JPH03227441A - Production of carbon fiber nonwoven fabric and apparatus therefor - Google Patents

Abstract

PURPOSE:To obtain the subject chemically stable nonwoven fabric having high uniformity by superposing many trays carrying sheetlike assemblies of pitch fiber placed thereon, subjecting the pitch fiber to infusibilizing treatment, further forming a continuous sheet and carbonizing the formed sheet. CONSTITUTION:Pitch fiber is continuously fed to porous trays 2 to form thin sheetlike assemblies of the pitch fiber on the trays 2. The resultant many trays 2 carrying the sheetlike assemblies placed thereon are then loaded onto a cart and fed into an infusibilizing furnace 7 to carry out infusibilization. Furthermore, the method for superposing the sheetlike assemblies is changed to move the assemblies from the upper part of the trays so as to partially overlap. Thereby, formation of a continuous sheet and carbonization thereof are carried out to afford the objective nonwoven fabric suitable as heat insulating materials, electromagnetic wave shielding materials, resistance heating elements, etc., used in a nonoxidizing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method and apparatus for manufacturing a pitch-based carbon fiber nonwoven fabric.

The present invention aims at making the sheet-like material thinner and making it infusible in order to equalize the temperature in the invulnerability process, which is the most difficult temperature control process in the manufacturing process of pitch-based carbon fiber sheets. The present invention relates to a spinning method and device that can handle an aggregate of fibers with very low strength without damaging the fibers, have a small device size, and have good thermal efficiency.

The nonwoven fabric produced by the present invention has high uniformity, is chemically stable, and exhibits excellent conductivity when the carbonization temperature is high. It shows excellent performance when used as materials, electrode materials, resistance heating elements, catalyst supports, and reinforcing fibers for composite materials.

(b) Prior Art Conventionally, pitch-based carbon fiber nonwoven fabrics have been made by centrifugal spinning or melt blow spinning of pitch.

According to the centrifugal spinning method, molten pitch is extruded through a die rotating at high speed and formed into a thread. The fibers blown away from the tie are transported by another air stream and received onto a belt-shaped receiver, where they are infusible and carbonized on the belt.In the case of the melt blow method, the pitch is extruded from a spinneret. is pulled by high-speed airflow and formed into a fiber.

The obtained fibers are received on a belt-shaped receiver and then infusible and carbonized on the belt. This entire process has conventionally been carried out substantially continuously.

This method has the advantage of simple equipment and easy operation, but if the pitch fiber layer is thick, it is likely to cause melting and foaming due to heat generation during infusibility, and if it is thin, the infusibility furnace will be very long. The disadvantage is that the cost is high. In order to improve this drawback, the air velocity in the infusibility furnace is increased, but since the pitch fibers in the infusibility stage are extremely weak, there is a problem that the fibers are damaged. Moreover, since the carbonization process is performed continuously with the infusibility process, it is often performed using a thin sheet, which poses a problem of increasing the size of the equipment and increasing the cost.

A common problem with these methods is that the fiber sheet deposited on the porous belt is uniform in the center but non-uniform in thickness and fiber orientation at both edges. In the case of nonwoven fabrics made of organic fibers, methods such as attaching a special scraping device to the belt or increasing suction from the back of the belt at the edge of the belt are used, but pitch fibers are brittle and weak, so such conditions are not possible. Forming a sheet into a sheet causes severe damage to the fibers, making it impractical.

In order to make the sheet uniform, conventional methods have been used to make it infusible or cut off both edges after carbonization, but unlike organic fibers, it is difficult to reuse nonwoven fabric scraps, and the yield is low. There is a problem of rising costs due to the decline.

(c) Problems to be Solved by the Invention The present invention solves the following problems in producing pitch-based carbon fiber nonwoven fabric:
In particular, the purpose is to solve the problem that processing with thin sheets is desired in the invulnerability process, which increases the size of equipment and increases costs.

Another object of the present invention is to solve the problem that a pitch-based carbon fiber nonwoven fabric is thin at both edges and has a different orientation from the center.

