Thermoplastic multi-layer packaging film and bags made therefrom

Description: TECHNICAL FIELD [Detailed description of the invention]

The present invention relates to thermoplastic multilayer heat shrinkable (ie, oriented) packaging films and bags or pouches formed from them. In particular, the present invention relates to films and bags having excellent heat shrinkage, orientation rate and abuse resistance. The heat-shrinkable thermoplastic film is used for packaging non-food products and food products such as meat, cheese, and edible birds. Many attempts have been made to combine abuse resistance or strength at all temperatures with excellent shrinkage, and also to formulate films at higher speeds. However, there is still room for improvement. The film known from US Pat. No. 3,741,253 [Borax] has a core layer of vinylidene chloride copolymer (saran) between the layer of ethylene-vinyl acetate copolymer and the layer of crosslinked ethylene-vinyl acetate copolymer. Including. Ethylene-vinyl acetate copolymer (EVA) has slightly improved properties over conventionally used polyethylene. Vinylidene chloride copolymer is a known barrier material for fluids such as oxygen. As disclosed in US Pat. No. 4,064,296 [Bonrstein], the core layer can also be a hydrolyzed ethylene-vinyl acetate copolymer (EVOH). It has the same oxygen barrier properties as vinylidene chloride copolymers and offers the advantage of being able to irradiate without discoloration, which will be described in detail below. A blend of low density polyethylene and ethylene vinyl acetate copolymer in the blended barrier film is disclosed in US Pat. No. 4,457,960 [Newsome], which claims the blended multilayer polymer film. The film consists of the following layers: (a) a first barrier layer, which has two opposing surfaces, (b) a second layer attached to one of the surfaces, the second layer is 10 ~ 90% linear low density polyethylene and 90-10% ethylene vinyl acetate, and (c) the other third layer adhering to the surface, the composition of the third layer is (i) ethylene vinyl acetate and (ii) Selected from the group consisting of a blend of 10-90% linear low density polyethylene and 90-10% ethylene vinyl acetate. So-called linear low-density polyethylenes have ethylene and copolymerized higher alpha-olefins, such as 5-10 carbon atoms / molecule (US Pat. No. 4,076,698) or 3-8 carbon atoms / molecule. (European Patent Application No. 120503, Union Carbide, Issued October 3, 1984) Alpha-olefin copolymers, such as ethylene and butene-1 copolymers, ethylene and octene-1 copolymers. Depending on their density, these materials are linear low density polyethylene (LLDPE) or very low density linear polyethylene (VLDPE) and their separation lines have a density of about 0.910 g / cc. Some properties of VLDPE are described in the following reference book: Plastic Technology, September 1984, p. 113. Plastic technology (Plastic) In the October 1984 issue of Technology), there was another treatise describing VLDPE entitled "A new type of polyethylene combines flexibility, toughness and thermal resistance". This paper lists a number of properties of VLDPE and compares them to EVA. VLDPE is also mentioned in a pamphlet of a company entitled "Stamylex PE", which was swelled by DMS in the Netherlands in February 1984. Their properties are described as a unique combination between the properties of standard polyethylene and polyolefin rubbers. Their sealability and compatibility with other polymers are stated. USSN911,936 (corresponding to European Patent Application No. 0217252, WR Grace, issued April 8, 1987) discloses a thermoplastic multilayer packaging film with excellent heat shrinkage and room temperature sealing properties. doing. If desired, the film has a barrier layer. The seal layer of this film consists of a copolymer of ethylene and higher alpha-olefin, which has a density lower than about 0.920 g / cc. Specifically, when having a copolymer of ethylene and butene, the comonomer content should be about 10-20% by weight based on the copolymer. Such copolymers are about 0.915 g / cm³Has a lower density. When using a copolymer of ethylene and octene, the conomonomeric content should be about 12-25% by weight based on the copolymer. Such copolymers have densities below about 0.920 g / cc. Also, the ethylene / alpha-olefin copolymer has a polymer up to 50% by weight based on the seal layer composition, which polymer is compatible with the ethylene / alpha-olefin copolymer. Such higher polymers are preferably linear low density polyethylene (LLDPE), linear high density polyethylene (LHDPE), low density polyethylene (LDPE), ethylene vinyl acetate (LLDPE) having a density of 0.920 g / cc or higher. EVA), acid-modified EVA, polypropylene, ethylene / propylene copolymers, Ionomer polymers, and ethylene / alkyl-allylate (EAA) copolymers (where the alkyl moiety has 1-8C atoms), especially ethimene / methyl-acrylate (EMA). ), Ethylene / ethyl-acrylate (EEA) and ethylene / butyl-acrylate (EBA). Ethylene / alkyl-acrylate copolymers that can be blended with ethylene / alpha-olefin copolymers in the heat sealable layer can consist of about 3-30% by weight alkyl acrylate. To achieve optimal results like USSN911,936, C₄Alpha-olefin (butene-1) to C₈When going to alpha-olefin (octene-1), the content of comonomer must be increased. US Pat. No. 4,640,856 [Inventor, Ferguson et al., Applicant, WR Grace] discloses a multilayer thermoplastic barrier film with at least three layers: (a) 0.910 g / cc. It has a layer consisting essentially of very low density polyethylene, a barrier layer selected from the group consisting of (b) (1) a copolymer of vinylene chloride and (2) a hydrolyzed ethylene-vinyl acetate copolymer, (c) heat. The thermoplastic polymer layer, said layer is on the side of the barrier layer opposite to the side of layer (a); and (d) shrinkage of layer (a) controls the shrinkage of the entire multilayer barrier layer, the multilayer film Formulated at 100 ° C (212 ° F) and heat shrinkable, the orientation is about 22 ° C (40 ° F) or more lower than the melting point of the very low density polyethylene. U.S. Pat. No. 4,579,920 [Inventor, Golike, Applicant, DuPont] (July 1986) states that ethylene and at least one C.