JP2011213766A - Manufacturing method of hydrogenated natural rubber, and rubber member obtained by using hydrogenated natural rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a hydrogenated natural rubber permitting the control of a hydrogenation ratio and to provide a rubber member excellent in heat resistance using the hydrogenated natural rubber.SOLUTION: The manufacturing method of a hydrogenated natural rubber comprises a hydrogenation catalyst addition step for adding a hydrogenation catalyst to a latex of a natural rubber or a deprotenized natural rubber and a hydrogenation step for causing hydrogen to react with the latex having the hydrogenation catalyst added thereto to hydrogenate at least a part of a carbon-carbon double bond of the natural rubber or the deprotenized natural rubber, where a royal water solution of palladium chloride comprising palladium chloride dissolved in royal water is used as the hydrogenation catalyst. The rubber member is manufactured by crosslinking a rubber composition comprising the hydrogenated natural rubber obtained by the manufacturing method.

Description

  The present invention relates to a method for producing hydrogenated natural rubber obtained by hydrogenating at least part of carbon-carbon double bonds of natural rubber, and a rubber member obtained by crosslinking a rubber composition containing hydrogenated natural rubber.

  Natural rubber has excellent properties such as high tensile strength and low heat generation due to vibration. For this reason, it is conventionally used for various rubber products such as tires and belts. In addition, natural rubber is being reviewed as an alternative material for synthetic rubber from the viewpoints of carbon dioxide emission regulations that contribute to global warming and the problem of exhaustion of petroleum resources. However, natural rubber has a problem that heat resistance, oil resistance, ozone resistance and the like are inferior to those of synthetic rubber.

  For example, in the automotive field, the temperature in the engine room tends to increase with fuel efficiency reduction and exhaust gas regulation measures. For this reason, anti-vibration rubber materials used for engine mounts and the like are required to have high heat resistance so that they can be used in higher temperature environments. Therefore, in order to use natural rubber as an anti-vibration rubber material, physical properties such as heat resistance must be improved.

  As a method for improving physical properties while utilizing the characteristics of natural rubber, for example, modification of natural rubber by grafting, epoxidation, hydrogenation, etc. is known (for example, Patent Documents 1 to 4, Non-Patent Documents). 1 and 2).

JP 2007-277343 A JP 2008-184572 A JP 2008-308601 A JP 2006-131807 A

Kojiro Ishizuka and three others, “Hydrogenation of natural rubber latex”, “Polymer Preprints, Japan” (Proceedings of the Society of Polymer Science), 2008, Vol. 57, no. 1, 3Pc157 Junichi Inoue and three others, “Synthesis of hydrogenated natural rubber”, “Polymer Preprints, Japan” (Proceedings of the Society of Polymer Science), 2007, Vol. 56, no. 2, 2Pa035

  When hydrogenating natural rubber, it is difficult to control the hydrogenation rate (ratio of hydrogenation of carbon-carbon double bonds in natural rubber) according to conventional methods. For this reason, there is a problem that it is difficult to obtain a hydrogenated natural rubber having a desired hydrogenation rate. Therefore, hydrogenated natural rubber and non-hydrogenated natural rubber are blended, or a plurality of hydrogenated natural rubbers having different hydrogenation rates are blended to improve physical properties such as heat resistance. However, since the compatibility of both is not good, the effect of improving physical properties by blending is small.

  This invention is made | formed in view of such a situation, and makes it a subject to provide the manufacturing method of the hydrogenated natural rubber which can control a hydrogenation rate. Another object of the present invention is to provide a rubber member having excellent heat resistance using the hydrogenated natural rubber obtained by the production method.

(1) The present inventor considered the reason why it is difficult to control the hydrogenation rate in the conventional method as follows. That is, as described in Patent Document 4 and Non-Patent Documents 1 and 2, in a hydrogenation reaction using natural rubber latex, as a hydrogenation catalyst, a chloride obtained by dissolving solid palladium chloride in water. An aqueous palladium solution is used. Alternatively, a palladium chloride / hydrochloric acid solution in which solid palladium chloride is dissolved in hydrochloric acid is used. In any solution, it is difficult to completely dissolve palladium chloride. For this reason, palladium chloride (PdCl ₂ ) and palladium tetrachloride ions ([PdCl ₄ ] ²⁻ ) are mixed in the solution depending on the degree of dissolution. That is, the dissolution state of palladium chloride differs for each hydrogenation reaction.

