JPH08218219A - Staple fiber for reinforcing rubber - Google Patents

Abstract

PURPOSE: To obtain a staple fiber excellent in reinforcing effects without causing the slipping off of single filaments by forming only the cross section of a cut end into a flat shape having a specific value or above of flatness degree. CONSTITUTION: This staple fiber for reinforcing rubber such as a polyester staple fiber is obtained by flattening only the cross section of a cut end thereof. The flatness degree which is a ratio of the maximum diameter to the minimum diameter of the cross section is >=3, preferably 5-8 and sufficient anchoring effects can be obtained. The cross section is preferably flattened by a method for press deforming the cut end by fusing and cutting with a heated cutter blade, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to short fibers for reinforcing rubber, and more particularly to short fibers used for reinforcing rubber products for industrial materials such as belts, hoses and tires.

[0002]

2. Description of the Related Art At present, in order to reinforce rubber products such as rubber, belts and tires, short fibers such as vinylon, nylon and polyester are blended in rubber. Such short fibers usually have a round cross-sectional shape, and the adhesion with rubber is not always sufficient, and the adhesive interface easily peels off due to excessive stress, repeated stress, etc., so single yarn loss easily occurs and the reinforcing effect is reduced. There is a problem to let.
In particular, polyester short fibers are suitable as rubber-reinforcing short fibers because of their high strength and high modulus,
Since the surface is inactive, adhesion with rubber is insufficient, the above tendency is remarkably exhibited, and a sufficient reinforcing effect cannot be exhibited. Therefore, various adhesive prescriptions have been proposed in order to improve the adhesion between the polyester short fibers and the rubber, but none have been found to be sufficient and the excellent characteristics have not been sufficiently exhibited.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a single yarn drop does not occur,
It is an object of the present invention to provide short fibers for rubber reinforcement having an excellent reinforcing effect.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, have found that the cross-sectional shape of the cut end portion of the short fiber may be modified, and the present invention has been completed. Came to do.

That is, according to the present invention, for reinforcing rubber, only the cross section of the cut end is flat, and the flatness ratio H (the maximum diameter of the cross section / the minimum diameter of the cross section) is 3 or more. Short fibers are provided.

Examples of the rubber-reinforcing short fibers of the present invention include short fibers such as cellulose, vinylon, nylon and polyester, and the material thereof is not limited, but particularly in the case of polyester short fibers, a remarkable effect is exhibited. be able to.

Examples of the polyester constituting the rubber-reinforcing short fibers of the present invention include polyesters having ethylene-2,6-naphthalate or ethylene terephthalate as a main repeating unit. In this case, ethylene-2,6 -A polymer containing 90 mol or more of naphthalate units or ethylene terephthalate units and 10 mol% or less of an appropriate third component may be used. As the third component, (a) a compound having two ester-forming functional groups, for example, an aliphatic dicarboxylic acid such as oxalic acid, succinic acid, adipic acid, sebacic acid, and dimer acid; cyclopropanedicarboxylic acid, cyclobutane Alicyclic dicarboxylic acids such as dicarboxylic acid and hexahydroterephthalic acid; phthalic acid, isophthalic acid, naphthalene-
Aromatic dicarboxylic acids such as 2,7-dicarboxylic acid and diphenyldicarboxylic acid; carboxylic acids such as diphenyletherdicarboxylic acid, diphenylsulfonic acid, diphenoxyethanedicarboxylic acid and sodium 3,5-dicarboxybenzenesulfonate; glycolic acid, p -Oxycarboxylic acids such as oxybenzoic acid and p-oxyethoxybenzoic acid; propylene glycol, trimethylene glycol, diethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentylene glycol, p-xylene glycol, 1,4-cyclohexanediene. Methanol, bisphenol A, p, p'-dihydroxydiphenyl sulfone, 1,4-bis (β-hydroxyethoxy) benzene, 2,2-bis (p-β-hydroxyethoxyphenyl) Propane, oxy compounds such as polyalkylene glycols; functional derivatives thereof;
High polymerization degree compounds derived from the above-mentioned carboxylic acids, oxycarboxylic acids, oxy compounds or their functional derivatives, and (b) compounds having one ester-forming functional group, for example, benzoic acid, benzyloxybenzoic acid. , Methoxypolyalkylene glycol and the like. Further, (c) a compound having three or more ester-forming functional groups such as glycerin, pentaerythritol, and trimethylolpropane can also be used within the range where the polymer is substantially linear. Among them, ethylene-2,
A polyester containing 6-naphthalate as a main repeating unit is preferably used. Needless to say, these polyesters may contain a matting agent such as titanium dioxide and a stabilizer such as phosphoric acid, phosphorous acid and their esters.

In the polyester staple fiber of the present invention,
The intrinsic viscosity is preferably 0.60 or more, more preferably 0.7 to 1.0. The intrinsic viscosity referred to here is a value obtained from the viscosity measured at 35 ° C. by dissolving the undrawn yarn in a mixed solvent of phenol and orthodichlorobenzene (volume ratio 6: 4). When the intrinsic viscosity is less than 0.60, the strength and toughness of the fiber are lowered. Fibers having an intrinsic viscosity of more than 1.0 tend to be defective in the spinning process and are difficult to manufacture.

