Aromatic polyamide fiber, rubber composition, rubber molded product, and method for producing the same

Abstract

To provide a fiber capable of obtaining high breaking tenacity, strength and durability when dispersed in rubber, and having high dispersibility in rubber and high adhesiveness to rubber.SOLUTION: The wholly aromatic polyamide fiber has ≥ 40m2 / g and ≤ 100m2 / g specific surface area measured by freeze-drying.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aromatic polyamide fiber, a rubber composition, a rubber molded product, and a method for producing the same. [Background technology]

[0002] In the past, in order to improve the mechanical properties of rubber molded articles, it has been considered to reinforce the rubber molded articles by blending short fibers such as cellulose fibers, nylon fibers, polyester fibers, and aramid fibers into the rubber. Among these short fibers, aramid fibers are widely used because of their excellent mechanical properties, fatigue resistance, heat resistance, and chemical properties.

[0003] However, since the surface of aramid short fibers is relatively inactive, they have low adhesive strength with the rubber to be reinforced and poor dispersibility when compounded with rubber, so that the inherent excellent properties of aramid short fibers cannot be fully exhibited.

[0004] Furthermore, even when short aramid fibers are blended into rubber, the short aramid fibers are not distributed completely uniformly in the molded product, and therefore wear progresses from the portions where no short aramid fibers are present, making it impossible to obtain sufficient wear resistance.

[0005] Generally, means for improving the adhesive strength between short reinforcing fibers and rubber include reducing the fiber diameter of the short reinforcing fibers or providing fibrils on the surface of the short reinforcing fibers to use them as fine short fibers, thereby increasing the contact area between the short reinforcing fibers and rubber.

[0006] For example, Patent Document 1 discloses a rubber molded article using aramid nanofibers with an average fiber diameter of 500 nm or less. However, with this technology, the fibers are too fine and therefore difficult to disperse during rubber mixing, and a sufficient reinforcing effect is not achieved. A long mixing time is required to achieve the reinforcing effect. Furthermore, aramid nanofibers tend to aggregate, and to prevent this aggregation, it is necessary to use a masterbatch obtained by mixing an aqueous dispersion containing aramid nanofibers with rubber latex and drying the mixture.

[0007] Patent Document 2 discloses a rubber molded product using existing finely divided aramid fibers, and Patent Document 3 discloses a rubber molded product using cellulose nanofibers. The fibers in these patents have low affinity with rubber, so peeling occurs between the rubber and the fiber, preventing sufficient reinforcing effect. Patent Document 4 also describes the use of aromatic polyamide short fibers for reinforcement by adhering an epoxy compound, a water-soluble nylon compound, and a water-soluble polyester resin to the fibers. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2022-184472 [Patent Document 2] Patent No. 3998692 [Patent Document 3] Patent No. 4948076 [Patent Document 4] Japanese Patent Application Publication No. 6-235170 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a fiber that can provide high breaking strength, strength, and durability when dispersed in rubber, has high dispersibility in rubber, and has high adhesiveness to rubber. [Means for solving the problem]

[0010] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved by using finely divided wholly aromatic polyamide fibers having a specific specific surface area. That is, the present invention is based on a freeze-dried sample having a specific surface area of ​​40 m 2 / g or more 100m 2 / g or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a fiber that, when dispersed in rubber, can achieve high breaking strength, strength, and durability, has high dispersibility in rubber, and has high adhesion to rubber. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below.

[0013] [Fully aromatic polyamide fiber] As the wholly aromatic polyamide fiber of the present invention, a para-type wholly aromatic polyamide fiber, a copolymer type aromatic polyamide fiber or a meta-type wholly aromatic polyamide fiber is used.

[0014] Examples of para-type wholly aromatic polyamide fibers include polyparaphenylene terephthalamide fibers (e.g., Twaron (registered trademark) manufactured by Teijin Aramid BV), copolymerized aromatic polyamide fibers include copolyparaphenylene-3,4'-oxydiphenylene terephthalamide fibers (e.g., Technora (registered trademark) manufactured by Teijin Limited), and meta-type wholly aromatic polyamide fibers include polymetaphenylene isophthalamide fibers (e.g., Conex (registered trademark) manufactured by Teijin Limited). Among the wholly aromatic polyamide fibers, it is preferable to use para-type wholly aromatic polyamide fibers or copolymer type aromatic polyamide fibers because they have high strength and elastic modulus.

