JPH0197215A - Production of pitch fiber - Google Patents

Abstract

PURPOSE:To industrially and stably obtain the title fiber capable of providing homogeneous carbon fibers having excellent physical properties, by filtering a molten pitch containing a diatomaceous filter aid, having specific properties and dispersed therein through a surface capturing type filter medium having specific properties and using the resultant filtered pitch. CONSTITUTION:A diatomaceous filter aid having 1X10<9>-5X10<10>m/kg filtration average specific resistance in an amount of 0.1-10wt.% is dispersed in a molten pitch with <=5wt.% infusible substance content at a melt spinning temperature to provide a molten pitch having 1-10,000P viscosity, which is then filtered through a surface capturing type filter medium having <=30mum particle diameter at a point of 95% collection efficiency. The resultant filtered pitch is subsequently melt spun to afford the aimed fiber. Furthermore, e.g. a wire net type filter medium, is used as the surface capturing type filter medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing pitch fibers in the process of producing carbon fibers from petroleum or coal-based pitch.

[Background of the invention]

It is known that pitch fibers obtained by melt-spinning pitch that does not contain solid matter (hereinafter referred to as foreign matter) that does not melt at the melt-spinning temperature provide excellent carbon fibers. For this reason, various methods have been devised and implemented to prevent the inclusion and generation of foreign substances in the process of manufacturing pitch using petroleum and coal as a starting material. However, until now, even pitch manufactured under strict conditions has inevitably contained trace amounts of foreign matter. Moreover, such a method significantly increases the manufacturing cost of pitch, making it difficult to put it into practical use industrially.

Therefore, when fishing on a boat, the pitch is filtered when it is melt-spun.
Foreign matter is removed by furnace.

Conventionally, this furnace-based removal has been carried out by 1) using a surface-trapping filter with a fine mesh, 2) using a mesh pre-coated with a filter aid, and 2) sintering or entangling metal powder or metal fibers. The deep layer formed is carried out by a method using a filter medium, and (2) a method using a packed layer of glass particles, metal particles, etc. Of these, (■) generally has low filtration accuracy, and it is easy for minute amounts of foreign matter to get mixed into the filtration pitch, and foreign matter often includes gel-like substances that pass through the mesh, so foreign matter is not sufficiently removed. It is. The disadvantage of method (2) is that it is not only difficult to pre-coat industrially, but also that there is a significant increase in filtration resistance because foreign matter is captured on the surface of the pre-coat. ③ is sufficient to remove foreign substances, but if the content of foreign substances reaches a high concentration of 0.1 wt% or more, the filtration life will be shortened, and there are disadvantages in that it is difficult to regenerate the filter medium. . (2) The particle size and the layer thickness of the packed bed are related to the filtration accuracy, and in order to obtain sufficient IP penetration, the filtration resistance of the pitch in the packed bed becomes extremely large, and the amount of foreign matter trapped in the packed bed is The disadvantage is that as the amount increases, it becomes difficult to regenerate or replace.

In other words, a method for producing pitch fibers by obtaining pitch that does not contain foreign substances in an industrially stable manner at low cost has not yet been known.

As a result of intensive research into methods for removing foreign substances from pitch using different furnaces, the inventors of the present invention were able to remove foreign substances with high filtration accuracy from high-concentration pitch containing up to a few percent of foreign substances. We have discovered a method for removing foreign matter in a separate furnace that can be easily regenerated and, therefore, industrially stable pitch free of foreign matter can be obtained at low cost.

[Purpose of the invention]

The present invention has been made based on the above-mentioned findings, and an object of the present invention is to provide a method for producing pitch fibers that can be suitably used to obtain carbon fibers that are uniform and have excellent physical properties.

[Structure of the invention]

In the present invention, the infusible content at the melt spinning temperature is 5wt.
Filtration average specific resistance 1.0X109 to pitch that is below %
5.0XIO”m/kg (7) Diatomaceous filter aid 0.1
Melt pitch with a viscosity of 1 to 10,000 poise dispersed at ~10 wt% is filtered through a surface trapping type filter medium whose particle size at the point of 95% collection efficiency is 30 μm or less, and the filtered pitch is used for melt spinning. The characteristic lies in the method of manufacturing pitch fiber.

