Laminates of ethylene vinyl acetate polymers and polymers of vinylidene chloride

PATENT OF INVENTION

Polio A / 19OO3.

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íow.e:

PROCEDURE FOR THE PRODUCTION OF COMPOSITIONS- ·. '· • * · *

FILM POEMERS.

&lt;3% &amp; άίαηί &amp; WRGRACE &amp; CO., American entity, resident in 3, Hanover Square, New York, New York-10004, USA. of A.

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This invention relates to a film of a oriented thermoplastic polymer and laminates containing said film. The film and laminates have excellent resistance to abuse and are

5. Of special use as packaging materials. A

M-2

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401296 -₂ Valuable partíau.lannen.te employment consists of food packaging, especially fresh, red meats to which bones have not been removed.

For many purposes, the materials of enva5. sado require a high resistance to abuse, to survive the latter during the transport and handling of containers. When the items inside the package are not soft or resi-

However, abuse can also occur from ·

10. the inside of the container during transport and handling. An example of articles particularly capable of making^: a bad internal treatment is meat with bone, that is, a piece of meat that contains bone. The:

• i

I breakage of the packaging material by the relative bones - j ii

fifteen. hard mind, whose break affects adversely, as is logically * f:

&gt;

Co, to the meat. Another great majority of consumer items k require packaging in a material that is highly resistant to abuse.

In accordance with the present invention, 20 is provided. a film of a polymer, or mixture of polymers, is oriented thermoplastic, characterized by, i

have a narrow molecular weight distribution, such as ί r

later it will be defined. 'p

I molecular weight distribution characterlsti25. ca is defined with reference to Figure 5 of the attached drawings. Figure 5 is a graph of the molecular weight distribution of polymers. The molecular weight of the polymer is plotted along the abscissa (x-axis) and the percentage of molecules that have that weight is plotted along

30 of the ordinates (y axis) The numbers present on the χ I axis

401296 ³they are a measure of the molecular weight in terms of the units normally used in the gel penetration curves. Figure 5 shows two curves, A and B.

Curve A is the moleeu5 weight distribution. lar of an alkylene / vinyl acetate polymer.

Curve B is the distribution of the molocular weight of another polymer between the same limits: the distribution shown by curve B is wider than that shown by curve A, that is, the area under the limited curve B.

10. along the x-axis and the ordinates x ^ yx₂, is smaller than the area bounded by the A curve. In other words, less of the total polymer is distributed between the narrow confines of molecular weight represented by the distance of a Xg along the x-axis.

15 · The molecular weight distribution indicated herein is determined by the use of a gel penetration chromatograph. It has been found that a polymer having the molecular weight distribution of curve A, of Figure 5, is satisfactory while a

twenty. polymer having a molecular weight distribution of 'curve B is less satisfactory for films of

<td colspan="4">this invention. These curves were analyzed by</td>

<td colspan="2">standard statistical techniques and it</td><td>performed</td><td>follow them</td>

<td>te determinations:</td><td></td><td>Curve A</td><td>B curve</td>

<td>Standard Deviation (SD)</td><td></td><td> 3,07</td><td> 3,65</td>

<td>Average molecular weight in number (M)</td><td></td><td> 28,96</td><td> 27,89</td>

<td>Coefficient of variation (100) (sd) M</td><td></td><td> 10,62</td><td> 13,08</td>

<td>Area under the curve, 10% of</td><td>M</td><td> 64,32</td><td> 50,72</td>

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Thus, it has been found that the polymer should have a coefficient of varlaoton that does not exoedn 13, the oual is referred to herein as a narrow moleoular weight distribution. ” The average molecular weight in

5. number is the heavy average molecular weight consisting of the sum of the molecular weight shown on the abscissa of Figure 5 plus the number of molecules of a given weight represented by the percentage shown on the ordinate.

More particularly it has been shown that for

10. polymers that have a number average molecular weight of approximately 28 (curves A and B) the area under the distribution curve should be larger than the area shown by curve B in an area limited by an abscissa of -10 $ of the weight number average moleoular (x ^ and Xg in Fig. 15.ra 5), ​​a lower ordinate of O and the upper ordinates represented by the distribution curve. Preferably, the area will not be smaller than the similar area for the curve A minus $ 50, more preferably 25 of the difference between the existing areas below

twenty. curves A and B. In other words, for polymers having a number average molecular weight of approximately 28, the area is greater than 50.72, - preferentially greater than 57.57, more preferably greater than 60.94 . The preferred minimum area, which is not smaller than the area

25. Under the curve A minus $ 25 is designated here as a very narrow molecular weight distribution.

The preferred molecular weight distribution is a distribution similar to curve A, that is, confined to the standard bell curve (bell-shaped).

30 The thermoplastic polymer of the film

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401296-.

The invention is molecularly oriented, which normally means that the film is obtained by drawing and contracting a polymer film of the required molecular weight distribution, ia

The invention also includes a method of manufacturing the film in this process.

