JP2777435B2 - Multi-layer laminate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multilayer laminate suitable for packaging materials such as beverages such as juice and coffee, and retort foods such as curries and soups. In particular, the present invention relates to a multilayer laminate having improved heat preservability and excellent heat sealability for aroma, which is one of the important commercial values of food.

[Prior Art] The aroma of food (hereinafter abbreviated as flavor) is made of organic compounds having various carbon numbers. For example, terpene hydrocarbons (d-limonene, myrcene, etc.), terpene alcohols (α-terpineol, linalool, geraniol, etc.), alcohols (octanol, isoamyl alcohol, etc.), aldehydes (octanal, citral, trans-2-) Hexanal), esters (ethylcaprate, amylbenzoate, ethylcinnamate, etc.).

The general structure of the multilayer laminate for food packaging in which these aromas should be preserved is, as a rule, a heat-sealable polyolefin resin layer as an inner layer, an ethylene-vinyl alcohol copolymer as a gas barrier layer in the middle, and a polychlorinated resin. Use a gas barrier resin such as vinylidene copolymer or polyamide resin or a metal foil such as aluminum, and a thermoplastic resin such as a polyolefin resin, polyester resin, vinyl chloride resin, or polystyrene resin as a support layer or a protective layer on the outside. It consists of a resin layer. These layers are generally laminated by an adhesive layer.

In particular, polyolefin resins are almost exclusively used for the heat seal layer, which is widely used for automation and efficiency of packaging. However, the polyolefin-based thermoplastic resin as the heat seal layer on the inner side has a problem in adhesiveness since it has no affinity with the gas barrier resin and the metal foil.

This can be easily imagined because the polyolefin-based thermoplastic resin represented by polyethylene and polypropylene is non-polar.

Therefore, in general, a dry laminating method of laminating through an adhesive such as polyester, acrylic or polyurethane; extruding and melt grafting a polyolefin resin simultaneously with an unsaturated carboxylic anhydride using an organic peroxide as a catalyst. A method of dissolving a polyolefin resin in hot xylene and a method of grafting an unsaturated carboxylic acid anhydride with an organic peroxide to obtain a multilayer laminate by a multilayer coextrusion method using a so-called modified polyolefin resin as an adhesive layer. Usually, it depends on the adhesive.

By the way, one of the important commercial values of packaged food is its flavor. This is one element of the flavor of food, and it is no exaggeration to say that the deterioration of flavor itself is the deterioration of food as a product. This flavor is made up of a large number of trace organic compound components contained in food, and the unique aroma of the food is formed by the balance of the vapor concentrations of these trace organic compound components.

However, polyolefin resin as a heat seal layer that is in direct contact with foodstuffs is required to make the heat seal layer thinner because it absorbs the flavor in the foodstuff to a considerable extent. The heat seal layer was liable to be damaged.

Watanabe Wataru et al. On the relationship between flavor retention and polymer properties; Journal of the Japan Food Industry Association, Vol 10 No.4 P118 (196
3) and food industry separate volume; food packaging and materials, Mitsuno (Showa 54)
Year), Yasushi Shigeyuki; March issue of Japan Food Science
P49 (1987), PRECEDING OF FUTURE-PAK87 (RYDER
ASSOCIATES INC) NOVEMBERP9 (1987).

As a conventional technique relating to flavor retention, there is a method of forming at least one of polyethylene terephthalate, ethylene-vinyl alcohol copolymer and nylon as the innermost layer in contact with the contents (JP-A-57-163654 and JP-A-60-1985).
48344), a method in which the innermost layer is a mixture of polyester and polyamide (JP-A-61-64449), a method in which a food flavor is kneaded into the resin forming the innermost layer (JP-A-59-174348,
59-174470), and a method using a mixture of polyesters having different molecular weights as an inner surface material (Japanese Patent Laid-Open No. 57-163654).