The fineness of the polyester short fibers is preferably less than 8 de, particularly preferably 2 to 7 de. As the fineness increases, poor dispersion in rubber easily occurs. The strength is preferably 8 g / de or more, and more preferably 9 g / de or more in order to enhance the reinforcing effect. The fiber length of the short fibers is preferably 0.3 to 10.0 mm, and particularly preferably 0.5 to 6.0 mm. If it is less than 0.3 mm, it is difficult to obtain the reinforcing effect by the short fiber, and it is 10.0 mm.
If it exceeds, the entanglement between the short fibers occurs, and the dispersion tends to be poor in the rubber.

It is important that the short polyester fiber of the present invention has a flat cross section only at the cut end and that the flatness ratio H expressed by the maximum diameter of the cross section / the minimum diameter of the cross section is 3 or more. If the flatness ratio is less than 3, a sufficient anchoring effect cannot be obtained, single yarn loss occurs, and the reinforcing effect becomes poor. The flatness ratio is particularly preferably 5 to 8.

The cross-sectional shape other than the cut end is arbitrary as long as it has a shape such that the minimum circumscribed circle diameter of the cross section is smaller than the maximum diameter of the end cross-section, but it is usually a round cross section.

To flatten only the cross section of the cut end, any method such as heating and pressing the cut end can be used, but when cutting the long fibers into short fibers, a heating cutter is used. It is preferable to use a method of fusing with a blade and deforming the cut end portion under pressure, because short fibers can be produced with good productivity. At this time, the flatness can be adjusted by changing the curvature radius R of the cutter blade and the heating temperature.

In the case of polyester short fibers, it is preferable that they are treated with an adhesive in order to improve the adhesiveness with rubber. The adhesion treatment agent is a composition containing resorcin-formalin rubber latex, and the resorcin-formalin rubber latex used here is usually called RFL and has any composition known as RFL. May be Examples of the rubber latex include natural rubber latex, styrene / butadiene / copolymer latex, vinylpyridine / styrene / butadiene terpolymer latex, and chloroprene rubber latex, which may be used alone or in combination.

[0014]

In the rubber-reinforcing short fiber of the present invention, only the cross section of the cut end is highly flattened. Therefore, when blended and dispersed in rubber, the flat cross section has an anchor effect which may be called physical adhesion. It is imparted, and the single yarn loss is unlikely to occur.

In the case of polyester short fibers, when the adhesive treatment is applied, the adhesive is attached to the surface of the polyester short fibers, but the adhesive is not attached to the cut end face, This cut end face does not contribute to the adhesion with rubber. By flattening the cut end portion, the area of the cut end surface that does not contribute to adhesion with rubber can be reduced, and the adhesiveness with rubber can be improved.

In the case of polyester short fibers, these effects are organically combined to significantly improve the rubber reinforcing effect.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. The physical properties are measured by the following methods.

(1) Strength and elongation of short fibers Using a tensile load measuring device (Autograph manufactured by Shimadzu Corporation),
It was measured according to JIS L-1074-64.

(2) Tensile strength at yield point and elongation at break of reinforced rubber product This shows the reinforcing effect and elongation of a rubber product reinforced with short fibers. According to JIS K6301, No. 3 dumbbell-shaped test piece was tested at 500 mm / min. The value obtained by dividing the load at the yield point when cutting at the tensile speed of 2 by the cross-sectional area of the test piece is the tensile strength at the yield point, and the elongation between marked lines at the time of cutting is the breaking elongation.

(3) Flexural Fatigue Life of Reinforced Rubber Product This is an index for judging the fatigue property of a rubber product reinforced with short fibers, using a Dematia flex fatigue tester manufactured by Toyo Seiki Co., Ltd.
The No. 3 dumbbell-shaped test piece was bent at a frequency of 5 Hz by 25%, and the number of times until cracking occurred was displayed.

[Examples 1 to 3, Comparative Examples 1 and 2] Three ethylene-2,6-naphthalate chips having an intrinsic viscosity of 0.65 were prepared.
After melting at a temperature of 10 ° C., 19 discharge holes with a hole diameter of 0.6 mm were formed.
It discharged from the spinneret which has 2 holes. The discharge rate was adjusted so that the single yarn fineness after spinning and drawing was 5 denier.
The discharged yarn is 370 ° C over a length of 400 mm.
After passing through the zone heated and maintained at 25 ° C., cooling air having a temperature of 25 ° C. and a wind speed of 0.3 m / sec was blown over a length of 330 mm to cool and solidify, and after applying an oil agent with an oiling roller, at a speed of 500 m / min. I wound up.

