JPH03241005A - Hollow acrylic fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having fine denier, high flexibility and improved bulkiness, water-absorption, etc., and usable as a precursor for carbon fiber by preparing a polymer soluble in a coagulation, washing or drawing solution of a wet or dry-wet spinning process and spinning a sheath-core conjugate fiber with a sheath-core spinneret using the above polymer as the core. CONSTITUTION:The objective fiber having a single fiber denier of <=1.5d (preferably <=1d) and containing a hollow core part continuing in the direction of fiber axis is produced by a wet or dry-wet spinning process with a sheath-core spinneret using a polymer soluble in a coagulation, washing or drawing solution (e.g. polyvinyl ether, PVA or polyethylene glycol) as the core.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to hollow acrylic fibers and a method for producing the same, particularly fine-grained hollow acrylic fibers and a method for producing the same.

[Prior Art] In recent years, the use of hollow acrylic fibers has been expanded, and applications are being developed that take advantage of their characteristics of low apparent specific gravity, bulk, and excellent heat retention, hygroscopicity, and water absorption. but,
Most conventional hollow acrylic fibers use a monohole ferrule that blows gas into the center with a hole diameter of 2 to 3 mm, and the single fiber denier is 10 deniers or more and the outer diameter is several tens of thousands of denier.
Most of them were very thick, 00 μm or more (for example, Japanese Patent Publication No. 56-21845, Japanese Patent Application Laid-Open No. 61-280).
14, JP-A-61-296115, etc.).

For this reason, there have been problems such as insufficient bulkiness, water absorption, etc., and limited use in clothing applications.

Conventionally, a technique has been proposed (Japanese Patent Application Laid-Open No. 73117/1983) in which polymers with different shrinkage rates are added to hollow acrylic fibers using a core-sheath die to make them finer. It is thick, with a denier or more, and there are large variations in fineness and shape between single fibers, and the sheath is easy to tear, making it difficult to form a complete hollow fiber. In addition, a technique has been proposed (Japanese Unexamined Patent Publication No. 142316/1983) that uses a joining type cap and makes it hollow under specific conditions.
Even the thinnest fibers have a diameter of 1.9 denier or more, and there are problems such as incomplete hollowness and roughness, large variations in fineness and shape among the single fibers, and large irregularities in the surface shape of the single fibers. Furthermore, when such hollow fibers are used as precursors for carbon fibers, the fibers tend to break due to the large amount of heat accumulated during the flameproofing process due to their particularly large fineness.
There were problems in that the carbon fibers could not be fired stably and the strength of the obtained carbon fibers was as low as 300 kg/mm2 or less.

[Problems to be Solved by the Invention] Therefore, the present inventors conducted extensive studies on fine-grained hollow acrylic fibers and arrived at the present invention. That is, an object of the present invention is to provide a hollow acrylic fiber with a fineness that could not be achieved using the above-mentioned conventional techniques, and a method for producing the same.

[Means for Solving the Problems] The above-mentioned problems of the present invention are as follows: (1) A hollow fiber characterized by having a single fiber denier of 1.5 denier or less and having a hollow part continuous in the fiber axis direction in the core part. Acrylic fiber (2) In a wet or dry-wet spinning method, a method for producing hollow acrylic fibers is characterized in that a polymer soluble in a coagulating, water-washing or drawing bath solution is introduced into the core using a core-sheath spinneret. It can be solved.

First, the hollow acrylic fiber of the present invention will be explained.

That is, the hollow acrylic fiber of the present invention is a hollow acrylic fiber characterized by having a single fiber denier of 1.5 denier or less and having a hollow part continuous in the fiber axis direction in the core, It is a hollow acrylic fiber with a fineness that is extremely difficult to use with this technology. The fineness of the material increases flexibility, and also significantly improves bulkiness, water absorption, etc. Furthermore, when this fiber is used as a separation membrane fiber, it is possible to increase the filling rate within the separation device, and the size of the separation device can be reduced. Furthermore, it can be used as a precursor for carbon fibers, greatly expanding its use in various applications.

