JP2012229339A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition that contains meta-type wholly aromatic polyamide short fiber that hardly causes a decrease in physical property even when used in an acidic atmosphere.SOLUTION: As meta-type wholly aromatic polyamide short fiber serving as a reinforcement material of a rubber composition, wholly aromatic polyamide short fiber whose single fiber fineness is within an specific range and in which the content of solvent remaining in fiber is equal to or less than a specific range is employed.

Description

  The present invention relates to a rubber composition. More specifically, the present invention relates to a rubber composition containing a meta-type wholly aromatic polyamide short fiber in which a decrease in physical properties in an acidic atmosphere is suppressed.

  Conventionally, it is known that wholly aromatic polyamides produced from aromatic diamines and aromatic dicarboxylic acid dihalides are excellent in heat resistance and flame retardancy. Among such wholly aromatic polyamides, polymetaphenylene isophthalamide is known. Meta-type wholly aromatic polyamide (sometimes referred to as “meta-aramid”) fibers represented by (2) are particularly useful as heat-resistant and flame-retardant fibers. For example, meta-type wholly aromatic polyamide fibers are widely used as rubber reinforcing materials for rubber belts, hoses and the like by taking advantage of such characteristics (see Patent Document 1), and meta-type wholly aromatic polyamide fibers are used as reinforcing materials. The rubber composition described above has been suitably used as a rubber composition used around automobile engines.

However, in recent years, the usage environment of fuel such as gasoline or alcohol / gasoline mixed fuel has changed to a higher temperature side as the fuel efficiency of automobile engines has increased. In a high temperature environment, it is known that fuel gasoline, etc. is oxidized and converted to acidic sour gasoline containing organic peroxide, and the generated sour gasoline is a rubber used around the engine. There has been a problem in that the deterioration of the composition is promoted, and as a result, the composition is damaged.
For this reason, there has been a strong demand for the appearance of a rubber composition containing acid-resistant meta-type wholly aromatic polyamide short fibers in which deterioration of physical properties in an acidic atmosphere is suppressed.

Japanese Patent Application Laid-Open No. 10-100364

  The present invention has been made in view of the above prior art, and an object of the present invention is to provide a rubber composition containing a meta-type wholly aromatic polyamide short fiber with little deterioration in physical properties even when used in an acidic atmosphere. It is to provide.

The present inventors have conducted intensive research to solve the above problems. As a result, as the meta-type wholly aromatic polyamide short fibers serving as a reinforcing material for the rubber composition, fully aromatic polyamide short fibers having a single yarn fineness in a specific range and a residual solvent content of a specific value or less are used. Thus, the present inventors have found that the above problems can be solved, and have completed the present invention.
That is, the present invention is a rubber composition comprising a meta type wholly aromatic polyamide short fiber, wherein the meta type wholly aromatic polyamide short fiber has a single yarn fineness of 10.0 to 50.0 dtex, and a residual solvent. The rubber composition is 1.0% by mass or less based on the total mass of the fiber.

  The rubber composition of the present invention is a rubber composition with little deterioration in physical properties even when used in an acidic atmosphere. Therefore, the rubber product obtained from the rubber composition of the present invention can withstand use in a harsher high-temperature acidic atmosphere, and can be suitably used, for example, as a rubber composition used for automotive parts. .

<Meta type wholly aromatic polyamide short fiber>
The meta-type wholly aromatic polyamide short fibers contained in the rubber composition of the present invention have the following specific physical properties. The physical properties, configuration, production method and the like of the meta-type wholly aromatic polyamide short fibers contained in the rubber composition of the present invention will be described below.

[Physical properties of meta-type wholly aromatic polyamide short fibers]
[Fineness of single fiber (single yarn fineness)]
The meta-type wholly aromatic polyamide short fiber used in the present invention is a fiber having a fineness of 10.0 to 50.0 dtex in the fineness of single fibers (single yarn fineness). When the fineness of the single fiber is less than 10.0 dtex, the acid resistance effect of the rubber reinforcement is insufficient, which is not preferable. On the other hand, it is difficult to obtain a meta-type wholly aromatic polyamide short fiber of 50.0 dtex or more, which is not realistic.

[Residual solvent amount]
Since the meta-type wholly aromatic polyamide fiber is usually produced from a spinning stock solution in which a polymer is dissolved in an amide solvent, the solvent necessarily remains in the fiber. However, in the meta type wholly aromatic polyamide short fiber used in the present invention, the amount of the solvent remaining in the fiber is 1.0% by mass or less based on the fiber mass. It is essential that it is 1.0 mass% or less, and it is more preferable that it is 0.5 mass% or less. Especially preferably, it is 0.01-0.1 mass%.
When the solvent remains in the fiber exceeding 1.0% by mass with respect to the mass of the fiber, yellowing easily occurs during processing and use in a high-temperature atmosphere exceeding 200 ° C. This is not preferable because a significant decrease in strength occurs.

  In order to reduce the amount of residual solvent in the meta-type wholly aromatic polyamide short fibers to 1.0% by mass or less, a specific coagulation bath is used in the fiber manufacturing process so as to take a dense solidification form without having a skin core. It is used for wet spinning, and the coagulated yarn is pulled up with a spinning draft within a specific range to obtain a fiber.

