JPH0881818A - Polyvinyl alcohol-based fiber subject to ready fibrillation - Google Patents

Abstract

PURPOSE: To obtain a fiber from a blend of a PVA-based polymer, PAN-based polymer and a specific graft copolymer, capable of easily forming fibrils by beating operation in an aqueous dispersion system thereof, thus useful as e.g. a substitutive material for asbestos or wood pulp. CONSTITUTION: This fiber is obtained from a blend of (A) a polyvinyl alcohol (PVA) >=1200 in degree polymerization and >=90mol% in degree of saponification, (B) a polyacrylonitrile-based polymer and (C) a graft copolymer prepared by grafting acrylonitrile to PVA. The blend contains 5-50wt.% (C) and 50-90wt.% total of the component A and the PVA component in the component C. For this fiber, the swellability of the phase involved in the component B is good, no component elutes into the water, and there is no trouble during its aftertreatment.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel easily fibrillizable polyvinyl alcohol (hereinafter abbreviated as PVA).
The present invention relates to a system fiber, and after being cut to 1.0 to 50 mm, it is easily fibrillated in water to form a pulp,
The present invention relates to a PVA-based easily fibrillated fiber which can be used as a reinforcing fiber for a cement product or the like as a substitute for asbestos, and can be used as a synthetic fiber raw material alone or mixed with wood pulp to produce a high quality synthetic fiber.

[0002]

2. Description of the Related Art In recent years, in order to protect the global environment and protect natural resources, mass consumption of wood pulp has been reconsidered, recycled paper and recycled pulp have been promoted, and PVA fibers such as vinylon and Demand for synthetic paper such as rayon, polypropylene, polyester, polyethylene is increasing.
In addition, restrictions on the use of asbestos have become stricter due to the theory of lung cancer in asbestos, and demand for alternative synthetic fibers such as vinylon and acrylic fibers is also increasing.

However, since these synthetic short fibers are too thick as compared with natural wood pulp and asbestos, the texture of the paper (surface texture) is poor, and the green (raw) strength of the slate is too weak. The use of wood pulp is limited or its use as special paper is limited, and development of ultrafine fibrillizable synthetic fibers is desired.

Attempts to fibrillate synthetic fibers in order to improve the quality of synthetic paper have been studied for a long time.
Among them, a technique for facilitating fibrillation by utilizing the phase separation behavior of a polymer alloy is well known. For example, Japanese Patent Publication No. 49-10617 and Japanese Patent Publication No. 50-3
No. 2326, Japanese Patent Publication No. 17-17608, Japanese Patent Publication No. 51-
In each publication such as 17609, polyacrylonitrile (hereinafter abbreviated as PAN) is used as a continuous phase, and PVA is graft-copolymerized with acrylonitrile (hereinafter abbreviated as AN) as an independent phase and oriented in the fiber axis direction. A technique is disclosed in which, when a material is cut and beaten in an aqueous dispersion system, fibrillation can be easily performed due to the water swelling property of the hydrophilic PVA portion, and a good synthetic fiber can be obtained. However, a series of these techniques is disclosed in, for example, Japanese Patent Publication No. 51-17609 (page 8, line 23), "The yarn obtained by such a series of operations has an island-shaped PVA part, It is a technique for modifying synthetic fibers in which an AN polymer is used as a continuous phase. When the content of PVA contained in the fiber is more than a certain value, the water resistance of the obtained fiber is lowered, the single yarns are stuck together, and the opacity of the obtained synthetic fiber is impaired. It has been pointed out that there are inconveniences such as foaming of the aqueous slurry and pollution of wastewater. These phenomena are such that in the process of promoting oriented crystallization of the polymer that constitutes the fiber by operations such as drawing and heat treatment, the oriented phase crystallized higher-order structure easily appears in the polymer forming the continuous phase, but the independent phase is formed. It tends to be difficult for oriented crystallization of the polymer to occur, and it is presumed that the crystallization of PVA, which is basically water-soluble, does not proceed and elutes in water.

