JP2018119129A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition capable of forming a molded body excellent in physical properties such as mechanical strength properties and further excellent in an appearance having a low surface gross, so-called, having a mat surface, and excellent in wear resistance.SOLUTION: Provided is a rubber composition comprising: [I] rubber (A) of 100 mass%; and [II] a cross-linked polymer olefin polymer (B) of 5 to 80 mass%; where (i) the melting point (T) measured by DSC is 120°C or higher; (ii) the intrinsic viscosity [η} measured in decalin heated to 135°C in accordance with ASTMD4020 lies in the range of 3 to 50 dl/g; and (iii)the average particle diameter dlies in the range of 1 to 200 μm.SELECTED DRAWING: None

Description

  The present invention relates to a rubber composition capable of forming a molded article having a low surface glossiness (gloss), an appearance having a so-called matte surface, and excellent wear resistance.

  In recent years, rubber parts have been used everywhere in daily life such as automobiles, buildings, OA equipment and the like. Rubber is usually used after being vulcanized, but there is a problem that the surface gloss is remarkably lowered due to surface wear, bloom, and bleed over a long period of use. Therefore, there is a need for a vulcanized rubber molded product having a uniform matte surface with a lower surface gloss than that during vulcanization molding. By the way, among the vulcanization methods, in the method in which the compounded rubber is continuously vulcanized after being extruded into a predetermined shape by an extruder, the compounded rubber is added by filling a large amount of carbon black or inorganic filler having a large particle size. The surface glossiness of the vulcanized rubber molding can be reduced. However, in such molding, when a matting mold is repeatedly used, the mold surface gradually becomes smooth due to contamination, and when it is transferred, the surface of the resulting vulcanized rubber molded article also becomes smooth. Become. Therefore, if polishing is performed in the sense of cleaning the mold surface, the product dimensions of the product obtained may not match, or the same matte mold surface as the first may not be obtained. Also, when the surface of the vulcanized rubber molded product is matted by secondary processing such as cutting the surface of the vulcanized rubber molded product or dipping it in a highly corrosive solvent to roughen the surface of the vulcanized rubber molded product. However, there is a problem that the process is complicated. Therefore, the appearance of a rubber composition capable of providing a vulcanized rubber molded article having a uniform matte surface with low surface glossiness even in the case of molding is desired.

  Patent Document 1 proposes a rubber composition in which a synthetic resin having a melting point measured by DSC of 120 ° C. or higher, a viscosity average molecular weight of 300,000 or higher, and an average particle diameter of 1 to 50 μm is blended. Yes.

JP-A-9-20838

  In Patent Document 1 described above, the rubber composition has the advantage that molding is possible and secondary processing is unnecessary, but the synthetic resin is dispersed without forming a continuous phase in the compounded rubber, and From the viewpoint of the roll operation of the compounded rubber, it was necessary to mix the mixed dispersion of the synthetic resin at a temperature below its melting point. The problem to be solved by the present invention is, in view of the various problems of the background art described above, more specifically, the mixing and dispersion of an ultrahigh molecular weight olefin polymer that is a synthetic resin in Patent Document 1 has a melting point. An object of the present invention is to provide a rubber composition capable of forming a molded article having a low surface glossiness (gloss), a so-called matte surface, and an excellent appearance and abrasion resistance.

The present inventors have intensively studied to solve the above problems. As a result, it has been found that the above problems can be solved by a rubber composition having the following constitution, and the present invention has been completed.
That is, the present invention relates to the following [1] to [7].

[1] [I] 100 parts by mass of rubber (A), and [II] an ultra-high cross-linked radiation high-molecular weight olefin polymer (B ′) satisfying the following requirements (i) to (iii) 5-80 parts by mass of a molecular weight olefin polymer (B),
Containing a rubber composition.
(I) The melting point (T _m ) measured by DSC is 120 ° C. or higher. (Ii) The intrinsic viscosity [η] measured in decalin at 135 ° C. according to ASTM D4020 is in the range of 3 to 50 dl / g ( iii) The average particle diameter d ₅₀ is in the range of 1 to 200 μm.
[2] The rubber composition according to [1], containing a vulcanizing agent (C).
[3] The rubber according to [1] or [2], including a step of kneading the rubber (A) and the crosslinked ultrahigh molecular weight olefin polymer (B) at a temperature of 120 to 170 ° C. A method for producing the composition.
[4] including a step of kneading the rubber (A) and the crosslinked ultrahigh molecular weight olefin polymer (B) at a temperature equal to or higher than the melting point of the ultra high molecular weight olefin polymer (B ′). [1] A method for producing a rubber composition according to any one of [3].
[5] including a step of obtaining the crosslinked ultrahigh molecular weight olefin polymer (B) by irradiating the ultrahigh molecular weight olefin polymer (B ′) with radiation having an irradiation dose of 20 to 700 kGy. [1] ] The manufacturing method of the rubber composition as described in any one of [4].
[6] A molded body formed from the rubber composition according to [1] or [2].
[7] The molded article according to [6], which is formed by mold vulcanization molding.

