JP7250583B2 - Aramid staple fiber bundle for rubber reinforcement and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aramid short fiber bundle for rubber reinforcement and a method for producing the same.

Aramid fiber is a synthetic fiber that combines high strength, high modulus, high heat resistance, non-conductivity, rust resistance, and other high functionality, as well as flexibility and lightness unique to organic fibers. It is used as a reinforcing material for rubber used in conveyors, etc.

However, since the aramid fiber has an inert surface, it has a problem of low adhesion to rubber and poor dispersibility when mixed with rubber. Therefore, aramid fiber bundles mixed with rubber are generally treated with resorcin-formaldehyde-latex (hereinafter referred to as "RFL").

In rubber reinforcing materials for tires and belts, it is necessary to improve the adhesiveness between the reinforcing materials and rubber at high temperatures (hereinafter referred to as "high-temperature adhesiveness") as the environmental temperature of tires and belts rises. Conventionally, latex with a small particle size has been used as a technique for improving high-temperature adhesion with rubber. It was a method of improving the adhesiveness with. However, if RFL-unattached single yarns are present inside the fiber bundle, fiber balls are likely to be formed when cutting into short fibers.

On the other hand, in rubber reinforcing short fibers obtained by uniformly attaching RFL to the single yarns present inside the fiber bundle and then cutting them to a specified length, the viscosity of the latex increases when the latex particle diameter is reduced, and the fiber bundle Since the permeability to the inside is deteriorated, it becomes difficult to apply the RFL uniformly. Furthermore, a large amount of RFL adheres to the surface of the fiber bundle, which causes problems such as the generation of process waste and a decrease in productivity.

In Patent Document 1, when ethylene propylene rubber is subjected to RFL treatment, polyester It is disclosed that the peel adhesion of fiber cords is improved. Patent Document 2 discloses that the use of a latex-containing sizing agent and wax improves cuttability and dispersibility in rubber.

JP-A-10-273880 (Claims, [0037] etc.) Japanese Patent Application Laid-Open No. 2018-111903 (Claims, etc.)

However, the methods disclosed in Patent Documents 1 and 2 have problems such as poor short fiber dispersibility during rubber kneading due to poor penetration into the fiber bundle, and high-temperature adhesion to rubber. Not suitable for rubber reinforcing short fibers that require adhesion.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber-reinforcing aramid short fiber bundle having good high-temperature adhesion to rubber and good dispersibility in rubber, and a method for producing the same. and

As a result of intensive studies to solve the above problems, the present inventors have found that a sizing agent containing a latex having a number average particle size within a specified range in aramid fibers having a high moisture content to which an epoxy compound has been applied in advance. The inventors have found that an aramid short fiber bundle having good high-temperature adhesiveness with rubber and good dispersibility in rubber can be obtained by adhering to the rubber, and completed the present invention.

That is, the present invention is as follows.
(1) Styrene-butadiene- , which is a bundle of aramid short fibers for reinforcing rubber, having an epoxy compound attached to or permeated on the fiber surface or in the fiber skeleton, and having a number average particle diameter in the range of 100 to 150 nm A bundle of aramid short fibers for rubber reinforcement, characterized in that a bundle containing a vinylpyridine copolymer latex is adhered thereto.
( 2 ) The rubber-reinforcing aramid short fiber bundle according to (1) , wherein the sizing agent further contains a resorcin-formaldehyde initial condensate, a blocked polyisocyanate compound and a chlorophenol compound.
( 3 ) The epoxy compound penetrates into the fiber skeleton and adheres to the fiber surface, and the amount of epoxy compound (A) that penetrates into the fiber skeleton and the amount of epoxy compound that adheres to the fiber surface ( The aramid short fiber bundle for reinforcing rubber according to (1) or (2) above, wherein the ratio (B)/(A) to B) is 0.5 or less.
( 4 ) The amount of epoxy compound permeated into the fiber skeleton is 0.1 to 10.0% by mass relative to the fiber mass when the moisture content of the aramid fiber is converted to 0%, and the epoxy attached to the fiber surface The rubber-reinforcing aramid short fiber bundle according to any one of (1) to ( 3 ), wherein the amount of the compound is 0.05 to 0.5% by mass.
( 5 ) The rubber according to any one of the above (1) to ( 3 ), wherein the amount of the sizing agent attached is 2 to 10% by mass with respect to the fiber mass when the moisture content of the aramid fiber is converted to 0%. Aramid staple fiber bundles for reinforcement.
( 6 ) Styrene- A sizing agent containing a butadiene-vinylpyridine copolymer latex is applied only once, dried and heat treated, and then cut to a fiber length of 0.1 to 10 mm. A method for manufacturing a fiber bundle.

