JP2694002B2 - LAMINATE AND ITS MANUFACTURING METHOD - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a laminate containing an ethylene-vinyl alcohol copolymer and a method for producing the same, particularly a laminate suitable for a packaging material such as food and a method for producing the same. It is about.

<Prior Art> Ethylene-vinyl alcohol copolymer is widely used as a packaging material for foods and the like because of its excellent oxygen barrier properties, but because of its poor properties such as moisture resistance and heat sealability,
Usually, it is used as a laminate with another resin. The laminate is produced by coextrusion molding, dry lamination molding, extrusion coating molding, or the like. However, since the copolymer has poor adhesion, a special adhesive resin is often used for the adjacent layer. As the adhesive resin, a polyolefin resin grafted with maleic anhydride was often used. The graft is excellent in adhesion to the copolymer, but has problems in hygiene, economy, and the like, and when used as an interlayer adhesive layer, from the viewpoint of adhesion to other layers, There is also a disadvantage that usable applications are limited.

On the other hand, although a copolymer of ethylene and an acid anhydride exists, it is necessary to introduce a considerable amount of an acid anhydride to develop sufficient adhesiveness, and the molecular weight of the polymer is inevitably reduced. I will. For this reason, the moldability was significantly reduced, and it was difficult to obtain a practically usable laminate.

<Problems to be Solved by the Invention> In a laminate containing an ethylene-vinyl alcohol copolymer as a single layer, the laminate having all of adhesiveness, hygiene, moldability, economy, etc. is not available until now. Therefore, an efficient method for producing the laminate has not been established. The substrate of the present invention solves this problem.

<Means for Solving the Problems> In the laminate containing at least one layer of the ethylene-vinyl alcohol copolymer, the present inventors have obtained at least an ethylene component and radical polymerization obtained by adding an antioxidant during the polymerization. It has been found that a target laminate can be efficiently produced by using a random copolymer containing a soluble acid anhydride component as an adhesive layer.

The ethylene-vinyl alcohol copolymer according to the present invention is obtained by saponifying an ethylene-vinyl acetate copolymer, and has an ethylene content of 20 to 70 mol% and a vinyl alcohol content of 30 to 80 mol%. If the ethylene content is less than 20 mol%, the extrudability is poor, and if it exceeds 70 mol%, the oxygen barrier property, which is a characteristic of the copolymer, becomes insufficient, and is not practical. If the vinyl alcohol content is less than 30 mol%, the oxygen barrier properties are insufficient, and if it exceeds 80 mol%, extrusion molding becomes difficult. MFR of this copolymer (JIS K-7210 2
30 ℃) is 0.5 to 50g / 10 minutes, preferably 3 to 20g / 1
0 minutes. If it is less than 0.5 g / 10 minutes, the melt flowability is insufficient, and molding at a normal speed cannot be performed. If it exceeds 50 g / 10 minutes, the moldability deteriorates due to a decrease in melt tension.

What is used as the adhesive layer in the present invention is a random copolymer containing at least an ethylene component and a radical-polymerizable acid anhydride component, which is obtained by adding an antioxidant during polymerization, and if necessary, other It may be a multi-order copolymer containing the radical-polymerizable comonomer (third comonomer) component of.

As a method for producing the random copolymer, a method for producing a high-pressure low-density polyethylene, which is generally well known, can be used as it is. That is, under a radical generator such as an organic peroxide, ethylene, a radical polymerizable acid anhydride and a third comonomer are polymerized at 100 to 300 ° C. and 1000 to 3500 atm to obtain a copolymer. At this time, an antioxidant is added to the polymerization system. The antioxidant is added by mixing the antioxidant with a radical-polymerizable acid anhydride or a third comonomer and injecting it into a reactor or an ethylene pipe upstream of the reactor by a pump. It is also possible to inject it alone. The injection site is not particularly specified, but injection into the suction line of the second-stage compressor is preferable in order to improve mixing with ethylene.

The content of ethylene component in the random copolymer is 55 mol
% Or more and less than 99.9 mol%. If it is less than 55 mol%, a good laminate cannot be obtained because moldability is extremely deteriorated.
If it is more than mol%, the adhesive strength is too small to be used as a laminate.

