Method for producing rubber composition

Abstract

To solve the problem in which: while silica is frequently incorporated into rubber compositions for improving fuel economy and driving performance, natural rubber has difficulty in sufficiently dispersing silica, and the use of a silane coupling agent results in low reactivity and insufficient desired performance.SOLUTION: A method for producing a rubber composition comprises: (1) a modification step of heating and mixing natural rubber latex with a saccharide to modify the natural rubber latex by the saccharide; (2) a drying step of drying the modified product following the modification step; and (3) a mixing step of mixing the dried product following the drying step with silica.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a rubber composition. [Background technology]

[0002] Natural rubber is widely and extensively used in the rubber industry due to its excellent physical properties and low cost. Natural rubber is made from rubber tree sap (natural rubber latex) collected by tapping on rubber plantations. Fresh latex immediately after harvesting contains not only rubber but also water, protein, lipids, inorganic salts, etc., and the rubber particles are protected by the proteins and lipids to form a dispersion liquid. Fresh latex generally contains preservatives such as ammonia to prevent bacterial growth and natural coagulation.

[0003] On the other hand, silica is often compounded into rubber compositions for tires to improve fuel economy and driving performance. However, it is difficult to sufficiently disperse silica in natural rubber, and even when a silane coupling agent is used, the reactivity is low, making it difficult to achieve the desired effect. Therefore, techniques have been proposed to improve the dispersibility of fillers by modifying natural rubber (see, for example, Patent Documents 1 and 2 listed below). However, these modification methods use petroleum-derived compounds, which have a significant environmental impact, and because the modification involves molecular scission, there are concerns that the mechanical properties of the rubber composition may be reduced. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6316716 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-40514 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for producing a rubber composition that can enhance the dispersibility of silica by a method that is simpler than conventional techniques and that suppresses environmental load and molecular chain scission. [Means for solving the problem]

[0006] The present invention provides a method for producing a rubber latex-modified cellulose rubber composition, comprising: (1) a modification step of heating and mixing natural rubber latex and a saccharide to modify the natural rubber latex with the saccharide; (2) a drying step of drying the modified product after the modification step; and (3) A method for producing a rubber composition, comprising a mixing step of mixing the dried product obtained after the drying step with silica. [Effects of the Invention]

[0007] According to the method for producing a rubber composition of the present invention, silica can be dispersed well in natural rubber by a method that is simpler than conventional techniques and that suppresses environmental load and molecular chain scission. As mentioned above, preservatives such as ammonia are added to fresh latex to prevent bacterial growth and natural coagulation. The modification process involves the sequential ene reaction of natural rubber latex with ammonia and the Maillard reaction between amino groups and sugars, modifying the natural rubber latex with the sugars. The presence of OH groups in the sugars causes an interaction with silica, resulting in good dispersion of silica in the natural rubber. This is expected to improve the physical properties of the natural rubber composition. [Brief explanation of the drawings]

[0008] [Figure 1] (1) IR difference spectrum of Example 2 with Comparative Example 1 as the reference for the natural rubber latex after the modification step. DETAILED DESCRIPTION OF THE INVENTION

[0009] The method for producing a rubber composition of the present invention includes (1) a modification step of heating and mixing natural rubber latex and saccharides to modify the natural rubber latex with the saccharides, (2) a drying step of drying the modified product obtained after the modification step, and (3) a mixing step of mixing the dried product obtained after the drying step with silica. Each step will be described below.

[0010] (1) Denaturation process The (1) modification step in the present invention is a step of heating and mixing natural rubber latex and sugars to modify the natural rubber latex with the sugars. The natural rubber latex used in the present invention can be rubber sap collected by tapping at rubber plantations as described above, and fresh latex immediately after collection contains ammonia or the like as a preservative. For example, the ammonia content of the entire natural rubber latex is about 0.4 to 1.0% by mass.