A preferred class of polymers are ethylene polymers, that is polymers that comprise (consist of or include) polymerized ethylene units.

10. Especially preferred are ethylene vinyl acetate copolymers containing 5-20 fi by weight of units derived from vinyl acetate. The ethylene / vinyl acetate copolymers indicated herein comprise (consist entirely of or simply include 15 as part) polymerized units of ethylene and vinyl acetate. In this way, other ingredients may be present; the polymer could be a terpolymer or another polymer that is not a copolymer as long as the predominant portions are derived from ethylene and

twenty. vinyl acetate To orient said polymers it is better to first perform the cross-linking thereof, the ways to carry out said cross-linking are known per se. for example, by irradiation #

In addition to a simple film, the invention

25. It also includes laminates containing said film.

In one version, the invention includes a flexible laminate comprising a substrate in the form of a film of the invention, said substrate carrying at least one other layer of a polymeric material.

30 A general method to make films

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and laminates of this invention, comprise biaxially stretching a thermoplastic oriented polymer film of narrow molecular weight distribution, either in the form of a single film or as the outer layer of a laminate. When a laminate is to be manufactured, a convenient method comprises melt extrusion on a non-stretched film of at least one diode polymer, a layer of another polymer, whereby a laminate is formed, and then biaxially stretch the laminate. '.

The invention also includes a flexible laminate, suitable for use in packaging operations, characterized in that it has an outer layer of an ethylene and vinyl acetate copolymer, oriented, preferably irradiated, being 5-20 # by weight of the units, units of vinyl acetate. Preferably, both outer layers (upper and lower layers) are of said copolymer. Between the outer layers a barrier layer may be present, which can be any of those described herein.

In this aspect, the invention is not limited by the nature of the molecular weight distribution of any of the .polymers.

The laminates of the present invention have various uses, both in packaging and in other fields of application. A preferred class of laminate for use in packaging, consists of one in the oual the substrate carries, in order, a barrier layer of low oxygen permeability and an opaque resistant to abuse. Said laminate can be manufactured by melt extrusion of a substrate film, cooling

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of the film to solidify it, extrusion in. cast on a barrier layer, solidification of the barrier layer and melt extrusion, on the barrier layer, of a film resistant to abuse, to sign a laminate, and biaxially stretch the laminate.

This kind of laminate will be described later in greater detail, but it should be understood that the invention is not limited in any way to such laminates.

The low permeability barrier layer &amp; Ϊ oxygen, the oual constitutes a particularly important requirement for a packaging laminate, is preferably manufactured from a vinylidene chloride copolymer with at least one other ethically unsaturated monomer, the copolymer containing at least 50 $ by weight of units derived from vinylidene chloride. Said copolymer is referred to herein as a vinylidene chloride polymer. Conveniently it is a copolymer of vinylidene chloride with vinyl chloride. This copolymer may contain, for example,

- $ 85 by weight of units derived from vinylidene chloride and $ 30-15 by weight of units derived from vinyl chloride. Other monomers suitable for polymerization with vinylidene chloride, in order to provide a barrier material, are quite well known and, therefore, will not be indicated herein. Although vinylidene chloride polymers are most commonly used as barrier layers, other materials such as vinyl chloride polymers, fluorinated carbon polymers and many others and the aforementioned pue30 layers have been used in espeoial.

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^ί? 401296 den be present in the laminates of the invention.

Laminates containing a barrier layer of vinylidene odoride polymer have already been described in US Patent No. 3 · 549.3θ9, Canadian Patent 5. No. 743 * 021, US Patent No. 3,031,332, Patent

USA No. 2,968,576 and US Patent No. 2,955,869. However, with such laminates it is usually necessary to use puncture protective means, such as those shown in US Patent No. 2,891,870. In

10. In addition, it can be seen that laminates of the prior art have required the formation of separate folds to provide the necessary resistance to abuse of a sheet, the necessary adhesive characteristics of other sheets and the barrier properties of

fifteen. another sheet or various special treatments to obtain a suitable adhesion characteristic between the folds. In addition, ethylene oopolymers having a substantial vinyl acetate content have not been found to be satisfactory for an outer sheet or in20. terior or a coating that should be resistant to abuse. In general, only those vinyl acetate / ethylene copolymers having a vinyl acetate content of less than 5% have been found suitable for such use. These are only a few

25. Disadvantages of prior art laminates.

Therefore, there is a need to find a laminate of a simplified construction that has all the characteristics necessary for packaging, especially for the packaging of cuts with

30 bone of card, without the use of special auxiliaries

401296 - · of packaging. Laminates that satisfy this need are obtained by the present invention.

The vinylidene polymer of the barrier layer of the laminates of the invention is preferably

5. a mixture of 5-40% by weight of polymer in suspension and 60-95 fi by weight of polymer in emulsion, preferably with an epoxy resin mixed with dioha mixed with an amount of 2-10 $ by weight, based on the polymer. Said mixture forms part of itself.

