JP2022087684A - Method for Producing Synthetic Polyisoprene Copolymer - Google Patents

Abstract

To provide a synthetic polyisoprene copolymer that can improve the mechanical strength of vulcanized rubber.SOLUTION: In the method for producing synthetic polyisoprene copolymer according to the embodiment, a latex containing a synthetic polyisoprene copolymer in which a vinyl monomer is graft-copolymerized on the surface of a synthetic polyisoprene rubber particle, and a polymerization initiator for the graft copolymerization is dried, and the obtained solid is immersed in a solvent in which the synthetic polyisoprene copolymer is not dissolved but the polymerization initiator is dissolved, and then the solid is taken out from the solvent.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a synthetic polyisoprene copolymer and a method for producing a vulcanized rubber using the method.

As a technique for modifying rubber, it is known that a vinyl monomer such as a styrene-based monomer or an acrylic-based monomer is graft-copolymerized with a rubber latex. For example, in Patent Document 1, by adding a vinyl monomer having alcoholicylan to a natural rubber latex and performing a graft copolymerization, the natural rubber particles are dispersed in a continuous phase formed by a graft chain in a phase-separated state. It is disclosed to obtain a natural rubber graft copolymer having a nanomatrix structure.

Patent Document 2 discloses that a nanomatrix-dispersed natural rubber having a nanomatrix structure formed by graft chains is synthesized by adding a styrene-based vinyl monomer to a deproteinized natural rubber latex and performing graft copolymerization. ..

On the other hand, Patent Document 3 discloses that a synthetic polyisoprene copolymer having a nanomatrix structure is obtained by graft-copolymerizing a vinyl monomer with a synthetic polyisoprene rubber latex.

Japanese Unexamined Patent Publication No. 2013-170268 Japanese Unexamined Patent Publication No. 2008-214481

Patent Document 3 discloses that the mechanical strength of an unvulcanized film of a synthetic polyisoprene copolymer having a nanomatrix structure is improved. However, when the synthetic polyisoprene copolymer was used as a rubber component and mixed with a filler to prepare a vulcanized rubber, it was found that the mechanical strength of the vulcanized rubber did not improve, but rather decreased.

In view of the above points, it is an object of the present invention to provide a method for producing a synthetic polyisoprene copolymer capable of improving the mechanical strength of vulcanized rubber.

In the method for producing a synthetic polyisoprene copolymer according to the embodiment of the present invention, a synthetic polyisoprene copolymer in which a vinyl monomer is graft-copolymerized on the surface of synthetic polyisoprene rubber particles and polymerization for the graft copolymerization are started. Drying the latex containing the agent, immersing the obtained solid in a solvent that does not dissolve the synthetic polyisoprene copolymer but dissolving the polymerization initiator, and removing the solid from the solvent. , Including.

The method for producing the vulcanized rubber according to the embodiment of the present invention is to produce a synthetic polyisoprene copolymer by the above method, dry-mix the obtained synthetic polyisoprene copolymer and a filler, and obtain. It involves vulcanizing the resulting mixture.

According to the embodiment of the present invention, a synthetic isoprene graft copolymer capable of improving the mechanical strength of the vulcanized rubber can be obtained.

Transmission electron micrograph of the rubber film obtained in Synthesis Example 1 Graph of strain-strain curve in tensile test of rubber film obtained in Synthesis Example 1

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

The present inventor considers the problem that the mechanical strength of the synthetic polyisoprene copolymer obtained by graft-copolymerizing a vinyl monomer on the surface of synthetic polyisoprene rubber particles does not improve when it is made into vulcanized rubber. During diligent studies, it was found that the polymerization initiator used for graft copolymerization causes vulcanization inhibition, which reduces the mechanical strength of the vulcanized rubber. Therefore, after taking out the solid material of the synthetic polyisoprene rubber from the synthetic polyisoprene copolymer latex by drying, the polymerization initiator is extracted from the solid material with a solvent, thereby solving the above-mentioned problems.

The method for producing a synthetic polyisoprene copolymer according to an embodiment includes the following steps.
(A) A step of drying a synthetic polyisoprene copolymer in which a vinyl monomer is graft-copolymerized on the surface of synthetic polyisoprene rubber particles and a latex containing a polymerization initiator for the graft copolymerization.
(B) A step of immersing the obtained solid material in a solvent in which the synthetic polyisoprene copolymer does not dissolve but the polymerization initiator dissolves, and
(C) A step of removing a solid substance from a solvent.