Examples of the radical polymerizable anhydride used in the random copolymer include maleic anhydride, itaconic anhydride,
Citraconic anhydride, Endic anhydride, 1-butene-
Examples thereof include 3,4-dicarboxylic acid anhydride. These may be used in combination of two or more. Of these, maleic anhydride and itaconic anhydride are particularly preferred.

The content of the radical polymerizable acid anhydride component in the present random copolymer is preferably in the range of 0.1 to 5 mol%, and particularly preferably 0.3 to 2 mol%. When the amount of the acid anhydride is less than 0.1 mol%, the interlayer adhesion is insufficient, and 5 mol%
Beyond is very difficult to produce commercially. Even if production is possible, it has no practical meaning, and only lowers economic efficiency and moldability.

Examples of the third comonomer that can be used in combination with the radical-polymerizable acid anhydride include ester compounds, amide compounds, acid compounds, ether compounds, hydrocarbon compounds and the like. If these are described specifically,
Ester compounds include vinyl acetate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl actylate, octyl acrylate,
Lauryl acrylate, benzyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, methyl fumarate, ethyl fumarate, propyl fumarate, fumaric acid Butyl, dimethyl fumarate, diethyl fumarate, dipropyl fumarate, dibutyl fumarate, methyl maleate, ethyl maleate, propyl maleate, butyl maleate, dimethyl maleate, diethyl maleate, dipropyl maleate, dibutyl maleate, etc. Can be illustrated. Amide compounds include acrylamide, methacrylamide, N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, N-
Butyl acrylamide, N-hexyl acrylamide,
Examples thereof include N-octylacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide, N, N-dimethylmethacrylamide, N, N-diethylmethacrylamide and the like. Examples of the acid compound include acrylic acid, methacrylic acid, maleic acid, fumaric acid and the like. Examples of the ether compound include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octadecyl vinyl ether, phenyl vinyl ether and the like. Hydrocarbon compounds include styrene, nonbornene,
Butadiene, acrylonitrile, methacrylonitrile,
Examples thereof include acrolein, crotonaldehyde, trimethoxyvinylsilane, vinyl chloride and vinylidene chloride. Of these, particularly preferred compounds include acrylic acid esters, methacrylic acid esters, maleic acid esters, fumaric acid esters, acrylic acid, and methacrylic acid. If necessary, two or more of these comonomers may be used in combination.

When the third comonomer is used in combination, the content of the third comonomer component in the random copolymer is at most 40 mol.
% Is preferred. If it is 40 mol% or more, the moldability is greatly reduced, and a laminate meeting the object of the present invention cannot be obtained.

Upon polymerizing the present random copolymer, an antioxidant is added to the polymerization system, and the antioxidant referred to in the present invention is a nucleus-substituted phenol, biphenol, bisphenol, etc., and at least in the phenol nucleus. One substituent is included. The kind of the substituent is not particularly limited, but an alkyl group and an alkenyl group having 4 or less carbon atoms, a vinyl group, a methyl-substituted vinyl group, an allyl group, an alkoxy group having 3 or less carbon atoms,
A hydroxyl group and the like are preferable. The number of substituents is preferably 2 or 3 or more, and mononuclear phenols are particularly preferable.
Specific examples of the antioxidant include parahydroxybenzaldehyde, hydroquinone monomethyl ether, paraaminophenol, 3,5-xylenol, 2,6-diisopropylphenol, 2-tert-butylhydroxyanisole, 4-tert-butylproton. Catechol, 2,4-
Bis (1,1-dimethylpropylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-methylenebis (2-methyl-6-tert-butylphenol), 4,4 ′ -Methylenebis (2,6-
Examples thereof include ditertiarybutylphenol), 2,6-ditertiarybutyl-4-methylphenol, and octadecyl 3- (3,5-ditertiarybutyl-4-hydroxyphenyl) propionate. Of these, 2,6-ditertiarybutyl-4-methylphenol, 4,4'-thiobis (3-methyl-6-tertiarybutylphenol), 3- (3,5-ditertiarybutyl-4-hydroxyphenyl) propion Octadecyl acid is preferred.

