JP6743006B2 - Resin composition and use thereof - Google Patents

Description

The present invention relates to a resin composition for a sealant, a lid material containing the sealant resin composition, and a food container having the lid material.

BACKGROUND ART Plastic containers having an easily-openable lid are widely used as various food and pharmaceutical containers such as jelly, pudding, yogurt, tofu, instant noodles and noodles. In particular, as containers for instant noodles in cups, noodles, juice powder, etc., expanded polystyrene sheets or those laminated with impact-resistant polystyrene film, impact-resistant polystyrene sheets, polyethylene laminated paper, etc. are widely used as containers. It is used. As a sealing material used for the lid of these plastic containers, various materials have been proposed and put to practical use in order to hermetically seal in an easily opened form. Among them, a composition mainly composed of a copolymer of ethylene and vinyl acetate or ethylene and an acrylic ester or a polyolefin resin has relatively good sealing property between the container body and the lid, and at the time of peeling the lid. It is widely used because its peel strength is generally appropriate.

For example, in Patent Document 1, an easy peeling containing a metal layer, a pressure-sensitive adhesive layer, a resin selected from an ethylene-vinyl acetate copolymer resin, an ethylene-acrylic acid ester copolymer resin and a polyolefin resin, and a tackifier It is described that a laminated body in which a functional resin layer is sequentially laminated is suitable as an easily peelable lid material for a bead expanded polystyrene container.

In Patent Document 2, a sealant composed of a composition containing an ethylene-(meth)acrylic acid copolymer, a polyolefin, a tackifying resin and a filler in a specific ratio is stronger than a known sealant but is peelable. It is described to provide a seal.

JP-A-3-79342 Japanese Patent Publication No. 2007-522276

On the other hand, the food container is naturally required to have hygiene so as not to impair the quality of the food that is the content. Therefore, some countries and regions have their own hygiene standards for food containers, and in Japan, the standards have already been established more than 50 years ago (foods and additives based on Article 18 of the Food Sanitation Act). Etc. standard standards (Ministry of Health and Welfare Notification No. 370 in 1959)). These standards basically limit the amount of container material extracted to various solvents, such as organic solvents and oils, with the goal of not transferring the components of the container to the food product that is the content. Avoiding such component transfer is a particularly important target for containers of oil-containing foods such as fried noodles and oil-cooked side dishes, in which component transfer from a plastic container is more concerned. Conventionally, materials satisfying such sanitary standards have been used as materials for food containers such as container bodies, lids, sealants, etc., but food sanitation standards such as solvent extraction tend to be stricter year by year, and are particularly strict. Some countries have standards.

However, even if it succeeds in lowering the solvent extraction amount of the sealant material so far, it cannot be said that the adhesiveness of the sealant material is always satisfied at the same time. Compatibility was not easy. Therefore, an excellent balance of adhesive strength and unsealing property with a container, and further, the elution of components into an organic solvent is extremely low, a sealant composition capable of meeting recent demands as a sealant material for food containers has not yet been obtained. Absent.

The present inventors have earnestly studied for an excellent sealant material that satisfies the stricter hygiene standards in addition to the adhesiveness required for the lid material of the food container. That is, an object of the present invention is to provide a sealant material, which can obtain a sealing property and a good unsealing property required for a lid material of a food container, and further, which has a smaller amount of solvent extraction and satisfies a stricter sanitary standard than before. ..

As a result, a resin composition containing a specific ethylene copolymer as a main component and an ethylene/α-olefin copolymer and a tackifying resin in a specific amount ratio satisfies the above problems, and is a sealant material for food containers. It was found to be excellent. That is, the present invention is as follows.

(Invention 1)
Ethylene/vinyl ester copolymer containing 90 mol% or more and 95 mol% or less of ethylene units and 5 mol% or more and 10 mol% or less of vinyl ester units (provided that the total of ethylene units and vinyl ester units is 100 mol%). at least one resin (a) 50 to 99 parts by weight selected from.)
1 at least one resin (B) selected from an ethylene/α-olefin copolymer and an ABA type block copolymer (A represents a polystyrene block and B represents an alkylene copolymer block). ~50 parts by mass,
A resin composition for a sealant, which contains 0 to 10 parts by mass of a tackifying resin (C) (however, the total amount of (A), (B), and (C) is 100 parts by mass) ,
Furthermore, 1 mass of the ethylene/unsaturated carboxylic acid ester copolymer resin (D) satisfying the following general formula (2) is added to 100 parts by mass of the resin (A), the resin (B), and the resin (C) in total. A resin composition for a sealant, which comprises not less than 60 parts by mass . T≧−3.0X+107 (2) (In the formula (2), X is the unsaturated carboxylic acid ester content (mol %), and T is the melting point (° C.) measured according to JIS K7121-1987. Represent)
(Invention 2)
Resin (A) 60 to 95 parts by weight, the resin (B) 5 to 40 parts by mass, the resin (C) 0 weight parts including body (the total of (A), (B), (C) The amount is 100 parts by mass.) , 5 parts by mass or more and 30 parts by mass or less of the resin (D) per 100 parts by mass of the resin (A), the resin (B), and the resin (C) in total. 1. The resin composition for sealant of 1.
(Invention 3 )
The resin composition for a sealant according to the invention 1 or 2 , which is used as a sealant between a container body and a lid base material.
(Invention 4 )
The resin composition for a sealant of the invention 3 , which is a container body in which at least a part in contact with the lid base material is made of impact-resistant polystyrene.
(Invention 5 )
The resin composition for a sealant according to any one of Inventions 1 to 4 , which is for a lid material for a food container.
(Invention 6 )
A lid member comprising a layer comprising the resin composition for a sealant according to any one of the inventions 1 to 5 and a base material layer.
(Invention 7 )
A food container comprising the lid member of the invention 6 .