In the present invention, the “amount of solvent remaining in the fiber” refers to a value obtained by the following method.
(Measurement method of residual solvent amount)
The fibers are sampled on the exit side of the washing step, and the fibers are subjected to a centrifuge (rotation speed: 5000 rpm) for 10 minutes, and the fiber mass (M1) at this time is measured. The fiber is boiled for 4 hours in methanol having a mass of 2 g, and the amide solvent and water in the fiber are extracted. The fiber after extraction is dried at 105 ° C. for 2 hours, and the fiber weight (P) after drying is measured. Further, the mass concentration (C) of the amide solvent contained in the extract is determined by gas chromatography.
The amount of solvent (amide solvent mass) N (%) remaining in the fiber is calculated by the following equation using M1, M2, P, and C described above.
N = [C / 100] × [(M1 + M2-P) / P] × 100

〔Breaking strength〕
The meta type wholly aromatic polyamide short fiber used in the present invention preferably has a breaking strength in the range of 5.0 to 6.5 cN / dtex. The range of 5.5 to 6.5 cN / dtex is more preferable, and the range of 5.8 to 6.5 cN / dtex is most preferable.
When the breaking strength is less than 5.0 cN / dtex, the resulting rubber composition has a low strength, which makes it difficult to withstand use. On the other hand, when it exceeds 6.5 cN / dtex, the elongation is significantly lowered, and problems such as difficulty in handling the product occur.

  In order to make the “breaking strength” within the above range in the meta type wholly aromatic polyamide short fiber, a specific coagulation bath is used in the fiber manufacturing process so as to take a dense solidification form without having a skin core. In addition to wet spinning, the coagulated yarn is pulled up with a spinning draft within a specific range, and plastic drawing is performed within a specific magnification range to obtain a fiber.

The “breaking strength” in the present invention refers to a value obtained by measurement under the following conditions using a model number 5565 manufactured by Instron as a measuring instrument based on JIS L1015.
(Measurement condition)
Grasp interval: 20mm
Initial load: 0.044 cN (1/20 g) / dtex
Tensile speed: 20 mm / min

〔Cross-sectional shape〕
The cross-sectional shape of the meta-type wholly aromatic polyamide short fiber used in the present invention is not particularly limited, and may be circular, elliptical, or any other shape, and a spinneret having a large number of spinning holes is used. Any cross-sectional shape obtained by wet spinning may be used.

[Elongation at break]
The meta-type wholly aromatic polyamide short fiber used in the present invention preferably has a breaking elongation of 15% or more, more preferably 18% or more, and particularly preferably 20% or more. When the elongation at break is less than 15%, the process passability in the post-processing step such as spinning is lowered, which is not preferable.

The “breaking elongation” of the meta-type wholly aromatic polyamide short fibers is obtained by wet spinning using a specific coagulation bath so as to take a dense solidification form without having a skin core in the coagulation step in the production method described later. Can be controlled. In order to achieve 15% or more, an amide solvent such as an aqueous solution of DMAc (N, N-dimethylacetamide) having a concentration of 50 to 60% by mass is used as the coagulation liquid, and the temperature of the bath liquid is set to 10 to 30 ° C. That's fine.
Here, “breaking elongation” refers to a value obtained by measurement under the above-mentioned “breaking strength” measurement conditions based on JIS L1015.

[Strength retention (acid resistance)]
As acid resistance of the meta type wholly aromatic polyamide short fiber used in the present invention, it is preferable that the strength retention after dipping in a 20% by mass sulfuric acid aqueous solution at 25 ° C. for 600 hours is 70% or more. More preferably, it is 75% or more, and particularly preferably 80% or more.
When the strength retention is less than 70%, if a product obtained from the rubber composition containing the meta type wholly aromatic polyamide short fiber is used in an acidic atmosphere over a long period of time, the mechanical strength of the fiber decreases. Deterioration occurs and eventually breaks.
In order to achieve a strength retention of 70% or more, in the fiber production process, the components or conditions of the coagulation bath are adjusted so that the coagulation form does not have a skin core, and after the washing process, dry heat treatment is performed at a specific temperature. To obtain a fiber.

In the present invention, “strength retention after immersion in a 20 mass% sulfuric acid aqueous solution at 25 ° C. for 600 hours” refers to a value obtained by the following method.
(Measurement method of strength retention (acid resistance))
A 20 mass% sulfuric acid aqueous solution is put into a separable flask, and 51 mm of fibers are immersed therein. Subsequently, the separable flask is immersed in a constant temperature water bath, maintained at a temperature of 25 ° C., and the fibers are immersed for 600 hours. For each of the fibers before and after the immersion, the breaking strength is measured, and the strength retention of the fibers after the immersion is obtained.

[Cut length]
The cut length of the meta-type wholly aromatic polyamide short fiber contained in the rubber composition of the present invention is preferably in the range of 0.3 to 10.0 mm. If the thickness is less than 0.3 mm, the reinforcing effect due to the short fibers is difficult to be obtained.

[Adhesion treatment of meta-type wholly aromatic polyamide short fibers]
The meta-type wholly aromatic polyamide short fibers contained in the rubber composition of the present invention are preferably subjected to adhesion treatment. The adhesive treatment agent is not particularly limited, and a known agent can be used so as to be compatible with the rubber to be used. For example, after processing with the 1st processing agent containing a polyepoxide compound, and drying and heat-processing, it is then processed with the 2nd processing agent containing resorcinol, formalin, rubber latex (RFL), and the method of drying and heat-processing is mentioned. .

<Meta-type wholly aromatic polyamide>
[Configuration of meta-type wholly aromatic polyamide]
The meta-type wholly aromatic polyamide used as the material of the meta-type wholly aromatic polyamide short fiber contained in the rubber composition of the present invention uses a meta-type aromatic diamine component and a meta-type aromatic dicarboxylic acid component as raw materials. Can be obtained by reacting. Further, other copolymer components such as a para type may be copolymerized within a range not impairing the object of the present invention.
In the present invention, it is a meta-type wholly aromatic polyamide mainly composed of a metaphenylene isophthalamide unit because it has excellent mechanical properties and has heat resistance and flame resistance that can withstand use in a high-temperature atmosphere. preferable. Furthermore, it is desirable that the meta-type wholly aromatic polyamide is composed of metaphenylene isophthalamide units, preferably 90 mol% or more, more preferably 95 mol% or more, particularly preferably 100 mol% of all repeating units.

