JPH11216725A - Manufacture of saponified ethylene-vinyl acetate copolymer pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop no breakage of a strand even during its continuous extrusion and satisfy the size accuracy of a pellet obtained by a method wherein the specified range amount of carboxylate is included in a coagulating liquid at the manufacture of pellets by cutting off the strand. SOLUTION: As a coagulating liquid, water and mixed solution of water and alcohol, and a solvent consisting of an aromatic hydrocarbon such as benzen or the like, a keton such as aceton, methyl ethyl keton or the like, or the like is employed and the preferable coagulating liquid is water or a mixed solution of water and alcohol. The coagulating liquid contains 1.0-15,000 ppm of a carboxylate. Extrusion is preferably carried out in the coagulating liquid containing 10-5,000 ppm of the carboxylate. If the carboxylate is below 1.0 ppm or beyond 15,000 ppm, trouble such as the longer hardening time of a strand, the breakage of the strand or the like occurs. In addition, a saponified ethylene-vinyl acetate copolymer solution is extruded in the coagulating liquid through a nozzle having an arbitrary shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a saponified ethylene-vinyl acetate copolymer pellet in which saponified ethylene-vinyl acetate copolymer pellets can be continuously produced and the size accuracy of the saponified pellet is excellent. Related to manufacturing method.

[0002]

2. Description of the Related Art Saponified ethylene-vinyl acetate copolymers are widely used in various applications such as films, sheets, containers and fibers because of their excellent properties such as oxygen barrier properties and mechanical strength. Among them, when a sheet or a film is produced by melt molding, the saponified copolymer is preferably in the form of pellets from the viewpoint of handling and molding. As a method for producing the pellets, for example, a method of extruding a saponified solution of an ethylene-vinyl acetate copolymer into water or a water / methanol solution in the form of a strand and then cutting the strand to produce a pellet is disclosed in
38634.

[0003]

However, in the disclosed technique, when the saponified ethylene-vinyl acetate copolymer is continuously extruded through a nozzle into a coagulation bath, the curing time of the strand is slow, and the strand breaks. In some cases, the size accuracy of the pellets obtained from the strand was not yet satisfactory.

[0004]

The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems.
In a method of continuously extruding a solution of a saponified vinyl acetate copolymer into a coagulating liquid in a strand form and then cutting the strand to produce pellets, the coagulating liquid contains 1.0 to 15000 ppm of a carboxylate. Then, the present inventors have found that the desired saponified ethylene-vinyl acetate copolymer pellets can be continuously obtained, and have completed the present invention.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The ethylene-vinyl acetate copolymer used as a raw material of the saponified ethylene-vinyl acetate copolymer used in the present invention is not particularly limited in ethylene content, but is preferably 15 to 60 mol%, and more preferably 20 to 55 mol%.

[0006] When the ethylene content is less than 15 mol%, precipitation in a strand form in a coagulation solution is incomplete,
A part of the strand is eluted, which is not preferable in operation, and it is necessary to pressurize or maintain the solution of the saponified ethylene-vinyl acetate copolymer in a uniform solution state, because it is necessary to heat the solution to a high temperature. Absent.

On the other hand, if it exceeds 60 mol%, it is difficult to prepare a homogeneous solution of the saponified ethylene-vinyl acetate copolymer, and the desired strand cannot be formed, which is not preferable.

The ethylene-vinyl acetate copolymer may contain, as well as ethylene and vinyl acetate, an ethylenically unsaturated monomer copolymerizable therewith as a copolymer component. Examples of the monomer include olefins such as propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; and unsaturated monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid. Acids or salts or mono- or dialkyl esters thereof, acrylonitrile, nitriles such as methacrylonitrile, acrylamide, amides such as methacrylamide, ethylenesulfonic acid, allylsulfonic acid, olefinsulfonic acid such as methallylsulfonic acid or a salt thereof, Alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallylvinylketone, N-vinylpyrrolidone, vinyl chloride,
Polyoxyalkylene (meth) allyl ethers such as vinylidene chloride, polyoxyethylene (meth) allyl ether, and polyoxypropylene (meth) allyl ether;
Polyoxyethylene (meth) acrylate, polyoxyalkylene (meth) acrylate such as polyoxypropylene (meth) acrylate, polyoxyethylene (meth) acrylamide, polyoxyalkylene (meth) acrylamide such as polyoxypropylene (meth) acrylamide, Polyoxyethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinyl Amines and the like.

