DE69407954T2 - Multi-layer gas barrier structure and heat-sealable packaging material containing it - Google Patents

Description

Background of the invention (1) Field of the invention

The present invention relates to a multilayer laminate which is useful as a good gas barrier against oxygen gas or the like, has good preservability for flavor components, and good bending and flexural fatigue strength, etc., and a heat-sealable packaging material containing the same and is useful as a packaging material having good preservability for food or the like.

(2) State of the art

The market for chilled, frozen and pre-packaged foods has grown rapidly in the food sector in recent times. These types of foods are characterized by extended shelf life, freshness and ease of preparation, and their widespread use as foods that meet consumer needs is expected to become increasingly widespread.

In the field of packaging materials for this type of food, for example, films, thin films, bags, Tubes, bottles, etc., i.e. materials suitable as a better gas barrier against oxygen gas or the like, are desired in order to enable an extended shelf life.

So far, laminates comprising a plastic substrate and a film of a metal or metal oxide formed on the surface of the plastic substrate have been developed as materials that are suitable as a good gas barrier layer.

For producing the laminate, the following methods have been proposed. For example, methods of vapor deposition of a thin film of metal such as aluminum, etc., and methods of laminating a thin film of metal oxide such as silicon oxide, etc. by vapor deposition or sputtering are described in JP-A-49-41469; JP-A-60-23037; U.S. Patent 3,442,686 and U.S. Patent 4,887,005. These laminates, after further laminating a polyolefin film such as polyethylene film or polypropylene film, have been used as protective films for preventing cracking due to bending or as an adhesive layer for imparting heat-adhesiveness to them.

In order to obtain laminates with very good gas barrier properties, it is necessary to make the thin film of metal or metal oxide significantly thicker than before. A metal or metal oxide is referred to below as "metal". However, the resulting thin film then becomes so brittle that cracks or fine holes can easily form. This means that the laminates are no longer effective as a gas barrier and have limited use as a gas barrier.

One of the most important economic significance of packaged foods is the preservation of flavor, a component contributing to the food's taste. A deterioration of the flavor itself can mean a deterioration of the food as a commercial product. The flavor consists of a variety of organic compounds contained in foods as micro-flavor components, and a specific flavor of the food is based on the balance of vapor concentrations or partial vapor pressures of the corresponding organic compounds as micro-flavor components. Micro-flavor components include, for example, terpene hydrocarbons, terpene alcohols, aldehydes, esters, etc.

In view of heat sealability, polyolefin resin is used for the heat sealable layer as the innermost layer of a food packaging material for retaining flavor. However, the polyolefin resin has a problem that the resin sorbs the flavor from the packaged food to a certain extent.

EP-A-0337316 describes a resin laminate comprising a layer of a styrene-based polymer having a mainly syndiotactic configuration and a thermoplastic resin layer; this laminate is used, for example, for electrostatic capacitors, hot stamping foils, flexible substrates for printed circuits, and films for packaging foodstuffs.

EP-A-0566053 relates to an olefin resin-based product having good gas barrier properties, comprising a crystalline olefin copolymer having formed thereon a thin layer of an inorganic metal oxide, wherein the crystalline olefin copolymer comprises repeating units obtained from ethylene or an α-olefin having 3 to 12 carbon atoms and 0.05 to 20 mol% of a diene; this olefin resin-based product is described as being useful as a packaging or packaging material for bagged foods or IC packages.

Summary of the invention

The object of the present invention is to provide a multilayer laminate which is suitable as a good gas barrier layer and has good aroma preservation properties and good bending and fatigue strength.

As a result of extensive investigations, the present inventors have surprisingly found that remarkably good gas barrier properties can be obtained by further laminating the surface of a laminate comprising a plastic substrate and a thin film of a metal or the like formed on the plastic substrate with a specific resin or resin emulsion composition, whereby the object of the present invention can be achieved.

The present invention relates to a multilayer laminate according to claim 1.

Preferred embodiments thereof are the subject of claims 2 to 11.

Another subject of the present invention is a heat-sealable packaging material according to claim 12.

Preferred embodiments thereof are the subject of claims 13 to 18.

A further object is the use of the inventive multilayer laminate and the heat-sealable packaging material for packaging, and preferably for packaging foodstuffs.

Detailed description of the invention

The present invention is described in more detail below:

The thermoplastic resin for the plastic substrate is selected from the group consisting of polypropylene, poly-4-methylpentene-1, complete saponification products of ethylene/vinyl acetate copolymer, polyacetal, polycarbonate, polyester (e.g. polyethylene terephthalate, polybutylene terephthalate, etc.), polyamide (hereinafter referred to as PA), polyphenylene oxide, polysulfone.

