JP2599766B2 - Gas barrier multilayer package - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Technical Field of the Invention The present invention relates to a multilayer package having a high gas barrier property and excellent storage properties, and particularly to prevent oxygen gas permeation in a retort treatment step. The present invention relates to a retort film packaging material, particularly a retort lid material or a retort pouch, which has a mechanism and has excellent transparency during storage. The present invention also includes a cup-shaped, tray-shaped, bottle-shaped or tube-shaped container having a high gas barrier property.

B. Prior art Retort container lids include aluminum foil, polyolefin (especially polypropylene) film laminate films, and metal lids for double seams, both of which have almost perfect gas barrier properties but are opaque. There are invisible drawbacks. The ability to see through the contents is necessary to motivate consumers to purchase.However, in order to prevent the contents from spilling when opening, or to partially open a hole in the lid material, use a microwave oven, etc. This is a necessary function for heating. However, currently available plastic film transparent lids are used only for limited applications due to their lack of gas barrier properties, especially oxygen gas barrier properties. That is, a representative gas barrier resin currently used as a lid material is a polyvinylidene chloride polymer (mainly a vinylidene chloride-vinyl chloride copolymer, sometimes abbreviated as PVDC hereinafter), and has a higher gas barrier property. A vinylidene chloride-acrylate copolymer film having the following formula is also known.

Non-PVDC-based gas barrier resins used for the lid material include metaxylylenediamine-adipic acid condensate (MX-nylon), polyamide, and PVDC-coated polyamide, all of which are oxygen gas. It is used for limited foods with low barrier property and little oxidative deterioration, or used only for foods distributed at low temperatures.

Further, the film packaging material for retort typified by a pouch is in a more severe environment. In other words, the lid material is a part of the container, whereas the transparent film packaging material used for pouches, skin packs, shrink wraps, deep draw wraps, rocket wraps, etc. constitutes the entire container. Currently, there is no transparent film packaging material for retort used for the purpose, which has sufficient gas barrier properties, and at present, all of the retort-sterilized products are distributed at a low temperature.

 Ethylene-vinyl alcohol copolymer resin (hereinafter referred to as EV
OH is sometimes the best gas barrier property at the moment
Is a thermoplastic resin that has 0.3% (60% R
H) ~ 0.75 (80% RH) cc / m^Two・ Day ・ atm oxygen transmission rate
(OTR) is used as a general-purpose brand
(EVAL manufactured by Kuraray Co., Ltd.) F type). EVOH is for cups and tofu
Widely used as gas barrier material in retort containers such as
EVOH is used for the middle layer and the inner and outer layers are made of PP with low moisture permeability.
The configuration of the multilayer package is adopted. In addition, preservation
Adhesive resin between PP layer and EVOH layer for further improvement
A method of including a desiccant in a layer (US Pat. No. 4,407,897)
No.) or a method of including a desiccant in the EVOH layer itself
(U.S. Pat. No. 4,425,510). However, EVOH
Oxygen gas when retort-treated by using it as Ilum packaging material
There are drawbacks that the transmittance is reduced and the transparency is reduced.

Further, in a lid material or a pouch using an aluminum foil, a method of facilitating the peeling of aluminum when heated in a microwave oven has been disclosed in Japanese Utility Model Laid-Open Publication No.
44473, etc., a laminate of an aluminum foil and an oxygen gas barrier resin film, particularly a laminate controlled so as to be easily peeled, is not known.

C. Problems to be Solved by the Present Invention As described above, since there is no lid or pouch having good storage stability and excellent transparency, a composite film of an opaque aluminum foil has been unavoidably used. The present inventors have conducted a detailed study on the preservability of retort food of the conventional oxygen gas barrier resin film, and found that most of the permeation of oxygen gas, which affects the preservability of food, occurs during retort processing. It was found that high oxygen gas barrier properties were maintained during storage. Based on this important finding, we have realized a retort packaging material that has never been considered as impossible before, such as a transparent gas barrier resin film equipped with a mechanism for preventing permeation of oxygen gas during retort processing. Things.

