JPH02209241A - Laminated long article - Google Patents

Abstract

PURPOSE:To keep the oxygen gas barrier properties of the intermediate layer of a base material by holding said intermediate layer to a dry state by a method wherein a specific ethylene/vinyl alcohol copolymer layer is set to an intermediate layer and polyolefin resin layers are provided to both surfaces of the base material laminated by interposing a hydrophobic adhesive resin layer so as not to be directly brought into contact with the intermediate layer mutually. CONSTITUTION:An ethylene/vinyl alcohol copolymer layer obtained by saponifying 90% of an ethylene/vinyl acetate copolymer wherein the copolymerization ratio of ethylene is 20-65 mol.% is set to an intermediate layer and an ethylene/ vinyl alcohol copolymer layer whose copolymerization ratio of ethylene is less than that of the ethylene/vinyl alcohol copolymer constituting the intermediate layer is provided to both surfaces of said intermediate layer through adhesive resin layers and propylene copolymer layers are provided to both surface layers of those ethylene/vinyl alcohol copolymer layers through respective adhesive resin layers. This laminated long article can be prepared by the generally used method in the field of this kind.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a material used in containers for retort foods, etc., which has high gas barrier properties even after retort sterilization, and has excellent preservability of contents. The present invention provides a laminated elongated material suitable for retort sterilization materials.

[Conventional technology]

Traditionally, packaging materials for foods, pharmaceuticals, etc. have been required to have excellent gas barrier and water vapor barrier properties to prevent deterioration due to oxidation of the packaged food, scattering of aromas, and penetration of penetrating liquids. has been done.

For this reason, a laminate using aluminum foil is generally used as a retort sterilizer laminate. Laminated materials using aluminum foil are preferable from the viewpoint of food preservation because they have excellent gas barrier properties and water vapor barrier properties.

On the other hand, as transparent laminate materials, many laminate materials using ethylene-vinyl alcohol copolymers with excellent gas barrier properties have been proposed. It is known that the gas barrier properties of this ethylene-vinyl alcohol copolymer change depending on humidity, and that the gas barrier properties are significantly reduced at high humidity.

For this purpose, hydrophobic polymeric substances with low transparency and moisture content, such as ethylene polymers and propylene polymers, are generally used by laminating them on both sides.

By the way, the reason why ethylene-vinyl alcohol copolymer has excellent gas barrier properties (particularly oxygen barrier properties) is that the intermolecular and intramolecular hydrogen bonds are more elastic than other polymeric substances. Not, but
One example is that the symmetry and polarity of the molecular chains contribute synergistically.

On the other hand, when the water content of the ethylene-vinyl alcohol copolymer increases, the adsorbed water molecules first bond to hydrophilic hydroxyl groups (OH groups), and as the water content increases, the adsorbed water moves between molecules. It is believed that the hydrogen bonds in the molecule are broken, allowing the molecular movement necessary for oxygen molecule diffusion, resulting in an increase in the oxygen permeability coefficient.

If the water content increases further from this state, free water will exist in addition to adsorbed water, and as a result, the intermolecular forces will further weaken, and the oxygen permeability coefficient will further increase due to the plasticizing effect on molecular motion. It is considered.

When using such an ethylene-vinyl alcohol copolymer as a transparent packaging container for retort sterilization, polyolefin resins such as ethylene polymers and propylene polymers are used to provide moisture-proofing and heat-sealing properties. Among them, propylene polymers are most suitable from the viewpoint of heat resistance to hot water or steam of about 120° C. during retort sterilization.

[Problem to be solved by the invention]

When aluminum foil is used as the laminated material for retort sterilization, the contents cannot be confirmed because it is opaque, and consumers can only check the contents after opening the package after purchase.

In addition, in the case of propylene-based polymers, when heated and pressurized during retort sterilization, the water vapor permeability increases by 15 to 20 times compared to at room temperature, so the water content of ethylene-vinyl alcohol copolymers rapidly increases. increases, and the oxygen gas barrier property decreases significantly.

Although the oxygen gas barrier properties of multilayer containers whose oxygen gas barrier properties have been significantly reduced by retort sterilization can be restored by storage after retort sterilization, it takes a long period of time, and the use of multilayer containers is limited to relatively low oxygen tolerance against deterioration. It is limited to large contents and items with a short shelf life.

