Rubber composition

Abstract

Rubber composition comprising - one or more rubber components comprising natural rubber in an amount of 5 to 100 parts by weight, - an oil obtained from the seeds of a plant of the Euphorbiaceae family selected from the group consisting of Vernicia cordata, Aleurites fordii, Jatropha curcas and Para rubber tree, in an amount of 1 to 60 parts by weight with respect to the total amount of the rubber component(s), when the total amount is considered to be 100 parts by weight, - 40 to 100 parts by weight of silica and 5 to 60 parts by weight of carbon black with respect to the total amount of rubber component(s), if the total amount is considered to be 100 parts by weight, and - one or more plasticiser components consisting of the vegetable oil in a proportion of 30% by weight or more in the rubber composition and of 10% by weight or more with respect to the total amount of the plasticiser component(s) and optionally wax and optionally oils from edible sources.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a rubber composition having particularly good processability, which is particularly suitable as a raw material for producing vulcanized rubbers for such tires which have excellent exothermic properties. BACKGROUND OF THE INVENTION

[0002] In rubber compositions used as raw materials for tire treads or other tire elements, a process oil, such as a flavor oil, is commonly used as a plasticizer. However, vulcanized rubber blended with a process oil tends to develop high exothermicity. When the vulcanized rubber is then used for a tire tread, for example, the tire's fuel efficiency may deteriorate due to a deterioration in rolling resistance, which in turn is a result of its hysteresis loss deterioration. Furthermore, there are concerns that flavor oils or the like are carcinogenic due to their polycyclic aromatic components. In recent years, therefore, due to increased environmental awareness, a demand for new plasticizers has arisen to replace flavor oils in rubber compositions.

[0003] JP 2010 132 864 A describes a process in which a naturally derived polyphenol is mixed into a rubber composition to prevent hardening of the composition as a result of aging of the composition.

[0004] JP 2005 213 415 A describes a process in which a fatty acid obtained from vegetable fats and oils having an iodine value of 80 or more is blended into a rubber composition to provide a tire tread whose energy loss is highly controllable over a wide frequency range and which has a high friction force, particularly on a wet road surface.

[0005] It has been shown that there is room for further improvement in the application of the rubber composition from the above-mentioned processes in a vulcanized rubber, particularly with regard to the exothermic properties of the resulting tires and with regard to the processability of the rubber composition.

[0006] JP H01 118551 A, JP H01 118548 A and DE 10 2013 226 505 A1 each show a rubber composition with tung oil as a plasticizer.

[0007] WO 2016 / 084984 A1 discloses a rubber composition containing a diene elastomer, reinforcing filler, a plasticizer comprising vegetable oils, and microparticles of a water-soluble sulfate of an alkali metal or an alkaline earth metal. DISCLOSURE OF THE INVENTION

[0008] The present invention has for its object to provide a rubber composition which can be used as a raw material for vulcanized rubbers and which has excellent workability, the tires produced therefrom being improved in their exothermic properties.

[0009] This object is achieved by a rubber composition according to claim 1. The rubber composition according to the invention is defined in claim 1 and therefore comprises an oil from a plant of the Euphorbiaceae family, whose compatibility with the rubber components, especially a diene rubber, is excellent. Therefore, the vegetable oil can improve the rubber composition in terms of its processability and further prevent the resulting vulcanized rubber from deteriorating in its physical properties, especially its low exothermic properties.

[0010] The invention makes it possible to improve, in a balanced manner, the rubber composition with regard to its processability and, on the other hand, the vulcanized rubber with regard to its low exothermic properties. DESCRIPTION OF PREFERRED EMBODIMENTS

[0011] The rubber composition of the present invention comprises the oil from a plant of the Euphorbiaceae family. The term "Euphorbiaceae plant oil" refers to an oily component obtained from a seed of a plant of the Euphorbiaceae family as a raw material.

