JPH10219517A - Production of polyvinyl alcohol-based fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a polyvinyl alcohol fiber, capable of being finely and rapidly fibrillated and easily developable into the field for reinforcing nonwoven fabrics or rubbers by spinning a specific spinning solution into a solidification bath and manufacturing a yarn under specified conditions. SOLUTION: A solution prepared by dissolving 55-80wt.% polyvinyl alcohol having >=1,500 polymerization degree and >=99.5mol% saponification degree and a polymer selected from the group consisting of polyacrylontrile, polymethyl methacrylate and cellulose acetate in dimethyl sulfoxide is spun into a solidification bath consisting essentially of methanol. The dimethyl sulfoxide is then extracted from the fiber until the dimethyl sulfoxide content in the fiber attains <=2wt.%. Ketones having >=4 carbon atoms in an amount of >=5wt.% and water are then applied to the fiber and the resultant fiber is subsequently dried until the solvent content attains <=50wt.% in a gas containing mthanol at 2-10vol.% concentration and <=150 deg.C and then drawn to afford a polyvinyl alcohol fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Polyvinyl alcohol to be fibrillated below (hereinafter P
More specifically, the present invention relates to a method for producing a fiber having preferable properties as a rubber reinforcing fiber or a nonwoven fabric fiber.

[0002]

2. Description of the Related Art Conventionally, fibrillated fibers are mainly melt-spun by mixing or compounding two or more polymers.
It is manufactured by extracting one polymer with a solvent. Such fibers are used as synthetic leather or non-woven fabrics because they have an extremely fine diameter of 2-3 μm or less and have an excellent texture, but their strength is low and their effects cannot be expected as reinforcing fibers, and the extraction process is complicated. It is. On the other hand, many fibers which split a 2-3 denier fiber into 10 to 20 fibers by melt composite spinning are also produced as filaments, but such fibers have a diameter of 3 to 5 μm (0.1 to 0.3 μm) even after splitting. (Denier), the adhesiveness to rubber is poor, and the strength is as low as 4 g / d at most. The reinforcing property is poor, and it is not suitable for rubber reinforcement. In addition, when processed into a nonwoven fabric, it is divided in the carding process and the process passability is poor, so that it is difficult to develop a dry nonwoven fabric for use.

[0003] The rubber reinforcing fiber is usually used after being subjected to an adhesive treatment such as resorcinol-formalin latex and embedded in the kneaded rubber. The fibril fiber of the present invention is cut into 3 mm or less and the above adhesive is used. The fibers are added to the rubber without any treatment, and the fibers fibrillate to a diameter of 1 μm or less during kneading, thereby increasing the surface area and bonding. In such applications, a certain degree of strength is required in order for the fiber strength to exert a reinforcing effect, but a high fibrillation rate is also required. Since the fibril is formed by kneading, if the speed is low, it is necessary to lengthen the kneading time, resulting in deterioration of the rubber.

[0004] On the other hand, nonwoven fabrics are produced by beating fibers with a refiner or a beater and then forming a sheet (beating method), or by making a wet papermaking sheet or a card web into fibrillated water by water entanglement (water-jet method). It is roughly divided into two. In the beating method, if the fibrillation rate is low, the beating requires a long time, and the fibers are entangled and a uniform sheet having a good formation cannot be obtained. Also, in the case of the water junction method, if the fibrillation rate is low, it is necessary to increase the water pressure and further reduce the line speed significantly.

In response to such demands, the present inventors have proposed a fibrillated fiber using PVA suitable for rubber reinforcement or nonwoven fabric in Japanese Patent Application No. 8-119922. This is a technique of dissolving two incompatible polymers in a common solvent, solidifying and extracting, replacing with a bath composed of a mixture of alcohol, ketone, and water, and drying. It has gained. However, as is apparent from the number of holes in the spinning nozzle used in the examples,
It was performed on a laboratory scale, not on an industrial scale.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to industrially produce fibers having both the strength required for rubber reinforcement and nonwoven fabric applications and the fibrillation rate.