On the other hand, in a fiber having PVA as a continuous phase, a component more swellable in water is dispersed as an independent phase in the fiber, and the cut fiber is dispersed in water and beaten to obtain PVA-based microfibrils. The method of obtaining is also known for a long time. For example, in Japanese Examined Patent Publication No. 47-31376, fully saponified PVA and partially saponified PVA are mixed at a fixed ratio, fiberized by wet spinning from an ordinary aqueous solution, then cut, dispersed in water and beaten. PVA
Methods for obtaining system fibrils are disclosed. The invention utilizes the difference in water swelling property due to the difference in saponification degree between two types of PVA, but in reality, a large amount of partially saponified PVA is used.
However, since PVA was contained in the fiber, elution of PVA from the fiber became a problem, and industrialization could not be achieved due to beating and foaming in the papermaking process.

[0006]

[Problems to be Solved by the Invention] PV among synthetic fibers
Since the A-based fibers have a hydrophilic group and have various excellent properties close to those of natural pulp such as asbestos and wood pulp, the appearance of PVA-based fibers that can be easily fibrillated is strongly desired. However, at present, the demand for fibrillated fibers containing PVA as a continuous phase is increasing, but in order to obtain PVA-based easily fibrillated fibers, in the above series of inventions,
The desired easily fibrillated fiber cannot be obtained simply by blending PVA with the graft copolymer to increase the content of PVA with respect to PAN to reverse the continuous phase and the independent phase. That is, just PV
If A is the continuous phase and PAN is the independent phase,
Fibrillation is not easy because the N phase is poor in water swelling.

In view of the above situation, the present inventors
PV is used as a continuous phase with VA as a continuous phase to easily form fibrils by beating in a dispersion system in water, and there is no component that elutes from the fiber into water, so that there is no trouble in the subsequent process such as foaming.
As a result of earnest efforts to develop an A-based easily fibrillated fiber, the present invention has been achieved.

[0008]

The present invention thus provides
(A) PVA having a polymerization degree of 1200 or more and a saponification degree of 90 mol% or more, (B) a polyacrylonitrile-based polymer, and (C) a graft copolymer in which acrylonitrile is graft-copolymerized with PVA. The proportion of the graft copolymer (C) is 5 to 50% by weight, and PVA
A fiber characterized in that the sum of (A) and the PVA component in the graft copolymer (C) is 50 to 90% by weight,
Further, the PVA component in the graft copolymer (C) is 9 to 67.
% Is more preferable, and the independent phase containing polyacrylonitrile as the main component is uniformly finely dispersed in the continuous phase containing PVA as the main component, and further, in the independent phase containing polyacrylonitrile as the main component. The PVA-based easily fibrillated fiber is characterized in that a third phase containing PVA as a main component is uniformly dispersed to form a structure having at least three phases.

The fiber of the present invention having the above-mentioned composition and having the above-mentioned structure can be easily fibrillated by a beating operation by being dispersed in water after being cut, and there is no elution component in water and foaming etc. A good quality pulp-like substance can be obtained without any trouble. Such a pulp-like substance is fine and has high strength, and is useful as a good substitute material for asbestos or wood pulp as a reinforcing fiber for cement products such as synthetic paper and slate.

The continuous phase of the fiber of the present invention has regularly the same hydrophilic hydroxyl groups as the cellulose of natural pulp, and when the molecules are stretch-oriented and crystallized, a strong crystal structure is formed by the intermolecular hydrogen bonds of the hydroxyl groups. Polymerization degree of 1
It must be 200 or more and PVA (A) having a saponification degree of 90 mol% or more. From the viewpoint of water resistance and strength of the obtained fibrils, the degree of polymerization and saponification of PVA used are preferably high, and the degree of polymerization is more preferably 1400 or more and the degree of saponification is more preferably 98 mol% or more, and the degree of polymerization is Over 1600,
Further, the saponification degree is more preferably 99.5 mol% or more.

The independent phase dispersed in the continuous phase of the fiber of the present invention is the phase separation behavior of PVA which is the continuous phase, the water resistance of the fiber,
Polyacrylonitrile (abbreviated as PVA) in terms of strength
The system polymer (B) must be the main component. In the case of other polymers, it is difficult to fibrillate due to the compatibility with PVA forming the continuous phase, and the water resistance and strength of the fibrils obtained even if fibrillated are unsatisfactory. The PAN-based polymer to be used in the present invention includes acrylic acid esters such as methyl acrylate, ethyl acrylate, and methyl methacrylate, vinyl esters such as vinyl acetate, acrylic acid, methacrylic acid, and sulfonic acid-modified monomers together with a homopolymer of acrylonitrile. A PAN-based copolymer obtained by copolymerizing an ionic monomer or the like at a ratio of 30 mol% or less is also a PA of the present invention.
It can be used as the N-based polymer (B).

