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 with an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group and a thioester group so that the ratio of the alkoxysilane is 1.0 pt.mass or more based on 100 pts.mass of a rubber component in the latex; 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 technology]

[0002] BACKGROUND ART Modified natural rubber obtained by adding an alkoxysilyl group-containing mercapto compound to natural rubber has been known as natural rubber used in tires and the like (for example, see patent documents). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-152045 Summary of the Invention [Problem to be solved by the invention]

[0004] In this situation, the present inventors produced the modified natural rubber described in the examples of Patent Document 1, used it in a rubber composition, and evaluated its toughness (hardness, M300). As a result, it became clear that further improvement is desirable in consideration of demands that are likely to increase in the future.

[0005] 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 problem]

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by changing the amount of alkoxysilane added to natural rubber, and have arrived at 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 with an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group so that the ratio of the alkoxysilane per 100 parts by mass of the rubber content in the latex is 1.0 part by mass or more, solidifying the resulting mixture, and heating and drying the resulting solid. (2) The modified natural rubber according to (1) above, wherein the proportion of the alkoxysilane is 1.0 to 30 parts by mass per 100 parts by mass of rubber in the latex. (3) a mixing step of mixing natural rubber latex with an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group so that the ratio of the alkoxysilane to 100 parts by mass of rubber in the latex is 1.0 part by mass or more; a solidification step of solidifying the mixture obtained in the mixing step; a heat drying step of heat drying the solidified product obtained in the solidification step. (4) A rubber composition containing the modified natural rubber described in (1) or (2) above. [Effects of the Invention]

[0008] As will be described below, the present invention can 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. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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 below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Each component may be used alone or in combination of two or more. When two or more components are used in combination, the content of the components refers to the total content unless otherwise specified. Furthermore, when a rubber composition is used, it exhibits excellent toughness or tear resistance, which is also referred to as simply exhibiting excellent toughness or tear resistance, or as having excellent effects of the present invention.

[0010] The modified natural rubber of the present invention is This modified natural rubber is obtained by mixing natural rubber latex with an alkoxysilane (hereinafter also referred to as the "specific alkoxysilane") having at least one group (hereinafter also referred to as the "specific group") selected from the group consisting of a sulfide group, a mercapto group, and a thioester group, so that the ratio of the alkoxysilane is 1.0 part by mass or more per 100 parts by mass of the rubber content in the latex, solidifying the resulting mixture, and heating and drying the resulting solid.

[0011] The modified natural rubber of the present invention has such a structure, and it is presumed that the above-mentioned effects are obtained. The reason for this is not clear, but is presumed to be as follows. It is believed that when natural rubber latex is mixed with a specific alkoxysilane, a specific group of the specific alkoxysilane undergoes an addition reaction with the carbon-carbon double bond of the natural rubber, resulting in a latex of natural rubber to which the specific alkoxysilane has been added (alkoxysilane-added natural rubber). Furthermore, when the alkoxysilane-added natural rubber obtained by solidifying this is heated and dried, it is believed that a modified natural rubber, which is a hydrolysis condensation product (intramolecular and intermolecular) of the alkoxysilyl groups of the alkoxysilane-added natural rubber, is obtained. Because this modified natural rubber of the present invention combines the flexibility of natural rubber with the rigidity of the hydrolysis condensation structure (siloxane bond) of the alkoxysilyl groups, it is believed to have extremely excellent toughness.

[0012] Here, the inventors have found from their research that toughness is dramatically improved when the ratio of specific alkoxysilane (hereinafter also referred to as "alkoxysilane amount") to 100 parts by mass of rubber content in the latex is 1.0 part by mass or more. It is thought that the crosslink density is dramatically improved by setting the alkoxysilane amount to 1.0 part by mass. Therefore, in the present invention, the alkoxysilane amount is limited to 1.0 part by mass or more.

[0013] As mentioned above, the modified natural rubber of the present invention is believed to be the product of intramolecular or intermolecular hydrolysis and condensation reactions between alkoxysilyl groups in alkoxysilane-added natural rubber. Therefore, its structure is extremely complex, and analyzing its structure is technically impossible, or identifying its structure would require excessive economic expenditure and time. Therefore, there are so-called "impossible or impractical circumstances" that make it impossible to identify the modified natural rubber of the present invention by its manufacturing method.

