JP2693990B2 - Multi-layer laminate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multilayer laminate suitable for packaging materials such as juice, beverages such as coffee and retort foods such as curry and soup. In particular, the present invention provides a multi-layer laminate capable of heat-sealing and improving the preservability of aroma, which is one of the important commercial values of foods.

(2) Conventional Technology The aroma of food (hereinafter abbreviated as flavor) is composed of organic compounds having various carbon numbers. For example, terpene hydrocarbons (d-limonene, myrcene, etc.), terpene alcohols (α-terpineol, linanol, geraniol, etc.), alcohols (octanol, isoamyl alcohol, etc.), aldehydes (octanal, citral, trans-2). -Hexanal, etc.), esters (ethyl caprate, amyl benzoate ethyl cinnamate, etc.) and the like. The general constitution of a multilayer laminate for food packaging in which these aromas should be preserved is a heat-sealable polyolefin resin layer as an inner layer, an ethylene-vinyl alcohol copolymer and a polyvinylidene chloride copolymer as a gas barrier layer in the middle. , A gas barrier resin such as a polyamide resin, a metal foil such as aluminum, and a thermoplastic resin layer such as a polyolefin resin, a polyester resin, a vinyl chloride resin, or a polystyrene resin as a supporting layer or a protective layer on the outside thereof. . These layers are generally laminated by an adhesive layer. In particular, the polyolefin resin as the heat seal layer on the inner surface side, the gas barrier resin, and the metal foil have no affinity for each other. This can be easily imagined because polyolefin resins such as polyethylene and polypropylene are non-polar.

Generally, a dry lamination method in which polyester, acrylic, or polyurethane adhesives are laminated, or a polyolefin resin extruded and melt-grafted with an organic peroxide and an unsaturated carboxylic acid anhydride, or heat A method of obtaining a multilayer laminate by a multilayer coextrusion method using a so-called modified polyolefin resin as an adhesive layer obtained by, for example, a method of dissolving a polyolefin resin in xylene and grafting an unsaturated carboxylic acid anhydride with an organic peroxide is well known. It is publicly known.

By the way, one of the important commercial values of packaged food is its flavor. This is one factor of the flavor of food, and it is no exaggeration to say that flavor deterioration itself is deterioration of food as a product. This flavor is made by a large number of trace organic compound components contained in food, and the flavor unique to the food is formed by the balance of vapor concentrations of these trace organic compound components.
However, if a polyolefin resin is used as the heat-sealing layer that comes into direct contact with the food, the flavor in the food will be sorbed to a considerable extent, so the heat-sealing layer must be thin, and the heat-sealing layer may be damaged. It was Regarding the relationship between flavor and fragrance and polymers, Watanabe et al .; Japan Society of Food Industry, Vol.10, No.4, P118 (19)
63), Food Industry Separate Volume; Food Packaging and Materials, Kosagi (Showa 54)
), Shigeyuki Harada; Japan Food Science, March issue P4
9 (1987), PRECEDING OF FUTURE-PAK '87 (PYDERASSO
CIATES INC.) NOV.P9 (1987) etc.

As a conventional technique relating to flavor retention, one or more of polyethylene terephthalate, ethylene-vinyl alcohol copolymer and nylon is used as the innermost layer in contact with the contents (JP-A-57-163654). And JP-A-60-48344), a method of using a mixture of polyester and polyamide as the innermost layer (JP-A-61-64449).
Japanese Patent Laid-Open Publication No. 59-174348), a method of kneading a food flavor into a resin forming an innermost layer (JP-A-59-174348 and 59-174470, and a method of using a mixture of polyesters having different molecular weights as an inner surface material (JP-A-57). No. 163654) is known.

Paper board having an ethylene-vinyl alcohol copolymer as the innermost layer in contact with the contents (Japanese Patent Laid-Open No. 63-3950) Paperboard having heat sealable glycol-modified polyethylene glycol as the innermost layer in contact with the contents JP-A-62-290534), the thickness of the ethylene-vinyl alcohol copolymer, which is laminated on the polyolefin layer and the polyolefin layer via an adhesive layer to form the inner surface of the package, is 5
There is known a method of adjusting the thickness to 40 μ (Japanese Utility Model Publication No. 63-21031).

However, all of these methods have a problem that the melting point is higher than that of the polyolefin resin and the heat sealability is poor, and when the food flavor is kneaded into the innermost layer resin due to the high kneading temperature, there is a problem that heat deterioration occurs. However, even if heat sealing is possible, there is a problem that the heat sealing property is poor and the heat sealing portion is easily damaged.