If the dissolved state of palladium chloride is different, the variation in particle diameter of palladium particles (Pd particles) produced by subsequent reduction increases. Specifically, the particle diameter of Pd particles produced through PdCl ₂ is considered to be larger than that of Pd particles produced through [PdCl ₄ ] ²⁻ . It is presumed that the hydrogenation reaction proceeds faster as the particle size of the Pd particles is smaller. Therefore, if the variation in the particle diameter of the Pd particles is large and the variation differs for each hydrogenation reaction, the reaction rate changes even if the hydrogenation reaction is performed under the same conditions. As a result, the hydrogenation rate of the resulting hydrogenated natural rubber varies.

  The method for producing a hydrogenated natural rubber of the present invention based on such knowledge includes a hydrogenation catalyst addition step of adding a hydrogenation catalyst to latex of natural rubber or deproteinized natural rubber, and the hydrogenation catalyst. A hydrogenation step in which hydrogen is reacted with the latex to which at least a part of carbon-carbon double bonds in the natural rubber or the deproteinized natural rubber is hydrogenated, The hydrogenation catalyst is characterized by being an aqueous palladium chloride solution in which palladium chloride is dissolved in aqua regia.

According to the method for producing hydrogenated natural rubber of the present invention, a palladium chloride aqua solution in which palladium chloride is dissolved in aqua regia is used as a hydrogenation catalyst. Aqua regia is a liquid in which concentrated hydrochloric acid and concentrated nitric acid are mixed at a volume ratio of 3: 1. By using aqua regia as a solvent, solid palladium chloride can be completely dissolved. Accordingly, palladium chloride exists as palladium tetrachloride ions ([PdCl ₄ ] ²⁻ ) in the aqueous palladium chloride solution. That is, the dissolved state of palladium chloride can be stabilized.

  By stabilizing the dissolved state of palladium chloride, the variation in the particle diameter of the Pd particles produced by the subsequent reduction is reduced. Therefore, the reaction rate of the hydrogenation reaction can be controlled by adjusting the particle size of the Pd particles. As a result, a hydrogenated natural rubber having a desired hydrogenation rate can be produced.

  (2) The rubber member of the present invention is obtained by crosslinking a rubber composition containing a hydrogenated natural rubber produced by the method for producing a hydrogenated natural rubber of the present invention.

  As described above, according to the method for producing a hydrogenated natural rubber of the present invention, a hydrogenated natural rubber having a desired hydrogenation rate can be easily obtained. Therefore, depending on the use, it is possible to obtain a rubber member having desired physical properties by preparing a rubber composition containing hydrogenated natural rubber having a suitable hydrogenation rate, and molding and crosslinking the rubber composition. it can. For example, the rubber member of the present invention using hydrogenated natural rubber having high heat resistance is suitable as a vibration isolating member used for automobiles and the like.

It is a graph which shows the relationship of the hydrogenation rate with respect to hydrogenation reaction time. It is a graph which shows the relationship between the hydrogenation reaction time and the hydrogenation rate in the hydrogenated natural rubber of Examples 1-4.

  Hereinafter, embodiments of the method for producing hydrogenated natural rubber and the rubber member of the present invention will be described. The method for producing hydrogenated natural rubber and the rubber member of the present invention are not limited to the following embodiments, and modifications, improvements, etc. that can be made by those skilled in the art are made without departing from the scope of the present invention. It can be implemented in various forms.

<Method for producing hydrogenated natural rubber>
The method for producing a hydrogenated natural rubber of the present invention includes a hydrogenation catalyst addition step and a hydrogenation step. First, the hydrogenation catalyst addition step will be described. In this step, a hydrogenation catalyst is added to latex of natural rubber or deproteinized natural rubber (hereinafter referred to as “latex” as appropriate).