10. invention .

Another barrier layer material consists of a molten extruded layer of a liquid coating grade vinylidene odoride polymer, described in more detail below. The invention not only

fifteen. it includes the laminates that have said barrier opase but generally extends to a foima- method. tion of an object, a film or not, whose method comprises melting a liquid coating grade vinylidene chloride copolymer. In a way

twenty. preferred, the liquid coating grade vinylidene odoride polymer is present in an amount of 5 - 100% constituting the remainder (if any) • 1 2 - 10 fi of an * epoxy resin and vinylidene chloride polymer Extrusion grade melt.

25. M preferred polymer material for the first layer (substrate) of the laminate is an ethylene with vinyl acetate oopolymer having 5-20, more preferably 8-12 fi by weight, of units derived from vinyl acetate and the weight distribution moleoular required.

30 The molecular weight distribution of the polymer is convex 10 401296

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neither in temente random in general and more preferably it is the distribution of ourva of. standard layer that is represented by line A in figure 5. It can be seen that this curve does not exactly constitute a curve of

5. Bell; an exact ourva should be unexpected in an oomercially produced product. The third layer, the one that is resistant to ill-treatment, is preferably of the same oopollomer and, if desired, can be precisely of the same copolymer used in the substrate.

10. The versions of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of the apparatus used in a preferred method of manufacturing

fifteen. a laminate of the invention.

Figure 2 is a cross-sectional view of a nozzle head that is part of this apparatus Figure 3 is a view taken along line 3-3 of Figure 2.

twenty. Figure 4 is a cross-sectional view of a laminate of the present invention.

Figure 5 is a graph of the moleoular weight distribution, as previously explained.

The percentages are expressed in weight unless

25. Let it be said otherwise.

With reference to figure 1 of the drawings, the tube 10 is extruded downwardly from the nozzle head 11 which is fed from the extruder 9.

The extruded tube has a thickness of 250 to 750 microns,

30 more preferably from 375 to 625 microns. After

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cooling by spraying water supplied from the cooling ring 12, the tube is crushed by crushing rollers 13 and fed through. an irradiation chamber 14 surrounded by a filler 15, in which chamber is irradiated with electrons from an accelerator-transformer with an iron core 16. Other accelerators such as the Van der (Jraff or resonance transformer) can be used. Radiation is not limited to electrons from an accelerator, any ionizing radiation being usable. The unit of radiation used in this report is the RAD which is defined as the amount of radiation that will dissipate 100 erg of energy (measured as absorbed energy) per gram of irradiated material. The MR is one million (10 ^) of RADS.

In special cases it may be desirable to cross-link the polymer by other means, such as by chemical removing agents. In the preferred method, however, irradiation is used and preferably as described below. The irradiation time of the ethylene / vinyl acetate copolymer tube, 10, is not critical but only needs to be sufficient to provide the dose required to perform crosslinking. In the present version, the tube 10 is preferably irradiated at a dose of 2-15 MR and more preferably at a dose of 2-10 MR.

The tube 10 is guided through the irradiation chamber 14 by rollers 17. After irradiation, the tube 10 is directed towards the crushing rollers 18. after which it is slightly inflated

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by a trapped gas bubble 20. The tube is not stretched significantly longitudinally before inflation, since the rollers 18 move at the same speed approximately as the previous rollers 13. The tube is inflated only to a sufficient degree to provide a practically circular tube without any significant transverse orientation.

The irradiated tube, slightly inflated, 10 · is passed through a vacuum chamber 21 towards a lamination or coating nozzle 22 disposed below the chamber 21. A second tubular film 23 is molten extruded, from the coating nozzle 22, and is coated on the irradiated tube 10, and directly adhered to the latter, to form a two-fold tubular laminate 24. The second tubular film 23 is preferably a barrier film. Preferably, said film is of a vinylidene polymer having at least $ 50 by weight of units derived from a vinylidene monomer and more preferably an oomposition consisting of copolymers of vinylidene chloride and vinyl chloride with 5-40 fi of units derived from vinyl odoride, more preferably 5-30 fi. This' • 4.

Composition is preferably 5-40 fi of polymer in suspension and 60-95 fi of emulsion polymer, more preferably 5-15 fi of polymer in suspension and 85-95 fi of polymer in emulsion. The preferred barrier layer also includes 2-10 fi, conveniently 4-6 fi, by weight of the layer, of epoxy resin. Thus, the preferred barrier layer is based on a copolymer of vinylidene chloride with vinyl chloride, having a 5-40 fi

401296 -,3

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of units derived from vinyl chloride, mixed with 2-10 # of epoxy resin the copolymer itself being a mixture of 5-40 fi of polymer in suspension and 60-95 fi of polymer in emulsion. The composition of the ba5 layer. Most preferred barrier comprises (a) a vinylidene chloride / vinyl chloride copolymer having 15-30 fi of units derived from vinyl odoride and (b) 4-6 fi of epoxy resin, the copolymer being a mixture of 5 - 15 fi of polymer in suspension and 85 - 95 fi of polymer in emul10. Zion.