The amount of the above antioxidant added is 50 to 2000 ppm, preferably 80 to 1500 ppm on a weight basis at the inlet of the reactor. 50
If it is less than ppm, the expected effect is not exhibited and the polymerization is not stable. If the added amount exceeds 2000 ppm, the antioxidant strongly acts as a polymerization inhibitor, so that favorable results cannot be obtained.

The MFR (JIS K-7210 190 ° C) of this random copolymer is 0.
It is in the range of 1 to 50 g / 10 minutes. Outside this range, the moldability during the production of the laminate will be significantly reduced, and a preferable laminate cannot be produced. In the present random copolymer, it is essential that the unreacted monomer is completely separated from the polymer and substantially not contained. The presence of unreacted monomers is not only problematic in terms of hygiene, but also causes a decrease in adhesiveness, which is also a problem in physical properties.

In high-pressure radical copolymerization of ethylene with a radical-polymerizable acid anhydride and a third comonomer, if the acid anhydride is introduced to the extent that it has sufficient adhesiveness when formed into a laminate, the chain-inhibiting effect of the acid anhydride And the chain transfer effect of the third comonomer makes it difficult to raise the molecular weight. For this reason, the melt tension of the resin is insufficient, and problems often occur during molding of the laminate. Although this problem can be solved by lowering the polymerization temperature, on the other hand, in the case of low temperature polymerization, the power required for stirring in the reactor increases and stable polymerization becomes difficult. By adding an antioxidant at the time of polymerization, stable polymerization at low temperature becomes possible. As a result, it is possible to obtain a copolymer having a molecular weight, melt tension, moldability and adhesiveness suitable for producing a laminate, and to produce a good laminate with an ethylene-vinyl alcohol copolymer. Is possible.

The laminate containing at least one layer of the ethylene-vinyl alcohol copolymer is a laminate having a thickness of 30 µm to 5 mm. The random copolymer layer containing the ethylene component and the radical-polymerizable acid anhydride component according to the present invention is used as a layer adjacent to the ethylene-vinyl alcohol copolymer layer. However, the present random copolymer layer does not necessarily have to be the intermediate layer, and can be used as the outermost layer in some cases. The shape of the laminate is not particularly limited, and it can be used in any form as needed, such as a film, a sheet, a bag, and a bottle.

The laminate is usually a polyolefin resin as the outermost layer,
Polystyrene-based resin, polyester-based resin and the like are used, but the random copolymer containing the ethylene component and the radical-polymerizable acid anhydride component according to the present invention exhibits high adhesiveness to any of these resins, and therefore is very It can be used in a wide range.

In manufacturing the laminate, various molding methods such as coextrusion molding, dry lamination molding, heat lamination molding, and extrusion coating molding can be used. In order to obtain a particularly good laminate by utilizing the characteristics of the present invention. It is desirable to utilize a coextrusion method.

<Example> Example 1 A structure having a polypropylene layer as both outer layers, an ethylene-vinyl alcohol copolymer (ethylene 32 mol%, vinyl alcohol 68 mol%, MFR 4 g / 10 min) layer in the middle, and an adhesive resin layer between both layers. Laminates of 5 layers of 3 types were produced by coextrusion.

As an adhesive resin, ethylene-methyl acrylate-maleic anhydride terpolymer (ethylene 95.5 mol%, methyl acrylate 3.5 mol%, maleic anhydride 1.0 mol%, MFR
2.5 g / 10 minutes) was used. This copolymer was produced by using a high-pressure polyethylene production facility having a 4 liter autoclave type reactor, 1000 ppm by weight at the inlet of the reactor, 2,6
-Ditertiarybutyl-4-methylphenol was added and polymerized.

Molding is performed using a co-extrusion multilayer film molding machine with three 65φ extruders and a T-die of 1300mm width, resin temperature 230 ° C,
With a take-off speed of 30 m / min, total thickness of 50 μm, adhesive layer thickness of 5
A μm laminate was produced.