[0012] Plants of the Euphorbiaceae family are plants, each derived from a non-edible source, and classified into the subfamilies Acalypha, Croton tiglium, and Euphorbia, among others. The Croton tiglium subfamily includes the genera Aleurites and Hevea. In the present invention, at least one of the plants of the Euphorbiaceae family is used, selected from the group consisting of Vernicia cordata, Aleurites fordii, Jatropha curcas, and Para rubber tree. Thus, the rubber composition can be advantageously improved in terms of processability and the resulting vulcanized rubber can be advantageously improved in terms of low exothermic properties in a balanced manner.When a vegetable oil containing an unsaturated fatty acid in a proportion of 50% or more by weight of the vegetable oil is used among the corresponding oils from plants of the Euphorbiaceae family, the compatibility of the oil with the rubber component(s), especially a diene rubber, is excellent. This can advantageously prevent the vulcanized rubber produced from the rubber composition comprising these oils from deteriorating in its physical properties, especially its low exothermic properties.

[0013] The rubber composition comprises the oil from the plant of the Euphorbiaceae family in an amount of preferably 1 to 60 parts by weight, more preferably 1 to 30 parts by weight, based on the total amount of the one or more rubber components of the composition, when this total amount is considered to be 100 parts by weight. When the rubber composition of the present invention comprises one or more plasticizer components and the vegetable oil in a proportion of 10% by weight or more based on the total amount of the plasticizer component(s), the compatibility of the plasticizers with the rubber component(s), particularly the diene rubber component, is improved. Therefore, this is one of the preferred embodiments. The vegetable oil is contained in the rubber composition in a proportion of 30% by weight or more. The definition of the plasticizers of the present invention is given below.

[0014] The rubber composition of the present invention comprises, as the rubber component(s), one or more diene rubbers. Examples of such a diene rubber include natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), polystyrene-butadiene rubber (SBR), chloroprene rubber (CR), and nitrile rubber (NBR). If necessary, rubbers obtained by modifying a molecular terminal of one of these rubbers (for example, terminal-modified SBR) and rubbers obtained by modifying one of these rubbers (for example, modified NR) to impart a desired property to the rubber can also be preferably used. Of these rubbers, NR is used, which has excellent compatibility with an oil from a plant of the Euphorbiaceae family, particularly a Para rubber tree.The rubber composition preferably comprises the NR in an amount of 5 to 100 parts by weight when the total amount of the rubber component(s) is considered to be 100 parts by weight.

[0015] The rubber composition of the present invention comprises silica as a filler and carbon black. The silica can be any type commonly used for rubber reinforcement, such as liquid silica, dry silica, sol-gel silica, or surface-treated silica, among which liquid silica is preferred. The blending amount of the silica is 40 to 100 parts by weight based on the total amount of the rubber component(s), when the total amount is considered to be 100 parts by weight.

[0016] The rubber composition of the present invention may comprise a silane coupling agent. The silane coupling agent is not limited to any particular one as long as it is one containing sulfur in its molecule. Various silane coupling agents, each blended with silica, are usable in the rubber composition. Examples thereof include sulfide silanes such as bis-(3-triethoxysilylpropyl) tetrasulfide (e.g., "Si69", manufactured by Degussa AG), bis-(3-triethoxysilylpropyl) disulfide (e.g.,"Si75", manufactured by Degussa AG), bis-(2-triethoxysilylethyl) tetrasulfide, bis-(4-triethoxysilylbutyl) disulfide, bis-(3-trimethoxysilylpropyl) tetrasulfide, and bis-(2-trimethoxysilylethyl) disulfide, mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane, and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane. The blending amount of the silane coupling agent is preferably 1 to 20 parts by weight, more preferably 3 to 10 parts by weight, per 100 parts by weight of silica.

[0017] In addition to the diene rubber(s), the vegetable oil of the Euphorbiaceae family, the silica, and the silane coupling agent each described above, the following additives may be blended into the rubber composition of the present invention: vulcanization additives, anti-aging agents, zinc oxide, stearic acid, plasticizers such as wax and oil, process-promoting agents, etc.

[0018] The type of carbon black can be any type of carbon black commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, GPF, or an electrically conductive type of carbon black, such as acetylene black or Ketjen black.

[0019] The carbon black is blended into the rubber composition of the invention in an amount of 5 to 60 parts by weight per 100 parts by weight of the diene rubber.

[0020] Examples of plasticizers usable in the present invention also include oils from edible sources such as olive oil, cottonseed oil, rapeseed oil, corn germ oil, sesame oil, soybean oil, and linseed oil, as well as process oils. However, it is preferred to minimize the blending amount of oils other than vegetable oils of the Euphorbiaceae family.

