JPH08337920A - P-aramid pulp and its production - Google Patents

Abstract

PURPOSE: To obtain the subject readily dispersible pulp having a high ability to retain the dispersed state of a powdery filler by spinning a low-polymerization degree p-aramid dope containing a p-aramid and an alkali (ne earth) metallic chloride in a polar amide-based solvent and then fibrillating the resultant fiber. CONSTITUTION: An optically anisotropic low-polymerization p-aramid dope containing 4-10wt.% p-aramid (having 1.0-2.5dl/g intrinsic viscosity) in a polar amide-based solvent and 2-10wt.% alkali metallic or alkaline earth metallic chloride is spun into an aqueous solvent. The resultant p-aramid fiber is washed and cut in a wet state thereof to afford staple fibers, which are then dispersed in a water in a raw material tank 2, fed to a refiner 4 for wet beating with a liquid feed pump 3, fibrillated and subsequently returned to a pulp slurry tank 1. Thereby, the resultant pulp have the Canadian freeness (xml) and the BET surface area (ym<2> /g) satisfy the formulas 0.000035x<2> -0.036x+12<=(y)<=0.000026x<2> -0.039x+17; 100<=(x)<=630 and 2<=(y)<=12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a para-aramid pulp obtained by fibrillating para-oriented aromatic polyamide (hereinafter abbreviated as para-aramid) fibers and a method for producing the same. Particularly, the present invention relates to a para-aramid pulp having excellent material properties such as filler retention, dispersibility, and reinforcing effect, which are useful in friction material applications, sliding material applications, gasket applications, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art As conventional para-aramid pulp, Tw
aron (trade name; made by Akzo Nobel), Kevlar (trade name: du)
(Made by Pont) is known. These para-aramid pulps are manufactured by a method in which dry continuous fibers are mechanically cut into short fibers and mechanically fibrillated by a refiner. And the conventional para-aramid pulp is manufactured by using a single disc type, a double disc type, or a multi-disc type refiner.

In general, as an index showing the degree of fibrillation of pulp, Canadian freeness (hereinafter sometimes referred to as freeness or freeness) and BET specific surface area (hereinafter sometimes referred to as specific surface area) are measured. The value is used. Generally, it can be said that the higher the degree of fibrillation is, the higher the specific surface area is and the lower the freeness is. Freeness is a measure of water retention, and low freeness means good water retention. In other words, pulp with low freeness is expected to have a high ability to maintain the dispersed state of various fillers and blends.

A friction material for brakes, which is one of the main uses of para-aramid pulp, is a molded product made of a mixture of a plurality of powdery fillers (fillers) having different specific gravities and containing para-aramid pulp. The role of para-aramid pulp in these components is to evenly disperse the powdered filler, to maintain a uniform dispersion, to reinforce the molding precursor called preform, and to reduce the amount of wear during use. It is to let.

The role of para-aramid pulp as a material for gaskets, which is another major application, is to disperse a mixture of a powdery filler having a different specific gravity and a rubber component and to reinforce it in the form of a sheet. It is an effect.

In any case, the dispersibility of the para-aramid pulp itself in the formulation has a significant effect on the performance of the product,
When para-aramid pulp having poor dispersibility is used, it is considered that the performance of the product is deteriorated. It has been considered that conventional para-aramid pulp requires sufficiently developed fibrils to maintain the dispersed state of the powdery filler. However, if the amount of fibrils is large, pills tend to be formed, and the dispersion of para-aramid pulp is often insufficient, and improvement has been desired.

For example, Japanese Patent Laid-Open No. 5-339859 discloses a method in which pulp is pre-opened and used in order to improve the dispersibility of para-aramid pulp in a blend.

[0008]

In addition to the high heat resistance inherent in para-aramid fibers, para-aramid pulp is easy to uniformly disperse in the mixture as pulp, and its ability to maintain the dispersed state of the powdery filler. Is expected and important. In order to maintain the dispersed state of the powdery filler, it is effective that the fibrils of the para-aramid pulp are sufficiently developed. However, if the amount of fibrils is too large, pills tend to be formed, and as a result, it becomes difficult to disperse the para-aramid pulp in the blend sufficiently uniformly.