Three main methods have been proposed to improve these problems. The first method is to impart hot water resistance to the ethylene-vinyl alcohol copolymer itself, and the second method is to increase the release rate of water absorbed by the ethylene-vinyl alcohol copolymer, thereby improving its oxygen gas barrier properties. The third method is to speed up the recovery, and the third method is to provide a protective layer on both sides of the ethylene-vinyl alcohol copolymer layer to prevent water from entering, thereby suppressing the deterioration of the oxygen gas barrier property.

In the first method, water resistance and hot water resistance are improved by increasing the ethylene content of the ethylene-vinyl alcohols polymer. However, as the ethylene content increases, the oxygen gas barrier properties of this wheat drop significantly, making it impractical.

In addition, in the second method, by making the thickness of the outer propylene polymer layer thinner than the inner propylene polymer layer, the ethylene-vinyl alcohol copolymer layer is reduced during storage after retort sterilization. This will speed up the release of absorbed water to the outside air and speed up the recovery of oxygen gas barrier properties. However, in this method, since the outer propylene polymer layer is thin, the ethylene-vinyl alcohol copolymer layer absorbs a large amount of water during retort sterilization.

For these reasons, even if the degree of decrease in oxygen gas barrier properties is large and the rate of recovery is fast, the cumulative amount of permeated oxygen can only be slightly reduced in the long term. Depending on the contents, this may accelerate deterioration due to the high oxygen concentration.

As a representative example of the third method, as proposed in JP-A-57-170748, water that enters during retort sterilization is prevented by protecting both sides of the ethylene-vinyl alcohol copolymer layer with a layer containing a desiccant. This is a method of trapping the ethylene-vinyl alcohol copolymer layer, reducing the increase in water content of the ethylene-vinyl alcohol copolymer layer, and suppressing the deterioration of the oxygen gas barrier property. With this method, deterioration in oxygen gas barrier properties due to retort sterilization can be suppressed. On the other hand, it contains a desiccant (10
~20% by weight), this naturally sacrifices transparency and results in an opaque container, which reduces the product's appeal by half, and furthermore, it is difficult to manufacture a multilayer container with a layer containing a desiccant. However, this method also became technically complex and increased the cost of the container.

Based on these facts, the object of the present invention is to maintain transparency in a multilayer container that can be retorted and sterilized using a conventional ethylene-vinyl alcohol copolymer as an oxygen gas barrier layer.
It also prevents the deterioration of oxygen gas barrier properties caused by retort sterilization, can be manufactured at low cost using conventional processing methods, and has a good shelf life for its contents. ).

[Means and effects for solving the problems] According to the present invention, these problems can be solved by saponifying at least 90% of an ethylene-vinyl acetate copolymer having an ethylene copolymerization ratio of 20 to 65 mol%. An ethylene-vinyl alcohol copolymer layer having a low ethylene-vinyl alcohol copolymerization ratio is used as an intermediate layer, and an adhesive resin layer is placed on both sides of the intermediate layer to form an ethylene-vinyl alcohol copolymer. It is a long product in which an ethylene copolymer layer is provided, and a propylene copolymer layer is provided on both surfaces of the ethylene-vinyl alcohol copolymer layer with adhesive resin layers interposed therebetween. Both the propylene polymer and the ethylene-vinyl alcohol copolymer have 30% adhesive resin at a temperature of 125°C.
Adhesive strength after retorting for minutes is 700 g/15
This problem can be solved by a laminated long article characterized by having a width of mm or more. The present invention will be specifically explained below.

(A) Ethylene-vinyl alcohol copolymer The ethylene-vinyl alcohol copolymer used to produce the gas barrier layer in the present invention generally has an ethylene copolymerization ratio of 20 to 65 mol% (preferably 20 to 65 mol%). ~
60 mol%, preferably 20 to 50 mol%) of a saponified ethylene and vinyl acetate copolymer. The saponification rate of this saponified product is usually 90% or more, preferably 95% or more, and particularly preferably 99% or more. If a saponified material with a saponification rate of less than 90 mol % is used, the barrier properties will be poor.

