JPH02259108A - Synthetic fiber excellent in alkali resistance and liquid holding property and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject fiber useful as a battery separator by mixing PVC with a carboxylic acid group-containing polymethyl methacrylate and polysulfone in a specific proportion, dissolving the resultant mixture in DMF, etc., and spinning the prepared spinning solution into a coagulation bath. CONSTITUTION:PVC having 800-2500 polymerization degree in an amount of 20-40wt.% is mixed with 20-65wt.% carboxylic acid group-containing polymethyl methacrylate and 15 to 40wt.% polysulfone so as to provide 2.4X10<-4> to 5.8X10<-4>mol/g content of the carboxyl acid groups. The resultant mixture is then dissolved and dispersed in a solvent selected from the group of dimethylacetamide, DMF, dimethyl sulfoxide and acetone and the prepared spinning solution is subsequently spun into a coagulation bath consisting of 20 to 60wt.% coagulant an 80-40wt.% same solvent as that in the spinning solution to afford the objective fiber having <=1.5wt.% weight loss of fiber after treatment thereof in a 30wt.% aqueous solution of KOH in a boiling state under ordinary pressure for 1hr and >=50wt.% liquid holding ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a synthetic fiber useful for battery separators that require alkali resistance and liquid retention properties, and a method for producing the same.

<Conventional technology> Conventionally, sealed alkaline batteries, such as nickel-cadmium alkaline batteries, have a nickel sintered substrate obtained by sintering carbonyl nickel powder, and an electrode plate in which an active material is impregnated and retained in the pores of the nickel sintered substrate. After cutting to size, they are wound spirally through a separator made of synthetic non-woven fabric to form a group of electrode plates, which are then placed in a battery can, injected with electrolyte, sealed and assembled. .

The material of the separator used here is generally a nonwoven fabric made of nylon fibers. However, in recent years, as battery operating temperatures have tended to rise, the material for separators has been changing to nonwoven polypropylene fibers, which have excellent alkali resistance at high temperatures.

However, a separator made of a non-woven fabric made of polypropylene fibers has better alkali resistance at high temperatures than a separator made of a non-woven fabric made of nylon fibers, but has a lower liquid retention property, so the electrolyte retention property of the separator is inferior. For this reason, when a battery using a separator made of a nonwoven polypropylene fiber fabric is repeatedly charged and discharged, the electrolyte in the separator decreases and the discharge characteristics deteriorate, and in the worst case, the battery becomes unable to discharge. Therefore, attempts have been made to modify the surface of nylon fibers and polypropylene fibers, such as by mixing nylon fibers with polypropylene fibers and by treating polypropylene fibers with surfactants. I can't say that.

In order to improve this drawback, Japanese Patent Application Laid-Open No. 62-51150 proposed a separator with excellent electrolyte retention properties by making polypropylene fibers porous, thereby creating a separator with excellent electrolyte retention properties. Methods have been proposed to improve the discharge cycle. This porous polypropylene fiber is obtained by superheating and kneading fine silica powder with polypropylene, performing injection molding, and then removing the fine silica powder with ultrasonic waves, but this method is not industrially suitable for fiber manufacturing. Improvements are desired.

<Problems to be Solved by the Invention> The present invention aims to provide a synthetic fiber useful for separators for alkaline storage batteries, which have excellent alkali resistance at high temperatures and require a high level of liquid retention, and a method for producing the same. be.

