Method for producing a hydroxyl group-modified diene rubber composition

Abstract

This invention provides a method for obtaining a rubber composition with a high bounce rubber content. [Solution] A method for producing a hydroxyl-modified diene rubber composition, comprising contacting a mixture containing 100 parts by mass of diene rubber and 20 to 150 parts by mass of at least one type of filler with a fluid containing supercritical carbon dioxide and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more, to obtain a composition containing hydroxyl-modified diene rubber.

Description

Technical Field

[0001] The present invention relates to a method for producing a hydroxyl group-modified diene rubber composition.

Background Art

[0002] Conventionally, a method for producing natural rubber having a hydroxyl group introduced into its main chain is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the method described in Patent Document 1 requires epoxidation of natural rubber, and the process is complicated. Further, as another method for introducing a hydroxyl group into the main chain of a diene rubber, for example, a method of putting a diene rubber and sulfuric acid into a mixer and mixing them at a high temperature can be considered. In this case, there are problems such as corrosion of the apparatus by sulfuric acid, the need to remove the acid remaining after the reaction by neutralization or the like, and molecular cleavage due to shear stress.

[0005] Under such circumstances, the present inventors have found that a diene rubber modified with a hydroxyl group (hydroxyl group-modified diene rubber) can be obtained by bringing a diene rubber into contact with a fluid containing supercritical carbon dioxide and water.

[0006] By the way, the hydroxyl groups introduced into the diene rubber are considered to interact with fillers such as silica and carbon fillers. As a method for evaluating the interaction between the rubber component and the filler in the rubber composition, there is the amount of bound rubber. Bound rubber is a rubber component firmly bonded to the filler, and the greater the amount thereof (amount of bound rubber), the more improvement in various properties is expected. The inventors mixed a filler with the hydroxyl-modified diene rubber described above and evaluated the amount of bounding rubber in the resulting composition. They found that while it was an improvement over the case using unmodified diene rubber, further improvement is desirable considering the increasing demands that are expected in the future.

[0007] Therefore, in view of the above circumstances, the present invention aims to provide a method for obtaining a rubber composition with a high amount of bounding rubber. [Means for solving the problem]

[0008] As a result of diligent research into the above-mentioned problems, the inventors of the present invention discovered that a composition with a high amount of bounding rubber can be obtained by mixing a specific proportion of filler with diene rubber and then bringing it into contact with a specific supercritical fluid, leading to the present invention. In other words, the inventors have found that the above problem can be solved by the following configuration.

[0009] (1) A mixture containing 100 parts by mass of diene rubber and 20 to 150 parts by mass of at least one type of filler, A fluid containing supercritical carbon dioxide and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more, A method for producing a hydroxyl group-modified diene rubber composition, comprising contacting the two materials to obtain a composition containing a hydroxyl group-modified diene rubber. (2) A method for producing the hydroxyl-modified diene rubber composition described in (1) above, wherein the diene rubber is natural rubber. (3) A method for producing the hydroxyl-modified diene rubber composition according to (1) or (2) above, wherein the filler is silica. (4) A method for producing the hydroxyl group-modified diene rubber composition according to any one of (1) to (3) above, wherein the pressure in the supercritical state is 10 MPa or more. (5) A method for producing a hydroxyl group-modified diene rubber composition according to any one of (1) to (4) above, wherein the amount of water relative to the carbon dioxide is 30% by mass or less. [Effects of the Invention]

[0010] As shown below, the present invention provides a method for obtaining a composition with a high amount of bounding rubber. [Modes for carrying out the invention]

[0011] The method for producing the hydroxyl-modified diene rubber composition of the present invention is described below. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. Furthermore, each component may be used individually or in combination of two or more. When two or more components are used in combination, the "content" of each component refers to the total content unless otherwise specified.

[0012] The method for producing the hydroxyl-modified diene rubber composition of the present invention (hereinafter also referred to as "the method of production of the present invention") is as follows: A mixture containing 100 parts by mass of diene rubber and 20 to 150 parts by mass of at least one type of filler, A fluid containing supercritical carbon dioxide and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more, This is a method for producing a hydroxyl-modified diene rubber composition, which involves contacting the rubber with a hydroxyl group to obtain a composition containing a hydroxyl-modified diene rubber.

[0013] In the production method of the present invention, as described above, a fluid (hereinafter also referred to as "specific fluid") containing carbon dioxide in a supercritical state and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more, is used. In the specific fluid, it is considered that carbon dioxide and water react to form carbonic acid. Here, since the carbon dioxide is in a supercritical state, the acidity of the generated carbonic acid is higher than normal (pH: about 3). Therefore, when a diene rubber comes into contact with the specific fluid, it is considered that an oxonium ion reacts with the double bond of the diene rubber, and a hydroxyl group is introduced into the main chain of the diene rubber. For example, when the diene rubber is natural rubber or polyisoprene, it is considered that a hydroxyl group is introduced as follows.