[0014] [1] Manufacturing method of modified natural rubber First, the method for producing the modified natural rubber of the present invention will be described. The method for producing modified natural rubber of the present invention comprises the steps of: a mixing step of mixing natural rubber latex with 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 so that the ratio of the alkoxysilane to 100 parts by mass of rubber in the latex is 1.0 part by mass or more; a solidification step of solidifying the mixture obtained in the mixing step; and a heat drying step of heat-drying the solidified product obtained in the solidification step.

[0015] Each step will be described below.

[0016] [Mixing process] The mixing step is a step of mixing natural rubber latex (hereinafter also referred to as "natural rubber latex") with 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, so that the ratio of the alkoxysilane (alkoxysilane amount) to 100 parts by mass of rubber in the latex is 1.0 part by mass or more. As described above, it is believed that in the mixing step, a specific group of the specific alkoxysilane undergoes an addition reaction with the carbon atom-carbon atom double bond of the natural rubber, thereby producing a latex of natural rubber to which the specific alkoxysilane has been added (alkoxysilane-added natural rubber).

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

[0018] [Natural rubber latex] The natural rubber latex used in the mixing step is not particularly limited, but examples thereof include field latex obtained by extracting and filtering rubber trees, and concentrated natural rubber latex obtained by processing the field latex. 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, for the reason that the modified natural rubber obtained will have better effects of the present invention. Hereinafter, "the modified natural rubber obtained will have better effects of the present invention" will also be simply referred to as "the modified natural rubber obtained will have better effects of the present invention."

[0019] [Specific alkoxysilane] As described above, in the mixing step, 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 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 this provides better effects of the present invention.

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

[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). There are no particular limitations on R (hydrocarbon group) of the thioester group, but examples include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a group that is a combination of these. The aliphatic hydrocarbon group may be linear, branched, or cyclic. Specific examples of the 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), and linear or branched alkynyl groups (particularly having 2 to 30 carbon atoms). Examples of the 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. The above 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) for reasons such as better effects of the present invention.

[0024] <Alkoxysilane> Alkoxysilane refers to a compound having an alkoxysilyl group (RO-Si≡: where R represents a hydrocarbon group). The alkoxysilyl group may be a monoalkoxysilyl group (RO-Si≡: where R represents a hydrocarbon group), a dialkoxysilyl group ((RO-)2Si<: where R represents a hydrocarbon group, and two Rs may be the same or different), or a trialkoxysilyl group ((RO-)3Si-: where R represents a hydrocarbon group, and three Rs may be the same or different). However, because the effects of the present invention are superior, a dialkoxysilyl group or trialkoxysilyl group is preferred, and a trialkoxysilyl group is more preferred. 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, but for reasons such as better effects of the present invention, a methyl group or an ethyl group is preferred, and an ethyl group is more preferred.

[0025] <Preferred embodiment> For reasons such as better effects of the present invention, 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 a compound represented by the following formula (S5) or a compound represented by the following formula (S), and even more preferably a compound represented by the following formula (S5).

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

[0027] [ka]

[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, and among these, an alkyl group having 1 to 5 carbon atoms is preferred. Specific examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a decyl group, and an octadecyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group, a tolyl group, and a naphthyl group. Specific examples of the alkenyl group having 2 to 10 carbon atoms include a vinyl group, a propenyl group, and a pentenyl group. 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 a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, and a decyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include the above-mentioned R 51 is the same as In the above formula (S5), n represents an integer of 1 to 10, and among these, an integer of 2 to 4 is preferable. In the above formula (S5), x represents a number of 1 to 6, and preferably 2 to 4. 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] [ka]