Then, the undrawn yarn is first fed between the heating supply roll (FR) at 160 ° C. and the first stage drawing roll (1R).
Stage stretching (magnification: 6.0 times) is performed, and then 280 ° C. between the first stage stretching roll and the second stage heating stretching roll (2R).
2nd stage drawing (1.1 times magnification) in a dry heat bath, and then relaxed by 3% with a heating roller at 160 ° C., and further 2
It was made to be 3% in a dry heat bath at 80 ° C. and wound at a speed of 300 m / min. The single yarn fineness of the obtained drawn yarn is 5 denier,
The strength was 9.0 g / de.

The drawn yarn thus obtained was dipped in a resorcin / formalin / latex adhesive and dried in an atmosphere of 175 ° C. for 1 minute, and then heat-treated in an atmosphere of 230 ° C. for 2 minutes. The adhesive-treated polyester fiber thus obtained was melted by changing the heating temperature and R of the cutter blade as shown in Table 1 and fusing so that the flatness of the cross section of the cut end became as shown in Table 1. A short fiber having a length of 3.0 mm was obtained.

5% by volume of each of these short fibers was mixed with natural rubber and unblended rubber containing styrene butadiene as a main component, and an MS type pressure kneader (DS3-10 MHHS Moriyama Seisakusho Co., Ltd.) was used. Kneaded for 3 minutes. A sheet was taken out to an appropriate thickness so that the short fibers were oriented, a rubber sheet was made by press vulcanization, and a sample was cut in the orientation direction of the short fibers to evaluate the performance. The results are shown in Table 1. A good reinforcing effect is obtained when the flatness of the cut end cross section of the short fiber is 3 or more (Examples 1 to 3), and particularly when the flatness is 5 to 5. Excellent effects were obtained in (Examples 2 and 3).

[0025]

[Table 1]

[Examples 4 to 6, Comparative Examples 3 and 4] 300 polyethylene terephthalate chips having an intrinsic viscosity of 1.00 were prepared.
After melting at a temperature of ° C, it was discharged from a spinneret having 192 discharge holes having a hole diameter of 0.6 mm. The discharge rate was adjusted so that the single yarn fineness after spinning and drawing was 5 denier. The discharged yarn passes through a zone heated and held at 350 ° C. over a length of 300 mm, then at a temperature of 25 ° C. and a wind speed of 0.3.
A cooling air of m / sec was blown over a blowing length of 330 mm to cool and solidify, an oiling agent was applied by an oiling roller, and then wound at a speed of 900 m / min.

Then, the undrawn yarn is subjected to the first stage drawing (magnification: 3.3 times) between the heating supply roll (FR) at 85 ° C. and the first stage drawing roll (1R), and then the first stage drawing is carried out. After performing the second stage stretching (magnification 1.6 times) in a dry heat bath at 280 ° C. between the roll and the second stage heating stretching roll (2R),
Relax by 3% with a heating roller at 120 ° C, then 280
It was made to be 3% in a dry heat bath at 0 ° C. and wound at a speed of 300 m / min. The obtained drawn yarn had a single yarn fineness of 5 denier and a strength of 8.8 g / de.

The drawn yarn thus obtained was dipped in a resorcin / formalin / latex type adhesive, dried in an atmosphere of 175 ° C. for 1 minute, and then heat-treated in an atmosphere of 230 ° C. for 2 minutes. The adhesive-treated polyester fiber thus obtained was melted by changing the heating temperature and R of the cutter blade as shown in Table 2 and fusing so that the flatness of the cross section of the cut end became as shown in Table 2. A short fiber having a length of 5.0 mm was obtained.

5% by volume of each of these short fibers was mixed with natural rubber and unblended rubber containing styrene-butadiene as a main component, and an MS type pressure kneader (DS3-10 MHHS Moriyama Seisakusho Co., Ltd.) was used. Kneaded for 3 minutes. A sheet was taken out to an appropriate thickness so that the short fibers were oriented, a rubber sheet was made by press vulcanization, and a sample was cut in the orientation direction of the short fibers to evaluate the performance. The results are as shown in Table 2, and when the flatness of the cut end cross section of the short fiber is 3 or more (Examples 4 to 6), a good reinforcing effect is obtained, and particularly, the flatness of 5 to 8 is obtained. In this case (Examples 5 and 6), excellent effects were obtained.

[0030]

[Table 2]

[0031]

EFFECTS OF THE INVENTION The short fiber of the present invention, when incorporated into rubber, does not cause single yarn loss, improves the adhesiveness with rubber, and has an excellent rubber reinforcing effect.

Claims (4)

[Claims] 1. A rubber-reinforcing short fiber characterized in that only the cross section of the cut end is flat, and the flatness ratio H represented by the following formula is 3 or more. Flatness ratio H = maximum diameter of cross section /
Minimum diameter of cross section 2. The short fiber for rubber reinforcement according to claim 1, wherein the short fiber is a polyester fiber. 3. The short fiber for rubber reinforcement according to claim 2, which has been treated with an adhesive. 4. The fineness is less than 8 de, the intrinsic viscosity is 0.6 or more, the strength is 8.0 g / de or more, and the fiber length is 0.3 to 1.
The short fiber for rubber reinforcement according to claim 2 or 3, which has a length of 0.0 mm.