JPH02235742A - Laminate and preparation thereof - Google Patents

Abstract

PURPOSE:To prepare effectively a laminate contg. an ethylene-vinyl alcohol copolymer as at least one layer by incorporating a random copolymer obtd. by incorporating an anti-oxidant when it is polymerized and contg. at least an ethylene component and a radical-polymerizable acid anhydride component as an adhesive layer. CONSTITUTION:An ethylene-vinyl alcohol copolymer is obtd. by saponifying an ethylene-vinyl acetate copolymer and consist of 20-70mol% ethylene and 30-80mol% vinyl alcohol. An adhesive layer used is a random copolymer contg. at least an ethylene component and a radical-polyemerizable acid anhydride component obtd. by incorporating an anti-oxidant when it is polymerized. The content of the radical-polymerizable acid anhydride component in the random copolymer is pref. in the range of 0.1-5mol% and especially pref. 0.3-2mol%. When said acid anhydride is less than 0.1mol%, an interlaminar adhesive strength is not sufficient and when it is above 5mol%, commercially profitable production thereof becomes very difficult.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a laminate containing an ethylene-vinyl alcohol copolymer and a method for producing the same, and particularly a laminate suitable for packaging materials for foods and the like and a method for producing the same. It is related to.

Prior art> Ethylene-vinyl alcohol copolymers are widely used as packaging materials for food products due to their excellent oxygen barrier properties, but because of their poor moisture-proofing, heat-sealing properties, and other properties, they are usually used in combination with other resins. It is used as a laminate with. The laminate is manufactured by coextrusion molding, dry lamination molding, extrusion coating molding, etc. However, since the above-mentioned copolymers have poor adhesive properties, a special adhesive resin is often used for the adjacent layer. Polyolefin resins grafted with maleic anhydride have often been used as adhesive resins. Although the graft has excellent adhesion with the above-mentioned copolymer, it has problems in terms of hygiene and economy, and when used as an interlayer adhesive layer, from the viewpoint of adhesion with other layers. It also had the disadvantage that its usable applications were limited.

On the other hand, there are copolymers of ethylene and acid anhydride,
In order to develop sufficient adhesive properties, it is necessary to introduce a considerable amount of acid anhydride, which inevitably lowers the molecular weight of the polymer. As a result, formability decreased significantly, making it difficult to obtain a laminate that could be used for practical purposes. Problems to be Solved by the Invention> There has never been a laminate containing an ethylene-vinyl alcohol copolymer as one layer that has all of the characteristics of adhesion, hygiene, moldability, economic efficiency, etc. Therefore, an efficient manufacturing method for the laminate has not been established. The purpose of the present invention is to solve this problem. <Means for Solving the Problems> The present inventors have discovered that, in a laminate containing at least one layer of an ethylene-vinyl alcohol copolymer, at least an ethylene component and a radical polymerization method obtained by adding an antioxidant during polymerization. It has been found that the desired laminate can be efficiently produced by using a random copolymer containing a polyhydric 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%. When the ethylene content is less than 20 mol%, extrusion moldability is poor;
If the vinyl alcohol content exceeds 70 mol%, the oxygen barrier property, which is a characteristic of the copolymer, will be insufficient, making it impractical. If the vinyl alcohol content is less than 30 mol%, the oxygen barrier property will be insufficient, and if it exceeds 80 mol%, extrusion molding will be difficult. becomes. MFR of the copolymer (JIS K-7210230℃
)teeth. 0.5 to 50 g/10 minutes, preferably 3 to 50 g/10 minutes
20g/10 minutes. 0.5g7 If it takes less than 10 minutes, the melt flowability will be insufficient and molding at normal speed will not be possible. 5
When it exceeds 0 g/10 minutes, moldability deteriorates due to a decrease in melt tension.

In the present invention, a random copolymer containing at least an ethylene component and a radically polymerizable acid anhydride component, which is obtained by adding an antioxidant during polymerization, is used as the adhesive layer. It may be a multi-component copolymer containing a radically polymerizable comonomer (third comonomer) component.