In view of easy processability, among these thermoplastic resins, polyolefin resins, especially polypropylene, poly-4-methylpentene-1, polyester and PA, or their mixtures are preferably used for the plastic substrate.

The metal for use in the invention for lamination with the plastic substrate includes, for example, simple metals such as aluminum, titanium, chromium, nickel, etc., and metal oxides such as aluminum oxide, silicon oxide, titanium oxide, ferrite, Indium oxide, etc. These metals and metal oxides can be deposited as a layer on the surface of the plastic substrate according to known vapor deposition techniques.

The polyvinyl alcohol copolymer emulsion used in the present multilayer laminate as components (a) and (b) (i) can be obtained by polymerizing vinyl acetate with ethylene in the presence of a known catalyst to produce polyvinyl alcohol, hereinafter referred to as PVA, in an aqueous emulsion as described in JP-A-60-96637 and JP-A-63-108016.

It appears that in the resulting PVA copolymer emulsion, PVA is integrated with ethylene-vinyl acetate copolymer, and the PVA copolymer emulsion has the form of copolymers comprising PVA, vinyl acetate and ethylene as components.

The PVA used in the reaction is a partial or complete saponification product of polyvinyl alcohol, and any saponification degree can be used. The preferred average saponification degree is 50 to 99%, and a particularly preferred average saponification degree is 8 to 99%, and the average polymerization degree is preferably 20 to 5000.

The amount of PVA initially present in the polymerization of the aqueous emulsion is 15 to 60% by weight, preferably 15 to 55% by weight, and more preferably 20 to 55% by weight, based on the total weight of vinyl acetate and PVA in the case of (a). If the amount of PVA initially present is less than 15% by weight, no better gas barrier properties can be obtained. while above 60 wt.% the viscosity is increased during the reaction, resulting in difficult temperature control.

In the case of (b) (i), the amount of PVA initially present is 3 wt% to less than 15 wt%, and preferably 5 to 14 wt%. When the amount of PVA initially present is less than 3 wt%, the polymerization is not stable during the reaction, while above 15 wt%, the compatibility with the aqueous solution of the PVA resin is sometimes deteriorated.

The content of ethylene as a component in the PVA copolymer obtained by the above-described method is 1 to 50% by weight, and preferably 10 to 45% by weight. If the content of ethylene as a component is more than 50% by weight, compatibility with PVA is deteriorated and therefore an ethylene content of more than 50% by weight is not suitable for the object of the present invention. Below 1% by weight, melt moldability is poor.

The content of vinyl acetate as another component is not particularly limited, but is preferably 1 to 89 wt. Below 1 wt. %, the melt formability is poor, while above 89 wt. %, no better gas barrier properties can be obtained.

The PVA copolymer resin may also be copolymerized with a third monomer component other than vinyl acetate monomer and ethylene monomer. Examples of this other third monomer component include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, Crotonic acid, maleic acid, fumaric acid, itaconic acid, etc., or their alkyl esters, and α-olefins such as propylene, butene, decene, octadecene, etc.

The PVA copolymer emulsion thus obtained has a solid concentration of preferably 50 wt% or more, and more preferably 20 to 70 wt%.

The PVA resin as component (b) (ii) in the resin emulsion composition (b) for use in the present multilayer laminate is a partially or fully saponified product of polyvinyl acetate or modified PVA.

The modified PVA is a partial or complete saponification product of the following copolymers: copolymers of vinyl acetate with olefins having 4 to 18 carbon atoms, copolymers of vinyl acetate with vinyl carboxylates such as vinyl versatate, vinyl stearate, etc., copolymers of vinyl acetate with alkyl vinyl ethers such as lauryl vinyl ether, methyl vinyl ether, etc., and copolymers of vinyl acetate with (meth)acrylates such as methyl methacrylate, etc., copolymers of vinyl acetate with acrylamide, methacrylamide, N,N-dimethylacrylamide, etc., copolymers of vinyl acetate with unsaturated carboxylic acids or their anhydrides or esters such as acrylic acid, crotonic acid, fumaric acid, itaconic acid, etc., copolymers of vinyl acetate with sulfonic acid monomers such as Vinylsulfonic acid, acrylsulfonic acid, etc., copolymers of vinyl acetate with cationic monomers such as dimethylaminoethyl methacrylate, vinylimidazole, vinylpyridine, vinylsuccinimide, etc., and copolymers of vinyl acetate with other monomers such as vinylene carbonate, allyl alcohol, allyl acetate, etc.

