Vinylidene chloride composition and film with controlled gas permeability

116050/3 mpnn u mmn bya onpi T>nbo ynbun nmonn

VINYLIDENE CHLORIDE COMPOSITION AND FILM WITH CONTROLLEDGAS PERMEABILITY CRYOVAC, INC.C:23586 42340 10

VINYLIDENE CHLORIDE COMPOSITION AND FILM WITH

CONTROLLED GAS PERMEABILITY

15 BACKGROUND OF THE INVENTION

The present invention relates to films made from vinylidenechloride polymers or copolymers; more particularly to a method,composition, and film for controlling the oxygen and carbon dioxide 20 transmission and stickiness, and enhancing the free flowability and thermal stability of monolayer and multilayer packaging films having aplasticized layer of vinylidene chloride copolymer film.

Thermoplastic packaging films made of vinylidene chloridecopolymer, here referred to as “saran”, have long been used to package 25 food such as cheese, fresh meat, etc. Saran is a good barrier to thetransmission of oxygen.

Methods of producing a multilayer film having a layer of saran aredisclosed in USP 4,112,181 (Baird) and USP. 3,741,253 (Brax et al), bothincorporated herein by reference. Saran is typically plasticized and 30 stabilized for purposes of extrusion. One example is 42340 epichlorohydrin/bisphenol A, and epoxy resin, and 2-ethyl hexyldiphenyl phosphate. USP 5,202,188 discloses a vinylidene chloride compositioncomprising 1 to 4% plasticizer, 1 to 4% acrylate/styrene polymer, andthe balance of 92 to 98% comprising a vinylidene chloride copolymer.Although this film has proven commercially useful in many packagingapplications requiring high oxygen barrier, it does not address the needsof packaging applications such as gas (CO2) producing cheeses, andproduce (vegetables) where a moderate O2 barrier combined withrelatively high CO2 transmission is often required. A commercial composition currently used to make film forpackaging gassing cheese includes 100 parts VDC/VC plus three liquidplasticizers: five parts of Plastolein 9759-A (a polymeric condensationproduct of azelaic acid and 1,3-butandiol), three parts of Plasthall HA7A,a polymeric plasticizer of polyester of adipic acid and propylene glycol,and one part Plas-chek 775, an epoxidized soybean oil. It has beenfound that blends with liquid plasticizers do not free flow very well andthus require a grinding step before extrusion. This process, coupledwith some migration of the liquid additives out of the VDC/VC matrix,causes inconsistency, i.e. lack of homogeneity in the composition of theresulting blend. This inconsistency in turn leads to inconsistency in theOj and CO2 transmission rates of packaging films made from the blend.This is important, because consistent O2 and CO2 transmission rates areneeded to insure a commercially acceptable package system. Whenthese gas rates can be controlled predictably, the amount of the additivescan be adjusted to optimize the transmission rates for the intended enduse.

Some cheese products are produced in such a way that the finalcheese product emits a significant amount of carbon dioxide over time.

In such cases, it is often desirable to provide a packaging material which 42340 is characterized by a relatively low oxygen transmission rate to protectthe cheese product from oxidative degradation in quality or shelf life. Itis also desirable to have a sufficiently high carbon dioxide transmissionto allow the naturally generated CO2 to escape from the package, andavoid undesirable ballooning of the package.

The present invention provides a composition, and film, with ahigher total amount of plasticizer and stabilizer than that shown in theart, and therefore a film suitable for packaging applications where Oj andCOj transmission rates are important. In preferred embodiments, theinvention provides not only a higher amount of plasticizer and stabilizer,but also a relatively lower amount of liquid plasticizer in the blend. Theresulting improvements in free flowability save an extra grinding step inpreparing the composition, and also offer a more controlled, consistentO2 and CO2 transmission.

The present invention also provides good thermal stability forsaran formulations, and they do not degrade to any significant extentduring extrusion. Methods for determining stability are well known, e.g.as described in USP 5,202,188 incorporated herein by reference.

SUMMARY OF THE INVENTION

In one aspect of the invention, an extrudable vinylidene chloridecomposition comprises 100 parts by weight of at least one vinylidenechloride copolymer; between 4 and 15 parts by weight of a plasticizer;and between 4 and 15 parts by weight of an acrylate/styrene copolymer;wherein the total amount of plasticizer and acrylate/styrene copolymercomprises at least 9 parts by weight.