The resin composition of the present invention is a sealant resin composition suitable for heat-sealing a food container body and a lid member. The resin composition for a sealant of the present invention is prepared by blending predetermined components, that is, the resin (A), the resin (B), the resin (C) and the resin (D) which is an optional component in a specific amount ratio. It was possible to achieve both excellent adhesion and extremely high hygiene, which is the issue of. By heat-sealing the main body of the food container and the lid material via the heat-sealing layer made of the resin composition for a sealant of the present invention, a food container having a good balance of good adhesiveness, easy opening and high hygiene is obtained. To be

The resin composition of the present invention contains 90 mol% or more and 95 mol% or less of ethylene units and 5 mol% or more and 10 mol% or less of vinyl ester units obtained by copolymerizing a vinyl ester monomer and ethylene in a specific ratio. An ethylene/vinyl ester copolymer (provided that the total of ethylene units and vinyl ester units is 100 mol %), and an unsaturated carboxylic acid ester monomer and ethylene are copolymerized at a specific ratio. An ethylene/unsaturated carboxylic acid containing 90 mol% or more and 95 mol% or less of ethylene units and 5 mol% or more and 10 mol% or less of unsaturated carboxylic acid ester units and having a specific relationship between the unsaturated carboxylic acid ester units and the melting point At least one resin (A) selected from ester copolymers, at least one resin (B) selected from ethylene/α-olefin copolymers and ABA type block copolymers, and tackifying The resin (C) is blended in a specific amount ratio.

[Resin (A)]
The resin (A) contained in the resin composition for a sealant of the present invention is at least one resin selected from an ethylene/vinyl ester copolymer and an ethylene/unsaturated carboxylic acid ester copolymer satisfying the following general formula (1). Is.
-3.0X+107>T... (1)
(In the formula (1), X represents an unsaturated carboxylic acid ester content (mol %), and T represents a melting point (°C) measured according to JIS K7121-1987).
The lower limit of T is preferably −3.0X+87.

The vinyl ester is, for example, vinyl acetate or vinyl propionate, preferably vinyl acetate. The ethylene/vinyl ester copolymer used in the present invention has an ethylene unit of 90 mol% or more and 95 mol% or less, preferably 90 mol% or more and 93 mol% or less, and a vinyl ester unit of 5 mol% or more and 10 mol% or less, preferably Is 7 mol% or more and 10 mol% or less (provided that the total of ethylene units and vinyl ester units is 100 mol %).

The ethylene/vinyl ester copolymer may be a binary copolymer or a multicomponent copolymer obtained by copolymerizing two kinds of the above vinyl esters with ethylene, and further, a vinyl ester copolymer. Inherently has, for example, other polar monomers such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride, unless the properties such as flexibility, elasticity and heat sealability are substantially changed. A small amount of itaconic anhydride, carbon monoxide or the like may be copolymerized.

An ethylene/vinyl ester copolymer satisfying the following general formula (1′) is more preferable from the viewpoint of solvent extraction amount.
-3.0X'+107>T'... (1')
(In the formula (1′), X′ represents a vinyl ester content (mol %), and T′ represents a melting point (° C.) measured according to JIS K7121-1987).
The lower limit of T'is preferably -3.0X+87.

The ethylene/vinyl ester copolymer as described above is produced by radical copolymerizing ethylene and vinyl ester at a high temperature and a high pressure according to a conventional method. It can be produced by either the autoclave method or the tubular method. The ethylene/vinyl ester copolymer satisfying the above formula (1') can be produced by a high pressure radical polymerization process by an autoclave method.

The unsaturated carboxylic acid ester is an alkyl ester of unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid having up to about 20 carbon atoms. The ethylene/unsaturated carboxylic acid ester copolymer used in the present invention has an ethylene unit content of 90 mol% or more and 95 mol% or less, preferably 90 mol% or more and 93 mol% or less, and an unsaturated carboxylic acid ester unit of 5 mol% or more. It is characterized by containing 10 mol% or less, preferably 7 mol% or more and 10 mol% or less (however, the total of ethylene units and unsaturated carboxylic acid ester units is 100 mol%). The ethylene/unsaturated carboxylic acid ester copolymer satisfying the formula (1) can be obtained by a high pressure radical polymerization process by an autoclave method.

The ethylene/unsaturated carboxylic acid ester copolymer satisfying the above formula (1) is not only a binary copolymer but also a multi-component copolymer obtained by copolymerizing ethylene with two or more kinds of the above carboxylic acid esters. Further, other polar monomers such as, for example, flexibility, elasticity, heat sealability and other polar monomers, which are inherently possessed by the ethylene/unsaturated carboxylic acid ester copolymer, may be used. A small amount of acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride, carbon monoxide or the like may be copolymerized.

When the content of the vinyl ester unit or unsaturated carboxylic acid ester unit is within this range, the adhesiveness and hygiene of the sealant resin composition are excellent. When the content of the vinyl ester unit or unsaturated carboxylic acid ester unit is lower than 5 mol %, the adhesive strength of the resin composition for sealant becomes low, which may cause a problem in the hermeticity of the container. When the content of the vinyl ester unit or the unsaturated carboxylic acid ester unit exceeds 10 mol %, the adhesive strength is high, but a blocking phenomenon is likely to occur, which may be unfavorable for the handleability of the processed product obtained from the resin composition for sealant. is there.

