Patch bag with patch containing high and low crystalinity ethylene copolymers

ES 2 239 985 T3

DESCRIPTION

Patch bag with patch containing high and low crystallinity ethylene copolymers.

Field of the invention

The present invention relates to the packaging of products in bags made of a flexible puncture resistant film. More particularly, the present invention relates to a patch bag, as well as to patch bag manufacturing processes.

Background of the invention

Various patch bags have been marketed for packaging fresh bone-in meat products, especially fresh red meat products and other bone-in meat products, such as whole bone-in pork chops etc. The patch reduces the likelihood of a perforation of the film by the protruding bones. The patch needs to have good resistance to perforation by bone. Optimally, the patch should also exhibit relatively high free shrinkage at a relatively low temperature.

US Patent No. 4,755,403 to Ferguson describes a patch bag having a heat shrinkable patch containing a blend of linear low density polyethylene mixed with ethylene vinyl acetate copolymer. US Patent 5,302,402 to Dudenhoeffer et al. Describes the use of various polymers, including very low density polyethylene, in a non-heat shrinkable patch for a patch bag. Au-B-40238/95 (based on Australian application 40238/95, published June 20, 1996) describes the use of a homogeneous ethylene / alpha-olefin copolymer in a patch for a patch bag. However, it is still desirable to provide a film that exhibits improved resistance to bone perforation, especially in combination with relatively high free shrinkage.

Summary of the invention

The present invention relates to a patch exhibiting a desirable combination: high free shrinkage in combination with improved resistance to bone perforation. A patch film of at least 70 percent by weight has been found to be a combination of a high crystallinity ethylene / alpha-olefin copolymer (such as LLDPE) and a heterogeneous low-grade ethylene / alpha-olefin copolymer. crystallinity (such as VLDPE), provides a patch that exhibits better performance in relation to drilling by bone, with respect to, for example to a patch using a linear low-density polyethylene blend with a minor proportion of ethylene / vinyl acetate copolymer. Preferably, the patch film is made from a blend of 50 to 95 weight percent VLDPE and 5 to 50 weight percent LLDPE. Surprisingly, the bone puncture resistance of the VLDPE / LLDPE blend is higher than if VLDPE alone or LLDPE alone is present as a bone puncture resistant polymer. Additionally, the VLDPE-LLDPE blend, if lacking ethylene / vinyl acetate copolymer and / or homogeneous ethylene / alpha-olefin copolymer, can provide the patch with increased resistance to bone puncture while also providing shrinkage. relatively high free at a temperature of, for example, 85 ° C. That is, even though the patch is made from a blend of VLDPE and LLDPE, if substantial amounts of ethylene / vinyl acetate copolymer and / or homogeneous ethylene / alpha-olefin copolymer are present in the VLDPE-LLDPE blend, it is reduced resistance to perforation by bone. Preferably, the heat shrinkable patch film comprises a blend of VLDPE-LLDPE, with less than 30 percent EVA or homogeneous ethylene / alpha-olefin copolymer present in the patch film.

As a first aspect, the present invention relates to a patch bag comprising a heat shrinkable patch adhered to a heat shrink bag. The heat shrinkable patch comprises a first heat shrink film and the heat shrink bag comprises a second heat shrink film. The first heat shrinkable film comprises: (A) a first component comprising an ethylene / alpha-olefin copolymer having a density greater than about 0.915 g / cm³ in an amount of at least about 5 percent, with respect to the total weight of the first film (preferably, at least 10, 20, 30, 40, 50, 60, 70, 80 or 90, or even up to 95 percent) and (B) a second component comprising a heterogeneous ethylene / alpha-olefin copolymer having a density less than about 0.915 g / cm³, where the second component is present in the first film in an amount of at least about 5 percent, relative to the total weight of the first film (preferably, at least 10, 20, 30, 40, 50, 60, 70, 80 or 90, or even up to 95 percent). The first and second components together make up at least 70 percent of the total weight of the first film (preferably, at least 75, 80, 85, 90, or 95, or even up to 100 percent). The first and the second components can be present in the same layer of the first heat shrinkable film, that is, as a mixture. Alternatively, the first film can be a multilayer film, with the first and second components present in separate layers.

Preferably, the first heat shrink film has a layer containing a mixture of the first component and the second component, the first component being present in the mixture in an amount of about 5 to 95 percent, based on the weight of the layer, and the second component being present in the mixture in a

ES 2 239 985 T3 amount from about 5 to 95 percent, based on the weight of the layer, and where the first component and the second component together constitute at least 70 percent of the total weight of the layer.

In a preferred embodiment, the first film has a total free shrink, at 85 ° C, of ​​at least 35 percent. Preferably, the first film and / or the second film have a total free shrink, at 85 ° C, of ​​at least about 45 percent.

In a preferred embodiment, the first film comprises a very low-density polyethylene blend in an amount of approximately 50 to 95 percent by weight (preferably 60-95%, more preferably 70-80%), relative to the total weight of the blend, and linear low-density polyethylene in an amount of about 5 to 50 percent (preferably 5-40%, more preferably 20-30%), relative to the total weight of the blend. Optionally, the blend may also comprise homogeneous ethylene / alpha-olefin copolymer having a density of 0.915 and below, but only in any amount up to about 20 percent, based on the total weight of the blend. Preferably, the mixture is present in an amount of at least about 70 percent by weight, based on the weight of the layer (more preferably, at least 75%, 80%, 85%, 90%, or 95%), in a layer having a thickness of at least about 0.6 mils (15.2 pm) (more preferably 0.6-5, 0.6-4, 0.6-3, 0.8-2 and 1-2 mils (15.2-127, 15.2-101.6, 15.2-76.2, 20.3-50.8 and 25.4-50.8 pm, respectively)).

Preferably, the patch film has a total free shrink, at 85 ° C, of ​​from about 50 percent to about 120 percent; more preferably, from about 50 percent to about 100 percent; and more preferably, from about 50 percent to about 80 percent. Preferably, the bag film has a total free shrink, at 85 ° C, of ​​from about 50 percent to about 120 percent; more preferably, from about 50 percent to about 100 percent; and more preferably, from about 50 percent to about 80 percent.

Preferably, the patch exhibits a failure rate in the conventional Rib Drop Test of at most 40 percent (i.e. 40 percent or less than 40 percent, or up to 40 percent, inclusive); more preferably 35 percent maximum; and more preferably, no more than 30 percent.

Preferably, the patch film is substantially free of homogeneous ethylene / alpha-olefin copolymer. That is, preferably, the patch film does not contain homogeneous ethylene / alpha-olefin copolymer. Alternatively and optionally, the blend may comprise homogeneous ethylene / alpha-olefin copolymer in an amount of from about 1 to about 20 percent, based on the weight of the blend; more preferably about 1 to 15 percent; more preferably, from about 1 to about 10 percent; and more preferably, from about 1 to about 5 percent.

Optionally, the blend may also comprise up to about 15 percent, relative to the total weight of the blend, of one or more members selected from the group consisting of a slip agent, filler, pigment, colorant, antioxidant radiation stabilizer , fluorescence additive, antistatic agent, elastomer and viscosity modifying agent.

Preferably, the patch comprises very low density polyethylene in an amount of about 70 to 80 weight percent, and linear low density polyethylene in an amount of about 20 to 30 weight percent.

Preferably, the bag comprises a first biaxially oriented heat shrink film comprising a resistant layer on the outside, an internal barrier layer for O₂ and a sealing layer on the inside, and the patch comprises a second biaxially oriented heat shrink film. Although the patch can adhere to the surface of the inside of the bag, preferably the patch adheres to the surface of the outside of the bag. Preferably, the patch is adhered to the bag with an adhesive.

The patch can be a monolayer film or a multilayer film. Preferably, the patch film comprises outer layers each containing the mixture, and an inner layer containing at least one member selected from the group consisting of ethylene / unsaturated ester copolymer (including ethylene / vinyl acetate, ethylene / methyl acrylate, ethylene / butyl acrylate), homogeneous ethylene / alpha-olefin copolymer, heterogeneous ethylene / alpha-olefin copolymer, ethylene / unsaturated acid copolymer (including ethylene / acrylic acid, ethylene / methacrylic acid), ionomer, and any other polymer capable of self-welding at the desired processing temperature.

Preferably, the multilayer film comprises an inner layer welded to itself and outer layers each comprising the blend. Preferably, the inner layer comprises ethylene / vinyl acetate copolymer in an amount of at least 50 percent, based on the weight of the inner layer; more preferably, at least 60 percent; more preferably, at least 70 percent; more preferably, at least 80 percent; more preferably at least 90 percent; and more preferably 100 percent. Preferably, the ethylene / vinyl acetate copolymer comprises vinyl acetate units in an amount of about 3-50 per cent.

ES 2 239 985 T3 weight percent, based on the weight of the ethylene / vinyl acetate copolymer; preferably, about 15 to 40 percent by weight; and preferably about 25 to 35 percent by weight.

Preferably, the multilayer film comprises at least two layers containing the mixture. Preferably, the multilayer film has a symmetrical cross section. Preferably, the two layers containing the mixture are the outer film layers of the patch film. In an alternative preferred embodiment, the multilayer patch film further comprises an intermediate layer that also contains the mixture. Preferably, the patch film has a symmetrical cross section. Preferably, the patch film comprises an inner layer containing ethylene / vinyl acetate in an amount of about 50 to 100 percent, the film further comprising two outer layers, each containing the mixture. Preferably, the blend comprises VLDPE in an amount of about 70 to 80 percent (based on the weight of the blend) and LLDPE in an amount of about 20 to 30 percent.

Preferably, the first film has an impact resistance (measured using ASTM D3763) of at least 0.5 joules / thousandth of an inch (19.6 Joules / pm) (preferably, at least 0.6, 0.7, 0, 8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5 Joules / thousandth of an inch (at least 23.6, 27.5, 31.4, 35 , 4, 39.3, 43.3, 47.2, 51.1, 55.1 and 59.0 Joules / pm, respectively)).

Brief description of the drawings

Figure 1 illustrates a plan view of an end sealed patch bag.

Figure 2 illustrates a cross-sectional view of the patch bag of Figure 1, taken through its section 2-2.

Figure 3 illustrates a cross-sectional view of a multilayer film for use in a preferred patch in accordance with the present invention.

Figure 4 illustrates a schematic view of a preferred process for manufacturing the multilayer film of Figure 3.

Figure 5 illustrates a cross-sectional view of a multilayer film for use in a preferred bag in accordance with the present invention.

