MXPA01006804A - Chloroprenebased rubber composition - Google Patents

Abstract

A chloroprenebased rubber composition characterized by containing a chloroprenebased rubber, a carbon black having an average stack height of layer planes in the direction of C axis within a crystallite i.e. Lc of 2 nm or more, and a zinc powder.

Description

COMPOSITION OF CHLOROPRENE TYPE HULE TECHNICAL FIELD The present invention relates to a chloroprene-type rubber composition. More particularly, it relates to a chloroprene-type rubber composition that provides a vulcanizate having a significantly improved heat resistance.

ANTECEDENTS OF THE TECHNIQUE Hitherto several methods have been proposed to improve the heat resistance of a vulcanizate of a chloroprene rubber composition. For example, JP-A-50-87437 discloses a method for improving heat resistance by adding a zinc powder and water to a chloroprene rubber; JP-A-2-34645 discloses a method for improving heat resistance by adding a thermal black and zinc powder, and in JP-A-3-81350 a method is described for improving heat resistance by adding a powder of zinc and 4,4 '- (a, a-dimethylbenzyl) diphenylamine to a chloroprene rubber. However, the requirement for heat resistance becomes strict with some applications, for example, automobile rubber components. Therefore, heat resistance is not always satisfactory with these methods, and it has been desired to improve the heat resistance.