[0021] The anti-aging agent may be an anti-aging agent commonly used for rubbers. Examples include aromatic amine-type, amine ketone-type, monophenol-type, bisphenol-type, polyphenol-type, dithiocarbamate-type, and thiourea-type anti-aging agents. Such anti-aging agents can be used singly or in a suitable mixture of two or more thereof. The anti-aging agent content is preferably 0.1 to 10 parts by weight per 100 parts by weight of the rubber component(s).

[0022] Examples of vulcanization admixtures include vulcanizing agents such as sulfur and organic peroxides, vulcanization accelerators, vulcanization accelerators, and vulcanization retarders.

[0023] The sulfur species as one of the vulcanization additives can be any common sulfur species for rubbers. Examples include powdered sulfur, precipitated sulfur, insoluble sulfur, and highly dispersible sulfur. In view of particularly favorable physical properties and durability of the resulting vulcanized rubber, the blending amount of sulfur is preferably 0.1 to 10 parts by weight per 100 parts by weight of the rubber component(s), with the amount being in terms of sulfur content.

[0024] The vulcanization accelerator may be a vulcanization accelerator commonly used for rubber vulcanization. Examples include sulfenamide-type, thiuram-type, thiazole-type, thiourea-type, guanidine-type, and dithiocarbamate-type vulcanization accelerators. Such vulcanization accelerators can be used singly or in the form of a suitable mixture of two or more thereof. The blending amount of the vulcanization accelerator(s) is preferably 0.1 to 10 parts by weight per 100 parts by weight of the rubber component(s).

[0025] The rubber component of the present invention can be obtained by using a kneading machine commonly used in the rubber industry, such as a Banbury mixer, a kneader, or a roller, to mix / knead the diene rubber(s), the vegetable oil of the Euphorbiaceae family, the silica and the silane coupling agent, each described above, and other optional components including, among others, carbon black, vulcanization additives, anti-aging agents, zinc oxide, stearic acid, plasticizers such as wax and oil, process-promoting agents.

[0026] The method of mixing the components together is not limited to any particular one and can be, for example: - a process in which admixture components other than the vulcanization additives, such as sulfur-containing vulcanizing agents and vulcanization accelerators, are mixed / kneaded beforehand to prepare a masterbatch, the remaining components are added thereto, and the entire components are further mixed / kneaded, or - a process in which each component is added in any order and the components are then mixed / kneaded, or - a process in which all the components are added and mixed / kneaded at the same time. EXAMPLES

[0027] The following describes specific examples 1 to 6, including Invention Example 4, which specifically demonstrates, among other things, the subject matter and advantageous effects of the present invention. Examples 1 to 3, 5, and 6 are provided for reference purposes but are not according to the invention. The examples and comparative examples were evaluated based on the evaluation criteria described below. The rubber samples were each obtained by heating and vulcanizing the respective rubber composition at 150°C for 30 minutes. (1) Low exothermic properties

[0028] A viscoelasticity meter manufactured by Toyo Seiki Seisaku-sho, Ltd. was used to measure the loss tangent tanδ of one of the samples from each of the above examples at a frequency of 10 Hz, a static load of 10%, a dynamic load of 1%, and a temperature of 60°C. For each of Examples 1 to 6 and Comparative Example 2, the measured value is represented as an index relative to the value of Comparative Example 1, with this value being regarded as 100. For each of Examples 7 to 9 and Comparative Example 4, the measured value is represented as an index relative to the value of Comparative Example 3, with this value being regarded as 100. The smaller the resulting numerical value, the better the rubber composition is in terms of its low exothermic properties. (2) Machinability

[0029] In accordance with JIS K6300, a rotorless Mooney gauge manufactured by Toyo Seiki Seisaku-sho, Ltd. was used to heat the vulcanized rubber from each of the above examples to 100°C for 1 minute using residual heat, and after 4 minutes, the torque value was measured in Mooney units. For each of Examples 1 to 6 and Comparative Example 2, the measured value is represented as an index relative to the value of Comparative Example 1, with this value being considered as 100. The smaller the resulting numerical value, the better the rubber composition in terms of processability. (Production of rubber compositions)

