JP3980001B2 - Rubber composition - Google Patents

Description

  The present invention relates to a rubber composition, and more particularly to a rubber composition formed by blending improved thermal expansive graphite coated with a basic substance.

  Currently, rubber compositions containing expanded graphite for various purposes are known. For example, a rubber composition excellent in conductivity in which expanded graphite expanded 20 to 500 times is blended with rubber is blended with Patent Document 1 and expanded graphite surface-treated with a titanate coupling agent. A rubber composition with improved thermal conductivity is disclosed in Patent Document 2, and a refractory rubber composition in which neutralized thermally expanded graphite is blended with rubber is disclosed in Patent Document 3. Moreover, it has already been reported by patent document 4 etc. that the rubber composition excellent in the friction performance on ice is obtained by mix | blending thermally expansible graphite with diene type rubber.

  These expanded graphites become graphite expanded bodies by the vaporization and expansion of the acidic substance impregnated inside the graphite layered crystals by heat, and the acidic components generated at this time are subjected to a vulcanization reaction of the rubber composition. There is a problem of delaying or reducing the crosslinking density. On the other hand, there is also a problem that the acidic component leaked from the expanded graphite particles partially destroyed at the time of kneading adversely affects other compounding agents.

JP 52-95645 A JP-A-3-70754 Japanese Patent Laid-Open No. 10-195251 Japanese Patent Laid-Open No. 2001-279020

  Therefore, an object of the present invention is to provide a rubber composition containing thermally expandable graphite in which the adverse effects due to acidic components that occur during expansion of expanded graphite in the above problems or leak during kneading are eliminated. .

  According to the present invention, a rubber composition comprising 0.5 to 20 parts by weight of thermally expandable graphite with respect to 100 parts by weight of diene rubber, the thermally expandable graphite is based on graphite particles. A rubber composition characterized in that the surface is coated with an organic basic substance in an amount of 0.5 to 20% by weight is provided.

（式中、Ｒ₁、Ｒ₂およびＲ₃は、それぞれ水素、または１〜２２個の炭素原子を有する脂肪族または芳香族炭化水素基である。）
で示される有機塩基性化合物である、上記ゴム組成物が提供される。 Also according to the present invention, the organic basic substance has the formula I:

(Wherein R ₁ , R ₂ and R ₃ are each hydrogen or an aliphatic or aromatic hydrocarbon group having 1 to 22 carbon atoms.)
The rubber composition is an organic basic compound represented by the formula:

  Furthermore, according to the present invention, in addition to the thermally expandable graphite whose surface is coated with a predetermined amount of the above organic basic substance, a rubber obtained by further blending a predetermined amount of thermally expandable microcapsules or a foaming agent-containing resin. A composition is provided.

  In the present invention, the acidic component leaked from the thermally expandable graphite particles partially destroyed at the time of rubber kneading is quickly neutralized with the basic substance coated in the vicinity of the particles. There is no adverse effect. For example, the thermally expandable microcapsule expands at a predetermined expansion start temperature without affecting the shell material of the thermally expandable microcapsule which is another compounding agent. In addition, when the rubber is vulcanized, the coated basic substance prevents the release of acidic components from the thermally expandable graphite particles into the compounding system, so that the vulcanization speed becomes appropriate and the rubber is vulcanized. Increases sulfur density. Therefore, when using the rubber composition of this invention for a tire member, it has the effect that various performances of a tire improve.

  The thermally expandable graphite whose surface is coated with an organic basic substance blended in the rubber composition of the present invention is, for example, a method in which a predetermined amount of an organic basic substance is dissolved or the expanded graphite is immersed in a dispersed liquid. Then, what is obtained by drying it is used. As the thermally expandable graphite, one whose surface is coated with an organic basic substance in an amount of 0.5 to 20% by weight, preferably 3 to 8% by weight, based on the graphite particles is used. If the coating amount is less than 0.5% by weight, the desired effect cannot be exhibited. Conversely, if the coating amount exceeds 20% by weight, the particles cannot be held on the surface of the particle, so that the vulcanization speed is increased. It is not preferable.