[Raw material for meta-type wholly aromatic polyamide]
(Meta-type aromatic diamine component)
Examples of the meta-type aromatic diamine component used as a raw material for the meta-type wholly aromatic polyamide include metaphenylene diamine, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfone, and the like, halogens in these aromatic rings, Derivatives having a substituent such as an alkyl group having 1 to 3 carbon atoms, such as 2,4-toluylenediamine, 2,6-toluylenediamine, 2,4-diaminochlorobenzene, 2,6-diaminochlorobenzene, etc. Can be illustrated. Of these, metaphenylenediamine alone or a mixed diamine containing metaphenylenediamine in an amount of 85 mol% or more, preferably 90 mol% or more, particularly preferably 95 mol% or more is preferable.

(Meta-type aromatic dicarboxylic acid component)
Examples of the meta-type aromatic dicarboxylic acid component that is a raw material for the meta-type wholly aromatic polyamide include a meta-type aromatic dicarboxylic acid halide. Examples of the meta-type aromatic dicarboxylic acid halide include isophthalic acid halides such as isophthalic acid chloride and isophthalic acid bromide, and derivatives having substituents such as halogen and alkoxy groups having 1 to 3 carbon atoms on the aromatic ring, such as 3 Examples thereof include chloroisophthalic acid chloride and 3-methoxyisophthalic acid chloride. Among them, isophthalic acid chloride alone or a mixed carboxylic acid halide containing isophthalic acid chloride at 85 mol% or more, preferably 90 mol% or more, particularly preferably 95 mol% or more is preferable.

(Copolymerization component)
Examples of copolymer components that can be used other than the above-mentioned meta-type aromatic diamine component and meta-type aromatic dicarboxylic acid component include, for example, paraphenylene diamine, 2,5-diaminochlorobenzene, 2,5- Benzene derivatives such as diaminobromobenzene and aminoanisidine, 1,5-naphthylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ketone, 4,4′-diaminodiphenylamine, 4,4′- And diaminodiphenylmethane. On the other hand, as the aromatic dicarboxylic acid component, terephthalic acid chloride, 1,4-naphthalenedicarboxylic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, 4,4′-biphenyldicarboxylic acid chloride, 4,4′-diphenylether dicarboxylic acid Examples include chloride.

  When the copolymerization ratio of these copolymerization components is too large, the properties of the meta-type wholly aromatic polyamide are likely to be lowered. It is preferable. In particular, a suitable meta-type wholly aromatic polyamide is a polyamide in which 90 mol% or more of all repeating units are metaphenylene isophthalamide units, and polymetaphenylene isophthalamide is particularly preferable.

[Method for producing meta-type wholly aromatic polyamide]
The production method of the meta-type wholly aromatic polyamide is not particularly limited. For example, it is produced by solution polymerization or interfacial polymerization using a meta-type aromatic diamine component and a meta-type aromatic dicarboxylic acid chloride component as raw materials. be able to.
In addition, the molecular weight of the meta-type wholly aromatic polyamide forming the fiber used in the present invention is not particularly limited as long as the fiber can be formed. In general, in order to obtain fibers having sufficient physical properties, molecular weight in which the intrinsic viscosity (IV) measured at 30 ° C. with a polymer concentration of 100 mg / 100 mL sulfuric acid in concentrated sulfuric acid is in the range of 1.0 to 3.0. Suitable polymers are those having a value in the range of 1.2 to 2.0.

<Method for producing meta-type wholly aromatic polyamide short fiber>
The meta-type wholly aromatic polyamide short fibers used in the present invention are prepared by using, for example, the aromatic polyamide obtained by the above-described production method, for example, a spinning solution preparation step, a spinning / coagulation step, and a plastic drawing bath described below. It is obtained by cutting long fibers produced through a drawing process, a washing process, a dry heat treatment process, and a heat drawing process.

[Spinning liquid preparation process]
In the spinning solution preparation step, the meta type wholly aromatic polyamide is dissolved in an amide solvent to prepare a spinning solution (meta type wholly aromatic polyamide polymer solution). In preparing the spinning solution, an amide solvent is usually used, and examples of the amide solvent used include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc). be able to. Of these, NMP or DMAc is preferably used from the viewpoints of solubility and handling safety.
The solution concentration may be appropriately selected from the viewpoint of the coagulation rate and the solubility of the polymer in the next spinning and coagulation step. For example, the polymer is a meta type such as polymetaphenylene isophthalamide. In the case of a wholly aromatic polyamide and the solvent is an amide solvent such as NMP, it is usually preferably in the range of 10 to 30% by mass.

[Spinning and coagulation process]
In the spinning / coagulation step, the spinning solution (meta-type wholly aromatic polyamide polymer solution) obtained above is spun into a coagulation solution and coagulated to obtain a coagulated yarn.
The spinning device is not particularly limited, and a conventionally known wet spinning device can be used. In addition, the number of spinning holes of the spinneret, the arrangement state, the hole shape and the like are not particularly limited as long as they can be stably wet-spun. For example, the number of holes is 1,000 to 20,000, the diameter of the spinning hole A multi-hole spinneret for sufu having a diameter of 0.07 to 0.2 mm may be used.
The temperature of the spinning solution (meta-type wholly aromatic polyamide polymer solution) when spinning from the spinneret is suitably in the range of 20 to 90 ° C.

