Rubber composition and method for producing the same

Abstract

To provide a rubber composition that is blended with a cellulosic material which improves its strength, and a method for producing the same.SOLUTION: There are provided a rubber composition that contains a pulverized material of a pulp sheet containing one or more hydrophobing agents selected from the group consisting of rosin, an alkyl ketene dimer, an alkanylsuccinic acid, and a styrene-acrylic resin, and a method for producing the rubber composition which includes a step of kneading the pulverized material with a rubber component. The pulp sheet preferably has a basis weight of 100 to 550 g / m2 and a Steckigt degree of 400 seconds or more, and a volume-based 50% average particle diameter of the pulverized material is preferably 100 μm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition and a method for producing the same.

Background Art

[0002] A rubber composition containing a rubber component and cellulose fibers is known to have excellent mechanical strength. For example, Patent Document 1 describes that a rubber composition containing a rubber component, microfibrillated plant fibers, and a rosin resin can improve the compatibility between the plant fibers and the rubber component, reduce energy loss, achieve both rigidity and elongation at break, and can be used for tires.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the rubber composition of Patent Document 1, the reinforcing effect of plant fibers may not be fully exerted, and further improvement in the strength of the rubber composition is required for applications in various fields.

[0005] An object of the present invention is to provide a rubber composition with improved strength and a method for producing the same in a rubber composition containing a cellulose-based material.

Means for Solving the Problems

[0006] The present invention provides the following. 〔1〕A rubber composition containing a pulverized product of a pulp sheet containing at least one hydrophobizing agent selected from the group consisting of rosin, alkyl ketene dimer, alkenyl succinic acid, and styrene-acrylic resin. 〔2〕The basis weight of the pulp sheet is 100 to 550 g / m2 The rubber composition according to [1]. 〔3〕The rubber composition according to [1] or [2], wherein the stiffness degree of the pulp sheet is 400 seconds or more. 〔4〕The rubber composition according to any one of [1] to [3], wherein the volume-based 50% average particle diameter (D50) measured by the laser diffraction / scattering method of the pulverized product of the pulp sheet is 100 μm or less. 〔5〕A method for producing a rubber composition, comprising a step of kneading a pulverized product of a pulp sheet containing at least one hydrophobizing agent selected from the group consisting of rosin, alkyl ketene dimer, alkenyl succinic acid, and styrene-acrylic resin with a rubber component.

Advantages of the Invention

[0007] According to the present invention, a rubber composition having good strength is provided, and a method for efficiently producing such a rubber composition is also provided.

Embodiments for Carrying Out the Invention

[0008] [1. Rubber Composition] The rubber composition contains a pulverized product of a pulp sheet.

[0009] [1.1 Pulp Sheet] In this specification, the pulverized product of the pulp sheet is a material obtained by pulverizing the pulp sheet.

[0010] [Pulp] In this specification, a pulp sheet is a material obtained by forming pulp into a sheet shape. Pulp includes pulp derived from wood such as softwood and hardwood, and non-wood-derived pulp such as bamboo, hemp, jute, kenaf, agricultural waste, and paper (e.g., waste paper, printing paper). Among these, wood-derived pulp and paper-derived pulp are preferred, softwood pulp, hardwood pulp, and waste paper pulp are preferred, and hardwood pulp and waste paper pulp are more preferred. Examples of wood-derived pulp include hardwood-derived pulp and softwood-derived pulp, and particularly preferred is hardwood-derived chemical pulp. The pulping method (digestion method) of these wood-derived chemical pulps is not particularly limited, and examples include sulfite digestion method, kraft digestion method, soda-quinone digestion method, organosolv digestion method, etc. Among these, the sulfite digestion method and the kraft digestion method are preferred. Further, treatments such as bleaching and beating may be performed. The resulting pulp may be any of unbleached pulp, bleached pulp, beaten pulp, and unbeaten pulp. Examples of chemical pulp include kraft pulp (KP), dissolved kraft pulp (DKP), sulfite pulp (SP), dissolved sulfite pulp (DSP), etc. Also, groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc. may be used, and it may be either unbleached chemical pulp or bleached chemical pulp. As mechanical pulp, mechanical pulps such as groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc. can also be used. Among these, chemical pulp is preferred. Examples of chemical pulp include, for example, hardwood kraft pulp (LKP), softwood kraft pulp (NKP), hardwood sulfite pulp (LSP), and softwood sulfite pulp (NSP), and LKP is preferred. Also, it is preferred in that it can become a pulp that exhibits high strength through beating treatment, and particularly preferred when the hydrophobizing agent is rosin.

