JP5400565B2 - Rubber composition - Google Patents

Description

  The present invention relates to a rubber composition containing aromatic polyamide short fibers, and relates to a rubber composition capable of improving mechanical strength and wear resistance.

  Conventionally, in order to improve the mechanical properties of rubber belts and the like, it has been studied to add and reinforced short fibers such as cellulose, vinylon, nylon and polyester to vulcanizable rubber. However, these reinforcing short fibers are organic fibers having low rigidity and have a drawback that they are difficult to uniformly disperse in the rubber in the kneading step of the rubber composition. Accordingly, attempts have been made to reinforce with short steel fibers. However, reinforcing with short steel fibers has the disadvantage that the advantages of weight reduction cannot be utilized, and the specific gravity of the short steel fibers is larger than that of the matrix rubber and cannot be uniformly dispersed in the rubber. For this reason, reinforcement with an organic fiber material having a specific gravity relatively similar to that of rubber has been desired. Among them, the aromatic polyamide short fiber is considered to be optimal as a rubber reinforcing fiber because it is excellent in mechanical properties, fatigue resistance, heat resistance and chemical properties. However, since the surface of the aromatic polyamide fiber is inactive, the adhesive strength with the rubber is low, and the dispersibility when blended with the rubber is poor. In addition, due to poor converging ability with multifilaments, when cut into short fibers, the short fibers may easily scatter and form fiber balls. In such situations, when kneading with rubber Further, not only the fibers cannot be introduced uniformly, but the dispersibility of the fibers becomes poor, and the excellent characteristics of the aromatic polyamide cannot be fully exhibited.

  In order to solve such a problem, Patent Documents 1 and 2 propose a method of treating fibers with RFL treatment, which is an adhesive with rubber. In such methods, the affinity between rubber and short fibers and Although the adhesiveness can be improved, the converging properties of the fibers are insufficient, and the RFL adhesive itself is sticky, so that the converging bodies adhere to each other to form a fiber ball. Further, Patent Document 3 describes a method for improving the adhesion to rubber by imparting unevenness to the fiber surface by ultraviolet pulse laser treatment after RFL treatment, but even in this method, adhesion to rubber is described. Although improved, the focusing property is poor and it is easy to form a fiber ball. On the other hand, Patent Document 4 describes a method of treating an epoxy compound, a water-soluble nylon compound, and a water-soluble polyester resin. However, since a reactive compound such as an epoxy compound is used, the single fibers are separated from each other. It will adhere | attach firmly and the dispersibility of the single fiber in rubber | gum will become inadequate. Further, in the above-described RFL adhesive treatment and reactive treatment such as epoxy compound, a large amount of the agent falls off on the contacting roller or the like during the drying after the agent treatment, and further, the lump of the removed agent is treated fiber. There is a problem that the adhesion of the agent to the short fiber finally obtained occurs and the dispersibility in the rubber is lowered.

JP-A-4-146221 Japanese Patent Laid-Open No. 7-268771 JP-A-8-109581 JP-A-6-184932

  The present invention has been made in view of the problems of the background art, and provides a rubber composition having good dispersibility of short fibers in rubber and excellent in mechanical strength and wear resistance. is there.

  As a result of intensive studies, the present inventors have found that the above-mentioned problem is a rubber composition in which an aromatic polyamide short fiber is contained in rubber, and (A) an ether in the main chain on the surface of the aromatic polyamide short fiber. A polyurethane resin containing a bond, and (B) a cationic activator, and a weight ratio (A) / (B) of (A) and (B) is 85/15 to 99/1, and (A ) And (B) have been found to be solved by a rubber composition characterized in that the total adhesion amount is 1 to 20% by weight based on the total weight of the aromatic polyamide short fiber, and the present invention has been achieved.

  According to the present invention, since an aromatic polyamide short fiber having good dispersibility and affinity in rubber is contained, a rubber composition excellent in mechanical strength and wear resistance can be provided.