In the fiber of the present invention, it is important that PVA contains a graft copolymer (C) obtained by graft copolymerizing acrylonitrile with PVA, in addition to the continuous phase PAN polymer (A) and the independent phase PAN polymer (B). That's the point. The graft polymer (C) improves the compatibility between the continuous phase and the independent phase by penetrating into the continuous phase or a part of the independent phase, and the PAN-based polymer is contained in the independent phase containing the PAN-based polymer (B) as a main component. It plays a very important role in forming the third phase containing PVA in the polymer (A) and the graft polymer (C) as a main component. When the fiber of the present invention is beaten in water, the third phase mainly composed of PVA dispersed in the PAN-based polymer (B) swells with water, which triggers and is an independent phase. PA
The N-based polymer (B) phase is swollen, and thus the entire fiber is divided into fibrils.

In order that the graft polymer (C) forms such a three-phase fiber structure and triggers fibrillation during water dispersion, the proportion of (C) in the total polymer is 5 to 5.
0% by weight, and the sum of the PVA-based polymer (A) and the PVA-based components in the graft polymer (C), that is, the total PVA of all polymers is 50 to 90% by weight (that is, the total PAN-based polymers in all the polymers). Of 10 to 50% by weight). If (C) is less than 5%, the effect of improving the compatibility between PVA and the PAN-based polymer is small, and the third phase containing PVA as the main component cannot be formed in the independent phase of the PAN-based polymer. Further, when (C) exceeds 50% by weight, the compatibility is improved and (B) becomes a partially continuous phase (that is, (A) is a partially independent phase), making it difficult to control the fiber structure. It is not possible to obtain the PVA-based easily fibrillating fiber that is the object of the invention. In addition, all PV in all polymers
A is less than 50% (that is, all PAN-based polymers are 50%
(A) is not satisfied, (A) does not form a continuous phase, and the PVA-based easily fibrillizable fiber aimed at by the present invention cannot be obtained. The total PVA in all polymers exceeds 90% (that is, the total PAN-based polymer is less than 10%).
Then, the amount of PAN-based polymer is small, and the continuous phase of (A) becomes too strong, so that split fibrillation cannot be performed.

P in the graft polymer (C)
When the content of VA is less than 9% by weight, the water swelling property of the independent phase is lowered, and the tendency toward fibrillation which is the object of the present invention tends to be lowered. When it is more than 67% by weight, the independent phase forming ability is increased. And the dispersibility of the independent phase becomes poor, and the desired fibrillation property tends to decrease, so P in (C)
When the content of VA is 9 to 67% by weight, it is easy to secure the easily fibrillating property of the fiber of the present invention, which is preferable. It is more preferable that the PVA content in (C) is 18 to 45% by weight.

Next, the PVA-based easily fibrillated fiber according to the present invention can be produced by the following method. That is, (A) a PVA-based polymer having a polymerization degree of 1200 or more and a saponification degree of 90 mol% or more, (B) a PAN-based polymer and (C) a graft copolymer obtained by graft-copolymerizing acrylonitrile with PVA, The proportion of the graft copolymer (C) in the polymer is 5 to 50% by weight, and PVA
The sum of the PVA component in (A) and the graph copolymer (C) is 5
A blend of 0 to 90% by weight is uniformly dissolved in a common solvent such as dimethyl sulfoxide (hereinafter abbreviated as DMSO), and then spun by a wet method or a dry-wet method, coagulated and dried, depending on the purpose. And stretching before and after drying to highly orientate and crystallize the polymer in the continuous phase containing PVA as a main component, and the independent phase containing PAN as a main component finely dispersed in the continuous phase and the independent phase. The PVA-based easily fibrillated fiber of the present invention can be produced by highly orienting it in the axial direction of the fiber of the third phase containing PVA as the main component uniformly dispersed therein.

