JP2018100375A - Method for producing rubber polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of obtaining a rubber polymer which improves storage elastic modulus and reduces loss elastic modulus.SOLUTION: A production method includes a step of adjusting a reaction system, which is obtained by adding at least a radical generator, a buffer agent having a pH of 7 and a buffer region on its both sides and a hydrophilic organic solvent having a boiling point of 80°C or higher to a latex containing a rubber polymer, where an amount of the hydrophilic organic solvent to be blended is 3-10 pts.mass with respect to 100 pts.mass of the rubber polymer in the latex, an amount of the radical generator to be blended is 0.05-0.3 pts.mass with respect to 1 pts.mass of the hydrophilic organic solvent, to a temperature at which a radical is generated from the radical generator.SELECTED DRAWING: None

Description

  The present invention relates to a production method for producing a modified rubber polymer using a rubber polymer as a raw material.

  Various means for improving the physical properties of rubber polymers have been studied. For example, as a means for improving the quality of natural rubber having many variations in physical properties due to impurities, Patent Document 1 discloses a method for improving the fracture resistance and wear resistance of natural rubber by increasing the high molecular weight component of natural rubber. Patent Document 2 discloses a method for improving crack resistance while maintaining the processability of natural rubber. Patent Document 3 discloses a high storage stability and a raw material such as an adhesive or a pressure-sensitive adhesive. And a method for obtaining a stable liquid epoxidized natural rubber having a narrow molecular weight distribution is disclosed.

  On the other hand, physical properties required for rubber polymers differ greatly depending on the use, and particularly rubber components blended in a rubber composition for tires are required to have high storage elastic modulus and low loss elastic modulus. However, methods for improving the storage elastic modulus of the rubber polymer and reducing the loss elastic modulus are not disclosed in Patent Documents 1 to 3, and are not yet known.

International Publication Number WO2013 / 168640 JP 2013-221669 A JP 2004-176013 A

  An object of this invention is to provide the manufacturing method of a rubber polymer in which the storage elastic modulus improved and the loss elastic modulus was reduced in view of the above point.

  The method for producing a rubber polymer according to the present invention comprises at least a latex containing a rubber polymer, a radical generator, a buffer having pH 7 and buffer regions on both sides thereof, and a hydrophilic organic solvent having a boiling point of 80 ° C. or higher. The amount of the hydrophilic organic solvent is 3 to 10 parts by mass with respect to 100 parts by mass of the rubber polymer in the latex, and the amount of the radical generator is 1 mass of the hydrophilic organic solvent. The production method has a step of adjusting the reaction system to a temperature at which radicals are generated from the radical generator, and 0.05 to 0.3 parts by mass with respect to parts.

  The radical generator may be a persulfate.

  The buffer may be a phosphate.

  The hydrophilic organic solvent can be propanol.

  The latex may be natural rubber latex.

  According to the production method of the present invention, a rubber polymer having improved storage elastic modulus and reduced loss elastic modulus can be obtained.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  The method for producing a rubber polymer according to the present embodiment comprises adding a radical generator, a buffer having a pH of 7 and a buffer region on both sides thereof, and a hydrophilic organic solvent having a boiling point of 80 ° C. or higher to latex, To generate radicals.

  The latex is not particularly limited, but is preferably a diene rubber latex. Specifically, natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), Examples of the latex include nitrile rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. Among these, natural rubber latex is preferable. Since natural rubber latex has many impurities and large variations in physical properties, the effects of the present invention are remarkably recognized. As the natural rubber latex, a concentrated latex, a fresh latex called a field latex, or the like can be used, and if necessary, a concentration adjusted by adding water may be used.

  The hydrophilic organic solvent is not particularly limited as long as the boiling point is 80 ° C. or higher, but is a lower aliphatic alcohol such as propanol or isopropanol, or a polyhydric alcohol such as 1,3-butylene glycol, propylene glycol, dipropylene glycol or glycerin. These may be used alone or in combination of two or more. More preferred is propanol, and more preferred is 2-propanol. When the boiling point is 80 ° C. or higher, the amount of the solvent that volatilizes in the reaction system in which the radical reaction is performed can be minimized.

