Modified natural rubber, method for producing modified natural rubber, and rubber composition

Abstract

To provide a modified natural rubber which exhibits excellent toughness when used for a rubber composition, a method for producing the modified natural rubber, and a rubber composition containing the modified natural rubber.SOLUTION: The modified natural rubber is obtained by: mixing a latex of a natural rubber, an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group and a thioester group, and at least one compound selected from the group consisting of peroxides and styrene; solidifying the obtained mixture; and heating and drying the obtained solid matter.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a modified natural rubber, a method for producing the modified natural rubber, and a rubber composition.

Background Art

[0002] Conventionally, as a natural rubber used in tires and the like, a modified natural rubber obtained by adding an alkoxysilyl group-containing mercapto compound to natural rubber is known (for example, Patent Document).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Under such circumstances, when the present inventors produced the modified natural rubber described in the examples of Patent Document 1 and used it in a rubber composition to evaluate its toughness (hardness, M300), it became clear that further improvement was desirable in consideration of future increasing requirements.

[0005] Therefore, in view of the above circumstances, an object of the present invention is to provide a modified natural rubber that exhibits excellent toughness when used in a rubber composition, a method for producing the modified natural rubber, and a rubber composition containing the modified natural rubber.

Means for Solving the Problems

[0006] As a result of intensive studies on the above problems, the present inventors have found that the above problems can be solved by further mixing a peroxide or styrene, and have reached the present invention. That is, the present inventors have found that the above problems can be solved by the following configuration.

[0007] (1) A modified natural rubber obtained by mixing natural rubber latex, an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group, and at least one compound selected from the group consisting of a peroxide and styrene, solidifying the obtained mixture, and heating and drying the obtained solid matter. (2) The modified natural rubber according to (1) above, wherein the ratio of the peroxide to 100 parts by mass of the rubber content in the latex is 0.05 to 0.5 parts by mass, and / or the ratio of the styrene to 100 parts by mass of the rubber content in the latex is more than 0 parts by mass and 2 parts by mass or less. (3) A mixing step of mixing natural rubber latex, an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group, and at least one compound selected from the group consisting of a peroxide and styrene, A solidifying step of solidifying the mixture obtained in the mixing step, A method for producing a modified natural rubber, comprising a heating and drying step of heating and drying the solid matter obtained in the solidifying step. (4) A rubber composition containing the modified natural rubber according to (1) or (2) above.

Advantages of the Invention

[0008] As shown below, an object of the present invention is to provide a modified natural rubber that exhibits excellent toughness when used in a rubber composition, a method for producing the modified natural rubber, and a rubber composition containing the modified natural rubber.

Modes for Carrying Out the Invention

[0009] Hereinafter, the modified natural rubber of the present invention, the method for producing the modified natural rubber, and the rubber composition containing the modified natural rubber will be described. In this specification, a numerical range represented by using "~" means a range including the numerical values described before and after "~" as a lower limit value and an upper limit value. Moreover, each component may be used alone or in combination of two or more. Here, when two or more of each component are used in combination, the content of that component refers to the total content unless otherwise specified. It is also said that when used in a rubber composition, it exhibits excellent toughness and low heat build-up, simply exhibits excellent toughness and low heat build-up, or has excellent effects of the present invention.

[0010] The modified natural rubber of the present invention is obtained by mixing a latex of natural rubber, an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group (hereinafter also referred to as "specific group") (hereinafter also referred to as "specific alkoxysilane"), and at least one compound selected from the group consisting of a peroxide and styrene (hereinafter also referred to as "specific compound"), solidifying the obtained mixture, and heating and drying the obtained solid matter.

[0011] Since the modified natural rubber of the present invention has such a configuration, it is presumed that the above-described effects can be obtained. The reason is not clear, but it is presumed as follows. When the latex of natural rubber and the specific alkoxysilane are mixed, it is considered that the specific group of the specific alkoxysilane undergoes an addition reaction to the carbon-carbon double bond of the natural rubber, and a latex of natural rubber to which the specific alkoxysilane is added (alkoxysilane-added natural rubber) is obtained. Furthermore, when the alkoxysilane-added natural rubber obtained by solidifying this is heated and dried, it is considered that a modified natural rubber, which is a hydrolysis condensate of alkoxysilyl groups (intramolecular and intermolecular) of the alkoxysilane-added natural rubber, is obtained. Such a modified natural rubber of the present invention is considered to have extremely excellent toughness because it has both the flexibility of natural rubber and the rigidity of the hydrolysis condensation structure (siloxane bond) of alkoxysilyl groups.

