JP2024005772A - Method for producing pellets of ethylene-vinyl ester copolymer saponification product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing EVOH pellets having high dimensional stability and productivity.

SOLUTION: There is provided a method for producing pellets of an ethylene-vinyl ester copolymer saponification product, which comprises: a coagulation step in which a solution of an ethylene-vinyl ester copolymer saponification product is extruded in a strand shape into a coagulation liquid to obtain a coagulated product; and a cutting step of cutting the coagulated product to obtain pellets, wherein in the solidification step, the discharge speed of the strand extruded into the coagulation liquid is 1.3 kg/(hour/hole) or more and the coagulation liquid contains at least one salt selected from the group consisting of an inorganic acid salt and an organic acid salt in an amount of 2 mass% or more and 25 mass% or less.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for producing saponified ethylene-vinyl ester copolymer pellets.

Saponified ethylene-vinyl ester copolymer (hereinafter sometimes abbreviated as EVOH) is a material with excellent oxygen barrier properties, oil resistance, non-static properties, mechanical strength, etc., and is used for films, sheets, containers, etc. It is molded and widely used. A common method for producing EVOH is to saponify an ethylene-vinyl ester copolymer obtained by polymerizing ethylene and a vinyl ester such as vinyl acetate in an organic solvent containing alcohol in the presence of a saponification catalyst. It is true.

As a post-treatment method for the EVOH alcohol solution obtained by saponification, the EVOH alcohol solution is extruded into a coagulating liquid such as water or a water/methanol solution in the form of a strand, and then the strand is cut to produce pellets. This method is widely used. At this time, it is important to stabilize the cuttability of the strands in order to prevent strand breakage and improve the dimensional stability of the pellets. Patent Document 1 describes that EVOH pellets with excellent size accuracy can be produced continuously by containing a predetermined amount of carboxylate in a coagulation liquid. On the other hand, it is stated that if the concentration of the carboxylic acid salt is too high or too low, problems such as a long curing time of the strands and breakage of the strands will occur.

Japanese Patent Application Publication No. 11-216725

In order to increase the production rate of EVOH, it is necessary to increase the discharge rate of the EVOH solution during pelletization. However, in conventional methods, when the discharge speed is increased, cutting errors may occur when cutting the strands, resulting in decreased productivity and insufficient dimensional stability of the resulting pellets. Ta. For this reason, there has been a demand for improvement in the cuttability of strands made of hydrous EVOH.

The present invention was made to solve the above problems, and an object of the present invention is to provide a method for producing EVOH pellets with high dimensional stability and high productivity.

The above-mentioned problem includes a coagulation step in which a solution of EVOH is extruded into a coagulation liquid in the form of a strand and solidified to obtain a coagulated product, and a cutting step in which the coagulated product is cut to obtain pellets. The discharge rate of the strand extruded into the liquid is 1.3 kg/(hour/hole) or more, and the coagulating liquid contains at least 2% by mass of at least one salt selected from the group consisting of inorganic acid salts and organic acid salts. The problem is solved by providing a method for producing EVOH pellets containing up to % by mass.

At this time, it is preferable that the coagulating liquid contains water and methanol. It is also preferable that the salt contained in the coagulation liquid is at least one selected from the group consisting of carboxylates, sulfates, nitrates, and carbonates.

In the production method of the present invention, EVOH pellets with high dimensional stability can be produced with good productivity because the strand-shaped coagulated material containing EVOH can be easily cut. The EVOH pellets thus obtained are suitably used as materials for various molded products.

The present invention includes a coagulation step in which a solution of EVOH is extruded into a coagulation liquid in the form of a strand and solidified to obtain a coagulated product, and a cutting step in which the coagulated product is cut to obtain pellets, and in the coagulation step, the coagulated The discharge rate of the strand extruded into the liquid is 1.3 kg/(hour/hole) or more, and the coagulating liquid contains at least 2% by mass of at least one salt selected from the group consisting of inorganic acid salts and organic acid salts. This is a method for producing EVOH pellets containing up to % by mass. In this method, since the strand-shaped coagulated material containing EVOH has good cutting properties, not only is productivity high, but also the resulting EVOH pellets have high dimensional stability. The present invention will be explained in detail below.