More specifically, a step of adding a vinyl monomer to the synthetic polyisoprene rubber latex (D) and performing graft copolymerization in the presence of a polymerization initiator may be included prior to the steps (A) to (C). That is, the method for producing the synthetic polyisoprene copolymer may include a step (D), a step (A), a step (B) and a step (C) in this order.

Further, in one embodiment, prior to step (D), (E) synthetic polyisoprene rubber latex (hereinafter, may be simply referred to as IR latex) is stirred under heating conditions of 50 ° C. or higher and centrifuged. It may include the step of purifying by. That is, the method for producing the synthetic polyisoprene copolymer may include a step (E), a step (D), a step (A), a step (B) and a step (C) in this order.

[Step (E)]
Step (E) is a step to remove the rosin-based surfactant from the surface of the rubber particles when the IR latex contains a rosin-based surfactant, and the graft copolymerization of the next step (D) is performed. It can be facilitated. The step (E) is an optional step and may not be carried out, for example, when the IR latex does not contain a rosin-based surfactant.

As the IR latex used as a starting material, a rubber latex containing cis-1,4-polyisoprene rubber can be used, and a commercially available product may be used. Examples of the rosin-based surfactant contained in a commercially available IR latex as an emulsifier include rosin acid soap and disproportionated rosin acid soap.

In the step (E), the heating temperature for stirring the IR latex is preferably 50 ° C. or higher, more preferably 60 ° C. or higher and 70 ° C. or lower, or 85 ° C. or higher and lower than 100 ° C., still more preferably 85. ° C or higher and 95 ° C or lower. The stirring time for stirring the IR latex is not particularly limited, and may be, for example, 10 to 200 minutes or 20 to 120 minutes.

The concentration of IR latex when stirring the IR latex is not particularly limited, and may be, for example, 10 to 60% by mass or 20 to 50% by mass in terms of rubber concentration (DRC: Dry Rubber Content).

When stirring the IR latex, a surfactant that does not inhibit the copolymerization reaction with the vinyl monomer may be added to the IR latex. As such a surfactant, an anionic surfactant, a nonionic surfactant, and a cationic surfactant can be used. Examples of the anionic surfactant include a carboxylic acid type, a sulfonic acid type, a sulfate ester type, a phosphoric acid ester type and the like. Examples of the nonionic surfactant include polyoxyalkylene ether type, polyoxyalkylene ester type, polyhydric alcohol fatty acid ester type, sugar fatty acid ester type, alkyl polyglycoside type and the like. Examples of the cationic surfactant include an alkylamine salt type, an alkylamine derivative type and a quaternary product thereof, and an imidazolinium salt type. The amount of the surfactant added may be 0.01 to 3% by mass or 0.05 to 2% by mass in terms of the concentration in IR latex.

After heating and stirring in this way, centrifugation is performed to separate the cream containing synthetic polyisoprene rubber and the serum containing serum. Purified synthetic polyisoprene rubber latex (purified IR latex) is obtained by adding water to the obtained cream and redispersing it.

Heating stirring and centrifugation may be repeated a plurality of times. That is, after the IR latex is heated and stirred and centrifuged, water and a surfactant are added to the cream when the cream is redistributed, and the mixture is stirred under the above heating conditions, and then the cream is centrifuged. It may be repeated multiple times. The number of repetitions is not particularly limited, and for example, heating and stirring and centrifugation may be performed 2 to 5 times.

The concentration of the purified IR latex is not particularly limited, and may be, for example, 10 to 60% by mass or 20 to 50% by mass in terms of rubber concentration (DRC). Further, a surfactant that does not inhibit the copolymerization reaction with the vinyl monomer may be added to the purified IR latex. The amount of the surfactant added may be 0.01 to 3% by mass or 0.05 to 2% by mass in terms of the concentration in the purified IR latex.

[Step (D)]
Step (D) is a step of graft-copolymerizing a vinyl monomer with IR latex. As the IR latex, the purified IR latex obtained in the step (E) may be used, or the IR latex not purified in the step (E) may be used.