[0011] By the pulping method (kraft method), lignin, which is a coloring substance in pulp, is dissolved and removed to whiten the pulp. By performing a bleaching treatment, the whiteness of the pulp can be further increased. The bleaching treatment method is not particularly limited, and a commonly used method can be used. For example, for pulp that has been optionally delignified by a normal method, chlorine treatment (C), chlorine dioxide bleaching (D), alkali extraction (E), hypochlorite bleaching (H), hydrogen peroxide bleaching (P), alkaline hydrogen peroxide treatment stage (Ep), alkaline hydrogen peroxide / oxygen treatment stage (Eop), ozone treatment (Z), chelating treatment (Q), etc. can be combined and carried out in sequences such as D-E / PD, C / D-E-H-D, Z-E-D-PZ / D-Ep-D, Z / D-Ep-D-P, D-Ep-D, D-Ep-D-P, D-Ep-P-D, Z-Eop-D-D, Z / D-Eop-D, Z / D-Eop-D-E-D, etc. (in the sequence, " / " means that the treatments before and after " / " are carried out continuously without washing). The whiteness of the pulp is preferably 80% or more based on ISO 2470.

[0012] [Hydrophobic agent] The pulp sheet contains a hydrophobizing agent. This can improve the water resistance of the pulp sheet and the uniformity during the rubber kneading of the pulverized product of the pulp sheet. Examples of the hydrophobizing agent include rosin (rosin, its derivatives, modified products, etc.), alkyl ketene dimer, alkenyl succinic acid (alkenyl succinic acid, alkenyl succinic anhydride, etc.), styrene-acrylic resin (styrene-acrylic resin, styrene-maleic acid-acrylic resin, etc.), styrene resin, and olefin resin. These may be used alone or in combination. Among these, rosin, alkyl ketene dimer, alkenyl succinic acid, and styrene-acrylic resin are preferred, and rosin and alkyl ketene dimer are more preferred. The content of the hydrophobizing agent is usually 0.15 parts by mass or more, preferably 0.2 parts by mass or more, based on 100 parts by mass of the pulp sheet. Thereby, the compounding effect of the hydrophobizing agent can be exerted. The upper limit is usually 3 parts by mass or less, preferably 2 parts by mass or less, more preferably less than 1 part by mass, even more preferably 0.8 parts by mass or less, and 0.5 parts by mass or less. Thereby, the plasticization tendency at high temperature can be suppressed, and as a result, the influence on the thermal stability after rubber vulcanization can be suppressed.

[0013] [Optional Component] The pulp sheet (and its pulverized product) may contain components other than the pulp and the hydrophobizing agent. Examples of such optional components include various organic components and / or inorganic components, such as paper strength enhancers, yield improvers, bulking agents, pigments, fillers, water repellency improvers, pH adjusters, defoamers, pitch control agents, and slime control agents (e.g., papermaking chemicals such as sulfuric acid band, polyacrylamide (amphoteric, cationic, anionic), cationized starch).

[0014] [Basis Weight] The basis weight of the pulp sheet is preferably 100 g / m 2 or more, more preferably 200 g / m 2 or more. The upper limit is preferably 550 g / m 2 or less, more preferably 400 g / m 2 or less. Therefore, it is preferably 100 to 550 g / m 2, more preferably 200 to 400 g / m 2 . By being in the above preferable range, the pulverized product of the pulp sheet can be stably produced.