An object of the present invention is to provide a para-aramid pulp having good dispersibility while having the ability to maintain the dispersed state of the powdery filler.

[0010]

The present invention comprises the following inventions. [1] The relationship between Canadian freeness and BET specific surface area is expressed by the following equation (1) 0.000035x ² − 0.036x + 12 ≦ y ≦ 0.000026x ² − 0.039x + 17 (1) (where x and y are respectively Represents Canadian freeness (ml) and BET specific surface area (m ² / g),
The range is 100 ≦ x ≦ 630 and 2 ≦ y ≦ 12. ) A para-aramid pulp characterized by being represented by.

[2] The weight-weighted average fiber length is 0.6 to 1.
Para-aramid pulp according to the above item [1], in the range of 2 mm.

[3] In the polar amide solvent, the intrinsic viscosity is
Para-aramid in the range of 1.0 to 2.5 dl / g 4
It is obtained by spinning a low-polymerization degree para-aramid dope containing 10 to 10% by weight and 2 to 10% by weight of a chloride of an alkali metal or an alkaline earth metal and having optical anisotropy in an aqueous solvent. After washing the para-aramid fiber, the fiber is cut in a wet state and then fibrillated by a viscous beating refiner, wherein the para-aramid pulp is produced.

The present invention will be described in detail below. The para-aramid pulp of the present invention is as described in the above item [1],
Para-aramid which is within the range of the formula (1) and in which the Canadian freeness (x) and the BET specific surface area (y) are in the ranges of 100 ≤ x ≤ 630 and 2 ≤ y ≤ 12, respectively. Defined as pulp. Further, among the para-aramid pulp of the present invention, more preferable one is within the range of the formula (1), and in the formula, x and y are 100 ≦.
It is a para-aramid pulp in the range of x ≦ 550 and 3 ≦ y ≦ 12.

The para-aramid pulp of the present invention is contained in the shaded area in FIG. 1, and the para-aramid pulp of the present invention contained in this area is compared with conventional commercially available para-aramid pulp. In comparison with the same specific surface area, the freeness is small and the water retention capacity is excellent. This means that when the para-aramid pulp of the present invention is mixed in a mixture of various powders, the para-aramid pulp of the present invention has a high ability to retain the powder. Actually, as described later, the para-aramid pulp of the present invention is easily dispersed uniformly in the blend, and is excellent in the ability to maintain the dispersed state of the powdery filler in a good condition. If the dispersibility of the para-aramid pulp and the powdery filler in the blend is good, the reinforcing effect of the para-aramid pulp will be high.

Regarding the range shown in the item [1], when the BET type specific surface area is larger than the range, it is difficult to obtain good dispersibility of the para-aramid pulp. On the other hand, if it is less than the above range, the powdery filler is insufficiently retained, and the strength of the molded article using the para-aramid pulp tends to be lowered, which is not preferable. The feature of the para-aramid pulp of the present invention is that the BET-type specific surface area is small even if it has the Canadian freeness equivalent to that of the conventional para-aramid pulp. As a result, while the para-aramid pulp of the present invention sufficiently maintains the dispersed state of the powdery filler,
It has the excellent feature of being uniformly dispersed in the formulation.

Regarding the range shown in the above item [1], when the freeness (Canadian freeness: x) is less than 100 ml, the fiber length of the pulp is shortened as a result, and in the case of gasket application, the strength of the gasket is Bring about a decline. In addition, 630m
When it exceeds 1, the powdery filler is insufficient in maintaining the dispersed state, which is not preferable.

The fiber length of the para-aramid pulp of the present invention is not particularly limited, but the weight-weighted average fiber length (hereinafter sometimes referred to as WL or fiber length) is 0 in order to reduce the amount of wear in friction material applications. It is preferably from 0.6 to 1.2 mm. When the fiber length exceeds 1.2 mm, the para-aramid pulp tends to be oriented in the direction parallel to the hot press plate, and the amount of abrasion increases. If the fiber length is less than 0.6 mm, the number of pills increases due to the entanglement of the ultrafine fibrils detached from the fibers, resulting in an unsatisfactory dispersion as pulp.