  In this step, either natural rubber latex or deproteinized natural rubber latex from which protein has been removed may be used. As the natural rubber latex, for example, a field latex or a commercially available ammonia-treated latex may be used. The latex rubber content (dry rubber mass, hereinafter the same) concentration is not particularly limited. For example, in consideration of the productivity of hydrogenated natural rubber, the latex rubber concentration is preferably 6% by mass or more. It is more preferable that it is 18 mass% or more. On the other hand, when the rubber content concentration of the latex becomes high, it tends to aggregate. Therefore, the rubber concentration is desirably 60% by mass or less.

  In order to stabilize the latex and facilitate the hydrogenation reaction, a surfactant may be added to the latex. As the surfactant, any of an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used. Examples of the anionic surfactant include carboxylic acid type, sulfonic acid type, and sulfuric acid ester type. Examples of the cationic surfactant include alkylamine salt type and imidazolinium salt type. Examples of nonionic surfactants include polyoxyalkylene ethers and polyhydric alcohol fatty acid esters.

  As the hydrogenation catalyst, an aqueous palladium chloride solution is used. The aqueous solution of palladium chloride can be prepared by dissolving palladium chloride in aqua regia. The concentration of palladium chloride in the aqueous palladium chloride solution is not particularly limited. For example, considering the rate of the hydrogenation reaction, the palladium chloride concentration is preferably 0.1 mol / L or more. On the other hand, considering the solubility of palladium chloride, the palladium chloride concentration is preferably 6 mol / L or less. Moreover, what is necessary is just to adjust the addition amount of palladium chloride aqua solution suitably with a density | concentration. For example, it is desirable to add palladium chloride in an amount of 0.01 to 1 part by mass with respect to 100 parts by mass of the rubber content of the latex.

After adding the hydrogenation catalyst, it is desirable to adjust the latex pH to near neutral in order to suppress the coagulation of the rubber. Specifically, it is preferable to adjust the pH of the latex to about 5 to 7 by adding an alkaline aqueous solution. As the alkaline aqueous solution, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a calcium hydroxide aqueous solution and the like are suitable. Palladium tetrachloride ions ([PdCl ₄ ] ²⁻ ) in the latex react with the added aqueous alkali solution to become palladium hydroxide (Pd (OH) ₂ ).

  The concentration of the alkaline aqueous solution may be determined so that the pH of the latex can be adjusted to near neutral according to the concentration of the aqueous solution of palladium chloride. For example, when the concentration of palladium chloride aqueous solution is around 3 mol / L and a sodium hydroxide aqueous solution is added, the concentration is preferably 0.1 mol / L or more and 6 mol / L or less. It is more preferable that the amount be 1 mol / L or more and 3 mol / L or less.

Further, as shown in the following examples, the progress of the hydrogenation reaction varies depending on the concentration of the alkaline aqueous solution and the addition rate. As described above, the rate of the hydrogenation reaction is considered to depend on the particle size of the Pd particles. Pd particles are produced by reducing palladium hydroxide (Pd (OH) ₂ ) particles produced by addition of an alkaline aqueous solution during the hydrogenation reaction. Therefore, if the particle diameter of the Pd (OH) ₂ particles is small, the particle diameter of the generated Pd particles is also small.

  For example, when the addition rate of the alkaline aqueous solution is decreased, that is, when the alkaline aqueous solution is slowly added, the particle diameter of the produced palladium hydroxide particles tends to be small. Therefore, by reducing the addition rate of the alkaline aqueous solution, the particle size of the Pd particles can be reduced, and as a result, the rate of the hydrogenation reaction can be improved. For example, in order to achieve the desired reaction rate by adding the above 0.1 mol / L or more and 6 mol / L or less sodium hydroxide aqueous solution, the addition rate is 0.05 g / 10 sec or more and 0.05 g / 3 sec. It is desirable to be (about 0.17 g / 10 seconds) or less.

  Next, the hydrogenation process will be described. In this step, the latex prepared in the previous hydrogenation catalyst addition step is reacted with hydrogen to hydrogenate at least part of the carbon-carbon double bonds in the natural rubber or deproteinized natural rubber. That is, hydrogenation reaction of natural rubber or deproteinized natural rubber is performed.

