Hollow particles, elastomer composition, and elastomer cross-linked molded article

Abstract

Provided are: hollow particles which are capable of reducing the weight of an elastomer cross-linked molded article and reducing the compression set of the elastomer cross-linked molded article; an elastomer composition containing the hollow particles; and a cross-linked molded article of the elastomer composition. Provided are: a hollow particle having a shell containing a resin and a hollow portion surrounded by the shell, and having an iodine value of 10 g / 100 g or more and 50 g / 100 g or less as measured in accordance with JIS K 0070; and an elastomer composition containing the hollow particle and a base elastomer.

Description

Technical Field

[0001] The present invention relates to hollow particles, an elastomer composition containing the hollow particles, and a cross-linked molded article thereof. Background Art

[0002] Elastomer products, focusing on the rubber-like elasticity and flexibility of elastomer raw materials, such as rubber, are used in a wide range of fields for applications such as shock absorbers, fluid barrier fillers, and tubes. Typically, the desired components are mixed with a base elastomer, and the resulting elastomer composition is kneaded in a molten state. The resulting elastomer composition is then formed through methods such as extrusion and compression molding, while the base elastomer is simultaneously crosslinked. This results in various elastomer product forms, including parts, coatings, and filler core materials.

[0003] As a method for reducing the weight of elastomer products, there is a known method of mixing a foaming agent into a base elastomer and foaming the mixture by heating during the molding process to form a foamed elastomer molded body. Patent Document 1, with the goal of providing a rubber composition for vulcanization molding capable of producing rubber products having excellent dimensional stability, good surface properties, and effectively reduced weight, describes a method for achieving this goal, wherein hollow particles are mixed with a base rubber having a specific Mooney viscosity at 100°C and the resulting rubber composition is used. The hollow particles are composed of an outer shell and a foaming agent enclosed in the outer shell and vaporized by heating, and the expansion margin is 20 to 80%. The outer shell is composed of a thermoplastic resin.

[0004] The method of Patent Document 1, mentioned above, identifies the production of a foamed elastomer molded article with excellent dimensional stability as one of its technical challenges. However, the method of producing a foamed elastomer molded article by mixing a foaming agent with a base elastomer is difficult to control the size of the pores formed by foaming, and therefore has a limit to the dimensional stability that can be achieved. Therefore, further improvement in dimensional stability is required in the production of elastomer molded articles.

[0005] On the other hand, as a method for introducing a plurality of micropores into a molded body to impart properties or functions such as lightweighting, heat insulation, and opacification, there is a known method using a molding material containing hollow particles in a base resin (Patent Documents 2 and 3). Since the cavities of the hollow particles contained in the molding material become pores, molding materials containing hollow particles in a base resin do not present the problem of controlling the size of the pores formed by foaming, as occurs when a foaming agent is used.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent No. 6116787;

[0009] Patent Document 2: International Publication No. 2020 / 261926;

[0010] Patent document 3: International Publication No. 2021 / 112110. Summary of the Invention

[0011] Problems to be solved by the invention

[0012] Furthermore, elastomer products are required to have low compression set. However, conventional elastomer products containing hollow particles in a base elastomer have not achieved improved compression set.

[0013] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide hollow particles capable of reducing the weight of a cross-linked elastomer molded product and reducing the compression set of the cross-linked elastomer molded product.

[0014] Another object of the present invention is to provide an elastomer composition containing the above-mentioned hollow particles and a cross-linked molded article thereof.

[0015] Solutions for solving problems

[0016] The present invention provides hollow particles having a shell made of a resin and a hollow portion surrounded by the shell, wherein the iodine value measured according to JIS K 0070 is 10 g / 100 g or more and 50 g / 100 g or less.

[0017] Furthermore, the present invention provides an elastomer composition comprising the hollow particles of the present invention and a base elastomer.

[0018] Furthermore, the present invention provides a cross-linked elastomer molded product obtained by cross-linking and molding the elastomer composition of the present invention.

[0019] Effects of the Invention

[0020] By using the hollow particles of the present invention as a filler for a cross-linked elastomer molded product, the cross-linked elastomer molded product can be made lighter and the compression set of the cross-linked elastomer molded product can be reduced.

[0021] Furthermore, according to the present invention, it is possible to provide a lightweight elastomer cross-linked molded article having reduced compression set, and an elastomer composition as a molding material thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a diagram illustrating an example of the method for producing hollow particles of the present invention. DETAILED DESCRIPTION

[0023] Hereinafter, the hollow particles of the present invention, the method for producing the hollow particles of the present invention, the elastomer resin composition of the present invention, and the elastomer cross-linked molded article of the present invention will be described in detail.

[0024] In the present invention, "to" in a numerical range means that the numerical values ​​described before and after it are included as the lower limit and the upper limit.

[0025] 1. Hollow particles

[0026] The hollow particles of the present invention are characterized by having a shell made of a resin and a hollow portion surrounded by the shell, and having an iodine value measured according to JIS K 0070 of 10 g / 100 g or more and 50 g / 100 g or less.

[0027] In the present invention, the iodine value measured according to JIS K 0070 may be simply referred to as the iodine value.

[0028] The iodine value of the hollow particles can be used as an indicator of the amount of reactive unsaturated bonds present on the outer surface of the hollow particles. The iodine value of the hollow particles of the present invention is 10g / 100g or more, so there is a specific amount of reactive unsaturated bonds on the outer surface. When the hollow particles of the present invention are mixed and kneaded with a base elastomer, and heated and pressed to obtain an elastomer cross-linked molded body, at least during the heating and pressing, the reactive unsaturated bonds present on the outer surface of the hollow particles react with the reactive unsaturated bonds possessed by the base elastomer to form a covalent bond. Therefore, in the elastomer cross-linked molded body containing the hollow particles of the present invention, the outer surface of the hollow particles is cross-linked with the base elastomer, and the adhesion of the interface between the hollow particles and the base elastomer is excellent, and the interface between the hollow particles and the base elastomer is not easy to peel off. In addition, compared with the base elastomer, the hollow particles have a high restoring force when an external force is applied, and are not easy to plastically deform. It is speculated that the compression set of the hollow particle-containing elastomer cross-linked molded article of the present invention is reduced because the base elastomer and the hollow particles are cross-linked, resulting in the base elastomer following the recovery of the hollow particles when an external force is applied. It is believed that in the hollow particle-containing elastomer cross-linked molded article, if the outer surfaces of the hollow particles are not cross-linked with the base elastomer, the plastic deformation of the base elastomer is not suppressed, resulting in an increase in compression set.

[0029] Furthermore, in the cross-linked elastomer molded article containing the hollow particles of the present invention, the hollow particles are not easily broken and their pores are easily maintained, thus achieving an excellent lightweighting effect. It is inferred that the reason why the hollow particles in the cross-linked elastomer molded article containing the hollow particles of the present invention are not easily broken is that the reactive unsaturated bonds on the surface of the hollow particles react with the reactive unsaturated bonds of the base elastomer to form a three-dimensional cross-linked structure near the surface of the hollow particles. It is believed that this three-dimensional cross-linked structure can increase the Young's modulus of the cross-linked elastomer molded article containing the hollow particles of the present invention, reduce compression set, and improve wear resistance.

[0030] When the iodine value of the hollow particles of the present invention is 10 g / 100 g or greater, sufficient crosslinking bonds are formed between the hollow particles and the base elastomer, thereby effectively reducing the compression set of the molded article. The iodine value of the hollow particles of the present invention is preferably 12 g / 100 g or greater, more preferably 15 g / 100 g or greater, even more preferably 20 g / 100 g or greater, and even more preferably 30 g / 100 g or greater.

[0031] On the other hand, when the iodine value of the hollow particles of the present invention exceeds 50 g / 100 g, the hollow particles are prone to agglomeration due to excessive reaction points on the outer surface of the hollow particles, resulting in cross-linking bonds being easily formed between the hollow particles. This deteriorates the dispersibility of the hollow particles and fails to sufficiently reduce the compression set of the molded article. From the perspective of reducing the compression set of the molded article, the iodine value of the hollow particles of the present invention is preferably 45 g / 100 g or less, and more preferably 40 g / 100 g or less.

[0032] The hollow particles of the present invention are particles having a shell (outer shell) containing a resin and a hollow portion surrounded by the shell, and have a reactive unsaturated bond on the outer surface of the shell.

[0033] Examples of the reactive unsaturated bond include reactive unsaturated bonds contained in vinyl groups, (meth)acryloyl groups, allyl groups, butenyl groups, maleimide groups, nadimide groups, propargyl groups, and ethynyl groups. Preferably, the reactive unsaturated bond is an ethylenic unsaturated bond, more preferably, an ethylenic unsaturated bond contained in at least one selected from vinyl groups, (meth)acryloyl groups, and allyl groups, and further preferably, an ethylenic unsaturated bond contained in at least one selected from vinyl groups and (meth)acryloyl groups.

[0034] In the hollow particles of the present invention, the reactive unsaturated bonds on the outer surface of the shell may be reactive unsaturated bonds contained in a cross-linking monomer unit or reactive unsaturated bonds contained in a coupling agent used for surface treatment, and are preferably reactive unsaturated bonds contained in a cross-linking monomer unit. In other words, it is preferred that at least one polymerizable functional group contained in the cross-linking monomer is present on the surface of the shell in an unreacted state.

[0035] In addition, the crosslinking monomer, coupling agent, etc. used for producing the hollow particles of the present invention will be described in detail in "2. Production method of hollow particles" described later.

[0036] The resin contained in the shell of the hollow particles of the present invention is typically a polymer of a polymerizable monomer used in the method for producing the hollow particles described below. The shell of the hollow particles may further contain a surface treatment agent or additives, etc., within the scope that does not impair the purpose of the present invention. In the hollow particles of the present invention, the content of the resin contained in the shell is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and even more preferably 98% by mass or more. The shell may also be composed of resin.

[0037] The shell of the hollow particles of the present invention may be a shell in which the outer surface of the resin layer comprising a polymer of a polymerizable monomer is surface-treated with a coupling agent. When the shell of the hollow particles of the present invention is surface-treated, it is preferred from the perspective of improving mechanical properties such as tensile strength, tensile stress, tear strength, and abrasion resistance in the elastomer cross-linked molded article containing the hollow particles of the present invention.

[0038] In the hollow particles of the present invention, the hollow portion is a cavity-like space clearly distinguishable from the shell. The shell of the hollow particle may have a porous structure, but in this case, the hollow portion has a size that clearly distinguishes it from the numerous microscopic spaces uniformly dispersed within the porous structure. From the perspective of mechanical strength, etc., the hollow particles of the present invention preferably have a dense shell.

[0039] Furthermore, from the viewpoint of the weight reduction effect, it is preferred that the hollow particles of the present invention have their hollow parts filled with a gas such as air.

[0040] The hollow particles of the present invention may have one or two or more hollow portions. However, from the perspective of maintaining a good balance between high porosity and mechanical strength, they preferably have only one or two hollow portions, and more preferably only one hollow portion. The proportion of the hollow particles of the present invention having only one hollow portion is preferably 90% or more, more preferably 95% or more, and even more preferably greater than 95%.

[0041] Furthermore, the shell of the hollow particles of the present invention and, when having two or more hollow parts, the partition walls separating adjacent hollow parts may be porous, but are preferably dense from the viewpoint of reducing the compression set of the molded article.

[0042] The shape of the hollow particles of the present invention may be, for example, spherical, ellipsoidal, or irregular, but is preferably spherical from the viewpoint of dispersibility and pressure resistance of the hollow particles.

[0043] An example of the shape of the hollow particles of the present invention is a bag formed of a thin membrane and filled with gas, and its cross-sectional view is as follows: Figure 1 The hollow particle 10 in (5) is shown. In this example, a thin membrane is provided on the outside, and the inside is filled with gas.

[0044] The hollow portion of the hollow particles can be confirmed by, for example, observing a cross section of the particles with an SEM or directly observing the particles with a TEM. The shape of the hollow particles can be confirmed by, for example, observing the hollow particles with an SEM or a TEM.