ADVANTAGE OF THE INVENTION According to this invention, the aramid short fiber bundle for rubber reinforcement which is excellent in the high-temperature adhesiveness with rubber, and the dispersibility with respect to rubber can be provided.
In the conventional method, the sizing agent attachment process for attaching the adhesive was required multiple times, but according to the present invention, the sizing agent attachment process can be performed only once, so excessive attachment of the sizing agent can be prevented. It is possible to eliminate the problem of process waste caused by a large amount of RFL adhering to the surface of the fiber bundle. In particular, it is possible to provide an aramid short fiber bundle for rubber reinforcement suitable for reinforcement with short fibers in a belt using chloroprene rubber.

The aramid short fiber bundle for rubber reinforcement of the present invention is an aramid fiber in which an epoxy compound is added to the surface of the aramid fiber or in the fiber skeleton, and the aramid fiber bundle has a fiber moisture content of 25% by mass or more, A sizing agent containing latex having a number average particle size within a specified range was applied, and then cut.

[Aramid fiber bundle]
In the present invention, the aramid fiber is a fiber having at least one optionally substituted divalent aromatic group in the repeating unit of the polymer forming the fiber, and having at least one amide bond. There is no particular limitation as long as it exists, and it may be what is called wholly aromatic polyamide fiber or aramid fiber. A “divalent aromatic group that may be substituted” means a divalent aromatic group that may have one or more substituents which may be the same or different.

As the aramid fiber, it is possible to appropriately select and use it from known ones, but the para-aramid fiber which is excellent in tensile strength is preferable. Aramid fibers are commercially available, and specific examples thereof include polyparaphenylene terephthalamide fiber (manufactured by DuPont, Toray Industries, Inc., trade name "Kevlar" (registered trademark)), copolyparaphenylene-3. , 4'-oxydiphenylene terephthalamide fiber (manufactured by Teijin Limited, trade name "Technora" (registered trademark)). Among these para-aramid fibers, polyparaphenylene terephthalamide fibers are particularly preferred.

In the present invention, as the aramid fiber, an aramid fiber having an epoxy compound attached to the surface of the fiber in advance, or an aramid fiber having an epoxy compound permeating the fiber skeleton in advance is used. Aramid fibers to which an epoxy compound has been applied in advance have the function of improving the adhesiveness of the latex contained in the sizing agent.

The aramid fiber to which the epoxy compound is attached in advance is obtained by a method of attaching the epoxy compound to the aramid fiber by a conventional method. The amount of the epoxy compound attached is preferably 0.05 to 0.5% by mass, more preferably 0.15 to 0.25% by mass, based on the fiber mass when the moisture content of the aramid fiber is converted to 0%.