  In order to obtain the fiber used in the present invention, it is important to use a specific coagulation bath. As the coagulation bath, an aqueous solution containing 50 to 60% by mass of an amide solvent that does not substantially contain an inorganic salt, The temperature of the bath liquid is used in the range of 10 to 30 ° C. It is essential to use an aqueous solution having an amide solvent concentration of 50 to 60% by mass as a bath liquid temperature range of 10 to 30 ° C., an amide solvent concentration of 53 to 60% by mass, and a bath liquid temperature of It is preferable to set it as 10-25 degreeC. Furthermore, it is particularly preferable that the concentration of the amide solvent is 55 to 60% by mass and the temperature of the bath liquid is 10 to 20 ° C.

  When the concentration of the amide solvent is less than 50% by mass, the skin formed on the surface of the obtained coagulated yarn has a thick structure, the cleaning efficiency in the subsequent cleaning process is lowered, and the residual solvent amount of the fiber is reduced. It becomes difficult. On the other hand, when the concentration of the amide solvent exceeds 60% by mass, uniform coagulation cannot be performed until reaching the inside of the fiber, so that it is difficult to reduce the residual solvent amount of the fiber.

  Moreover, in order to obtain the fiber used in the present invention, it is essential to use a specific coagulation bath and pull up the coagulated yarn with a specific range of spinning draft, and the spinning draft is in the range of 0.1 to 0.5. And The range is preferably 0.1 to 0.4, and more preferably 0.1 to 0.3.

  When the spinning draft is less than 0.1, the tension of the coagulated yarn is too low so that adjacent single yarns come into contact with each other, the process condition becomes unsatisfactory, and it becomes difficult to pull up the coagulated yarn. On the other hand, when the spinning draft exceeds 0.5, the liquid resistance by the coagulating liquid increases, so that the desolvation of the surface layer portion of the coagulated yarn proceeds and a skin layer is formed. As a result, since a uniform fiber structure cannot be obtained, not only the physical properties of the fiber are lowered, but also the washing efficiency in the subsequent washing step is lowered, and it becomes difficult to reduce the amount of residual solvent of the fiber. In addition, the range of 0.1-30 seconds is suitable for the immersion time of the fiber in a coagulation bath.

  Here, the coagulating liquid substantially free of an inorganic salt means a coagulating liquid substantially composed of only an amide solvent and water. However, since inorganic salts such as calcium chloride and calcium hydroxide are extracted from the polymer solution, the coagulating liquid actually contains a small amount of these salts. A suitable concentration of the salt in industrial implementation is in the range of 0.3% by mass to 10% by mass with respect to the entire coagulating liquid. In order to make the inorganic salt concentration less than 0.3% by mass, the recovery cost for purification in the recovery process of the coagulating liquid becomes remarkably high, which is not appropriate. On the other hand, when the inorganic salt concentration exceeds 10% by mass, the coagulation rate becomes slow, so that the fiber immediately after being discharged from the spinneret is likely to be fused, and the coagulation time is long. Therefore, the coagulation equipment must be enlarged, which is not preferable.

By setting the conditions of the coagulation bath and the spinning draft as described above, the skin formed on the fiber surface can be thinned to have a uniform structure up to the inside of the fiber, and the breaking elongation of the obtained fiber can be further increased. Can be improved.
By this spinning / coagulation step, a fiber (tow) made of a coagulated yarn of a porous meta-type wholly aromatic polyamide is formed in the coagulation bath, and then drawn from the coagulation bath into the air.

[Plastic stretching bath stretching process]
In the plastic drawing bath drawing step, the fiber is drawn in the plastic drawing bath while the fiber obtained by coagulation in the coagulation bath is in a plastic state.
It does not specifically limit as a plastic drawing bath liquid, A conventionally well-known thing can be employ | adopted. For example, an aqueous solution composed of an aqueous solution of an amide solvent and substantially free of salts can be used, and industrially, it is particularly preferable to use the same type of solvent as that used in the coagulation bath. That is, the amide solvents used for the polymer solution, the coagulation bath, and the plastic stretching bath are preferably the same. By using the same kind of amide solvent, the recovery process can be integrated and simplified, which is economically beneficial.

  The temperature and composition of the plastic stretching bath are closely related to each other, but can be suitably used as long as the mass concentration of the amide solvent is 20 to 70% by mass and the temperature is in the range of 20 to 70 ° C. . In a region lower than this range, plasticization of the porous fibrous material does not proceed sufficiently, and it becomes difficult to obtain a sufficient stretching ratio in plastic stretching. On the other hand, in a region higher than this range, the surface of the porous fiber is melted and fused, making it difficult to produce a good yarn.

  In order to obtain the fiber used in the present invention, the draw ratio in the plastic drawing bath needs to be in the range of 3.5 to 10.0 times, more preferably in the range of 4.0 to 6.5 times. And The breaking strength of the fiber finally obtained can be ensured by performing stretching in the plastic stretching bath within the range of the magnification and increasing the molecular chain orientation by stretching.

When the draw ratio in the plastic drawing bath is less than 3.5 times, it becomes difficult to obtain a fiber having a breaking strength of 5.0 cN / dtex or more. On the other hand, when the draw ratio exceeds 10.0 times, single yarn breakage occurs, resulting in poor production stability.
The temperature of the plastic stretching bath is preferably in the range of 20 to 90 ° C. When the temperature is in the range of 20 to 90 ° C., the process condition is good, which is preferable. The temperature is more preferably 20 to 60 ° C.