[0014] [Chemical formula]

[0015] Since the above-mentioned reaction occurs simply by bringing the diene rubber into contact with the specific fluid, molecular cleavage as in the case of using a mixer is unlikely to occur.

[0016] Also, when using a bulk (mass) of diene rubber, the introduction of the above-mentioned hydroxyl group proceeds on the surface of the bulk, and gradually the introduction of the hydroxyl group also proceeds inside the bulk. In the production method of the present invention, since it is made into a mixture with a specific amount of filler and then brought into contact with the specific fluid, paths derived from the filler exist in the bulk, and as a result, it is considered that carbonic acid easily penetrates and the introduction of the hydroxyl group easily proceeds.

[0017] In addition, in the production method of the present invention, since carbon dioxide in a supercritical state is used, carbonic acid can be volatilized as carbon dioxide simply by returning the system to normal pressure after the introduction of the hydroxyl group. That is, the acid remaining after the reaction can be easily removed.

[0018] The production method of the present invention comprises at least the following two steps. The production method of the present invention may also include other steps. (1) Mixture preparation step Step of obtaining a mixture containing 100 parts by mass of a diene rubber and 20 to 150 parts by mass of at least one filler (2) Supercritical fluid contact step Step of obtaining a composition containing a diene rubber modified with a hydroxyl group by bringing the above mixture into contact with a specific fluid

[0019] Hereinafter, each step will be described.

[0020] [1] Mixture preparation step The mixture preparation step is a step of obtaining a mixture (hereinafter, also referred to as "the mixture of the present invention") containing 100 parts by mass of a diene rubber and 20 to 150 parts by mass of at least one filler.

[0021] [Diene rubber] The above diene rubber is not particularly limited. One kind or two or more kinds of the above diene rubber may be used.

[0022] 〔Specific examples〕 Specific examples of the above diene rubber include natural rubber (NR), butadiene rubber (polybutadiene) (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (polyisoprene) (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Specific examples of the above aromatic vinyl-conjugated diene copolymer rubber include styrene butadiene rubber (SBR), styrene isoprene copolymer rubber, etc.

[0023] 〔Molecular weight〕 The weight average molecular weight (Mw) of the above diene 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 for the reason that the effects of the present invention are more excellent.

[0024] In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are standard polystyrene equivalent values ​​obtained by gel permeation chromatography (GPC) measurement.

[0025] [Preferred Embodiment] The above-mentioned diene rubber preferably contains isoprene units, more preferably natural rubber or polyisoprene, and even more preferably natural rubber, for the reasons that the effects of the present invention are superior.

[0026] [Filler] The filler is not particularly limited, but specific examples include carbon black, silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, calcium sulfate, etc. Among these, carbon black and silica are preferred, and silica is more preferred, because they provide superior effects in the present invention. One type of filler may be used, or two or more types may be used.

[0027] [Carbon Black] The carbon black (CB) mentioned above is not particularly limited, and various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF, GPF, and SRF can be used.

[0028] 〔silica〕 Examples of silica include wet silica, dry silica, fumed silica, and diatomaceous earth. Biomass-derived silica, such as rice husks, may also be used. The above silica may be used alone or in combination of two or more types.

[0029] [Content] In the mixture of the present invention, the content of the filler is 20 to 150 parts by mass per 100 parts by mass of the diene rubber described above. The content of the above-mentioned filler is preferably 30 to 100 parts by mass, and more preferably 40 to 70 parts by mass, per 100 parts by mass of the above-mentioned diene rubber, for the reason that the rubber modification effect by carbon dioxide in the present invention is superior.

[0030] [Optional ingredients] The mixture of the present invention may optionally contain components other than those described above (optional components). Examples of such components include various additives commonly used in rubber compositions, such as thermally expandable microcapsules, zinc oxide (zinc oxide), stearic acid, antioxidants, waxes, processing aids, liquid polymers, vulcanizing agents (e.g., sulfur), vulcanization accelerators, and vulcanization activators.

[0031] [Content] In the mixture of the present invention, the content of optional components is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, particularly preferably 5 parts by mass or less, and most preferably 1 part by mass or less, per 100 parts by mass of the diene rubber, for reasons that the effects of the present invention are superior. The lower limit of the content of optional components is not particularly limited and is 0 parts by mass.