（式中、Ｒ₁、Ｒ₂およびＲ₃は、それぞれ、水素、またはメチル基、ブチル基、ドデシル基、ステアリル基等の１〜２２個の炭素原子を有する脂肪族または芳香族炭化水素基であり、直鎖や分岐構造を問わず、また、部分的に不飽和結合を有するものも含む。）
で示される塩基性化合物が使用される。 As the organic basic substance used for such coating, those which are solid at room temperature are used, for example, primary amines such as laurylamine, stearylamine and oleylamine, secondary amines such as distearylamine, and dimethylstearylamine. And tertiary amines such as dimethyl behenylamine. Particularly preferred are the following formulas I:

(Wherein, R _1, R ₂ and R ₃ are each hydrogen or a methyl group, butyl group, dodecyl group, aliphatic or aromatic hydrocarbon radical having 1 to 22 carbon atoms such as stearyl group, Yes, regardless of whether it is a straight chain or branched structure, and also includes those having a partially unsaturated bond.)
The basic compound shown by is used.

  Further, as the expanded graphite to be coated with the organic basic substance, the following expanded graphite is used. That is, expanded graphite is a known material and is produced by a known production method. Generally, it is manufactured by immersing graphite particles in a mixed solution of a strong acid substance and an oxidizing agent, and inserting an acid between the layers of the graphite particles by an intercalation treatment. For example, concentrated sulfuric acid is used as the strong acid substance, and nitric acid is used as the oxidizing agent, thereby obtaining expanded graphite in which sulfuric acid is inserted between the particles. Expanded graphite expands when the interlayer opens when the intercalation compound volatilizes by heat treatment. Expanded graphite in which sulfuric acid is used as an interlayer material usually expands by heat treatment at 300 ° C. or higher. However, the expansion start temperature can be reduced by modifying the interlayer material or using other low-boiling acid compounds (eg nitric acid). Expanded graphite lowered to 300 ° C. or lower is manufactured and sold. The processing temperature of the rubber composition containing diene rubber as a main component in the present invention is 200 ° C. or less, and in the present invention, a predetermined effect is exhibited by using expanded graphite having an expansion start temperature of 190 ° C. or less. Is done. As such expanded graphite having an expansion start temperature of 190 ° C. or less, for example, “Graph Guard 160-50” or “Graph Guard 160-80” manufactured by UCAR Graphtech of the United States is commercially available from Sakai Industries, It is available. Expanded graphite, in terms of term, refers to an unexpanded product (Expandable) immediately after acid treatment, but may also refer to an expanded product after heat treatment. The expanded graphite used for the coating treatment in the present invention is an unexpanded product before heat treatment.

  The expanded graphite to be subjected to the coating treatment in the present invention is a powder substance having a particle size of 30 to 600 μm, preferably 100 to 350 μm, which contains an acidic substance that is vaporized by heat between the graphite particles. It is preferable to expand by heat to become a graphite expanded body. In the present invention, it is desirable that the expanded graphite does not expand in the rubber composition kneading process and the extrusion molding process, but expands in the vulcanization process, and preferably has an expansion start temperature of 120 to 190 ° C., more preferably. Is 140 to 170 ° C. If the expansion start temperature is less than 120 ° C., the expanded graphite expands during kneading or extrusion, and the rubber specific gravity may change during the process, which may impair the workability. Further, when the expansion start temperature exceeds 190 ° C, the processing temperature in the vulcanization process must be set to 190 ° C or higher, and the thermal deterioration of the diene rubber molecules as the main component of the rubber composition is remarkable. Tend to be. On the other hand, expanded graphite has a skeletal structure consisting of carbon atoms, so it has good affinity with rubber matrix and carbon black, and even when added to rubber, there is little decrease in wear resistance of vulcanized rubber. There is an advantage.

  The heat-expandable graphite subjected to the coating treatment of the present invention is used by blending 0.5 to 20 parts by weight, preferably 2 to 8 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount is less than 0.5 parts by weight, the desired effect cannot be obtained, which is not preferable. Conversely, if the blending amount exceeds 20 parts by weight, when used as a tire tread member, the distance between the rubber surface and the ice road surface is not preferable. Since the contact area at the micro level is reduced, the frictional force on ice is lowered, which is not preferable.

