JP7151151B2 - Natural rubber composition, rubber composition for tire, and method for producing tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a natural rubber composition and a rubber composition for tires using the same.

Natural rubber (NR) used in the rubber industry is solidified sap (latex) collected from a rubber tree called Hevea brasiliensis, which is cultivated in tropical regions. As a solidification method, it is produced by coagulating with an acid such as formic acid, making it into a sheet, and drying it, or by allowing it to coagulate naturally in a cup for extracting latex at a rubber plantation, or by adding acid to the cup to coagulate it. There is a method in which the cup lump obtained by the above method is repeatedly pulverized, washed, dried and then pressed.

Since it is produced as described above, natural rubber contains many non-rubber components such as proteins, lipids and sugars in addition to the polyisoprene component. Therefore, these components putrefy during the storage period prior to drying, causing offensive odors. In particular, cup lumps tend to have a long storage period due to storage in farms, storage in processing factories, and transportation, and are prone to odor problems. In recent years, however, natural rubber made from cup lumps has been widely used in tire applications because of ease of production and cost. The putrid odor of natural rubber has become a problem not only in natural rubber processing factories but also in rubber product manufacturing factories such as tires, as it deteriorates the working environment of the factories and affects the environment around the factories.

Furthermore, after production, natural rubber has a storage period until it is processed. During this period, the viscosity increases and it hardens. There is an influence such as not being able to knead, and it may also adversely affect the physical properties of the tire after processing.

Patent Literature 1 discloses a technique for reducing odor by adding a proteolytic enzyme and a surfactant to natural rubber latex and reacting them to remove proteins, which are one of the causes of putrefaction.

Patent Literature 2 discloses a technique for reducing odor by adding an antioxidant to natural rubber latex and further lowering the drying temperature.

Patent Document 3 describes a natural rubber containing natural rubber that achieves constant viscosity over a long period of time by blending natural rubber with an aminoguanidine compound as a viscosity stabilizing agent and an odor suppressing agent, and that has significantly reduced odor. It is reported that compositions can be provided.

JP-A-8-81505 JP 2011-74392 A JP 2015-117323 A

However, the methods described in Patent Document 1 and Patent Document 2 can only be applied when latex is used as a raw material, and there is a problem that the odor cannot be reduced with regard to natural rubber made from cup lump as a raw material. In addition, in the method described in Patent Document 3, since most of the aminoguanidine compounds are strong acids, the pH of the compound becomes close to acidic, and in the case of a silica compound tire composition such as a studless compound, silica and cup There is a problem that the reaction of the ring agent becomes worse.

Therefore, the present invention provides a method for producing an odor-reduced and viscosity-stabilized natural rubber composition that can be used regardless of whether it is latex or cup lump, a natural rubber composition obtained by the production method, and An object of the present invention is to provide a tire rubber composition containing the natural rubber composition, and a tire comprising a tire member composed of the tire rubber composition.

In view of the above problems, the present inventors have found that by bringing natural rubber into contact with an aqueous citric acid solution and then mixing it with a predetermined amount of a hydrazide compound, it is possible to reduce the odor of the resulting natural rubber while maintaining a constant viscosity. I found that I could do it, and completed the present invention.

That is, the present disclosure
[1] A first step of contacting natural rubber with an aqueous citric acid solution;
A second step of mixing the natural rubber and the hydrazide compound after the first step, wherein the hydrazide compound is added in an amount of 0.1 to 3 parts by mass, preferably 1.5 to 2.0 parts by mass, based on 100 parts by mass of the natural rubber. A method for producing a natural rubber composition of 5 parts by mass,
[2] The method for producing a natural rubber composition according to [1] above, wherein the drying temperature during the production process of the natural rubber composition is 140°C or lower, preferably 125°C or lower, more preferably 120°C or lower;
[3] A method for producing a natural rubber composition according to [1] or [2] above, which comprises the step of immersing natural rubber in an aqueous solution of a basic substance;
[4] The method for producing a natural rubber composition according to [3] above, wherein the aqueous solution of the basic substance contains a surfactant;
[5] A natural rubber composition produced by the production method described in [1] to [4] above,
[6] A rubber composition for tires containing the natural rubber composition described in [5] above; and [7] A tire comprising a tire member composed of the rubber composition for tires described in [6] above.

A method for producing a natural rubber composition according to the present invention, comprising the first step of contacting the natural rubber with an aqueous citric acid solution, and the second step of mixing the natural rubber and a predetermined amount of hydrazide compound after the first step. According to this, it is possible to provide a natural rubber composition with a reduced odor peculiar to natural rubber and a constant viscosity, and a composition for tires containing the natural rubber composition, and a rubber composition for tires. It is possible to provide a tire comprising a molded tire component.

