JPH04209840A - Production of pill-like carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber capable of being filled in a space at an optional filling density due to excellent bulkiness and resiliency by carrying out conjugate spinning of two or more kinds of pitches having different softening points and linear shrinkage factors in carbonizing, and using the resultant conjugate single filaments. CONSTITUTION:Two or more kinds of pitches, having <=10 deg.C difference between softening point and providing >=5% maximum difference in linear shrinkage factor in the fiber axial direction in carbonization after spinning are separately fed to a spinning apparatus, and simultaneously melt discharged from a conjugate nozzle. The resultant 50-10000 conjugate single filaments are then bundled and cut to 3-15mm length. The cut conjugate single fiber bundle is subsequently subjected to infusibilization treatment and then carbonization treatment to afford the objective fiber. Furthermore, the conjugate single filaments are preferably bundled by fixing positions in the transverse direction of the filaments using ethyl alcohol, etc.

Description

[Detailed description of the invention]

[00011

[Industrial Field of Application] The present invention relates to a method for producing fluffy carbon fibers having excellent bulk and elasticity. [0002] [0002] Conventionally, pitch-based carbon fibers having a high elastic modulus have been used as fillers for insulation materials and filters, catalysts,
Electromagnetic shielding materials and various matrices (e.g. plastics, metals, carbon, concrete, ceramics, etc.)
It is used as a reinforcing material in a wide range of fields such as space and aviation, general industry, and sports and leisure. [0003] However, since this type of pitch-based carbon fiber has a linear form, when it is used as a filler for insulation materials, filters, etc., the linear fibers are either woven as a cloth or Alternatively, carbon fibers can be laminated into a mat shape and formed into a binder with predetermined spaces.Also, when used as a reinforcing material for a three-dimensional matrix, carbon fibers are woven into a three-dimensional shape using a complicated three-dimensional weaving process. Afterwards, the matrix must be impregnated and shaped. For this reason, in the former case, not only is it extremely difficult to manufacture a structure with a certain gap, but it cannot be used at all for filling a three-dimensional space or for applications that require compressive elasticity. Moreover, in the latter case, there are problems such as requiring complicated processing steps for carbon fibers. [0004] Furthermore, when processing carbon fibers having a linear shape, there is a problem in that fluff formed by single yarn breakage generates carbon dust, which is undesirable in terms of work hygiene. [0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems associated with the use of conventional pitch-based carbon fibers. [0006]

[Means for Solving the Problems] That is, the present invention provides that (i) the difference in softening point is within 10°C, and the maximum difference in linear shrinkage rate during carbonization in the direction of the fiber axis after spinning is 5°C. % or more of two or more types of pitches are separately supplied to a spinning device t\ and simultaneously melted and discharged from a composite nozzle to prepare a composite single fiber,
(2) After bundling 50 to 10,000 composite single fibers, cutting them into lengths of 3 to 15 mm, (iii) subjecting the composite single fiber bundle to infusible treatment, and then subjecting it to carbonization treatment. The present invention relates to a method for producing a fluffy carbon fiber characterized by the following. [00071 The pitch used as the spinning raw material in the present invention is appropriately selected from the group consisting of petroleum-based pitch or coal-based pitch conventionally known in the field, for example, optically isotropic pitch and optically anisotropic pitch. All you have to do is select from the above. However, in this case, two or more pitches must be selected that have a softening point difference within 10°C and a maximum difference in linear shrinkage rate during carbonization in the fiber axis direction after spinning of 5% or more. Must be. [00081 Usually, the viscosity of the spinning pitch changes greatly depending on the temperature, so the optimal spinning temperature range is narrow, and in order to perform good spinning, it is a preferable condition that the viscosity of the pitch at the spinning temperature is similar, In the present invention, the difference in softening point between two or more pitches is within 10°C. If the softening point exceeds 10° C., stable spinning for a long period of time becomes impossible, which is not preferable. [0009] Furthermore, if the maximum difference in the linear shrinkage rate during carbonization in the fiber axis direction of the spinning pitch is smaller than 5%, the single fibers will simply be crimped separately, and a fluff-like fiber that is twisted together as a whole will not be obtained. do not have. [00101 Composite single fibers are prepared by separately supplying two or more pitches that meet the above conditions to a spinning device and melting and discharging them simultaneously from a composite nozzle. The spinning conditions depend on the type of spinning pitch, etc., and are not particularly limited, but for example, a sheath core type nozzle or a side-by-side type nozzle can be used. In addition, in this case, the discharge ratio of pitches with a large linear shrinkage rate is set to 30 to 90.
% is preferable. [0011] The obtained composite single fibers are bundled so that the number of filaments is 50 to 10,000, and then the number of filaments is 3 to 15]
It is cut to a length of 1111. When converging, it is preferable to fix the lateral orientation of the fibers using, for example, ethyl alcohol, a mixture of ethyl alcohol and water, or a mixture of ethyl alcohol and a silicone oil/water emulsion. [00121 According to electron micrographs and the like, the fluffy carbon fiber obtained by the present invention has a U-shaped shape as a whole with each filament twisted together, but the number of bundled filaments is 50. If the number of filaments is less than 1000, the single fibers will simply be crimped separately, and an overall twisted form will not be obtained, and the number of bundles of filaments will be less than 1000.
If it exceeds 0, it is not preferable because a U-shaped shape cannot be obtained as a whole and the bulkiness and elasticity deteriorate. Furthermore, the length of the cut composite single fiber is 3IIL.
[If the diameter is less than 11 mm or greater than 15 mm, a carbon fiber having a U-shaped shape as a whole cannot be obtained. Further, as for the sizing agent, it is important to use a sizing agent that has an appropriate focusing power. [0013] The fluff-like carbon fiber according to the present invention is obtained by subjecting the cut composite single fibers prepared as described above to an infusible treatment and then to a carbonization treatment. [0014] The infusibility treatment is carried out, for example, by filling a can or the like with the above-mentioned cut composite single fibers, and heating the cut composite fibers in an oxidizing gas for about 2 hours.
The carbonization treatment is carried out at about 600 to 3000°C in an atmosphere of an inert gas such as nitrogen. In this carbonization process, since the linear shrinkage rates of the components constituting the cut composite single fibers are different, each fiber is twisted mutually, and the cut composite single fibers as a whole take a U-shaped form. [0015]