[0015] [Degree of Stickiness Size] The degree of stickiness size of the pulp sheet is preferably 400 seconds or more, more preferably 600 seconds or more. Thereby, the uniformity during rubber kneading of the pulverized product of the pulp sheet can be improved. The degree of stickiness size can be measured according to JIS P 8122:2004.

[0016] [Method for Producing Pulp Sheet] The method for producing the pulp sheet is not particularly limited. For example, there can be mentioned a method of forming a pulp slurry containing a raw material containing pulp and a hydrophobizing agent. The solvent of the pulp slurry is usually water. The concentration (solid content concentration) of pulp in the pulp slurry is usually 0.5% by mass or more, preferably 0.7% by mass or more. The upper limit is usually 5% by mass or less, preferably 3% by mass or less. The forming can be carried out using a paper-making machine such as a pulp machine.

[0017] [1.2 Pulverized Product of Pulp Sheet] The pulverized product of the pulp sheet can be obtained by pulverizing the above-mentioned pulp sheet.

[0018] [Size of Pulverized Product (Average Particle Diameter, etc.)] The pulverized product is usually in powder form. The average particle diameter of the pulverized product is usually 100 μm or less, preferably 80 μm or less, more preferably 60 μm or less, still more preferably 55 μm or less, or 50 μm or less. Thereby, kneading with the rubber component can be made easier. The lower limit is usually 5 μm or more, preferably more than 10 μm. In this specification, the average particle diameter is the volume 50% average particle diameter (D50) measured by the laser light scattering method (laser diffraction method), and can be measured with a laser diffraction / scattering type particle size distribution measuring instrument (in the following examples, manufactured by Malvern, instrument name: Mastersizer 3000) etc.

[0019] [Optional treatment] The ground product of pulp may contain components other than pulp and hydrophobizing agent. Such optional components include various organic components and / or inorganic components. For example, paper strength enhancer, yield improver, bulking agent, pigment, filler, drainage improver, pH adjuster, defoaming agent, pitch control agent, slime control agent (e.g., sulfuric acid band, polyacrylamide (amphoteric, cationic, anionic), cationized starch), etc. papermaking chemicals. Also, the ground product of pulp may be subjected to modification treatment such as chemical treatment. The modification treatment is preferably carried out within a range that does not significantly impair the degree of polymerization of the pulp raw material used as the raw material. The purpose of adding optional components and optional treatment may be to improve various functions, etc., and is not particularly limited. The addition amount of the optional component can be appropriately determined according to the type and necessity of the formulation.

[0020] [Method for producing ground product of pulp sheet] The method for producing the ground product of pulp sheet is not particularly limited. For example, grinding treatment using a grinder can be mentioned.

[0021] [-Grinding treatment-] Examples of grinders that can be used in the grinding treatment include cutting mills, impact mills, air classifying mills, hammer mills, vertical roller mills, media mills, media agitation mills, and cryogenic grinders. They can be used alone or in combination of two or more. Specifically, the following can be exemplified.

[0022] Cutting mill: Mesh mill HA series (manufactured by Horai Co., Ltd.), Knife mill (manufactured by Palman), Cutter mill (manufactured by Tokyo Atomizer Co., Ltd.), Centricutter (manufactured by Nippon Coke Industry Co., Ltd.), Rotary cutter mill (manufactured by Nara Machinery Co., Ltd.), Turbo cutter (manufactured by Floyd Turbo Co., Ltd.), etc.

[0023] Hammer mills: Joe crusher (manufactured by Makino Co., Ltd.), Atomizer TAP (manufactured by Tokyo Atomizer Manufacturing Co., Ltd.), Micro Pulverizer (manufactured by Hosokawa Micron Corporation), Fine Impact Mill (manufactured by Hosokawa Micron Corporation), Atomizer (manufactured by Seishin Enterprise Co., Ltd.), and Hammer Crusher (manufactured by Mieno Industries Co., Ltd.).