<Method for producing natural rubber composition>
The method for producing a natural rubber composition of the present invention comprises a first step of bringing natural rubber into contact with an aqueous citric acid solution, and a second step of mixing the natural rubber with a predetermined amount of hydrazide compound after the first step. In this production method, by mixing with a predetermined amount of hydrazide compound after contact with an aqueous citric acid solution, the obtained natural rubber composition has a reduced odor and a constant viscosity natural rubber composition that suppresses an increase in viscosity over time. becomes rubber.

The odor of natural rubber is caused by the decomposition of proteins, lipids, sugars, etc., which are non-rubber components of natural rubber, during storage and decomposition during drying, resulting in the generation of odor-causing substances such as lower fatty acids and accompanying aldehydes. This is thought to be the cause. In addition, it is considered that the putrid proteins and sugars are contained in the water contained in the natural rubber and in the gaps between the rubber components. Curing during storage is believed to occur by cross-linking with aldehydes.

The effect of the present invention described above is that the hydrazino group (—NHNH ₂ ) of the hydrazide compound reacts with the carbonyl group (C=O moiety) of the aldehydes to trap the aldehydes, thereby reducing odor and aldehyde cross-linking. It is thought that it is possible to prevent hardening during storage. Furthermore, by bringing the aqueous citric acid solution into contact with the natural rubber in the previous step of mixing the hydrazide compound, the metal ions are removed, the PO (degradation index) and PRI (oxidation index) are improved, and it is thought that this contributes to constant viscosity. The combination of such contact with the aqueous citric acid solution and mixing with the hydrazide compound further promotes the reaction between the aldehydes and the hydrazide compound, resulting in a significant odor reduction effect and a constant viscosity effect due to early prevention of aldehyde cross-linking. it is conceivable that. In addition, since the hydrazide group also reacts with the carbonyl group of the carboxylic acid attached to the lower fatty acid, it is thought that many of the odorous components of natural rubber can be trapped.

Moreover, the present invention can be applied to a production process using cup lumps instead of latex, and can stably reduce the odor of natural rubber regardless of raw materials.

Further, the lower fatty acid generated in a small amount even in the above production method can be neutralized and removed by immersing the sheet in an aqueous solution of a basic substance, thereby further reducing the odor. Furthermore, adding a small amount of surfactant makes it easier to extract odor-causing components inside, and by making it easier to penetrate basic substances, odor components are more efficiently neutralized and removed, resulting in even more odor. can be reduced.

The natural rubber used as a raw material is raw latex collected by tapping rubber trees (field latex), concentrated latex obtained by concentrating raw latex by centrifugation or creaming (purified latex, high ammonia latex by adding ammonia in the usual way). , LATZ latex stabilized with zinc white and TMTD (tetramethylthiuram disulfide) and ammonia), as well as natural coagulation in rubber plantation cups or cups for collecting latex. Cup lumps obtained by a method of solidification by adding an acid are mentioned, and cup lumps are preferred from the viewpoint of workability, cost, and availability of raw materials.

The citric acid aqueous solution can be used by dissolving commercially available citric acid in water, and the concentration of citric acid is usually preferably 0.01% by mass or more, more preferably 0.1% by mass or more. Also, the concentration of citric acid is generally preferably 30% by mass or less, more preferably 20% by mass or less. When the citric acid concentration in the aqueous citric acid solution is within the above range, the PRI-improving effect tends to be further improved.

The hydrazide compound is not particularly limited, but specifically, general formula (1):
Ra- _{CONHNH2 (} 1)
(In the formula, R _a is any one of an alkyl group having 1 to 30 carbon atoms, an unsaturated hydrocarbon group having 2 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, and an aryl group having 6 to 30 carbon atoms. indicates.)
A compound represented by the general formula (2):
NH2NHCO- _Rb - _CONHNH2 ( ₂ )
(Wherein, R _b is a divalent alkylene group having 1 to 30 carbon atoms, a divalent unsaturated hydrocarbon group having 2 to 30 carbon atoms, a divalent cycloalkylene group having 3 to 30 carbon atoms, divalent any aryl having 6 to 30 carbon atoms.)
The compound represented by is mentioned.

Specific examples of the compound represented by the general formula (1) include acetohydrazide, propionic hydrazide, butyl hydrazide, lauric hydrazide, palmitic hydrazide, stearic hydrazide, cyclopropyl hydrazide, cyclohexyl hydrazide, cycloheptyl hydrazide, Benzoic hydrazide, salicylic hydrazide, o-, m- or p-tolylhydrazide, p-methoxyphenylhydrazide, 3,5-xylylhydrazide, 1-naphthylhydrazide, etc., represented by the general formula (2) Specific examples of the compound include adipic acid dihydrazide, isophthalic acid dihydrazide, sebacic acid dihydrazide, salicylic acid dihydrazide, dodecanediohydrazide, and the like.

