Organic particles, methods for producing the same, and materials

Abstract

This invention provides highly solvent-resistant organic particles using polymers with a cis-1,4-polyisoprene core, such as natural rubber. [Solution] A method for producing organic particles comprising the steps of: dissolving a polymer having cis-1,4-polyisoprene as the main skeleton in a solvent and carrying out a cyclization reaction to obtain a cyclized rubber with a cyclization rate of 60-90%; and suspend polymerization of the cyclized rubber and a vinyl monomer in the presence of water and a suspension stabilizer, wherein the Mooney viscosity [ML(1+4)100℃] of the polymer having cis-1,4-polyisoprene as the main skeleton is 18-65 as defined in JIS K 6300, and the vinyl monomer includes 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 Art

[0002] Particles such as acrylic beads, polystyrene beads, and polyurethane beads are used in various products such as paints, plastics, adhesives, and cosmetics. In particular, the need for particles on the micrometer scale is increasing.

[0003] As particles on the micrometer scale, a cyclized natural rubber organic solvent solution is suspended in a medium that does not dissolve or only slightly dissolves in the organic solvent to form a suspension, and this suspension is heated to simultaneously evaporate the organic solvent during the crosslinking reaction to form spherical particles of cyclized natural rubber (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the rubber particles disclosed in Patent Document 1 do not have perfect solvent resistance, and there are still quite a few parts that dissolve in the solvent. In order to improve the solvent resistance, it is necessary to reduce the cyclization rate of natural rubber and increase the double bond component. However, it has been found that if the cyclization rate of the rubber particles disclosed in Patent Document 1 is further reduced, the tack (surface adhesiveness) becomes strong and particle formation becomes difficult. An object of the present invention is to provide organic particles with high solvent resistance using a polymer having a cis-1,4-polyisoprene main skeleton represented by natural rubber.

Means for Solving the Problems

[0006] To achieve the above objectives, the present invention employs the following configuration. [1] The process involves dissolving a polymer with cis-1,4-polyisoprene as the main skeleton in a solvent and carrying out a cyclization reaction to obtain a cyclized rubber with a cyclization rate of 60-90%, and suspend polymerization of the cyclized rubber and a vinyl monomer in the presence of water and a suspension stabilizer. The Mooney viscosity [ML(1+4)100℃] of the polymer having the cis-1,4-polyisoprene as its main backbone is 18 to 65, as defined in JIS K 6300. A method for producing organic particles, wherein the vinyl monomer includes 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 its main skeleton is obtained by kneading raw rubber. [3] The method for producing organic particles according to [2], wherein the raw material rubber is natural rubber. [4] The monofunctional vinyl monomer is one or more selected from the group consisting of monofunctional aromatic vinyl monomers having only one vinyl group bonded to a benzene ring and monofunctional (meth)acrylic monomers having only one (meth)acryloyl group. A method for producing organic particles according to any one of [1] to [3], wherein the crosslinkable vinyl monomer is one or more selected from the group consisting of a crosslinkable aromatic vinyl monomer having a plurality of vinyl groups bonded to a benzene ring, and a plurality of (meth)acryloyl groups, or a crosslinkable (meth)acrylic monomer having 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 backbone is cyclized with a cyclization rate of 60-90%, and a vinyl monomer, The Mooney viscosity [ML(1+4)100℃] of the polymer having the cis-1,4-polyisoprene as its main backbone is 18 to 65, as defined in JIS K 6300. Organic particles comprising 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 its main skeleton is obtained by kneading raw rubber. [7] The organic particles according to [6], wherein the raw material rubber is natural rubber. [8] The monofunctional vinyl monomer is one or more selected from the group consisting of monofunctional aromatic vinyl monomers having only one vinyl group bonded to a benzene ring and monofunctional (meth)acrylic monomers having only one (meth)acryloyl group, The organic particle according to any one of [5] to [7], wherein the crosslinkable vinyl monomer is one or more selected from the group consisting of a crosslinkable aromatic vinyl monomer having a plurality of vinyl groups bonded to a benzene ring, and a plurality of (meth)acryloyl groups, or a crosslinkable (meth)acrylic monomer having a (meth)acryloyl group and an allyl group. [9] Organic particles as described in any of [5] to [8], having an average particle size of 1 μm to 300 μm.