The method for producing the fiber of the present invention will be described in more detail below. First, PVA which is the main component of the independent phase which is the core of fibrillation of the PVA-based easily fibrillated fiber according to the present invention
And a method for producing a graft copolymer of acrylonitrile (abbreviated as AN) will be described. The method for producing the graft copolymer is described in JP-B-48-38790, JP-B-49-5621, JP-B-49-11471 and JP-B-51-583.
The PVA used in the graft copolymer has a degree of polymerization of 500 or more and a degree of saponification of 80 or more from the viewpoint of water swellability which is a core at the time of fibrillation, graft reactivity, and water resistance when formed into fibers.
It is desirable to use the same mol% or more as the PVA as the continuous phase, but in the fiber as the continuous phase of the PVA of the present invention, the degree of polymerization and saponification are preferably higher than those of the PVA used in the continuous phase. It is desirable to use a slightly smaller one. However, when PVA having a polymerization degree of 500 or less or a saponification degree of 80 mol% or less is used, about 25% of PVA is obtained when AN is graft-polymerized, for example, when the reaction rate of AN monomer is 50%. Since it remains as an unreacted homopolymer, there is a risk of causing inconvenience such as causing sticking during spinning and generating bubbles during fibrillation.

The content of PVA in the graft copolymer is preferably 9 to 67% by weight. To achieve this composition range, the reaction rate of AN monomer and the formation of PAN homopolymer are taken into consideration. It is preferable that the amount of the AN monomer is 0.5 to 10.0 times the amount of PVA in the initial weight charging ratio. In the present invention in which PVA is used as the continuous phase, the graft copolymer composition obtained preferably has a large PAN component, and a more preferable initial weight charging ratio in consideration of the reaction rate of AN monomer and the formation of AN homopolymer is AN monomer. Is 1.5 to 5 times the amount of PVA

In the production of the graft copolymer,
It is also possible to replace a part of the AN monomer with another vinyl-based monomer, that is, vinyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, etc. In general, the monomer other than AN is 25% by weight based on the total amount of the monomer. It is desirable to stop within. The graft copolymer is obtained by a solution polymerization method, and the solvent used at this time is DMSO,
Examples thereof include dimethylformamide (hereinafter abbreviated as DMF), dimethylacetamide, an aqueous solution of zinc halide, an aqueous solution of potassium rhodanate, and the like. In terms of solution stability of the obtained graft copolymer and handleability in the spinning step, DM
SO is most preferable, and the fiber obtained from the spinning dope uniformly dissolved in such a good solvent is easy to form a higher-order structure, and a fiber excellent in fibrillation resistance, water resistance, strength, etc. is obtained. easy.

Next, a specific method for producing the graft copolymer will be described. First, PVA is heated and dissolved in the above-mentioned solvent in the range of 1 to 10% by weight at 5 to 80 ° C, and when a uniform solution is obtained, the temperature is kept at 45 to 60 ° C and a predetermined amount of monomer such as AN is gradually stirred. In addition, a predetermined amount of chain transfer agent is added. Next, while observing the progress of the graft polymerization, a predetermined amount of the polymerization catalyst is added little by little, stirring is continued for a predetermined time to proceed with the polymerization, and finally the chain transfer agent is added in excess to terminate the polymerization.

As the catalyst used in the graft polymerization reaction, ammonium persulfate (APS), potassium persulfate (KPS), azobisvaleronitrile, azobisisobutynitrile, benzoyl persulfate and the like can be used. KPS is preferred. The addition amount of the catalyst is preferably 0.01 to 3.0% by weight with respect to the monomer.
Further, as the chain transfer agent used in the graft polymerization reaction,
Dodecyl mercaptan (DM), thioglycolic acid, stearyl mercaptan, etc. can be used, but DM
Is preferred, and the amount used is 0.5 to AN monomer.
5.0% by weight is preferred.

The polymerization time depends on the polymerization temperature, catalyst, chain transfer agent,
Generally 1-2 depending on the amount of AN monomer.
It is 0 hours, and it is particularly important to control the conversion rate of the AN monomer in order to prevent gelation of the reaction system. That is, economically A
Ideally, the conversion rate of N monomer should be 100%, but in order to prevent gelation, the conversion rate is 30-80%.
It is preferable to terminate the polymerization at the stage of. A solution of the graft copolymer, which has been completely polymerized, is prepared separately from PVA.
The mixed spinning dope is very stable because it contains a graft copolymer, and is mixed at 40-80 ° C. Stable and no phase separation even if left for 1 to 2 days.