In the production of natural rubber, it is common to repeat crushing and washing after coagulation, followed by molding and drying. Prior to crushing, the latex coagulated solid is passed through a scraper and rolls to reduce the water content. It can be confirmed that the odor is further improved by using it.

The natural rubber latex coagulate is not particularly limited, and examples include unsmoked sheet (latex coagulated with acid, sheeted and dried), smoked sheet (smoked unsmoked sheet), and cups. There are lumps (latex spontaneously solidified in the cup), slabs or mixtures thereof.

These coagulates are then repeatedly cut, washed, and formed into sheets, and finally cut into small particles (crumbs). The grain size of the crumbs is preferably 10 mm or less, more preferably 2 to 5 mm, from the viewpoint of ease of hot air drying.

(First step)
The first step of contacting the aqueous citric acid solution with the natural rubber is not particularly limited as long as it is performed before adding the hydrazide compound, but it is carried out by sprinkling the aqueous citric acid solution at the stage of forming a sheet by creper treatment. is preferred. This process facilitates sheeting, removes metal ions that promote deterioration of natural rubber, improves PO (deterioration index) and PRI (oxidation index), and suppresses viscosity increase over time. Alternatively, the natural rubber and the aqueous citric acid solution can be brought into contact by immersing the cut product in the aqueous citric acid solution during the cutting and washing steps. The particle size of the cut product when it comes into contact with the aqueous citric acid solution is, for example, 200 mm or less, and preferably 100 mm to 1 mm from the viewpoint of improving the effects of the present invention. The particle size of the cut product can be adjusted by combining a plurality of known slab cutters, rotary cutters, sheeting by creper treatment, and cutting by shredder treatment.

The contact time between the natural rubber and the aqueous citric acid solution is, for example, preferably 20 minutes or longer, more preferably 30 minutes or longer. By setting the contact time to 20 minutes or more, the reaction between the metal ions and citric acid tends to reach almost parallel and the effect tends to be maximized, that is, the effect of stabilizing the viscosity tends to increase. In other words, the citric acid aqueous solution is sufficiently immersed in the cut pieces of natural rubber to remove metal ions, which tends to improve PO and PRI. Further, the contact time between the natural rubber and the aqueous citric acid solution is preferably 60 minutes or less, more preferably 50 minutes or less. Even if the contact time is longer than 60 minutes, there is no change in the effect on constant viscosity, and there is no particular change in the effect of constant viscosity. By setting the contact time to 60 minutes or less, the amount of modification of non-rubber components is small, and only unnecessary metal elements tend to be removed, and the natural rubber molecules themselves deteriorate due to long-term contact with the acidic aqueous solution. tend to be able to prevent

It is preferable that the cut product that has been completely contacted with the aqueous citric acid solution is further subjected to a drying step after undergoing each step of forming a sheet by a creper treatment, washing, and pulverizing (crumbing) by a shredder treatment.

(Second step)
The second step of mixing the hydrazide compound with the natural rubber treated with the aqueous citric acid solution is not particularly limited as long as it is after the treatment with the aqueous citric acid solution, but the natural rubber before drying is immersed or sprayed. It can be added as a raw material, or it can be kneaded into the rubber after drying. In such a case, the hydrazide compound is preferably dissolved in a solvent or the like before blending. Alternatively, it is desirable to dissolve it in water during the final water washing step.

The amount of the hydrazide compound added to 100 parts by mass of natural rubber is 0.1 parts by mass or more, preferably 1 part by mass or more, and more preferably 1.5 parts by mass or more. If the amount of the hydrazide compound added is less than 0.1 parts by mass, the amount of aldehyde trapping is insufficient, and it is difficult to obtain the effect of reducing odor and increasing the constant viscosity. The amount of hydrazide compound added is 3 parts by mass or less, preferably 2.5 parts by mass or less, and more preferably 2 parts by mass or less. Even if the amount of the hydrazide compound added exceeds 3 parts by mass, there is a tendency that it is difficult to obtain an effect commensurate with the cost.

In the drying step, the drying temperature is preferably 140° C. or lower, more preferably 125° C. or lower, and even more preferably 120° C. or lower. By setting the drying temperature to 140° C. or less, there is a tendency to reduce the possibility of causing deterioration of the physical properties of natural rubber. The lower limit of the drying temperature in the drying step is not particularly limited as long as it is a temperature at which the rubber can be dried, but the drying temperature is preferably 75° C. or higher from the viewpoint of facilitating evaporation of water used in washing. , 100° C. or higher is more preferable.