Figure 6 illustrates a schematic view of a preferred process for manufacturing the multilayer film of Figure 5.

Figure 7 illustrates a plan view of a "wide patch" patch bag, used in the conventional rib drop test.

Figure 8 illustrates a cross-sectional view of the patch bag of Figure 7, taken through section

Detailed description of the invention

As used herein, the term "bag" includes L seal bags, side seal bags, back seam bags, and sacks. An L seal bag has an open top, a bottom seal, a side seal along a first side edge, and a second seamless side edge (ie, folded, not sealed). A side seal bag has an open top and a seamless bottom edge, each of its two side edges having a seal along its length. Although the seals along the side and / or bottom edges may be very to the edge (ie, seals of a type commonly referred to as "welt seals"), preferably, the seals are spaced apart from the side edges of the bag. inward (preferably by a distance of 1/4 to 1/2 inches (6.35 to 12.7 mm, more or less), and preferably performed using an impulse type heat sealing apparatus, which uses a bar that heats up quickly and then cools down quickly. A back seam bag is a bag that has an open top, a seal running the length of the bag in which the bag film is flap-sealed or flap-sealed, two seamless side edges, and a seal bottom along a bottom edge of the bag.

As used herein, the terms "heat shrinkable" and "heat shrink" and the like refer to the tendency of a film, generally an oriented film, to contract upon application of heat, that is, to contract after being heated, from such that the size (area) of the film is reduced if it is not impeded when heated. Similarly, the tension of a heat shrink film increases after the application of heat if the shrinkage of the film is prevented. As a corollary, the term "heat-shrunk" refers to a heat-shrinkable film, or a portion thereof, that has been exposed to heat such that the film or portion thereof is in a heat-shrunk state, that is, of reduced in size (without impediments to contraction) or under greater stress (with impediments to contraction). Preferably, the heat shrink film has a total free shrink (i.e., machine direction plus cross direction), as measured by ASTM D 2732, of at least 5 percent at 185 ° C, more preferably of at least a 7 percent, even more preferably at least 10 percent, and even more preferably at least 20 percent.

ES 2 239 985 T3

As used herein, the phrase "heterogeneous polymer" refers to products of a polymerization reaction with a relatively wide variation in molecular weight and a relatively wide variation in composition distribution, that is, it refers to typical polymers. prepared, for example, using conventional Ziegler-Natta catalysts. Heterogeneous copolymers typically contain a relatively wide diversity of chain lengths and percentages of comonomers.

As used herein, the phrase "homogeneous polymer" refers to products of a polymerization reaction with a relatively narrow molecular weight distribution and a relatively narrow composition distribution. Homogeneous polymers are useful in various layers of the multilayer film used in the present invention. Homogeneous polymers are structurally different from heterogeneous polymers in that homogeneous polymers exhibit relatively uniform comonomer sequencing within a chain, a reflection of the sequence distribution across all chains, and a similarity in the length of all chains. , that is, a narrower molecular weight distribution. Furthermore, homogeneous polymers are typically prepared using metallocene, or other single-site type catalyst, rather than using Ziegler Natta catalysts.

More particularly, homogeneous ethylene / alpha-olefin copolymers can be characterized by one or more processes known to those skilled in the art, such as molecular weight distribution (Mw / Mn), Mz / Mn, distribution width index of the composition (CDBI) and narrow melting point range and single melting point behavior. The molecular weight distribution (Mw / Mn), also known as polydispersity, can be determined by size exclusion chromatography. The homogeneous ethylene / alpha-olefin copolymers useful in this invention generally have a (Mw / Mn) of less than 2.7; preferably about 1.9 to 2.5; more preferably about 1.9 to 2.3. The composition distribution breadth index (CDBI) of such homogeneous ethylene / alpha-olefin copolymers will generally be greater than about 70 percent. The CDBI is defined as the percentage by weight of the copolymer molecules that have a comonomer content within 50 percent (ie, plus or minus 50%) of the average total molar comonomer content. The CDBI of linear polyethylene, which does not contain a comonomer, is defined as 100 percent. The composition distribution width index (CDBI) is determined by the temperature rise elution fractionation (TREF) technique. The CDBI determination clearly distinguishes homogeneous copolymers (narrow composition distribution assessed by CDBI values ​​generally above 70%) from commercially available VLDPEs which generally have a broad composition distribution as assessed by generally lower CDBI values 55%. The CDBI of a copolymer is easily calculated from data obtained by methods known in the art, such as, for example, elution fractionation with elevation of temperature as described, for example, in Wild et al., J. Poly. Sci. Poly. Phys. Ed., Vol. 20, p. 441 (1982). Preferably, the homogeneous ethylene / alpha-olefin copolymers have a CDBI of greater than about 70%, that is, a CDBI of about 70% to 99%. In general, the homogeneous ethylene / alpha-olefin copolymers of the patch bag of the present invention also exhibit a relatively narrow melting point range, compared to "heterogeneous copolymers", that is, polymers that have a lower CDBI. 55%. Preferably, homogeneous ethylene / alpha-olefin copolymers exhibit essentially unique melting point characteristics, with a maximum melting point (Tm), determined by differential scanning calorimetry (DSC), of about 60 ° C to 110 ° C. Preferably, the homogeneous copolymer has a maximum DSC Tm of about 80 ° C to 100 ° C. As used herein, the phrase "essentially individual melting point" means that at least about 80% by weight of the material corresponds to a single peak of Tm at a temperature within the range of about 60 ° C to 110 ° C. , and essentially no substantial fraction of the material has a maximum melting point above about 115 ° C, as determined by DSC analysis. DSC measurements are performed on a Perkin Elmer System 7 thermal analysis system. The melt information presented is the second melt data, i.e. the sample is heated at a programmed rate of 10 ° C / min to a temperature below its critical range. The sample is then reheated (second melt) at a programmed rate of 10 ° C / minute. The presence of higher melting peaks is detrimental to film properties such as optical clarity and compromises the possibility of a significant reduction in the start temperature of the final film seal.

In general, a homogeneous ethylene / alpha-olefin copolymer can be prepared by the copolymerization of ethylene and any one or more alpha-olefins. Preferably, the alpha-olefin is an alpha-monoolefin of 3 to 20 carbon atoms, more preferably an alpha-monoolefin of 4 to 12 carbon atoms and, even more preferably, an alpha-monoolefin of 4 to 8 carbon atoms. Even more preferably, the alpha-olefin comprises at least one member selected from the group consisting of butene-1, hexene-1, and octene-1, ie, 1-butene, 1-hexene, and 1-octene, respectively. Most preferably the alpha-olefin comprises octene-1 and / or a mixture of hexene-1 and butene-1.

Processes for preparing and using homogeneous polymers are described in US Patent No. 5,206,075, US Patent No. 5,241,031 and PCT International Application WO 93/03093. Additional details regarding the production and use of ethylene copolymers describe additional details regarding the production and use of ethylene copolymers in PCT International Publication No. homogeneous / alpha-olefin.

In US Patent No. 5,272,236 to LAI et al., And in US Patent No. 5,278,272 to LAI et al. Yet another genus of homogeneous ethylene / alpha-olefin copolymers is disclosed. Each of these patents

ES 2 239 985 T3 describes long chain, homogeneous and substantially linear branched ethylene / alpha-olefin copolymers produced and sold by The Dow Chemical Company.

As used herein, the phrase "ethylene / alpha-olefin copolymer" and "ethylene / alpha-olefin copolymer" refer to materials such as linear low-density polyethylene (LLDPE) and very low-density polyethylene. ultra low density (VLDPE and ULDPE); and homogeneous polymers such as metallocene catalyzed polymers such as EXACT resins^® available from Exxon Chemical Company, and TAFMER resins^® available from Mitsui Petrochemical Corporation. All of these materials generally include copolymers of ethylene with one or more comonomers selected from C4-10 alpha-olefins such as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. wherein the copolymer molecules comprise long chains with relatively few side chain branches or crosslinked structures. This molecular structure should be contrasted with that of conventional low or medium density polyethylenes which are more branched than their respective counterparts. Heterogeneous ethylene / alpha-olefin copolymers commonly known as LLDPE have a density typically in the range of about 0.91 grams per cubic centimeter to about 0.94 grams per cubic centimeter. Also included are other ethylene / alpha-olefin copolymers, such as the long chain branched homogeneous ethylene / alpha-olefin copolymers available from the Dow Chemical Company, known as AFFINITY resins.^®, as another type of homogeneous ethylene / alpha-olefin copolymer useful in the present invention.

In general, the ethylene / alpha-olefin copolymer comprises a copolymer resulting from the copolymerization of about 80 to 99 percent by weight of ethylene and 1 to 20 percent by weight of alpha-olefin. Preferably, the ethylene / alpha-olefin copolymer comprises a copolymer resulting from the copolymerization of about 85 to 95 weight percent ethylene and 5 to 15 weight percent alpha-olefin.

As used herein, the phrase "very low density polyethylene" refers to heterogeneous ethylene / alpha-olefin copolymers having a density of 0.915 g / cc and below, preferably about 0.88 to 0.915 g / cc. . As used herein, the phrase "linear low-density polyethylene" refers to, and includes, both heterogeneous and homogeneous ethylene / alpha-olefin copolymers, having a density of at least 0.915 g / cc, preferably 0.916. at 0.94 g / cc.

As used herein, the phrases "inner layer" and "inner layer" refer to any layer of a multilayer film that has its two major surfaces adhered directly to another layer of the film.

As used herein, the phrase "outer layer" refers to any layer of the film that has fewer than two of its major surfaces adhered directly to another layer of the film. The phrase includes monolayer and multilayer films. In multilayer films, there are two outer layers, each having a major surface adhered only to a different layer of the multilayer film. In monolayer films, there is only one layer, which of course is an outer layer since neither of its two main surfaces are adhered to another layer of the film.

As used herein, the phrase "inside layer" refers to the outer layer of a multilayer film that wraps a product, which is closest to the product relative to the other layers of the multilayer film.

As used herein, the phrase "outer layer" refers to the outer layer of a multilayer film that wraps a product, which is farthest from the product relative to the other layers of the multilayer film. Similarly, the "outside surface" of a bag is the surface away from the product that is packaged within the bag.

As used herein, the term "adhered" includes films that adhere directly to each other using heat seal or other means, as well as films that adhere to each other using an adhesive that is between the two films.