  The rubber composition of the present invention is a rubber composition in which aromatic polyamide short fibers are contained in rubber, and (A) a polyurethane resin containing an ether bond in the main chain on the surface of the aromatic polyamide short fibers, And (B) a cationic activator is attached, the weight ratio (A) / (B) of (A) and (B) is 85/15 to 99/1, and (A) and (B) The total adhesion amount is 1 to 20% by weight based on the total weight of the aromatic polyamide short fibers.

  Examples of the rubber used in the present invention include acrylic rubber, acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber, isoprene rubber, urethane rubber, ethylene-propylene rubber, epichlorohydrin rubber, chlorosulfonated polyethylene rubber, chloroprene rubber, and silicone rubber. Styrene-butadiene rubber, polysulfide rubber, natural rubber, butadiene rubber, butyl rubber, fluorine rubber, and the like. These may be used alone or in a blend. Further, organic fillers such as coumarone resin and phenol resin, softeners such as naphthenic oil, anti-aging agents, vulcanization aids, processing aids and the like may be included as necessary.

  On the other hand, the aromatic polyamide fiber used in the present invention is a fiber in which 80 mol% or more, preferably 90 mol% or more of the repeating units constituting the polyamide are aromatic homopolyamide or aromatic copolyamide. Here, the aromatic groups to be fibers may be the same or different aromatic groups. The hydrogen atom of the aromatic group may be substituted with a halogen atom, a lower alkyl group, or a phenyl group.

  Examples of such aromatic polyamide fibers include conventionally known fibers and fibers obtained by a conventionally known production method, such as JP-A Nos. 49-10032, 47-10863, and 58. -144152, JP-A-4-65513 and the like can be used.

  In addition, the aromatic polyamide fiber is preferably a para-type aromatic polyamide fiber from the viewpoint of excellent heat resistance and strength. The para-type aromatic polyamide fiber is a fiber made of polyamide in which the chain bond of the aromatic polyamide is coaxial or parallel and faces in the opposite direction.

  Specifically, polyparaphenylene terephthalamide fiber (for example, “Twaron” manufactured by Teijin Aramid BV) or copolyparaphenylene 3,4′-oxydiphenylene which is a copolymer type aromatic polyamide fiber. Terephthalamide fiber (for example, “Technola” manufactured by Teijin Techno Products Co., Ltd.) is exemplified, and the latter, which is a copolymer type, is particularly preferable because of its high mechanical strength, particularly impact strength, when used as a composite material.

  The single fiber fineness of the aromatic polyamide short fiber is preferably in the range of 0.1 to 5.5 dtex, more preferably 0.3 to 2.5 dtex. When the single fiber fineness is less than 0.1 dtex, there are many difficult points in the spinning technology, and not only is it difficult to stably produce good quality fibers due to the occurrence of yarn breakage and fluff, but also the cost Since it becomes high, it is not preferable. On the other hand, if the single fiber fineness exceeds 5.5 dtex, the mechanical properties of the fiber, in particular, the strength is lowered, and it tends to be difficult to uniformly disperse the fiber in the rubber.

  The aromatic polyamide short fiber has a fiber length of 0.5 to 12 mm, preferably 1 to 10 mm. When the fiber length is less than 0.5 mm, it becomes difficult to obtain a substantially columnar short fiber in which a plurality of single fibers are converged. It is not preferable because the single fibers are entangled with each other and are liable to cause poor dispersion.

  In the present invention, (A) a polyurethane resin containing an ether bond in the main chain, and (B) a cationic activator are attached to the surface of the aromatic polyamide short fiber, and the weight of (A) and (B) The ratio (A) / (B) is 85/15 to 99/1, and the total adhesion amount of (A) and (B) is 1 to 20% by weight with respect to the total weight of the aromatic polyamide short fibers. It is important. The present inventor has said that (A) and (B), when (A) and (B) are added to the fiber surface in an appropriate amount, the entanglement of the aromatic polyamide short fibers is suppressed, and the rubber It has been found that the dispersibility of short fibers is improved, the adhesion between short fibers and rubber is also improved, and the mechanical strength and wear resistance of the rubber composition are remarkably improved.

