JP2002194009A - Method for producing ethylene-vinyl acetate copolymer, saponified material of the copolymer obtained by the same, and molded product containing the saponified material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve (1) the melting extrusion stability and (2) the melting moldability and to reduce (3) the development of coloration and (4) the development of gel in the production of an ethylene-vinyl acetate copolymer saponified material (EVOH). SOLUTION: In the production of an ethylene-vinyl acetate copolymer (EVA) having the ethylene content of 5-60 mol% by copolymerizing an ethylene and a vinyl acetate using a polymerization initiator, an aliphatic alcohol of 4C or less is used as a polymerization solvent, the contents of acetaldehyde and a saturated ester acetate with respect to the vinyl acetate are 200 ppm or less and 10-1,500 ppm, respectively, and the polymerization is carried out at 30-150 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a melt extrusion stability,
The present invention relates to a method for producing an ethylene-vinyl acetate copolymer (EVA), which gives a saponified ethylene-vinyl acetate copolymer (EVOH) having excellent melt moldability and less coloring and gelling.

[0002]

2. Description of the Related Art Conventionally, EVOH is industrially produced by copolymerizing ethylene and vinyl acetate with a polymerization initiator to obtain EVA, and saponifying the EVA. However, in the conventional method, when the EVOH is melt-extruded, the load of the extruder easily changes, and the melt-extrusion stability is not always sufficient. In addition, drawdown, neck-in fluctuation and the like are likely to occur when EVOH is melt-extruded, and the melt moldability is not always sufficient. Further, in the conventional method, coloring or gel is easily generated in the formed EVOH.

In order to solve these problems, for example, Japanese Patent Application Laid-Open Nos. 49-134763 and 62-1439
Various methods have been proposed in Japanese Patent Laid-Open No. 54, JP-A-1-135852 and the like. However, further improvement is desired in view of the performance level required for molding materials and the like in recent years.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the stability of melt extrusion by EVOH obtained by saponifying a specific EVA, to improve the melt moldability, and to reduce the occurrence of coloring. And reducing the generation of gel.

[0005]

The present invention provides a method for producing an ethylene-vinyl acetate copolymer having an ethylene content of 5 to 60 mol% by copolymerizing ethylene and vinyl acetate using a polymerization initiator. Using an aliphatic alcohol having 4 or less carbon atoms as a polymerization solvent, the content of acetaldehyde to vinyl acetate in a raw material vinyl acetate or an aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms was 200 pp.
m or less, the content of saturated acetate in vinyl acetate is 10 to 1500 ppm, and the temperature is 30 to 150 ° C.
It is characterized by being polymerized by.

[0006] The present invention relates to E
It also includes EVOH obtained by saponifying VA. The present invention also includes a molded article containing the EVOH.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In the present invention, the ethylene content of EVA is 5 to 60 mol%. Preferred EVA has an ethylene content of at least 7 mol%, more preferably at least 10 mol%, especially at least 20 mol%. Further, it is preferably at most 58 mol%, more preferably at most 55 mol%, still more preferably at least 53 mol%.
It is as follows. When the ethylene content is less than 5 mol%, the effect of reducing the coloring and gel of EVOH obtained after saponification decreases, and when the ethylene content exceeds 60 mol%, the melt formability of EVOH obtained after saponification is inferior.

In the present invention, an aliphatic alcohol having 4 or less carbon atoms is used as a polymerization solvent. If an aliphatic alcohol or aromatic alcohol having 5 or more carbon atoms is used, the effects of the invention cannot be sufficiently obtained. Examples of the aliphatic alcohol having 4 or less carbon atoms include methanol, ethanol, propanol, and butanol. In order to sufficiently obtain the effects of the present invention, aliphatic alcohols having 3 or less carbon atoms are preferable, and fatty acids having 1 carbon atom are preferable. Group alcohols, ie, methanol, are more preferred.

In the present invention, the content of acetaldehyde to vinyl acetate is set to 200 ppm or less in the raw material vinyl acetate or an aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms. Acetaldehyde is introduced as an impurity when supplying vinyl acetate. For this reason, the content of acetaldehyde in the raw material vinyl acetate or the aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms is set to 200 ppm or less based on vinyl acetate. The content of acetaldehyde is preferably 150 ppm or less, more preferably 100 ppm or less, and still more preferably 50 ppm or less. If the content of acetaldehyde to vinyl acetate exceeds 200 ppm, the resulting E
Melt extrusion stability and melt moldability of VOH deteriorate, and coloring and gel become apparent when EVOH is used as a molded product. When an aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms is used as the raw material, the same alcohol solution as the polymerization solvent, particularly a methanol solution, is preferable as the aliphatic alcohol solution having 4 or less carbon atoms.

[0010] The cause of the adverse effects based on acetaldehyde is not always clear. At present, acetaldehyde acts as a chain transfer agent during polymerization, affecting the degree of polymerization, degree of polymerization distribution, branching, etc. of EVA obtained by copolymerization. As a result, the melt extrusion stability and melt moldability of EVOH are reduced. It is thought that the adverse effect has been exerted. Regarding coloring and gel, it is considered that acetaldehyde is condensed during polymerization of ethylene and vinyl acetate, etc., and changes to a condensate which easily causes coloring and gel, and the condensate cannot be removed in the subsequent polymer purification step. It is thought that there is a cause.

When ethylene and vinyl acetate are polymerized by reducing the content of acetaldehyde present as an impurity in vinyl acetate by a commonly used method such as precision distillation and the use of an ion exchange resin, a very good effect is obtained. Was obtained. But that was not always enough. The present inventors have further studied and found that the conventional polymerization system is essentially a system that easily generates acetaldehyde.