Although the films used in the patch bag according to the present invention can be monolayer films or multilayer films, the patch bag comprises at least two films laminated together. Preferably, the patch bag comprises films that together constitute a total of 2 to 20 layers; more preferably 2 to 12 layers; and even more preferably, 4 to 12 layers. In general, the multilayer film (s) used in the present invention may have any desired overall thickness, as long as the film provides the desired properties for the particular packaging operation in which the film is used, for example, abuse resistance ( especially puncture resistance), modulus, seal strength, optical properties, etc.

FIG. 1 is a plan view of a preferred end seal patch bag 20 in a flat extended position, this patch bag being in accordance with the present invention; Figure 2 is a cross-sectional view of patch bag 20, taken through section 2-2 of Figure 1. Looking at Figures 1 and 2 together, patch bag 20 comprises a bag 22, a first patch 24, a second patch 26, an open top 28, and an end seal 30.

The portions of bag 22 to which patches 24 and 26 adhere are "covered", ie, protected, by patches 24 and 26 respectively. The upper and lower end portions 32 and 34 (respectively) of the bag

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22, preferably not covered by patch 24, to facilitate end sealing 26, which is preferably done before putting the product in the bag, as well as top sealing (not illustrated) which is preferably done after putting the product in the bag. Unless done correctly, heat sealing through the bag and patch 22 and patch 24 together can result in burns and / or a weaker seal. For a special process of sealing through the patch and the bag together, see USSN 60/042664, on behalf of DePoorter et al, entitled "PATCH BAG HAVlNG SEAL THROUGH PATCHES". filed April 4, 1997.

Figure 3 illustrates a schematic view of a preferred film for use as a patch film, for example, in the patch bag illustrated in Figures 1 and 2. In Figure 3, the multilayer film 36 has outer layers 38 and 40, intermediate layers 42 and 44 and self-welded layers 46 and 48.

Figure 4 illustrates a schematic of a preferred process for producing the multilayer film for use in the patch of the patch bag of the present invention, for example, the patch film illustrated in Figure 3. In the process illustrated in Figure 4, solid polymeric beads (not illustrated) are supplied to a plurality of extruders 52 (for simplicity, only one extruder is illustrated). Within extruders 52, the polymer beads are advanced, melted, and degassed, after which the resulting bubble-free melt is advanced into a die head 54, and extruded through a annular die resulting in a tube 56 having a thickness of 5-40 mils (0.127-1.01 mm), more preferably 20-30 thousandths of an inch (0.50-0.76mm) and even more preferably about 25 thousandths of an inch (0.63mm).

After cooling or quenching by spraying water from the cooling ring 58, the tube 56 is collapsed by collecting cylinders 60 and subsequently supplied through the irradiation chamber 62 surrounded by a protective cover 64, where the tube 56 is irradiated. with high energy electrons (ie ionizing radiation) from an iron core transformer accelerator 66. Tube 56 is guided through irradiation chamber 62 onto cylinders 68. Preferably, the tube 56 is irradiated at a level of about 10 megarads ("MR").

After irradiation, the irradiated tube 70 is directed over a guide cylinder 72, after which the irradiated tube 70 passes into a hot water bath tank 74 containing hot water 76. The now collapsed irradiated tube 70 is immersed in the hot water for a retention time of at least about 5 seconds, that is, for a period of time to bring the film to the desired temperature, after which a complementary heating means ( not illustrated), including a plurality of steam cylinders around which the irradiated tube 70 is partially wound, and optionally hot air insufflators, they raise the temperature of the irradiated tube 70 to a desired targeting temperature of approximately 240 ° F to 250 ° F (115.56 ° C-121.11 ° C). A preferred means of heating the irradiated tube 70 is with an infrared oven (not illustrated), by exposure to infrared radiation for approximately 3 seconds, which also raises the tube to a temperature of approximately 240-250 ° F (115.56 ° C). -121.11 ° C). Subsequently, the irradiated film 70 is directed towards pressure cylinders 78, and the bubble 80 is blown, thereby extending the irradiated tube 70 transversely. Furthermore, while blowing, that is, spreading transversely, the irradiated film 70 is stretched (that is, in the longitudinal direction) between the pressure cylinders 78 and the pressure cylinders 86, since the pressure cylinders 86 have a greater surface velocity than the surface velocity of pressure cylinders 78. As a result of the transverse extension and longitudinal stretching, the irradiated biaxially oriented blown tube film 82 is produced, this blown tube having preferably been extended in a ratio of about 1: 1.5-1: 6, and having been stretched by a ratio of about 1: 1.5-1: 6. More preferably, the extension and stretching are performed at a ratio of about 1: 2-1: 4. The result is a biaxial orientation of about 1: 2.25-1: 36, more preferably 1: 4-1: 16. While holding bubble 80 between collecting cylinders 78 and 86, blown tube 82 collapses by cylinders 84 and is subsequently conveyed through pressure cylinders 86 and transverse guide cylinder 88, and then wound onto a winding cylinder 90. Complementary cylinder 92 ensures good winding.

Preferably, the reserve film from which the bag is formed has a total thickness of about 1.5 to 5 thousandths of an inch (0.038-0.127 mm); more preferably about 2.5 mils (0.063mm). Preferably, the reserve film from which the bag is formed is a multilayer film having 3 to 7 layers; more preferably 4 layers.

Figure 5 illustrates a cross-sectional view of a preferred multilayer film 110 for use as a tube film stock material from which bag 22 is formed. The multilayer film 110 has a physical structure, in terms of the number of layers, thickness of layers, and arrangement and orientation of layers in the patch bag, and a chemical composition in terms of the various polymers, etc., present in each of the layers, as indicated in Table 1 below.

ES 2 239 985 T3

TABLE I

<td>Layer Designation</td><td>Layers Function</td><td>Chemical Identity of Layers</td><td>Layer Thickness (thousandths of an inch)</td>

<td> 112</td><td>Outer part layer rior and resistant</td><td>90% EVA N^d 1 10% HDPE No. 1</td><td>0.58 (14.73 pm)</td>

<td> 114</td><td>O barrier layer₂</td><td>2% epoxidized soybean oil; Y 2% buA / MA / bu-MA terpolymer</td><td>0.19 (4.8 pm)</td>

<td> 116</td><td>Puncture resistant ration</td><td>85% of LLDPÉ Ν^ώ 1 and 15% of EBA N ° 1</td><td>1.15 (29.2 pm)</td>

<td> 118</td><td>Sealant layer and interior part</td><td>80% of SSPÉ Ñ ° 1 20% LLDPE No. 1</td><td>0.48 (12.19 pm)</td>

LLPD No. 1 was DOWLEX® 2045 linear low-density polyethylene, obtained from the Dow Chemical Company of Midland, Michigan. LLDPE No. 2 was ESCORENE® LL3003.32 linear low density polyethylene, obtained from Exxon Chemical Company Baytown, Texas. SSPE No. 1 was AFFINITY® metallocene catalyzed ethylene / octene copolymer obtained from the Dow Chemical Company of Midland, Michigan. HDPE No. 1 was Fortiflex® T60-500-119 high density polyethylene, obtained from Solvay Polymers of Deer Park, Texas. EVA No. 1 was ESCORENE® LD318.92 ethylene / vinyl acetate copolymer having a melt index of 2.0, a density of 0.930 g / cc, and a vinyl acetate monomer content of 9 percent, this resin being obtained from the Exxon Chemical Company. EBA No. 1 was ethylene / butyl acrylate copolymer SP1802 containing 18% butyl acrylate, obtained from Chevron Chemical Company of Houston, Texas. VDC / MA No. 1 was vinylidene chloride / methyl acrylate copolymer SARAN® MA-134, obtained from the Dow Chemical Company. The epoxidized soybean oil was PLAS-CHEK® 775 epoxidized soybean oil obtained from Bedford Chemical Division of Ferro Corporation, Walton Hills, Ohio. The Bu-A / MA / bu-MA terpolymer was butyl acrylate / methyl methacrylate / butyl methacrylate METABLEN® L-1000 terpolymer, obtained from Elf Atochem North America, Inc., 2000 Market Street, Philadelphia, Pennsylvania, 19103.

Figure 6 illustrates a schematic of a preferred process for producing the multilayer film of Figure 5. In the process illustrated in Figure 6, solid polymeric beads (not illustrated) are supplied to a plurality of extruders 120 (for simplicity, only illustrates an extruder). Within extruders 120, the polymeric beads are advanced, melted, and degassed, after which the resulting bubble-free melt is advanced into a die head 122, and extruded through an annular die. , resulting in a tube 124 having a thickness of 10 to 30 mils (0.25-0.76 mm), more preferably 15 to 25 mils (0.38-0.63 mm).

After cooling or quenching by spraying water from the cooling ring 126, the tube 124 is collapsed by collecting cylinders 128 and is subsequently supplied through the irradiation chamber 130 surrounded by a protective cover 132, where the tube 124 is irradiated. with high energy electrons (ie ionizing radiation) from an iron core transformer accelerator 134. Tube 124 is guided through irradiation chamber 130 onto cylinders 136. Preferably, tube 124 is irradiated at a level of approximately 4.5 MR.

After irradiation, the irradiated tube 138 is directed through pressure cylinders 140, after which the tube 138 is inflated slightly, causing trapped bubbles 142 to remain. However, in the trapped bubble zone 142, the tube does not stretch significantly longitudinally, as the surface velocity of pressure cylinders 144 is approximately the same as the speed of pressure cylinders 140. Furthermore, the irradiated tube 138 inflates only sufficiently to provide a substantially circular tube without significant transverse orientation, ie, no extension.

The slightly inflated irradiated tube 138 is passed through a vacuum chamber 146 and subsequently directed through the coating die 148. From the coating die 148 a second tubular film 150 is melt extruded and applied as a coating on the slightly inflated irradiated tube 138, to form a two-layer tubular film 152. The second tubular film 150 preferably comprises an O-barrier layer₂, which does not pass through ionizing radiation. Additional details of the coating step described above are generally set forth in US Patent No. 4,278,738 to BRAX et al., Which is incorporated herein by reference in its entirety.

