JP2016060806A - Manufacturing method of modified diene rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a modified diene rubber capable of suppressing residue of a halogen content derived from perhalogen acid and increasing purity when modifying a diene rubber by using perhalogen acid.SOLUTION: There is provided a manufacturing method of a modified diene rubber including a process of modifying a diene rubber with a modification method including a process of oxidation cleavage by using perhalogen acid to obtain latex containing the modified diene rubber and a process of cooling the resulting latex preferably under an acidic condition to solidify the modified diene rubber.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a modified diene rubber.

  In order to improve the properties of rubber products such as tires, it is known to modify the diene rubber compounded in the rubber composition. For example, in Patent Document 1, after adding an oxidizing agent such as perhalogen acid to a diene rubber latex to oxidatively cleave the diene rubber, the acid basicity of the latex containing the decomposed diene rubber is changed. In order to obtain a modified diene rubber. In Patent Document 1, methanol is specifically used when coagulating the modified diene rubber from the latex containing the modified diene rubber. However, in such a coagulation method, perhalogenate contained in the latex remains in the modified diene rubber.

  By the way, conventionally, as a technique for removing a non-rubber component from a rubber latex, Patent Document 2 discloses mixing natural rubber latex in an organic solvent that does not dissolve the rubber component and dissolves the non-rubber component. Yes. However, solidification with such an organic solvent cannot suppress the residual perhalogenate. Also, coagulation with an organic solvent requires safety and hygiene measures against volatilization of the organic solvent that occurs in the work environment.

  In Patent Document 3, a polymer latex having a glass transition temperature of −20 to 60 ° C. of an outermost layer polymer obtained by emulsion polymerization is frozen at a temperature of −5 ° C. or lower to solidify the polymer. It is disclosed. However, this method requires freezing for coagulation, and it is not disclosed that residual perhalogenate contained in the latex can be suppressed by coagulation by cooling.

  In Patent Document 4, after mixing a modified diene rubber latex and a slurry solution of a filler, coagulation is promoted by changing the temperature by steam heating or freezing when the obtained mixture is coagulated. Is disclosed. However, this method is for coagulating a mixture of a rubber latex and a slurry solution to obtain a wet master batch, and it is possible to suppress the residual perhalogenate contained in the latex by coagulation by cooling. Not disclosed.

JP 2013-177579 A JP 2009-256482 A JP-A-6-263819 JP 2010-261002 A

  The present invention provides a method for producing a modified diene rubber that can suppress the residual halogen content derived from perhalogen acid and increase the purity when the diene rubber is modified using perhalogen acid. With the goal.

  The method for producing a modified diene rubber according to the present invention includes a step of obtaining a latex containing a modified diene rubber by modifying the diene rubber by a modification method including a step of oxidative cleavage using a perhalogen acid. And a step of coagulating the modified diene rubber by cooling the obtained latex.

  According to the present invention, by cooling a latex containing a modified diene rubber modified with a perhalogen acid, the modified diene rubber can be coagulated without using an organic solvent. Residues of halogens derived from acids in the modified diene rubber can be suppressed, and a high purity modified diene rubber can be obtained.

  The method for producing a modified diene rubber according to this embodiment includes a step of obtaining a latex containing a modified diene rubber by modifying the diene rubber by oxidative cleavage using a perhalogen acid, and cooling the obtained latex. And a step of coagulating the modified diene rubber.

  In a preferred embodiment, the step of obtaining the latex containing the modified diene rubber includes a step of decomposing the diene rubber latex by oxidative cleavage by adding a perhalogen acid to the diene rubber latex, and a decomposed diene rubber. A step of changing the acid basicity so that the latex is basic in the case of acidity and acidic in the case of basicity. As a modification method for modifying the diene rubber through such steps, for example, the modification method disclosed in Patent Document 1 can be used.

  In this embodiment, examples of the diene rubber to be modified include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), and chloroprene. Examples thereof include rubber (CR), butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. Among these, it is preferable to use at least one selected from the group consisting of natural rubber, synthetic isoprene rubber, styrene butadiene rubber, and butadiene rubber. The number average molecular weight (Mn) of the diene rubber is not particularly limited, and may be, for example, 60,000 to 1,000,000, or 80,000 to 800,000.