The vinyl monomer is not particularly limited as long as it can be grafted on the surface of synthetic polyisoprene rubber particles, and is styrene-based such as styrene, methylstyrene, ethylstyrene, propylstyrene, butylstyrene, pentylstyrene and other alkylstyrenes. Monomers; Vinyl alkoxysilane monomers such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (2-methoxyethoxy) silane, vinylmethyldimethoxysilane; (meth) acrylic acid, (meth) methyl acrylate, 2-hydroxyethyl ( (Meta) acrylic acid-based monomers such as (meth) acrylate; (meth) acrylamide-based monomers such as (meth) acrylamide and alkyl (meth) acrylamide; vinyl ester-based monomers such as vinyl acetate; nitrile vinyl monomers such as acrylonitrile; vinyl Examples thereof include pyrrolidone. Any one of these may be used, or two or more thereof may be used in combination. Here, "(meth) acrylic acid" means one or both of acrylic acid and methacrylic acid, and "(meth) acrylate" means one or both of acrylate and methacrylate. "(Meta) acrylamide" means one or both of acrylamide and methacrylamide.

The amount of the vinyl monomer added is not particularly limited, but is preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass with respect to 100 parts by mass of the synthetic polyisoprene rubber. By setting such an addition amount, it is possible to secure the graft amount of the vinyl monomer and enhance the modification effect, and suppress the formation of homopolymer to enhance the graft efficiency.

A polymerization initiator is added to the IR latex to graft-copolymerize the vinyl monomer. Examples of the polymerization initiator include benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, 2,2-azobisisobutyronitrile, potassium persulfate and the like. It is preferable to use a redox-based initiator consisting of an oxide in combination with a reducing agent such as tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ion, and ascorbic acid, and more preferably tert-butyl hydroperoxide. It is a combination of a hydroperoxide such as, and an amine such as tetraethylenepentamine. The amount of the polymerization initiator added is not particularly limited, and may be, for example, 0.3 to 10 mol% with respect to 100 mol of the vinyl monomer.

Synthetic polyisoprene obtained by graft-copolymerizing a vinyl monomer on the surface of synthetic polyisoprene rubber particles by charging IR latex, vinyl monomer and polymerization initiator into a reaction vessel and carrying out a reaction at 25 to 80 ° C. for 1 to 10 hours. A latex containing a polymer can be obtained. The latex further contains a polymerization initiator.

After the reaction is completed, the unreacted vinyl monomer may be removed under reduced pressure. At that time, there may be a polymerization initiator that is removed together with the vinyl monomer, but in the following steps, the latex of the synthetic polyisoprene copolymer containing the polymerization initiator that is not removed even at this stage is treated.

[Step (A)]
In step (A), the latex containing the synthetic polyisoprene copolymer and the polymerization initiator is dried. Specifically, by vaporizing water from the latex and drying it, a solid synthetic polyisoprene copolymer can be obtained.

By drying the latex in this way to obtain a solid substance, a synthetic polyisoprene rubber copolymer having a nanomatrix structure in which synthetic polyisoprene rubber particles are dispersed in a continuous phase formed by a graft chain in a phase-separated state. Can be obtained in an advantageous manner. That is, for example, a solid synthetic polyisoprene copolymer can be recovered by coagulating the latex with methanol, but the synthetic polyisoprene copolymer thus obtained has the above-mentioned nanomatrix structure. It was found that it was difficult to form. By vaporizing water by drying to obtain a solid substance, a synthetic polyisoprene copolymer having a nanomatrix structure can be obtained more advantageously.

The drying method may be heat drying or vacuum drying. In the case of heat drying, the drying temperature is not particularly limited as long as water can be vaporized from the latex, and may be, for example, 30 to 100 ° C. or 50 to 70 ° C.

At the time of drying, in order to increase the area in contact with the solvent in the step (B) of the next step and improve the extraction efficiency of the polymerization initiator, it is preferable to form the solid into a shape having a large surface area after drying. Therefore, it is preferable to mold the sheet of the synthetic polyisoprene copolymer as the solid substance by, for example, cast molding. The thickness of the sheet of the synthetic polyisoprene copolymer is not particularly limited, and may be, for example, 0.5 to 10 mm or 1 to 5 mm. The sheet referred to here is a concept including a thin film generally called a film.

There may be a polymerization initiator that is vaporized or decomposed and removed by drying the latex, but there are polymerization initiators that are not removed in the drying step. Therefore, the obtained solid contains a polymerization initiator together with the synthetic polyisoprene copolymer. Examples of the polymerization initiator contained in such a solid substance include tetraethylenepentamine, sodium bisulfite, reducing metal ions, ascorbic acid and the like.