Paper board having an innermost layer of an ethylene-vinyl alcohol copolymer in contact with the contents (JP-A-63-3950), and paperboard having a heat-sealable glycol-modified polyethylene glycol as the innermost layer in contact with the contents (JP-A-63-3950) 62−
290534), a method in which a polyolefin layer and an ethylene-vinyl alcohol copolymer which is laminated on the polyolefin layer via an adhesive layer and constitutes the inner surface of the package have a thickness of 5 to 40 μm (Public Utility 63-21031). A method has been proposed in which the inner layer is a polyolefin resin layer and the amount of the polyolefin resin is 0.5% or less based on 100% (weight) of the food to be filled (Japanese Patent Laid-Open No. 62-268640).

However, all of these methods use a resin having a melting point higher than that of the polyolefin resin on the surface used as the innermost layer, so that there is a problem that heat sealability is poor, or kneading when mixing a fragrance. Due to the high temperature, there is a problem that heat deterioration occurs when kneading the food flavor into the innermost layer resin, and even if heat sealing can be performed, the heat sealing performance is poor and the heat sealing part is easily damaged, etc. Or the problem of JP-A-62-2686.
In order to reduce the amount of polyolefin to 0.5% or less with respect to the amount of filled food 100% (weight) as in Japanese Patent Publication No. 40, specifically, it is necessary to make the low-density polyethylene very thin as 10 μm, At the time of heat sealing, the outer layer made of a resin having a higher melting point than low-density polyethylene became unmelted, resulting in poor heat seal strength and a problem of breakage.

Some of them are effective in the case of large-volume filled foods, but in the case of small-volume filled foods, there are inevitably restrictions on reducing the thickness of the polyolefin or the size of the container. Restrictions.

[Problem to be Solved by the Invention] In the conventional technology using a gas barrier resin as the innermost layer, the flavor barrier property is superior to the polyolefin resin, but the heat sealability is inferior to the polyolefin resin, so that the workability and quality are maintained. There was a problem from the point of view.

For example, regarding the flavor barrier property, ethylene-
Although the vinyl alcohol copolymer was the most excellent, the heat sealability was higher than that of the polyolefin resin due to the higher heat melting temperature, and the heat seal temperature was higher, and the heat seal strength was poor due to lack of toughness.

As a solution to this, there is a method of selecting an ethylene-vinyl alcohol copolymer having a high ethylene content,
As the ethylene content increases, the heat sealing property is slightly improved, but the flavor barrier property is worsened, and contradictory problems of the heat sealing property and the flavor barrier property cannot be solved at the same time.

Accordingly, an object of the present invention is to obtain a multilayer laminate having excellent heat sealing properties, and also excellent flavor barrier properties and mechanical strength.

Means for Solving the Problems The present invention has been made to solve the above problems, and polyvinyl alcohol is at least 10% by weight based on the total amount of polyvinyl alcohol and vinyl acetate monomer.
At least one polyvinyl alcohol-based copolymer resin layer composed of units of polyvinyl alcohol, vinyl acetate, and ethylene having an ethylene content of 1 to 50% by weight obtained by emulsion polymerization of a vinyl acetate monomer and an ethylene monomer in an existing state. A layer of a polyolefin-based thermoplastic resin layer or an adhesive layer and a layer of a polyolefin-based thermoplastic resin layer having a thickness of not less than 2 μm and not exceeding 30 μm adjacent to the resin layer, and when the article is wrapped, An object of the present invention is to provide a multilayer laminate excellent in heat sealability, flavor barrier properties and mechanical strength by using a resin layer as a heat seal surface.

The production method of the polyvinyl alcohol copolymer resin of the present invention is described in JP-A-60-96637 and JP-A-63-108016.

As an example of a method for producing this resin, the average degree of polymerization is 20 to
It is obtained by emulsion copolymerization of vinyl acetate and ethylene using a known catalyst in the presence of 5000 polyvinyl alcohol.

The polyvinyl alcohol used can have an average saponification degree of 50 to 99%, but preferably has an average saponification degree of 80 to 99%. During the polymerization of vinyl acetate and ethylene, the amount of polyvinyl alcohol present in the aqueous emulsion must be at least 10% by weight, based on the total amount of vinyl acetate and polyvinyl alcohol. If it is less than this, the sorption of the flavor becomes large and is not suitable for the purpose of the present invention.

The ethylene content in the polyvinyl alcohol-based copolymer produced by the above method is 1 to 50% by weight, preferably 10 to 45% by weight.