(3) Problems to be Solved by the Invention According to the above-mentioned conventional techniques, there is a drawback that the flavor barrier property is superior to the polyolefin resin but the heat seal property is inferior to the polyolefin resin. Regarding the flavor barrier property, the ethylene-vinyl alcohol copolymer is the most excellent, but the heat seal property is inferior to the polyolefin resin. The ethylene-vinyl alcohol copolymer has a higher heat melting temperature than the polyolefin resin. Therefore, the heat-sealing temperature was high, and the toughness was lacking, so that the heat-sealing strength was poor. As a solution to these problems, it is necessary to select an ethylene-vinyl alcohol copolymer having a high ethylene content, but the heat sealability is slightly improved as the ethylene content is increased, but on the contrary, the flavor barrier property is poor and the heat sealability is poor. There was a problem that both the flavor barrier property and the flavor barrier property were not compatible. Therefore, it is an object of the present invention to obtain a multi-layer laminate having excellent heat sealability, flavour barrier properties and mechanical strength.

(4) Means for Solving Problems The present invention has been made to solve the above problems, and its gist is that polyvinyl alcohol is at least 10% by weight based on the total amount of polyvinyl alcohol and vinyl acetate monomer. When present, it has at least one or more polyvinyl alcohol-based copolymer resin layers having an ethylene content of 1-50 wt% obtained by emulsion polymerization of vinyl acetate monomer and ethylene monomer, and is composed of one or more thermoplastic resins. A multilayer having excellent heat sealability, flavor barrier properties, and mechanical strength by using a multilayer laminate in which a polyvinyl alcohol-based copolymer resin layer is used as a heat seal layer when the article is packaged. To obtain a laminate.

The polyvinyl alcohol-based copolymer resin constituting the present invention can be obtained by the method described in JP-A-60-96637. As an example of the method for producing this resin, it can be obtained by copolymerizing with vinyl acetate and ethylene using a known catalyst in the presence of polyvinyl alcohol having an average degree of polymerization of 20 to 5000. The polyvinyl alcohol used may have any degree of hydrolysis, that is, an average degree of saponification of 50 to 50.
99% can be used, but those with an average saponification degree of 80 to 99% are preferred. The amount of polyvinyl alcohol present in the aqueous emulsion during the polymerization of vinyl acetate and ethylene should be at least 10% by weight, based on the total amount of vinyl acetate and polyvinyl alcohol. If it is less than this, the flavor sorption becomes large, which is not suitable for the purpose of the present invention. In addition, the content of ethylene in the polyvinyl alcohol-based copolymer produced by the above method is 1 to 50% by weight, and 10 to 45% by weight.
Is preferred. When the ethylene content exceeds 50% by weight, the heat-sealing property becomes good, but the flavor sorption increases, which is not suitable for the purpose of the present invention. If it is less than 1% by weight, it cannot be used because of poor melt moldability.

The content of vinyl acetate unit is preferably 1 to 89% by weight. If it is less than 1% by weight, the melt moldability is poor,
If it exceeds 89% by weight, flavor sorption increases.

This polyvinyl alcohol-based copolymer resin has an additional 10
It is possible to copolymerize monomers having an ethylenically unsaturated bond within a weight percentage. Examples of these monomers include unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, or alkyl esters thereof, propylene, butene, decene, octadecene α-olefin, and the like.

On the other hand, as the thermoplastic resin laminated on the polyvinyl alcohol resin layer, polyethylene resin, polypropylene resin, polybutene resin, 4-methylpentene-1 resin, EV
A, polyolefin resin such as copolymer resin of ethylene and α-olefin having 3 to 12 carbon atoms or its modified product (hereinafter abbreviated as PO), polystyrene resin (hereinafter abbreviated as PS)
Polyethylene terephthalate resin (hereinafter abbreviated as PET),
Examples include biaxially oriented polypropylene (hereinafter abbreviated as OPP), polyvinyl chloride resin (hereinafter abbreviated as PVC), polycarbonate resin (hereinafter abbreviated as PC), polyamide resin (hereinafter abbreviated as NY), and the like. An example of a copolymer resin of ethylene and an α-olefin having 3 to 12 carbon atoms is ethylene-butene-
1 copolymer, ethylene-4 methylpentene-1 copolymer, ethylene-hexene-1 copolymer and the like.
Further, modified polypropylene blended with ethylene-propylene rubber, modified polybutene, modified poly-4 methylpentene-1 or the above-mentioned polyolefin polymer is grafted with an unsaturated carboxylic acid or an anhydride thereof under an organic peroxide. Contains PO also copolymerized with other monomers (eg methyl methacrylate, ethyl acrylate, etc.).