[0045] The hollow particles of the present invention may contain a small amount of particles with low circularity due to particle breakage, deformation, etc. as impurities. However, from the perspective of achieving a lightweight effect and reducing the compression set of the molded article, the proportion of particles with a circularity of 0.85 or less in 100% by mass of the hollow particles is preferably less than 15% by mass, more preferably less than 10% by mass, and even more preferably less than 8% by mass.

[0046] Particles with a circularity of 0.85 or less typically produce deformations or cracks such as dents, and are sometimes referred to as "irregular-shaped particles" in the present invention. Compared to spherical hollow particles, such irregular-shaped particles have a lower porosity and, therefore, a poorer lightweighting effect. Therefore, by reducing the proportion of irregular-shaped particles contained in the hollow particles, the lightweighting effect of the hollow particles can be improved. In addition, compared to spherical particles, irregular-shaped particles have the problem of being easily aggregated when dispersed in the base elastomer and having poor dispersibility. Therefore, by reducing the proportion of irregular-shaped particles contained in the hollow particles, the dispersibility of the hollow particles can be improved, and as a result, the compression set of the molded body can be further reduced. Furthermore, irregular-shaped particles are easily subjected to external pressure locally, and therefore have a problem of poor pressure resistance compared to spherical particles. When irregular-shaped particles are dispersed in the base elastomer, aggregates are easily generated, and the aggregates are easily subjected to external pressure, resulting in even poorer pressure resistance. Therefore, by reducing the proportion of irregular-shaped particles contained in the hollow particles, the pressure resistance of the hollow particles can be improved.

[0047] Circularity is defined as the diameter of a circle with the same area as the projected image of the particle (area-equivalent diameter) divided by the diameter of a circle with the same circumference as the projected image of the particle (circumference-equivalent diameter). If the particle is a perfect sphere, the circularity is 1. The more complex the surface shape of the particle, the smaller the circularity value.

[0048] The average circularity of the hollow particles of the present invention may be 0.950 to 0.995.

[0049] In the present invention, the circularity is measured using a flow particle imaging measurement device at an image resolution of 0.185 μm / pixel.

[0050] A flow-type particle imaging measuring instrument, for example, the IF-3200 manufactured by JASCO International, Inc., can be preferably used. The measurement sample is prepared by, for example, dispersing a mixture of 0.10 to 0.12 g of the hollow particles in an aqueous solution of sodium linear alkylbenzene sulfonate (concentration 0.3%) using an ultrasonic cleaner for 5 minutes.

[0051] The average circularity is the average value of the circularities of 1,000 to 3,000 particles selected at random.

[0052] The porosity of the hollow particles of the present invention is not particularly limited. From the perspective of weight reduction, it is preferably 60% or greater, more preferably 65% ​​or greater, and even more preferably 70% or greater. The upper limit of the porosity of the hollow particles is not particularly limited. From the perspective of suppressing a decrease in the strength of the hollow particles and making them less susceptible to breakage, it is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less.

[0053] The porosity of the hollow particles is calculated from the apparent density D1 and true density D0 of the hollow particles.

[0054] The apparent density D1 of the hollow particles is determined as follows. First, a volume of 100 cm 3 Fill the volumetric flask to about 30 cm 3 The mass of the hollow particles was accurately weighed. Next, the volumetric flask filled with the hollow particles was filled with isopropyl alcohol up to the mark, while being careful not to mix in bubbles. The mass of the isopropyl alcohol added to the volumetric flask was accurately weighed, and the apparent density D1 (g / cm 3 ).

[0055] Formula (I)

[0056] Apparent density D1 = [mass of hollow particles] / (100-[mass of isopropyl alcohol] / [specific gravity of isopropyl alcohol at the measurement temperature])

[0057] The apparent density D1 corresponds to the specific gravity of the entire hollow particle when the hollow portion is regarded as a part of the hollow particle.

[0058] The method for determining the true density D0 of hollow particles is as follows: After crushing the hollow particles in advance, 3 Fill a volumetric flask with about 10 g of hollow particle fragments and accurately weigh the mass of the filled fragments. Then, add isopropyl alcohol to the volumetric flask in the same manner as the above-mentioned apparent density measurement, accurately weigh the mass of isopropyl alcohol, and calculate the true density D0 (g / cm2) of the hollow particles based on the following formula (II): 3 ).

[0059] Formula (II)

[0060] True density D0 = [mass of hollow particle fragments] / (100 - [mass of isopropyl alcohol] / [specific gravity of isopropyl alcohol at the measurement temperature])

[0061] The true density D0 corresponds to the specific gravity of only the shell portion of the hollow particle. As is clear from the above-described measurement method, when calculating the true density D0, the hollow portion is not considered as part of the hollow particle.

[0062] The porosity (%) of the hollow particles is calculated from the apparent density D1 and true density D0 of the hollow particles using the following formula (III).

[0063] Formula (III)

[0064] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0065] The volume average particle size of the hollow particles of the present invention is not particularly limited. As a lower limit, it is preferably 0.1 μm or more, more preferably 1 μm or more, and as an upper limit, it is preferably 100 μm or less, more preferably 80 μm or less, and further preferably 50 μm or less. When the volume average particle size of the hollow particles of the present invention is above the above lower limit, since the aggregation of the hollow particles is suppressed and the dispersibility is improved, the effect of reducing the compression set of the molded body is improved. When the volume average particle size of the hollow particles of the present invention is below the above upper limit, the reduction in the specific surface area of ​​the hollow particles is suppressed. As a result, since the reduction in the interface between the hollow particles and the substrate elastomer is suppressed, the amount of cross-linked bonds formed between the hollow particles and the substrate elastomer increases, and the effect of reducing the compression set of the molded body is improved.

[0066] The particle size distribution (volume average particle size (Dv) / number average particle size (Dp)) of the hollow particles is not particularly limited, but is preferably 1.05 to 1.30, more preferably 1.10 to 1.30. When the particle size distribution is 1.30 or less, the compression set of the molded article tends to be significantly reduced, and particles with less variation in performance between particles can be obtained. Furthermore, when the particle size distribution is 1.30 or less, for example, when the cross-linked elastomer molded article of the present invention is formed into a sheet, the thickness uniformity can be improved.

[0067] About the volume average particle diameter (Dv) and number average particle diameter (Dp) of hollow particles, for example, the particle diameter of hollow particles can be measured by a particle size distribution measuring device based on the Coulter counter method, and the number average and volume average are calculated respectively, and the obtained values ​​are used as the number average particle diameter (Dp) and volume average particle diameter (Dv) of the particles. Particle size distribution is the value obtained by dividing the volume average particle diameter by the number average particle diameter. The Coulter counter method is a method for measuring particle diameter by a resistance method called the Coulter principle.

[0068] The residual volatile content of the hollow particles of the present invention is not particularly limited, but is preferably less than 100 ppm. When the residual volatile content of the hollow particles is high, residual volatiles are present on the outer surface of the hollow particles. The residual volatiles present on the outer surface of the hollow particles hinder the reaction of the reactive unsaturated bonds on the outer surface of the hollow particles with the reactive unsaturated bonds of the base elastomer. Therefore, when the residual volatile content of the hollow particles is high, the adhesion of the hollow particles contained in the elastomer cross-linked molded body to the base elastomer will deteriorate, resulting in an increase in the compression set of the molded body. In contrast, if the residual volatile content of the hollow particles is less than 100 ppm, the increase in the compression set of the molded body can be fully suppressed. From the viewpoint of reducing the compression set of the molded body, the residual volatile content of the hollow particles of the present invention is more preferably less than 50 ppm, and further preferably less than 30 ppm.

[0069] The residual volatile components are generally organic compounds having a molecular weight of 500 or less, and specifically include residual polymerizable monomers, residual hydrophobic solvents, and decomposition products of polymerization initiators. Furthermore, the residual volatile content refers to the ratio of the mass of the residual volatile components contained in the hollow particles to the mass of the hollow particles.

[0070] The lower limit of the residual volatile content of the hollow particles of the present invention is not particularly limited, but from the viewpoint of ease of production, it may be, for example, 1 ppm or more, 2 ppm or more, or 3 ppm or more.

[0071] The residual volatile content of the hollow particles can be measured by purge and trap / gas chromatography (P&T / GC). Specifically, the measurement method described in the examples below can be used.

[0072] The total content of the surfactant and water-soluble polymer stabilizer (hereinafter referred to as "surfactant etc.") present on the outer surface of the hollow particles of the present invention is preferably less than 500ppm, more preferably less than 200ppm, further preferably less than 100ppm, and more preferably less than 50ppm. In addition, the water-soluble polymer stabilizer can be any one of an organic system or an inorganic system. When the content of the surfactant etc. present in the outer surface of the hollow particles is below the above-mentioned upper limit value, the reduction of the reactivity of the hollow particles and the substrate elastomer is suppressed, and therefore the effect of reducing the compression set of the formed body is improved. By using only an inorganic dispersion stabilizer as a dispersion stabilizer in the manufacture of the hollow particles described later, the content of the surfactant etc. present on the hollow particle surface can be made less than the detection limit.

[0073] In the present invention, the content of surfactants and the like present on the outer surface of the hollow particles refers to the ratio of the mass of the surfactants and the like present on the outer surface of the hollow particles to the mass of the hollow particles. The surfactants and the like present on the outer surface of the hollow particles can be extracted by, for example, ultrasonically treating the hollow particles in water. The type and mass of the surfactants and the like extracted into the water can be determined based on the 1 The peak position and peak intensity of the H-NMR spectrum are used to determine the amount of the surfactant and the like present on the surface of the hollow particles. In this method, the detection limit of the amount of the surfactant and the like present on the surface of the hollow particles is usually 0.05 ppm.

[0074] The thermal decomposition starting temperature of the hollow particles of the present invention is not particularly limited, but is preferably 345° C. or higher, more preferably 350° C. or higher from the viewpoint of heat resistance. The upper limit of the thermal decomposition starting temperature of the hollow particles is not particularly limited, but may be, for example, 400° C. or lower.

[0075] In the present invention, the thermal decomposition starting temperature of the hollow particles is the temperature at which the weight is reduced by 5%, and can be measured using a TG-DTA apparatus under a nitrogen atmosphere at a nitrogen flow rate of 230 mL / min and a heating rate of 10°C / min.

[0076] The hollow particles of the present invention are added to an elastomer composition, which is a molding material for a cross-linked elastomer molded article, to reduce the weight of the cross-linked elastomer molded article and reduce its compression set. In addition to reducing the weight and compression set of the cross-linked elastomer molded article, the hollow particles of the present invention can also impart various properties to the cross-linked elastomer molded article, such as thermal insulation and retention of functional ingredients such as antimicrobial agents. The uses of the elastomer composition containing the hollow particles of the present invention and the cross-linked molded article thereof are described in detail below in "3. Elastomer Compositions."

[0077] In addition, hollow particle of the present invention can give the multiple characteristics such as these material lightweighting, heat insulation, low dielectric, sound insulation, vibration reduction, light scattering by adding in resin, coating or various molded bodies etc. Therefore, hollow particle of the present invention can be used for the light-reflecting material, anti-glare film, light diffusion film and light diffusion material plate such as used in the various fields such as automobile, electricity, electronics, building, aviation, aerospace, etc., light diffusion material, heat insulating material, sound insulating material and low dielectric body, the buoyancy materials such as parts, food containers, sports shoes, sandals and shoes, household appliance parts, bicycle parts, stationery, tool, the wire rod of 3D printer, composite foam plastics etc. In addition, hollow particle of the present invention has high porosity, is not easily broken, and heat resistance is also excellent, therefore satisfies the heat insulation, cushioning (vibration reduction (Cushion) property) required by primer, also satisfies the heat resistance that meets thermal paper purposes. In addition, hollow particle of the present invention is also useful as the plastic pigment of excellence such as gloss, hiding power.

