Organic particles, their manufacturing method, and materials

Abstract

The present invention provides organic particles with high solvent resistance, which are made from a polymer having a main skeleton of cis-1,4-polyisoprene, a typical example of which is natural rubber. [Solution] A method for producing organic particles includes the steps of dissolving a polymer having cis-1,4-polyisoprene as a main skeleton in a solvent and carrying out a cyclization reaction to obtain a cyclized rubber having a cyclization rate of 60 to 90%, and suspension polymerizing the cyclized rubber and a vinyl monomer in the presence of water and a suspension stabilizer, wherein the polymer having cis-1,4-polyisoprene as a main skeleton has a Mooney viscosity [ML(1+4)100°C] specified in JIS K 6300 of 18 to 65, and the vinyl monomer contains a monofunctional vinyl monomer having only one vinyl group and a crosslinkable vinyl monomer having multiple vinyl groups.

Description

[Technical Field]

[0001] The present invention relates to organic particles, a method for producing the same, and materials. [Background technology]

[0002] Particles such as acrylic beads, polystyrene beads, and polyurethane beads are used in a variety of products such as paints, plastics, adhesives, and cosmetics. In particular, there is a growing need for micrometer-scale particles.

[0003] A method has been proposed for producing micrometer-scale particles by suspending an organic solvent solution of cyclized natural rubber in a medium that is insoluble or only slightly soluble in the organic solvent, and then heating the suspension to evaporate the organic solvent simultaneously with the crosslinking reaction, thereby forming spherical particles of cyclized natural rubber (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7153412 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the rubber particles disclosed in Patent Document 1 are not completely solvent-resistant, and a significant portion dissolves in the solvent. To improve solvent resistance, it is necessary to reduce the cyclization rate of the natural rubber and increase the double bond content, but it has been found that further reducing the cyclization rate of the rubber particles disclosed in Patent Document 1 increases tack (surface stickiness), making particle formation difficult. An object of the present invention is to provide organic particles having high solvent resistance, which are made of a polymer having a main skeleton of cis-1,4-polyisoprene, a typical example of which is natural rubber. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention employs the following configuration. [1] A method for producing a cyclized rubber having a cyclization rate of 60 to 90% by dissolving a polymer having cis-1,4-polyisoprene as a main skeleton in a solvent and carrying out a cyclization reaction therein; and a method for suspension polymerization of the cyclized rubber and a vinyl monomer in the presence of water and a suspension stabilizer, the polymer having cis-1,4-polyisoprene as a main skeleton has a Mooney viscosity [ML(1+4)100°C] as defined in JIS K 6300 of 18 to 65; The method for producing organic particles, wherein the vinyl monomer comprises a monofunctional vinyl monomer having only one vinyl group and a crosslinkable vinyl monomer having multiple vinyl groups. [2] The method for producing organic particles according to [1], wherein the polymer having cis-1,4-polyisoprene as a main skeleton is obtained by masticating raw rubber. [3] The method for producing organic particles according to [2], wherein the raw rubber is natural rubber. [4] The monofunctional vinyl monomer is at least one selected from the group consisting of a monofunctional aromatic vinyl monomer having only one vinyl group bonded to a benzene ring and a monofunctional (meth)acrylic monomer having only one (meth)acryloyl group, The method for producing organic particles according to any one of [1] to [3], wherein the crosslinkable vinyl monomer is at least one selected from the group consisting of a crosslinkable aromatic vinyl monomer having a plurality of vinyl groups bonded to a benzene ring, and a crosslinkable (meth)acrylic monomer having a plurality of (meth)acryloyl groups, or a (meth)acryloyl group and an allyl group. [5] Organic particles obtained by polymerizing a cyclized rubber in which a polymer having cis-1,4-polyisoprene as the main skeleton is cyclized at a cyclization rate of 60 to 90% and a vinyl monomer, the polymer having cis-1,4-polyisoprene as a main skeleton has a Mooney viscosity [ML(1+4)100°C] as defined in JIS K 6300 of 18 to 65; The organic particles, wherein the vinyl monomer comprises a monofunctional vinyl monomer having only one vinyl group and a crosslinkable vinyl monomer having multiple vinyl groups. [6] The organic particles according to [5], wherein the polymer having cis-1,4-polyisoprene as a main skeleton is obtained by masticating raw rubber. [7] The organic particles according to [6], wherein the raw rubber is natural rubber. [8] The monofunctional vinyl monomer is at least one selected from the group consisting of a monofunctional aromatic vinyl monomer having only one vinyl group bonded to a benzene ring and a monofunctional (meth)acrylic monomer having only one (meth)acryloyl group, The organic particles according to any one of [5] to [7], wherein the crosslinkable vinyl monomer is at least one selected from the group consisting of a crosslinkable aromatic vinyl monomer having a plurality of vinyl groups bonded to a benzene ring, and a crosslinkable (meth)acrylic monomer having a plurality of (meth)acryloyl groups, or a (meth)acryloyl group and an allyl group. [9] The organic particles according to any one of [5] to [8], which have an average particle size of 1 μm to 300 μm.

[10] The organic particles according to any one of [5] to [9], which have a gel fraction of 80% or more as determined by the following method: (How to determine gel fraction) The organic particles are placed in a container and their mass (W1) is precisely weighed. Toluene is added so that the organic particle concentration becomes 0.625% by mass. 24 hours after the toluene addition, the liquid in the container is filtered through filter paper (particle retention size: 1 μm), and the resulting residue on the filter paper (toluene-insoluble matter) is dried at 110°C for 2 hours, and the mass (W2) of the toluene-insoluble matter is measured. The gel fraction is calculated based on the obtained masses W1 and W2 using the following formula (2). Gel fraction (%) = (W2 / W1) × 100 (2)

[11] A material containing the organic particles according to any one of [5] to

[10] . [Effects of the Invention]

[0007] According to the present invention, organic particles with high solvent resistance can be obtained by using a polymer having a main skeleton of cis-1,4-polyisoprene, which is typified by natural rubber. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an electron microscope photograph of organic particles obtained in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this specification and claims, the term "(meth)acryloyl group" means one or both of a methacryloyl group and an acryloyl group. Furthermore, the term "(meth)acrylic monomer" refers to either or both of a methacrylic monomer and an acrylic monomer. Moreover, "(meth)acrylic acid" means one or both of methacrylic acid and acrylic acid. Also, (meth)acrylate means either or both of acrylate and methacrylate. Also, PEG means polyethylene glycol. Furthermore, a numerical range expressed by "to" means a numerical range in which the numbers before and after "to" are the lower and upper limits.

[0010] <Method of manufacturing organic particles> The method for producing organic particles according to the present disclosure includes a step of dissolving a polymer having cis-1,4-polyisoprene as a main skeleton in a solvent and carrying out a cyclization reaction to obtain a cyclized rubber having a cyclization rate of 60 to 90% (cyclization step), and a step of suspension polymerizing the cyclized rubber and a vinyl monomer in the presence of water and a suspension stabilizer (suspension polymerization step).