[0024] Impact mills: ACM Pulverizer (manufactured by Hosokawa Micron Corporation), Micro Pulverizer (Hosokawa Micron Corporation), Inomizer (manufactured by Hosokawa Micron Corporation), CUM type centrifugal mill (manufactured by Nippon Coke & Engineering Co., Ltd.), Xceed Mill (manufactured by Mieno Industries Co., Ltd.), Ultraplex (manufactured by Mieno Industries Co., Ltd.), Contrapex (manufactured by Mieno Industries Co., Ltd.), Colopex (manufactured by Mieno Industries Co., Ltd.), Impeller Mill (manufactured by Seishin Enterprise Co., Ltd.), Tornade Mill (manufactured by Sanjo Industries Co., Ltd.), Near Mill (manufactured by Dalton Co., Ltd.), HT type fine crusher (manufactured by Horai Co., Ltd.), Free Crusher (manufactured by Nara Machinery Co., Ltd.), New Cosmomizer (manufactured by Nara Machinery Co., Ltd.), Turbo Mill (manufactured by Freund Turbo Co., Ltd.), Spar Powder Mill (manufactured by Nishimura Machinery Co., Ltd.), Blade Mill (manufactured by Nisshin Engineering Co., Ltd.), Super Rotor (manufactured by Nisshin Engineering Co., Ltd.), Wiley Pulverizer (manufactured by Yoshida Manufacturing Co., Ltd.), and Universal Mill (manufactured by Tokuju Works Co., Ltd.).

[0025] Air jet mills: Gather Mill (manufactured by Polarist Co., Ltd.), CGS type jet mill (manufactured by Nippon Coke & Engineering Co., Ltd.), Spiral Jet (manufactured by Hosokawa Micron Corporation), Counter Jet Mill (manufactured by Hosokawa Micron Corporation), Micron Jet (manufactured by Hosokawa Micron Corporation), Cross Jet Mill (manufactured by Kurimoto Iron Works Co., Ltd.), Supersonic Jet Pulverizer (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), Super Jet Mill (manufactured by Nisshin Engineering Co., Ltd.), Selen Mirror (manufactured by Masayuki Sangyo Co., Ltd.), New Micro Cyclotmat (manufactured by Masuno Manufacturing Co., Ltd.), Cryptron (manufactured by Earth Technica Co., Ltd.), and Current Jet (manufactured by Nisshin Engineering Co., Ltd.).

[0026] Vertical roller mills: vertical roller mills (manufactured by Seishin Enterprise Co., Ltd.), roller mills (manufactured by Kotobuki Giken Kogyo Co., Ltd.), VX mills (manufactured by Kurimoto Iron Works, Ltd.), KVM vertical mills (manufactured by Earth Technica Co., Ltd.), and IS mills (manufactured by IHI Plant Engineering Co., Ltd.).

[0027] Among these, it is preferable to use airflow pulverizers such as Micro Pulverizer (manufactured by Hosokawa Micron Corporation), Free Mill (manufactured by Nara Machinery Co., Ltd.), Turbo Mill (manufactured by Freund Industry Co., Ltd.), Spar Powder Mill (manufactured by Nishimura Machinery Co., Ltd.), Blade Mill (manufactured by Nisshin Engineering Co., Ltd.), which are excellent in fine pulverization; vertical roller mills (manufactured by Seishin Enterprise Co., Ltd.); Mesh Mill HA series (manufactured by Horai Co., Ltd.), Knife Mill (manufactured by Palman Co., Ltd.); supersonic jet pulverizers (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and Current Jet (manufactured by Nisshin Engineering Co., Ltd.).

