JPH10195208A - Rubber-reinforcing fiber and production of rubber-molded product using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject fiber that can increase uniform dispersion of fibers without damage to the physical properties of the rubber molding product and has increased adhesion to the matrix rubber by applying a liquid rubber excellent in compatibility the rubber on the surface of the reinforcing fiber. SOLUTION: This objective fiber is produced by applying >=1wt.% of a liquid rubber (or rubber in liquid at room temperature), particularly an isoprene liquid rubber with a molecular weight of 10,000-70,000, to the fiber that can be divided or f'ibrillated by the mechanical shear force caused in the mixing or molding in the rubber-molding step (Banbury or roll kneading step), preferably comprises (A) a polyvinyl alcohol polymer and (B) an acrylonitrile polymer where the cross sections of the fibers are islands or either A or B is islands and the other is the sea (matrix) and the weight A/B ratio is 90/10-20/80. This fiber and the matrix rubber are kneaded, molded by extrusion molding, when desired, vulcanized (hot-press vulcanization treatment) to give a fiber-reinforced rubber molding product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber used for reinforcing matrix rubber and a method for producing a molded rubber article using the reinforcing fiber.

[0002]

2. Description of the Related Art Rubber (fiber reinforced rubber) containing reinforcing fibers for improving physical properties such as strength and abrasion has been used in various rubber application fields. In order for the reinforcing effect to be sufficiently exhibited, it is important that the fibers are uniformly dispersed in the matrix rubber while ensuring good adhesion between the fibers and the rubber. If the adhesion between the reinforcing fiber and the matrix is low, the reinforcing effect will not be sufficiently exhibited, and if the fiber dispersion becomes uneven, a large difference will occur in the performance of each part of the product and the quality of the product will only be insufficient. In addition, a sufficient reinforcing effect cannot be obtained. Normal short fibers have low uniform dispersibility due to easy entanglement between fibers and poor slippage between fibers.
It is necessary to knead the fibers for a long time in order to disperse the fibers uniformly in the rubber, and even if the fibers are kneaded for a long time, the dispersibility tends to be insufficient.

[0003] In view of the above, various studies have been made to enhance fiber dispersibility. For example, a method has been proposed in which a single fiber bundle obtained by using a thermoplastic resin having a low melting point is added and kneaded in rubber. According to this method, first, the bundled yarn is dispersed in the rubber, and then the thermoplastic resin is melted by the heat generated in the rubber kneading step to separate the fibers, so that an excellent effect in terms of uniform dispersion of the fibers is obtained. can get.

[0004]

However, this chemical bonding process requires a relatively large cost, and there are cases where a sufficient bonding force cannot be obtained depending on the fibers and the matrix. Since the thermoplastic resin remains therein, the original performance of the rubber may be impaired. In view of the above, an object of the present invention is to provide an excellent rubber reinforcing fiber which is excellent in uniform dispersibility and reinforcing property and does not impair the inherent properties of rubber.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a rubber molded article obtained by heating and vulcanizing a rubber reinforcing fiber to which liquid rubber is adhered, and a mixture of the rubber reinforcing fiber to which liquid rubber is adhered and a matrix rubber. And a method for producing the same.

[0006] By adhering a liquid rubber having excellent compatibility with rubber to the fiber surface, the wettability between the fiber and the rubber is improved and at the same time the melt viscosity of the matrix rubber is reduced. Can be significantly increased. Furthermore, if a normal thermoplastic resin is present in the matrix rubber, the inherent performance of the rubber may be impaired.In the present invention, however, the liquid rubber is co-vulcanized with the matrix rubber in the rubber vulcanization step. The physical properties of the molded product are not impaired, and the adhesiveness between the matrix rubber and the reinforcing fibers is enhanced, so that an excellent effect can be obtained.

[0007] The liquid rubber in the present invention refers to a rubber which is liquid at normal temperature, and has a melting point of 50 ° C in terms of fiber dispersibility and handleability.
The following are preferred. More specifically, liquefied natural rubber (which is obtained by subjecting ordinary natural rubber having a molecular weight of about 1,000,000 or more to thermal decomposition to a molecular weight of about tens of thousands), liquid isoprene-based synthetic rubber, and liquid nitrile / butadiene / rubber (NB
R), liquid styrene-butadiene rubber (SBR), liquid butadiene rubber (BR), and the like, and these may be used in combination. It is preferable to use one having a molecular structure similar to that of the matrix rubber. Of these, isoprene-based liquid rubber is preferred, and those having a molecular weight of 10,000 to 70,000 are particularly preferred. From the viewpoint of adhesion to rubber, a liquid isoprene rubber modified with maleic acid or itaconic acid is preferable within a range not exceeding 30 mol%, and a liquid isoprene rubber and a molecular weight of 1
More preferably, about 50,000 liquefied natural rubber is used in combination.

