AU658375B2

AU658375B2 - Cheese packaging laminate

Info

Publication number: AU658375B2
Application number: AU87716/91A
Authority: AU
Inventors: Walter Brendt Mueller
Original assignee: WR Grace and Co Conn; WR Grace and Co
Current assignee: WR Grace and Co Conn
Priority date: 1990-11-16
Filing date: 1991-11-08
Publication date: 1995-04-13
Anticipated expiration: 2011-11-08
Also published as: CA2053707A1; ZA918226B; JPH04269533A; AU8771691A; JP3043868B2

Description

658375

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): W. R. Grace Co.-Conn.

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ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Cheese packaging laminate The following statement is a full description of this invention, including the best method of performing it known to me/us:- S 9 Ct S

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9 0 *5 The present invention is directed to a laminated structure useful in the packaging of food items, particularly soft cheeses.

Soft cheeses such as Camembert and Brie are currently packaged in a variety of different materials including polyethylenes with and without ethylene/vinyl-acetate copolymers, polypropylenes, nylon/polyethylene laminates, and polyester/polyethylene laminates. The oxygen and carbon dioxide transmission rates of such structures are of primary importance in the packaging of many soft cheeses, as well as other food items which require a packaging material of high gas permeability such as many fruits and. vegetables. High Soxygen permeability is of primary importance in the packaging of cheeses which, like Brie, require an aerobic atmosphere to support fungal growth on the surface of the cheese. Other cheeses respire CO 2 in amounts that require a permeable packaging material in order to preclude gassing of the package. In the case of produce packaging, regulation of the transmission of 02 and CO 2 minimizes enzymatic browning of cut surfaces and the damaging effects of product anaerobiosis.

However, in most cases, materials having the desired oxygen and carbon dioxide transmission rates required in the above-discussed applications also have minimal abuse resistance and machinability properties. Conversely, film structures which are abuse resistant and machinable generally 2/901004.2/TXTLPG 11/12/90 -2lack the gas permeability and sealing properties required by such applications.

The present application requires a structure which combines heat resistancoe, low extensibility and strength with high gas permeability und sealing. To prevent drying of the packaged food product, a low water vapor transmission rate is also required.

Such requirements were met by the structure of U.S. Pat.

No. 4,935,271 to Schirmer which discloses a multilayer laminate for use in the packaging of lettuce and the like having a first impermeable film of propylene homopolymer or copolymer having perforations defined therein, and a second permeable film bonded to the first film which includes a bonding layer of ethylene vinyl acetate copolymer and an outer heat sealable layer. In that laminate, machinability is provided by the polypropylene film which is perforated in order to render it permeable. The gas permeable second film contributes the properties of low moisture transmission and sealability to the overall structure. However, for the Schirmer structure, disposition of the soft, flexible second film adjacent the relativelT stiff, heat set polypropylene, results in curling of the overall structure and, thus, poor 25 machining performance.

SUMMARY OF THE INVENTION In accordance with the present invention there is 30 provided a multilayer laminate comprising: a) a first component film having perforations defined 4therein; and b) a gas permeable second component film, bonded to one side of the first component film, the second component film including a bonding layer and at least one layer comprising butadiene styrene copolymers.

95209,p:\opr\mna,87716-91.040,2 -3- The multilayer laminate of the present invention is particularly useful in providing an improved material for the packaging of cheese and the like which is machinable, having heat resistance, non-extensibility and strength.

The multilayer laminate may further provide a packaging laminate having high gas permeability in addition to strength, heat resistance, and low extensibility which precludes moisture transmission and tends to remain in a planar configuration during processing.

There is further provided a method of making a multilayer laminate comprising: a) providing a strong non-extensible perforated, machinable film; b) coextruding a second film having a bonding layer and at least one layer for imparting stiffness to said second film wherein said second film having a high permeability and a low moisture transmission; and c) bonding a web of the second film to one side of the perforated film.

There is further provided a method of making a multilayer laminate comprising providing a perforated film 25 preferably comprising a propylene homopolymer or copolymer, coextruding a second film having a bonding layer, and preferably an interior styrene butadiene layer, and bonding the second film to the perforated film.