The weight-weighted average fiber length (WL) is 0.6-1.
By controlling to 2 mm, a sliding material molded body containing para-aramid pulp and polytetrafluoroethylene (hereinafter sometimes referred to as PTFE) as main components,
A remarkable effect of reducing the amount of wear is recognized.

The mechanism by which the amount of wear is reduced is not always clear, but the weight-weighted average fiber length (WL) is from 0.6 to 1.2.
By controlling to mm, the orientation of the para-aramid pulp in the sliding material tends to be random, and as a result, when the frictional force acts, peeling and dropping of the aramid pulp fibrils due to the frictional force hardly occur. It is thought to be because.

The above-mentioned effect of the para-aramid pulp of the present invention was remarkably observed in the PTFE-based sliding material, but the same effect is expected in other various friction materials including the friction material for brakes. It

In the present invention, para-aramid (para-oriented aromatic polyamide) is obtained by polycondensation of para-oriented aromatic diamine and para-oriented aromatic dicarboxylic acid halide, and the amide bond is at the para position of the aromatic ring or Aligned position according to it (for example, 4,4'-biphenylene, 1,5
-Naphthalene, 2,6-naphthalene, etc., which is an aromatic polyamide consisting essentially of repeating units bound in opposite orientations which extend coaxially or parallel to each other.

Specifically, for example, poly (paraphenylene terephthalamide), poly (4,4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylene dicarboxylic acid terephthalamide), poly ( Aromatic polyamides having a polypara-oriented type or a structure close to the para-oriented type, such as paraphenylene-2,6-naphthalenedicarboxylic acid amide). Of these, poly (paraphenylene terephthalamide) is typical.

The method for producing para-aramid pulp according to the present invention has an intrinsic viscosity of 1.0 to 2.5 in a polar amide solvent.
An optically anisotropic para-aramid dope containing 4 to 10% by weight of para-aramid (dl / g) and 2 to 10% by weight of a chloride of an alkali metal or an alkaline earth metal is spun in an aqueous solvent to prepare a polar amide. This is a method in which after removing the system solvent by washing, fibers in a wet state are obtained, the obtained fibers in a wet state are cut, and then fibrillated using a refiner for viscous beating.

As a preferred industrially rationalized production method of the para-aramid pulp of the present invention, the above-mentioned para-orientation is carried out in a polar amide solvent containing 2 to 10% by weight of a chloride of an alkali metal or an alkaline earth metal. An optically anisotropic para-aramid polymerization solution containing 4 to 10% by weight of para-aramid having an intrinsic viscosity of 1.0 to 2.5 dl / g by condensation polymerization of aromatic diamine and para-oriented aromatic dicarboxylic acid halide ( Dope) is prepared, the dope is spun in an aqueous solvent, the polar amide solvent is removed by washing, a wet fiber is obtained, and then the obtained wet fiber is cut, followed by viscous beating. There is a method to fibrillate using a refiner.

Refining of making fibers into pulp
The beater is called a refiner. Generally, the purpose of beating is (1) fiber swelling, (2) fiber cutting,
(3) It is said that there are three points of fibrillation of fibers. (2)
The beating mainly in the cutting of the fiber of is called free beating, and the beating mainly in the fibrillation of the fiber of (3) is called the viscous beating. Depending on which of these two types of beating methods is adopted, the type of refiner to be selected, the blade shape, the operating conditions, etc. are different.

The method for producing para-aramid pulp of the present invention is characterized by using a refiner for viscous beating, that is, for example, a cylindrical type, a conical type or a double disc type refiner when fibrillating para-aramid fibers. Among these viscous beating refiners, cylindrical and conical refiners are particularly preferable.

A typical process for fibrillating para-aramid short fibers used in the method for producing para-aramid pulp of the present invention is illustrated in FIG. The process comprises a raw material tank (2), a pulp slurry tank (1), a liquid feed pump (3) and a refiner (4).