(d) Means for Solving the Problems The present invention involves stacking thin sheet-like aggregates of pitch fibers placed on porous trays, stacking a large number of trays while still being placed on the trays, and then infusibleizing them. This is a method for producing a carbon fiber nonwoven fabric, which is characterized in that the stacking method of the sheet-like aggregates is changed and the sheet-like aggregates are moved from a tray so that they partially overlap to form a continuous sheet, and then carbonized.

BACKGROUND ART The method of stacking a large number of articles to be heat treated on trays and charging them into a kiln has been used for a long time in bread baking ovens and the like. Furthermore, when firing ceramics, it is widely practiced to stack a large number of molded objects in pods on a trolley, and then pass them through a tunnel kiln for firing. Such a firing method has the advantage of reducing the installation area of the kiln and increasing thermal efficiency.

However, in cases where the objects are continuously supplied, such as heat treatment of fiber sheets, stacking them again requires extra manpower and equipment, and often damages the fibers, so this has rarely been done in the past. I never got hurt.

However, it has been found that when the sheet-like aggregates, which have been cut to a certain size and made invincible by placing them on a tray, are overlapped so that some of them overlap, there are various quality advantages that cannot be seen with conventional methods.

In one embodiment of the present invention, as shown in FIG. 1, the step of placing pitch fibers on a porous tray is preferably carried out by continuously supplying the tray and sucking it from the back of the tray. The pitch fibers are collected in sheet form.

After cutting the pitch fibers placed on the tray into each tray,
For example, as shown in FIG. 2, they are stacked and subjected to infusibility treatment in a tunnel kiln. In the case of small-scale equipment, the infusibility treatment can also be carried out in a batchwise manner using a box-shaped furnace.

The step of converting the sheet-like aggregate of pitch fibers placed on the tray of the present invention into a continuous sheet is carried out at a heat treatment temperature of 450 to 100.
Lightly carbonized pitch-based carbon fibers, which are preferably placed after mild carbonization at 0°C, have higher elongation than fibers before carbonization or highly carbonized fibers, and are less prone to entanglement and other problems that occur when they are made into continuous sheets. It has the advantage of less damage to the fibers during processing.

The sheet-like aggregate of pitch fibers placed on a tray is preferably formed into continuous sheets by needle punching, collision of columnar liquid streams, or entanglement by collision of high-speed air streams. This allows the sheet-like aggregate to have a large and uniform thickness. In addition, it is possible to reduce the number of thin layer structures by transferring the fibers between the eyebrows to the sheet-like aggregate formed in many thin layers when collecting on the tray.

When forming a sheet-like aggregate of pitch fibers placed on a tray into continuous sheets, the sheet-like aggregate is changed in direction by 90° from the direction of travel of the tray, as shown in Fig.
It is preferable that ~90% (area) be overlapped. This eliminates the non-uniformity in the basis weight and orientation of the edges of each sheet, making it unnecessary to remove the edges. If the overlapping ratio of each sheet is less than 10%, the orientation of the fibers in the overlapped portion will be strong in the direction parallel to the seam, making it easy to tear, which is undesirable. This is not preferable because the number of sheets to be overlapped becomes 10 or more, which tends to cause defects due to peeling between the eyebrows. The ratio of overlapping each sheet is preferably 50
~85%.

The device used in the invulnerability process of the carbon fiber nonwoven fabric of the present invention is as follows:
Preferably, the apparatus for infusibility of sheet-like aggregates of pitch fibers placed on trays is a tunnel-shaped furnace into which a large number of trays stacked on a cart are continuously fed. One embodiment of this furnace is shown in FIG.

The apparatus used in the carbonization process of the carbon fiber nonwoven fabric of the present invention is preferably a hearth roller furnace. A mesh belt type furnace is not preferred because it requires a cooling zone from the viewpoint of the belt's heat resistance, which increases costs.

Preferably, the wrapping device used in the spinning process of pitch fibers, which is the raw material for the carbon fiber nonwoven fabric of the present invention, transfers the pitch fibers floating in the air immediately after melt spinning onto a porous tray that transfers them while sucking them from the back side. It is collected as a sheet-like aggregate having substantially the same dimensions as the tray.