Odor components of natural rubber can be further reduced by immersing it in an aqueous solution of a basic substance. Specifically, the method is not particularly limited as long as it is a method of bringing the coagulated rubber into contact with a basic substance. are mentioned. Aqueous solutions of basic substances can be prepared by diluting and dissolving each basic substance in water. The treatment with an aqueous solution of a basic substance may be performed on a natural rubber sheet cut into small pieces. The step of immersing in the aqueous solution of the basic substance is not particularly limited, but after the first step of contacting the aqueous citric acid solution with the natural rubber, the natural rubber treated with the aqueous citric acid solution is mixed with a hydrazide compound. It is preferable to carry out before the second step. Immersion of natural rubber in an aqueous solution of a basic substance is not particularly limited as long as it is after treatment with an aqueous citric acid solution, and can be performed during crumbing, that is, cutting, washing with water, and sheeting. When treatment with an aqueous citric acid solution is performed in the second cutting, washing, and sheeting, it can be performed in the subsequent cutting, washing, and sheeting, and since the crumbs are smaller, it should be performed in the final washing step. is preferred, and it is more preferred to carry out before the drying step.

Although the basic substance is not particularly limited, basic inorganic compounds are preferable from the viewpoint of the ability to remove proteins and the like. Basic inorganic compounds include metal hydroxides such as alkali metal hydroxides and alkaline earth metal hydroxides; metal carbonates such as alkali metal carbonates and alkaline earth metal carbonates; alkali metal hydrogencarbonates and the like. metal phosphates such as alkali metal phosphates; metal acetates such as alkali metal acetates; metal hydrides such as alkali metal hydrides; and ammonia.

Alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Alkaline earth metal hydroxides include magnesium hydroxide, calcium hydroxide, barium hydroxide and the like. Alkali metal carbonates include lithium carbonate, sodium carbonate, potassium carbonate and the like. Alkaline earth metal carbonates include magnesium carbonate, calcium carbonate, barium carbonate and the like. Alkali metal hydrogencarbonates include lithium hydrogencarbonate, sodium hydrogencarbonate, potassium hydrogencarbonate and the like. Alkali metal phosphates include sodium phosphate, sodium hydrogen phosphate and the like. Alkali metal acetates include sodium acetate, potassium acetate and the like. Examples of alkali metal hydrides include sodium hydride and potassium hydride. Among them, from the viewpoint of saponification efficiency and ease of treatment, metal hydroxides, metal carbonates, metal hydrogen carbonates, metal phosphates, and ammonia are preferable, and sodium hydroxide, which is an alkali metal hydroxide, and water Potassium oxide is more preferred. These basic substances may be used alone or in combination of two or more.

The content of the basic substance in 100% by mass of the aqueous solution of the basic substance is preferably 0.1% by mass or more, more preferably 0.3% by mass or more. By setting the concentration of the basic substance to 0.1% by mass or more, there is a tendency that odorous components can be sufficiently removed. The content of the basic substance in 100% by mass of the aqueous solution of the basic substance is preferably 10% by mass or less, more preferably 5% by mass or less. By setting the concentration of the basic substance to 10% by mass or less, there is a tendency to obtain efficiency commensurate with the cost.

The treatment temperature in the treatment of immersing natural rubber in an aqueous solution of a basic substance is not specifically defined, but is preferably 10 to 50°C, more preferably 15 to 35°C. The treatment time is usually 5 minutes or longer, preferably 10 minutes or longer, and more preferably 30 minutes or longer. If the treatment time is set to 5 minutes or more, there is a possibility that the odor reduction effect may not be obtained satisfactorily. Although there is no upper limit, from the viewpoint of productivity, it is preferably 48 hours or less, more preferably 24 hours or less, and particularly preferably 16 hours or less.

The aqueous solution of the basic substance preferably contains a surfactant. Addition of a surfactant tends to improve the removal efficiency of odorous components and increase the odor reduction effect. In addition, the affinity between the hydrophobic rubber surface and the aqueous solution of the basic substance is improved, which tends to improve the reaction rate and shorten the treatment time.

At least one of anionic surfactants, nonionic surfactants and amphoteric surfactants can be used as the surfactant. Examples of anionic surfactants include carboxylic acid-based, sulfonic acid-based, sulfate-based, and phosphate-based anionic surfactants. Examples of nonionic surfactants include polyoxyalkylene ester-based, polyoxyalkylene ester-based, polyhydric alcohol fatty acid ester-based, glycolipid ester-based, and alkylpolyglycoside-based nonionic surfactants. Amphoteric surfactants include, for example, amphoteric surfactants of amino acid type, betaine type, amine oxide type and the like.