  The rubber body composition of the present invention can be produced by a simpler process, has excellent physical properties such as mechanical strength characteristics, and has a low surface gloss (gloss) appearance, a so-called matte surface, and wear resistance. It is possible to form a molded article excellent in the above.

  Hereinafter, the rubber composition according to the present invention will be specifically described. The rubber composition according to the present invention comprises at least one rubber (A) selected from natural rubber and synthetic rubber, a crosslinked ultrahigh molecular weight olefin polymer (B), and a vulcanizing agent (C) as necessary. It is composed of

  By using the crosslinked ultrahigh molecular weight olefin polymer (B), even if the kneading temperature with the rubber (A) is higher than the melting point, the unevenness of the surface of the vulcanized rubber molded product becomes fine and an excellent matte state is obtained. Can be obtained. In this invention, a bridge | crosslinking ultra high molecular weight olefin type polymer (B) is 5-80 mass parts with respect to 100 mass parts of rubber | gum (A), Preferably it is 10-70 mass parts, More preferably, it is 20-60. Used in the ratio of parts by mass. When the amount of the crosslinked ultrahigh molecular weight olefin polymer mixed and dispersed in the rubber (A) is less than 5 parts by mass, a vulcanized rubber molded article having a matte surface cannot be obtained. On the other hand, if the amount of the crosslinked ultrahigh molecular weight olefin polymer (B) exceeds 80 parts by mass, the workability of the compounded rubber (unvulcanized) and the mechanical properties of the vulcanized rubber molded product are deteriorated, which is not preferable. .

<Rubber (A)>
The rubber (A) according to the present invention is natural rubber (NR) or synthetic rubber. Specific examples of the synthetic rubber include ethylene / propylene copolymer rubber (EPR) and ethylene / propylene / diene copolymer rubber (EPDM). Of these, polyolefin-based rubbers such as EPR and EPDM are preferably used for exterior materials that require weather resistance.

<Crosslinked Ultra High Molecular Weight Olefin Polymer (B)>
The crosslinked ultra high molecular weight olefin polymer (B) according to the present invention is a radiation cross-linked product of the ultra high molecular weight olefin polymer (B ′).

  In the present invention, the ultrahigh molecular weight olefin polymer (B ′) is a homopolymer such as polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or ethylene and a small amount of other α. -Copolymers with olefins such as propylene, 1-butene, 1-hexene, 1-octene and 4-methyl-1-pentene, preferably ethylene polymers, particularly preferably ethylene It is a homopolymer and is usually a polymer having a higher molecular weight than the olefin polymer to be molded.

In the present invention, the ultra high molecular weight olefin polymer (B ′) is produced by the following requirement (i):
Although it will not specifically limit if-(iii) is satisfy | filled, For example, it can manufacture by the method disclosed by the following literature.
(1) International Publication No. 2006/054696 (2) International Publication No. 2008/013144 (3) International Publication No. 2009/011231 (4) International Publication No. 2010/074073

The ultrahigh molecular weight olefin polymer (B ′) according to the present invention satisfies the following requirements (i) to (iii).
Requirement (i)
The ultrahigh molecular weight olefin polymer (B ′) according to the present invention has a melting point of 120 ° C. or higher measured by DSC (differential scanning calorimeter). There is a risk that a crosslinked product of an ultrahigh molecular weight olefin polymer having a melting point of less than 120 ° C. is melted when mixed using a practical kneader such as a Banbury mixer and cannot be processed after being cooled. In addition, a vulcanized rubber molded product obtained by using a crosslinked product of an ultra-high molecular weight olefin polymer having a melting point of less than 120 ° C. has properties at high temperatures, for example, thermal properties such as increased compression set. Getting worse. Therefore, in this invention, the ultra high molecular weight olefin type polymer which has melting | fusing point below the temperature which vulcanizes at the temperature of 120 degreeC or more is used as a raw material of a crosslinked body.

Requirement (ii)
The intrinsic viscosity [η] of the ultrahigh molecular weight olefin polymer (B ′) according to the present invention measured in a 135 ° C. decalin solvent is 3 to 50 dl / g, preferably 5 to 35 dl / g, more preferably 5 to 30 dl. / G. By using such an ultrahigh molecular weight olefin polymer, a uniform surface state can be obtained without the ultrahigh molecular weight olefin polymer being flattened or flowing in the flow direction of the compounded rubber during vulcanization. . Further, it is more preferable because it is excellent in wear resistance and self-lubrication.