The slurry, in which para-aramid short fibers are placed in the raw material tank (2) and dispersed in water, is fed to the refiner (4) by the liquid feed pump (3), treated by the refiner (4), and then pulp. Return to the slurry tank (1).

This cycle is performed once or more to obtain the para-aramid pulp of the present invention having the predetermined BET specific surface area, Canadian freeness and weight-weighted average fiber length. By dividing the raw material tank (2) and the pulp slurry tank (1) into tanks, the number of passages through the refiner can be made uniform.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The test evaluation methods or criteria in Examples and Comparative Examples are as follows.

(1) Intrinsic viscosity In the present invention, the intrinsic viscosity is defined by the following measuring method. For a solution prepared by dissolving 0.5 g of para-aramid polymer in 100 ml of 96-98% sulfuric acid and 96-98% sulfuric acid, the flow time was measured at 30 ° C. by a capillary viscometer, and the ratio of the calculated flow times was used to calculate the following formula. The intrinsic viscosity was determined by. Intrinsic viscosity = ln (T / T ₀ ) / C
[Unit: dl / g] Here, T and T ₀ are the flow times of the para-aramid sulfuric acid solution and sulfuric acid, respectively, and C represents the para-aramid concentration [g / dl] in the para-aramid sulfuric acid solution.

(2) Canadian Freeness In Canadian freeness, the Canadian standard freeness was measured according to JIS P8121 "Pulp freeness test method".

(3) Weight-Weighted Average Fiber Length (WL) The fiber length is the weight-weighted average fiber length (WL) measured by using a fiber length analyzer FS-200 type commercially available from KAJAANI Electronics. ).

(4) BET-type specific surface area The BET-type specific surface area was measured by using a Flowsorb 2 2300 model manufactured by Micromeritics Co., Ltd. and using an alumina standard sample having a specific surface area of 12 m ² / g for the purpose of assay.

(5) Coefficient of Dynamic Friction and Wear Coefficient The coefficient of dynamic friction and the coefficient of wear were measured with a Suzuki type wear tester by preparing a test piece from a sliding material compact by cutting. Test condition: Surface pressure: 6 kgf / cm ² Sliding speed: 40 m / min Sliding area: 2 cm ² Test temperature: Room temperature Test time: 24 hours Counterpart material: Aluminum (JIS A5052P)

(6) Production and Evaluation of Joint Sheet The production and evaluation of the joint sheet were carried out as follows. As a blending material, para-aramid pulp (9.9
% By weight), rock wool (9.9% by weight), barium sulfate (16.8% by weight), magnesium oxide (9.9% by weight), catarpo (24.8% by weight), silica ER (9.9).
% By weight), NBR (14.9% by weight), vulcanization system (3.0
%) And ultramarine blue (1.0% by weight). An MTI mixer (manufactured by Tsukishima Kikai Co., Ltd.) is used as a kneading machine, and an appropriate amount of toluene is added as the compounding material and the solvent,
Kneading was performed.

The compound-like kneaded material obtained by kneading was vulcanized by a calender roll (manufactured by Hitachi Mechanical Engineering Co.) at a heating roll temperature of about 150 ° C. to obtain a joint sheet having a thickness of 1.5 mm. JI
According to the test method of JIS K6301 based on S R3453, after 24 hours from the sheeting, 1
After storing at 00 ℃ for 1 hour and then at room temperature for 3 hours in a desiccator, punch out the test piece with JIS No. 1 dumbbell.
A strength measurement sample was prepared. This is an Instron type 4301 tensile tester with a crosshead speed of 300.
mm / min. The strength was measured at a pulling speed of.

The winding direction when manufacturing the joint sheet
This is called the MD direction, and the direction perpendicular to this is called the TD direction. In the evaluation of the present invention, the latter TD direction was compared.

(7) Evaluation of Friction Material (Sieve Residual Rate and Dispersibility) (i) Sieve Residual Rate The screen residual rate, which is one of the evaluation indexes of the brake friction material, was evaluated by the method described below. The composition of the powder blend, which is the raw material of the friction material for brakes, is as follows. Para-aramid pulp (5.0% by weight), pulp rock wool (5.0% by weight), kaolin (32.5% by weight), barium sulfate (47.5% by weight), phenol resin (1
0.0% by weight). The above mixture was stirred with a 5-liter supermixer (manufactured by Kawata) (stirring speed 2000 rpm, stirring time 5 minutes) to prepare a uniform powder mixture.