<Means for Solving the Problems> The present invention provides polyvinyl chloride (
PvC) 20 to 40% by weight, carboxylic acid group-containing polymethyl methacrylate (PMMA) 20 to 65% by weight, and polysulfone (PSF) 15 to 40% by weight, and the content of carboxylic acid groups in the fiber is 2. 4 X
10-4 to 5.8 x 10-' mol/g, the fiber loss after being treated in a 30 wt% KOH aqueous solution at normal pressure boiling for 1 hour is 1.5 wt% or less, and the water conduction shrinkage rate Synthetic fibers with excellent alkali resistance and liquid retention properties, characterized by having a liquid retention rate of 25% or less and a liquid retention rate of 50% or more by the measurement method shown in the text, and a polymerization degree of 800.
-2500 PvC 20-40% by weight, carboxylic acid group-containing PMMA 20-65% and PSF 15-40% by weight with a carboxylic acid group content of 2.4 x 10-4-5.
8 X'I O-' mol/g and dissolved and dispersed in a solvent selected from the group of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, and acetone, a spinning stock solution is mixed with 20 to 60% by weight of a coagulant and a spinning agent. The present invention provides a method for producing synthetic fibers having excellent alkali resistance and liquid retention properties, which is characterized by spinning into a coagulation bath containing 80 to 40% by weight of the same solvent as the stock solution.

The first requirement for the fiber of the present invention is 20 to 40% by weight of PVC,
Carboxylic acid group-containing PMMΔ20-65% by weight and PS
It consists of F15 to 40% and contains 2 carboxylic acid groups.
．． The content is 4X10-4 to 5.8X10-4 mol/g.

When PVC is less than 20% by weight, it becomes difficult to produce fibers with practically sufficient physical properties, and when PvC exceeds 40% by weight, alkali resistance decreases, and specifically, KO
The fiber loss after treatment in a 30% by weight f1 aqueous solution at normal pressure boiling for 1 hour exceeds 1.5% by weight.

If the amount of carboxylic acid group-containing PMMA exceeds 65% by weight, the physical properties of the fiber will deteriorate, making it impossible to obtain a fiber with practically desirable physical properties.

If the content of PSF is less than 15% by weight, the water conduction shrinkage rate of the fiber will exceed 25%, which is not preferable in terms of fiber physical properties. Furthermore, if the PSF exceeds 40, the strength and elongation of the fibers will be insufficient.

The content of carboxylic acid groups in the fiber is 2.4X10-4~5
．． It is necessary that the amount is 8 x 10-' mol/g. The content of carboxylic acid groups is 2.4 X 10-'
If it is less than mol/g, a sufficient liquid retention rate will not be obtained, specifically, the liquid retention rate will be less than 50% by weight. On the other hand, if the content of carboxylic acid groups exceeds 5.8 x 10-' mol/g, the liquid retention rate of the fiber improves, but the alkali resistance decreases, and the fiber cannot be boiled at normal pressure in a 30% by weight aqueous solution of KOJI. 1 in condition
Fiber loss after time treatment exceeds 1.5% by weight.

Introduction of carboxylic acid groups into the fibers is achieved by blending a carboxylic acid group-containing polymer with PVC/PMMA/PSF and wet spinning. However, the carboxylic acid group-containing polymer must be one that does not impair the alkali resistance of the obtained fibers, and furthermore, in consideration of process passability in the spinning process, it is important that it can be dissolved or dispersed in the spinning solvent. A preferred method is to make PMMA itself contain a required amount of carboxylic acid groups, and to copolymerize methyl methacrylate with a monomer containing a carboxylic acid group, such as acrylic acid, methacrylic acid, or a salt thereof. Therefore, carboxylic acid group-containing PMM^ is obtained, and in the case of acrylic acid copolymerization, it is preferable to copolymerize with 3 to 20% by weight, and in the case of methacrylic acid, to copolymerize with 3.5 to 24% by weight of methyl methacrylate.

The degree of polymerization of the PvC polymer used is 800 to 2500.
If the degree of polymerization is less than 800, it will not be possible to impart sufficient strength and elongation to the fiber properties, and if the degree of polymerization exceeds 2,500, gelation of the spinning solution will easily occur, making it difficult to stably form the fiber. It becomes difficult to manufacture. There is no particular regulation regarding the degree of polymerization of carboxylic acid group-containing PMMA or PSF, but any polymer that is normally used for films and molding materials may be used.

Furthermore, PMMA containing a carboxylic acid group that can be used in the present invention does not mean only methyl methacrylate monopolymer, but PMMA containing a small amount of plastic component.
This refers to all MMA-based polymers. As mentioned above, PMMA used in the present invention contains an appropriate carboxylic acid group, but even in this case, there is no problem even if a small amount of plasticizing component is contained.