The resin (A) contained in the resin composition for a sealant of the present invention preferably exhibits appropriate fluidity. The melt flow rate (MFR, measured at 190° C. and 2160 g load) of the ethylene/vinyl ester copolymer and the ethylene/unsaturated carboxylic acid ester copolymer is generally 1 g/10 min or more and 50 g/10 min or less. Is preferably 10 g/10 minutes or more, and more preferably 14 g/10 minutes or more. When the MFR of the resin (A) is extremely low, it becomes difficult to laminate the resin composition on the base material and process it into a sheet-like material such as a lid material, which may not be preferable.

The resin (A) of the present invention may contain at least one selected from the above ethylene/vinyl ester copolymers and ethylene/unsaturated carboxylic acid ester copolymers, and two or more ethylene. A vinyl ester copolymer or a mixture of two or more ethylene/unsaturated carboxylic acid ester copolymers may be used. When using a mixture of two or more kinds of ethylene/vinyl ester copolymers or two or more kinds of ethylene/unsaturated carboxylic acid ester copolymers, the content of vinyl ester units or unsaturated carboxylic acid ester units in the mixture is It suffices if it is within the above-mentioned predetermined range, and the MFR of the mixture is preferably within the above-mentioned range.

As the ethylene/vinyl ester copolymer, an ethylene/vinyl ester copolymer (A1) having a relatively low MFR and an ethylene/vinyl ester copolymer (A2) having a relatively high MFR can be used in combination, and , An ethylene/unsaturated carboxylic acid ester copolymer having a relatively low MFR (A1′) and an ethylene/unsaturated carboxylic acid ester (A2′) having a relatively high MFR ) Can also be used together.

Examples of the above (A1) and (A2) include an ethylene unit of 90 mol% or more and 95 mol% or less, a vinyl ester unit of 5 mol% or more and 10 mol% or less, and an MFR of 1 g/10 min or more and 50 g/10 min or less. , Preferably 5 g/10 min or more and 30 g/10 min or less, more preferably 7 g/10 min or more and 25 g/10 min or less ethylene-vinyl ester copolymer (A1), and 90 mol% or more and 95 mol% of ethylene units. The vinyl ester unit is contained in an amount of 5 mol% or more and 10 mol% or less, and the MFR thereof is 80 g/10 min or more and 300 g/10 min or less, preferably 100 g/10 min or more and 250 g/10 min or less, more preferably 120 g/10 min or more. The ethylene/vinyl ester copolymer (A2) of 250 g/10 minutes or less is preferably 1:9 to 9:1 (mass ratio (A1):(A2)), more preferably 5:5 to 8:2. Can be used together in the amount ratio of.

Examples of the above (A1′) and (A2′) include ethylene units of 90 mol% or more and 95 mol% or less, unsaturated carboxylic acid ester units of 5 mol% or more and 10 mol% or less, and MFR of 1 g/10 min or more. 50 g/10 minutes or less, preferably 5 g/10 minutes or more and 30 g/10 minutes or less, more preferably 7 g/10 minutes or more and 25 g/10 minutes or less ethylene-unsaturated carboxylic acid ester copolymer (A1′), and ethylene 90 mol% or more and 95 mol% or less, unsaturated carboxylic acid ester unit is contained in 5 mol% or more and 10 mol% or less, and MFR is 80 g/10 min or more and 300 g/10 min or less, preferably 100 g/10 min or more and 250 g/ 10 minutes or less, more preferably 120 g/10 minutes or more and 250 g/10 minutes or less of the ethylene/unsaturated carboxylic acid ester copolymer (A2′), preferably 1:9 to 9:1 (mass ratio (A1′ ):(A2′)), more preferably 5:5 to 8:2. The resin (A) may be a combination of (A1) and (A2') or a combination of (A1') and (A2).

[Resin (B)]
The resin (B) of the resin composition for a sealant of the present invention is an ethylene/α-olefin copolymer obtained by copolymerizing ethylene with an α-olefin having 3 to 18 carbon atoms, preferably 4 to 10 carbon atoms, and It is at least one resin selected from ABA type block copolymers (A represents a polystyrene block and B represents an alkylene copolymer block). The ethylene/α-olefin copolymer is, for example, ethylene and an α-olefin other than ethylene, for example, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4 It is a copolymer with one or more α-olefins selected from -methyl-1-pentene. Considering the adhesiveness of the resin composition of the present invention, the ethylene/α-olefin copolymer used as the resin (B) in the present invention preferably has a density of 850 kg/m ³ or more and 910 kg/m ³ or less, more preferably 870 kg / ^{m 3} or more 900 kg / ^{m 3} or less of ethylene · alpha-olefin copolymer. The MFR (190° C., 2160 g load) of the ethylene/α-olefin copolymer used in the present invention is generally 1 g/10 minutes or more and 100 g/10 minutes or less, preferably 1 g/10 minutes or more and 60 g/10 minutes or less, and more preferably Is 1 g/10 minutes or more and 20 g/10 minutes or less. The above-mentioned ethylene/α-olefin copolymer is a heterogeneous olefin polymerization catalyst such as a highly active Ziegler-Natta catalyst or Phillips catalyst composed of a highly active titanium catalyst component and an organic aluminum compound, or a homogeneous olefin such as a metallocene catalyst. It is produced by copolymerizing ethylene and the above α-olefin by a process such as a gas phase method, a solution method, a high pressure method or a slurry method using a polymerization catalyst or the like.