In another aspect, a polymeric film comprises at least one layercomprising 100 parts by weight of at least one vinylidene chloridecopolymer; between 4 and 15 parts by weight of a plasticizer; andbetween 4 and 15 parts by weight of an acrylate/styrene copolymer; 42340 wherein the total amount of plasticizer and acrylate/styrene copolymercomprises at least 9 parts by weight.

DEFINITIONS

As used herein: “Plasticizer” means a material incorporated in a film to increaseflexibility, workability, or extrudability of the film. “Acrylate/styrene polymer” means an additive that has acrylate orstyrene moieties, or both, such as methyl methacrylate/butylacrylate/styrene terpolymer, methyl methacrylate/butyl acrylate/butylmethacrylate terpolymer, or poly (alpha-methyl styrene).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventive composition preferably comprises 100 partsby weight of at least one vinylidene chloride copolymer; between 5 and 15parts by weight of a plasticizer; and between 5 and 15 parts by weight ofan acrylate/styrene copolymer.

More preferably, the present composition comprises 100 parts byweight of at least one vinylidene chloride copolymer; between 6 and 12parts by weight of a plasticizer; and between 6 and 12 parts by weight ofan acrylate/styrene copolymer.

Most preferably, the present composition comprises 100 parts byweight of at least one vinylidene chloride copolymer; between 8 and 10parts by weight of a plasticizer; and between 8 and 10 parts by weight ofan acrylate/styrene copolymer.

Preferably, the total amount of plasticizer plus acrylate/styrenecopolymer is at least 10 parts (to be added to 100 parts of the vinylidenechloride copolymer composition). More preferably, the total amount ofthese additives is at least 12 parts, even more preferably at least 14parts. Most preferably, at least 16 parts of the additives are used. . ,- c 42340

Higher total levels of plasticizer and acrylate/styrene copolymer inthe composition provide O2 and CO2 transmission that is very suitablefor packaging gassing cheese. In addition, as the total level of theseadditives goes up, the CO2 transmission typically increases 5 proportionally more than the O2 transmission. This can be seen in Table3, where the CO2/O2 ratio shows an increase with an increased totalamount of plasticizer plus acrylate/styrene copolymer. Some of thisincrease is dependent on the specific materials used.

The advantage of this ratio increase is that the CO2 transmission10 rate can be beneficially increased (very useful in gassing cheese applications) while effecting a smaller increase in the O2 transmissionrate. This latter value is desirably kept relatively low so that oxidativedegradation of the cheese or other product is retarded.

The composition can be made into monolayer or multilayer film, 15 oriented or unoriented, by means well known in the art.

In a preferred embodiment, a film comprises a four layer filmstructure: sealant layer/core layer/barrier layer/abuse layer where: sealant layer = 90% ethylene vinyl acetate copolymer (EVA) (6%VA)+ 10% linear low density polyethylene (LLDPE) which is an 20 ethylene/octene copolymer (6.5% octene); core layer = ethylene vinyl acetate copolymer (EVA) (15%VA);barrier layer = (as defined in the Tables); and abuse layer = 92.5% ethylene vinyl acetate copolymer (EVA) (9% VA) and 7.5% linear low density polyethylene (LLDPE) which is an 25 ethylene/octene copolymer (6.5% octene).

The sealant and abuse layers can comprise any suitable polymeric material, but preferably comprise an ethylene alpha olefin copolymer, anethylene unsaturated ester copolymer, an ethylene acid copolymer, otherpolyolefins, or any combination or blend thereof. The core layer, which is 30 optional, can also comprise any of these materials. Ethylene alpha olefin 42340 copolymers are preferably copolymers of ethylene with one or morecomonomers selected from Ca to Cm alpha olefins. Both heterogeneousand homogeneous materials can be used. Examples of heterogeneousmaterials include LLDPE (linear low density polyethylene), VLDPE (verylow density polyethylene), ULDPE (ultra low density polyethylene), andthe like. Homogeneous materials can include metallocene catalyzedpolymers (MCP) such as those available from Exxon under the EXACTtrademark, and available from Dow under the AFFINITY trademark.

Ethylene unsaturated ester copolymer refers to materials such asethylene vinyl acetate copolymer (EVA), ethylene alkyl acrylatecopolymers such as ethylene ethyl acrylate copolymer (EEA), ethylenemethyl acrylate copolymer (EMA), and ethylene n-butyl acrylatecopolymer (EnBA). It also refers to ethylene methyl methacrylatecopolymer (EMMA).

Ethylene acid copolymer refers to materials such as ethyleneacrylic acid copolymer (EAA), and ethylene methacrylic acid copolymer(EMAA). Metal salt neutralized or partially neutralized versions of thesematerials, such as ionomer, are also included herein.