D. Means for Solving the Problems The multilayer package of the present invention has a substantially gas-impermeable layer on the outer layer, for example, a metal thin film layer such as aluminum foil, and a transparent ethylene-vinyl alcohol layer on the inner layer. A gas barrier resin layer containing a polymer is provided, and the above outer layer and inner layer are laminated via an easily peelable adhesive layer. This multilayer package does not transmit oxygen gas during retort. After the retort treatment, the above outer layer portion can be made transparent by peeling and removing the outer layer portion, and the contents in the package can be seen through. Thus, a new retort wrapping material having high preservability and having transparency at the time of preservation has been completed.

E. More Detailed Description of the Invention As the substantially gas impermeable layer used for the outer layer of the present invention, a metal foil such as an aluminum foil is most suitable, but aluminum, zinc oxide or silicon oxide. A film in which inorganic glass is deposited on the surface of a plastic film can also be used. Although the thickness of the aluminum foil is arbitrary, it can be usually used in the range of 5 to 80 μm.
The outer surface of the aluminum foil is preferably coated with various resins for the purpose of corrosion protection or laminated with a polyester film, a nylon film, a stretched polypropylene (PP) film, or the like. The inner surface of the aluminum foil may be left as it is, but the above-mentioned resin films may be laminated to reinforce the aluminum.

As the resin forming the gas barrier resin layer containing the transparent ethylene-vinyl alcohol copolymer contained in the inner layer of the present invention, ethylene-vinyl alcohol copolymer, ethylene-vinyl alcohol copolymer and polyamide resin The composition etc. can be mentioned as a representative,
However, the oxygen permeation rate (20
℃, 65% RH) 20cc / m ²・ day ・ atm or less, especially 5
cc / m ²・ day ・ atm or less, more preferably 1.5cc / m ²・ day ・ atm
A film having a thickness of atm or less is desirable for storage performance.

Among the above-mentioned gas barrier resins, ethylene-vinyl alcohol copolymer or a composition comprising polyamide and ethylene-vinyl alcohol copolymer are preferable because they exhibit excellent barrier properties.

Ethylene-vinyl alcohol copolymer (EVOH) includes any one obtained by hydrolyzing a vinyl acetate unit in a copolymer of ethylene and vinyl acetate. In particular, the content of ethylene units is between 20 and 50 mol%, especially between 27 and 40 mol%,
Those having a degree of saponification of vinyl acetate units of 96% or more, particularly 99% or more, may be used.
Examples of the value of g) include a range of 0.2 to 60 g / 10 minutes. The EVOH referred to in the present invention may be modified with a copolymer monomer in a range of 5 mol% or less. Examples of the modifying monomer include propylene, 1-butene, 1-hexene,
-Methyl-1-pentene, acrylic acid ester, methacrylic acid ester, maleic acid, fumaric acid, itaconic acid,
Higher fatty acid vinyl ester, alkyl vinyl ether,
N- (2-dimethylaminoethyl) methacrylamides or quaternary compounds thereof, N-vinylimidazole or quaternary compounds thereof, N-vinylpyrrolidone, Nn-butoxymethylacrylamide, vinyltrimethoxysilane, vinylmethyldimethoxy Examples thereof include silane and vinyldimethylmethoxysilane.

In addition, EVOH alone may have reduced transparency immediately after retorting, or a wave pattern may be present, but the composition of EVOH and polyamide does not cause such defects even after retorting, and transparency is particularly high. Excellent and preferred.