In the present invention, pitch fibers are manufactured using a spunbond spinning method in which molten pitch is spun from an ordinary spinneret and pulled by an air stream or rollers, or by spinning from a spinning hole or slit having an outlet in a high-speed air stream. It is preferable to produce it by either a melt-blowing spinning method, or a centrifugal spinning method, in which the liquid is dispersed by centrifugal force from a high-speed rotating pot.Among them, the melt-blowing method is particularly preferable.

Melt blowing methods include a method in which spinning holes are arranged in a line or a slit is provided in a slit-shaped high-speed airflow discharge hole, and a method in which one or several spinning holes are provided in a high-speed airflow discharge hole in a thank you letter. is known, but either method can be used for the present invention.

The pitch used in the present invention is a high softening point pitch that can be melt-spun and rendered invincible. The pitch may be isotropic or optically anisotropic.

(E) Function The present invention is capable of infusibility treatment by stacking a sheet-like aggregate of pitch fibers placed on a porous tray together with the tray and placing it on a transfer device such as a trolley, thereby reducing the volume of the infusibility device. It increases efficiency and improves energy efficiency. In addition, there is an advantage that there is no large increase in cost even if the sheet-like aggregate of pitch fibers is made thinner by stacking them together with the tray, and problems such as fiber deterioration, fusion, and foaming due to heat generation during infusibility treatment are avoided. There are advantages to avoiding it.

In the present invention, a large number of sheets of pitch fibers made invincible in this manner are stacked one on top of the other so as to partially overlap each other to form a continuous sheet. As a result, not only a long sheet with a large basis weight can be obtained, but also the uniformity of the sheet is increased, and the disadvantage that the sheet easily peels off into thin layers due to entanglement during overlapping is also eliminated.

Furthermore, the problem that when forming pitch fibers into sheets, the date and performance of the edges are different from those of the center can be solved by rotating the sheets by 90 degrees when stacking them.

(f) Example Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A spinning yarn with a diameter of 0.8 rm that uses petroleum pitch with a softening point of 285°C and an optical anisotropy fraction of 100% as a raw material and has a built-in tubular nozzle for discharging raw materials with an inner diameter of 0.3 fi and an outer diameter of 0.6 nm. Using a spinneret with holes, heated air was blown out from around the tubular nozzle to pull the molten pitch and perform spinning. Pitch discharge amount, 12g/80# hole/min, pitch temperature 310°C, mouth temperature 370°C1 heated air flow rate 0.4
The temperature of the heated air was 370°C, and the pressure of the heated air was 1.5 kIr/am2G.

The spun fibers are continuously fed into a tray made of stainless steel wire mesh with a collection section of 20 meshes in the manner shown in Figure 1, and are sucked from the back of the tray and placed onto the tray. Collected. Tray dimensions are 120 CIIX 12
The amount of pitch fibers collected was 60 g per tray.

20 sheets of pitch fibers were loaded onto a cart together with a tray, and the sheets were fed into an infusibility furnace as shown in FIG. 2, where they were infusible by air oxidation. The maximum temperature of the furnace was 300°C, the travel time to the maximum temperature position was 100 minutes, and the remaining residence time to the exit was 15 minutes.

Immediately after leaving the infusibility furnace, the crab was carbonized in an inert gas. The maximum temperature was 630°C, and the temperature increase rate was 10°C/min.

The conveyance direction of the obtained carbon fiber sheets was changed by 90", each sheet was overlapped by 75%, and 65 punches/C1+2 were formed.
After performing needle punching at a density of , carbonization was performed at 1400°C to obtain a carbon fiber male nonwoven fabric.

The obtained nonwoven fabric with a basis weight of 220 g/m2 has a high degree of symmetry;
It showed excellent strength and chemical resistance.

Example 2 Pitch fibers were produced by using a spinneret having 320 spinning holes in a row with a diameter of 0.15 am in a slit with a width of 0.3 mm in place of the spinning apparatus of Example 1. Pitch discharge amount 5
The pitch temperature was 305° C., the heated air temperature was 310° C., and the heated air pressure was 1.2 kg/a++2G.

When the same devices as in Example 1 were used as the fiber collection device, infusibility device, and carbonization device, a similarly excellent carbon fiber nonwoven fabric was obtained.