Requirement (iii)
The average particle size d ₅₀ of the ultrahigh molecular weight olefin polymer (B ′) according to the present invention is a value at which the integrated value of the particle shape distribution is 50% by mass by measurement of the weight-based particle size distribution by the Coulter counter method. The average particle diameter d ₅₀ is in the range of 1 to ₂₀₀ μm, preferably 1 to ₅₀ μm, more preferably 1 to 40 μm, still more preferably 1 to 35 μm, particularly preferably 5 to 35 μm, and particularly preferably 5 to 20 μm.

<Preparation of crosslinked ultrahigh molecular weight olefin polymer (B)>
The crosslinked ultrahigh molecular weight olefin polymer according to the present invention is obtained by irradiating the above-described ultrahigh molecular weight olefin polymer (B ′) with radiation.
By irradiating the ultrahigh molecular weight olefin polymer (B ′) with radiation, the molecular chain is broken and crosslinked, and as a result, the molecular chain is bound at the crosslinking point. As a result, the molecular chain cannot flow freely even at the glass transition temperature or higher than the melting point, and the high temperature characteristics are improved. Furthermore, the shape can be maintained even under stress, and the mechanical properties can be maintained.

As radiation, there are α rays, β rays, γ rays, electron rays, ions, etc., and any of them can be used, but electron rays or γ rays are suitable.
Although the irradiation dose of radiation varies depending on the monomer species constituting the ultrahigh molecular weight olefin polymer (B ′) to be used, it is usually 20 to 700 kGy, preferably 100 to 500 kGy.

  When the irradiation dose is within the above range, the crosslinking reaction of the ultrahigh molecular weight olefin polymer (B ′) proceeds efficiently, and the crosslinked ultrahigh molecular weight olefin polymer (B) thus obtained is converted to olefin. When used in a polymer composition, reaggregation of particles can be suppressed.

  On the other hand, when the irradiation dose is 700 kGy or more, the polymer is deteriorated severely, and when the irradiation dose is 20 kGy or less, the crosslinking of the polymer chain does not proceed or is not preferable.

<Vulcanizing agent (C)>
The vulcanizing agent (C) may or may not be contained in the rubber composition according to the present invention. When the rubber composition according to the present invention containing no vulcanizing agent (C) is vulcanized, the vulcanizing agent (C) is blended.
Examples of the vulcanizing agent (C) used in vulcanization include sulfur, sulfur compounds and organic peroxides.

<Sulfur and sulfur compounds>
Specific examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur and the like.

  Specific examples of the sulfur compound include sulfur chloride, sulfur dichloride, and polymer polysulfide. Also use sulfur compounds that release active sulfur at the vulcanization temperature, such as morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide, dipentamethylenethiuram tetrasulfide, selenium dimethyldithiocarbamate. Can do. Of these, sulfur is preferably used.

Sulfur or a sulfur compound is used in a proportion of 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the rubber (A).
Moreover, when using sulfur and a sulfur compound as a vulcanizing agent (C), it is preferable to use a vulcanization accelerator together.

<Vulcanization accelerator>
Specifically, as a vulcanization accelerator,
Sulfenamide compounds such as N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolsulfenamide, N, N-diisopropyl-2-benzothiazolsulfenamide;
Thiazole compounds such as 2-mercaptobenzothiazole, 2- (2 ′, 4′-dinitrophenyl) mercaptobenzothiazole, 2- (4′-morpholinodithio) benzothiazole, dibenzothiazyl disulfide;
Guanidine compounds such as diphenylguanidine, diorthotolylguanidine, diorthonitrile guanidine, orthonitrile biguanide, diphenylguanidine phthalate;
Aldehyde amines or aldehydes such as acetaldehyde-aniline reactant, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde ammonia
Ammonia compounds;
Imidazoline compounds such as 2-mercaptoimidazoline;
Thiourea compounds such as thiocarbanilide, diethylthiourea, dibutylthiourea, trimethylthiourea, diorthotolylthiourea;
Thiuram compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, pentamethylenethiuram tetrasulfide;
Dithioacid salts such as zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc di-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, selenium dimethyldithiocarbamate, tellurium dimethyldithiocarbamate Compounds;
Xanthate compounds such as zinc dibutylxanthate;
A compound such as zinc white can be mentioned.
These vulcanization accelerators are used in a proportion of 0.1 to 20 parts by mass, preferably 0.2 to 10 parts by mass with respect to 100 parts by mass of the rubber (A).