[10] Organic particles according to any of [5] to [9], wherein the gel fraction determined by the method below is 80% or more. (How to determine gel fraction) Organic particles are placed in a container and their mass (W1) is accurately weighed. Toluene is added to the container so that the concentration of organic particles reaches 0.625% by mass. After 24 hours have elapsed since the addition of toluene, the liquid in the container is filtered through filter paper (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. Based on the obtained masses W1 and W2, the gel fraction is calculated using the following formula (2). Gel fraction (%) = (W2 / W1) × 100 ... (2) A material containing organic particles as described in any of

[11] , [5], or

[10] . [Effects of the Invention]

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

[0008] [Figure 1] This is an electron microscope image of the organic particles obtained in Example 1. [Modes for carrying out the invention]

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

[0010] <Method for producing organic particles> The method for producing organic particles according to the present disclosure comprises a step of dissolving a polymer having cis-1,4-polyisoprene as the main backbone in a solvent and carrying out a cyclization reaction to obtain a cyclized rubber with a cyclization rate of 60 to 90% (cyclization step), and a step of suspension polymerization of 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 this disclosure may include a suspension polymerization step, a step of removing the solvent from the suspension to obtain an aqueous dispersion in which organic particles are dispersed in water (solvent removal step), a step of performing solid-liquid separation of the aqueous dispersion obtained in the solvent removal step 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 the cyclization step] In the cyclization step, a polymer having a cis-1,4-polyisoprene as the main chain is used. "Having a cis-1,4-polyisoprene as the main chain" means that the cis-1,4-polyisoprene units constituting the polymer account for 98% by mass or more of all the units constituting the polymer.

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

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

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

[0016] The above Mooney viscosity can be adjusted by kneading the raw rubber to reduce the molecular weight. Generally, kneading is performed to adjust the elasticity and plasticity to a state easy to process. Conventional methods can be used for mixing, including mechanical shear force, the action of oxygen in the air, a peptizer, heat, or a combination of these. Among these, the method using mechanical shear force is preferred because it is simple and allows for easy control of Mooney viscosity. Methods using mechanical shear force include pressurized kneaders, Banbury mixers, and open roll mixers. Mixing accelerators may also be used during mixing.

[0017] The raw material rubber used in this disclosure may be either so-called natural rubber extracted from plants (such as rubber trees, dandelions, or eucalyptus trees), or synthetic rubber polymerized from naphtha and biomass-derived isoprene monomers. Examples of synthetic rubber include Nipol® IR2200 and IR2200L from Zeon Corporation, and IR2200 from ENEOS Material Corporation.

[0018] The raw rubber may contain non-rubber components as long as they do not impair the effects of the present invention. For example, natural rubber obtained from the sap of plants such as the Para rubber tree contains not only polymers with cis-1,4-polyisoprene as the main backbone, but also water and non-rubber components (impurities such as proteins, fatty acids, and inorganic salts).

[0019] From the perspective of the SDGs (Sustainable Development Goals), natural rubber is preferable as the raw material. As for the natural rubber, you may use commercially available natural rubber latex (emulsion of natural rubber) obtained by salting it out and drying, or you may use 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 using commercially available natural rubber latex (emulsion of natural rubber) obtained by salting out and drying as the raw material 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% by mass, more preferably 20 to 70% by mass, and even more preferably 30 to 60% by mass. A value above the lower limit of the above range is preferable because it increases the yield of the target organic particles. A value below the upper limit of the above range is also preferable because it improves the dispersibility of natural rubber in the suspension.

[0022] The cyclization process is carried out in a rubber solution in which a polymer with cis-1,4-polyisoprene as the main backbone is dissolved in a solvent. At this time, it is preferable that the amount of water in the rubber solution be as low as possible. Therefore, it is preferable that the natural rubber latex be solidified by salting out the natural rubber and then dried before the cyclization process, and recovered in a solid state (salting out process).

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

[0024] Examples of coagulants include aluminum sulfate, sodium chloride, and calcium chloride. The coagulant may be used alone or in combination of two or more types. 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 above the lower limit, the natural rubber latex can be sufficiently salted out, but if it exceeds the upper limit, the effect of the coagulant plateaus, and the cost only increases.

[0025] 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. Surfactants may be used individually or in combination of two or more types.

[0026] The amount of surfactant added is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of natural rubber in the natural rubber latex. If the amount of surfactant added is above the lower limit, the natural rubber can be easily extracted as a slurry without significant aggregation. If the amount of surfactant added is below the upper limit, costs can be reduced. A preferred combination of coagulant and 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 component are as described above.