The saponified ethylene-vinyl acetate copolymer used in the present invention is obtained by saponifying the above-described ethylene-vinyl acetate copolymer. The saponification reaction is usually carried out in the presence of an alkali catalyst. As the alkali catalyst, a conventionally known catalyst used for a saponification reaction of polyvinyl acetate or an ethylene-vinyl acetate copolymer with an alkali catalyst can be used as it is. In particular,
Alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, sodium methylate, t
An alkali metal alcoholate such as potassium butoxy,
1,8-diazabicyclo [5,4,10] undecene-
Strongly basic amines represented by 7 (DBU), furthermore, alkali metal carbonates, alkali metal hydrogencarbonates, etc. are exemplified, but use of sodium hydroxide is preferred from the viewpoint of easy handling, catalyst cost and the like.

The amount of the catalyst used varies depending on the required degree of saponification, the reaction temperature and the like, but is used in an amount of 0.05 equivalent or less based on the residual vinyl acetate groups in the ethylene-vinyl acetate copolymer.
Preferably it is 0.03 equivalent or less. Further, instead of the alkali catalyst, an acid catalyst such as hydrochloric acid and sulfuric acid can be used.

In the saponification, the ethylene-vinyl acetate copolymer is dissolved in an alcohol or a medium containing an alcohol so as to have a concentration of usually about 20 to 60% by weight, and an alkali catalyst is added thereto to obtain a solution of 40 to 140% by weight. React at a temperature of ° C. As the alcohol, methanol, ethanol, alcohol such as propanol is used,
Preferably, methanol is used.

As the saponification reaction proceeds, ethylene-
Although a saponified vinyl acetate copolymer is produced, the final concentration of the saponified product in the present invention is not particularly limited as long as the saponified product is not precipitated in an alcohol medium for the following stranding step. However, usually, the concentration of the saponified product is adjusted so as to be 10 to 50% by weight, preferably 15 to 45% by weight.

The saponification degree of the vinyl acetate component of the saponified ethylene-vinyl acetate copolymer is 70 to
Advantageously, it is 100 mol%, preferably 80-100 mol%. If the saponification degree is less than 70 mol%, the thermal stability when melt-molding using the saponified ethylene-vinyl acetate copolymer becomes poor.

Next, the alcohol solution of the saponified ethylene-vinyl acetate copolymer obtained as described above may be used as it is, but preferably, only water is added, or water is added, and the concentration of the saponified solution is adjusted appropriately. Then, a solution for strand production is obtained as an alcohol / water solution. In addition, the concentration of the saponified product in the saponified solution of the ethylene-vinyl acetate copolymer at this time is preferably 15 to 55% by weight,
More preferably, it is 20 to 50% by weight. If the amount is less than 15% by weight, coagulation in the coagulation liquid becomes difficult, and
If the content exceeds 5% by weight, the porosity of the pellets is reduced, which adversely affects the thermal stability at the time of molding.

At this time, a saturated aliphatic amide (eg, stearic acid amide, etc.), an unsaturated fatty acid amide (eg, olefinic acid amide, etc.), a bisfatty acid amide (eg, ethylene bisstearic acid amide, etc.), a fatty acid metal salt (eg, Lubricants such as, for example, calcium stearate), low molecular weight polyolefins (eg, low molecular weight polyethylene having a molecular weight of about 500 to 10,000, or low molecular weight polypropylene), inorganic salts (eg, hydrotalcite), plasticizers (eg, ethylene glycol, glycerin, etc.) Aliphatic polyhydric alcohols such as hexanediol).

The weight ratio of alcohol to water in the medium in the saponified solution is 9/1 to 3/7, preferably 8 to 13.
It is desirable to adjust so as to be / 2 to 4/6. If the ratio of alcohol to water exceeds 9/1, the saponified solution becomes slightly unstable and the porosity of the strand decreases, while
If the ratio is less than / 7, the saponified solution becomes unstable and a precipitate may be generated in the saponified solution.

Examples of the coagulating liquid include water or a water / alcohol (mixed) solution, aromatic hydrocarbons such as benzene, acetone,
Solvents such as ketones such as methyl ethyl ketone and ethers such as dipropyl ether are used, and water or a water / alcohol (mixed) solution is preferable. In the case of a water / alcohol (mixed) solution, the weight mixing ratio is 9 /. It is desirable to adjust so as to be 1/5. As the alcohol, alcohol such as methanol, ethanol and propanol is used, and preferably, methanol is used.