The epoxy resin means a wearable temoendure resin that contains epoxy groups, of high viscosity, which should not be confused with the epox oils that constitute the usual epoxy plasticizers and that

fifteen. They are usually formed from epoxidized natural oil and are much less viscous.

It is completely unexpected that the mixture of emulsion and suspension resins, particularly those of the vinylidene polymer, can be melt-free

twenty. and conform to a biaxially oriented movie of good quality. Normally, it should be expected that the suspended resin will cause the formation of wales in the emulsion resin during extrusion. However, in the present case the suspension polymer pare25. It must act as a stabilizer instead of causing the formation of gels in the emulsion polymer film. Although the requesting entity does not attempt to rely on any theory, it is believed that the suspension polymer melts more slowly in the ex30 cylinder. truder and act as a cleaning agent during the step

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of the mixture through the extruder avoiding the deposition of the polymer on the surface of the extruder cylinder and thereby preventing its decomposition. In other words, the emulsion polymer tends to stick when it melts and the suspension polymer acts somewhat in foxma similar to ball bearings, moving it along the oil cylinder. Of course, the total mixture of oopolymers eventually melts and is extruded. . „

It has been found that when the content in.

't- V

Λ suspension polymer of the polymer mixture is greater than 'li “, to 20 #, it is difficult to orientate the film. Only with careful handling is it possible to use a mixture that contains up to 40 # of polymer in suspension. The reason for this difficulty of orientation arises from the fact that crystals form more rapidly in a polymer film in suspension. In this way, the suspension polymer acts as a contaminant in the emulsion polymer in the sense that the suspension polymer crystallizes too quickly so that a sufficient desosaous (film thickness reduction) is obtained during the orientation step.

It has been found that it is possible to operate at tem •• t '.

extrusion covers between normal processing conditions for emulsion and suspension polymerized polymers, in other words at temperatures of 138 to 171^fiC for most of the preferred compositions. Oon previously it was not believed that the mixed materials were compatible in the molten polymer state because of the differences in melt rates in these two polymers.

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Thus, extruder 25 is preferably operated at a cylinder temperature of 43 to 1602G ', more preferably 121 to 149^fiC and the nozzle of. Extrusion is preferably operated at a temperature of 13θ to 17120, more preferably at 146-157²O. The extruded tube has a thickness of 25 to 125 microns, more preferably 50 to 100 microns.

Extruder 25 is conventional, for example; a standard 8.2 cm extruder.

The details of the nozzle 22 can be better appreciated with reference to Figures 2 and 3. The nozzle 22 is a circular cross head nozzle having an adapter 26 coupled thereto to provide, in its preferred form, an opening 27 of 8.9 cm for the slightly inflated tube 10. The opening 27, through which the inflated substrate passes, has been formed through the mandrel 28, which is attached to the housing of the nozzle 29. The path of the molten coating material 23 is indicated by the arrows in Figures 2 and 3 · The vacuum chamber 21 supplies a soft vacuum, for example, in the range of 0 to 6.4 cm of water, on the nozzle 22 to drag or suck the extruded film 23 while it is still in the molten state against the inflated tube 10 in order to avoid the formation of occluded bubbles in the laminate 24. The vacuum chamber 21 may simply consist of a cylindrical housing or inner diameter closely conforms to the outer diameter of the inflated tube. A vacuum may be applied through outlet 30 by conventional means producing

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401296 vacuum (not shown).

Another preferred material for the barrier layer consists of a coating material of the type used to deposit a polymer coating or

5. vinylidene from a solvent or emulsion. In addition, dioho material has normally been applied from a solution in a solvent, at room temperature, then drying the oapa. This liquid coating polymer can replace the poly10 polymer. Merit in suspension of the preferred barrier composition described above. It is believed that this liquid coated vinylidene polymer material acts exactly the opposite of the suspension polymer, has a lower melt viscosity and enhances

fifteen. the flow of the barrier layer composition in the form of a lubricant. Liquid-coated vinylidene polymers were not believed to be melt extrudable. In other cases, it has been found possible to replace the entire vinylidene polymer of the

twenty. composition and of the barrier layer by the liquid coating vinylidene polymer, by melt extrusion. As can be understood, it is surprising that a good film can be formed in this way. The vinylidene polymers liner25. They are also normally polymerized in emulsion but have established a distinctive character in the Teonica. With preference, this vinylidene polymer contains 5-15 # by weight of units derived from vinyl chloride.