When the ethylene content exceeds 50% by weight, the heat sealability is improved, but the sorption of flavor is increased, which is not suitable for the purpose of the present invention. On the other hand, if it is less than 1% by weight, it cannot be used because the melt moldability is inferior.

The content of vinyl acetate units 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.

A monomer having an ethylenically unsaturated bond within 10% by weight can be further copolymerized with the present polyvinyl alcohol copolymer resin. Examples of these monomers include unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, and alkyl esters thereof, and α-olefins such as propylene, butene, decene, and octadecene.

On the other hand, as the thermoplastic resin of the heat seal layer to be laminated on the polyvinyl alcohol-based copolymer resin layer, polyethylene resin, polypropylene resin, polybutene resin, 4-methylpentene-1 resin, EVA, ethylene and ethylene having 3 to 1 carbon atoms are used.
And polyolefin resins such as copolymer resins with α-olefins (2) or modified products thereof (hereinafter, referred to as polyolefin resins), and blends thereof.

Examples of a copolymer resin of ethylene and an α-olefin having 3 to 12 carbon atoms include ethylene-butene-1 copolymer,
Ethylene-4 methylpentene-1 copolymer, ethylene-
Hexene-1 copolymer and the like. Ethylene-
Modified polypropylene, modified polybutene, modified poly-4 methylpentene-1 blended with propylene rubber, etc.
Alternatively, in the present invention, a polyolefin polymer obtained by grafting an unsaturated carboxylic acid or its anhydride to the above-mentioned polyolefin polymer in the presence of an organic peroxide or copolymerizing it with another monomer (eg, methyl methacrylate, ethyl acrylate, etc.) is also used. It is contained in resin.

Generally, a polyolefin-based resin is used for a heat seal layer for packaging foods and the like, but the flavor component of the content is sorbed by the polyolefin resin, and sometimes the flavor component is lost from the content. The sorption referred to herein is a phenomenon in which low molecular organic substances dissolve and diffuse into a solid such as a polymer.

The present inventors have conducted intensive studies on this sorption problem and have found that polyvinyl alcohol resin obtained by emulsion polymerization of vinyl acetate monomer and ethylene monomer in the presence of at least 10% by weight of polyvinyl alcohol, vinyl acetate, Laminating a polyolefin-based thermoplastic resin layer or an adhesive layer and a polyolefin-based thermoplastic resin layer having a total thickness of 2 μm to 30 μm adjacent to the resin having at least one layer of a polyvinyl alcohol-based copolymer composed of ethylene units. When a polyolefin-based thermoplastic resin layer is used as the innermost layer, that is, a heat seal layer, when packaging an article using a multilayered laminate obtained as described above, a multilayer having excellent content resistance, flavor barrier properties, heat sealability, and mechanical strength. It was found to be effective as a laminate.

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

However, in the dry lamination method, if the thickness of the polyolefin-based thermoplastic resin layer film is too small, it may cause breakage or wrinkling of the film in the dry lamination. Therefore, the thickness is preferably 10 μm or more.

Further, in the coextrusion molding method, as the polyolefin-based thermoplastic resin resin which is laminated on the polyvinyl alcohol-based copolymer to form a heat seal layer, polyethylene, ethylene-vinyl acetate copolymer, ionomer resin, polyethylene-based ternary resin There are resins of the polyethylene family such as copolymers, which can be laminated without an adhesive layer. To obtain stronger interlayer adhesive strength, unsaturated carboxylic acids or their anhydride-modified polyolefin resins or urethane-based, acrylic-, polyester-based adhesives for dry lamination, which are usually used for bonding ethylene-vinyl alcohol resins, etc. May be used for the adhesive resin layer.

As examples of the multilayer laminate according to the present invention, B is a polyvinyl alcohol-based copolymer resin layer, A is a polyolefin-based resin layer having a thickness of 2 μm to 30 μm, and C is an adhesive resin layer.
+ C is set to 2 μm to 30 μm. ), And other thermoplastic resins are represented by D as follows. A / B, A / C / B, A / B / C /
D, A / B / metal foil / D, A / C / B / metal foil / D, and the like.