It is considered that vinyl acetate undergoes a transesterification reaction with a lower aliphatic alcohol used as a polymerization solvent to form acetaldehyde and an acetate as shown in the following formula (1).

[0013]

Embedded image

Here, R represents a lower alkyl group. That is, even if acetaldehyde in vinyl acetate before polymerization is reduced, in a system of vinyl acetate and a lower aliphatic alcohol, when a certain amount of heat is applied, it is estimated that acetaldehyde is newly generated by the transesterification reaction. You. Since this reaction is an equilibrium reaction, an effect of preventing generation of acetaldehyde to some extent can be obtained by adding an acetic ester or removing a lower aliphatic alcohol. The present inventor has examined both of them, and found that gel and coloring tend to increase more easily in the latter, which is not appropriate, and that in the former, specific conditions are preferable.

In the present invention, a saturated acetate is used. Saturated acetic ester refers to an ester composed of acetic acid and a saturated aliphatic alcohol. If an ester other than a saturated acetic acid ester, for example, an acetic acid unsaturated ester or an acid ester other than acetic acid, is used, the effect of the present invention cannot be sufficiently exerted, and the polymerization may be adversely affected. Preferred examples of the saturated acetate include an ester of acetic acid and an aliphatic alcohol having 4 or less carbon atoms, and more preferred examples include methyl acetate and ethyl acetate. A further preferred embodiment is to select a saturated acetate corresponding to the alcohol of the polymerization solvent. For example, when methanol is used as the polymerization solvent, it is recommended to use methyl acetate as the saturated acetate. Similarly, when ethanol is used as the polymerization solvent, it is recommended to use ethyl acetate as the saturated acetate. As shown in this example, a combination in which the polymerization solvent contains methanol and / or ethanol and the saturated acetate contains the acetate of the alcohol used as the polymerization solvent, specifically, methyl acetate and / or ethyl acetate is preferred. This saturated acetate is introduced into the polymerization vessel together with vinyl acetate or a solution of vinyl acetate.

In the present invention, in the raw material vinyl acetate or in an aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms, the content of saturated acetate relative to vinyl acetate is set to 10 to 1500 ppm. The content of the saturated acetic ester is preferably 1300 ppm or less, more preferably 1200 ppm or less, further preferably 1000 ppm or less, and preferably 30 ppm or more, more preferably 50 ppm or more, and still more preferably 100 ppm or more. In the present invention, a plurality of saturated acetates may be used in combination. In this case, the content of saturated acetate means the total amount of the content of each saturated acetate.

From the viewpoint of suppressing the generation of acetaldehyde, considering the equilibrium reaction represented by the equation (1),
It is preferable that the content of the saturated acetate is as large as possible. However, in reality, when the content of the saturated acetic ester relative to vinyl acetate exceeds 1500 ppm, a new problem arises in that the melt moldability of EVOH deteriorates. When the content of saturated acetate is less than 10 ppm, EVO
The effect of improving the melt extrusion stability and melt moldability of H is reduced, and the effect of suppressing coloring and generation of gel is also reduced.

In the present invention, from the viewpoint of achieving a sufficient effect, when the content of saturated acetate to vinyl acetate is E (ppm) and the content of acetaldehyde to vinyl acetate is A (ppm), > A
Is preferable, E> 3A is more preferable, E> 5A is more preferable, and E> 10A
Is most preferable. It is preferable to use vinyl acetate or a solution of vinyl acetate prepared in advance to satisfy these relationships.

In the present invention, the polymerization is carried out at a temperature of 30 to 150 ° C. The polymerization temperature is preferably 35 ° C. or higher, more preferably 40 ° C. or higher, and further preferably 45 ° C. or higher. Further, it is preferably 120 ° C. or less, more preferably 1 ° C.
The temperature is not higher than 00 ° C, more preferably not higher than 95 ° C. When the polymerization temperature is higher than 150 ° C., the effect of the invention is reduced. When the polymerization temperature is lower than 30 ° C., melt extrusion stability, productivity and the like are reduced, and gel is easily generated.

In the present invention, it is preferable that ethylene, vinyl acetate, a polymerization initiator and a polymerization solvent are continuously introduced into a polymerization tank, and EVA is continuously discharged from the polymerization tank. ~ (C) is more preferable. (A) vinyl acetate or an aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms is introduced into a heat exchanger provided with a cooling means, and ethylene discharged from a polymerization tank is introduced into the heat exchanger; Absorbing at least a portion of the ethylene into the vinyl acetate or vinyl acetate solution in the exchanger; and (B) introducing the ethylene-absorbed vinyl acetate or vinyl acetate solution into the polymerization tank and mixing with the polymerization solution. And (C) vaporizing ethylene present in the polymerization tank in excess of the solubility of ethylene in the polymerization solution and leading it to a heat exchanger.

Such a process is described, for example, in JP-A-60-535.
The method can be carried out with reference to the method described in Japanese Patent Publication No. According to the method including each of the steps (A) to (C), the heat (polymerization heat) generated in the polymerization tank due to the vaporization of ethylene is effectively removed, so that the temperature in the polymerization tank partially increases. Is suppressed. The reaction of the formula (1) tends to proceed as the temperature increases near the polymerization temperature. For this reason, the reaction which generates acetaldehyde is suppressed by preventing a partial temperature rise in the polymerization tank. As a result, melt moldability and melt extrusion stability are further improved, and coloring and gel are further reduced.

In such a continuous production method, it is preferable to introduce the entire amount of vinyl acetate into the polymerization tank through a heat exchanger. However, depending on the amount of heat generated, a part of vinyl acetate passes through the heat exchanger. And the remainder may be introduced directly into the polymerization vessel.