[0015] The wholly aromatic polyamide fiber of the present invention has a specific surface area of ​​40 m 2 / g or more 100m 2 / g or less, preferably 40m 2 / g or more 70m 2 / g or less. This specific surface area is 40m 2 If the adhesive strength is less than 1 / g, the adhesion to rubber will decrease. If the adhesive strength to rubber is low, peeling will occur at the interface between the fiber and rubber during stretching of the rubber composition, preventing the reinforcing properties of the fiber from being exhibited and reducing the rubber strength. Generally, rubber molded products used in tires, belts, and hoses are repeatedly stretched and compressed during use. If the adhesive strength to rubber is low, peeling will occur at the interface between the fiber and rubber during use, reducing the durability of the rubber molded product.

[0016] The specific surface area measured after freeze-drying is 100m 2 If the fiber density exceeds 1 / g, the wholly aromatic polyamide fibers are difficult to disperse during mixing with the rubber, and a sufficient reinforcing effect is not achieved. Generally, rubber moldings are kneaded with a roll to disperse the fibers in the rubber and orient them in the direction of roll rotation, thereby achieving rubber reinforcing performance. If dispersion and orientation are difficult, a sufficient reinforcing effect cannot be achieved, and rubber with a high modulus cannot be obtained.

[0017] In the present invention, the specific surface area of ​​the freeze-dried wholly aromatic polyamide fiber is 40 m 2 / g or more 100m 2 / g or less, the wholly aromatic polyamide fibers are uniformly dispersed and well oriented in the rubber, and the wholly aromatic polyamide fibers and the rubber are bonded together, thereby obtaining a rubber composition with high rubber strength, elastic modulus, and durability.

[0018] The wholly aromatic polyamide fiber of the present invention preferably has a fiber length of 0.01 mm or more and 1.0 mm or less. A fiber length of less than 0.01 mm is undesirable because it reduces adhesion to rubber. If adhesion to rubber is poor, peeling occurs at the interface between the wholly aromatic polyamide fiber and the rubber during stretching of the rubber composition, preventing the reinforcing properties of the wholly aromatic polyamide fiber from being exhibited and reducing rubber strength. Furthermore, a shorter fiber length reduces the aspect ratio of the fiber, preventing sufficient reinforcing effect and reducing the rubber modulus. On the other hand, a fiber length of more than 1.0 mm results in large fiber size, resulting in poor rubber molding. Furthermore, the fibers are difficult to disperse during rubber mixing, preventing sufficient reinforcing effect from being exhibited. In particular, uneven dispersion of the wholly aromatic polyamide fiber within the rubber occurs, and this unevenness becomes a defect, resulting in reduced rubber strength and durability.

[0019] In the present invention, by using a wholly aromatic polyamide having a fiber length of 0.01 mm or more and 1.0 mm or less, the reinforcing performance is fully exhibited, and a rubber composition having high rubber strength, elastic modulus, and durability can be obtained, and also a rubber composition having good moldability can be obtained.

[0020] The wholly aromatic polyamide fibers of the present invention are used by dispersing them in water, an organic solvent, or rubber, and in this case, the wholly aromatic polyamide fibers preferably account for 10% by weight or more and 90% by weight or less of the total weight of the fiber composition.

[0021] That is, according to the present invention, there is provided a wholly aromatic polyamide fiber composition comprising the above-mentioned wholly aromatic polyamide fiber and water, an organic solvent, or a rubber, wherein the wholly aromatic polyamide fiber accounts for 10 wt% or more and less than 90 wt% of the total weight of the fiber composition. In this case, the water, organic solvent, or rubber is preferably water.