The polymerization degree of the PVA resin thus obtained is not particularly limited, and can be selected as appropriate in view of the application field, etc. Normally, a PVA resin having a polymerization degree of 100 to 3000 is preferred. From the viewpoint of coatability, melt flowability, mechanical strength, etc., in particular, a PVA resin having a polymerization degree of 200 to 1800 is preferred. The saponification degree is preferably 50 mol% or more. In view of gas barrier properties and melt flowability, a saponification degree of 70 to 99.5 mol% is particularly preferred. Below a saponification degree of less than 50 mol%, better mechanical strength cannot be obtained, while above 99.5 mol%, better melt flowability cannot be obtained.

The mixing ratio of the component (b) (i) to the component (b) (ii) in the resin emulsion composition must be such that the total weight of the vinyl alcohol component is 15% by weight or more, and preferably 20 to 90% by weight, based on the total weight of the vinyl alcohol component and the vinyl acetate component. If the total weight of the vinyl alcohol component is less than 15% by weight, the gas barrier properties are not satisfactory and thus the object of the present invention is not achieved. Above 90% by weight, the coating film becomes hard and brittle.

The PVA copolymer emulsion (a) and the resin emulsion composition (b) must be coated to a thickness of 3 µm or more, and preferably 5 µm or more. based on the solid balance after drying. If the thickness is less than 3 µm, better gas barrier properties cannot be obtained and thus the object of the present invention cannot be achieved. The thickness has no particular upper limit, but from an economical point of view, the thickness is preferably not more than 80 µm.

Saponified resins of the olefin/vinyl acetate copolymer (c) for use in the present invention can be prepared by saponifying the copolymer obtained by radical polymerization of olefin with vinyl acetate.

Olefins for use in the saponified resin of the olefin-vinyl acetate copolymer (c) include, for example, α-olefins having 2 to 12 carbon atoms, among which ethylene is not preferred from the viewpoint of easy polymerization and excellent gas barrier properties of the saponified product of the ethylene/vinyl acetate copolymer.

The olefin content and the saponification degree of the saponified product of the olefin/vinyl acetate copolymer (c) are not particularly limited, but the olefin content is preferably 15 to 60 mol%, and particularly 20 to 50 mol%. If the olefin content is less than 15 mol%, extrusion molding is difficult to perform, while above 60 mol%, the gas barrier properties are sometimes reduced.

The degree of saponification is preferably 90 mol% or more, and more preferably 96 mol% or more. If the degree of saponification is less than 90 mol%, the gas barrier properties are not satisfactory.

The thickness of the saponified resin layer of the olefin-vinyl acetate copolymer (c) in the present multilayer laminate must be at least 1 µm. Below 1 µm, the desired gas barrier properties cannot be achieved. The greater the thickness, the better the gas barrier properties. In view of the gas barrier properties and economy, it is not necessary for the thickness to be more than 50 µm. Normally, a thickness of 3 to 40 µm is selected from this point of view.

The PA resin (d) for use in the present invention is not particularly limited, and the resins described in "Polyamide resin Handbook" published by Nikkan Kogyo Shinbun-sha, Japan, on January 30, 1988 can be used. For example, polycondensates of dibasic acids and diamines can be used. Specifically, they include polymers of ε-caprolactam, aminolactam, enantholactam, 11-aminoundecanoic acid, 7-aminopentanoic acid, 9-aminononanoic acid, α-pyrrolidone, α-piperidone, etc.; Polycondensates of diamines, such as hexamethylenediamine, nonamethylenediamine, undecamethylendiamine, dodecamethylenediamine, metaxylylenediamine etc. with dicarboxylic acids, such as terephthalic acid, isophthalic acid, adipic acid, sebacic acid, dodecanedioic acid, glutaric acid, etc., or their copolymers. In particular, they also include, for example, nylon-4, nylon-6, nylon-7, nylon-8, nylon-11, nylon-12, nylon-6,6, nylon-6,9, nylon-6,10, nylon-6,11, nylon-6,12, nylon MXD.

The thickness of the PA resin layer must be at least 1 µm, because below 1 µm the gas barrier properties are not satisfactory. From an economic point of view, the thickness is preferably 3 to 40 µm.

The PVA resin (e) for use in the invention is the same PVA as that of (b) (ii).

The thickness of the PVA resin layer (e) must be at least 3 µm. Below 3 µm, the desired gas barrier properties cannot be achieved. The greater the thickness, the better the gas barrier properties. From the standpoint of gas barrier properties and economy, a thickness of more than 50 µm is not necessary. Normally, a thickness of 3 to 40 µm is selected from this point of view.