ES 2 239 985 T3

After irradiation and coating, the two-layer tube film 152 is wound onto a winding cylinder 154. Subsequently, the winding cylinder 154 is removed and installed as an unwinding cylinder 156, in a second stage of the process. of tube film fabrication as ultimately desired. Two-layer tubular film 152, from unwind roll 156, is unwound and passed over guide roll 158, after which two-layer tubular film 152 passes into a hot water bath tank 160 containing hot water 162. The now collapsed, irradiated, coated tubular film 152 is immersed in hot water 162 (having a temperature of about 210 ° F (98.89 ° C) for a retention time of at least about 5 seconds, that is, for a sufficient period of time for the film to reach the desired temperature for biaxial orientation. Subsequently, the irradiated tubular film 152 is directed through pressure cylinders 164, and a bubble 166 is blown, thereby extending the tubular film 152 transversely. Furthermore, while blowing, that is, extending transversely, the pressure cylinders 168 stretch the tubular film 152 in the longitudinal direction, since the pressure cylinders 168 have a surface velocity greater than the surface velocity of the pressure cylinders 164. . As a result of the transverse extension and longitudinal stretching, a coated, irradiated, biaxially oriented blown tube film 170 is produced, this blown tube having preferably been extended in a ratio of about 1: 1.5-1: 6, and having stretched in a ratio of about 1: 1.5-1: 6. More preferably, the extension and stretching are done in a ratio of about 1: 2-1: 4. The result is a biaxial orientation of about 1: 2.25-1: 36, more preferably 1: 4-1: 16. While bubble 166 is held between collection cylinders 164 and 168, blown tube film 170 is collapsed by cylinders 172, and is subsequently conveyed through pressure cylinders 168 and through guide cylinder 174, and then is it winds over the winding cylinder 176. The complementary cylinder 178 ensures good winding.

Figure 7 is a schematic illustration of another preferred patch bag 180 substantially in its flat configuration, this patch bag being a "wide patch" patch bag. This is the bag used in the conventional rib drop test explained below. Figure 8 illustrates a cross-sectional view of a patch bag 180 taken through section 8-8 of Figure 7. Looking at both Figure 7 and Figure 8, patch bag 180 comprises a bag 182 having an end seal 184, an open top 186, a first side edge 188, and a second side edge 190. To the surface of Adhered to the outside of bag 180 is a first patch 192 and a second patch 194. The first patch 192 has a first protrusion 196 protruding from the first lateral edge 188, and a second protrusion 198 protruding from the second lateral edge 190. The second patch 194 has a third protrusion 200 protruding from the first lateral edge 188 and adheres to the first projection 196, and a fourth projection 202 protruding from second side edge 190 and adhering to second projection 198. In this way, along the length of bag 182 on which a first patch 192 and a second patch 194 adhere, the full width of bag 182 is "covered" by the combination of patch 192 and 194, that is that is, together, patches 192 and 194 constitute a "full width" coverage of bag 182. The end portions 204 and 206 of the bag 182 are not covered by the patches 192 and 194, so that strong seals can be made through the bag 182, without having to seal the patches 192 and / or 194 through the bag.

The polymeric components used to make multilayer films in accordance with the present invention may also contain appropriate amounts of other additives normally included in such compositions. These include anti-blocking agents (such as talc), slip agents (such as fatty acid amides), fillers, pigments and colorants, radiation stabilizers (including antioxidants), fluorescence additives (including a material that emits fluorescence with ultraviolet radiation), antistatic agents, elastomers, viscosity modifying substances (such as fluoropolymer processing aids) and similar additives known to those skilled in the art of packaging films.

The multilayer films used to make the patch bag of the present invention are preferably irradiated to induce crosslinking, in addition to being corona treated to roughen the surface of the films to be adhered to each other. In the irradiation process, the film is subjected to energetic radiation treatment, such as corona discharge, plasma, flame, ultraviolet radiation, X-rays, gamma rays, beta rays, and high-energy electron treatment, which induces crosslinking between the molecules of the irradiated material. In US Patent No. 4,064,296 to bOrNSTEIN et al., Irradiation of polymeric films is described. BORNSTEIN et al. describes the use of ionizing irradiation for crosslinking of the polymer present in the film.

Radiation dosages are referred to in this document in terms of the radiation unit "RAD", denoted one million RADS, also known as megarad, "MR", or in terms of the radiation unit kiloGray (kGy), representing 10 kiloGray 1 MR, as those skilled in the art know. A suitable high energy electron radiation dosage is in the range of up to about 16 to 166 kGy, more preferably about 40 to 90 kGy, and even more preferably 55 to 75 kGy. Preferably, the irradiation is carried out by an electron accelerator and the dosage level is determined by conventional dosimetry processes. Other accelerators such as a van der Graaf or resonance transformer can be used. Radiation is not limited to electrons from an accelerator, as any ionizing radiation can be used.

As used herein, the phrases "corona treatment" and "corona discharge treatment" refer to subjecting the surfaces of thermoplastic materials, such as polyolefins, to corona discharge, that is, the ionization of such a gas. as air very close to the surface of a film and ionization initiated by a high

ES 2 239 985 T3 voltage passed across a nearby electrode, and cause oxidation and other changes to the surface of the film, for example by providing roughness to the surface.

BONET US Patent No. 4,120,716, issued October 17, 1978, describes the corona treatment of polymeric materials. This patent describes better adhesion characteristics of the polyethylene surface by corona treatment, to oxidize the polyethylene surface. US Patent No. 4,879,430 to HOFFMAN describes the use of corona discharge for treating plastic nets for use in cook-in packaging of meat, with corona treatment. of the surface of the inner part of the net to increase the adhesion of the meat to the protein material. Although corona treatment is a preferred treatment of multilayer films used to make the patch bag of the present invention, plasma treatment of the film can also be used.

Lamination of the patch on the bag can be accomplished by a variety of methods, including the use of an adhesive, corona treatment, or even heat sealing. Adhesives are the preferred means of laminating. Examples of suitable types of adhesives include thermoplastic acrylic emulsions, solvent-based adhesives and high solids adhesives, ultraviolet radiation cured adhesive, and electron beam cured adhesive, as is known to those skilled in the art. A preferred adhesive is a thermoplastic acrylic emulsion known as RHOPLEX® N619 (thermoplastic acrylic emulsion, obtained from the Rohm &amp; Haas Company, at Dominion Plaza Suite 545, 17304 Preston Rd., Dallas, Texas 75252, with Rohm &amp; Haas headquartered in the 7th floor, Independence Mall West, Philadelphia, Penn. 19105.

Returning to preferred embodiments of the film from which the patch is made, although the first component may be a homogeneous ethylene / alpha-olefin copolymer or a heterogeneous ethylene / alpha-olefin copolymer, preferably the first component comprises a copolymer ethylene / alpha-olefin heterogeneous. Preferably, the first component comprises an ethylene / alpha-olefin copolymer having a density of at least about 0.915 g / cm³; more preferably greater than about 0.916, more preferably greater than about 0.917; more preferably greater than about 0.918; more preferably greater than about 0.919; and more preferably greater than about 0.920. Preferably, the first component comprises an ethylene / alpha-olefin copolymer having a density less than about 0.960 g / cm³; more preferably less than about 0.940; more preferably less than about 0.935; more preferably less than about 0.930; more preferably less than about 0.928; and more preferably less than about 0.926.

Although the first and second components are preferably present as a mixture, they may alternatively be present in separate film layers. Preferably, the first film comprises the first component in an amount less than about 90% relative to the weight of the first film; more preferably less than about 80%; more preferably less than about 70%; more preferably less than about 60%; and more preferably less than about 50%. Preferred ranges include 10-90%, 10-50%, 10-40%, and 20-30%.

Preferably, the first component comprises an ethylene / alpha-olefin copolymer which is a copolymer of ethylene and at least one member selected from the group consisting of olefin of 3 to 20 carbon atoms; more preferably an alpha-monoolefin of 3 to 20 carbon atoms, more preferably an alpha-monoolefin of 4 to 12 carbon atoms, and even more preferably an alpha-monoolefin of 4 to 8 carbon atoms. Even more preferably, the alpha-olefin comprises at least one member selected from the group consisting of butene-1, hexene-1 and octene-1, ie 1-butene, 1-hexene and 1-octene respectively. Preferably, the alpha-olefin comprises octene-1 and / or a mixture of hexene-1 and butene-1. The first component may comprise an ethylene / alpha-olefin copolymer containing ethylene units and units of at least two different comonomers in addition to the ethylene unit.

Preferably, the second component comprises a heterogeneous ethylene / alpha-olefin copolymer having a density less than about 0.915 g / cm³. In one embodiment, the ethylene / alpha-olefin copolymer has a density of less than 0.914; more preferably less than about 0.913; more preferably less than about 0.910; more preferably less than about 0.908; more preferably less than about 0.906; more preferably less than about 0.904; more preferably less than about 0.902; more preferably less than about 0.900; more preferably less than about 0.898; more preferably less than about 0.895; more preferably less than about 0.890; more preferably less than about 0.885; and more preferably less than about 0.88. Preferred density ranges include 0.88 to 0.915, 0.89 to 0.915, 0.90 to 0.915, 0.900 to 0.912, and 0.900 to 0.910 g / cc. Some examples of resins that can be used as a second component include various ATTANE® polymers from Dow Chemical (eg ATTANE® 4203) and polymers called ULDPE / VLDPE, manufactured by Union Carbide Chemicals and Plastics Company (eg DFDA 1137).

Preferably, the second component contains an ethylene / alpha-olefin copolymer in which the alpha-olefin comonomer comprises at least one comonomer selected from the group consisting of olefin of 3 to 20 carbon atoms; more preferably, alpha-monoolefin of 3 to 20 carbon atoms, more preferably alpha-monoolefin of 4 to 12 carbon atoms, and even more preferably alpha-monoolefin of 4 to 8 carbon atoms. Preferably, the alpha-olefin comprises at least one member selected from the group consisting of butene10

ES 2 239 985 T3

1, hexene-1 and octene-1, i.e. 1-butene, 1-hexene and 1-octene, respectively. Preferably, the alpha-olefin comprises octene-1 and / or a mixture of hexene-1 and butene-1. The second component may comprise an ethylene / alpha-olefin copolymer consisting of two or more comonomers.

Preferably, the second component is present in the first film in an amount of about 5 to 95 percent by weight, preferably 30-95, 50-90, 60-90, and 70-80 percent by weight.

In a preferred embodiment, the first film comprises a first layer comprising a mixture of the first component and the second component, each having a chemical composition as described above. In one embodiment, the first layer comprises the first component in an amount of at least about 5 percent, based on the total weight of the blend. Preferably, the mixture comprises the first component in an amount of about 5-70%, more preferably 10-50%, more preferably 10-40%, and most preferably 20-30%. In this same embodiment, the first layer preferably comprises the second component in an amount of at least about 5 percent, based on the total weight of the mixture. Preferably, the mixture comprises the second component in an amount of about 3099%, more preferably 50-90%, more preferably 60-90%, and most preferably 70-80%.