[0022] [Rubber] The rubber may be unvulcanized or uncrosslinked. Specific examples include unvulcanized natural rubber (NR), styrene butadiene rubber (SBR), nitrile rubber (NBR), polyisoprene rubber (IR), butadiene rubber (BR), butyl rubber (IIR), ethylene propylene rubber (EPM), chloroprene rubber (CR), acrylic rubber (ACM), silicone rubber (Q), and fluororubber (FKM). Multiple types of these rubbers may be used.

[0023] [Rubber composition] According to the present invention, there is provided a rubber composition containing the above-mentioned wholly aromatic polyamide fiber and water, an organic solvent, or a rubber, wherein the wholly aromatic polyamide fiber accounts for 10% by weight to 90% by weight of the total weight of the rubber composition. This rubber composition is a composition used for rubber moldings. This rubber composition is used when producing a rubber molded product, and a rubber molded product can be obtained by compounding this rubber composition with additional rubber and vulcanizing the rubber.

[0024] In a rubber composition, if the content of wholly aromatic polyamide fibers exceeds 90% by weight, the fibers will aggregate together, making it difficult for the fibers to open up and disperse in the rubber during kneading. Therefore, by limiting the content of wholly aromatic polyamide fibers to 90% by weight or less of the total weight of the rubber composition and allowing water, an organic solvent, or rubber to adhere to the surface of the wholly aromatic polyamide fibers, it is possible to suppress the aggregation of the wholly aromatic polyamide fibers. On the other hand, if the content is less than 10% by weight, the wholly aromatic polyamide fibers will not blend with the rubber during kneading, making it difficult for them to disperse in the rubber.

[0025] In the rubber composition, any one of water, organic solvent, and rubber may be used, or a combination of two or more thereof may be used, in which case, they may be mixed. From the viewpoints of practicality and environmental load, the water, organic solvent, or rubber used in the rubber composition is preferably water. That is, the wholly aromatic polyamide fiber of the present invention is preferably used in the form of an aqueous dispersion.

[0026] When water or an organic solvent is used during kneading, it is preferable to evaporate it before vulcanization. If a large amount of water or an organic solvent is contained in the rubber composition, it will evaporate within the rubber composition during vulcanization, causing unevenness in the rubber molded product, which is undesirable.

[0027] [Rubber molding] The rubber molding obtained by the present invention is a rubber molding containing wholly aromatic polyamide fibers and rubber, and the wholly aromatic polyamide fibers account for 0.1 to 20 parts by weight of the rubber in the rubber molding.

[0028] This rubber molded product can be obtained by blending the wholly aromatic polyamide fiber of the present invention with water, an organic solvent or rubber to form a rubber composition, and then blending further rubber therein and crosslinking the rubber.

[0029] The wholly aromatic polyamide fiber of the present invention preferably accounts for 0.1 to 20 parts by weight, more preferably 0.5 to 20 parts by weight, of the rubber in the rubber molding. If the content is less than 0.1 part by weight, a sufficient reinforcing effect cannot be exhibited, which is undesirable. On the other hand, if the content exceeds 20 parts by weight, it becomes difficult to sufficiently disperse the wholly aromatic polyamide fiber during rubber kneading, which makes it difficult to exhibit a sufficient reinforcing effect and causes molding defects, which is undesirable.

[0030] [Manufacturing method] The wholly aromatic polyamide fiber of the present invention can be obtained by fibrillating a wholly aromatic polyamide dope under a gas flow using a jet spinning nozzle. The dope, which is a solution of a wholly aromatic polyamide polymer, exhibits low kinematic viscosity and can be fibrillated at temperatures below 60°C, preferably at room temperature.

[0031] The wholly aromatic polyamide fibers of the present invention can also be obtained by treating the wholly aromatic polyamide fibers under high shear force. Examples of the method for treating under high shear force include beating with a millstone refiner (Hypermass Colloider MKZA-20JA, manufactured by Masuko Sangyo Co., Ltd.) and beating with a high-pressure homogenizer (N-2000 110, manufactured by Kos21 Co., Ltd.). These methods can increase the specific surface area to the range of the present invention and make the fiber length fall within the range of the present invention. It is preferable to use these methods in combination.

