JP2019094479A - Molded article - Google Patents

Abstract

To provide a molded article which has desired lubricating performance from the start of use thereof, and has lubricating performance and wear performance for a long period of time.SOLUTION: The present invention relates to a molded article formed by polishing the surface of a precursor molded article with abrasive grains (Y) having an average particle diameter dtwice or less that of an ultra-high molecular weight olefin polymer (B), the precursor molded article being formed from a rubber composition comprising 100 pts.mass of rubber (A) and 5 to 80 pts.mass of the ultra-high molecular weight olefin polymer (B) which satisfies the following (i) to (iii): (i) the melting point (T) as measured by DSC is 120°C or higher; (ii) the intrinsic viscosity [η] measured according to ASTM D4020 in decalin of 135°C is in a range of 3 to 50 dl/g; and (iii) the average particle diameter dis in a range of 1 to 200 μm.SELECTED DRAWING: None

Description

  The present invention relates to a molded article having a low coefficient of dynamic friction, so-called slipperiness and excellent in abrasion resistance, and a method for producing the same.

In recent years, rubber parts are used in automobiles, buildings, office automation equipment, etc. in every part of daily life. Various methods such as a method of applying a silicone grease, a method of blending a wax, and a method of blending a silicone oil are employed in order to improve the sliding property between the rubber and the counterpart material. However, when a method of applying silicone grease to the contact portion between rubber and a partner material is adopted, there is a problem that the number of assembly steps increases, leading to an increase in cost, and a method of compounding silicone oil in a rubber composition was adopted. In this case, the coefficient of friction is low at the beginning of use, but there is a problem that the rubber surface wears when used for a long time.
As a method of reducing the frictional resistance of a molded article made of a rubber composition, several proposals have been made to blend ultra-high molecular weight polyethylene powder into rubber (Patent Documents 1 to 3).

  However, according to Patent Document 1, when the ultra high molecular weight polyethylene powder is only blended into the rubber, the ultra high molecular weight polyethylene is not sufficiently exposed to the rubber surface particularly in the early stage of use, so the slip property is not sufficient. It is necessary to combine fatty acid amide and silicone oil in combination in order to impart.

  In addition, Patent Document 4 proposes a high pressure rubber hose in which an ultrahigh molecular weight polyethylene powder is attached to the surface of a high pressure rubber hose, or an ultrahigh molecular weight polyethylene powder is formed in a layer and integrated. Since it is necessary to provide a layer made of ultrahigh molecular weight polyethylene powder on the rubber composition before the high pressure hose is vulcanized, there is a problem that the production cost is too high and injection vulcanization is difficult.

JP 9-20838 A Japanese Patent Application Laid-Open No. 63-95241 Unexamined-Japanese-Patent No. 1-217049 JP, 2005-144833, A

  An object of the present invention is to obtain a molded article having desired sliding performance from the beginning of use of the molded article and having sliding performance and wear performance over a long period of time.

As a result of earnestly examining in order to solve the above-mentioned subject, by carrying out polish processing of the surface of the precursor compact which consists of a rubber composition which blended the powder of the ultra high molecular weight olefin polymer with the abrasive material which has a specific abrasive grain. When used for sliding parts between the molded body and rubber or sliding parts between the molded body and metal, the sliding property is secured even at the beginning of use, and the ultra-high molecular weight olefins even when the surface of the molded body is worn It has been found that the ultra-high molecular weight polyethylene exposed to the surface of the rubber molded article can provide a molded article having sliding performance and wear performance over a long period of time by ensuring that the base polymer powder is always present on the surface.
That is, the present invention relates to the following [1] to [4].