When hydrogen is reacted with the latex to which the hydrogenation catalyst has been added, the Pd (OH) ₂ particles are reduced to become Pd particles. Using the produced Pd particles as a catalyst, carbon-carbon double bonds in natural rubber or deproteinized natural rubber are hydrogenated. All of the carbon-carbon double bonds may be hydrogenated (hydrogenation rate 100%), or only a part of them may be hydrogenated.

  The hydrogenation reaction may be performed in the presence of hydrogen, and any of batch, semi-batch, and continuous methods may be employed. For example, it can be performed while hydrogen is supplied, such as bubbling hydrogen into the latex.

  In order to advance the hydrogenation reaction at a practical rate, the reaction temperature is desirably 25 ° C. or higher. More preferably, the temperature is 60 ° C or higher. On the other hand, if the reaction temperature is too high, the latex may coagulate or the rubber may have a low molecular weight. Therefore, the reaction temperature is desirably 90 ° C. or lower. More preferably, it is 80 ° C. or lower. About reaction time, what is necessary is just to adjust suitably according to reaction temperature, reaction pressure, etc. so that a desired hydrogenation rate may be obtained.

What is necessary is just to determine a hydrogenation rate suitably considering the use etc. of the hydrogenated natural rubber manufactured. For example, when used as an anti-vibration rubber material, the hydrogenation rate is desirably 1% or more and 98% or less. In addition, what is necessary is just to obtain | require about a hydrogenation rate by < ¹ > H-NMR measurement.

It is desirable to remove the catalyst from the latex after the hydrogenation step. The removal of the catalyst can be performed, for example, as follows. First, an oxidant such as hydrogen peroxide is added to the latex after the hydrogenation reaction to oxidize the Pd particles (Pd + H ₂ O ₂ + 2H ⁺ → Pd ²⁺ + 2H ₂ O). Next, dimethylglyoxime or the like is added to form a complex with Pd ²⁺ . And after leaving still, a complex is removed by means, such as filtration. After removing the catalyst, hydrogenated natural rubber is precipitated from the filtrate (latex) and further dried to obtain hydrogenated natural rubber.

<Rubber member>
The rubber member of the present invention is formed by crosslinking a rubber composition containing a hydrogenated natural rubber produced by the method for producing a hydrogenated natural rubber of the present invention. The rubber composition may contain compounding agents such as a cross-linking agent, a cross-linking accelerator, a processing aid, a plasticizer, an anti-aging agent, a reinforcing agent, and a colorant as necessary. First, a hydrogenated natural rubber, a compounding agent, and the like are kneaded with a roll or a kneader to prepare a rubber composition. Next, the prepared rubber composition is molded into a predetermined shape and crosslinked. By doing so, the rubber member of the present invention can be manufactured.

  Next, the present invention will be described more specifically with reference to examples.

<Relationship between dissolved state of palladium chloride and hydrogenation rate>
By changing the kind of palladium chloride solution of the hydrogenation catalyst, we investigated how the hydrogenation rate changes depending on the dissolution state of palladium chloride.

[Production of deproteinized natural rubber latex]
A deproteinized natural rubber latex was produced as follows. As the natural rubber latex, high ammonia latex (rubber content concentration 60 mass%) manufactured by VON was used. First, the high ammonia latex was diluted so that the rubber concentration was 30% by mass. Next, 1.0 part by mass of sodium dodecyl sulfate (SDS: anionic surfactant) was added to 100 parts by mass of the rubber content of the diluted latex to stabilize the latex. Next, 0.1 part by mass of urea was added to 100 parts by mass of the rubber content of the latex, and the protein was decomposed by stirring at room temperature for 10 minutes at a rotation speed of 200 rpm. Thereafter, the latex after completion of the proteolytic treatment was centrifuged at a rotation speed of 8000 rpm for 45 minutes. The separated upper layer was taken out and centrifuged twice as described above. Finally, 0.03 parts by mass of SDS was added to the obtained cream of the upper layer and stirred at room temperature for 30 minutes at a rotation speed of 300 rpm to obtain a deproteinized natural rubber latex.