₈-C₁₈It discloses a method of making a shrinkable film by strecthing a film made from an alpha-olefin copolymer without pre-crosslinking, the copolymers having two copolymers below 128 ° C. It has a well-defined crystal melting point, the difference between these melting points is at least 10 ° C, and stretching is carried out at temperatures within the range defined by these melting points. An object of the present invention, to provide a packaging film and bags made therefrom have a that improved orientation properties than those of very good, or have been used in the past material is Rukoto. This means that the alignment rate during processing should be faster. Another object of the present invention is to provide a packaging film and a bag made from it, which have excellent heat shrinkability compared to the materials used in the past. Another object of the present invention is to provide packaging films and bags made from them, which have the above two properties and also have excellent abuse resistance and strength compared to the materials used in the past. Provided, thereby minimizing the risk of destruction when using bags made from this film material in automated loading methods. Last and most importantly, the object of the present invention is a film that combines these three advantages: excellent shrinkage properties, excellent orientation properties and excellent abuse resistance. And to provide materials for bags. Therefore, according to the present invention, it comprises at least one layer of ethylene and an alpha-olefin copolymer having 6 or more carbon atoms, said ethylene / alpha-olefin copolymer being about 0.910 g / cc. Provided are thermoplastic multilayer heat-shrinkable packaging films characterized by having a density of less than or equal to and a melt index of about 2 or less. Further, according to the present invention, it is composed of an outer polymer layer, a heat-sealing layer and an inner layer between the heat-sealing layer and the outer layer, and the inner layer is ethylene and 6 / molecule or more carbon atoms. The ethylene / alpha-olefin copolymer is composed of an alpha-olefin copolymer having an excellent abuse resistance and shrinkage resistance, which is characterized by having a density of about 0.910 g / cc or less and a melt index of about 2 or less. And a thermoplastic multilayer heat-shrinkable packaging film having a compoundability is provided. Further, according to the present invention, at least one layer of (I) ethylene and an alpha-olefin copolymer having 6 or more carbon atoms is extruded, and the ethylene / alpha-olefin copolymer is about 0.910 g / g. Thermoplastics having a density of cc or less and a melt index of about 2 or less, (II) orienting the extruded polymer in at least one direction, and (III) recovering a heat-shrinkable polymer film. A method for producing a multilayer heat-shrinkable packaging film is provided. On the other side, according to the present invention, there is provided a bag made from the film of the present invention and characterized by having side seals and / or edge seals. Ethylene / alpha-olefin copolymers suitable for use in at least one layer of the thermoplastic multilayer heat-shrinkable packaging film of the present invention are in the class known as very low density linear polyethylene (VLDPE). Belongs. VLDPE is detailed below. Suitable for use in the films of the present invention, VLDPEs have an alpha-olefin comonomer with a density of about 0.910 g / cc or less, a melt index of about 2 or less, and 6 or more carbon atoms. Have. Such comonomer includes, but is not limited to: 4-methyl-pentene-1, hexene-1- and octene-1. Some of the suitable commercially available VLDPEs are: XPRO545 Series [Dow (D)_OW)], XU61512.08L resin [Dow (D)_OW), And DEFD1629 resin [supplied by Union Carbide]. This VLDPE is preferably present in the inner layer of the multilayer film. If desired, the films of the invention have a barrier layer, such as a layer of EVOH or Saran. Typically, in the production of films, a suitable polymer, usually in the form of pellets, is placed in a heated area, where it is melted and heated to its extrusion temperature of the polymer feed, and tubular from an annular die. Extrude as a "blown bubble". Other methods, such as "slot die" extrusion, in which the resulting extrusion is flat rather than tubular, are also well known. If a heat shrinkable film is desired, the film is typically cooled and then "tenter framing" or "trapped". By inflating using "bubbles", the film is stretched, i.e. oriented, to give the film heat shrinkability. This will be described later. If desired, irradiation, typically irradiation with an electron beam, can be performed after stretching the film for compounding, but preferably before stretching the film for compounding. However, in the present invention, such irradiation is unnecessary because a very suitable packaging film can be obtained without using irradiation. The general methods of making and / or making films are detailed below. Next, the irradiation will be described in detail. More specifically, shrinkage, i.e., the production of blended films, generally involves heating a thermoplastic resin material to a temperature at or above the flow point or melting point, eg, in the form of a tubular or flat (sheet). This can be achieved by extruding or co-extruding from a co-extrusion die (single-layer film) or co-extruding (multilayer film) and then extruding and then cooling. Stretching to orient the film can be performed during cooling while the film is still hot and within its compounding temperature range, and then completes cooling. Alternatively, after cooling after extrusion, the relatively hot "tape" extrusion is reheated within its blending temperature range and stretched to blend or align the crystallites and / or molecules of the material and then cool again. The compounding temperature range of a given one or more materials will vary with the polymers of the different resins that make up the material and / or their blends. However, it can be stated that the compounding temperature range for a given thermoplastic material is generally below the melting point of the crystals of the material, but above its secondary transition temperature (sometimes referred to as the glass transition temperature). it can. Within this temperature range, the material can be effectively stretched to provide a heat shrinkable film. The term "orienting" or "oriented" here generally extends in the lateral, longitudinal, or both directions (during post-extrusion cooling or extrusion, as described in the previous article). Of the resin, which was then heated to a temperature within its orientation temperature range (during subsequent reheating) and the conformation