JPH04269533A - Cheese packing laminate - Google Patents

Abstract

PURPOSE: To obtain a soft cheese packaging substance having low moisture transmission and high gas permeability by adhesively laminating a multilayer film of a second component film on a first component film having perforations therein. CONSTITUTION: A multilayer laminate 100 comprises a first film 12 having perforations 14 therein. A film 16 has a bonding layer 18 for bonding the film 16 to the film 12, a layer 20 for giving rigidity to a flexible permeable film, and a heat sealable outside layer 22. The perforated film 12 is manufactured by extruding a polypropylene, ethylene-propylene copolymer, polyester or nylon film, orienting and thermosetting it and then perforating by a conventional known means, and the film 16 is manufactured by a conventional technology. A web of the film 16 is bonded to one side of the film 12 by corona treating the bonded surfaces of the films 12, 16 and then adhering the two webs by heating and pressurizing.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION This invention relates to a laminate structure useful for packaging food products, particularly soft cheese.

[0002] In recent years, camembert
) and Brie, soft cheeses such as ethylene/vinyl acetate copolymers, polypropylene, nylon/polyethylene laminates or polyester/polyethylene laminates, with or without ethylene/vinyl acetate copolymers, polyethylene laminates, etc. packaged with material. The oxygen and carbon dioxide permeability of such structures is extremely important. High oxygen permeability is extremely important when packaging cheeses, such as Brie, which require an air atmosphere to support bacterial growth on the surface of the cheese. Other cheeses emit significant amounts of carbon dioxide and therefore require permeable packaging materials to exclude gases from the packaging. In the case of product packaging, oxygen and carbon dioxide permeability needs to be adjusted to minimize the damaging effects of enzymatic browning of cut surfaces and anaerobic product anaerobicization.

However, in most cases, materials with the desired oxygen and carbon dioxide permeability necessary for the above applications also have minimal abuse resistance and machinability. Abuse-resistant and machinable film structures typically lack the gas permeability and sealing properties necessary for such applications.

[0004] This application requires a structure that combines heat resistance, low elongation and strength with high gas permeability and sealing properties. A low water vapor transmission rate is also required to avoid drying out of the packaged food product.

These needs have been met by the structure described in Schirmer, US Pat. No. 4,935,271, which discloses a multilayer laminate for use in packaging lettuce, etc. a first impermeable film of propylene homopolymer or copolymer having defined pores therein; a tie layer and a heat sealable outer layer of ethylene/vinyl acetate copolymer; a second transparent film bonded to the film. In such laminates, machinability is provided by a polypropylene film that is perforated to provide permeability. The gas permeable second film contributes to the low moisture permeability and sealability of the entire structure. However, with respect to Schirmer's structure, as a result of placing a soft and flexible second film adjacent to the relatively stiff, thermoset polypropylene,
The entire structure curls, thereby impairing machinability.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved material for soft cheese packaging that has low moisture permeability and high gas permeability.

[0007] Another object of the present invention is to provide a material that can be machined;
An object of the present invention is to provide an improved material for packaging cheese, etc., which has heat resistance, non-extensibility and strength.

A further object of the present invention is to provide a packaging laminate that has high gas permeability in addition to strength, heat resistance, and low elongation, prevents moisture permeation, and easily maintains a flat shape during processing. That's true.

[0009] These objectives, as well as other objectives, include a tough and non-extensible first component film with defined pores therein and a high permeability and low moisture permeation bond bonded to the first component film. This is achieved by providing a multi-layer laminate consisting of a second component film having a bonding layer and a layer imparting stiffness to the second film.

[0010] Furthermore, such an objective is achieved by providing a perforated film, preferably consisting of a propylene homopolymer or copolymer, coextruding a second film having a tie layer and a styrene/butadiene inner layer, and , is achieved by providing a method of manufacturing a multilayer laminate comprising bonding a second film to the perforated film.

DEFINITIONS As used herein, the term "ethylene copolymer" refers to a copolymer of ethylene and vinyl acetate, alkyl acrylate or alpha copolymer.
- Refers to copolymers with olefins. Also included within the scope of this definition are chemically modified derivatives of these substances.

[0012] The term "EVA" as used herein refers to ethylene/vinyl acetate copolymer.

[0013] As used herein, the term "linear low density polyethylene" (LLDPE) encompasses a group of ethylene/α-olefin copolymers with limited branched side chains and a density of 0.916 g/cc~0.
Refers to a range of 940g/cc. Density is 0.926
Linear polyethylene ranging from g/cc to 0.940 g/cc is sometimes referred to as linear medium density polyethylene (LMDPE).
) is called. Representative product names include Dow Chem.
ical's Dowlex, Mitsui Petrochemical Co., Ltd.'s Ultzex and Neozex, and Du Pont.
There is a company named Sclair. The α-olefin copolymers are generally of butene-1, pentene-1, hexene-1, octene-1, and the like.