The two-fold film 24 is passed to the

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coating or lamination nozzle 32, preferably while still hot. In a discontinuous process, it would be possible to cool the tube 24 before passing it to the second lining nozzle 32 but this would also normally require a re-inflation and a reheating of the tube, to obtain an excess bond between the second layer and the first layer, the first layer, considering the tube from outside §1. Faithful, would be both the outer layer or the inner layer of the tube.

From the lining nozzle 32, a third opal is molten extruded, which is reduced by rubbing the two-fold tubular laminate 24, adhering directly thereto, to form a tubular laminate of two-fold tares 34. The tubular laminate 33 is a parefearenol oon. A chosen composition involves those that are propounded when explaining the tubular film 10 above. Although it is not necessary to have the same composition as the tubular film 10, it is convenient that it be the same. The coating process on the nozzle 32 is identical to that of the soarito on the nozzle 22. The vacuum chamber 36 serves the same purpose as the vacuum chamber 21 and operates in an identical manner by applying a hole through the outlet 37. the film Tubular or fold 33 has a thickness of 75-375 microns, more preferably 100-300 microns.

The tubular lamiaiado of folds 34 is cooled by spraying water supplied from the cooling ring 39. The water is normally at 7²C. the crushing rollers 40 crush then 30.

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This is the three-fold tubular film and the latter is wound on a winding roller 41. Alternatively, in a continuous process, the film would not be rolled on the pickup roller 41, but would be driven directly to the next stage of the process sequence (stretched). „

As shown in Fig. 1, the delivery roller 42, which is a pickup roller 41 'annealy prepared, is unwound on the guide roller 43 · The laminate 34 does not stretch or orient virtually as it passes over the roller guide 43. The film passes, from the guide roller 43, into a hot water bath 44 containing water 45. The reheating temperature or the preferred hot water temperature is 70 to 1008C, more preferably 82 to 968C.

The crushed three-fold tubular film is immersed in the hot water for at least 5 seconds. This time is normally necessary to bring the temperature of the film to that required to perform orientation stretching.

A typical retention time in the water bath is ·, &lt;. &lt;

about 20 seconds Glutton rollers 46 and 47 guide the crushed tube through the water bath 45.

After obtaining the appropriate orientation temperature, the bubble 54 is blown into the film that is out of the water and the film is stretched both in the transverse direction or in the longitudinal direction, in a preferred ratio of 1: 1.5-1x6, more preferably 1: 2 - 1: 4 which would be a bi30 orientation.

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axial of 1: 2.25 - 1: 3.60 and 1: 4 - 1:16, respectively. The thicknesses of the layers are substantially reduced in equal proportions. The bubble 54 is held inside the crushing rollers 48 and 49. The tube is crushed by the rollers 50 and the laminate, which passes through the crushing rollers 49, overrides the guide roller 51 and under the tensioner roller 53, is enraged. roller 52 is left over.

In Fig. 4, a cross section of the oriented laminate 34 is illustrated. The first applied layer, which is the inner side of the tube, and the layer 10, which has a preferred thickness of 12-125 microns, more preferably 25- 50 microns The barrier layer is that indicated by number 23 and has a preferred thickness of 1.25-50 microns, preferably 2.5 to 6 microns. The terroera oapa, 33, which is the outer protective layer of the tube, has a thickness of 2.5-100 micraB, more preferably 6-25 microns. These after layers can be joined directly without interstate layers. The lapped mine has a contraction tension of 14 - 35 kg / cm, ρ

a preferential rate of 14-28 kg / cnr and a pound contraction of at least $ 40, more preferably of at least $ 50, at 96® C, and a pound contraction of at least $ 20, more preferably of at least minus $ 30, to 8520.

In another preferred method for producing the laminate, the second and third coatings, applied, can be co-extruded over the preformed tube, from a co-extrusion nozzle. This will produce the same laminated end product but it is a procedure

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something more difficult to carry out.

The tubular film produced from the tube of this invention produces an excellent barrier bag, the layer 10 joining very well thereto at tempe5. natures between 93 and 177 ^ 0 without substantially distortion occurring when thermally sealed or with a thermal pulse sealer. «·».

Layer 10 also provides excellent puncture resistance to said bag. The thin 10. barrier layer provides the necessary barrier characteristics with minimal thickness and expense. The outer layer of non-irradiated copolymer provides a high degree of resistance to abuse at low temperatures as well as improved tear resistance15. Give those bags.

An advantageous method for employing bags made from the tube of this invention is described in our US patent 3,552,090. After the bags are evacuated, they are properly closed 20. by staples, for example, as shown in US Pat. No. 3,3-3,746. In the US patent application, SN 844,883, filed on July 25, 1969, whose inventor is Dave L. Owen, an appropriate evacuation device is described.

25. The invention provides a method for packaging an article, especially a food, by enclosing said article in a molecularly oriented thermoplastic polymer film of narrow molecular weight distribution or in a laminate containing said film30. cula as an outer layer thereof, on the inside

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or outside of the container, the film or laminate being in contact with the article, and applying heat to the film or laminate to make the contraction.