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

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

[0029] The solvent is not particularly limited as long as it can dissolve polymers with cis-1,4-polyisoprene as the main backbone, but examples 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 types.

[0030] The content of the polymer with a cis-1,4-polyisoprene main skeleton relative to the total mass of the polymer solution is preferably 5 to 60% by mass, and more preferably 10 to 40% by mass. Within this preferred range, the viscosity of the polymer solution with a cis-1,4-polyisoprene main skeleton becomes manageable. When preparing a polymer solution, the solvent may be heated to facilitate the dissolution of the polymer, which has cis-1,4-polyisoprene as its main backbone. The heating temperature is preferably 20 to 120°C, and more preferably 40 to 100°C.

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

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

[0033] The cyclization catalyst may be used alone or in combination of two or more types. It is preferable that the acidic cyclization catalyst be neutralized after the cyclization reaction. It is preferable that the acidic catalyst residue generated after neutralization be 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 alkali metal bicarbonate (e.g., sodium bicarbonate) to the cyclized rubber solution and stirring. The neutralized cyclization catalyst is readily soluble in aqueous solution. When the stirring is stopped, the organic phase of the cyclized rubber solution and the aqueous phase of the aqueous solution separate naturally, so the aqueous solution containing the neutralized cyclization catalyst can be easily removed.

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

[0035] A preferred combination of solvent and cyclization catalyst constituting the polymer solution with cis-1,4-polyisoprene as the main skeleton is, for example, a combination of aromatic hydrocarbons such as toluene and organic sulfonic acids 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 process is carried out so that the cyclization rate of the resulting cyclized rubber is 60-90%. Preferably, it is carried out so that the cyclization rate of the resulting cyclized rubber is 65-85%. If the cyclization rate is 60% or higher, the cyclized rubber can be easily atomized without being affected by its tackiness. If the cyclization rate is 90% or lower, the remaining double bonds can be expected to improve the crosslinking rate. The cyclization rate of cyclized rubber can be adjusted by controlling the amount of cyclization catalyst used. Generally, the higher the amount of cyclization catalyst used, the higher the cyclization rate tends to be.

[0037] "Cyclization rate" refers to the proportion of cyclized parts in cyclized rubber. 1 This is determined by 1H-NMR. Specifically, the peak area (S0) of protons originating from the double bonds of the polymer with cis-1,4-polyisoprene as the main backbone before the cyclization reaction and the peak area (S1) of protons originating from the double bonds of the polymer with cis-1,4-polyisoprene as the main backbone 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 determined from the following formula (1). In addition, 1 The measurement conditions for H-NMR are as shown in the examples described below. Cyclization rate (%)={1-(S1 / S0)}×100 (1)

[0038] By using a polymer with cis-1,4-polyisoprene as the main backbone to create a cyclized rubber, the chemical resistance, heat resistance, and weather resistance of the resulting organic particles are enhanced. In addition, adhesion to non-polar polymers such as polyolefins, polar polymers such as polyester, polyurethane, and alkyd resins, and metals such as iron is also improved.

[0039] [Vinyl monomers used in the suspension polymerization process] The vinyl monomers used in the suspension polymerization process include monofunctional vinyl monomers having only one vinyl group and crosslinkable vinyl monomers having multiple vinyl groups. The monofunctional vinyl monomer is preferably one or more selected from the group consisting of monofunctional aromatic vinyl monomers having only one vinyl group bonded to a benzene ring and monofunctional (meth)acrylic monomers 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 monomers such as styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, triethylstyrene, propylstyrene, butylstyrene, hexylstyrene, heptylstyrene, octylstyrene, fluorostyrene, chlorostyrene, bromostyrene, dibromostyrene, chloromethylstyrene, iodide styrene, 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 esterified (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, glycidyl (meth)acrylate, and others.

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

[0043] The number of vinyl groups in a crosslinkable vinyl monomer is not particularly limited, but it is preferable to have two, as this results in less polymerization shrinkage and less polymerization heat generation. 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, propion oxide-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, Examples include 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 ratio of crosslinkable vinyl monomer to the total amount of monofunctional vinyl monomer and crosslinkable vinyl monomer is preferably 1 to 50% by mass, and more preferably 2 to 30% by mass. If the ratio of crosslinkable vinyl monomer is above the preferred lower limit, it is easier to obtain organic particles that are sufficiently crosslinked and have high solvent resistance. If it is below the preferred upper limit, it is easier to avoid the particles becoming hard and brittle.