[1] It was formed from a rubber composition containing 100 parts by mass of rubber (A) and 5 to 80 parts by mass of an ultrahigh molecular weight olefin polymer (B) satisfying the following requirements (i) to (iii) the surface of the precursor molded body, formed by polishing the surface with an average particle diameter d ₅₀ of the ultra high molecular weight olefin polymer (B) mean twice less is abrasive particle size d ₅₀ (Y), the molded body .
(I) The melting point (T _m ) measured by DSC is 120 ° C. or more.
(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 molded article according to [1], wherein the rubber composition contains a vulcanizing agent (C).
[3] The molded article according to [1] or [2], wherein the average particle diameter d ₅₀ of the ultrahigh molecular weight olefin polymer (B) is in the range of ₅ to 35 μm.
[4] A step of polishing the surface of the precursor molded article with the abrasive grains (Y) described in [1] after obtaining the precursor molded article by mold-vulcanizing the rubber composition described in [1] A method of producing a molded body comprising:

  The molded product of the present invention is excellent in physical properties such as mechanical strength and the like in addition to being able to be manufactured in a simpler process, and also ensures slipperiness at the beginning of use. The molecular weight olefin polymer powder is always exposed (present) on the surface of the molded body, and is excellent in sliding performance and wear performance over a long period of time.

Hereinafter, the rubber composition suitable for obtaining the molded object concerning this invention is demonstrated concretely. In the present invention, “A to B” indicating a numerical range indicates A or more and B or less unless otherwise specified.
The rubber composition according to the present invention comprises at least one rubber (A) selected from natural rubber and synthetic rubber, an ultrahigh molecular weight olefin polymer (B), and, if necessary, a vulcanizing agent (C) It is configured.

  In the present invention, the ultrahigh molecular weight olefin polymer (B) is 5 to 80 parts by mass, preferably 10 to 70 parts by mass, more preferably 20 to 60 parts by mass with respect to 100 parts by mass of the rubber (A). Used in proportions of parts. If the amount of the ultrahigh molecular weight olefin polymer mixed and dispersed in the rubber (A) is less than 5 parts by mass, it is not possible to obtain a molded article having excellent slipperiness and wear characteristics. When the amount of the ultrahigh molecular weight olefin polymer (B) exceeds 80 parts by mass, the processability of the compounded rubber (unvulcanized) and the molding obtained by vulcanizing the compounded rubber (rubber composition) It is not preferable because the mechanical properties of the body deteriorate.

<Rubber (A)>
The rubber (A) according to the present invention is a natural rubber (NR) or a synthetic rubber. Specifically as a synthetic rubber, ethylene propylene copolymer rubber (EPR), ethylene propylene diene copolymer rubber (EPDM), etc. are mentioned. Among these, polyolefin-based rubbers such as EPR and EPDM are preferably used for applications of the exterior material where weather resistance is required.

<Ultra-high molecular weight olefin polymer (B)>
The ultrahigh molecular weight olefin polymer (B) according to the present invention is a homopolymer such as polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, etc., and ethylene and a small amount of other α Copolymers with olefins, such as, for example, propylene, 1-butene, 1-hexene, 1-octene and 4-methyl-1-pentene, preferably ethylene-based polymers, particularly preferably ethylene It is a homopolymer and is usually a polymer having a larger molecular weight than the olefin polymer to be molded.

In the present invention, the method for producing the ultrahigh molecular weight olefin polymer (B) is not particularly limited as long as it satisfies the following requirements (i) to (iii), but, for example, by the methods disclosed in the following documents It can be manufactured.
(1) WO 2006/054696 pamphlet (2) WO 2008/013144 pamphlet (3) WO 2009/011231 pamphlet (4) WO 2010/074073 pamphlet

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). The 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 there is a possibility that the rubber composition can not be processed after being cooled. In addition, a molded product obtained by vulcanizing a rubber composition obtained using an ultrahigh molecular weight olefin polymer having a melting point of less than 120 ° C. has a high temperature property, for example, a thermal effect such as an increase in compression set. Characteristics deteriorate. Therefore, in the present invention, it is preferable to use an ultra-high molecular weight olefin polymer having a melting point lower than the temperature at which vulcanization is performed at a temperature of 120 ° C. or higher.

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 It is in the range of g. By using such an ultrahigh molecular weight olefin polymer, a molding having a uniform surface state without the ultrahigh molecular weight olefin polymer being flattened or flowing in the flow direction of the rubber composition at the time of vulcanization You can get the body. Further, the resulting molded product is more preferable because it is excellent in wear resistance and self-lubricity.