[0007]

That is, the present invention comprises 55 to 80% by weight of polyvinyl alcohol having a polymerization degree of 1500 or more and a saponification degree of 99.5 mol% or more, polyacrylonitrile, polymethyl methacrylate, and cellulose acetate. A polymer selected from the group is dissolved in dimethyl sulfoxide, and the obtained solution is spun into a solidification bath mainly composed of methanol, and dimethyl sulfoxide is removed from the fiber until the content of dimethyl sulfoxide in the obtained fiber becomes 2% by weight or less. After extraction, ketones having 4 or more carbon atoms are added to the fiber by adding 5% by weight or more to the fiber and water, and then the methanol concentration is 10% by volume or less until the solvent content becomes 50% by weight or less. The film is dried in a gas at 150 ° C. or lower and stretched.

The fibrillation index, which indicates the degree of fibrillability of the fiber obtained by the method of the present invention, is measured by the following method. 400 g of 4 g of fiber cut into 2 mm
A commercial mixer (National MX-
X40), beat at 11000 rpm for 5 minutes, drain the water, measure the weight without drying, collect 1/8 of the weight (0.5 g in terms of fiber), and re-weigh 400 cc.
And dispersed in water at 20 ° C. for 20 seconds using a mixer with a blade dropped, and water is added to make a total amount of 750 cc to obtain a sample. This is transferred to a cylinder having an inner diameter of 63 mm provided with a 17 mm diameter stopper and a 350 mesh filter at the bottom, and the time required for 750 cc to be filtered after removing the stopper is used as the fibrillation index. The time index is 2.1 seconds.

When the method of the present invention is used, an index having an index of 50 seconds or more can be obtained. This index is 50 seconds, 30m /
Whether a fibril is formed when water is applied to both sides of a nonwoven fabric with a basis weight of 100 g / m ² at a line speed of 80 kg / cm ^{2 at} a pressure of 80 kg / cm ² , or a fiber cut 2 mm into natural rubber 140 ° C after adding 20% by weight,
This corresponds to the boundary of whether or not to knead at 200 rpm for 15 minutes to fibrillate. By further strengthening the water-bridging conditions and kneading conditions, fibrillation can be sufficiently performed even if the fibrillation index is less than 50 seconds, but it is preferably 50 seconds or more in order to cope with any apparatus.

[0010] The strength of the obtained fiber is generally 3 g / d or more, as long as it generally satisfies the process passability for nonwoven fabric applications, but is preferably higher for rubber reinforcement applications, and is 7 g / d.
/ D, or more preferably, 9 g / d or more. In order to obtain such high strength, it is important that PVA, which is a strong component, is blended in the polymer of the fiber.
It must be 0 or more, and the degree of saponification must be 99.5 mol% or more. As for the copolymerization of PVA, copolymerization of a hydrophobic substance such as ethylene or an acrylate ester may be carried out as long as it is at most 10 mol%, but there is no advantage in using the copolymerized PVA.

If the PVA content is less than 55% by weight, not only is it difficult to satisfy the strength, but also process defects such as deterioration of the nozzle condition and increase in elution of the polymer into the solidification bath are caused.
Further, if any one of the degree of polymerization and the degree of saponification deviates from the scope of the present invention, similarly insufficient strength and process failure,
Further, in a wet beating or water-bending step, PVA is eluted, which leads to a problem that the liquid used in the treatment foams. On the other hand, when the content of PVA exceeds 80% by weight, the fibrillation rate decreases, and the desired performance cannot be obtained.

On the other hand, the polymer to be mixed with PVA must be dissolved in dimethyl sulfoxide (hereinafter abbreviated as DMSO) as a solvent and phase-separated from PVA in a DMSO-dissolved stock solution, and polyacrylonitrile (hereinafter abbreviated as PAN) is required. , Polymethyl methacrylate (hereinafter abbreviated as PMMA), cellulose acetate (hereinafter abbreviated as CA) and the like are preferably used. These polymers are undiluted PVA
It is necessary that these polymers have a phase-separated structure, that is, PVA is a sea, and that these polymers have a so-called sea-island structure. Further, from the viewpoint of spinning stability, the size of the island is preferably about 50 μm or less in diameter. For this purpose, it is necessary to appropriately select the molecular weight of these polymers. As long as the molecular weight of PAN or PMMA is in the range of 300 to 2,000, vinyl acetate or methyl methacrylate may be copolymerized at 20 mol% or less. As CA, any of mono, di, and triacetate can be used.