The present multilayer laminate can be used for various applications, e.g., as heat-sealable packaging materials. When the layer materials (a), (b), (c) and (d) of the present invention are used as heat-sealable layers, the thickness of the laminate must be at least 5 µm in terms of solid balance after drying, in view of the sealing strength.

When a multilayer laminate comprising the layer material (e) is used as a heat-sealable packaging material, it is necessary to further laminate a polypropylene layer as a heat-sealable layer.

The present layer materials (a), (b), (c), (d) and (e) are applied to the surface of a thin film of a metal or metal oxide deposited on a plastic substrate is applied by the following coating method: The PVA copolymer emulsion composition (a) and the resin emulsion composition (b) are directly applied in the emulsion state to the surface of a thin film of metal or metal oxide formed on the plastic substrate and dried, or the emulsions are dried and the resulting dried materials are extrusion-laminated onto the surface of the thin film by means of an extruder, or the lamination can be carried out with a known anchor coating agent or a dry coating adhesive.

The layer materials (c), (d) and (e) can be laminated according to a known method, e.g. by dissolving in a solvent and coating the resulting solution, by laminating films obtained by extrusion molding, or by simultaneous extrusion lamination.

The coating can be carried out according to a known coating method, for example, by means of an air brush method, a gravure roll method, a reverse roll coating, a bar coating method, a dip coating method, a spray method, a brush coating method, an electrostatic coating method, a centrifuge coating method, a spreader coating method, an electrophoresis coating method, or their combinations. The coating can be carried out in one step or by a multi-step coating including a two-step coating.

After coating, drying is carried out in an arc-shaped drying oven, a floating-type drying oven or the like, or in a high-frequency hot dryer.

Preferred embodiments of the invention

The present invention will be described in detail below with reference to Examples using the following test methods.

Determination of the volume of permeated oxygen

The oxygen transmission rate was determined using an OXTRAN Type 10/50 A manufactured by Modern Control, Ltd. under the conditions of temperature of 23 ºC and relative humidity of 65% and temperature of 23 ºC and relative humidity of 90% according to ASTM D3985-81.

Bending fatigue test

The laminates were subjected to a fatigue test by using a Gelbo bending tester manufactured by Tester Sangyo KK, Japan, with a cylinder diameter of 90 mm, a stroke of 178 mm, a twist angle of 440 º, a twist stroke of 89 mm, a linear stroke of 63.5 mm and a repetition rate of 40 cycles/minute, by bending the laminate every 10 passes up to 100 bending passes and every 100 bending passes. The bending pass number of the Gelbo bending tester was changed and permeated oxygen was measured at each stage at 23 ºC and 65 % RH, whereby the volume of permeated oxygen increases after breakage of the vapor-deposited layer due to bending fatigue. Bending fatigue can therefore be easily determined by this method.

Aroma preservation test

Bags were made from multilayer laminates and a solution containing various flavor components was sealed in the bags. After a certain time, the flavor components sorbed into the inside of the film of each bag were extracted and quantified by gas chromatography. The greater the amount of sorbed flavor components, the lower the flavor preservation.

A specific method for determination is given below:

Multilayer laminates for the flavor preservation test were prepared by dry laminating an aluminum foil with a thickness of 9 µm to the surface corresponding to the outer surfaces of bags using a polyethylene terephthalate film with a thickness of 12 µm. An adhesive AD 950 A/B manufactured by Toyo Morton K.K., Japan, was used for dry lamination, followed by aging in a thermostat room at 40 ºC for 4 days. The adhesive was applied at 4 g/m² based on the solid balance after drying.

The aroma preservation test was carried out using some examples and Comparative Examples. Bags having a size of 18 cm × 10 cm were prepared by heat sealing so that in the Examples the resin layer of the present invention could be provided on the inner surface and in the Comparative Examples a polypropylene resin layer could be provided on the inner surface. Then, 300 ml of an aqueous surfactant solution containing various flavor components (an aqueous 0.5% solution of Ryoto Sugar Ester S-1170, manufactured by Mitsubishi Kasei Shokuhin KK, Japan) was sealed in each of the bags and kept in a thermostatic room at 23 °C for 70 days. The bags were then opened and the flavor components sorbed into the film on the inner surface of each of the bags were extracted with ether, and the flavor components remaining in the aqueous detergent solution were also extracted with ether. Then, the extracted flavor components were quantitatively determined by gas chromatography, and the amount of sorbed components and that of the remaining components were calculated based on the concentrations in the original aqueous solution. From the results thus obtained, the distribution ratio of the sorbed flavor components was obtained according to the following formula:

Distribution ratio = amount of sorbed components/ amount of remaining components

That is, the larger the distribution ratio, the greater the sorption of the flavor components. With a distribution ratio of 1, half of the flavor components contained in the aqueous solution before sealing are in the inner layer of each of the bags sorbed, and if the distribution ratio is greater than 1, the concentration of aroma components remaining in the aqueous solution is reduced.

