JP4014119B2 - Process for producing saponified pellets of ethylene-vinyl acetate copolymer - Google Patents

Description

【００４５】
【発明の効果】
本発明では、エチレン−酢酸ビニル共重合体ケン化物の溶液を凝固液中にストランド状に連続的に押し出し、次いで該ストランドを切断してペレットを連続的に製造する方法において、凝固液中のカルボン酸の含有量を１〜１００００ｐｐｍにしているため、連続的にしかもサイズの精度が優れたエチレン−酢酸ビニル共重合体ケン化物ペレットが製造できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing ethylene-vinyl acetate copolymer saponified pellets, in which ethylene-vinyl acetate copolymer saponified pellets can be continuously produced and the size accuracy of the saponified pellets is excellent.
[0002]
[Prior art]
Saponified ethylene-vinyl acetate copolymer is widely used in various applications such as films, sheets, containers and fibers because of its excellent properties such as oxygen barrier properties and mechanical strength.
Among them, when a sheet or film is produced by melt molding, the copolymer saponification product is preferably in the form of pellets from the handling surface and molding surface, and as a method for producing the pellet, for example, ethylene-vinyl acetate is used. A method for producing pellets by extruding a saponified copolymer solution into water or an aqueous methanol solution in the form of strands and then cutting the strands is known.
[0003]
[Problems to be solved by the invention]
However, the known technique does not contain carboxylic acid in the coagulation liquid, and there is a drawback that strand breakage occurs when the saponified ethylene-vinyl acetate copolymer is continuously extruded through the nozzle into the coagulation bath. It became clear that there was. Furthermore, when the pellets obtained by the disclosed technology are used for extrusion molding, fluctuations in the feeding to the extruder, load fluctuations of the extruder, etc. occur, making it difficult to perform a stable molding operation, and thus the shape is uniform. Ethylene-vinyl acetate copolymer saponified pellets are desired.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the inventor continuously extruded a solution of a saponified ethylene-vinyl acetate copolymer into a coagulation liquid in a strand shape, and then the strand was cut to form a pellet. In the method of continuously producing the carboxylic acid in the coagulating liquid, the objective ethylene-vinyl acetate copolymer saponified pellets are found to be obtained when the carboxylic acid is contained in an amount of 1 to 10,000 ppm, and the present invention is completed. It was.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail for each step.
The ethylene-vinyl acetate copolymer used as a raw material for the saponified ethylene-vinyl acetate copolymer used in the present invention is not particularly limited as the ethylene content, but is preferably 15 to 60 mol%, 20-55 mol%.
[0006]
If the ethylene content is less than 15 mol%, the precipitation in the form of strands in the coagulation liquid is incomplete, and part of the strands are eluted, which is undesirable in operation. Also, an ethylene-vinyl acetate copolymer solution is not used. It is not preferable because it is necessary to pressurize or heat to a high temperature in order to maintain a uniform solution state.
[0007]
On the other hand, if it exceeds 60 mol%, it is difficult to prepare a homogeneous solution of a saponified ethylene-vinyl acetate copolymer, and the desired strand cannot be produced.
[0008]
In addition to ethylene and vinyl acetate, such an ethylene-vinyl acetate copolymer may contain an ethylenically unsaturated monomer copolymerizable therewith as a copolymerization component. Examples of the monomer include olefins such as propylene, isobutylene, α-octene, α-dodecene, and α-octadecene, and unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid. Acids or salts thereof or mono- or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, or salts thereof, Alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (Meth) allyl ether, polyoxyalkylene (meth) allyl ether such as polyoxypropylene (meth) allyl ether, polyoxyalkylene (meth) acrylate such as polyoxyethylene (meth) acrylate and 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 vinylamine, etc. It is below.
[0009]
The saponified ethylene-vinyl acetate copolymer used in the present invention is obtained by saponifying the ethylene-vinyl acetate copolymer as described above. The saponification reaction is 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 ethylene-vinyl acetate copolymer with an alkali catalyst can be used as it is. Specifically, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, alkali metal alcoholates such as sodium methylate and t-butoxy potassium, 1,8-diazabicyclo [5,4,10] undecene -7 (DBU) in typified by strong basic amines, further although alkali metal carbonate, and the like alkali metal bicarbonate is ease of handling, the use of sodium hydroxide from the catalyst cost and the like are preferable.