[Step (B)]
In the step (B), the solid substance obtained in the step (A), that is, the solid substance containing the polymerization initiator together with the synthetic polyisoprene copolymer is immersed in the solvent.

As the solvent, a solvent that does not dissolve the synthetic polyisoprene copolymer but dissolves the polymerization initiator is used. As a result, the polymerization initiator is extracted from the solid material. Examples of such a solvent include acetone, methanol, ethanol, water and the like. Any one of these solvents may be used alone or in combination of two or more.

The solvent temperature when the solid material is immersed in the solvent is not particularly limited, and may be, for example, 0 to 50 ° C. or 20 to 30 ° C. The immersion time is also not particularly limited, and may be, for example, 12 to 240 hours or 72 to 120 hours. The dipping method is also not particularly limited, and the solid substance may be immersed in the solvent by standing still, or may be immersed while stirring or shaking, and the sheet-shaped solid substance may be continuously immersed in the bathtub containing the solvent. You may put it in the bathtub and run it in the bathtub to soak it.

[Step (C)]
In the step (C), the solid material immersed in the solvent in the step (B) is taken out from the solvent. As a result, a synthetic polyisoprene copolymer in which the polymerization initiator is removed or reduced by extraction can be obtained. Therefore, the inhibition of vulcanization by the polymerization initiator is suppressed, and the decrease in the mechanical strength of the vulcanized rubber can be suppressed.

In the step (C), after removing the solid matter from the solvent, it is usually dried. The drying method may be heat drying or vacuum drying. In the case of heat drying, the drying temperature is not particularly limited, and may be, for example, 30 to 100 ° C. or 50 to 70 ° C.

The solid substance taken out from the solvent may be used as it is as a rubber component for producing vulcanized rubber. This is because the solvent can be vaporized and removed by heating during kneading of the rubber composition.

[Synthetic polyisoprene copolymer]
The synthetic polyisoprene copolymer obtained by the above production method is obtained by graft-copolymerizing a vinyl monomer on the surface of synthetic polyisoprene rubber particles, and is also referred to as a synthetic polyisoprene graft copolymer. The synthetic polyisoprene copolymer has a nanomatrix structure in which synthetic polyisoprene rubber particles are dispersed in a continuous phase having a thickness of 1 to 100 nm formed by a graft chain in a phase-separated state.

The synthetic polyisoprene copolymer may be composed of only a synthetic polyisoprene copolymer having a nanomatrix structure, or may contain a homopolymer composed of the vinyl monomer. That is, in the case of graft copolymerization, not only the graft copolymer but also homopolymers are usually produced from vinyl monomers, so a mixture containing such homopolymers in a mixed state may be used.

In the synthetic polyisoprene copolymer having such a nanomatrix structure, the particle size of the synthetic polyisoprene rubber particles depends on the particle size of the raw material IR latex and is not particularly limited, but the average particle size is 0.01. It may be up to 20 μm or 0.04 to 3.0 μm. Here, the average particle size is obtained as an additive average by measuring the diameters of 100 randomly selected particles from a transmission electron microscope (TEM) image. The diameter of the particle is, for example, the average value of the diameter measured in 2 degree increments by connecting two points on the outer circumference of the particle and passing through the center of gravity using the image processing software "Image-Pro Plus" of Media Cybernetics. Can be. When measuring the particle size of synthetic polyisoprene rubber particles using IR latex as a raw material, the value of D50 measured using a laser diffraction type particle size distribution measuring device may be used.

In the nanomatrix structure, the graft chain, which is a polymer of vinyl monomer, forms a continuous phase (that is, a matrix phase) having a thickness of 1 to 100 nm. The continuous phase intervenes between the particles of the synthetic polyisoprene rubber particles to phase-separate the rubber particles, and is formed in a layer between the rubber particles. The thickness of the continuous phase is more preferably 5 to 50 nm. Here, the thickness of the continuous phase is added by measuring the thickness of the graft chain formed between 100 sets of randomly selected rubber particles from the image of a transmission electron microscope (TEM). Obtained as an average.

In the synthetic polyisoprene copolymer, the content of the graft chain made of vinyl monomer is not particularly limited, and may be, for example, 3 to 30% by mass, 5 to 25% by mass, or 8 to 20% by mass. Here, the content of the graft chain is the ratio of the mass of the graft chain portion to the mass of the entire synthetic polyisoprene copolymer.