[0032] [Preparation method] The method for preparing the mixture of the present invention is not particularly limited, and examples include kneading each of the above-mentioned components using known methods and apparatus (e.g., Banbury mixer, kneader, roll, etc.).

[0033] [2] Supercritical fluid contact process The supercritical fluid contact process is a process of obtaining a composition containing a hydroxyl-modified diene rubber by contacting the mixture of the present invention described above with a fluid (specific fluid) containing supercritical carbon dioxide and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more. Hereinafter, contact with the specific fluid will also be referred to as "processing".

[0034] [Mixture] The mixture of the present invention is as described above.

[0035] [Specified fluid] The specific fluid used in the manufacturing method of the present invention is a fluid containing supercritical carbon dioxide and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more.

[0036] [Supercritical carbon dioxide] Supercritical carbon dioxide is carbon dioxide subjected to temperatures above the critical temperature (31.1°C) and pressures above the critical pressure (7.38 MPa).

[0037] <Temperature> The temperature of the supercritical state described above is preferably 40°C or higher, and more preferably 50°C or higher, for the reasons that the effects of the present invention are superior. While there is no particular upper limit to the temperature of the supercritical state described above, it is preferably 100°C or lower, more preferably 90°C or lower, even more preferably 80°C or lower, and particularly preferably 70°C or lower, for reasons that the effects of the present invention are superior.

[0038] <Pressure> The pressure in the supercritical state described above is preferably 10 MPa or higher, more preferably 15 MPa or higher, and even more preferably 20 MPa or higher, for the reasons that the effects of the present invention are superior. While there is no particular upper limit to the pressure in the supercritical state described above, it is preferably 50 MPa or less, more preferably 40 MPa or less, and even more preferably 30 MPa or less, for reasons that the effects of the present invention are superior.

[0039] <Content> The carbon dioxide content in the specific fluid is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 60 to 99% by mass, more preferably 70 to 95% by mass, and even more preferably 80 to 90% by mass.

[0040] <Quantity relative to diene rubber> The amount of carbon dioxide relative to the diene rubber described above is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100 to 2000% by mass, more preferably 300 to 1500% by mass, even more preferably 500 to 1000% by mass, and particularly preferably 700 to 800% by mass.

[0041] 〔water〕

[0042] <Water / carbon dioxide> In a specific fluid, the amount of water relative to the carbon dioxide (hereinafter also referred to as "water / carbon dioxide") is 5% by mass or more. The water / carbon dioxide ratio is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 15% by mass or more, for which the effects of the present invention are superior. While there is no particular upper limit to the water / carbon dioxide ratio, it is preferably 100% by mass or less, more preferably 50% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less, for reasons that the effects of the present invention are superior.

[0043] <Content> The water content in the specific fluid is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass.

[0044] <Quantity relative to diene rubber> The amount of water in the diene rubber described above is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 10 to 500% by mass, more preferably 30 to 300% by mass, even more preferably 50 to 150% by mass, and particularly preferably 80 to 120% by mass.

[0045] 〔temperature〕 The temperature of the specific fluid is above the critical temperature of carbon dioxide (31.1°C). The preferred temperature for a particular fluid is the same as the temperature of the supercritical state described above.

[0046] 〔pressure〕 The pressure of the specific fluid is above the critical pressure of carbon dioxide (7.38 MPa). The preferred pressure configuration for a particular fluid is the same as the pressure in the supercritical state described above.

[0047] [Iss] The pH of the specific fluid is not particularly limited, but for the reasons that the effects of the present invention are superior, it is preferably 6 or less, more preferably 5 or less, even more preferably 4 or less, particularly preferably 3 or less, and most preferably 2 or less. While there are no particular limitations on the lower limit of the pH of the specific fluid, it is preferable that it be 1 or higher for better effects of the present invention. The pH of a particular fluid can be adjusted, for example, by adding an acid.

[0048] 〔acid〕 The specific fluid may contain an acid other than carbonic acid (for example, phosphoric acid).

[0049] <Content> When a specific fluid contains the above-mentioned acid, the content of the acid in the specific fluid is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 0.001 to 1% by mass, and more preferably 0.01 to 0.1% by mass.

[0050] <Quantity relative to diene rubber> When a specific fluid contains the above-mentioned acid, the amount of the above-mentioned acid relative to the diene-based rubber is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 0.01 to 10% by mass, and more preferably 0.1 to 1% by mass.

[0051] [Contact method] The method for bringing the mixture of the present invention described above into contact with the specific fluid described above is not particularly limited, but for example, one method is to seal the mixture of the present invention and water in a pressure vessel, fill it with supercritical carbon dioxide, and then allow it to stand. The temperature inside the vessel should be above the critical temperature of carbon dioxide, and the pressure should be above the critical pressure of carbon dioxide. The standing time is not particularly limited, but for better effects of the present invention, it is preferably 1 to 600 minutes, more preferably 10 to 300 minutes, and even more preferably 60 to 120 minutes.