[0010]
The amount of the catalyst used varies depending on the required degree of saponification, reaction temperature, etc., but 0.05 equivalent or less is used with respect to the remaining acetate groups in the ethylene-vinyl acetate copolymer, preferably 0.03 equivalent or less. . Moreover, it is also possible to use acid catalysts, such as hydrochloric acid and a sulfuric acid, instead of an alkali catalyst.
[0011]
In the saponification, the ethylene-vinyl acetate copolymer is dissolved in an alcohol or an alcohol-containing medium so as to have a concentration of usually about 20 to 60% by weight, and an alkali catalyst or an acid catalyst is added to add 40 to 140. React at a temperature of ° C. The concentration of the saponified product is not particularly limited as long as the saponified ethylene-vinyl acetate copolymer is not precipitated at the solution temperature, but the concentration of the saponified product is usually 10 to 55% by weight, preferably 15%. What is necessary is just to make it become -50weight%.
[0012]
The saponification degree of the vinyl acetate component of the saponified ethylene-vinyl acetate copolymer obtained by such saponification is preferably 70 to 100 mol%, and more preferably 80 to 100 mol%. When the saponification degree is less than 70 mol%, the thermal stability when melt-molding using the saponified ethylene-vinyl acetate copolymer pellets is deteriorated.
[0013]
Next, the ethylene-vinyl acetate copolymer saponified alcohol solution obtained above may be used as it is, but preferably, water is added directly, or the saponified solution is appropriately concentrated or diluted, and then water is added to the strand. Prepared into a solution for production. At this point, saturated aliphatic amide (such as stearic acid amide), unsaturated fatty acid amide (such as olefinic acid amide), bisfatty acid amide (such as ethylenebisstearic acid amide), fatty acid metal salt (such as calcium stearate), etc. Lubricants, low molecular weight polyolefins (for example, low molecular weight polyethylene having a molecular weight of about 500 to 10,000, or low molecular weight polypropylene), inorganic salts (for example, hydrotalcite), plasticizers (for example, ethylene glycol, glycerin, hexanediol, etc.) Or other aliphatic polyhydric alcohols).
[0014]
Next, the ethylene-vinyl acetate copolymer saponified solution is extruded into a coagulating solution in a strand form and precipitated. The concentration of the saponified product in the ethylene-vinyl acetate copolymer saponified solution is preferably 15 It is -55 weight%, More preferably, it is 20-50 weight%. If it is less than 15% by weight, it is difficult to solidify in the coagulation liquid. Conversely, if it exceeds 55% by weight, the void ratio of the pellet is lowered, which adversely affects the thermal stability during molding.
[0015]
It is also desirable to adjust the weight mixing ratio of alcohol and water in the saponified solution to 9/1 to 3/7, preferably 8/2 to 4/6.
If the ratio of alcohol to water exceeds 9/1, the solution becomes slightly unstable, and the porosity at the time of strand precipitation slightly decreases. On the other hand, if the ratio is less than 3/7, the solution becomes unstable and saponification may be precipitated. is there.
[0016]
As coagulation liquid, water or water / alcohol mixed solvent, aromatic hydrocarbons such as benzene, ketones such as acetone and methyl ethyl ketone, ethers such as dipropyl ether, organic acids such as methyl acetate, ethyl acetate and methyl propionate Esters are used, but water or water / alcohol mixed solvents are preferred.
[0017]
In the present invention, the maximum characteristic is that 1 to 10,000 ppm of carboxylic acid is contained in the coagulation liquid, and preferably 50 to 5000 ppm. If the content of carboxylic acid is less than 1 ppm, the curing time of the strand becomes long and strand breakage is unsuitable, and if it exceeds 10,000 ppm, it is unsuitable because strand breakage occurs.
[0018]
The carboxylic acid is not particularly limited, and examples include formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, crotonic acid, maleic acid, itaconic acid, and preferably acetic acid. Used.
[0019]
When the water / alcohol mixed solvent is used, the alcohol concentration is preferably equal to or lower than the alcohol content of the alcohol / water mixed solution in the copolymer saponified solution. Polymer loss at the time increases, which is not preferable.
[0020]
As the alcohol, alcohols such as methanol, ethanol, propanol and the like are used, and methanol is preferably used.
