Vulcanizate and tire using same

Abstract

To solve the problem in which an unvulcanized rubber composition containing unvulcanized rubber is known to undergo a change in vulcanization time and physical properties of the vulcanized rubber due to a change in moisture content: for example, fluctuations in storage conditions of the unvulcanized rubber composition cause a change in moisture content, leading to a decrease in elongation or a variation in physical properties.SOLUTION: A vulcanizate is prepared by vulcanizing an unvulcanized rubber composition containing unvulcanized rubber and having a moisture content of less than 0.2 mass%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a vulcanizate and a tire using the same. [Background technology]

[0002] It is known that the vulcanization time and physical properties of vulcanized rubber change with the change in the moisture content of an unvulcanized rubber composition. In general, in order to improve productivity, rubber is mixed and extruded in a factory, and then the rubber is cooled with water. Therefore, the moisture content in the unvulcanized rubber composition varies from lot to lot, resulting in reduced elongation and uneven physical properties. Therefore, for example, Patent Document 1 discloses a method for measuring the moisture content of unvulcanized rubber, and the moisture content of unvulcanized rubber is grasped to control its quality.

[0003] On the other hand, a pneumatic tire is mainly composed of a pair of bead portions and sidewall portions on the left and right, and a tread portion connected to both sidewall portions. A carcass layer is provided on the inside of the tire, and both ends of the carcass layer are folded back so as to enclose the bead cores from the inside to the outside of the tire. The tread portion is composed of a cap tread and an undertread, and a belt layer is disposed between the undertread and the carcass layer. Since the belt layer is subjected to strong impacts and large loads, a metal reinforcing cord such as a steel cord is used as a reinforcing material, and the rubber covering the steel cord is required to have good adhesion to the steel cord. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-20192 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a vulcanizate which is capable of improving elongation and reducing the variation in physical properties, and which has particularly good adhesion to metal reinforcing cords, and a tire using the same. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above problems can be solved by appropriately adjusting the water content of the unvulcanized rubber composition, and have thus completed the present invention.

[0007] That is, the present invention provides a vulcanizate obtained by vulcanizing an unvulcanized rubber composition that contains unvulcanized rubber and has a water content of less than 0.2 mass %. Effect of the Invention

[0008] In the present invention, the water content of the unvulcanized rubber composition is less than 0.2% by mass, so that the water content in the unvulcanized rubber composition is less likely to vary from lot to lot, improving elongation. Furthermore, by keeping the storage conditions of the unvulcanized rubber constant, it is possible to provide a vulcanizate with reduced variation in physical properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will now be described in further detail.

[0010] The unvulcanized rubber composition in the present invention contains unvulcanized rubber and has a water content of less than 0.2% by mass. If the water content of the unvulcanized rubber composition is 0.2% by mass or more, the elongation of the vulcanized product cannot be improved. In addition, the physical properties of the vulcanized product vary. The water content of the unvulcanized rubber composition is preferably less than 0.2% by mass, and more preferably from 0.05% by mass to less than 0.2% by mass. The water content in the present invention means a value measured by the Karl Fischer method.

[0011] The method for adjusting the moisture content of the unvulcanized rubber composition in the present invention is not particularly limited, but for example, a adjusting step of storing the unvulcanized rubber composition at a relative humidity of less than 30% for 12 hours or more to adjust the moisture content of the unvulcanized rubber composition to less than 0.2 mass% can be performed. The atmospheric temperature in this adjusting step is preferably, for example, 10 to 40°C. Furthermore, by carrying out a mixing step of mixing the unvulcanized rubber composition at 100° C. or higher and / or a molding step of extruding the unvulcanized rubber composition prior to the adjusting step, the moisture content of the unvulcanized rubber composition can be easily adjusted to less than 0.2% by mass or less. When cooling the unvulcanized rubber after the mixing step or molding step, it is preferable to perform air cooling using, for example, a fan in order to prevent the unvulcanized rubber from absorbing moisture.

[0012] Next, each component that can be blended in the unvulcanized rubber composition of the present invention will be described. The unvulcanized rubber composition of the present invention contains at least an unvulcanized rubber.

[0013] (Unvulcanized rubber) The unvulcanized rubber used in the present invention may be, for example, a diene rubber, and examples of the diene rubber include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), and acrylonitrile-butadiene copolymer rubber (NBR). When the vulcanizate of the present invention is used as a vulcanizate for metal bonding, it is preferable to set the amount of NR and / or IR to 80 parts by mass or more when the total diene rubber is 100 parts by mass. The molecular weight and microstructure of the unvulcanized rubber are not particularly limited, and the rubber may be terminally modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl, or the like, or may be epoxidized.

[0014] (Other ingredients) Furthermore, when the vulcanizate of the present invention is used as a vulcanizate for metal bonding, the adhesion to metal components can be further enhanced by blending an organic acid cobalt salt into the unvulcanized rubber composition (hereinafter sometimes referred to as a rubber composition for metal bonding). Examples of the organic acid cobalt salts include cobalt naphthenate, cobalt neodecanoate, cobalt stearate, cobalt rosinate, cobalt versatate, cobalt tall oil acid, cobalt borate neodecanoate, and cobalt acetylacetonate. The mixing ratio of the organic acid cobalt salt is preferably 0.1 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, based on 100 parts by mass of the unvulcanized rubber.