[0014] As used herein, the terms "very low density polyethylene" (VLDPE) and "ultra low density polyethylene" (ULDPE) have a density of about
Less than 0.915g/cc, especially normal 0.912
g/cc or less and may be 0.89 g/cc or less. Representative VLDPE resins include UnionCarbid
e company under the designation DFDA, which is believed to have butene or isobutene primarily or usually as a comonomer. Very low density polyethylene compared to LLDPE usually contains a much higher content of copolymers and has distinctly different properties making it a distinct type of polymer. Resins typically designated as "ULDPE" resins are commercially available from Dow and are believed to have octene as a comonomer. These polymers have slight differences in properties that are believed to be due to the comonomers. “0.9” used herein
Linear ethylene with a density less than 15 g/cc/
The term "α-olefin copolymer" includes both VLDPE and ULDPE.

“Butadiene/styrene copolymer” (BD
The term S) is used herein to refer to thermoplastic copolymers, particularly block copolymers containing large amounts (greater than 50%) of styrene and small amounts (less than 50%) of butadiene comonomers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to laminates for use in packaging soft cheese and other products requiring packaging having the properties described herein. Packaging soft cheese requires packaging materials with low moisture permeability and high gas permeability. Additionally, process automation requires machinable materials. Machinability is defined as encompassing strength, low elongation, and heat resistance. Additionally, a machinable film must be capable of retaining a substantially flat shape during various types of manipulation and processing. Typically,
Materials with high gas permeability do not exhibit adequate machinability and vice versa. The present invention is strong, non-stretchable, heat resistant, but non-permeable and non-sealing.
All the requirements of the above applications are met by first providing a machinable film which is also capable of forming a film, and then perforating the film, thereby making it permeable. A permeable, heat-sealable film is bonded to one side of the perforated film to provide sealing capabilities while retaining permeability and providing a moisture-impermeable structure. Curling of the final laminate structure, which is expected when a highly permeable film is laminated to a tough, non-stretchable film, is prevented by including a stiffening layer within the soft permeable film. The relative gas and moisture permeability of the final structure is determined by the thickness and permeability of the second film and the pore size and number of the non-permeable first film.

Referring to FIG. 1, the multilayer laminate 100 includes:
It contains a first film 12 having holes 14 therein. In a preferred embodiment, layer 12 is comprised of propylene homopolymer (PP), although propylene copolymers such as ethylene/propylene copolymer (EPC) may also be used. Various homopolymers and copolymers of polypropylene are commercially available and known in the art. One particularly preferred film in the present invention is Cryovac Divi
sion of W. R. Grace & Co.
There is a commercially available film supplied by -Conn under the designation PY. Other machinable films are also included within the scope of the invention. Generally, such films are first stretch oriented and then heat set, ie, held in the stretched configuration, by heating to a temperature above the original stretch temperature but below the melt temperature. Shrinkage occurs at such temperatures, but not at the original stretching temperature. Such processing provides strength, low elongation and heat resistance. Besides polypropylene, polyester and nylon are
It is stretched and heat cured to provide the properties necessary for good machinability as required by the present invention.

A coextruded second component film 16 is also shown in FIG. A web of film 16 is bonded to one side of film 12. Although it is within the scope of the present invention to have a web of film 16 bonded to both sides of film 12, it will be appreciated that such is not necessary or generally preferred. The second web of film 16 "balances" the structure of the present invention.
e out)" is not necessary to prevent curling of the machinable film for relatively flexible and transparent films. Rather, the film 16 is attached to the inner layer 20, as explained in detail below. However, applying a heat-sealable layer to both outer surfaces of the final structure, such as when a lap seal is required where sealing one side of the laminate also requires sealing the opposite side. If desired, film 1 is placed on both sides of film 12.
Preferably, 6 webs are laminated. however,
Providing film 16 on only one side of film 12 is only possible for fin sealing, where one side of the laminate is sealed to itself, but such a sealing method only applies to heat-resistant film 12. advantageously in contact with the sealing jaws.

Film 16 of the present invention must contain a tie layer 18 for bonding film 16 to film 12. Preferably, bonding layer 18 comprises Du
A product of Pont Corporation, it consists of an ethylene/vinyl acetate copolymer such as Elvax 3165, which is 18% vinyl acetate EVA. However, other materials that provide a film 16 with a corona-laminable surface may also be used.
It falls within the scope of the present invention. As a preferred example, layer 1
8 is EVA and anti-blocking agent (antiblock)
A blend of, preferably about 80% Elvax 3130, which is DuPont's 12% vinyl acetate EVA.
, and 90% polyethylene from TeknorColor
and Syloid 10% blend of EPE-8
It consists of about 20% of an antiblocking agent masterbatch such as 160. In another embodiment, bonding layer 18 is made of DuPo
Alathon 318 commercially available from nt.
High vinyl acetate low melting point EVA (melt index 23-27 g/10 min, vinyl acetate content approx.
29% by weight, density approximately 0.948 g/cc ~ 0.954
g/cc).