Requirement (iii)
The average particle diameter d ₅₀ of the ultrahigh molecular weight olefin polymer (B) according to the present invention is a value such that the integrated value of particle shape distribution becomes 50% by mass by measurement of weight-based particle size distribution by Coulter counter method The average particle diameter d50 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, and particularly preferably 5 to 35 μm. In order to further improve the sliding performance of the molded body, the range of 5 to 15 μm is more preferable.

The ultrahigh molecular weight olefin polymer blended in the rubber (A) may be irradiated with radiation to the above-mentioned ultrahigh molecular weight olefin polymer (B).
By irradiating the ultrahigh molecular weight olefin polymer (B) with radiation, cleavage and crosslinking of the molecular chain occur, and as a result, the molecular chains are linked at the crosslinking point. As a result, molecular chains can not flow freely even at the glass transition temperature or the melting point or higher, and the high temperature characteristics are improved. Furthermore, the form can be maintained even under stress, and mechanical properties can be maintained.

Examples of radiation include α-rays, β-rays, γ-rays, electron beams, and ions, and any of them can be used, but electron beams or γ-rays are suitable.
The irradiation dose of radiation varies depending on the type of monomers constituting the ultrahigh molecular weight olefin polymer (B) to be used, but is usually 20 to 700 kGy, preferably 100 to 500 kGy.

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

  A crosslinking reaction can be advanced efficiently, without degrading a polymer as the said irradiation dose is 700 kGy or less. In addition, it is preferable that the irradiation dose is 20 kGy or more, as crosslinking of polymer chains proceeds at a sufficient crosslinking rate.

<Vulcanizing agent (C)>
The vulcanizing agent (C) may not be contained in the rubber composition according to the present invention, or may be contained. In the rubber composition according to the present invention not containing the vulcanizing agent (C), the vulcanizing agent (C) is blended when performing vulcanization (when obtaining a molded product).
The vulcanizing agent (C) used in the vulcanization includes 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 sulfur compounds include sulfur chloride, sulfur dichloride, and polymeric polysulfides. In addition, use is also made of sulfur compounds which release active sulfur at the vulcanization temperature to be vulcanized, such as morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide, dipentamethylenethiuram tetrasulfide, selenium dimethyldithiocarbamate and the like. Can. Among them, sulfur is preferably used.

The sulfur or 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 a 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-based compounds such as N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, N, N-diisopropyl-2-benzothiazolesulfenamide;
Thiazole compounds such as 2-mercaptobenzothiazole, 2- (2 ′, 4′-dinitrophenyl) mercaptobenzothiazole, 2- (4′-morpholinodithio) benzothiazole, dibenzothiazyl disulfide;
Guanidine compounds such as diphenyl guanidine, diolstril guanidine, diolsonitrile guanidine, ortho nitrile biguanide, diphenyl guanidine phthalate and the like;
Aldehyde amines such as acetaldehyde-aniline reactant, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde ammonia and the like;
Imidazoline compounds such as 2-mercaptoimidazoline;
Thiourian compounds such as thiocarbanilide, diethylthiourea, dibutylthiourea, trimethylthiourea, diorsotrillthiourea and the like;
Thiuram compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, pentamethylenethiuram tetrasulfide and the like;
Dithioacid salts such as zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc di-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, selenium dimethyldithiocarbamate and tellurium dimethyldithiocarbamate System compounds;
Xanthate compounds such as zinc dibutyl xanthate;
Compounds such as zinc flower can be mentioned.
These vulcanization accelerators are used in a ratio 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 peroxides >>
Any organic peroxide may be used so long as it is usually used for peroxide vulcanization of rubber. 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-butylperoxyne) hexyne-3,2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2 Examples include 5-mono (t-butylperoxy) -hexane, α, α'-bis (t-butylperoxy-m-isopropyl) benzene and the like. Among these, dicumyl peroxide, di-t-butyl peroxide, and di-t-butylperoxy-3,3,5-trimethylcyclohexane are preferably used. These organic peroxides may be used alone or in combination of two or more.