In the present invention, in the above continuous polymerization method, the temperature of the vinyl acetate or the vinyl acetate solution having absorbed ethylene introduced into the polymerization tank is set to T ₁ (° C.), and the temperature of the polymerization solution in the polymerization tank is set to T ₁ (° C.). When T ₂ (° C.), it is preferable that the relationship of T ₁ <T ₂ is satisfied. T ₁ <It is more preferable to satisfy the relationship of _{T 2 -10, -15 ≦ T 1} <T 2 -2
More preferably, the relationship of 0 is satisfied.

When vinyl acetate or a solution of vinyl acetate is allowed to pass through a wet-wall multitubular heat exchanger provided with a cooling means in the form of a thin film, the ethylene absorption efficiency can be increased. In the heat exchanger, as a method for contacting vinyl acetate or a solution of vinyl acetate with ethylene, any of a countercurrent contact method and a cocurrent contact method may be adopted, but in order to sufficiently obtain the effects of the invention, A countercurrent contact method is preferred.

The polymerization initiator is preferably at least one selected from diacyl peroxide-based initiators, valeronitrile-based initiators and peroxydicarbonate-based initiators. By using these polymerization initiators, melt extrusion stability and melt moldability can be further improved. Further, generation of coloring and gel can be further reduced.

Examples of the diacyl peroxide-based polymerization initiator include acetyl peroxide, dipropyl peroxide, isobutyryl peroxide, benzoyl peroxide, dilauroyl peroxide and the like. Examples of the valeronitrile-based polymerization initiator As 2,
2'-azobis (2,4,4'-trimethylvaleronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (4-methoxy-2,
4-dimethylvaleronitrile), 2,2'-azobis (4-ethoxy-2,4-diethylvaleronitrile),
2,2'-azobis (4,4'-diethoxy-2-methylvaleronitrile) and the like. Examples of the peroxydicarbonate-based polymerization initiator include dicyclohexylperoxydicarbonate, bis- (4-t -Butylcyclohexyl) peroxydicarbonate, di-n-propylperoxydicarbonate and the like. Among these, acetyl peroxide, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), di-n-propylperoxydicarbonate, and dicyclohexylperoxydicarbonate are sufficient for the effects of the invention. It is preferable to obtain 2,2'-azobis (4-
Methoxy-2,4-dimethylvaleronitrile) is more preferred.

In the present invention, the effect of the present invention becomes more remarkable by adding a compound having a conjugated double bond having a molecular weight of 1,000 or less to the solution after polymerization of EVA.
Specifically, at least two carbon-carbon double bonds described in JP-A-61-197603, JP-A-61-197604, JP-A-9-71620 and the like have one carbon-carbon double bond. A compound having a structure connected through a single bond may be used. Examples of this compound include 2
A conjugated diene having a structure in which two carbon-carbon double bonds and one carbon-carbon single bond are alternately connected;
A conjugated triene having a structure in which a carbon double bond and two carbon-carbon single bonds are alternately connected, and a structure in which a larger number of carbon-carbon double bonds and a carbon-carbon single bond are alternately connected. Certain conjugated polyene compounds are included. Therefore, a conjugated triene compound such as 2,4,6-octatriene is also included in the compound having a conjugated double bond. Further, a plurality of conjugated double bonds may be independently present in one molecule. For example, a compound having three conjugated trienes in the same molecule, such as tung oil, is also included in the compound having a conjugated double bond in the present invention.

Compounds having a conjugated double bond include other functional groups such as carboxyl groups and salts thereof, hydroxyl groups, ester groups, carbonyl groups, ether groups, amino groups, imino groups, amide groups, cyano groups, diazo groups, Has various functional groups such as nitro group, sulfone group, sulfoxide group, sulfide group, thiol group, sulfonic acid group and its salt, phosphoric acid group and its salt, phenyl group, halogen atom, double bond and triple bond May be. Such a functional group may be directly bonded to a carbon atom in the conjugated double bond, or may be bonded to a position remote from the conjugated double bond. Therefore,
The multiple bond in the functional group may be located at a position capable of conjugating with the conjugated double bond. For example, 1-phenyl-1,3-butadiene having a phenyl group, sorbic acid having a carboxyl group, myrcene having an olefinic double bond, and the like are also included in the compound having a conjugated double bond in the present invention. Furthermore, the conjugated double bond referred to in the present invention includes not only the above-described conjugated double bond between aliphatic groups but also 2,4-diphenyl-4-methyl-1-pentene and 1,3-diphenyl-1-pentene. Contains conjugated double bonds of aliphatic and aromatic such as butene.

Among them, compounds having a conjugated double bond between aliphatic groups, or
Having a carboxyl group and its salt, a polar group such as a hydroxyl group,
Further, a compound having a conjugated double bond is preferable, and a compound having a polar group and having a conjugated double bond between aliphatic groups is more preferable.

The compound having a conjugated double bond preferably has a molecular weight of 1,000 or less. Molecular weight 10
If it exceeds 00, sufficient effects cannot be obtained in terms of melt extrusion stability, prevention of gel generation, and the like.

The compound having a conjugated double bond is added to EVOH after saponification of EVA obtained by polymerization in an amount of 0.
It is preferable to add so as to be in the range of 1 to 3000 ppm. It is more preferably at least 1 ppm, still more preferably at least 3 ppm, and most preferably at least 5 pp.
m or more. Further, more preferably 2,000 ppm or less, more preferably 1500 ppm or less,
Most preferably, it is 1000 ppm or less. The compound having a conjugated double bond may be used as a mixture of two or more kinds. In this case, the added amount of the compound refers to the total amount of each.