Furthermore, the composition of the fiber of the present invention is not limited to PVC, carboxylic acid group-containing PMMA, PSF, but PvC, carboxylic acid group-containing PMMA,
Any polymer that can be mixed or dispersed in PSF to form fibers can be added as a composition, but the amount added is preferably less than 5% by weight. Furthermore, the added polymer must not impair alkali resistance.

It is also possible to add a small amount of light-resistant and heat-resistant stabilizers.

The fiber of the present invention is manufactured by a wet spinning method. As a solvent for the spinning dope, PvC, carboxylic acid group-containing PM
A single solvent or a mixed solvent can be used as long as it has the ability to dissolve and disperse MA and PSF. These solvents include dimethylacetamide, dimethylformamide, dimethylsulfoxide and acetone, with dimethylacetamide and dimethylformamide being advantageously used. A spinning stock solution is prepared by mixing, dissolving and dispersing PvC, carboxylic acid group-containing PMMA, and PSF in these solvents.The spinning stock solution is prepared by mixing polymers in advance and mixing them in a solvent, or by dissolving individual polymers in a solvent. Obtained by mixing solutions. The viscosity of the spinning stock solution at 50°C is often 100 to 2000 poise, preferably 150 to 1000 poise, and the solid content concentration of the stock solution is adjusted to these values. In spinning, it is preferable that the amount is 50% by weight or less.

The obtained spinning dope is extruded from a spinneret into a coagulation bath and shaped into fibers. The size of the spinneret is appropriately selected depending on the target thickness of the fiber. As the coagulant in the coagulation bath, water, alcohol, etc., which are non-solvents for the polymer, are used, but water is most preferred from an industrial standpoint. The coagulation bath consists of a mixed solution of the same solvent and coagulant used in the spinning stock solution.
The mixing ratio is 20-60% by weight of coagulant and 80-4% by weight of solvent.
A composition of 0% by weight is desirable. Coagulant ratio is 2
If the proportion of the coagulant is less than 0% by weight, the fibers discharged into the coagulation bath will adhere, whereas if the proportion of the coagulant exceeds 60% by weight, the coagulated filaments will not adhere, but a large amount of voids will form in the coagulated filaments, causing the fibers to stick together. This impairs the stretchability necessary to provide appropriate strength and elongation. Although the temperature of the coagulation bath is not particularly limited, it is preferably 20 to 40°C.

The obtained coagulated thread is stretched and washed in boiling water, and further stretched and washed as necessary to give it more suitable physical properties as a fiber. The fibers are collected dry or undried and used as raw materials for sheets such as paper for battery separators, knitted fabrics, and nonwoven fabrics. The method of washing, stretching, and drying the undrawn yarn after leaving the coagulation bath can be determined at the appropriate time depending on the polymer composition in the fiber, but it is especially important that the conditions do not impair the liquid retention rate of the produced fiber. There are no restrictions.

The fiber of the present invention has excellent alkali resistance at high temperatures, and specifically, the alkali resistance is 30% by weight
It is necessary that the fiber loss after 1 hour of immersion in an H aqueous solution and boiling under normal pressure is 1.5% by weight or less, and this value is lower than the value of polypropylene fibers measured by the same method.

Furthermore, in order to produce a superior battery separator for alkaline batteries, the fiber must have excellent liquid retention properties, and specifically, the fiber was soaked in deionized water for 24 hours and centrifuged for 10 minutes in an IOC. It is necessary that the liquid retention rate calculated from the following formula by measuring the dry weight of the fiber (width wi) and the dry weight of this fiber is 50% by weight or more.