Polyamide resins (PA) used in this composition include polycapramide (nylon-6), poly-ω-aminoheptanoic acid (nylon-7), poly-ω-aminononanoic acid (nylon-9), polyundecaneamide (Nylon-11), polylaurin lactam (nylon-12), polyethylenediamine adipamide (nylon-2,6), polytetramethylene adipamide (nylon-4,6), polyhexamethylene adipamide (nylon -6,6), polyhexamethylene sebacamide (nylon-6,10), polyhexamethylene dodecamide (nylon-6,12), polyoctamethylene adipamide (nylon 8,6), polydecamethylene adipamide Pamide (nylon-10,6), polydodecamethylene sebacamide (nylon-10,8), or caprolactam / laurin lactam copolymer (na Ron -6/12),
Caprolactam / ω-aminononanoic acid copolymer (nylon-6 / 9), caprolactam / hexamethylene diammonium adipate copolymer (nylon-6 / 6,6), laurin lactam / hexamethylene diammonium adipate copolymer (nylon) -12 / 6,6), hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymer (nylon-6,6 / 6,10), ethylene diammonium adipate / hexamethylene diammonium adipate copolymer (nylon -2,6 / 6,6), caprolactam / hexamethylenediammonium adipate / hexamethylenediammonium sebacate copolymer (nylon-6 / 6,6 / 6,10).

Among these PAs, the most preferred one for the present invention is a caprolactam / laurin lactam copolymer, that is, nylon-6 / 12. The composition of 6 and 12 components in nylon-6 / 12 is not particularly limited, but 12 components are 5
Preferably, it is from about 60 mol%, more preferably from 10 to 50 mol%. Further, its relative viscosity is in the range of 2.0 to 3.6, more preferably 2.2 to 3.2.

A polyamide having a polyether bond in the polymer chain may be obtained by adding a polyether diamine and a dicarboxylic acid (such as dimer acid) at the time of polycondensation of these PAs, especially nylon-6 / 12. During the condensation, aliphatic amines such as hexamethylenediamine, laurylamine and laurylamine, and aromatic amines such as metaxylenediamine and methylbenzylamine were added to reduce the amount of carboxyl end groups in the polyamide. Those are also preferred. In that case, when the amino terminal group is 8 × 10 ⁻⁵ equivalent / g or more,
In addition, the carboxyl terminal group is preferably at most 3 × 10 ⁻⁵ equivalent / g.

The amount of PA to EVOH is 5 to 50% by weight, preferably
10 to 30% by weight.

These gas barrier resin layers can be used as the innermost layer, but in many packages, it is preferable to provide a heat seal layer as the innermost layer inside the gas barrier resin layer. The resin used for the heat seal layer is selected in consideration of heat resistance, heat sealability, and transparency.

For many purposes, polypropylene is suitable as the resin for the innermost layer (heat seal layer), but other thermoplastic resins can be used. Examples include polyolefin resins other than polypropylene (such as polyethylene), polyamide resins, polyester resins, polystyrene resins, polyvinyl chloride resins, acrylic resins, polyvinylidene chloride resins, polyacetal resins, and polycarbonate resins. And the like, and these resins are used alone or in a laminated form. When the inner layer portion (the gas barrier resin layer and the innermost layer) is produced by a co-extrusion method, an ordinary technique of laminating an adhesive resin is adopted. Adhesive resins such as polypropylene, polyethylene, or resins obtained by modifying polyolefins such as copolymers of ethylene with copolymerizable monomers (such as vinyl acetate and acrylic acid ester) with addition of maleic anhydride, etc. Is used.

Further, another resin film may be laminated on the outer side of the gas barrier resin of the inner layer for the purpose of reinforcement or printing. For example, there are a biaxially stretched nylon film, a non-stretched nylon film, a polyester film, a biaxially stretched PP film, a non-stretched PP film, a polycarbonate film and the like.

The lamination for producing the inner layer or the outer layer respectively,
Dry lamination, co-extrusion, sand lamination,
Extrusion lamination, coextrusion lamination, and the like are employed.

The lamination of the outer layer including the substantially gas impermeable layer and the inner layer including the transparent gas barrier resin layer is performed via the easily peelable adhesive layer. This easily peelable adhesive layer must adhere well until after the retort treatment, and after the retort treatment, the adhesive strength can be controlled to be low so that the outer layer can be peeled off.