The compound having a conjugated double bond is preferably added after the polymerization of EVA and before the step of removing vinyl acetate from the EVA polymerization solution from the viewpoint of sufficiently obtaining the effects of the invention. . This compound is EV
It is thought that it functions as a kind of stabilizer for preventing the alteration of A.

In the present invention, another polymerizable monomer may be simultaneously introduced during the polymerization of EVA for copolymerization. Examples of the polymerizable monomer used for the copolymerization include propylene, n-butene, i-butene, 4-methyl-1-
Olefins such as pentene, 1-hexene and 1-octene; unsaturated carboxylic acids such as itaconic acid, methacrylic acid, acrylic acid and maleic acid, salts thereof, partially or completely esterified products thereof, amides thereof and anhydrides thereof; vinyl Vinyl silane compounds such as trimethoxysilane; unsaturated sulfonic acids or salts thereof; alkyl thiols; vinyl pyrrolidones. The addition amount of these polymerizable monomers is preferably within a range that does not impair the above object of the invention.

The EVA obtained according to the present invention can be saponified by a known saponification method using an alkali, a metal alcoholate or the like to obtain EVOH. The degree of saponification of EVOH is preferably at least 90%, more preferably 9%.
It is at least 5%, more preferably at least 97%, most preferably at least 99%. If the saponification degree is less than 90%, the melt moldability and the stability of melt extrusion are likely to deteriorate, and
The generation of gel becomes remarkable.

The EVOH obtained according to the present invention preferably contains a boron compound. This gives E
The melt extrusion stability and melt moldability of VOH are further improved. Examples of such boron compounds include boric acids, borate esters, borates, borohydrides and the like. Specifically, the boric acids include orthoboric acid, metaboric acid, tetraboric acid, and the like, and the borate esters include triethyl borate, trimethyl borate, and the like.
Examples of the borate include alkali metal salts, alkaline earth metal salts, and borax of the various boric acids. Of these compounds, orthoboric acid is preferred.

The content of the boron compound is from 20 to 2000 ppm, preferably from 50 to 1000 pp in terms of boron element.
m. By setting such a range, EVOH
Is further improved in melt extrusion stability and melt moldability. 2
If the amount is less than 0 ppm, such an effect is small.
If it exceeds pm, gelation tends to occur rather easily, resulting in poor moldability.

The melt flow rate (MFR) of EVOH obtained by the present invention is preferably 0.1 to 100 g from the viewpoint of improving melt extrusion stability and melt moldability.
/ 10 min, more preferably 0.2 to 20 g / 10
Min, more preferably 0.3 to 10 g / 10 min, and most preferably 0.4 to 8 g / 10 min. Here, the MFR of EVOH is JIS (Japanese Industr
ial Standard) Based on K7210, 190 ° C, 216
The value measured under a load of 0 g. However, the melting point is 190 ° C
In the vicinity or exceeding 190 ° C, the temperature was measured at a plurality of temperatures above the melting point under a load of 2160 g, and the reciprocal of the absolute temperature was plotted on the semi-logarithmic graph as the horizontal axis, and the MFR was plotted on the vertical axis (logarithmic). The value inserted.

The EVOH obtained according to the present invention may contain various additives as required. Examples of such additives include antioxidants, plasticizers, heat stabilizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, and other thermoplastic resins.

The EVOH obtained according to the present invention can be formed into various molded products by a known molding method. According to the present invention, even when melt molding EVOH alone, good melt moldability such as drawdown resistance and neck-in variability can be obtained, but coextrusion molding with other thermoplastic resins is particularly possible. Sometimes it shows better melt moldability.
Examples of extrudates include films, sheets, pipes,
Tubes, bottles and the like can be mentioned.

Examples of other thermoplastic resins coextruded in combination with the EVOH obtained according to the present invention include:
Examples thereof include polyolefin, polyamide, polyester, and polystyrene. Polyolefins include low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, and high-density polyethylene; vinyl acetate, (meth) acrylate, butene, hexene, 4-methyl-1-pentene Polyethylene, which is obtained by copolymerizing ethylene, butane, propylene homopolymer or ethylene, butene, hexene, 4-methyl-1-
Polypropylene copolymerized with olefins such as pentene; poly 1-butene; poly 4-methyl-1-pentene;
Further, there may be mentioned carboxylic acid-modified polyolefins based on the above-mentioned polyolefins. Among these polyolefins, particularly excellent melt moldability can be obtained by coextrusion molding with a carboxylic acid-modified polyolefin.

The carboxylic acid-modified polyolefin is a polyolefin having a carboxyl group in the molecule. E
The excellent effect of the co-extruded product of VOH and carboxylic acid-modified polyolefin is due to the interaction between the hydroxyl group of EVOH and the carboxyl group of carboxylic acid-modified polyolefin or its anhydride at the interface between the EVOH layer and the carboxylic acid-modified polyolefin layer. It is estimated to be based on Examples of the carboxylic acid-modified polyolefin include those obtained by graft-modifying a polyolefin with α, β-unsweetened carboxylic acid or an anhydride thereof, or olefin monomer and α, β-
Examples thereof include those obtained by random copolymerization of an unsaturated carboxylic acid or an anhydride thereof. Examples of α, β-unsaturated carboxylic acids or anhydrides include acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride,
And itaconic anhydride. Of these, maleic acid and maleic anhydride are preferred. Further, in the carboxylic acid-modified polyolefin, as represented by an ionomer, all or a part of the carboxyl group may be present in the form of a metal salt.