between the molecules of the material was altered by the physical alignment of the microcrystals and / or molecules of the material. The steps of the method obtained by cooling the thermoplastic polymer material substantially immediately to improve certain mechanical properties of the film, eg, shrink tension and relieve stress, and resulting. Used to describe the properties of the product. Both of these properties can be measured according to ASTM D 2838-81. When stretching force is applied in one direction, uniaxial orientation occurs. When stretching force is applied in two directions, biaxial orientation occurs. The term orientation is also used here in compatibility with "heat shrinkability" and these terms refer to a material that has been stretched and fixed by cooling while the material retains its stretched dimensions. Oriented (ie, heat shrinkable) materials tend to return to their original non-stretchable (non-stretchable) dimensions when heated to a suitable high temperature. However, "orientation properties or properties", when used herein, are specifically intended to mean the rate of orientation during processing when making an oriented film. When referring to the% shrinkage of a film and a bag made from it, the term "heat shrinkage property or property" or the term "shrinkage property or property" is used herein. Returning to the basic manufacturing method of the film described above, the film is oriented by being extruded once (or co-extruded in the case of a multilayer film) and then stretched within a temperature range within that alignment range. Stretching for orientation can be achieved in many ways, for example by "trapped bubble" techniques or "tenter framing". These methods are well known in the art and refer to orientation procedures that stretch the material laterally (TD) and / or longitudinally or mechanically (MD). After stretching, the film is rapidly cooled while the film substantially retains its stretched dimensions, thus fixing the oriented molecules in a three-dimensional arrangement. The film produced is then stored in rolls and can be used to wrap a wide variety of articles. If the material is manufactured by "inflated bubble" technology, the material can still be in the form of tubulars, or it can be slit and opened to form a sheet of film material. In this regard, the product to be packaged is first taken into the material, if necessary and appropriate, by heat-sealing the film against itself to form a pouch or bag, and then inserting the product into it. Can be surrounded. Alternatively, it can be wrapped using a sheet of material. All of these packaging methods are well known in the art. When the material is of the heat shrinkable (ie oriented) type, it is packaged after packaging, for example, by passing the packaged product through a hot air tunnel or by placing the packaged product in hot water. The product can be exposed to high temperatures. This causes the enclosed heat shrinkable film to shrink around the product, creating a tight packaging that closely adapts to the contours of the product. As mentioned above, film sheets or tubes can be formed into bags or pouches and then used for product packaging. In this case, if the film is formed as a tube, it would be preferable to first slit the tubular film to form a sheet of film and then form the sheet in a bag or pouch. Methods of forming such bags or pouches are also well known in the art. The general overview of producing films is not meant to be all-encompassing, as such methods are well known in the art. For example, see the following US patents: US Pat. No. 4,274,900, US Pat. No. 4,299,241, US Pat. No. 4,194,039, US Pat. No. 4,188,443, US Pat. No. 4,048,428, US Pat. .. The disclosures of these patents generally represent such methods and are added herein by citation. Another method of producing this type of film is known in the art. One well-known alternative is, as described above, a method of forming a multilayer film by extruding a coating in combination with an extrusion or co-extrusion method. When extruding the coating, one or more first tubular layers are extruded and then one or more additional layers are simultaneously or subsequently coated on the outer surface of the first tubular layer or continuous layer. An example of this method is US Pat. No. 3,741,253. This patent is generally representative of extrusion coating methods and is added herein by reference. Many variants of film formation are well known in the art. For example, conventional thermoforming or laminating techniques can be used. For example, multiple support layers are first extruded by the blow bubble method and then additional layers are extruded or laminated onto it, or two multilayer tubes are extruded simultaneously and then one tube is extruded over the other. Can be coated or laminated. In a preferred embodiment as exemplified in the following examples, the multilayer film of the present invention contains a barrier layer. This layer is a barrier to fluids, such as gases. The barrier layer consists of a layer of vinylidene chloride copolymer (commonly known as saran) or hydrolyzed ethylene-vinyl acetate copolymer (EVOH), preferably at least 50%, most preferably about 90%. It can be composed of a layer composed of those hydrolyzed as described above, or can be composed of both a layer composed of a vinylidene chloride copolymer and a layer composed of EVOH. When the barrier layer is composed of a layer of EVOH, the molar% of vinyl acetate before hydrolysis should be at least 29%. This is because for smaller amounts, the effectiveness of the hydrolyzed copolymer as a barrier for fluids, eg gases, is substantially reduced. In addition, the barrier copolymer preferably has a melt flow that is generally compatible with the melt flow of the other components of the multilayer film, preferably having a melt flow of about 3-10 (melt flow is generally according to ASTM D1238). It is determined). The main gas is oxygen, and the permeation rate is 70cc / m²When less than / mil thickness / 24 hours / atom (measured according to ASTM D-1434), the permeation is considered to be sufficiently low, i.e. the barrier material is considered to be relatively gas impermeable. The multilayer barrier shrinkable film according to the embodiment of the barrier film of the present invention has a transmission rate lower than this value. EVOH can be advantageously used in the films of the present invention. This is because the irradiation high energy electron treatment