30 DEFINITIONS The term "ethylene copolymers" as used herein refers to copolymers of ethylene and vinyl acetate, alkyl acrylate or alpha-olefin. Also within the scope of the present definition are chemically modified derivatives of these materials.

V 3 950209,p:\opcr\mla87716-91.040,3 3A The term "EVA" as used herein designates ethylene/vinylacetate copolymers.

The term "linear low density p:olyethylene" (LLDPE) as herein includes that group of ethylene/ alpha- olef in copolymers having limited side chain branching and which fall into a density range of 0.916 g/cc to 0.940 g/cc. Sometimes linear polyethylene in the density range from 0.926 g/cc to 950209,p:\operniLa.87716-91.043.3 0.940 g/cc is referred to as linear medium density polyethylene (12DPE). Typical brand names are Dowlex from Dow Chemical Company, Ultzex and Neozex from Mitsui Petro Chemical Company, and Sclair from DuPont. The alpha-olefin copolymers are typically butene-l, pentene-1, hexene-l, octene-l, etc.

The terms "very low density polyethylene" (VLDPE) and "ultra-low density polyethylene" (ULDPE) as used herein refer to ethylene/alpha-olefin copolymers which have a density of less than about 0.915 g'cc and, more specifically, usually 0.912 g/cc or be.low and may be below 0.89 g/cc.

Typical VLDPE resins are those designated DFDA by Union Carbide and are believed to principally or usually have butene or isobutene as a comonomer. The very low density polyethylenes as compared to LLDPE, usually have significantly higher copolymer content and distinctly different properties making them a distinct class of polymers. Typically, resins designated "ULDPE" resins come from Dow and are believed to have octene as the comonomer. There is a -slight difference in properties which is thought to be attributable to the comonomer. As used herein the term "linear ethylene/alpha-olefin copolymer having a density of less than S0.915 g/cc" encompasses both VLDPE and ULDPE.

The term "butadiene styrene copolymer" (BDS) is used herein to denote thermoplastic copolymers, especially block copolyr~;rs containing a major portion (greater .than of styrene and a minor proportion (less than 50%) of butadiene comcnomer.

BRIEF DESCRIPTION OF THE DRAWINGS The invention can be further understood by reference to the drawing figures, wherein: a 1004.2/TXTLPG FIG. 1 is a schematic cross sectional view of one embodiment of the multilayer laminate of the present invention; and FIG. 2 is a schematic cross sectional view of another embodiment of a multilayer laminate in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMMODIMENTS The present invention is directed to a laminate for

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use in the packaging of soft cheese and other items which S require a packaging material having the properties disclosed herein. The packaging of soft cheeses requires a packaging material having a low moisture transmission rate and a high gas transr~ission rate. Further, automation of the process requires the material to be machinable. MachinabilLty may be defined as including the properties of strength, low extensi- S* bility, and heat resistance. Further, for a film to be mas chinable it must be capable of maintaining a substantially planar configuration during many types of handling and processing. Typically, those materials having high gas permeabilities do not demonstrate adequate machinability and vice- S versa. The present invention meets all of the prerequisites of this application by first providing a machinable film which is strong, non-extensible and heat resistant, but also impermeable and nonsealable, and then perforating it, thereby rendering it permeable. In order to provide sealability while maintaining permeability and providing for a moisture impermeable structure, a permeable, heat sealable film is bonded to one side of the perforated film. Curling of the final laminate structure, which is expected when a highly permeable film is laminated onto a strong, non-extensible film, is precluded by including a stiffness imparting layer within the otherwise coft, permeable film. Relative gas and moisture transmission rates of the ultimate structure are 2/901004.2/TXTLPG 11/12/90 determined by the size and number of perforations in the first, impermeable fi:Lm, as well as the thickness and permeability of the second film.

Referring to Figure 1, the multilayer laminate 100 includes an first film 12 having perforations 14 therein. In the preferred embodiments, layer 12 comprises a propylene homopolymer although a propylene copolymer such as ethylene propylene copolymer 'EPC) may be used. Various homopolymers and. copolymers of polypropylene are commercially available and well known in the art. One film especially preferred for the present invention is a commercial film designated PY, supplied by the Cryovac Division of W. R.