  As the polyurethane resin (A) to be attached to the aromatic polyamide short fiber, a polyurethane resin containing an ether bond in the main chain is used. The polyurethane resin is a polycondensation product of an isocyanate group and an alcohol group, and includes an ether bond in the main chain, that is, a polyurethane resin produced using a polyether polyol as a compound having an alcohol group. The polyurethane resin can realize a high adhesive force between the short fiber and the rubber due to the amine group and the carbonyl group contained in the resin.

  Examples of the polyether polyol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, glycerin, Trimethylolethane, trimethylolpropane, sorbitol, sucrose, aconite sugar, trimellitic acid, hemimellitic acid, phosphoric acid, ethylenediamine, diethylenetriamine, triisopropanolamine, pyrogallol, dihydroxybenzoic acid, hydroxyphthalic acid, 1,2,3-propane One or more compounds having at least two active hydrogen atoms such as trithiol as initiators for ethylene oxide, propylene oxide, butylene oxine Id, styrene oxide, epichlorohydrin, tetrahydrofuran, and the like that one or two or more monomers, such as cyclohexylene by addition polymerization by a conventional method.

  Examples of the polyol component used in the production of the (A) polyurethane resin include polyester polyol, polycarbonate polyol, polyacrylate polyol, polyacetal polyol, polyesteramide polyol, and the like in addition to the polyether polyol. To aromatic polyamide short fibers, a polyurethane resin blended with a polyether polyol is attached in terms of interfacial adhesion between rubber and short fibers, fiber dispersibility when mixing rubber, and improvement in mechanical properties of the rubber composition. Is the best.

  The (A) polyurethane resin preferably has a 100% modulus of 0.1 to 10 MPa. If the 100% modulus is less than 0.1 MPa, the strength tends to decrease, such being undesirable. On the other hand, when the 100% modulus exceeds 10 MPa, the flexibility is lowered, and the specific length is easily broken when cut and cut. The 100% modulus is more preferably 0.5 to 5 MPa, still more preferably 0.5 to 3.0 MPa. The breaking elongation of the polyurethane resin is preferably 200% or more. If it is less than 200%, it becomes undesirably easy to break into a specific length at the time of cutting. The breaking elongation is more preferably 500% or more, and still more preferably 600% or more.

  As the (B) cation activator to be attached to the aromatic polyamide short fiber of the present invention, any activator may be used as long as the hydrophilic group is a positively charged surfactant. For example, a primary amine salt Secondary amine salts, tertiary amine salts (hereinafter collectively referred to as amine salt type activators), quaternary ammonium salts, and the like. Also, ethylene oxide adducts of higher aliphatic amines and fatty acid amides can be used with some cationic properties, although they are nonionic activators.

  An amine salt type activator is produced by neutralizing a primary amine, secondary amine, or tertiary amine with an acid such as hydrochloric acid, nitric acid, formic acid, acetic acid, phosphoric acid, or lactic acid, Specific examples of amines include alkylamines such as methylamine, dimethylamine, trimethylamine, laurylamine and stearylamine, alcohol amines such as methanolamine and ethanolamine, polyethyleneamines such as ethylenediamine and diethylenetriamine, and higher alkylamines. Examples include ethylene oxide adducts, ethylene oxide / propylene oxide adducts of higher alkylamines, N, N-diethylethylenediamine, aminoethylethanolamine, pyridine, morpholine, guanidine, hydrazine, piperazine and the like.

  The quaternary ammonium salt is produced by the reaction of a tertiary amine and an alkylating agent. Specifically, alkyl dimethyl such as lauryl trimethyl ammonium hydrochloride, alkyl dimethyl such as lauryl dimethyl ethyl ammonium bromate, and the like. Alkyldimethylbenzylammonium salts such as ethylammonium salt, lauryldimethylbenzylammonium hydrochloride, cetyldimethylbenzylammonium hydrochloride, alkyl such as laurylpyridinium hydrochloride, cetylpyridinium hydrochloride, cetylpyridinium bromate, stearamide methylpyridinium hydrochloride Pyridinium salts, alkyldimethylhydroxyethylammonium salts such as lauryldimethylhydroxyethylammonium nitrate, laurylhydroxyethylimidazolinium et Alkyl hydroxyethyl imidazolinium salts such as Rufeto are exemplified.