[0011] The method for producing organic particles according to the present disclosure may include, after the suspension polymerization step, a step of removing the solvent from the suspension to obtain an aqueous dispersion in which the organic particles are dispersed in water (solvent removal step), a step of subjecting the aqueous dispersion obtained in the solvent removal step to solid-liquid separation and washing the recovered organic particles with water (washing step), and a step of drying the washed organic particles (drying step).

[0012] [Polymer to be subjected to cyclization step] In the cyclization step, a polymer having cis-1,4-polyisoprene as the main skeleton is used. "Having cis-1,4-polyisoprene as the main skeleton" means that the cis-1,4-polyisoprene units constituting the polymer account for 98% by mass or more of all units constituting the polymer.

[0013] The polymer having cis-1,4-polyisoprene as the main skeleton has a Mooney viscosity [ML(1+4)100°C] of 18 to 65 as defined in JIS K 6300. The Mooney viscosity [ML(1+4)100°C] of the polymer having cis-1,4-polyisoprene as the main skeleton is preferably 20 to 60, and more preferably 30 to 50.

[0014] The Mooney viscosity is a value measured at 100° C. in accordance with JIS K 6300. The symbol (ML1+4) has the following meaning. M: Mooney viscosity. L: Uses a large rotor. 1+4: The measured value when the sample was heated for 1 minute and then the rotor was rotated at 2 rpm for 4 minutes.

[0015] If the Mooney viscosity is 18 or more, the polymer can be easily granulated without being affected by the tackiness of the polymer having cis-1,4-polyisoprene as the main skeleton.If the Mooney viscosity is 65 or less, the plasticity is not too high, and the viscosity when dissolved in a solvent is not too high, so the polymer can be easily granulated.

[0016] The Mooney viscosity can be adjusted by masticating the raw rubber to reduce the molecular weight. Generally, mastication is carried out to adjust the elasticity and plasticity to a state that makes it easier to process. As a mastication method, a conventional method using mechanical shearing force, the action of oxygen in the air, a peptizer, heat, or a combination of these can be used. Among these, a method using mechanical shearing force is preferred because it is simple and makes it easy to control the Mooney viscosity. For the method using mechanical shearing force, a pressure kneader, a Banbury mixer, an open roll, or the like can be used. A mastication accelerator may be used during mastication.

[0017] The raw rubber used in the present disclosure may be either so-called natural rubber collected from plants (such as Hevea brasiliensis, dandelion, or Eucommia ulmoides), or synthetic rubber obtained by polymerizing isoprene monomers derived from naphtha and biomass. Examples of synthetic rubber include Nipol (registered trademark) IR2200 and IR2200L from Zeon Corporation, and IR2200 from ENEOS Materials Corporation.

[0018] The raw rubber may contain non-rubber components as long as the effects of the present invention are not impaired. For example, natural rubber, obtained from the sap of plants such as the Hevea tree, contains a polymer with a cis-1,4-polyisoprene backbone as well as water and non-rubber components (such as impurities such as proteins, fatty acids, and inorganic salts).

[0019] From the perspective of the SDGs (Sustainable Development Goals), natural rubber is preferred as the raw material. The natural rubber to be used may be one obtained by salting out and drying commercially available natural rubber latex (an emulsion of natural rubber), or may be commercially available solid natural rubber.

[0020] Commercially available solid natural rubber includes ribbed smoked sheet (RSS), pale crepe, standard Malaysian rubber (SMR), standard Vietnamese rubber (SVR), and thick pale crepe (TPC).

[0021] When a rubber obtained by salting out and drying a commercially available natural rubber latex (an emulsion of natural rubber) is used as the raw rubber, the content of the rubber component (i.e., natural rubber) relative to the total mass of the natural rubber latex is preferably 10 to 80 mass%, more preferably 20 to 70 mass%, and even more preferably 30 to 60 mass%. A concentration of at least the lower limit of the above range is preferred because the yield of the desired organic particles is increased, whereas a concentration of at most the upper limit of the above range is preferred because the dispersibility of the natural rubber in the suspension is increased.

[0022] The cyclization step is carried out in the form of a rubber solution in which a polymer having cis-1,4-polyisoprene as a main skeleton is dissolved in a solvent, and the lower the water content in the rubber solution, the better. Therefore, it is preferable to recover the natural rubber latex in the form of a solid by salting out the natural rubber prior to the cyclization step, drying it, and then recovering it (salting out step).

[0023] (Salting out process) The salting-out step is a step in which natural rubber latex is salted out to separate the natural rubber from the dispersion medium such as water. In the salting out step, the natural rubber latex is coagulated by salting out using a coagulant, and then the solid matter is recovered by solid-liquid separation and dried to obtain a solid natural rubber.

[0024] Examples of the coagulant include aluminum sulfate, sodium chloride, and calcium chloride. The coagulant may be used alone or in combination of two or more kinds. The amount of coagulant added is preferably 5 to 200 parts by mass, and more preferably 10 to 150 parts by mass, per 100 parts by mass of natural rubber in the natural rubber latex. If the amount of coagulant added is equal to or greater than the above-mentioned lower limit, the natural rubber latex can be sufficiently salted out, but if the amount exceeds the above-mentioned upper limit, the effect of the coagulant reaches a plateau, and costs only increase.

[0025] The salting out may be carried out in the presence of a surfactant. The surfactant is not particularly limited, and known anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc. can be used. The surfactant may be used alone or in combination of two or more kinds.

[0026] The amount of surfactant added is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of natural rubber in the natural rubber latex. When the amount of surfactant added is at least the above-mentioned lower limit, the natural rubber can be easily extracted as a slurry without significant aggregation. When the amount of surfactant added is at most the above-mentioned upper limit, costs can be reduced. A preferred combination of a coagulant and a surfactant is, for example, a combination of aluminum sulfate and an anionic surfactant such as sodium lauryl sulfate. In this preferred combination, the preferred amounts of each agent added are as described above.

[0027] The drying temperature is preferably 50 to 120°C, more preferably 70 to 100°C. The drying time is preferably 10 to 48 hours, more preferably 15 to 24 hours.

[0028] [Cyclization process] The cyclization step is a step in which a polymer having cis-1,4-polyisoprene as the main skeleton is dissolved in a solvent and subjected to a cyclization reaction to obtain a cyclized rubber with a cyclization rate of 60 to 90%. In the cyclization step, first, a polymer having cis-1,4-polyisoprene as the main skeleton is dissolved in a solvent to prepare a solution of the polymer having cis-1,4-polyisoprene as the main skeleton.

[0029] The solvent is not particularly limited as long as it can dissolve a polymer having cis-1,4-polyisoprene as its main skeleton, and examples thereof include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and n-octane; and alicyclic hydrocarbons such as cyclopentane and cyclohexane. Among these, toluene is preferred from the viewpoint of boiling point. The solvent may be used alone or in combination of two or more kinds.