[0008] The molecular weight of the liquid rubber is preferably 5,000 or more and 100,000 or less. Those having such a molecular weight are preferred in terms of fiber dispersibility and processability of adhering to fibers because the performance of the matrix rubber is hardly impaired and the viscosity is moderate. The amount of the liquid rubber adhered to the fiber is 1% by weight or more, particularly 8% by weight or more, and more preferably 10 to 30%.
It is preferably 0% by weight, more preferably 15 to 150% by weight. In the present invention, since the co-vulcanizable liquid rubber is used, the influence on the matrix rubber is extremely small, and it can be used in a large amount. However, even if the adhesion amount is increased to a certain degree or more, the fiber dispersibility is not so much improved, which is not economically preferable.

The aspect ratio of the fibers is preferably from 30 to 1500, particularly preferably from 50 to 800, from the viewpoint of fiber dispersibility and reinforcing effect. If the aspect ratio is reduced, the dispersibility of the fiber is improved, but the surface area of the fiber is reduced and a sufficient adhesive force cannot be secured, so that the reinforcing effect is hardly exhibited. In the present invention, since the liquid rubber is adhered, even if a fiber having a large aspect ratio is used, the dispersibility is hardly reduced and an excellent reinforcing effect can be obtained. The aspect ratio in the present invention is a value obtained by dividing the fiber length by the diameter of a circle having the same area as the cross section of the fiber. In addition, a single fiber may be used as a bundled yarn bundled with liquid rubber, and the bundled yarn is also included in the present invention.

The material of the fiber used in the present invention is not particularly limited. For example, organic synthetic fibers such as polyester fibers (including polyarylate fibers), polyvinyl alcohol fibers, paraamide fibers, and metaaramid fibers are used. Inorganic fibers such as fiber, glass fiber, alumina fiber and carbon fiber can be used. As the thickness of the fiber, 0.1-20 denier,
Particularly, those having 1 to 10 denier are preferable. Fiber strength is 5
g / d or more, particularly preferably 7 g / d or more, and Young's modulus is preferably 100 g / d or more, particularly preferably 150 g / d or more.

The fiber is preferably one in which the fiber is divided and reduced in diameter by the mechanical shearing force generated during mixing or molding in the rubber molding process (for example, Banbury and roll kneading process). Is more preferably 2/3 or less before mixing. At this time, the average fiber diameter after division is 9 μm or less, particularly 5 μm or less, and more preferably 0.03 to
It is preferably 3 μm. When such fibers are used, good dispersibility can be obtained, and at the same time, an excellent reinforcing effect can be obtained.

In the reinforcing fiber, even if the entire cross section of the yarn is divided and reduced in diameter, or only the periphery thereof is divided and reduced while leaving the trunk.
The diameter may be reduced, and the latter partial division and reduction in diameter are more preferable because the entanglement of the fibers in the matrix is small. It is more preferable in terms of uniform dispersion of the fibers that the splitting / diameter reduction when shearing force is applied mainly occurs at a shearing rate of 1 × 10 ⁻⁵ sec ⁻¹ or more. Depending on the method, the fibers are also split in a preparatory step before production of the rubber product such as fiber cutting, and as a result, the fibers are entangled with each other, causing a problem in dispersion. It is preferable to apply a shearing force in any of the processes for producing a rubber molded product to reduce the diameter of the fibers by dividing them. Specifically, a Banbury mixer, a rubber kneading roll, a roll gap of a calender, a rotation speed ratio Or adjust the injection,
In the extrusion molding process, the amount of rubber discharged, the groove structure of the extrusion screw, the rotation speed or the gate to the mold
There is a method of adjusting the gap, and the like.