  The amount of the hydrophilic organic solvent is preferably 3 to 10 parts by mass and more preferably 4 to 9 parts by mass with respect to 100 parts by mass of the rubber polymer in the latex. When the amount is 3 parts by mass or more, a radical reaction with respect to the rubber polymer is likely to occur, and when the amount is 10 parts by mass or less, the micelles of the rubber polymer are easily stabilized.

  Although it does not specifically limit as a radical generator, For example, an azo compound, an organic peroxide, etc. are mentioned, The thing which generate | occur | produces a radical by heat irradiation and the thing which generate | occur | produces a radical by light irradiation are contained. Examples of the azo compound include azobisisobutyronitrile (AIBN), 1,1′-azobis (cyclohexanecarbonitrile) (ABCN), and the like. Examples of organic peroxides include persulfate, di-tert-butyl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, methyl ethyl ketone peroxide, and the like. Among these, persulfate is preferable, and sodium persulfate and potassium persulfate are more preferable.

  The compounding amount of the radical generator is preferably 0.05 to 0.3 parts by mass, more preferably 0.05 to 0.1 parts by mass with respect to 1 part by mass of the hydrophilic organic solvent. When the amount is 0.05 to 0.3 parts by mass, the radical reaction tends to occur uniformly with respect to the rubber polymer.

  The buffer is not particularly limited as long as it has pH 7 and buffer regions on both sides thereof. For example, phosphate is preferable, and sodium phosphate and potassium phosphate are more preferable. A buffer having “pH 7 and a buffer region on both sides” has a buffer region straddling an acidic region and a basic region, and becomes acidic or basic in a chemical equilibrium state. To do. The pH range in which the buffering action can be obtained is generally said to be the range of pKa-1 to pKa + 1 of the buffering agent. Therefore, the pKa of the buffering agent is preferably larger than 6, preferably 6.2 or more. More preferably, it is 6.4 or more. Moreover, it is preferable that it is less than 8, It is more preferable that it is 7.8 or less, It is further more preferable that it is 7.6 or less.

  Although the compounding quantity of a buffering agent is not specifically limited, It is preferable that it is 0.005-0.7 mass part with respect to 100 mass parts of rubber polymers in latex, and it is 0.017-0.66 mass part. Is more preferable.

  In the reaction system of the production method according to the present embodiment, a surfactant may be included depending on the type of latex subjected to the reaction. For example, natural rubber latex contains ammonia, and ammonia has a role of stabilizing the micelles of the rubber polymer in the latex. However, if ammonia is contained, the pH of the reaction system is unlikely to change, and the effects of the present invention may not be obtained. Therefore, by adding a nonionic surfactant to the reaction system, it is possible to suppress the influence of ammonia on the pH and to stabilize the micelle instead of ammonia. It is possible to create an environment where an effect can be easily obtained. As the nonionic surfactant, a general one can be used, and is not particularly limited, and examples thereof include sodium lauryl sulfate.

  The metal salt contained in the radical generator, the buffer, and the surfactant is preferably a salt made of a common metal from the viewpoint of minimizing the influence in the reaction system, for example, a radical generator. When is a sodium salt, the buffering agent and the surfactant are also preferably sodium salts.

  The manufacturing method according to the present embodiment includes a step of adjusting the temperature of the reaction system including at least the latex, the radical generator, the buffer, and the organic solvent to a temperature at which radicals are generated from the radical generator. The temperature adjustment can be performed by heating and cooling as necessary while stirring the reaction system by means usually used.