[0011] The sugars used in the present invention include one or more selected from monosaccharides and disaccharides, with monosaccharides being preferred. Examples of monosaccharides include aldoses, ketoses, and derivatives thereof. Examples of aldoses include glyceraldehyde, erythrose, threose, ribose, arabinose, xylose, lyxose, glucose, galactose, allose, altrose, mannose, gulose, idose, and talose. Examples of ketoses include dihydroxyacetone, erythrulose, xylulose, ribulose, fructose, psicose, and sorbose. Examples of disaccharides include disaccharides composed of the above monosaccharides, such as maltose, sucrose, lactose, trehalose, and cellobiose.

[0012] In the (1) modification step, natural rubber latex and sugars are mixed while being heated, and the natural rubber latex is modified with the sugars. The ratio of the natural rubber latex and sugars used in the (1) modification step is, for example, 0.01 to 30 parts by mass, and preferably 0.01 to 5 parts by mass, of the sugars per 100 parts by mass of the natural rubber latex (including preservatives). It is preferable to use water during modification, and the amount of water used is, for example, 1 to 200 parts by mass per 100 parts by mass of the natural rubber latex (including preservatives). In this specification, 100 parts by mass of natural rubber latex is synonymous with 100 parts by mass of the total fresh latex. The heating temperature is preferably 70 to 130°C, and more preferably 60 to 90°C. The mixing time is preferably 0.01 to 24 hours, more preferably 3 to 12 hours. There is no need to set special conditions for the mixing method, and for example, a known mixer may be used.

[0013] In the (1) modification step, a portion of the silica described below may be used, and the natural rubber latex, saccharides, and silica may be heated and mixed. This configuration provides the effect of further increasing dispersibility due to interactions between the silica, saccharides, and rubber. When silica is used in the (1) modification step, the amount of silica is, for example, 1 to 50 parts by mass, and preferably 1 to 20 parts by mass, per 100 parts by mass of natural rubber latex (including preservatives).

[0014] (2) Drying process Next, in the present invention, the modified product obtained in the (1) modification step is dried in the (2) drying step. The drying temperature is, for example, 40 to 100°C, preferably 40 to 60°C, and the drying time is preferably 0.1 to 12 hours, more preferably 1 to 6 hours. During the (2) drying step, the ammonia preservative volatilizes and the natural rubber latex coagulates to form a solid.

[0015] (3) Mixing process Next, in the present invention, the dried product obtained in the drying step (2) is mixed with silica in the mixing step (3). The silica is not particularly limited, but examples thereof include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. These may be used alone or in combination of two or more. It is also suitable to use silica derived from biomass materials such as rice husks. If the sugars are derived from natural sources, the petroleum-derived materials used in the present invention are not used, which is environmentally preferable. (3) In the mixing step, the mixing time is preferably 0.01 to 1 hour, more preferably 0.01 to 0.25 hours. There is no need to set special conditions for mixing, and for example, a known mixer may be used under normal conditions for mixing rubber and silica.

[0016] In the (3) mixing step, the amount of silica used is preferably 5 to 200 parts by mass, more preferably 5 to 100 parts by mass, per 100 parts by mass of natural rubber latex (including preservatives). Even when silica is used in the (1) modification step, the total amount of silica used is preferably in the above-mentioned ratio. According to the production method of the present invention, by going through the steps (1) to (3), the natural rubber latex is modified with the sugars, and the presence of OH groups in the sugars causes an interaction with the silica, resulting in good dispersion of the silica in the natural rubber.

[0017] The rubber composition obtained by the production method of the present invention contains at least natural rubber and may contain various conventionally known additives as other components. The weight-average molecular weight (Mw) of the natural rubber is not particularly limited, but is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000, to achieve superior effects of the present invention. In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are values ​​calculated using standard polystyrene standards obtained by gel permeation chromatography (GPC). Examples of additives include various additives commonly used in rubber compositions, such as vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, silane coupling agents, zinc oxide, various fillers, antioxidants, plasticizers, and reinforcing materials. These additives can be kneaded into a composition by a conventional method and used for vulcanization or crosslinking. The amounts of these additives used can be the same as those used in the past. The additives are preferably added and mixed in the above-mentioned (3) mixing step.