[0078] Furthermore, the hollow particles of the present invention can enclose useful ingredients such as fragrances, chemicals, pesticides, and ink components by methods such as impregnation, reduced pressure or pressurized impregnation, and can therefore be used for various applications depending on the ingredients contained therein.

[0079] Furthermore, the hollow particles of the present invention are also preferably used as rust inhibitors. The hollow particles of the present invention are also useful as additives that reduce electrical conductivity. Therefore, for example, a coating containing the hollow particles of the present invention can be used as an anti-rust coating (coating substrate, lubricating coating, etc.) for improving the corrosion resistance and rust resistance of steel materials, etc. In addition, the hollow particles added to the anti-rust coating can also contain an anti-rust additive.

[0080] 2. Method for manufacturing hollow particles

[0081] The hollow particles of the present invention can be produced by, for example, the production method described below based on the suspension polymerization method.

[0082] As one embodiment of the method for producing hollow particles of the present invention, there can be cited a method for producing hollow particles having the following steps: a step of preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer and an aqueous medium; a step of preparing a suspension in which droplets of a monomer composition containing the polymerizable monomer, the hydrophobic solvent and the polymerization initiator are dispersed in the aqueous medium by suspending the above-mentioned mixed solution; a step of preparing a precursor composition in which precursor particles are dispersed in the above-mentioned aqueous medium by subjecting the above-mentioned suspension to a polymerization reaction, wherein the above-mentioned precursor particles have a hollow portion surrounded by a shell containing a resin and the above-mentioned hollow portion is filled with the above-mentioned hydrophobic solvent; and a step of removing the above-mentioned hydrophobic solvent from the above-mentioned precursor particles.

[0083] In the present invention, hollow particles whose hollow parts are filled with a hydrophobic solvent are considered to be intermediates of hollow particles whose hollow parts are filled with a gas and are sometimes referred to as “precursor particles.” In the present invention, a “precursor composition” refers to a composition containing precursor particles.

[0084] In the above-mentioned production method, a suspension is prepared by suspending a mixed liquid containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium to form droplets of a monomer composition dispersed in an aqueous medium. The liquid monomer composition has a distribution structure in which the polymerizable monomer and the hydrophobic solvent undergo phase separation, with the polymerizable monomer concentrated on the surface and the hydrophobic solvent concentrated in the center. When this suspension is subjected to a polymerization reaction, polymer begins to precipitate on the surface of the monomer composition droplets. As the polymerization reaction proceeds, the surface of the droplets solidifies to form a shell, resulting in hollow particles having a hollow portion filled with the hydrophobic solvent.

[0085] By incorporating a crosslinkable monomer into the mixed liquid, a reactive unsaturated bond can be introduced into the outer surface of the shell.

[0086] Above-mentioned manufacture method comprises the operation of preparation mixed solution, the operation of preparation suspension, suspension is supplied to the operation of polyreaction, from precursor particles, removes the operation of hydrophobic solvent, can also comprise the operation except these.In addition, as long as technically feasible, then can carry out simultaneously as a operation two or more in above-mentioned each operation and other additional operation, also can swap order and carry out.For example, can carry out simultaneously the mode of suspending simultaneously with the material that drops into preparation mixed solution, in an operation, carry out preparation and the suspension of mixed solution simultaneously.

[0087] As a preferred example of a method for producing hollow particles, there can be mentioned a method including the following steps.

[0088] (1) Mixed liquid preparation process

[0089] A step of preparing a mixed solution comprising a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium;

[0090] (2) Suspension process

[0091] A step of preparing a suspension in which droplets of a monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator are dispersed in the aqueous medium by suspending the mixed liquid;

[0092] (3) Polymerization process

[0093] a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition in which precursor particles are dispersed in the aqueous medium, wherein the precursor particles have a hollow portion surrounded by a shell containing a resin and the hollow portion is filled with the hydrophobic solvent;

[0094] (4) Solid-liquid separation process

[0095] a step of obtaining a solid component containing precursor particles by solid-liquid separation of the precursor composition; and

[0096] (5) Solvent removal process

[0097] A step of removing the hydrophobic solvent from the precursor particles obtained in the solid-liquid separation step to obtain hollow particles.

[0098] Figure 1 This is a schematic diagram illustrating an example of the production method of the present invention. Figure 1 (1) to (5) in the figure correspond to the above steps (1) to (5). The white arrows between the figures indicate the order of the steps. Figure 1 The schematic diagrams are merely for illustration, and the manufacturing method of the present invention is not limited to the manufacturing method shown in the drawings. In addition, the structure, size, and shape of the materials used in the manufacturing method of the present invention are not limited to the structure, size, and shape of the various materials in these drawings.

[0099] Figure 1 (1) is a schematic cross-sectional view showing one embodiment of a mixed solution in the mixed solution preparation step. As shown in this figure, the mixed solution includes an aqueous medium 1 and a low-polarity material 2 dispersed in the aqueous medium 1. Here, the low-polarity material 2 refers to a material with low polarity that is not easily miscible with the aqueous medium 1. In the present invention, the low-polarity material 2 includes a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator.

[0100] Figure 1 (2) is a cross-sectional schematic diagram showing an embodiment of the suspension in the suspension process. The suspension includes an aqueous medium 1 and droplets 8 of a monomer composition dispersed in the aqueous medium 1. The droplets 8 of the monomer composition contain polymerizable monomers, a hydrophobic solvent, and a polymerization initiator, but the distribution within the droplets is uneven. The droplets 8 of the monomer composition have the following structure: the hydrophobic solvent 4a and the material 4b other than the hydrophobic solvent containing the polymerizable monomer are phase-separated, the hydrophobic solvent 4a is concentrated in the center, the material 4b other than the hydrophobic solvent is concentrated on the surface side, and a dispersion stabilizer (not shown) is attached to the surface.

[0101] Figure 1(3) is a schematic cross-sectional view showing an embodiment of a precursor composition comprising precursor particles containing a hydrophobic solvent in a hollow portion obtained by a polymerization step. The precursor composition comprises an aqueous medium 1 and precursor particles 9 containing a hydrophobic solvent 4a in a hollow portion, which are dispersed in the aqueous medium 1. The shell 6 forming the outer surface of the precursor particles 9 is formed by polymerization of the polymerizable monomer in the droplets 8 of the monomer composition, and the polymer containing the polymerizable monomer serves as a resin.

[0102] Figure 1 (4) is a schematic cross-sectional view showing one embodiment of the precursor particles after the solid-liquid separation step. Figure 1 (4) shows that from the above Figure 1 The state (3) is the state after removing the aqueous medium 1.

[0103] Figure 1 (5) is a schematic cross-sectional view showing one embodiment of the hollow particles after the solvent removal step. Figure 1 (5) shows that from the above Figure 1 The state (4) is the state after the hydrophobic solvent 4a is removed. By removing the hydrophobic solvent from the precursor particles, hollow particles 10 having a hollow portion 7 filled with gas inside the shell 6 are obtained.

[0104] Hereinafter, the above five steps and other steps will be described in sequence.

[0105] (1) Mixed liquid preparation process

[0106] This step is a step of preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium. The mixed solution may further contain other materials within a range that does not impair the purpose of the present invention.

[0107] The materials of the mixed solution will be described in the order of (A) polymerizable monomer, (B) hydrophobic solvent, (C) polymerization initiator, (D) dispersion stabilizer, and (E) aqueous medium.

[0108] (A) polymerizable monomer

[0109] In the present invention, a polymerizable monomer refers to a compound having a functional group capable of addition polymerization (sometimes simply referred to as a polymerizable functional group in the present invention). In the present invention, a compound having an ethylenically unsaturated bond as a functional group capable of addition polymerization is generally used as a polymerizable monomer. As the polymerizable functional group, a free radical polymerizable group is preferred. From the perspective of excellent reactivity, at least one selected from a (meth)acryloyl group, a vinyl group, and an allyl group is particularly preferred, and at least one selected from a (meth)acryloyl group and a vinyl group is more preferred.

[0110] In the present invention, a polymerizable monomer having only one polymerizable functional group is referred to as a non-crosslinking monomer, and a polymerizable monomer having two or more polymerizable functional groups is referred to as a crosslinking monomer. A crosslinking monomer can form crosslinks in a polymer through a polymerization reaction. The crosslinking monomer becomes the crosslinking monomer unit in the shell, and the non-crosslinking monomer becomes the non-crosslinking monomer unit in the shell.

[0111] In the present invention, a polymerizable monomer composed of carbon and hydrogen is referred to as a hydrocarbon monomer, a crosslinkable monomer composed of carbon and hydrogen is referred to as a crosslinkable hydrocarbon monomer, and a non-crosslinkable monomer composed of carbon and hydrogen is referred to as a non-crosslinkable hydrocarbon monomer. Furthermore, a polymerizable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as an acrylic monomer, a crosslinkable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as a crosslinkable acrylic monomer, and a non-crosslinkable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as a non-crosslinked acrylic monomer. In a crosslinkable acrylic monomer, at least one polymerizable functional group may be a (meth)acryloyl group, but preferably all polymerizable functional groups are (meth)acryloyl groups.

[0112] In the present invention, (meth)acrylate refers to acrylate and methacrylate, (meth)acrylic acid refers to acrylic acid and methacrylic acid, and (meth)acryloyl refers to acryloyl and methacryloyl.

[0113] As the polymerizable monomer, any known polymerizable monomer conventionally used in the production of hollow particles can be used without particular limitation. To ensure that the iodine value of the hollow particles falls within the aforementioned range, it is preferred that at least a crosslinking monomer be included. It is speculated that the iodine value of the hollow particles falls within the aforementioned range by allowing a portion of the reactive unsaturated bonds of the crosslinking monomer to remain unreacted on the outer surface of the shell.

[0114] In addition, when comprising crosslinking monomer as polymerizable monomer, when suspension is supplied to polyreaction, the crosslinking density of the polymer separated out on the surface of droplet becomes high, and then precipitate is also crosslinked each other, therefore can improve the crosslinking density of shell.Therefore, easily form the shell of excellent strength, in addition, hollow particle easily becomes spherical, easily forms the hollow part clearly distinguished from shell in particle.The more excellent the intensity of shell, the more difficult for hollow particle to plastically deform, therefore by improving the intensity of shell, can improve the effect of reducing the compression set of formed body.

[0115] Examples of the crosslinking monomer include aromatic divinyl monomers such as divinylbenzene, divinylbiphenyl, and divinylnaphthalene; linear or branched dienes such as butadiene, isoprene, 2,3-dimethylbutadiene, pentadiene, and hexadiene; and alicyclic dienes such as dicyclopentadiene, cyclopentadiene, and ethylenetetracyclododecene; crosslinking macromonomers such as polybutadiene, polyisoprene, block copolymers of styrene and butadiene (SBS), and block copolymers of styrene and isoprene (SIS); and crosslinking hydrocarbon monomers such as allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 3-(meth)acryloyloxy-2-hydroxypropyl (meth)acrylate, 1,3-bis(methacryloyloxy)-2-hydroxypropyl (meth)acrylate. Bifunctional cross-linking acrylic monomers such as propane, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and bisphenol A di(meth)acrylate; trifunctional or higher cross-linking acrylic monomers such as trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and dipentaerythritol poly(meth)acrylate; and cross-linking acrylic monomers such as ethoxylates thereof; cross-linking allyl monomers such as diallyl phthalate; and cross-linking macromonomers such as polyphenylene ether modified with vinyl groups at both ends and polyphenylene ether modified with (meth)acrylic acid at both ends. These crosslinking monomers can be used alone or in combination of two or more.

[0116] In the present invention, from the perspectives of maintaining the iodine value of the hollow particles within the above-mentioned range, improving the shell strength, and reducing the compression set of the molded article, the crosslinking monomer preferably contains at least one selected from a crosslinking acrylic monomer and a crosslinking hydrocarbon monomer. It is more preferred that at least a crosslinking acrylic monomer be contained, and it is particularly preferred that a combination of a crosslinking acrylic monomer and a crosslinking hydrocarbon monomer be contained.