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

[0047] Cyclic rubber and vinyl monomer can be suspended by mixing the cyclic rubber solution and vinyl monomer in a dispersion medium consisting of water with a suspension stabilizer. The cyclized rubber content in the cyclized rubber solution is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass. If the cyclized rubber content is above the preferred lower limit, the yield increases and productivity improves. If it is below the preferred upper limit, the viscosity does not become too high, making it easy to handle.

[0048] The content of cyclized rubber in the cyclized rubber solution can be adjusted by concentrating the cyclized rubber solution obtained in the cyclization process or by further diluting it with a solvent. Examples of solvents used for dilution include those previously described in the explanation of the cyclization process.

[0049] The ratio of cyclized rubber (excluding solvent) to the total amount of cyclized rubber and vinyl monomer to be polymerized (excluding solvent) is preferably 5 to 95% by mass, more preferably 10 to 70% by mass, and even more preferably 20 to 50% by mass. If the ratio of cyclized rubber is above the preferred lower limit, organic particles with rubber properties will be obtained. If it is below the preferred upper limit, the solvent resistance of the resulting organic particles will be improved.

[0050] The total amount of cyclized rubber and vinyl monomer (excluding solvent) in the suspension is preferably 5 to 50% by mass, and more preferably 10 to 30% by mass. If the total amount of cyclized rubber and vinyl monomer is above the preferred lower limit, the yield will increase and productivity will improve. If it is below the preferred upper limit, stable suspension can be achieved.

[0051] Examples of suspension stabilizers include cellulosic water-soluble resins (e.g., methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, etc.), polyvinyl alcohol, polyacrylates, polyethylene glycol, polyvinylpyrrolidone, polyacrylamide, and tertiary phosphates. A suspension stabilizer may be used alone or in combination of two or more types.

[0052] The amount of suspension stabilizer used is preferably 1 to 30 parts by mass, and more preferably 10 to 30 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 suspension stabilizer used is within the above range, the suspension state can be sufficiently stabilized.

[0053] To further stabilize the suspension, a surfactant may be used in combination with a suspension stabilizer. The surfactant is not particularly limited, and known anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc., can be used. Surfactants may be used individually or in combination of two or more types.

[0054] The amount of surfactant added is preferably 0.1 to 30 parts by mass, and 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 above the lower limit, the suspension state can be sufficiently stabilized. If it exceeds the upper limit, the effect of the surfactant plateaus, and the cost increases. It is preferable to add the surfactant to the dispersion medium before mixing the cyclized rubber solution with the vinyl monomer.

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

[0056] The 10-hour half-life temperature of the radical polymerization initiator is preferably 35 to 150°C, and more preferably 45 to 130°C. If the 10-hour half-life temperature of the radical polymerization initiator is above the lower limit, runaway reactions can be suppressed, and handling becomes easier. If the 10-hour half-life temperature of the radical polymerization initiator is below the upper limit, deactivation of the radical polymerization initiator residue by heating is easy.

[0057] For example, organic peroxides and azo compounds can be used as radical polymerization initiators. Examples of 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), and cumyl peroxyneodecanoate (10-hour half-life temperature: 38°C). Examples include t-butyl peroxy-2-ethylhexanoate (10-hour half-life temperature: 77°C), octanoyl peroxide (10-hour half-life temperature: 62°C), decanoyl peroxide, t-butyl peroxy-2-ethylhexanoate (10-hour half-life temperature: 72°C), t-butyl peroxyisopropyl carbonate (10-hour half-life temperature: 99°C), cumyl peroxyoctaate, 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-carbonitride) (10-hour half-life temperature: 88°C).

[0059] Among these, organic peroxides are preferred from the viewpoint of crosslinking point formation by hydrogen abstraction, and t-butyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, and t-hexyl peroxypivalate are more preferred. Radical polymerization initiators may be used individually or in combination of two or more.

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

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

[0062] The temperature at which the suspension is heated (the reaction temperature for suspension polymerization) is preferably 40 to 150°C, and more preferably 60 to 130°C. If the reaction temperature is above the preferred lower limit, the reaction will proceed rapidly. If it is below the upper limit, excessive reaction will be suppressed and the reaction will be easier to control. The reaction time for suspension polymerization is preferably 0.5 to 10 hours, and more preferably 2 to 5 hours. If the reaction time is above the preferred lower limit, unreacted material is less likely to remain. If it is below the upper limit, the reaction process is shortened, and productivity is improved.