The content of the surfactant in 100% by mass of the aqueous solution of the basic substance is preferably 0.01% by mass or more, more preferably 0.05% by mass or more. By setting the content of the surfactant in the aqueous solution of the basic substance to 0.01% by mass or more, there is a tendency that the removal efficiency of the odorous component can be improved. The content of the surfactant in the aqueous solution of the basic substance is preferably 5% by mass or less, more preferably 3% by mass or less. By setting the content of the surfactant in the aqueous solution of the basic substance to 5% by mass or less, there is a tendency to obtain an effect commensurate with the cost.

After removing the substance used for treating the basic substance, washing treatment is performed as necessary. The washing method includes, for example, a method of diluting the rubber with water, washing and then centrifuging, and a method of allowing the rubber to float by allowing it to stand still and discharging only the aqueous phase to take out the rubber.

The treatment temperature may be appropriately selected, but is preferably 10 to 50°C, more preferably 15 to 35°C. Also, the treatment time is generally preferably 3 seconds or longer, more preferably 10 seconds or longer, and still more preferably 30 seconds or longer. If the time is less than 3 seconds, the odorous component cannot be sufficiently neutralized and removed, and the effects of the present invention may not be obtained satisfactorily. Although there is no upper limit, it is preferably 24 hours or less, more preferably 10 hours or less, and still more preferably 5 hours or less from the viewpoint of productivity.

The natural rubber composition obtained by the production method of the present invention achieves a constant viscosity over a long period of time and has a significantly reduced odor. This eliminates the need to masticate the natural rubber before use, for example, when it is used in a rubber composition for tires, and suppresses the generation of offensive odors throughout the manufacturing process. Therefore, the natural rubber composition obtained by the production method of the present invention is preferably used as a rubber component of a rubber composition for tires.

<Rubber composition for tires>
The rubber composition for tires containing the natural rubber composition obtained by the production method of the present invention is optionally blended with other components generally used in the production of rubber compositions for tires in addition to the above-described natural rubber composition. can be By way of example, such optional ingredients include other rubber components, fillers, silane coupling agents, liquid SBR, oils, tackifying resins, waxes, antioxidants, stearic acid, zinc oxide, vulcanizing agents, vulcanizing agents, Sulfur accelerator and the like.

(rubber component)
The rubber is not particularly limited, but natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene (SIR), styrene isoprene butadiene rubber ( SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), and the like. A diene rubber may be used in combination. Among these, it is more preferable to contain SBR from the viewpoint of obtaining better grip performance.

SBR is not particularly limited, and includes solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), modified SBR (modified S-SBR, modified E-SBR), and the like. Examples of modified SBR include terminal and/or main chain modified SBR, tin, modified SBR coupled with a silicon compound (condensate, branched structure, etc.), hydrogenated SBR (SBR), etc. are mentioned. The SBR may also be oil extended.

BR is not particularly limited, and includes high-cis 1,4-polybutadiene rubber (high-cis BR), butadiene rubber containing 1,2-syndiotactic polybutadiene crystals (SPB-containing BR), modified butadiene rubber (modified BR), Examples include rare earth BR. BR may be used in combination.

(filler)
Examples of fillers include, but are not limited to, carbon black, silica, diatomaceous earth, calcium carbonate, sodium hydroxide, and talc.

Carbon black is not particularly limited. Examples of carbon black include furnace black, acetylene black, thermal black, channel black, and graphite. These carbon blacks may be used in combination.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 40 m ² /g or more, more preferably 60 m ² /g or more, from the viewpoint of improving durability. In addition, N ₂ SA is preferably 300 m ² /g or less, more preferably 140 m ² /g or less, from the viewpoint of ensuring good dispersibility of carbon black and good thermal conductivity. preferable. The N ₂ SA of carbon black is a value measured by the BET method according to ASTM D3037-81.

The content of carbon black is preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component, because the obtained rubber composition can obtain sufficient ultraviolet crack resistance and reinforcing properties, and the thermal conductivity is excellent. 3 parts by mass or more is more preferable. Moreover, the content of carbon black is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, from the viewpoint of excellent elongation at break and crack growth.

Silica is not particularly limited. By way of example, silica commonly used in the tire industry can be used. Examples of silica include those manufactured and sold by Rhodia, Evonik Degussa, and the like.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 20 m ² /g or more, more preferably 30 m ² /g or more, from the viewpoint of obtaining sufficient reinforcing properties. The N ₂ SA of silica is preferably 250 m ² /g or less, more preferably 240 m ² /g or less. The N ₂ SA of silica is a value measured by the BET method according to ASTM D3037-81.