Although the first layer can be an outer layer or an inner layer; preferably, it is an outer layer. The first layer as described above, preferably has a thickness of from about 0.001 to about 0.2mm; more preferably, from about 0.003mm to about 0.2mm; more preferably, from about 0.005mm to about 0.15mm; more preferably, from about 0.007 to about 0.15mm; more preferably, from about 0.01mm to about 0.15mm; more preferably, from about 0.015mm to about 0.15mm; more preferably, from about 0.02mm to about 0.10mm; more preferably, from about 0.03mm to about 0.08mm; more preferably, from about 0.04mm to about 0.08mm; and even more preferably, from about 0.04mm to about 0.06mm. Generally, the thickness of the first layer is from about 1 to about 100%, relative to the total thickness of the multilayer film; more preferably, from about 5 to about 100%; more preferably, from about 10 to about 40%; more preferably, from about 20 to about 100%; and more preferably, from about 25% to about 100%. In a preferred embodiment, the first layer has a thickness of at least about 10%; more preferably, at least about 20%; more preferably, at least about 30%; more preferably, at least about 40%; more preferably, at least about 50%; more preferably, at least about 60%; more preferably, at least about 70%; more preferably, at least about 80%, and more preferably, at least about 90%, relative to the total thickness of the multilayer film.

Preferably, the first layer contains one or more polymers having a melt index of from about 0.3 to about 50; more preferably about 0.5-20; more preferably about 0.5-10, more preferably about 0.5-5, more preferably about 0.5-3, more preferably about 0.7-2, more preferably about 0.7-1, 5, and more preferably about 0.7-1.2 (measured by ASTM D1238). Preferably, the first component comprises a polymer having a melt index of less than about 5, more preferably less than about 3; more preferably, less than about 2.5; more preferably less than about 2.0; more preferably less than about 1.5, more preferably less than about 1.3; and more preferably, less than about 1.2. In some embodiments, it is preferable that the first component comprises a polymer having a melt index of less than about 1, more preferably less than about 0.9.

Preferably, the second component comprises a polymer having a melt index of about 0.3-50, more preferably about 0.5-20; more preferably about 0.5-10, more preferably about 0.5-5, more preferably about 0.5-3, more preferably about 0.7-2, more preferably about 0.7-1, 5, and more preferably about 0.7-1.2. Preferably, the second component comprises a polymer having a melt index of less than about 5, more preferably less than about 3; more preferably, less than about 2.5; more preferably less than about 2.0; more preferably less than about 1.5, more preferably less than about 1.3; and more preferably, less than about 1.2. In some embodiments, it is preferable that the second component comprises a polymer having a melt index of less than about 1, more preferably less than about 0.9.

Although the first film could be a monolayer film, preferably, the first film comprises a second layer in addition to the first layer described above. This second layer preferably comprises at least one member selected from the group consisting of polyolefin, polystyrene, polyamide, polyester, and polyurethane; more preferably a polyolefin. The second layer preferably comprises at least one member selected from the group consisting of polyethylene homopolymer, polyethylene copolymer, polypropylene homopolymer, polypropylene copolymer, polybutene homopolymer, and polybutene copolymer. The polyolefin can be a homogeneous polyolefin or a heterogeneous polyolefin. Preferably, the polyolefin includes at least one member selected from the group consisting of ethylene / alpha-olefin copolymer, ethylene / ester copolymer

ES 2 239 985 T3 unsaturated and ethylene / unsaturated acid copolymer. Preferred ethylene / alpha-olefin copolymers are as described above in the description of the first layer. However, in a preferred embodiment, the second layer comprises a self-welding polymer, preferably having a melting point of less than 125 ° C, more preferably less than 110 ° C, more preferably less than 100 ° C, more preferably less than 90 ° C, more preferably less than 85 ° C and more preferably less than 80 ° C. Although the second layer can be an inner layer or an outer layer, preferably the second layer is an inner layer.

The second layer, as described above, preferably has a thickness of from about 0.001 to about 0.2mm; more preferably about 0.003 to about 0.2mm; more preferably about 0.005 to about 0.15mm; more preferably, from about 0.007 to about 0.15mm; more preferably, from about 0.01mm to about 0.10mm; more preferably, from about 0.015mm to about 0.10mm; more preferably, from about 0.02mm to about 0.07mm; more preferably, from about 0.03mm to about 0.07mm; more preferably, from about 0.03mm to about 0.05mm. Generally, the thickness of the second layer is from about 1 to about 95% with respect to the total thickness of the multilayer film; more preferably, from about 5 to about 95%; more preferably, from about 10 to about 95%; more preferably about 20 to about 95%; and more preferably from about 25 to about 95%. If the second layer does not comprise an ethylene / alpha-olefin copolymer, it preferably has a thickness of less than 30%, more preferably less than 20% and more preferably less than 10%, relative to the total thickness of the film.

Preferably, the second layer contains at least one polymer having a melt index of from about 0.3 to about 50, as measured by ASTM D1238; more preferably from about 0.5 to about 20; more preferably from about 0.7 to about 10; even more preferably from about 1 to about 8; and more preferably from about 1 to about 6.

Optionally, the first film may comprise a third layer, the third layer having a thickness and composition as described above in the description of the second layer. Optionally, the first film may further comprise a fourth layer and / or a fifth layer, these having a thickness and composition as described above in the description of the second layer.

Preferably, the first film has a free shrink in the transverse direction at 85 ° C of at least about 5%; more preferably, at least about 8%; more preferably, at least about 10%; more preferably at least about 15%; more preferably, at least about 18%; more preferably, at least about 20%; more preferably, at least about 22%; more preferably, at least about 24%; more preferably, at least about 26%; more preferably, at least about 28%; more preferably, at least about 30%; and more preferably, at least about 32%.

Preferably, the first film has a free shrink in the longitudinal direction at 85 ° C of at least 5%; more preferably at least 8%; more preferably at least 10%; more preferably at least 12%; more preferably at least 14%; more preferably, at least about 16%; more preferably, at least about 18%; more preferably, at least about 20%; and more preferably, at least about 22%.

Preferably, the first film has a total free shrink at 85 ° C (i.e., L + T at 85 ° C) of at least 5%, more preferably at least 10%, more preferably at least 20%, plus preferably at least 25%, more preferably at least 30%, more preferably at least 35%, more preferably at least 40%, more preferably at least 50%, more preferably at least 52%, more preferably at less 54%, more preferably at least 56%, more preferably at least 58%, and more preferably at least 60%.

The first film of the present invention preferably has a total thickness of from about 0.01 to about 0.25mm, more preferably from about 0.03 to about 0.20mm, more preferably from about 0.04 to about 0.18 mm, even more preferably about 0.06 to about 0.16 mm; more preferably, from about 0.07 to about 0.14mm; more preferably about 0.07 to about 0.13mm; more preferably, from about 0.07 to about 0.12mm; more preferably, from about 0.07 to about 0.11mm; and more preferably, from about 0.07 to about 0.10mm. Preferably, the first film is less than about 0.2mm thick, more preferably less than about 0.18mm; more preferably, less than about 0.16mm; more preferably, less than about 0.14mm; more preferably less than about 0.13mm; and more preferably, less than about 0.12mm; and more preferably, less than about 0.11 mm. Preferably, the first film also has a thickness of at least about 0.01mm; more preferably, at least about 0.03mm; more preferably, at least about 0.04mm; more preferably, at least about 0.06mm; and more preferably, at least about 0.07mm.

ES 2 239 985 T3

Preferably, the first film according to the present invention comprises a total of 1 to 20 layers; more preferably 1 to 10 layers; more preferably 1 to 8 layers; more preferably 1 to 6 layers. Preferably, the multilayer film of the invention consists of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 layers. Although the adjacent layers may have identical or similar compositions, preferably the adjacent layers have different compositions.

The first heat shrinkable film of the present invention can be irradiated and / or corona treated. The term "irradiation" refers to subjecting a film material to radiation such as corona discharge, plasma, flame, ultraviolet radiation, X-rays, gamma rays, beta rays and treatment with high energy electrons, altering any of these treatments. the surface of the film and / or inducing crosslinking between molecules of the contained polymers. In US Patent No. 4,064,296 (Bornstein et al.) The use of ionizing radiation to crosslink polymers present in a polymeric structure is described. Irradiation can produce a crosslinked polymer network and improves the orientation process used to make the first heat shrinkable film. In addition, the irradiation process can improve the impact resistance of the first heat shrinkable film. It has also been discovered that for certain preferred films of this invention, the irradiation process can improve the overall free shrinkage of the first film, especially at higher dosages. This discovery can be used to produce a first heat shrink film having a total free shrink closer to that of the second heat shrink film, thus providing good compatibility between the total free shrink of the first film and the second film. This full free shrink compatibility can provide a superior patch pocket that exhibits fewer punctures and other leak points. Irradiation can also improve interfold adhesion between the various layers of the first film, if the first film is a multilayer film.

Radiation dosages are referred to herein in terms of the radiation unit "RAD", denoting one million RADS, also known as megarad, "MR", or in terms of the radiation unit kiloGray (kGy), representing 10 kiloGrays 1 MR, as is known to those skilled in the art. To produce crosslinking, the polymer is subjected to a dosage of suitable high energy electron radiation, preferably using an electron accelerator, a dosage level being determined by conventional dosimetry methods. A suitable radiation dosage of high energy electrons is in the range of up to about 13-200 kGy, more preferably about 30-175 kGy, more preferably 50-150 kGy. Preferably, the radiation dosage is at least about 20 kGy; more preferably at least 40 kGy; more preferably at least 50 kGy, more preferably at least 60 kGy; more preferably at least 70 kGy, more preferably at least 80 kGy; more preferably at least 90 kGy; more preferably at least 100 kGy, more preferably at least 110 kGy; more preferably at least 120 kGy; and more preferably at least 125 kGy. Preferably, the radiation dosage is less than 300 kGy; and more preferably less than 200 kGy. Preferably, the irradiation is carried out by an electron accelerator and the dosage level is determined by conventional dosimetry methods. However, other accelerators such as a Van de Graaf or resonance transformer can be used. The radiation is not limited to electrons from an accelerator, as any ionizing radiation can be used. The preferred amount of radiation depends on the film and its end use.

Preferably, the difference between the total free shrinkage of the second film and the total free shrinkage of the first film, both measured at 85 ° C, is less than about 60%, 50%, 40%, 35%, 30% and 25%.