[0028] The pulverization treatment may be in one stage or two or more stages. Examples of the pulverization treatment in two or more stages include a first pulverization step of obtaining a first pulverized product with an average particle size of 100 μm or less from a pulp sheet, and then further pulverizing the first pulverized product to obtain a second pulverized product with an average particle size of 50 μm or less, including such a treatment.

[0029] When preparing the pulverized product of the pulp sheet, it is also possible to mix the pulp sheet with other optional components (for example, organic components and / or inorganic components) alone or in any ratio of two or more types and then pulverize them.

[0030] -Optional treatment- When preparing the pulverized product of the pulp sheet, treatments other than pulverization may be performed. For example, chemical treatment can be performed on the pulverized product after pulverization or on the pulp sheet before pulverization.

[0031] [1.3 Rubber component] The rubber composition contains a rubber component. Examples of the rubber component include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM), fluororubber (FKM), epichlorohydrin rubber (CO, ECO), urethane rubber (U), silicone rubber (Q), halogenated butyl rubber, polysulfide rubber and other synthetic rubbers, and are not particularly limited. Further, thermoplastic elastomers such as polystyrene-based thermoplastic elastomers, polypropylene-based thermoplastic elastomers, polydiene-based thermoplastic elastomers, chlorine-based thermoplastic elastomers, and engineering plastics-based elastomers can also be used. Among these, natural rubber (NR) is preferred.

[0032] [1.4 Optional Components] The rubber composition may further contain one or more optional components according to the requirements such as the use of the rubber composition. Examples of the optional components include, firstly, crosslinking agents.

[0033] -Crosslinking Agent- In a rubber composition, the rubber component usually exists in a crosslinked state. The crosslinking treatment is generally carried out by a vulcanization system that combines sulfur or a sulfur - donating compound with various general - purpose vulcanization accelerators such as sulfenamide - based and thiuram - based compounds. Crosslinking with organic peroxides is also possible. Examples of organic peroxides include tert - butyl peroxide, dicumyl peroxide, tert - butyl cumyl peroxide, 1,1 - bis(tert - butylperoxy) - 3,3,5 - trimethylcyclohexane, 2,5 - dimethyl - 2,5 - bis(tert - butylperoxy)hexane, 2,5 - dimethyl - 2,5 - bis(tert - butylperoxy)hexyne - 3, 1,3 - bis(tert - butylperoxyisopropyl)benzene, 2,5 - dimethyl - 2,5 - bis(benzoylperoxy)hexane, tert - butyl peroxybenzoate, tert - butyl peroxyisopropyl carbonate, n - butyl - 4,4 - bis(tert - butylperoxy)valerate, bis(α,α - dimethylbenzyl)peroxide, cumene peroxide, and other peroxides. When crosslinking with organic peroxides, it is preferable to use a polyfunctional unsaturated compound in combination, such as triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, N,N’ - m - phenylenebismaleimide. In addition, generally used crosslinking agents such as quinone dioximes, organic polyvalent amine compounds, and alkylphenol resins having a methylol group can also be used.

[0034] Examples of optional components other than the crosslinking agent include reinforcing agents (e.g., silica, carbon black), fillers other than cellulose fillers (e.g., calcium carbonate, clay), silane coupling agents, vulcanization accelerators, vulcanization accelerator aids, oils, curing resins, waxes, antioxidants, colorants, foaming agents, and other compounding agents that can be used in the rubber industry, and papermaking chemicals added to pulp sheets. One or a combination of two or more of these can be appropriately selected and used.