[0032] A rubber composition can be produced by dispersing the wholly aromatic polyamide fiber of the present invention in water, an organic solvent, or rubber, and then kneading the composition with rubber, followed by evaporating the water or organic solvent, and then vulcanizing the rubber to produce a rubber molded article. [Example]

[0033] The present invention will be described in more detail below with reference to examples. The evaluation methods used in the examples are as follows.

[0034] (1) Specific surface area A water dispersion of the fiber material was frozen and then dried under reduced pressure to 20 Pa while maintaining a temperature of -5°C, to obtain a sample for measuring the specific surface area. The specific surface area of ​​the sample was measured using a flow-type automatic specific surface area measuring device (Shimadzu Corporation, FlowSorbIII).

[0035] (2) Fiber length The fiber material was measured using a fully automatic pulp analyzer, Pulp Expert (registered trademark) FS (Metso). The weight average fiber length was used as the fiber length.

[0036] (3) Breaking strength A sample was cut from the vulcanized rubber composition sheet in the orientation direction of the fiber material, and a tensile test was carried out using a dumbbell No. 3 according to JIS K6251 to measure the stress at break. The higher the stress, the better the strength.

[0037] (4) Stress at 50% elongation Similar to the evaluation method (3) above, a tensile test was carried out to measure the stress at 50% elongation. The higher the stress, the better the modulus of elasticity.

[0038] (5) Durability In a tensile test, the vulcanized rubber composition sheet was stretched to an elongation of 100% and then returned to an elongation of 10%, repeated 50 times. It was then stretched to break, and the strength at break was measured. The strength retention rate was calculated by subtracting the initial strength from the obtained strength, and durability was evaluated.

[0039] (6) Fiber dispersion A cross section of the vulcanized rubber composition sheet was cut, and a photograph of the cut surface was enlarged with an optical microscope (300x magnification) and visually observed to determine the dispersion state of the fiber material according to the following criteria. A: No lumps due to poor dispersion are observed. B: Slightly poorly dispersed lumps are observed. C Poor dispersion of fibers is observed throughout the rubber sheet.

[0040] (7) Rubber adhesion After the tensile test, the fracture surface of the vulcanized rubber composition sheet was observed, and the adhesiveness of the wholly aromatic polyamide fiber was visually evaluated according to the following criteria. A: No delamination between the fiber and rubber is observed. B: Slight delamination between the fiber and rubber is observed. C Peeling between fibers and rubber is observed throughout the rubber sheet.

[0041] [Materials 1 to 6] As materials for producing vulcanized rubber sheets, materials 1 to 6 described below were produced or prepared.

[0042] [Material 1] Micronized aramid fibrids A hydrous molding made of para-type wholly aromatic polyamide fibers was obtained according to the following method. 2.5m 3 Polymerization of para-phenylene terephthalamide (PPTA) was carried out using a Drais reactor. The reactor was thoroughly dried, and 1140 L of NMP / CaCl (N-methylpyrrolidone / calcium chloride) containing 2.5 wt% CaCl was added to the reactor. Next, 27.50 kg of para-phenylenediamine (PPD) was added and dissolved at room temperature.

[0043] The PPD solution was then cooled to 10°C, and 51.10 kg of terephthalic acid dichloride (TDC) was added. After the addition of TDC, the polymerization reaction was carried out for 45 minutes. The polymer solution was then neutralized with a calcium oxide / NMP suspension (14.10 kg of CaO in 28 L of NMP). After the addition of the CaO suspension, the polymer solution was further stirred for at least 15 minutes. This neutralization reaction was carried out to remove hydrogen chloride (HCl) generated during the polymerization. A gel-like polymer solution with a para-phenylene terephthalamide (PPTA) concentration of 4.5 wt% and a relative viscosity of 2.8 (in 0.25 wt% H2SO4) was obtained.

[0044] The polymer solution was fed to a spinning pump (feed rate 120 L / h) to feed a spinning nozzle with 20 circular holes of 350 μm diameter. The spinning temperature was ambient (20°C). PPTA was spun through the nozzle into a low-pressure zone. An air jet (160 Nm) at 6 bar was used. 3 / h (normal cubic meters per hour) was independently fed perpendicular to the polymer flow into the same region where the air expanded through a ring-shaped channel.

