Paraffin wax compositions and rubber compositions into which paraffin wax compositions are incorporated

Abstract: A paraffin wax composition comprises straight-chain saturated hydrocarbons, wherein the content of each of the straight-chain hydrocarbons having a number of carbons from 22 to 44, respectively, is not less than 2% by weight relative to the entire straight-chain saturated hydrocarbons. A rubber composition is also disclosed, which comprises a rubber and this paraffin wax composition, wherein 1 to 10 parts by weight of the above paraffin wax composition is blended relative to 100 parts by weight of a diene-based rubber.

Description: The present invention relates to paraffin wax compositions which can prevent degradation of rubber articles with ozone and afford good appearance upon the rubber articles over a wide temperature range from a low temperature zone to a high temperature zone. The invention also relates to rubber compositions into which such paraffin wax compositions are incorporated. In order to prevent rubber from being cracked with air or sun light, it is formerly known that a wax-based antioxidant is used in rubber. When the wax-based antioxidant is blended with rubber, the antioxidant oozes out onto the surface of rubber and forms a thin film thereon. This thin film prevents the rubber from contacting ozone, and thus prevents degradation thereof. Although a variety of wax-based rubber antioxidants have been commercially available for a long time, the function of the antioxidant to ooze out and form a thin film and a phenomenon that the thin film once formed peels off differ depending upon temperatures. Under the circumstances, in order to improve these problems, there are proposed antioxidants in which the number of the carbons of a wax-based rubber antioxidant is distributed over a wide range of 16-41 (U.S. Patent No. 3,423,348) and antioxidants containing 25-70% by weight straight chain hydrocarbons having a number of carbons of 26-29 and 30-75% by weight straight chain hydrocarbons having a number of carbons of 34-40 (Japanese patent publication No. 54-25,062). Japanese patent application Laid-open Nos. 48-91,141 and 63-145,346 disclose wax-based rubber antioxidants having a so-called two peak distribution consisting of greater amounts of wax components having a number of carbons of 26-29 and a wax component having a number of carbons of 34-40 and a smaller amount of a wax component having a number of carbons of 30-33. Further, Japanese patent application Laid-open No. 1-230,648 discloses antioxidants capable of improving ozone resistance at relatively high temperatures by increasing the content of normal saturated hydrocarbons having a number of carbons of 36-51. However, the above-mentioned conventional wax-based antioxidants all damage the appearance of rubber articles, and have poor ozone resistance at relatively low temperatures. Therefore, they are unsuitable for rubber compositions which are to be used under conditions of high ozone even at low temperatures. Attention is also drawn to the disclosures of DE-A-2311965 and DE-A-3840202. DE-A-2311965, which corresponds to US-A-3826735, is directed to a wax composition which is useful for preventing rubber from being degraded or otherwise damaged in contact with ozone in the atmosphere and is characterized in that the weight percentage (x) of straight chain hydrocarbons having a carbon number of C26 to C29 and the weight percentage (y) having a carbon number of C34 to C40 satisfy the relation shadowed in Fig. 2. That is, in Fig. 2, x = 25 to 70, y = 30 to 75, and x + y is not greater than 100. DE-A-3840202, which corresponds to US-A-4877456, discloses a wax composition wherein the content of normal saturated hydrocarbon is at least 75%, and which contains the normal saturated hydrocarbon having a carbon number of 36 to 51 of from 20 to 45% and the normal saturated hydrocarbon having a carbon number of 21 to 26 of from 5 to 25%. The present invention aims to overcome the above-mentioned problems, and to provide a wax-based antioxidant of a paraffin wax composition and a rubber composition including such a paraffin wax composition, which paraffin wax composition and rubber composition can favourably prevent deterioration with ozone under a stationary condition over a wide temperature range from relatively low temperatures to high temperatures, for example over 0°C to 60°C, be free from a wax-blooming phenomenon, and afford good appearance upon the surface of rubber. The present invention provides a paraffin wax composition which is a microcrystal wax containing straight-chain saturated hydrocarbons termed normal paraffin, non-linear saturated hydrocarbons termed isoparaffin, and alicyclic hydrocarbons termed cycloparaffin, as well as aromatic hydrocarbon; characterized in that the content of each of the said straight-chain saturated hydrocarbons having a number of carbons from 31 to 44, respectively, is not less than 2% by weight relative to the entire straight-chain saturated hydrocarbons; and in that the content of each of the straight-chain saturated hydrocarbons having a number of carbons from 22 to 30, respectively, is not less than 4% by weight relative to the entire straight-chain saturated hydrocarbons. It is preferable that the content of non-linear saturated hydrocarbons having a number of carbons from 30 to 60 is 16 to 30% by weight relative to the entire paraffin wax composition. The invention also provides a rubber composition comprising a rubber and a paraffin wax composition, wherein said paraffin wax composition is a