The pitch used in the method of the present invention needs to have an infusible content of 5 wt% or less at the melt spinning temperature, preferably 1 wt% or less.

If the content of infusible substances exceeds 5 wt%, it becomes impossible to obtain pitch free of foreign substances with high productivity.

Pitch having an infusible matter content of 5 wt% or less at the melt spinning temperature, preferably 1 wt% or less, is obtained by a conventionally known pitch production method using petroleum-free coal or the like as a starting material,
Alternatively, it can be obtained by further subjecting the obtained pitch to a conventionally known fractionation operation such as sedimentation separation or centrifugation at a temperature around the melt spinning temperature.

In addition, the diatom 'I filter aid has a filtration average specific resistance, that is,
Resistance to the mass of the auxiliary material per unit surface when the auxiliary material is a filter layer (for example, Iwanami Zensho "Chemical Engineering ■" 1964
The resistance described as average resistivity α1 on p. 118 of the October 30, 2015 edition) is 1.0 x 10'~1.0 x 10' and cannot be removed sufficiently, and 5.0 x 10'' s+/
If it exceeds kg, the filtration resistance becomes extremely large and the filtration operation becomes difficult.

Diatomaceous filter aids can be dispersed into pitch by adding and mixing the aids to pitch such as solid particles, then melting the pitch and stirring, or by adding the aids to the molten pitch and stirring. The addition amount of the auxiliary material needs to be in the range of 0.1 to 10 wt%, preferably 0.3 to 5 wt%, based on the pitch. If the amount added is 0.1 wt%, the ability of the auxiliary material to collect foreign matter will decrease, and if it exceeds 10-t%, the rate of formation of a separation cake will become too fast, and the period during which pitch can be efficiently filtered will be shortened. Becomes shorter.

The pitch in which the auxiliary material is dispersed has a viscosity of 1 to 10,000 poise, preferably 10 to 1,000 poise in a molten state.
0-4572, the particle size at the 95% point of collection efficiency is 30 μm or less (captures 95% or more of particles with a particle size of 30 μm). . If the viscosity of the pitch is less than 1 poise, the temperature will be too high than the spinning temperature that gives a viscosity of 100 to 2000 boys in normal melt spinning, and the removal of foreign matter by furnace will not be sufficient at the melt spinning temperature. On the other hand, if it exceeds 10,000 poise, the resistance when the material passes becomes too large, making filtration difficult. In addition, if the filter medium has a particle size exceeding 30 μm at the 95% collection efficiency point (particle size does not exceed 30 μm, it will not capture 95% or more), the filter aid material may form a cake on the surface of the filter medium. Until the filter is formed, leakage of the filter aid will occur, resulting in the filter aid being mixed into the filter pitch and making it difficult to regenerate the filter. As the surface-trapping type filter medium, conventionally known ones such as a wire mesh, a wire ring type filter medium, or a combination of these in multiple layers can be used.

As described above, filtration can be carried out stably for a long period of time, foreign matter in the raw material pitch is completely separated in the furnace together with the filter aid, and overpitched material with almost no foreign matter can be obtained. Additionally, if a separation cake grows on the surface of the filter medium during filtration and the filtration resistance becomes high, at an appropriate time, the material pitch can be switched from the previous filtration means to a similar means installed in parallel. . The material used for filtration up until now can be easily recycled by peeling off the cake layer formed on the surface using a mechanical peeling method or a method of applying reverse pressure using nitrogen gas, etc. can.

The filtration pitch is spun using a conventionally known melt spinning device under normal melt spinning conditions. As a result, uniform pitch fibers are obtained, and by carbonizing these pitch fibers by a conventionally known carbonization process, uniform carbon fibers with excellent physical properties can be obtained.

〔Example〕

The present invention will be further explained below using specific examples and comparative examples.