[0021]
The contact time between the coagulation liquid and the saponified ethylene-vinyl acetate copolymer is preferably 10 seconds to 1 hour.
[0022]
The temperature at which the saponified ethylene-vinyl acetate copolymer solution is brought into contact with the coagulation liquid is −10 to 40 ° C., preferably 0 to 20 ° C. Since the above organic solvent is a non-solvent for the saponified product, there is little concern that the saponified product will dissolve in the coagulation liquid and cause resin loss, but operation at as low a temperature as possible is safe.
[0023]
Next, the saponified ethylene-vinyl acetate copolymer solution is extruded into a coagulating liquid in a strand form by a nozzle having an arbitrary shape.
[0024]
The shape of the nozzle is not particularly limited, but a cylindrical shape is preferable. The length at that time is 1 to 100 cm, preferably 3 to 30 cm, and the inner diameter is 0.1 to 10 cm, preferably 0.2. ~ 5.0 cm. In particular, a cylindrical shape having a length to inner diameter ratio (length / inner diameter) of 8 to 40 is preferable, and the thickness of the nozzle is 0.01 to 0.5 cm, preferably 0.1 to 0.3 cm.
[0025]
The cross-sectional shape of the nozzle is preferably circular as described above, but may be oval, square, rhombus, star, or the like depending on circumstances.
[0026]
Moreover, the strand does not necessarily need to be one, and can be extruded in an arbitrary series of several to several hundreds.
[0027]
The saponified ethylene-vinyl acetate copolymer extruded in a strand form is sufficiently solidified, and then the strand is cut, pelletized, and washed with water as necessary.
[0028]
As the water washing conditions, the pellets are washed in a water bath at a temperature of 10 to 60 ° C. By washing with water, oligomers and impurities in the saponified ethylene-vinyl acetate copolymer are removed, and particularly sodium acetate is removed to 0.5% by weight or less.
[0029]
The pellets washed with water are preferably subjected to acid treatment, and examples thereof include acetoacetic acid, formic acid, acetic acid, adipic acid, phosphoric acid, boric acid and the like, and more preferably acetic acid is used.
As conditions for the acid treatment, for example, washing is performed in an acetic acid aqueous solution of 3% by weight or less, and the treatment is performed so that the pH of the washing solution becomes 3 to 8.
[0030]
The shape of the pellet is not particularly limited, but the diameter is 2 to 5 mm and the length is 2 to 5 mm in the case of a cylindrical shape from the viewpoint of workability and handling during molding, and the diameter is 2 to 5 mm in the case of a spherical shape. Something is practical.
[0031]
Thus, although the pellet of the present invention can be produced, the pellet is melt-molded and formed into a desired molded product. The temperature condition for melt molding is preferably about 160 to 260 ° C. In molding, an appropriate amount of a known additive such as a reinforcing material such as glass fiber or carbon fiber, a stabilizer such as a filler, a colorant, or hydrotalcite, a foaming agent, or a drying agent may be blended. Further, an appropriate amount of a thermoplastic resin for modification can be blended in the saponified ethylene-vinyl acetate copolymer.
[0032]
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 employed. Among these, the extrusion molding method includes a T-die method, a hollow molding method, a pipe extrusion method, a linear extrusion method, a deformed die extrusion method, an inflation method, etc., but molding of an ethylene-vinyl acetate copolymer saponified product alone. Coextrusion of not only products (films, sheets, tapes, bottles, pipes, filaments, profile cross-section extrudates, etc.) but also saponified ethylene-vinyl acetate copolymer layers and other thermoplastic resin layers is possible. .
[0033]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples. In the examples, “parts” and “%” are based on weight unless otherwise specified.
[0034]
Example 1
A methanol solution containing 0.017 equivalents of sodium hydroxide with respect to acetic acid groups in the copolymer and methanol 150 were added to 100 parts of a methanol solution containing 50% ethylene-vinyl acetate copolymer having an ethylene content of 35 mol%. Parts were supplied and saponified . Next, 60 parts of an aqueous methanol solution mixed at a ratio of 50 parts of water to 100 parts of methanol was supplied at an azeotropic point. The reaction temperature was 128 to 140 ° C., and the pressure was 5 kg / cm ² G. The obtained ethylene-vinyl acetate copolymer saponified solution (resin concentration 40%) was a completely transparent homogeneous solution. The saponification degree of the vinyl acetate component of the ethylene-vinyl acetate copolymer saponified product was 99.8 mol. %Met.