In order to industrially produce the fiber of the present invention, these polymers are dissolved in DMSO, spun into a solidification bath mainly composed of methanol to extract DMSO to 2% by weight or less, and then the carbon number is reduced. 5 or more ketones per fiber
% Or more and water, and then the methanol concentration is reduced to 2-1 until the solvent content of the fiber becomes 50% by weight or less.
It is necessary to adopt a method of drying in a gas at 0% by volume and 150 ° C. or lower, and performing stretching and heat treatment. In the present invention, the above numerical values of weight% are all based on the polymer.

The method for dissolving the polymer is not particularly limited, and two types of polymers may be dissolved alone in DMSO and mixed at an appropriate ratio. Either a method of adding and dissolving a polymer and a method of dissolving two kinds of polymers at the same time can be adopted. It is not possible to use an acid or an antioxidant as a polymer stabilizer in the spinning dope. It can be done without any problem. The concentration of the polymer in the stock solution is preferably from 10 to 30% by weight. Further, the temperature of the spinning solution is preferably from 50 to 140 ° C.

The spinning may be carried out by a wet or dry / wet method in a solidifying bath mainly composed of methanol. Generally, a mixed bath of methanol and DMSO is used as a solidification bath, and its composition is methanol / DMSO (weight ratio) = 40.
/ 60 to 90/10, and preferably 50/50 to 70/30 from the viewpoint of spinning condition and solvent recovery.

The extraction of DMSO can be carried out using methanol. However, it is necessary to extract DMSO to 2% by weight or less based on the polymer before adding water and ketones having 4 or more carbon atoms. . When a large amount of DMSO remains, the fibrillation performance is remarkably deteriorated. Therefore, it is preferable to perform extraction to 2% by weight or less, preferably 1% by weight or less, more preferably 0.5% by weight or less.

After extraction, ketones having 4 or more carbon atoms must be provided together with water in an amount of 5% by weight or more based on the weight of the polymer. Ketones include methyl ethyl ketone (M
EK), methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK) and the like having a carbon number of 4 or more may be used, but MEK or MIBK having a relatively low boiling point is preferable from the viewpoint of easy drying. Further, these can be used in combination. The application of such ketones may be carried out by using a mixed solution of methanol, water and ketones for the fiber after extraction, or after applying a mixed solution of methanol and water in advance, and mixing the above three kinds of liquids and ketones. It is also possible to apply a methanol mixture. The amount of ketones to be applied is required to be 5% by weight or more, and the larger the amount, the better the fibrillation performance.
The amount of water to be applied is preferably 3% by weight or more from the viewpoint of fibrillation performance. In addition, in addition to ketone and water, it is preferable to simultaneously contain methanol from the viewpoint of fibril properties,
The content of methanol in the fiber is preferably 20% by weight or more.

The fiber is subsequently dried, but must be dried and dried in a gas having a methanol concentration of 2 to 10% by volume and 150 ° C. or less until the content of the solvent (methanol, water and ketone) becomes 50% by weight or less. Must. As described above, in the dryer, methanol, water, and ketone are evaporated from the fiber, so that the solvent gas concentration in the atmosphere is inevitably high, especially when the methanol concentration is high, or when the drying temperature is high, This is because the fibrillation performance is extremely impaired. Therefore, for efficient industrial production, it is necessary that the methanol concentration in the dry atmosphere be 2% by volume or more, and from the viewpoint of the fibrillation rate, it is 10% by volume or less, preferably 8% by volume or less, and more preferably 5% by volume or less. % Or less, and the drying temperature is preferably 100 ° C. or less. On the other hand, the concentration of ketone or water in the dry atmosphere hardly affects the fibrillation performance. The fiber is usually 1
The drying atmosphere is entered in a state containing about 00% by weight of a solvent, but if the remaining solvent amount is reduced to 50% by weight or less with respect to the polymer (fiber) under the above conditions, then the methanol concentration is increased or the temperature is increased. However, there is no problem if high drying conditions are adopted.

After drying, 220-240 ° C. according to a conventional method.
Dry stretching is performed so that the total stretching ratio becomes 6 to 15 times.
The stretching ratio is appropriately adjusted since the required strength and elongation vary depending on the application. Here, the total stretching ratio is a value represented by the product of the wet stretching ratio and the dry stretching ratio. Further, heat treatment may be performed if necessary, but it is preferable not to shrink during the heat treatment because the fibrillation performance is not impaired.