The use for which the previous laminate was specifically projected, although it could obviously be used for many other uses, is as a packaged material to wrap or package cuts of fresh meat that have bones. For this purpose, a three-layer laminate manufactured from

10. of the preferred materials described above.

A laminate could be used that has a different and inferior barrier layer but this is detrimental to the processing capacity in the preparation of the laminate and the oality of the laminate. The laminate is not

15 · toxic and generally suitable for food packaging.

It can be understood that when a bag is used to package a piece of fresh meat that has not been frozen and that is not to be frozen, but will be packaged # held at low temperatures, for example, 0 - 7⁵0,

twenty. The laminate encloses the cut of meat with bones and the exposed bones collide with the inner layer of the bag.

In the preferred packaging process, meat with bones is inserted into the three fold laminate

25. which is biaxially oriented and thermally contractable. The laminate thus encloses a cut of meat with bones and depending on the cut of meat, it can always collide with an exposed bone. The bag is evacuated and sealed to preserve the vacuum. The bag

30 then it contracts thermally on the meat.

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In the preferred form of this invention, it is important that the irradiation dose is within the established limits because if this is done, an adherent coating is obtained that has sufficient tensile strength to provide good processability, Good resistance to bone punctures and good rolling orientation. The irradiation should be sufficient to increase the tensile strength without greatly decreasing the elongation, since the material should stretch over the bone when meat cuts with bones are wrapped. At the same time, it is desirable that the bag sticks to soft meat and bones when the bones protrude from the meat. Fresh meat can soften and let bones move or float inside it. In the event that the film is irradiated in large quantities, the elongation decreases and the bone will pierce the container after impact. If the content of vinyl acetate is higher than specified, the melting point of the polymer decreases, adversely affecting the high temperature properties required for shrink packaging.

In addition to the loss of resistance to treatment at thermal shrinkage temperatures, the heat seal becomes delaminated when the vinyl acetate content is much greater than $ 18 on this particular laminate. If the vinyl acetate content decreases to an amount less than $ 5, the low temperature elasticity decreases and the modulus of elasticity increases to such an extent that the bag cannot

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perform your functions in the manner required for an efficient packaging operation.

The preferred three-layer laminate has a number of very desirable characteristics, some of these being good shrinkage at a moderately high temperature, an elongation of at least 50 #, more preferably 100-125 #, a transmission speed of oxygen not exceeding 70 cmVl m / hours / 1 atmosphere, at 22.8sC, and a relative humidity of 0 fi (ASTM L 1434) i and more normally not exceeding □ O cm-y ™ / 24 hours / 1 atmosphere at 73^BC, relative humidity of 0 fi (ASTM D 1434). In its preferred form, the film has a hello impact resistance of at least 25 om-kg, measured in a test apparatus number 13-8 of Tessting Machines Inc. using a standard hemispherical head.

Various aspects of the invention can be used independently or in other combinations, with advantage over the materials normally employed in this way. Barrier layer compositions can be formed in independent films. The compositions have the superior extrusion characteristics already enumerated, such as being coated by melt extrusion or melted, as independent self-supporting films. Naturally, to be self-supporting, the exempted vinylidene polymer film must be at least 2-3 microns thick if it is extruded as a tube using conventional appropriate extrusion techniques. In addition, it has been found that the oriented film forms' l

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It is based on an emulsion polymerized polymer mixture in emulsion and in suspension that has an unexpected tear and puncture resistance compared to the strength of conventional films5. . Polymers of vinylidene chloride / vinyl chloride polymers.

In certain cases, it may be desirable to replace another polymer in the outer layer of the laminate,

This layer is what the resistance to cor10 must have. tear and tear. These other polymers should have a relatively narrow molecular weight distribution or preferably with a random molecular weight distribution, more. It seems to be a general distribution of the standard bell curve. Examples of such policies15. mere are polypropylene, polyamides, polyesters and the like, and copolymers, terpolymers and other polymers of such materials. Such groups of coating polymers are well known. Of course, in certain applications, the outer (third) oapa and even the

twenty. The first (internal) layer could not have the advantages of this invention but the other sheet may be necessary and thus the invention includes preferred packages and modifications thereof containing only some of the materials present in the pre-packaged containers.

The film of the invention and the various layers of the laminates of the invention may include compatible additives, such as stabilizers, pigmentation agents, processing aids, such as 0030. waxes, deodorant agents, antistatic agents and anti-blocking agents.

This invention is further illustrated by the following examples.

EXAMPLE 1

5 · Following the procedure schematically represented in Figure 1, an ethylene / vinyl acetate copolymer containing 10 # of vinyl acetate with a melt index of about 2 and a weight distribution is fed onto the hopper of extruder 9

10. molecular as shown by line A of Figure 5, and sold as EU 637 by the US Industrial Chemicals Division of National Distillers. The extruder is a structor of 8.9 om and is operated at the following temperatures: rear zone 1212C, middle cylinder 172 ^ 0, cilin15. front dro 143^fiC »adapter 149^CC and nozzle 16620.