[0012] Here, from the studies of the present inventors, it has been found that by further mixing peroxides and styrene, the toughness is rapidly improved. The addition reaction of specific alkoxysilanes is promoted by these compounds, and it is conceivable that these compounds crosslink natural rubbers with each other, and as a result, the crosslink density is significantly improved. Therefore, peroxides and styrene are essential components in the present invention.

[0013] As described above, the modified natural rubber of the present invention is considered to be one in which the alkoxysilyl groups of the alkoxysilane - added natural rubber have undergone a hydrolysis - condensation reaction intramolecularly and intermolecularly. Furthermore, it may be crosslinked by peroxides and styrene. Therefore, its structure is extremely complex, and it is considered technically impossible to analyze its structure, or that the work of specifying its structure requires an extremely large economic expenditure and time. Therefore, there are so - called "impossible and impractical matters" in specifying the modified natural rubber of the present invention by the production method.

[0014] [1] Method for producing modified natural rubber First, the method for producing the modified natural rubber of the present invention will be described. The method for producing the modified natural rubber of the present invention comprises a mixing step of mixing a latex of natural rubber, an alkoxysilane (specific alkoxysilane) having at least one group (specific group) selected from the group consisting of a sulfide group, a mercapto group, and a thioester group, and at least one compound (specific compound) selected from the group consisting of a peroxide and styrene; a solidifying step of solidifying the mixture obtained in the above mixing step; and a heat - drying step of heat - drying the solid obtained in the above solidifying step. It is a method for producing modified natural rubber.

[0015] Hereinafter, each step will be described.

[0016] [Mixing step] The mixing step is a step of mixing a latex of natural rubber (hereinafter also referred to as "natural rubber latex") with an alkoxysilane having at least one group (specific group) selected from the group consisting of a sulfide group, a mercapto group, and a thioester group (specific alkoxysilane) and at least one compound (specific compound) selected from the group consisting of a peroxide and styrene. As described above, in the mixing step, it is considered that the specific group of the specific alkoxysilane undergoes an addition reaction with the carbon-carbon double bond of the natural rubber, and a latex of natural rubber to which the specific alkoxysilane is added (alkoxysilane-added natural rubber) is obtained. In addition, as described above, there is a possibility that natural rubbers are crosslinked by the specific compound.

[0017] First, each material used in the mixing step will be described.

[0018] 〔Natural rubber latex〕 The latex of natural rubber (natural rubber latex) used in the mixing step is not particularly limited, and examples thereof include field latex collected from rubber trees and filtered, and concentrated natural rubber latex obtained by treating the same. The rubber content (solid content) in the natural rubber latex is not particularly limited, but is preferably 10 to 90% by mass and more preferably 50 to 70% by mass because the effects of the present invention and the like on the obtained modified natural rubber are more excellent. Hereinafter, "the effects of the present invention and the like on the obtained modified natural rubber are more excellent" will also be simply referred to as "the effects of the present invention and the like are more excellent".

[0019] 〔Specific alkoxysilane〕 As described above, in the mixing step, an alkoxysilane having at least one group (specific group) selected from the group consisting of a sulfide group, a mercapto group, and a thioester group (specific alkoxysilane) is used. The specific alkoxysilane is not particularly limited as long as it is an alkoxysilane having a specific group.

[0020] <Specific group> The specific group is at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group. The specific group is preferably a sulfide group or a thioester group, and more preferably a sulfide group (particularly a polysulfide group), because the effects of the present invention are more excellent.

[0021] (Sulfide group) The sulfide group is a group represented by -Sx- (where x represents a number of 1 or more). The sulfide group is preferably a group represented by a polysulfide group (-Sx- (where x represents a number of 2 or more (preferably 2 to 5))), because the effects of the present invention are more excellent.

[0022] (Mercapto group) The mercapto group is a group represented by -SH.