Grace Co.-Conn. Also within the scope of the present invention are other machinable films. Generally, such films are first stretch-oriented and then heat set, that is, held in a stretched configuration and heated to some. temperature higher than the original orientation temperature but below the melt temperature such that shrinkage will occur at such temperature and not at the original orientation temperature. Such processing provides strength, low elongation and heat resistance. In addition to polypropylenes, polyesters and nylons may be oriented and heat set to provide the properties needed for good machinability required by the present invention.

feet%,: pA coextruded second component film 16 is also depicted in Figure 1. A web of film 16 is bonded to one side of film 12. It should be noted that although it is within the scope of the present invention to bond a web of film 16 to both sides of film 12, such is not necessary and is, generally, not preferred. A second web of film 16 is not required to "balance out" the present structure and prevent curling of a machinable film about a relatively flexible, permeable film. Instead, the present film 16 is stiffened by an interior layer 20, discussed in greater detail below. However, lamination of a web of film 16 to both sides of film 12 may be preferred when it is desirable to provide heat sealable layers on both outer surfaces of the final structure such as 2/901004.2/TXTLPG 11/12/90 -7when lap sealing, which requires the sealing of one surface of the laminate to the opposite surface, is required.

However, while the provision of film 16 on only one side of film 12 allows only for fin sealing, wherein one surface of the laminate is sealed to itself, such sealing method advantageously subjects only the heat resistant film 12 to contact with the sealing jaws.

The film 16 of the present invention must include a bonding layer 18 for bonding film 16 to film 12. Preferably, bonding layer 18 comprises an ethylene vinyl acetate copolymer such as Elvax 3165, an 18% by weight vinyl acetate EVA from DuPont. However, other materials which provide film 16 with a corona laminatable surface are also within the scope of the present invention. In a preferred embodiment, layer 18 comprises a blend of EVA and antiblock, preferably about 80% by weight of Elvax 3130, a 12% by weight vinyl acetate EVA from DuPont, and about 20% by weight of an antiblock masterbatch such as EPE-8160, a 90% by weight polyethylene, 10% by weight Syloid blend from Teknor Color.

In an alternative embodiment, bonding layer 18 is composed of a high vinyl acetate, low melting point EVA such as Alathon 3180 available from DuPont, having a melt index of between 23 and 27 grams/10 minutes, a vinyl acetate content by weight of 25 between about 27% and 29%, and a density of between about 0.948 g/cc and 0.954 g/cc.

SAlso required in film 16 is a layer 20 which imparts stiffness to the otherwise pliant permeable film. As 30 discussed above, it is this stiffness imparting layer which precludes curling of the final laminate structure 10. A preferred material for layer 20 is a butadiene styrene (BDS) copolymer, although any material having the combined properties of stiffness and high gas permeability is within the scope of the present invention. One example of a commercially available resin for use in layer 20 is a BDS copolymer designated DK 10, one of the K-resin series 950209,p:\opr\mi,87716-9040,7 7A available from Phillips Chemical Company. It should be noted that, although layer 20 is illustrated as an interior layer in Figure 1, *6 4* 6 a 6*66 a a 66 6*6 a.

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0 *606 a 950209,p:%oper~nla,87716-9.4,7 when a BDS copolymer is employed for stiffness imparting layer 20, a further sealing layer is not required because of the wide sealing range provided by such material. Note that in Examples 3 and 5 below, an outer BDS layer serves as a heat sealable layer. In order to provide the requisite stiffness for the present application either two or more FPS layers are required, or, if only one BDS layer is provided, it must be a relatively thick layer, comprising from about .o% to about of the total thickness of film 16.

In Figure 1, an outer heat sealable layer is designated at 22. Layer 22 is preferably an ethylene vinyl acetate copclymer and can be comprised of the same material as layer 18. A preferred EVA is Elvax 3165 from DuPont, which S has a vinyl acetate content of about 18 4 Layer 22 can also be a very low density polyethylene (VLDPE) or a VLDPE/EVA blend.