As for the production method of this random copolymer, the well-known production method of high-pressure low-density polyethylene can be used as is. That is, in the presence of a radical generator such as an organic peroxide, ethylene, a radically polymerizable acid anhydride, and a third comonomer are heated at 100 to 300°C and 1000 to 3000°C.
Polymerize at 500 atm to obtain a copolymer. At this time, an antioxidant is added to the polymerization system. The antioxidant is added by making a mixed solution of the antioxidant with a radically polymerizable acid anhydride or a third comonomer, and injecting the mixture into the reactor or the ethylene piping upstream of the reactor using a pump. It is also possible to inject it alone. Although there are no particular restrictions on where to inject it, it is preferable to inject it into the suction line of the second stage compressor in order to improve mixing with ethylene.

The content of ethylene component in this random copolymer is 55 mo
It is preferably 1% or more and less than 99.9 mol%. 55mo1
If it is less than 99.9%, the moldability will be extremely deteriorated and a good FAN product will not be obtained, and if it is more than 99.9no1%, the adhesive strength will be so small that it cannot be used as an adhesive layer.

Examples of radically polymerizable acid anhydrides used in this random copolymer include maleic anhydride, itaconic anhydride, citraconic anhydride, endic anhydride, ■-butene-3
, 4-dicarboxylic acid anhydride, and the like. Two or more of these may be used in combination. Among these, maleic anhydride and itaconic anhydride are particularly preferred.

The content of the radically polymerizable acid anhydride component in the present random copolymer is preferably in the range of 0.1 to 5 mol%, particularly preferably 0.3 to 2 mol%. If the acid anhydride content is less than 0.1 mol%, interlayer adhesion is insufficient, and if it exceeds 5 mol%, it is extremely difficult to commercially produce. Even if it were possible to produce it, it would have no practical meaning and would only lead to a decline in economic efficiency and formability. Examples of the third comonomer that can be used in combination with the radically polymerizable acid anhydride include ester compounds, amide compounds, acid compounds, ether compounds, and hydrocarbon compounds.

Specifically, ester compounds include vinyl acetate, methyl acrylate, ethyl acrylate, probyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, benzyl acrylate, and methacrylate. Methyl, ethyl methacrylate, probyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, methyl fumarate, ethyl fumarate, proyl fumarate, butyl fumarate, dimethyl fumarate, diethyl fumarate, Examples include dipropyl fumarate, dibutyl fumarate, methyl maleate, ethyl maleate, probyl maleate, butyl maleate, dimethyl maleate, diethyl maleate, dipropyl maleate, and dibutyl maleate. Amide compounds include acrylamide, methacrylamide, N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, N-butylacrylamide, N-hexylacrylamide, N-octylacrylamide.
Examples include N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dimethylmethacrylamide, and N,N-diethylmethacrylamide. Examples of compounds a include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Examples of ether compounds include methyl vinyl ether, ethyl vinyl ether, probyl vinyl ether, butyl vinyl ether, octadecyl vinyl ether, and phenyl vinyl ether. Examples of the hydrocarbon compound include styrene, norbornene, butadiene, acrylonitrile, methacrylonitrile, acritonitrile, crotonaldehyde, trimethoxyvinylsilane, vinyl chloride, and vinylidene chloride. Among these, particularly preferred compounds are acrylic esters.
Examples include methacrylic esters, maleic esters, fumaric esters, acrylic acid, and methacrylic acid.

If necessary, two or more of these comonomers may be used in combination.

When the above third comonomer is used in combination, the content of the third comonomer component in the random copolymer is at most 40 mo
Preferably, it is less than 1%; if it exceeds 40+io1%, the moldability will be significantly reduced, making it impossible to obtain a laminate that meets the purpose of the present invention.

When polymerizing this random copolymer, an antioxidant is added to the polymerization system, and the antioxidants referred to in the present invention include nuclear-substituted phenols, biphenols, bisphenols, etc., and at least Contains one substituent. The type of substituent is not particularly limited, but includes alkyl groups and alkenyl groups having 4 or less carbon atoms, vinyl groups, methyl-substituted vinyl groups, allyl groups, alkoxy groups having 3 or less carbon atoms,
Hydroxyl group etc. are preferred. The number of substituents is preferably two or three or more, and mononuclear phenols are particularly preferred.