[0023] (Thioester group) The thioester group is a group represented by R-CO-S- (where R represents a hydrocarbon group). R (hydrocarbon group) of the thioester group is not particularly limited, and examples thereof include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a group combining these. The above aliphatic hydrocarbon group may be linear, branched, or cyclic. Specific examples of the above aliphatic hydrocarbon group include linear or branched alkyl groups (particularly having 1 to 30 carbon atoms), linear or branched alkenyl groups (particularly having 2 to 30 carbon atoms), linear or branched alkynyl groups (particularly having 2 to 30 carbon atoms), and the like. Examples of the above aromatic hydrocarbon group include aromatic hydrocarbon groups having 6 to 18 carbon atoms such as a phenyl group, a tolyl group, a xylyl group, and a naphthyl group. R (hydrocarbon group) is preferably an aliphatic hydrocarbon group, more preferably an alkyl group, and even more preferably a linear alkyl group (particularly having 1 to 10 carbon atoms), because the effects of the present invention are more excellent.

[0024] <Alkoxysilane> An alkoxysilane refers to a compound having an alkoxysilyl group (R-O-Si≡: where R represents a hydrocarbon group). The alkoxysilyl group may be a monoalkoxysilyl group (R-O-Si≡: where R represents a hydrocarbon group), a dialkoxysilyl group ((R-O-)2Si<: where R represents a hydrocarbon group, and the two Rs may be the same or different), or a trialkoxysilyl group ((R-O-)3Si-: where R represents a hydrocarbon group, and the three Rs may be the same or different). However, for better effects of the present invention, etc., it is preferably a dialkoxysilyl group or a trialkoxysilyl group, and more preferably a trialkoxysilyl group. Specific examples and preferred embodiments of R (hydrocarbon group) of the alkoxysilyl group are the same as those of R of the thioester group described above. However, for better effects of the present invention, etc., it is preferably a methyl group or an ethyl group, and more preferably an ethyl group.

[0025] <Preferred embodiment> For better effects of the present invention, etc., the specific alkoxysilane is preferably a compound represented by the following formula (S5), a compound represented by the following formula (S), or a copolymer having a repeating unit represented by the following formula (A3) and a repeating unit represented by the following formula (A4). More preferably, it is a compound represented by the following formula (S5) or a compound represented by the following formula (S). Even more preferably, it is a compound represented by the following formula (S5).

[0026] (Compound represented by formula (S5))

[0027]

Chemical formula

[0028] In the above formula (S5), R 51represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms. Among them, an alkyl group having 1 to 5 carbon atoms is preferable. Specific examples of the alkyl group having 1 to 20 carbon atoms include, for example, methyl group, ethyl group, propyl group, butyl group, hexyl group, octyl group, decyl group, octadecyl group and the like. Specific examples of the aryl group having 6 to 10 carbon atoms include, for example, phenyl group, tolyl group, naphthyl group and the like. Specific examples of the alkenyl group having 2 to 10 carbon atoms include, for example, vinyl group, propenyl group, pentenyl group and the like. In the above formula (S5), R 52 represents an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 10 carbon atoms include, for example, methyl group, ethyl group, propyl group, butyl group, hexyl group, octyl group, decyl group and the like. Specific examples of the aryl group having 6 to 10 carbon atoms are the same as those of the above R 51 . In the above formula (S5), n represents an integer of 1 to 10, and among them, an integer of 2 to 4 is preferable. In the above formula (S5), x represents a number of 1 to 6, and among them, 2 to 4 is preferable. In the above formula (S5), y represents an integer of 1 to 3.

[0029] (Compound represented by formula (S)) (C n H 2n+1 O)3-Si-C m H 2m -S-CO-C k H 2k+1 Formula (S) In formula (S), n represents an integer of 1 to 3, m represents an integer of 1 to 5 (preferably an integer of 2 to 4), and k represents an integer of 1 to 15 (preferably an integer of 5 to 10).

[0030] (Copolymer having a repeating unit represented by formula (A3) and a repeating unit represented by formula (A4))

[0031]