<Organic peroxide>
Any organic peroxide may be used as long as it is usually used for rubber peroxide vulcanization. Specifically, dicumyl peroxide, di-t-butyl peroxide, di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butyl hydroperoxide, t-butylcumyl peroxide, benzoyl Peroxide, 2,5-dimethyl-2,5-di (t-butylperoxin) hexyne-3, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2 , 5-mono (t-butylperoxy) -hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, and the like. Of these, dicumyl peroxide, di-t-butyl peroxide, and di-t-butylperoxy-3,3,5-trimethylcyclohexane are preferably used. These organic peroxides are used alone or in combination of two or more.

  The organic peroxide is used in a proportion of 0.0003 to 0.05 mol, preferably 0.001 to 0.03 mol, based on 100 g of the rubber (A). It is desirable to determine the optimum amount as appropriate.

When an organic peroxide is used as the vulcanizing agent (C), it is preferable to use a vulcanization aid in combination. Specific examples of the vulcanization aid include sulfur; quinone dioxime compounds such as p-quinone dioxime; methacrylate compounds such as polyethylene glycol dimethacrylate; allyl compounds such as diallyl phthalate and triallyl cyanurate; Other maleimide compounds; divinylbenzene and the like.
Such a vulcanization aid is used in an amount of 0.5 to 2 mol, preferably about equimolar to 1 mol of the organic peroxide used.

<Other ingredients>
In the rubber composition according to the present invention, depending on the intended use and performance of the vulcanizate, in addition to the rubber (A), the crosslinked ultrahigh molecular weight olefin polymer (B) and the vulcanizing agent (C), Types of rubber reinforcing agents, fillers and softeners and their blending amounts, types of compounds such as vulcanization aids and their blending amounts, types of antioxidants, processing aids and their blending amounts, and foaming as necessary The type of compound for foaming, such as an agent and a foaming aid, and the blending amount thereof, a defoaming agent, and a step of producing a vulcanizate can be appropriately selected.

  The total amount of the rubber (A) and the crosslinked ultrahigh molecular weight olefin polymer (B) in the vulcanized product can be appropriately selected according to the intended performance and use of the vulcanized product. Preferably it is 25 mass% or more.

[Rubber reinforcement and filler]
The rubber reinforcing agent has an effect of enhancing mechanical properties such as tensile strength, tear strength, and wear resistance of the vulcanized rubber.

  Specific examples of such rubber reinforcing agents include those that are surface-treated with carbon black such as SRF, GPF, FEF, MAF, HAF, ISAF, SAF, FT, and MT, silane coupling agents, and the like. Examples thereof include carbon black, silica, activated calcium carbonate, fine talc, fine silicate.

The filler is used for the purpose of increasing the hardness of the rubber product or reducing the cost without significantly affecting the physical properties.
Specific examples of such fillers include light calcium carbonate, heavy calcium carbonate, talc, and clay.

Further, the hardness of the rubber product can be increased by using the crosslinked ultrahigh molecular weight olefin polymer (B).
The types and blending amounts of these rubber reinforcing agents and fillers can be appropriately selected depending on the application, but these blending amounts are usually 300 parts by weight at maximum with respect to 100 parts by weight of rubber (A), preferably at most 200 parts by mass.

[Softener]
As the softener, a softener usually used for rubber can be used.
Specifically, petroleum-based softeners such as process oil, lubricating oil, paraffin, liquid paraffin, petroleum asphalt, and petroleum jelly;
Coal tar softeners such as coal tar and coal tar pitch;
Fatty oil-based softeners such as castor oil, linseed oil, rapeseed oil, coconut oil;
Tall oil;
sub;
Waxes such as beeswax, carnauba wax, lanolin;
Fatty acids and fatty acid salts such as ricinoleic acid, palmitic acid, barium stearate, calcium stearate, zinc laurate;
Examples thereof include synthetic polymer materials such as petroleum resin, atactic polypropylene, and coumarone indene resin. Of these, petroleum softeners are preferably used, and process oil is particularly preferably used.

  The blending amount of these softening agents can be appropriately selected depending on the use of the vulcanizate. The blending amount is usually 150 parts by mass at the maximum with respect to 100 parts by mass of the rubber (A), preferably 100 parts by mass at the maximum. is there.

[Anti-aging agent]
If an anti-aging agent is used, the material life can be further extended. This is the same as in the case of ordinary rubber.

As an anti-aging agent used in the present invention, specifically,
Aromatic secondary amine stabilizers such as phenylnaphthylamine, 4,4 ′-(α, α-dimethylbenzyl) diphenylamine, N, N′-di-2-naphthyl-p-phenylenediamine; 2,6-di- phenolic stabilizers such as t-butyl-4-methylphenol, tetrakis- [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane;
Thioether stabilizers such as bis [2-methyl-4- (3-n-alkylthiopropionyloxy) -5-tert-butylphenyl] sulfide;
Benzimidazole stabilizers such as 2-mercaptobenzimidazole;
Dithiocarbamate stabilizers such as nickel dibutyldithiocarbamate;
Examples include quinoline stabilizers such as a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline. These anti-aging agents are used alone or in combination of two or more.