In the ABA type block copolymer, A represents a styrene polymer block and B represents an alkylene copolymer block. Examples of the alkylene copolymer block include an ethylene/butene copolymer block and an ethylene/propylene copolymer block. Such a block copolymer is obtained by hydrogenating a butadiene polymer unit or an isoprene polymer unit of a styrene-butadiene-styrene block copolymer or a styrene-isoprene-styrene block copolymer, and generally SEBS or It is called SEPS. Here, the content of the styrene polymer block is preferably 1% by mass to 40% by mass, more preferably 5% by mass to 30% by mass, based on the total mass of the ABA type block copolymer. is there. The melt flow rate (MFR) of the ABA type block copolymer at 230° C. under a load of 2160 g is preferably 0.1 g/10 minutes to 500 g/10 minutes, more preferably 1 g/10 minutes. ~100 g/10 minutes. The MFR of the A-B-A type block copolymer is a value measured by a method according to JIS K7210-1999 at 230°C and a load of 5000 g. Specific examples of the ABA type block copolymer include Kraton G1657 manufactured by Kraton Japan Co., Ltd. and Tuftec H1221 manufactured by Asahi Kasei Chemicals Corporation.

As the resin (B) of the present invention, one kind of the above ethylene/α-olefin copolymers may be used, or a mixture of two or more kinds of ethylene/α-olefin copolymers may be used. When a mixture of two or more kinds of ethylene/α-olefin copolymers is used, the density or MFR of the mixture is preferably within the above-mentioned predetermined range. As the resin (B) of the present invention, one kind of the above ABA type block copolymer may be used, or a mixture of two or more kinds of ABA type block copolymers may be used. May be. Further, as the resin (B) of the present invention, a mixture of one or more kinds of the ethylene/α-olefin copolymer and one or more kinds of the ABA type block copolymer may be used.

The resin (C) that may be contained in the resin composition for a sealant of the present invention in a certain amount or less is a tackifying resin. The resin (C) can be selected from resins having a function of imparting tackiness, and is preferably an alicyclic hydrocarbon resin, aromatic hydrocarbon resin, aliphatic hydrocarbon resin, polyterpene resin, rosin, styrene. It is selected from a series of resins.

Examples of the alicyclic hydrocarbon resin include a resin obtained by polymerizing a spent C4 or C5 fraction after cyclization and dimerization, a resin obtained by polymerizing a cyclic monomer such as cyclopentadiene, a hydrogenated product thereof, or an aromatic compound. It is a resin in which a hydrocarbon resin or an aliphatic/aromatic copolymerized hydrocarbon resin is hydrogenated in the nucleus. Even if the alicyclic hydrocarbon resin (partially hydrogenated petroleum resin) in which some of the unsaturated double bonds in the resin are partially hydrogenated, all of the unsaturated double bonds in the resin are hydrogenated. The alicyclic hydrocarbon resin (completely hydrogenated petroleum resin) may be used.

As the aromatic hydrocarbon resin, a resin obtained by polymerizing a fraction containing at least one unsaturated aromatic hydrocarbon having 3 to 10 carbon atoms such as vinyltoluene, isopropenyltoluene, indene and α-methylstyrene, Resins obtained by copolymerizing these fractions and aliphatic hydrocarbon fractions can be used without limitation.

The aliphatic hydrocarbon resin is, for example, a polymer containing, as a main component, an olefin or a diene having 4 to 5 carbon atoms. The polyterpene resin is, for example, a polymer such as α-pinene, β-pinene or dipentene, a terpene/phenol resin or a hydrogenated terpene resin. The above-mentioned rosins are, for example, rosin, polymerized rosin, hydrogenated rosin, rosin ester, hydrogenated products or polymers thereof. The styrene-based resin is, for example, a polymer such as styrene, vinyltoluene, α-methylstyrene, isopropenyltoluene, or a low molecular weight polymer such as an intercopolymer thereof. As the resin (C), a hydrogenated petroleum resin is preferable among the above-exemplified products when color tone, odor, food hygiene and the like are important as the performance of the resin composition of the present invention.

[Amount Ratio of Resins (A), (B), (C)]
The resin composition for a sealant of the present invention contains the above resins (A), (B), and (C) in a specific amount ratio. That is, 50 to 99 parts by mass of the resin (A), 1 to 50 parts by mass of the resin (B), and 0 to 10 parts by mass of the resin (C) are mixed. However, the total amount of (A), (B), and (C) is 100 parts by mass. The resin composition of the present invention is preferably 60 to 95 parts by mass of resin (A), 5 to 40 parts by mass of resin (B), 0 to 10 parts by mass of resin (C), and more preferably resin (A). ) Is 70 to 95 parts by mass, the resin (B) is 5 to 30 parts by mass, the resin (C) is 0.5 to 8 parts by mass, and more preferably the resin (A) is 70 to 95 parts by mass, the resin (B). In an amount of 5 to 20 parts by mass and the resin (C) in an amount of 1.0 to 5 parts by mass.

If the blending amount of the resin (B) is less than 1 part by mass, the adhesive strength of the resin composition for a sealant, particularly the adhesive strength with respect to high impact polystyrene is lowered, which is not preferable. When the compounding amount of the resin (B) exceeds 50 parts by mass, the processability of the resin composition for sealant is lowered, or the solvent extractable component is increased and the food hygiene is inferior, which is not preferable. When the compounding amount of the tackifying resin (C) exceeds 10 parts by mass, the adhesive strength of the resin composition for sealant is high, but the solvent extractable content increases and the food hygiene is inferior, which is not preferable.