Aramid fibers in which an epoxy compound is pre-permeated into the fiber skeleton can be obtained by the method described in JP-A-2012-207326. The permeation amount (A) of the epoxy compound is preferably 0.1 to 10.0% by mass, more preferably 0.25 to 2.0% by mass, based on the fiber mass when the moisture content of the aramid fiber is converted to 0%. preferable.
As a specific example, a viscous solution of 18 to 20% by mass of polyparaphenylene terephthalamide dissolved in concentrated sulfuric acid is extruded from a spinneret, and washed and neutralized with water. A method of imparting an epoxy compound to a polyparaphenylene terephthalamide fiber having a moisture content of 15 to 200% by mass which has been dried for up to 20 seconds can be mentioned. If the moisture content is less than 15% by mass, it becomes difficult to uniformly permeate the epoxy compound into the fiber skeleton. On the other hand, if the moisture content exceeds 200% by mass, there is a risk that the impregnated epoxy compound will fall off together with moisture when it comes into contact with a guide or the like before the winding process, and the winding process of the fiber will become difficult. More preferably, the moisture content is 15 to 100% by mass. In order to allow the epoxy compound to uniformly penetrate into the fiber skeleton, the polyparaphenylene terephthalamide fiber preferably does not have a history of being dried to a moisture content of less than 15% by mass after being spun.

In the above process, the epoxy compound permeates into the fiber skeleton and also adheres to the surface of the fiber. The surface adhesion amount (B) of the epoxy compound at this time is preferably 0.05 to 0.5% by mass, preferably 0.15 to 0.25, with respect to the fiber mass when the moisture content of the aramid fiber is converted to 0%. % by mass is more preferred.

The ratio (B)/(A) between the amount (A) of the epoxy compound permeating into the fiber skeleton and the amount (B) of the epoxy compound adhering to the surface of the fiber is preferably 0.5 or less. . Aramid fibers in which the epoxy compound exists in such a state are not easily affected by the type of latex, and there is no need to provide a special pretreatment process for uniformly attaching the sizing agent containing latex. A bundle of aramid short fibers that are applied more uniformly can be obtained. On the other hand, when the above (B)/(A) exceeds 0.5, the generation of short fiber clumps and dregs becomes significant.

In the rubber-reinforcing aramid short fiber bundle of the present invention, the moisture content of the aramid fiber when attaching the sizing agent containing latex is preferably 25% by mass or more, more preferably 25 to 70% by mass, 25 to 50% by weight is particularly preferred. When the moisture content of the aramid fibers is 25% by mass or more, the sizing agent easily adapts to the fiber surface and adheres more uniformly. Furthermore, if the sizing agent is applied with a moisture content of 70% by mass or less, the latex can be prevented from falling off together with moisture when it comes into contact with a guide or the like during the drying or heat treatment process after the sizing agent is applied. can.

The aramid fiber with the epoxy compound permeated into the fiber skeleton is wound on a bobbin in the winding process while maintaining the above moisture content, and the moisture content is kept in an unheated state until a sizing agent containing latex is applied. is preferably maintained at 25 to 70% by mass, and aging treatment may be performed as necessary.

In order to more uniformly penetrate the epoxy compound into the aramid fiber skeleton, the epoxy compound may be diluted with water, a solvent, or the like and applied. Alternatively, it may be applied together with an oiling agent generally used for aramid fibers, and specific examples of the oiling agent include low-molecular-weight fatty acid esters having 18 or less carbon atoms, polyethers, mineral oils, and the like. As a method for infiltrating the epoxy compound into the aramid fiber skeleton, a known method can be used, and examples thereof include immersion oiling, spray oiling, roller oiling, and guide oiling using a metering pump.

The number of single filaments of the aramid short fiber bundle constituting the bundle is preferably 100 to 3,000, more preferably 500 to 2,500. If the number of single yarns is 100 or more, there is no risk of yarn breakage during the immersion treatment with the sizing agent. not significantly damaged.

Although the single filament fineness of the aramid fibers constituting the fiber bundle is not particularly limited, it is preferably in the range of 0.5 to 10 dtex, more preferably 1 to 5 dtex. If it is 0.5 dtex or more, the physical properties of the rubber can be improved without any difficulty in spinning technology, and if it is 10 dtex or less, the short fiber bundles can be uniformly dispersed in the rubber. .