  By using the activator, short fibers are uniformly dispersed in the rubber, and a rubber composition having excellent mechanical properties and wear resistance can be obtained. Although this mechanism is not clear, the end face of the aromatic polyamide short fiber is likely to be negatively charged, but the neutralization occurs due to the presence of the cationic activator and the polyurethane resin on the surface and inside of the short fiber, and the rubber When mixing and kneading short fibers, the short fibers are prevented from opening and entangled and a fiber lump (fiber ball) is suppressed, and the short fibers are uniformly dispersed and have the above excellent characteristics. It is believed that a rubber composition is obtained.

  In the present invention, the weight ratio of the (A) polyurethane resin to the (B) cationic activator is (A) / (B) = 85/15 to 99/1, preferably 90/10 to 97/3. is there. The (A) polyurethane resin and (B) cationic activator can also be used as a treatment liquid dispersed in an aqueous solution when producing a rubber composition, but the polymerization ratio of the cationic activator is (A) and ( If it exceeds 15% of the total of B), it may be difficult to obtain a uniform aqueous solution. Moreover, even when not preparing mixed aqueous solution, since the mechanical characteristic of the rubber composition obtained falls, it is unpreferable. In addition, when the weight ratio of the cation activator is less than 1% of the total of (A) and (B), sufficient antistatic property is obtained even when the total adhesion amount of (A) and (B) described later is increased. This is not preferable because the handling becomes difficult.

  In the present invention, the total amount of the (A) polyurethane resin and the (B) cationic activator is 1 to 20% by weight, preferably 2 to 19% by weight, based on the total weight of the aromatic polyamide short fibers. Preferably it is 3 to 18% by weight. When the adhesion amount is less than 1% by weight, the short fibers are not sufficiently converged, the handling property is deteriorated, the short fiber bundle is easily opened in the process of mixing with rubber, and a fiber lump is generated. In addition, if the adhesion amount exceeds 20% by weight, the production becomes difficult, which is not preferable.

  In addition, it includes functional agents such as flame retardants, light proofing agents, ultraviolet absorbers, antioxidants, rust inhibitors, antibacterial agents, pigments, silane coupling agents, and inorganic fine particles as long as they do not hinder the purpose of the present invention. Alternatively, the treatment agent (oil agent or the like) applied in the fiber production process may be used as it is without being removed.

  Aromatic polyamide short fibers are manufactured through a series of steps of application, drying, and cutting of a treatment agent (for example, an aqueous solution obtained by mixing them) containing the (A) polyurethane resin and (B) cationic activator. The method is not limited, and any method capable of obtaining a substantially cylindrical short fiber may be used. Moreover, a cationic activator may be provided by methods, such as a spray, after cutting, without mixing a cationic activator with a processing agent.

  Examples of the method of applying the treatment agent include a method of immersing in a liquid bath filled with the treatment solution, a method of bringing a driving roller provided with the treatment agent into contact with the traveling yarn, and the like. Of course, you may provide in a fiber manufacturing process.

  Examples of the method for drying the aromatic polyamide fiber to which the treatment agent has been applied include a method in which the aromatic polyamide fiber is brought into contact with a heated metal roll or the like, a method in which the aromatic polyamide fiber is passed through a non-contact heater, and a method in which high-temperature steam is imparted. Further, in order to make it easy to obtain cylindrical short fibers, a circular nozzle guide may be passed before the drying step, or a heated mold having a cylindrical hole may be passed. In any case, the temperature is preferably 120 ° C. to 200 ° C. and the residence time is 0.05 to 10 minutes, but the conditions are set after appropriately adjusting according to the amount of sizing liquid attached. It is necessary.

  In addition, as a method for cutting aromatic polyamide short fibers, it may be cut using any cutter capable of cutting the fibers, and specifically, it may be cut using a rotary cutter, a guillotine cutter, or the like. .

  In the present invention, by containing the aromatic polyamide short fibers described above in the rubber, the handleability during production is good, the fibers are uniformly dispersed and arranged in the rubber, and the mechanical strength is also excellent. A rubber composition can be provided.