composition according to the first aspect of the invention, and wherein 1 to 10 parts by weight of the said paraffin wax composition is blended relative to 100 parts by weight of a diene-based rubber. The paraffin wax composition, which blooms over a wide range from low temperatures to high temperatures, exhibits effective ozone resistance and particularly effective stationary ozone resistance in use under conditions over a wide atmospheric temperature range. The paraffin wax composition according to the present invention complies with such requirements. When the content of each of the straight-chain saturated hydrocarbons having a number of carbons from 22 to 44 is not less than 2% by weight relative to the entire straight-chain saturated hydrocarbons, blooming of the wax can be maintained over a wide temperature range from low temperatures (e.g. 0°C) to high temperatures (e.g. 60°C), and excellent ozone resistance under stationary conditions can be also maintained. In the paraffin wax composition according to the present invention, when the content of each of the straight-chain saturated hydrocarbons having a number of carbons from 22 to 30 is not less than 4% by weight relative to the entire straight-chain saturated hydrocarbons, the blooming speed of the wax becomes faster at a low temperature range (0°C-30°C). Further, even if the film of the wax is broken or cracked depending upon exterior stimulation conditions such as changes in temperature ranges and changes in strains, the film is speedily repaired, so that desirable ozone resistance can be exhibited. On the other hand, if the content of the total straight-chain saturated hydrocarbons is too high, the antioxidant contained in the blended rubber composition blooms together with the blooming of the wax to change the appearance with sun light or ultraviolet rays, although the initial stage ozone resistance under stationary conditions is good. In view of this, in order to control the blooming speed of the wax particularly at high temperatures (30°C-60°C) and realize both prevention of deterioration of the appearance owing to the colour change and maintenance of the function of the wax, the content of the non-linear saturated hydrocarbons having a number of carbons from 30 to 60 is preferably 16 to 30% by weight relative to the entire paraffin wax composition. The paraffin wax composition according to the present invention is called a microcrystal wax which contains straight-chain saturated hydrocarbons termed normal paraffin, isoparaffin (non-linear saturated hydrocarbons), cycloparaffin (alcyclic hydrocarbons) as well as a small amount of aromatic hydrocarbon. The diene-based rubber used in the rubber composition according to the present invention is suitably a rubber polymer selected from the group consisting of natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, styrene-isoprene copolymer rubber, and styrene-butadiene-isoprene terpolymer rubber. These rubbers may be used singly or in a blended state. In the rubber composition according to the present invention, if the blended amount of the paraffin wax composition is less than 1 part by weight relative to 100 parts by weight of the diene rubber, a blooming amount of the wax onto the surface of the rubber is so small that the function of the bloomed film is insufficient. On the other hand, the blended amount of the paraffin wax composition is unfavourably more than 10 parts by weight, because the blooming amount is too high and the appearance is deteriorated, and tenacity of the rubber is lowered. A process for producing the paraffin wax composition according to the present invention is not limited to any specific process. For example, a desired paraffin wax composition may be obtained directly from a conventionally known petroleum-originated wax or synthesized wax by distillation. Alternatively, the paraffin wax composition of the invention may be obtained by blending an appropriate wax containing sufficient straight-chain hydrocarbons having a number of carbons of 22 to 30 with another appropriate straight-chain hydrocarbon having a number of carbons of 31-44. The paraffin wax composition of the present invention can be usually obtained by the following specific process. That is, a crude oil is distilled under ordinary pressure, oil in a bottom of a distillation tower is further distilled under reduced pressure; and an aromatic component is removed from a distilled oil by subjecting the distilled oil to extraction with a solvent such as phenol or furfural. Then, the oil is purified by hydroxylation, and is subjected to dewaxing with a solvent such as a ketone or an aromatic mixed solution. Thereby, a crude wax is obtained in the dewaxing step as a byproduct being produced when the dewaxed wax oil is obtained as a base oil for a lubricant. After that, a deoiled wax is obtained by removing a low melting point wax from the crude wax through deoiling the crude oil with a solvent. Alternatively, the deoiled wax may be obtained by deoiling the crude wax through sweating. The deoiled wax may be purified by treating it with sulfuric acid or white clay. In order to separate a normal paraffin, for example, a method disclosed in Japanese patent application Laid-open Nos. 56-14,583, 56-15,218, and 56-15,219 may be employed. The paraffin wax composition according to the present invention may be obtained as follows: The deoiled wax obtained by the above-mentioned ordinary process is distilled to obtain a desired paraffin wax composition. Alternatively, a crude oil is appropriately selected as a starting material, and