Generally, a packaged object such as a food uses a polyolefin resin for a heat-sealing layer, but the flavor component of the content is sorbed on the polyolefin resin, and the flavor component is lost from the content in a severe case. As used herein, sorption refers to a phenomenon in which a low molecular weight organic substance is dissolved and diffused in a solid such as a polymer. Due to this sorption phenomenon, the low molecular weight organic substance, which is the flavor component of the contents, is dissolved and diffused in the polyolefin resin forming the portion in contact with the contents, and the scent is lost from the contents.

As a result of intensive studies on the problem of sorption, the present inventors have found that polyvinyl alcohol resin is obtained by emulsion-polymerizing vinyl acetate monomer and ethylene monomer in the presence of at least 10% by weight of polyvinyl alcohol, Use a multilayer laminate having at least one polyvinyl alcohol copolymer resin composed of vinyl acetate and ethylene units and laminating one or more thermoplastic resin layers, and when packaging an article, use a polyvinyl alcohol copolymer copolymer It was found that when the combined resin layer is used as the innermost layer, that is, the heat seal layer, it is effective as a multilayer laminate excellent in flavor barrier property, heat seal property, and mechanical strength.

As a method for laminating the multilayer laminate of the present invention, urethane-based,
It is carried out by a known dry lamination method or sand lamination method using an acrylic-based dry lamination adhesive, or co-extrusion lamination, co-extrusion method (feed block, multi-manifold method) co-injection method, co-extrusion pipe molding method. Etc. can be obtained.

Further, in the coextrusion molding method, polyvinyl alcohol-based copolymer resin and polyolefin resin, polyethylene,
Ethylene-vinyl acetate copolymer, ionomer resin,
For polyethylene family resins such as polyethylene terpolymers, it is possible to laminate without an adhesive layer, but to obtain a stronger interlayer adhesive strength, an acid anhydride modified polyolefin resin used for ethylene-vinyl alcohol resin, Alternatively, a modified polyolefin resin may be used in the adhesive resin layer.

As an example of the multilayer laminate according to the present invention, when the polyvinyl alcohol copolymer resin layer is represented by A, the adhesive resin layer is represented by B, and the other thermoplastic resin is represented by C, A / C, A / B / C, A / Examples include B / metal foil / C. The combination of these resins can be appropriately changed in these layer structures depending on the required physical properties. For example, more specifically, A / PO / B / PET, A / PO / B / NY, A / PO / B / PS, A / PO / B /
PVC, A / PO / B / PC, A / PO / B / OPP, A / B / PET, A / B / NY, A / B / PS, A / B
/ PVC, A / B / PC, A / B / OPP, A / B / NY / B / PET, A / B / NY / B / PC, A / B / P
ET / PO, A / B / NY / PO, A / B / PS / NY, A / B / PVC / PO, A / B / PC / PO, etc.

Further, an ethylene-vinyl alcohol copolymer, a polyvinylidene chloride copolymer, an acrylonitrile copolymer, a metal foil such as an aluminum foil, which is a gas barrier material, may be laminated as an intermediate layer.

The combination of these multi-layer laminates is not particularly limited, and layer A is used as the outermost layer in the construction of the multi-layer laminate, and when the article is packaged, it is used as the heat-sealing surface, that is, the innermost layer of the package. Due to flavor barrier properties,
It is possible to obtain a multilayer laminate having excellent heat-sealing properties, and the use of layer A as the intermediate layer has no effect.

(5) Action When an article is packaged with a multilayer laminate containing the polyvinyl alcohol-based copolymer resin of the present invention, when the resin is used as a heat seal layer, the reason why the flavor barrier property is excellent and the heat seal property is also excellent is explained. I'm not sure. Generally, the gas barrier property of a resin having a hydroxyl group such as a polyvinyl alcohol-based copolymer resin depends on the diffusion rate of gas molecules in these resins. It is said that the binding force between the molecules is weakened, the mobility between polymer chains is increased, and the diffusion rate of gas molecules is also increased. However, regarding the flavor sorption, the compatibility of the polyvinyl alcohol-based copolymer resin and the flavor component molecule greatly contributes, and in the range of the flavor component molecule that can be usually perceived as an odor, a large sorption property is obtained. It depends on the absence of the molecule shown. On the other hand, regarding the heat-sealing property, the side chain of a copolymer such as ethylene-vinyl alcohol copolymer has only a hydroxyl group, and moreover, a hydrogen bond is taken between adjacent hydroxyl groups and most of them have a hydroxyl group, that is, a vinyl alcohol component. Therefore, it is brittle, and the heat sealability is poor because it is difficult to melt. On the other hand, the polyvinyl alcohol-based copolymer resin used in the present invention is expected to have an ethylene-vinyl acetate copolymer crafted into polyvinyl alcohol, so that it is easily melted at the time of heat-sealing and the heat-sealing portion firmly adheres. I think that the. Hereinafter, the present invention will be described with reference to examples.