DETAILED DESCRIPTION OF THE INVENTION The present invention resides in a composition comprising a chloroprene-type rubber, and a specific carbon black and zinc powder incorporated in said rubber, and it is an object of the present invention to improve the heat resistance of a vulcanizate thereof. That is, the present inventors have made extensive studies to improve the heat resistance of a vulcanizate of a chloroprene-type rubber composition, and as a result have discovered that it is possible to achieve the object by a combination of a chloroprene-type rubber, a carbon black having an average stacking height Lc of at least 2 nm in a C-axis direction of the layer planes in the crystallites, and a zinc powder. The present invention has been made based on this discovery. The present invention will now be described in detail. The chloroprene rubber in the chloroprene rubber composition of the present invention contains a chloroprene rubber as the main component, but may contain in addition to the chloroprene rubber, for example, natural rubber, SBR, butyl rubber, BR, NBR or EPDM, as the case may require. The chloroprene-type rubber of the present invention may be a chloroprene homopolymer or a copolymer (hereinafter frequently referred to as a chloroprene-type rubber) obtained by polymerization of a mixture (hereinafter referred to as a monomer of type). chloroprene) comprising chloroprene and at least one other monomer copolymerizable with chloroprene. The monomers copolymerizable with chloroprene include, for example, 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, sulfur, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene as well as acrylic acid, acid methacrylic and esters thereof and can be used within a scale to satisfy the purpose of the present invention. With respect to the polymerization method to obtain the chloroprene rubber to be used in the present invention, there is no particular limitation and a conventional polymerization method can be employed. That is, the chloroprene-type monomer can be polymerized by emulsion by a conventional method in the presence of a polymerization initiator that is commonly used for chloroprene polymerization to obtain the chloroprene rubber. The emulsifier to be used for this emulsion polymerization is not particularly limited, and, for example, an emulsifier commonly used for chloroprene emulsion polymerization can be used, such as an alkali metal salt of a fatty acid of Saturated or unsaturated Cß-22, an alkali metal salt of rosin or disproportionate rosin acid, or an alkali metal salt of a condensate of ß-naphthalenesulfonic acid formalin. Chloroprene rubbers are classified in a type modified by sulfur, type modified by mercaptan and a type modified by xanthogen, depending on the type of the molecular weight modifier. The sulfur-modified type is obtained by copolymerizing sulfur and chloroprene to obtain a polymer and plasticizing the polymer with thiuram disulfide to have a predetermined Mooney viscosity. The mercaptan modified type is obtained using an alkyl mercaptan such as n-dodecyl mercaptan, tert-dodecyl mercaptan, or octyl mercaptan as the molecular weight modifier. In the same manner, the modified xanthogen type is prepared using an alkylxanthogen compound as a molecular weight modifier. As the chloroprene rubber of the present invention, any modified type can be used. In addition, a chloroprene-type rubber modified by a combination of sulfur, mercaptan and xanthogen can also be used. However, the sulfur modified type has a poor heat resistance of the polymer itself as compared to the mercaptan modified or modified by xanthogen type, and therefore, it is preferred to use the modified mercaptan type or modified by xanthogen in the case in which greater resistance to heat is required. Specific examples of the alkyl xanthogen compound to be used for the xanthogen-modified type include dimethylxanthogen disulfide, diethylxanthogen disulfide, diisopropylxanthogen disulfide and disobutylxanthogen disulfide. The amount of the alkyl xanthogen compound is selected such that the molecular weight of the chloroprene-type polymer (or viscosity) Mooney of a chloroprene-type rubber obtainable by polymer isolation) will be appropriate. Generally, it is employed in an amount within a scale of 0.05 to 5.0 parts by weight, preferably 0.3 to 1.0 parts by weight, based on 100 parts by weight of the chloroprene-type monomer, although the amount may vary depending on the structure of the alkyl group or the desired molecular weight. As the polymerization initiator, potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide or an organic peroxide known as t-butyl hydroperoxide, which are commonly used for chloroprene emulsion polymerization, can be used. In the present invention, the polymerization temperature and the final conversion of the monomer are not particularly limited. However, the polymerization temperature is preferably 0 to 50 ° C, more preferably 20 to 50 ° C. In addition, the polymerization is preferably carried out so that the final conversion of the monomer will be within a range of 50 to 90%, and where this conversion has been achieved, a small amount of polymerization inhibitor can be added to finish the polymerization. For example, an inhibitor commonly used as thiodiphenylamine, 4-tert-butylcatechol or 2,2-methylenebis-4-methyl-6-tert-butylphenol can be used as the polymerization inhibitor. For example, an unreacted monomer can be removed by steam scrubbing, and then the pH of the latex is adjusted, followed by example, by solidification by conventional freezing, washing with water and drying with hot air to isolate the polymer. The carbon black to be incorporated into the chloroprene-type rubber composition of the present invention can be any of thermal black and acetylene black prepared by a method of thermal decomposition and black furnace and black channel prepared by a method of incomplete combustion. However, it is necessary that those blacks have an average stacking height Lc of at least 2 nm in a C-axis direction of the layer planes in the crystallites, and particularly one which has an average Lc averaging height of at least 2.5 nm in a C-axis direction of the layer planes. In addition, a preferred carbon black is one having a maximum average particle size of 60 nm, and having a DBP oil absorption preferably of 100 to 350 ml / 100 g., more preferably from 120 to 300 ml / 100 g, in particular, preferably from 140 to 300 ml / 100 g. If the average stacking height Lc is less than 2 nm in a C-axis direction