[Resin (D)]
The resin composition for a sealant of the present invention may further contain an ethylene/unsaturated carboxylic acid ester copolymer resin satisfying the general formula (2) in addition to the resins (A), (B) and (C). it can. The ethylene/unsaturated carboxylic acid ester copolymer (hereinafter referred to as resin (D)) in the present embodiment is a copolymer of ethylene and an unsaturated carboxylic acid alkyl ester.

Examples of unsaturated carboxylic acid alkyl esters include alkyl esters of unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid having up to about 20 carbon atoms.
Examples of the alkyl ester of acrylic acid or methacrylic acid include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, isopropyl acrylate, isobutyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and methacrylic acid. Examples thereof include ethyl acid, n-propyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, n-butyl methacrylate, dimethyl maleate, and diethyl maleate. Among these, (meth)acrylic acid alkyl ester having an alkyl ester having 2 to 4 carbon atoms is preferable from the viewpoint of easy availability, performance and price balance.

Examples of the preferable copolymer (D) include ethylene-ethyl acrylate copolymer, ethylene-n-propyl acrylate copolymer, ethylene-isopropyl acrylate copolymer, ethylene-n-butyl acrylate copolymer. , Ethylene-isobutyl acrylate copolymer, ethylene-ethyl methacrylate copolymer, ethylene-n-propyl methacrylate copolymer, ethylene-isopropyl methacrylate copolymer, ethylene-n-butyl methacrylate copolymer, ethylene- Examples thereof include isobutyl methacrylate copolymer. The copolymer (D) in the present embodiment is a random binary copolymer, but a copolymer obtained by copolymerizing a plurality of (meth)acrylic acid alkyl esters with ethylene is also in the category of a random binary copolymer. to go into. The copolymer (D) satisfies the following formula (2) with respect to its melting point T (° C.) (according to JIS K7121-1987) and unsaturated carboxylic acid ester unit content (X mol %).
T≧−3.0X+107 (2)
The upper limit of T is preferably -3.0X+125.

The copolymer (D) can be obtained by a high pressure radical polymerization process by a tubular method. For example, the total amount of ethylene gas and (meth)acrylic acid alkyl ester monomer and the organic peroxide are introduced from the inlet of the tubular reactor, and the average reaction temperature in the reactor is set in the range of 150 to 250°C. When the polymerization is carried out, a copolymer (D) satisfying the above formula (2) is obtained. Since the reactivity between ethylene and the alkyl (meth)acrylate is different, the concentration of the alkyl (meth)acrylate monomer in ethylene gas changes between the inlet and outlet of the tubular reactor. That is, the concentration of the (meth)acrylic acid alkyl ester monomer in ethylene gas is high at the inlet and low at the outlet, and a copolymer having a high (meth)acrylic acid alkyl ester content and a copolymer having a low (meth)acrylic acid alkyl ester content are mixed. To generate. Among them, a copolymer having a low content of (meth)acrylic acid alkyl ester provides higher melting point and heat resistance. Therefore, when the average value of the (meth)acrylic acid alkyl ester contents of the copolymer is the same, the melting point of the copolymer obtained by the tubular method becomes higher than that by the autoclave method, so that the above condition is satisfied. The resin (D) can be obtained.

The resin (D) may be a binary copolymer or a multicomponent copolymer obtained by copolymerizing two or more kinds of the above unsaturated carboxylic acid esters with ethylene, and further, an unsaturated carboxylic acid ester copolymer. Other polar monomers such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, and anhydrous, as long as the properties inherent to the polymer, such as flexibility, elasticity, and heat sealability, are not substantially changed. A small amount of maleic acid, itaconic anhydride, carbon monoxide or the like may be copolymerized.

The unsaturated carboxylic acid ester unit constituting the resin (D) is in the range of generally 1 to 22 mol% and preferably 5 to 14 mol% based on 100 mol% of the total of ethylene units and unsaturated carboxylic acid ester units. It is in. The MFR (190° C., 2160 g load) of the resin (D) used in the present invention is preferably in the range of 2 to 50 g/10 minutes from the viewpoint of the adhesive seal strength of the resulting sealant composition, and further the workability. And particularly preferably 3 to 20 g/10 minutes.

When the resin (D) is, for example, an ethylene/(meth)acrylic acid alkyl ester copolymer, the (meth)acrylic acid alkyl ester unit content X in the above formula (2) is equal to (meth)acrylic acid alkyl ester. It is measured by the assigned infrared absorption spectrum (IR). For example, in the case of ethyl acrylate (EA), it is determined from the absorbance at 860 cm ⁻¹ belonging to EA.
However, the calibration curve is obtained by determining the EA concentration by nuclear magnetic resonance spectrum (NMR) and correlating with the absorbance at 860 cm ⁻¹ of IR. The method of calculating X in formula (1) and X′ in formula (1′) also conforms to the above example of the method of calculating X.

The resin composition for a sealant of the present invention preferably contains the resin (D) in an amount of 1 part by mass or more and 60 parts by mass or less based on 100 parts by mass of the resin (A), the resin (B) and the resin (C). The content can be more preferably 5 parts by mass or more and 30 parts by mass or less, and further preferably 8 parts by mass or more and 30 parts by mass or less. When the blending amount of the resin (D) exceeds 60 parts by mass, the adhesive strength of the resin composition is high, but the solvent-extracted component increases and the food hygiene is inferior, which is not preferable in some cases.