In order to sufficiently obtain the effects of the present invention, it is preferable to use an α, β-unsaturated carboxylic acid graft-modified polyethylene, particularly a density of 0.88 to 0.93 g / cm ³ , M
FR 1.0 to 7.0 g / 10 min (190 ° C., 2160
It is particularly preferable to use the α, β-unsaturated carboxylic acid graft-modified linear low-density polyethylene of g). In this case, the content of the α, β-unsaturated carboxylic acid or its anhydride is preferably 0.01 to 5% by weight, more preferably 0.03% by weight, from the viewpoint of sufficiently exerting the effects of the invention.
-4% by weight, more preferably 0.05-3% by weight. Also, 100% of the modified polyolefin can be used, but a blend of a highly modified polyolefin and an unmodified polyolefin having a final modification amount within the above range is used. This is more cost effective.

The polyamide coextruded in combination with the EVOH obtained according to the present invention includes nylon-
6, nylon-6 / 12, nylon-6 / 6,6, nylon-11, nylon-12 and the like. Among these polyamides, copolymerized polyamides containing a caproamide component, particularly nylon-6 / 6,6, are preferable from the viewpoint that the effects of the invention can be sufficiently exhibited.

Examples of the polyester include polyethylene terephthalate, polybutylene terephthalate, polyethylene (terephthalate / isophthalate), poly (ethylene / cyclohexane dimethylene) terephthalate, and the like. Ethylene glycol, butylene glycol,
Diols such as cyclohexane dimethanol, neopentyl glycol, pentanediol, or isophthalic acid, benzophenone dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenylmethane dicarboxylic acid, propylene bis (phenylcarboxylic acid), diphenyl oxide dicarboxylic acid, oxalic acid, Also included are those containing dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and diethylsuccinic acid.

As the polystyrene, not only a styrene homopolymer but also a copolymer of a polymerizable monomer other than styrene or a blend of a resin obtained by polymerizing a polymerizable monomer other than styrene is used. Is also good. Specifically, styrene homopolymer, so-called HIPS (high impact polystyrene) containing a small amount of rubber component, ABS
(Acrylonitrile-butadiene-styrene copolymer), AS (acrylonitrile-styrene copolymer),
Styrene-diene copolymer and hydrogenated product thereof, styrene-
And maleic anhydride copolymers.

The EVOH obtained according to the present invention can be formed into various molded products such as films, sheets, pipes, tubes, bottles, etc. by melt molding. These molded products can be pulverized and molded again. Further, a film, a sheet, or the like may be uniaxially or biaxially stretched to form a stretched film or a sheet, and it is also useful to form a container such as a tray or a cup by thermoforming. As the melt molding method, a known method such as an extrusion molding method using a T-die, an inflation molding method, and a blow molding method can be employed. The melt molding temperature is usually 1 from the viewpoint of sufficiently obtaining the effects of the invention.
50 to 300 ° C, preferably 165 to 280 ° C,
More preferably, the temperature is 170 to 250 ° C., especially EVOH
Tm (° C.), Tm + 10 to Tm + 5
It is recommended to select from the range of 0 (° C).

[0047]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the invention thereto. Also, in the following description, except for those specifying the content of acetaldehyde and saturated acetate,
The raw material used was substantially free of acetaldehyde and saturated acetate. The analysis method and the evaluation method in the present invention are as follows.

(1) Analytical method (1-1) Determination of acetaldehyde and saturated acetic ester The determination is performed according to the gas chromatography method described in JIS K6724. (1-2) Quantification of 2,4-diphenyl-4-methyl-1-pentene (DPMP) and sorbic acid A calibration curve was prepared in advance using a sample of DPMP and sorbic acid, and was subjected to high-performance liquid chromatography. Do. (1-3) Determination of Boron Compound EVOH of a sample is put in a magnetic crucible and incinerated in an electric furnace. The obtained ash was converted to a 0.01 N aqueous nitric acid solution 200.
It is dissolved in mL, quantified by atomic absorption analysis, and the content of the boron compound is calculated as a value in terms of boron element.

(2) Evaluation method (2-1) Extrusion film formation Two extruders having a diameter of 55 mmφ (for EVOH) and 70 mmφ (for other thermoplastic resins) were prepared, and a screw tip breaker plate of each extruder was prepared. A stainless steel screen was attached to the part in a five-sheet configuration of 50 mesh / 100 mesh / 300 mesh / 100 mesh / 50 mesh. Using a co-extrusion film forming apparatus having a feed block with a selector plug and a T die having a lip opening width of 750 mm, a single-layer melt of EVOH or a laminate melt of EVOH and another thermoplastic resin was polished to a 95 mmφ chrome-plated mirror surface. Extruded film was formed on a roll. Air gap (distance from die lip to contact point of molten resin on first roll) is 2
It was 5 cm. When changing the layer configuration, the setting of the selector plug of the feed block was changed.

(2-2) Melt Extrusion Stability In the single-layer extrusion or multilayer co-extrusion film formation described in (2-1), screw load fluctuation of an extruder for EVOH after 30 minutes from the start of film formation. The melt extrusion stability was evaluated from the situation described above. The evaluation is based on the following criteria. A: The screw load fluctuation range is extremely small at about 4 amps, and there is no problem in operation. B: The fluctuation range of the screw load is as small as about 6 to 7 amps, and there is no problem in operation. C: The screw load fluctuation range is slightly large at about 9 to 10 amps, and there is a slight hindrance in operation. D: The screw load fluctuation range exceeds 10 amps, and there is a problem in operation.