  More specifically, for example, it can be performed by the following operation. That is, water and a surfactant, sodium lauryl sulfate, are added to natural rubber latex and stirred. Next, an aqueous solution in which 2-propanol, which is a hydrophilic organic solvent, disodium hydrogen phosphate, which is a buffering agent, and sodium peroxodisulfate, which is a radical generator, is dissolved, is prepared and charged into the natural rubber latex prepared above. . After these mixed solutions are placed in a water bath at room temperature, they are heated to a temperature at which radicals are generated from the radical generator, for example, 40 to 70 ° C. and stirred. Subsequently, the rubber component is taken out by adding ethanol to make it a poor solvent, washed with distilled water, and then dried with a hot-air circulating dryer, whereby a modified natural rubber latex can be produced. Thus, the storage elastic modulus can be improved and the loss elastic modulus can be reduced by performing a radical reaction of the rubber polymer in the presence of pH 7 and a buffer having a buffer region on both sides thereof. The mechanism is not clear, but can be estimated as follows. That is, a radical is generated by the radical generator, and a part of the molecular chain of the rubber polymer is cut by the radical. At this time, the reaction system is temporarily made basic by the buffer, so that the cut portions of the rubber polymer are bonded again. It is considered that when the rubber polymer is once cut and bonded again, the part where the molecular chains of the rubber polymer are entangled in a complicated manner is eliminated, and the distribution of molecular chains and the molecular weight distribution are optimized.

  The rubber polymer obtained by the production method according to the present embodiment includes reinforcing fillers such as carbon black and silica, process oil, zinc white, stearic acid, softener, and plasticizer that are used in the normal rubber industry. Further, compounding chemicals such as wax, anti-aging agent, vulcanizing agent, vulcanization accelerator and the like can be appropriately blended within a normal range to obtain a tire rubber composition.

  The rubber composition for tires can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll or other mixer. That is, in the first mixing stage, the rubber polymer produced is mixed with a reinforcing filler and other additives except for the vulcanizing agent and the vulcanization accelerator, and then the resulting mixture is finally mixed. A rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator in stages.

  The rubber composition thus obtained includes pneumatic tires for passenger cars, treads for various tires such as heavy duty tires such as trucks and buses, sidewalls, rim strips, covering rubbers such as belt cords and carcass cords, inner It can be used for parts such as liners and bead fillers. It can be suitably used for sidewalls and the like that require particularly high rigidity.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

<Manufacturing method 1>
0.6 parts by mass of sodium lauryl sulfate and 50 parts by mass of water were added to 100 parts by mass of the natural rubber latex and stirred for 24 hours. In addition, 4 parts by mass of 2-propanol, 0.34 parts by mass of disodium hydrogen phosphate, and 0.2 parts by mass of sodium peroxodisulfate were dissolved in 50 parts by mass of water and charged into the natural rubber latex. These mixed solutions were placed in a water bath at room temperature, heated to 60 ° C., and then stirred for 24 hours. Next, ethanol was added to make it a poor solvent, and the rubber component was taken out, washed with distilled water, and then dried at 30 ° C. for 24 hours with a hot-air circulating dryer to obtain a solid of modified rubber 1.

  The modified rubbers 2 to 8 were produced by the same method as the production method 1 except that the blends shown in Table 1 were changed.

  Using a Banbury mixer, in accordance with the formulation (parts by mass) shown in Table 2, in the first kneading step (non-pro kneading step), components other than the vulcanization accelerator and sulfur were added and kneaded (discharge temperature = 100 ° C.), then In the second kneading step (professional kneading step), the obtained kneaded product was kneaded with a vulcanization accelerator and sulfur (discharge temperature = 80 ° C.) to prepare a rubber composition.