First, a method for synthesizing EVOH will be explained. EVOH is obtained by saponifying an ethylene-vinyl ester copolymer. As the vinyl ester, fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate can be used, and vinyl acetate is preferred. The polymerization of ethylene and vinyl ester may be carried out by any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization, but solution polymerization is preferred. Further, either a continuous type or a batch type may be used.

The solvent used in solution polymerization is preferably alcohol, but other organic solvents (such as dimethyl sulfoxide) that can dissolve ethylene, vinyl ester, and ethylene-vinyl acetate copolymer can also be used. As the alcohol, methanol, ethanol, 1-propanol, 2-propanol, etc. can be used, and methanol is industrially preferred.

As a polymerization catalyst, 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methyl-2,4-dimethylvaleronitrile) ), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), azonitrile-based initiators such as 2,2-azobis-(2-cyclopropylpropionitrile), and isobutyryl peroxide, Organic compounds such as cumyl peroxyneodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide. A peroxide-based initiator or the like can be used.

The polymerization temperature is preferably 20 to 90°C, more preferably 40 to 70°C. The polymerization time (average residence time in the case of continuous system) is preferably 2 to 15 hours, more preferably 3 to 11 hours. The polymerization rate is preferably 10 to 90 mol%, more preferably 30 to 80 mol%, based on the vinyl ester charged. The polymer concentration in the solution after polymerization is preferably 5 to 85% by mass, more preferably 20 to 70% by mass. The ethylene unit content of the ethylene-vinyl ester copolymer is the same as the ethylene unit content of EVOH, which will be explained later. In addition, the ethylene-vinyl ester copolymer can be copolymerized with a small amount of other monomers, but the type and amount of the other monomers are the same as in the case of EVOH, which will be explained later. .

After polymerization for a predetermined time and reaching a predetermined polymerization rate, a polymerization inhibitor is added as necessary, unreacted ethylene gas is removed by evaporation, and unreacted vinyl ester is expelled. As a method for expelling unreacted vinyl ester from an ethylene-vinyl ester copolymer solution in which ethylene has been removed by evaporation, for example, the copolymer solution is continuously fed at a constant rate from the upper part of a column packed with a Raschig ring. A method of blowing organic solvent vapor such as methanol from the bottom of the column, distilling a mixed vapor of the organic solvent such as methanol and unreacted vinyl ester from the top of the column, and taking out the copolymer solution from which unreacted vinyl ester has been removed from the bottom of the column. etc. will be adopted.

An alkali catalyst is added to the ethylene-vinyl ester copolymer solution from which unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified. The saponification method can be either a continuous method or a batch method, but it is preferable to carry out the saponification reaction continuously using a tower reactor and take out the EVOH solution from the bottom of the tower. As the alkali catalyst, sodium hydroxide, potassium hydroxide, alkali metal alcoholate, etc. are used. Moreover, as the solvent used for saponification, alcohols such as methanol and ethanol are preferable, and methanol is more preferable from an industrial standpoint. When using a column reactor, it is preferable to supply methanol vapor from the bottom of the column and distill methyl acetate from the top of the column.

Suitable saponification conditions are as follows. The concentration of the ethylene-vinyl ester copolymer in the reaction solution is preferably 10 to 50% by mass, more preferably 20 to 45% by mass. The reaction temperature is preferably 70 to 150°C, more preferably 80 to 140°C. The amount of the catalyst used is preferably 0.005 to 1 equivalent, more preferably 0.01 to 0.5 equivalent, relative to the number of moles of vinyl ester units. The reaction time (average residence time in the case of a continuous system) is preferably 10 minutes to 6 hours, more preferably 15 minutes to 2 hours. In this way, the saponification reaction is allowed to proceed, and a solution of EVOH is obtained. The content of EVOH in the solution is preferably 10 to 50% by mass, more preferably 20 to 45% by mass.