[0035] - Vulcanization accelerators, vulcanization accelerator aids - Examples of vulcanization accelerators include guanidine - based ones such as diphenylguanidine (DPG), thiazole - based ones such as di - 2 - benzothiazolyldisulfide (MBTS) and 2 - mercaptobenzothiazole (MBT), sulfenamide - based ones such as N - cyclohexyl - 2 - benzothiazolylsulfenamide (CBS), N - tert - butyl - 2 - benzothiazolylsulfenamide (BBS), N - oxyethylene - 2 - benzothiazolylsulfenamide (OBS), N,N - dicyclohexyl - 2 - benzothiazolylsulfenamide (DZ), thiourea - based ones such as ethylene thiourea (EU), diethylthiourea (EUR), trimethylthiourea (TMU), thiuram - based ones such as tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), thiocarbamate - based ones such as zinc dimethyldithiocarbamate (ZnMDC), zinc di - n - butyldithiocarbamate (ZnBDC), and xanthate - based vulcanization accelerators such as zinc isopropylxanthate (ZIX). These can be used alone or in combination of two or more. Examples of vulcanization accelerator aids include zinc oxide and stearic acid.

[0036] [1.5 Content of Each Component] The content of the ground product of the pulp sheet is usually 5 parts by mass or more, preferably 10 parts by mass or more, based on 100 parts by mass of the rubber component. Thereby, the compounding effect of the pulp sheet can be fully obtained. The upper limit is usually 100 parts by mass or less, preferably 50 parts by mass or less, more preferably 30 parts by mass or less. Thereby, the influence on the strength of the rubber composition can be suppressed.

[0037] [Content of Optional Components] The content of the optional components can be appropriately determined for each component. For cross - linking agents and vulcanization accelerators, an example is as follows.

[0038] The content of the crosslinking agent is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and even more preferably 0.5 part by mass or more with respect to 100 parts by mass of the rubber component. The upper limit is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less.

[0039] The content of the vulcanization accelerator is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and even more preferably 0.4 part by mass or more with respect to 100 parts by mass of the rubber component. The upper limit is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0040] [2. Manufacturing method] Examples of the method for producing the rubber composition include a method including a step of kneading a pulverized product of a pulp sheet containing a hydrophobizing agent with a rubber component.

[0041] [Kneading step] In the kneading step, the pulverized product of the pulp sheet and the rubber component are kneaded to obtain a mixture. The amounts of the respective components are as described above. It is preferable that the crosslinking agent and the vulcanization accelerator are added after the kneading of the above two components.

[0042] The form of each component to be kneaded is not particularly limited. Examples include solids of each component, a dispersion (in the case of a rubber component, latex) dispersed in a dispersion medium, and a solution dissolved in a solvent. Examples of the dispersion medium and the solvent (hereinafter also collectively referred to as "liquid") include water and organic solvents, and water is preferable. The amount of the liquid is preferably 10 to 1000 parts by mass with respect to 100 parts by mass of the rubber solid content (when using two or more rubber components, the total amount thereof). The dispersion and the solution may contain a dispersant as necessary. The pulverized product of the pulp sheet and the rubber component to be kneaded are preferably solids (not dispersed in a dispersion medium) respectively. Thereby, the drying step after mixing can be omitted, and simplification of the process, acceleration of processing, and low cost can be achieved.

[0043] Kneading may be carried out using a kneader according to a known method. Examples of kneaders include open kneaders such as two-roll and three-roll kneaders, intermeshing Banbury mixers, tangential Banbury mixers, pressure kneaders, homodispersers, super mixers, and other equipment. Kneading may be a multi-step process. For example, a combination of kneading with a closed kneader in the first step and then re-kneading with an open kneader may be mentioned. When kneading is carried out as a dispersion or solution, it is preferable to perform a drying treatment once after kneading, and then add a crosslinking agent and a vulcanization accelerator. Drying can be carried out using a drying device such as an oven or a drum dryer.

[0044] The kneaded product obtained by kneading may be used as a masterbatch as it is or, if necessary, after further kneading (for example, kneading with a kneader such as a roll kneader). Also, arbitrary additives such as rubber components, crosslinking agents, and vulcanization aids may be additionally added to these masterbatches, kneaded again (secondary kneading), and used as a final product (vulcanized rubber, crosslinked rubber).