The following method can be adopted for such purpose. Intermittently (partially or partially) a resin having a relatively low adhesive strength to at least one of the resins, for example, an acrylic resin, a polyamide resin, a silicone resin, a vinyl chloride resin, etc. ) Is applied by a part coat method. Examples of the application pattern are shown in FIGS. 1 and 2 (a) to (d). As shown in the drawing, the portion where the resin is not applied forms a pattern such as a linear shape, a dot shape, a lattice shape, and a stripe shape. In some cases, the adhesive surface of the present invention can be formed even when a resin is applied to the entire surface.

Next, the inner layer and the outer layer are bonded using an adhesive. Here, a normal laminating adhesive is suitably used as the adhesive. By this method, both layers can be satisfactorily adhered to each other until the retort treatment is completed, and after the retort treatment is completed, the outer layer can be peeled off and the inner layer can be left as part or all of the packaging material. To facilitate peeling, the package may be provided with perforations such as those that do not affect the gas barrier properties. It is preferable to use a resin and an adhesive having relatively low adhesive strength that have higher adhesive strength to the outer layer than to the inner layer because the adhesive layer does not remain in the inner layer when the outer layer is peeled off after the retort treatment.

The easily peelable adhesive layer of the package of the present invention is composed of the above-mentioned resin layer having relatively low adhesive strength, or a combination of this resin layer and the adhesive layer.

The multilayer package of the present invention is most effective mainly as a lid material or a pouch, but can also be made into a tray shape, a cup shape, a bottle shape or a tube shape.

These packages can be subjected to a heat treatment known as retort sterilization or boil sterilization. For the retort treatment, various methods such as a recovery method, a replacement method, a steam method, a shower method, and a spray method are employed.

The above-described multilayer package of the present invention is filled with food,
If necessary, the inside is degassed by a known means, or the inside is replaced with an inert gas such as nitrogen gas or a single gas, and then sealed by means such as a heat seal, and then retort sterilization is performed.

Suitable foods are cooked or semi-cooked foods that are eaten as they are, but are heated prior to eating. Next, examples of foods are shown.

Pre-cooked curry, pre-cooked Hayashi, beef shichiyu, borscht, meat sauce, sweet and sour pork, sukiyaki, Chinese bean, Hachiho greens, meatballs, oden, asparagus boiled, sweet corn, Matsushiyu room, tuna cream boiled, consommé,
Attached foods such as various soups such as potage soup, miso soup, pork juice, kenchin soup, cooked rice, red rice, pot rice, fried rice, pilaf, porridge, spaghetti, soba, udon, ramen, noodles, rice cooked with rice, and rice with Chinese soba , Yuzuzuki, Zenzai,
Anmitsu, meat dumpling, hamburger, beef steak, roast pork, pork saute, corned beef, ham, sausage, grilled fish, grilled meat, grilled chicken, roast chicken, pork kechijap, fish meat kunsei, bacon, kamaboko, pudding,
Jelly, yokan, various pet foods. Further, the multilayer package of the present invention is a fruit product such as mandarin orange, peach, pineapple, cherry, olive, soy sauce, sauce, vinegar,
Mirin, dressing, mayonnaise, kechiyap, edible oil, miso, seasonings such as lard, tofu, jam, butter, margarine, fruit juse, vegetable juse, beer, cola, lemonade, sake, shochu, fruit liquor, wine, whiskey, Excellent as a container for brandy. In addition, medicines such as Ringer's solution, pesticides, cosmetics,
Detergent, benzene, toluene, xylene, acetone, methyl ethyl ketone, normal hexane, cyclohexane,
It can also be used as a container for organic liquid chemicals such as carbon tetrachloride, gasoline, kerosene, petroleum benzene, thinner, and grease.

Hereinafter, the present invention will be described more specifically with reference to examples. The parts are parts by weight.