When silica is used as the filler, it preferably contains a silane coupling agent. The silane coupling agent is not particularly limited, but any silane coupling agent conventionally used in combination with silica in the rubber industry can be used in combination, for example, bis(3-triethoxysilylpropyl ) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl sulfides such as benzothiazolyl tetrasulfide and 3-triethoxysilylpropyl methacrylate monosulfide; mercaptos such as 3-mercaptopropyltrimethoxysilane; vinyls such as vinyltriethoxysilane; glycidoxy-based such as γ-glycidoxypropyltriethoxysilane; nitro-based such as 3-nitropropyltrimethoxysilane; chloro-based such as 3-chloropropyltrimethoxysilane; These silane coupling agents may be used alone or in combination of two or more. Among these, sulfide-based compounds are preferred, and bis(3-triethoxysilylpropyl)disulfide is particularly preferred, because of their good reactivity with silica.

When a silane coupling agent is used, the content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, relative to 100 parts by mass of silica. The content of the silane coupling agent is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of silica. When the content of the silane coupling agent is 2 parts by mass or more, the dispersibility of the filler in the rubber composition can be improved. In addition, when the content of the silane coupling agent is 20 parts by mass or less, the filler is well dispersed in the rubber composition, and the reinforcement of the obtained tire is likely to be improved.

(Liquid diene polymer)
Liquid diene-based polymers include liquid styrene-butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), and the like. be done. Among these, liquid SBR is preferable because it provides a good balance between wear resistance and stable steering stability performance during running. The liquid diene-based polymer in the present specification is a diene-based polymer that is in a liquid state at room temperature (25° C.).

The polystyrene-equivalent weight average molecular weight (Mw) of the liquid diene-based polymer measured by gel permeation chromatography (GPC) is preferably 1.0×10 ³ or more from the viewpoints of abrasion resistance, breaking properties, and durability. 3.0×10 ³ or more is more preferable. From the viewpoint of productivity, it is preferably 2.0×10 ⁵ or less, more preferably 1.5×10 ⁴ or less. The Mw of the liquid diene-based polymer in this specification is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

When the liquid diene-based polymer is contained, the content of the liquid diene-based polymer is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, relative to 100 parts by mass of the rubber component. Moreover, the content of the liquid diene-based polymer is preferably 30 parts by mass or less, more preferably 20 parts by mass or less. When the content of the liquid diene-based polymer is within the above range, there is a tendency that good wet grip performance and an effect of improving initial wet grip performance are likely to be obtained.

(tackifying resin)
Examples of the tackifying resin include resins commonly used in conventional rubber compositions for tires, such as aromatic petroleum resins. Examples of aromatic petroleum resins include phenolic resins, coumarone-indene resins, terpene resins, styrene resins, acrylic resins, rosin resins, and dicyclopentadiene resins (DCPD resins). Examples of phenolic resins include Cholecin (manufactured by BASF) and Tackyroll (manufactured by Taoka Chemical Industry Co., Ltd.). Examples of the coumarone-indene resin include coumarone (manufactured by Nichinuri Chemical Co., Ltd.), Esclone (manufactured by Nippon Steel Chemical Co., Ltd.), and neopolymer (manufactured by Nippon Petrochemical Co., Ltd.). Styrene resins include, for example, Sylvatraxx (registered trademark) 4401 (manufactured by Arizona Chemical Co.). Examples of terpene resins include TR7125 (manufactured by Arizona Chemical Co.) and TO125 (manufactured by Yasuhara Chemical Co.).

The softening point of the tackifying resin is preferably 40°C or higher, more preferably 60°C or higher. A softening point of 40° C. or higher tends to provide sufficient grip performance. Also, the softening point is preferably 120° C. or lower, more preferably 100° C. or lower. By setting the softening point to 120° C. or lower, there is a tendency to obtain sufficient grip performance. The softening point of the resin is the temperature at which the ball descends when the softening point specified in JIS K 6220-1:2001 is measured with a ring and ball type softening point measuring device.

The content of the tackifying resin with respect to 100 parts by mass of the rubber component is preferably 3 parts by mass or more, more preferably 5 parts by mass or more. By setting the content of the tackifying resin to 3 parts by mass or more, there is a tendency for sufficient grip performance to be obtained. Moreover, 30 mass parts or less are preferable, and, as for content of tackifying resin, 25 mass parts or less are more preferable. By setting the content of the tackifying resin to 30 parts by mass or less, there is a tendency that sufficient wear resistance performance and good fuel economy performance can be obtained.