(2-3) Melt Formability (2-3-1) Drawdown Resistance In the single-layer extrusion or multilayer coextrusion film formation described in (2-1), 30 minutes have elapsed since the start of film formation. The drawdown property of the molten resin discharged from the die lip at that time was evaluated. The evaluation is based on the following criteria. A: There is almost no drawdown, and there is no problem in operation. B: Drawdown is slightly observed, but there is no problem in operation. C: Drawdown was recognized, and there was some difficulty in operation. D: Drawdown is remarkable, and there is a problem in operation.

(2-3-2) Neck-in variability In the single-layer extrusion or multilayer co-extrusion film formation described in (2-1), the melt discharged from the die lip 30 minutes after the start of film formation. The neck-in variability was evaluated from the state of neck-in variability on both sides of the resin die. The evaluation is based on the following criteria. A: Almost no change in neck-in is observed, and there is no problem in operation. B: Neck-in fluctuation is slightly observed, but there is no problem in operation. C: Neck-in fluctuation was observed, and there was some trouble in operation. D: Neck-in fluctuation is remarkable, and there is a problem in operation.

(2-4) Coloring In the single-layer extrusion or multilayer co-extrusion film formation described in (2-1), the film is wound into a paper tube in a roll form after 30 minutes from the start of film formation. Evaluation was made from the yellowness of the end face of this roll. The evaluation is based on the following criteria. A: Almost no coloring is observed, and it has a sufficient commercial value. B: Although coloring is very slightly recognized, it is within a range without any problem and has commercial value. C: Coloring is recognized, and the commercial value is small. D: Coloring is remarkable and has no commercial value.

(2-5) Gel A film was collected from the roll of (2-4) and evaluated from the state of gel formation on the film surface. In this case, in the case of lamination co-extrusion film formation, a film is formed by replacing the maleic anhydride graft-modified linear low density polyethylene used as the adhesive layer with an unmodified linear low density polyethylene having low adhesiveness,
The EVOH layer was peeled off from the co-extruded film, and the gel generated in the EVOH layer was evaluated. The evaluation is based on the following criteria. A: Almost no gel is recognized, and it has a sufficient commercial value. B: Gel is very slightly recognized, but within a range without any problem and has commercial value. C: Gel is recognized and commercial value is small. D: The gel is remarkable and has no commercial value.

Example 1 A polymerization tank having a heat transfer area of 4 m ² and an internal volume of 750 L connected to a vertical wet-wall multi-tube heat exchanger having 10 tubes was used. Vinyl acetate having an acetaldehyde content of 10 ppm and a methyl acetate content of 500 ppm was introduced into the polymerization tank at a rate of 31 kg / hr through a heat exchanger. On the other hand, ethylene was used as a polymerization initiator at a rate of 6 kg / hr at 2,2'-azobis- (4-methoxy-
2,4-Dimethylvaleronitrile) (AMV) was converted to 1/2000 of the vinyl acetate supply, that is, 15.5 g / hr.
At a rate of 2.3 kg / h of methanol as a polymerization solvent
At a rate of r, each was directly introduced into the polymerization tank. The other materials introduced into the polymerization tank do not substantially contain either acetaldehyde or methyl acetate. Therefore,
Also in the polymerization solution, the content of acetaldehyde and methyl acetate with respect to the supplied vinyl acetate is the same as the above value.

In the polymerization tank, continuous polymerization of EVA was started under the conditions of a polymerization temperature of 60 ° C. (T ₂ ) and a polymerization pressure of 45 kg / cm ² . Outside the heat exchanger, a coolant (−30 ° C.) at −2 ° C.
% Methanol aqueous solution) was circulated at a rate of 1.8 m ³ / hr. The vinyl acetate flows down in the heat exchanger in a thin film state, comes into countercurrent contact with the vaporized ethylene from the polymerization tank, is introduced into the polymerization tank in a state in which the ethylene is absorbed and dissolved, and is mixed with the liquid in the polymerization tank. Mixed. The temperature (T ₁ ) of vinyl acetate in which ethylene was absorbed and dissolved was 5 ° C. In this way, a polymerization reaction solution was continuously obtained at a rate of 39 kg / hr.

The polymerization solution continuously taken out from the lower part of the polymerization vessel was added with 2,4-diphenyl-4-methyl-1 at the exit of the polymerization vessel.
-A solution of pentene (DPMP) in methanol was added and unreacted ethylene was evaporated off. EVA obtained
The methanol solution of EVA is continuously flowed down from the top of the effluent tower filled with Raschig rings, and methanol vapor is blown from the bottom of the tower to remove unreacted vinyl acetate together with methanol vapor from the top of the tower, and remove it to remove EVA. A 35% by weight methanol solution was obtained. This methanol solution of EVA was charged into a saponification reactor, and sodium hydroxide (80 g) was added.
/ L methanol solution) was added so as to be 0.55 equivalent to the vinyl acetate component in EVA, and methanol was further added to adjust the EVA concentration to 15% by weight. The solution was heated to 60 ° C. and reacted for 5 hours while blowing nitrogen gas into the reactor. Thereafter, the reaction was stopped by neutralization with acetic acid, and the contents were taken out of the reactor and left at room temperature to precipitate solids into particles. The operation of removing the precipitated particles by a centrifugal separator, adding a large amount of water, and removing the liquid was repeated.

The obtained particles were treated with acetic acid and orthoboric acid (O
BA) was treated at a bath ratio of 20 using an aqueous solution containing 0.5 g of acetic acid and 0.4 g of orthoboric acid in 1 L of an aqueous solution, dried, and then pelletized by an extruder set at 215 ° C. The thus obtained EVOH pellets were treated with chloroform in a Soxhlet extractor for 48 hours,
The additives and the like in OH were extracted and removed and purified. Purified E
When the composition of VOH was determined by nuclear magnetic resonance (NMR), the ethylene content was 31 mol% and the saponification degree was 9
It was 9.5%. Also, differential scanning calorimeter (DSC)
The melting point was 185 ° C. Furthermore,
MFR under a load of 2160 g at 190 ° C. is 1.5 g
/ 10 minutes.