In forming the first heat shrinkable film according to the invention, various combinations of layers can be used. Below are some examples of preferred combinations where letters are used to represent film layers. Although only 1-3 layer embodiments are provided for illustrative purposes, the multilayer films of the invention may also include more layers, as follows:

"A" represents a first component comprising an ethylene / alpha-olefin copolymer having a density greater than about 0.915 g / cm³, as described in the description of the first component.

"B" represents a second component comprising a heterogeneous ethylene / alpha-olefin copolymer having a density less than about 0.915 g / cm³ , as described in the description of the second component.

"C" represents a polymer comprising at least one member selected from the group consisting of polyolefin, polystyrene, polyamide, polyester, and polyurethane, as described in the description of the second layer.

"X" represents a layer comprising an ethylene / alpha-olefin copolymer having a density greater than about 0.915 g / cm³, as described in the description of the first component.

"Y" represents a layer containing a second component comprising a heterogeneous ethylene / alpha-olefin copolymer having a density less than about 0.915 g / cm³, as described in the description of the second component.

"Z" represents a layer comprising at least one member selected from the group consisting of polyolefin, polystyrene, polyamide, polyester, and polyurethane, as described in the description of the second layer.

ES 2 239 985 T3

The film can be a monolayer film comprising (1) A and B, or (2) A, B and C. Some preferred two-layer films are depicted in Table II below.

TABLE II

<td>Movie No.</td><td>I^to cap</td><td> 2^to cap</td>

<td> 1</td><td>TO</td><td>B</td>

<td> 1</td><td>TO</td><td>"B + A</td>

<td> 3</td><td>TO</td><td>B + C</td>

<td> 4</td><td>TO</td><td>B + C + A</td>

<td> 5</td><td>B</td><td>A + B</td>

<td> 6</td><td>B</td><td>A + C</td>

<td></td><td>B</td><td>A + B + C</td>

<td> 8</td><td>"A + B</td><td>C</td>

<td> 9</td><td>A + faith</td><td>A + B</td>

<td> 10</td><td>A + B</td><td>"A + C</td>

<td> 11</td><td>"A + B</td><td>B + C</td>

<td> 12</td><td>A + C</td><td>B + C</td>

<td> 13</td><td>T + C</td><td>A + B</td>

<td> 14</td><td>B + C</td><td>A + C</td>

Some preferred three-layer films include: X / Y / X; X AND Z; Y / X / Y; Y / X / Z; X / Z / Y; A + B / Z / C; A + C / Z / B; and B + C / Z / A. In any one of these multilayer structures, a plurality of layers of the same compositions or different modified compositions can be formed and one or more bonded layers can be added.

Examples

The identity of the resins used in Examples 1-11 is as follows:

TABLE III

<td>Resin Code</td><td>Tradename</td><td>Fusion Index</td><td>Density (g / m³)</td><td>Comonomer Type / Comonomer Content</td><td>Maker</td>

<td>VLDPE</td><td>ATTANE</td><td> 0,8</td><td> 0,905</td><td>11.5 &amp; / C,</td><td>Dow</td>

<td>N ° 1</td><td> 4203</td><td></td><td></td><td></td><td></td>

<td>LLDPE N ° 1</td><td>DOWLEX 2045.03</td><td> 1,1</td><td> 0,920</td><td>0.5% / C,</td><td>Dow</td>

<td>LLPbE Ñ^or 2</td><td>SClaIr ' 11C1</td><td>Or, 8</td><td> 0^18</td><td> ...</td><td>Nova Chemi- cals</td>

<td>EVA N ° 1</td><td>'ESCÓRÉNE' LD318.92</td><td> 2,0</td><td>Ί5Ϊ930</td><td>Acetate vinyl / 9%</td><td>Exxon Che- mical Company</td>

<td>EVAN^d2</td><td>choose me * LD761.36</td><td> 5,7</td><td> 0^50</td><td>Acetate vinyl / 28%</td><td>Exxon Che- mical Company</td>

<td>Additive N ° 1</td><td>L-710-AB (anti-blocking agent and additive of fluorescence UV)</td><td> 4,5</td><td> ”07945</td><td>T7A ^!</td><td>Bayshore Industrial, Inc.</td>

<td>HEAO N ° 1</td><td>'A'FFIÑITV DPF 1150.01</td><td> 0,9</td><td>0.90ό</td><td>C_g/ 12.5fc</td><td>Dow</td>

ES 2 239 985 T3

Example 1

Patch Film No. 1 (Comparison)

A coextruded double layer tubular tape having a thickness of approximately 17 thousandths of an inch (0.431 mm) was molded, containing an "A layer" that made up 82 percent of the tape thickness and a "B layer" that made up 18% of the tape thickness. Layer A was comprised of a blend of 87 percent VLDPE # 1, 10 percent by weight EVA # 1, and 3 percent additive package # 1. Layer B was comprised of 100% EVA No. 2. The double-layer tube was cooled until a solid phase was obtained in a water bath, and electronically cross-linked with an exposure level of 90 to 100 kilograys (kGy).

The resulting cross-linked double-layer tube was heated by hot water to 205-212 ° F and subsequently oriented by stretching and extending approximately 300 to 330 percent, in each of the machine and transverse directions respectively, using a trapped air bubble held between two sets of pressure cylinders. Orientation produced a 2.25 mil (0.057 mm) thick double layer film in the form of a tube.

TABLE IV

<td>Layer Designation</td><td>Layer Function</td><td>Chemical Identity of the Layer</td><td>Layer thickness (thousandths of an inch)</td>

<td>TO</td><td>From outside, resistant to drilling</td><td>87% VLDPE No. 1 10% EVA No. 1 3% Additive Package # 1</td><td>1.84 (46.73 pm)</td>

<td>B</td><td>Inner Union</td><td>100% EVA No. 2</td><td>0.41 (10.4 pm)</td>

Film # 1 was determined to have free shrink at 185 ° F (by ASTM 2732) and instrumented impact (by ASTM D3763), as indicated in Table VIII below.

An alternative to patch film # 1 is a two-layer film approximately 2.25 thousandths of an inch (57.1 pm) thick, with approximately 82 percent of the film thickness being layer A, and with about 18 percent of the film thickness being layer B, which was the layer on the inside of the 2-layer tube. This film could be produced using a flat die, rather than a circular die, followed by cooling, crosslinking, heating, and orientation.

Example 2

Patch Movie N ° 2

Patch film No. 2 was prepared by the same processes used to make patch film No. 1, except that in patch film No. 2 layer A was composed of a mixture of 43.5 Weight percent No. 1 LLDPE, 43.5 weight percent VLDPE No. 1, 10 weight percent EVA No. 1, and 3 percent additive package No. 1. Layer B, which was the layer on the inside of the two-layer tube, was identical to layer B of patch film No. 1. In addition, in patch film No. 2, layer A constituted a 82 weight percent of the tape thickness and layer B made up 18 percent of the tape thickness. Table VIII below shows the results of free shrinkage and instrumented impact of patch film No. 2.

Example 3

Patch Film N ° 3 (Comparative)

Patch Film No. 3 was prepared by the same processes used to make Patch Film No. 1, except that in Patch Film No. 3, Layer A was composed of a mixture of 87 percent. weight percent LLDPE # 1, 10 weight percent EVA # 1, and 3 weight percent additive package # 1. Layer B was identical to layer B of patch film N 1 and was the layer on the inside of the two-layer tube. In addition, in patch film No. 3, Layer A made up 82 percent of the tape thickness, and Layer B made up 18% of the tape thickness. The free shrinkage and instrumented impact results for patch film # 3 are provided in Table VIII below. Patch film # 3 was a comparative example, as it did not contain VLDPE.

ES 2 239 985 T3

TABLE V

<td>Movie No.</td><td>Contraction Free at 185 ° F (%)</td><td>Load Maximum Impact (N)</td><td>Load Maximum Indexed (N / thousandth of an inch)</td><td>Energy from Impact from Break (J)</td><td>Indexed Impact Energy (J / / thousandth of an inch)</td><td>Thickness (thousandth of an inch)</td><td>Composition that Provides Impact (% in layer of the outer part)</td>

<td> 1</td><td> 75</td><td> 15$</td><td>60 (2.36 N / m)</td><td>i, i</td><td>03 (0.032 J / m)</td><td>2. 3. 4 (67.05 p.m)</td><td>~ S7% dé " VLDPE No. 1 10 of EVA N ° 1</td>

<td> —2—</td><td> 61</td><td>Ϊ52</td><td>71 (2.79 N / m)</td><td> 575</td><td>1.11 (0.043 J / m)</td><td>2 / ñ (68.83 p.m)</td><td>433% VLDPE No. 1 43.5% LLDPE No. 1 10 of EVA N ° 1</td>

<td> 3</td><td> 49</td><td> 195</td><td>78 (3, () 1 N / m)</td><td> 2,9</td><td>Γϊδ (0.045 J / m)</td><td>230 (63.5 p.m)</td><td>"87% give" LLDPE No. 1 10 of EVA N ° 1</td>

Patch Movie N ° 4

A coextruded double-layer tubular tape was molded having a thickness of approximately 26 thousandths of an inch (0.66 mm), the tape having an A layer that made up 85 percent of the tape thickness and a B layer that made up a 15 percent of the tape thickness. Layer A was comprised of 75 weight percent VLDPE No. 1, 20.5 weight percent LLDPE No. 2, and 4.5 weight percent additive package No. 1. Layer B, which was the layer on the inside of the two-layer tube, was composed of 100 weight percent EVA No. 2. The two-layer tube was cooled in a water bath until a solid phase, and electronically crosslinked with a 500 keV beam at a level of approximately 90-110 kGy.

The resulting cross-linked bilayer tube was heated by steam to a temperature of about 220 to 226 ° F (104.44-107.78 ° C) and then by hot air to a temperature of about 270 to 275 ° F (132, 22135 ° C). Subsequently, orientation was performed by stretching and spreading approximately 320-400 percent in the machine and transverse direction respectively, using a trapped air bubble held between two sets of pressure cylinders. Orientation produced a 2.25 mil (57.1 pm) two-layer film in the shape of a tube.

After orientation, the tube resulting from the heat-shrinkable flat tube was passed through a pair of heated pressure cylinders, causing the inner B-layer to bond with itself as the tube collapsed, according to U.S. Patent No. 4,765,857 to Ferguson. This produced a four layer film, with the intermediate layers being layer B on the inside of the tube bonded to itself. The resulting film had a nominal thickness of 4.5 mils (0.114 mm). Patch film No. 4 was made up of the above three layers, the middle layer being made up of the inner tube layer. Patch film # 4 was determined to have the 185 ° F free shrink (via ASTM 2732) and instrumented impact (via ASTM D3763) values ​​listed in Table VIII below. The composition of patch film No. 4 is indicated in Table VI below.