[Epoxy compound]
In the present invention, the epoxy compound may be either an aliphatic epoxy compound or an epoxy compound having an aromatic ring, or may be used in combination. is preferred.

Aliphatic epoxy compounds can be appropriately selected from known ones and used, but in the present invention, one selected from glycidyl ether compounds of trihydric or higher polyhydric alcohols such as glycerol, sorbitol, and polyglycerol, or A mixture of two or more is preferred.
Specific examples of aliphatic epoxy compounds include glycerol diglycidyl ether, glycerol triglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether and the like. Among the above epoxy compounds, glycerol diglycidyl ether, glycerol triglycidyl ether, sorbitol polyglycidyl ether, and polyglycerol polyglycidyl ether are more preferred.

If necessary, a curing agent may be used together with the epoxy compound. As the curing agent, an amine compound is preferred, and a tertiary amine compound is particularly preferred. Examples thereof include dimethyloctylamine, dimethyldecylamine, dimethyllaurylamine, and long-chain alkylpolyoxyethylene-type tertiary amines obtained by adding ethylene oxide to primary aliphatic amines.

[Sizing agent]
The latex used in the sizing agent of the present invention may be appropriately selected from known ones, and specific examples thereof include styrene-butadiene-vinylpyridine copolymer latex, styrene-butadiene copolymer latex, acrylonitrile- Butadiene copolymer latex, chloroprene polymer latex, chlorosulfonated polyethylene polymer latex, butadiene polymer latex, acrylate latex, and natural rubber latex. These latexes can be used alone or in combination of two or more. Among these, the styrene-butadiene-vinylpyridine copolymer latex is most suitable because of its excellent bundling properties of aramid short fibers, dispersibility in rubber, and heat-resistant adhesion between aramid short fibers and rubber.

As the latex, one having a number average particle size in the range of 100 to 150 nm is used. When the number average particle size is less than 100 nm, latex non-adhesive threads are generated inside the aramid fiber bundle due to the increase in latex viscosity, and a large amount of latex adheres to the fiber surface, resulting in the formation of fiber balls when short fibers are cut. becomes easier. When the short fiber bundle and the rubber are kneaded, lumps are generated, and the heat-resistant adhesion between the short fiber and the rubber is also lowered when exposed to high temperatures. On the other hand, when the number average particle size exceeds 150 nm, the permeability of the latex particles to the inside of the aramid fiber bundle is reduced, and latex-unattached single yarns are likely to occur, resulting in reduced heat-resistant adhesion to rubber. The number average particle size referred to in the present invention is the number average of particle sizes measured by electron microscopy.

The sizing agent of the present invention preferably contains 20% by mass or more, more preferably 50% by mass or more, of the latex based on the total solid content of the sizing agent. If the content is too small, the effect of specifying the number average particle size of the latex may not be sufficiently obtained.

The sizing agent of the present invention preferably contains a resorcin-formaldehyde initial condensate. Here, the resorcin-formaldehyde initial condensate is a product obtained by condensing resorcin and formaldehyde in the presence of an alkali catalyst or an acid catalyst. As the resorcinol-formaldehyde initial condensate, a known one can be used, and a commercially available product (eg, "Sumikanol 700S" manufactured by Sumitomo Chemical Co., Ltd.) can also be used.

Resorcin-formaldehyde latex (RFL) is obtained by mixing and maturing the resorcin-formaldehyde precondensate and the latex.