The spindle speed is 37 rprn. and the pressure

Or it is 267 kg / cm. The diameter of the nozzle is 8.9 cm and the circumference of the tube produced is 20.3^;cm.

The water in the cooling ring 12 has a temperature of

twenty. 7 &amp; C. The crushing rollers 13 operate at a speed of 10.7 meters per minute and the thickness of the crushed tube is approximately 460 microns.

The crushed tube is passed through an irradiation unit such as that illustrated in Figure 1,

25. operating at 500 kilo-eleotronvolts, 20 MA and a speed of 10.7 meters per minute »Four passes are made and the tube receives a dose of approximately 6 mega-radios.

The irradiated substrate film is passed in 30. oes to a coating nozzle 22, where it is re401296

<img file="ES401296A1_D0025.tif" />

5.

10.

15.

20.

25.

Dress with a barrier material. The barrier material contains a slightly plasticized mixture of vinylidene chloride copolymers with vinyl chloride. The copolymer mixture consists of 10% suspension polymerized copolymer and 90% emulsion polymerized copolymer. The suspension polymerized copolymer consists of 70% of units derived from chloride of__;vinylidene and in 30% of units derived from vinyl chloride, approximately, and the polymerized copolymer in suspension consists, approximately, in 80% of units "» "derived from vinylidene chloride and 20% of units derived from chloride of vinyl. These materials are supplied by the Dow Chemical Company and UP 925 dome (the emulsion polymerized resin) and SP 4θ9 (the suspension polymerized resin) are sold. Other ingredients of the barrier layer are: 5 fi or an epoxy epoxy resin / bisphenol A resin sold as EPON 828 resin by the Shell Chemical Company and approximately 0.5 fi from a microcrystalline paraffin wax supplied by Sun Ohemioal Company and sold oomo Wax 5512. The three resins are mixed in a high-intensity Trodex-Henschel mixer, at high speed, and the mixture is fed to the hopper of extruder 25 which consists of a 5 om Trodex extruder with a crosshead nozzle of the type illustrated in Figures 2 and 3 * This extruder is operated under the following temperatures: back zone, 99^SC, medium oil cylinder, 1272C, front cylinder, 149^SC adapter 141^fiC and nozzle, 1602C. The spindle speed is 34 rpm and the pressure is 390 kg / cm ^. The diameter of the nozzle is 8.9 cm

30.

5.

10.

15.

20.

25.

<img file="ES401296A1_D0026.tif" />

and the circumference of the tube is 20.3 cm. The upper rollers 18 are operated at a speed of 10.7 m per minute and the thickness of the coating is approximately 75 microns.

Next, a third layer is formed using the same resin as in the first oapa. The resin is extruded through the extruder 35, operated in an identical manner to the extruder 9, except that the temperatures are as follows: back zone, 1212C, middle cylinder, 13220, front cylinder, 193⁵θ, adapter, 2272C and nozzle, 23280. The coating nozzle 32 is of identical design to the coating nozzle 22. The lower rollers 40 are operated at a speed of&gt; 1.0 meters per minute and the water of the cooling ring 39 it is encased at a temperature of 720. The thickness of the coating is approximately 150 microns.

Biaxial orientation is done by worrying the tube in water at approximately 8880, as shown in 44 in Figure 1, and passing the tube thus heated through the crushing rollers operating at 5.8 meters per minute to the rollers Inflators operating at 21.4 meters per minute and blowing the 10 cm tube last year to produce a film with a width of approximately 41 cm and a film thickness of approximately 61 microns. This tube is then rolled up on a storage roller which is then converted into bags by sealing the tube transversely in intervals, to form bottoms in the conventional manner and by opening the tube into the desired bag lengths.

30.

- 28 EXAMPLE 2

<img file="ES401296A1_D0027.tif" />

The above procedure is repeated, except that the barrier layer is varied by adding 2 $ of 2-ethyl-exyl-diphene phosphate plasticizer5. what is supplied by Monsanto under the designation Santicizer 141 and reducing the epoxy resin content to $ 3.

EXAMPLE 3

The procedure of example 1 is repeated_F with

10. the exception that the composition of the barrier layer ee of $ 66 of vinylidene chloride / vinyl chloride copolymer resin UP 925, $ 30 of a liquid coated vinylidene chloride polymer resin, supplied by Dow Chemical Company and sold15. gives as QX 2168, $ 2 of Epon 828 resin and $ 2 of Santicizer 141.

EXAMPLE 4

The procedure of example 3 is repeated, except that the saran of the barrier layer composition

twenty. It was made up entirely of QX 2168.

EXAMPLES 5 .V 6

The procedures of Examples 3 and 4 are repeated except that QX 2168 is replaced by a liquid coated vinylidene chloride polymer.