[0045] The fibrids were then coagulated in the same area by supplying a coagulant jet (600 L / h) through the ring-shaped channel at an angle to the direction of the polymer flow (HO / 30 wt% NMP / 1.3 wt% CaCl), and the resulting fibrids were collected on a filter and washed to obtain aramid fibrids.

[0046] Water was added to this aramid fibrid to prepare a 1% by weight aqueous dispersion of fibrids. This aqueous dispersion was beaten three times in a high-pressure homogenizer (manufactured by Kos21 Co., Ltd., N-2000 110) with a clearance of 100 μm and a rotation speed of 1,500 rpm, to obtain an aqueous dispersion of finely divided aramid fibrids. The specific surface area and fiber length of the obtained finely divided aramid fibrids were as shown in Table 1.

[0047] [Material 2] Aramid nanofiber 202 g of Twaron (registered trademark) pulp (product number: Type 1094) manufactured by Teijin Aramid Co., Ltd. (solids weight: 50 g, moisture weight: 152 g), 64 g of additional water, 25 g of potassium hydroxide, and 1,950 g of dimethyl sulfoxide (DMSO) were placed in a 2 L plastic container and mixed at room temperature to prepare a mixed liquid, which was then kept in a dryer set to 70°C for 3 hours.

[0048] After 3 hours at 70°C, the color of the mixture changed from yellow to reddish brown, and no pulp-like substance was observed in the mixture. At this point, the mixture was returned to room temperature, and it was visually confirmed that the viscosity had increased compared to immediately after mixing.

[0049] A sufficient amount of water was then added to the mixture to coagulate the aramid fibers derived from the Twaron pulp. While removing the DMSO, potassium hydroxide, and water mixture, water was added continuously to obtain an agglomerate of aramid fibers. The agglomerate was passed through a wet mill to obtain an aqueous dispersion of aramid nanofibers. The specific surface area and fiber length of the resulting aramid nanofibers are shown in Table 1.

[0050] [Material 3] Cellulose nanofiber As an example of a fine fiber material other than aromatic polyamide fiber, cellulose nanofiber (product name BiNFi-s, product number FMa-10005) manufactured by Sugino Machine Co., Ltd. was used. The specific surface area and fiber length of the cellulose nanofiber were as shown in Table 1.

[0051] [Material 4] Fully aromatic polyamide fiber "Tiara" A wholly aromatic polyamide fiber "Tiara product name, KY-100S" manufactured by Daicel Chemical Industries, Ltd. was used. The specific surface area and fiber length of the wholly aromatic polyamide fiber were as shown in Table 1.

[0052] [Material 5] Aramid fibrid A hydrous molding made of para-type wholly aromatic polyamide fibers was obtained according to the following method. 2.5m 3 Polymerization of para-phenylene terephthalamide (PPTA) was carried out using a Drais reactor. The reactor was thoroughly dried, and 1140 L of NMP / CaCl (N-methylpyrrolidone / calcium chloride) containing 2.5 wt% CaCl was added to the reactor. Next, 27.50 kg of para-phenylenediamine (PPD) was added and dissolved at room temperature.

[0053] The PPD solution was then cooled to 10°C, and 51.10 kg of terephthalic acid dichloride (TDC) was added. After the addition of TDC, the polymerization reaction was carried out for 45 minutes. The polymer solution was then neutralized with a calcium oxide / NMP suspension (14.10 kg of CaO in 28 L of NMP). After the addition of the CaO suspension, the polymer solution was further stirred for at least 15 minutes. This neutralization reaction was carried out to remove hydrogen chloride (HCl) generated during the polymerization. A gel-like polymer solution with a para-phenylene terephthalamide (PPTA) concentration of 4.5 wt% and a relative viscosity of 2.8 (in 0.25 wt% H2SO4) was obtained.

[0054] The polymer solution was fed to a spinning pump (feed rate 120 L / h) to feed a spinning nozzle with 20 circular holes of 350 μm diameter. The spinning temperature was ambient (20°C). PPTA was spun through the nozzle into a low-pressure zone. An air jet (160 Nm) at 6 bar was used. 3 / h (normal cubic meters per hour) was independently fed perpendicular to the polymer flow into the same region where the air expanded through a ring-shaped channel.