  As the diene rubber to be modified, it is preferable to use a water-based emulsion, that is, a latex, which is micellar in water, which is a protic solvent. Although the density | concentration (rubber solid content density | concentration) of diene type rubber latex is not specifically limited, It is preferable that it is 5-70 mass%, More preferably, it is 10-50 mass%.

  In order to oxidatively cleave the carbon-carbon double bond of the diene rubber, perhalogen acid is used as an oxidizing agent in this embodiment. The diene rubber can be oxidatively cleaved by adding perhalogen acid to the diene rubber latex and stirring. Periodic acid is preferably used as the perhalogen acid. The amount of perhalogen acid used is not particularly limited as long as it can be oxidatively cleaved. For example, it may be 0.1 to 10 parts by mass or 1 to 5 parts by mass with respect to 100 parts by mass of the diene rubber in the latex.

  Diene rubber is decomposed by oxidative cleavage, and a diene polymer having a carbonyl group (> C═O) or a formyl group (—CHO) at the terminal is obtained. As one embodiment, the decomposed diene rubber has a structure represented by the following formula (1) at the end.

式中、Ｒ¹は、水素原子、メチル基又はクロロ基である。分解したジエン系ゴムは、その分子鎖の少なくとも一方の末端に上記式（１）で表される構造を持つ。

In the formula, R ¹ is a hydrogen atom, a methyl group or a chloro group. The decomposed diene rubber has a structure represented by the above formula (1) at at least one end of its molecular chain.

  The molecular weight of the decomposed diene rubber decreases due to the oxidative cleavage. The number average molecular weight (Mn) after decomposition is not particularly limited, and may be, for example, 3 to 500,000, or 5 to 100,000.

  When the diene rubber is decomposed as described above, the latex containing the decomposed diene rubber (hereinafter referred to as depolymerized latex) is basic (that is, alkaline) when acidic, and is basic when basic. The acid basicity is changed to be acidic. By changing the acid basicity in this way, a coupling reaction (aldol condensation reaction) that is a reverse reaction to cleavage proceeds preferentially. At that time, the diene polymer fragments may be recombined with each other without adding a separate modifier to the depolymerized latex, or a modifier having a carbonyl group and / or a formyl group may be added to the depolymerized latex. In addition, a further modifying group may be introduced at the end of the diene polymer fragment. When the diene polymer fragments are recombined, a polymer containing a linking group represented by the following formulas (2) to (5) can be generated.

ここで、Ｒ¹が水素原子である末端構造を持つポリマー断片同士が結合する場合、式（４）及び／又は式（５）で表される連結基となり、Ｒ¹が水素原子である末端構造を持つポリマー断片とＲ¹がメチル基である末端構造を持つポリマー断片が結合する場合、式（２）及び／又は式（３）で表される連結基となる。

Here, when polymer fragments having a terminal structure in which R ¹ is a hydrogen atom are bonded to each other, a linking group represented by formula (4) and / or formula (5) is obtained, and a terminal structure in which R ¹ is a hydrogen atom. When a polymer fragment having a terminal structure in which R ¹ is a methyl group and a polymer fragment having R ¹ are bonded to each other, a linking group represented by formula (2) and / or formula (3) is obtained.

  In addition, adjustment of pH at the time of changing acid basicity can be performed by adding an acid or a base to the depolymerized latex, and is not particularly limited. Examples of acids include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. , Formic acid, acetic acid and the like, and examples of the base include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like.

  As described above, as one embodiment, a latex containing a modified diene rubber in which at least one of the linking groups represented by formulas (2) to (5) is introduced into the main chain (hereinafter referred to as a modified rubber latex). Is obtained. The content rate of a coupling group is not specifically limited, For example, 0.001-25 mol% may be sufficient as the sum total of the coupling group of Formula (2)-(5), and 0.1-15 mol% may be sufficient. Here, the content of the linking group is the ratio of the number of moles of the linking group to the number of moles of all the constituent units constituting the modified diene rubber. When a modifying agent is added separately, a modified diene rubber having a modifying group derived from the modifying agent is obtained. The number average molecular weight (Mn) of the modified diene rubber is not particularly limited, and may be, for example, 60,000 to 1,000,000, or 80,000 to 800,000.