of the completely co-extruded film does not deteriorate the EVOH barrier layer as in the case of the barrier layer of the vinylidene chloride copolymer. Further, as described below, when vinylidene chloride (PVDC) is used as a barrier layer in place of or with EVOH, irradiation is preferably performed prior to applying the Saran layer to avoid its degradation. Should be. The application can be achieved by the well-known extrusion coating method as described above. More specifically, when one or more layers of a film are subjected to a treatment that can be detrimental to one or more other layers, the extrusion coating method for film formation preferably simultaneously extrudes the entire film. That is. An example of such a case is a barrier composed of one or more copolymers of vinylidene chloride (ie, saran), eg, copolymers of vinylidene chloride and acrylonitrile or vinylidene chloride and vinyl chloride or vinylidene chloride and methyl acrylate. This is a case where one or more layers of a film containing a layer are to be irradiated with high-energy electrons. In other words, the barrier layer is added to or instead of the EVOH layer and includes a Saran layer. As recognized in the art, irradiation with high energy electrons is generally detrimental to the composition of such a saran barrier layer, as it degrades and discolors the saran to a brownish tint. Thus, when performing full co-extrusion and orientation, followed by high energy electron irradiation of the multilayer structure on the film with the saran layer, the irradiation should be performed at low levels with caution. Alternatively, this case can be avoided by using an extruded coating. Thus, by extrusion coating, one or more layers are first extruded or co-extruded, the layers are exposed with high energy, then the Saran layer is extruded and coated, and for that, the outer surface of the extruded and pre-irradiated tube. Other subsequent layers on top, which can be irradiated or unirradiated layers, can be extruded simultaneously or subsequently. This order allows the first and subsequent layers to be irradiated with one or more layers without exposing the saran barrier layer to harmful discoloration effects. Irradiation can be achieved by the use of high energy electrons, ultraviolet light, X-rays, gamma rays, beta particles and the like. Preferably, the electrons are used up to a level of about 20 megarad (MD) dose. The source of irradiation can be any electron beam generator operating in the range of about 150 kilovolts to about 6 megavolts, with a power output capable of delivering the desired dose. The voltage can be adjusted to a suitable level, which can be, for example, 1,000,000 or 20,000,000 or 3,000,000 or 6,000,000 or more or less. Many devices that irradiate film are known in the art. Irradiation is usually performed at doses up to about 20 MR, typically in the range of 1 MR to about 20 MR, preferably about 2 MR to about 12 MR. Irradiation can conveniently be carried out at room temperature, but higher and lower temperatures, such as 0 ° C to 60 ° C, can be used. In the examples below, the multilayer film is formed by a conventional manufacturing method that combines tubular simultaneous extrusion (colloquially called hot blow valve technology) and extrusion coating to form an oriented (heat shrinkable) film. Made by doing. Utilizing a tubular method, co-extruded tubes of multi-layer support cores are extruded and coated with saran and other layers simultaneously, then the selected structures are cooled and crushed and then reheated to make the tubes and valves. By inflating, it was biaxially stretched in the lateral and longitudinal directions. The determined valve was then cooled and crushed, and the deflated oriented film was rolled as a flat, seamless, tubular film, which was later used to make bags, overlaps, etc. Prior to coating the Saran layer and additional layers, the core of the support is guided through the field of ionized radiation, for example through the beam of an electron accelerator, and the radiation dose of growth of about 4-6 megarads (MR). give. VLDPE with 6 or more carbon atom comonomer, melt index (MI) of about 0.910 g / cc or less or about 2 or less can be blended with one or more of various other polymers. , One or more of the various other polymers are present in an amount of up to about 50%, more preferably up to about 35%, and most preferably up to about 25%. These various other polymers can also be used for heat sealing inside the preferred multilayer barrier film of the present invention. Many of these other polymers are also suitable for use in other layers of the film of the invention, whether or not the film is a barrier film. Other suitable polymers include, but are not limited to: ethylene vinyl acetate (EVA) copolymers, LLDPE, LDPE, HDPE, MDPE, polypropylene, ethylene / propylene copolymers, ethylene / alkyl-acrylate copolymers ( EAA) [eg, ethylene / methyl-acrylate (EMA), ethylene / methyl-acrylate (EEA) and ethylene / butyl-acrylate (EBA)], acid-modified EVA, copolymers of (i) and (ii), where (i) i) is the formula RHC = CH₂(R in the formula is H or C₁-C₈Aflua-olefins (which are alkyl), and (ii) are alpha, beta-ethylene unsaturated carboxylic acids, and mixtures thereof. Preferably RHC = CH of olefins and carboxylic acids₂In the copolymer, the olefin is ethylene and the carboxylic acid is acrylic acid or methacrylic acid. Equation RHC = CH₂(R in the formula is H or C₁-C₈Copolymers of alpha-olefins (which are alkyl) and alpha, beta-ethylene unsaturated carboxylic acids are typically Primacor.) (Dow Chemical Company, Midland, Michigan). Primacol is produced by free radical copolymerization of carboxylic acids of ethylene and its comonomer, such as acrylic acid or methacrylic acid. Also, the formula RHC = CH₂(R in the formula is H or C₁-C₈The copolymer of alpha-olefin and alpha, beta-ethylene unsaturated carboxylic acid (which is alkyl) can be a neutralized metal salt, eg, a Na salt. Thus, the copolymer can be an ionomer. Typically, such ionomer materials are Surlyn.) Is commercially available from E.I. Du Pont de Nimoas Company (Wilmington, Delaware, USA) and is detailed in US Pat. No. 3,355,319 and US Pat. No. 3,845,163. .. In general, these polymers described in the above theory can be blended with each other, and as in the previously issued European Patent 0217252, 0.920 g / in an amount up to 50% based on the seal layer. Many of the materials can be blended with ethylene and higher alpha-olefin