The sizing agent of the present invention can contain a blocked polyisocyanate compound and a chlorophenol compound, and can contain a cross-linking agent, a vulcanizing agent, a vulcanization accelerator, an ultraviolet absorber, an antioxidant and the like. One or more of these compounds can be used.
A blocked polyisocyanate is an adduct of a polyisocyanate compound and a blocking agent, and is a compound in which the blocking agent component is liberated by heating to produce an active polyisocyanate compound. Examples of polyisocyanate compounds include polyisocyanates such as tolylene diisocyanate, metaphenylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, and triphenylmethane triisocyanate, or these polyisocyanates and active hydrogen atoms. A polyol containing a terminal isocyanate group obtained by reacting a compound having two or more groups, such as trimethylolpropane, pentaerythritol, etc., at a molar ratio of isocyanate group (--NCO) to hydroxyl group (--OH) exceeding 1. and adduct polyisocyanate. Among them, aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenyl isocyanate are preferred. Examples of blocking agents include phenols such as phenol, cresol and resorcin, lactams such as ε-caprolactam and valerolactam, oximes such as acetoxime, methyl ethyl ketone oxime and cyclohexanone oxime, and ethyleneimine. Other examples include compounds such as 2,4-toluenediisocyanate dimer, in which the polyisocyanate compound itself also serves as a blocking agent.
Chlorophenol compounds are co-condensates of parachlorophenol, resorcin and formaldehyde. Specific examples include 2,6-bis(2′,4-dihydroxy-phenylmethyl)4-chlorophenol (“Casabond” manufactured by Thomas Wan, “Denabond” manufactured by Nagase Chemical Industries, Ltd., etc.). Among them, from the standpoint of adhesiveness, those containing a chlorophenol compound having 3 or more benzene nuclei as a main component are preferred.

The method of attaching the latex-containing sizing agent to the aramid fibers may be a known method. Examples thereof include a method of immersing an aramid fiber bundle in an aqueous solution of a sizing agent, and a method of contacting a running aramid fiber bundle with a driving roller provided with a solution of a sizing agent. The immersion method is preferable because it has excellent permeability into the inside of the fiber bundle.

The amount of the sizing agent attached to the rubber-reinforcing aramid short fiber bundle of the present invention is preferably 1 to 20% by mass with respect to the fiber mass when the moisture content of the aramid fibers is converted to 0%. If the adhesion amount of the sizing agent is 1% by mass or more, latex can be applied even to the single yarns constituting the bundle of short fibers. It is possible to apply the sizing agent to the inside of the fiber bundle without making it too thick. The adhesion amount of the sizing agent is more preferably 2 to 15% by mass, particularly preferably 3 to 10% by mass.

Then, the aramid fiber bundle to which the latex-containing sizing agent is adhered is heated and dried at an appropriate temperature and time by a known method such as a heating roll, heater, steam, etc. to obtain an aramid fiber bundle.

After that, by using a known guillotine cutter or rotary cutter, the fibers are cut into fibers having a length of 0.1 mm to 10 mm by a known method to obtain bundles of short aramid fibers for reinforcing rubber. The fiber length is more preferably 1 mm to 10 mm, particularly preferably 1 mm to 5 mm. If the fiber length is 0.1 mm or more, the reinforcing effect of the short fibers to the rubber is exhibited, and if the fiber length is 10 mm or less, the short fibers may be entangled with each other when the short fiber bundle and the rubber are mixed. In addition, short fibers are not easily cut by shearing in the mixer to form fiber balls of short fibers, and the dispersibility in rubber is good.

In the present invention, the number of treatments for attaching the latex-containing sizing agent is preferably one. If the treatment is performed twice or more, the sizing agent adheres only to the surface of the fiber bundle and tends to cause scum.

In the rubber-reinforcing aramid short fiber bundle of the present invention, since RFL is applied to each single yarn, the single yarn is evenly distributed during rubber kneading, compared to the general adhesion method by RFL treatment. distributed. In addition, since the elastic modulus of rubber reinforced by the aramid short fiber bundle is expected to be improved and the orientation of the short fiber is expected to be improved, various power transmission belts, tires (sidewall members, tread members, etc.), rubber hoses, rubber It can be used as a reinforcing material for various rubber products such as sheets. The type of rubber is not particularly limited.