[0030] The content of the polymer having cis-1,4-polyisoprene as the main skeleton relative to the total mass of the polymer solution is preferably 5 to 60 mass%, more preferably 10 to 40 mass%, Within this preferred range, the viscosity of the polymer solution having cis-1,4-polyisoprene as the main skeleton becomes easy to handle. When preparing the polymer solution, the solvent may be heated to facilitate dissolution of the polymer having cis-1,4-polyisoprene as the main skeleton in the solvent. The temperature during heating is preferably 20 to 120°C, more preferably 40 to 100°C.

[0031] Next, a cyclization catalyst is added to the polymer solution with cis-1,4-polyisoprene as the main skeleton, and the cyclization reaction is carried out. The polymer with cis-1,4-polyisoprene as the main skeleton is cyclized through the cyclization reaction to form cyclized rubber. The cyclized rubber is obtained in the form of a solution (cyclized rubber solution).

[0032] Examples of the cyclization catalyst include sulfuric acid, organic sulfonic acids such as p-toluenesulfonic acid, monofluoromethanesulfonic acid, difluoromethanesulfonic acid, xylenesulfonic acid, and alkylbenzenesulfonic acid, and metal halide compounds such as boron trifluoride, boron trichloride, tin tetrachloride, titanium tetrachloride, aluminum chloride, diethylaluminum monochloride, aluminum bromide, antimony pentachloride, tungsten hexachloride, and iron chloride. Among these, organic sulfonic acids are preferred from the viewpoint of removing acid catalyst residues, and p-toluenesulfonic acid is more preferred.

[0033] The cyclization catalyst may be used alone or in combination of two or more. The acidic cyclization catalyst is preferably neutralized after the cyclization reaction. The acid catalyst residue generated after neutralization is preferably removed from the cyclized rubber solution. The acidic cyclization catalyst can be neutralized by adding an aqueous solution of an alkali metal carbonate (e.g., sodium carbonate) or an alkali metal bicarbonate (e.g., sodium bicarbonate) to the cyclized rubber solution and stirring. The neutralized cyclization catalyst is easily dissolved in the aqueous solution. When the stirring is stopped, the organic phase of the cyclized rubber solution and the aqueous solution, which is the aqueous phase, naturally separate, allowing the aqueous solution containing the neutralized cyclization catalyst to be easily removed.

[0034] The amount of the cyclization catalyst added is preferably 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of the polymer having cis-1,4-polyisoprene as a main skeleton in the polymer solution having cis-1,4-polyisoprene as a main skeleton. When the amount of the cyclization catalyst added is within the above range, it is easy to adjust the cyclization rate of the cyclized rubber to a desired value. The reaction temperature for the cyclization reaction is preferably 50 to 150°C, more preferably 80 to 110°C. The reaction time for the cyclization reaction is preferably 0.5 to 10 hours, more preferably 2 to 5 hours.

[0035] A preferred combination of a solvent and a cyclization catalyst for forming the polymer solution having cis-1,4-polyisoprene as the main skeleton is, for example, a combination of an aromatic hydrocarbon such as toluene and an organic sulfonic acid such as p-toluenesulfonic acid. In this preferred combination, the preferred content of natural rubber, the preferred amount of cyclization catalyst added, and the preferred reaction temperature and reaction time for the cyclization reaction are as described above.

[0036] The cyclization step is carried out so that the cyclization rate of the resulting cyclized rubber is 60 to 90%, and preferably so that the cyclization rate of the resulting cyclized rubber is 65 to 85%. If the cyclization rate is 60% or higher, the cyclized rubber can be easily granulated without being affected by adhesion. If the cyclization rate is 90% or lower, the remaining double bonds can be expected to improve the crosslinking rate. The cyclization rate of the cyclized rubber can be adjusted by adjusting the amount of the cyclization catalyst used. The cyclization rate tends to increase as the amount of the cyclization catalyst used increases.

[0037] "Cyclization rate" means the proportion of cyclized moieties in the cyclized rubber, 1 It can be determined by H-NMR. Specifically, the peak area (S0) of protons derived from double bonds in a polymer having cis-1,4-polyisoprene as the main skeleton before the cyclization reaction and the peak area (S1) of protons derived from double bonds in a polymer having cis-1,4-polyisoprene as the main skeleton after the cyclization reaction (cyclized rubber) are measured. Based on the obtained peak areas S0 and S1, the cyclization rate of the cyclized rubber is calculated using the following formula (1). In addition, 1 The measurement conditions for H-NMR are as shown in the Examples below. Cyclization rate (%)={1-(S1 / S0)}×100 (1)

[0038] By converting a polymer having a cis-1,4-polyisoprene skeleton into a cyclized rubber, the resulting organic particles have improved chemical resistance, heat resistance, and weather resistance, as well as improved adhesion to non-polar polymers such as polyolefins, polar polymers such as polyesters, polyurethanes, and alkyd resins, and metals such as iron.

[0039] [Vinyl monomer to be subjected to suspension polymerization process] The vinyl monomers to be subjected to the suspension polymerization step include monofunctional vinyl monomers having only one vinyl group and crosslinkable vinyl monomers having multiple vinyl groups. The monofunctional vinyl monomer is preferably at least one selected from the group consisting of a monofunctional aromatic vinyl monomer having only one vinyl group bonded to a benzene ring and a monofunctional (meth)acrylic monomer having only one (meth)acryloyl group.

[0040] Examples of monofunctional aromatic vinyl monomers having only one vinyl group bonded to a benzene ring include styrene-based monomers such as styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, triethylstyrene, propylstyrene, butylstyrene, hexylstyrene, heptylstyrene, octylstyrene, fluorostyrene, chlorostyrene, bromostyrene, dibromostyrene, chloromethylstyrene, styrene iodide, nitrostyrene, acetylstyrene, and methoxystyrene.

[0041] Examples of monofunctional (meth)acrylic monomers having only one (meth)acryloyl group include (meth)acrylic acid, esters of (meth)acrylic acid, and nitrile derivatives of (meth)acrylic acid. Specific examples of esters of (meth)acrylic acid having only one (meth)acryloyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, 1-butyl (meth)acrylate, t-butyl (meth)acrylate, amyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and glycidyl (meth)acrylate.

[0042] The crosslinkable vinyl monomer is preferably at least one selected from the group consisting of crosslinkable aromatic vinyl monomers having multiple vinyl groups bonded to a benzene ring, and crosslinkable (meth)acrylic monomers having multiple (meth)acryloyl groups or having a (meth)acryloyl group and an allyl group.

[0043] The number of vinyl groups that the crosslinkable vinyl monomer has is not particularly limited, but is preferably two in order to reduce polymerization shrinkage and polymerization heat. Specific examples of crosslinkable aromatic vinyl monomers having multiple vinyl groups bonded to a benzene ring include divinylbenzene and divinylbiphenyl.