[0117] Among the crosslinkable monomers, crosslinkable acrylic monomers are preferred from the viewpoint of improving the shell strength, while crosslinkable hydrocarbon monomers are preferred from the viewpoint of easily introducing reactive unsaturated bonds into the outer surface of the shell.

[0118] As the crosslinkable hydrocarbon monomer, an aromatic divinyl monomer is particularly preferred, and divinylbenzene is particularly preferred.

[0119] The cross-linkable acrylic monomer is preferably any of the above-mentioned bifunctional cross-linkable acrylic monomers and trifunctional or higher cross-linkable acrylic monomers. From the perspective of increasing shell strength and reducing compression set of the molded article, it is preferred to include at least a bifunctional cross-linkable acrylic monomer, and more preferably a combination of a bifunctional cross-linkable acrylic monomer and a trifunctional or higher cross-linkable acrylic monomer. The bifunctional cross-linkable acrylic monomer is particularly preferably at least one selected from ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate. The trifunctional or higher cross-linkable acrylic monomer is particularly preferably at least one selected from trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate.

[0120] In the present invention, the content of the crosslinking monomer in 100% by mass of the polymerizable monomer is preferably 50% by mass or greater, more preferably 70% by mass or greater, even more preferably 90% by mass or greater, and even more preferably 95% by mass or greater, in order to maintain the iodine value of the hollow particles within the above range, improve shell strength, and reduce compression set of the molded article. In the present invention, the polymerizable monomer may be composed solely of the crosslinking monomer or may further contain a non-crosslinking monomer as described below. Therefore, the content of the crosslinking monomer in 100% by mass of the polymerizable monomer may be, for example, 99% by mass or less, 98% by mass or less, or 97% by mass or less.

[0121] The content of each monomer in 100% by mass of the polymerizable monomer corresponds to the content of each monomer unit in 100% by mass of all monomer units constituting the polymer contained in the shell.

[0122] Furthermore, from the perspective of maintaining the iodine value of the hollow particles within the above-mentioned range, improving the shell strength, and reducing the compression set of the molded article, the content of the crosslinkable hydrocarbon monomer in 100% by mass of the polymerizable monomer is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more as a lower limit. The upper limit is not particularly limited and may be 100% by mass, but is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0123] Furthermore, from the same viewpoint, the content of the cross-linkable acrylic monomer in 100% by mass of the polymerizable monomer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more as the lower limit, and is preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less as the upper limit.

[0124] Furthermore, in the case of a combination of a bifunctional crosslinkable acrylic monomer and a trifunctional or higher crosslinkable acrylic monomer, from the perspective of maintaining the iodine value of the hollow particles within the above-mentioned range, improving the shell strength, and reducing the compression set of the molded article, the content of the bifunctional crosslinkable acrylic monomer relative to the total of 100 mass% of the bifunctional crosslinkable acrylic monomer and the trifunctional or higher crosslinkable acrylic monomer is preferably 20 mass% or more as a lower limit, more preferably 30 mass% or more, and even more preferably 40 mass% or more as an upper limit, and preferably 70 mass% or less, more preferably 60 mass% or less, and even more preferably 50 mass% or less as an upper limit.

[0125] From the perspectives of maintaining the iodine value of the hollow particles within the above-mentioned range, improving the shell strength, and reducing the compression set of the molded article, when the cross-linking monomer comprises a cross-linking acrylic monomer and a cross-linking hydrocarbon monomer, the content of the cross-linking acrylic monomer relative to 100% by mass of the total of the cross-linking acrylic monomer and the cross-linking hydrocarbon monomer is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more as a lower limit, and preferably 70 parts by mass or less, more preferably 60 parts by mass or less as an upper limit, with respect to 100% by mass of the total of the cross-linking acrylic monomer and the cross-linking hydrocarbon monomer.

[0126] In the present invention, from the perspective of maintaining the iodine value of the hollow particles within the above range, improving the shell strength, and reducing the compression set of the molded article, the total content of the crosslinkable acrylic monomer and the crosslinkable hydrocarbon monomer is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, and even more preferably 99 parts by mass or more per 100 parts by mass of the crosslinkable monomer.

[0127] In the present invention, a non-crosslinking monomer may be contained as a polymerizable monomer.

[0128] Examples of the non-crosslinking monomer include aromatic monovinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, and ethylvinylnaphthalene; linear or branched monoolefins such as ethylene, propylene, and butene; and alicyclic monoolefins such as vinylcyclohexane, norbornene, tricyclododecene, and 1,4-methylene-1,4,4a,9a-tetrahydrofluorene; and non-crosslinking hydrocarbon monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, and propylene glycol. Ester, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-aminoethyl (meth)acrylate, (meth)acrylic acid, (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, methoxy polyethylene glycol (meth)acrylate, ethoxy polyethylene glycol (meth)acrylate , propoxy polyethylene glycol (meth) acrylate, butoxy polyethylene glycol (meth) acrylate, hexyl polyethylene glycol (meth) acrylate, octyl polyethylene glycol polypropylene glycol (meth) acrylate, lauryl polyethylene glycol (meth) acrylate, stearyl polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol polypropylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol tetra Non-crosslinking acrylic monomers such as methylene glycol (meth)acrylate, propylene glycol polybutylene glycol mono(meth)acrylate, and monoethylene glycol mono(meth)acrylate; carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated aromatic vinyl monomers such as halogenated styrene; halogenated vinyl monomers such as vinyl chloride; vinylidene halide monomers such as vinylidene chloride; vinyl pyridine monomers; non-crosslinking macromonomers such as polystyrene terminally modified with (meth)acrylic acid, and polymethyl methacrylate terminally modified with (meth)acrylic acid. These non-crosslinking monomers can be used alone or in combination of two or more.

[0129] From the perspective of maintaining the iodine value of the hollow particles within the above range and suppressing a decrease in shell strength, the content of the non-crosslinking monomer in 100% by mass of the polymerizable monomer is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less. The lower limit of the content of the non-crosslinking monomer in 100% by mass of the polymerizable monomer is not particularly limited and may be, for example, 1% by mass or more, 2% by mass or more, or 3% by mass or more.

[0130] The content of the polymerizable monomer in the mixed liquid is not particularly limited. From the perspective of balancing the porosity, particle size, and mechanical strength of the hollow particles, it is preferably 15 to 50% by mass, and more preferably 20 to 40% by mass, relative to 100% by mass of the total mass of the components in the mixed liquid excluding the aqueous medium.

[0131] Furthermore, from the perspective of suppressing a decrease in the strength of the obtained hollow particles, the content of the polymerizable monomer is preferably 96% by mass or more, and more preferably 97% by mass or more, relative to 100% by mass of the total mass of the solid components excluding the hydrophobic solvent in the material forming the oil phase in the mixed liquid.

[0132] In the present invention, the solid content refers to all components excluding the solvent, and liquid polymerizable monomers and the like are included in the solid content.

[0133] (B) Hydrophobic solvent

[0134] The hydrophobic solvent used in the production method of the present invention is a non-polymerizable organic solvent that is poorly soluble in water.

[0135] The hydrophobic solvent acts as a spacer, forming a hollow space within the particles. In the suspension step described below, a suspension is obtained in which droplets of the monomer composition containing the hydrophobic solvent are dispersed in an aqueous medium. Phase separation occurs within the monomer composition droplets during the suspension step, causing the low-polarity hydrophobic solvent to accumulate within the droplets. Ultimately, the hydrophobic solvent is distributed within the monomer composition droplets, while other materials, excluding the hydrophobic solvent, are distributed at the edges according to their respective polarities.

[0136] In the polymerization step described below, an aqueous dispersion containing precursor particles containing a hydrophobic solvent is obtained. That is, the hydrophobic solvent accumulates inside the particles, forming a hollow portion filled with the hydrophobic solvent inside the obtained precursor particles.

[0137] The hydrophobic solvent can be appropriately selected from known hydrophobic solvents without particular limitation. Examples thereof include esters such as ethyl acetate and butyl acetate; ether esters such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; and hydrocarbon solvents. Hydrocarbon solvents are particularly preferred, and hydrocarbon solvents having 5 to 8 carbon atoms are more preferred.

[0138] Examples of hydrocarbon solvents include aliphatic hydrocarbons including chain hydrocarbon solvents such as pentane, hexane, heptane, octane, 2-methylbutane and 2-methylpentane, paraffin solvents, and cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane and cycloheptane; and aromatic hydrocarbons such as benzene, toluene and xylene.

[0139] These hydrophobic solvents can be used alone or in combination of two or more.

[0140] In the suspension step, the hydrophobic solvent is preferably an organic solvent having a lower solubility in water than the crosslinking monomer contained in the polymerizable monomer, because the polymerizable monomer and the hydrophobic solvent are easily phase-separated in the droplets of the monomer composition.

[0141] In addition, when the polymerizable monomer contains a hydrocarbon monomer at a ratio of 30% by mass or more, the hydrophobic solvent is preferably a hydrocarbon solvent, more preferably a chain hydrocarbon solvent, further preferably a chain hydrocarbon solvent having 5 to 8 carbon atoms, and further preferably at least one selected from pentane, hexane, heptane and octane.

[0142] In addition, the boiling point of the hydrophobic solvent is not particularly limited. From the perspective of easy removal in the solvent removal step described later, it is preferably 130°C or lower, more preferably 100°C or lower. On the other hand, from the perspective of easy inclusion in the precursor particles, it is preferably 50°C or higher, more preferably 60°C or higher.

[0143] In addition, when the hydrophobic solvent is a mixed solvent containing multiple hydrophobic solvents and has multiple boiling points, the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent is preferably below the above-mentioned upper limit value, and the boiling point of the solvent with the lowest boiling point among the solvents contained in the mixed solvent is preferably above the above-mentioned lower limit value.

[0144] Furthermore, the hydrophobic solvent preferably has a relative dielectric constant of 2.5 or less at 20°C. The relative dielectric constant is one of the indicators indicating the polarity of a compound. It is believed that when the relative dielectric constant of the hydrophobic solvent is sufficiently low, at 2.5 or less, phase separation in the droplets of the monomer composition proceeds rapidly, facilitating the formation of hollow portions.

[0145] Examples of hydrophobic solvents having a relative dielectric constant of 2.5 or less at 20° C. are as follows. The values ​​in parentheses are relative dielectric constants.

[0146] Pentane (1.8), hexane (1.9), heptane (1.9), octane (1.9), cyclohexane (2.0).

[0147] Regarding the relative dielectric constant at 20°C, reference can be made to values ​​described in known literature (e.g., "Basic Handbook of Chemistry" edited by the Chemical Society of Japan, revised 4th edition, Maruzen Co., Ltd., published on September 30, 1993, pages II-498 to II-503) and other technical information. Examples of methods for measuring the relative dielectric constant at 20°C include a relative dielectric constant test conducted in accordance with Section 23 of JIS C 2101:1999, with the measurement temperature set at 20°C.

[0148] The porosity of the hollow particles can be adjusted by varying the amount of hydrophobic solvent in the mixed liquid. In the suspension step described below, the oil droplets containing the polymerizable monomers undergo polymerization while encapsulating the hydrophobic solvent. Therefore, the porosity of the resulting hollow particles tends to increase with increasing hydrophobic solvent content.

[0149] In the present invention, from the aspects of easily controlling the particle size of the hollow particles, easily increasing the porosity while maintaining the strength of the hollow particles, and easily reducing the amount of residual hydrophobic solvent in the particles, the content of the hydrophobic solvent in the mixed solution is preferably 100 parts by mass or more and 650 parts by mass or less relative to 100 parts by mass of the polymerizable monomer. The content of the hydrophobic solvent in the mixed solution is more preferably 120 parts by mass or more and 500 parts by mass or less, and further preferably 140 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the polymerizable monomer.