copolymers with densities below cc. Definition The term "saran" or "PVDC", when used herein, consists of one or more unsaturated monomers in which the major amount of copolymer consists of vinylidene chloride and a small amount of copolymer can copolymerize with it, vinylidene chloride. Means a copolymer of. Examples of unsaturated monomers copolymerizable with vinylidene chloride are vinyl chloride, acrylonitrile, and alkyl acrylates having 1-18 carbon atoms in the alkyl group. The term "extrusion", when used herein, is intended to include simultaneous extrusion, extrusion coating, or a combination thereof, also by tubular, flattening, or combinations thereof. An "oriented" or "heat-shrinkable" material will here be free-shrinked by about 5% or more in at least one linear direction when heated to a suitable temperature above room temperature (eg, 96 ° C). Defined as a material. Unless otherwise stated and defined, or otherwise limited, the terms "polymer" or "polymer resin" are generally used herein in homopolymers, copolymers such as blocks, grafts, random and alternating. Includes, but is not limited to, copolymers, terpolymers, etc., and blends and variants thereof. Moreover, unless otherwise limited in particular, the term "polymer" or "polymeric resin" will include the three-dimensional arrangement of all possible molecules of the material. These structures include, but are not limited to, the three-dimensional arrangement of isotactic, syndiotactic and random molecules. The term "polyethylene", when used herein, when used in the films of the present invention, is the ethylene C of bright charcoal.₂H₂Means a family of resins selected by substantially polymerizing. By modifying the comonomer, catalyst and method of polymerization, properties such as density, melt index, crystallinity, degree of branching, molecular weight and molecular weight distribution can be adjusted over a wide range. Further modifications are selected by other methods, such as halogenation and compounding additives. Low molecular weight polymers of ethylene are fluids used as lubricants, medium molecular weight polymers are paraffin-miscible waxes, and high molecular weight polymers are resins that can generally be used in the plastics industry. Polyethylene with a density in the range of about 0.900 g / cc to about 0.935 g / cc is called low density polymer (LDPE), whereas it has a density in the range of about 0.935 g / cc to about 0.940 g / cc. Polyethylene is called medium density polymer (MDPE), and polyethylene with densities in the range of about 0.941 g / cc to about 0.965 g / cc is called high density polymer (HDPE). Older classic low density types of polyethylene are usually polymerized at high pressures and temperatures, whereas older classic high density types are usually polymerized at relatively low temperatures and pressures. The term "Linear Low Density Polyethylene" (LLDPE), when used here, is a major amount of ethylene and a small amount of C.₃~ About C₁₀Or a newer copolymer of one or more comonomer selected from higher alpha-olefins, such as butene-1, pentene-1, hexene-1, octene-1, etc. The molecule consists of a long chain with a slight side chain or branched structure achieved by low pressure copolymerization. The existing flanking will be shorter compared to non-linear polyethylene. The molecular differences in linear polymers can be entangled, but the forces that tend to hold the molecules together are physical rather than chemical, and thus weakened by the energy applied in the form of heat. Can be done. The low density linear polyethylene preferably has a density in the range of about 0.911 g / cc to about 0.935 g / cc, more preferably in the range of about 0.912 g / cc to about 0.928 g / cc for the purpose of making a film. The maltoin flow dex of linear low density polyethylene is generally in the range of about 0.1 to about 10 g / 10 min, preferably about 0.5% to about 3.0 g / 10 min. This type of LLDPE is commercially available and is manufactured by low pressure vapor and liquid phase methods using transition metal catalysts. Very low density linear low density polyethylene (VLDPE) has a density of about 0.910 g / cc to about 0.860 g / cc or even lower. The term "ethylene vinyl acetate copolymer" (EVA), when used herein, has ethylene and vinyl acetate in which the ethylene inducible units in the copolymer are present in major amounts and in small amounts vinyl acetate (VA) in the copolymer. Means a copolymer produced from the monomer of. The VA content of EVA is preferably about 3% to about 25% for the purpose of forming a film. The term "ethylene / alkyl-acrylate copolymer" (EAA), when used herein, has an alkyl moiety having 1-8 carbon atoms, and the ethylene inductive units in the copolymer are present in major amounts, and the copolymer. It means a copolymer produced from ethylene and alkyl-acrylate monomers with a small amount of alkyl-acrylate in it. The term "ethylene / methyl-acrylate copolymer" (EMA), when used herein for the type of polyethylene, means a copolymer produced from ethylene and methyl acrylate monomers. The term "ethylene / ethyl-acrylate copolymer" (EEA), when used herein for the type of polyethylene, means a copolymer produced from ethylene and ethyl acrylate monomers. The term "ethylene / butyl-acrylate copolymer" (EBA), when used herein for the type of polyethylene, means a copolymer produced from ethylene and butyl acrylate monomers. Many suitable EBAs are commercially available, and they have a butyl acrylate content of about 3% to about 18% by weight. USI is a commercial supplier of Resin No. 4895, which has a melt index of about 3% by weight butyl acrylate and 3 and a melting point of about 106-107 ° C. The following examples describe preferred embodiments of the present invention and their comparisons. These examples do not limit the invention. Materials used in the examples A suitable adhesive type of polymer used in the films of the present invention is commercially available as Bynel CXA3101. It is functionally an ethylene-based adhesive with a combination of ester and acid comonomer (ie, acid-modified EVA) and is supplied by DuPont. One of the LLDPEs used in the examples was Dowlex 2045.03 with a melt index of 1.1 and a density of 0.920. It was sourced from Dow Chemical. The comonomer was acten. Some of the LLDPEs used in the examples were Dowlex 4002 LLDPE with a melt index of 3.3 and a density of 0.912, and some were Dowle 4001 with a melt index of 1 and a density of 0.912. It was