[Manufacture of hydrogenated natural rubber]
Using three kinds of palladium chloride solutions as a hydrogenation catalyst, a hydrogenation reaction was performed on the produced deproteinized natural rubber latex. The following catalysts (a) to (c) were used as the palladium chloride solution. The dissolution days are days when palladium chloride is dissolved in a solvent (hydrochloric acid).
Catalyst (a): Aqueous palladium chloride solution (2.8 mol / L; manufactured by Ishifuku Metal Industry Co., Ltd.)
Catalyst (b): Palladium chloride hydrochloric acid solution (1 mol / L, dissolution days 1 day)
Catalyst (c): Palladium chloride / hydrochloric acid solution (same as above, dissolution days: 5 days)
First, distilled water was added to deproteinized natural rubber latex to dilute the rubber concentration to 18% by mass. Next, while stirring the diluted latex at a rotation speed of 200 rpm, 0.03 parts by mass of SDS was added to the latex with respect to 100 parts by mass of the rubber content of the latex. Subsequently, the palladium chloride solutions (a) to (c) above were respectively added dropwise to the latex. In any of the cases (a) to (c), 0.57 parts by mass was dropped with respect to 100 parts by mass of the rubber content of the latex. Then, an aqueous sodium hydroxide solution (1 mol / L) was added to the latex at an addition rate of 0.05 g / 3 seconds to adjust the pH in the latex to about 6. The latex was then heated to about 70 ° C. in a warm bath.

Next, hydrogen was bubbled into the latex at a flow rate of 0.1 L / min, and a hydrogenation reaction was performed for a predetermined time. After finishing the hydrogenation reaction, the latex was cooled to about 40 ° C., hydrogen peroxide was added, and the mixture was stirred for 1 hour. Subsequently, dimethylglyoxime was added and stirred for 1 hour. Then, it left still at room temperature for 12 hours, and solid content (hydrogenation catalyst) was separated by filtration. And the obtained filtrate was dried and hydrogenated natural rubber was obtained. About the obtained hydrogenated natural rubber, < ¹ > H-NMR measurement was performed and the hydrogenation rate was computed. ¹ H-NMR measurement was performed using an NMR apparatus “INOVA-400” manufactured by Varian.

[Hydrogenation rate of hydrogenated natural rubber]
About the manufactured hydrogenated natural rubber, the relationship of the hydrogenation rate with respect to hydrogenation reaction time was investigated for every catalyst (a)-(c) used. The results are shown in FIG.

  As shown in FIG. 1, it can be seen that the hydrogenation rate varies depending on the type of solvent of the hydrogenation catalyst and the number of days of dissolution even when the hydrogenation reaction is performed under the same conditions. For example, when catalysts (b) and (c) using hydrochloric acid as a solvent are used, hydrogenation of the hydrogenated natural rubber obtained is possible even if the dissolution time of palladium chloride is different and it is reacted with hydrogen for the same time. The rate has changed. The reason for this is considered to be that, because the dissolution state of palladium chloride differs depending on the number of days of dissolution, even if the hydrogenation reaction was performed under the same conditions, the reaction rate was different. Thus, when a conventional hydrogenation catalyst is used, it is difficult to control the hydrogenation rate.

<Production of hydrogenated natural rubber using aqueous palladium chloride solution>
Using the palladium chloride aqueous solution of the catalyst (a), in the above production method, the concentration or the addition rate of the aqueous sodium hydroxide solution was changed to produce further three types of hydrogenated natural rubber. A total of four types of manufactured hydrogenated natural rubber were made into Examples 1-4. Table 1 shows the concentration of sodium hydroxide aqueous solution, the addition rate, and the hydrogenation rate after 3.4 hours from the start of the hydrogenation reaction for the hydrogenated natural rubbers of Examples 1 to 4. FIG. 2 shows the relationship between the hydrogenation reaction time and the hydrogenation rate in the hydrogenated natural rubbers of Examples 1 to 4.

  As shown in FIG. 2, it is understood that when the aqueous solution of palladium chloride is used, the hydrogenation rate can be controlled by adjusting the concentration and the addition rate of the aqueous sodium hydroxide solution.