Details of each component in Tables 1 and 2 are as follows.
・ Rubber Latex: Natural Rubber Latex “HA-NR” manufactured by Residex Co., Ltd., DRC (Dry Rubber Content) = 60 mass%
-Raw rubber: solid content obtained by drying the rubber latex-Modified rubber 1-8: Modified rubber 1-8 obtained by the above production method
・ Hydrophilic organic solvent: 2-propanol Nacalai Tesque Co., Ltd. Nacalai Standard Class 1 ・ Buffer: Disodium hydrogen phosphate Nacalai Tesque Co., Ltd. Nacalai Standard Class 1 ・ Radical generator: Sodium peroxodisulfate Nacalai Tesque ( Nacalai Standard Grade 1, Surfactant: Sodium Lauryl Sulfate Nacalai Tesque, Ltd. Nacalai Standard Grade 1, Carbon Black: Tokai Carbon Co., Ltd. “Seast 3”
・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Corporation
Silane coupling agent: bis (3-triethoxysilylpropyl) tetrasulfide, “Si69” manufactured by Evonik
・ Process oil: “X-140” manufactured by Japan Energy Co., Ltd.
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
Anti-aging agent: “NOCRACK 6C” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Sulfur: Hosoi Chemical Co., Ltd. “Powder sulfur for rubber 150 mesh”
・ Vulcanization accelerator: “Noxeller CZ” manufactured by Ouchi Shinsei Chemical Co., Ltd.

  About each obtained rubber composition, the test piece of the predetermined shape was produced by vulcanizing for 20 minutes at 160 degreeC. About the obtained test piece, using a dynamic viscoelasticity measuring apparatus (USM company fully automatic viscoelasticity analyzer VR-7110), a dynamic viscoelasticity test is carried out on the conditions of frequency 50Hz, static strain 10%, and dynamic strain 2%. The storage elastic modulus and the loss elastic modulus were evaluated. Each evaluation method is as follows.

-Storage elastic modulus E ': The storage elastic modulus E' was measured under the condition of a temperature of 60 ° C, and an index with Comparative Example 1 as 100 is shown. The larger the value, the higher the storage elastic modulus E ′ and the higher the rigidity.

Loss elastic modulus E ″: The loss elastic modulus E ″ is measured under the condition of a temperature of 60 ° C., and the reciprocal is indicated by an index with Comparative Example 1 as 100. The larger the value, the better the loss elastic modulus E ″.

  The results are as shown in Table 2. Examples 1 to 3 were superior to Comparative Example 1 in both the storage elastic modulus E ′ and loss elastic modulus E ″ of the rubber polymer.

  In Comparative Examples 2 to 6, the blending amount of the radical generator with respect to 1 part by mass of the hydrophilic organic solvent is more than 0.3 parts by mass. Compared with Comparative Example 1, Comparative Example 2 has a deteriorated storage elastic modulus E ′. In Comparative Examples 3 to 6, both the storage elastic modulus E ′ and the loss elastic modulus E ″ deteriorated. This is presumably due to the radical reaction being dominant and the molecular chain of the rubber polymer being cut more than necessary. .

  The rubber polymer obtained by the production method of the present invention can be used in tire rubber compositions for various tires such as passenger cars, light trucks and buses.

Claims (5)

To the latex containing the rubber polymer, a radical generator, pH 7 and a buffer having a buffer region on both sides thereof, and a hydrophilic organic solvent having a boiling point of 80 ° C. or higher are added to form a reaction system,
The amount of the hydrophilic organic solvent is 3 to 10 parts by mass with respect to 100 parts by mass of the rubber polymer in the latex,
The amount of the radical generator is 0.05 to 0.3 parts by mass with respect to 1 part by mass of the hydrophilic organic solvent,
A method for producing a rubber polymer, comprising the step of adjusting the reaction system to a temperature at which radicals are generated from the radical generator.   The method for producing a rubber polymer according to claim 1, wherein the radical generator is a persulfate.   The method for producing a rubber polymer according to claim 1, wherein the buffer is a phosphate.   The method for producing a rubber polymer according to claim 1, wherein the hydrophilic organic solvent is propanol. The method for producing a rubber polymer according to any one of claims 1 to 4, wherein the latex is natural rubber latex.