  The organic peroxide is used at a ratio of 0.0003 to 0.05 mol, preferably 0.001 to 0.03 mol, per 100 g of the rubber (A), but depending on the required physical properties. It is desirable to determine the optimal amount accordingly.

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; divinyl benzene and the like can be mentioned.
Such a vulcanizing coagent is used in an amount of 0.5 to 2 moles, preferably about equimole, to 1 mole of the organic peroxide used.

<Other ingredients>
In the rubber composition according to the present invention, in addition to the rubber (A), the ultrahigh molecular weight olefin polymer (B) and the vulcanizing agent (C), depending on the intended use and performance of the vulcanized product, the rubber Types and amounts of reinforcing agents, fillers and softeners, types of compounds such as vulcanizing aids and their amounts, types of antiaging agents and processing aids, and amounts of foaming agents as required The kind and compounding amount of compounds for foaming such as foaming aids, defoaming agents, and the step of producing a vulcanized product (step of obtaining a molded product) can be appropriately selected.

  The total amount of the rubber (A) and the ultrahigh molecular weight olefin polymer (B) in the vulcanizate can be appropriately selected according to the intended performance and use of the vulcanizate, but it is usually at least 20 mass%, preferably Is 25 mass% or more.

[Rubber reinforcing agents and fillers]
The rubber reinforcing agent has the effect of enhancing mechanical properties such as tensile strength, tear strength and abrasion resistance of the resulting molded body.

  As such rubber reinforcing agents, specifically, those surface-treated with carbon black such as SRF, GPF, FEF, MAF, HAF, ISAF, SAF, SAF, MT, silane coupling agent, etc. Carbon black, silica, activated calcium carbonate, finely powdered talc, finely powdered silicic acid and the like can be mentioned.

The above-mentioned filler is used for the purpose of increasing the hardness of the obtained molded product or reducing the cost without significantly affecting the physical properties.
Specific examples of such fillers include light calcium carbonate, ground calcium carbonate, talc, clay and the like.

Moreover, it is possible to make high the hardness of the molded object obtained by using an ultrahigh molecular weight olefin polymer (B).
Although the kind and compounding quantity of these rubber reinforcing agents and fillers can be suitably selected according to the use, these compounding quantities are usually a maximum of 300 mass parts, preferably the maximum with respect to 100 mass parts of rubber (A). It is 200 parts by mass.

[Softener]
As the above-mentioned 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, petrolatum and the like;
Coal tar softeners such as coal tar and coal tar pitch;
Fatty oil softeners such as castor oil, linseed oil, rapeseed oil, coconut oil, etc.
Tall oil;
sub;
Waxes such as beeswax, carnauba wax and lanolin;
Fatty acids and fatty acid salts such as ricinoleic acid, palmitic acid, barium stearate, calcium stearate, zinc laurate;
Synthetic polymer substances such as petroleum resin, atactic polypropylene and coumarone-indene resin can be mentioned. Among them, petroleum-based softeners are preferably used, and in particular, process oils are preferably used.

  The blending amount of these softeners can be appropriately selected according to the application of the vulcanized product, but the blending amount is usually at most 150 parts by mass, preferably at most 100 parts by mass with respect to 100 parts by mass of rubber (A). is there.

[Anti-aging agent]
The use of an antiaging agent can further prolong the material life. This is similar to the case of normal rubber.

Specifically as the anti-aging agent used in the present invention,
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, etc .;
Thioether stabilizers such as bis [2-methyl-4- (3-n-alkylthiopropionyloxy) -5-t-butylphenyl] sulfide;
Benzimidazole-based stabilizers such as 2-mercaptobenzimidazole;
Dithiocarbamate stabilizers such as nickel dibutyl dithiocarbamate;
Quinoline type | system | group stabilizers, such as a polymer of 2,2,4-trimethyl 1, 2- dihydroquinoline, etc. are mentioned. These anti-aging agents may be used alone or in combination of two or more.

  Such an antiaging agent is used in a proportion of 5 parts by mass or less, preferably 3 parts by mass or less based on 100 parts by mass of the rubber (A), but the optimum amount is appropriately determined according to the required physical property value It is desirable to do.