  Such an anti-aging agent is used at a ratio of 5 parts by mass or less, preferably 3 parts by mass or less, with respect to 100 parts by mass of the rubber (A), but the optimum amount is appropriately determined according to the required physical property values. It is desirable to do.

[Processing aid]
As said processing aid, the compound used for processing of normal rubber can be used. Specifically, higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid and lauric acid, higher fatty acid salts such as barium stearate, zinc stearate and calcium stearate, ricinoleic acid ester, stearic acid ester, palmitic acid ester and lauric acid And higher fatty acid esters such as acid esters.

  Such a processing aid is usually used at a ratio of 10 parts by mass or less, preferably 5 parts by mass or less with respect to 100 parts by mass of the rubber (A), but an optimum amount is appropriately selected according to the required physical property values. It is desirable to decide.

[Foaming agent and foaming aid]
As described above, the rubber composition according to the present invention can be obtained by blending a foaming agent and a foaming aid that are usually used in rubber as necessary, and performing molding, foaming, and vulcanization.

Specifically, as a foaming agent,
Inorganic foaming agents such as sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, ammonium nitrite;
Nitroso compounds such as N, N′-dimethyl-N, N′-dinitrosotephthalamide, N, N′-dinitrosopentamethylenetetramine;
Azo compounds such as azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene, barium azodicarboxylate;
Sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, p, p′-oxybis (benzenesulfonyl hydrazide), diphenylsulfone-3,3′-disulfonyl hydrazide;
Examples include azide compounds such as calcium azide, 4,4-diphenyldisulfonyl azide, and p-toluenesulfuronyl azide.

These foaming agents are used in a proportion of 0.5 to 30 parts by mass, preferably 1 to 20 parts by mass with respect to 100 parts by mass of the rubber (A).
If necessary, the foaming aid used in combination with the foaming agent acts to lower the decomposition temperature of the foaming agent, promote decomposition, and make the bubbles uniform. Examples of such foaming aids include organic acids such as salicylic acid, phthalic acid, stearic acid, and oxalic acid, urea, and derivatives thereof.

  These foaming assistants are used in a proportion of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of rubber (A), but depending on the required physical property values. It is desirable to determine the optimum amount as appropriate.

[Defoamer]
When the rubber composition is vulcanized, bubbles may be formed or the degree of foaming may be different depending on the moisture contained therein. In order to prevent these, calcium oxide may be added as a defoaming agent.

  Such a defoaming agent is usually used in a proportion of 20 parts by mass or less, preferably 10 parts by mass or less, with respect to 100 parts by mass of rubber (A). It is desirable to decide.

Preparation of rubber composition The rubber composition according to the present invention comprises a rubber (A), a crosslinked ultra-high molecular weight olefin polymer (B), and the vulcanizing agent (C) used as necessary. Accordingly, rubber compounding agents such as vulcanization accelerators, vulcanization aids, rubber reinforcing agents, fillers, softeners, anti-aging agents, processing aids, foaming agents, foaming aids, defoaming agents within the above range are included. A predetermined amount can be mixed and prepared by a general method for preparing a rubber compound.

  In the rubber composition according to the present invention, it is important that the crosslinked ultrahigh molecular weight olefin polymer (B) is dispersed in the compounded rubber without forming a continuous phase. In Patent Document 1, it is necessary to perform mixing and dispersion of an ultrahigh molecular weight olefin polymer at a temperature lower than its melting point.

In the present invention, by using the crosslinked ultrahigh molecular weight olefin polymer (B), even if the mixed dispersion exceeds its melting point, it is dispersed without forming a continuous phase in the compounded rubber.
In Patent Document 1, when an ultrahigh molecular weight olefin polymer is mixed with rubber (A) at a temperature equal to or higher than the melting point, the ultrahigh molecular weight olefin polymer forms a continuous phase or is compatible with rubber (A). As a result, the viscosity of the compounded rubber once cooled to the melting point or less significantly increases. Therefore, this compounded rubber becomes difficult to roll at temperatures below the melting point, that is, below 120 ° C., and cannot be actually molded.

In the present invention, by using the crosslinked ultrahigh molecular weight olefin polymer (B), this compounded rubber can be rolled at a temperature of the melting point or higher, for example, 120 ° C. or higher.
Therefore, the rubber composition (unvulcanized compounded rubber) according to the present invention is prepared, for example, by the following method.