  Next, the modified diene rubber is solidified by cooling the resulting modified rubber latex. The modified rubber latex is formed as a uniform dispersion system due to the charge balance between the solvent water and latex particles, but when cooled below the Kraft point, the charge balance is lost and aggregation occurs, causing the modified diene rubber to coagulate. . In general, rubber latex is stabilized with a surfactant, and in that case, the resulting modified rubber latex is also stabilized with a surfactant. By cooling below the Kraft point, the solubility of the surfactant is increased. By lowering, the balance of charges is lost, and the modified diene rubber can be solidified. In one embodiment, the cooling temperature is 5 ° C. or lower, and may be 5 to −20 ° C. In order to solidify without freezing, the cooling temperature is preferably 0 ° C. or higher, more preferably 5 to 0 ° C.

  The Kraft point here is the temperature at which coagulation of the modified diene rubber begins when the modified rubber latex is cooled, regardless of whether the modified rubber latex is stabilized with a surfactant. It can be determined by lowering the temperature using the target modified rubber latex.

  In this embodiment, the modified rubber latex is coagulated by cooling, and the coagulation is performed in water. Therefore, the modified diene rubber can be coagulated without using an organic solvent. In addition, the modified diene rubber can be coagulated while a halogen component derived from perhalogen acid (specifically, for example, a perhalogenate) remains in water.

  In the present embodiment, the coagulation is preferably performed under acidic conditions. That is, it is preferable to coagulate the modified diene rubber by cooling the modified rubber latex under acidic conditions. Solidification can be promoted by cooling under acidic conditions. For example, when the resulting modified rubber latex is acidic by changing the depolymerized latex from basic to acidic in the modification step, the modified rubber latex is cooled and solidified while still acidic. On the other hand, by changing the depolymerized latex from acidic to basic in the modification step, if the resulting modified rubber latex is basic, it is changed from basic to acidic, and the modified rubber latex is subjected to acidic conditions. Cool and solidify. In order to make the modified rubber latex acidic, acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid may be added, and sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate You may adjust pH by adding bases, such as.

  The acidic condition, that is, the pH of the modified rubber latex when coagulating the modified diene rubber is preferably 2.5 to 5.5, and more preferably 3 to 5. By coagulating under such acidic conditions, the modified rubber latex can be coagulated without freezing. For this reason, it is not necessary to thaw after freezing, and productivity can be improved. When the pH is 2.5 or more, the modified diene rubber can be prevented from undergoing oxidative cleavage again.

  In addition, the density | concentration (rubber solid content density | concentration) of the modified rubber latex at the time of coagulating is not specifically limited, For example, 5-70 mass% may be sufficient, and 10-50 mass% may be sufficient.

  The production method according to this embodiment preferably includes a step of drying a solid rubber (that is, a modified diene rubber) that is a coagulated product obtained by cooling the modified rubber latex. By drying, water as a solvent can be removed. For drying, for example, a normal dryer such as a vacuum dryer or a hot air dryer can be used. Note that the solidified product may be washed with water before drying.

  According to this embodiment, a modified diene rubber having a functional group introduced can be obtained by modification with perhalogen acid. At that time, latex containing modified diene rubber modified with perhalogen acid is cooled below the Kraft point and solidified to suppress perhalogenate in the modified diene rubber that promotes deterioration. can do. Therefore, a high-purity modified diene rubber from which impurities are removed can be obtained, and the characteristics of the rubber composition can be improved.

  The modified diene rubber obtained as described above can be used as a rubber component in various rubber compositions. When used in a rubber composition, the rubber component may be the modified diene rubber alone or may be blended with other diene rubbers. Further, the rubber composition can contain a filler such as silica and carbon black together with the rubber component, and as other additives, softeners, plasticizers, anti-aging agents, zinc white, stearin. Various additives generally used in a rubber composition such as an acid, a vulcanizing agent, and a vulcanization accelerator can be blended. The use of the rubber composition is not particularly limited, and the rubber composition can be used for various rubber members such as tires, anti-vibration rubbers, and conveyor belts. Preferably, it is used for tires, and rubber parts (for example, tread parts, sidewall parts, bead parts, tire cord coatings) of various pneumatic tires are formed by vulcanization molding at 140 to 180 ° C. according to a conventional method. Rubber etc.).