The molding could be carried out without any problems. The obtained laminate has good appearance and transparency, and after aging at 40 ° C. for 2 days, the 90 ° peel strength between the polypropylene layer and the ethylene-vinyl alcohol copolymer layer was measured (peeling speed 300 mm / min). It had a peel strength of 580 g / 15 mm with no problems. Oxygen permeability under 35 ℃ drying condition is 0.5cc ・ 20μm / m
^It is as low as ²・ 24Hr ・ atm and can be judged to be a laminate suitable for packaging materials.

Example 2 Polystyrene (HI grade MFR2.0g / 10
Min), adhesive resin, ethylene-vinyl alcohol copolymer, adhesive resin, linear low-density polyethylene (MFR2.2g /
10 minutes, density 0.922) and normal low density polyethylene (MFR6.
A 5 layer laminate was produced which was a mixture with 8g / 10min, density 0.917). In molding, first, three layers from the outer layer were used in Example 1.
After co-extrusion molding by the molding method shown in, the other two layers are co-extrusion coated with the laminate as a base material to give a total thickness of 30
A 0 μm sheet was obtained. The adhesive resin and ethylene-vinyl alcohol copolymer used are the same as in Example 1.

The moldability is not particularly problematic, and the peel strength between the layers is 40 on the outer layer side.
The strength was 0 g / 15 mm and the inner layer side was 720 g / 15 mm, and had practically no problem. This sheet has excellent heat-sealing properties and thermocompression bonding properties, has oxygen permeability equivalent to that of the laminate of Example 1, and is particularly suitable as a food packaging material.

Examples 3 to 7 Instead of the adhesive resin used in Example 1, Table 1
A laminate was produced in the same manner as in Example 1 except that the random copolymer shown in 1 was used. As shown in Table 1, there was no problem in moldability and film appearance, and the interlayer adhesion was practically sufficient.

Comparative Example 1 A laminate was produced under the conditions of Example 1 by using a copolymer polymerized without adding 2,6-ditertiarybutyl-4-methylphenol as an adhesive resin. In this case, it was necessary to raise the polymerization temperature to maintain the polymerization stability, and as a result, only a copolymer having an MFR of 13 g / 10 min was obtained. In addition, the molten film was not stable during molding, and the thickness unevenness of the film was remarkable. The interlayer adhesive strength was uneven, and it was impossible to use it as a laminate.

Comparative Example 2 A laminate was produced under the same conditions as in Example 1 except that modified polypropylene (MFR 5.5 g / 10 min, maleic anhydride 0.28% by weight) obtained by grafting maleic anhydride onto polypropylene was used as the adhesive resin. did. The modified polypropylene was prepared by dispersing and mixing 1.8% by weight of maleic anhydride and 1.2% by weight of benzoyl peroxide in polypropylene powder with a Henschel mixer, followed by performing a graft reaction with an extruder and pelletizing.

There was no particular problem in molding, but gels and fish eyes, which are considered to be due to ungrafted maleic anhydride, were noticeable, and the adhesive strength was weak at 270 g / 15 mm, and the practical performance as a laminate was poor.

<Effects of the Invention> A random copolymer containing at least an ethylene component and a radical-polymerizable acid anhydride component of the present invention is excellent in moldability, adhesiveness, hygiene and the like, and the copolymer is used as an adhesive layer. By using it, it is possible to effectively produce a laminate containing an ethylene-vinyl alcohol copolymer as at least one layer. This laminate can be used in a wide range, and is particularly suitable for packaging materials such as foods.

Claims (2)

(57) [Claims] 1. A random copolymer containing at least an ethylene component and a radical-polymerizable acid anhydride component, which is obtained by adding an antioxidant during polymerization in a laminate containing at least one layer of an ethylene-vinyl alcohol copolymer. A laminate using a polymer as an adhesive layer. 2. A laminate comprising an ethylene-vinyl alcohol copolymer as at least one layer, which is obtained by adding an antioxidant at the time of polymerization and contains at least an ethylene component and a radical-polymerizable acid anhydride component. A method for producing a laminate, which comprises using a polymer as an adhesive layer.