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

The combination of these multilayer laminates is not particularly limited, and layer A may be the outermost layer in the configuration of the multilayer laminate, and
Multilayer laminate with excellent flavor barrier properties and heat sealability by laminating a polyvinyl alcohol copolymer resin adjacent to the layer and using it as the innermost layer of the package when packaging an article. Can be obtained by laminating the B layer next to the A layer,
Or it is necessary to laminate the B layer on the A layer via the C layer,
There is no effect if the layer B is separated from the layer A and used as an intermediate layer. When the layer B is laminated on the layer A via the layer C, A
There is no effect unless the total thickness of the layer and the C layer is 30 μm or less.

If the thickness of the polyolefin-based thermoplastic resin used as the heat seal layer is 2 μm or less, molding is difficult, and
If it is 30 μm or more, the sorption amount of the flavor component becomes large, which is not preferable. It is preferable to laminate the polyolefin-based thermoplastic resin or the resin layer and the C layer so that the total thickness thereof is in the range of 5 μm to 20 μm.

On the other hand, the thickness of the resin layer of the polyvinyl alcohol-based copolymer is not particularly limited.
It is good to make it below μm.

[Operation] When an article is wrapped using the multilayer laminate containing the polyvinyl alcohol-based copolymer resin used in the present invention, the thickness is 2
When using a polyolefin-based thermoplastic resin layer of μm to 30 μm as a heat-sealing layer, it is not clear why the flavor barrier property is excellent and the heat-sealing property is excellent, but it contains hydroxyl groups as in a polyvinyl alcohol-based copolymer resin. The gas barrier properties of a resin depend on the diffusion rate of gas molecules in these resins, and the resin contains water, which absorbs moisture and weakens the binding force between polymer chains, resulting in mobility between polymer chains. It is said that the diffusion rate of gas molecules also increases with the increase in gas diffusion.

However, regarding the flavor sorption, the compatibility between the polyvinyl alcohol-based copolymer resin and the flavor component molecules greatly contributes, and within the range of the flavor component molecules that we can usually feel as a fragrance, a large sorption property is exhibited. This is probably due to the absence of a molecule indicating

On the other hand, with regard to heat sealability, the side chain of a copolymer such as an ethylene-vinyl alcohol copolymer has only a hydroxyl group, and further, adjacent hydroxyl groups take a hydrogen bond with each other,
In addition, most of them are hydroxyl groups, that is, vinyl alcohol components, so that they are brittle and hard to melt, so that heat sealability is poor.

However, in the polyvinyl alcohol copolymer resin used in the present invention, ethylene-
Since the vinyl acetate copolymer is expected to be grafted, it is easily melted during heat sealing, so that the layer A is exposed to severe heat sealing conditions, and a portion of this layer flows, and the polyolefin-based thermoplastic resin layer It is considered that even if the heat-sealing portion is absent, the heat-sealing portion is strongly bonded due to the heat-sealing performance of the polyvinyl alcohol-based copolymer resin layer itself, which is an adjacent layer.

 Hereinafter, the present invention will be described with reference to examples.

[Examples] (Examples 1 to 9 and Comparative Examples 1 to 10) << Preparation of polyvinyl alcohol-based copolymer >> The degree of polymerization was determined using an autoclave having a content of 20 liters.
Using PVA205 manufactured by Kuraray Co., Ltd., which is a partially saponified polyvinyl alcohol resin having a saponification degree of 500% and having a ratio of vinyl acetate monomer as shown in the left column of Table 1, the catalysts ammonium persulfate and Emulsion polymerization was carried out while changing the pressure of ethylene gas while adding sodium metabisulfite, to obtain a copolymer emulsion shown in the right column of Table-1. This emulsion is added at -20 ° C for 20
The polymer was frozen for a period of time to precipitate. 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.