[Processing aid]
As the above-mentioned processing aids, compounds used for processing of ordinary rubbers 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, lauric acid Examples thereof include higher fatty acid esters such as acid esters.

  Such a processing aid is generally used in a proportion of 10 parts by mass or less, preferably 5 parts by mass or less, based on 100 parts by mass of the rubber (A), but the optimum amount is appropriately selected according to the required physical properties. It is desirable to determine

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

Specifically as a foaming agent,
Inorganic blowing 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, azocyclohexyl nitrile, azodiaminobenzene, barium azodicarboxylate and the like;
Sulfonyl hydrazide compounds such as benzene sulfonyl hydrazide, toluene sulfonyl hydrazide, p, p′-oxybis (benzene sulfonyl hydrazide), diphenyl sulfone-3,3′-disulfonyl hydrazide and the like;
An azide compound such as calcium azide, 4,4-diphenyldisulfonyl azide, p-toluenesulfonyl azide and the like can be mentioned.

These foaming agents are used in a ratio 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, accelerate the decomposition, and homogenize the cells. Examples of such a foaming aid 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 mass, preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the rubber (A), depending on the required physical property values. It is desirable to determine the optimal amount accordingly.

[Defoamer]
When the rubber composition is vulcanized, bubbles may be generated or the degree of foaming may differ depending on the contained water. In order to prevent these, calcium oxide may be added as a defoamer.

  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 the rubber (A), but the optimum amount is appropriately selected according to the required physical properties. It is desirable to make a decision.

Preparation of Rubber Composition The rubber composition according to the present invention comprises a rubber (A), an ultrahigh molecular weight olefin polymer (B), the above-mentioned vulcanizing agent (C) used as needed, and, if necessary, Rubber compounding agents such as vulcanization accelerators, vulcanization aids, rubber reinforcing agents, fillers, softeners, anti-aging agents, processing aids, foaming agents, foaming aids, defoamers, etc. within the above range The determination can be mixed and prepared according to the general method of rubber compounding preparation.

  The rubber composition (unvulcanized blended rubber) according to the present invention is prepared, for example, by the following method. That is, after mixing the rubber (A) and the additives such as the filler and the softener at a temperature of 80 to 190 ° C. for 3 to 10 minutes by an internal mixer such as a Banbury mixer, a kneader or an intermix, open roll Using ultra-high molecular weight olefin polymer (B), vulcanizing agent, if necessary, vulcanizing accelerator or auxiliary agent, blowing agent, temperature of less than 200 ° C. Add mix below. Preferably, in consideration of the deterioration of the rubber and the vulcanizing agent, additional mixing is carried out at a temperature of less than 160 ° C., more preferably less than 140 ° C., particularly preferably less than 120 ° C. After kneading at a roll temperature of 40 to 80 ° C. for 5 to 30 minutes, it can be prepared by dispensing.

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

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

  The unvulcanized compounded rubber prepared as described above can be molded and vulcanized by various molding methods, but it can be molded and vulcanized by molding such as compression molding, injection molding and injection molding. When it does, it can exhibit the characteristic most.

  That is, in the case of compression molding, an unvulcanized compounded rubber weighed in advance is put in a mold, and after closing the mold, the target precursor molded body is heated at a temperature of 120 to 270 ° C. for 30 seconds to 120 minutes. Is obtained.

  In the case of injection molding, a ribbon-like or pellet-like compounded rubber is supplied to the pot in a predetermined amount by a screw. Subsequently, the preheated compounded rubber is fed into the mold by the plunger in 1 to 20 seconds. By injecting the compounded rubber and then heating for 30 seconds to 120 minutes at a temperature of 120 to 270 ° C., a target precursor molded body is obtained.

  In the case of injection molding, the previously weighed compounded rubber is put into a pot and injected into the mold by a piston in 1 to 20 seconds. By injecting the compounded rubber and heating at a temperature of 120 to 270 ° C. for 30 seconds to 120 minutes, a target precursor molded body is obtained.