(oil)
Oil is not particularly limited. By way of example, the oils are paraffinic process oils, aromatic process oils, naphthenic process oils, castor oil (for vulcanized bladders), and the like. A process oil may be used in combination.

When oil is contained, the content of oil is not particularly limited. To give an example, the process oil has little effect on mold releasability, and from the viewpoint of plasticizing rubber and improving filler dispersion, it is preferable that the amount of process oil is 1 part by mass or more with respect to 100 parts by mass of the rubber component. , 2 parts by mass or more. In addition, the amount of oil is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, relative to 100 parts by mass of the rubber component, since a large amount of grip-improving resin can be blended. However, in high-viscosity, high-grip formulations for racing, the oil content may be 30 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

(Antiaging agent)
The anti-aging agent is not particularly limited. The anti-aging agent can be used by arbitrarily selecting from various anti-aging agents that have been commonly used in rubber compositions. Examples of anti-aging agents include quinoline anti-aging agents, quinone anti-aging agents, phenol anti-aging agents, and phenylenediamine anti-aging agents. An antioxidant may be used in combination.

When an anti-aging agent is contained, the content of the anti-aging agent is not particularly limited. For example, the content of the anti-aging agent is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the rubber component. Moreover, the content of the anti-aging agent is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, with respect to 100 parts by mass of the rubber component. When the content of the anti-aging agent is within the above range, the filler tends to have improved oxidation deterioration resistance and good tensile properties. Moreover, the resulting rubber composition is easily kneaded. Anti-aging agents (for example, phenylenediamine-based anti-aging agents) have a slower bleeding speed than waxes containing branched alkanes and the like. However, for example, when the phenylenediamine anti-aging agent is contained in an amount of 4 parts by mass or more with respect to 100 parts by mass of the rubber component, the bleeding speed increases and the static ozone resistance can be improved even immediately after production.

In addition, as stearic acid, zinc oxide, etc., those conventionally used in the rubber industry can be used.

(vulcanizing agent)
The vulcanizing agent is not particularly limited, and those commonly used in the rubber industry can be used, but those containing sulfur atoms are preferred, such as powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, Insoluble sulfur etc. are mentioned.

(Vulcanization accelerator)
Vulcanization accelerators are not particularly limited, but examples include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, and imidazoline. and xanthate-based vulcanization accelerators. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferable because the effect of improving the initial wet grip performance can be more preferably obtained.

<Method for producing a rubber composition for tires>
The method for producing the rubber composition for tires is not particularly limited, and known methods can be used. For example, it can be produced by kneading each of the above components using a rubber kneading apparatus such as an open roll, Banbury mixer, or internal kneader, followed by vulcanization. For example, in the kneading step, kneading is performed at 80° C. to 170° C. for 1 minute to 30 minutes, and in the vulcanizing step, vulcanization is performed at 130° C. to 190° C. for 3 minutes to 20 minutes.

<Tire Manufacturing Method>
A tire having a tire member composed of the tire rubber composition can be produced by a conventional method using the tire rubber composition. That is, the tire composition obtained by blending the compounding agent with the diene rubber component as necessary is extruded in accordance with the shape of a specific tire member, and together with other tire members on a tire building machine. An unvulcanized tire is formed by bonding and molding by a normal method, and a tire can be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizer.

Tires can be used for tires in general, such as tires for passenger cars, high-performance tires for passenger cars, tires for heavy loads such as trucks and buses, and tires for racing.

The present invention will be specifically described based on examples. The invention is not limited to these examples.

Various chemicals used in Examples (including Reference Examples when referred to comprehensively; the same shall apply hereinafter) and Comparative Examples are shown below.
・Raw rubber 1: Cup lump ・Raw rubber 2: Natural rubber latex ・Hydrazide compound 1: Propionic acid hydrazide/hydrazide compound 2: Otsuka Chemical Co., Ltd.: isophthalic acid dihydrazide/hydrazide compound 3: Stearic acid hydrazide/citric acid manufactured by Tokyo Chemical Industry Co., Ltd.: manufactured by Wako Pure Chemical Industries, Ltd. Basic substance 1: sodium carbonate (Na ₂ CO ₃ ) manufactured by Sigma-Aldrich Co., Ltd.
- Basic substance 2: Sodium bicarbonate ( _NaHCO3 ) manufactured by Sigma-Aldrich
・ Surfactant 1: Emar E-27C (sodium polyoxyethylene lauryl ether sulfate, active ingredient 27% by mass) manufactured by Kao Corporation
・Surfactant 2: Emal 20C (sodium polyoxyethylene lauryl ether sulfate, active ingredient 25%) manufactured by Kao Corporation