[0045] After kneading, shaping may be carried out if necessary. Examples of shaping include, for example, mold shaping, injection molding, extrusion molding, blow molding, and foam molding, and the device may be appropriately selected according to the shape, use, and molding method of the final product.

[0046] After kneading, preferably after shaping, it is more preferable to further heat. When the rubber composition contains a crosslinking agent (preferably a crosslinking agent and a vulcanization accelerator), crosslinking (vulcanization) treatment is performed by heating. Also, even when the rubber composition does not contain a crosslinking agent and a vulcanization accelerator, the same effect can be obtained by adding them later and heating. The heating temperature is preferably 150°C or higher, and the upper limit is preferably 200°C or lower, more preferably 180°C or lower. Therefore, about 150 to 200°C is preferable, and about 150 to 180°C is more preferable. Examples of heating devices include vulcanization devices such as mold vulcanization, can vulcanization, continuous vulcanization, and injection molding vulcanization.

[0047] Before using the kneaded product as the final product, finishing treatment may be performed as necessary. Examples of the finishing treatment include polishing, surface treatment, lip finishing, lip cutting, and chlorine treatment. Only one of these treatments may be performed, or a combination of two or more may be performed.

[0048] [3. Use of the rubber composition] The use of the rubber composition is not particularly limited, and any composition for obtaining a rubber product as the final product may be used. That is, it may be an intermediate (masterbatch) for rubber production, an unvulcanized rubber composition containing a vulcanizing agent, or a rubber product as the final product.

[0049] The use of the final product is not particularly limited. For example, it includes transportation equipment such as automobiles, trains, ships, and airplanes (e.g., tires, vibration-proof rubber); electrical appliances such as personal computers, televisions, telephones, and watches; mobile communication devices such as mobile phones; portable music players, video players, printing machines, copying machines, and sports goods; building materials (e.g., seismic isolation rubber); office equipment such as stationery; containers; and containers. Even if it is other than these, it can be applied to members using rubber or flexible plastics.

Examples

[0050] Hereinafter, the present invention will be described more specifically with reference to experimental examples of the present invention, but the present invention is not limited to these experimental examples. Unless otherwise specified, "parts" and "%" indicate parts by mass and mass%, respectively, and numerical ranges are described as including their endpoints.

[0051] [1. Materials used] Natural rubber: solid rubber (RSS3: Ribbed Smokes Sheet grade 3 of smoked sheet rubber)

[0052] Hydrophobic agent: · Rosin (Harsize NES105, manufactured by Harima Kasei Co., Ltd.), added 0.3 part per 100 parts of pulp · Alkyl ketene dimer (AD1614, manufactured by Seiko PMC Co., Ltd.), added 0.4 part per 100 parts of pulp

[0053] Sulfuric acid band (0.15 part): Paper strength enhancer, yield improver

[0054] Vulcanization reagent · Zinc oxide: Manufactured by Fujifilm Wako Pure Chemical Corporation · Stearic acid: Manufactured by Fujifilm Wako Pure Chemical Corporation · Sulfur: Manufactured by Fujifilm Wako Pure Chemical Corporation · Vulcanization accelerator: N - oxyethylene - 2 - benzothiazolylsulfenamide (Nocceler MSA - G manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0055] [2. Manufacturing method] [Manufacture of pulp pulverized product] Examples 1 - 4 For 100 parts by mass of hardwood bleached kraft pulp (LBKP) with a Canadian standard drainage degree of 420 ml, a pulp slurry with a concentration of 1.12% to which a hydrophobizing agent of the type shown in Table 2 (the addition amount is as described above) and 0.15 part by mass of sulfuric acid band were added was made into a pulp sheet at a forming speed of 110 m / min using a pulp machine, with a basis weight of 320 g / m 2 , and a pulp sheet with a Stoke sizing degree (measured according to JIS P 8122:2004, the same hereinafter) of 980 seconds for Examples 1 and 2, and 960 seconds for Examples 3 and 4 was formed. This pulp sheet was pulverized using a vertical roller mill to prepare a pulp pulverized product. The particle size of the pulp pulverized product was adjusted under the pulverization conditions.