  Examples of the diene rubber component used in the present invention include any diene rubber conventionally used for tires, such as natural rubber (NR), polyisoprene rubber (IR), and various styrene-butadiene copolymers. Examples thereof include rubber (SBR), various polybutadiene rubbers (BR), acrylonitrile-butadiene copolymer rubber, and the like. These rubbers can be used alone or in any blend. The diene rubber of the present invention preferably has an average glass transition temperature (Tg) of −55 ° C. or lower, preferably −90 to −60 ° C. (that is, when used for a winter tire).

  In the rubber composition of the present invention, in addition to the surface-coated thermally expandable graphite, the thermally expandable microcapsule is further added in an amount of 0.5 to 20 parts by weight, preferably 3 to 10 parts per 100 parts by weight of the diene rubber. You may mix | blend in the quantity of a weight part. If the amount is less than 0.5 parts by weight, the desired effect cannot be obtained. Conversely, if the amount exceeds 20 parts by weight, the abrasion resistance of the rubber composition is remarkably lowered, which is not preferable.

  The heat-expandable microcapsule used in the rubber composition of the present invention is a heat-expandable thermoplastic resin particle in which a liquid that is vaporized by heat to generate gas is encapsulated in a thermoplastic resin, and the particle is expanded. By heating and expanding at a temperature equal to or higher than the start temperature, usually 140 to 190 ° C., gas-encapsulated thermoplastic resin particles in which a gas is encapsulated in an outer shell made of the thermoplastic resin are obtained. The particle size of the heat-expandable microcapsule is not particularly limited, but is preferably 5 to 300 μm even before expansion, more preferably 10 to 200 μm. As such a thermally expandable microcapsule, for example, the trade name “Expancel 091DU-80” or “Expancel 092DU-120” is currently available from EXPANCEL of Sweden, or the trade name “ Matsumoto Microsphere F-85 "or" Matsumoto Microsphere F-100 "is available.

  The thermoplastic resin constituting the outer shell component of the gas-filled thermoplastic resin particles has an expansion start temperature of 100 ° C or higher, preferably 120 ° C or higher, and a maximum expansion temperature of 150 ° C or higher, preferably 160 ° C or higher. Are preferably used. As such a thermoplastic resin, for example, a polymer of (meth) acrylonitrile or a copolymer having a high (meth) acrylonitrile content is preferably used. As the other monomer (comonomer) in the case of the copolymer, monomers such as vinyl halide, vinylidene halide, styrene monomer, (meth) acrylate monomer, vinyl acetate, butadiene, vinylpyridine, chloroprene are used. . The above thermoplastic resins are divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, It may be crosslinkable with a crosslinking agent such as allyl (meth) acrylate, triacryl formal, triallyl isocyanurate or the like. The crosslinked form is preferably uncrosslinked, but may be partially crosslinked so as not to impair the properties as a thermoplastic resin. Examples of the liquid that is vaporized by heat to generate a gas include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, and petroleum ether, methyl chloride, methylene chloride, dichloroethylene, trichloroethylene, Liquids such as chlorinated hydrocarbons such as trichloroethylene.

  Furthermore, in addition to the above surface-coated thermally expandable graphite, the rubber composition of the present invention further comprises a foaming agent-containing resin containing a chemical foaming agent with respect to 100 parts by weight of the diene rubber. Parts, preferably 2-8 parts by weight. If the blending amount is less than 0.5 parts by weight, the desired effect cannot be achieved. On the other hand, if it exceeds 20 parts by weight, the shape stability of the vulcanized rubber is impaired and the wear resistance of the rubber is remarkably impaired. Absent.

  When the rubber composition containing the foaming agent-containing resin is used as a tread member for a tire, a microcapsule-shaped resin-coated bubble is formed inside the rubber without greatly reducing the hardness after rubber vulcanization. By simultaneously removing the micro water film between the rubber and ice due to the surface irregularities appearing on the rubber surface and the scratching effect on the ice surface by the resin component exposed on the surface along with the bubbles, the friction force between the rubber and ice can be reduced. It can be greatly improved. Since the foaming agent pre-coated with the polyolefin resin is blended, the processing temperature can be selected regardless of the softening point of the resin as long as it is below the decomposition temperature of the foaming agent. It is formed. In addition, since the polyolefin resin does not have co-crosslinking properties with the diene rubber, the resin layer does not unnecessarily diffuse into the rubber phase during high temperature processing or vulcanization, and the rubber phase and the resin part are clearly separated. A microcapsule-shaped resin-coated bubble is obtained. In addition, the air bubbles that have been improved in airtightness by the resin coating are less likely to escape from the mold contact surface during vulcanization, and as a result, the vulcanized rubber has a more uniform distribution of microcapsule bubbles from the surface layer to the center. It becomes the property. An icy and snowy road surface tire using such a rubber composition is a tire that can exhibit a high on-ice frictional force from the beginning of use.