[0150] (C) Polymerization initiator

[0151] In the production method of the present invention, the mixed liquid preferably contains an oil-soluble polymerization initiator as a polymerization initiator. The oil-soluble polymerization initiator is not particularly limited as long as it is a lipophilic polymerization initiator with a solubility in water of 0.2% by mass or less. Examples thereof include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxydiethylacetate, and t-butyl peroxypivalate; and azo compounds such as 2,2′-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, and 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile).

[0152] The content of the polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass relative to 100 parts by mass of the polymerizable monomer in the mixed solution. When the content of the polymerization initiator is above the above lower limit, the polymerization reaction can proceed sufficiently. When the content of the polymerization initiator is below the above upper limit, the possibility of the polymerization initiator remaining after the polymerization reaction is completed is small, and the possibility of unexpected side reactions is also small.

[0153] (D) Dispersion stabilizer

[0154] The dispersion stabilizer is an agent that disperses the droplets of the monomer composition in the aqueous medium during the suspension step. Examples of the dispersion stabilizer include inorganic dispersion stabilizers, organic or inorganic water-soluble polymer stabilizers, and surfactants.

[0155] In the present invention, an inorganic dispersion stabilizer is preferably used as the dispersion stabilizer from the viewpoints of easily controlling the particle size of droplets in the suspension, facilitating removal of the dispersion stabilizer by a washing step, and preventing the shell from becoming too thin and thus reducing the strength of the hollow particles.

[0156] Examples of the inorganic dispersion stabilizer include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and iron hydroxide; and inorganic compounds such as silicon dioxide. These inorganic dispersion stabilizers can be used alone or in combination of two or more.

[0157] As the inorganic dispersion stabilizer, an inorganic dispersion stabilizer that is poorly soluble in water can be preferably used. Here, poorly soluble in water means that the solubility in water at 25° C. is preferably less than 1 g / L.

[0158] As the poorly water-soluble inorganic dispersion stabilizer, metal hydroxides are particularly preferred, and magnesium hydroxide is more preferred.

[0159] In the present invention, it is particularly preferred to use the sparingly water-soluble inorganic dispersion stabilizer dispersed in the aqueous medium in the form of colloidal particles, i.e., in the form of a colloidal dispersion containing the sparingly water-soluble inorganic dispersion stabilizer colloidal particles. This allows the inorganic dispersion stabilizer to be easily removed in the washing step described below.

[0160] The colloidal dispersion containing the sparingly water-soluble inorganic dispersion stabilizer colloidal particles can be prepared, for example, by reacting at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides with a water-soluble polyvalent metal salt (excluding alkaline earth metal hydroxides) in an aqueous medium.

[0161] Examples of the alkali metal hydroxide salt include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. Examples of the alkaline earth metal hydroxide salt include barium hydroxide, calcium hydroxide, etc.

[0162] The water-soluble polyvalent metal salt may be any water-soluble polyvalent metal salt other than the compounds belonging to the above-mentioned alkaline earth metal hydroxide salts. Examples thereof include magnesium metal salts such as magnesium chloride, magnesium phosphate, and magnesium sulfate; calcium metal salts such as calcium chloride, calcium nitrate, calcium acetate, and calcium sulfate; aluminum metal salts such as aluminum chloride and aluminum sulfate; barium salts such as barium chloride, barium nitrate, and barium acetate; and zinc salts such as zinc chloride, zinc nitrate, and zinc acetate. Among these, magnesium metal salts, calcium metal salts, and aluminum metal salts are preferred, magnesium metal salts are more preferred, and magnesium chloride is particularly preferred.

[0163] The method for reacting at least one selected from the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with the above-mentioned water-soluble polyvalent metal salt in an aqueous medium is not particularly limited. For example, it is sufficient to mix an aqueous solution of at least one selected from the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with an aqueous solution of a water-soluble polyvalent metal salt.

[0164] Furthermore, colloidal silica can also be used as a colloidal dispersion containing colloid particles of an inorganic dispersion stabilizer that is poorly soluble in water.

[0165] Examples of organic water-soluble polymer stabilizers include polyvinyl alcohol, polycarboxylic acids (polyacrylic acid, etc.), celluloses (hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, etc.), polyvinyl pyrrolidone, polyacrylic acid imide, polyethylene oxide, and poly(hydroxystearic acid-g-methyl methacrylate-co-methacrylic acid) copolymers.

[0166] Examples of the inorganic water-soluble polymer stabilizer include sodium tripolyphosphate.

[0167] The surfactant refers to a compound having both a hydrophilic group and a hydrophobic group in one molecule, and examples thereof include ionic surfactants such as well-known anionic surfactants, cationic surfactants, and amphoteric surfactants, and nonionic surfactants.

[0168] Furthermore, the solubility of the water-soluble polymer stabilizer and surfactant in water at 25° C. is usually 1 g / L or more.

[0169] The content of the dispersion stabilizer is not particularly limited, but is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, relative to a total of 100 parts by mass of the polymerizable monomer and the hydrophobic solvent. By setting the content of the dispersion stabilizer above the lower limit, the droplets of the monomer composition can be fully dispersed in the suspension without aggregation. On the other hand, by setting the content of the dispersion stabilizer below the upper limit, an increase in the viscosity of the suspension during granulation can be prevented, thereby avoiding the problem of clogging of the suspension in the granulator.

[0170] The content of the dispersion stabilizer is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of the aqueous medium.

[0171] In the present invention, from the perspective of suppressing the decrease in reactivity between the hollow particles and the base elastomer, the lower the residual amount of dispersion stabilizer, the more preferred. It is most preferred that the dispersion stabilizer be absent, and particularly preferred that the dispersion stabilizer be absent, including water-soluble polymer stabilizers and surfactants. By using only an inorganic dispersion stabilizer as the dispersion stabilizer, hollow particles can be obtained in which the levels of both water-soluble polymer stabilizers and surfactants are below the detection limit.

[0172] (E) Aqueous media

[0173] In the present invention, the aqueous medium refers to a medium selected from water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent.

[0174] When a mixture of water and a hydrophilic solvent is used, it is important that the polarity of the mixture as a whole does not become too low from the perspective of forming droplets of the monomer composition. In this case, the mass ratio of water to hydrophilic solvent (water:hydrophilic solvent) can be, for example, 99:1 to 50:50.

[0175] The hydrophilic solvent in the present invention is not particularly limited as long as it is a solvent that is fully miscible with water without phase separation. Examples of the hydrophilic solvent include alcohols such as methanol and ethanol; tetrahydrofuran (THF); and dimethyl sulfoxide (DMSO).

[0176] The content of the aqueous medium is not particularly limited. From the viewpoint of ensuring that the particle size and porosity of the hollow particles are within the preferred ranges described below, the lower limit is preferably 200 parts by mass or more, more preferably 400 parts by mass or more, and even more preferably 600 parts by mass or more, relative to 100 parts by mass of the polymerizable monomer contained in the mixed liquid. The upper limit is preferably 1000 parts by mass or less, and more preferably 800 parts by mass or less.

[0177] The mixed liquid may further contain other materials different from the above-mentioned materials (A) to (E) within a range not impairing the effects of the present invention.

[0178] A mixed solution is obtained by mixing the above-mentioned materials and other materials as needed, followed by appropriate stirring. In this mixed solution, an oil phase containing the above-mentioned (A) polymerizable monomer, (B) hydrophobic solvent, (C) polymerization initiator, and other lipophilic materials is dispersed in particles of approximately several millimeters in an aqueous phase containing (D) dispersion stabilizer and (E) aqueous medium. Depending on the type of materials, the dispersion state of these materials in the mixed solution may also be visually observable.

[0179] In the mixed solution preparation step, the above-mentioned materials and other materials as needed can be simply mixed and stirred to obtain a mixed solution. From the perspective of easily achieving uniform shell formation, it is preferred to prepare the mixed solution by separately preparing an oil phase containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator, and an aqueous phase containing a dispersion stabilizer and an aqueous medium, and then mixing these. In the present invention, a colloidal dispersion prepared by dispersing a sparingly water-soluble inorganic dispersion stabilizer in the form of colloidal particles in an aqueous medium can be preferably used as the aqueous phase.

[0180] By preparing the oil phase and the water phase separately in advance and then mixing them, hollow particles having a uniform composition of the shell portion can be produced, and the particle size of the hollow particles can also be easily controlled.

[0181] (2) Suspension process

[0182] The suspension step is a step of preparing a suspension in which droplets of the monomer composition containing a hydrophobic solvent are dispersed in an aqueous medium by suspending the mixed liquid.

[0183] The method for suspending the droplets of the monomer composition is not particularly limited, and a known suspension method can be employed. Examples of dispersers used to prepare the suspension include horizontal or vertical inline dispersers such as the Milder manufactured by Ohyo Kiko Co., Ltd., the Cavitron manufactured by Eurotec, and inline dispersers manufactured by IKA (e.g., the DISPAX-REACTOR (registered trademark) DRS); and emulsifying dispersers such as the Homomixer MARK II series manufactured by Plemix Co., Ltd.

[0184] In the dispersion for preparing a suspension, the rotation speed of the disperser is preferably 100 rpm or more, more preferably 200 rpm or more, and further preferably 300 rpm or more, from the perspective of forming a hollow portion and ensuring that the volume average particle size of the hollow particles is within the above-mentioned preferred range. On the other hand, from the perspective of reducing the proportion of irregular-shaped particles, the rotation speed is preferably 30,000 rpm or less, more preferably 10,000 rpm or less, and further preferably 5,000 rpm or less.

[0185] In the suspension prepared in the suspension step, droplets of the monomer composition containing the lipophilic material and having a particle size of approximately 0.1 to 100 μm are uniformly dispersed in the aqueous medium. While these droplets of the monomer composition are difficult to observe with the naked eye, they can be observed using known observation equipment such as an optical microscope.

[0186] During the suspension process, phase separation occurs within the monomer composition droplets, so the low-polarity hydrophobic solvent tends to accumulate within the droplets. As a result, the resulting droplets contain the hydrophobic solvent within them and materials other than the hydrophobic solvent at their edges.

[0187] The droplets of the monomer composition dispersed in the aqueous medium are formed by surrounding the oil-soluble monomer composition with a dispersion stabilizer. The droplets of the monomer composition contain an oil-soluble polymerization initiator, a polymerizable monomer, and a hydrophobic solvent.

[0188] The droplets of the monomer composition are fine oil droplets, and the oil-soluble polymerization initiator generates polymerization initiation radicals inside the fine oil droplets. Therefore, precursor particles of a target particle size can be produced without excessive growth of the fine oil droplets.

[0189] In such a suspension polymerization method using an oil-soluble polymerization initiator, the polymerization initiator has no opportunity to come into contact with the polymerizable monomer dispersed in the aqueous medium. Therefore, the use of an oil-soluble polymerization initiator can suppress the by-production of unwanted resin particles, such as relatively small, dense particles, in addition to the target hollow resin particles.

[0190] (3) Polymerization process

[0191] This step involves subjecting the suspension obtained in the suspension step to a polymerization reaction to prepare a precursor composition comprising precursor particles dispersed in an aqueous medium. The precursor particles have a hollow portion surrounded by a shell containing a resin and filled with a hydrophobic solvent. The precursor particles are formed by polymerizing polymerizable monomers contained in droplets of a monomer composition, and the shells of the precursor particles contain a polymer of the polymerizable monomers as the resin.

[0192] The polymerization method is not particularly limited, and for example, a batch method (intermittent method), a semi-continuous method, a continuous method, and the like can be adopted.

[0193] The polymerization temperature is preferably 40 to 90°C, more preferably 50 to 80°C.

[0194] Furthermore, the polymerization reaction time is preferably 1 to 48 hours, more preferably 1 to 36 hours.

[0195] In the polymerization step, the shell portions of the monomer composition droplets containing the hydrophobic solvent are polymerized, and thus, as described above, hollow portions filled with the hydrophobic solvent are formed inside the obtained precursor particles.