<< Preparation of Multilayer Laminate >> The polyvinyl alcohol copolymer shown in Table 1 was used to make the thickness of the layer 20 μm, and this was mixed with linear low density polyethylene (LLDPE, MI 0.8 g / 10 min, density 0.918 g / cc) and unsaturated. Carboxylic anhydride modified polyethylene adhesive resin (MI 3.5g /
A multilayer laminate was obtained with a 40 mmφ multilayer molding machine using a resin composition in which 10 min, density 0.92 g / cc) was mixed one-to-one (Example 1).
-5, Comparative Examples 1-5). On the other hand, the linear low-density polyethylene was changed to polypropylene (MFR 9 g / 10 min) and the unsaturated carboxylic anhydride-modified polypropylene-based adhesive resin (MFR
R 5.5 g / 10 min, density 0.8 g / cc) (Examples 6 to 9 and Comparative Examples 6 to 8), and a polyvinyl alcohol-based copolymer resin was used with Kuraray Co., Ltd. EVAL EPG110 (EVOH, ethylene content 4
7 mol%), PP was changed to LLDPE, and unsaturated carboxylic acid anhydride-modified polyethylene-based adhesive resin (MI 3.5 g / 10 min, density was used for adhesion of linear-low-density polyethylene and ethylene-vinyl alcohol copolymer resin) 0.92 g / cc) (Comparative Example 9), LLDPE was changed to PP with the same EVOH, and unsaturated carboxylic anhydride-modified polypropylene-based adhesive resin ( MFR
9g / 10min) (Comparative Example 10) to obtain a multilayer T-die film shown in Table-2.

<< Evaluation of heat seal strength >> Using a tester Sangyo (manufactured) heat seal tester TP701, the pressure of each film was 2 (Kg / cm ² ), the heat seal time was 1 second, the heat seal temperature was changed, and the width 15
The sample for heat seal evaluation having mm was obtained. Next, the heat seal strength was measured using Tensilon manufactured by Toyo Seiki Co., Ltd.
T-shaped peeling was performed at a peeling speed of 300 mm / min, and the heat seal strength was determined. The heat seal strength was 500g / 1
Table 2 shows the temperature at which it becomes 5 mm or more.

<< Evaluation of Sorption of Flavor >> A 9 μm-thick aluminum foil and a 12 μm-thick polyethylene terephthalate film were dry-laminated on the multilayer laminate film of the present invention shown in Table 2 to obtain a multilayer laminate.
Dry laminate AD95 manufactured by Toyo Morton Co., Ltd.
Using 0A / B, the coating amount was adjusted to 4 g / m ² when dried, and then aging was performed in a constant temperature room at 40 ° C. for 4 days. Heat-sealed so that the polyolefin-based thermoplastic resin layer becomes the inner surface using the multilayer laminate of the present invention, 18 cm
A × 10 cm pouch was made. 300 ml of a surfactant aqueous solution (Ryoto Sugar Ester S-1170 0.5% aqueous solution, manufactured by Mitsubishi Kasei Food Co., Ltd.) in which various flavor components were dissolved was sealed in the pouch, and kept at a constant temperature of 23 ° C. for 70 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 = sorbed amount / remaining amount (1) That is, the larger the distribution ratio, the stronger the flavor sorption. When the distribution ratio is 1, half of the flavor is contained in the aqueous solution before encapsulation, and half of the flavor is on the inner layer side of the pouch. The concentration of flavor remaining in the aqueous solution decreases as the distribution ratio becomes greater than 1. The results of flavor sorption evaluated in this way are shown in Table-3.

[Effects] The multilayer laminate of the present invention is excellent in flavor barrier properties, heat sealability, and mechanical strength, and is useful as a food packaging material, a medical packaging material, and other packaging materials requiring flavor barrier properties. Further, the multilayer laminate of the present invention can be laminated with metal, paper and the like.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B32B 1/00-35/00

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-based copolymer resin layer composed of units of polyvinyl alcohol, vinyl acetate and ethylene having an ethylene content of 1 to 50% by weight obtained by emulsion polymerization of a vinyl acetate monomer and an ethylene monomer in a state of being present in an amount of 1% by weight. When having a laminate of a polyolefin-based thermoplastic resin layer or an adhesive layer and a layer made of a polyolefin-based thermoplastic resin layer having a thickness of not less than 2 μm and not exceeding 30 μm, which is adjacent to the resin layer, And a multilayer laminate having a polyolefin-based thermoplastic resin layer as a heat sealing surface.