[0052] [3] Hydroxyl-modified diene rubber As described above, the manufacturing method of the present invention yields a composition containing hydroxyl-modified diene rubber.

[0053] [Method for confirming hydroxyl group denaturation] The presence of hydroxyl groups in diene rubber can be confirmed, for example, by measuring the IR (infrared spectroscopy) spectrum.

[0054] The following examples illustrate specific methods for confirming hydroxyl group modification. First, the IR spectrum of 2-methyl-2-butanol (a model compound for hydroxyl-modified natural rubber or hydroxyl-modified polyisoprene) is measured. The measured IR spectrum shows 3370 cm⁻¹. -1 A broad peak originating from hydroxyl groups (OH stretching vibrations) is observed in the vicinity. Next, the IR spectra of natural rubber (raw material), polyisoprene (raw material), and the compositions obtained in the examples were measured. The IR spectrum of the compositions obtained in the examples was 3370 cm⁻¹. -1 Since a peak is observed in the vicinity, it can be said that hydroxyl groups have been introduced into the hydroxyl-modified natural rubber or hydroxyl-modified polyisoprene contained in the composition obtained in the example.

[0055] [Degeneration rate] In the hydroxyl group-modified diene rubber of the present invention, the percentage (%) of repeating units into which hydroxyl groups have been introduced out of the total repeating units (hereinafter also referred to as the "modification rate") is not particularly limited, but it is preferably 0.1% or more, more preferably 0.5% or more, even more preferably 1% or more, and particularly preferably 2% or more. The upper limit of the above-mentioned rate of denaturation is not particularly limited, but it is preferably 90% or less, more preferably 50% or less, even more preferably 10% or less, and particularly preferably 5% or less.

[0056] The following examples illustrate specific methods for determining the rate of denaturation. In the IR spectrum described above, 2940 cm⁻¹ -1 The peak observed in the vicinity is a peak originating from CH stretching vibrations. The aforementioned 3370 cm is the relative intensity of this peak. -1 The denaturation rate is determined from the ratio of nearby peak intensities (hereinafter also referred to as the "peak intensity ratio"). Specifically, the peak intensity ratio for 2-methyl-2-butanol is determined, and this peak intensity ratio is set as the denaturation rate of 100%. The denaturation rates for each example are then determined from their respective peak intensity ratios. [Examples]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] [Manufacturing of hydroxyl-modified natural rubber composition] The following hydroxyl-modified natural rubber compositions were prepared.

[0059] [Example 1]

[0060] <Mixture preparation process> 50 parts by mass of silica were mixed with 100 parts by mass of natural rubber. The mixing conditions were a temperature of 80°C, a time of 2 minutes, and a mixing speed of 30 rpm (rotation per minute).

[0061] <Supercritical fluid contact process> Next, 20 mL of the obtained mixture and 20 g of water were sealed in a 200 mL pressure-resistant container (manufactured by Toyo Koatsu Co., Ltd.), and then filled with supercritical carbon dioxide. The temperature inside the container was 60°C and the pressure was 25 MPa. In this way, the mixture was brought into contact with a fluid containing water and supercritical carbon dioxide (water / carbon dioxide: 17.3% by mass, pH: approximately 3). This was left to stand for 2 hours. After that, the container was opened and the carbon dioxide was allowed to volatilize. Next, the mixture was removed from the container, and its IR spectrum was measured, confirming that hydroxyl groups had been introduced into the natural rubber. In this way, a composition containing hydroxyl-modified natural rubber (hydroxyl-modified natural rubber composition) was obtained.

[0062] [Example 2] The mixture preparation and supercritical fluid contact steps were carried out in the same manner as in Example 1, except that 50 parts by mass of carbon black were used instead of 50 parts by mass of silica. The mixture was removed from the container and its IR spectrum was measured, confirming that hydroxyl groups had been introduced into the natural rubber. In this way, a composition containing hydroxyl-modified natural rubber (hydroxyl-modified natural rubber composition) was obtained.

[0063] [Example 3] The mixture preparation step and supercritical fluid contact step were carried out in the same manner as in Example 1, except that 100 parts by mass of polyisoprene were used instead of 100 parts by mass of natural rubber. The mixture was removed from the container and its IR spectrum was measured, confirming that hydroxyl groups had been introduced into the polyisoprene. In this way, a composition containing hydroxyl-modified polyisoprene (hydroxyl-modified polyisoprene composition) was obtained.