Chemical formula

[0032] In the above formulas (A3) and (A4), R 31 and R 41 each independently represent an alkylene group having 1 to 5 carbon atoms. Specific examples thereof include a methylene group, an ethylene group, a propylene group, etc. Among them, a propylene group is preferred. A plurality of R 31 and R 41 may be the same or different from each other. In the above formulas (A3) and (A4), R 32 and R 42 each independently represent a linear or branched alkylene group having 1 to 30 carbon atoms, a linear or branched alkenylene group having 2 to 30 carbon atoms, or a linear or branched alkynylene group having 2 to 30 carbon atoms. Among them, those having 3 to 20 carbon atoms are preferred. When R 32 is at the terminal, R 32 represents a hydrogen atom, a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched alkenyl group having 2 to 30 carbon atoms, or a linear or branched alkynyl group having 2 to 30 carbon atoms. Among them, those having 3 to 20 carbon atoms are preferred. When R 42 is at the terminal, the definition, specific examples and preferred embodiments of R 42 are the same as those of the above R 32 . A plurality of R 32 and R 42 may be the same or different from each other. In the above formulas (A3) and (A4), R 33 and R 43 each independently represent a hydrogen atom, a halogen atom, a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched alkenyl group having 2 to 30 carbon atoms, a linear or branched alkynyl group having 2 to 30 carbon atoms, a linear or branched alkyl group having 1 to 30 carbon atoms and having a hydroxyl group or a carboxyl group at the terminal, or a linear or branched alkenyl group having 2 to 30 carbon atoms and having a hydroxyl group or a carboxyl group at the terminal. R 43Preferably, it is a group having a hydroxyl group at the terminal. R 32 and R 33 may form a ring with R 32 and R 33 . R 42 and R 43 may form a ring with R 42 and R 43 . A plurality of R 33 and R 43 may be the same or different from each other. In the above formula (A3), R 34 represents an alkyl group having 1 to 13 carbon atoms, and among them, an alkyl group having 3 to 10 carbon atoms is preferable. Specific examples of the alkyl group having 3 to 10 carbon atoms include, for example, hexyl group, heptyl group, octyl group and the like. A plurality of R 34 may be the same or different from each other.

[0033] <Specific examples>

[0034] (Sulfide group) Specific examples of the alkoxysilane having a sulfide group include Si266, Si69, Si75 (all manufactured by Evonik) and the like.

[0035] (Mercapto group) Specific examples of the alkoxysilane having a mercapto group include Si363 (the following structure) (manufactured by Evonik), KBE-803 (3-mercaptopropyltriethoxysilane), KBM-803 (3-mercaptopropyltrimethoxysilane), 9457F (the following structure) and the like.

[0036] Si363

Chemical formula

[0037] 9457F (where Et represents an ethyl group, and m, n and l represent the molar ratio of each repeating unit)

Chemical formula

[0038] (Thioester group) Specific examples of the alkoxysilane having a thioester group include NXT (the following structure, manufactured by Momentive Performance Materials), NXT-Low VOC (the following structure), and the like.

[0039] NXT [Chemical formula]

[0040] NXT-Low VOC [Chemical formula]

[0041] (Sulfide group, mercapto group) Specific examples of the alkoxysilane having a sulfide group and a mercapto group include 9511D (the following structure) and the like.

[0042] 9511D (where Et represents an ethyl group, and m, n, o, and l represent the molar ratios of each repeating unit) [Chemical formula]

[0043] (Mercapto group, thioester group) Specific examples of the alkoxysilane having a mercapto group and a thioester group include NXT-Z (the following structure) and the like.

[0044] NXT-Z (where the curve bonded to the oxygen atom represents an alkyl group having 1 to 30 carbon atoms, and the curve having one bonded to the oxygen atom and the other bonded to the hydroxy group represents an alkylene group having 1 to 30 carbon atoms) [Chemical formula]

[0045] 〔Specific compound〕 As described above, in the mixing step, at least one compound (specific compound) selected from the group consisting of peroxide and styrene is used. The specific compound preferably contains styrene, and more preferably contains peroxide and styrene, because the effects of the present invention are more excellent.

[0046] <Peroxide> Examples of the peroxide include inorganic peroxides and organic peroxides. Examples of the inorganic peroxide include hydrogen peroxide solution; persulfate compounds such as persulfuric acid, sodium bisulfate persulfate, and potassium bisulfate persulfate. Examples of the organic peroxide include t-butyl hydroperoxide, m-chloroperbenzoic acid (mCPBA), performic acid, peracetic acid, and propionic acid. The peroxide is preferably an organic peroxide because the effects of the present invention are more excellent.

[0047] 〔Procedure of mixing step〕 In the mixing step, natural rubber latex, a specific alkoxysilane, and a specific compound are mixed.

[0048] <Temperature> The temperature of the mixing step is not particularly limited, but is preferably 10 to 30°C, and more preferably room temperature, because the effects of the present invention are more excellent.