[0056] Examples 5 and 6 Using 100 parts by mass of beaten hardwood bleached kraft pulp (LBKP) with a Canadian standard drainage degree of 368 ml as the raw material pulp, a pulp sheet was manufactured under the same conditions as in Examples 1 - 4 except that the same hydrophobizing agent shown in Table 2 was used, and a pulp pulverized product was obtained. The particle size of the pulverized product was adjusted under the pulverization conditions. The Stoke sizing degree of the pulp sheet before pulverization was 1070 seconds.

[0057] Example 7 Using 100 parts by mass of waste paper pulp (Canadian standard drainage degree 420 ml) as the raw material pulp, a pulp pulverized product was obtained under the same pulverization conditions as in Example 3. The Stoke sizing degree of the pulp sheet before pulverization was 990.

[0058] Comparative Examples 1 to 3 Except that no hydrophobizing agent was added, pulp pulverized materials were obtained in the same manner as in Examples 1, 2, and 7, respectively.

[0059] [Manufacture of Vulcanized Rubber Sheet] Each pulp pulverized material was dried at 70°C for 12 hours. The solid rubber was kneaded for 1 minute at 70°C using a laboratory plastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd., 50MR), and then a predetermined amount of the pulp pulverized material was added and kneaded for another 5 minutes. Thereafter, vulcanization reagents (stearic acid, zinc oxide, sulfur, vulcanization accelerator) were added and kneaded using a roll kneader (open roll: manufactured by Kansai Roll Co., Ltd.). The compounding parts of the vulcanization reagents were unified as 6.0 parts of zinc oxide, 0.5 part of stearic acid, 3.5 parts of sulfur, and 0.7 part of vulcanization accelerator per 100 parts of rubber. Thereafter, vulcanization molding (press crosslinking at 150°C) was performed to obtain a 2-mm-thick vulcanized rubber sheet.

[0060] [Table 1]

[0061] [3. Tests] Each of the obtained vulcanized rubber sheets was subjected to each test. ·Tensile test (JIS K6251 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Properties", dumbbell No. 3) ·Rubber hardness test (in accordance with JIS K6253-3, durometer hardness) ·Dynamic viscoelasticity test (frequency 10 Hz), measuring the storage elastic modulus at 23°C The results are shown in Table 2.

[0062] [Table 2]

[0063] Compared with the sample without the hydrophobizing agent (comparative example), the sample with the hydrophobizing agent (example) was able to overall improve the basic rubber physical properties such as intermediate stress and storage modulus without significantly impairing the strength and elongation. This is considered to be due to the improved compatibility with rubber and the increased reinforcement efficiency by using the pulverized product of the hydrophobized pulp sheet by adding the hydrophobizing agent.

[0064] These results indicate that the present invention provides a rubber composition with good strength and also provides a method for efficiently manufacturing such a rubber composition.

Claims

1. A rubber composition containing a pulverized product of a pulp sheet containing at least one hydrophobizing agent selected from the group consisting of rosin, alkyl ketene dimer, alkenyl succinic acid, and styrene-acrylic resin.

2. The rubber composition according to claim 1, wherein the basis weight of the pulp sheet is 100 to 550 g / m ２ .

3. The rubber composition according to claim 1 or 2, wherein the Stoke's sizing degree of the pulp sheet is 400 seconds or more.

4. The rubber composition according to claim 1 or 2, wherein the volume-based 50% average particle diameter (D50) of the pulverized product of the pulp sheet measured by the laser diffraction / scattering method is 100 μm or less.

5. A method for producing a rubber composition, comprising a step of kneading a pulverized product of a pulp sheet containing at least one hydrophobizing agent selected from the group consisting of rosin, alkyl ketene dimer, alkenyl succinic acid, and styrene-acrylic resin with a rubber component.

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