[0064] [Comparative Example 1] Without performing the mixture preparation step, the supercritical fluid contact step was carried out in the same manner as in Example 1, using natural rubber instead of the mixture. When the natural rubber was removed from the container and its IR spectrum was measured, it was confirmed that hydroxyl groups had been introduced into the natural rubber. In this way, hydroxyl-modified natural rubber (hydroxyl-modified natural rubber) was obtained. Next, 50 parts by mass of silica were mixed with 100 parts by mass of the obtained hydroxyl-modified natural rubber. In this way, a composition containing hydroxyl-modified natural rubber (hydroxyl-modified natural rubber composition) was obtained.

[0065] [Comparative Example 2] The mixture preparation and supercritical fluid contact steps were carried out in the same manner as in Example 1, except that the amount of silica was changed to 10 parts by mass. When the mixture was removed from the container and its IR spectrum was measured, it was confirmed that hydroxyl groups had been introduced into the natural rubber. Next, 40 parts by mass of silica were mixed with 100 parts by mass of hydroxyl-modified natural rubber. In this way, a composition containing hydroxyl-modified natural rubber (hydroxyl-modified natural rubber composition) was obtained.

[0066] [Bounce rubber amount] The amount of bounding rubber (hereinafter also referred to as "amount of bounding rubber after treatment") was evaluated for each hydroxyl-modified natural rubber composition obtained. In addition, for each hydroxyl-modified natural rubber composition, the amount of bounding rubber (hereinafter also referred to as "amount of bounding rubber before treatment") was evaluated for the mixture obtained in the mixture preparation step (the mixture before the supercritical fluid contact step). For Comparative Examples 1 and 2, the amount of bounding rubber was evaluated for the mixture obtained by mixing 50 parts by mass of silica with 100 parts by mass of natural rubber, and this was taken as the amount of bounding rubber before treatment. For each example, the ratio of the amount of bounding rubber after treatment to the amount of bounding rubber before treatment × 100 (hereinafter also referred to as the "index") was calculated. The results are shown in Table 1. A higher index indicates a higher amount of bound rubber after treatment.

[0067] The method for evaluating the amount of bounce rubber is as follows: A certain amount of the composition or mixture is shredded, placed in a cage made of 325-mesh wire mesh, and immersed in toluene for 48 hours. The toluene-insoluble portion is air-dried and its mass is measured. Then, the amount of band rubber is calculated using the following formula. Bound rubber volume = [(Sample mass after toluene immersion and drying) - (Filler mass)] / (Diene rubber mass before toluene immersion)

[0068] [Table 1]

[0069] As can be seen from Table 1, the hydroxyl-modified diene rubber compositions obtained by the methods of Examples 1 to 3, in which a specific proportion of filler was mixed with diene rubber and then brought into contact with a specific fluid, showed a significant improvement in the amount of bounding rubber compared to before treatment. Furthermore, comparing Examples 1 and 2, Example 1, in which silica was used as the filler, showed a greater improvement in the amount of bounding rubber. Furthermore, a comparison between Example 1 and Example 3 revealed that Example 1, in which the diene rubber was natural rubber, showed a greater improvement in the amount of bounding rubber.

[0070] On the other hand, the hydroxyl-modified diene rubber composition obtained by the method of Comparative Example 1, in which the diene rubber was treated alone and then mixed with a filler, showed a slight improvement in the amount of bounding rubber compared to before treatment, but the rate of improvement was small. Furthermore, the hydroxyl-modified diene rubber composition obtained by the method of Comparative Example 2, in which the proportion of filler was less than 20 parts by mass per 100 parts by mass of diene rubber, also showed a slight improvement in the amount of bounding rubber compared to before treatment, but the rate of improvement was small.

Claims

1. A mixture containing 100 parts by mass of diene rubber and 20 to 150 parts by mass of at least one type of filler, A fluid containing supercritical carbon dioxide and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more, A method for producing a hydroxyl group-modified diene rubber composition, comprising contacting the two materials to obtain a composition containing a hydroxyl group-modified diene rubber.

2. A method for producing a hydroxyl group-modified diene rubber composition according to claim 1, wherein the diene rubber is natural rubber.

3. A method for producing a hydroxyl-modified diene rubber composition according to claim 1 or 2, wherein the filler is silica.

4. A method for producing a hydroxyl group-modified diene rubber composition according to claim 1 or 2, wherein the pressure of the supercritical state is 10 MPa or more.

5. A method for producing a hydroxyl group-modified diene rubber composition according to claim 1 or 2, wherein the amount of water relative to the carbon dioxide is 30% by mass or less.

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