[0020] Film 16 requires a layer 20 that provides stiffness to the flexible transparent film. As explained above, it is this stiffening layer that prevents curling of the final laminate structure 100. Preferred materials for layer 20 include butadiene/styrene (BDS) copolymers, although any material that has the properties of both stiffness and high gas permeability is within the scope of the invention. One example of a commercially available resin used for layer 20 includes Phillips Ch
1 of the K resin series commercially available from chemical company.
There is a BDS copolymer designated as DK10. Although layer 20 is shown as an inner layer in FIG.
It will be appreciated that if a DS copolymer is used as the stiffening layer 20, no further sealing layer is required since such a material provides a wide seal. In Examples 3 and 5 below, it can be seen that the BDS outer layer acts as a heat sealable layer. To provide the necessary stiffness for the above applications, two or more BDS layers are required, or if only one BDS layer is provided, approximately % of the total thickness of the film 16. ~
It should be a relatively thick layer consisting of approx.

In FIG. 1, the heat sealable outer layer is 2
2. Layer 22 is preferably an ethylene/vinyl acetate copolymer and may be comprised of the same material as layer 18. A preferred EVA is Elvax, a product of Du Pont, whose vinyl acetate content is about 18%.
There are 3165. Layer 22 is very low density polyethylene (VLDPE)
Or it may be a VLDPE/EVA blend.

Referring to FIG. 2, a multilayer stack 200 similar to FIG. 1 is shown, but the filler layer 24' is a thinned BD.
It is located between the S layer 20'. Such a structure is preferred because it provides the stiffness of the thick BDS layer 20 of FIG. 1 above at a lower cost, since the filler layer may be comprised of a polymeric material that is less expensive than BDS. Such a packed layer is preferably an ethylene/α-olefin copolymer. A preferred resin for layer 24' is VLDPE, such as DFDA 1137, supplied by Union Carbide.
However, high vinyl acetate EVA copolymer or EVA/V
Other materials with high gas permeability such as LDPE blends may also be used.

The connection between the filling layer 24' and the thinned BDS layer 20' is provided by an intermediate connecting layer 26'. Each intermediate connection layer is
The polymeric adhesive preferably comprises a copolymer of ethylene, more preferably an ethylene/vinyl acetate copolymer (EVA). A preferred EVA is one in which the vinyl acetate content is about 18% by weight of the copolymer. Other polymeric materials may also be used as layer 26' so long as they provide the requisite high gas permeability required by the present invention. Mixtures of polymeric materials and polymeric adhesives may also be used as intermediate layer 26'. Additionally, it will be appreciated that a tie layer may be used as necessary within the film 16 to bond adjacent layers that are susceptible to delamination during handling. For example, in Example 2 below, a tie layer is used between the BDS inner layer and each of the tie layer and heat sealable layer.

Typically, perforated film 12 is made by extruding a polypropylene, ethylene/propylene copolymer, polyester or nylon film, stretching and heat curing the film, and then subjecting it to flame or needle perforation techniques known in the art. It can be manufactured by drilling by means such as. Multilayer film 16 may be manufactured by standard coextrusion techniques.

The web of multilayer film 16 is preferably corona treated on the bonding surfaces of both film 12 and film 16 and then bonded to the perforated film 12 by bonding the two webs together under some heat and pressure. Joined on one side. Although it is within the scope of the present invention to corona treat only film 16 or only film 12, optimal lamination is achieved when both bonding surfaces are treated. The bond between the two films is labeled 40 in the figure.

Other bonding techniques may also be used, including the use of common lamination adhesives. However, bonding techniques that utilize other adhesives are less preferred in that such adhesives may block pores in the film 12.

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

[0028]
Table 1 Example 1 PP//EVA/BDS/EVA
(Consolidated)/VLDPE/EVA (Consolidated)/BDS/EV
A 2 PP//EVA/EVA (consolidated)/BDS/EVA (consolidated)/EVA 3
PP//EVA/BDS/EVA (consolidated)/VLD
PE/EVA (consolidated)/BDS/EVA/BDS
4 PP//EVA/BDS/EVA 5
PP//EVA/BDS In the laminate of Example 3, the tie layer of approximately 20% EVA contains an antiblock masterbatch premixed with the EVA prior to extrusion. The antiblocking agent used contains 90% low density polyethylene mixed with 10% colloidal silica. Such structures were tested for water vapor permeability and oxygen and carbon dioxide permeability. Water vapor transmission rate is 100°F and 100
Average approximately 2.73g/100 in2-24 at %RH
It was hrs. The oxygen permeability averages about 4858.9 cm3/m2-atm. at 73°F. -24 hours
It was rs. The permeability of carbon dioxide averages about 30204.0 cm3/m2 -atm. at 73°F. −
It was 24 hours.