[Function] The carbon fiber according to the present invention has two
It becomes fluffy due to the difference in linear shrinkage rate during carbonization between different spinning pitches, and not only exhibits excellent bulk and elasticity, but also has good processability and can be handled as a granular material. be. [0016]

[Examples] The present invention will be explained below with reference to Examples. [0017] Example 1 An optically anisotropic spinning pitch with a linear shrinkage rate of 5.8% in the fiber axis direction during carbonization and an optically isotropic spinning pitch with a linear shrinkage rate of 12.9%, Composite spinning is performed using a sheath core type composite nozzle in which the inner diameter of the inner nozzle is 0.2 mm and the inner diameter of the outer nozzle is 0.5 mm.
A composite fiber having a fiber diameter of 5μ and an optically isotropic spinning pitch of 70% was obtained. Using a sizing agent, this fiber is
After bundling into 0 filaments, they were cut into lengths of 7 mm, infusible at 290°C in air, and then heated at 1000°C in nitrogen.
Carbonized at °C. The obtained fluffy carbon fibers had a U-shape as a whole, with the fibers twisting each other. [0018] When this fluffy carbon fiber is filled into a container with its own weight to a height of 10 cm, the bulk density is 0.125.
It had a low 8/CC and had excellent heat insulation properties. Furthermore, if this is pressurized at 3 kg/cm2, the filling height will be 2.8
Compressed to a centimeter, bulk density is 0.44g
/cc. In this way, this fluffy carbon fiber can fill any space with 0.12
It was possible to use it by filling it with an arbitrary bulk density of 5 to 0 and 44 g/cc. Then, when the pressure was released, the filling height returned to nearly the original height and had good elasticity. Further, during this operation, almost no fiber waste was observed to fall off, and the product had excellent handling properties. [0019]

Effects of the Invention The fluffy carbon fiber according to the present invention can be handled as a granular material with excellent bulk and elasticity, so it can be used in any space as a filling material for machinery, in addition to insulation and filters. It can be used by filling with various packing densities, and various three-dimensional molded objects can be easily produced by composite molding with various binders and matrices. It should be noted that during processing and other handling of the fluff-like carbon fiber according to the present invention, almost no carbon dust is generated due to fluff formed by single filament breakage.

Claims (3)

[Claims] Claim 1: (i) Spinning two or more types of pitches in which the difference in softening point is within 10°C and the maximum difference in linear shrinkage rate during carbonization in the fiber axis direction after spinning is 5% or more. (ii) prepare composite single fibers by supplying them separately to an apparatus and simultaneously melting and discharging them from a composite nozzle;
After converging 00 pieces, cut them into lengths of 3 to 15 mm, and (
iii) After subjecting the cut composite single fiber bundle to an infusible treatment,
A method for producing a fluffy carbon fiber characterized by further subjecting it to carbonization treatment. 2. A fluffy carbon fiber produced by the method according to claim 1. 3. A three-dimensional molded article obtained by composite molding the fluffy carbon fiber according to claim 2 with a matrix.