20 g of this powder blend was added to an inner diameter of 100 mm,
It is put into a 60-mesh screen and the screen is vibrated (vibration speed 1500 rpm, vibration time 10 minutes). The screen residual rate is calculated by the following formula.

(Ii) Evaluation of dispersibility The powder mixture obtained as described above was baked and solidified at 200 ° C. for 5 hours to obtain a compact (friction material). The molded body was divided into two, and the dispersibility of the para-aramid pulp in the cross section was visually observed and evaluated. (In the table, ◎ is excellent, ○ is good, △ is acceptable,
X means failure. )

Example 1 (1) Preparation of poly (paraphenylene terephthalamide) dope Using a 100-liter glass-lined polymerization reactor equipped with a stirring blade, a thermometer, a nitrogen inflow tube and a powder addition port, poly Polymerization of (paraphenylene terephthalamide) was performed.

After the polymerization reactor is sufficiently dried, N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).
116.4 kg and 7.60 kg of dried calcium chloride
Was added, and calcium chloride was completely dissolved at an internal temperature of 85 ° C. Then, after cooling the internal temperature to room temperature, paraphenylenediamine (hereinafter sometimes referred to as PPD).
3.35 kg was added and dissolved, and 6.12 kg of terephthaloyl chloride (hereinafter sometimes referred to as TDC) was gradually added while maintaining the internal temperature at 18 to 22 ° C. After the addition of TDC was completed, the mixture was aged at a temperature of 18 to 22 ° C. for 1 hour to obtain a stable polymerization liquid having optical anisotropy (hereinafter sometimes referred to as dope). The poly (paraphenylene terephthalamide) concentration in the dope was 6.24% by weight, and the calcium chloride concentration was 5.75% by weight. The intrinsic viscosity of poly (paraphenylene terephthalamide) is 1.98.
(Dl / g).

(2) Spinning and Evaluation of Dope of Poly (paraphenylene terephthalamide) Para-aramid fiber was spun from the dope obtained in (1). The dope was filled in a 500-liter SUS304 tank kept cold at 10 ° C., and after defoaming in vacuum, the pressure was 3 kg / cm ² G with dry nitrogen. The tank outlet was connected to a gear pump (KAP-1-2.92, manufactured by Kawasaki Heavy Industries, Ltd.), and the gear pump outlet was connected to a spinneret holder through a filter. The spinneret has a pore size of 70 μm or 50 μm,
The L / D of the nozzle holes was 1, and the number of holes was 10,000.

The dope is passed through the spinneret to an aqueous solvent (NMP
Was extruded into an aqueous solution containing 30% by weight) and spun. The spun fiber was fed by a godet roll so that the fiber was not loosened. The fiber that has passed through the godet roll is washed with water to remove the solvent, and stretched with several Nelson rolls,
I put it on the winder.

(3) Pulping and its evaluation The obtained continuous para-aramid filaments in a wet state were cut into 10 mm by a roving cutter. 5.0 kg of this short para-aramid fiber was dispersed in 95.0 liters of ion-exchanged water using a disintegrator having an internal volume of 300 liters to obtain a uniform dispersion liquid (slurry). At this time, since the water content in the fiber was 75% by weight (polymer content was 25% by weight), the wet fiber concentration in the slurry was 5.0% by weight and the solid polymer content was 1.25% by weight.

The slurry was refined (made by Aikawa Tekko Co., Ltd.
It was fibrillated by pumping it to Deluxe Finer 50 type). At this time, the flow rate was adjusted to 380 L / min. The refiner rotor and stator were made of basalt. The rotor was pressed against the stator (pressing pressure was 1 kg / cm ² gauge), and the gap between the rotor and the stator was 0 mm and beaten for 10 minutes. The beating conditions are summarized in Table 1. During this time, the water temperature is 19 ℃ ~ 38 ℃
Rose to. After the beating was completed, the pulp slurry was dehydrated with a centrifuge, dried, and then opened using a Fine Victory Mill FVP-1 machine manufactured by Hosokawa Micron.