[0044] Examples of crosslinkable (meth)acrylic monomers having multiple (meth)acryloyl groups include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, propionoxide-modified bisphenol A di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1, 4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 3-methyl-1,5 pentanediol di(meth)acrylate, 2-methyl-1,8 octanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, ethoxylated polypropylene glycol di(meth)acrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, glycerin di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, and allyl (meth)acrylate.

[0045] The proportion of the crosslinkable vinyl monomer relative to the total amount of the monofunctional vinyl monomer and the crosslinkable vinyl monomer is preferably 1 to 50% by mass, more preferably 2 to 30% by mass. If the proportion of the crosslinkable vinyl monomer is equal to or greater than the preferred lower limit, it is easy to obtain organic particles that are sufficiently crosslinked and have high solvent resistance. If the proportion is equal to or less than the preferred upper limit, it is easy to avoid the particles becoming hard and brittle.

[0046] [Suspension polymerization process] The suspension polymerization process is a process in which a cyclized rubber and a vinyl monomer are suspension-polymerized in the presence of water and a suspension stabilizer. By polymerizing the cyclized rubber and the vinyl monomer in a suspended state, organic particles are obtained that are dispersed in water as an oil together with a solvent.

[0047] The cyclized rubber and the vinyl monomer can be suspended by mixing a solution of the cyclized rubber and the vinyl monomer in a dispersion medium prepared by adding a suspension stabilizer to water. The content of the cyclized rubber in the cyclized rubber solution is preferably 5 to 30% by mass, more preferably 10 to 20% by mass. If the content of the cyclized rubber is equal to or greater than the preferred lower limit, the yield increases and productivity improves. If the content is equal to or less than the preferred upper limit, the viscosity does not become too high and the solution is easy to handle.

[0048] The content of the cyclized rubber in the cyclized rubber solution can be adjusted by concentrating the cyclized rubber solution obtained in the cyclization step or further diluting it with a solvent. Examples of the solvent used for dilution include the solvents exemplified above in the description of the cyclization step.

[0049] The proportion of the cyclized rubber (excluding the solvent) relative to the total amount (excluding the solvent) of the cyclized rubber and vinyl monomer to be polymerized is preferably 5 to 95 mass%, more preferably 10 to 70 mass%, and even more preferably 20 to 50 mass%. If the proportion of the cyclized rubber is equal to or greater than the preferred lower limit, the organic particles will have rubber properties. If it is equal to or less than the preferred upper limit, the solvent resistance of the resulting organic particles will be improved.

[0050] The total amount of the cyclized rubber and the vinyl monomer (excluding the solvent) in the suspension is preferably 5 to 50% by mass, more preferably 10 to 30% by mass. If the total amount of the cyclized rubber and the vinyl monomer is equal to or greater than the preferred lower limit, the yield increases and productivity improves. If the total amount is equal to or less than the preferred upper limit, stable suspension can be achieved.

[0051] Examples of suspension stabilizers include water-soluble cellulose resins (such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose), polyvinyl alcohol, polyacrylates, polyethylene glycol, polyvinylpyrrolidone, polyacrylamide, and tertiary phosphates. The suspension stabilizer may be used alone or in combination of two or more kinds.

[0052] The amount of suspension stabilizer used is preferably 1 to 30 parts by mass, more preferably 10 to 30 parts by mass, per 100 parts by mass of the total amount of the cyclized rubber and vinyl monomer (excluding the solvent) in the suspension. If the amount of suspension stabilizer used is within the above range, the suspension state can be sufficiently stabilized.

[0053] For the purpose of further stabilizing the suspension state, a surfactant may be used in combination with the suspension stabilizer. The surfactant is not particularly limited, and known anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc. can be used. The surfactant may be used alone or in combination of two or more kinds.

[0054] The amount of surfactant added is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass, per 100 parts by mass of the total amount of cyclized rubber and vinyl monomer (excluding solvent) in the suspension. If the amount of surfactant added is equal to or greater than the lower limit, the suspension state can be sufficiently stabilized. If the amount exceeds the upper limit, the effect of the surfactant will plateau, resulting in increased costs. The surfactant is preferably added to the dispersion medium before mixing the cyclized rubber solution with the vinyl monomer.

[0055] The cyclized rubber and vinyl monomer in the suspension can be polymerized by heating in the presence of a radical polymerization initiator. The polymerization initiator may be mixed with the cyclized rubber solution and the vinyl monomer, or may be added to the dispersion medium in advance. In view of good reaction efficiency, it is preferred to mix the cyclized rubber solution and the vinyl monomer to form a polymerization solution, and then add this polymerization solution to the dispersion medium while stirring to form a suspension.

[0056] The 10-hour half-life temperature of the radical polymerization initiator is preferably 35 to 150°C, more preferably 45 to 130°C. When the 10-hour half-life temperature of the radical polymerization initiator is equal to or higher than the lower limit, runaway reaction can be prevented, and handling becomes easy. When the 10-hour half-life temperature of the radical polymerization initiator is equal to or lower than the upper limit, residues of the radical polymerization initiator can be easily inactivated by heating.

[0057] As the radical polymerization initiator, for example, an organic peroxide or an azo compound can be used. Organic peroxides include benzoyl peroxide (10-hour half-life temperature: 74°C), dilauroyl peroxide (10-hour half-life temperature: 62°C), t-butyl peroxybenzoate (10-hour half-life temperature: 104°C), m-toluyl peroxide, diisopropyl peroxydicarbonate (10-hour half-life temperature: 41°C), t-butyl peroxypivalate (10-hour half-life temperature: 58°C), cumyl peroxyneodecanoate (10-hour half-life temperature: 38°C), Examples include t-butylperoxy-2-ethylhexanoate (10-hour half-life temperature: 77°C), octanoyl peroxide (10-hour half-life temperature: 62°C), decanoyl peroxide, t-butylperoxy-2-ethylhexanoate (10-hour half-life temperature: 72°C), t-butylperoxyisopropyl carbonate (10-hour half-life temperature: 99°C), cumyl peroxyoctoate, and t-hexyl peroxypivalate (10-hour half-life temperature: 53°C).

[0058] Examples of azo compounds include 2,2-azobisisobutyronitrile (10-hour half-life temperature: 65°C), 2,2-azobis(2,4-dimethylvaleronitrile) (10-hour half-life temperature: 51°C), and 1,1-azobis(cyclohexane-1-carbonitrile) (10-hour half-life temperature: 88°C).

[0059] Among these, organic peroxides are preferred from the viewpoint of forming crosslinking points by hydrogen abstraction, and t-butyl peroxypivalate, t-butylperoxy-2-ethylhexanoate, and t-hexyl peroxypivalate are more preferred. The radical polymerization initiator may be used alone or in combination of two or more kinds.

[0060] The radical polymerization initiator is preferably one or more types arbitrarily selected from the group exemplified above for organic peroxides, more preferably two or more types, and even more preferably three or more types. In particular, when a plurality of radical polymerization initiators having different 10-hour half-life temperatures are used in combination, the polymerization initiator that generates radicals early at low temperatures (polymerization initiator with low half-life temperatures) promotes the radical generation of the polymerization initiator that generates radicals later at high temperatures (polymerization initiator with high half-life temperatures), thereby enabling the crosslinking reaction to proceed quickly.