Example 1 Initial boiling point 350 obtained from a fluid catalytic cracker for petroleum fractions
°C decant oil is subjected to thermal decomposition polymerization reaction at 450 °C under a pressure of 0.5 kg/cm"G, and then at 450 °C.
Pitch was obtained by removing light components under conditions of an absolute pressure of 20 mm and 1 g. The obtained pitch had a viscosity of 400 poise at 360°C, and observation using a polarizing microscope showed that the mesophase content was approximately 100%. The optimum spinning temperature for this pitch is about 355°C, at which time the opening resistance is 4
Add 2wt% of diatomaceous filter aid of 9m/kg, mix well, melt at 360°C, and filter using a Fuji Plate filter made by Fuji Filter Co., Ltd. whose material is a surface-trapping type. went.

This filter has a particle size of 20μ at the 95% collection efficiency point.
m, the filtration area was 0.03927a+2. The obtained overpitch was spun at a temperature of 355° C. from a spinning nozzle having a single hole and wound at a winding speed of 800 m/win to obtain a pitch fiber having a fiber diameter of 12 μm. The pitch fibers were made infusible in air, and spinning was carried out stably for more than 30 minutes without yarn breakage. The obtained pitch fibers were carbonized at 1300° C. using a conventionally known carbonization device to obtain carbon fibers. This carbon fiber has a fiber diameter of 10.5 μm.

It was uniform and had excellent strength with a strength of 300 kg/mm''.

On the other hand, after a predetermined amount of filtration has been performed, the cake formed on the surface of the filter is easily peeled off by passing heated nitrogen gas in the opposite direction to the filtration process, and the cake is easily regenerated to its original condition. We were able to.

Comparative Example 1 Pitch was filtered under the same conditions as in Example 1, except that no silicon thin filter aid was added to the raw material pitch fibers. In this case, the filter became clogged in a short period of time, and the amount of filtration pitch obtained was less than 20% of that in Example 1. Further, when spinning was carried out in the same manner as in Example 1 using the obtained filtration pitch, yarn breakage occurred frequently and the longest time that spinning could be continued was about 5 minutes. Furthermore, when the obtained pitch fiber was carbonized in the same manner as in Example 1, the resulting carbon fiber had a fiber diameter of 10.5 μTI and a strength of 240 kg/mm, and compared to the carbon fiber of Example 1, the uniformity was 1 strength. It was inferior.

On the other hand, the same regeneration method as in Example 1 was performed on the clogged filter, but is it possible to easily regenerate it to its original state? “There wasn’t.

Example 2 The same method as in Example 1 was applied to coal tar hard pitch, which has a quinoline dissolution content of 0.1 wt%, is almost completely optically isotropic, and has a viscosity of 200 poise at 260°C. 4-
Filtration was carried out under the same conditions as in Example 1, except that 1% was added and the filtration temperature was 260°C. Using the obtained filtration pitch, the spinning temperature was 250°C using the same spinning device as in Example 1.
2 Spinning at a winding speed of 500 m/min to obtain a fiber diameter of 1
It was possible to obtain uniform pitch fibers of 0 μm. Spinning was carried out stably for more than 30 minutes without yarn breakage. Furthermore, the filter could be regenerated easily in the same manner as in Example 1.

Comparative Example 2 Filtration and spinning were carried out in the same manner as in Example 2, except that a surface-trapping filter with a particle size of 35μ at the point of 95% collection efficiency was used as the filter medium, but the spinning was unstable and the yarn broke. It happened frequently. In order to continue spinning for more than 30 minutes without yarn breakage, conditions had to be met to obtain pitch fibers with a fiber diameter of 15 μm or more.

Furthermore, the filter could not be regenerated as easily as in Examples 1 and 2.

〔Effect of the invention〕

According to the method of the present invention, pitch fibers that provide uniform carbon fibers with excellent physical properties can be produced industrially stably and at low cost.

Claims (1)

[Claims] Filtration average specific resistance 1.0 x 10^9 to 5.0
10^1^0m/kg diatomaceous filter aid is 0.1-10
It is characterized by filtering molten pitch with a viscosity of 1 to 10,000 poise dispersed in wt% through a surface trapping type filter medium whose particle size at the point of 95% collection efficiency is 30 μm or less, and then performing melt spinning using the filtered pitch. A method for producing pitch fiber.