As the resin (D) of the present invention, one kind of the above-mentioned ethylene/unsaturated carboxylic acid ester copolymer may be used, and a mixture of two or more kinds of the ethylene/unsaturated carboxylic acid ester copolymer is used. May be. When a mixture of two or more kinds of ethylene/unsaturated carboxylic acid ester copolymers is used, the content of the mixture may be in the above predetermined range, and the MFR of the mixture is preferably in the above range.

[Arbitrary ingredients]
The resin composition for a sealant of the present invention may contain other resins as long as the characteristics of the composition are not impaired. The resin composition for a sealant of the present invention may further contain various additives, if necessary. Examples of such additives are antioxidants, ultraviolet absorbers, light stabilizers, heat stabilizers, pigments, dyes, antistatic agents, processing aids such as lubricants and release agents.

The sealant resin composition of the present invention is produced by mixing the resins (A), (B), (C) and optionally the resin (D) and the optional components simultaneously or sequentially. The mixing method follows the standard method. For example, it is preferable to melt-mix using a single-screw extruder, a twin-screw extruder, a Banbury mixer, various kneaders, etc., and the mixing order is not particularly limited. The melt mixing temperature is preferably 140°C to 230°C.

Considering extrusion processability and adhesive strength, the resin composition for a sealant of the present invention has an MFR (190° C., 2160 g load) of 0.1 to 100 g/10 minutes, preferably about 1 to 30 g/10 minutes. It is desirable to be prepared.

The sealant resin composition of the present invention is suitable as a sealant material for plastic containers. When the main body of the container and the lid material are sealed with the resin composition of the present invention, the lid material having a layer made of the resin composition of the present invention and the container body are usually heat-sealed according to a conventional method. The above-mentioned lid material is preferably formed by molding a multilayer laminate including a layer made of the resin composition for a sealant and a lid base material in the present invention. The lid base material is not particularly limited, and includes paper, aluminum plate (eg, aluminum foil), non-woven fabric, polyester, polyethylene, polypropylene, polystyrene (eg, impact-resistant polystyrene), aluminum vapor deposition polyester, aluminum vapor deposition polypropylene, silica vapor deposition polyester. Etc. are used. The lid base material may be a single layer or a laminate of two or more layers. Although the thickness of the lid base material layer is not particularly limited, it is generally about 1 to 500 μm, preferably 10 to 200 μm.

When laminating the resin composition for a sealant of the present invention on a lid base material, a film is previously formed from the resin composition by a casting method or an inflation method, and a method of laminating the film to the lid base material by a dry lamination method, the resin composition Adopting a method of directly coating an object on a lid base material, a method of using polyethylene or the like for an adhesive layer and laminating via an adhesive layer by sandwich lamination, a coextrusion of the lid base material and the resin composition, and the like. You can Among these methods, a method of coextrusion molding a two-layer or three-layer or more multilayer material composed of a single-layer or two-layer or more lid base material and the resin composition for a sealant of the present invention is a T-die method. preferable. The thickness of the layer composed of the resin composition for a sealant of the present invention is not particularly limited, but is generally about 1 to 500 μm, preferably 10 to 200 μm.

Examples of the material of the plastic container body include polyolefins such as polyethylene and polypropylene, polystyrene, styrene polymers such as impact-resistant polystyrene, polyesters such as polyethylene terephthalate, polycarbonate, polyvinyl chloride and the like. Such materials may be in the form of foam. Among these materials for the main body, the high impact polystyrene is generally used as the main body of a container for instant foods and has good adhesiveness to the resin composition for a sealant of the present invention. Therefore, as the main body of the plastic container that is heat-sealed using the resin composition for a sealant of the present invention, a high impact polystyrene container or a container made of a material containing high impact polystyrene is preferable. The container body may be a single layer or a laminate of two or more layers.

One of the features of the resin composition for a sealant of the present invention is that the amount of solvent extracted is small and the hygienic property is higher even when measured under stricter conditions than conventional ones. As a more severe measurement condition than the conventional condition, for example, a film-like sealant of 300 cm ² is used as a sample, and 600 ml of n-hexane is contacted with one side of the sample at room temperature for 2 hours to elute the n-hexane. A method of measuring the weight (actual elution amount (mg)) can be mentioned. The resin composition for a sealant of the present invention has an actual elution amount measured by this method example of preferably 30 mg or less, more preferably 20 mg or less.

In the case of a food container, in order for the container to be sufficiently sealed and the container user to open the container without difficulty, it is desirable that the main body of the container and the lid member are bonded to each other with a moderate strength. One of the features of the resin composition for a sealant of the present invention is that it is useful for such a food container. The peeling strength between the lid member and the container body when the seal material including the sealant layer made of the resin composition for a sealant of the present invention and the lid base material and the container body are heat-sealed via the sealant layer. It fits within the appropriate strength range. This peel strength is, for example, a multi-layer material obtained by heat-sealing a lid material including a sealant layer made of the resin composition for a sealant of the present invention and a lid base material, and a plastic layer constituting a container body via the sealant layer. It can be measured as the maximum stress when a test piece having a width of 15 mm cut out from is pulled by peeling (180° peeling) on both sides in the horizontal opposite direction. The peeling strength of the resin composition for a sealant of the present invention measured by such a method is preferably 5 N/15 mm or more and 15 N/15 mm or less, more preferably 7 N/15 mm or more and 14 N/15 mm or less.

Further, the resin composition for a sealant of the present invention is one in which the occurrence of blocking is suppressed by optimizing the composition. For this reason, the multilayer film having the sealant resin composition of the present invention as the sealant layer does not cause blocking, or even if it does occur, it remains only to a slight extent. Six multi-layer films including a sealant layer made of the resin composition for a sealant of the present invention and a base material are stacked in the order of sealant layer/cover base material, and aged at 40° C. for 2 days under a load of 5 kgf/cm ^2. In this case, the blocking strength between the test pieces is preferably less than 100 g/50 mm, more preferably less than 10 g/50 mm.