[0055] Then, the fibrids were coagulated in the same area by supplying a coagulant jet (600 L / h) through the ring-shaped channel at an angle to the direction of the polymer flow (HO / 30 wt% NMP / 1.3 wt% CaCl), and the resulting fibrids were collected on a filter and washed to obtain aramid fibrids. The specific surface area and fiber length of the obtained aramid fibrids were as shown in Table 1.

[0056] [Material 6] Fully aromatic polyamide fiber "Twaron (registered trademark) pulp" Twaron (registered trademark) pulp (product number: Type 1094) manufactured by Teijin Aramid Co., Ltd. was used. The specific surface area and fiber length of this Twaron pulp were as shown in Table 1.

[0057] [Table 1]

[0058] [Unvulcanized rubber compound] As unvulcanized rubber compound 1, an unvulcanized rubber compound having the composition shown in Table 2 was prepared, and as unvulcanized rubber compound 2, an unvulcanized rubber compound having the composition shown in Table 3 was prepared.

[0059] [Table 2]

[0060] [Table 3]

[0061] Example 1 Water was added to the finely divided aramid fibrids of Material 1 so that the solid content concentration was 1% by weight, and the mixture was heated and stirred to prepare an aqueous dispersion with a solid content concentration of 20% by weight. This aqueous dispersion was mixed with unvulcanized rubber compound 1 so that 5 parts by weight of micronized aramid fibrids were mixed with 100 parts by weight of the rubber (natural rubber and styrene-butadiene rubber) of unvulcanized rubber compound 1, and the mixture was kneaded at 100 ° C for 60 minutes in an MS pressure kneader (DS3-10MHHS, manufactured by Moriyama Seisakusho Co., Ltd.) to evaporate the water contained in the mixture, and an unvulcanized rubber composition was obtained. This unvulcanized rubber composition was left standing overnight at 50 ° C, and the water remaining in the unvulcanized rubber composition was evaporated. Then, it was left to cool at 20 ° C for 30 minutes and solidified.

[0062] To this solid material, sulfur and N-cyclohexyl-2-benzothiazolylsulfenamide as a vulcanization accelerator were added in amounts of 2% by weight each relative to the solid material, and the solid material was sheeted to a thickness of approximately 2 mm using an open roll (Kansai Roll Co., Ltd., 9-inch test roll) to obtain an unvulcanized rubber composition sheet. One sheet of this unvulcanized rubber composition was placed in a 2 mm deep mold and pressed at 150°C for 30 minutes under 1 MPa to vulcanize the rubber, producing a 2 mm thick vulcanized rubber composition sheet. The properties of the resulting vulcanized rubber composition sheet are shown in Table 4.

[0063] Example 2 By mixing the finely divided aramid fibrids of material 1 with natural rubber latex (manufactured by Regitex Co., Ltd., product number: ULACOL, containing 61% by weight of natural rubber) and diluting with water, a mixture was obtained in which the weight ratio of the finely divided aramid fibrids to the natural rubber latex was 20:80 and the total solid concentration of the finely divided aramid fibrids and the natural rubber latex was 5% by weight. This mixture was heated and stirred until all the water was gone, and a finely divided fiber rubber master batch was obtained.

[0064] This microfiber rubber master batch was mixed with unvulcanized rubber compound 1 so that the amount of microfiber aramid fibrids mixed was 5 parts by weight per 100 parts by weight of the total of the rubber in the microfiber rubber master batch and unvulcanized rubber compound 1 to obtain a rubber composition, which was kneaded at 100 ° C. for 60 minutes in an MS pressure kneader (DS3-10MHHS, manufactured by Moriyama Seisakusho Co., Ltd.) to evaporate the water contained in the rubber composition, thereby obtaining an unvulcanized rubber composition. The obtained unvulcanized rubber composition was left to cool overnight and solidified. An unvulcanized rubber sheet and a vulcanized rubber sheet were obtained from this solid matter in the same manner as in Example 1. The properties of the obtained vulcanized rubber composition sheets are shown in Table 4.