[0063] Through 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. Furthermore, when the double bonds remaining in the cyclized rubber react, a different double bond than the one consumed by cyclization reacts and 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 process that, after the suspension polymerization step, removes the solvent from the suspension to obtain an aqueous dispersion in which organic particles are dispersed in water. As described above, the organic particles are obtained dispersed in water as oil along with the solvent. Therefore, by removing the solvent from the suspension in the solvent removal process, 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 process, the suspension can be heated. The heating temperature is preferably 70 to 120°C, and more preferably 80 to 100°C. The heating time is preferably 1 to 10 hours, and more preferably 2 to 5 hours.

[0065] [Washing process] The washing process involves solid-liquid separation of the aqueous dispersion obtained in the solvent removal process and washing the recovered organic particles with water. The method of washing with water is not particularly limited; for example, one method is to suspend the organic particles in water and then recover the organic particles by solid-liquid separation such as filtration or precipitation.

[0066] [Drying process] The drying process is the process of drying the organic particles after washing. Drying methods include, for example, heat drying, airflow drying, vacuum drying, and infrared drying. When applying the heat drying method, the drying temperature is preferably 40 to 120°C, and more preferably 60 to 100°C. The drying time is preferably 2 to 48 hours, and more preferably 6 to 24 hours.

[0067] <Organic particles> The organic particles of this disclosure are organic particles obtained by polymerizing a cyclized rubber, in which a polymer having a cis-1,4-polyisoprene main skeleton is cyclized with a cyclization rate of 60-90%, with a vinyl monomer, wherein the Mooney viscosity [ML(1+4)100℃] of the polymer having a cis-1,4-polyisoprene main skeleton is 18-65 as defined in JIS K 6300, 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 this disclosure, and the raw rubber for obtaining the cyclized rubber, are the same as those described in the method for producing the organic particles described above, and the preferred embodiments are also the same.

[0069] Furthermore, because the organic particles in this disclosure are three-dimensionally cross-linked, their structure is too complex to be represented by a general formula (structure). Furthermore, while the organic particles of this disclosure possess characteristics such as a high gel fraction, these characteristics alone are not sufficient to identify the organic particles of this disclosure. In other words, the organic particles of this disclosure cannot be directly identified by their structure or characteristics; they can only be identified by the process (manufacturing method) used to obtain them.

[0070] The average particle size of the organic particles in this 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 this invention, the "average particle diameter" is the particle diameter (volume-average particle diameter) corresponding to 50% of the cumulative distribution on a volume basis measured by a laser diffraction particle size analyzer. Here, the volume-average particle diameter is the median diameter (d50).

[0071] The organic particles of this disclosure preferably have a gel fraction of 80% or more, and more preferably 85-100%, as determined by the method described below. A higher gel fraction indicates superior solvent resistance.

[0072] (How to determine gel fraction) Organic particles are placed in a container and their mass (W1) is accurately weighed. Toluene is added to the container so that the concentration of organic particles reaches 0.625% by mass. After 24 hours have elapsed since the addition of toluene, the liquid in the container is filtered through filter paper (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. Based on the obtained masses W1 and W2, the gel fraction is calculated using the following formula (2). Gel fraction (%) = (W2 / W1) × 100 ... (2)

[0073] The organic particles of this disclosure are copolymerized from a cyclized rubber polymer with a cis-1,4-polyisoprene backbone and a vinyl monomer, and have a three-dimensionally crosslinked structure. Therefore, they can be easily formed into particles and have high solvent resistance. The organic particles of this disclosure can be used as naturally derived microbeads for use in paints, plastics, adhesives, cosmetics, paper coatings, textile processing materials, writing instruments, markers, and other fillers.

[0074] <Material> The materials disclosed herein are materials containing the organic particles disclosed herein. Specifically, these include paints, plastics, adhesives, cosmetics, paper coatings, textile processing materials, writing instruments, markers, and the like. [Examples]

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

[0076] <Measurement method> [Cyclization rate] The cyclization rate of cyclized rubber is determined using a nuclear magnetic resonance apparatus. 1 This was determined by measuring H-NMR. Specifically, 1H-NMR was measured under the following measurement conditions to determine the peak area (S0) of protons originating from the double bonds of the polymer with cis-1,4-polyisoprene as the main backbone before the cyclization reaction, and the peak area (S1) of protons originating from the double bonds of the polymer with cis-1,4-polyisoprene as the main backbone after the cyclization reaction (cyclized rubber). The cyclization rate of the cyclized rubber was then determined 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. • Total number of times: 32. • Amount of polymer with cis-1,4-polyisoprene as the main backbone used as the measurement sample: 0.02 mg.