The most important feature of the present invention is that the coagulating solution contains 1.0 to 15000 ppm of a carboxylate, and the coagulating solution is preferably extruded into a coagulating bath containing 10 to 5000 ppm. When the amount of the carboxylate is less than 1.0 ppm or more than 15000 ppm, inconveniences such as a long curing time of the strand and breakage of the strand occur.

The carboxylate is not particularly restricted but includes sodium formate, potassium formate, magnesium formate, calcium formate, sodium acetate, potassium acetate, magnesium acetate, etc., preferably sodium acetate.

Next, the saponified ethylene-vinyl acetate copolymer solution is extruded in a strand form into the coagulating liquid by a nozzle having an arbitrary shape.

The shape of the nozzle is preferably a cylindrical shape. The length of the nozzle is 1 to 100 cm, preferably 3 to 30 cm, and the inner diameter is 0.1 to 10 cm, preferably 0.2 to 5.0 cm. It is preferable to have a cylindrical shape with a ratio of length to inner diameter (length / inner diameter) of 8 to 40.
The cross-sectional shape of the nozzle is usually circular, but may be elliptical, square, rhombic, star-shaped or the like in some cases.

The number of nozzle openings is not necessarily one, and any number between several and several hundreds can be extruded.

The contact time between the coagulating liquid and the saponified ethylene-vinyl acetate copolymer is preferably 10 seconds to 1 hour. The temperature for contacting is -10 to 40C, preferably 0 to 20C. Since the coagulation liquid is a non-solvent for the saponified product, there is almost no fear that the saponified product dissolves in the coagulating liquid and causes resin loss, but operation at a low temperature is safe as much as possible.

The saponified ethylene-vinyl acetate copolymer extruded in the form of a strand is cut after sufficient coagulation, cut into pellets, and optionally washed with water. The water washing is performed by immersing the pellets in a water bath at a temperature of 10 to 60 ° C., and may be carried out by any method such as bringing them into countercurrent contact. By washing with water, impurities such as oligomers in the saponified ethylene-vinyl acetate copolymer are removed.Especially, when sodium hydroxide is used as the saponification catalyst, the sodium acetate content in the saponified ethylene-vinyl acetate copolymer is reduced. It is removed to 0.5% by weight or less.

The washed pellets are preferably subjected to an acid treatment. Examples of the acid include formic acid, acetic acid, adipic acid, phosphoric acid, boric acid and alkali metal salts or alkaline earth metal salts of these acids. Acetic acid is more preferably used. In the acid treatment, for example, saponified ethylene-vinyl acetate copolymer pellets are immersed in a 3% by weight or less aqueous acetic acid solution (pH: about 3 to 8).

Although the shape of the pellet as the final product is not particularly limited, it is preferable that the diameter of the pellet is 2 from the viewpoint of workability during molding and handling.
A cylindrical shape having a length of 2 to 5 mm and a spherical shape having a diameter of 2 to 5 mm is practical.

Thus, the pellets of the present invention can be produced. The pellets are melt-molded to form a desired molded product. Is desirable. At the time of molding, if necessary, known additives such as reinforcing materials such as glass fibers and carbon fibers, fillers, coloring agents, stabilizers such as hydrotalcite, foaming agents, and drying agents may be appropriately blended. The saponified ethylene-vinyl acetate copolymer may also contain a suitable amount of a modifying thermoplastic resin.

As the melt molding method, any molding method such as an injection molding method, a compression molding method, and an extrusion molding method can be adopted. Examples of the extrusion molding method include a T-die method, a hollow molding method, a pipe extrusion method, a linear extrusion method, a deformed die extrusion method, an inflation method and the like, and a molding of a saponified ethylene-vinyl acetate copolymer alone. Objects (films, sheets, tapes,
Bottles, pipes, filaments, extruded shaped sections, etc.)
In addition, coextrusion molding of the saponified ethylene-vinyl acetate copolymer layer and another thermoplastic resin layer is also possible.

[0029]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Example 1 To 100 parts of a methanol solution containing 50% of an ethylene-vinyl acetate copolymer having an ethylene content of 35 mol%, 0.017 equivalent of sodium hydroxide was added to the vinyl acetate group in the copolymer. Supply 150 parts of methanol solution containing
The saponification reaction was performed at 18 to 130 ° C. and a pressure of 4 kg / cm ² G for 30 minutes. The resulting methanol solution of a saponified ethylene-vinyl acetate copolymer (saponification degree: 99.8 mol%) had a resin concentration of 30%. Next, a water content of 62.5
% Methanol aqueous solution is supplied azeotropically to the methanol solution of the saponified ethylene-vinyl acetate copolymer,
Methanol was distilled off at 100 to 110 ° C. under a pressure of 3 kg / cm ² G until the concentration of the resin component in the saponified ethylene-vinyl acetate copolymer methanol / water solution became 40%,
A completely clear methanol / water homogeneous solution was obtained.