[0030] The rubber compositions of each of Examples 1 to 6 and Comparative Examples 1 to 2 were formulated according to the compounding formulations in Table 1 and then kneaded using a conventional Banbury mixer to prepare a rubber composition. The admixtures shown in Table 1 are listed below. In Table 1, the blending amount of each of the admixtures is given as a numerical value (in parts by weight) based on 100 parts by weight of the rubber component(s). a) Plasticizer components - Process oil: “PROCESS P200”, manufactured by Jomo Sun-Energy Co., Ltd. - Palm oil (edible vegetable oil from oil palms), manufactured by Yamakei Sangyoi, Ltd.; percentage of unsaturated fatty acids: 46% by weight - Vernicia cordata seed oil: "KlRIYU", manufactured by Yamakei Sangyo Ltd.; percentage of unsaturated fatty acids: 82% by weight - Jatropha curcas seed oil, produced by Nippon Biodiesel Fuel; percentage of unsaturated fatty acids: 78% by weight - Para rubber tree seed oil, produced by Viet Delta Corporation; percentage of unsaturated fatty acids: 55% by weight b) Rubber components - SBR 1 (non-terminally modified SBR): “VSL5025-0HM”, manufactured by Lanxess AG - SBR 2 (terminal-modified SBR): “HPR 350”, manufactured by JSR Corporation - No.: “RSS #3” - BR: “BR150B”, manufactured by Ube Industries Ltd. c) Silica: “NIPSIL AQ”, manufactured by Tosoh Silica Corporation d) Carbon black: “DIABLACK N341”, manufactured by Mitsubishi Chemical Corporation e) Silane coupling agent: “Si69”, manufactured by Evonik Degussa GmbH f) Spangle: “Spangle No. 1”, manufactured by Mitsui Mining & Smelting Co., Ltd. g) Anti-aging agent: “ANTIGEN 6C”, manufactured by Sumitomo Chemical Co., Ltd. h) Stearic acid: “LUNAC S-20”, manufactured by Kao Corporation i) Wax: “OZOACE 0355”, manufactured by Nippon Seiro Co., Ltd. j) Sulphur: “5% oil-blended powdered sulphur”, manufactured by Tsurumi Chemical Industry Co., Ltd. k) Vulcanization accelerators: - Vulcanization accelerator 1: “SOXINOL CZ”, manufactured by Sumitomo Chemical Co., Ltd. - Vulcanization accelerator 2: “NOCCELER D”, manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.

[0031] From the results in Table 1, it can be seen that the vulcanized rubber of the rubber composition according to Examples 1 to 6 is excellent in processability and further that the vulcanized rubbers obtained from the compositions are excellent in low exothermic properties. [Table 1] Comparison examples Examples 1 2 1 2 3 4 5 6 Process oil 40 20 Palm oil 40 Oil from Vernicia cordata seeds 40 Oil from Jatropha curcas seeds 40 Oil from Para rubber tree seeds 40 20 40 40 SBR (1) 70 70 70 70 70 70 70 SBR (2) 70 natural rubber 30 30 30 30 30 30 30 30 BR Silica 70 70 70 70 70 70 70 40 Coupling agent 7 7 7 7 7 7 7 7 CB 10 10 10 10 10 10 10 40 Silane coupling agent 7 7 7 7 7 7 7 3,5 Spangle 3,0 3,0 3,0 3,0 3,0 3,0 3,0 3,0 Anti-aging products 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 Stearic acid 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 wax 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 sulfur 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 Vulcanization accelerator 1,8 1,8 1,8 1,8 1,8 1,8 1,8 1,8 Workability 100 98 92 90 95 90 98 86 Exothermic properties 100 98 92 90 93 95 70 88

Claims

[1] A rubber composition comprising - one or more rubber components comprising natural rubber in an amount of 5 to 100 parts by weight, - an oil obtained from the seeds of a plant of the Euphorbiaceae family selected from the group consisting of Vernicia cordata, Aleurites fordii, Jatropha curcas and Para rubber tree, in an amount of 1 to 60 parts by weight with respect to the total amount of the rubber component(s), when the total amount is considered to be 100 parts by weight, - 40 to 100 parts by weight of silica and 5 to 60 parts by weight of carbon black with respect to the total amount of rubber component(s), if the total amount is considered as 100 parts by weight, and - one or more plasticiser components consisting of the vegetable oil in a proportion of 30% by weight or more in the rubber composition and of 10% by weight or more with respect to the total amount of the plasticiser component(s) and optionally wax and optionally oils from edible sources.