The BET specific surface area, Canadian freeness and weight-weighted average fiber length of the obtained para-aramid pulp were measured. The measurement results are shown in Table 2. The relationship between the BET specific surface area and the Canadian freeness of the obtained para-aramid pulp satisfied the above mathematical expression 1.

Then, a gasket sheet was prepared using the obtained para-aramid pulp, and its tensile strength was measured. Further, a composition for a friction material was prepared using the para-aramid pulp, and the residual ratio of the sieve was measured. A friction material was prepared using the para-aramid pulp, and the dispersibility of the para-aramid pulp in the friction material was evaluated. The results are shown in Table 2.
It was noted in.

Examples 2, 3, 5, 8 and 10 Example 1 was repeated except that the solid content concentration in the slurry, the slurry flow rate, the gap between the stator and the rotor, the stator pressing pressure and the beating time were changed as shown in Table 1. Para-aramid pulp was produced according to The obtained para-aramid pulp was evaluated according to Example 1, and the results are shown in Table 2.

Example 4 The continuous para-aramid filaments in a wet state obtained in Example 1 were cut into mm by a roving cutter. The obtained short fibers (5.6 kg) were dispersed in ion-exchanged water (94.3 liters) using a disintegrator having an internal volume of 300 liters to obtain a uniform slurry. At this time, the moisture content in the fiber is 7
Since it was 5% (polymer content 25%), the wet fiber concentration in the slurry was 5.6% and the solid polymer content was 1.4%.

The slurry was sent to Aikawa Iron Works Deluxe Finer Model 50 for fibrillation. At this time, the flow rate was adjusted to 240 L / min. The refiner rotor and stator were made of basalt. The wet yarn in the slurry was circulated for 10 minutes to completely disperse it.
During this time, the water temperature rose to 19 ° C to 27 ° C. Subsequently, the rotor was pressed against the stator with a gap of 0.07 mm and beaten for 10 minutes. During this time, the water temperature rose to 27 ° C to 40 ° C. The slurry was dehydrated, dried and opened in the same manner as in Example 1.

Then, a friction material was prepared using the obtained para-aramid pulp, and the dispersibility in the friction material was measured and evaluated. Table 2 shows the results.

Example 9 The continuous para-aramid filaments in a wet state obtained in Example 1 were cut into 13 mm with a roving cutter. 4.5 kg of the short fibers thus obtained were mixed with 9 parts of ion-exchanged water.
Dispersed into 5.5 liters using a disintegrator having an internal volume of 300 liters to obtain a uniform slurry. At this time, since the water content in the fiber was 78% (polymer content 22%), the wet fiber concentration in the slurry was 4.5% and the solid polymer content was 1.0%.

The slurry was fed to a deluxe finer model 50 manufactured by Aikawa Iron Works and fibrillated. At this time, the flow rate is 2
It was adjusted to 40 L / min. The refiner rotor and stator were made of basalt. During this time, the water temperature rose to 20.0 ° C to 46 ° C. Subsequently, the rotor was pressed against the stator so that the gap became 0.07 mm, beaten for 30 minutes, and similarly made the gap 0 mm, and further beaten for 10 minutes. The pulp slurry was dehydrated in the same manner as in Example 1,
It was dried and opened. Next, the dispersibility in the friction material was measured and evaluated using the obtained para-aramid pulp. Table 2 shows the results
Shown in

Comparative Examples 1 to 3 A joint sheet and a friction material were prepared in the same manner as in Example 1 except that three types of commercially available para-aramid pulp were used, and the tensile strength, the residual sieve ratio, the dispersibility and the like were evaluated. Table 3 shows the results.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

[Table 3]

Reference Example 1 Para-aramid pulp of the present invention (20% by weight), PTFE (8
A molded body (sliding material) made of 0% by weight) was produced as follows. The following PTFE was used. PTF
E: Fluon G168 (trade name, manufactured by Asahi Glass Co., Ltd., average particle size 25 μm)