when an oil remaining on distillation under ordinary pressure is to be distilled under reduced pressure to obtain a distilled oil, the distillation is effected in such a narrow boiling point range that the hydrocarbons having the composition defined in the present invention may be substantially distilled out. Thereby, for example, a fraction containing hydrocarbons having a number of carbons of 22-30 and a fraction substantially containing hydrocarbons having a number of carbons of 31-44 are obtained, and the paraffin wax composition is obtained by mixing these fractions. As the petroleum paraffin wax according to the present invention, a polyolefine obtained by polymerizing an olefine such as ethylene, a pyrolyzed polyolefine, or a wax synthesized by Hisshar-Tropis process or products obtained by further subjecting them to distillation or extraction to produce the composition including hydrocarbons having the given number of carbons may be used. The composition of the paraffin wax composition was determined by a machine of capillary GC (tradename HP-5890) and a capillary column having a column coated with alumina (manufactured under tradename CBM-1 by Shimazu Manufacturing Co., Ltd., 25 m length) in the state that helium was passed as a carrier gas at a flow rate of 4 mm/min., and the temperature and the heating rate of the column were set at 180°C to 390°C and 15°C/min., respectively. The present invention will be explained in more detail with reference to the following specific examples and comparative examples. Seven kinds of paraffin wax compositions shown in Table 1 were used, and fourteen kinds of rubber compositions were kneaded according to the compounding recipes shown in Tables 2 and 3 in terms of parts by weight. Then, a rubber sheet was obtained by vulcanizing each of the kneaded mixtures at 155°C for 30 minutes. The characteristics of the thus obtained rubber sheets were examined in the following ways. Ozone resistance Each of the fourteen kinds of the thus obtained rubber sheets as test pieces was held by an expanding holder, and appearance of the rubber sheet was examined by visually observing a crack-occurred percentage after the rubber sheet was allowed to be left in an ozone weather meter at an ozone concentration of 100 pphm in a stationary condition for 72 hours (i) under an expanded percentage of 50% at a temperature of 5°C and (ii) under an expanded percentage of 30% at a temperature of 60°C. Appearance Appearance of the rubber was evaluated by three steps through visually evaluating each test piece which had been allowed to be left in a thermostat vessel at a temperature of 50°C for one week. "Good", "acceptable" and "bad" in Tables 2 and 3 denote the test piece of which the surface did not become whitish, the test piece of which the surface became slightly whitish, and the test piece of which the surface become conspicuously whitish to remarkably deteriorate the appearance, respectively. In Table 2, the appearance was relatively evaluated by index by taking an index of the rubber composition in Comparative Example 1 and the state completely free from occurrence of cracks as 100 and 0, respectively. In Table 3, the appearance was similarly relatively evaluated by index by taking the index of the rubber composition in Comparative Example 1. As is seen from Tables 1, 2 and 3, the rubber compositions according to the present invention exhibited excellent ozone resistance both at the low and high temperatures (5°C and 60°C) as compared with Comparative Examples which did not contain the paraffin wax compositions defined in the present invention. As having been explained above, according to the present invention, the contents of the straight-chain saturated hydrocarbons having the specified numbers of carbons are set at the specific ranges, respectively. Thereby, the rubber compositions into which a given amount of such paraffin wax compositions is incorporated can prevent deterioration of the rubber articles with ozone in the stationary condition over a wide range from low temperatures to high temperatures, and exhibit an acceptable appearance.

Claims: A paraffin wax composition which is a microcrystal wax containing straight-chain saturated hydrocarbons termed normal paraffin, non-linear saturated hydrocarbons termed isoparaffin, and alicyclic hydrocarbons termed cycloparaffin, as well as aromatic hydrocarbon; characterized in that the content of each of the said straight-chain saturated hydrocarbons having a number of carbons from 31 to 44, respectively, is not less than 2% by weight relative to the entire straight-chain saturated hydrocarbons; and in that the content of each of the straight-chain saturated hydrocarbons having a number of carbons from 22 to 30, respectively, is not less than 4% by weight relative to the entire straight-chain saturated hydrocarbons. A paraffin wax composition as claimed in claim 1, characterized in that the content of non-linear saturated hydrocarbons having a number of carbons from 30 to 60 is 16 to 30% by weight relative to the entire paraffin wax composition. A rubber composition comprising a rubber and a paraffin wax composition, characterized in that said paraffin wax composition is a composition as claimed in claim 1 or 2, and in that 1 to 10 parts by weight of the said paraffin wax composition is blended relative to 100 parts by weight of a diene-based rubber.

Inventors: IKEDA NOBUMASA, TAJIMA MASANORI, IKEDA, NOBUMASA, TAJIMA, MASANORI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1991
Main classification: C08L21
IPC codes: C08L91, C08L21