[0061] The total amount of radical polymerization initiator added is preferably 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of the total amount of the cyclized rubber and vinyl monomer (excluding the solvent) to be polymerized. If the amount of radical polymerization initiator added is equal to or greater than the lower limit, the cyclized rubber can be sufficiently crosslinked. If the amount exceeds the upper limit, the effect of the radical polymerization initiator will plateau, resulting in increased costs.

[0062] The temperature to which the suspension is heated (reaction temperature of suspension polymerization) is preferably 40 to 150°C, more preferably 60 to 130°C. If the reaction temperature is equal to or higher than the preferred lower limit, the reaction proceeds quickly. If the reaction temperature is equal to or lower than the preferred upper limit, excessive reaction is suppressed, making it easier to control the reaction. The reaction time of the suspension polymerization is preferably 0.5 to 10 hours, more preferably 2 to 5 hours. If the reaction time is equal to or greater than the preferred lower limit, unreacted materials are less likely to remain. If the reaction time is equal to or less than the preferred upper limit, the reaction process is shortened, improving productivity.

[0063] By the suspension polymerization, the double bonds remaining in the cyclized rubber and the double bonds of the vinyl monomer react and crosslink, thereby improving the solvent resistance of the resulting organic particles. When the double bonds remaining in the cyclized rubber react, double bonds other than those consumed by cyclization react to form crosslinks, so the cyclization rate of the cyclized rubber does not change before and after suspension polymerization.

[0064] [Solvent removal process] The solvent removal step is a step in which the solvent is removed from the suspension after the suspension polymerization step to obtain an aqueous dispersion in which organic particles are dispersed in water. As described above, the organic particles are obtained in a state where they are dispersed in water as an oil together with the solvent. Therefore, by removing the solvent from the suspension in the solvent removal step, an aqueous dispersion in which the organic particles are dispersed in water is obtained. To remove the solvent from the suspension after the suspension polymerization step, the suspension may be heated. The heating temperature is preferably 70 to 120° C., more preferably 80 to 100° C. The heating time is preferably 1 to 10 hours, more preferably 2 to 5 hours.

[0065] [Cleaning process] The washing step is a step of subjecting the aqueous dispersion obtained in the solvent removal step to solid-liquid separation and washing the recovered organic particles with water. The method for washing with water is not particularly limited, and examples thereof include a method in which the organic particles are suspended in water and then recovered by solid-liquid separation such as filtration or precipitation.

[0066] [Drying process] The drying step is a step of drying the organic particles after washing. As the drying method, for example, a heat drying method, an air flow drying method, a vacuum drying method, an infrared drying method, or the like is applied. When the heat drying method is applied, the drying temperature is preferably 40 to 120° C., more preferably 60 to 100° C. The drying time is preferably 2 to 48 hours, more preferably 6 to 24 hours.

[0067] <Organic particles> The organic particles of the present disclosure are organic particles obtained by polymerizing a cyclized rubber obtained by cyclizing a polymer having cis-1,4-polyisoprene as a main skeleton at a cyclization rate of 60 to 90% with a vinyl monomer, wherein the polymer having cis-1,4-polyisoprene as a main skeleton has a Mooney viscosity [ML(1+4)100°C] as defined in JIS K 6300 of 18 to 65, and the vinyl monomer includes a monofunctional vinyl monomer having only one vinyl group and a crosslinkable vinyl monomer having multiple vinyl groups.

[0068] The cyclized rubber and vinyl monomer constituting the organic particles of the present disclosure, and the raw rubber for obtaining the cyclized rubber, are the same as those explained in the method for producing organic particles above, and preferred embodiments are also the same.

[0069] It should be noted that the organic particles of the present disclosure are three-dimensionally crosslinked, and therefore their structure is too complex to be expressed by a general formula (structure). Furthermore, although the organic particles of the present disclosure have properties such as a high gel fraction, the organic particles of the present disclosure cannot be identified by such properties alone. That is, the organic particles of the present disclosure cannot be directly identified by their structure or properties, and can only be identified by the process (manufacturing method) for obtaining the organic particles.

[0070] The average particle size of the organic particles of the present disclosure is preferably 1 μm to 500 μm, more preferably 1 μm to 300 μm, even more preferably 1 μm to 200 μm, and particularly preferably 1 μm to 180 μm. In particular, organic particles with an average particle size of 1 μm to 300 μm are suitable for use in paints and the like. In the present invention, the "average particle size" refers to the particle size (volume average particle size) corresponding to 50% of the cumulative distribution on a volume basis measured with a laser diffraction particle size distribution analyzer. Here, the volume average particle size is the median diameter (d50).

[0071] The organic particles of the present disclosure preferably have a gel fraction of 80% or more, more preferably 85 to 100%, as determined by the following method. A higher gel fraction means better solvent resistance.

[0072] (How to determine gel fraction) The organic particles are placed in a container and their mass (W1) is precisely weighed. Toluene is added so that the organic particle concentration becomes 0.625% by mass. 24 hours after the toluene addition, the liquid in the container is filtered through filter paper (particle retention size: 1 μm), and the resulting residue on the filter paper (toluene-insoluble matter) is dried at 110°C for 2 hours, and the mass (W2) of the toluene-insoluble matter is measured. The gel fraction is calculated based on the obtained masses W1 and W2 using the following formula (2). Gel fraction (%) = (W2 / W1) × 100 (2)

[0073] The organic particles disclosed herein are copolymerized with a cyclized rubber and a vinyl monomer using a polymer with a cis-1,4-polyisoprene backbone, and have a three-dimensional crosslinked structure, which allows for easy particle formation and high solvent resistance. The organic particles of the present disclosure can be used as naturally occurring microbeads for fillers in paints, plastics, adhesives, cosmetics, paper coating materials, textile processing materials, writing instruments, markers, and the like.

[0074] <Material> The materials of the present disclosure are materials blended with the organic particles of the present disclosure, and specifically include paints, plastics, adhesives, cosmetics, paper coating materials, textile processing materials, writing implements, markers, and the like. [Example]

[0075] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following descriptions.

[0076] <Measurement method> [Cyclization rate] The cyclization rate of cyclized rubber was measured using a nuclear magnetic resonance spectrometer. 1 It was determined by measuring H-NMR. Specifically, 1H-NMR was measured under the following measurement conditions, and the peak area (S0) of protons derived from double bonds in the polymer having cis-1,4-polyisoprene as the main skeleton before the cyclization reaction and the peak area (S1) of protons derived from double bonds in the polymer having cis-1,4-polyisoprene as the main skeleton after the cyclization reaction (cyclized rubber) were measured, and the cyclization rate of the cyclized rubber was calculated using the following formula (1). Cyclization rate (%)={1-(S1 / S0)}×100 (1)

[0077] (Measurement conditions) Equipment: JEOL Ltd., "JNM-ECP600". · Solvent: Chloroform-d1. ·Concentration: 0.01g / mL. ·Resonance frequency: 600MHz. -Number of times accumulated: 32 times. The amount of polymer with cis-1,4-polyisoprene as the main skeleton used as the measurement sample: 0.02 mg.