  That is, by an internal mixer such as a Banbury mixer, a kneader, or an intermix, the rubber (A) and additives such as a filler and a softener are added at 80 to 190 ° C, 80 to 170 ° C, preferably 100 to 170 ° C. More preferably, the mixture is kneaded at a temperature of 120 to 170 ° C., particularly preferably 140 to 160 ° C. for 3 to 10 minutes, and then a crosslinked ultrahigh molecular weight olefin polymer using a roll such as an open roll or a kneader. (B), a vulcanizing agent and, if necessary, a vulcanization accelerator or vulcanization aid and a foaming agent are additionally mixed at a temperature of less than 200 ° C. Preferably, in consideration of deterioration of the rubber and the vulcanizing agent, additional mixing is performed at a temperature of less than 160 ° C., more preferably less than 140 ° C. After kneading at a roll temperature of 40 to 80 ° C. for 5 to 30 minutes, it can be prepared by dispensing.

Even if the mixing temperature in the internal mixer is high, the crosslinked ultrahigh molecular weight olefin polymer (B), the vulcanizing agent, the vulcanization accelerator, the foaming agent, etc. can be simultaneously used together with the polymer, the filler, the softening agent and the like. You may knead.
The rubber composition prepared as described above can be used for various applications including automobile parts, and can be particularly suitably used for applications prepared by molding.

<Preparation of molded product>
In order to prepare a molded body from the rubber composition according to the present invention, an unvulcanized compounded rubber (rubber composition) is prepared once by the method described above, as in the case of molding a general rubber, Next, vulcanization may be performed after the compounded rubber is formed into an intended shape.

  The unvulcanized compounded rubber prepared as described above can be molded and vulcanized by various molding methods, but molded by mold vulcanization molding such as compression molding, injection molding, injection molding, The characteristics can be exhibited most when vulcanized.

  That is, in the case of compression molding, an unvulcanized compounded rubber that has been weighed in advance is put into a mold, and after closing the mold, it is heated at a temperature of 120 to 270 ° C. for 30 seconds to 120 minutes, thereby achieving the desired vulcanized rubber. A molded body is obtained.

  In the case of injection molding, a ribbon-shaped or pellet-shaped compounded rubber is supplied to the pot by a preset amount with a screw. Subsequently, the preheated compounded rubber is fed into the mold by a plunger in 1 to 20 seconds. After injecting the compounded rubber, it is heated at 120 to 270 ° C. for 30 seconds to 120 minutes to obtain the intended vulcanized rubber molded product.

  In the case of injection molding, a pre-weighed compounded rubber is placed in a pot and injected into the mold by a piston in 1 to 20 seconds. After injecting the compounded rubber, the target vulcanized rubber molded article is obtained by heating at a temperature of 120 to 270 ° C. for 30 seconds to 120 minutes.

  In the present invention, in the case of these molds, the crosslinked ultrahigh molecular weight olefin polymer (B) has a larger volume expansion than the rubber (A) or other compounding agents during vulcanization, and cooling after molding. It is important to return to the original volume.

  The surface gloss of the rubber molded body obtained by vulcanization as described above is preferably 50% or less. More preferably, it is 40% or less. A method for measuring the surface gloss will be described later in Examples.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
The physical properties of the ultrahigh molecular weight olefin polymer (B ′) used in Examples and Comparative Examples were measured according to the following methods.

(1) melting point by DSC (T _m) measured melting point (Tm) were measured by DSC. Using DSC (DSC220C, manufactured by Seiko Instruments Inc.), a sample of about 5 mg was put in an aluminum pan for measurement, heated to 200 ° C. and melted, then cooled to 30 ° C. at −10 ° C./min. The melting point (Tm) was calculated from the peak apex of the crystal melting peak when the temperature was raised at ° C / min.

(2) Measurement of intrinsic viscosity [η] The intrinsic viscosity [η] was measured in decalin at a temperature of 135 ° C. by dissolving the ultrahigh molecular weight olefin polymer (B ′) in decalin.
More specifically, about 15 mg of a measurement sample was dissolved in 50 ml of decalin, and the specific viscosity η _sp was measured in an oil bath at 135 ° C. After adding 5 ml of decalin solvent to the decalin solution for dilution, the specific viscosity η _sp was measured in the same manner. This dilution operation was further repeated twice, and the value of η _sp / C when the concentration (C) was extrapolated to 0 as shown in the following formula was determined as the intrinsic viscosity [η] (unit: dl / g).
[Η] = lim (η _sp / C) (C → 0)

The measured average particle size d ₅₀ (3) Average particle size d _50, using the Beckman Multisizer threes, was calculated from the weight-based particle size distribution by Coulter counter method.
Moreover, the test methods of the tensile test, the hardness test, the compression set test, and the gloss measurement test performed on the rubber sheets formed from the rubber compositions obtained in Examples and Comparative Examples are as follows.