Subsequently, a methanol / water solution of the obtained saponified ethylene-vinyl acetate copolymer was treated with a water / methanol solution containing 100 ppm of sodium acetate (weight ratio: 9%).
5/5) into a coagulation bath maintained at 5 ° C. from a cylindrical nozzle having an inner diameter of 0.3 cm and a length of 6.0 cm.
The extruded strand was extruded into a strand at a rate of 10 kg / hour, and the produced strand was drawn out of the coagulation liquid by a take-off roller attached to the end of the coagulation liquid tank so that the residence time in the coagulation liquid was 3 minutes. Here, there were 10 nozzle openings, and the number of strands was 10. The strand was cut with a cutter to obtain a porous pellet. The obtained pellets were uniform in shape and had no deformation. The pellets were washed in a water bath at a temperature of 30 ° C. for 1 hour, and this was repeated four times to remove sodium acetate, further washed in an aqueous solution of acetic acid at a temperature of 30 ° C. for 1 hour, and then dried. (A cylindrical white pellet having an average diameter of 3.8 mm and an average length of 4 mm). The following items were evaluated in the above manufacturing process.

(1) Evaluation of Strands Curing time The strands immersed in the coagulation liquid were taken out over time, and the time until the hardness reached 30 degrees was measured and evaluated as follows. The hardness is measured according to JISK 630.
According to No. 1, the test was performed using a spring-type hardness tester (Shimadzu Corporation). ○ ・ ・ ・ less than 40 seconds △ ・ ・ ・ 40 seconds or more and less than 60 seconds × ・ ・ ・ 60 seconds or more

Breakage of Strands The number of breakage of the strands during the operation for 72 hours out of 10 strands was measured.

Pellet size accuracy The diameter and length of 100 pellets were measured with calipers, and the diameter and length of the pellets were 3.8 ± 0.2 mm and 4 mm ±.
The proportion of pellets falling within the range of 0.2 mm was measured and evaluated as follows. ◎ ・ ・ ・ 95% or more ○ ・ ・ ・ 90% or more and less than 95% △ ・ ・ ・ 80% or more and less than 90% × ・ ・ ・ less than 80%

Example 2 A pellet of the present invention was produced in the same manner as in Example 1 except that the composition of the coagulating solution was adjusted so that the content of sodium acetate in the coagulating solution was 400 ppm. evaluated.

Comparative Example 1 Pellets were produced and evaluated in the same manner as in Example 1, except that the content of sodium acetate in the coagulating liquid was changed to 0 ppm.

Comparative Example 2 Pellets were produced and evaluated in the same manner as in Example 1, except that the content of sodium acetate in the coagulating liquid was changed to 20,000 ppm. Table 1 shows the evaluation results of Examples 1 and 2 and Comparative Examples 1 and 2.

[0038]

[Table 1]

[0039]

According to the present invention, there is provided a method for continuously extruding a solution of a saponified ethylene-vinyl acetate copolymer into a coagulating liquid in the form of a strand and then cutting the strand to produce pellets. Carboxylate to 1.
Since it is contained in an amount of 0 to 15000 ppm, saponified ethylene-vinyl acetate copolymer pellets having continuous and excellent size accuracy can be produced.

Claims (5)

[Claims] 1. A solution of a saponified ethylene-vinyl acetate copolymer is continuously extruded into a coagulating solution in a strand form,
Next, in a method for producing a pellet by cutting the strand, a carboxylate is added to the coagulation solution in an amount of 1.0 to 1500.
A method for producing saponified ethylene-vinyl acetate copolymer pellets, characterized by containing 0 ppm. 2. A carboxylate is added to the coagulation solution in an amount of 10 to 500.
The method for producing saponified ethylene-vinyl acetate copolymer pellets according to claim 1, wherein 0 ppm is contained. 3. The method for producing saponified ethylene-vinyl acetate copolymer pellets according to claim 1, wherein the solution is methanol or methanol / water solution. 4. The method for producing saponified ethylene-vinyl acetate copolymer pellets according to claim 1, wherein the coagulating liquid is water or a water / methanol solution. 5. The method for producing saponified ethylene-vinyl acetate copolymer pellets according to claim 1, wherein sodium carboxylate is used as the carboxylate.