EXAMPLES The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to them. In addition, in the following examples and the like, "% by mass" is abbreviated as "%" and "parts by mass" is abbreviated as "parts" unless otherwise specified. The method for evaluating the rubber-reinforcing aramid short fiber bundles described in the examples is as follows.

(1) Moisture Content of Aramid Fiber Measure the mass of about 5 g of sample (mass before drying). After heat treatment at 300° C. for 20 minutes, the sample is allowed to stand at 25° C. and 65% RH for 5 minutes, and the mass (mass after drying) is measured again.
Moisture content (mass%) = [(mass before drying - mass after drying) / (mass after drying)] x 100

(2) Epoxy compound adhesion amount The total adhesion amount was measured by the heating weight loss method, and the surface adhesion amount was measured by the solvent extraction method. The difference between the total adhesion amount and the surface adhesion amount was taken as the amount of permeation into the fiber skeleton.

(3) Rubber Adhesion According to Adhesion-A method of JIS L 1017, a sizing agent-treated cord was embedded in unvulcanized rubber, press vulcanized at 150° C. for 30 minutes under pressure, and then allowed to cool. . After that, the pull-out load (N/cm) was measured by pulling out the cord from the rubber block at a speed of 30 cm/min. Chloroprene unvulcanized rubber was used as the rubber compound in adhesion evaluation.

(4) Adhesiveness to rubber after aging As in the evaluation of adhesiveness to rubber, a sizing agent-treated cord was embedded in unvulcanized chloroprene rubber, press-vulcanized under pressure, and allowed to cool. After that, heat treatment was performed under the conditions of 120°C x 1 week, and after leaving it for 24 hours at a temperature of 25°C and a humidity of 55% RH, the cord was pulled out from the rubber block at a speed of 30 cm/min to obtain a pull-out load after aging. (N/cm) was measured.

(5) Lump generation rate Put 200 g of short fibers into a sieve with a mesh size of 2 mm x 2 mm, and after sieving for a sufficient time until the short fibers do not pass through the sieve, the short fibers that did not pass are generated as lumps. rate was calculated.
Occurrence rate (%) = (amount of lumps / amount of input) x 100

(6) Process dregs It was judged whether or not dregs were generated when the fibers after the dry heat treatment were run for 2,000 m.

(Example 1)
1 kg of polyparaphenylene terephthalamide (PPTA) (molecular weight: about 20,000) obtained by a known method was dissolved in 4 kg of concentrated sulfuric acid, and was passed through a die having 1,000 holes with a diameter of 0.1 mm at a shear rate of 30, 000 sec ⁻¹ and spun in water at 4° C., then neutralized with a 10 mass % aqueous sodium hydroxide solution at 10° C. for 15 seconds. Then, it was dehydrated and dried at a low temperature of 110° C. to adjust the moisture content to 50%.
An oil agent (a mixture of diisostearyl adipate/dioleyl adipate/hydrogenated castor oil ethylene oxide/mineral oil) containing 50% by mass of sorbitol polyglycidyl ether as an epoxy compound was added to the PPTA fiber, and the moisture content was converted to 0%. After applying 1.0% to the fiber mass at that time, it was wound on a bobbin in the winding process.

Separately, 100 parts (solid content) of styrene-butadiene-vinylpyridine copolymer latex (number average particle diameter: 140 nm) in the presence of sodium hydroxide, resorcin and formaldehyde in the presence of sodium hydroxide in advance molar ratio 15 parts (solid content) of the initial condensate reacted at a ratio of resorcin/formaldehyde = 3/1 were mixed and aged to prepare liquid (C). An aqueous dispersion of diphenylmethane-bis-4,4′-methylethylketoneoxycarbamate was added to the prepared liquid (C) as a blocked isocyanate compound so that the mass ratio (solid content) with the liquid (C) was 5:1. to prepare an RFL treatment liquid.

