JPH01221556A - Production of carbon fiber nonwoven cloth having high bulk density - Google Patents

Abstract

PURPOSE:To obtain a nonwoven cloth of carbon fiber having high bulk density and uniform porosity and exhibiting excellent performance as a filter material, electrode material, etc., by heat-treating an infusibilized pitch fiber sheet in an inert atmosphere and carbonizing the product. CONSTITUTION:An infusibilized pitch fiber sheet is heat-treated in an inert atmosphere at a temperature between the softening point of the pitch fiber and (softening point + 100 deg.C) in a state pinched between a number of press rollers applying forces perpendicular to the surface of the sheet. The pressing force is e.g. 0.1-10kg/cm<2> and the ratio of the roller gap to the thickness of the sheet supplied to the roller is e.g. 50-95%. The heat-treated fiber sheet is carbonized to obtain an excellent carbon fiber resistant to interlaminar peeling in use.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for producing a carbon fiber nonwoven fabric having a high bulk density.

The carbon fiber nonwoven fabric produced by the present invention has a high bulk density and uniform porosity, and can be used as a filtration material, a packing material, a brake lining material, an electrode material, a catalyst carrier, an electromagnetic shielding material, a heat-resistant container, and a fiber. Demonstrates excellent performance when used as a reinforcing material for composite materials.

(Example) Conventional technology The production of pitch-based carbon fiber nonwoven fabrics, like other types of carbon fibers, is carried out by cutting the carbonized fibers and performing the same process as for ordinary synthetic fibers. Further, as a method specific to pitch-based carbon fibers, a method is used in which melt-spun pitch fibers are immediately collected in the form of a nonwoven fabric.

This method of immediately collecting pitch fibers in the form of a non-woven fabric after melt-spinning is almost the same as the spunbond method for synthetic fibers and the method widely used for manufacturing glass wool (short glass fibers) and rock wool. It was similar.

In the spunbond method for synthetic fibers, the melt-spun fibers are immediately drawn or pulled at a speed that is sufficient to cause oriented crystallization to stabilize the fiber structure, and then the fibers are stretched on a porous/textured belt such as a net conveyor or porous. The material is deposited in a sheet form on a drum by suction or other operations to form a nonwoven fabric.

In the case of short glass fibers or rock wool nonwoven fabrics, the spun glass melt is atomized by air current or centrifugal force, and deposited on a porous belt or drum by suction by air current or by heavy crab. Make it into a sheet.

Even in the case of synthetic fibers, glass short 1! Similar to the male method, there is a known method known as the melt blow method, in which the melt is pulled and thinned by air current to form a non-woven fabric.

Application of the spunbond method, centrifugal spinning method, and melt blowing method is also being considered in the case of pitch-based carbon li fiber nonwoven fabric, and the centrifugal spinning method was described in Japanese Patent Publication No. 47-3214.
No. 8, etc., and the melt blow method is described in JP-A-62-9 (
The technology is disclosed in No. 1320 and the like.

A common problem with these technologies is that they only disclose electrostatic treatment for non-melting and carbonization, but do not disclose what kind of nonwoven fabric can be produced by treatment in other conditions. That's true. - The nonwoven fabric produced by immediately collecting the melt-spun pitch fibers has a thickness of 1% in the thickness direction. It has the disadvantage that there is very little intertwining of miscellaneous objects, and it is easy to cause i4I separation between the eyebrows. In addition, it is difficult to process the fibers to make them bulky by crimping, twisting, or loosening them, and it is almost impossible to make them tight by entangling or shrinking them, so it is difficult to change the bulk. be.

C) Problems to be Solved by the Invention The present invention addresses the disadvantages of pitch-based carbon fiber nonwoven fabrics, which are that there is very little entanglement in the thickness direction, which tends to cause peeling between the eyebrows, and bulking or tightness processing. This solves the problem that it is difficult to make much change in blue height because it is difficult to
The purpose is to form a nonwoven fabric with high bulk density.

2) Means for solving the problem The present invention uses pitch fiber sheets that have been rendered invulnerable.
After heat treatment at a temperature above the softening point of the pitch fibers that have undergone the invulnerability treatment and below (softening point + 300>'C) while applying pressure in a direction substantially perpendicular to the surface of the sheet in an inert atmosphere, This is a method for producing a high bulk density carbon fiber nonwoven fabric, which is characterized by carbonization.

In the present invention, the sheet is pressurized during the carbonization treatment under static load or by being sandwiched between a number of pressing rollers.