F. Example Example 1 and Comparative Example 1 From the outermost layer, (1) a corrosion-resistant coated aluminum foil (40
μ), (2) polyester film (12μ), (3) 2
A film was prepared by laminating an axially stretched nylon film (15 μm), (4) a film of a composition of EVOH and polyamide (20 μm), and (5) a non-stretched polypropylene film (50 μm). EVOH contained in the fourth layer has an ethylene monomer unit content of 28 mol% and a melt index (190 ° C., 2160 ° C.).
g) is 1.2g / 10min, while polyamide is polyamide-6 / 1
The two copolymers (copolymerization ratio is 80/20 by weight) and the blend ratio is 80/20 (weight ratio). As an adhesive for dry lamination of the first and second layers, the third and fourth layers, and the fourth and fifth layers, Takerat A-385 (manufactured by Takeda Pharmaceutical Co., Ltd.) is used as the main agent. 50 (manufactured by the company) was used as a curing agent, and after lamination, curing was carried out at 40 ° C. for 3 days.

Next, a silicon resin was partially applied to the surface of the third layer by a part coating method. Fig. 2 (a)
It is. Next, the adhesive for dry lamination was applied to the surface of the second layer, and after lamination with the third layer, curing was performed at 40 ° C. for 3 days.

Using the thus obtained laminated film as a lid material, it was heat-bonded to a gas-barrier cup-shaped container of PP / EVOH / PP containing a food (tomato pyule) by a heat sealer with the fifth unstretched PP layer as the inner surface. . The retort equipment (Hisaka Manufacturing Co., Ltd., high-temperature high-pressure cooking sterilization tester, RC
Using S-40R TGN), a retort treatment was performed at 120 ° C. for 30 minutes. The first, which is the outer layer of the lid material after retort treatment,
The two layers were peeled off, leaving the third to fifth layers in the container. The remaining lid material had good transparency and appearance. 20 containers
After storage at 65 ° C. and 65% RH for 6 months, the tomato pickle inside was taken out, but the color and taste were good, and the storage stability of the container was good. (Color difference 1.2) For comparison, in Example 1 described above, the outer layers 1 and 2 were used.
The retort treatment and the storage test were performed in the same manner as in Example 1 except that the laminated film was used as the lid material only for the third to fifth layers without laminating the layers. At the time of the retort treatment, discoloration of the tomato pyule was observed (color difference 4.7). After storage for 6 months, the degree of discoloration is almost the same as immediately after retort, and there is little change during storage (color difference 5.4).

In the above evaluation, the color difference was measured by a Z-1001DP colorimeter using Nippon Denshoku Industries Co., Ltd.

Example 2 and Comparative Example 2 A laminated film was produced in the same manner as in Example 1 except that the various films shown in Table 1 were used in place of the EVOH / polyamide composition film in the fourth layer. And
It was evaluated as a lid material for food containers. The results are summarized in Table 1. Although the lid material of Example 2 has high preservability, the lid material of Comparative Example 2 has insufficient preservability.

G. Effects of the InventionThe package of the present invention has a mechanism having a high gas barrier property, particularly a mechanism for preventing oxygen gas permeation in the retort treatment step, and has excellent transparency and gas barrier property during storage. Have When the outer layer includes a metal thin film such as an aluminum foil, a process such as a microwave oven can be directly performed by peeling the outer layer.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the basic structure of the package of the present invention. FIG. 2 is a plan view showing four examples of patterns of the intermittent resin layer 3. 1 is an outer layer including a substantially gas-impermeable layer, 2 is an adhesive layer, 3 is a resin layer having relatively low adhesive strength, and 4 is an inner layer including a gas barrier resin layer.

Claims (4)

(57) [Claims] An outer layer containing a gas-impermeable layer and an inner layer containing a gas-barrier resin layer containing an ethylene-vinyl alcohol copolymer, wherein both layers form an easily peelable adhesive layer. Gas barrier multi-layer package that is laminated through the intermediary. 2. A heat seal layer as an innermost layer.
The gas barrier multilayer package according to the above. 3. A pouch for a retort comprising the multilayer package according to claim 1. 4. A lid for a retort container comprising the multilayer package according to claim 1.