[0196] (4) Solid-liquid separation process

[0197] This step is a step of obtaining a solid component containing precursor particles by solid-liquid separation of the precursor composition containing precursor particles obtained in the above-mentioned polymerization step.

[0198] The method for solid-liquid separation of the precursor composition is not particularly limited, and known methods can be used. Examples of solid-liquid separation methods include centrifugation, filtration, and static separation. Filtration is particularly preferred because it is easy to operate and has a high removal efficiency for the dispersion stabilizer.

[0199] After the solid-liquid separation step and before the solvent removal step described below, an optional step such as a pre-drying step may be performed. Examples of the pre-drying step include a step of pre-drying the solid component obtained after the solid-liquid separation step by passing it through a drying device such as a dryer or a drying apparatus such as a hand dryer.

[0200] (5) Solvent removal process

[0201] This step is a step of removing the hydrophobic solvent contained in the precursor particles.

[0202] For example, after the solid-liquid separation step, the hydrophobic solvent contained in the precursor particles is removed in the gas, and the hydrophobic solvent inside the precursor particles is replaced with air, thereby obtaining hollow particles filled with gas.

[0203] " in gas " in this process strictly refers to under the environment that there is no liquid component at all outside of precursor particles and under the environment that there is only the very small amount of liquid component of the degree that does not affect the removal of hydrophobic solvent in the outside of precursor particles. " in gas " can change and be expressed as the state that precursor particles are not present in slurry, and also can change and be expressed as the state that precursor particles are present in dry powder. That is, in this process, it is important to remove hydrophobic solvent under the environment that precursor particles are in direct contact with outside gas.

[0204] The method for removing the hydrophobic solvent in the precursor particles in a gas is not particularly limited, and a known method can be employed, such as reduced pressure drying, heat drying, airflow drying, or a combination of these methods.

[0205] In particular, when using a heat drying method, the heating temperature needs to be above the boiling point of the hydrophobic solvent and below the maximum temperature at which the shell structure of the precursor particles does not collapse. Therefore, although it depends on the composition of the shell in the precursor particles and the type of hydrophobic solvent, the heating temperature can be set to, for example, 50 to 200°C, 70 to 200°C, or even 100 to 200°C.

[0206] By the drying operation in the gas, the hydrophobic solvent inside the precursor particles is replaced by the external gas, resulting in hollow particles in which the gas occupies the hollow portion.

[0207] The drying environment is not particularly limited and can be suitably selected according to the purpose of the hollow particle. As the drying environment, for example, air, oxygen, nitrogen, argon, etc. can be considered. In addition, after the gas is temporarily filled with the hollow particle inside, drying under reduced pressure is carried out, thus also hollow particles that are temporarily vacuum can be obtained inside.

[0208] As another method, instead of performing solid-liquid separation of the slurry-like precursor composition obtained in the polymerization step, the hydrophobic solvent contained in the precursor particles may be removed from the slurry containing the precursor particles and the aqueous medium.

[0209] In this method, the hydrophobic solvent contained in the precursor particles can be removed by blowing an inert gas into the precursor composition at a temperature equal to or higher than the temperature obtained by subtracting 35° C. from the boiling point of the hydrophobic solvent.

[0210] Here, when the hydrophobic solvent is a mixed solvent containing multiple hydrophobic solvents and has multiple boiling points, the boiling point of the hydrophobic solvent in the solvent removal step refers to the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, that is, the highest boiling point among the multiple boiling points.

[0211] From the perspective of reducing the residual amount of the hydrophobic solvent in the hollow particles, the temperature at which the inert gas is bubbled into the precursor composition is preferably at least the temperature obtained by subtracting 30°C from the boiling point of the hydrophobic solvent, and more preferably at least the temperature obtained by subtracting 20°C from the boiling point of the hydrophobic solvent. The temperature during the bubble is generally set to be at least the polymerization temperature in the polymerization step described above. While not particularly limited, the bubble temperature can be set to 50°C to 100°C.

[0212] The inert gas to be blown in is not particularly limited, and examples thereof include nitrogen and argon.

[0213] The aeration conditions can be appropriately adjusted according to the type and amount of the hydrophobic solvent to remove the hydrophobic solvent contained in the precursor particles. The aeration conditions are not particularly limited. For example, the inert gas can be aerated at 1 to 3 L / min for 1 to 10 hours.

[0214] This method can produce a slurry of hollow particles containing an inert gas. The slurry is subjected to solid-liquid separation to obtain hollow particles, which are then dried to remove the aqueous medium remaining in the hollow particles, thereby obtaining hollow particles in which the gas occupies the hollow portion.

[0215] Regarding a method for obtaining hollow particles whose hollow portions are filled with gas by removing the hydrophobic solvent in the precursor particles in a gas after solid-liquid separation of a slurry-like precursor composition, and a method for obtaining hollow particles whose hollow portions are filled with gas by removing the hydrophobic solvent contained in the precursor particles in a slurry containing the precursor particles and an aqueous medium, and then removing the aqueous medium remaining in the hollow particles in a gas after solid-liquid separation, when the two methods are compared, the former method has the advantage that the hollow particles are not easily broken during the step of removing the hydrophobic solvent, and the latter method has the advantage that the residual amount of the hydrophobic solvent is reduced due to the use of an inert gas for blowing.

[0216] In addition, as a method for removing the hydrophobic solvent contained in the precursor particles without performing solid-liquid separation on the slurry-like precursor composition obtained in the polymerization step after the polymerization step and before the solid-liquid separation step, for example, a method of distilling off the hydrophobic solvent contained in the precursor particles from the precursor composition at a specified pressure (high pressure, normal pressure or reduced pressure); a method of introducing an inert gas such as nitrogen, argon, helium or water vapor into the precursor composition at a specified pressure (high pressure, normal pressure or reduced pressure) to thereby distill off the hydrophobic solvent.

[0217] (6) Others

[0218] As steps other than the above-mentioned (1) to (5), for example, the following (6-a) surface treatment step, (6-b) screening step, (6-c) washing step, and (6-d) particle internal replacement step may be added.

[0219] (6-a) Surface treatment process

[0220] The method for producing hollow particles of the present invention may include a surface treatment step of treating the outer surface of the shell with a coupling agent after the polymerization step.

[0221] The coupling agent has a functional group capable of bonding with organic matter and a functional group capable of bonding with inorganic matter in one molecule, which can improve the affinity between organic and inorganic materials.

[0222] The coupling agent preferably has a functional group in its molecular structure that is capable of undergoing a cross-linking reaction with the base elastomer described below. The functional group capable of undergoing a cross-linking reaction with the base elastomer is appropriately selected depending on the type of the base elastomer and is not particularly limited. Examples thereof include hydroxyl groups, carboxyl groups, carbonyl groups, amino groups, mercapto groups, halogen groups, vinyl groups, methacryloyl groups, acryloyl groups, siloxy groups, peroxide groups, and epoxy groups. Of these functional groups, carboxyl groups, carbonyl groups, and epoxy groups are preferred, with epoxy groups being particularly preferred.

[0223] Examples of the coupling agent include a silane coupling agent, a titanium coupling agent, and an aluminum coupling agent.

[0224] Here, examples of the silane coupling agent include alkoxysilanes having a vinyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltri(β-methoxyethoxy)silane; alkoxysilanes having a methacryl group or an acryl group such as γ-acryloxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane; γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropylmethyl Alkoxysilanes having an epoxy group, such as diethoxysilane; alkoxysilanes having an amino group, such as γ-aminopropyltriethoxysilane, N-β-(aminoethyl)γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)γ-aminopropylmethyldimethoxysilane; alkoxysilanes having a mercapto group, such as γ-mercaptopropyltrimethoxysilane; alkoxysilanes having a halogen group, such as γ-chloropropyltrimethoxysilane; silanes having a vinyl group and a halogen group, such as vinyltrichlorosilane; methyltriacetoxysilane, etc.

[0225] Examples of the titanium coupling agent include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tri(dioctyl pyrophosphate) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis[ditridecyl phosphite] titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis[ditridecyl]phosphite titanate, and bis(dioctyl phosphite) titanate. octyl pyrophosphate)oxyacetate titanate, bis(dioctyl pyrophosphate)ethylene titanate, isopropyl trioctyl titanate, isopropyl dimethacryloyl isostearyl titanate, isopropyl isostearyl diacryloyl titanate, isopropyl tri(dioctyl pyrophosphate) titanate, isopropyl tri(N-amidoethylaminoethyl) titanate, dicumylphenoxyacetate titanate, diisostearyl ethylene titanate, and the like.

[0226] Examples of the aluminum coupling agent include acetoalkoxyaluminum diisopropylate and the like.

[0227] Silane coupling agents are particularly preferred, and alkoxysilanes having an epoxy group, such as γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane, are particularly preferred.

[0228] The coupling agent is used directly or dissolved in a solvent.

[0229] Furthermore, the hollow particles used in the present invention may also have polar groups such as amino groups or acidic groups on the particle surface. Examples of methods for introducing polar groups onto the surface of the hollow particles include a method of reacting a modifier for introducing polar groups, a method of surface treatment with a coupling agent having polar groups, and a method of using a polymerizable monomer having polar groups.

[0230] (6-b) Screening process (foreign matter removal process)

[0231] The method for producing hollow particles of the present invention preferably includes a sieving step after the solvent removal step. By performing the sieving step, coarse powder and aggregates can be removed, and foreign matter can be easily removed.

[0232] As a screening method, a known method can be adopted, which is not particularly limited. For example, a metal mesh such as a stainless steel mesh or a resin mesh such as a nylon mesh can be used for screening. More specifically, the net on which the hollow particles are placed is vibrated to obtain hollow particles passing through the net, thereby obtaining hollow particles after screening. The pore size of the net used in the screening process is appropriately selected according to the size of the hollow particles. In the hollow particles obtained, it is preferred that the proportion of particles having a circularity of less than 0.85 reaches an pore size of less than 15% by mass.

[0233] (6-c) Cleaning process

[0234] The washing step is a step of adding an acid or an alkali to remove the residual dispersion stabilizer in the precursor particles or hollow particles. When the dispersion stabilizer used is an inorganic dispersion stabilizer soluble in acid, it is preferred to add an acid to the slurry containing the precursor particles or hollow particles for washing. On the other hand, when the dispersion stabilizer used is an inorganic dispersion stabilizer soluble in alkali, it is preferred to add an alkali to the slurry containing the precursor particles or hollow particles for washing.

[0235] Furthermore, when an acid-soluble inorganic dispersion stabilizer is used as the dispersion stabilizer, it is preferred to add an acid to the slurry containing the precursor particles or hollow particles to adjust the pH of the slurry to preferably 6.5 or less, more preferably 6 or less. As the acid to be added, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as formic acid and acetic acid can be used. Sulfuric acid is particularly preferred from the perspectives of high dispersion stabilizer removal efficiency and low burden on production equipment.

[0236] (6-d) Replacement process inside the particle

[0237] The particle internal replacement process is a process in which the gas or liquid inside the hollow particle is replaced with another gas or liquid. This replacement can change the internal environment of the hollow particle, selectively enclose molecules within the hollow particle, or modify the chemical structure of the hollow particle to suit the intended use.

[0238] 3. Elastomer composition

[0239] The elastomer composition of the present invention is characterized by comprising the hollow particles of the present invention and a base elastomer, and is used as a molding material for producing a cross-linked elastomer molded article.

[0240] According to the elastomer composition of the present invention, it is possible to provide a cross-linked elastomer molded article that is lightweight and has reduced compression set.

[0241] [Hollow particles]

[0242] The hollow particles contained in the elastomer composition of the present invention are the hollow particles of the present invention described above.