[Washing process]
In the washing step, the fibers drawn in the plastic drawing bath are thoroughly washed. Washing is preferably performed in multiple stages because it affects the quality of the resulting fiber. In particular, the temperature of the cleaning bath in the cleaning step and the concentration of the amide solvent in the cleaning bath liquid affect the state of extraction of the amide solvent from the fibers and the state of penetration of water from the cleaning bath into the fibers. For this reason, it is preferable to control the temperature condition and the concentration condition of the amide solvent by setting the washing process in multiple stages for the purpose of bringing them into an optimum state.

  The temperature condition and the concentration condition of the amide solvent are not particularly limited as long as the quality of the finally obtained fiber can be satisfied, but if the initial washing bath is at a high temperature of 60 ° C. or higher, water Intrusion into the fiber occurs at a stretch, generating huge voids in the fiber, leading to quality degradation. For this reason, it is preferable that the first washing bath has a low temperature of 30 ° C. or lower.

  If the solvent remains in the fiber, coloring or discoloration (particularly yellowing) of the fiber at high temperatures cannot be suppressed, and physical properties and shrinkage, limiting oxygen index (LOI), etc. Give rise to For this reason, the amount of solvent contained in the fiber used in the present invention must be 1.0% by mass or less, and more preferably 0.5% by mass or less. Especially preferably, it is the range of 0.01-0.1 mass%.

[Dry heat treatment process]
In order to obtain the fiber used in the present invention, a dry heat treatment step is preferably performed on the fiber that has undergone the above washing step. In the dry heat treatment step, the fiber that has been washed in the washing step is preferably subjected to a dry heat treatment in the range of 100 to 250 ° C., more preferably 100 to 200 ° C. Here, the dry heat treatment is not particularly limited, but a constant length is preferable.
If the drying heat treatment is subsequently applied after the washing step, the fluidity of the polymer can be improved moderately, and the crystallization can be suppressed while the orientation proceeds, and the densification of the fibers can be promoted. In addition, the temperature of said dry heat processing says the preset temperature of fiber heating means, such as a hot plate and a heating roller.

[Hot drawing process]
Subsequently, a heat stretching step is performed on the fiber that has undergone the dry heat treatment step. In the hot stretching process, it is preferable to perform stretching 1.2 to 1.8 times while applying heat treatment at 310 to 335 ° C. When the heat treatment temperature in the hot stretching process is higher than 335 ° C., the yarn is colored and severely deteriorates to reduce the breaking strength, and in some cases, the yarn may be broken. On the other hand, at a temperature lower than 310 ° C., sufficient crystallization of the fiber cannot be achieved, and it becomes difficult to express desired fiber physical properties, that is, mechanical properties such as breaking strength and thermal properties.

There is a close relationship between the treatment temperature in the hot drawing step and the density of the resulting fiber. In order to obtain a product having a particularly good fiber density, it is preferable that the heat treatment temperature in the hot stretching step is in a range of 310 to 335 ° C. The heat treatment is particularly preferably a dry heat treatment, and the heat treatment temperature in the heat drawing step refers to a set temperature of a fiber heating means such as a hot plate or a heating roller.
Further, the draw ratio in the heat drawing step is closely related to the strength and elastic modulus expression of the obtained fiber. In order to obtain the fiber used in the present invention, it is usually preferable to set the range of 1.2 to 1.8 times, preferably 1.2 to 1.5 times. Necessary strength and elastic modulus can be expressed while maintaining excellent heat stretchability.

[Adhesion treatment process]
The meta-type wholly aromatic polyamide short fibers contained in the rubber composition of the present invention are preferably subjected to adhesion treatment. The method for applying the adhesive treatment agent is not particularly limited. For example, it is preferable in production that a bundle of meta-type wholly aromatic polyamide long fibers is treated with the treatment agent, dried and heat-treated before cutting. .
The treating agent and the treating method to be used are not particularly limited. For example, the meta-type wholly aromatic polyamide long fiber bundle is dipped into the first treating agent containing the polyepoxide compound and dried at 130 ° C. Examples include a method in which heat treatment is performed at 240 ° C., followed by dipping into a second treatment agent containing resorcin / formalin / rubber latex (RFL), followed by drying and heat treatment in the same manner.

[Cut process]
Subsequently, the meta type wholly aromatic polyamide short fibers used in the present invention are finally obtained by cutting the long fibers preferably subjected to the adhesion treatment.
The method for cutting is not particularly limited, and a known method can be adopted. For example, there is a method of cutting long fibers into a predetermined fiber length using a guillotine cutter.

<Rubber composition>
The rubber composition of the present invention is a composition containing the above-mentioned meta-type wholly aromatic polyamide short fibers.

[Rubber type]
The type of rubber used in the present invention is not particularly limited and can be appropriately selected depending on the application. For example, chloroprene (CR), natural rubber, nitrile rubber (NBR), H-NBR, chlorosulfonated polyethylene and the like can be mentioned, and any rubber that requires vulcanization can enjoy the effects of the present invention. preferable. In the present invention, natural rubber is particularly preferable because it can be used in a wide range of applications such as tires, holes, and belts.

[Meta-type wholly aromatic polyamide short fiber content]
The compounding amount of the meta-type wholly aromatic polyamide short fibers contained in the rubber composition of the present invention is 1.0 to 50.0 parts by mass with respect to 100 parts by mass of the rubber. More preferably, it is 5.0-30.0 mass parts. If it is less than 1.0 part by mass, the effect of fiber reinforcement of the resulting rubber composition is small, so that the fatigue resistance is insufficient. Moreover, when it exceeds 50.0 mass parts, since the softness | flexibility of the product obtained is impaired, fatigue resistance becomes inadequate.