Symbols for aroma components:

A: Myrcen

B: d-Limonen

C: n-caproic acid ester

D: Linabol

E: n-octyl alcohol

Examples and comparisons Secreted film

(1) Substrat

PET: Lumilar pH, manufactured by Toray K.K., Japan, 12 µm thick

CPP: Sho-Allomer, manufactured by Showa Denko K.K., Japan,

50 µm thick, for all examples using CPP and Comparative Examples 1, 5, 9 and 12;

60 µm thick for comparative example 13

Annotation:

PET: Polyester film

CPP: Cast polypropylene film

(2) Vapor-deposited film

Materials: SiO (silicon monoxide)

Al (aluminium)

Deposit thickness: 30, 50, 60 and 110 nm (300, 500, 600 and 1100 Å) for Examples 1 to 16 and Comparative Examples 1 to 7

70 nm (700 A) for Examples 17 to 53 and Comparative Examples 8 to 14

Laminate materials (1) PVA copolymer emulsion (hereinafter abbreviated as EP)

Note: PVA content: ratio of polyvinyl alcohol to the total amount of polyvinyl alcohol and vinyl acetate (by weight) (2) Resin emulsion composition (hereinafter abbreviated as CP) (3) EVOH (hereinafter abbreviated as EV)

Note: EVOH: saponified product of ethylene/vinyl acetate copolymer

(4) PA resin (hereinafter abbreviated as PA)

PA-1 Amylan CM4000, manufactured by Toray K.K., Japan, solution

PA-2 Amylan CM4001, manufactured by Toray K.K., Japan, solution

PA-3 Amylan CM8000, manufactured by Toray K.K., Japan, solution

PA-4 Nylon-6, 1022B, manufactured by Ube Kosan K.K., Japan, melting point 196 ºC

(5) PVA resin (hereinafter referred to as PV)

PV-1 Gohsenol GL 03, aqueous solution, manufactured by Nihon Gohsei Kagaku K.K., Japan, Polymerization degree: 300; Saponification degree: 86.5-89 mol%

PV-2 Poval PVA 105, aqueous solution, manufactured by Kuraray K.K., Japan, degree of polymerization: 500; saponification degree: 98.5 ± 0.5 mol%

PV-3 Poval PVA 117, aqueous solution, manufactured by Kuraray K.K., Japan, degree of polymerization: 1700; saponification degree: 98.5 ± 0.5 mol%

PV-4 Poval PVA 224, aqueous solution, manufactured by Kuraray K.K., Japan, degree of polymerization: 2400; degree of saponification: 88.0 ± 1.5 mol%.

Vapor deposition of a thin film of metal or metal oxide onto the surface of a plastic substrate

On one side of a commercially available PET or CPP, SiO or Al was vacuum deposited to a certain thickness The vacuum deposition was carried out in a vacuum deposition apparatus, type EBH6, manufactured by Nippon Shinku Gizyutsu KK, Japan, using a tungsten pad as a heating resistor, with the vapor source having a purity of 99.99% or more at a vacuum degree of 2 × 1300 Pa (2 × 10 Torr). The thickness of the vacuum vapor-deposited film was calculated on a weight basis.

(a) Preparation of PVA copolymer emulsions

Emulsion polymerization was carried out in an autoclave having a net content of -30 l using a partially saponified PVA resin having a polymerization degree of 500 and a saponification degree of 88 mol%, PVA 205, manufactured by Kurare K.K., Japan, sequentially adding ammonium persulfate and sodium metabisulfite as catalysts and changing the vinyl acetate concentration and ethylene gas pressure to obtain PVA copolymer emulsions (EP-1 to EP-4). The emulsions thus obtained had a solid concentration of about 20 to about 60 wt%.

(b) Preparation of resin emulsion compositions

PV (PV-1) was dissolved in water at 70 ºC with heating to prepare an aqueous solution having a viscosity (23 ºC) of 2.7 Pa.s (2700 cps) and a polymer concentration of 30 wt%, which was then mixed with the above-mentioned PVA copolymer emulsion (EP-3) to prepare the emulsion compositions (CP-1 to CP-4) having various PVA contents.