LLDPE. Both were sourced from Dow Chemical. For both, the comonomer was octene. One of the LLDPEs used in the examples was Dowlex XU 61502.36 LLDPE with a melt index of 1 and a density of 0.917. It was sourced from Dow Chemical. The comonomer was octene. One of the LLDPEs used in the examples was HS7028 with a melt index of 1.0 and a density of 0.918. It was supplied by Union Carbide. The comonomer was hexene-1. One of the LLDPEs used in the examples was LL3001.CR1 with a melt index of 1.0 and a density of 0.918. It was sourced from Exxon. The comonomer was hexene-1. The HDPE used in the examples was Alathon 7850 with a melt index of 18 and a density of 0.960. It was supplied by DuPont. One of the VLDPEs used in the examples was XPR0545-36568-5N with a melt index of 0.8 and a density of 0.901. The comonomer was octene-1. It was sourced from Dow Chemical. One of the VLDPEs used in the examples was XPR0545-36568-6A with a melt index of 0.8 and a density of 0.905. The comonomer was octene-1. It was sourced from Dow Chemical. One of the VLDPEs used in the examples was XPR0545-36568-6A with a melt index of 0.8 and a density of 0.910. The comonomer was octene-1. It was sourced from Dow Chemical. Dow XU 61612.08L is a VLDPE supplied by Dow Chemical. It had octene as a comonomer. Density = 0.905 and melt index = 0.80. One of the VLDPEs used in the examples was DEFD1419 with a melt index of 1.0 and a density of 0.900. The comonomer was butene-1. It was supplied by Union Carbide. One of the VLDPEs used in the examples was XPR0545-36568-12D with a melt index of 0.8 and a density of 0.900. The comonomer was octene-1. It was sourced from Dow Chemical. One of the VLDPEs used in the examples was XPR0545-36568-12E with a melt index of 0.8 and a density of 0.905. The comonomer was octene-1. It was sourced from Dow Chemical. One of the VLDPEs used in the examples was XPR0545-36568-12F with a melt index of 0.8 and a density of 0.910. The comonomer was octene-1. It was sourced from Dow Chemical. One with VLDPE was XPR0545-36568-12G. It was sourced from Dow Chemical. It had octene as a comonomer. Density = 0.900 and melt index = 0.60. One of the VLDPEs used in the examples was XPR-0545-33 260-46L with a melt index of 3.3 and a density of 0.907 to 0.908. The comonomer was octene-1. It was sourced from Dow Chemical. Some of the LLDPE and VLDPE used were Stamylex resin supplied by Dutch State Mines. The comonomer was octene. Each had the following melt index and density: Stamylex 1016, Melt Index = 1.1, Density = 0.920; Stamylex 1026, Melt Index = 2.2, Density = 0.920; Stamylex ) 08-026, Melt Index = 2.2, Density = 0.911; Stamylex 2H287, Melt Index = 2.2, Density = 0.906; Stamylex 2H286, Melt Index = 2.2, Density = 0.902. One of the LLDPEs used was DEFD resin supplied by Union Carbide. The comonomer was hexacene-1. Each had the following melt index and density: DEFD1568, Melt Index = 0.50, Density = 0.913; DEFD1569, Melt Index = 1.0, Density = 0.912; DEFD1263, Melt Index = 1.0, Density = 0.915; DEFD1624, Melt Index = 0.5, Density = 0.914; DEFD1626, Melt Index = 0.8, Density = 0.911, DEFD1627, Melt Index = 0.8, Density = 0.912; DEFD1628, Melt Index = 0.8, Density = 0.915; DEFD1630, Melt Index = 0.5, Density = 0.913; DEFD1567, melt index = 1.0, density = 0.913; DEFD1565, melt index = 0.5, density = 0.912. One of the LLDPEs used was DEFD 1629 supplied by Union Carbide. The comonomer of DEFD1629 was hexacene-1. Melt index = 0.5, density = 0.910. One of the VLDPEs used in the examples was 1137 with a melt index of 0.8 and a density of 0.906. One was 1491 with a melt index of 1.0 and a density of 0.900. Both comonomer was butene. Both were supplied by Union Carbide. USI was the commercial supplier of the EBA used, Resin N.4895. It has about 3% by weight butyl acrylate (the butyl group is n-butyl, not tert-butyl) and a melt index of 3. The saran used in some of the laboratory examples is Ixan supplied by Solvay Corporation.) It was WV320. It is a copolymer of vinylden chloride and vinyl chloride. The other Saran used in some of the laboratory examples [labeled Saran-MA in the examples below] was XU32027.01 supplied by Dow Chemical. It is a copolymer of vinylene chloride and methyl acrylate. One of the EVAs used in the laboratory examples was LD318.92, which contained 9% vinyl acetate and had a melt index of 2.0. It was supplied by Exxon. The EVA used in some of the laboratory examples was LD720.62, which contained 18% vinyl acetate and had a melt index of 1.5. It was supplied by Exxon. We also used Elvax 3165. This is an EVA with 18% vinyl acetate and 0.7 melt index. One of the EVAs used in the examples was PE3508. This is an EVA with 12% vinyl acetate and a melt index of 0.35. The EVA was PE3507-1. This is an EVA with 6% vinyl acetate and a melt index of 2.7. These were supplied by DuPont. Example The percentages shown in the examples were calculated as% by weight. The film was first made by hot blowing a two-layer extruded tube, layer 1 / layer 2 as a structure and support, through an annular die. A layer of saran (barrier layer 3) and another layer (outer layer 4) were then extruded and coated onto it. The resulting four-layer structure was then cooled and crushed. The tubes were oriented by reheating and stretching laterally 4: 1 and laterally 3: 1 through an inflatable bubble, and the total biaxial formulation was 12: 1. Making such a film on the bag, the heat seal layer 1 was the "inner" layer because it was on the "inside" of the bag, and the "outer" layer 4 was on the "outer" of the bag. The test layer 2 and the barrier layer 3 were the "inner" layers of the multilayer film. When irradiation was shown in the sample, the two-layer support was irradiated with the MR shown before coating the saran and outer layers. Various properties, namely orientation rate, abuse resistance [Carson spear or ball burst)] was measured for the film as shown in the table below. It should be noted that the device was operational due to the fastest orientation rate, but could not exceed 24.4 m (80 ft) / min. Sphere bursts and contractions were measured according to the procedures described in ASTM D3420 and ASTM D2732. The Calson spear is an impact test that measures the impact resistance of a film by the method of a free-falling spear. The device used for the free-falling spear impact was described in ASTM D1079. The spear weighed about 41.5 g. A sample of film about 17.8 x 17.8 cm (7 x 7 inches) was cut. Samples and equipment were equilibrated at room temperature for 36-40 hours prior to testing. Three specimens of each type of film were placed sequentially in the clamp of the device, with the inside of the sample (layer 1 of the film below) facing up. Selected the height of destruction, and released the spear. The height was lowered by 2.54 cm (1 inch), and the tests on the other three specimens were repeated. The 2.54 cm (1 inch) descent was repeated continuously until all three samples were not destroyed by the impact of the spear. Example I A film with four layers was made, and as shown below, the polymer in layer 2 was varied for the various films made, whereas layers 1, 3 and 4 were kept identical.