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The melt flow rate (MFR) was measured at 190° C. under a load of 2160 g according to JIS K7210-1999.
[Examples 1 to 6, Comparative Examples 1 to 7]
The following resins were mixed at the compounding ratios shown in Tables 1 and 2 so that the charged amount was 10 kg. A resin composition was prepared by introducing the resin composition into an extruder (65 mmφ, L/D=28, tip dullage flight screw) and melt-kneading at a processing temperature of 180° C. to obtain the resin composition of the present invention (Example). A resin composition for comparison (comparative example) was obtained.
-EVA1: ethylene-vinyl acetate copolymer ethylene unit content 92.9 mol%, vinyl acetate unit content 7.1 mol%, MFR (190°C, 2160 g load) 15 g/10 minutes, melting point 84°C. It was produced by high pressure radical polymerization by an autoclave method.
EVA2: ethylene/vinyl acetate copolymer ethylene unit content 92.9 mol%, vinyl acetate unit content 7.1 mol%, MFR (190°C, 2160 g load) 150 g/10 minutes, melting point 79°C. It was produced by high pressure radical polymerization by an autoclave method.
EVA3: ethylene-vinyl acetate copolymer: ethylene unit content 96.5 mol%, vinyl acetate unit content 3.5 mol%, MFR (190°C, 2160 g load) 9 g/10 minutes, melting point 94°C. It was produced by high pressure radical polymerization by an autoclave method.
EVA4: Ethylene/vinyl acetate copolymer Ethylene unit content 88.8 mol%, vinyl acetate unit content 11.2 mol%, MFR (190°C, 2160 g load) 15 g/10 minutes, melting point 71°C. It was produced by high pressure radical polymerization by an autoclave method.
PO-1: ethylene/butene random copolymer elastomer MFR manufactured by Mitsui Chemicals, Inc. (190° C., 2160 g load) 3.7 g/10 min Density 885 kg/m ³ .
PO-2: Mitsui Chemicals, Inc. ethylene/hexene random copolymer MFR (190° C., 2160 g load) 3.7 g/10 min Density 905 kg/m ³ .
SEBS: Styrene/ethylene/butylene/styrene block copolymer "Clayton G1657" manufactured by Kraton Japan. MFR (230°C, 5000 g load) 22 g/10 minutes, density 900 kg/m ³ .
Tackifying resin: fully hydrogenated aromatic hydrocarbon resin Arakawa Chemical Co., Ltd. product. Ring and ball softening point 115°C.
EMA: ethylene/methyl acrylate copolymer ethylene unit content 92.5 mol %, methyl acrylate unit content 7.5 mol %, MFR (190° C., 2160 g load) 8 g/10 minutes, melting point 92° C. Manufacturing method: Manufactured by high pressure radical polymerization by the tubular method.
EMAA: ethylene/methacrylic acid copolymer ethylene unit content 96.1 mol%, methacrylic acid unit content 3.9 mol%, MFR (190° C., 2160 g load) 8 g/10 minutes.

The obtained resin composition was evaluated from the following viewpoints.
[Adhesion strength to HIPS]
A polyethylene terephthalate layer (PET), a polyethylene layer (PE), and a methacrylic acid unit content of 3.9 mol% of ethylene. It was laminated with a methacrylic acid copolymer layer (EMAA). A PET, PE, EMAA, and resin composition were laminated in this order to obtain a laminate having a configuration of PET (12 μm)/PE (15 μm)/EMAA (20 μm)/resin composition (10 μm). This laminate was heat-sealed on a commercially available HIPS sheet having a thickness of 0.4 mm under the conditions of a pressing force of 0.2 MPa, a heating temperature of 120° C. and a heating time of 1.0 second, and left at room temperature for 24 hours. Then, both sides of a 15 mm wide test piece cut out from the laminate were pulled in opposite directions (in a peeling direction of 180° C.) to determine the maximum stress. This maximum stress (N/15 mm) was defined as the adhesive strength (N/15 mm) of the resin composition to HIPS at a heat sealing temperature of 120°C. The measurement was performed in the same manner as above except that the heat sealing temperature was changed, and the adhesive strength of the resin composition to HIPS at the heat sealing temperatures of 140° C. and 160° C. was also obtained. The measurement results are shown in Tables 1 and 2.

The adhesive strength to HIPS was judged according to the following criteria. The judgment results are shown in Tables 1 and 2.
・A: Especially good. 7 N/15 mm or more and 14 N/15 mm or less B: Good. 5 N/15 mm or more and less than 7 N/15 mm, more than 14 N/15 mm and 15 N/15 mm or less C: Somewhat bad. 3 N/15 mm or more and less than 5 N/15 mm, more than 15 N/15 mm and 20 N/15 mm or less-D: Fail. Less than 3N/15mm or more than 20N/15mm.

[Blocking resistance]
Six samples each having a width of 50 mm cut out from the laminate having the configuration of PET (12 μm)/PE (15 μm)/EMAA (20 μm)/resin composition (10 μm) are stacked in an atmosphere of 40° C. under a load of 5 kgf/cm ^2. Aged for 2 days. Then, the peel strength between the six samples was measured with a measuring machine VG-35 manufactured by Vangard. The obtained strength (g/50 mm) is shown in Tables 1 and 2 as blocking resistance.