Referring to Figure 2, a multilayer laminate 200 like that of Figure I is shown, but in which a filler layer 24' is disposed between reduced BDS layers 20'. Such structure is preferred because it provides the stiffening properties of the thick BDS layer 20 of Figure i above at less a expense as the filler layer may be composed of a polymeric material which is less expensive than BDS. Such filler layer S is preferably an ethylene/alpha-olefin copolymer. The preferred resin for layer 24' is a VLDPE such as DFDA 1137 supplied by Union Carbide, although other materials having high gas permeability, such as high vinyl acetate EVA copolymers or EVA/VLDPE blends may also be employed.

Bonding reduced BDS layers 20' to filler layer 24' are intermediate tie layers 26', each comprising a polymeric adhesive and preferably a copolymer of ethylene, and more preferably an ethylene vinyl acetate copolymer (EVA). A preferred EVA is one having a vinyl acetate content at about 18% by weight of the copolymer. Other polymeric materials may be used for layers 26' as long as they provide the neces- J 29 01004.2/TXTLPG S12/90 sary high gas permeability required by the present invention. Blends of polymeric materials and polymeric adhesives can also be used for intermediate layers 26'. Further, it should be noted that tie layers may be employed as needed in film 16 for bonding adjacent layers which may otherwise be susceptible to delamination during handling. For example, in Example 2 below, tie layers are employed between an interior BDS layer and each of the bonding layer and the heat sealable layer.

Generally, perforated film 12 may be made by extruding a polypropylene, ethylene propylene copolymer, polyester or nylon film, orienting and heat setting the film and perforating same by means well known in the art such as flame or needle perforation. Multilayer film 16 can be made by standard coextrusic' techniques.

A of multilayer film 16 is bonded to one side of perforated film 12 preferably by corona treating the bond- Sing surfaces of both fri; 12 and film 16, and then, under some heat and pressure, adhering the two webs together.

Although it is within the scope of the present invention to corona treat only film 16 or only film 12, optimum lamination S is achieved when both bonding surfaces are treated. The bond between the two films is designated at 40 in the drawings.

SOther bonding techniques, including the use of conventional lamination adhesives, may also be used. However, bonding techniques in which a separate adhesive is utilized may be less desirable in that such adhesive may block the perforaticus of film 12.

The invention may be further understood by reference to Table 1 indicating specific laminate structures made in accordance with the present invention.

2/901004.2/TXTLPG 11/12/90 TABLE. 1

EXAMPLE

1 PP//EVA/BDS/EVA(tie )/VLDPE/EVA(tie)/BDS/EVA 2 PP//EVA/EVA(tie)/BDS/EVA(tie)/EVA 3 PP//EVA/BDS/EVA(tie)/VLDPE/EVA(tie)/BDS/EVA/BDS 4 PP//EVA/BDS/EVA 5 PP//EVA/BDS In the laminate of Example 3, about 20% of the EVA of bonding layer comprised, an antiblocking agent masterbatch which had been preblended with the EVA prior to extrusion.

The antiblockir.g agent used included 90%low density polyethylene blended with 10%of a colloidal silica. Such structure was tested for water vapor transmission and 0, and CO 2 o permeability. The water vapor transmission rate averaged S about 2.73 g/100 in 2 -24 hrs. at 100 0 F and 100% RH. The Soxygen transmission rate averaged about 4858.9 cm'/m 2 -atm.-24 hrs. at 73°F. The carbcn dioxide transmission rate averaged about 30204.0 cm 3 /m'-atm.-24 hrs. at S 73OF.

Although the outer permeable films, generally 16, of the present invention are represented as composites of varying numbers of layers, it is to be understood that the relative thickness of any film 16 is not necessarily a function of the number of layers comprising such. For example, the permeable film of Example 4 above may have a thickness as great as that of Example 1. In Example 1, the VLDPE core is included in order to add bulk between the stiffness imparting BDS layers at a reduced cost. In Examples 4 and. 5 the BDS S2901004 2/TYTLPG t ^ll2/90 I I">1

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layer is thickened in order to provide the thickness and stiffness of the film of Example 1.

Although the present invention h3s been described by reference to the specific embodiments and examples, a latitude of modification change and. substitution is intended in the foregoing disclosure, those skilled in the art would readily understand that modifications may be made by one skilled in the art after a review of this description without departing from the spirit and scope of the claims which follow.