For comparison, PV-1 was mixed with EP-4 to produce CP-6.

(c) Production of EVOH solutions

Soarnol DT having an ethylene content of 29 mol% and a saponification degree of more than 99 mol%, a product manufactured by Nihon Gohsei K.K., Japan, and Soarnol A having an ethylene content of 44 mol% and a saponification degree of more than 90 mol%, a product manufactured by Nihon Gohsei Kagaku K.K., Japan, were used as EVOH and dissolved in a solvent mixture of distilled water and n-propyl alcohol at a mixing ratio of the former to the latter of 45/55 wt% with stirring at 70 ºC to make a polymer concentration of 15 wt%, thereby preparing EVOH solutions (EV-1 or EV-2).

As a commercially available EVOH solution, Soarnol 30L, a product manufactured by Nihon Gohsei Kagaku K.K., Japan, was used at a copolymer concentration of 30 wt% in a mixed solvent of water and alcohol (EV-3).

(d) Preparation of PA resin solutions

Amylan CM4000, Amylan CM4001 and Amylan CM8000, manufactured by Toray K.K., Japan, as alcohol-soluble nylon products, were dissolved to prepare PA resin solutions (PA-1 to PA-3) with stirring at 60 ºC at a polymer concentration of 10 wt%.

(e) Preparation of PVA solutions

Gohsenol GL03 (a product manufactured by Nihon Gohsei K.K., Japan; degree of polymerization: 300; saponification degree: 86.5-89 mol%), Poval PVA 105 (a product manufactured by Kuraray K.K., Japan; degree of polymerization: 500; saponification degree: 98.5 ± 0.5 mol%), Poval PVA 117 (a product manufactured by Kuraray K.K., Japan; degree of polymerization: 1700; saponification degree: 98.5 ± 0.5 mol%) and Poval PVA 224 (a product manufactured by Kuraray K.K., Japan; degree of polymerization: 2400; saponification degree: 88.0 ± 1.5 mol%) were each dissolved in water under heating and stirring at 60 ºC at a polymer concentration of 15 wt%, thereby preparing aqueous PVA solutions (PV-1 to PV-4).

Production of multilayer laminates

The resin emulsion compositions and resin solutions (a), (b), (c), (d) and (e) thus prepared were coated on the surface of a vapor-deposited film of the metal or metal oxide to a certain thickness. The coated films thus obtained were dried in air for one day and then dried in vacuum at 50 °C for 7 days, thereby obtaining multilayer laminates of the present invention.

The vapor-deposited films using EP and CP and those of Comparative Examples 7 and 13 were previously primed with an aqueous dry laminate adhesive Adcord Ab 335E, a product manufactured by Toyo Morton K.K., Japan, to a thickness of about 4 µm on the vapor-deposited surface.

The multilayer laminates of the examples and comparative examples were subjected to a quantitative determination of the oxygen permeation rate, the aroma preservation test, and the bending fatigue test.

Examples 1 to 16

Examples 1 to 3 relate to cases using PVA copolymer emulsions (a), and Examples 4 to 9 to cases using resin emulsion compositions (b). Examples 10 to 12 relate to cases using the compositions (b) while changing the coating thickness, and Examples 13 to 15 to cases using the compositions (b) in which the PVA content was changed.

Example 16 uses CPP as a substrate for the vapor deposited film.

The flavor preservation test was conducted in Examples 3 and 5, and the bending fatigue test was conducted in Examples 5 and 7. The results are shown in Table 1.

Comparative examples 1 to 7

Comparative Example 1 uses CP-5, where cold deposition was carried out at 20 ºC for 20 hours, followed by freeze-pulverization and freeze-drying of the resulting polymers, vacuum drying at 80 ºC, and extrusion lamination at 220 ºC.

Comparative Examples 2 to 5 relate to cases using only a vapor-deposited film, Comparative Example 6 to a case using CP-6 having a PVA content of 10 wt%, and Comparative Example 7 to a case using CPP.

The flavor preservation test was conducted in Comparative Example 7, and the bending fatigue test was conducted in Comparative Example 2. The results are shown in Table 1.

Examples 17 to 28

Examples 17 to 26 relate to cases using EVOH as a vapor-deposited film on the PET substrate, Examples 21 to 24 relate to cases using CPP as a substrate, and Examples 25 to 28 relate to cases where the film thickness of the EVOH was changed.

The flavor preservation test was carried out in Examples 17 to 19, 21, 24 and 25. The results are given in Table 2.

Comparative examples 8 to 13

Comparative Example 8 concerns a case of extrusion lamination of Soanol DT at 220ºC.