<img file="JP2733249B2_D0001.tif" />* When EVA was used (control sample 1), layer 2 was 100% EVA. However, when using LLDPE or VLDPE (Samples 2-32), Layer 2 is a blend of 7% by weight Bynel CXA3101 and 93% by weight LLDPE or 7% by weight Bynel CXA3101 and 93% by weight. It was a blend of VLDPE. ** After compounding, the total thickness of the four layers of film ranged from about 0.056 mm (2.2 mils) to about 0.064 mm (2.5 mils).<img file="JP2733249B2_D0002.tif" /><img file="JP2733249B2_D0003.tif" />Sample description Control 1 (Layer 2 was EVA) and 2A-2D (Layer 2 was LLDPE): (Compare them below with Samples 10-18 illustrating the present invention). As can be seen from EVA sample 1, abuse resistance is poor (17.8 cm for spear and 25 cm kg for ball burst), good orientation rate [17.37 m (57 ft / min)], and% shrinkage. Was very good (44% horizontal; 27% vertical). For control samples 2A-2D of LLDPE (density = 0.920; comonomer = octene), abuse resistance was very good (for 2A and 2D, 38.1 cm and 30.5 cm spear, respectively) or good (for 2C and 2B, respectively). , 48.3 cm and 50.8 cm spear), good formulation (46-60 ft / min), and excellent shrinkage (34% T for 2A, 23% L for 23%, and 33% for 2B. T, 22% L) to good (28% T for 2C, 16% L, and 28% T for 2D, 18% L). For the LLDPE sample compared to EVA control sample 1, the abuse resistance was even better, the% shrinkage was not very good, and the orientation rate was similar. In summary, in LLDPE, abuse resistance is improved and contraction is exacerbated, whereas in EVA, contraction is improved and abuse resistance is exacerbated. Samples 3-6: These were other comparative samples, where layer 2 was LLDPE with octene as a comonomer, similar to LLDPE control samples 2A-2D. Samples 3-6 had substantially similar orientations, still poor abuse resistance, and corresponding% shrinkage compared to control samples 2A-2D. Samples 7-9: These are samples where layer 2 is VLDPE, VLDPE has octene as a comonomer, but has a high melt index 2.2 for samples 8 and 9 and a high melt index 3.3 for samples 7A and 7B. Had.

Their performance at [14.9 ~ 17.1 m (49 ~ 56 ft) / min] and% shrinkage was also substantially similar to those of LLDPE control samples 2A ~ 2D, but sample 8 had better shrinkage (14.9 ~ 17.1 m (49 ~ 56 ft) / min). It has 41% T and 29% L). In terms of their abuse resistance, it was not very high in LLDPE control samples 2A-2D. Furthermore, it should be noted that VLDPE samples 7-9, where VLDPE has a high melt index, did not show the very good orientation of the samples of the invention, samples 10-18, as described in the next two sections below. Is. Samples 10-17: These were samples of preferred embodiments. They were samples in which layer 2 was octene as a comonomer and VLDPE with a low melt index of about 2.0 or less. For these samples, all three performance properties, orientation,% shrinkage and abuse resistance were constantly excellent. On the other hand, as mentioned above, for a particular control sample, one or two of the three properties were excellent or very good, but for a particular control sample, all three properties were by no means very good. There wasn't. Sample 18: This was another sample of the preferred embodiment. It was VLDPE with layer 2 hexene as a comonomer and a low melt index of about 2 or less. As in Samples 10-17, the orientation,% shrinkage and abuse resistance were very good. Samples 19-28: These were other comparative samples, where layer 2 was LLDPE with hexene as a comonomer.

Their performance properties of [excluding samples 20 with a poor orientation of 13.3 m (38 ft) / min] and% shrinkage were substantially similar to those of LLDPE control samples 2A-2D, but they. Abuse resistance (excluding sample 20 with a 35.6 cm Calson spear) was not very high at 2A-2D. In fact, for sample 28, the abuse resistance was inferior, 15.2 cm. Samples 29-32: These were samples in which layer 2 was LLDPE or VLDPE with butene as a comonomer. Their performance properties of% orientation and shrinkage are also substantially similar to those of LLDPE control samples 2A-2D, with the exception of sample 29, which had an inferior orientation of only 10.4 m (34 ft / min). Met. However, for all of Samples 29-32, the abuse resistance is not very high for Control Samples 2A-2D, and for some of them, ie, for Samples 29 and 32, the abuse resistance is inferior, ie, Calson. The spears were 16.5 cm and 12.7 cm, respectively. In summary, EVA Control 1 has excellent contraction (44% lateral; 27% longitudinal), good orientation [17.4 m (57 ft / min)], and poor abuse resistance (7 cm for spear and ball burst). 25 cm · kg). On the other hand, the LLDPE control sample 2A-2D had a good orientation rate [16.1-21 m (46-60 ft) / min] and the control sample 2A-2D abuse resistance (Carson spear 30.5-50.8 cm). Was in the very good or good range, and the shrinkage (eg, 28% lateral and 16% longitudinal for 2C) was good. Surprisingly, for samples 10-18 where the polymer in layer 2 is a VLDPE with a melt index of about 2.0 or less, the film has very good abuse resistance, very good shrinkage and very good orientation rate. Was discovered. Thus, for Samples 10-18, all three performance properties were excellent. Example II Films were made as in Example I, except that Saran-MA was used for barrier layer 3 and the polymer was varied in each of layers 1, 2 and 4.