As a preferred specific example of the fiber, a solvent-spun cellulose obtained by a method of spin-dry spinning a cellulose stock solution obtained by dissolving cellulose in an amino oxide-based solvent in water to precipitate cellulose. Fiber ("TENCEL" manufactured by Coulters Co., Ltd., UK) and splittable polyester fiber. Liquid rubber having a molecular weight of 5,000 to 100,000 is particularly preferred.
% By weight or more, wherein the fibers are composed of at least a polyvinyl alcohol-based polymer (A) and an acrylonitrile-based polymer (B), and have a sea-island cross-section, wherein either A or B is an island component The other is a sea component, and a fiber having a weight ratio of A / B of 90/10 to 20/80 is preferable.

Even if a fiber having an aspect ratio with good dispersibility, that is, a fiber having a relatively low aspect ratio is used at the time of adding and dispersing the fiber, the fiber is divided and reduced in diameter in a subsequent processing step, so that an excellent reinforcing effect is obtained. Is obtained. A polyvinyl alcohol-based polymer is used because the fiber obtained therefrom has an extremely high strength, and an acrylonitrile-based polymer is used together therewith.
The combination of a polyvinyl alcohol-based polymer and an acrylonitrile-based polymer is preferred in terms of fiber division / diameter reduction and high strength, and a solvent spinning method typified by a wet spinning method is more preferably used as a method for producing a polyvinyl alcohol-based fiber. However, when dimethyl sulfoxide (DMSO) is used as a solvent for the spinning solution at that time, an acrylonitrile-based polymer is also soluble in DMSO, and therefore, a combination of a polyvinyl alcohol-based polymer and an acrylonitrile-based polymer is preferable from the viewpoint of production. .

The polyvinyl alcohol polymer may be completely saponified, partially saponified, or copolymerized with another monomer. The acrylonitrile-based polymer only needs to have acrylonitrile in an amount of 70 mol% or more. Therefore, for example, (meth) acrylates such as methyl acrylate, ethyl acrylate, and methyl methacrylate; vinyl esters such as vinyl acetate and vinyl butyrate; Vinyl compounds such as vinyl chloride, acrylic acid,
It may be copolymerized with a monomer such as an unsaturated carboxylic acid such as methacrylic acid or maleic anhydride, a vinyl compound containing a sulfonic acid, or a monomer co-vulcanizable with a rubber such as butadiene or isoprene. In order to improve the solubility in the undiluted solvent, 0.5 to 10 mol%, more preferably 2 to 10 mol% of other monomers is used as compared with the PAN homopolymer.
Acrylonitrile-based polymers copolymerized at ８8 mol% are preferred.

A preferred method for producing the sea-island fiber is that the sea component polymer and the island component polymer are dissolved in a common solvent, wet-spun or dry-spun, and then wet-drawn (they need not be used in the case of dry-spinning). Further, it is preferable to perform dry heat stretching. In order to increase the fiber strength and achieve more excellent division and reduction in diameter, it is preferable to increase the draw ratio.

The method for adhering the liquid rubber of the present invention is not particularly limited. For example, tow-like fiber bundles, monofilaments or multifilaments obtained by single yarn or pulling, can be used as a liquid rubber or an organic solvent diluted liquid, or a liquid rubber. Is preferably immersed in, for example, emulsified with an emulsifier and then squeezed and dried to remove the solvent, water and the like. The fiber may be cut after or before the liquid rubber is attached. The fiber cutting method is not particularly limited, and a known method such as an EC cutter or a guillotine cutter can be employed. Further, in addition to the present invention, the use of the conventional adhesive treatment such as RFL and isocyanate on the fibers before the liquid rubber is adhered does not reduce the effect of the present invention, and a higher adhesive force can be obtained. Is preferred.

The method for kneading the reinforcing fiber and the matrix rubber of the present invention and the step of adding the reinforcing fiber are not particularly limited. For example, in a Banbury mixer or a roll kneading step, it is charged together with a matrix / rubber compound (rubber, vulcanizing agent, vulcanization accelerator, antioxidant, carbon, etc.) and kneaded, or mixed with fiber and matrix. There is a method in which a rubber compound is charged at the stage where rubber is pre-kneaded. The kneading time of the matrix rubber and the reinforcing fibers is 1 to 40 minutes, especially 3
It is preferably set to about 20 minutes. It is preferable to employ the latter from the viewpoint of fiber dispersibility. In particular, when kneading with a Banbury mixer, the rubber compound reaches a high temperature of 100 ° C. or more due to frictional heat generated during kneading, and vulcanization proceeds during kneading. Therefore, only the matrix rubber and the liquid rubber-adhered fiber are kneaded. After the fibers are sufficiently dispersed in the rubber, it is preferable to add and knead a vulcanizing agent, a vulcanization accelerator and the like.