(Examples and Comparative Examples)
According to the formulation shown in Table 1 or 2, the raw rubber (for Reference Example 5, a sheet obtained by adding formic acid to natural rubber latex collected from a normal rubber plantation and hardening it beforehand is used) is cut. , Washing with water, forming into a sheet with a creper, and cutting to a diameter of about 10 mm. In the course of cutting, washing with water, and sheeting, the cut product is immersed in a 10% by mass aqueous citric acid solution for the time shown in Table 1 or 2. Finally, a crumb of 5 mm or less is obtained. After drying the obtained crumbs with a dryer at the temperature shown in Table 1 or 2 for 4 hours, an aqueous solution of each hydrazide compound shown in Table 1 or 2 was added to 100 parts by mass of natural rubber, followed by rolling with a twin-screw roll. It is kneaded to obtain a natural rubber composition for each test. Only in Comparative Example 5, the hydrazide compound was added at the timing of the initial water washing step before immersion in the aqueous citric acid solution. The basic substance is an aqueous solution having a concentration described in Table 1 or 2, and an aqueous solution containing a surfactant at a concentration described in Table 1 or 2 is used. After contact with the aqueous citric acid solution is completed, it is dried. A natural rubber sheet is immersed in the solution prior to the process.

Each index shown in Table 1 or 2 or a value close thereto is obtained by performing the following evaluation on the test natural rubber composition obtained as described above.

<Odor component index>
Main substances causing the odor of natural rubber include lower fatty acids and their aldehydes such as acetic acid, valeric acid, isovaleric acid, isovaleric aldehyde and butyric acid. Therefore, the peak area ratio of the above components contained in natural rubber detected using Head-Space GCMS is corrected by the olfactory threshold of each component, and the sum of all is taken as the amount of odor components. As an evaluation,
Odor component index = 1/(amount of odor component in each example/amount of odor component in Comparative Example 1) x 100
is represented by A larger index indicates less odorous components.

<Constant viscosity index (Mooney viscosity increase value)>
Mooney viscosity (ML 1+4/130°C) immediately after production and Mooney viscosity (ML _{1+4 /} 130°C) one month after production (stored at 30°C) were measured. Viscosity is indexed with 100 being the Mooney viscosity immediately after manufacture. The Mooney viscosity was measured at 130°C according to the method for measuring Mooney viscosity according to JIS K 6300-1 "Unvulcanized rubber-Physical properties-Part 1: Determination of viscosity and scorch time by Mooney viscometer". Perform under temperature conditions. It should be noted that the closer the value is to 100, the better the constant viscosity.

In this embodiment, the target value of the odor component index is 125 or more, and the target value of the constant viscosity index is 90-110.

Claims (7)

a first step of contacting natural rubber with an aqueous citric acid solution;
A method for producing a natural rubber composition, comprising a second step of mixing a natural rubber and a hydrazide compound after the first step, wherein the hydrazide compound is added in an amount of 0.1 to 3 parts by mass based on 100 parts by mass of natural rubber. and
The contact between the natural rubber and the aqueous citric acid solution is carried out by immersing the cut pieces of natural rubber in the aqueous citric acid solution,
The hydrazide compound has the general formula (2):
NH2NHCO- _Rb - _CONHNH2 ( ₂ )
(Wherein, R _b is a divalent alkylene group having 1 to 30 carbon atoms, a divalent unsaturated hydrocarbon group having 2 to 30 carbon atoms, a divalent cycloalkylene group having 3 to 30 carbon atoms, divalent any arylene group having 6 to 30 carbon atoms.)
A method for producing a natural rubber composition, which is a compound represented by 2. The method for producing a natural rubber composition according to claim 1, wherein the drying temperature during the production process of the natural rubber composition is 140[deg.] C. or less. 3. The method for producing a natural rubber composition according to claim 1 or 2, comprising the step of immersing the natural rubber in an aqueous solution of a basic substance. 4. The method for producing a natural rubber composition according to claim 3, wherein the aqueous solution of said basic substance contains a surfactant. The method for producing a natural rubber composition according to any one of claims 1 to 4, wherein the concentration of the aqueous citric acid solution is 10% by mass or more and 30% by mass or less. A method for producing a rubber composition for tires, comprising the step of kneading raw materials for kneading containing the natural rubber composition produced by the production method according to any one of claims 1 to 5. A step of processing the tire rubber composition produced by the method for producing a tire rubber composition according to claim 6 into a tire member;
and a step of manufacturing a tire using the tire member.