[0065] Example 3 A vulcanized rubber composition sheet was obtained in the same manner as in Example 1, except that unvulcanized rubber compound 2 was used instead of unvulcanized rubber compound 1. The performance of the obtained vulcanized rubber composition sheet is shown in Table 4.

[0066] [Table 4]

[0067] Comparative Example 1 A vulcanized rubber composition sheet was obtained in the same manner as in Example 1, except that aramid nanofibers (Material 2) were used instead of the finely divided aramid fibrids (Material 1). The performance of the obtained vulcanized rubber composition sheet is shown in Table 5.

[0068] Comparative Example 2 A vulcanized rubber composition sheet was obtained in the same manner as in Example 1, except that cellulose nanofibers (Material 3) were used instead of the finely divided aramid fibrids (Material 1). The performance of the obtained vulcanized rubber composition sheet is shown in Table 5.

[0069] Comparative Example 3 A vulcanized rubber composition sheet was obtained in the same manner as in Example 2, except that cellulose nanofibers (Material 3) were used instead of the finely divided aramid fibrids (Material 1). The performance of the obtained vulcanized rubber composition sheet is shown in Table 5.

[0070] Comparative Example 4 A vulcanized rubber composition sheet was obtained in the same manner as in Example 1, except that the tiara of material 4 was used instead of the finely divided aramid fibrids of material 1. The performance of the obtained vulcanized rubber composition sheet is shown in Table 5.

[0071] Comparative Example 5 A vulcanized rubber composition sheet was obtained in the same manner as in Example 1, except that the aramid fibrids of Material 5 were used instead of the finely divided aramid fibrids of Material 1 in Example 1. The performance of the obtained vulcanized rubber composition sheet is shown in Table 6.

[0072] Comparative Example 6 A vulcanized rubber composition sheet was obtained in the same manner as in Example 2, except that the aramid fibrids of Material 5 were used instead of the finely divided aramid fibrids of Material 1. The performance of the obtained vulcanized rubber composition sheet is shown in Table 6.

[0073] Comparative Example 7 A vulcanized rubber composition sheet was obtained in the same manner as in Example 1, except that Twaron (registered trademark) pulp was used as material 6 instead of the finely divided aramid fibrids as material 1. The performance of the obtained vulcanized rubber composition sheet is shown in Table 6.

[0074] [Table 5]

[0075] [Table 6]

[0076] Compared to the rubber vulcanized sheets of Comparative Examples 1 to 7, the vulcanized rubber composition sheets of Examples 1 and 2 had well-dispersed fibers in the rubber, exhibited high rubber adhesion, and exhibited high rubber strength, elastic modulus, and durability. [Industrial Applicability]

[0077] The wholly aromatic polyamide fiber of the present invention can be used as a reinforcing material for rubber moldings for applications such as tires, power transmission belts, underwater clothing, various sealing materials such as rubber packings, oil seals, and waterproofing materials, vehicle shock absorbers, rubber vibration isolators, and rubber soundproofing materials.

Claims

1. The specific surface area after freeze-drying is 40m ２ / g or more 100m ２ / g or less.

2. 2. The wholly aromatic polyamide fiber according to claim 1, having a fiber length of 0.01 mm or more and 1.0 mm or less.

3. A rubber composition comprising the wholly aromatic polyamide fiber according to claim 1 and water, an organic solvent, or a rubber, wherein the wholly aromatic polyamide fiber accounts for 10% by weight or more and 90% by weight or less of the total weight of the composition.

4. The rubber composition according to claim 3, wherein the water, organic solvent or rubber is water.

5. A rubber molding comprising the wholly aromatic polyamide fiber of claim 1 and rubber, wherein the wholly aromatic polyamide fiber of claim 1 accounts for 0.1 to 20 parts by weight of the rubber in the rubber molding.

6. A method for producing a rubber molding, comprising kneading the rubber composition according to claim 3 with rubber, evaporating the water or organic solvent, and vulcanizing the rubber to produce a rubber molding.

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