  In addition, in Example 4 in which the addition rate of the aqueous sodium hydroxide solution was small, that is, in the case where the aqueous sodium hydroxide solution was added slowly, the reaction rate was higher than that in Example 1 having the same concentration. The reason is considered as follows. That is, when a sodium hydroxide aqueous solution is added slowly, the particle diameter of the produced palladium hydroxide particles becomes small. The palladium hydroxide particles are reduced during the hydrogenation reaction to become Pd particles. That is, when the sodium hydroxide aqueous solution is added slowly, the particle size of the Pd particles becomes small. As a result, the speed of the hydrogenation reaction is improved.

<Heat resistance evaluation of hydrogenated natural rubber>
Heat resistance of hydrogenated natural rubber of five kinds of hydrogenation rates (19%, 33%, 51%, 72%, 98%) produced using the above-mentioned catalyst (a) palladium chloride aqua solution evaluated. First, each hydrogenated natural rubber was subjected to a tensile test according to JIS K 6251 (2004), and the tensile strength (TS) and elongation at break (E _b ) were measured. For the tensile test, a dumbbell-shaped No. 7 test piece was used. Next, each test piece was heat-aged by holding at 120 ° C. for 72 hours. Thereafter, a tensile test was performed in the same manner, and tensile strength (TS) and elongation at break (E _b ) were measured. And the change rate of TS and _Eb after carrying out heat aging for 72 hours was computed by following Formula (1), (2).
TS change rate (%) = [(TS after heat aging) − (initial TS)] / [initial TS] × 100 (1)
E _b change rate (%) = [(E _b after heat aging) − (initial E _b )] / [initial E _b ] × 100 (2)
Table 2 shows the initial (before heat aging) TS and E _{b of} each hydrogenated natural rubber and the rate of change of TS and E _b after 72 hours of heat aging.

For comparison, natural rubber (NR), deproteinized natural rubber (DPNR), and ethylene-propylene-diene rubber (EPDM) were also subjected to the same test, and the rate of change in TS and _Eb was calculated. . These results are shown in Table 3. The materials used for comparison are as follows.
Natural rubber: RSS (Ribbed Smoked Sheet).
Deproteinized natural rubber: produced from the deproteinized natural rubber latex produced in this example.
EPDM: “Esplen (registered trademark) E505” manufactured by Sumitomo Chemical Co., Ltd.

  As shown in Tables 2 and 3, for natural rubber and deproteinized natural rubber, the tensile strength and elongation at break were significantly reduced by heat aging. On the other hand, all of the hydrogenated natural rubber produced by the production method of the present invention had a tensile strength equal to or higher than that of EPDM. In addition, the elongation at break was also improved compared to natural rubber and deproteinized natural rubber. In particular, in hydrogenated natural rubber having a high hydrogenation rate, elongation at break did not decrease.

  Thus, according to the production method of the present invention, a hydrogenated natural rubber having a desired hydrogenation rate can be easily produced. Thereby, the rubber member which has a required physical property according to a use can be obtained easily.

  For example, the rubber member of the present invention using hydrogenated natural rubber having high heat resistance is suitable for a vibration isolating member, a seismic isolation member and the like used for automobiles.

Claims (3)

A hydrogenation catalyst addition step of adding a hydrogenation catalyst to latex of natural rubber or deproteinized natural rubber;
A hydrogenation step in which hydrogen is reacted with the latex to which the hydrogenation catalyst has been added to hydrogenate at least part of the carbon-carbon double bonds in the natural rubber or the deproteinized natural rubber;
Have
The method for producing hydrogenated natural rubber, characterized in that the hydrogenation catalyst is an aqueous palladium chloride solution in which palladium chloride is dissolved in aqua regia.   2. The method for producing hydrogenated natural rubber according to claim 1, wherein, in the hydrogenation catalyst addition step, after adding the hydrogenation catalyst, an alkaline aqueous solution is added to adjust the pH of the latex to near neutrality.   A rubber member obtained by crosslinking a rubber composition containing hydrogenated natural rubber produced by the method for producing hydrogenated natural rubber according to claim 1 or 2.

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