[0018] The rubber composition obtained by the present invention is preferably used for tires, more preferably pneumatic tires. Pneumatic tires can be manufactured according to conventional manufacturing methods and can be filled with air, inert gases such as nitrogen, and other gases. [Example]

[0019] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0020] Examples 1 to 3 and Comparative Example 1 Natural rubber latex containing 0.6% by mass of ammonia as a preservative was prepared and used in the following experiments.

[0021] (1) Denaturation process Natural rubber latex, water, and glucose were mixed using an aluminum block thermostatic bath equipped with a stirrer as a mixer according to the formulation (parts by mass) shown in Table 1. During mixing, conditions of a heating temperature of 80°C and a mixing time of 6 hours were adopted, and (1) the modification step was carried out to obtain a modified product. (2) Drying process The modified product obtained in the (1) modification step was dried at a drying temperature of 50°C for 3 hours, and then subjected to the (2) drying step to obtain a dried product. As shown in Table 1, various natural rubbers, NR1 to NR5, were obtained. (3) Mixing process The components excluding the vulcanization accelerator and sulfur were kneaded in the formulation (parts by mass) shown in Table 2 below using a Brabender mixer at 135°C, 60 rpm, and for 5 minutes, and the rubber was then discharged from the mixer and cooled to room temperature. The rubber was then re-added to the mixer, and the vulcanization accelerator and sulfur were added, followed by further kneading at 90°C, 40 rpm, and for 3 minutes to obtain a rubber composition. 0.3 g of each rubber composition (unvulcanized) was cut, placed in a wire mesh basket, and immersed in 300 mL of toluene at room temperature for 48 hours, then removed and dried. The mass of the sample was measured and the amount of bound rubber was calculated using the following formula. We also investigated the Payne effect, which is described below. The results are shown in Table 2.

[0022] <Amount of bound rubber> The results are expressed as an index, with the value of Comparative Example 1 being 100. The larger the index, the more bound rubber (rubber reacted with silica) there is, and the higher the dispersibility of silica in the rubber composition. Bound rubber mass = [(mass of sample after toluene immersion and drying) - (mass of silica and zinc oxide)] / (mass of rubber component) <Pain Effect> Each of the resulting rubber compositions (unvulcanized) was press-vulcanized in a mold (15 cm×15 cm×0.2 cm) at 160° C. for 15 minutes to prepare a vulcanized rubber sheet. The shear strain modulus G' at 0.28% strain and the shear strain modulus G' at 30.0% strain were measured for the vulcanized rubber sheet using a shear strain tester (RPA2000, manufactured by α-Technology Co., Ltd.), and the difference G'0.28 (MPa) - G'30.0 (MPa) was calculated as the Payne effect. The results are expressed as an index, with Comparative Example 1 being 100. A smaller index indicates better silica dispersibility.

[0023] Example 4 Examples 1 to 3 and Comparative Example 1 were repeated, except that 10 parts by mass of the total 50 parts by mass of silica used was used in the (1) modification step and mixed with natural rubber latex, water, and sugars. The results are shown in Table 2.

[0024] Comparative Example 2 Examples 1 to 3 and Comparative Example 1 were repeated except that the (1) modification step was not performed, the (2) drying step and the (3) mixing step of the natural rubber latex were performed, and glucose was added during the (3) mixing step. The results are shown in Table 2.

[0025] [Table 1]

[0026] [Table 2]

[0027] *1: NR (natural rubber obtained by the above manufacturing method) *2: Glucose (manufactured by Kanto Chemical Co., Ltd.) *3: Xylose (manufactured by Kanto Chemical Co., Ltd.) *4: Silica (manufactured by Solvay Fine Chemical Additives (Qingdao) Co., Ltd., product name ZEOSIL 1165MP) *5: Silane coupling agent (Si69 manufactured by Evonik) *6: Zinc oxide (Zinc oxide type 3 manufactured by Seido Chemical Industry Co., Ltd.) *7: Stearic acid (NOF Corporation Beads Stearic Acid YR) *8: Anti-aging agent (Flexis Santoflex 6PPD) *9: Sulfur (Kinka brand oil-filled fine sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.) *10: Vulcanization accelerator (product name: Sancerer CM-G, manufactured by Sanshin Chemical Industry Co., Ltd.)