The resulting graft copolymer solution contains unreacted homo-PVA and non-graftable homo-PAN in addition to the unreacted AN monomer. These contents can be quantified by reprecipitating the polymer content from the reaction stock solution with methanol and then separately performing Soxhlet extraction with acetone, DMF, and hot water. That is, since only unreacted AN monomer can be removed with acetone, AN monomer and homo-PAN can be extracted with DMF, and AN monomer and unreacted homo-PVA can be extracted with hot water, the yield of the graft copolymer can be calculated from them. it can. When the unreacted AN monomer contained in the reaction stock solution is wet- or dry-wet spun as it is contained in the spinning stock solution,
It is possible to release it in the coagulation bath for recovery. However, because of its toxicity, it is preferable to heat and decompress the reaction stock solution before spinning if possible. The above-mentioned graft copolymer is an essential component in the constitution of the PVA-based easily fibrillated fiber according to the present invention, and in a system in which PVA and PAN are simply blended, the stability of the spinning dope is poor and phase separation occurs. It is easy to occur, so the spinning condition is bad and it is easy to break the thread,
Furthermore, as a result of observing the cross section of the fiber, the distribution of the independent phase is non-uniform, and fluff occurs during the drawing process, resulting in extremely poor processability.

The PVA forming the continuous phase of the easily fibrillated fiber according to the present invention has a degree of polymerization of 1200 or more and a degree of saponification of 90.
Mol% or more, preferably 98 mol% or more, and in view of mechanical properties of the obtained fibers and fibrils, water resistance, and phase separation behavior with the graft copolymer, the degree of polymerization is as high as possible and the degree of ken is as high as possible. Degree of polymerization is preferably 15 and degree of polymerization is 15.
It is more preferable that the saponification degree is 00 or more and the saponification degree is 99.5 mol% or more.

In the present invention, a polyacrylonitrile (co) polymer prepared separately is added when the PAN component to form an independent phase is insufficient depending on the condition of the graft reaction, that is, the reaction rate of the AN monomer. Add all P
The AN component is adjusted to be 10 to 50% by weight.

The PVA and the polyacrylonitrile (co) polymer optionally added are heated and dissolved in the same solvent as the solvent of the graft copolymer solution and mixed with the graft copolymer solution to prepare a spinning dope. There is a feature in that. Although the dissolved concentration varies depending on the degree of polymerization or saponification of PVA, it is preferably 3 to 30% by weight, and is governed by the viscosity of the mixed spinning dope. That is, generally, when a high degree of polymerization PVA is used, it should be a low concentration,
In the case of low degree of polymerization PVA, the concentration should be high, and the viscosity of the spinning dope should be adjusted to tens to hundreds of poise at the spinning temperature.

The spinning of the PVA-based easily fibrillated fiber according to the present invention should be carried out by a wet method or a dry-wet method that undergoes a coagulation process, and a preferable phase separation structure that facilitates fibrillation is not realized until the coagulation condition is controlled. To be done. The dry-wet method in which an air gap of 0.1 to several cm is provided between the spinneret and the coagulation bath is effective especially when the temperature difference between the spinning dope and the coagulation bath is large, but the concentration of the dope is low. It is disadvantageous when spinning a low viscosity stock solution. On the other hand, in the wet method in which the spinneret is in contact with the coagulation bath, when the temperature difference between the spinning stock solution and the coagulation bath is large, the stock solution is easily affected by the temperature of the coagulation bath at the time of discharging from the spinneret, resulting in viscosity unevenness Although it is likely to cause spots and requires some ingenuity, it has the advantages that a low-viscosity stock solution can be spun and that spinning can be performed without sticking even if the number of holes in the die is large. The selection of such a wet method or a dry-wet method should be judged depending on the state of the stock solution and the spinning conditions, and also affects the phase separation structure and productivity of the PVA-based easily fibrillated fiber of the present invention.

The spinneret from which the undiluted solution is discharged may be of the same size as that used in ordinary PVA spinning. The selection of the coagulation bath is particularly important for the expression of the fiber structure and the phase separation structure, and an aqueous solution of Glauber's salt, an aqueous solution of caustic soda, an aqueous solution of a mixture of glauber's salt and caustic soda can be used. In particular, an aqueous solution of Glauber's salt is particularly preferable. Further, from the viewpoint of developing the fiber structure and the phase separation structure, it is important to select the coagulation bath temperature and the draft ratio. Especially, when the PVA fiber having high strength and high elastic modulus is to be obtained, the coagulation bath with respect to the discharge speed is The draft ratio, which is the ratio of the ascending winding speed, is brought to the reverse draft side of 1.0 or less so that the polymer chain is sufficiently shrunk during solidification, and then the polymer chain can be formed along the fiber axis by stretching. It is important to orient as long as possible.