[0035]
Subsequently, the ethylene-vinyl acetate copolymer saponification product solution was placed in a coagulation liquid tank maintained at 5 ° C. consisting of 5% methanol containing 95 ppm acetic acid and 95% water at a rate of 10 kg / hour. After being extruded into a strand from a cylindrical nozzle having a length of 3 cm, a length of 6.0 cm and a thickness of 0.2 cm, the strand was brought into contact with the coagulating liquid for 3 minutes by a take-off roller attached to the end of the coagulating liquid tank. Pulled from the coagulation liquid.
The strand was cut with a cutter to obtain porous pellets. The obtained pellets were uniform in shape and had no deformation. The porous pellet was washed with water in a water bath at a temperature of 30 ° C. for 1 hour, and this was repeated four times. After removing sodium acetate, the one washed for 1 hour in acetic water at a temperature of 30 ° C. was dried and dried. An inventive pellet (a white pellet having a diameter of 3.8 mm and a length of 4 mm) was obtained. The following items were evaluated during the manufacturing process of the ethylene-vinyl acetate copolymer saponified product pellets.
[0036]
(1) Evaluation of Strand (1) Curing Time The strand immersed in the coagulating liquid was taken out over time, and the time until the hardness reached 30 degrees or more was measured and evaluated as follows. The hardness was measured with a spring type hardness tester (Shimadzu Corporation) according to JIS K 6301.
○: Less than 40 seconds Δ: 40 seconds or more and less than 60 seconds × ... 60 seconds or more [0037]
(2) Strand breakage The number of strand breaks during 72 hours of operation was measured, and there were 10 strands, which were expressed as the number of strand breaks per 10 strands.
[0038]
(3) Accuracy of pellet size The diameter and length of 100 pellets were measured with a vernier caliper, and the proportion of pellets whose diameter and length were 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
In Example 1, the pellets of the present invention were produced in the same manner as in Example 1 except that the content of acetic acid in the coagulation liquid was 1000 ppm, and evaluated in the same manner.
[0041]
Example 4
In Example 1, the pellet of this invention was manufactured similarly to Example 1 except having used propionic acid instead of acetic acid, and evaluated similarly.
[0042]
Comparative Example 1
In Example 1, except that the content of acetic acid in the coagulation liquid was 0 ppm, the pellets of the present invention were produced in the same manner as in Example 1 and evaluated in the same manner.
[0043]
Comparative Example 2
In Example 1, the pellets of the present invention were produced in the same manner as in Example 1 except that the content of acetic acid in the coagulation liquid was 20000 ppm, and evaluated in the same manner.
The evaluation results of Examples 1 , 2 , and 4 and Comparative Examples 1 and 2 are shown in Table 1.
[0044]
[Table 1]

[0045]
【The invention's effect】
In the present invention, a solution of a saponified ethylene-vinyl acetate copolymer is continuously extruded into a coagulating liquid in a strand form, and then the strand is cut to continuously produce pellets. Since the acid content is set to 1 to 10,000 ppm, saponified ethylene-vinyl acetate copolymer pellets having excellent size accuracy can be produced continuously.

Claims (5)

  In the method of continuously extruding a solution of a saponified ethylene-vinyl acetate copolymer into a coagulation liquid in a strand form, and then cutting the strand to continuously produce pellets, A method for producing ethylene-vinyl acetate copolymer saponified pellets, containing 10,000 ppm.   The process for producing saponified pellets of ethylene-vinyl acetate copolymer according to claim 1, wherein the coagulating liquid contains 5 to 5000 ppm of carboxylic acid.   3. The method for producing saponified pellets of ethylene-vinyl acetate copolymer according to claim 1, wherein the solution is methanol or methanol / water solution.   The method for producing saponified pellets of ethylene-vinyl acetate copolymer according to any one of claims 1 to 3, wherein the coagulation liquid is water or a water / methanol solution.   The method for producing saponified pellets of ethylene-vinyl acetate copolymer according to any one of claims 1 to 4, wherein acetic acid is used as the carboxylic acid.