[0243] The content of hollow particles in the elastomer composition of the present invention is not particularly limited. The lower limit is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, relative to 100 parts by mass of the base elastomer. The upper limit is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less. When the content of hollow particles is at least the lower limit, the hollow particles provide excellent lightweighting effects and reduce the compression set of the molded article. When the content of hollow particles is at most the upper limit, deterioration in the dispersibility of the hollow particles is suppressed, resulting in an excellent effect of reducing the compression set of the molded article. Furthermore, since the base elastomer can be sufficiently contained, an elastomer composition having excellent rubber properties can be obtained.

[0244] [Base elastomer]

[0245] The elastomer composition of the present invention contains an elastomer, ie, a polymer having rubber-like elasticity, as a base material. The elastomer contained as the base material of the elastomer composition is referred to as a "base elastomer" in the present invention.

[0246] The base elastic body is not particularly limited, and examples thereof include rubber and thermoplastic elastomer.

[0247] Examples of the rubber include natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), ethylene-α-olefin copolymer rubber, ethylene-propylene-diene terpolymer (EPDM) and other ethylene-α-olefin-non-conjugated diene copolymer rubbers, halogenated ethylene-α-olefin-non-conjugated diene copolymer rubbers, sulfonated ethylene-α-olefin-non-conjugated diene copolymer rubbers, maleated ethylene-α-olefin-non-conjugated diene copolymer rubbers, butyl rubber, isobutylene isoprene rubber, polyurethane rubber, silicone rubber, chlorosulfonated polyethylene, acrylic rubber, epichlorohydrin rubber, fluororubber, polysulfide rubber, and propylene oxide rubber.

[0248] Thermoplastic elastomers generally refer to polymers that exhibit rubber-like elasticity at room temperature (25°C) and can be plasticized and molded at high temperatures. Examples of thermoplastic elastomers include thermoplastic elastomers that have been used as molding resins, such as polyurethane elastomers, styrene elastomers, olefin elastomers, amide elastomers, and ester elastomers.

[0249] These base elastic bodies can be used alone or in combination of two or more.

[0250] In the elastomer composition of the present invention, it is preferred to select from these base elastomers one having an iodine value of 5 g / 100 g or greater. This allows sufficient cross-linking to form between the hollow particles and the base elastomer, resulting in a molded body with sufficiently reduced compression set. The iodine value of the base elastomer is more preferably 10 g / 100 g or greater, and even more preferably 15 g / 100 g or greater. While the upper limit of the iodine value of the base elastomer is not particularly limited, it is preferably 50 g / 100 g or less, more preferably 40 g / 100 g or less, and even more preferably 30 g / 100 g or less.

[0251] The base elastomer preferably comprises at least one selected from ethylene-α-olefin-non-conjugated diene copolymer rubber, butadiene rubber, styrene-butadiene rubber, natural rubber, isoprene rubber, acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber, butyl rubber, fluororubber, silicone rubber, acrylonitrile-butadiene rubber, chloroprene rubber, acrylic rubber, chlorosulfonated polyethylene rubber, chlorinated polyethylene rubber, polyurethane rubber, isobutylene-isoprene rubber, polysulfide rubber, propylene oxide rubber, and epichlorohydrin rubber. More preferably, it comprises at least one selected from ethylene-α-olefin-non-conjugated diene copolymer rubber, butadiene rubber, styrene-butadiene rubber, natural rubber, isoprene rubber, acrylic rubber, acrylonitrile-butadiene rubber, and hydrogenated acrylonitrile-butadiene rubber. Further preferably, it comprises at least one selected from ethylene-α-olefin-non-conjugated diene copolymer rubber, acrylonitrile-butadiene rubber, and hydrogenated acrylonitrile-butadiene rubber. It is particularly preferably, it comprises ethylene-α-olefin-non-conjugated diene copolymer rubber.

[0252] In addition, although not particularly limited, the content of the above-mentioned preferred base elastomer contained in the entire base elastomer (100 mass%) is preferably 50 mass% or more, more preferably 70 mass% or more, further preferably 90 mass% or more, and particularly preferably 100 mass%.

[0253] Ethylene-α-olefin-non-conjugated diene copolymer rubber is a random copolymer of ethylene, α-olefin and non-conjugated diene. As α-olefin, propylene, 1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene etc. can be mentioned. Among these, propylene, 1-hexene, 1-octene are preferred, and propylene is particularly preferred. These α-olefins can be used alone or in combination of two or more. The molar ratio of ethylene to α-olefin (ethylene / α-olefin) is not particularly limited, and is preferably 40 / 60 to 95 / 5, more preferably 50 / 50 to 85 / 15, and further preferably 60 / 40 to 80 / 20.

[0254] As non-conjugated dienes, 1,4-hexadiene, 3-methyl-1,4-hexadiene, 1,7-octadiene, 1,9-decadiene, 5-ethylidene-2-norbornene, 5-isopropylidene-2-norbornene, 5-isobutenyl-2-norbornene, cyclopentadiene, dicyclopentadiene, norbornadiene, etc. can be mentioned. Among these, 5-ethylidene-2-norbornene and dicyclopentadiene are preferred. These non-conjugated dienes can be used alone or in combination of two or more.

[0255] [Crosslinking agent]

[0256] The elastomer composition of the present invention may contain a crosslinking agent for crosslinking the base elastomer. Examples of the crosslinking agent include sulfur such as powdered sulfur, precipitated sulfur, colloidal sulfur, and insoluble sulfur; sulfur-containing inorganic compounds such as sulfur chloride, selenium, and tellurium; sulfur-containing organic compounds such as morpholine disulfide, alkylphenol disulfides, thiuram disulfides, and dithiocarbamates; and organic peroxides such as 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, di-tert-butyl peroxide, dicumyl peroxide, tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,3-bis(tert-butylperoxyisopropyl)benzene. These crosslinking agents may be used alone or in combination of two or more.

[0257] The content of the crosslinking agent can be appropriately selected depending on the type thereof, and is generally in the range of 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the base elastic body.

[0258] [Other ingredients]

[0259] The elastomer composition of the present invention may contain additives such as plasticizers (softeners), reinforcing agents, fillers, vulcanization accelerators, vulcanization accelerator aids, processing aids, antioxidants, ultraviolet absorbers, foaming agents, foaming aids, lubricants, pigments, colorants, dispersants, and flame retardants as needed, within the scope not impairing the purpose of the present invention.

[0260] Furthermore, the reinforcing agent and filler contained in the elastomer composition of the present invention may be surface-treated with the coupling agent described above for use in the hollow particles of the present invention. It is preferred that at least one of the reinforcing agent and filler be surface-treated with the coupling agent described above, from the perspective of improving the mechanical properties of the cross-linked elastomer molded article, such as tensile strength, tensile stress, tear strength, and abrasion resistance. It is more preferred that the hollow particles of the present invention and at least one of the reinforcing agent and filler be surface-treated with the coupling agent described above.

[0261] As the plasticizer (softener), those generally used as plasticizers or softeners in applications such as vehicle-mounted materials, general plastics, and rubber products, or those having a component that imparts flexibility can be used. Examples of plasticizers include process oil, lubricating oil, paraffin, liquid paraffin, petroleum asphalt, and vaseline; coal tar softeners such as coal tar and coal tar pitch; fatty oil softeners such as castor oil, linseed oil, rapeseed oil, and coconut oil; tall oil; waxes such as beeswax, carnauba wax, and lanolin; fatty acids and fatty acid salts such as ricinoleic acid, palmitic acid, barium stearate, calcium stearate, and zinc laurate; synthetic polymers such as petroleum resins, atactic polypropylene, and coumarone-indene resins; ester plasticizers such as dioctyl phthalate, dioctyl adipate, and dioctyl sebacate; carbonate plasticizers such as diisododecyl carbonate; other microcrystalline waxes, rubber substitutes (vulcanized oils), liquid polybutadiene, modified liquid polybutadiene, liquid mercaptans, and hydrocarbon-based synthetic lubricants. These plasticizers can be used alone or in combination of two or more.

[0262] The content of the plasticizer (softener) in the elastomer composition is not particularly limited, but is usually 10 to 200 parts by mass, preferably 35 to 100 parts by mass, and more preferably 45 to 90 parts by mass per 100 parts by mass of the base elastomer.

[0263] Reinforcing agents have the effect of improving the mechanical properties of elastomers, such as tensile strength, tensile stress, tear strength, and abrasion resistance. It is speculated that in cross-linked molded articles containing reinforcing agents, bonded rubber is formed at the interface of the reinforcing agent, thereby improving these mechanical properties.

[0264] Specific examples of such reinforcing agents include carbon black such as SRF, GPF, FEF, FF, HAF, HAF-LS, HAF-HS, ISAF, ISAF-LS, ISAF-HS, SAF, FT, and MT, as well as silica. Examples of silica include natural silica such as quartz powder and silica powder, and synthetic silica such as anhydrous silicic acid (silica gel, aerogel, etc.), hydrous silicic acid, hydrous silicates, and finely powdered silicic acid. These reinforcing agents can be used alone or in combination of two or more.

[0265] The amount of the reinforcing agent blended is not particularly limited, but is generally less than 230 parts by mass per 100 parts by mass of the base elastomer. From the viewpoint of improving the mechanical properties of the cross-linked molded article, the amount of the reinforcing agent is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more per 100 parts by mass of the base elastomer. On the other hand, from the viewpoint of facilitating kneading of the elastomer composition, the amount of the reinforcing agent is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less.

[0266] As carbon black, it is preferred to use carbon black having a nitrogen adsorption specific surface area of ​​5 m 2 / g and above and 150m 2 / g or less, and from the perspective of excellent compatibility with the base elastomer, it is particularly preferred to use a carbon black having a nitrogen adsorption specific surface area of ​​5m 2 / g or more and less than 25m 2 / g of carbon black. From the viewpoint of excellent compatibility with the base elastomer, the nitrogen adsorption specific surface area of ​​carbon black is more preferably 5m 2 / g or above and 20m 2 / g or less, more preferably 5m 2 / g or above and 15m 2 / g or less, particularly preferably 5m 2 / g or more and 10m 2 / g or less.

[0267] In addition, the specific examples of the above carbon black are all in the nitrogen adsorption specific surface area of ​​5m 2 / g and above and 150m 2 / g or less. Among them, the nitrogen adsorption specific surface area is 5m 2 / g or more and less than 25m 2 / g, it is preferred to use FT carbon (nitrogen adsorption specific surface area: 13m 2 / g) and MT carbon (nitrogen adsorption specific surface area: 7m 2 / g), MT carbon is particularly preferred.

[0268] The nitrogen adsorption specific surface area of ​​carbon black is measured in accordance with JIS K6217-2.

[0269] As a reinforcing agent, from the perspective of excellent effect of improving the above-mentioned mechanical properties of the cross-linked molded body, at least one selected from carbon black and silica can be preferably used. Carbon black is preferred from the perspective of particularly excellent effect of improving the above-mentioned mechanical properties of the cross-linked molded body and further from the perspective of reducing the compression set of the cross-linked molded body. On the other hand, when a cross-linked molded body contains carbon black, it will turn black. Therefore, in applications where blackening is allowed, it is preferred to use carbon black as a reinforcing agent. On the other hand, in applications where blackening is not allowed, it is preferred to use silica as a reinforcing agent. In this way, the type of reinforcing agent can be appropriately selected according to the application of the cross-linked molded body.

[0270] Furthermore, as described above, the reinforcing agent may be one that has been surface-treated with the coupling agent described above that can be used for hollow particles. In applications where blackening is not permitted, silica treated with a coupling agent is particularly preferred as a reinforcing agent.

[0271] Examples of fillers include inorganic fillers such as calcium carbonate, light calcium carbonate, heavy calcium carbonate, magnesium carbonate, talc, clay, glass beads, and glass balloons; and organic fillers such as high styrene resins, coumarone-indene resins, phenolic resins, lignin, modified melamine resins, and petroleum resins. Inorganic fillers are particularly preferred. These fillers can be used alone or in combination of two or more.

[0272] The amount of the filler to be added is not particularly limited, but is usually 30 to 200 parts by mass per 100 parts by mass of the base elastomer.