[Physical properties of rubber composition]
[Bending fatigue retention (acid resistance)]
As the acid resistance of the rubber composition of the present invention, it is preferable that the bending fatigue retention after being immersed in a 20% by mass sulfuric acid aqueous solution at 25 ° C. for 60 hours is 60% or more. More preferably, it is 65% or more, and particularly preferably 70% or more.
When the bending fatigue retention is less than 60%, if the rubber composition containing the meta-type wholly aromatic polyamide short fiber is used in an acidic atmosphere for a long period of time, deterioration occurs due to a decrease in mechanical strength, and consequently breakage. Resulting in.
In order to make the bending fatigue retention 60% or more, a rubber composition is obtained using the meta-type wholly aromatic polyamide short fibers described above.

In the present invention, the “bending fatigue retention after immersion in a 20 mass% sulfuric acid aqueous solution at 25 ° C. for 600 hours” refers to a value obtained by measurement by the following measurement method.
(Measurement method of bending fatigue retention rate (acid resistance))
A No. 3 dumbbell-shaped test piece is prepared from a rubber composition containing short fibers. A 20% by mass sulfuric acid aqueous solution is put into a separable flask, and the prepared test piece is immersed and fixed. Then, the separable flask is immersed in a constant temperature water bath, maintained at a temperature of 25 ° C., and the sample is immersed for 600 hours. . Remove after 600 hours, wipe off any excess aqueous solution adhering to the surface within 3 minutes and leave at room temperature for 4 hours or more. The bending fatigue test described below is performed on each of the test pieces before and after the immersion, and the bending fatigue retention rate is measured from the obtained number of bendings.
(Bending fatigue test)
A No. 3 dumbbell-shaped test piece is bent 25% at a cycle of 5HZ using a Deathia bending fatigue tester manufactured by Toyo Seiki Co., Ltd., and the number of times until cracking is measured.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and the like, but the present invention is not limited to these examples and the like. “Part” and “%” are based on “mass” unless otherwise specified, and “quantity ratio” indicates “mass ratio” unless otherwise specified. Further, the polymer concentration (PN concentration) in the polymer solution (spinning stock solution) used for spinning is “% by mass of polymer” with respect to “total mass part”, that is, [polymer / (polymer + solvent + others)]. × 100 (%).

<Measurement method>
Each physical property value in Examples and Comparative Examples was measured by the following method.
[Intrinsic viscosity (IV)]
After the aromatic polyamide polymer was isolated from the polymer solution and dried, it was measured in concentrated sulfuric acid at a polymer concentration of 100 mg / 100 mL sulfuric acid at 30 ° C.
[Single yarn fineness]
According to JIS L1015, the measurement based on the A method of a positive fineness was implemented, and it described with the apparent fineness.
[Breaking strength, breaking elongation, initial elastic modulus]
Measurement was performed under the following conditions based on JIS L1015 using a tensile tester (Instron, model: 5565).
(Measurement condition)
Grasp interval: 20mm
Initial load: 0.044 cN (1/20 g) / dtex
Tensile speed: 20 mm / min [Amount of solvent remaining in fiber (residual solvent amount) N (%)]
The fibers were sampled on the exit side of the washing step, and the fibers were subjected to a centrifuge (rotation speed: 5,000 rpm) for 10 minutes, and the fiber mass (M1) at this time was measured. This fiber was boiled in methanol having a mass of 2 g for 4 hours to extract the amide solvent and water in the fiber. The fiber after extraction was dried at 105 ° C. for 2 hours, and the fiber mass (P) after drying was measured. Moreover, the mass concentration (C) of the amide solvent contained in the extract was determined by gas chromatography.
The amount of solvent (amide solvent mass) N (%) remaining in the fiber was calculated by the following formula using M1, M2, P, and C described above.
N = [C / 100] × [(M1 + M2-P) / P] × 100
[Fiber strength retention (acid resistance)]
A 20 mass% sulfuric acid aqueous solution was put into a separable flask, and 50 mm of unbonded sample yarn was fixed by immersion. Subsequently, the separable flask was immersed in a constant temperature water bath, maintained at a temperature of 25 ° C., and the sample yarn was immersed for 600 hours. For each of the sample yarns before and after immersion, the breaking strength was measured by the measurement method described above, and the strength retention of the fibers after immersion was determined.
[Bending fatigue retention of rubber composition (acid resistance)]
A No. 3 dumbbell-shaped test piece was prepared from a rubber composition containing short fibers. A 20 mass% sulfuric acid aqueous solution was put into a separable flask, and the prepared test piece was immersed and fixed. Subsequently, the separable flask was immersed in a constant temperature water bath, maintained at a temperature of 25 ° C., and the sample was immersed for 600 hours. . It was taken out after 600 hours had passed, and the excess aqueous solution adhering to the surface was wiped off within 3 minutes and left at room temperature for 4 hours or more. The bending fatigue test described below was performed on each of the test pieces before and after the immersion, and the bending fatigue retention rate was measured from the obtained number of bendings.
(Bending fatigue test)
A No. 3 dumbbell-shaped test piece was bent 25% at a cycle of 5HZ using a Deathia bending fatigue tester manufactured by Toyo Seiki Co., Ltd., and the number of times until cracking was measured.