Furthermore, if the ethylene copolymerization ratio of the ethylene-vinyl acetate copolymer is less than 20 mol%, the decomposition temperature and melting point are close to each other, resulting in significantly poor moldability. On the other hand, if it exceeds 65 mol%, the barrier properties against oxygen are poor.

Furthermore, M I (2) described below is usually 0.1 to 50 g/
10 minutes, preferably 0.5-50g/10 minutes, 0
．． 5 to 40 g/10 minutes is suitable. When M I (2) is less than 0.1 i/10 minutes, moldability is poor. on the other hand,
If it exceeds 50 g/10 minutes, it will be difficult to construct these layers when manufacturing a laminated long article.

(B) Propylene-based polymer In the present invention, the propylene-based polymer used for both surface layers is a propylene homopolymer, ethylene containing at least 70% by weight of propylene, or other α-based polymers.
- random copolymers with olefins or random or block copolymers with α-olefins, and when the container is obtained by thermoforming, e.g. vacuum forming, 1.0 to 5
A good product is obtained when 0% by weight of ethylene-based polymer is mixed with propylene-based polymer. The melt index of these propylene polymers [JIS K-7210
14, hereinafter referred to as rM I (1) J] is 0.005 to 80 g/10 min, and 0101
~60g/10min is preferable, especially 0.01
~40 g/10 min of propylene polymer is preferred.

If a propylene polymer with an M I (1) of less than 0.005 g/10 min is used, the molding processability to obtain long objects or containers will be poor, and good long objects or containers will not be obtained.
If a propylene-based polymer with a content exceeding the lo content is used, the impact resistance of the container will be weak and the container will not be suitable for practical use.

As the propylene polymer in the present invention, one to which an inorganic filler described later may be added may be used.

In this case, when forming a container and filling the container with food, from the viewpoint of food hygiene, a propylene polymer that does not contain an inorganic filler is added inside the inner layer of the propylene polymer that contains an inorganic filler. It is preferable to provide a layer of.

The inorganic filler is generally one widely used in the fields of synthetic resins and rubber.

These inorganic fillers are preferably inorganic compounds that do not react with oxygen and water and do not decompose during kneading and molding.

Examples of the inorganic filler include oxides of metals such as aluminum, copper, iron, lead, nickel, magnesium, calcium, barium, zinc, zirconium, molybdenum, silicon, antimony, and titanium, and hydrates (hydroxides) thereof; It is broadly classified into compounds such as sulfates, carbonates, and silicates, their double salts, and mixtures thereof. Representative examples of the inorganic filler are described in Japanese Patent Application No. 124481/1981.

Among these inorganic fillers, those in powder form have a diameter of 3
Preferably, the blood concentration is 0 or less (preferably 10 IlfB or less). In addition, in the case of fibrous materials, the diameter is 1 to 500 Il! a
(preferably 1 to 300 m), the length is 0.1 to G,
Oan (preferably 0.1 to 5.0 dragons) is desirable. Furthermore, the plate-like one is 30 μm or less (preferably l
(1zcm or less) is preferable. Among these inorganic fillers, those in the form of flat plates (flake) and those in the form of powder are particularly suitable.

The composition ratio (content ratio) of the inorganic filler in the inorganic filler-containing propylene polymer is at most 70% by weight, preferably 5 to 65% by weight, particularly preferably 5 to 60% by weight. .

If the composition ratio of the inorganic filler in the inorganic filler-containing propylene polymer exceeds 70% by weight, the impact resistance of the resulting container will be significantly reduced, resulting in a container that is not suitable for practical use.

(C) Adhesive resin In the present invention, between the ethylene-vinyl alcohol copolymer constituting the gas barrier layer and the propylene polymer or the mixture of the propylene polymer and inorganic filler constituting both surface layers. The adhesive resin used has an adhesive strength of 700 z/15+ after retorting for 30 minutes at a temperature of 125°C with any of these polymers.
nn+ width or more (preferably 800g/15mm width or more). If the adhesive strength is less than 700g/15+u width, problems such as peeling and delamination may occur, which is not preferable.

As the adhesive resin, commonly used adhesive resins such as urethane adhesives and chlorinated polypropylene can be used. These adhesive resins are used after being dissolved in an inert organic solvent.

Therefore, it is not preferable for molding by coextrusion molding, which is an industrially easy method. Therefore, the following adhesive resins are preferably used in the present invention.