[0049] <Amount of alkoxysilane> The ratio of the specific alkoxysilane to 100 parts by mass of the rubber content in the natural rubber latex in the mixing step (hereinafter, also referred to as "amount of alkoxysilane") is not particularly limited, but is preferably 0.1 part by mass or more, more preferably 1.0 part by mass or more, further preferably 2.0 part by mass or more, particularly preferably 5.0 part by mass or more, and most preferably 8.0 part by mass or more, because the effects of the present invention are more excellent. The upper limit of the amount of alkoxysilane is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 40 parts by mass or less, particularly preferably 30 parts by mass or less, and most preferably 20 parts by mass or less, because the effects of the present invention are more excellent.

[0050] <Amount of peroxide> The ratio of peroxide to 100 parts by mass of the rubber content in natural rubber latex in the mixing step (hereinafter also referred to as "amount of peroxide") is not particularly limited, but is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.2 parts by mass or more because the effects of the present invention are more excellent. The upper limit of the amount of peroxide is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 2 parts by mass or less, particularly preferably 1 part by mass or less, and most preferably 0.5 parts by mass or less because the effects of the present invention are more excellent.

[0051] <Amount of styrene> The ratio of styrene to 100 parts by mass of the rubber content in natural rubber latex in the mixing step (hereinafter also referred to as "amount of styrene") is not particularly limited, but is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and still more preferably 1.0 parts by mass or more because the effects of the present invention are more excellent. The upper limit of the amount of styrene is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 4 parts by mass or less, particularly preferably 3 parts by mass or less, and most preferably 2 parts by mass or less because the effects of the present invention are more excellent.

[0052] [Curing step] The curing step is a step of curing the mixture obtained in the above-described mixing step. As described above, in the solidification step, it is considered that by solidifying the mixture (latex) obtained in the mixing step, natural rubber (alkoxysilane - added natural rubber) to which a specific alkoxysilane is added can be obtained. In addition, as described above, there is also a possibility that natural rubbers are cross - linked by a specific compound.

[0053] The method of solidification is not particularly limited. For example, a method of drying (leaving it standing) at room temperature can be mentioned.

[0054] [Heating and Drying Step] The heating and drying step is a step of heating and drying the solidified product obtained in the above - described solidification step. As described above, in the heating and drying step, it is considered that hydrolysis condensates of alkoxysilyl groups (intramolecular and intermolecular) of natural rubber (alkoxysilane - added natural rubber) to which a specific alkoxysilane is added can be obtained. In addition, as described above, there is also a possibility that natural rubbers are cross - linked by a specific compound.

[0055] [Temperature] The temperature of the heating and drying step is preferably 40°C or higher, more preferably 50°C or higher, for the reason that the effects of the present invention are more excellent. The upper limit of the above temperature is not particularly limited, but is preferably 200°C or lower, more preferably 100°C or lower, for the reason that the effects of the present invention are more excellent.

[0056] [2] Modified Natural Rubber The modified natural rubber of the present invention is a modified natural rubber obtained by mixing a latex of natural rubber, an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group (hereinafter, also referred to as a "specific group") (hereinafter, also referred to as a "specific alkoxysilane"), and at least one compound selected from the group consisting of a peroxide and styrene (hereinafter, also referred to as a "specific compound"), solidifying the obtained mixture, and heating and drying the obtained solid.

[0057] Each material and procedure used in the modified natural rubber of the present invention is as described above.

[0058] [3] Rubber composition The rubber composition of the present invention (hereinafter, also referred to as "the composition of the present invention") is a rubber composition containing the modified natural rubber of the present invention described above.

[0059] [Modified natural rubber] The modified natural rubber of the present invention is as described above.

[0060] [Content] In the composition of the present invention, the content of the modified natural rubber of the present invention in all rubber components is not particularly limited. However, for the reason that the rubber composition exhibits better toughness and lower heat generation, it is preferably 10% by mass or more, more preferably 30% by mass or more, still more preferably 50% by mass or more, particularly preferably 70% by mass or more, and most preferably 90% by mass or more. The upper limit of the content of the modified natural rubber of the present invention in all rubber components is not particularly limited and is 100% by mass. Hereinafter, "the rubber composition exhibits better toughness and lower heat generation" is also referred to as "the effects of the present invention are more excellent".