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

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

[0080] [Confirmation of organic particle shape] Electron microscope images were taken to confirm the shape of the organic particles.

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

[0082] <Manufacturing example> [Ecogenic Rubber A] 3800g of deionized water was placed in a 5L separable flask equipped with a stirrer. 800g of natural rubber latex (Sumitomo Rubber Industries, Ltd., "SeLatex® 1100", natural rubber content: 60% by mass, dispersion medium content such as water: 40% by mass) and 4.8g of sodium lauryl sulfate were added to prepare a latex solution. 267.2g of a 33.6% by mass aqueous aluminum sulfate solution was then added to perform salting out of the natural rubber latex. The solid was then recovered by solid-liquid separation using a filter cloth and dried at 80°C for 20 hours to obtain a solid natural rubber with a Mooney viscosity of 91 (salting out process). 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. Solid natural rubber was kneaded using a Laboplast Mill (registered trademark) (Toyo Seiki, "10S-100") and adjusted to a Mooney viscosity of 23.2.

[0083] 120 g of solid natural rubber and 480 g of toluene were placed in a 2 L separable flask equipped with a stirrer, and the mixture was heated to 100°C to dissolve the natural rubber in toluene, preparing a 20% by mass natural rubber solution. Next, 12 g of p-toluenesulfonic acid was added, and the cyclization reaction was started at 100°C. Two and a half hours after the addition of p-toluenesulfonic acid, 19.2 g of a 25% by mass sodium carbonate aqueous solution was added to stop the reaction, obtaining 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. Note that the p-toluenesulfonic acid reacted with sodium carbonate and dissolved in the sodium carbonate aqueous solution.

[0084] The toluene solution of the obtained cyclized rubber A (excluding the added sodium bicarbonate aqueous solution; the same applies hereafter) contained 20% by mass of cyclized rubber (cyclized natural rubber) and 80% by mass of toluene, relative to the total mass. Furthermore, the cyclization rate of cyclized rubber A was 83.5%. To measure the cyclization rate, a portion of the cyclized rubber solution was collected, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0085] [Ecogenic 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 cyclic rubber (cyclic natural rubber) content of the obtained cyclic rubber B in the toluene solution was 20% by mass, and the toluene content was 80% by mass. Furthermore, the cyclization rate of cyclized rubber B was 67.8%.

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

[0087] 120 g of solid natural rubber and 480 g of toluene were placed in a 2 L separable flask equipped with a stirrer, and the mixture was heated to 100°C to dissolve the natural rubber in toluene, preparing a 20% by mass natural rubber solution. Next, 12 g of p-toluenesulfonic acid was added, and the cyclization reaction was started at 100°C. Two and a half hours after the addition of p-toluenesulfonic acid, 19.2 g of a 25% by mass sodium carbonate aqueous solution was added to stop the reaction, and a toluene solution of cyclized rubber C was obtained (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 sodium carbonate aqueous solution.

[0088] The cyclic rubber (cyclic natural rubber) content of the obtained cyclic rubber C in the toluene solution was 20% by mass, and the toluene content was 80% by mass. Furthermore, the cyclization rate of the cyclized rubber was 77.5%. To measure the cyclization rate, a portion of the cyclized rubber solution was collected, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0089] [Ecological Rubber D] A toluene solution of cyclized rubber D was obtained in the same manner as for cyclized rubber C, except that it was kneaded until its Mooney viscosity was 41.9. The toluene solution of the obtained cyclized rubber D contained 20% by mass of cyclized rubber (cyclized natural rubber) and 80% by mass of toluene. Furthermore, the cyclization rate of cyclized rubber D was 80.5%. To measure the cyclization rate, a portion of the cyclized rubber solution was collected, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0090] [Ethylene-based rubber E] A toluene solution of cyclized rubber D was obtained in the same manner as for cyclized rubber C, except that it was kneaded until its Mooney viscosity was 59.6. The cyclic rubber (cyclic natural rubber) content of the obtained cyclic rubber E in the toluene solution was 20% by mass, and the toluene content was 80% by mass. Furthermore, the cyclization rate of cyclized rubber D was 78.2%. To measure the cyclization rate, a portion of the cyclized rubber solution was collected, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0091] [Ecogenic Rubber F] Synthetic rubber (ENEOS Material Co., Ltd., "IR2200", Mooney viscosity ML(1+4)100℃=82, cis-1,4 bond; 98%) was kneaded in a Laboplast Mill (Toyo Seiki, "10S-100") to obtain a synthetic rubber solid with a Mooney viscosity of 35.3.