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

[Examples 1 to 5]
A modified rubber latex was prepared according to the procedure of Example 1 of Patent Document 1. In detail, natural rubber latex (“LA-NR” manufactured by Residex, DRC = 60 mass%, Mn = 26.9 million) is adjusted to DRC = 30 mass%, sodium lauryl sulfate (manufactured by Nacalai Tesque) Was added to a concentration of 1% by mass, and 3.3 g of periodic acid (H ₅ IO ₆ ) was added to 100 g of the polymer mass in the natural rubber latex, followed by stirring at 23 ° C. for 3 hours. The rubber was oxidatively cleaved. To the resulting depolymerized latex (pH 6.2), 0.1 g of pyrrolidine-2-carboxylic acid was added, 1N sodium hydroxide was added so that the pH of the reaction solution was 10, and the mixture was stirred at 23 ° C. for 12 hours. The modified natural rubber having a linking group represented by the above formulas (2) to (5) by reacting (Mn = 300,000, the content of the linking group (total of formulas (2) to (5)) = 1. A modified rubber latex containing 3 mol%) was obtained. Here, Mn is a value in terms of polystyrene measured by gel permeation chromatography (GPC), the content of the linking group is a value measured by NMR, and the pH is a portable pH meter “HM-30P type manufactured by Toa DKK Co., Ltd.” These are measured values according to the method described in Patent Document 1.

  Subsequently, 2 mL of modified rubber latex (DRC = 30% by mass) was taken into a test tube, and after adjusting the pH as described in Table 1 using formic acid (manufactured by Nacalai Tesque), the temperature was changed to the temperature shown in Table 1 for 18 hours. After cooling, the solidified state was examined. The results are shown in Table 1 with the visual observation of “O” for solidified and “X” for non-solidified. In addition, about what was cooled at -18 degreeC, since latex was frozen, the frozen thing was thawed with running water, and it returned to room temperature, and obtained the coagulum. The solidified product was washed with water and then vacuum dried at 40 ° C. for 48 hours using a vacuum drying oven to obtain a modified natural rubber.

[Comparative Examples 1 and 2]
2 mL of the modified rubber latex (DRC = 30% by mass) obtained above was changed to 10 mL of ethanol (manufactured by Nacalai Tesque, first grade) in Comparative Example 1, and ethanol / water = 2/1 (mass ratio) in Comparative Example 2. The modified natural rubber was coagulated by pouring each into 10 mL of a mixed solvent and stirring and mixing. When coagulation did not proceed, the pH was adjusted to less than 5 with formic acid (manufactured by Nacalai Tesque). Thereafter, the coagulated modified natural rubber was washed with water and then vacuum dried at 40 ° C. for 48 hours using a vacuum drying oven to obtain a modified natural rubber.

[Comparative Example 3]
Take 2 mL of the modified rubber latex (DRC = 30% by mass) obtained above in a test tube, adjust to pH 5 using formic acid (manufactured by Nacalai Tesque), and then heat in a water bath set at 85 ° C. for 5 minutes. The modified natural rubber was coagulated. The coagulated modified natural rubber was washed with water and then vacuum dried at 40 ° C. for 48 hours using a vacuum drying oven to obtain a modified natural rubber.

[Measurement of iodine content]
The gas produced when the modified natural rubber obtained above was completely burned at 1000 ° C. under a stream of oxygen using a combustion apparatus AQF-100 manufactured by Mitsubishi Chemical Analitech. Using GA-100, absorption and oxidation were performed with an absorbing solution, and a Dionex column IonPacAS12A was connected to a Dionex ion chromatograph IC-1500 for measurement. The eluent AS12A for analysis of dionex ion chromatograph anions analyzed by Kanto Chemical Co., Ltd. is used as the eluent, the phosphoric acid standard solution manufactured by Wako Pure Chemical Industries is used as the internal standard, and N-iodo manufactured by Tokyo Chemical Industry Co., Ltd. as a sample for preparing a calibration curve for iodine amount. Succinimide was used. In the table, “not detected” means below the detection limit.

  The results are as shown in Table 1. The modified rubber latex did not coagulate at 8 ° C, but could be coagulated by cooling to 0 ° C or -18 ° C. In particular, in Examples 3 to 5 having a low pH, it was solidified even at 0 ° C. and could be solidified without freezing. Further, in the modified natural rubber of Examples 1 to 5 solidified by cooling, the iodine content was below the detection limit, and Comparative Example 1 was coagulated using an organic solvent such as ethanol or a mixed solvent of ethanol / water. The residual amount of iodine can be significantly reduced as compared with 2, and the residual amount of iodine is reduced as compared with Comparative Example 3 which is heated to 85 ° C. and solidified.