[0061] [Other rubber components] The composition of the present invention may contain rubber components other than the modified natural rubber of the present invention (other rubber components). Specific examples of such rubber components (preferably diene rubbers) include butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), and the like. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, and the like.

[0062] [Content] In the composition of the present invention, the content of other rubber components in all rubber components is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 90% by mass or less, more preferably 70% by mass or less, still more preferably 50% by mass or less, particularly preferably 30% by mass or less, and most preferably 10% by mass or less. The lower limit of other rubber components in all rubber components is not particularly limited and is 0% by mass.

[0063] [Carbon black] The composition of the present invention preferably contains carbon black for the reason that the effects of the present invention are more excellent. The above carbon black is not particularly limited, and for example, various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF can be used. The nitrogen adsorption specific surface area (N2SA) of the above carbon black is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 50 to 200 m 2 / g, and more preferably 70 to 150 m 2 / g. Here, the nitrogen adsorption specific surface area (N2SA) is a value measured according to JIS K6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method" for the amount of nitrogen adsorbed on the carbon black surface.

[0064] [Content] In the composition of the present invention, the content of carbon black is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, and still more preferably 3 to 10 parts by mass with respect to 100 parts by mass of the rubber component.

[0065] [Silica] The composition of the present invention preferably contains silica for the reason that the effects of the present invention are more excellent. The above-mentioned silica is not particularly limited, and any conventionally known silica compounded in a rubber composition for applications such as tires can be used. Specific examples of silica include wet silica, dry silica, fumed silica, diatomaceous earth, etc. Among them, wet silica is preferred because the effects of the present invention are more excellent. The above silica may be used alone or in combination of two or more kinds of silica. The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of silica is not particularly limited, but it is preferably 100 to 300 m 2 / g, and more preferably 150 to 200 m 2 / g, for reasons that the effects of the present invention are more excellent. In this specification, the CTAB adsorption specific surface area is a value measured according to JIS K6217-3:2001 "Part 3: Method for determining specific surface area - CTAB adsorption method" for the amount of CTAB adsorbed on the silica surface.

[0066] 〔Content〕 In the composition of the present invention, the content of silica is not particularly limited, but it is preferably 10 to 300 parts by mass, more preferably 20 to 200 parts by mass, and even more preferably 30 to 100 parts by mass with respect to 100 parts by mass of the rubber component, for reasons that the effects of the present invention are more excellent.

[0067] [Silane coupling agent] The composition of the present invention preferably contains a silane coupling agent for reasons that the effects of the present invention are more excellent. The silane coupling agent is not particularly limited as long as it is a silane compound having a hydrolyzable group and an organic functional group. The hydrolyzable group is not particularly limited, and examples thereof include an alkoxy group, a phenoxy group, a carboxyl group, an alkenyloxy group, etc. Among these, from the reason that the effects of the present invention are more excellent, an alkoxy group is preferable. When the hydrolyzable group is an alkoxy group, the number of carbon atoms of the alkoxy group is preferably 1 to 16, more preferably 1 to 4, from the reason that the effects of the present invention are more excellent. Examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, etc.

[0068] The above organic functional group is not particularly limited, but it is preferably a group capable of forming a chemical bond with an organic compound. For example, an epoxy group, a vinyl group, an acryloyl group, a methacryloyl group, an amino group, a sulfide group (especially, a polysulfide group (-S n -: n is an integer of 2 or more)), a mercapto group, a blocked mercapto group (protected mercapto group) (for example, an octanoylthio group), etc. are mentioned. Among these, from the reason that the effects of the present invention are more excellent, a sulfide group (especially, a disulfide group, a tetrasulfide group), a mercapto group, a blocked mercapto group are preferable. The silane coupling agent may be used alone or in combination of two or more.

[0069] From the reason that the effects of the present invention are more excellent, the above silane coupling agent is preferably a sulfur-containing silane coupling agent.

[0070] Specific examples of the above silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazole tetrasulfide, triethoxysilylpropyl-methacrylate-monosulfide, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, 3-octanoylthio-1-propyltriethoxysilane, etc. Among these, one kind may be used alone, or two or more kinds may be used in combination.

[0071] In the composition of the present invention, the content of the silane coupling agent is not particularly limited. However, for the reason that the effects of the present invention are more excellent, it is preferably 2 to 20% by mass, more preferably 5 to 15% by mass, based on the content of the above-mentioned silica.