  The rubber composition of the present invention is obtained by blending 0.5 to 30 parts by weight, more preferably 2 to 30 parts by weight of aromatic polyamide short fibers with respect to 100 parts by weight of rubber. When the content of the aromatic polyamide short fiber is less than 0.5 parts by weight, there is a tendency that sufficient effects cannot be obtained in terms of improvement in fatigue resistance and wear resistance. On the other hand, when the content of the aromatic polyamide short fiber is more than 30 parts by weight, not only the rubber composition itself becomes too hard, but also in the step of kneading the aromatic polyamide short fiber and the rubber, the aromatic polyamide short fiber Tends to be difficult to disperse.

  As a method for producing the rubber composition of the present invention, a known method can be employed. The timing of mixing the aromatic polyamide short fibers and the rubber is preferably performed at the time of kneading the unvulcanized rubber in the process of manufacturing the rubber composition. Furthermore, the aromatic polyamide short fiber can be formed into an arbitrary shape by subjecting the unvulcanized rubber to vulcanization treatment at a temperature, time, and pressure suitable for various rubbers.

  Hereinafter, the present invention will be described in more detail with reference to examples. The evaluation methods used in the examples are as follows.

(1) Total adhesion amount of (A) and (B) A constant weight of fiber was put into a mixed solvent of methanol / acetone = 1/1, and the weight of the Soxhlet extracted at 80 ° C. for 1 hour, the following formula was obtained. Used to calculate. Moreover, when giving a processing agent to the thread | yarn which the oil agent for fibers adhered, it computed by deducting the adhesion amount of the oil agent for fibers.
Total adhesion amount (%) = (fiber weight before extraction−fiber weight after extraction) / fiber weight after extraction × 100

(2) Dispersibility of short fibers Short fibers are blended in unvulcanized rubber mainly composed of chloroprene rubber shown in Table 1 not containing carbon black, kneaded for 5 minutes with a pressure kneader, and then transparent acrylic plate The thickness was set to about 1 mm with a press. This was visually determined according to the following criteria.
○: Fiber dispersion is good and the presence of fiber is difficult to understand Δ: Slightly has fiber balls ×: Fiber dispersion is poor and fiber balls are scattered

(3) Primary yield point tensile strength of rubber composition According to JIS-K6301, a No. 3 dumbbell-shaped test piece was 500 mm / min. The primary yield point tensile strength is the value obtained by dividing the primary yield point load by the cross-sectional area of the test piece at the tensile speed of.

(4) Abrasion resistance This is one standard for judging the reinforcing effect of short fibers. If the rubber is uniformly dispersed in the rubber, even if the surface of the short fiber reinforced rubber is rubbed with a metal, the wear rate becomes slow and the wear amount per unit time becomes small. The amount of wear was indexed in comparison with a rubber plate without short fiber reinforcement to judge wear resistance. Here, a steel ring is rotated and worn on the surface of a rubber plate having a thickness of 5 mm at a peripheral speed of 50 cm / min using a friction wear tester manufactured by Orientec Co., Ltd. with a load of 5 kg. A method was used in which the amount of wear was determined from the change in weight and compared.

[Example 1]
As the treatment liquid, (A) a polyether-based water-based polyurethane resin (“Bondic 8510” manufactured by Dainippon Ink and Chemicals, Inc.) and (B) lauryldimethylhydroxyethylammonium hydrochloride have a solid content ratio of (A ) / (B) = 90/10, and then blended with ion-exchanged water to prepare a solid concentration of 15% by weight. To this treatment liquid, a twist of 40 times / m in the S direction was given, and the fineness of the fiber bundle was 1670 dtex and the number of single fibers was 1000 copolyparaphenylene-3.4'-oxydiphenylene terephthalamide fibers (Teijin Techno Products ( Co., Ltd., “Technola T-200H”) is continuously dipped, and then passed through a dryer at a temperature of 150 ° C. for 1 minute, so that the solid content (that is, the total amount of (A) and (B)) is A 5.2% by weight aromatic polyamide long fiber was obtained. Subsequently, this long fiber was cut into a length of 3 mm with a guillotine cutter to obtain an aromatic polyamide short fiber. The obtained short fibers are blended in an unvulcanized rubber mainly composed of chloroprene rubber shown in Table 1 in an amount of 5 to 10% by volume, and an MS pressure type kneader (DS3-10MHHS manufactured by Moriyama Manufacturing Co., Ltd.) is used. After kneading for 3 minutes, the sheet was taken out, a rubber sheet was formed by press vulcanization, a sample was cut out in the orientation direction of the short fibers, and subjected to performance evaluation. The results are shown in Table 2.