(6) Example Example 1-5, Comparative Example 1-6 (Preparation of Polyvinyl Alcohol Copolymer Resin) An autoclave with an internal capacity of 30 liters was used, and the degree of polymerization was
Using PVA205 manufactured by Kuraray Co., Ltd., a partially saponified polyvinyl alcohol resin with a saponification degree of 500 and 88%, the concentration of vinyl acetate and the pressure of ethylene gas were changed while adding ammonium persulfate and sodium metabisulfite as catalysts. Emulsion polymerization was carried out to obtain a polyvinyl alcohol-based copolymer resin having the composition shown in Table 1 right. The solid content of the polymerized emulsion was about 20-60% by weight. This emulsion was left standing at -20 ° C for 20 hours to freeze-precipitate to obtain a polymer. The resulting polymer was then freeze ground and vacuum dried at a temperature of 80 ° C. In addition, the ratio of the ethylene component of the polymer was determined by an alkali saponification method.

(Evaluation of heat-sealing strength) Heat-sealing tester TP701 (manufactured by Tester Sangyo Co., Ltd.) was used, the thickness of each film was 60 μm, the pressure was 2 (Kg / cm ² ), and the heat-sealing time was 1 second. An evaluation sample was obtained. Next, this heat seal strength was T-type peeled at a peeling speed of 300 mm / min using Tensilon manufactured by Toyo Seiki Co., Ltd. to obtain the heat seal strength. The heat seal strength of these measurements is 400g
Table 2 shows the temperatures at which the temperature is above / mm.

(Evaluation of Flavor Sorption) A multilayer laminate was obtained by dry laminating a 30 μm thick film, a 9 μm thick aluminum foil and a 12 μm thick polyethylene terephthalate film of the polyvinyl alcohol copolymer resin of the present invention in Table-2. . The dry laminate was prepared by using an adhesive AD950A / B manufactured by Toyo Morton Co., Ltd. so that the coating amount was 4 g / m ² when dried, and then aging was performed in a constant temperature room at 40 ° C. for 4 days. Using a multilayer laminate, heat sealing was performed so that the resin composition of the present invention was on the inner surface, and a pouch of 18 cm × 10 cm was prepared. An aqueous solution of a surfactant in which various flavor components are dissolved in this pouch (Ryot Sugar Ester S-1170 0.5%
Aqueous solution, 300 ml of Mitsubishi Kasei Foods Co., Ltd., sealed, 23 ℃
It was kept at a constant temperature of 50 days. Thereafter, the pouch was opened, the flavor component adsorbed by the film on the inner surface of the pouch was extracted with ether, and the flavor component remaining in the aqueous solution was also extracted with ether. Next, the sorbed amount and the residual amount converted to the original aqueous solution concentration were quantified for each flavor component using gas chromatography. From the obtained results, the distribution ratio of flavor sorption was calculated according to the following equation. Here, the distribution ratio is defined as in equation (1).

Distribution ratio = Sorption amount / Residual amount (1) That is, the larger the distribution ratio is, the stronger the flavor sorption is. When the distribution ratio is 1, half the flavor is contained in the aqueous solution and half of the flavor is the inner surface layer of the pouch. The concentration of flavor remaining in the aqueous solution decreases as the distribution ratio becomes larger than 1. Table 3 shows the results of flavor sorption evaluated in this way.

(7) Effects The multilayer laminate of the present invention has excellent flavor barrier properties, heat seal properties, and mechanical strength, and is useful as a food packaging material, a medical packaging material, and other packaging materials required to have flavor barrier properties. Further, the multilayer laminate of the present invention can be laminated with metal, paper and the like.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Houji Tanaka 3 2224-2 Higashi Akeno, Oita City, Oita Prefecture

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the polyvinyl alcohol is at least 10% based on the total amount of the polyvinyl alcohol and the vinyl acetate monomer.
At least one polyvinyl alcohol copolymer resin layer having an ethylene content of 1 to 50% by weight, which is obtained by emulsion polymerization of vinyl acetate monomer and ethylene monomer in the state of being present in an amount of 1% by weight, and at least one thermoplastic resin. A multilayer laminate in which the polyvinyl alcohol-based copolymer resin layer serves as a heat seal layer when the article is packaged.