[0032] In the above formulas (A3) and (A4), R 31 and R 41 are each independently an alkylene group having 1 to 5 carbon atoms, and specific examples thereof include a methylene group, an ethylene group, and a propylene group. Of these, a propylene group is preferred. 31 and R 41 may be the same or different. In the above formulas (A3) and (A4), R 32 and R 42 R each independently represents 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, and among these, those having 3 to 20 carbon atoms are preferred. 32 If is terminal, R 32 R 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, and among these, those having 3 to 20 carbon atoms are preferred. 42 If is terminal, R 42 The definition, specific examples and preferred embodiments of R 32 It is the same as multiple R 32 and R 42 may be the same or different. In the above formulas (A3) and (A4), R 33 and R 43 R each independently represents 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 terminal hydroxyl group or carboxyl group, or a linear or branched alkenyl group having 2 to 30 carbon atoms and having a terminal hydroxyl group or carboxyl group. 43is preferably a group having a hydroxyl group at the terminal. 32 and R 33 is R 32 and R 33 and R may form a ring. 42 and R 43 is R 42 and R 43 A ring may be formed by combining multiple R 33 and R 43 may be the same or different. In the above formula (A3), R 34 represents an alkyl group having 1 to 13 carbon atoms, and among these, an alkyl group having 3 to 10 carbon atoms is preferred. Specific examples of the alkyl group having 3 to 10 carbon atoms include a hexyl group, a heptyl group, and an octyl group. 34 may be the same or different.

[0033] <Example>

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

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

[0036] Si363 [ka]

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

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

[0039] NXT [ka]

[0040] NXT-Low VOC [ka]

[0041] (sulfide group, mercapto group) A specific example of an alkoxysilane having a sulfide group and a mercapto group is 9511D (structure shown below).

[0042] 9511D (wherein Et represents an ethyl group, and m, n, o, and l represent the molar ratio of each repeating unit) [ka]

[0043] (mercapto group, thioester group) A specific example of an alkoxysilane having a mercapto group and a thioester group is NXT-Z (structure shown below).

[0044] NXT-Z (wherein the curved line bonded to the oxygen atom represents an alkyl group having 1 to 30 carbon atoms, and the curved line bonded to one oxygen atom and the other hydroxyl group represents an alkylene group having 1 to 30 carbon atoms). [ka]

[0045] [Mixing process procedure] In the mixing step, the natural rubber latex and the specific alkoxysilane are mixed.

[0046] <Temperature> The temperature in the mixing step is not particularly limited, but is preferably 10 to 30°C, more preferably room temperature, for reasons such as better effects of the present invention.

[0047] <Amount of alkoxysilane> In the mixing step, the natural rubber latex and the specific alkoxysilane are mixed so that the ratio of the specific alkoxysilane (alkoxysilane amount) to 100 parts by mass of the rubber content in the natural rubber latex is 1.0 part by mass.

[0048] The amount of alkoxysilane is preferably 2.0 parts by mass or more, more preferably 5.0 parts by mass or more, and even more preferably 8.0 parts by mass or more, for reasons such as better effects of the present invention. The upper limit of the amount of alkoxysilane is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even 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, for reasons such as better effects of the present invention.

[0049] [Solidification process] The solidification step is a step of solidifying the mixture obtained in the above-mentioned mixing step. As described above, in the solidification step, the mixture (latex) obtained in the mixing step is solidified, and it is believed that natural rubber to which a specific alkoxysilane has been added (alkoxysilane-added natural rubber) is obtained.

[0050] The method for solidifying is not particularly limited, but examples thereof include a method of drying (leaving) at room temperature.

[0051] [Heat drying process] The heat drying step is a step of heat drying the solidified material obtained in the solidification step described above. As described above, the heat drying step is thought to produce a hydrolysis condensation product (intramolecular and intermolecular) of alkoxysilyl groups in natural rubber to which a specific alkoxysilane has been added (alkoxysilane-added natural rubber).

[0052] 〔temperature〕 The temperature in the heat drying step is preferably 40° C. or higher, more preferably 50° C. or higher, for reasons such as better effects of the present invention. There is no particular upper limit to the temperature, but for reasons such as better effects of the present invention, it is preferably 200° C. or lower, more preferably 100° C. or lower.

[0053] [2] Modified natural rubber The modified natural rubber of the present invention is This modified natural rubber is obtained by mixing natural rubber latex with an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group so that the ratio of the alkoxysilane is 1.0 part by mass or more per 100 parts by mass of the rubber content in the latex, solidifying the resulting mixture, and heating and drying the resulting solid.

[0054] The materials and procedures used in the modified natural rubber of the present invention are as described above.

[0055] [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 above-mentioned modified natural rubber of the present invention.

[0056] [Modified natural rubber] The modified natural rubber of the present invention is as described above.