  The resin component constituting the foaming agent-containing resin used in the rubber composition of the present invention must not have co-crosslinking properties with the diene rubber, and specifically includes a polyolefin resin as a main component. Is used. Here, the main component means 75% by weight or more, preferably 85% by weight or more of the polyolefin resin component, and other components include, for example, unreacted residues of olefin monomers, polymerization initiators and the like. Residues such as catalysts, processing aids, and polymeric resins other than polyolefin-based resins are exemplified. This resin component is preferably one in which no double bond remains in the main chain of the molecule in order to prevent co-crosslinking with the diene rubber. As the polyolefin resin, at least one selected from polyethylene, polypropylene, poly-4-methylpentene-1, polybutylene-1, and the like can be used, and a mixture or copolymer thereof can also be used.

  The content of the chemical foaming agent in the foaming agent-containing resin is 5 to 65% by weight, preferably 15 to 50% by weight. If the content is too small, the void formation effect may be insufficient. Conversely, if the content is too large, the thickness of the shell formed may be reduced, and the scratching effect as a microcapsule may be insufficient. is there. The decomposition temperature of the chemical foaming agent is 120 to 180 ° C, preferably 140 to 160 ° C. When this temperature is too low, a sufficiently large resin-coated bubble cannot be formed during the extrusion process. In addition, when this decomposition temperature is too high, a decomposition temperature can also be adjusted to 120-180 degreeC by combined use with foaming adjuvants, such as urea. Foaming aids are available, for example, as “cell paste” from Eiwa Chemical Industries.

As the component of the chemical foaming agent, at least one selected from azo compounds, nitroso compounds, hydrazine derivatives, azo compounds, and bicarbonates can be used. Specifically, azodicarbonamide (ADCA), N, N′-dinitrosopentamethylenetetramine (DPT), 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH), hydrazodicarbonamide (HDCA), barium azodicarboxylate (Ba / AC), sodium bicarbonate ( NaHCO ₃ ), etc., which are “Vinihole” (ADCA), “Cellular” (DPT), “Neoselbon” (OBSH), “Exceller” (DPT / ADCA), “Span Cell” ( ADCA / OBSH), “Selbon” (NaHCO ₃ ) and the like are commercially available.

  The particle diameter of the foaming agent-containing resin blended in the rubber composition of the present invention is preferably 10 to 200 μm. If it is smaller than this, unevenness of a sufficiently large size cannot be formed on the rubber surface, and if it is too large, the mechanical strength of the rubber is significantly lowered. Such a foaming agent-containing resin is commercially available as “cell powder” from Eiwa Kasei Kogyo Co., Ltd., for example. In addition, although the microcapsule-like bubbles formed in the vulcanized rubber composition are spherical, the shape of the foaming agent-containing resin at the raw material stage need not be spherical.

In the rubber composition of the present invention, any carbon black that is usually blended in a rubber composition can be blended as a rubber reinforcing agent. Also, carbon black surface-treated with silica can be used. Furthermore, silica can also be used. Carbon black is used in an amount of 20 to 80 parts by weight, preferably 30 to 60 parts by weight, based on 100 parts by weight of the rubber component. If the blending amount is too small, the rubber cannot be sufficiently reinforced, and therefore, for example, the wear resistance is deteriorated, which is not preferable. On the contrary, if the amount is too large, the hardness becomes too high or the workability is decreased. Further, the precipitated or dry silica is preferably added in an amount of 0 to 50 parts by weight, more preferably 0 to 20 parts by weight, based on 100 parts by weight of the rubber component. Silica does not need to be used, and if used, it should be used in a blending amount in a range where the viscoelastic properties of the vulcanized rubber such as tan δ are improved. Since the cohesive force of the reinforcing agent becomes strong and dispersion during kneading becomes insufficient, it is not preferable. The carbon black compounded in the rubber composition of the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of preferably 70 m ² / g or more, more preferably 80 to 20070 m ² / g, and dibutyl phthalate (DBP) oil absorption. The amount is preferably 95 mL / 100 g or more, more preferably 105 to 140 mL / 100 g.