Specific examples of antioxidants include parahydroxybenzaldehyde, hydroquinone monomethyl ether, paraaminophenol, 3.5-xylenol, 2,6-diisopropylphenol, 2-tert-butylhydroxyanisole, and 4-tert-hydroxybenzaldehyde. butylpyrocatechol,
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-tert-butylphenol) butylphenol)
．． 2.8-ditertiarybutyl-4-methylphenol. Examples include octadecyl 3-(3,5-ditertiarybutyl-4-hydroxyphenyl)probionic acid. Of these, 2,6-ditertiarybutyl-
4-Methylphenol. 4.4'-thiobis(3-
Methyl-6-tert-butylphenol), 3-(
Octadecyl 3.5-ditertiarybutyl-4-hydroxyphenyl)propionate is preferred.

The amount of the antioxidant added is 50 to 2000 ppm, preferably 80 to 15 ppm by weight at the inlet of the reactor.
00 ppm. If the amount is less than 50 ppm, the expected effect will not be exhibited and polymerization will not be stable. Addition amount is 2000ppm
If this value is exceeded, the antioxidant acts strongly as a polymerization inhibitor, and favorable results cannot be obtained. Liver R of this random copolymer (JIS K-7210 1
90°C) is in the range of 0.1 to 50 g/10 minutes. Outside this range, the moldability during the production of a laminate will be significantly reduced, making it impossible to produce a preferred laminate. Furthermore, in this random copolymer, it is essential that unreacted monomers be completely separated from the polymer and substantially not contained therein.

The presence of unreacted monomers not only poses a hygiene problem, but also
It is also a physical problem because it causes a decrease in adhesion. In the high-pressure radical copolymerization of ethylene, a radically polymerizable acid anhydride, and a third comonomer, if an attempt is made to introduce the acid anhydride to an extent that will provide sufficient adhesion when formed into a laminate, the chain inhibition effect of the acid anhydride will occur. Also, the chain transfer effect of the third comonomer makes it difficult to increase the molecular weight. As a result, the melt tension of the resin is insufficient, which often causes problems when forming laminates. This problem can be solved by lowering the polymerization temperature, but on the other hand, in the case of low-temperature polymerization, the power required for stirring inside the reactor increases, making stable polymerization difficult. Adding an antioxidant during polymerization enables stable polymerization at low temperatures. As a result, a copolymer with molecular weight, melt tension, moldability and adhesive properties suitable for producing 'f'AN products can be obtained, and a good laminate with an ethylene-vinyl alcohol copolymer can be obtained. It becomes possible to manufacture.

The laminate containing at least one layer of ethylene-vinyl alcohol copolymer is a laminate having a thickness of 30 μm to 5+ m. The random copolymer layer containing an ethylene component and a radically polymerizable acid anhydride component according to the present invention is used as a layer adjacent to the ethylene-vinyl alcohol copolymer layer. However, this random copolymer layer does not necessarily have to be an intermediate layer, and can also be used as an outermost layer in some cases. There are no particular restrictions on the shape of the laminate, and it can be used in any desired shape, such as a film, sheet, bag, or bottle.

The laminate usually uses polyolefin resin, polystyrene resin, polyester resin, etc. as the outermost layer, but the random copolymer containing an ethylene component and a radically polymerizable acid anhydride component according to the present invention can be made of any of these resins. It exhibits high adhesion to other resins, so it can be used in a very wide range of applications.

Various molding methods such as coextrusion molding, dry lamination molding, heat lamination molding, and extrusion coating molding can be used to manufacture the laminate, but in order to obtain a particularly good laminate by taking advantage of the characteristics of the present invention. It is desirable to use a coextrusion method.

Example 1 Polypropylene layer on both outer layers, ethylene-vinyl alcohol copolymer (ethylene 32 mo1%, vinyl alcohol 68 mo1%. MFR 4κ/10 min) N,
Three types of 5N laminates having a structure of adhesive resin layers between both layers were manufactured by coextrusion molding.