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

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

[0094] [Ecologically oxidized rubber G] A toluene solution of cyclized rubber F was prepared in the same manner as for cyclized rubber C, except that it was kneaded until its Mooney viscosity was 69.0. The cyclic rubber (cyclic natural rubber) content of the obtained cyclic rubber G in the toluene solution was 20% by mass, and the toluene content was 80% by mass. Furthermore, the cyclization rate of cyclized rubber E was 70.5%. To measure the cyclization rate, a portion of the cyclized rubber solution was collected, the solvent was removed, and the resulting residue was dried and used for the measurement.

[0095] [Ecogenic rubber H] A toluene solution of cyclized rubber G was prepared in the same manner as for cyclized rubber C, except that it was kneaded until its Mooney viscosity reached 16.3. The cyclic rubber (cyclic natural rubber) content of the obtained cyclic rubber H in the toluene solution was 20% by mass, and the toluene content was 80% by mass. Furthermore, the cyclization rate of cyclized rubber G was 82.2%. To measure the cyclization rate, a portion of the cyclized rubber solution was collected, the solvent was removed, and the resulting residue was dried and used for the measurement.

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

[0097] Furthermore, a polymerization solution was prepared by mixing 36 g of styrene and 4 g of divinylbenzene with 200 g of a toluene solution of cyclized rubber A obtained in the production example, and adding 1.2 g of t-butyl peroxypivalate, 1.2 g of t-butyl peroxy-2-ethylhexanoate, and 1.2 g of t-hexyl peroxypivalate as radical polymerization initiators.

[0098] A suspension was prepared by adding the polymerization solution while stirring the dispersion medium at a stirrer speed of 400 rpm. The suspension was heated to 80°C while continuing to stir, and the 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 cyclized rubber.

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

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

[0101] Furthermore, a polymerization solution was prepared by mixing 9 g of styrene and 1 g of divinylbenzene with 200 g of a toluene solution of cyclized rubber A obtained in the production example, and adding 1.2 g of t-butyl peroxypivalate, 1.2 g of t-butyl peroxy-2-ethylhexanoate, and 1.2 g of t-hexyl peroxypivalate as radical polymerization initiators.

[0102] A suspension was prepared by adding the polymerization solution while stirring the dispersion medium at a stirrer speed of 250 rpm. The suspension was heated to 80°C while continuing to stir, and the 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 cyclized rubber.

[0103] The suspension after the suspension polymerization step was heated to 100°C and held at 100°C for 1 hour to remove toluene from the suspension, obtaining an aqueous dispersion in which organic particles were dispersed in water (solvent removal step). The aqueous dispersion was cooled to room temperature (20°C), then solid-liquid separation was performed, and the recovered organic particles were washed with water (washing step). The organic particles after washing were dried at 70°C for 20 hours to obtain new organic particles. The obtained organic particles were confirmed by electron microscopy. The volume-average particle size and gel fraction were measured for the obtained organic particles. 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 toluene solution of cyclized rubber A obtained in the production example was set 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 electron microscopy observation. The volume-average particle size and gel fraction were measured for the obtained organic particles. 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 a toluene solution of cyclized rubber B obtained in the production example was used instead of 200 g of a toluene solution of cyclized rubber A obtained in the production example. The obtained organic particles were confirmed by electron microscopy observation. The volume-average particle size and gel fraction were measured for the obtained organic particles. 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 a toluene solution of cyclized rubber C obtained in the production example was used instead of 200 g of a toluene solution of cyclized rubber A obtained in the production example. The obtained organic particles were confirmed by electron microscopy observation. The volume-average particle size and gel fraction were measured for the obtained organic particles. 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 a toluene solution of cyclized rubber D obtained in the production example was used instead of 200 g of a toluene solution of cyclized rubber A obtained in the production example. The obtained organic particles were confirmed by electron microscopy observation. The volume-average particle size and gel fraction were measured for the obtained organic particles. 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 a toluene solution of cyclized rubber E obtained in the production example was used instead of 200 g of a toluene solution of cyclized rubber A obtained in the production example. The obtained organic particles were confirmed by electron microscopy observation. The volume-average particle size and gel fraction were measured for the obtained organic particles. 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 a toluene solution of cyclized rubber F obtained in the production example was used instead of 200 g of a toluene solution of cyclized rubber A obtained in the production example. The obtained organic particles were confirmed by electron microscopy observation. The volume-average particle size and gel fraction were measured for the obtained organic particles. The results are shown in Table 1.