ES 2 239 985 T3

TABLE VI

<td>Layer Designation</td><td>Layer Function</td><td>Chemical Identity of the Layer</td><td>Layer thickness (thousandths of an inch)</td>

<td>TO</td><td>From outside, resistant to drilling</td><td>75% of VLDPÉ N^or 1 20.5% LLDPE No. two 4.5% Additive Package # 1</td><td>1.91 (48.5 pm)</td>

<td>B</td><td>Internal, united and self- welded</td><td>100% EVA No. 2</td><td>0.34 (8.6 pm)</td>

An alternative to patch film # 4 is a two-layer flat film (i.e., a non-annular film) with a thickness of approximately 4.5 mils (0.11 mm), approximately 82 being composed of percent of the film in layer A and being made up about 18 percent of the film in layer B. This film could be produced using a flat die, rather than a circular die, followed by cooling, crosslinking, heating and orientation.

Patch Film No. 5 (Comparison)

Patch Film No. 5 was prepared by the same process used to make Patch Film No. 4, except that in Patch Film No. 5, Layer A was 95.5 percent by weight of VLDPE # 1 and 4.5 percent by weight of additive package # 1. Layer B was identical to layer B of patch film # 4. In addition, in patch film # 5, Layer A made up 85 percent of the tape thickness, while Layer B, which was the inner tube layer, made up the remaining 15 percent of the thickness. of the tape. The free shrinkage of the No. 5 patch film, the instrumented impact, and the results of the conventional Covered Bone Puncture Bag Drop Test (Covered Bone Puncture Bag Drop Test) are listed below in Table VIII.

Patch Film No. 6 (Comparative)

Patch Film No. 6 was prepared by the same processes used to make Patch Film No. 4, except that in Patch Film No. 6, Layer A was comprised of 95.5 percent by weight of LLDPE # 2 and 4.5 percent by weight of additive package # 1. Layer B was identical to layer B of patch film # 4. In addition, in patch film # 6, Layer A made up 85 percent of the tape thickness, while Layer B, which was the inner tube layer, made up the remaining 15 percent of the thickness. of the tape. The results of free shrinkage, instrumented impact, and the conventional bag drop test to check for perforation by covered bones are listed below in Table VIII. Patch Film No. 6 is a comparative patch film, because it does not contain any VLDPE.

Patch Film No. 7 (Comparison)

A # 7 patch film was prepared by the same processes used to make the # 4 patch film, except that the # 7 patch film was composed of five layers having C / A / B // B / A / C. Layer C was comprised of 75 weight percent VLDPE No. 1, 20.5 weight percent LLDPE No. 2, and 4.5 weight percent additive package. No. 1. Layer B was identical to layer B of patch film No. 4. Layer A was composed of 50 weight percent homogeneous ethylene / alpha-olefin No. 1 ("HEAO No. 1"), 45.5 weight percent LLDPE No. 2, and 4.5 percent by weight. Additive package weight percent No. 1. Additionally, in patch film No. 7, Layer A made up 60 percent of the tape thickness, Layer B made up 15 percent of the tape thickness, and Layer C made up 25 percent of the tape's thickness.

ES 2 239 985 T3

TABLE VII

<td>Layer Designation</td><td>Layer Function</td><td>Chemical Identity of the Layer</td><td>Layer thickness (thousandths of an inch)</td>

<td>-c-</td><td>From the outside, puncture resistant</td><td>75% VLDPE # 1 20.5% LLDPE No. two 4.5% Additive Package # 1</td><td>0.56 (14.22 pm)</td>

<td>B</td><td>Inner union and self-welding</td><td>100% EVA No. 2</td><td>0.34 (8.63 pm)</td>

<td>TO</td><td>Internal, resistant to drilling</td><td>50% HEAO N ° 1 45.5% LLDPE No. two 4.5% Additive Package # 1</td><td>1.35 (34.29 pm)</td>

The results of free shrinkage, instrumented impact, and the conventional bag drop test to check for perforation by covered bones are shown in Table VIII below. Patch Film No. 7 is a comparative patch film in that the majority layer was made from a blend of 50 weight percent homogeneous ethylene / alpha-olefin copolymer and 45.5 weight percent LLDPE.

TABLE VIII

<td>Movie- butt No.</td><td>Free Shrinkage at 185 ° F (%)</td><td>Load Maxi made Im- covenant (N)</td><td>Load Maximum Indexed (N / mil made inch)</td><td>Impact Energy of Sign ra (J)</td><td>Energy Index since Break (J / / mil made flea- gives)</td><td>Thickness (thousandths of an inch)</td><td>Test Conventional Drop Ribs¹(%) (n = 96)</td><td>Composition of Majority Layer</td>

<td> 4</td><td></td><td> 530</td><td>98 (3.85 N / m)</td><td> 9,4</td><td>1.74 (0.06 J / m)</td><td>5.4 (0.137 mm)</td><td> ¿5</td><td>Mix of VLDPE and LLDPE</td>

<td> 5</td><td>_g7</td><td> 527......</td><td>98 (3.85 N / m)</td><td> 9,5</td><td>1.75 (0.06 J / m)</td><td>5.4 (0.137 mm)</td><td>3X5</td><td>VEDFE</td>

<td> 6</td><td> 28</td><td> ~355^-</td><td>1Ú1 (3.9? (N / m)</td><td> 6,3</td><td>1.40 ..... (0.055 J / m)</td><td>4.5 (0.114 mm)</td><td>3X5</td><td>....... LLDPE</td>

<td> 7</td><td> 48</td><td> 482</td><td>93 (3.66 '...... N / m)</td><td>SW</td><td>1.54 (0.060 J / m)</td><td>5.2 (0.132 mm)</td><td>357S</td><td>Mix of HEAO and LLDPE</td>

¹ Bone perforation was measured according to the conventional bag drop test for covered bone perforation described above.

The Conventional Rib Drop Test

The standard rib drop test was performed as follows. Two pieces of cut beef back ribs (total package weight 4 to 5 pounds (1.8-2.2 kg)) were placed in a 7-inch (17, 78 cm) in width and 24 inches (60.96 cm) in length, referred to as a "wide patch bag" due to the fact that the patches extend beyond the side edges of the bag. The

ES 2 239 985 T3 film on the bag was as indicated in Table I, presented above, and had a thickness of 2.4 mils (60.96 μιη). Only the film on the patch varied with the test being performed. The patch bag had a patch attached to each flat side, with each patch having a length of 19 inches (48.26 cm) and a width of 8.5 inches (21.59 cm). The bottom edge of the patches was placed approximately 5/16 inches above the end seal of the bag. The patches extended beyond the side edges of the bag, the protruding portions of the patches adhering to each other. The top 4 11/16 inches of the bag were not covered by a patch on the flat side. The patch bag, which had the two cut ribs inside, was placed in a Cryovac® Model 8600B-18 rotary chamber vacuum packaging machine, which removed the air from the bag, sealed the bag and cut the excess bag length. The resulting package was then processed through a Cryovac® Model 6570E hot water shrink tunnel in which the water temperature was 200 ° F (93.33 ° C). The bag contracted to fit the product as a result of passage through the shrink tunnel.

Test data was generated as follows. Six different patch formulations were tested for puncture resistance in actual use. The patch bags for each of the formulations were tested with six different sets of cut beef short ribs, with 16 ribs per set. For the first series of ribs, the first patch bag formulation was tested by packaging the ribs in pairs each of eight patch bags of a first formulation. The packages were drained of air, sealed, and excess length removed, as described above. Afterwards, each air-emptied package was put on end, that is, with the tips of the ribs facing down (the most vulnerable position) in a cardboard box with a width of 400 mm by a length of 600 mm by a height of 235mm manufactured by Weyerhauser of Amarillo, Texas, the case being of a type known as XB3-07046. The box, which had all eight packages inside, each rib tips down, dropped once from a height of 3 feet (91 cm), using an Accu Drop® 130 drop tester, produced by MT Lab, Lab Division, of Onondaga Street, Skaneateles, New York, 13152. The packages were then removed from the box and inflated with air while submerged to determine if the patch had been punctured. The total number of packages with perforated patches (ie, leak points) was recorded for the series of eight packages tested.

The ribs were then removed from the tested bags and placed in a second series of eight patch bags, each being the second patch formulation, which of course differed from the first patch formulation. The test was then repeated in the same manner as the first series of patch bags, ie, as described above; it was repeated again for a third series of patch bags, and so on, until six different series of patch bags were tested with the same series of cut beef short ribs. To generate this data series, a total of 48 bags were dropped.

However, as the ribs could, in theory at least, have become dull from repeated falls, repetitive trials were structured to allow each set of patch bags to be the first set tested with a new set of ribs, the second set tested, and so on. successively. To accomplish this, a second data set was generated in an identical manner to the generation of the first data set, with the exception that the second patch bag formulation was the first tested, etc., with the first formulation being the one tested. last rehearsed of the series and, otherwise, the rehearsal order being the same. A third data set was then generated with the third patch bag formulation being the first tested, etc., up to six different data sets, each patch bag formulation being the first tested with a particular set of ribs, the second tested , etc. In this manner, each series of patch bags was subjected to total perforation abuse which, in theory, was equivalent to the other series of patch bags tested. Subsequently, after the six data series were generated as a first "data grid", the entire data grid was repeated with the same ribs, in the same order as in the first data grid. In total, 576 data points were generated, with each patch bag formulation being dropped to produce a total of 96 data points, including data from the two grids.

Surprisingly, the bone puncture resistance of the film containing the VLDPE / LLDPE blend was higher than if VLDPE alone or LLDPE alone were present as a bone puncture resistant polymer. Compare the results of the standard rib drop test for Example 4 versus Examples 5, 6 and 7. Furthermore, the patch film comprising the VLDPE-LLDPE blend, if substantially free of ethylene / vinyl acetate copolymer and / or homogeneous ethylene / alpha-olefin copolymer, i.e., preferably contained no more than 30 percent of these polymers (more preferably no more than 25, 20, 15, 10, 5, 0), it provided the patch with increased resistance to bone piercing while also providing relatively high free shrinkage at a temperature of, for example, 85 ° C. That is, even though the patch is made from a blend of VLDPE and LLDPE, if substantial amounts of ethylene / vinyl acetate copolymer and / or homogeneous ethylene / alpha-olefin copolymer are present in the patch film, the strength is reduced. to perforation by bones. Preferably, the heat shrinkable patch film comprises a VLDPE-LLDPE blend, with no EVA or homogeneous ethylene / alpha-olefin copolymer present in the patch film.