  In the case of these moldings, during vulcanization, the ultrahigh molecular weight olefin polymer (B) has a greater volume expansion than the rubber (A) and other compounding agents, and the volume of the original polymer after being cooled after molding It is important to return to

[Method for producing molded body]
The molded object of this invention can obtain the molded object of this invention by grind | polishing the surface of the precursor molded object obtained by the said manufacturing method by the abrasive grain (Y) shown below. Since the ultrahigh molecular weight olefin polymer (B) inside the preformed body is deposited on the surface of the shaped body by polishing, the obtained shaped body can maintain slippage even at the beginning of use. In addition, since the ultrahigh molecular weight polyethylene (B) is always present on the surface of the molded product even if the surface of the molded product is worn, the molded product can have sliding performance and wear performance over a long period of time.

<Abrasive grain (Y)>
The average particle size d ₅₀ of the abrasive grain according to the present invention (Y), the 2 times the average particle size d ₅₀ ultra high molecular weight olefin polymer (B) or less, preferably 1.5 times or less, more preferably It is less than 1 time. The average particle size d ₅₀ of the abrasive grains (Y) is preferably 0.5 μm or more.
Abrasive average particle size d ₅₀ of (Y) is, the greater than 2 times the average particle size d ₅₀ ultra high molecular weight olefin-based polymer (B), the molded body surface ultrahigh molecular weight olefin polymer (B Since it does not expose, it is inferior to sliding performance.

  As the abrasive grains (Y) according to the present invention, general abrasives can be used. Specifically, alumina, silicon carbide, chromium oxide, iron oxide, cerium oxide, zirconia, silica, diamond, CBN or the like can be used.

  The method of polishing the surface of the precursor molded body according to the present invention includes a grinder, a polisher, a lapping machine, a polishing machine, a honing machine, a buff polisher, a CMP apparatus, and the like, and any method may be used.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples.
Physical properties of the ultrahigh molecular weight olefin polymer (B) used in Examples and Comparative Examples were measured according to the following method.

(1) Melting point (T _m ) measurement by DSC Melting point (Tm) was measured by DSC. Using DSC (DSC 220C, Seiko Instruments Inc.), about 5 mg of the sample is placed in an aluminum pan for measurement, heated to 200 ° C to melt the sample, and then cooled to 30 ° C at -10 ° C / min. The melting point (Tm) was calculated from the peak 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 diluting 5 ml of decalin solvent to the decalin solution to dilute, the specific viscosity _{sp sp} was measured in the same manner. This dilution operation was further repeated twice, and the value of _{sp sp} / C when the concentration (C) was extrapolated to 0 as shown in the following formula was determined as the limiting viscosity [η] (unit; dl / g).
[Η] = lim (( _sp / C) (C → 0)

(3) Measurement of Average Particle Size d ₅₀ The average particle size d ₅₀ was calculated from a weight-based particle size distribution by Coulter Counter method using a Multiman-made by Beckman Corporation.
Further, the tensile test, the hardness test, the compression set test and the test method of the dynamic friction coefficient performed on the rubber sheet formed from the rubber composition obtained in Examples and Comparative Examples are as follows.

(Test method)
(1) Tensile test A test piece was obtained by punching a 2 mm-thick precursor molded article (vulcanized rubber sheet) with a No. 3 type dumbbell described in JIS K6251. Using this test piece, a tensile test is conducted under the conditions of a measuring temperature of 25 ° C. and a tensile speed of 500 mm / min according to the method defined in the same JIS K6251, tensile stress at break (T _B ) and tensile elongation at break (E) _B ) was measured.

(2) Hardness test In the hardness test, six sheets of a precursor molded body (vulcanized rubber sheet) having 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, 6 sheets of 2 mm thick precursor molded articles (vulcanized rubber sheet) are stacked and attached to a compression device according to the method described in JIS K6262, and the height of the test piece Was compressed to 3/4 of the height before loading, and the mold was heat treated in a 70 ° C. gear oven for 22 hours.
After the heat treatment, the test piece was taken out of the compression apparatus, 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 test piece before test t ₁ : height of test piece after heat treatment and cooling for 30 minutes t ₂ : height of test piece mounted on mold

(4) Dynamic coefficient of friction measurement The coefficient of dynamic friction of the surface of the precursor molded product (vulcanized rubber sheet) and the molded product formed by polishing the surface of the precursor molded product is as follows. The rubber was horizontally slid and measured at a test speed of 300 mm / min.