Although the transparent outer film of the present invention, generally designated 16, is depicted as a composite of several layers, the relative thickness of any film 16 does not necessarily vary from one such film to another. It is understood that this is not a function of the number of layers. For example, the transparent film of Example 4 above may be as thick as the film of Example 1. In Example 1, a core of VLDPE has bulk between the BDS layers to provide stiffness at low cost.
) is contained to increase the In Examples 4 and 5, the thickness of the BDS layer is increased to provide thickness and stiffness to the film of Example 1.

Although the invention has been described with reference to specific embodiments and embodiments, modifications and substitutions thereof are within the scope of the foregoing disclosure and, upon reviewing the description of the invention, those skilled in the art will appreciate that
It will be readily apparent to those skilled in the art that modifications may be made without departing from the spirit and scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing one specific example of the multilayer laminate of the present invention.

FIG. 2 is a schematic cross-sectional view showing another specific example of the multilayer laminate of the present invention.

[Explanation of symbols]

12 Perforated film 16 Multilayer film 18 Tie layer 20 Stiffening layer 22 Heat sealable outer layer 20'
BDS layer 24' Filled layer 26' Connection layer

Claims (22)

[Claims] Claim 1: a) a first tube having a hole defined therein;
A multilayer laminate consisting of a component film and b) a gas permeable second component film bonded to one side of the first component film and containing a tie layer and at least one layer consisting of a butadiene/styrene copolymer. 2. The multilayer laminate according to claim 1, wherein the first component film comprises a propylene homopolymer or copolymer. 3. The multilayer laminate of claim 1, wherein the tie layer of the second component film comprises an ethylene/vinyl acetate copolymer. 4. The multilayer laminate of claim 1 further comprising a heat sealable outer layer on the second component film. 5. The heat-sealable outer layer is made of ethylene/
The multilayer laminate according to claim 4, comprising a vinyl acetate copolymer. 6. The multilayer laminate of claim 5, wherein the heat sealable outer layer of the second component film is the same material as the tie layer. 7. The heat sealable outer layer of the second component film comprises very low density polyethylene.
The multilayer laminate described in . 8. The multilayer laminate of claim 4, wherein the heat sealable outer layer of the second component film comprises a butadiene/styrene copolymer. 9. The multilayer laminate of claim 1, wherein the tie layer of the second component film comprises a blend of an ethylene/vinyl acetate copolymer and an antiblocking agent masterbatch. 10. The multilayer laminate of claim 9, wherein the tie layer of the second component film comprises a blend of about 80% ethylene/vinyl acetate copolymer and about 20% antiblocking agent masterbatch. 11. The multilayer laminate of claim 1, wherein the first component perforated film comprises polyester. 12. The multilayer laminate of claim 1, wherein the first component perforated film comprises nylon. 13. The multilayer laminate according to claim 1, wherein the first component perforated film is stretched. 14. The multilayer laminate according to claim 13, wherein the first component film is stretched and thermoset. 15. The second component film comprises butadiene/
comprising at least two layers of styrene copolymer;
The multilayer laminate of claim 1 further comprising a filler layer disposed between the at least two butadiene/styrene layers. 16. The multilayer laminate of claim 15, wherein the filler layer comprises very low density polyethylene. 17. The multilayer laminate according to claim 15, wherein the filler layer comprises an ethylene/vinyl acetate copolymer. 18. The multilayer laminate of claim 15, wherein the filler layer comprises a blend of very low density polyethylene and ethylene/vinyl acetate copolymer. 19. Further comprising an additional layer disposed between the filler layer and each of the two butadiene/styrene layers,
16. The multilayer laminate of claim 15, wherein the additional layer connects each butadiene/styrene layer and filler layer. 20. A method for producing a multilayer laminate, comprising: a
a) providing a first film; b) perforating the first film; c) coextruding a second film having a tie layer and at least one layer consisting of a butadiene/styrene copolymer; and d) bonding a second web of film to a perforated film. 21. The method of claim 20, including the step of corona treating the second film at its bonding surface prior to bonding the web of second film to the perforated film. 22. A method for producing a multilayer laminate, comprising: a
b) coextruding a second film having a tie layer and at least one layer imparting stiffness to the second film; and c) providing a perforated film on one side of the perforated film. A method comprising bonding a second web of film.