[Manufacturing method of vulcanized rubber]
The method for producing a vulcanized rubber according to one embodiment includes a step of producing a synthetic polyisoprene copolymer as described above, and then (F) a dry mixing step of the obtained synthetic polyisoprene copolymer and a filler. , (G) The step of vulcanizing the obtained mixture.

[Step (F)]
In the step (F), a synthetic polyisoprene copolymer is used as a rubber component, and a filler or the like is dry-mixed with the synthetic polyisoprene copolymer to prepare an unvulcanized rubber composition.

The rubber component may be only a synthetic polyisoprene copolymer, or may be used in combination with another diene-based rubber together with the synthetic polyisoprene copolymer. The other diene rubber is not particularly limited, and for example, natural rubber (NR), polybutadiene rubber (BR), styrene butadiene rubber (SBR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and the like. Examples thereof include styrene-isoprene-butadiene copolymer rubber, and these can be used alone or in combination of two or more.

Examples of the filler include carbon black, silica and the like. The blending amount of the filler is not particularly limited, and may be, for example, 1 to 150 parts by mass, 3 to 100 parts by mass, or 10 to 50 parts by mass with respect to 100 parts by mass of the rubber component.

In addition to the above components, unvulcanized rubber compositions generally include, for example, zinc oxide, stearic acid, oil, wax, antiaging agents, vulcanizing agents (eg sulfur), vulcanization accelerators, and the like. Various additives used can be blended and may be dry mixed with the filler.

For dry-type mixing, a mixer such as a Banbury mixer, a kneader, or a roll can be used, and kneading may be performed according to a conventional method. For example, in the first mixing step (non-professional kneading step), additives other than the vulcanizing agent and the vulcanization accelerator are added and mixed with the rubber component together with the filler. Next, an unvulcanized rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator in the final mixing step (professional kneading step) to the obtained mixture.

[Process (G)]
In the step (G), a vulcanized rubber is obtained by vulcanizing the mixture obtained in the step (F), that is, the unvulcanized rubber composition.

At the time of vulcanization, the unvulcanized rubber composition is formed into a shape suitable for its intended use and heated. For example, when the unvulcanized rubber composition is used for a part of a tire such as a pneumatic tire, an unvulcanized tire using the unvulcanized rubber composition for the part thereof is produced, and the unvulcanized tire is used. By vulcanization molding, a tire containing vulcanized rubber made of the unvulcanized rubber composition can be obtained. Even when used in various rubber products such as anti-vibration rubber, condoms, rubber gloves, and other medical fields and household products, the above unvulcanized rubber composition should be vulcanized into a predetermined shape alone or in combination with other members. Therefore, a rubber product containing a vulcanized rubber made of the above-mentioned unvulcanized rubber composition can be obtained.

The temperature (vulcanization temperature) at which the unvulcanized rubber composition is vulcanized is not particularly limited, and may be, for example, 100 to 200 ° C. or 130 to 180 ° C. The vulcanization time is also not particularly limited, and may be, for example, 5 to 100 minutes or 10 to 50 minutes.

Hereinafter, the present embodiment will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Reagents used]
-Raw material IR latex: "IRL701" manufactured by BST Specialty Co., Ltd.
・ Sodium dodecyl sulfate: manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. ・ tert-Butyl hydroperoxide: manufactured by Tokyo Chemical Industry Co., Ltd. ・ Tetraethylenepentamine: manufactured by Tokyo Chemical Industry Co., Ltd. Made by Acetone: Made by Nacalai Tesque Co., Ltd. Polyisoprene rubber: Made by JSR Corporation "JSR IR2200"
-Carbon black: "N339 Seast KH" manufactured by Tokai Carbon Co., Ltd.
・ Zinc Oxide: “Zinc Oxide Type 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
-Stearic acid: "Lunac S-20" manufactured by Kao Corporation
・ Sulfur: “Powdered sulfur 150 mesh for rubber” manufactured by Hosoi Chemical Industry Co., Ltd.
・ Vulcanization accelerator 1: "Noxeller CZ" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
・ Vulcanization accelerator 2: "Noxeller NS-P" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