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Claims

1. A multilayer laminate comprising: a) an first component film having perfora- tions defined therein; and b) a gas permeable second component film, bonded to one side of the first component film, the second component film including a bonding layer and at least one layer comprising butadiene styrene copolymers.

2. A multilayer laminate according to claim 1 S" wherein said first component film comprises a propylene homo- polymer or copolymer.

3. A multilayer laminate according to claim 1 wherein the bonding layer of the second component film com- prises an ethylene vinyl acetate copolymer. a 4. A ilultilayer laminate according to claim 1 further including an outer heat sealable layer on the second component film. A multilayer laminate according to claim 4 wherein said outer heat sealable layer comprises an ethylene vinyl acetate copolymer. 6 A multilayer laminate according to claim wherein the outer heat sealable layer of the second component film is the same material as that of the bonding layer.

7. A multilayer laminate according to claim 4 wherein the outer heat sealable layer of the second component film comprises a very low density polyethylene. 2/901004.2/TXTLPG 11/12/90

8. A multilayer laminate according to claim 4 wherein the outer heat sealable layer of the second component film comprises a butadiene styrene copolymer.

9. A multilayer laminate according to claim 1 wherein the bonding layer of the second component film com- prises a blend of ethylene vinyl acetate copolymer and an antiblocking agent master batch. A multilayer laminate according to claim 9 wherein the bonding layer of the second component film com- prises a blend of about 80% 4 ethylene vinyl acetate copolymer and. about 2 0%Aof an antiblocking agent master batch. 0 S.. 0 '11. A multilayer laminate according to claim 1 wherein the first component perforated film comprises a polyester.

12. A multilayer laminate according to claim 1 wherein the first component perforated film comprises a nylon. 0*%

13. A multilayer laminate according to claim 1 wherein the fi. .t component perforated film is oriented.

14. A multilayer laminate according to claim 13 wherein the first component film is oriented and heat set. A multilayer laminate according to claim 1 wherein said second component film comprises at least two layers comprising butadiene styrene copolymers and further including a filler layer disposed between two of said at least two butadiene styrene layers;

16. A multilayer laminate according to claim wherein said filler layer comprises very low density polyeth- ylene. 2 q 04.2/TXTLPG 1

17. A multilayer laminate according to claim wherein said filler layer comprises ethylene vinyl acetate copolymer.

18. A multilayer laminate according to claim wherein said filler layer comprises a blend of very low densi- ty polyethylene and ethylene vinyl acetate copolymer.

19. A multilayer laminate according to claim further including additional layers disposed between said filler layer and each of said two butadiene styrene layers, said additional layers bonding each of said butadiene styrene layers to said filler layer. 4 i 20. A method of making a multilayer laminate com- prising: a) providing a first film; b) perforating said first film; or** c) coextruding a second film having a bonding layer and at least one layer comprising- Sbutadiene styrene copolymers; and d) bonding a web of the second film to the perforated film.

21. A method according to claim 20 including the step of corona treating the second film at its bonding sur- face prior to bonding a web thereof to the perforated film.

22. A method of making a, multilayer laminate com- prising: stroong e-.-ye'ns'\\e a) providing a4perforated, machinable film; C, ,4901004.2/'rTLPG 11/12/90 15 b) coextruding a second f ilm haiving a bonding layer and at least one layer for imparting stiffness to said second film wherein said second film having a high 4permeability; and c) bonding a web of the second f ilm to one side of the perforated film.

23. A multilayer laminate according to claim 1, or a metho~d of making a said laminate, substantially as hereinbefore described with reference to the drawings and/or Examples. Dated this 9th day of February, 1995 W. R. GRACE CO.-CONN by DAVIES COLLISON CAVE Patent Attorneys for the applicant(s) 0 $see *0

0090.. 950209,p:opcr\mla,8716-9.O40,15 ABSTRA~CT OF THE DISCLOSURE A multilaye.. laminate comprises a machinable film with perforations defined therein, preferably of a propylene homopolymer or copolymer, and a second component film bonded to one side of the machinable film, such laminate providing the combined properties of machinability, high gas. permeabii:-- ty and low moisture transmission while maintaining. a substan- tial~ly planar configuration. 00 0 j 0o