D in the extract obtained by Soxhlet extraction
The content of PMP was quantified by the above method and converted to the content in EVOH pellets, which was 180 ppm. Further, the content of orthoboric acid in the EVOH pellets was quantified by the above method, and it was 230 ppm in terms of boron element.

Using an EVOH pellet, a single-layer EVOH film having a thickness of 20 μm was formed by the method described in the column of evaluation method and evaluated. The film forming temperature at this time is 220
° C. Table 1 shows the above analysis results and evaluation results.

Example 2 Linear low density polyethylene (density 0.92 g / cm ³ , MFR 1.5 g / 10 min (19
0160 ° C., 2160 g) as both outer layers, a linear low-density polyethylene (maleic anhydride-modified amount) in which EVOH obtained in Example 1 was used as an intermediate layer, and maleic anhydride was graft-modified between both outer layers and the intermediate layer. 0.5% by weight, density 0.91g
/ Cm ³ , MFR 1.5 g / 10 min (190 ° C., 216
0g)) as an adhesive layer and a coextruded film of five layers of three types (thickness of each layer: 20 μm / 10 μm / 15 μm / 10 μ)
m / 20 μm, total thickness 75 μm) was formed by the method described in the column of evaluation method and evaluated. The extrusion temperature of each resin at this time was all 220 ° C. Table 1 shows the evaluation results.

(Embodiment 3) In Embodiment 1, the DPMP
Was added in the same manner as in Example 1 except that no EVOH was added.
Pellets were prepared and analyzed, and EVOH monolayer films were formed and evaluated. Table 1 shows the analysis results and the evaluation results.

(Example 4) In Example 2, EVOH
A coextruded film was formed and evaluated in the same manner as in Example 2 except that was changed to that obtained in Example 3. Table 1 shows the evaluation results.

Example 5 An EVOH pellet was produced and analyzed in the same manner as in Example 1 except that the treatment with orthoboric acid was omitted, and the evaluation was performed by forming an EVOH single-layer film. . Table 1 shows the analysis results and the evaluation results.

(Example 6) In Example 2, EVOH
Was changed to that obtained in Example 5, a coextruded film was formed in the same manner as in Example 2, and evaluated. Table 1 shows the evaluation results.

Example 7 In Example 1, the polymerization initiator was changed to di-n-propylperoxydicarbonate (NP
An EVOH pellet was manufactured and analyzed in the same manner as in Example 1 except that the method was changed to P), and an EVOH single-layer film was formed and evaluated. Table 1 shows the analysis results and the evaluation results.

Example 8 Example 7 was made by using polypropylene (“B200” manufactured by Mitsui Petrochemical Industries, Ltd.) as the inner and outer layers.
The EVOH obtained in the above was used as an intermediate layer, and maleic anhydride graft-modified polypropylene (“Admer QB550” manufactured by Mitsui Petrochemical Industry Co., Ltd.) was disposed between the inner and outer layers and the intermediate layer as an adhesive layer. Machine ((with)
Suzuki Iron Works TB-ST-6P type, screw diameter: 45
mmφ, 40mmφ, 35mmφ, 35mmφ), outer diameter 70mmφ, body thickness 700μm, capacity 1000
3 types of 5 layers (each layer thickness: outer layer 250 μm /
A hollow molded container (20 μm / 20 μm / 20 μm / 390 μm inner layer, total thickness 700 μm) was molded and evaluated. The temperature of the die at this time is 220 ° C.
Hot water at 0 ° C. was circulated so that the condition was gradually cooled. Table 1 shows the evaluation results.

Example 9 A batch polymerization tank having a cooling device and a stirrer was charged with an acetaldehyde content of 20 ppm.
2000 ppm of vinyl acetate with an ethyl acetate content of 350 ppm
0 parts by weight, 2,000 parts by weight of ethanol as a polymerization solvent, and acetyl peroxide (AP) as a polymerization initiator.
O), 10 parts by weight of O), nitrogen replacement with stirring, and introduction of ethylene, polymerization temperature of 75 ° C, polymerization pressure of 6
The temperature and pressure were adjusted to 0 kg / cm ² , and the mixture was stirred for 5 hours to carry out polymerization.

Next, the polymerization solution was taken out from the lower part of the polymerization tank, and sorbic acid (SA: 1.5% by weight methanol solution) was added at a polymerization tank outlet at a ratio of 0.05% by weight to vinyl acetate (10% by weight as sorbic acid). ) And unreacted ethylene was removed by evaporation. The polymerization rate was 40% based on the charged vinyl acetate. The operation after the removal of unreacted vinyl acetate was performed in the same manner as in Example 1, and the EVOH
Pellets were prepared and analyzed, and EVOH monolayer films were formed and evaluated. Table 1 shows the analysis results and the evaluation results.

(Embodiment 10) In the embodiment 2, the EVO
Example 2 except that H was changed to that obtained in Example 9.
A co-extruded film was formed and evaluated in the same manner as described above. Table 1 shows the evaluation results.

Example 11 In Example 1, the vinyl acetate was changed to a 95% by weight methanol solution of vinyl acetate (acetaldehyde content to vinyl acetate: 10 ppm and methyl acetate content: 500 ppm), and the methanol concentration in the polymerization tank was changed. In the same manner as in Example 1, except that the supply amount of methanol (containing substantially no acetaldehyde and saturated acetic ester) directly introduced into the polymerization tank was changed so as to be the same as in Example 1, EVOH pellets were prepared and analyzed, and an EVOH monolayer film was formed and evaluated. Table 1 shows the analysis results and the evaluation results.