The method of the present invention comprises the steps of extracting,
The application of water and ketones, drying method is specific,
In the process leading up to the present invention while verifying or modifying the hypothesis, the following is theoretically interpreted as follows. In the method of the present invention using a DMSO solution as a spinning solution, the stock solution is PVA
Despite the phase separation between the polymer and the dissimilar polymer, they interact with each other, so simply extruding from the nozzle and fibrillating does not cause fibrillation due to interfacial peeling as in the case of melt composite spinning, but solidification, extraction, and drying processes To promote the phase separation and reduce the interfacial adhesion.

It is known that PVA has no affinity for ketones, and particularly that ketones having 4 or more carbon atoms tend to cause aggregation of molecules. In addition, when the ketones are added to the fiber after extraction together with water, the ketone easily moves in the PVA in which the hydrogen bond is relaxed by the water, and easily reaches the heterogeneous polymer such as PAN or PMMA which is an island component. . Conversely, ketones hardly reach the island component without water. Next, in the drying step, the ketones act on the PVA at the sea-island interface to aggregate the PVA molecules at the interface, whereby the sea-island phase separation is completed. However, if the methanol concentration in the dry atmosphere is high, drying of the methanol from the fiber is slow, and when PVA aggregates at the interface due to the action of ketones, the effect is hindered by the presence of the methanol.
When the drying temperature is higher than 150 ° C., the drying of methanol is fast but the drying of ketones is also fast, so that the agglomeration of PVA cannot be exerted at the interface. In order for the mechanism of the formation of the sea-island phase separation structure to follow such a process, it is only necessary to prepare conditions for the ketones to work well in the initial stage of drying, and the boundary is equivalent to 50% of the remaining solvent. Has no particular restrictions.

[0022]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The elongation and solvent content in the examples were measured by the following methods. Strong elongation; measured in accordance with JIS L-1013. Solvent content; gas chromatograph (GC7, Shimadzu Corporation)
A), column HR-20M, detector TCD DMSO analysis: 1.5 g of a sample was dissolved in 100 g of water added with 2% by weight of triglyme and measured. An undissolved polymer insoluble in water such as PAN remains, but this is ignored. Analysis of water, MIBK, and methanol: 1.5 g of a sample was dissolved in 20 g of DMSO to which 2% by weight of triglyme was added to measure.

Example 1 PA having a polymerization degree of 1000 obtained by copolymerizing 5% by weight of vinyl acetate.
80 kg of N was added to 800 kg of DMSO together with 1 kg of 10% sulfuric acid as a stabilizer of PAN, and dissolved at 100 ° C. Then, the polymerization degree was 1700 and the saponification degree was 99.
120 kg of 8 mol% of PVA was added and dissolved at 100 ° C. to prepare a stock solution. (PVA 60%, PAN 40%) The undiluted solution was passed through a nozzle having 20,000 holes and a hole diameter of 0.08 mm, and methanol / DMSO was 7/3 (weight ratio).
Was wet-spun into a solidification bath at 5 ° C. with a spinning draft of 0.3 times. Subsequently, the DMSO was extracted with methanol at 20 ° C. to the remaining 0.1% while stretching by 3 times, and then methanol / MIBK / water = 40/40/20 (weight ratio).
10% by weight of MIBK and 15% by weight of water
It was applied to the fibers (total solvent content after immersion was 90% by weight). Next, the resultant was dried (first drying) with hot air at 80 ° C. (3% by volume of methanol at the time of blowing) until the residual solvent amount became 20% by weight, and then dried at 180 ° C. (second drying). The film was further stretched and wound at 230 ° C. so that the total stretching ratio became 14 times. The obtained fiber has a denier of 2 and a strength of 10.6 g.
/ D, elongation 7.2% and a fibrillation index of 150 seconds, which was excellent. Further, if the methanol concentration in the dryer is to be 1% by volume, the number of holes must be 6000 or less, and it is difficult to produce industrially at such a low concentration.

Example 2, Comparative Example 1 Fibers were produced in the same manner as in Example 1, except that the amount of residual DMSO after extraction was changed by changing the extraction time. Table 1 shows the results in that case.