[0057] [Content] In the composition of the present invention, the content of the modified natural rubber of the present invention in the total rubber component is not particularly limited, but is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, particularly preferably 70% by mass or more, and most preferably 90% by mass or more, because the rubber composition exhibits superior toughness and tear resistance. The upper limit of the content of the modified natural rubber of the present invention in the total rubber component is not particularly limited, and is 100% by mass. Hereinafter, "the rubber composition exhibits superior toughness and tear resistance" is also referred to as "the effects of the present invention are superior."

[0058] [Other rubber components] The composition of the present invention may contain a rubber component (other rubber component) other than the modified natural rubber of the present invention. 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), etc. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, etc.

[0059] [Content] In the composition of the present invention, the content of other rubber components in all rubber components is not particularly limited, but in order to achieve better effects of the present invention, it is preferably 90% by mass or less, more preferably 70% by mass or less, even 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 the other rubber components in all rubber components is not particularly limited, and is 0% by mass.

[0060] [Carbon black] The composition of the present invention preferably contains carbon black, as this will provide better effects of the present invention. The carbon black is not particularly limited, and various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, and FEF can be used. The nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited, but is preferably 50 to 200 m for reasons such as the superior effects of the present invention. 2 / g, and 70 to 150m 2 / g is more preferred. Here, the nitrogen adsorption specific surface area (N2SA) is the amount of nitrogen adsorbed onto the surface of carbon black measured according to JIS K6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0061] [Content] In the composition of the present invention, the content of carbon black is not particularly limited, but in order to obtain better effects of the present invention, the content is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, and even more preferably 3 to 10 parts by mass, per 100 parts by mass of the rubber component.

[0062] [silica] The composition of the present invention preferably contains silica, as this will provide better effects of the present invention. The silica is not particularly limited, and any conventionally known silica that is compounded in rubber compositions for use in tires and the like can be used. Specific examples of silica include wet silica, dry silica, fumed silica, and diatomaceous earth. Among these, wet silica is preferred because it provides better effects of the present invention. The silica may be used alone or in combination of two or more types. The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of ​​silica is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferred that the specific surface area be 100 to 300 m 2 / g, and 150 to 200m 2In this specification, the CTAB adsorption specific surface area is a value obtained by measuring the amount of CTAB adsorbed on the silica surface in accordance with JIS K6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method."

[0063] [Content] In the composition of the present invention, the content of silica is not particularly limited, but in order to achieve better effects of the present invention, the content 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, per 100 parts by mass of the rubber component.

[0064] [Silane coupling agents] The composition of the present invention preferably contains a silane coupling agent because it provides better effects of the present invention, etc. 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, and an alkenyloxy group. Of these, an alkoxy group is preferred because it provides better effects of the present invention. When the hydrolyzable group is an alkoxy group, the number of carbon atoms in the alkoxy group is preferably 1 to 16, and more preferably 1 to 4, because it provides better effects of the present invention. Examples of alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, and a propoxy group.

[0065] The organic functional group is not particularly limited, but is preferably a group capable of forming a chemical bond with an organic compound, such as an epoxy group, a vinyl group, an acryloyl group, a methacryloyl group, an amino group, a sulfide group (particularly, 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), and the like. Among these, a sulfide group (particularly a disulfide group or a tetrasulfide group), a mercapto group, and a blocked mercapto group are preferred because they provide better effects of the present invention. The silane coupling agents may be used alone or in combination of two or more.

[0066] The silane coupling agent is preferably a sulfur-containing silane coupling agent because it provides better effects of the present invention.

[0067] Specific examples of the 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, and the like. One of these may be used alone, or two or more may be used in combination.

[0068] In the composition of the present invention, the content of the silane coupling agent is not particularly limited, but in order to obtain better effects of the present invention, it is preferably 2 to 20 mass % relative to the content of silica described above, and more preferably 5 to 15 mass %.

[0069] [Other ingredients] The composition of the present invention may contain, as necessary, components other than the above-mentioned components (other components) within the scope that does not impair the effects or purposes of the composition. Examples of such components include various additives commonly used in rubber compositions, such as 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), and vulcanization accelerators.