[0078] [Volume average particle size] The volume average particle size of the organic particles was measured using a laser diffraction particle size distribution analyzer ("SALD2100" manufactured by Shimadzu Corporation).

[0079] [Mooney viscosity] The Mooney viscosity of the polymer having cis-1,4-polyisoprene as the main skeleton before the cyclization reaction was measured using a Mooney viscometer (Ueshima Seisakusho Co., Ltd., product name "VR1132") with an L-shaped rotor in accordance with JIS K 6300. The measurement temperature was 100°C, and after preheating the sample at the test temperature for 1 minute, the rotor was rotated at 2 rpm, and the torque after 4 minutes was measured and taken as the Mooney viscosity (ML(1+4)).

[0080] [Confirming the shape of organic particles] To confirm the shape of the organic particles, electron microscope photographs were taken.

[0081] [Gel fraction] To evaluate the solvent resistance, the organic particles were dissolved in toluene and the gel fraction was determined as follows. The organic particles were precisely weighed (W1) in a container, and toluene was added thereto so that the concentration of the organic particles became 0.625% by mass. After 24 hours, the liquid in the container was filtered through filter paper (particle retention diameter: 8 μm), and the resulting residue on the filter paper (toluene-insoluble matter) was dried at 110°C for 2 hours. The mass (W2) of the toluene-insoluble matter was measured, and the gel fraction was calculated using the following formula (2). Gel fraction (%) = (W2 / W1) × 100 (2)

[0082] <Production example> [Cyclated rubber A] A 5-liter separable flask equipped with a stirrer was charged with 3,800 g of ion-exchanged water, and 800 g of natural rubber latex (Sumitomo Rubber Industries, Ltd., "SeLatex® 1100," natural rubber content: 60% by mass, dispersant content such as water: 40% by mass) and 4.8 g of sodium lauryl sulfate were added to prepare a latex solution. 267.2 g of an aqueous aluminum sulfate solution with a concentration of 33.6% by mass was then added to salt out the natural rubber latex. The solid matter was then recovered by solid-liquid separation using a filter cloth and dried at 80°C for 20 hours to obtain a natural rubber solid matter with a Mooney viscosity of 91 (salting out step). The amount of sodium lauryl sulfate added was 1 part by mass, and the amount of aluminum sulfate added was 18.7 parts by mass, per 100 parts by mass of natural rubber. The natural rubber solid was masticated using a Labo Plastomill (registered trademark) (Toyo Seiki, "10S-100") to adjust the Mooney viscosity to 23.2.

[0083] A 2L separable flask equipped with a stirrer was charged with 120g of natural rubber solids and 480g of toluene, and the mixture was heated to 100°C. The natural rubber was dissolved in toluene to prepare a natural rubber solution with a concentration of 20% by mass. Next, 12g of p-toluenesulfonic acid was added, and the cyclization reaction was initiated at 100°C. Two and a half hours after the addition of p-toluenesulfonic acid, 19.2g of a 25% by mass aqueous sodium carbonate solution was added to terminate the reaction, yielding a toluene solution of cyclized rubber A (cyclization step). The amount of p-toluenesulfonic acid added was 10 parts by mass per 100 parts by mass of natural rubber. The p-toluenesulfonic acid reacted with sodium carbonate and dissolved in the aqueous sodium carbonate solution.

[0084] The content of cyclized rubber (cyclized natural rubber) relative to the total mass of the obtained toluene solution of cyclized rubber A (not taking into account the added aqueous sodium bicarbonate solution; the same applies below) was 20 mass% and the content of toluene was 80 mass%. The cyclization rate of cyclized rubber A was 83.5%. When measuring the cyclization rate, a portion of the cyclized rubber solution was sampled, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0085] [Cyclated rubber B] A toluene solution of cyclized rubber B was obtained in the same manner as for cyclized rubber A, except that the amount of p-toluenesulfonic acid added was changed to 3 g. The amount of p-toluenesulfonic acid added was 2.5 parts by mass per 100 parts by mass of natural rubber. The content of the cyclized rubber (cyclized natural rubber) relative to the total mass of the obtained toluene solution of cyclized rubber B was 20 mass %, and the content of toluene was 80 mass %. The cyclization rate of cyclized rubber B was 67.8%.

[0086] [Cyclated rubber C] A natural rubber sheet (Nomura Trading, "TCP-1X", Mooney viscosity ML(1+4)100℃=94, cis-1,4 bond; 100%) was masticated in a Labo Plastomill (Toyo Seiki, "10S-100") to obtain a natural rubber solid with a Mooney viscosity of 33.8.

[0087] A 2L separable flask equipped with a stirrer was charged with 120g of natural rubber solids and 480g of toluene, and the mixture was heated to 100°C. The natural rubber was dissolved in toluene to prepare a natural rubber solution with a concentration of 20% by mass. Next, 12g of p-toluenesulfonic acid was added, and the cyclization reaction was initiated at 100°C. Two and a half hours after the addition of p-toluenesulfonic acid, 19.2g of a 25% by mass aqueous sodium carbonate solution was added to terminate the reaction, yielding a toluene solution of cyclized rubber C (cyclization step). The amount of p-toluenesulfonic acid added was 10 parts by mass per 100 parts by mass of natural rubber. The p-toluenesulfonic acid reacted with sodium carbonate and dissolved in the aqueous sodium carbonate solution.

[0088] The content of the cyclized rubber (cyclized natural rubber) relative to the total mass of the obtained toluene solution of cyclized rubber C was 20 mass %, and the content of toluene was 80 mass %. The cyclization rate of the cyclized rubber was 77.5%. When measuring the cyclization rate, a portion of the cyclized rubber solution was sampled, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0089] [Cyclated rubber D] A toluene solution of cyclized rubber D was obtained in the same manner as cyclized rubber C, except that mastication was carried out so that the Mooney viscosity became 41.9. The content of the cyclized rubber (cyclized natural rubber) relative to the total mass of the obtained toluene solution of cyclized rubber D was 20 mass %, and the content of toluene was 80 mass %. The cyclization rate of cyclized rubber D was 80.5%. When measuring the cyclization rate, a portion of the cyclized rubber solution was sampled, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0090] [Cyclated rubber E] A toluene solution of cyclized rubber D was obtained in the same manner as cyclized rubber C, except that mastication was carried out so that the Mooney viscosity was 59.6. The content of the cyclized rubber (cyclized natural rubber) relative to the total mass of the obtained toluene solution of cyclized rubber E was 20 mass %, and the content of toluene was 80 mass %. The cyclization rate of cyclized rubber D was 78.2%. When measuring the cyclization rate, a portion of the cyclized rubber solution was sampled, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0091] [Cyclated rubber F] Synthetic rubber (ENEOS Materials Corporation, "IR2200," Mooney viscosity ML(1+4)100°C=82, cis-1,4 bond; 98%) was masticated in a Labo Plastomill (Toyo Seiki, "10S-100") to obtain a synthetic rubber solid with a Mooney viscosity of 35.3.