A hollow part that is continuous in the fiber axial direction is a hollow part that is continuous without being divided midway in the fiber axial direction and has no holes on the fiber surface. This refers to the inside of the fibers that contain them. That is, for various separation purposes, it is essential that the hollow portion be continuous. Particularly when used as a precursor for carbon fibers, a collection of discontinuous voids is undesirable because it causes internal defects and deteriorates physical properties. The cross-sectional shape of the hollow part is preferably circular;
The closer the shape is to a perfect circle, the less likely local distortion will occur, which is preferable. The hollowness ratio is generally about 2 to 90%, more preferably about 4 to 70%, and is preferably adjusted depending on the purpose.

The single fiber denier is preferably 1.5 denier or less, more preferably 1 denier or less. That is, the thinner the carbon fiber, the better the flexibility, bulkiness, water absorption, filling rate into the separation device, and firing processability of carbon fibers.

Next, an example of a method for manufacturing the hollow acrylic fiber of the present invention will be explained.

That is, a wet spinning method and a wet-dry spinning method can be adopted as a method for spinning acrylic fibers, but a wet-dry spinning method is preferred because it can easily obtain fineness. In either case, it is important to use a core/sheath die to introduce a polymer soluble in the coagulation, water washing, or drawing bath solution into the core.

Polymers that are soluble in coagulation, water washing, or stretching bath solutions include various solvents used in coagulation bath solutions, such as organic solvents such as acetone, methanol, acetonitrile, dimethyl sulfoxide, and dimethyl formamide, or zinc chloride, nitric acid, and rhodan soda.

those soluble in any inorganic solvent such as rhodan nitrate;
and those soluble in any of the solvents used in water washing and stretching bath solutions, such as water, hot water, steam, and glycerin. Specifically, polyvinyl ether.

Polyvinyl alcohol, polyethylene glycol.

Polypropylene glycol, polyacrylamide.

Synthetic polymers such as polyacrylic acid, polyvinylpyrrolidone, polyethyleneimine, sodium polyphosphate, and semi-synthetic polymers such as viscose, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxylmethylcellulose, dextrin, dialdehyde starch, carboxyl starch, and also starch ,dextrin.

T selected from natural polymers such as rubber tragacanth
It indicates a species or a mixture of two or more species.

The acrylic polymer to be put into the sheath is at least 8
5 mol% or more of acrylonitrile and 15 mol% or less of a copolymerizable vinyl monomer, such as acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts;
Examples include copolymers with ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and their salts or alkyl esters.

The polymerization method is conventionally known solution polymerization.

Suspension polymerization, emulsion polymerization, etc. can be applied, but the degree of polymerization is generally set to an intrinsic viscosity ([η]) of 1.0 or more, preferably 1.5 or more. Furthermore, when used as a separation membrane, it is effective to add additives to create a porous structure.

By adjusting the discharge amount of these cores and sheaths, the hollowness ratio can be freely adjusted. As the cap, a well-known core/sheath cap can be used, but since an eccentric type has a hollow portion unevenly positioned, a concentric cap is preferable.

The number of die holes is generally about 300 to 10,000, but it is preferable to optimize from the viewpoint of productivity, die cost, etc.

The stretching ratio is generally about 2 to 15 times, but if the ratio is too high, the hollow space may be crushed, so
About 10 times is preferable. As for the stretching method, a combination of bath stretching, dry heat stretching, or wet heat stretching can be used, but a combination of bath stretching or wet heat stretching is preferred since the hollows are less likely to collapse. Even in the drying and densification process, excessive drying may cause the hollow to collapse, so
It is preferable to carry out at a low temperature of -150°C, preferably 100-130°C.

The hollow acrylic fibers of the present invention thus obtained can be widely used as clothing fibers, two-separation membrane fibers, precursors for carbon fibers, and the like.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Using a copolymer consisting of 99.4 mol% acrylonitrile (AN) and 0.6 mol% methacrylic acid, the concentration was 20%.
A dimethyl sulfoxide (DMSO) solution (Polymer A) with a concentration of 6% by weight was prepared, and a DMSO solution with a concentration of 6% by weight (Polymer A) was prepared using polyvinyl alcohol with a degree of polymerization of 4000.
Polymer B) was produced. Polymer A and Polymer B
Both were adjusted to a temperature of 35°C, and as polymers for the sheath and core, the pore diameter was O1↓2mmφ and the number of holes was 500.
Once discharged into the air through a concentric type core-sheath cap and run through a space of about 3-3, the temperature was 5℃.