In order to develop a fiber structure for imparting high strength and high elastic modulus or a phase-separated structure for facilitating fibrillation to the filament solidified by such a method, a polymer chain or an independent phase is added to the fiber. It is necessary to orient in the axial direction, and appropriate washing, drying, stretching and heat setting steps are required. First, for the purpose of removing an inorganic salt and a solvent that are obstacles in the stretching step, the solvent is sufficiently washed with water which is also a swelling agent to replace the solvent, and then heat drying is performed to remove a residual solvent and a swelling agent.
If too much heat or too much time is used in the drying step, crystallization of PVA or PAN will proceed, which will adversely affect the subsequent stretching step, so efficient drying is important. Stretching is roughly divided into wet stretching performed in a liquid bath in a swollen state before drying and dry heat stretching with hot air or a hot plate after drying, but it is also effective to combine both and usually 3 to It is desirable to be stretched 20 times. When it is desired to emphasize easy fibrillation, it is better to refrain from dry heat stretching mainly by wet stretching, while dry heat stretching is preferred mainly when high strength and high elastic modulus and hot water resistance are desired. . Finally, for the purpose of completing crystallization and expressing dimensional stability, heat setting is performed at a temperature slightly higher than the dry heat drawing temperature, but the heat setting conditions should be as mild as possible for easy fibril formation. good.

The PVA fiber according to the present invention further comprises 1.
After being cut to a cut length of 0 to 50 mm, it is dispersed in water, sufficiently swelled, and then beaten with a device such as a mixer, a refiner or a beater to easily finely disperse along the fiber axis direction to form fibrils. To do. Furthermore, since there are few fluffs between the fibrils, the fibrils are dispersed without being entangled in a pill shape. This is a major feature of the easily fibrillated fiber of the present invention. Furthermore, because of its hydrophilicity, it is finely dispersed in a pulp form and exhibits excellent properties as raw material fibers for various materials such as synthetic paper and reinforcing fibers for cement products. The PVA-based easily fibrillated fiber according to the present invention can be continuously and endlessly produced as a yarn or tow, and can be cut into various cut lengths by a general synthetic fiber cutter, but at this point, it is divided and fibrillated. It is important for processability that no occurrence occurs.

The excellent properties of the easily fibrillated fiber of the present invention as a synthetic pulp are first exhibited by the complex three-phase structure formed inside the PVA type easily fibrillated fiber of the present invention. That is, P which is formed by phase separation in the solidification step and is scattered in the independent phase containing PAN as a main component and stretched along the fiber axis in the drawing step.
It is considered that the third phase containing VA as a main component is also present in the form of a layer or a rod along the fiber axis, and the third phase PV
The phase containing A as a main component has a much lower degree of oriented crystallization than the PVA phase forming a continuous phase, is most water-swellable, and does not dissolve in water due to the presence of the graft copolymer component. It is considered to be a thing. Thus, it is considered that the presence of this third phase facilitates fibrillation only when swollen by water.

The finely fibrillated pulp-like material can be left in a water-dispersed state without settling and solidifying, and can be used alone or in a mixture with a cellulosic natural pulp, such as tappies, round nets, It is possible to make paper with various paper making machines such as Fourdrinier, has excellent paper strength even without using a binder, and has a good texture (surface smoothness). It is possible to manufacture a synthetic fiber paper similar to such high-grade Japanese paper. It is also suitable as a binder fiber for various functional papers by taking advantage of the characteristics of fine pulp having excellent strength, and particularly in the production of functional papers containing a large amount of inorganic particles such as kaolin, talc and zeolite, according to the present invention. It is noteworthy that fibrils made from PVA-based fibers have excellent retention of inorganic particles, so that the green strength immediately after papermaking is increased and the productivity is improved.