[0092] A 2L separable flask equipped with a stirrer was charged with 120g of synthetic rubber solids and 480g of toluene, and the mixture was heated to 100°C. The synthetic rubber was dissolved in toluene to prepare a synthetic rubber solution with a concentration of 20% by mass. Next, 12g of p-toluenesulfonic acid was added, and the cyclization reaction was initiated at 100°C. Two and a half hours after the addition of p-toluenesulfonic acid, 19.2g of a 25% by mass aqueous sodium carbonate solution was added to stop the reaction, yielding a toluene solution of cyclized rubber C (cyclization step). The amount of p-toluenesulfonic acid added was 10 parts by mass per 100 parts by mass of synthetic rubber. The p-toluenesulfonic acid reacted with sodium carbonate and dissolved in the aqueous sodium carbonate solution.

[0093] The content of the cyclized rubber (cyclized synthetic rubber) relative to the total mass of the obtained toluene solution of cyclized rubber F was 20 mass %, and the content of toluene was 80 mass %. The cyclization rate of cyclized rubber E was 77.9%. When measuring the cyclization rate, a portion of the cyclized rubber solution was sampled, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0094] [Cyclated rubber G] A toluene solution of cyclized rubber F was prepared in the same manner as cyclized rubber C, except that the cyclized rubber F was masticated to a Mooney viscosity of 69.0. The content of the cyclized rubber (cyclized natural rubber) relative to the total mass of the obtained toluene solution of cyclized rubber G was 20 mass %, and the content of toluene was 80 mass %. The cyclization rate of cyclized rubber E was 70.5%. When measuring the cyclization rate, a portion of the cyclized rubber solution was sampled, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0095] [Cyclated rubber H] A toluene solution of cyclized rubber G was prepared in the same manner as cyclized rubber C, except that the cyclized rubber G was masticated to a Mooney viscosity of 16.3. The content of the cyclized rubber (cyclized natural rubber) relative to the total mass of the obtained toluene solution of cyclized rubber H was 20 mass %, and the content of toluene was 80 mass %. The cyclization rate of cyclized rubber G was 82.2%. When measuring the cyclization rate, a portion of the cyclized rubber solution was sampled, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0096] <Examples 1 to 7 and Comparative Examples 1 to 4> [Example 1] A 2 L separable flask equipped with a stirrer was charged with 600 g of water, and 15 g of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., "Metolose (registered trademark) 90SH-100") was added and dissolved in the water to prepare a dispersion medium.

[0097] In addition, 36 g of styrene and 4 g of divinylbenzene were mixed with 200 g of a toluene solution of cyclized rubber A obtained in Production Example, and a solution (polymerization solution) was prepared by adding 1.2 g of t-butyl peroxypivalate, 1.2 g of t-butylperoxy-2-ethylhexanoate, and 1.2 g of t-hexyl peroxypivalate as radical polymerization initiators.

[0098] The polymerization solution was added to the dispersion medium while stirring at a stirrer speed of 400 rpm to prepare a suspension. The suspension was heated to 80°C while continuing stirring, and a suspension polymerization reaction was carried out at 80°C for 2 hours (suspension polymerization step). The amount of hydroxypropyl methylcellulose added was 25 parts by mass per 100 parts by mass of the cyclized rubber.

[0099] The suspension after the suspension polymerization step was heated to 100°C and maintained at 100°C for 1 hour to remove toluene from the suspension, thereby obtaining an aqueous dispersion in which organic particles were dispersed in water (solvent removal step). After the aqueous dispersion was cooled to room temperature (20° C.), solid-liquid separation was carried out, and the recovered organic particles were washed with water (washing step). The washed organic particles were dried at 70° C. for 20 hours to obtain organic particles. As shown in FIG. 1, the obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0100] [Example 2] A 2 L separable flask equipped with a stirrer was charged with 600 g of water, and 9 g of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., "Metolose 90SH-100") was added thereto and dissolved in the water to prepare a dispersion medium.

[0101] In addition, 9 g of styrene and 1 g of divinylbenzene were mixed with 200 g of a toluene solution of the cyclized rubber A obtained in Production Example, and a solution (polymerization solution) was prepared by adding 1.2 g of t-butyl peroxypivalate, 1.2 g of t-butylperoxy-2-ethylhexanoate, and 1.2 g of t-hexyl peroxypivalate as radical polymerization initiators.

[0102] The polymerization solution was added to the dispersion medium while stirring at a stirrer speed of 250 rpm to prepare a suspension. The suspension was heated to 80°C while continuing stirring, and a suspension polymerization reaction was carried out at 80°C for 2 hours (suspension polymerization step). The amount of hydroxypropyl methylcellulose added was 25 parts by mass per 100 parts by mass of the cyclized rubber.

[0103] The suspension after the suspension polymerization step was heated to 100°C and maintained at 100°C for 1 hour to remove toluene from the suspension, thereby obtaining an aqueous dispersion in which organic particles were dispersed in water (solvent removal step). After the aqueous dispersion was cooled to room temperature (20° C.), solid-liquid separation was carried out, and the recovered organic particles were washed with water (washing step). The washed organic particles were dried at 70° C. for 20 hours to obtain organic particles. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0104] [Example 3] Organic particles were obtained in the same manner as in Example 1, except that the amount of the toluene solution of cyclized rubber A obtained in Production Example was changed to 32 g, the amount of styrene to 64 g, and the amount of divinylbenzene to 8 g. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0105] [Example 4] Organic particles were obtained in the same manner as in Example 1, except that 200 g of the toluene solution of cyclized rubber B obtained in Production Example was used instead of 200 g of the toluene solution of cyclized rubber A obtained in Production Example. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0106] [Example 5] Organic particles were obtained in the same manner as in Example 1, except that 200 g of the toluene solution of cyclized rubber C obtained in Production Example was used instead of 200 g of the toluene solution of cyclized rubber A obtained in Production Example. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0107] [Example 6] Organic particles were obtained in the same manner as in Example 1, except that 200 g of the toluene solution of cyclized rubber D obtained in Production Example was used instead of 200 g of the toluene solution of cyclized rubber A obtained in Production Example. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0108] [Example 7] Organic particles were obtained in the same manner as in Example 1, except that 200 g of the toluene solution of cyclized rubber E obtained in Production Example was used instead of 200 g of the toluene solution of cyclized rubber A obtained in Production Example. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0109] [Example 8] Organic particles were obtained in the same manner as in Example 1, except that 200 g of the toluene solution of cyclized rubber F obtained in Production Example was used instead of 200 g of the toluene solution of cyclized rubber A obtained in Production Example. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 1.