Example 3 When a spunbond spinning machine was used instead of the spinning machine of Example 1, a similarly excellent carbon fiber nonwoven fabric was obtained.

Comparative Example 1 Using the same spinning machine as in Example 1, a sheet was collected using a porous belt as a pitch fiber collecting device, and the obtained sheet was continuously subjected to infusibility treatment and carbonization treatment. The belt speed was slowed down so that the basis weight of the sheet and the final fabric weight of the nonwoven fabric obtained during collection were the same as in Example 1. (Conventional method) Because the obtained sheet is thick, it tends to become uneven due to heat generation during infusibility, and the temperature increase rate cannot be increased, and the transfer time to the highest temperature point in the furnace is 320 minutes. The above was necessary.

(G) Effects of the Invention The present invention relates to a method and apparatus for producing a pitch-based carbon fiber nonwoven fabric.

The present invention aims at making the sheet-like material thinner and making it infusible in order to equalize the temperature in the invulnerability process, which is the most difficult temperature control process in the manufacturing process of pitch-based carbon fiber sheets. The present invention relates to a spinning method and device that can handle an aggregate of fibers with very low strength without damaging the fibers, have a small device size, and have good thermal efficiency.

The nonwoven fabric produced by the present invention has high uniformity, is chemically stable, and exhibits excellent conductivity when the carbonization temperature is high. It shows excellent performance when used as materials, electrode materials, resistance heating elements, catalyst supports, and reinforcing fibers for composite materials.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a vertical cross section of a collecting device for pitch m fibers in an apparatus for producing a pitch-based carbon fiber nonwoven fabric according to the present invention. FIG. 2 is a schematic diagram showing a longitudinal section of the infusibility device. FIG. 3 is a schematic view of a laminated sheet viewed diagonally from above, illustrating an overview of a lamination method in which sheets of rendered pitch fiber or carbon fiber are laminated to form a continuous sheet. DESCRIPTION OF SYMBOLS 1... Fiber sheet, 2... Tray, 3... Suction duct, 4... Spinning machine, 5... Spinning cylinder, 6... Cutting device, 7... Infusibility furnace, 8・−・Tray transport vehicle. Applicants: Vetoso Patent Attorney Yatabe Sasai (411 people) Figure 1

Claims (7)

[Claims] (1) Thin sheet-like aggregates of pitch fibers placed on porous trays are piled up and infusible while many trays are stacked on top of each other, and the sheet-like aggregates are overlapped in a later process. 1. A method for producing a carbon fiber nonwoven fabric, characterized in that the carbon fiber nonwoven fabric is moved from a tray so that some parts overlap to form a continuous sheet, and then carbonized. (2) The step of placing the pitch fibers on a porous tray according to claim 1 is a step of continuously feeding the tray and sucking from the back side of the tray to collect the spun pitch fibers in a sheet form. A method for producing a carbon fiber nonwoven fabric, characterized by the following. (3) The sheet-like aggregate of pitch fibers placed on the tray according to any one of claims 1 or 2 is formed into a continuous sheet after mild carbonization at a heat treatment temperature of 450 to 1000°C. Method for producing carbon fiber nonwoven fabric. (4) The sheet-like aggregate of pitch fibers placed on the tray according to any one of claims 1 or 3 is formed into a continuous sheet by needle punching, collision of a columnar liquid flow, or high-speed air flow in addition to a partial overlap. A method for producing a carbon fiber nonwoven fabric, characterized in that the method involves entanglement due to collision. (5) When forming the sheet-like aggregate of pitch fibers placed on the tray according to any one of claims 1 or 4 into a continuous sheet, changing the direction by 90 degrees from the traveling direction of the tray,
A method for producing a carbon fiber nonwoven fabric characterized by overlapping. (6) A method for producing a carbon fiber nonwoven fabric, characterized in that the sheet-like aggregate of pitch fibers according to claim 1 or 5 is carbonized in a hearth roller furnace. (7) Pitch fibers floating in the air immediately after melt spinning are collected on a porous tray that is transferred while being sucked from the back side as a sheet-like aggregate with substantially the same size as the tray, and is used in subsequent steps. A method for producing a carbon fiber nonwoven fabric, characterized by sending the carbon fiber nonwoven fabric.