Comparative Examples 9 to 12 relate to cases using only the vapor-deposited film, and Comparative Example 13 to a case using CPP.

The flavor preservation test was conducted in Comparative Example 13, and the bending fatigue test in Comparative Example 9. The results are shown in Table 2.

Examples 29 to 40

Examples 29 to 32 relate to cases using PA resin on the vapor-deposited film on the PET substrate, Examples 33 to 36 relate to cases using CPP as the substrate, and Examples 37 to 40 relate to cases where the film thickness of the PA resin was changed.

The flavor preservation test was conducted in Examples 29 to 31 and 37, and the bending fatigue test was conducted in Examples 29 and 37. The results are shown in Table 3.

Comparison example 14

Comparative Example 14 relates to a case of extrusion lamination of nylon-6 at 230 ºC, wherein adhesives LX703 and KP90, products manufactured by Dainihon Ink Kagaku Kogyo K.K., Japan, were used at about 3 g/m2 in the extrusion lamination as a primer.

Examples 41 to 53

Examples 41 to 46 relate to cases using PVA resin on the vapor-deposited SiO film, Examples 47 to 50 relate to cases using a vapor-deposited Al film, and Examples 51 to 53 relate to cases where the coating thickness of the PVA resin was changed.

The bending fatigue test was carried out on Example 43. The results are given in Table 3.

The multilayer laminates of the present invention have good gas barrier properties against oxygen gas, good flavor preservation properties, and good bending and flexural fatigue strength, and can be preferably used as a packaging material for foods, medicines, cosmetics, etc., or as a heat-sealable packaging material such as a container material for preserving foods which require long-term preservation. Table 1 Table 1 (continued)

* PVA content: ratio of polyvinyl alcohol to the total amount of polyvinyl alcohol and vinyl acetate (by weight) Table 2 Table 2 (continued) Table 3 Table 3 (continued)

Claims (22)