As the adhesive resin, ethylene-methyl acrylate-maleic anhydride terpolymer (ethylene 95.5 mol%,
Methyl acrylate 3.5mol1%, maleic anhydride 1.
0 mol%, MFR 2.5 g/10 minutes) was used.

This copolymer was polymerized using a high-pressure polyethylene production facility with 42 autoclave reactors, and adding 1000 ppm (by weight) of 2,6-di-tert-butyl-4-methylphenol at the inlet of the reactor. I got it.

Molding was carried out using a coextrusion multilayer film molding machine with three 65φ extruders and a 1300mm T-die, at a resin temperature of 230°C and a take-up speed of 30m/min, with a total thickness of 50mm.
A laminate with a μm thickness and an adhesive layer thickness of 5 μm was manufactured.

Molding was carried out without any particular problems. The obtained laminate had good appearance and transparency, and when the 90 degree peel strength between the polypropylene layer and the ethylene-vinyl alcohol copolymer layer was measured after aging at 40°C for 2 days (peeling speed 300 mm/
), and had a peel strength of 580 g/15+nm, which was no problem for practical use. The oxygen permeability under drying conditions at 35° C. was as low as 0.5 cc·20 μm/m”24 Hr-atm, and the laminate was judged to be suitable for packaging materials.

Example 2 Polystyrene (HI grade MFR2.0
g/10 min), adhesive resin, ethylene-vinyl alcohol copolymer, adhesive resin, linear low-density polyethylene (
A 5-layer laminate was prepared which was a mixture of MFR 2.2 k/10 min, density 0.922) and regular low density polyethylene (MFR 6.8 g/10 min, density 0.917).

For molding, first the three outer layers were coextruded using the molding method shown in Example 1, and then the other two layers were coextruded and coated using the laminate as a base material, resulting in a total thickness of 300 μm.
m sheets were obtained. The adhesive resin and ethylene-vinyl alcohol copolymer used were the same as in Example 1. There were no particular problems with moldability, and the peel strength between the layers was 40 on the outer layer side.
0g/15m+a. 720g/15+++ on the inner layer side
m, and had a strength that poses no problem in practical use. This sheet has excellent heat-sealing properties and swallow-pressing properties, and 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 Laminates were manufactured in the same manner as in Example 1, except that the random copolymers shown in Table 1 were used instead of the adhesive resin used in Example 1. As shown in Table 1, there were no problems in moldability or film appearance, and the interlayer adhesion strength was sufficient for practical use.

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

Comparative Example 2 Modified polypropylene (HFRS.5κ/10
A laminate was produced under the same conditions as in Example 1, except that 0.28% by weight of maleic anhydride was used. Modified polypropylene is made by adding 1 part maleic anhydride to polypropylene powder.
．． After dispersing and mixing 8% by weight and 1.2% by weight of benzoyl peroxide using a Henschel mixer, a graft reaction was carried out using an extruder and the mixture was formed into pellets. Although there were no particular problems in molding, gel and fish eyes, which were thought to be caused by ungrafted maleic anhydride, were noticeable, and the adhesive strength was weak at 270 g/15+Ila+, resulting in poor practical performance as a laminate.

(The following is a blank space) <Effects of the Invention> The random copolymer of the present invention containing at least an ethylene component and a radically polymerizable acid anhydride component has excellent moldability, adhesiveness, sanitary properties, etc. By using this as an adhesive layer, a laminate containing at least one layer of ethylene-vinyl alcohol copolymer can be effectively produced.

This laminate can be used in a wide range of applications, and is particularly suitable for packaging materials such as food products.

Patent applicant: Showa Denko Co., Ltd. teenager buried Man

Claims (1)

[Claims] 1. In a laminate containing at least one layer of ethylene-vinyl alcohol copolymer, at least an ethylene component and a radically polymerizable acid anhydride component obtained by adding an antioxidant during polymerization. A laminate characterized by using a random copolymer containing the same as an adhesive layer. 2. In a laminate containing at least one layer of ethylene-vinyl alcohol copolymer, a random copolymer containing at least an ethylene component and a radically polymerizable acid anhydride component, which is obtained by adding an antioxidant during polymerization. A method for producing a laminate characterized by its use as an adhesive layer.