Pressurization by a static load is performed by using a weight, pressurization by fluid pressure such as a hydraulic machine, pressurization by a screw, or the like. In the case of pressurization by static load, it is possible to use not only normal pressurization to the sheet surface but also isotropic pressurization.

The magnitude of pressurization under static load is 0", 1g~10kg/
an”, preferably 1-1000 g/e, m”
If the pressure is too large, the pitch fibers will be damaged, and if the pressure is too small, the effect of increasing the bulk density will be poor.

A pair of rollers rotating at approximately the same surface speed is used for applying pressure with the squeezing roller. If necessary, press rollers can be used.
You can hang an apron on it. Since the apron is required to have heat resistance, it is preferable to use a gold side made of a heat-resistant alloy or a woven fabric made of carbon fiber.

The surface of the squeezing roller is preferably made of a material such as ceramic, which has excellent heat resistance and high abrasion resistance.6 For example, it is preferable to use a roller made of thermally sprayed ceramic.

Squeezing can be done in one step, but it is preferable to do it little by little in multiple stages, especially when rollers are used. Sudden squeezing has the advantage of entangling the fibers, but it can damage the fibers. This is undesirable because it easily causes loss of fibers, and the floating fibers contaminate the manufacturing process equipment environment.

The compression is performed after a certain amount of infusibility treatment has been performed, and the pitch fibers after this treatment are referred to as pitch fibers that have undergone infusibility treatment. Pitch wI fibers before infusibility treatment have a low softening point and have the advantage of producing a pressurizing effect at low temperatures, but they have low strength and low elongation, so they have the disadvantage that the fibers are easily damaged during compression processing, and they are bulky. This is considered to be disadvantageous for increasing density. It is preferable that the infusibility treatment is carried out to a value of 20 to 90% of the lowest oxygen content at which complete infusibility is achieved. Although it is possible to produce the high bulk density carbon fiber nonwoven fabric of the present invention even if the oxygen content exceeds the level specified by There is a problem that the service life is short, and the yield of carbon fiber nonwoven fabric from pitch is low.

The compression rate is preferably 50% to 95% as a ratio of the roller gap to the thickness of the sheet fed to the rollers. If the compression rate is large, the compression effect will be small, and if the compression rate is small, the fibers will be This is undesirable because it tends to cause damage.

The number of stages of compression is preferably 3 to 50, most preferably 5.
If the number of 0 stages (~15 stages) is too small, the squeezing effect will be reduced and the fibers will be damaged, which is undesirable.If the number of stages is too large, the equipment cost will increase and the effect will tend to be saturated, which is undesirable.

The temperature of the compression treatment is higher than the softening point of the infusible pitch fiber and lower than (softening point +300°C).Preferably, the softening point +
25) °C~(softening point +150>'C).

Moreover, it is preferable that this temperature does not exceed 500°C.

When pressure treatment is carried out at 500 to 1400°C, there is a problem that the effect is not noticeable when it is carried out successively at a lower temperature.If pressure treatment is suddenly started in this temperature range, the elastic modulus of the fiber has already increased. Perhaps because of this, the compression does not proceed!
! ! ! The main problem is that the fibers are damaged. In addition, the squeezing that occurs when pressurized in this temperature range is at even higher temperatures (especially 88
There is a problem in that it is difficult to recover by carbonization treatment at a temperature of 00° C. or higher, and the bulk density is difficult to increase.

The softening point of pitch fibers is measured by determining the temperature at which compaction due to plastic deformation of the test sample ends when measuring the specific volume with a flow tester under constant rate heating conditions. The temperature is measured using a "Koka Type Flow Tester" manufactured by Shimadzu Corporation at a heating rate of 2° C./min.

In the present invention, the pitch fiber sheet used as a raw material is preferably produced by immediately collecting melt-spun pitch fibers.

Specifically, the molten pitch is spun through a normal spinneret,
Spunbond spinning method, which is pulled by an air stream or rollers; Melt-blown spinning method, which involves spinning from a spinning hole or spool with one outlet in a high-speed air stream; Although any centrifugal spinning method can be used, the melt blowing method is particularly preferred.

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. Preferably it is an optically anisotropic pitch, most preferably a pitch that is substantially 100% optically anisotropic.

The pitch used in the present invention may be one type pitch, or two or more types may be used.