Comparative Example 1 EVOH pellets were produced and analyzed in the same manner as in Example 1 except that the content of vinyl acetate was changed to 250 ppm and the content of methyl acetate was changed to 5 ppm. EVOH
A single-layer film was formed and evaluated. Table 1 shows the analysis results and the evaluation results.

Comparative Example 2 EVOH pellets were produced and analyzed in the same manner as in Example 1 except that the content of vinyl acetate was changed to 10 ppm and the content of methyl acetate was changed to 5 ppm. An EVOH monolayer film was formed and evaluated. Table 1 shows the analysis results and the evaluation results.

Comparative Example 3 EVOH pellets were produced and analyzed in the same manner as in Example 1 except that the content of vinyl acetate was changed to 10 ppm and the content of methyl acetate was changed to 2000 ppm. EV
An OH monolayer film was formed and evaluated. Table 1 shows the analysis results and the evaluation results.

Comparative Example 4 EVOH pellets were produced and analyzed in the same manner as in Example 1 except that the polymerization solvent was not used, and the evaluation was made by forming an EVOH single-layer film. Table 1 shows the analysis results and the evaluation results.

Comparative Example 5 EVOH pellets were prepared and analyzed in the same manner as in Example 1 except that the ethylene feed rate was increased. The EVOH had a content of ethylene units of 65 mol%. In addition, an EVOH single layer film was formed and evaluated. Table 1 shows the analysis results and the evaluation results.

[0077]

[Table 1]

[0078]

EVA obtained by the production method of the present invention
By saponifying, the melt extrusion stability is improved,
An EVOH having improved melt moldability and less coloring and less gelation is provided.

Continued on the front page F-term (reference) 4F071 AA15 AA28 AA29 AB27 AC17 AE22 AF34 AH03 AH04 BB06 BB09 BB13 BC01 BC04 BC05 BC17 4J011 AA01 AA05 AB02 BB04 DA04 DB07 HA03 HB02 HB03 HB06 HB10 HB12 HB22 H24

Claims (11)

[Claims] An aliphatic alcohol having 4 or less carbon atoms for producing an ethylene-vinyl acetate copolymer having an ethylene content of 5 to 60 mol% by copolymerizing ethylene and vinyl acetate using a polymerization initiator. Is used as a polymerization solvent, the content of acetaldehyde to vinyl acetate is 200 ppm or less in the raw material vinyl acetate or an aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms, and the content of saturated acetate in vinyl acetate is 10 to 10. A method for producing an ethylene-vinyl acetate copolymer, wherein the polymerization is performed at 1500 ppm and at a temperature of 30 to 150 ° C. 2. The ethylene according to claim 1, wherein ethylene, vinyl acetate, a polymerization initiator and a polymerization solvent are continuously introduced into a polymerization tank, and an ethylene-vinyl acetate copolymer is continuously discharged from the polymerization tank. -A method for producing a vinyl acetate copolymer. 3. The method for producing an ethylene-vinyl acetate copolymer according to claim 2, comprising the following steps: (A) vinyl acetate or an aliphatic alcohol solution of vinyl acetate having 4 or less carbon atoms is introduced into a heat exchanger provided with cooling means, and ethylene discharged from a polymerization tank is introduced into the heat exchanger; Absorbing at least a portion of the ethylene into the vinyl acetate or vinyl acetate solution in the exchanger; (B) introducing the ethylene-absorbed vinyl acetate or vinyl acetate solution into the polymerization tank and mixing with the polymerization solution And (C) vaporizing ethylene present in the polymerization tank in excess of the solubility of ethylene in the polymerization solution and leading it to a heat exchanger. 4. The method according to claim 1, wherein the temperature of the vinyl acetate or the solution of vinyl acetate which has been introduced into the polymerization tank and which has absorbed ethylene is T ₁ (° C.),
When the temperature of the polymerization solution in the polymerization tank is T ₂ (° C.), T ₁ <
Satisfy the relation of T _2, ethylene according to claim 3, wherein - method for producing vinyl acetate copolymer. 5. The ethylene-vinyl acetate copolymer according to claim 3, wherein vinyl acetate or a solution of vinyl acetate is passed in the form of a thin film through a wet-wall multitubular heat exchanger provided with cooling means. Production method. 6. The method according to claim 1, wherein the aliphatic alcohol having 4 or less carbon atoms is at least one selected from methanol and ethanol, and the saturated acetate is at least one selected from methyl acetate and ethyl acetate. A method for producing an ethylene-vinyl acetate copolymer according to any one of the preceding claims. 7. The polymerization initiator according to claim 1, wherein the polymerization initiator is at least one selected from a diacyl peroxide-based initiator, a valeronitrile-based initiator, and a peroxydicarbonate-based initiator. A method for producing the ethylene-vinyl acetate copolymer according to the above. 8. A compound having a conjugated double bond having a molecular weight of 1,000 or less is added to the solution after polymerization.
The method for producing an ethylene-vinyl acetate copolymer according to any one of the above. 9. A saponified ethylene-vinyl acetate copolymer obtained by saponifying an ethylene-vinyl acetate copolymer obtained by the production method according to claim 1. Description: 10. The saponified ethylene-vinyl acetate copolymer according to claim 9, comprising a boron compound. 11. A molded article comprising the saponified ethylene-vinyl acetate copolymer according to claim 9 or 10.