[0070] [Application] The composition of the present invention is suitably used for, for example, tires, conveyor belts, hoses, vibration-proof materials, rubber rolls, outer covers of railway vehicles, etc. It is particularly suitable for use in tires (particularly treads). [Example]

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0072] [Production of modified natural rubber] Modified natural rubbers 1 to 4 and comparative modified natural rubbers were produced as follows. Modified natural rubbers 1 to 4 are modified natural rubbers obtained by mixing natural rubber latex with Si69 (alkoxysilane having a sulfide group) or NXT (alkoxysilane having a thioester group), solidifying the resulting mixture, and heating the resulting solidified product, and since the amount of alkoxysilane is 1.0 part by mass or more, they fall under the above-mentioned modified natural rubber of the present invention. On the other hand, comparative modified natural rubber is modified natural rubber obtained by mixing natural rubber latex with Si69 (alkoxysilane having a sulfide group), solidifying the resulting mixture, and heating the resulting solidified product, but since the amount of alkoxysilane is less than 1.0 part by mass, they do not fall under the above-mentioned modified natural rubber of the present invention.

[0073] <Modified natural rubber 1> Modified natural rubber 1 was produced as follows.

[0074] (Mixing process) Natural rubber latex (rubber content: 60% by mass) (100 parts by mass as the rubber component) and 10 parts by mass of Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) (manufactured by Evonik) were mixed and stirred at room temperature for about 1 hour.

[0075] (solidification process) The resulting mixture (latex after the mixing step) was transferred to a tray and dried at room temperature to solidify.

[0076] (heat drying process) The solidified material was dried by heating at 50°C. In this way, a modified natural rubber was obtained. The modified natural rubber obtained is also referred to as modified natural rubber 1.

[0077] <Modified natural rubber 2> A modified natural rubber was obtained in the same manner as for modified natural rubber 1, except that NXT (3-octanoylthio-1-propyltriethoxysilane) (a compound represented by the above formula (S), where in the above formula (S), n = 2, m = 3, and k = 7) (manufactured by Momentive Performance Materials) was used instead of Si69 in the mixing step. The obtained modified natural rubber is also referred to as modified natural rubber 2.

[0078] <Modified natural rubber 3> A modified natural rubber was obtained in the same manner as in the above-mentioned modified natural rubber 1, except that the amount of Si69 in the mixing step was changed to 50 parts by mass. The obtained modified natural rubber is also referred to as modified natural rubber 3.

[0079] <Modified natural rubber 4> A modified natural rubber was obtained in the same manner as in the above-mentioned modified natural rubber 1, except that the amount of Si69 in the mixing step was changed to 1 part by mass. The obtained modified natural rubber is also referred to as modified natural rubber 4.

[0080] <Comparative modified natural rubber> A modified natural rubber was obtained in the same manner as in the above-mentioned modified natural rubber 1, except that the amount of Si69 in the mixing step was changed to 0.5 parts by mass. The obtained modified natural rubber is also referred to as comparative modified natural rubber.

[0081] <Analysis> When the solidified materials of Modified Natural Rubbers 1 to 4 and Comparative Modified Natural Rubber were subjected to acetone extraction after the solidification step, no unreacted Si69 or NXT was detected. From this, it is believed that all of the Si69 or NXT used reacted (addition reaction) with the natural rubber. Furthermore, when the modified natural rubbers 1 to 2, 4, and the comparative modified natural rubber were analyzed after the heat drying process, no alkoxysilyl groups were detected. This suggests that all of the alkoxysilyl groups in Si69 or NXT had reacted (hydrolysis condensation reaction). On the other hand, when the modified natural rubber 3 was analyzed after the heat drying process, a small amount of alkoxysilyl groups was detected. The analysis results suggest that approximately 80% of the alkoxysilyl groups in Si69 had reacted (hydrolysis condensation reaction), with the remainder remaining as alkoxysilyl groups.

[0082] [Preparation of Rubber Composition] The components shown in Table 1 below were mixed in the proportions (parts by mass) shown in the same table. Specifically, first, all components other than sulfur and the vulcanization accelerator were mixed in a 1.8 L (liter) internal mixer at 130°C for 5 minutes, and the masterbatch was discharged. Then, sulfur and the vulcanization accelerator were added to the masterbatch, and the mixture was mixed using an open roll at 80°C to prepare each rubber composition.

[0083] 〔evaluation〕 The rubber compositions thus obtained were evaluated as follows.