It was coagulated in an aqueous DMSO solution with a concentration of 30%. The withdrawal speed was 40 m/min. The discharge amount ratio was 1 for the core and 4 for the sheath. After washing the coagulated yarn with water, it was stretched 3 times in a 3-stage hot water stretching bath, and a silicone-based elastomer was applied.
It is dried and densified by contacting it with the roller surface heated to ℃,
Further 3. The fiber bundle was drawn three times in pressurized steam at 7 kg/d to obtain a fiber bundle with a single yarn fineness of 1 d and a total denier of 500 D.

The obtained acrylic fiber had a hollow part continuous in the fiber axis direction in the core, and was a concentric type perfectly circular hollow acrylic fiber. The hollowness ratio was about 20%.

By using this hollow fiber as a membrane fiber for separation,
Compared to conventional hollow acrylic fibers with an outer diameter of 300 μm, the filling rate could be increased by more than 10 times.

In addition, the obtained fiber bundles are heated in air at 240 to 270°C to convert them into flame-resistant fibers, and then heated to a maximum temperature of 1400°C.
By firing in a nitrogen atmosphere, it was possible to stably produce a hollow carbon fiber having a hollow portion continuous in the fiber axis direction in the core.

Moreover, the apparent specific gravity of the obtained hollow carbon fiber was as low as 1.5, and the strength was as high as 500 kg/mm2.

Example 2 In Example (■), DM with a concentration of 12% by weight of corn starch (starch) manufactured by Sanei Toka Co., Ltd. was used as Polymer B.
An acrylic fiber bundle having a single fiber fineness of 1 d and a total denier of 500 D was obtained by spinning in the same manner as in Example 1 except that the SO solution was used. . The obtained acrylic fiber had a hollow part continuous in the fiber axis direction in the core, and was a concentric type perfectly circular hollow acrylic fiber. The hollow ratio is also about 20 as in Example 1.
%Met.

Comparative Example 1 Except for adding polymer A to the core in Example ↓,
Acrylic fibers were produced by spinning in the same manner as in Example ↓. The obtained acrylic fibers did not have hollow spaces, and only solid fibers were obtained.

When the obtained fiber bundle was fired to obtain carbon fibers in the same manner as in Example 1, the obtained carbon fibers had hollow portions and had a high apparent specific gravity of 1.8.

Comparative Example 2 Silk spinning was carried out in the same manner as in Example 1, except that air was blown into the core in Example 1, but dripping occurred during spinneret extraction and stable spinning could not be achieved.

Comparative Example 3 Silk spinning was carried out in the same manner as in Example 1 except that the discharge amounts of the core and sheath polymers were both increased by 2.5 times.
A hollow acrylic fiber having a single fiber denier of 2.5 denier was obtained. When the obtained hollow acrylic fibers were fired in the same manner as in Example 1, the fibers broke due to heat accumulation at the same flame resistance temperature, so flame resistance was achieved by lowering the maximum temperature by 20°C.

Furthermore, as in Example 1, firing was performed in a nitrogen atmosphere at a maximum temperature of 1500° C., but at the same speed thread breakage occurred and stable firing could not be achieved. As a result of firing at a lower firing speed of ↓/2, the obtained carbon fiber was a hollow carbon fiber with a hollow part continuous in the fiber axis direction in the core, but it had a lot of fuzz and the strength was 300 kg / wn 2 I could only get something low.

[Effects of the Invention] The hollow acrylic fibers of the present invention are hollow acrylic fibers that have a fineness that is extremely difficult to achieve with conventional techniques and have a complete hollow section, and are more supple than conventional thick hollow acrylic fibers. Along with this increase, bulkiness and water absorption properties have improved, and it has also become possible to use it as a precursor for carbon fibers, greatly expanding its use in a variety of applications.

Claims (2)

[Claims] (1) A hollow acrylic fiber having a single fiber denier of 1.5 denier or less and having a hollow portion continuous in the fiber axis direction in the core. (2) A method for producing hollow acrylic fibers, which comprises adding a polymer soluble in a coagulating, water-washing or drawing bath solution to the core using a core-sheath spinneret in a wet or wet-dry spinning method.