[0028] As is clear from Tables 1 and 2 above, the unvulcanized rubber compositions in each example had a high bound rubber amount and a Payne effect reduced to 70 or less, indicating that silica was well dispersed in the natural rubber. The bound rubber amount and Payne effect are generally correlated. In these examples, the state of modification of the rubber varied depending on the sugar concentration and type. However, by undergoing steps (1) to (3) of the present invention, the interaction between natural rubber and silica was favorably controlled, providing a rubber composition with improved silica dispersibility. Furthermore, in Example 4, where silica is present during rubber modification, the dispersion of silica is better. In contrast, in Comparative Example 1 (1), no sugars were used in the modification step, and therefore the amount of bound rubber was low. Comparative Example 2 is an example in which glucose was not used in the (1) modification step but was used in the (3) mixing step, resulting in a low amount of bound rubber and a small reduction in the Payne effect.

[0029] Fig. 1 shows the IR difference spectrum of the natural rubber latex after the (1) modification step in Example 2 relative to Comparative Example 1. From Fig. 1, it can be seen that the peak at 1090-1020 cm resulting from the ene reaction is -1 C-N bond, 1640cm from the Maillard reaction -1 The C=O bond and sugar modification are confirmed at 3300cm -1 The OH bond was confirmed.

[0030] The present invention includes the following aspects. Embodiment 1: (1) a modification step of heating and mixing natural rubber latex and sugars to modify the natural rubber latex with the sugars; (2) a drying step of drying the modified product after the modification step; and (3) A method for producing a rubber composition, comprising a mixing step of mixing the dried product obtained after the drying step with silica. Embodiment 2: The method for producing a rubber composition according to embodiment 1, wherein a part of the silica used in the (3) mixing step is used in the (1) mixing step, and the (1) mixing step is a step of heating and mixing the natural rubber latex, the saccharides, and the silica, and modifying the natural rubber latex with the saccharides. Embodiment 3: 3. The method for producing a rubber composition according to embodiment 1 or 2, wherein the saccharide is at least one selected from monosaccharides and disaccharides. Embodiment 4: 4. The method for producing a rubber composition according to any one of embodiments 1 to 3, wherein the heating temperature in the (1) modification step is 60 to 90°C. Embodiment 5: 5. The method for producing a rubber composition according to any one of embodiments 1 to 4, wherein the total amount of silica used is 5 to 200 parts by mass per 100 parts by mass of the natural rubber latex. Embodiment 6: 6. The method for producing a rubber composition according to any one of embodiments 1 to 5, wherein the rubber composition is a rubber composition for tires.

Claims

1. (1) a modification step of heating and mixing natural rubber latex and a sugar to modify the natural rubber latex with the sugar; (2) a drying step of drying the modified product after the modification step; and (3) A method for producing a rubber composition, comprising a mixing step of mixing the dried product obtained after the drying step with silica.

2. 2. The method for producing a rubber composition according to claim 1, wherein a part of the silica used in the (3) mixing step is used in the (1) mixing step, and the (1) mixing step is a step of heating and mixing the natural rubber latex, the saccharides, and the silica, and modifying the natural rubber latex with the saccharides.

3. 2. The method for producing a rubber composition according to claim 1, wherein the saccharide is at least one selected from the group consisting of monosaccharides and disaccharides.

4. 2. The method for producing a rubber composition according to claim 1, wherein the heating temperature in the modification step (1) is 60 to 90°C.

5. 2. The method for producing a rubber composition according to claim 1, wherein the total amount of silica used is 5 to 200 parts by mass per 100 parts by mass of the natural rubber latex.

6. 2. The method for producing a rubber composition according to claim 1, wherein the rubber composition is a rubber composition for tires.

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