<img file="JP2733249B2_D0004.tif" /><img file="JP2733249B2_D0005.tif" /><img file="JP2733249B2_D0006.tif" /> As can be seen from Tables II A-B, three performance properties, namely orientation,% shrinkage and abuse resistance, were constantly excellent for samples 8 and 9. These were samples in which layer 2 consisted of octene as a comonomer and VLDPE with a low melt index of about 2 or less. It should be noted that for these samples 8 and 9, the VLDPE in layer 2 was a blend with another polymer compatible with it, here EBA. Nevertheless, all three properties of Samples 8 and 9 in Table II were excellent. As can be concluded, films consisting of octene as a comonomer and VLDPE with a low melt index of about 2 or less have two very good properties, even when the VLDPE layer is a blend with other polymers compatible with it. Will have all of the orientation rate, abuse resistance and% shrinkage of. In addition, Table II For Sample 9 in A and B in particular, the VLDPE used in the outer layer 4, ie the resin XPR054-33260-46L with octene as the comonomer but with a high melt index of 3.3, is the sample 7A and in Table I. Also identical to the VLDPE used in the inner layer 2 of 7B, sample 9 has an excellent orientation rate of 21.3 m (70 ft) / min, whereas samples 7A and 7B are slightly It should be noted that it had only a good orientation rate of 15.2 m (50 ft) / min. The reason for this is that Samples 9 in Tables II A and B also have a VLDPE layer, i.e. layer 2, where VLDPE has octene as a comonomer, but has a low melt index, i.e. a melt index at 0.8. The resin was XU6151.2.08L. Such layers using VLDPE with a low melt index were not present in Samples 7A and 7B of Table I, and for this reason they showed excellent orientation. Table II compared to Sample 9 in Table I For Sample 7 in Samples A-B, each had a layer of the same VLDPE [resin XU61512.08L] (layer 4 of sample 7 and layer 2 of sample 9) with octene as a comonomer and a low melt index of 0.8. , And each showed comparable excellent orientation rates and% shrinkage. However, Samples 7 in Tables II A to B showed inferior abuse resistance (Calson spear = 15.2 cm), whereas Sample 9 in Table I had excellent abuse resistance (Calson spear = 25.4 cm). )showed that. Not bound by any theory, this is because the VLDPE layer of sample 7 has a pre-orientation thickness of only 0.165 Mm (6.5 mils), whereas the VLDPE layer of sample 9 has a thickness of 0.37 mm (14.5 mils). It is believed that this is due to the thickness of the mill) before orientation. Sample 7 is repeated, but if the layer of VLDPE was 0.37 mm (14.5 mil) thick, good abuse resistance would also be obtained. Although certain representative embodiments and details have been presented for illustrative purposes, numerous modifications could be made to the aforementioned formulations without departing from the present invention disclosed herein. The main aspects and features of the present invention are as follows. It comprises at least one layer of ethylene and an alpha-olefin copolymer having 6 or more carbon atoms, said ethylene / alpha-olefin copolymer having a density of less than about 0.910 g / cc and about 2 A thermoplastic multilayer heat-shrinkable packaging film having the following melt indexes. 2. The film according to the above item 1, wherein the ethylene and the copolymer of alpha-olefin having 6 or more carbon atoms are blended with other polymers. 3. The film according to paragraph 1 above, further comprising a barrier layer. 4. The film according to the above item 1, wherein at least one layer of the ethylene / alpha-olefin copolymer is an inner layer. 5. The film according to paragraph 1 above, wherein at least one layer of the ethylene / alpha-olefin copolymer is irradiated with a dose of up to about 20 MR. 6. Consists of an outer polymer layer, a heat-sealing layer and an inner layer between the heat-sealing layer and the outer layer, the inner layer of ethylene and alpha-olefin having 6 / molecule or more carbon atoms. Consisting of the copolymer, the ethylene / alpha-olefin copolymer has excellent heat resistance, shrinkage and orientation, characterized by a density of about 0.910 g / cc or less and a melt index of about 2 or less. Plastic multilayer heat-shrinkable packaging film. 7. The inner layer further contains up to 50% by weight of polymer based on the layer composition, the polymer is compatible with the ethylene / alpha-olefin copolymer, and the ethylene / alkyl-acrylate copolymer, wire. Low Density Polyethylene (LLDPE), High Density Polymer (HDPE), Linear Medium Density Polyethylene (LMDPE), Linear High Density Polyethylene (LHDPE), Low Density Polyethylene (LDPE), Medium Density Polyethylene (MDPE), Ethylene / Acetate Vinyl (EVA), acid modified EVA, polypropylene, ethylene / propylene copolymer, formula RHC = CH₂(R in the formula is H or C₁-C₈The film according to item 6 above, which is selected from copolymers of alpha-olefins and alpha, beta-ethylene unsaturated carboxylic acids having (alkyl), and mixtures thereof. 8. The film according to item 6, further comprising a barrier layer between the heat-sealing layer and the outer layer. 9. The film according to item 6 above, wherein the inner layer is irradiated with a dose of up to about 20 MR. 10, (I) Extruded at least one layer of ethylene and an alpha-olefin copolymer having 6 or more carbon atoms, said ethylene / alpha-olefin copolymer having a density of about 0.910 g / cc or less and about. For thermoplastic multilayer heat shrinkable packaging characterized by having a melt index of 2 or less, (II) orienting the extruded polymer in at least one direction, and (III) recovering the heat shrinkable polymer film. How to make a film. 11. The method according to paragraph 10 above, further comprising extruding the barrier layer prior to the alignment step. 12. The method according to paragraph 10 above, wherein the ethylene and alpha-olefin copolymers having 6 or more carbon atoms are blended with other polymers. 13. The method of paragraph 10 above, further comprising irradiating the layer of the ethylene / alpha-olefin copolymer with a dose of up to about 20 MR prior to the orientation step. 14. Thermoplastic multilayer heat-shrinkable packaging film, said film comprising at least one layer of ethylene and an alpha-olefin copolymer having 6 or more carbon atoms, said ethylene /. The alpha-olefin copolymer has a density of about 0.910 g / cc or less and a melt index of about 2 or less, and the film is characterized by having excellent abuse resistance properties, excellent shrinkage properties and excellent orientation properties. Thermoplastic multilayer heat-shrinkable packaging film. 15. A bag formed from the film according to paragraph 1 above, characterized by having end seals, side seals, or a combination thereof. 16. The bag according to paragraph 15 above, further comprising a barrier layer. 17, The bag according to item 15 above, wherein at least one layer of the ethylene / alpha-olefin copolymer is an inner layer.