The cross-sectional shape of the fiber of the present invention is not particularly limited, and can be selected from various shapes as long as it does not impair alkali resistance and liquid retention properties at high temperatures. In order to increase the bulk of the separator, which is a sheet-like molded product, and improve its liquid retention properties, the fiber cross section is changed from circular to flat, cross, or Y-shaped.
It is also effective to increase the voids between the fibers, and such irregular cross-section has the effect of further increasing the liquid retention properties of the separator, which is a sheet-like material. Further, the fineness of the fiber of the present invention is preferably 3 deniers or less, preferably 2 deniers or less. Such fine denier fibers enable the production of thinner separators, providing separators suitable for downsizing batteries. As the separator becomes thinner, the voids between the fibers that make up the separator decrease, which causes a decrease in liquid retention.However, when the fibers themselves have high liquid retention, such as the fibers of the present invention, the separator becomes thinner. It is possible to effectively compensate for the decrease in liquid retention caused by

<Example> The present invention will be explained below with reference to Examples.

Example 1 Using dimethylacetamide as a solvent, the degree of polymerization was 110.
PMMA and PSF, which are copolymerized with 0 PvC and 10% by weight of methacrylic acid (MAA), were dissolved and dispersed in a solvent at the mixing ratio shown in Table 1 to obtain a spinning stock solution. The solid content concentration at this time was adjusted so that the viscosity at 50°C was around 200 voids.

This spinning stock solution was discharged into a coagulation bath containing 60% by weight of dimethylacetamide and 40% by weight of deionized water at a temperature of 30°C.
An undrawn yarn was obtained. This undrawn yarn was stretched approximately 3 times in spring water, and after further washing in spring water, the yarn had a fineness of 1.0.
Obtained denier fiber. The performance of the obtained fibers is shown in Table 1.

The weight loss and liquid retention rate after KOI+ treatment shown in Table 1 are as follows:
This is a value processed and measured using the method shown in the text.

As shown in Table 1, if the PVC content is less than 20% by weight, sufficient stretchability cannot be obtained and spinning becomes impossible;
If it exceeds % by weight, the alkali resistance will be impaired.

Example 2 Using dimethylacetamide as a solvent, PvC and M
AAIO weight% copolymerized PMMΔ and PSF at a composition ratio of 30
The polymerization degree of PVC was changed to 150/20 as shown in Table 2, and the mixture was dissolved and dispersed in a solvent to obtain a spinning dope.

These spinning stock solutions were mixed with 60% by weight of dimethylacetamide,
It was discharged into a coagulation bath containing 40% by weight of deionized water and a temperature of 30°C to obtain an undrawn yarn. This undrawn yarn was stretched approximately 3 times in spring water, and after further washing in spring water, the yarn had a fineness of 1
．． A fiber of 0 denier was obtained. The content of carboxylic acid groups in the obtained fibers was 5.8 x 10-' mol/
It is g. Furthermore, the performance of the obtained fibers is shown in Table 2.

Table 2 Example 3 Using dimethylacetamide as a solvent, polymerization degree 110
0 pvc and 18 10% by weight copolymerized PMMA, PSP composition by changing the mixing ratio of PSP as shown in Table 3.
The mixture was dissolved and dispersed in a solvent to obtain a spinning stock solution.

These spinning stock solutions were mixed with 60% by weight of dimethylacetamide,
40% by weight of deionized water was discharged into a coagulation bath at a temperature of 30''C to obtain an undrawn yarn.This undrawn yarn was stretched approximately 3 times in boiling water, and further washed in boiling water. , fineness 1
．． A fiber of 0 denier was obtained. In addition, the amount of carboxylic acid groups contained in the obtained fiber was 5.8 x 10-' mol
/g.

The performance of the obtained fibers is shown in Table 3.

As shown in Table 3, when the PSF content is less than 15% by weight, the fresh water shrinkage rate of the fiber increases and thermal stability is impaired. On the other hand, if it exceeds 40% by weight, the physical properties of the fibers, particularly the strength, will deteriorate and the fibers will no longer be of practical use.

Example 4? Using dimethylacetamide as a container, PvC and M
AA copolymer PMMA, PSF composition is 30150/2
The content of carboxylic acid groups in the resulting fiber was adjusted by changing the copolymerization amount of MAA in PMMA, and the resulting fiber was dissolved and dispersed in a solvent to obtain a spinning dope.