[Purification of IR latex]
Sodium dodecyl sulfate (SDS) and ion-exchanged water were added to the raw material IR latex to prepare the SDS concentration to 1% by mass and the TSC (total solid content of the latex) to 30% by mass. The obtained TSC 30% by mass IR latex was stirred at a normal pressure of 200 rpm for 60 minutes using a stirrer after setting the stirring temperature to 90 ° C. Then, the IR latex was centrifuged (12000 G, 30 ° C., 30 minutes) and separated into a cream component and a serum component. Distilled water and SDS were added to this cream content and redistributed so that the concentration of SDS was 0.5% by mass and the DRC was 30% by mass. After stirring at 200 rpm for 60 minutes, centrifugation (12000 G, 30 ° C., 30 minutes) was performed. After repeating this redispersion, heating and stirring and centrifugation once more, distilled water and SDS were added to the cream obtained by the final centrifugation, and the concentration of SDS was 0.1% by mass and the DRC was 30. Purified IR latex was obtained by redispersing to a mass%.

[Graft copolymerization]
The purified IR latex was replaced with nitrogen for 1 hour with stirring at 30 ° C. and 200 rpm. Then, tert-butyl hydroperoxide (TBHPO) and tetraethylenepentamine (TEPA) were sequentially added dropwise in the amounts shown in Table 1 as the polymerization initiator. Further, after adding the styrene monomer in the amount shown in Table 1, the polymerization reaction was carried out at 30 ° C. and 400 rpm for 2 hours. The unreacted styrene monomer was removed from the latex after the reaction at 90 ° C. using a rotary evaporator to obtain the latex of Synthesis Examples 1 to 3 containing the synthetic polyisoprene copolymer. At that time, the polymerization initiator TBHPO is decomposed or vaporized together with the unreacted styrene monomer and removed from the latex. Then, the latex containing the synthetic polyisoprene copolymer was cast on a tray and vacuum dried for 3 days to obtain an ascast film having a thickness of about 2 mm. The amount in Table 1 is a molar amount (mol / kg) with respect to 1 kg of rubber in IR latex.

The formula for calculating the styrene content in Table 1 is as follows.

[Observation of morphology of ascast film]
The ascast film obtained from the latex of Synthesis Example 1 was dyed with _OsO4 , and then ultrathin sections were prepared using a cryomicrotome (Leica EM FC6 / UC6 manufactured by Leica), and a transmission electron microscope (TEM, FEI) was prepared. The phase separation structure was observed with a Talos F200X manufactured by Talos F200X and an acceleration voltage of 200 kV).

As a result, the synthetic polyisoprene rubber particles are phase-separated from the grafted polystyrene, and the synthetic polyisoprene rubber particles having a diameter of about 1 μm are dispersed in the grafted styrene continuous phase having a thickness of several nm to several tens of nm. A phase separation state between the grafted styrene continuous phase and the synthetic polyisoprene rubber particle dispersed phase was observed. FIG. 1 is a transmission electron micrograph of the ascast film, in which the black phase shows synthetic polyisoprene rubber particles and the white phase shows polystyrene.

[Tensile test of ascast film]
A tensile test was performed on the ascast film obtained from the latex of Synthesis Example 1 and the ascast film obtained from the raw material IR latex according to JIS K6251. The tensile test was carried out by punching an ascast film with a dumbbell-shaped No. 3 shape at room temperature and a tensile speed of 500 mm / min. The ascast film of the raw material IR latex was prepared as a film having a thickness of about 2 mm by casting the raw material IR latex on a tray and vacuum-drying it for 3 days in the same manner as in Synthesis Example 1.

As a result of the tensile test, the strain-strain curve is shown in FIG. While the breaking stress of the film obtained from the raw material IR latex was 0.23 MPa, the breaking stress of the synthetic polyisoprene copolymer film obtained from the latex of Synthesis Example 1 increased to about 2 MPa. From this result, it can be seen that the breaking strength increases due to the formation of the nanomatrix structure.

[Examples 1 to 3]
The latex containing the synthetic polyisoprene copolymer obtained in Synthesis Examples 1 to 3 (which contains the polymerization initiator TEPA) was cast on a tray, air-dried, and then air-dried at 50 ° C. under vacuum. By vacuum drying for one day, an ascast film having a thickness of 2 mm was obtained.

80 g of the obtained ascast film was immersed in 500 mL of acetone at 25 ° C. for 3 days to extract TEPA into acetone. Then, the ascast film was taken out from acetone and vacuum dried for 1 day to obtain the synthetic polyisoprene copolymer of Examples 1 to 3.