The blocking resistance was evaluated according to the following criteria. The samples judged to be excellent here are those in which the blocking phenomenon is less likely to occur. Tables 1 and 2 show the results of determination regarding blocking property.
・A: Especially good. Less than 10 g/50 mm.
・B: Good. 10 g/50 mm or more and less than 100 g/50 mm.
・C: Bad. 100 g/50 mm or more.

[Organic solvent extraction test]
It tested using the single-sided extractor used for the Ministry of Health and Welfare notification No. 370 test. In this extraction container, a laminate having the above-mentioned PET (12 μm)/PE (15 μm)/EMAA (20 μm)/resin composition (10 μm) was placed with the resin composition layer on top, and 300 cm ² on one side of the laminate was placed. The mixture was allowed to stand at room temperature for 2 hours while being in contact with 600 ml of a solvent, n-hexane. After that, the solvent was evaporated and the amount of residue (mg) was measured. The amount of this residue was taken as the amount of solvent extracted from the laminate (mg). The measurement results are shown in Tables 1 and 2.

The solvent extraction amount (mg) thus obtained was judged according to the following criteria. The judgment results are shown in Tables 1 and 2.
・A: Especially good. 20 mg or less.
・B: Good. More than 20 mg and 30 mg or less.
-C: Fail. Over 30 mg.
-: Not measured

In Comparative Examples 1, 2, and 3 using the ethylene-vinyl acetate copolymer having an excessively small amount of vinyl acetate units, the adhesive strength to HIPS is low and sufficient container sealing property cannot be expected. Comparative Example 4, which does not use the resin (A), has a large blocking tendency and a high solvent extraction amount, so that desired hygiene cannot be obtained. In Comparative Example 5, which uses an ethylene/vinyl acetate copolymer having an excessive amount of vinyl acetate units, the solvent extraction amount and the blocking tendency are large, and it is expected that there are problems in hygiene, handleability of the lid material, and processability. .. Comparative Example 6 in which the amount of the resin (A) blended is too small has extremely poor workability. Comparative Example 7 containing no resin (B) had a lower adhesive strength to HIPS than Comparative Example 1.
As described above, the resin composition for a sealant of the comparative example has a problem in any of adhesiveness, solvent extraction amount, and processability, and is not suitable for practical use.

On the other hand, the resin composition for a sealant of the example shows a moderate adhesive strength to HIPS in a wide temperature range, and the amount of solvent extracted is extremely low. Moreover, the resin composition for a sealant of the example has a low blocking tendency and is excellent in the usability as a heat-sealing layer of the lid material. As described above, the resin composition for a sealant of the example has a well-balanced adhesiveness, hygiene property, and processability with which the container can be opened well.

The resin composition for a sealant of the present invention can be expected as a next-generation sealant material that can be used for heat sealing of containers that require higher hygiene and safety. The container to which the sealant resin composition of the present invention can be applied may be any container as long as the container body and the lid member are bonded to each other by heat sealing. For example, a container composed of a container body made of impact-resistant polystyrene or a material mainly containing it and a lid member is preferable in that the container can be opened without difficulty. In addition, a food container is suitable because there is less risk of component migration from the heat-sealing resin composition of the present invention to the food product that is the content. Examples of food containers using the resin composition for a sealant of the present invention include, for example, snacks, cereals, jellies, puddings, yogurts, tofu, prepared foods, instant foods (for example instant noodles, instant soups), beverages, and fresh foodstuffs thereof. Examples include processed products. The sealant resin composition of the present invention has a high practical value even in countries and regions where stricter hygiene standards are set for food containers.

Claims (7)

Ethylene/vinyl ester copolymer containing 90 mol% or more and 95 mol% or less of ethylene units and 5 mol% or more and 10 mol% or less of vinyl ester units (provided that the total of ethylene units and vinyl ester units is 100 mol%). at least one resin (a) 50 to 99 parts by weight selected from.)
1 at least one resin (B) selected from an ethylene/α-olefin copolymer and an ABA type block copolymer (A represents a polystyrene block and B represents an alkylene copolymer block). ~50 parts by mass,
A resin composition for a sealant, which contains 0 to 10 parts by mass of a tackifying resin (C) (however, the total amount of (A), (B), and (C) is 100 parts by mass) ,
Furthermore, 1 mass of the ethylene/unsaturated carboxylic acid ester copolymer resin (D) satisfying the following general formula (2) is added to 100 parts by mass of the resin (A), the resin (B), and the resin (C) in total. A resin composition for a sealant, which comprises not less than 60 parts by mass .
T≧−3.0X+107 (2)
(In the formula (2), X represents an unsaturated carboxylic acid ester content (mol %), and T represents a melting point (°C) measured according to JIS K7121-1987). Resin (A) 60 to 95 parts by weight, the resin (B) 5 to 40 parts by mass, the resin (C) 0 weight parts including body (the total of (A), (B), (C) The amount is 100 parts by mass.) , and the resin (D) is contained in an amount of 5 parts by mass or more and 30 parts by mass or less based on 100 parts by mass of the resin (A), the resin (B), and the resin (C). Item 1. The sealant resin composition according to Item 1. The sealant resin composition according to claim 1 or 2 , which is used as a sealant between a container body and a lid base material. The resin composition for a sealant according to claim 3 , wherein at least a part of the container body in contact with the lid base material is a container body made of impact-resistant polystyrene. A lid member of the food containers, the sealant resin composition according to any one of claims 1-4. Consisting sealant resin composition according to any one of claims 1-5 and a layer and the substrate layer, the cover member. A food container comprising the lid member according to claim 6 .