[Examples 6 to 10]
A modified rubber latex was prepared according to the procedure of Example 5 of Patent Document 1. Specifically, styrene butadiene rubber latex (“SBR Latex LX110, DRC = 50 mass%, Mn = 324,000) manufactured by Nippon Zeon Co., Ltd.) was adjusted to DRC = 30 mass%, and the polymer mass in the rubber latex Periodic acid (H ₅ IO ₆ ) 3.3 g was added to 100 g, and the styrene-butadiene rubber was oxidatively cleaved by stirring for 3 hours at 23 ° C. In the obtained depolymerized latex (pH 5.9), Add 0.1 g of pyrrolidine-2-carboxylic acid, add 1 N sodium hydroxide so that the pH of the reaction solution becomes 10, and stir at 23 ° C. for 12 hours to react, and the above formulas (4) and (5) A modified rubber latex containing a modified styrene butadiene rubber having a linking group represented by the formula (Mn = 280,000, linking group content (sum of formulas (4) and (5)) = 1.8 mol%) It was.

  Subsequently, 2 mL of modified rubber latex (DRC = 30% by mass) was taken into a test tube, and after adjusting the pH as shown in Table 2 using formic acid (manufactured by Nacalai Tesque), the temperature was changed to the temperature shown in Table 2 for 18 hours. After cooling, the solidified state was examined. As for the one cooled at −18 ° C., since the latex was frozen, the frozen product was thawed with running water and returned to room temperature to obtain a coagulated product. The solidified product was washed with water and then vacuum dried at 40 ° C. for 48 hours using a vacuum drying oven to obtain a modified styrene butadiene rubber.

[Comparative Examples 4 and 5]
2 mL of the modified rubber latex (DRC = 30% by mass) obtained in Example 6 was changed to 10 mL of ethanol (manufactured by Nacalai Tesque, first grade) in Comparative Example 4, and ethanol / water = 2/1 (mass ratio) in Comparative Example 5. ) Was mixed with 10 mL of the mixed solvent and mixed by stirring to coagulate the modified styrene butadiene rubber. When coagulation did not proceed, the pH was adjusted to less than 5 with formic acid (manufactured by Nacalai Tesque). Thereafter, the coagulated product was washed with water and then vacuum-dried at 40 ° C. for 48 hours using a vacuum drying oven to obtain a modified styrene-butadiene rubber.

[Comparative Example 6]
2 mL of the modified rubber latex (DRC = 30% by mass) obtained in Example 6 was taken into a test tube, adjusted to pH 5 using formic acid (manufactured by Nacalai Tesque), and then placed in a water bath set at 85 ° C. for 5 minutes. Heated to coagulate the modified styrene butadiene rubber. Thereafter, the coagulated product was washed with water and then vacuum-dried at 40 ° C. for 48 hours using a vacuum drying oven to obtain a modified styrene-butadiene rubber.

  About modified styrene butadiene rubber obtained above, it carried out similarly to Example 1, and measured iodine content. The results are as shown in Table 2. In the case of the modified styrene butadiene rubber, the modified rubber latex can be coagulated by cooling, as in the case of the modified natural rubber. The residual amount of can be greatly reduced.

Claims (4)

Modifying the diene rubber by a modification method including a step of oxidative cleavage using a perhalogen acid to obtain a latex containing the modified diene rubber;
A step of coagulating the modified diene rubber by cooling the obtained latex;
A process for producing a modified diene rubber.   The modified diene rubber according to claim 1, wherein in the step of coagulating the modified diene rubber, the modified diene rubber is coagulated by cooling the latex containing the modified diene rubber under acidic conditions. Method.   The method for producing a modified diene rubber according to claim 1 or 2, wherein the perhalogenic acid is periodic acid.   The step of obtaining the latex containing the modified diene rubber includes a step of decomposing the diene rubber latex by adding perhalogen acid to oxidative cleavage of the diene rubber, and a step of decomposing the latex containing the decomposed diene rubber from acidity. A step of coagulating the modified diene rubber, wherein the latex containing the modified diene rubber is changed from basic to acidic and cooled under acidic conditions. The method for producing a modified diene rubber according to any one of claims 1 to 3.