25 · sold by WR Grace &amp; Co. as Daran CR 6795-H.

EXAMPLE 7

The procedure of example 1 is repeated, except that 5 $ of epoxy resin is replaced by $ of an epoxidized soybean oil (which is not to be fused with the epoxy resin) sold by Swift &amp; Co. as

<img file="ES401296A1_D0028.tif" />

- 29 5.

Epoxol 7-4. EXAMPLE 8

10.

15.

20.

25.

The procedure of example 1 is repeated, except that 5 # of epoxy resin is replaced by 4 # of 2-ethyl-exyl diphenyl phosphate plasticizer and 1 # of magnesium oxide.

EXAMPLE 9

The procedure of example 1 is repeated, except that a mixture of 53 »3 # by weight of isotactic polypropylene '(ioyamont * P007), 33.3% polybutene-1 (Mobil * PB 103) is used to form the third layer )'.Y

13.3 # of atactic polypropylene (Novamont * Lot 2030 ·) ·.

The atactic and isotactic polypropylene is first added, in an appropriate proportion, to a Banbury mixer and the melt is mixed for approximately 8 minutes at 204BC and then extruded into a sheet which is cut into pellets. These pellets are combined with polybutene-1 pellets in a rotating drum and this mixture is loaded into the hopper of extruder 35. Extruder 35 is operated at the following temperatures: back zone 196b0j middle zone 204^andCj drive zone 2320C, adapter 2O4.BC and nozzle 218BC

Example 10

The composition used in Example 2 to form the barrier opase, except that 4 # of the epoxy resin is used, and the UP 925 resin content is reduced to 1 is extruded as a self-supporting single layer film under the Extrusion conditions of Example 2. A propylene glycol coating is applied to the inside of the tube to avoid sticking when the

30.

<img file="ES401296A1_D0029.tif" />

ae tube crushes before biaxial orientation. The process is continued, the bubble 54 forming before crushing the tube but without winding the tube. In addition, the water bath is maintained at approximately 3820. The spesor

5 · of the extruded film is 125 microns and the thickness of the substantially oriented film is approximately 19 microns after a stretched, total disorientation ratio of 12: 1 biaxially. The movie turns out • f.

have a tear and puncture resistance sor10. very high for a oriented film compared to the usual known oriented films of vinylidene chloride / vinyl chloride copolymers.

OON TESTS REGARDING THE BAD TREATMENT OF THE CONTAINER

fifteen. The following test procedure is performed. The test bags were preselected and conditioned for 24 hours at 7-102C. Bags chosen at random were used to package cuts of meat with bones, weighing 11.3 - 13.6 kg. The bags had a

twenty. width of 41 om for a depth of 70 or 81 cm. The containers were evacuated and the bags stapled, sealed by shrinkage and dried in a stream of air. The containers were then placed in boxes in corrugated containers coated with wax, three in

25. each container the containers were then closed with a filamentous mono nylon tape.

In the oaida test, the individual containers were dropped from a height of 0.91 meters from a moving transport. In the essay of the

3θ · abuse in transport, the containers were

<img file="ES401296A1_D0030.tif" />

stored to 3²C for 24 hours and then shaken for 7.5 minutes at 1 gram on a LAB vibration test apparatus with synchronized movement to produce a movement similar to that produced on the road for 200 km.

In both tests the containers were bombs-oon air and are submerged in water to determine the leaks. A leaking container is considered useless.

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TABLE I

<td>BAG</td><td>THICKNESS OF THE LAMINATE You look</td><td>SURVIVAL IN FI IN THE FALL TEST (RESISTANCE TO BONE PUNCHES)</td><td>supehv: fi IN E3 OF MAK IN THE 0</td>

<td>Manufactured in substantial accordance with Example 1</td><td> 61</td><td> 75</td><td> £</td>

<td>Manufactured in substantial accordance with Example 1</td><td> 69</td><td> 73 # ;</td><td> 9</td>

<td>Manufactured substantially according to Example 2</td><td> 51</td><td> 63 #</td><td> 8</td>

<td>Standard oxymer bag of Tinilidene chloride / vinyl chloride, produced by WRGrace ~ &amp; C</td><td> 48 0.</td><td> 25 #</td><td> 4</td>

<td>Perflex 66 oxymer bag of vinylidene chloride / vinyl chloride, supplied by Union Carbide</td><td></td><td>23 fi</td><td> 3&lt;</td>

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<td>SURVIVENCE IN $ IN SL TEST OF BAD TREATMENT IN THE TRANSPORT</td><td>OXYGEN BARBER cc. (1 m²/ 24 hrs./l atom.)</td>

<td> 82 $</td><td> 45</td>

<td> 92 $</td><td> 40-45</td>

<td> 80 $</td><td> 35</td>

<td> • 45 $</td><td> 150</td>

<td> 36,6 $</td><td> 150</td>

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