[Comparative Example 1]
The latex containing the synthetic polyisoprene copolymer obtained in Synthesis Example 1 was cast on a tray and air-dried, and then vacuum-dried at 50 ° C. under vacuum for 2 days to obtain an ascast film having a thickness of 2 mm. This was used as the synthetic polyisoprene copolymer of Comparative Example 1.

[Examples 4 to 8, Comparative Examples 2 to 5]
An unvulcanized rubber composition was prepared using a Banbury mixer according to the formulations (parts by mass) shown in Tables 2 and 3 below. Specifically, first, in the first mixing step, a compounding agent excluding sulfur and a vulcanization accelerator was added to the rubber component and kneaded (emission temperature = 160 ° C.). Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product in the final mixing step and kneaded (emission temperature = 90 ° C.). In the table, the copolymers of Examples 1 to 3 and Comparative Example 1 indicate the synthetic polyisoprene copolymers of Examples 1 to 3 and Comparative Example 1, respectively.

The obtained unvulcanized rubber composition was vulcanized at 150 ° C. for 25 minutes, and the tensile stress of the vulcanized rubber sample was evaluated. Specifically, a tensile test (dumbbell-shaped No. 7 type) conforming to JIS K6251 was performed on the vulcanized rubber sample, and the stress at the time of 300% elongation was determined. Then, Comparative Example 3 and Examples 4 to 6 in Table 2 are displayed as an index with the value of Comparative Example 2 as 100, and Comparative Example 5 and Examples 7 and 8 in Table 3 are displayed in Comparative Example 4. It was displayed as an index with the value set to 100. The larger the index, the better the fracture characteristics (mechanical strength).

As shown in Table 2, in Examples 4 to 6 using the synthetic polyisoprene copolymers of Examples 1 to 3 extracted with acetone, compared with Comparative Example 2 using the polyisoprene rubber not graft-copolymerized. The breaking characteristics have been improved. In particular, in Example 4 using the synthetic polyisoprene copolymer of Example 1 having a high styrene content, the fracture characteristics were significantly improved.

On the other hand, in Comparative Example 3 using the synthetic polyisoprene copolymer of Comparative Example 1 which was not extracted with acetone, although the synthetic polyisoprene copolymer having a high styrene content was used, the breakdown characteristics were The improvement was small. As is clear when comparing Example 4 and Comparative Example 3 having the same styrene content, the fracture characteristics of the ascast film obtained by performing acetone extraction are remarkable as compared with those without acetone extraction. It was improving. In Comparative Example 3, it is considered that vulcanization inhibition is caused by the remaining TEPA.

As shown in Table 3, even when the blending amount of carbon black was increased to 30 parts by mass, graft copolymerization was not carried out in Examples 7 and 8 using the synthetic polyisoprene copolymers of Examples 1 and 2. The fracture characteristics were improved as compared with Comparative Example 4 using the polyisoprene rubber, and in particular, the improvement range was large in Example 7 having a high styrene content. In Comparative Example 5, although the synthetic polyisoprene copolymer having a high styrene content was used, the fracture property was lower than that of the unmodified Comparative Example 4. That is, when the amount of carbon black is increased, the influence of the deterioration of the fracture characteristics due to the inhibition of vulcanization tends to be large, and as is clear from the comparison between Example 7 and Comparative Example 5, the fracture characteristics are significantly improved by the acetone extraction. The effect was seen.

Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments, omissions, replacements, changes, etc. thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

Claims (4)

Drying a latex containing a synthetic polyisoprene copolymer in which a vinyl monomer is graft-copolymerized on the surface of synthetic polyisoprene rubber particles and a polymerization initiator for the graft copolymerization.
The obtained solid material is immersed in a solvent in which the synthetic polyisoprene copolymer is not dissolved but the polymerization initiator is dissolved, and
Extracting the solid from the solvent,
A method for producing a synthetic polyisoprene copolymer containing the above. The method for producing a synthetic polyisoprene copolymer according to claim 1, wherein the polymerization initiator contains tetraethylenepentamine. The method for producing a synthetic polyisoprene copolymer according to claim 1 or 2, wherein the solvent comprises at least one selected from the group consisting of acetone, methanol, ethanol and water. Producing a synthetic polyisoprene copolymer by the method according to any one of claims 1 to 3.
Dry-mixing the obtained synthetic polyisoprene copolymer and the filler, and
Vulcanizing the resulting mixture,
A method for producing vulcanized rubber including.

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