  The rubber composition for tires of the present invention further includes vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, oils, antioxidants, fillers, plasticizers, softeners, and other general rubbers that are usually used. Various additives and compounding agents can be blended, and the blending amounts of these additives and blending agents can be the conventional general blending amounts as long as the object of the present invention is not violated. .

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further, it cannot be overemphasized that the scope of the present invention is not limited to these Examples.

Preparation of improved expanded graphite The improved expanded graphite used in Table 1 was prepared by the following production method.
Expanded graphite graph guard 160-80 and 4% by weight of oleylamine (Farmin O manufactured by Kao) with respect to the expanded graphite were mixed at 100 ° C. with stirring, and then slowly cooled to room temperature to obtain base-treated expanded graphite. Prepared.

Mixing rubber compounds for testing Using a 1.7-liter closed Banbury mixer, the compounding agents such as rubber and carbon black shown in Table 1 below are mixed for 5 minutes, and the rubber mixture is released to the outside of the mixer. After cooling to room temperature, the vulcanization accelerator and sulfur, and predetermined expanded graphite, improved expanded graphite, thermally expandable microcapsule, and foaming agent-containing resin were blended and mixed in the same Banbury mixer.

Test method and evaluation 1) Vulcanization rate: Each compound was measured using a rheometer at 165 ° C based on JIS K6300, and the reciprocal of the time to reach 95% vulcanization at that time was a measure of the vulcanization rate. It was. The result was evaluated by an index. The larger the value, the higher the vulcanization speed.
2) Crosslink density: Each compound was vulcanized in a 6 inch square, 2 mm thick mold at 165 ° C. for 15 minutes, and after vulcanization, the rubber composition was sufficiently cooled in water to room temperature in accordance with ISO 37 Tensile tests were conducted, and the elastic modulus (M100) at 100% during elongation was used as a measure of the crosslinking density. The result was evaluated by an index. The larger the value, the higher the crosslink density.
3) Friction force on ice: A sheet-like rubber piece obtained by vulcanizing each compound was attached to a flat cylindrical base rubber, and measured using an inside drum type ice friction tester at a measurement temperature of -3.0 ° C and a load of 5.5 kg. The friction coefficient on ice was measured under the conditions of / cm ³ and a drum rotation speed of 25 km / hour. The result was evaluated by an index. The larger the index, the greater the frictional force on ice.

Examples 1-3 and Comparative Examples 1-3
The results are shown in Table 1 below.

  According to the above results, the rubber composition blended with the improved expanded graphite of the present invention has markedly improved both the crosslinking speed, the crosslinking density and the frictional force on ice compared with those blended with the conventional expanded graphite. I understand that. Further, in the rubber composition in which the improved expanded graphite of the present invention is used in combination with the conventional heat-expandable microcapsule or the foaming agent-containing resin, the rubber using the conventional heat-expandable microcapsule or the foaming agent-containing resin alone. Similarly, it can be seen that both the crosslinking speed, the crosslinking density, and the frictional force on ice are significantly improved as compared with the composition.

  Based on the above, the rubber composition of the present invention can be used extremely effectively as, for example, a tread member of a pneumatic tire.

Claims (5)

  A rubber composition comprising 0.5 to 20 parts by weight of thermally expandable graphite with respect to 100 parts by weight of diene rubber, wherein the thermally expandable graphite is 0.5 to 20 weights with respect to graphite particles. A rubber composition having a surface coated with an organic basic substance in an amount of%. Said organic basic substance is of formula I:

(Wherein R ₁ , R ₂ and R ₃ are each hydrogen or an aliphatic or aromatic hydrocarbon group having 1 to 22 carbon atoms.)
The rubber composition of Claim 1 which is an organic basic compound shown by these.   The rubber composition according to claim 1 or 2, further comprising 0.5 to 20 parts by weight of thermally expandable microcapsules.   The rubber composition according to claim 1 or 2, further comprising 0.5 to 20 parts by weight of a foaming agent-containing resin.   A pneumatic tire using the rubber composition according to any one of claims 1 to 4 for a tread portion.