Comparative Example 1
100 parts by mass of ethylene / propylene • 5-ethylidene-2-norbornene ternary copolymer [trade name: Mitsui EPT 4021, manufactured by Mitsui Chemicals, Inc.],
5 parts by mass of zinc flower,
1 part by mass of stearic acid,
1 part by mass of polyethylene glycol # 4000
65 parts by mass of FEF carbon black,
40 parts by mass of paraffinic process oil were kneaded for 5 minutes with a 1.7-liter volume Banbury mixer, and the mixture at 120 ° C. was discharged.

  Furthermore, after winding this composition on an 8 inch roll having a surface temperature of 50 ° C., 1.5 parts by mass of N-cyclohexyl-2-benzothiazolylsulfenamide, with respect to 212 parts by mass of this composition, dimethyldithiocarbamic acid 0.2 parts by mass of zinc [vulcanization accelerator], 0.5 parts by mass of zinc di-n-butyl dithiocarbamate [vulcanization accelerator], 2.0 parts by mass of sulfur [vulcanizing agent], and defoaming agent 4 The parts by mass were added and kneaded for 8 minutes, and the resulting mixture was allowed to cool.

  The mixture was vulcanized at 180 ° C. for 5 minutes using a press molding machine to prepare a 2 mm-thick rubber sheet. The rubber block for the compression set test was prepared by vulcanizing at 180 degrees for 10 minutes.

  With respect to the precursor molded body obtained as described above, the tensile test, the hardness test and the compression set test, and the dynamic friction measurement test of the surface of the precursor molded body and the molded body obtained by polishing the surface of the precursor molded body It carried out by the above-mentioned method. The results are shown in Table 1.

Comparative Example 2
The surface of the precursor molded article (vulcanized rubber sheet) obtained in Comparative Example 1 is accumulated with a grain size of # 120 (the lowermost stage, the fifth step, 90 μm) of the abrasive (sandpaper abrasive paper) Using an upper amount of 96% or more), a molded product was obtained by sliding at 1000 reciprocations at a speed of 48 times / min and reciprocating 1000 times at a load of 1000 g to obtain a molded body. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Comparative Example 3
The surface of the precursor molded article (vulcanized rubber sheet) obtained in Comparative Example 1 was subjected to particle size # 240 (average particle size d ₅₀ : 58.5 μm ± 2.0 μm) of the abrasive (sandpaper abrasive paper) Polishing was carried out in the same manner as in Comparative Example 1 to obtain a molded body. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Comparative Example 4
The surface of the precursor molded article (vulcanized rubber sheet) obtained in Comparative Example 1 was subjected to particle size # 320 (average particle size d ₅₀ : 46.2 μm ± 1.5 μm) of the abrasive (sandpaper abrasive paper) Polishing was carried out in the same manner as in Comparative Example 1 to obtain a molded body. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Comparative Example 5
The surface of the vulcanized rubber sheet obtained in Comparative Example 1 was treated in the same manner as Comparative Example 1 using particle size # 800 (average particle size d ₅₀ : 21.8 μm ± 1.0 μm) of the abrasive (sandpaper abrasive paper). It grind | polished by the method and the molded object was obtained. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Comparative Example 6
It is the same as Comparative Example 1 except that 40 parts by mass of ultra high molecular weight polyethylene (B) [melting point: 136 ° C., intrinsic viscosity [η] 13.0 dl / g, average particle diameter d ₅₀ : 30 μm] is added. The results are shown in Table 1.