[0072] [Other Components] The composition of the present invention can contain, if necessary, components other than the above-mentioned components (other components) within a range that does not impair its effects and purposes. Examples of such components include fillers other than carbon black and silica, terpene resins (preferably aromatic-modified terpene resins), thermally expandable microcapsules, zinc oxide (zinc white), stearic acid, antioxidants, waxes, processing aids, process oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), vulcanization accelerators, and various additives generally used in rubber compositions.

[0073] [Uses] The composition of the present invention is suitably used, for example, in tires, conveyor belts, hoses, vibration isolators, rubber rolls, outer covers of railway vehicles, etc. In particular, it is suitably used in tires (especially treads).

Examples

[0074] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

[0075] 〔Production of modified natural rubber〕 Modified natural rubbers 1 to 4 were produced as follows. Note that modified natural rubbers 1 to 4 are modified natural rubbers obtained by mixing natural rubber latex, Si69 (alkoxysilane having a sulfide group), tert-butyl hydroperoxide (peroxide) and / or styrene, solidifying the obtained mixture, and heating the obtained solidified product, and thus correspond to the modified natural rubber of the present invention described above.

[0076] <Modified natural rubber 1> Modified natural rubber 1 was produced as follows.

[0077] (Mixing step) Natural rubber latex (rubber content: 60% by mass) (100 parts by mass as rubber content), 10 parts by mass of Si69 (bis(3-triethoxysilylpropyl)tetrasulfide), and 0.25 part by mass of tert-butyl hydroperoxide were mixed and stirred at room temperature for about 1 hour.

[0078] (Solidification step) The obtained mixture (latex after the mixing step) was transferred to a tray and dried at room temperature to be solidified.

[0079] (Heating and drying step) The obtained solidified product was heated and dried at 50°C. Thus, a modified natural rubber was obtained. The obtained modified natural rubber is also referred to as modified natural rubber 1.

[0080] <Modified natural rubber 2> A modified natural rubber was obtained according to the same procedure as modified natural rubber 1 described above, except that 15 parts by mass of styrene was further mixed in the mixing step. The obtained modified natural rubber is also referred to as modified natural rubber 2.

[0081] <Modified natural rubber 3> In the mixing process, a modified natural rubber was obtained according to the same procedure as the above-mentioned modified natural rubber 2, except that the amount of styrene was changed to 8 parts by mass. The obtained modified natural rubber is also referred to as modified natural rubber 3.

[0082] <Modified natural rubber 4> In the mixing process, a modified natural rubber was obtained according to the same procedure as the above-mentioned modified natural rubber 2, except that the amount of tert-butyl hydroperoxide was changed to 3 parts by mass. The obtained modified natural rubber is also referred to as modified natural rubber 4.

[0083] <Analysis> When acetone extraction of the cured products after the curing process was carried out for modified natural rubbers 1 to 4, unreacted Si69 was not detected. From this, it is considered that all of the Si69 used reacted (addition reaction) with natural rubber. Also, when the modified natural rubbers 1 to 4 were analyzed after the heat drying process, alkoxysilyl groups were not detected. From this, it is considered that all of the alkoxysilyl groups of Si69 reacted (hydrolysis condensation reaction).

[0084] 〔Preparation of rubber composition〕 Each component shown in Table 1 below was mixed at the ratio (parts by mass) shown in the same table. Specifically, first, the components other than sulfur and vulcanization accelerator were mixed in a 1.8 L (liter) closed mixer under the condition of 130 °C for 5 minutes, and the masterbatch was discharged. Then, sulfur and vulcanization accelerator were added to the above masterbatch and mixed using an open roll under the condition of 80 °C to prepare each rubber composition.

[0085] 〔Evaluation〕 The following evaluations were performed on each of the obtained rubber compositions.

[0086] <HS(20 °C)> Each of the obtained rubber compositions (unvulcanized) was press-vulcanized at 160 °C for 20 minutes in a mold (15 cm × 15 cm × 0.2 cm) to produce a vulcanized rubber sheet. Regarding the obtained vulcanized rubber sheet, in accordance with JIS K6253-3, the hardness (type A durometer hardness) was evaluated at 20°C. The results are shown in Table 1. The results are expressed as an index with the value of Comparative Example 1 being 100. The larger the index, the higher the hardness, which means excellent toughness. Practically, the index is preferably 105 or more.