of the layer planes in the crystallites, the heat resistance of a vulcanizate obtained by vulcanization of the chloroprene-type rubber composition will be inadequate. In addition, acetylene black is a carbon black obtained by thermally decomposing acetylene gas, and the chloroprene-type rubber composition using acetylene black is more preferred since the The effect to improve the heat resistance of its vulcanization is significant, because the crystallization is significantly advanced, the structure is highly developed and the absorption of oil is great. The amount of the carbon black is preferably 10 to 70 parts by weight, more preferably 20 to 60 parts by weight, based on 100 parts by weight of the chloroprene rubber. If the amount exceeds 70 parts by weight, the processability tends to be deficient, it is likely to be burned, and the temperature at which the vulcanizate becomes brittle tends to be high. If the amount is less than 10 parts by weight, the tensile strength and modulus tend to be low. With respect to the grain size of the zinc powder to be used in the present invention, one which passes through a 200 mesh screen is preferred. The amount of the zinc powder is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, based on 100 parts by weight of the chloroprene-type rubber. If the amount of the zinc powder is less than 1 part by weight, the heat resistance of the vulcanized will not improve adequately, and if it is greater than 30 parts by weight, the mechanical properties of the vulcanized tend to be lower. The vulcanizer to be used in the present invention is not particularly limited, but is preferably a metal oxide. Specifically, for example, mention may be made of zinc oxide, magnesium oxide, lead oxide, triplyl tetraoxide, iron trioxide, titanium dioxide or calcium oxide. They can be used in combination as a mixture of two or more of them. The amount of that vulcanizer is preferably from 3 to 15 parts by weight based on 100 parts by weight of the chloroprene-type rubber. In addition, by using said vulcanizer in combination with the following vulcanization accelerator, vulcanization can be carried out more efficiently. As the vulcanization accelerator, a vulcanization accelerator of the thiourea type, guanidine type, thiuram type, thiazole type or triazine type, which is commonly used for chloroprene rubber vulcanization, can be used. However, one of the thiourea type is preferred. As the thiourea type vulcanization accelerator, for example, it is mentioned, ethylenethiourea, diethylthiourea, trimethylthiourea, triethylthiourea or N, N'-diphenylthiourea, and particularly trimethylthiourea is preferred. In addition, a vulcanization accelerator may also be used as a mixture comprising 3-methylthiazolidin thione-2 or thiadiazole and phenylenedimaleimide, or dimethylammonium hydrogen isophthalate or a derivative of 1,2-dimercapto-1,4-thiadiazole. The above vulcanization accelerators can be used in combination as a mixture of two or more of them. A type of peroxide vulcanization can also be used. The amount of that vulcanization accelerator is preferably 0.5 to 5 parts by weight based on 100 parts by weight of the chloroprene-type rubber. To the chloroprene rubber composition of the present invention, several additives may be incorporated, when required. as a softening agent, a plasticizer, a processing aid, an aging prevention agent, a lubricant, a filler, etc. As the aging prevention agent, a common aging prevention agent of, for example, amine type, imidazole type, metal carbamate, phenol type or wax type can be used. As a kind of aging prevention agent which has a significant effect in improving heat resistance, there may be mentioned, for example, the amine type such as 4,4'-bis- (a, a-dimethylbenzyl) diphenylamine or octylated diphenylamine. . Particularly, 4,4'-bis' (a, a-dimethylbenzyl) diphenylamine can further improve the heat resistance of the chloroprene rubber composition of the present invention. These aging prevention agents can be used alone or in combination as a mixture. As the softening agent, a common softening agent can be used as an oil-type softening agent as a lubricating oil, processing oil, paraffin, liquid paraffin, petrolatum or petroleum asphalt, or an aliphatic softening agent such as colaza oil, flaxseed oil, castor oil or coconut oil. A common plasticizer such as dioctyl phthalate or dioctyl adipate can be used as the plasticizer. As a plasticizer which will not inhibit or increase the heat resistance of the chloroprene rubber composition of the present invention, an ether / thioether type plasticizer such as vulcanol OT (registered trademark, manufactured by Bayer Ltd.), a vegetable oil or an ester-type plasticizer or an ether / ester-type plasticiser such as Adekacizer RS-700, RS-735 (registered trademarks, manufactured by Asahi Denka Kogyo K.k.). Particularly preferred is an ether / thioether type plasticizer because it has effects to improve the low temperature resistance as well as to increase the heat resistance and it is excellent in the balance between both. Said plasticizers can be used alone or in combination as a mixture of two or more of them, depending on the required properties. With respect to methods for kneading and vulcanizing the rubber composition in the present invention, methods commonly carried out in the rubber industry can be employed. Commonly, the rubber composition is mixed in a kneading machine such as a kneader, a Banbury mixer or a roller mill, followed by molding in the desired shape to obtain a molded vulcanizate. Specifically, several components are kneaded at a temperature no greater than the vulcanization temperature, and the kneaded product is molded into the desired shape, followed by vulcanization. The vulcanization temperature and time can be set appropriately. The vulcanization temperature is preferably 140 to 190 ° C, more preferably 150 to 180 ° C. The vulcanizate obtained from the chloroprene-type rubber composition of the present invention is excellent, in addition to the mechanical properties of the rubber, in the heat resistance, the oil resistance and the resistance to low temperatures. Therefore, it is suitable for industrial components, for which resistance to heat, resistance to oil and resistance to low temperatures is required, such as boots, hoses, belts, rubber vibration isolators, vibration dampers, electric cables, gaskets, oil seals and gaskets, particularly for automotive rubber components, for which a strict guarantee of quality and resistance to heat is required.