The degree of saponification of the vinyl ester unit of EVOH thus obtained is preferably 80 to 100 mol%. From the viewpoint of obtaining a molded product with excellent barrier properties, the content is more preferably 95 mol% or more, still more preferably 98 mol% or more, and particularly preferably 99 mol% or more. If the degree of saponification is less than 80 mol%, barrier properties, long-run properties, and moisture resistance may deteriorate.

In the present invention, the ethylene unit content of EVOH is preferably 20 to 60 mol% from the viewpoint of obtaining a molded product with excellent barrier properties and melt moldability. If the ethylene unit content is less than 20 mol%, melt moldability may deteriorate. The ethylene unit content is more preferably 23 mol% or more. On the other hand, if the ethylene unit content exceeds 60 mol%, the barrier properties may become insufficient. The ethylene unit content is more preferably 55 mol% or less, still more preferably 50 mol% or less.

EVOH can also be copolymerized with a small amount of other monomers as long as the purpose of the present invention is not impaired. Examples of copolymerizable monomers include alkenes such as propylene, butylene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4- Diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2- Methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6- Alkenes having ester groups such as acyloxy-1-hexene, 5,6-diasiloxy-1-hexene, 1,3-diacetoxy-2-methylenepropane, or saponified products thereof; acrylic acid, methacrylic acid, crotonic acid, itaconic acid, etc. unsaturated acids or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefins such as vinylsulfonic acid, allylsulfonic acid, and methalylsulfonic acid. Sulfonic acid or its salt; vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers, vinyl ketone, N-vinylpyrrolidone, vinyl chloride , vinylidene chloride, etc. When EVOH has other monomer units, the copolymerized amount thereof is preferably 10 mol% or less, more preferably 5 mol% or less.

The solvent used in the EVOH solution to be subjected to the coagulation step is not particularly limited as long as it is a good solvent for EVOH, but a mixed solvent containing water and alcohol is preferred. That is, it is preferable to use a water/alcohol solution of EVOH in the coagulation step. Here, the water/alcohol solution of EVOH refers to a solution in which EVOH is dissolved in the mixed solvent containing water and alcohol. Examples of the alcohol used at this time include methanol, ethanol, propanol, butanol, and the like, with methanol being industrially preferred.

The method for producing the EVOH solution to be subjected to the coagulation step is not particularly limited. The EVOH solution after the saponification reaction may be directly subjected to the coagulation step, or the EVOH solution after the saponification reaction may be further added with a solvent, or at least a part of the solvent in the EVOH solution after the saponification reaction may be used. A solvent substituted with the same or different solvent may be subjected to the coagulation step.

As the EVOH water/alcohol solution to be subjected to the coagulation step, one obtained by replacing a portion of the alcohol in the EVOH solution after the saponification reaction with water can be subjected to the coagulation step. . At this time, as a method to replace a portion of the alcohol in the EVOH alcohol solution with water, a mixed vapor of solvent (alcohol) and water is added to the alcohol solution in the container to remove the solvent (alcohol) from the solution. A method of vaporization is preferred. As the container at this time, a column-type container such as a tray column or a packed column is preferable. In this case, the alcoholic solution of EVOH is introduced from the upper part of the tower, a mixed vapor of solvent (alcohol) and water is introduced from the lower part of the tower type container, and the solvent (alcohol) and water are brought into countercurrent contact, and the solvent (alcohol) and water are introduced from the upper part of the tower. The mixed vapor is led out and a part of the solvent present in the supplied alcoholic EVOH solution is replaced with water, so that a highly concentrated water/alcoholic solution of EVOH can be obtained from the bottom of the column. Furthermore, it is preferable that the water content in the mixed steam is 20 to 70% by mass. The solvent used for the mixed vapor is preferably an alcohol having a boiling point of 130° C. or lower, and examples of such alcohol include alcohols such as methanol, ethanol, propanol, and butanol. Alcohols having a boiling point of 100° C. or lower are more preferred, and methanol is particularly preferred because it is easily available, inexpensive, has a low boiling point, and is easy to handle. By replacing the solvent in this way, a water/alcohol solution of EVOH can be obtained. The water/alcohol mass ratio of the EVOH water/alcohol solution to be subjected to the coagulation step is preferably 10/90 to 60/40, more preferably 20/80 to 50/50. .