The adhesive resin is obtained by graft polymerizing the propylene polymer or the ethylene resin described later with an unsaturated carboxylic acid or a derivative thereof described later. This graft polymerization is generally carried out in the presence of a radical initiator (generally an organic peroxide) as described below.

As the ethylene resin, ethylene homopolymer, ethylene and carbon number at most 12 (preferably 3 to 8)
(The copolymerization ratio of α-olefin is usually 20% by weight or less, preferably 15% by weight or less, preferably 12% by weight or less) and ethylene as the main component (generally 65% by weight or less). % or more, preferably 70% or more by weight) with a monomer having a polar group (for example, vinyl acetate, (meth)acrylic acid, or an alkyl ester thereof).

In producing the graft polymer, the melt index of these ethylene resins (measured according to JIS K7210 under conditions 4, hereinafter referred to as rM I (2) J
] and M I (1) of the propylene polymer are generally 0. O1 to 100 g/10 minutes, preferably 0602 to 50 g/10 minutes,
Particularly suitable is 0.05 to 50 g/10 minutes.

When a propylene polymer or ethylene resin having M I (1) or M I (2) below the lower limit is used, it is difficult to uniformly carry out the graft reaction. On the other hand, if the amount exceeding the upper limit is used, the strength of the resulting adhesive resin will be poor, and the adhesive strength will also be poor.

In producing the graft polymer, among these ethylene resins and propylene polymers, low density and high density ethylene homopolymers, propylene homopolymers, copolymers of ethylene and propylene, and ethylene or propylene are used. A copolymer of α-olefin and other α-olefins is desirable.

(D) A-layer elongated product and its manufacturing method A partially enlarged sectional view of a typical laminated elongated product of the present invention is shown in FIG. 1st
In the figure, 1 is an ethylene-vinyl alcohol copolymer layer (hereinafter referred to as "first gas barrier layer"), and 2 and 2' are adhesive resin layers. Further, 3 and 3' are layers of an ethylene-vinyl alcohol copolymer having a lower copolymerization ratio of ethylene than the ethylene-vinyl alcohol copolymer constituting the gas barrier layer (hereinafter referred to as "second gas barrier layer"). 4 and 4' are adhesive resin layers, and 5 and 5' are propylene polymer layers.

In the laminated long article of the present invention, the thickness of each layer varies greatly depending on its intended use, but the proportion of each propylene polymer layer to the total of the first gas barrier layer and the second gas barrier layer is usually 10-100 (preferably 3-100)
80). Regarding the thickness of the second gas barrier layer, the total amount of the second gas barrier layer is generally 10 to 90% of the total amount of the thickness of the first gas barrier layer and the second gas barrier layer. Desirably, preferably 20~
It is 80%.

Moreover, the thickness of the adhesive layer is usually 5 to 100 μm, especially! 0-50 blood is preferred. If the thickness of the adhesive layer is less than 5 mm, it is difficult to produce a multilayer long article with a uniform thickness, and uneven adhesion occurs after retort processing or the like. On the other hand, if the amount exceeds 100 blood, not only is there an economical problem, but the container may turn yellow. In addition, the thickness of the inner layer and outer layer (propylene polymer layer) is generally 10
00 m or less, and the gas barrier layer is 110 l1 or more. Furthermore, the second gas barrier layer is only 10% thicker.

The laminated elongated article of the present invention can be manufactured by a method commonly practiced in this type of field.

In the case of manufacturing by multilayer coextrusion, the resin of each layer is melt-kneaded using an extruder corresponding to the resin, and then extruded into a predetermined shape through a multilayer die such as a T-die or a circular die. It can also be manufactured by lamination methods such as dry lamination, sandwich lamination, and extrusion coating.

Moreover, the molded article can take the form of a film, a sheet, a preform for forming a bottle or a tube, or the like. Forming a container from a parison or preform can be easily accomplished by pinching off the extrudate with a pair of split dies and blowing fluid into the interior thereof. Furthermore, after cooling the preform, it is heated to a stretching temperature, stretched in the axial direction, and blow-stretched in the circumferential direction using fluid pressure, thereby obtaining a stretched-blown container or the like. Further, by subjecting the film or sheet to vacuum forming, pressure forming, plug assist forming, etc., containers such as cup-shaped and tray-shaped containers can be manufactured.