[0110] [Comparative Example 1] A 2 L separable flask equipped with a stirrer was charged with 600 g of water, and 15 g of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., "Metolose 90SH-100") was added thereto and dissolved in the water to prepare a dispersion medium.

[0111] While stirring the dispersion medium at 400 rpm, 300 g of the toluene solution of cyclized rubber A obtained in Production Example was added to prepare a suspension. While continuing stirring, the suspension was heated to 80°C and subjected to a suspension crosslinking reaction at 80°C for 2 hours (suspension polymerization step). The amount of hydroxypropyl methylcellulose added was 25 parts by mass per 100 parts by mass of the cyclized rubber.

[0112] The suspension after the suspension polymerization step was heated to 100°C and maintained at 100°C for 1 hour to remove toluene from the suspension, thereby obtaining an aqueous dispersion in which organic particles were dispersed in water (solvent removal step). After the aqueous dispersion was cooled to room temperature (20° C.), solid-liquid separation was carried out, and the recovered organic particles were washed with water (washing step). The washed organic particles were dried at 70° C. for 20 hours to obtain organic particles. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 2.

[0113] Comparative Example 2 A 2 L separable flask equipped with a stirrer was charged with 600 g of water, and 15 g of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., "Metolose 90SH-100") was added thereto and dissolved in the water to prepare a dispersion medium.

[0114] In addition, a solution (polymerization solution) was prepared by adding 1.2 g of t-butyl peroxypivalate, 1.2 g of t-butylperoxy-2-ethylhexanoate, and 1.2 g of t-hexyl peroxypivalate as radical polymerization initiators to 200 g of a toluene solution of the cyclized rubber A obtained in Production Example.

[0115] The polymerization solution was added to the dispersion medium while stirring at a stirrer speed of 400 rpm to prepare a suspension. The suspension was heated to 80°C while continuing stirring, and a suspension polymerization reaction was carried out at 80°C for 2 hours (suspension polymerization step). The amount of hydroxypropyl methylcellulose added was 25 parts by mass per 100 parts by mass of the cyclized rubber.

[0116] The suspension after the suspension polymerization step was heated to 100°C and maintained at 100°C for 1 hour to remove toluene from the suspension, thereby obtaining an aqueous dispersion in which organic particles were dispersed in water (solvent removal step). After the aqueous dispersion was cooled to room temperature (20° C.), solid-liquid separation was carried out, and the recovered organic particles were washed with water (washing step). The washed organic particles were dried at 70° C. for 20 hours to obtain organic particles. The obtained organic particles were confirmed by observation with an electron microscope. The volume average particle size and gel fraction of the obtained organic particles were measured, and the results are shown in Table 2.

[0117] Comparative Example 3 An attempt was made to produce organic particles in the same manner as in Example 1, except that 200 g of a toluene solution of cyclized rubber G obtained in the production example was used instead of 200 g of a toluene solution of cyclized rubber A obtained in the production example. However, the viscosity of the cyclized rubber solution was very high, making it difficult to produce particles.

[0118] Comparative Example 4 An attempt was made to produce organic particles in the same manner as in Example 1, except that 200 g of a toluene solution of cyclized rubber H obtained in Production Example 6 was used instead of 200 g of a toluene solution of cyclized rubber A obtained in Production Example 6. However, the particles aggregated together, making it difficult to produce particles.

[0119] [Table 1]

[0120] [Table 2]

[0121] As is clear from Tables 1 and 2, the organic particles obtained in each Example were superior in solvent resistance to the organic particles obtained in the Comparative Examples.

Claims

1. The method comprises the steps of: dissolving a polymer having cis-1,4-polyisoprene as a main skeleton in a solvent and carrying out a cyclization reaction to obtain a cyclized rubber having a cyclization rate of 60 to 90%; and suspension polymerizing the cyclized rubber and a vinyl monomer in the presence of water and a suspension stabilizer; the polymer having cis-1,4-polyisoprene as a main skeleton has a Mooney viscosity [ML(1+4)100°C] as defined in JIS K 6300 of 18 to 65; The method for producing organic particles, wherein the vinyl monomer comprises a monofunctional vinyl monomer having only one vinyl group and a crosslinkable vinyl monomer having multiple vinyl groups.

2. 2. The method for producing organic particles according to claim 1, wherein the polymer having cis-1,4-polyisoprene as a main skeleton is obtained by masticating raw rubber.

3. The method for producing organic particles according to claim 2, wherein the raw rubber is natural rubber.

4. the monofunctional vinyl monomer is at least one selected from the group consisting of a monofunctional aromatic vinyl monomer having only one vinyl group bonded to a benzene ring and a monofunctional (meth)acrylic monomer having only one (meth)acryloyl group, 3. The method for producing organic particles according to claim 1, wherein the crosslinkable vinyl monomer is at least one selected from the group consisting of a crosslinkable aromatic vinyl monomer having a plurality of vinyl groups bonded to a benzene ring, and a crosslinkable (meth)acrylic monomer having a plurality of (meth)acryloyl groups or a (meth)acryloyl group and an allyl group.

5. The organic particles are obtained by polymerizing a cyclized rubber in which a polymer having a cis-1,4-polyisoprene main skeleton is cyclized at a cyclization rate of 60 to 90% and a vinyl monomer, the polymer having cis-1,4-polyisoprene as a main skeleton has a Mooney viscosity [ML(1+4)100°C] as defined in JIS K 6300 of 18 to 65; The organic particles, wherein the vinyl monomer comprises a monofunctional vinyl monomer having only one vinyl group and a crosslinkable vinyl monomer having multiple vinyl groups.

6. the monofunctional vinyl monomer is at least one selected from the group consisting of a monofunctional aromatic vinyl monomer having only one vinyl group bonded to a benzene ring and a monofunctional (meth)acrylic monomer having only one (meth)acryloyl group, The organic particles according to claim 5, wherein the crosslinkable vinyl monomer is at least one selected from the group consisting of a crosslinkable aromatic vinyl monomer having a plurality of vinyl groups bonded to a benzene ring, and a crosslinkable (meth)acrylic monomer having a plurality of (meth)acryloyl groups or a (meth)acryloyl group and an allyl group.

7. 7. The organic particles according to claim 5, having an average particle size of 1 μm to 300 μm.

8. 7. The organic particles according to claim 5, wherein the gel fraction determined by the following method is 80% or more. (How to determine gel fraction) The organic particles are placed in a container and their mass (W1) is precisely weighed. Toluene is added to the container so that the organic particle concentration becomes 0.625% by mass. 24 hours after the toluene addition, the liquid in the container is filtered through filter paper (retention particle size: 1 μm), and the resulting residue on the filter paper (toluene-insoluble matter) is dried at 110°C for 2 hours, and the mass (W2) of the toluene-insoluble matter is measured. The gel fraction is calculated based on the obtained masses W1 and W2 using the following formula (2): Gel fraction (%)=(W2 / W1)×100 (2)

9. A material containing the organic particles according to claim 5 or 6.

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