[0025]

[Table 1]

As is clear from Table 1, the fibrillation index is greatly affected by the residual amount of DMSO at the time of adding MIBK and water. I can't get it.

Examples 3 to 5, Comparative Examples 2 and 3 With respect to MIBK in Example 1, the amount applied and the type of ketone were changed. Table 1 shows the respective conditions and the fibrillation index together with Example 2.

[0028]

[Table 2]

As a result, the ketones used have 4 carbon atoms.
When the amount is less than 5% by weight, or when the amount is less than 5% by weight, the fibrillation performance is remarkably reduced, and it is found that the fiber targeted by the present invention cannot be obtained.

Comparative Example 4 In Example 1, the fibers were immersed in a bath of methanol / MIBK = 50/50 (weight ratio) without using water when MIBK was applied. The strength and elongation of the obtained fiber were the same as in Example 1, but the fibrillation index was 7 seconds and hardly fibrillated.

Examples 6 to 8 and Comparative Examples 5 to 7 Fibers were produced in the same manner as in Example 1, except that the first drying conditions were variously changed. Table 3 shows the results.

[0032]

[Table 3]

From Table 3, it can be seen that the initial (first) drying conditions greatly affect the fibrillation, and the fibers of the present invention cannot be obtained under the drying conditions outside the range specified in the present invention. The strength and elongation were almost the same as those of Example 1.

Example 9, Comparative Examples 8 and 9 In Example 1, the proportion of PVA was changed. Table 4 shows the physical properties and process passability of the obtained fiber.

[0035]

[Table 4]

Comparative Example 8, that is, when the PVA ratio was 50% by weight, the fibrillation performance was good, but the polymer eluted into the solidification bath was large and the processability was poor. On the other hand, if the PVA ratio exceeds 80% by weight, the strength is increased, but fibers having a fibrillation index of 50 seconds or more cannot be obtained.

Example 10 PM of polymerization degree 1200 obtained by copolymerizing 5% by weight of vinyl acetate
A solution of MA in DMSO at a concentration of 20% by weight;
A solution in which PVA used in Example 1 was dissolved at 20% by weight was mixed and stirred at a ratio of 45/55 (weight ratio) to prepare a stock solution. (PVA / PMMA = 55/45) This was spun in the same manner as in Example 1 to obtain a fiber having a strength of 1
It had good physical properties of 1.0 g / d, 7.0% and a fibrillation index of 170 seconds, and also had good processability without any problem.

Comparative Examples 10 and 11 Spinning was carried out under the same conditions as in Example 10 except that the degree of polymerization of PVA was changed to 1000 (Comparative Example 10) and the degree of saponification was changed to 98.2 mol% (Comparative Example 11). In Comparative Example 10 in which the degree of polymerization was lower than the range of the present invention, poor solidification caused many yarn breakage on the nozzle surface, and the polymer was eluted into the solidification bath so that spinning was impossible. On the other hand, in Comparative Example 11 having a low degree of saponification, although there was no particular problem in the processability, PVA was insufficiently crystallized, so that PVA was dissolved and foamed by mixer beating in the fibrillation index.

[0039]

According to the present invention, it has become possible to provide a PVA-based fibril fiber which can be ultrafinely and quickly fibrillated, and the development of nonwoven fabric and rubber in the field of reinforcement has been facilitated.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akio Omori 1621 Sazu, Kurashiki City, Okayama Prefecture Kuraray Co., Ltd.

Claims (1)

[Claims] 1. A polymerization degree of 1500 or more and a saponification degree of 99.5.
55% to 80% by weight of polyvinyl alcohol of at least mol%
And a polymer selected from the group consisting of polyacrylonitrile, polymethyl methacrylate, and cellulose acetate dissolved in dimethyl sulfoxide, and the resulting solution is spun into a solidification bath mainly composed of methanol, and the dimethyl sulfoxide in the obtained fiber is dissolved. After extracting dimethyl sulfoxide from the fiber until the content becomes 2% by weight or less, the fiber is provided with 5% by weight or more of ketones having 4 or more carbon atoms and water, and subsequently, the solvent content is reduced to 50% by weight or less. A method for producing a polyvinyl alcohol fiber, comprising drying in a gas having a methanol concentration of 2 to 10% by volume and a temperature of 150 ° C. or lower until drawing, and stretching.