(A) 30 g of para-aramid pulp obtained in Example 1 and 120 g of PTFE were stirred using a 5-liter super mixer (manufactured by Kawata) (stirring speed 2000 rp).
m stirring time 2 minutes) to prepare a uniform mixture. (B) 120 g of the mixture was filled in a vinyl chloride pipe having a diameter of 38 mm, and a surface pressure of 3 kgf / cm ² was applied,
A molding intermediate having a height of 170 mm was produced. (C) The molding intermediate was dried at 120 ° C. for 30 minutes.

(D) An inner diameter of 40 m of the dried molding intermediate
m, height 280 mm, and then pressurizing (100 kgf / cm ² , 1 while degassing with a vacuum pump).
Then, a preform having a diameter of 40 mm and a height of 50 mm was prepared at room temperature. The degassing here was performed through a hole having a diameter of 2 mm provided on the side surface of the mold. (E) Under normal pressure, the preformed body is heated at 380 ° C for 1
After holding for a while, a desired molded body was produced. From room temperature to 3
The temperature increase rate up to 80 ° C. and the temperature decrease rate from 380 ° C. to room temperature were both 50 ° C./hour. The obtained molded body was cut to produce a sliding material.

Evaluation results of sliding material Dynamic friction coefficient: 0.17 Wear coefficient: 7 [× 10 ^-5 mm / (km kgf / cm
² )]

Comparative Reference Example 1 A molded article (sliding material) was prepared in the same manner as in Reference Example 1 except that a commercially available product was used as para-aramid pulp.
The wear coefficient was measured.

Evaluation result of sliding material Dynamic friction coefficient: 0.17 Wear coefficient: 9 [× 10 ^-5 mm / (km kgf / cm
² )]

[0066]

INDUSTRIAL APPLICABILITY The para-aramid pulp of the present invention is particularly excellent in the dispersibility of the para-aramid pulp in the mixture of the para-aramid pulp and the powdered filler when it is used for a friction material, a gasket, etc. It has an excellent ability to maintain the dispersed state of the powdery filler in the product. Further, the molded article reinforced with the para-aramid pulp of the present invention, for example, the molded article containing para-aramid pulp and polytetrafluoroethylene as the main components is excellent in mechanical strength and abrasion resistance. Especially weight-weighted average fiber length (WL) is 0.6-1.2m
When the para-aramid pulp of the present invention in the range of m is used as a friction material and a sliding material, it has a feature that the amount of wear is small.

[Brief description of drawings]

FIG. 1 shows the relationship between BET specific surface area and Canadian freeness of para-aramid pulp of the present invention.

FIG. 2 represents the process of fibrillation of para-aramid pulp of the present invention.

[Explanation of symbols]

 1. Pulp slurry tank 2. Raw material tank 3. Liquid delivery pump 4. Refiner

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Takahashi 6 Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd.

Claims (3)

[Claims] 1. The relationship between Canadian freeness and BET specific surface area is expressed by the following formula (1) 0.000035x ² − 0.036x + 12 ≦ y ≦ 0.000026x ² − 0.039x + 17 (1) (where x and y are , Canadian freeness (ml) and BET specific surface area (m ² / g),
The range is 100 ≦ x ≦ 630 and 2 ≦ y ≦ 12. ) A para-aramid pulp characterized by being represented by. 2. A weight-weighted average fiber length of 0.6 to 1.2 mm.
The para-aramid pulp according to claim 1, which is within the range. 3. An intrinsic viscosity of 1.0 in a polar amide solvent.
~ 4 dl of para-aramid in the range of ~ 2.5 dl / g
%, Containing 2 to 10% by weight of chloride of alkali metal or alkaline earth metal, para-aramid dope having a low degree of polymerization and having optical anisotropy, is spun in an aqueous solvent,
The method for producing para-aramid pulp according to claim 1, wherein after the obtained para-aramid fiber is washed, the fiber is cut in a wet state and then fibrillated by a viscous beating refiner.