[Examples and comparative examples]

Hereinafter, the present invention will be explained in more detail with reference to Examples.

In the Examples and Comparative Examples, five types and nine layer multilayer sheet forming machines (manufactured by Toshiba Machine Co., Ltd., two 05 mm diameter, three 40 mm diameter, die width 800 mm) were used to form each multilayer sheet at a die temperature of 230°C. was molded. Each sheet was molded using a vacuum forming machine (manufactured by Asano Research Institute, model FLV441) to a diameter of 81.2 mm, a depth of 70 mm, and a capacity of 230 mm.
A cc container was molded. Each container obtained in this way is filled with water so that 5% of the total content becomes a space,
A lid made of propylene polymer with a thickness of 80 m on both sides with a 2011A thick aluminum foil interposed therebetween was heated at a temperature of 200°C and a pressure of 2.5 kg/cd for 3 hours.
Ring sealing was performed for seconds to obtain a container filled with water.

The container filled with the obtained water was subjected to retort treatment at a temperature of 110° C. for 30 minutes using a retort pot (manufactured by Daiwa Can Co., Ltd., model KHR-W-101-M).

Then, the oxygen permeability was measured using an oxygen permeability measuring device [manufactured by Modern Control (USA)].

The measurement temperature was 23° C., the relative humidity inside the container was 90%, and the relative humidity outside the container was 60%.

Propylene-based ffi used in Examples and Comparative Examples
The types, manufacturing methods, physical properties, etc. of the ethylene-vinyl alcohol copolymer and adhesive resin are shown below.

[(A) Propylene polymer]

As a propylene polymer, M I (1) is 1. Og/
Propylene homopolymer [hereinafter referred to as rPP(A)
J], Ml(1) is 0.5 g/10 min, and the ethylene copolymerization ratio is 18% by weight.
Propylene block copolymer [r P P (B)
J] 85 parts by weight and M I (2) is 0.2
g/10 minutes and a density of 0.955 g/ci, 15 parts by weight of ethylene homopolymer [hereinafter referred to as rPE(1)J] was heated to a resin temperature of 220 using an extruder with a screw diameter of 65 mm. Composition [pellets, hereinafter referred to as "composition (I)"] produced while kneading at °C, the above PP (B) 6
0 parts by weight, PE (1) L mouth overlapping part and average particle size of 5.
A composition [pellets, hereinafter referred to as "composition (■)"], produced by kneading 30 parts by weight of talc having an aspect ratio of about 01lA and an aspect ratio of about 20, PP (
B) A composition [pellets,
Hereinafter referred to as "composition (■)"] and M! (1)
Propylene homopolymer with a ratio of 0.003i/10 min
Hereinafter referred to as r P P (C) J] was used.

[(B) Ethylene-vinyl alcohol copolymer] Also,
A saponified product obtained by saponifying an ethylene-vinyl acetate copolymer having an ethylene copolymerization ratio of 38 mol% as an ethylene-vinyl alcohol copolymer [saponification degree 99%, M I (2) 4.0 g /1
0 minutes, hereinafter referred to as rEVOH(1)J], a saponified product obtained by saponifying an ethylene-vinyl acetate copolymer with an ethylene copolymerization ratio of 25 mol% [saponification degree 99%, M! (2) 5.0 g/10 minutes, hereinafter referred to as rEVOH (2) 90%, Ml(2) 5.5g/10min, hereinafter r
EVOH (3) J] and a saponified product obtained by saponifying an ethylene-vinyl acetate copolymer with an ethylene copolymerization ratio of 89 mol% [saponification degree 91%, M I (2) 6.0 g/10 minutes, hereinafter referred to as rEVOH(4)J].

[(C) Adhesive resin]

Furthermore, 0.5g/M I (1) as adhesive resin
100 parts by weight of propylene homopolymer, 0.
3 parts by weight of maleic anhydride and 0.2 parts by weight of benzoyl peroxide were triblended in advance for 5 minutes using a Henschel mixer.

Modified polypropylene (M I (1)
25 g/10 minutes, hereinafter referred to as "modified product"] was used.