These spinning stock solutions were mixed with 60% by weight of dimethylacetamide,
It was discharged into a coagulation bath containing 40% by weight of deionized water and a temperature of 30°C to obtain an undrawn yarn. This undrawn yarn was stretched approximately 3 times in spring water, and after further washing in spring water, the yarn had a fineness of 1
, O denier fibers were obtained.

Table 4 shows the performance of the obtained fibers.

As shown in Table 4, the content of carboxylic acid groups in the fiber is 2
．． If it is less than 4 x 10-' mol/g, sufficient liquid retention will not be obtained, and specifically, the liquid retention rate will be less than 50% by weight. On the other hand, if it exceeds 5.8 x 10-' mol/g, the liquid retention property of the fibers will increase, but the alkali resistance will be impaired.

Example 5 Using dimethylacetamide as a solvent, the degree of polymerization was 110.
0(7) 30% by weight of PVC, % by weight of MAAIO copolymerized P
A spinning dope was prepared by dissolving and dispersing in a solvent at a mixing ratio of 50% by weight of MMA and 20% by weight of PSF so that the solid content concentration was 35% by weight. The viscosity of the spinning dope at this time at 50°C was 204 voids.

This spinning stock solution was discharged into a coagulation bath of dimethylacetamide and deionized water having the mixing ratio shown in Table 5 to obtain an undrawn yarn. This undrawn yarn was drawn approximately 3 times in boiling water and further washed in boiling water to obtain fibers shown in Table 5.

Example 6 A paper was made by mixing 85% by weight of short fibers obtained by compressing the fibers obtained in Example 1, No. 1 into 6 embryos, and 15% by weight of polyethylene fibers with a cut length of 3InI11 as binder fibers, and bonding them by thermocompression. A nonwoven fabric with a weight of 50 g/rtT was obtained. The alkali resistance of this nonwoven fabric and the liquid retention rate of a 30% by weight aqueous KOH solution were measured.

As a result, as shown in Table 6 G, it was found that the electrolyte retaining property was superior to that of commercially available nonwoven fabrics.

Table 6 Note that the liquid retention rates in the above examples were evaluated using the evaluation method shown below.

Evaluation method for liquid retention rate (wt%) of KOI + aqueous solution: Cut out three test pieces of 5 cm x 5 cm from any part of the nonwoven fabric and weigh them (old). This test piece was mixed with KOH 30% by weight.
After being immersed in an aqueous solution (20° C.) for 1 hour, the droplet was cut off for 10 minutes, the weight (wi) was measured, and the weight (wi) was calculated using the following formula.

<Effect of the invention>

Claims (2)

[Claims] (1) Polyvinyl chloride 20 with a degree of polymerization of 800 to 2500
-40% by weight, 20-65% by weight of carboxylic acid group-containing polymethyl methacrylate, and 15-40% by weight of polysulfone, and the content of carboxylic acid groups in the fiber is 2.4 x 10^-^4-5 .8×10^-^4mol/
g, which has a fiber loss of 1.5% by weight or less after being treated in a 30% by weight KOH aqueous solution at normal pressure boiling for 1 hour, and has a liquid retention rate of 50% by weight or more by the measurement method shown in the text. A synthetic fiber with excellent alkali resistance and liquid retention properties. (2) Polyvinyl chloride 20 with a degree of polymerization of 800 to 2500
~40% by weight, 20~65% by weight of carboxylic acid group-containing polymethyl methacrylate and 15~40% by weight of polysulfone, with a content of carboxylic acid groups of 2.4 x 10^-^4 ~
A spinning solution prepared by mixing 5.8 x 10^-^4 mol/g and dissolving and dispersing it in a solvent selected from the group of dimethylacetamide, dimethylformamide, dimethyl sulfoxide and acetone is mixed with 20 to 60% by weight of coagulant and A method for producing synthetic fibers having excellent alkali resistance and liquid retention properties, which comprises spinning the fibers into a coagulation bath containing 80 to 40% by weight of the same solvent as the spinning dope.