Further, the holding power of the inorganic particles is important in the use of the asbestos substitute fiber in the production of slate products. Since the conventional substitute fibers such as vinylon and acrylic fiber are too thick as compared with asbestos, the cement particles at the time of papermaking. Omission occurs,
In order to compensate for this, it was necessary to use cellulose-based natural pulp together. The synthetic pulp obtained from the PVA-based easily fibrillated fiber according to the present invention does not need to be mixed with such a natural pulp because it is finely divided, and a cement product has an excellent reinforcing effect by adding a small amount of an organic fiber. Is advantageous in fire resistance performance. In the field of brake shoes and clutch plates, it is difficult to substitute asbestos due to the synthetic pulp obtained from the PVA-based easily fibrillated fiber according to the present invention, which is difficult to replace asbestos with the conventional organic synthetic fiber because it is thick and lacks retention of inorganic particles. But it became possible to substitute.

[0033]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples. Example 1 <Synthesis of graft copolymer>; 25 parts of commercial PVA 7.50 parts by weight having a degree of polymerization of 1250 and a degree of saponification of 99.0 mol% were used.
22.50 parts by weight of an AN monomer of a special grade reagent which was dissolved in 9.4 parts by weight of DMSO at 60 ° C. and was replaced with nitrogen gas and then the polymerization inhibitor was removed (PVA / AN = 1/3 weight ratio), polymerization A predetermined amount of dodecyl mercaptan (DM) as a degree adjusting agent and ammonium persulfate (APS) as a polymerization initiator were dispersed in 10 parts by weight of DMSO and then 0.31 part by weight was added, and the mixture was stirred in a separable flask. Graft copolymerization was carried out at 60 ° C. for 60 minutes. Finally, DM as a polymerization terminator was added to lower the temperature to stop the reaction. The total amount of DM added was 0.3 parts by weight. The obtained graft copolymer solution was dropped into acetone to coagulate, vacuum-dried and then Soxhlet-extracted separately with acetone, DMF, and water. From the weight reduction amount, the reaction rate of AN monomer, the grafting efficiency of PVA, and AN Grafting efficiency was determined. As a result, the reaction rate of AN monomer was 50%, PV
The grafting efficiency of A and AN was 75%. Therefore, the PVA content in the graft polymer was 40%.

<Preparation of spinning dope> Polymerization degree 1750 for forming continuous phase by mixed spinning, saponification degree 99.9 mol%
37.5 parts by weight of commercial PVA of 153.1 parts by weight of DM
A solution dissolved in SO was prepared in advance, and the solution immediately after the graft copolymerization was mixed to obtain the PVA component and P in all the polymers.
A spinning dope having an AN component weight composition ratio of PVA / PAN = 80/20 and a concentration of 12% by weight was prepared. In addition,
The proportion of graft copolymer in the total polymer is 25% by weight. Since gelation occurs when the temperature of the solution is lowered, 60 to 7
Immediately before spinning, degassing was performed while keeping the temperature at 0 ° C. <Spinning / Drawing>; The stock solution was heated to 100 ° C and the diameter was 0.08.
It was discharged from a spinneret of 100 mm × 100 holes into a coagulation bath made of an aqueous solution of Glauber's salt having a specific gravity of 1.23 and a temperature of 33 ° C. at a discharge speed of 2.4 g / min, and wet spinning was performed at a spinning speed of 1.1 m / min.
The spinning condition was good, and the yarn could be taken off continuously for a long time. The obtained yarn was subsequently subjected to 4-fold wet drawing in a drawing bath of the same composition as the coagulation bath at 90 ° C., washed with water and dried. The maximum draw ratio was as high as 9 times. The thickness of the obtained fiber is single yarn 3
It was denier and had a strength of about 5 g / d and an elongation of 18.

FIG. 1 is a faithful copy of a transmission electron micrograph (60,000 times) of the cross section of the obtained fiber. The obtained fiber was acetalized and fixed in size to water, then embedded in epoxy resin, cross-sectioned with an ultramicrotome, further stained with ruthenium oxide vapor, and then observed with a transmission electron microscope. is there. In the figure, the densely dotted portions are the PAN components, and have a three-phase structure in which the PVA-based third phase is further interspersed with the PAN-based independent phase.

<Fibrillation / papermaking> The obtained yarn was cut into a length of 2 mm with a guillotine cutter, made into an aqueous dispersion of 3 g / liter, and beaten through a disc refiner. The obtained pulp was fibrillated into fine fibers with a diameter of 0.1 micron or less, had good water dispersibility, and had no pill-like lumps. Then, using a tappy paper machine, paper making was carried out aiming at a basis weight of 40 g / square meter to obtain a synthetic fiber paper. The obtained paper has the texture of high-quality Japanese paper like a banknote, the surface smoothness is good, and the paper strength is about twice as high as that of the material made from the cellulosic natural pulp simultaneously made as a control, especially the wet strength. Was excellent.