Further, a so-called master batch in which reinforcing fibers are compounded in rubber at a high ratio is produced, and this is called a matrix batch.
The method of adding to and mixing with rubber is more preferable in terms of fiber dispersibility. The fiber mixing ratio in the master batch is 10 to 5
It is preferred to be 0% by weight / master-batch total weight, more preferably 20-40% by weight / master-batch total weight. The kneading time of fiber and rubber to obtain a master batch is 1 to
40 minutes, preferably about 3 to 20 minutes,
The rubber constituting the master batch and the matrix rubber may be the same or different rubbers. The compounding ratio of the fibers in the rubber molding is preferably 1 to 50% by weight / the total weight of the rubber molding, particularly preferably 3 to 20% by weight / the total weight of the rubber molding.

After kneading the matrix rubber and the reinforcing fibers, the mixture is molded by a known extrusion molding method, calendar molding method, injection molding method or the like, and then vulcanization treatment (hot press vulcanization treatment or the like) is performed if desired. For example, a fiber-reinforced rubber molded product can be obtained.
The vulcanization treatment is preferably performed at 80 to 250 ° C, particularly 120 to 200 ° C, and the treatment time is 5 to 60 minutes, particularly 10 to
Preferably, it is 30 minutes. The form of the rubber molded product obtained by the present invention is not particularly limited, and can be appropriately selected, such as a sheet shape and a tubular shape.

[0021]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Degree of polymerization 1750, degree of saponification 9
Acrylonitrile-based polymer (abbreviated as PAN) obtained by copolymerizing 60 parts by weight of 9.9 mol% of polyvinyl alcohol (hereinafter abbreviated as PVA) and 5 mol% of methyl methacrylate
40 parts by weight were added to dimethyl sulfoxide (DMSO), and the mixture was stirred and dissolved under a nitrogen stream at 80 ° C. for 8 hours at 200 rpm to obtain a mixed spinning dope having a total polymer concentration of 20% by weight. This undiluted solution is opaque when observed with the naked eye, and has a phase structure having a particle diameter of 2 to 8 μm when the undiluted solution is observed for its phase structure.
It was confirmed that the A component was a dispersion medium component (sea component) and the PAN component was a dispersion component (island component).

The stock solution is wet-spun through a spinneret having 1,000 holes and a hole diameter of 0.08 mmφ in a coagulation bath at a temperature of 5 ° C. at a weight ratio of DMSO / methanol of 45/55, and wet-stretched three times. After DMSO in the yarn was extracted with methanol, the yarn was dried with hot air at 80 ° C., and subjected to dry heat drawing at 230 ° C. with a total draw ratio of 16 times to obtain 1800 d / 1000.
Thus, a PVA / PAN blend fiber of f was obtained. The fiber had a strength of 8.5 g / d and a Young's modulus of 180 g / d.
This fiber is cut to a length of 2 mm (aspect ratio 140) using a guillotine cutter, and 100 parts by weight of the cut yarn is liquid isoprene rubber (isoprene having a molecular weight of 50,000).
Oligomer LIR-50) manufactured by Kuraray Co., Ltd.
0 parts by weight were adhered. Next, 1 liter Banbury
Mixer (blade rotation speed: one blade 52 rp)
m, natural rubber (RSS #) on the other blade (44 rpm)
3) 320 g was charged and kneaded for about 1 minute, and then 160 g of the above liquid isoprene rubber-adhered fiber was charged and kneaded for 15 minutes to prepare a master batch (MB).

This master batch is 7.51 inφ × 2
One of the rolls is 11.5 mm / min and the other is 13.
The sheet was kneaded at a rotation speed of 0 m / min, a roll interval of 0.5 mm, and a roll temperature of 50 to 55 ° C. for 5 minutes to form a sheet having a thickness of about 1.0 mm. When the inside of the rubber of the sheet was visually observed, the presence of the fiber itself could not be confirmed because the fiber was well dispersed. Further, in order to confirm the fiber diameter, the sheet was cut at right angles to the longitudinal direction of the sheet, and the cross section was observed with a scanning electron microscope at a magnification of 1,000 times. The fiber diameter was 0.4 to 1.4 μm ( 0.8 μm on average), which is significantly smaller than the fiber diameter of 15 μm before kneading.
From the cross-sectional area ratio, it was found that it was divided into about 300 by the shearing force.