(Test method)
(1) Tensile test A test piece was obtained by punching out from a vulcanized rubber sheet having a thickness of 2 mm with a No. 3 type dumbbell described in JIS K6251. Using this test piece, in accordance with the method defined in JIS K6251, a tensile test is performed under the conditions of a measurement temperature of 25 ° C. and a tensile speed of 500 mm / min, and the tensile breaking point stress (T _B ) and tensile breaking point elongation (E _B ) was measured.

(2) Hardness test In the hardness test, six vulcanized rubber sheets with a thickness of 2 mm were stacked, and the hardness (JIS-A) was measured according to JIS K6253.

(3) Compression set test In the compression set test, six vulcanized rubber sheets with a thickness of 2 mm are stacked and attached to a compression device according to the method described in JIS K6262, before the height of the test piece applies a load. The mold was compressed to 3/4 of the height and heat-treated in a gear oven at 70 ° C. for 22 hours together with the mold.
After the heat treatment, the test piece was taken out from the compression device and allowed to cool for 30 minutes, and then the height of the test piece was measured, and the compression set was calculated by the following formula.
Compression set [%] = [(t _O −t ₁ ) / (t _O −t ₂ )] × 100
t _O : Height of the test piece before the test t ₁ : Height after heat-treating the test piece and allowing it to cool for 30 minutes t ₂ : Height of the test piece attached to the measuring mold

(4) Gloss measurement test The surface glossiness of the vulcanized rubber sheet was measured using a gloss meter [Gloss Checker IG-310, incident angle 60 °, light receiving angle 60 °: manufactured by HORIBA, Ltd.] on the surface of the vulcanized rubber sheet. Measured against

[Comparative Example 1]
100 parts by mass of ethylene / propylene / 5-ethylidene-2-norbornene terpolymer [trade name: Mitsui EPT4021, manufactured by Mitsui Chemicals, Ltd.]
5 parts by mass of zinc white,
1 part by weight of stearic acid,
1 part by weight of polyethylene glycol # 4000,
65 parts by mass of FEF carbon black,
40 parts by mass of paraffinic process oil was kneaded for 5 minutes with a 1.7 liter Banbury mixer, and the mixture at 145 ° C. was discharged.

Furthermore, after winding this compound around an 8-inch roll having a surface temperature of 50 ° C., N-cyclohexyl-2-benzothiazolylsulfenamide 1 was added to 212 parts by mass of this compound.
. 5 parts by mass, zinc dimethyldithiocarbamate [vulcanization accelerator] 0.2 parts by mass, zinc di-n-butyldithiocarbamate [vulcanization accelerator] 0.5 parts by mass, sulfur [vulcanizing agent] 2.0 parts by mass And 4 parts by mass of defoaming agent were added and kneaded for 8 minutes, and the resulting blend was allowed to cool.

The compound was vulcanized at 180 ° C. for 5 minutes using a press molding machine to prepare a rubber sheet having a thickness of 2 mm. A rubber block for compression set test was prepared by vulcanization at 180 degrees for 10 minutes.
About the vulcanizate obtained as described above, a tensile test, a hardness test, a compression set test, and a gloss measurement test were performed by the above methods. The results are shown in Table 1.

[Comparative Example 2]
Ultra-high molecular weight polyethylene (B′-1) [melting point: 136 ° C., intrinsic viscosity [η] is 13.0 dl / g, average particle size: 30 μm] It knead | mixed with the mixer and discharged | emitted the compound of 145 degreeC. This formulation was wound on an 8-inch roll having a surface temperature of 50 ° C., but as the formulation was cooled, it quickly cured and could not be rolled.

[Comparative Example 3]
Ultra-high molecular weight polyethylene (B′-2) [melting point: 136 ° C., intrinsic viscosity [η] is 12.9 dl / g, average particle diameter: 125 μm] It knead | mixed with the mixer and discharged | emitted the compound of 145 degreeC. This formulation was wound on an 8-inch roll having a surface temperature of 50 ° C., but as the formulation was cooled, it quickly cured and could not be rolled.

[Comparative Example 4]
Ultrahigh molecular weight polyethylene (B′-3) [Melting point: 136 ° C., intrinsic viscosity [η] is 13.0 dl / g, average particle diameter: 10.5 μm] And kneaded with a Banbury mixer, and the mixture at 145 ° C. was discharged. This formulation was wound on an 8-inch roll having a surface temperature of 50 ° C., but as the formulation cooled, it quickly cured and could not be rolled.