Comparative Example 1 PVA / PAN = 80/20 was used as a raw material without using a graft copolymer, using PVA having a polymerization degree of 1700 and a saponification degree of 99.9 mol% and commercially available acrylic fiber cotton as a defatted PAN.
A simple blend compounded in a weight ratio is added to DMSO.
A stock solution having a concentration of 12% by weight was prepared by dissolving in, and wet spinning was tried in the same manner as in Example 2. However, the stock solution was very unstable, and it remained moggy during stirring. The stock solution temperature was lowered to 65 ° C, and the discharge speed was slowed down to spin the fiber, but the spinning condition was extremely poor and frequent yarn breakage occurred, resulting in normal operation. Spinning could not be done.

Comparative Example 2 PV used in Example 1 to form the continuous phase
A PVA-based fiber was wet-spun by the same method except that the degree of polymerization A was 1000 and the degree of saponification was 99.9 mol%. However, because the degree of polymerization of PVA used was too low, the maximum draw ratio was as low as 5 times, and the strength of the obtained drawn yarn was about 2 g /
It was as low as d. Therefore, the strength of the paper when it is made into synthetic paper is also reduced, and the purpose could not be achieved.

Comparative Example 3 PV used in Example 1 to form the continuous phase
PVA-based fibers were wet-spun by the same method except that the degree of polymerization A was 1700 and the degree of saponification was 88.0 mol%. However, since the degree of saponification of PVA used was too low, the yarn ejected from the coagulation bath was severely stuck, and continuous spinning was difficult. Further, it was attempted to cut the fibers barely obtained to make paper, but the wet strength of the obtained synthetic fiber paper was extremely weak, and almost no paper to be used for physical property measurement could be obtained.

Comparative Example 4 PVA10 having a degree of polymerization of 1250 and a degree of saponification of 99.0 mol%
4 parts by weight of the special grade AN monomer was added to parts by weight, and graft copolymerization was carried out in the same manner as in Example 1 to obtain a graft copolymer solution having an AN monomer reaction rate of 50% and PVA and AN graft efficiency of 75%. PVA in graft copolymer
Was 83%. Furthermore, DMSO solution of 1 part by weight of PVA prepared separately was added to prepare a spinning dope. The proportion of graft copolymer in the total polymer is about 69% by weight,
The proportion of the VA component was about 85% by weight. Then, wet spinning was performed in the same manner as in Example 1 to obtain a PVA fiber. Further, it was tried to cut the obtained fiber and fibrillate it by the same method as in Example 1, but it was difficult to fibrillate. It is presumed that the cause is that the proportion of the graft copolymer in the total polymer is too high.

[0041]

EFFECTS OF THE INVENTION Synthetic paper and functional paper obtained by making synthetic pulp obtained from the PVA-based easily fibrillated fiber according to the present invention are excellent in strength, water resistance, texture and the like, and substitute asbestos for the cement product. As the reinforcing fiber, it is possible to provide a fiber characterized by being excellent in retention of inorganic particles.

[Brief description of drawings]

FIG. 1 is a faithful copy of a photograph (60,000 times) taken by a transmission electron microscope of a part of the cross section of the fiber of the present invention.

[Explanation of symbols]

 a PVA component b PAN component c PVA component in PAN component d Fiber surface

Claims (2)

[Claims] 1. (A) Polymerization degree of 1200 or more, saponification degree of 9
A graft copolymer (C) comprising 0 mol% or more of polyvinyl alcohol, (B) a polyacrylonitrile polymer, and (C) a graft copolymer obtained by graft-copolymerizing acrylonitrile with polyvinyl alcohol.
Is 5 to 50% by weight, and the sum of the polyvinyl alcohol components in the polyvinyl alcohol (A) and the graft copolymer (C) is 50 to 90% by weight. Fibrillated fiber. 2. An independent phase containing polyacrylonitrile as a main component is uniformly finely dispersed in a continuous phase containing polyvinyl alcohol as a main component, and polyvinyl alcohol is added to the independent phase containing polyacrylonitrile as a main component. The polyvinyl alcohol-based easily fibrillated fiber according to claim 1, wherein the third phase as a main component is uniformly dispersed to form a structure having at least three phases.