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

[0111] A suspension was prepared by adding 300 g of a toluene solution of cyclized rubber A obtained in the production example to the dispersion medium while stirring with a stirrer at a rotation speed of 400 rpm. The suspension was heated to 80°C while continuing to stir, and the suspension crosslinking 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 cyclized rubber.

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

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

[0114] Furthermore, a polymerization solution was prepared by adding 1.2 g of t-butyl peroxypivalate, 1.2 g of t-butyl peroxy-2-ethylhexanoate, and 1.2 g of t-hexyl peroxypivalate as radical polymerization initiators to 200 g of a toluene solution of cyclized rubber A obtained in the production example.

[0115] A suspension was prepared by adding the polymerization solution while stirring the dispersion medium at a stirrer speed of 400 rpm. The suspension was heated to 80°C while continuing to stir, and the 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 cyclized rubber.

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

[0117] [Comparative Example 3] We attempted to produce organic particles in the same manner as in Example 1, except that we used 200g of a toluene solution of cyclized rubber G obtained in the production example instead of 200g 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 particle formation difficult.

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

[0119] [Table 1]

[0120] [Table 2]

[0121] As is clear from Tables 1 and 2, the organic particles obtained in each example showed superior solvent resistance compared to the organic particles obtained in the comparative example.

Claims

1. The process comprises the steps of: dissolving a polymer with cis-1,4-polyisoprene as the main skeleton in a solvent and carrying out a cyclization reaction to obtain a cyclized rubber with a cyclization rate of 60-90%; and suspend polymerization of the cyclized rubber and a vinyl monomer in the presence of water and a suspension stabilizer. The Mooney viscosity [ML(1+4)100℃] of the polymer having cis-1,4-polyisoprene as its main skeleton is 18 to 65 as defined in JIS K 6300. A method for producing organic particles, wherein the vinyl monomer includes 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 claim 1, wherein the polymer having cis-1,4-polyisoprene as its main skeleton is obtained by kneading raw rubber.

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

4. The monofunctional vinyl monomer is one or more selected from the group consisting of monofunctional aromatic vinyl monomers having only one vinyl group bonded to a benzene ring and monofunctional (meth)acrylic monomers having only one (meth)acryloyl group. The method for producing organic particles according to claim 1 or 2, wherein the crosslinkable vinyl monomer is one or more selected from the group consisting of a crosslinkable aromatic vinyl monomer having a plurality of vinyl groups bonded to a benzene ring, and a plurality of (meth)acryloyl groups, or a crosslinkable (meth)acrylic monomer having a (meth)acryloyl group and an allyl group.

5. Organic particles obtained by polymerizing a cyclized rubber, in which a polymer with cis-1,4-polyisoprene as the main backbone is cyclized with a cyclization rate of 60-90%, and a vinyl monomer. The Mooney viscosity [ML(1+4)100℃] of the polymer having cis-1,4-polyisoprene as its main skeleton is 18 to 65 as defined in JIS K 6300. Organic particles comprising a monofunctional vinyl monomer having only one vinyl group and a crosslinkable vinyl monomer having multiple vinyl groups.

6. The organic particles according to claim 5, wherein the polymer having cis-1,4-polyisoprene as its main skeleton is obtained by kneading raw rubber.

7. The organic particles according to claim 6, wherein the raw material rubber is natural rubber.

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

9. The organic particles according to claim 5 or 6, wherein the average particle diameter is 1 μm to 300 μm.

10. The organic particles according to claim 5 or 6, wherein the gel fraction determined by the method described below is 80% or more. (How to determine gel fraction) Organic particles are placed in a container and their mass (W1) is accurately weighed. Toluene is added to the container so that the concentration of organic particles is 0.625% by mass. After 24 hours have elapsed since the addition of toluene, the liquid in the container is filtered through filter paper (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. Based on the obtained masses W1 and W2, the gel fraction is calculated using the following formula (2). Gel fraction (%) = (W2 / W1) × 100 ... (2)

11. A material comprising the organic particles described in claim 5 or 6.

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