PREFERRED MODALITY OF THE INVENTION The present invention will now be explained in detail with reference to the examples. However, it should be understood that the present invention is in no way restricted to said specific examples.

EXAMPLES 1 TO 5 AND COMPARATIVE EXAMPLES 1 TO 4 In accordance with the formulation of the combination as identified in Tables 1 and 2, kneading was carried out using 20.32 cm rolls to prepare a sheet having a thickness of 2.3 mm. The sheet was subjected to pressure vulcanization at 150 ° C for 20 minutes to prepare a vulcanized sheet having a thickness of 2 mm. Physical properties tests were performed using No. 3 weights, the stress test was carried out in accordance with JIS K6251, and the hardness was measured according to with JIS K6253. In addition, its operation at low temperatures was evaluated with the measurement of a Gehman torsion test according to JIS K6261, and it was represented by T10 (the temperature at which the specific module as the value for the module at 23 ° C). convert to 10). With respect to heat resistance, using a test sample preserved in a 140 ° C equipment furnace for 9 days according to JIS K6257, the stress test and the hardness measurement were carried out in accordance with measurement methods mentioned above, and the heat resistance was represented by the rates of change in tensile strength and elongation and the amount of change in hardness. The average stacking height Lc (nm) was calculated in a C-axis direction of the layer planes in the crystallites according to the following formula of a diffracted beam (002) in an X-ray diffraction method using a beam of Cu-Ka: Lc = (18O-K-?) / (P-ß-cos0j K: form factor (using 0.9)?: Wavelength (0.154nm) of the XT ray: Angle representing the maximum value in the band Diffracted beam absorption (002) ß: Amplitude of half the value in the diffracted beam absorption band (002) when represented by an angle.

TABLE 1 The materials used in Table 1 are as follows: 1) Mercaptan-modified chloroprene rubber (S-40V), manufactured by Denki Kagaku Kogyo K.K. 2) Denka Black granulated product (Lc: 3.5nm, DBP oil absorption: 210ml / 100g), manufactured by Denki Kagaku Kogyo K.K. 3) Sheast 116 (Lc: maximum 1.8nm, oil absorption DBP: 133ml / 100g), manufactured by Tokai Carbon K.K. 4) Sheast 3 (Lc: maximum 1.8nm, oil absorption DBP: 101ml / 100g) manufactured by Tokai Carbon K.K. 5) Asahi Thermal FT (Lc: maximum 1.8nm, DBP oil absorption: 28ml / 100g), manufactured by Asahi Carbon K.K. 6) Ether / thioether type plasticizer, manufactured by Bayer Ltd. (Germany).

TABLE 2 As shown in tables 1 and 2, the chloroprene-type rubber composition of the present invention, comprising chloroprene rubber and a carbon black having an average stacking length Lc of at least 2 nm in a direction of C axis of the layer planes in the crystallites and a zinc powder incorporated in said chloroprene rubber, provides a vulcanizate that has an excellent resistance to heat.

Claims (3)

NOVELTY OF THE INVENTION CLAIMS

1. - A chloroprene-type rubber composition comprising a chloroprene-type rubber, a carbon black having an average stacking height Lc of at least 2 nm in a C-axis direction of the layer planes in the crystallites, and a zinc powder.

2. The chloroprene-type rubber composition according to claim 1, further characterized in that 10 to 70 parts by weight of the carbon black and from 1 to 30 parts by weight of the zinc powder are mixed based on 100 parts by weight. of the chloroprene type rubber.

3. A vulcanizate obtained by vulcanization of the chloroprene rubber composition according to claim 1 or 2.