<Example 1>
[Production of meta-type wholly aromatic polyamide fiber]
[Spinning solution (spinning dope for spinning) adjustment process]
20.0 parts by mass of polymetaphenylene isophthalamide powder having an intrinsic viscosity (IV) of 1.9 produced by an interfacial polymerization method according to the method described in Japanese Patent Publication No. 47-10863 is cooled to -10 ° C. , N-dimethylacetamide (DMAc) was suspended in 80.0 parts by mass to form a slurry. Subsequently, the suspension was heated to 60 ° C. to dissolve the polymetaphenylene isophthalamide powder to obtain a transparent polymer solution.
[Spinning and coagulation process]
The obtained polymer solution was spun as a spinning stock solution from a spinneret having a pore diameter of 0.11 mm and a pore number of 1500 into a coagulation bath having a bath temperature of 30 ° C. The composition of the coagulation liquid was water / DMAc (mass ratio) = 45/55, and spinning was performed by discharging into a coagulation bath at a yarn speed of 7 m / min and a spinning draft of 0.20.
[Plastic stretching process]
Subsequently, the film was stretched at a draw ratio of 5.0 in a plastic stretching bath having a composition of water / DMAc (mass ratio) = 40/60 at a temperature of 40 ° C.
[Washing process]
After plastic stretching, 20 ° C. water / DMAc (mass ratio) = 70/30 bath (immersion length 1.8 m), followed by 20 ° C. water bath (immersion length 3.6 m), 60 ° C. hot water bath (immersion) Long 5.4 m), and then passed through a warm water bath (7.2 m) at 80 ° C. for sufficient washing.
[Dry heat treatment process]
The washed fibers were subsequently subjected to a drying heat treatment under constant tension with a hot roller having a surface temperature of 150 ° C.
[Heat drawing process]
Subsequently, a heat drawing process of drawing 1.3 times while applying heat treatment was performed with a heat roller having a surface temperature of 330 ° C., and finally polymetaphenylene isophthalamide fiber was obtained.
[Physical properties of fibers]
Various measurement evaluation was implemented with respect to the obtained fiber (tow). The results are shown in Table 1.

[Production of meta-type wholly aromatic polyamide short fibers for rubber reinforcement]
[Adhesion treatment process]
(Preparation of first treatment agent)
DENOGOL EX-611 (manufactured by Nagase Sangyo Co., Ltd., sorbitol polyglycidyl ether) 1.9 g, Neocor SW-30 (Daiichi Kogyo Seiyaku Co., Ltd., diacrylylsulfosuccinate sodium salt 30% aqueous solution as a surfactant) ) 1.6 g was added and dissolved uniformly. This was added to 200 g of water with stirring and dissolved uniformly. Next, 29.9 g of ε-caprolactam block body of 4,4′-diphenylmethane diisocyanate was added and stirred, and 0.5 g of Nippon 1562 (manufactured by Nippon Zeon Co., Ltd., acrylonitrile-butadiene latex 40% water emulsion) was added. In addition, it was dissolved uniformly. The obtained liquid mixture was used as the first treatment agent.
(Preparation of second treatment agent)
4.7 g of 10% sodium hydroxide aqueous solution was added to 300.8 g of water and stirred well to obtain an aqueous solution. In the obtained aqueous solution, 14.5 g of resorcin and 14.9 g of formalin (37% aqueous solution) were added and dispersed with sufficient stirring. This solution was allowed to stand in an atmosphere at 20 to 25 ° C. for 2 to 3 hours to cause initial condensation of resorcin and formalin.
Next, the solution of the resorcin / formalin initial condensate was added to 239.1 g of Nippon 1562 (manufactured by Nippon Zeon Co., Ltd., acrylonitrile-butadiene latex 40% aqueous emulsion) while slowly stirring. Finally, 427.5 g of water was added to make a second treating agent.
(Adhesion treatment)
The polymetaphenylene isophthalamide fiber bundle (tow) obtained above was drawn to a thickness of 660,000 dtex to obtain a supply fiber.
The supplied fiber was dipped in the first treatment agent, dried at 130 ° C., heat treated at 240 ° C., then dipped in the second treatment agent, dried and heat treated in the same manner to obtain an adhesion treated fiber bundle. .
[Cut process]
The obtained adhesion-treated fiber bundle was cut into a fiber length of 3.0 mm with a guillotine cutter to obtain a meta-type wholly aromatic polyamide short fiber for rubber reinforcement.
[Production of rubber sheet]
The resulting short fiber was blended with a carcass-blended unvulcanized rubber containing natural rubber as a main component so that the blending amount was 5.0% by mass, and an MS pressure type kneader (Moriyama Seisakusho Co., Ltd., model: DS3) -10 MHHS) for 3 minutes. The sheet was put out to an appropriate thickness so that the short fibers were oriented, and a rubber sheet was produced by press vulcanization at 170 ° C. for 180 minutes. From the obtained rubber sheet, a sample was cut out in the orientation direction of the short fibers, held in a 20 mass% sulfuric acid aqueous solution at 25 ° C for 600 hours, and then subjected to a bending fatigue test. The obtained results are shown in Table 1.