The EVOH content in the EVOH solution to be subjected to the coagulation step is preferably 20 to 50% by mass. By setting the EVOH content within this range, the fluidity of the EVOH solution is ensured, and efficient resin production is possible. From the viewpoint of increasing the production amount per unit time, the content is more preferably 25% by mass or more, and even more preferably 35% by mass or more. The content of components other than EVOH and the solvent in the EVOH solution is usually 10% by mass or less.

As the coagulating liquid used in the coagulating step, one containing a poor solvent for the EVOH is used. The poor solvent is preferably water or a mixed solvent containing water and alcohol, and more preferably a mixed solvent containing water and alcohol. As the alcohol used in the mixed solvent, methanol, ethanol, propanol, etc. are used, and methanol is preferably used industrially. The mass ratio of water and alcohol (water/alcohol) contained in the mixed solvent is preferably 70/30 to 98/2. It is more preferable that the mass ratio (water/alcohol) is 80/20 or more. The content of the poor solvent in the coagulation liquid is preferably 60% by mass or more, more preferably 75% by mass or more. On the other hand, the content is preferably 98% by mass or less.

The coagulating liquid needs to contain at least 2% by mass and not more than 25% by mass of at least one salt selected from the group consisting of inorganic salts and organic salts. Conventionally, a method of adding a predetermined amount of a carboxylic acid salt to a coagulating liquid has been known as a method for improving the cuttability of a strand obtained by extruding an EVOH solution into a coagulating liquid. However, when the discharge speed of the EVOH solution is increased to increase the production rate of EVOH, cutting errors occur when cutting the strands, resulting in decreased productivity and insufficient dimensional stability of the resulting pellets. There was a need for improvement. On the other hand, as a result of intensive studies to improve the cutting performance, the inventors found that when the salt concentration was increased and the discharge speed of the EVOH solution was increased, as will be described later, the cutting performance of the strands was improved. I discovered that. Conventionally, it has been known that if the concentration of carboxylate in the coagulation solution is too high, the curing time of the strands increases and the cuttability tends to decrease, so it is truly surprising that such an effect can be obtained. It is. The salt contained in the coagulation liquid is preferably an organic salt. Examples of the organic salts include carboxylates, sulfonates, and the like, with carboxylates being preferred. Examples of the inorganic salts include sulfates, nitrates, carbonates, hydrochlorides, phosphates, and the like, with sulfates, nitrates, and carbonates being preferred. Further, the cation constituting the salt is preferably a cation of a metal belonging to Group 1 or 2 of the periodic table, and more preferably a cation of a metal belonging to Group 1 of the periodic table. Examples of cations of metals belonging to Group 1 of the periodic table include sodium ions, potassium ions, and lithium ions, with sodium ions and potassium ions being preferred, and sodium ions being more preferred. Examples of cations of metals belonging to Group 2 of the periodic table include calcium ions and magnesium ions. Specifically, sodium acetate is preferred from the viewpoint of ease of handling.

When the content of the salt contained in the coagulation liquid is 2% by mass or more, the effect of improving cutting performance can be obtained. Further, the content is 25% by mass or less from the viewpoint of suppressing salt precipitation in the coagulation liquid.

The temperature of the coagulating liquid is preferably -10°C or more and 40°C or less. If the temperature is less than -10°C, the coagulation liquid may freeze. The temperature is more preferably -5°C or higher, and even more preferably 0°C or higher. On the other hand, if the temperature exceeds 40°C, the EVOH may not solidify sufficiently. The temperature is more preferably 30°C or lower, further preferably 25°C or lower, even more preferably 20°C or lower, and particularly preferably 15°C.