Comparative Example 7
The surface of the vulcanized rubber sheet obtained in Comparative Example 6 was made to have a particle size # 120 of the abrasive (sandpaper abrasive paper) (the lowermost screen, the fifth step of which was 90 μm and the cumulative mesh weight was 96% or more). Using the same method as in Comparative Example 1 to obtain a molded body. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Example 1
The surface of the vulcanized rubber sheet obtained in Comparative Example 6 was treated in the same manner as in Comparative Example 1 using particle size # 240 (average particle size d ₅₀ : 58.5 μm ± 2.0 μm) of the abrasive (sandpaper abrasive paper). It grind | polished by the method and the molded object was obtained. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Example 2
The surface of the vulcanized rubber sheet obtained in Comparative Example 6 was treated in the same manner as Comparative Example 1 using particle size # 320 (average particle size d ₅₀ : 46.2 μm ± 1.5 μm) of the abrasive (sandpaper abrasive paper). It grind | polished by the method and the molded object was obtained. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

[Example 3]
The surface of the vulcanized rubber sheet obtained in Comparative Example 6 was treated in the same manner as Comparative Example 1 using particle size # 800 (average particle size d ₅₀ : 21.8 μm ± 1.0 μm) of the abrasive (sandpaper abrasive paper). It grind | polished by the method and the molded object was obtained. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Example 4
The surface of the vulcanized rubber sheet obtained in Comparative Example 6 was treated in the same manner as Comparative Example 1 using particle size # 1200 (average particle size d ₅₀ : 15.3 μm ± 1.0 μm) of the abrasive (sandpaper abrasive paper). It grind | polished by the method and the molded object was obtained. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

Comparative Example 8
It is the same as Comparative Example 1 except that 40 parts by mass of ultrahigh molecular weight polyethylene (B) (melting point: 136 ° C., intrinsic viscosity [極限] 12.7 dl / g, average particle diameter d ₅₀ : 10 μm) is added. The results are shown in Table 1.

[Example 5]
The surface of the vulcanized rubber sheet obtained in Comparative Example 8 was treated in the same manner as Comparative Example 1 using particle size # 1200 (average particle size d ₅₀ : 15.3 μm ± 1.0 μm) of an abrasive (sandpaper abrasive paper). It grind | polished by the method and the molded object was obtained. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

[Example 6]
The surface of the vulcanized rubber sheet obtained in Comparative Example 8 is the same as Comparative Example 1 using particle size # 2500 (average particle size d ₅₀ : 8.4 μm ± 0.5 μm) of the abrasive (sandpaper abrasive paper) It grind | polished by the method and the molded object was obtained. The dynamic friction coefficient of the surface of the obtained molded product is shown in Table 1.

As apparent from Table 1, the average particle diameter d ₅₀ of the grindstone of the molded product (precursor molded product) obtained by vulcanization as described above is the average of the ultrahigh molecular weight olefin polymer (B) Ultra high molecular weight olefin-based weight inside the precursor molded body by polishing with a particle diameter d ₅₀ or less twice as large (Example 1 and Example 2 and Example 3 and Example 4 and Example 5 and Example 6) It can be seen that since the united (B) is exposed on the surface of the molded body, the slipperiness is good even at the beginning of the use of the molded body. Furthermore, when the average particle diameter d _{50 of} the ultrahigh molecular weight olefin polymer (B) is in the range of 5 to 15 μm (Examples 5 and 6), the resulting molded article has a smaller coefficient of dynamic friction, It can be seen that the sliding performance is better.

Claims (4)

A precursor molded article formed from a rubber composition containing 100 parts by mass of rubber (A) and 5 to 80 parts by mass of an ultrahigh molecular weight olefin polymer (B) satisfying the following requirements (i) to (iii) surface, mean average twice less is abrasive particle size d ₅₀ (Y) formed by polishing the surface of a molded body of the particle size d ₅₀ ultra high molecular weight olefin polymer (B) of the.
(I) The melting point (T _m ) measured by DSC is 120 ° C. or more.
(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 molded article according to claim 1, wherein the rubber composition contains a vulcanizing agent (C). The average particle size d ₅₀ ultra high molecular weight olefin polymer (B) is in the range of 5 to 35 m, the molded body according to claim 1 or 2.   After the rubber composition according to claim 1 is molded and vulcanized to obtain a precursor molded body, the method includes the step of polishing the surface of the precursor molded body with the abrasive grains (Y) according to claim 1 And a method of producing a molded article.