[Example 2]
In Example 1, it implemented like Example 1 except having made the weight ratio of (A) and (B) into (A) / (B) = 97/3, and processing agent adhesion amount was 5.0%. Aromatic polyamide short fibers were obtained, and a rubber sheet was made to prepare a sample. The results are shown in Table 2.

[Example 3]
(B) The same procedure as in Example 1 was carried out except that the component was lauryldimethylhydroxyethylammonium nitrate, and an aromatic polyamide short fiber having a solid content of 5.5% was obtained. Created.

[Example 4]
The same procedure as in Example 1 was performed except that the component (A) was a polyether-based aqueous polyurethane resin (“Bondic 1940NE” manufactured by Dainippon Ink and Chemicals, Inc.), and the solid content adhesion amount was 6.0%. An aromatic polyamide short fiber was obtained, and a rubber sheet was further made to prepare a sample. The results are shown in Table 2.

[Comparative Example 1]
The same as in Example 1 except that the weight ratio of (A) and (B) was (A) / (B) = 99.5 / 0.5. A group polyamide short fiber was obtained, and a rubber sheet was made to prepare a sample. The results are shown in Table 2.

[Comparative Example 2]
Aromatic polyamide short fiber having a solid content of 7.5%, which was carried out in the same manner as in Example 1 except that the weight ratio of (A) to (B) was (A) / (B) = 80/20 A rubber sheet was made to make a sample. The results are shown in Table 2.

[Comparative Example 3]
In Example 1, except that the component (B) was changed to lauryl sulfate potassium salt, the same procedure as in Example 1 was carried out to obtain an aromatic polyamide short fiber having a solid content of 5.5%, and a rubber sheet. A sample was made. The results are shown in Table 2.

[Comparative Example 4]
(B) The same procedure as in Example 1 was performed except that the component was an adduct of 10 moles of ethylene oxide of lauryl alcohol to obtain an aromatic polyamide short fiber having a solid content of 5.5%, and a rubber sheet. A sample was made. The results are shown in Table 2.

[Comparative Example 5]
(A) It implemented similarly to Example 1 except having set it as the polyester-type water-based polyurethane resin (Dainippon Ink Chemical Co., Ltd. product "Bondic 1980NE"), and solid content adhesion amount is 6.0% Aromatic polyamide short fibers were obtained, and a rubber sheet was made to prepare a sample. The results are shown in Table 2.

[Comparative Example 6]
Except that the immersion treatment and drying of the water-based polyurethane resin were not performed, the same procedure as in Example 1 was performed to obtain a short aromatic polyamide fiber having a length of 3 mm, and further a rubber sheet was prepared to prepare a sample. The results are shown in Table 2.

  The rubber composition of the present invention is excellent in mechanical strength and abrasion resistance, and can be suitably used for applications such as a conveyor belt and a conductive belt.

Claims (3)

  A rubber composition comprising an aromatic polyamide short fiber in rubber, wherein (A) a polyurethane resin containing an ether bond in the main chain, and (B) a cationic activator on the surface of the aromatic polyamide short fiber The weight ratio (A) / (B) of (A) and (B) is 85/15 to 99/1, and the total adhesion amount of (A) and (B) is short of aromatic polyamide. A rubber composition characterized by being 1 to 20% by weight based on the total weight of the fiber.   The rubber composition according to claim 1, wherein the aromatic polyamide short fibers have a fiber length of 0.5 to 12 mm.   The rubber composition according to claim 1 or 2, wherein the aromatic polyamide fiber is a para-type aromatic polyamide fiber.