[0087] <m300> Regarding the vulcanized rubber sheet produced as described above, in accordance with JIS K6251:2010, a JIS No. 3 dumbbell-shaped test piece (thickness 2 mm) was punched out, and the 300% modulus (stress at 300% deformation) was measured under the conditions of a temperature of 20°C and a tensile speed of 500 mm / min. The results are shown in Table 1. The results are expressed as an index with Comparative Example 1 taken as 100. A larger index means better toughness. Practically, the index is preferably 103 or more.

[0088] <tanδ(60°C)> Regarding the vulcanized rubber sheet produced as described above, in accordance with JIS K6394:2007, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.), tanδ(60°C) was measured under the conditions of a strain rate of 10% ± 2% in extension, a vibration frequency of 20 Hz, and a temperature of 60°C. The reciprocal of tanδ(60°C) is shown in Table 1. The results are expressed as an index with the reciprocal of Comparative Example 1 taken as 100. A larger index means better low heat generation property.

[0089]

Table 1

[0090] The details of each component in Table 1 are as follows. · NR: TSR20 (natural rubber, glass transition temperature: -62°C) · Modified natural rubber 1 - 4: Modified natural rubber 1 - 4 produced as described above · Styrene: Styrene · Peroxide: tert-Butyl hydroperoxide · Carbon black: Show black N339 (manufactured by Cabot Japan Ltd.) · Silica: ZEOSIL 1165MP (CTAB adsorption specific surface area: 159 m 2 / g, manufactured by Rhodia) · Stearic acid: Bead stearic acid (manufactured by NOF Corporation) · Zinc oxide: Zinc oxide type 3 (manufactured by Sho-Dowa Chemical Industry Co., Ltd.) · Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) · Vulcanization accelerator: Sanseler NS-P (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) (N-tert-butyl-2-benzothiazolylsulfenamide) · Sulfur: Jinhua Indian Ink Microfine Sulfur (sulfur content 95.24% by mass, manufactured by Tsurumi Chemical Industry Co., Ltd.)

[0091] As can be seen from Table 1, the rubber compositions of Examples 1 to 4 containing the modified natural rubber of the present invention exhibited excellent toughness. From the comparison of Examples 1 to 4, Examples 2 to 4 in which the specific compound used in the modified natural rubber contains styrene showed better toughness (hardness). Among them, Examples 2 to 3 in which the peroxide amount of the modified natural rubber is 0.05 to 0.5 parts by mass showed even better toughness (hardness, M300). Among them, Example 2 in which the styrene amount of the modified natural rubber is more than 0 part by mass and 2 parts by mass or less showed even better toughness (hardness) and low heat generation. Also, from the comparison of Examples 1 to 4, Examples 1 to 3 in which the peroxide amount of the modified natural rubber is 0.05 to 0.5 parts by mass showed better toughness (M300). Among them, Examples 2 to 3 in which the specific compound used in the modified natural rubber contains styrene showed even better toughness (hardness). Among them, Example 2 in which the styrene amount of the modified natural rubber is more than 0 part by mass and 2 parts by mass or less showed even better toughness (hardness) and low heat generation.

[0092] On the other hand, Comparative Examples 1 to 5 containing unmodified natural rubber instead of the modified natural rubber of the present invention had insufficient toughness.

Claims

1. Natural rubber latex, an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group, a peroxide, or a mixture of a peroxide and styrene, and the resulting mixture is solidified, and the resulting solid is heat-dried to obtain a modified natural rubber.

2. The ratio of the peroxide to 100 parts by mass of the rubber content in the latex is 0.05 to 0.5 parts by mass, or, the ratio of the peroxide to 100 parts by mass of the rubber content in the latex is 0.05 to 0.5 parts by mass, and the ratio of the styrene to 100 parts by mass of the rubber content in the latex is more than 0 parts by mass and 2 parts by mass or less. The modified natural rubber according to Claim 1.

3. Natural rubber latex, an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group, a mixing step of mixing a peroxide, or a peroxide and styrene, a solidifying step of solidifying the mixture obtained in the mixing step, a heat-drying step of heat-drying the solid obtained in the solidifying step, and a method for producing a modified natural rubber comprising the steps.

4. A rubber composition containing the modified natural rubber according to Claim 1 or 2.

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