The carbon fiber nonwoven fabric produced according to the present invention can be highly carbonized to provide high electrical conductivity. Carbon fiber nonwoven fabric with high electrical conductivity can be used as electromagnetic wave shielding material, surface heating element, and more! It can be used as an electrode material, catalyst carrier, etc.

The non-woven fabric produced according to the present invention can contain galvanic tA, carbon fiber fabric, ceramic 11 fabric, etc. inside or on the surface to improve electrical conductivity, shape stability, etc. Further, it is possible to have an adhesive layer or a pressure-sensitive adhesive layer for bonding with other materials. It is also possible to perform flocking, flocking, resin coating, lamination with film, etc.

Example 1 A petroleum-based pitch with a softening point of 285°C and an optical anisotropy fraction of 100% was used as a raw material, and a diameter of 0.81 was used, which had a built-in tubular nozzle for discharging the raw material with an inner diameter of 0.3 + s - outer diameter of 0.6 mm. Using a nozzle with a spinning hole, heated air was blown out from around the tubular nozzle to pull the molten pitch and perform spinning.

Pitch discharge! 12g/80H・min, pitch temperature 320
℃, base temperature 420℃, heated air flow rate 0.43kg/
The temperature was 420°C.

The spun fibers were collected on the belt by suction from the back side of a belt whose collecting portion was made of 20 mesh stainless wire mesh.

The obtained sheet was infusible under conditions such that the oxygen content was 75% of the complete infusibility treatment, and was further charcoalized while being compressed in an inert gas furnace.

The number of stages of compression was 7, and the compression rate of each stage was 80%.

The temperature was 250°C in the first stage, and the temperature was increased by 30°C in each subsequent stage for compression treatment.

The obtained carbon fiber nonwoven fabric had an apparent specific gravity of 0.22 and a basis weight of 80 Fi/am'. This nonwoven fabric has almost no delamination.
did not occur.

Comparative Example 1 A fiber sheet spun under the same conditions as Example 1 was subjected to infusibility treatment by a conventional method, and then carbonized without compression. The obtained carbon fiber nonwoven fabric has an apparent specific gravity of 0.0.
8, and the delamination was severe, and it separated into many thin fiber layers just by rubbing lightly.

Example 2 A fiber sheet spun under the same conditions as Example 1 was slightly infusible and then carbonized while being compressed under various conditions.The appearance of the obtained carbon fiber nonwoven fabric was determined by specific gravity and interlayer Checked for peeling. The results are shown in Table 1.

Table 1 Pressing conditions during carbonization and glabella peeling example 3 Using high softening point isotropic petroleum pitch with a softening point of 237°C as raw material, 30 spinning holes with a diameter of 0 and 15 mm were arranged in 3 linear rows.
The fiber is spun from a nozzle having 00 pieces, and immediately after cooling, it is suctioned by a slit-shaped traction nozzle, and is ejected into a space with an apex angle of 60° sandwiched between two net conveyors to be deposited.
Collected in sheet form.

The obtained sheet was infusible by a conventional method, and then carbonized while being squeezed with a roller in an inert gas. The treatment was carried out in seven stages, with a compression ratio of 80% in each stage and a temperature of 150°C in the first stage, increasing the temperature by 40°C in each stage.

The obtained sheet had an apparent specific gravity of 0.25, and almost no delamination occurred.

On the other hand, in the case of carbonization treatment without ordinary compression, the resulting sheet had an apparent specific gravity of 0.02 and severe peeling occurred between the eyebrows.

E) Functions and Effects of the Invention The present invention relates to a method for producing a carbon fiber nonwoven fabric having a high bulk density.

The carbon fiber nonwoven fabric produced according to the present invention has a high bulk density and a uniform porosity, and has a characteristic that it is difficult to cause so-called glabellar peeling, which causes destruction from a place where the fibers are less entangled during use.

The carbon fiber nonwoven fabric produced according to the present invention includes a carbon fiber material,
It exhibits excellent performance when used in packing materials, brake lining materials, electrode materials, catalyst carriers, electromagnetic shielding materials, heat-resistant containers, reinforcing materials for fiber composite materials, etc.

that's all

Claims (1)

[Claims] A sheet of pitch fibers that has undergone infusibility treatment is pressed in an inert atmosphere in a direction substantially perpendicular to the surface of the sheet, and the pitch fibers that have undergone infusibility treatment are heated at a temperature above the softening point of the pitch fibers (
A method for producing a high bulk density carbon fiber nonwoven fabric, which comprises carbonizing the fabric after heat treatment at a temperature below the softening point +300)°C.