[0015] The rubber composition for metal bonding in the present invention may contain a reinforcing filler, examples of which include carbon black, silica, clay, mica, talc, calcium carbonate, aluminum oxide, and titanium oxide.

[0016] When carbon black is blended in the rubber composition for metal bonding in the present invention, the amount is preferably more than 40 parts by mass and not more than 80 parts by mass, more preferably 50 to 70 parts by mass, per 100 parts by mass of the unvulcanized rubber. When the amount of carbon black is more than 40 parts by mass, it is advantageous in terms of elongation and breaking properties, and when it is 80 parts by mass or less, it is advantageous in terms of low heat build-up.

[0017] In addition to the above-mentioned components, the unvulcanized rubber composition or the rubber composition for metal bonding of the present invention can be blended with various additives that are generally blended in rubber compositions, such as vulcanizing agents, vulcanization accelerators, various fillers, various oils, antioxidants, antiaging agents, plasticizers, etc., and these additives can be kneaded in a general manner to prepare a composition and used for vulcanization. The blending amounts of these additives can be conventional general blending amounts as long as they do not go against the object of the present invention.

[0018] When sulfur is used as a vulcanizing agent, from the viewpoint of further enhancing adhesion to the metal reinforcing cord, the amount of sulfur blended is preferably 4 parts by mass or more and less than 10 parts by mass, and more preferably 5 to 8 parts by mass, per 100 parts by mass of unvulcanized rubber.

[0019] On the other hand, the rubber composition for bonding metal in the present invention has good adhesion to metal reinforcing cords and can be suitably used, for example, as a rubber coating for a belt (steel cord) embedded in an undertread. The steel cord is preferably brass-plated.

[0020] The vulcanization conditions of the unvulcanized rubber composition or the rubber composition for metal bonding of the present invention are not particularly limited and can be appropriately determined depending on the application. From the viewpoint of further reducing the variation in physical properties, the vulcanization temperature is preferably 160 to 190°C, more preferably 170 to 180°C. When the vulcanizate of the present invention is used for a tire, the conventional tire manufacturing method can be followed. The tire of the present invention is preferably a pneumatic tire, and can be filled with air, an inert gas such as nitrogen, and other gases. EXAMPLES

[0021] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0022] Examples 1 to 8 and Comparative Examples 1 to 4 Sample preparation In the formulation (parts by mass) shown in Tables 1 and 2, the components other than the vulcanization accelerator and sulfur were kneaded in a 1.7-liter closed Banbury mixer for 5 minutes, and the rubber was discharged outside the mixer and cooled at room temperature. The rubber was then placed back into the mixer, and the vulcanization accelerator and sulfur were added and further kneaded to obtain an unvulcanized rubber composition. This unvulcanized rubber composition was stored under the conditions shown in Tables 1 and 2, and the moisture content of the unvulcanized rubber composition was examined by the Karl Fischer method. Next, the unvulcanized rubber composition was press-vulcanized in a specified mold under the conditions shown in Tables 1 and 2 to obtain vulcanized rubber test pieces, and the physical properties of the vulcanized rubber test pieces were measured by the test methods shown below.

[0023] Breaking elongation (EB): Evaluated at 100° C. in a tensile test in accordance with JIS K6251. The results are expressed as an index, with the value of Comparative Example 2 or 4 being 100. A larger index indicates better breaking elongation. Belt peeling force: Each sample was peeled off and the peeling force was evaluated according to JIS K6256. The results were expressed as an index, with the value of Comparative Example 2 or 4 being 100. A larger index indicates better belt peeling force. The results are shown in Tables 1 and 2.

[0024] [Table 1]

[0025] [Table 2]

[0026] *1:NR(RSS#3) *2: Carbon black (Tokai Carbon Co., Ltd., Seast 300) *3: Zinc oxide (Zinc oxide type 3 manufactured by Seido Chemical Industry Co., Ltd.) *4: Cobalt stearate (DIC Corporation) *5: Anti-aging agent 6PPD (Flexis Santoflex 6PPD) *6: Anti-aging agent RD (Nocrac 224, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *7: Vulcanization accelerator DCBS (Noccela DZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *8: Sulfur (Akzo Nobel Krystex HS OT 20)

[0027] As is clear from Tables 1 and 2 above, the unvulcanized rubber composition in each Example contains unvulcanized rubber and has a moisture content of less than 0.2 mass%, and is superior in breaking elongation and belt peeling force compared to Comparative Examples 2 and 4. In contrast, in Comparative Examples 1 and 3, since the water content of the unvulcanized rubber composition was 0.2 mass % or more, no improvement was observed in the breaking elongation and belt peeling force compared to Comparative Examples 2 and 4. Examples 1 to 4 and Comparative Example 1 are contrasted with the results of Comparative Example 2, and Examples 5 to 8 and Comparative Example 3 are contrasted with the results of Comparative Example 4.

Claims

[Claim 1] A method for producing a rubber composition comprising the steps of: storing an unvulcanized rubber composition containing 100% by mass of natural rubber at a relative humidity of less than 30% for 12 hours or more; and adjusting the moisture content of the unvulcanized rubber composition to less than 0.2% by mass; Prior to the preparation step, a mixing step of mixing the unvulcanized rubber composition at 100° C. or higher and / or a molding step of extruding the unvulcanized rubber composition are carried out. A storage method comprising the steps of:

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