1. A multilayer laminate comprising a plastic substrate, a vapor-deposited film of a metal or metal oxide formed on the surface of the substrate, and a layer formed on the surface of the vapor-deposited film, characterized in that the plastic substrate is selected from the group consisting of polypropylene, poly-4-methylpentene-1, the complete saponification products of ethylene/vinyl acetate copolymer, polyacetal, polycarbonate, polyester, polyamide, polyphenylene oxide and polysulfone, and the layer is selected from the group consisting of: (a) a layer formed from a polyvinyl alcohol copolymer emulsion having an ethylene content of 1 to 50% by weight obtainable by aqueous emulsion polymerization of a vinyl acetate monomer, an ethylene monomer and a polyvinyl alcohol, the polyvinyl alcohol initially being present in an amount of 15 to 60% by weight based on the total weight of polyvinyl alcohol and vinyl acetate monomer; (b) a layer formed from a resin emulsion composition obtainable by mixing (i) a polyvinyl alcohol copolymer emulsion having an ethylene content of 1 to 50% by weight obtainable by aqueous emulsion polymerization a vinyl acetate monomer, an ethylene monomer and a polyvinyl alcohol, wherein the polyvinyl alcohol is initially present in an amount of 3 to less than 15 weight percent based on the total weight of polyvinyl alcohol and vinyl acetate monomer, with (ii) an aqueous solution of a polyvinyl alcohol resin, wherein the weight ratio of the weight of the polyvinyl alcohol to the weight of the polyvinyl alcohol and the vinyl acetate monomer in the resin composition is 15% or more; (c) a layer formed from a saponified resin solution of an olefin/vinyl acetate copolymer; (d) a layer formed from a polyamide resin solution; and (e) a layer formed from a polyvinyl alcohol resin solution 2. Multilayer laminate according to claim 1, characterized in that the metal is aluminum. 3. Multilayer laminate according to claim 1, characterized in that the metal oxide is silicon oxide. 4. Multilayer laminate according to claim 1, 2 or 3, characterized in that a layer of the polyvinyl alcohol copolymer emulsion (a) in a thickness of 3 µm or more, based on the solid balance after drying, is provided on the thin film of the metal or metal oxide. 5. Multilayer laminate according to claim 1, 2 or 3, characterized in that on the thin film of the metal or metal oxide there is provided a layer of the resin emulsion composition (b) in a thickness of 3 µm or more, based on the solid balance after drying. 6. A multilayer laminate according to claim 1, 2, 3 or 5, characterized in that the polyvinyl alcohol resin (b) (ii) comprises a vinyl alcohol component and a vinyl acetate component and has a polymerization degree of 100 to 3000 and a saponification degree of 70 mol% or more. 7. Multilayer laminate according to claim 1, 2 or 3, characterized in that a layer of the saponified product of the olefin/vinyl acetate copolymer (c) in a thickness of at least 1 µm is provided on the thin film of the metal or metal oxide. 8. Multilayer laminate according to claim 1, 2, 3 or 7, characterized in that the olefin of the saponification product of the olefin/vinyl acetate copolymer is ethylene, and the saponification product has an ethylene content of 15 to 60% by weight and a saponification degree of vinyl acetate of 90 mol% or more. 9. Multilayer laminate according to claim 1, 2 or 3, characterized in that a layer of the polyamide resin (d) in a thickness of at least 1 µm is provided on the thin film of the metal or metal oxide. 10. Multilayer laminate according to claim 1, 2 or 3, characterized in that a layer of the polyvinyl alcohol resin (e) in a thickness of at least 3 µm is provided on the thin film of the metal or metal oxide. 11. Multilayer laminate according to claim 1, 2, 3 or 10, characterized in that the polyvinyl alcohol resin (e) comprises 30 to 100 mol% vinyl alcohol component and not more than 70 mol% vinyl acetate component, and has a degree of polymerization of 100 to 5000. 12. A heat-sealable packaging material comprising a multilayer laminate comprising a plastic substrate, a vapor-deposited film of a metal or metal oxide formed on the surface of the substrate, and a layer formed on the surface of the vapor-deposited film, characterized in that the plastic substrate is selected from the group consisting of polypropylene, poly-4-methylpentene-1, the complete saponification products of ethylene/vinyl acetate copolymer, polyacetal, polycarbonate, polyester, polyamide, polyphenylene oxide and polysulfone, and the layer is selected from the group consisting of: (a) a layer formed from a polyvinyl alcohol copolymer emulsion having an ethylene content of 1 to 50% by weight obtainable by aqueous emulsion polymerization of a vinyl acetate monomer, an ethylene monomer and a polyvinyl alcohol, the polyvinyl alcohol initially being present in an amount of 15 to 60% by weight based on the total weight of polyvinyl alcohol and vinyl acetate monomer; (b) a layer formed from a resin emulsion composition obtainable by mixing (i) a polyvinyl alcohol copolymer emulsion having an ethylene content of 1 to 50 wt.% obtainable by aqueous emulsion polymerization of a vinyl acetate monomer, an ethylene monomer and a polyvinyl alcohol, the polyvinyl alcohol initially being present in an amount of 3 to less than 15 wt.% based on the total weight of polyvinyl alcohol and vinyl acetate monomer, with (ii) an aqueous solution of a polyvinyl alcohol resin, the weight ratio of the weight of the polyvinyl alcohol to the weight of the vinyl acetate monomer in the resin composition being 15% or more; (c) a layer formed from a saponified resin solution of an olefin/vinyl acetate copolymer; (d) a layer formed from a polyamide resin solution; and (e) a layer formed from a polyvinyl alcohol resin solution. 13. Heat-sealable packaging material according to claim 12, characterized in that the metal is aluminum . 14. Heat-sealable packaging material according to claim 12, characterized in that the metal oxide is silicon oxide. 15. Heat-sealable packaging material according to claim 12, 13 or 14, characterized in that on the thin film of the metal or metal oxide, at least one layer selected from the materials (a), (b), (c), (d) and (e) is provided in a thickness of 5 µm or more, based on the solid balance after drying. 16. A heat-sealable packaging material according to claim 12, 13, 14 or 15, characterized in that the polyvinyl alcohol resin (b) (ii) comprises a polyvinyl alcohol component and a vinyl acetate component and has a polymerization degree of 100 to 3000 and a saponification degree of 70 mol% or more. 17. Heat-sealable packaging material according to claim 12, 13, 14 or 15, characterized in that the olefin of the saponification product of the olefin/vinyl acetate copolymer (c) is ethylene, and the saponification product has an ethylene content of 15 to 60 wt.% and a saponification degree of vinyl acetate of 90 mol% or more. 18. Heat-sealable packaging material according to claim 12, 13, 14 or 15, characterized in that the polyvinyl alcohol resin (e) comprises 30 to 100 mol% of a vinyl alcohol component and not more than 70 mol% of a vinyl acetate component and has a polymerization degree of 100 to 5000. 19. Use of a multilayer laminate according to one of claims 1 to 11 for packaging. 20. Use of a heat-sealable packaging material according to one of claims 12 to 18 for packaging. 21. Use according to claim 19 for packaging foodstuffs. 22. Use according to claim 20 for packaging foodstuffs.