The EVOH solution is extruded into the coagulation liquid in the form of a strand through a nozzle having an arbitrary shape. The shape of such a nozzle is not particularly limited, but a cylindrical shape is preferable. The inner diameter of the nozzle may be adjusted as appropriate depending on the diameter of the target EVOH pellet, but is usually 1 to 10 mm.

In the present invention, it is necessary that the discharge rate of the strand extruded into the coagulation liquid is 1.3 kg/(hour/hole) or more. This improves the production rate of EVOH, and as mentioned above, by increasing the salt concentration in the coagulation liquid, the cutting performance of the strands is stable even when the discharge speed is high, so EVOH can be produced with extremely high productivity. can be manufactured. Here, the discharge rate [kg/(hour/hole)] means the amount (kg) of strand (EVOH solution) extruded per hour from the hole (discharge port) of one nozzle. From the viewpoint of further improving the production rate of EVOH, the discharge amount is preferably 1.8 kg/(hour/hole) or more, and more preferably 2.5 kg/(hour/hole) or more. On the other hand, from the viewpoint of further improving cutting performance, the discharge amount is preferably 10 kg/(hour/hole) or less, and more preferably 5 g/(hour/hole) or less. In the present invention, the number of strands to be extruded does not necessarily need to be one, but any number between several to several hundred strands can be extruded. That is, the number of nozzles (strand discharge ports) does not have to be one, and can be any number between several to several hundred.

The contact time between the EVOH extruded into a strand and the coagulation liquid is preferably 5 seconds or more. If the contact time is less than 5 seconds, the EVOH solution may not solidify sufficiently. The contact time is more preferably 10 seconds or more, further preferably 20 seconds or more, even more preferably 30 seconds or more, and particularly preferably 40 seconds or more. On the other hand, from the viewpoint of productivity, the contact time is preferably 30 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less.

The EVOH extruded into a strand is pulled out from the coagulation bath by a take-up roller attached to the end of the coagulation bath, and then cut to obtain EVOH pellets. Depending on the take-up speed of the take-up roller, the contact time with the coagulation liquid, the diameter of the EVOH pellets obtained, etc. can be adjusted. The take-up speed of the take-up roller is preferably 1.5 to 5.0 m/min, more preferably 2.0 to 4.5 m/min, even more preferably 2.5 to 4.5 m/min.

The EVOH-containing strand-shaped coagulated material thus obtained is cut to obtain EVOH pellets. The method for cutting the coagulated material is not particularly limited, and examples thereof include methods using a strand cutter, hot cutter, underwater cutter, and the like. Among these, it is preferable to cut the coagulated material using a strand cutter. The length of the EVOH pellet immediately after cutting is preferably 1 to 10 mm. When the EVOH pellet is cylindrical, it is preferable that its diameter is 1 to 10 mm.

In order to further improve cuttability, the moisture content of the EVOH pellets immediately after cutting is preferably 30 to 80% by mass. The moisture content is more preferably 35% by mass or more. On the other hand, the water content is more preferably 70% by mass or less, even more preferably 50% by mass or less, and particularly preferably 45% by mass or less.

The water-containing EVOH pellets thus obtained may be subjected to a washing step and a drying step, if necessary. Examples of the cleaning liquid used in the cleaning step include water, an aqueous solution containing an acid such as acetic acid, an aqueous solution containing an alcohol such as methanol, and the like. The drying method for the water-containing EVOH pellets used in the drying step includes hot air drying, infrared irradiation, and the like.

The water-containing EVOH pellets may be subjected to chemical treatment, if necessary. Examples of the treatment include a method of impregnating the water-containing EVOH pellets with an aqueous solution containing an arbitrary additive. Examples of such additives include carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts.

The EVOH pellets thus obtained are melt-molded into various molded bodies such as films, sheets, containers, pipes, and fibers.

Hereinafter, the present invention will be explained in more detail using Examples, but the present invention is not limited to these Examples in any way.