[Example 1]
Comparative Example 1 except that 20 parts by mass of crosslinked ultra-high molecular weight polyethylene (B-1) [average particle size: 30 μm] was added, kneaded with a Banbury mixer in the same manner as Comparative Example 1, and the 145 ° C. mixture was discharged. A rubber sheet was prepared in the same manner as described above. Crosslinked ultra high molecular weight polyethylene (B-1) was obtained by irradiating ultra high molecular weight polyethylene (B′-1) with an electron beam of 200 kGy. The results are shown in Table 1.

[Example 2]
A rubber sheet was prepared in the same manner as in Example 1 except that the rubber discharge temperature after the Banbury mixer kneading was 160 ° C. The results are shown in Table 1.

[Example 3]
A rubber sheet was prepared in the same manner as in Example 1 except that the amount of the crosslinked ultrahigh molecular weight polyethylene (B-1) [average particle size: 30 μm] was 40 parts by mass. The results are shown in Table 1.

[Example 4]
A rubber sheet was obtained in the same manner as in Example 1 except that 40 parts by mass of the crosslinked ultrahigh molecular weight polyethylene (B-2) [average particle diameter: 125 μm] was added instead of the crosslinked ultrahigh molecular weight polyethylene (B-1). Was prepared. Cross-linked ultra high molecular weight polyethylene (B-2) was obtained by irradiating ultra high molecular weight polyethylene (B′-2) with an electron beam of 200 kGy. The results are shown in Table 1.

[Example 5]
A rubber sheet was obtained in the same manner as in Example 1, except that 20 parts by mass of the crosslinked ultrahigh molecular weight polyethylene (B-3) [average particle size: 10 μm] was added instead of the crosslinked ultrahigh molecular weight polyethylene (B-1). Was prepared. The crosslinked ultra high molecular weight polyethylene (B-3) was obtained by irradiating an ultra high molecular weight polyethylene (B′-3) with an electron beam of 200 kGy. The results are shown in Table 1.

[Example 6]
A rubber sheet was prepared in the same manner as in Example 5 except that the rubber discharge temperature after kneading the Banbury mixer was set to 160 ° C. The results are shown in Table 1.

[Example 7]
A rubber sheet was obtained in the same manner as in Example 1 except that 40 parts by mass of the crosslinked ultrahigh molecular weight polyethylene (B-3) [average particle size: 10 μm] was added instead of the crosslinked ultrahigh molecular weight polyethylene (B-1). Was prepared. The crosslinked ultra high molecular weight polyethylene (B-3) was obtained by irradiating an ultra high molecular weight polyethylene (B′-3) with an electron beam of 200 kGy. The results are shown in Table 1.

  As is apparent from the results shown in Table 1, when the ultrahigh molecular weight olefin polymer is mixed and kneaded at a temperature equal to or higher than the melting point, the processability of the rubber composition is poor (Comparative Example 2, Comparative Example 3 and Comparative Example). 4) However, by using a crosslinked ultra-high molecular weight olefin polymer, the processability of the rubber composition is good and the effect of reducing the gloss of the resulting vulcanized molded article (more excellent in matteness) is good. I know that there is.

Claims (7)

[I] 100 parts by mass of rubber (A);
[II] 5 to 80 parts by mass of the crosslinked ultrahigh molecular weight olefin polymer (B), which is a radiation crosslinked body of the ultrahigh molecular weight olefin polymer (B ′) that satisfies the following requirements (i) to (iii): ,
Containing a rubber composition.
(I) The melting point (T _m ) measured by DSC is 120 ° C. or higher. (Ii) The intrinsic viscosity [η] measured in decalin at 135 ° C. according to ASTM D4020 is in the range of 3 to 50 dl / g ( iii) The average particle diameter d ₅₀ is in the range of 1 to 200 μm.   The rubber composition according to claim 1, comprising a vulcanizing agent (C).   The manufacturing method of the rubber composition of Claim 1 or 2 including the process of knead | mixing the said rubber | gum (A) and the said bridge | crosslinking ultrahigh molecular weight olefin type polymer (B) at the temperature of 120-170 degreeC. .   The method includes the step of kneading the rubber (A) and the crosslinked ultrahigh molecular weight olefin polymer (B) at a temperature equal to or higher than the melting point of the ultra high molecular weight olefin polymer (B ′). The manufacturing method of the rubber composition in any one of -3.   The process of obtaining the said bridge | crosslinking ultra high molecular weight olefin polymer (B) by irradiating the radiation of 20-700 kGy to the said ultra high molecular weight olefin polymer (B ') is included. The manufacturing method of the rubber composition in any one of.   A molded body formed from the rubber composition according to claim 1.   The molded body according to claim 6, which is formed by mold vulcanization molding.