The resulting PPTA fibers (fineness 1,670 dtex when converted to moisture content of 0%, filament number 1,000) were impregnated with a sizing agent composed of the above RFL treatment liquid, and the RFL was given in Table 1 with respect to the PPTA fiber mass. It was made to adhere so that the solid content adhesion amount would be . The moisture content of the PPTA fibers immediately before being impregnated with the sizing agent was 50%. After that, drying and heat treatment were performed at 250° C. for 2 minutes. The obtained PPTA fibers were cut to 3.5 mm by a known method to obtain bundles of short fibers.

(Comparative example 1)
The same sorbitol polyglycidyl ether as in Example 1 was applied to the PPTA fibers obtained in Example 1 and having a moisture content of 10% in a dipping bath. After the polyparaphenylene terephthalamide fibers were impregnated with a sizing agent in the same manner as in Example 1 to attach RFL, a bundle of short fibers was obtained in the same manner as in Example 1.

(Comparative example 2)
A short fiber bundle was obtained in the same manner as in Example 1, except that a styrene-butadiene-vinylpyridine copolymer latex (number average particle size: 172 nm) was used.

(Comparative Example 3)
A short fiber bundle was obtained in the same manner as in Example 1, except that a styrene-butadiene-vinylpyridine copolymer latex (number average particle size: 90 nm) was used.

Table 1 shows the evaluation results of the bundled short fibers obtained above.

From the results in Table 1, the aramid short fiber bundle obtained in Example 1 had good adhesiveness to rubber, high-temperature adhesiveness, and dispersibility in rubber. Since the RFL is uniformly applied to the inside, there is no problem of generation of process waste. In contrast, the aramid short fiber bundles obtained in Comparative Examples 1 to 3 were inferior in heat resistance to rubber.

The aramid short fiber bundle of the present invention is useful as a reinforcing material for various rubbers.

Claims (6)

A styrene-butadiene-vinylpyridine co-polymer which is an aramid short fiber bundle for rubber reinforcement, has an epoxy compound attached to or permeates the fiber surface or in the fiber skeleton, and has a number average particle size in the range of 100 to 150 nm. A bundle of aramid short fibers for rubber reinforcement, characterized by being attached with a sizing agent containing a polymer latex. 2. The rubber-reinforcing aramid short fiber bundle according to claim 1 , wherein the sizing agent further contains a resorcin-formaldehyde initial condensate, a blocked polyisocyanate compound and a chlorophenol compound. The epoxy compound penetrates into the fiber skeleton and adheres to the surface of the fiber, and the amount of epoxy compound (A) that penetrates into the fiber skeleton and the amount of epoxy compound that adheres to the fiber surface (B). 3. The rubber-reinforcing aramid short fiber bundle according to claim 1 , wherein the ratio of (B)/(A) is 0.5 or less. The amount of epoxy compound permeated into the fiber skeleton is 0.1 to 10.0% by mass with respect to the fiber mass when the moisture content of the aramid fiber is converted to 0%, and the amount of epoxy compound attached to the fiber surface is The rubber-reinforcing aramid short fiber bundle according to any one of claims 1 to 3 , wherein the content is 0.05 to 0.5% by mass. The aramid short fiber bundle for rubber reinforcement according to any one of claims 1 to 3 , wherein the amount of the sizing agent attached is 2 to 10% by mass with respect to the fiber mass when the moisture content of the aramid fiber is converted to 0%. body. Styrene-butadiene- vinylpyridine having a number average particle size in the range of 100 to 150 nm in an aramid fiber bundle having an epoxy compound attached to or permeated into the fiber or fiber skeleton and having a moisture content of 25% by mass or more. A bundle of aramid short fibers for reinforcing rubber, characterized by applying a sizing agent containing a copolymer latex only once, followed by drying and heat treatment, and then cutting the fiber length to 0.1 to 10 mm. Production method.