[Evaluation method]
(1) Strand cutability evaluation During the manufacturing process of the hydrous EVOH pellets obtained in Examples and Comparative Examples, the hydrous EVOH pellets (approximately 2500 pellets) obtained by cutting 10 m of strand-shaped hydrous EVOH (coagulated material) were visually inspected. and evaluated the following items.
・Is it possible to cut the strands continuously?
・Number of times (times) the cutter was stopped due to a defective cut in which pellets continued for 3 cm or more
・Number of pellets that cannot be cut and are a series of water-containing EVOH pellets
・Number of hydrous EVOH pellets with a crushed cross section (units)

(2) Water content of water-containing EVOH pellets The water content of the water-containing EVOH pellets obtained in Examples and Comparative Examples immediately after cutting was measured using a halogen moisture meter "HR73" manufactured by Mettler.

(3) Dimensional stability Select 100 EVOH pellets obtained in Examples and Comparative Examples, measure the diameter and length, and the diameter and length of the pellets fall within ±0.2 mm of the average value. The percentage of pellets was determined.

[Example]
(Example 1)
EVOH (saponified ethylene-vinyl acetate copolymer) with an ethylene unit content of 27 mol% and a saponification degree of 99 mol% is placed in a container having a nitrogen inlet and a cylindrical nozzle with an inner diameter of 0.3 cm and a length of 6.0 cm. By adding an EVOH solution (water/methanol solution (mass ratio 50/50)) containing 40% by mass of It was discharged in the form of a strand into a coagulation bath consisting of a 5° C. water/methanol solution (mass ratio 95/5) containing 3% by mass of sodium acetate at a speed of (h/hole). The produced strand-shaped coagulated material was pulled out from the coagulation liquid by a take-up roller attached to the end of the coagulation bath so that the residence time in the coagulation bath was 60 seconds. The strand pulled out from the coagulation liquid was cut with a cutter to obtain porous water-containing EVOH pellets. To cut the strands, use a φ60mm/100mm rotary blade with 8 equally spaced blades, adjust the rotational speed of the blade so that the circumferential speed of the blade is equal to the take-up speed + 0.05m/min, and cut the strand. did. The resulting water-containing EVOH pellets were evaluated for strand cutability and water content according to the methods described in evaluation methods (1) and (2) above. The results are shown in Table 1. The water-containing EVOH pellets were washed with water for 1 hour in a water tank at a temperature of 30°C, this process was repeated 4 times, and further washed in acetic acid water at a temperature of 30°C for 1 hour, dried, and the EVOH pellets of the present invention (average A cylindrical white pellet with a diameter of 3.8 mm and an average length of 4 mm was obtained.

(Examples 2 to 7, Comparative Examples 1 to 4)
Water-containing EVOH pellets and EVOH pellets were produced and evaluated in the same manner as in Example 1, except that the discharge speed and coagulation bath conditions were changed as shown in Table 1. The results are shown in Table 1. In addition, in Comparative Example 4, the salt concentration in the coagulation bath was too high and sodium acetate precipitated in the coagulation bath, so that the strand could not be stably discharged and evaluation could not be performed.

Claims (3)

The coagulating step includes a coagulating step of obtaining a coagulated product by extruding a solution of saponified ethylene-vinyl ester copolymer into a coagulating liquid in the form of a strand and coagulating it, and a cutting step of cutting the coagulated product to obtain pellets. , the discharge rate of the strand extruded into the coagulation liquid is 1.3 kg/(hour/hole) or more, and the coagulation liquid contains at least one salt selected from the group consisting of inorganic acid salts and organic acid salts. A method for producing saponified ethylene-vinyl ester copolymer pellets containing from % by mass to 25% by mass. The method for producing saponified ethylene-vinyl ester copolymer pellets according to claim 1, wherein the coagulation liquid contains water and methanol. The saponified ethylene-vinyl ester copolymer pellet according to claim 1 or 2, wherein the salt contained in the coagulation liquid is at least one selected from the group consisting of carboxylates, sulfates, nitrates, and carbonates. manufacturing method.