Patch Film No. 8 (Comparison)

A coextruded double-layer tubular tape was molded, having a thickness of approximately 26 mils (0.66 mm), the tape having an A layer that constituted 85% of the tape thickness and a B layer that constituted a 15% of the tape thickness. Layer A was composed of 97% LLDPE No. 2 and 3 percent Additive No. 1. Layer B was composed of 100% EVA No. 2. The double-layer tube was cooled until

ES 2 239 985 T3 a solid phase was obtained in a water bath and electronically crosslinked with a 500 keV beam at a level of about 90-110 kGy.

The resulting cross-linked double-layer tube was steam heated to a temperature of approximately 220-275 ° F (104.44-107.78 ° C), and subsequently heated with hot air to approximately 270-275 ° F (132.22- 135 ° C). Subsequently, orientation was performed by stretching and spreading approximately 320-400%, in each of the machine and transverse directions respectively, using a trapped air bubble held between two sets of pressure cylinders. The orientation produced a nominally 2.25 mil (0.057 mm) double layer film in the shape of a tube.

After orientation, the resulting heat-shrinkable flat film tube was passed through a pair of hot pressure cylinders, causing the inner B-layer to bond to itself as the tube collapsed. This produced a four layer film, with the interlayers being the inner part B layer bonded to itself. The resulting film had a nominal thickness of 4.5 mils (114.3 jum). The composition of film No. 8 was indicated in Table IX, presented below.

TABLE IX

<td>Layer Designation</td><td>Layer Function</td><td>Chemical Identity of the Layer</td><td>Layer thickness (thousandths of an inch)</td>

<td>TO</td><td>External, resistant to drilling</td><td>97% LLDPE No. 2 3% Additive Package # 1</td><td>1.91 (48.5 pm)</td>

<td>fc ......</td><td>Inner union</td><td>10056 of EVA N ° 2</td><td>0.34 (8.63 pm)</td>

Patch film No. 8 was composed of the above three layers, the middle layer of the inner tube layer being adhered to itself. Patch film # 8 was determined to have 185 ° F free shrink (by ASTM 2732) and instrumented impact (by ASTM D3763) as indicated in Table X below.

An alternative to patch film # 8 is a two-layer film approximately 4.5 mils (114.3 jum) thick, with approximately 85% of the film being made up of layer A and approximately 15% of the film made up of layer B. This film could be produced using a flat die, rather than a circular die, followed by cooling, crosslinking, heating and orientation.

Patch Movie N ° 9

Patch Film No. 9 was prepared by the same processes used in Patch Film No. 8, except that in Patch Film No. 9 Layer A was comprised of a 50 percent mix in weight of VLDPE # 1 and 47 percent by weight of LLDPE # 2 and 3 percent by weight of additive package # 1. Layer B was identical to layer B of patch film # 8 . In addition, in patch film No. 9, Layer A made up 85 percent of the tape thickness and Layer B made up 15 percent of the tape thickness. Free shrinkage and instrumented impact for patch film # 9 are shown in Table X below.

Patch Film N ° 10

Patch Film No. 10 was prepared by the same processes used in Patch Film No. 4, except that in Patch Film No. 10, Layer A was composed of a 75 percent blend. by weight of VLDPE No. 1 and 23 percent by weight of LLDPE No. 2 and 3 percent by weight of additive package No.

1. Layer B was identical to Layer B of Patch Film No. 8. In addition, in Patch Film No. 10, Layer A made up 85 percent of the tape thickness and Layer B made up 15 percent of the tape. hundred of the thickness of the tape. Free shrinkage and instrumented impact for patch film # 10 are shown in Table X below.

Patch Film No. 11 (Comparison)

Patch Film No. 11 was prepared by the same processes used in Patch Film No. 8, except that in Patch Film No. 11, Layer A was comprised of a 97 percent blend. by weight of VLDPE No. 1 and 3 percent by weight of additive package No. 1. Layer B was identical to layer B of patch film No. 8. In addition, in patch film No. 11, Layer A made up 85 percent of the tape thickness and Layer B made up 15 percent of the tape thickness. Free shrinkage and instrumented impact for patch film # 11 are shown in Table X below.

ES 2 239 985 T3

TABLE X

<td>Movie of Patch No.</td><td>Total Free Shrinkage at 185 ° F (%)</td><td>Maximum Impact Load (N)</td><td>Load Maximum Indexed (N / thousandth of an inch)</td><td>Impact Energy of Break (J)</td><td>Energy Indexed Breaking (J / thousandth of an inch)</td><td>Thickness (thousandths of an inch)</td><td>Composition of Majority Layer</td>

<td>8 (Comparison he)</td><td> 55</td><td> 513</td><td>112 (4,409 N / m)</td><td> 6,7</td><td>Γ76 ^!(0.057 J / m)</td><td>4.6 (116.8 p.m)</td><td>97% of LLDPE N ° 2</td>

<td>9 (Inven- tion)</td><td> 56</td><td> 529</td><td>110 (4,330 N / m)</td><td> 8.1</td><td>Ñ69 (0.066 J / m)</td><td>4.8 (121.92 pin)</td><td>Mix of 50% VLDPE No. 1 and 47% of LLDPE No. two</td>

<td>10 (Invention)</td><td> 44</td><td> 509</td><td>106 (4,173 N / m)</td><td> 8,0</td><td>Ñ57 (0.065 J / m)</td><td>4.8 (121.92 p.m)</td><td>Mix of 75% VLDPE No. 1 and 23% of LLDPE No. two</td>

<td>eleven (Comparison he)</td><td> 48</td><td> 479</td><td>100 (3,937 N / m)</td><td> 7,5</td><td>1.56 (0.061 J / m)</td><td>4.8 (121.92 p.m)</td><td>97% of VLDPE No. 1</td>

Examples 8-11 demonstrate that films for patching according to the present invention exhibit higher breaking energy relative to various comparative films designed for patching. Higher breaking energy is associated with better performance in a conventional rib drop test.

The data from the various examples above indicate that the films of this invention (for example, the films of Examples 2, 4, 9 and 10) have an impact energy that is comparable to or greater than the impact energy of various films of prior art.

A blend of a high crystallinity ethylene / alpha-olefin copolymer and a low crystallinity heterogeneous ethylene / alpha-olefin copolymer has been found to be advantageous for use in a heat shrinkable patch film adhered to a heat shrink bag film. Although the high-crystallinity ethylene / alpha-olefin copolymer provides higher stiffness (ie, higher modulus) and higher abrasion resistance, it is difficult to spread films dominated by high-crystallinity polymers. The low crystallinity polymer provides greater elongation (i.e., it is easier to extend, especially at relatively low solid-state orientation temperatures), as well as providing greater puncture resistance than ethylene / alpha-olefin copolymers of high crystallinity.

Importantly, the combination of a high crystallinity ethylene / alpha-olefin copolymer and the heterogeneous low-crystallinity ethylene / alpha-olefin copolymer, together with crosslinking, can be used to optimize link chain concentration, providing a best combination of properties, such as the combination of impact resistance, puncture resistance and abrasion resistance. In addition, it is believed that the combination of high crystallinity ethylene / alpha-olefin copolymer and low crystallinity heterogeneous ethylene / alpha-olefin copolymer can provide better impact resistance at low temperatures, due to the presence of the low crystallinity polymer. in the movie. The incorporation of the component with the highest crystallinity provides greater resistance to abrasion, especially on the outer surface of the film.

In prior art commercial patch bags, the dominance of the patch film by the high crystallinity ethylene / alpha-olefin copolymer has made it difficult to obtain high abrasion resistance in combination with high free shrinkage, because high-density, high-crystallinity ethylene / alpha-olefin copolymers (especially those with a value of 0.92 or higher) have forced the patch film to have a total free shrink at 185 ° F less than The desired. As a result, the total free contraction of the patch has been

ES 2 239 985 T3 significantly less than the total free shrinkage of the bag to which the film has adhered. As a result, the total free shrinkage of the patch-bag laminate has been less than desired. The minor shrinkage of such a patch bag adversely affects the appearance of the resulting packaged product. More particularly, the high crystallinity LLDPE in the patch film makes such films more difficult to orient.

However, it has been found that this drawback can be reduced or eliminated by providing the patch with a heterogeneous low crystallinity ethylene / alpha-olefin copolymer to facilitate film orientation. If the low crystallinity polymer is an ethylene / alpha-olefin copolymer, it must be a heterogeneous ethylene / alpha-olefin copolymer because the higher molecular weight distribution of such polymers provides the film with abrasion resistance and abrasion resistance. impact that is greater than if the low crystallinity polymer were a homogeneous ethylene / alpha-olefin copolymer. In addition, the heterogeneous ethylene / alpha-olefin copolymer provides increased free shrinkage. Compare Examples 4 and 7 above. As can be seen, the use of a heterogeneous ethylene / alpha-olefin copolymer with a density of at least 0.915 provides superior impact strength, as measured by indexed energy at break, and superior performance in the conventional rib drop test. . This is quite unexpected.

Finally, providing the patch film with a total of the high-crystallinity ethylene / alpha-olefin copolymer and the low-crystallinity heterogeneous ethylene / alpha-olefin copolymer in an amount of at least 70 percent, based on total weight of the film, the film has better properties of impact resistance and abrasion resistance, compared to films containing other components, such as ethylene / vinyl acetate copolymer, in an amount greater than 30 percent, with respect to the total weight of the film.

Although, in general, the bag according to the present invention can be used in the packaging of any product, the bag of the present invention is especially advantageous for packaging food products, especially fresh meat products containing bone, especially cut bone ends. on or near the surface of the fresh meat product. Preferably, the meat product comprises at least one member selected from the group consisting of poultry, pork, beef, lamb, goat, horse, and fish. More preferably, the meat product comprises at least one member selected from the group consisting of ham, spare ribs, picnic, back rib, tenderloin, short rib, whole turkey, and pork tenderloin. Even more preferably, the meat product comprises bone-in ham, including both smoked and processed ham, fresh bone-in ham, turkey, chicken, and jerky. Ribs are a particularly preferred cut for packaging in the patch bag of the present invention.

Although the present invention has been described in connection with preferred embodiments, it should be understood that modifications and variations may be used without departing from the principles and scope of the invention, as will be readily understood by those skilled in the art. Accordingly, such modifications can be practiced within the scope of the following claims.