Examples 1 to 5, Comparative Examples 1 to 4 As shown in Figure 1, the inner and outer surface layers were a layer mainly composed of a propylene polymer whose type and thickness are shown in Table 1, and the intermediate layer was a layer whose thickness was as shown in Table 1. A gas barrier layer (hereinafter referred to as "layer A") made of ethylene-vinyl alcohol copolymer (EVOH) shown in Table 1, an inner surface layer and an AWI
and an ethylene-vinyl alcohol copolymer layer (hereinafter referred to as "layer B" and "layer 0" respectively) whose thickness and type are indicated between the outer surface layer,
Inner surface layer and B layer, outer surface layer and 0 layer, and B layer and A
Adhesive resin (modified material) layer (hereinafter referred to as "
A five-layer, nine-layer multilayer sheet manufacturing device (manufactured by Toshiba Machine Co., Ltd., fed-block method, screw diameter: 40 mm)
A sheet was molded using 5 extruders (5 units) (however, the numerical values for the thickness of each layer in Table 1 indicate the thickness at the multilayer sheet stage).

Containers were made from each of the multilayer sheets thus obtained and filled with water as described above. The container filled with each layer was subjected to retort treatment as described above. The oxygen permeability of the retort treated capacity and untreated retort capacity was measured using an oxygen permeation measuring device. The results obtained are shown in Table 2. It is clear from Table 2 that the barrier properties of the plastic containers of the present invention hardly change before and after retort treatment.

In Figure 1, 1 is an ethylene-vinyl alcohol copolymer layer (A layer), 2 and 2' are adhesive resin layers (F layer,
G layer), 3 and 3' are ethylene-vinyl alcohol copolymer layers (B layer).

0 layer), 4 and 4' mean adhesive resin layers (D layer, E layer), and 5 and 5' mean propylene polymer layers (inner surface layer, outer surface layer).

(Left below) Table 1) cc/oxygen 1 atm, 24 hours/piece 2) 12
Adhesive strength after retort treatment at a temperature of 5°C for 30 minutes In Comparative Example 3, E
VOH (3) decomposed and could not be molded.

〔Effect of the invention〕

The laminated elongated article of the present invention is a base material which has an ethylene-vinyl alcohol copolymer layer as an intermediate layer, and is laminated with a hydrophobic adhesion resin layer interposed so that the intermediate layer and the intermediate layer do not come into direct contact with each other. It is characterized by having a polyolefin resin layer on both sides of the base material, and when used after being molded into a container for retort food, water vapor that has entered from the polyolefin resin layer during retort sterilization will be adjacent to the polyolefin resin layer on both sides of the base material. The two hydrophobic resin layers absorb and trap moisture, and the intermediate layer consisting of the ethylene-vinyl alcohol copolymer layer at the center of the base material is kept dry, maintaining oxygen gas barrier properties.

It is believed that the laminated elongated article of the present invention can be formed into a container and utilized over the other side.

Typical uses are shown below.

(1) Various processed seasoning food containers (2) Various liquid food containers (3) Various food containers

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged cross-sectional view of the elongated VT layer manufactured in Examples and Comparative Examples. 1... Ethylene-vinyl alcohol copolymer layer (A layer) 2.2'... Adhesive resin layer (F layer 9G layer) 3.3'.
...Ethylene-vinyl alcohol ff1 combined layer (B layer, 0 layer) 4.4'...Adhesive resin layer (D layer, E layer) 5.5'
...Propylene polymer layer (inner surface layer, outer surface layer) Figure 1

Claims (1)

[Claims] An ethylene-vinyl alcohol copolymer layer obtained by saponifying at least 90% of an ethylene-vinyl acetate copolymer having an ethylene copolymerization ratio of 20 to 65 mol% is used as an intermediate layer, and adhesive is attached on both sides of the intermediate layer. An ethylene-vinyl alcohol copolymer layer having a lower copolymer proportion of ethylene than the ethylene-vinyl alcohol copolymer constituting the intermediate layer is provided via the ethylene-vinyl alcohol copolymer layer. It is a long article in which propylene copolymer layers are provided on both surface layers with adhesive resin layers on both sides, and both adhesive resins are made of the propylene polymer and the ethylene-vinyl alcohol copolymer. 3 at a temperature of 125 °C for both coalescence
Adhesive strength after 0 minute retort treatment is 700g/15
A laminated long article characterized by having a width of mm or more.