<Example 2>
[Production of meta-type wholly aromatic polyamide fiber]
[Process for preparing spinning dope (spinning dope)]
In a reaction vessel under a dry nitrogen atmosphere, 721.5 parts by mass of N, N-dimethylacetamide (DMAc) having a moisture content of 100 ppm or less was weighed, and 97.2 parts by mass (50.18 mol) of metaphenylenediamine was added to the DMAc. %) Was dissolved and cooled to 0 ° C. To this cooled DMAc solution, 181.3 parts by mass (49.82 mol%) of isophthalic acid chloride (hereinafter abbreviated as IPC) was added while gradually stirring to carry out a polymerization reaction. After the change in viscosity stopped, stirring was continued for 40 minutes to complete the polymerization reaction.
Next, 66.6 parts by mass of calcium hydroxide powder having an average particle size of 10 μm or less was weighed and slowly added to the polymer solution after completion of the polymerization reaction to carry out a neutralization reaction. After the addition of calcium hydroxide was completed, the mixture was further stirred for 40 minutes to obtain a transparent polymer solution.
When polymetaphenylene isophthalamide was isolated from the obtained polymer solution and IV was measured, it was 1.25. The polymer concentration in the polymer solution was 20%.
[Spinning and coagulation process]
The obtained polymer solution was spun as a spinning solution from a spinneret having a pore diameter of 0.15 mm and a number of holes of 1500 into a coagulation bath having a bath temperature of 30 ° C. The composition of the coagulation liquid was water / NMP (quantity ratio) = 45/55, and spinning was performed by discharging into a coagulation bath at a yarn speed of 5 m / min and a spinning draft of 0.16.
[Plastic stretching process]
Subsequently, stretching was performed at a stretching ratio of 6.0 times in a plastic stretching bath having a composition of water / NMP (quantity ratio) = 40/60 at a temperature of 40 ° C.
[Washing process]
After plastic stretching, 20 ° C. water / NMP (quantity ratio) = 70/30 bath (immersion length 1.8 m), followed by 20 ° C. water bath (immersion length 3.6 m), 60 ° C. hot water bath (immersion) Long 5.4 m), and then passed through a warm water bath (7.2 m) at 80 ° C. for sufficient washing.
[Dry heat treatment process]
The washed fibers were subsequently subjected to a drying heat treatment under constant tension with a hot roller having a surface temperature of 150 ° C.
[Heat drawing process]
Subsequently, a heat drawing step of drawing 1.2 times while applying heat treatment was performed with a heat roller having a surface temperature of 330 ° C., and finally polymetaphenylene isophthalamide fibers were obtained. Table 1 shows various measurement results for the obtained fibers.
[Physical properties of fibers]
Various measurement evaluation was implemented with respect to the obtained fiber (tow). The results are shown in Table 1.
[Production of meta-type wholly aromatic polyamide short fibers for rubber reinforcement]
Using the obtained fiber, a meta-type wholly aromatic polyamide short fiber for reinforcing rubber was produced in the same manner as in Example 1.
[Production of rubber sheet]
Using the obtained meta-type wholly aromatic polyamide short fiber, a rubber sheet was produced in the same manner as in Example 1. Table 1 shows the bending fatigue test results of the obtained rubber sheet.

<Comparative Example 1>
[Production of meta-type wholly aromatic polyamide fiber]
In the spinning step, polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that the base used was changed to a hole diameter of 0.07 mm and the spinning draft was 0.63. Table 1 shows various measurement results for the obtained fibers.
[Production of meta-type wholly aromatic polyamide short fibers for rubber reinforcement]
Using the obtained fiber, a meta-type wholly aromatic polyamide short fiber for reinforcing rubber was produced in the same manner as in Example 1.
[Production of rubber sheet]
Using the obtained meta-type wholly aromatic polyamide short fiber, a rubber sheet was produced in the same manner as in Example 1. Table 1 shows the bending fatigue test results of the rubber sheets obtained.

<Comparative example 2>
[Production of meta-type wholly aromatic polyamide fiber]
In the spinning process, polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that the used die was changed to a pore diameter of 0.11 mm and the spinning draft was 0.06. Table 1 shows various measurement results for the obtained fibers.
[Production of meta-type wholly aromatic polyamide short fibers for rubber reinforcement]
Using the obtained fiber, a meta-type wholly aromatic polyamide short fiber for reinforcing rubber was produced in the same manner as in Example 1.
[Production of rubber sheet]
Using the obtained meta-type wholly aromatic polyamide short fiber, a rubber sheet was produced in the same manner as in Example 1. Table 1 shows the bending fatigue test results of the obtained rubber sheet.

<Comparative Example 3>
[Production of meta-type wholly aromatic polyamide fiber]
In the spinning solution (spinning dope) preparation step, the solvent used is changed to N-methyl-2-pyrrolidone (NMP) to produce a polymer solution. In the spinning step, the die used has a pore diameter of 0.26 mm and a pore number of 1500. A polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that the spinning draft was changed to 1.13. Table 1 shows various measurement results for the obtained fibers.
[Production of meta-type wholly aromatic polyamide short fibers for rubber reinforcement]
Using the obtained fiber, a meta-type wholly aromatic polyamide short fiber for reinforcing rubber was produced in the same manner as in Example 1.
[Production of rubber sheet]
Using the obtained meta-type wholly aromatic polyamide short fiber, a rubber sheet was produced in the same manner as in Example 1. Table 1 shows the bending fatigue test results of the obtained rubber sheet.

  The rubber composition of the present invention is a rubber composition with little deterioration in physical properties even when used in an acidic atmosphere. Therefore, the rubber product obtained from the rubber composition of the present invention can be used even in a severer high temperature acidic atmosphere, and cannot be used in a rubber composition using conventional meta type wholly aromatic polyamide short fibers. It can also be used in other fields.

Claims (3)

A rubber composition comprising a meta-type wholly aromatic polyamide short fiber,
The meta-type wholly aromatic polyamide short fiber is a rubber composition having a single yarn fineness of 10.0 to 50.0 dtex and a residual solvent amount of 1.0% by mass or less based on the total mass of the fiber.   The rubber composition according to claim 1, wherein the bending fatigue retention after being immersed in a 20 mass% sulfuric acid aqueous solution at 25 ° C for 600 hours is 60% or more.   The rubber composition according to claim 1, wherein the breaking strength of the meta-type wholly aromatic polyamide short fibers is 5.0 to 6.5 cN / dtex.