EXAMPLES

Table 1 identifies the compositions used in the examples.

Nine compositions of the present invention, as well as a controlcomposition, were tested for thermal stability (shown as degradation inminutes) and free flowability. The results are shown in Table 2.

Table 3 shows the O2 and CO2 transmission rates of fouradditional examples, compared with the same control. The controlcomposition forms part of the B 625 bag commercially made by CryovacDivision of W.R. Grace & Co.-Conn. Oxygen transmission is measuredby ASTM 3985; carbon dioxide transmission is by a coulometric testmethod; both properties were measured using Mocon equipment. 42340 TABLE 1

MATERIAL TRADENAME SOURCE VDC, PV324 SOLVAY VDCa MA134 DOW P, Plastolein 9759-A HENKEL Pa Plasthall HA7A C.P. HALL Pa Plas-Chek 775 FERRO Pa Citroflex A-4 MORFLEX s, Metablen P700 ATOCHEM Sa Metablen LI000 ATOCHEM where: VDCi = vinylidene chloride/vinyl chloride copolymer; VDCj = vinylidene chloride/methyl acrylate copolymer;

Pi = polymeric condensation product of azelaic acid and 1,3-butandiol;

Pa = polymeric plasticizer of polyester of adipic acid and propyleneglycol;

Pa = epoxidized soybean oil;

Pa = plasticizer of acetyl tri-n-butyl citrate;

Si = methyl methacrylate/butyl acrylate/styrene terpolymer; and

Sj = methyl methacrylate/butyl acrylate/butyl methacrylateterpolymer.

In the tables, “phr” means pounds per hundred (weight units) ofmaterial. For example, in the control, 100 pounds of saran was blendedwith 5 pounds of Pi, 3 pounds of Pa, and 1 pound of P3. An equivalent is“parts by weight”. 42340 !' . TABLE 2 EXAMPLE COMPOSITION......................WM................... DEGRADATION (minutesl FREE FLOW 1 (Control) 100 VDCt + 5 P, + 3 P2 + 1 Pa 21.0 very poor 2 100 VDC, + 4 Pa . 5 S. 24.0 excellent 3 100 VDC. + ' 4 Pa + 10 S, 21.0 excellent 4 100 VDC. + 8 Pa + 5 S, 43.0 very good 5 100 VDC. + 8 Pa + 10 S. 38.0 very good 6 100 vdc2 + 4 P3 > 5 S, 44.0 excellent 7 100 VDC2 + 4 P3 + 10 s. 68.0 excellent 8 100 VDC2 + 4 Pa+ 10 S. 54.0 excellent 9 100 VDC2 + 4 P3 + 10 s, 70.0 very good 10 100 vdc2 + 4 Pa + 10 S, 70.0 very good 42340 TABLE 3 EXAMPLE fphrl 1 100 VDCi + 5 Pi + (Control) 3 P2 + 1 Pa 11 100 VDCi + 8 P3 > 8 S2 12 100 VDCi + 5 Pa + 10 S, 13 100 VDC, + 6 Pa +10 s, 14 100VDC.+ 8 Ρί't-ίο Si

COMPOSITION O2 trans.cc/dav.m·2 CO2 trans. cc/dav.m2 CO2/O ratio 41.0 248.0 6.05 38.0 245.0 6.45 31.0 200.0 6.45 40.0 248.0 6.2 37.0 278.0 7.5 5

Those skilled in the art will understand that modifications to thepresent invention can be made after review of the disclosure. Suchmodifications are deemed to be within the scope of the invention asclaimed. 10 For example, although four layer embodiments are disclosed as examples, those in the art will readily understand that one or morelayers can be made into a film having the benefits described.

The examples were made by a tubular extrusion coating process,well known in the art. However, other processes, such as flat cast 15 extrusion or coextrusion, lamination, extrusion coating, extrusion 42340 c- ( ' lamination and the like can be employed. These alternative processes are well known in the art.

The examples were made by irradiating a substrate (sealant and core layer) prior to extrusion coating of the barrier and abuse layers, and 5 prior to orientation. Alternatively, films of the invention can be totallycrosslinked by conventional means such as electronic or chemicalcrosslinking; post-irradiated, i.e. irradiated after orientation; or madewithout crosslinking, or without orientation.

Orientation is accomplished by conventional means such as blown10 bubble or tenterframe. Orientation ratios can be at any suitable range orratio, including 1:1 to 6:1 in either or both of the machine and transverse directions. 10