[0084] <HS(20℃)> Each of the resulting rubber compositions (unvulcanized) was press-vulcanized in a mold (15 cm×15 cm×0.2 cm) at 160° C. for 20 minutes to prepare a vulcanized rubber sheet. The hardness (Type A durometer hardness) of the obtained vulcanized rubber sheet was evaluated at 20°C in accordance with JIS K6253-3. The results are shown in Table 1. The results are expressed as an index, with the value of Comparative Example 1 being 100. A larger index indicates higher hardness and superior toughness. For practical purposes, an index of 105 or more is preferable.

[0085] <m300> From the vulcanized rubber sheets prepared as described above, JIS No. 3 dumbbell-shaped test pieces (thickness: 2 mm) were punched out in accordance with JIS K6251:2010, and the 300% modulus (stress at 300% deformation) was measured at 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 being 100. A larger index means better toughness. In practice, an index of 103 or more is preferred.

[0086] <Tear> For the vulcanized rubber sheets prepared as described above, the maximum tear strength was measured at a temperature of 23°C and a pulling speed of 500 mm / min using angle-type test pieces (thickness 2 mm) in accordance with JIS K6252:2015 to determine the tear strength. The results are shown in Table 1. The results are expressed as an index, with Comparative Example 1 being 100. A larger index means better tear resistance.

[0087] [Table 1]

[0088] Details of each component in Table 1 are as follows: NR:TSR20 (natural rubber, glass transition temperature: -62°C) Modified natural rubbers 1 to 4: Modified natural rubbers 1 to 4 produced as described above Comparative modified natural rubber: Comparative modified natural rubber produced as described above Carbon black: Show Black N339 (manufactured by Cabot Japan) ·Silica: ZEOSIL 1165MP (CTAB adsorption specific surface area: 159m 2 / g, manufactured by Rhodia) Stearic acid: Bead stearic acid (NOF Corporation) Zinc oxide: Three types of zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.) Silane coupling agent 1: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) Silane coupling agent 2: NXT mentioned above Vulcanization accelerator: Sancerer NS-P (Ouchi Shinko Chemical Industry Co., Ltd.) (N-tert-butyl-2-benzothiazolyl sulfenamide) Sulfur: Kinkaji oil-filled fine sulfur (sulfur content 95.24% by mass, manufactured by Tsurumi Chemical Industry Co., Ltd.)

[0089] 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. In particular, Examples 1 to 4, in which the amount of alkoxysilane in the modified natural rubber was 1.0 to 30 parts by mass, exhibited excellent tear resistance. Of these, Examples 1 and 2, in which the amount of alkoxysilane in the modified natural rubber was 5 to 20 parts by mass, exhibited even better toughness and tear resistance. Furthermore, a comparison between Example 1 and Example 2 revealed that Example 1, in which the specific alkoxysilane used in the modified natural rubber had a polysulfide group, exhibited superior toughness (M300).

[0090] On the other hand, Comparative Examples 1 to 3, which contained unmodified natural rubber instead of the modified natural rubber of the present invention, and Comparative Example 4, which contained modified natural rubber in which the amount of alkoxysilane was less than 1.0 part by mass, had insufficient toughness.

Claims

1. A modified natural rubber obtained by mixing natural rubber latex with an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group so that the ratio of the alkoxysilane per 100 parts by mass of rubber in the latex is 1.0 part by mass or more, solidifying the resulting mixture, and heating and drying the resulting solid, The modified natural rubber, wherein the alkoxysilane has an alkoxysilyl group that is a trialkoxysilyl group.

2. 2. The modified natural rubber according to claim 1, wherein a ratio of the alkoxysilane per 100 parts by mass of a rubber content in the latex is 1.0 to 30 parts by mass.

3. a mixing step of mixing natural rubber latex with an alkoxysilane having at least one group selected from the group consisting of a sulfide group, a mercapto group, and a thioester group so that the ratio of the alkoxysilane to 100 parts by mass of a rubber content in the latex is 1.0 part by mass or more; a solidification step of solidifying the mixture obtained in the mixing step; a heat drying step of heat drying the solidified product obtained in the solidification step, The method for producing a modified natural rubber, wherein the alkoxysilyl group in the alkoxysilane is a trialkoxysilyl group.

4. A rubber composition comprising the modified natural rubber according to claim 1 or 2.

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