The above MB 120 g, natural rubber (RSS #
3) 100 g, SBR (JSR 1500 manufactured by Nippon Gosei)
20 g is again put into Banbury and kneaded for 2 minutes,
2 g of a peptizing accelerator, Lenasit 7 (manufactured by Bayer), 180 g of carbon black H (manufactured by Mitsubishi Kasei), 20 g of zinc white # 3 (manufactured by Mitsui Kinzoku), 10 g of stearic acid, process oil (Swaflex # 200: Maruzen) 20 g of sulfuric acid) was added and kneaded, 9.6 g of sulfur was further added, 2 g each of Succinol CM and Socynol DM manufactured by Sumitomo Chemical as vulcanization accelerators, and an anti-aging agent (Ouchi Shinko Chemical's Antigen 3C).
4 g was added and kneaded for 1 minute. The obtained kneaded material was heated at a temperature of 50 to 55 with the same two rolls of 7.51 inφ as described above.
The mixture was kneaded at a temperature of 5 ° C. for 5 minutes to form a sheet having a thickness of about 1 mm, and then press-vulcanized at 150 ° C. for 30 minutes to produce a rubber molded body.

This vulcanized sheet is JIS K6251-1
The sheet was punched out with a No. dumbbell, and the strength to strain curve was measured at 20 ° C. and a tensile speed of 500 mm / min. Further, when this measurement was carried out n = 20 and the fluctuation rate of the stress at the time of 10% strain was obtained, the fluctuation rate was extremely low at 5.1%, indicating that the fibers were uniformly dispersed in the rubber. I understand. The fluctuation rate in the present invention is a value obtained by dividing the standard deviation of the measured value of n = 20 by an average value, and the value is expressed as a percentage.

Comparative Example 1 The same procedure as in Example 1 was carried out except that no liquid isoprene rubber was attached. The fiber dispersion is poor, many lumps of fiber are present in the rubber, the stress at 10% of the vulcanized sheet is as low as 3.5 MPa, and the fluctuation rate is 2%.
The variation was as large as 6.8%.

[Examples 2 to 7, Comparative Example 2] PVA-based fiber (Kuraray; trade name: Vinylon, brand name T-16) having a single fiber fineness of 2 dr, a strength of 10.5 g / dr and an elongation of 8% was used. Cut to 3 mm length (aspect ratio 200), isoprene oligomer of molecular weight 50,000 (L made by Kuraray Co., Ltd.)
As shown in Table 1, 0 to 300% of IR-50) was adhered using a double-armed kneader. 100% by weight
The following was applied by a method in which a liquid isoprene rubber was dissolved in trichloroethylene and subjected to an adhesion treatment and dried at 50 ° C. Next, the obtained reinforcing fiber 20
The same procedure as in Example 1 was carried out except that 100 parts by weight of the unvulcanized natural rubber was mixed and kneaded with a Banbury mixer for 5 to 30 minutes. Table 1 shows the result 1. In addition, the uniform dispersibility of the fiber was evaluated as follows: a rubber sheet having a large number of fiber lumps was x, a fiber lumpy was slightly present was △, and the fiber lumps were substantially absent and the fibers were uniform. Those that were dispersed were evaluated as ○.

[0029]

[Table 1]

[0030]

According to the present invention, there can be obtained a rubber reinforcing fiber having excellent dispersibility and reinforcing property without impairing the basic performance of the matrix rubber. The rubber reinforcing fiber of the present invention can be used for reinforcing any rubber, and can be used for various transmission belts, tires, hoses, gaskets, diagrams, piston caps, exterior parts of automobiles, and the like.

Claims (4)

[Claims] 1. A rubber reinforcing fiber to which liquid rubber has adhered. 2. A fiber to which liquid rubber is adhered, and which is divided and reduced in diameter by mechanical shearing force at the time of mixing or molding in a rubber molding process. 3. A fiber to which a liquid rubber is attached, wherein the fiber is at least a polyvinyl alcohol-based polymer (A).
And the acrylonitrile-based polymer (B), and its fiber cross section is a sea-island shape, either A or B is an island component and the other is a sea component, and the weight ratio of A / B is 90/10
20/80 rubber reinforcing fibers. 4. A method for producing a molded rubber article, comprising heating and vulcanizing a mixture comprising a rubber reinforcing fiber and a matrix rubber to which liquid rubber has adhered.