[0273] Specific examples of the vulcanization accelerator include aldehyde amines such as hexamethylenetetramine; guanidines such as diphenylguanidine, di(o-tolyl)guanidine, and o-tolylbiguanide; thioureas such as symmetrical diphenylthiourea, di(o-tolyl)thiourea, N,N′-diethylthiourea, and dilaurylthiourea; thiazoles such as mercaptobenzothiazole, dibenzothiazole disulfide, and N,N′-bis(ethylthiocarbamoylthio)benzothiazole; N-tert-butyl-2-(2-methyl-1-thiophene)-1-ol; Sulfenamides such as benzothiazolesulfenamide; thiurams such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, and tetramethylthiuram monosulfide; carbamates such as zinc dimethylthiocarbamate, sodium dimethyldithiocarbamate, copper dimethyldithiocarbamate, tellurium dimethylthiocarbamate, and iron dimethylthiocarbamate; xanthates such as zinc butylthioxanthate, etc. These vulcanization accelerators can be used alone or in combination of two or more.

[0274] The amount of the vulcanization accelerator to be added is generally in the range of 0.1 to 20 parts by mass, preferably in the range of 0.2 to 10 parts by mass, relative to 100 parts by mass of the base elastomer.

[0275] Specific examples of the vulcanization accelerator include metal oxides such as magnesium oxide and zinc oxide; and organic acids (salts) such as stearic acid, oleic acid, and zinc stearate. Zinc oxide and stearic acid are particularly preferred. These vulcanization accelerators can be used alone or in combination of two or more.

[0276] The amount of the vulcanization accelerating agent added is usually in the range of 0.5 to 20 parts by mass relative to 100 parts by mass of the base elastomer.

[0277] Examples of processing aids include higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid, and lauric acid; salts of higher fatty acids such as barium stearate, zinc stearate, and calcium stearate; and esters of higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid, and lauric acid. Examples of antioxidants include amine-based, hindered phenol-based, and sulfur-based antioxidants.

[0278] Examples of lubricants include hydrocarbons such as liquid paraffin, fatty acids such as stearic acid, fatty acid amides such as stearic acid amide, esters such as butyl stearate, alcohols such as stearyl alcohol, and compounds or mixtures thereof, and metal soaps.

[0279] Examples of the pigment include: inorganic pigments such as titanium dioxide, zinc oxide, ultramarine, red iron oxide, lithopone, lead, cadmium, iron, cobalt, aluminum, hydrochloride, and nitrate; azo pigments, phthalocyanine pigments, quinacridone pigments, quinacridonequinone pigments, dioxane pigments, and the like; Organic pigments such as azine pigments, anthrapyrimidine pigments, anthraquinone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, perinone pigments, diketopyrrolopyrrole pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindoline pigments, and carbon black.

[0280] The crosslinked molded article obtained by melt molding or the like using the elastomer composition of the present invention as a molding material may be, for example, an elastomer part integrally molded with an elastomer part or a part made of another material, a coating, or a core material for filling.

[0281] A molded article obtained by cross-linking and molding the elastomer composition of the present invention contains the hollow particles of the present invention, thereby achieving a lighter weight and reduced compression set.

[0282] Examples of uses for the cross-linked elastomer molded article produced using the elastomer composition of the present invention include various rubber parts used in various fields such as automobiles, electrical and electronic products, construction, aviation, and aerospace. More specifically, examples include automotive parts such as hoses, sealants, vibration-damping rubber, and weather stripping; building materials such as waterproof sheets and sealants; electrical rubber parts such as high-voltage cables and connectors; and industrial products such as heat-resistant conveyor belts, chemical-resistant rollers, and heat-resistant hoses. Since sealing properties decrease when a sealing material plastically deforms, a low compression set is particularly desired. The cross-linked elastomer molded article containing the hollow particles of the present invention exhibits a low compression set and is therefore particularly preferably used in applications such as sealing materials that require a low compression set.

[0283] Furthermore, examples of uses of the elastomer cross-linked molded article of the present invention include topcoat materials or basecoat materials requiring heat insulation, cushioning (shock absorption) properties, etc., cushioning materials (shock absorption materials) for shoes such as sports shoes and sandals, home appliance parts, bicycle parts, stationery, tools, 3D printer wires, buoyancy materials such as composite foam plastics, etc.

[0284] [Method for producing elastomer composition]

[0285] The elastomer composition of the present invention can be produced by conventional methods without particular limitation. Examples of methods for producing the elastomer composition of the present invention include a method in which, while kneading a base elastomer, the hollow particles of the present invention and, if necessary, other components such as a crosslinking agent are added to the base elastomer, followed by further kneading. Alternatively, a method in which a raw material mixture containing a base elastomer, the hollow particles of the present invention, and, if necessary, other components such as a crosslinking agent is prepared and then kneaded can be used.

[0286] The base elastomer or the raw material mixture is kneaded at a temperature at which the base elastomer softens. The kneading machine used for this kneading includes, for example, a single-shaft kneading machine, a twin-shaft kneading machine, a kneader, a Banbury mixer, a pressurized kneader, a roll kneader, and other known kneading machines. Kneading that applies a high shear force, such as roll kneading, is particularly preferred. As a kneading machine for roll kneading, for example, a twin mixing roll can be used, more specifically, a mixing roll DY6-15 (manufactured by Daihan Co., Ltd.).

[0287] Furthermore, in the production of the elastomer composition of the present invention, pre-kneading at a temperature at which the base elastomer softens may be performed to homogenize the ingredients, followed by finishing kneading such as roll kneading with the application of high shear forces. This can yield an elastomer composition in which the ingredients are further homogenized and refined.

[0288] Furthermore, when the elastomer composition is cross-linked and molded, the elastomer composition before cross-linking recovered from the molding apparatus can be reused as a raw material mixture.

[0289] The kneading conditions for the base elastomer or raw material mixture are not particularly limited. When a free radical initiator is used as a crosslinking agent, the kneading temperature is preferably below the 10-hour half-life temperature of the crosslinking agent (free radical initiator). The kneading temperature herein refers to the set temperature of the kneading apparatus. Furthermore, the kneading time is preferably less than 1 hour. By setting these kneading conditions, crosslinking reactions of the base elastomer during kneading can be prevented, thereby preventing scorching and enabling uniform mixing of the ingredients.

[0290] As an example, kneading can be performed using the following method: Using a roll kneader, set the kneading temperature to 70°C to 90°C. After the kneader temperature stabilizes, add the base elastomer. Subsequently, while rotating the kneader rotor at 10 to 35 rpm, add the hollow particles, crosslinking agent, and other components in any order. After all materials have been added, knead for 10 to 30 minutes. This yields the elastomer composition of the present invention.

[0291] 4. Elastomer cross-linked molding

[0292] The cross-linked elastomer molded article of the present invention is a molded article obtained by cross-linking and molding the elastomer composition of the present invention.

[0293] The elastomer composition of the present invention is cross-linked and molded, thereby causing a cross-linking reaction of the base elastomer to proceed, and the reactive unsaturated bonds of the hollow particles react with the reactive unsaturated bonds of the base elastomer to form cross-linked bonds, thereby obtaining the elastomer cross-linked molded product of the present invention.

[0294] The method for cross-linking and molding the elastomer composition can be appropriately selected from known methods depending on the type of the base elastomer, the type and content of the hollow particles and other additives, and the shape of the desired molded article. Examples of known methods for cross-linking and molding the elastomer composition include melt molding methods such as extrusion molding, compression molding, extrusion lamination, injection molding, press molding, and blow molding.

[0295] The temperature at which the elastomer composition of the present invention is cross-linked and molded is not particularly limited. However, when a free radical initiator is used as the cross-linking agent, the temperature is preferably not less than the 10-hour half-life temperature of the cross-linking agent, from the viewpoint of sufficiently proceeding the cross-linking reaction of the base elastomer and the reaction between the hollow particles and the base elastomer. The upper limit of the temperature at which the elastomer composition of the present invention is cross-linked and molded is not particularly limited. However, when a free radical initiator is used as the cross-linking agent, the temperature is preferably not more than the 1-minute half-life temperature.

[0296] The conditions for cross-linking and molding the elastomer composition of the present invention are not particularly limited. The pressure can be, for example, 1 MPa to 20 MPa, and the heating and pressing time can be 1 minute to 180 minutes.

[0297] The form of the cross-linked elastomer molded product of the present invention is not particularly limited. For example, the molten elastomer composition can be formed into a long sheet, a block, a filler, etc., or it can be processed into a roll by winding the long sheet, or into a strip by cutting the long sheet into a specified length.

[0298] The crosslinked elastomer molded article of the present invention preferably has a compression set of less than 60%, more preferably less than 40%, as measured at room temperature according to JIS K 6262: 2013. The lower limit of the compression set of the crosslinked elastomer molded article of the present invention is not particularly limited, but is usually 10% or more.

[0299] Furthermore, the elastomer composition of the present invention used as a molding material for the elastomer cross-linked molded article of the present invention usually has the above-mentioned compression set of 60% or more before cross-linking molding.

[0300] Example

[0301] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, parts and % are by mass unless otherwise specified.

[0302] [Preparation of hollow particles]

[0303] [Production Example 1 (Hollow Particles A)]

[0304] (1) Mixed liquid preparation process

[0305] First, mix the following materials to prepare the oil phase.

[0306] Cross-linking acrylic monomer: 25 parts of ethylene glycol dimethacrylate;

[0307] Cross-linking acrylic monomer: 30 parts of trimethylolpropane trimethacrylate;

[0308] Cross-linking hydrocarbon monomer: 45 parts of divinylbenzene;

[0309] Oil-soluble polymerization initiator: 3 parts of 2,2′-azobis(2,4-dimethylvaleronitrile);

[0310] Hydrophobic solvent: 160 parts of hexane.

[0311] On the other hand, in a stirred tank, at room temperature, to an aqueous solution obtained by dissolving 17.1 parts of magnesium chloride (water-soluble polyvalent metal salt) in 494 parts of ion-exchanged water, an aqueous solution obtained by dissolving 12.1 parts of sodium hydroxide (alkali metal hydroxide) in 121 parts of ion-exchanged water was slowly added under stirring to prepare a magnesium hydroxide colloid (a poorly water-soluble metal hydroxide colloid) dispersion (4 parts of magnesium hydroxide), thereby forming an aqueous phase.

[0312] A mixed liquid is prepared by mixing the obtained aqueous phase with the oil phase.

[0313] (2) Suspension process

[0314] The mixed solution obtained in the mixed solution preparation step was stirred at 4000 rpm for 1 minute using a disperser (manufactured by Plemicus Co., Ltd., product name: Homomixer) to suspend the mixture, thereby preparing a suspension in which droplets of the monomer composition containing a hydrophobic solvent were dispersed in water.

[0315] (3) Polymerization process

[0316] The suspension obtained in the above suspension step was stirred under a nitrogen atmosphere at 65° C. for 1 hour and 30 minutes to perform a polymerization reaction, thereby obtaining a precursor composition containing precursor particles enclosing a hydrophobic solvent.

[0317] (4) Cleaning process and solid-liquid separation process

[0318] The precursor composition was washed with dilute sulfuric acid (25°C, 10 minutes) to a pH of 5.5 or less. The water was then separated by filtration, and 200 parts of ion-exchanged water was added for reslurry. The water washing process (washing, filtration, and dehydration) was repeated several times at room temperature (25°C), and the solid component was separated by filtration. The resulting solid component was dried in a dryer at 40°C to obtain precursor particles containing a hydrophobic solvent.

[0319] (5) Solvent removal process

[0320] The precursor particles obtained in the solid-liquid separation step were heated in a vacuum dryer at 200° C. in a nitrogen atmosphere for 12 hours to remove the hydrophobic solvent contained in the particles, thereby obtaining hollow particles.

[0321] (6) Screening process

[0322] The hollow particles obtained in the solvent removal step were sieved using a nylon mesh having a pore size of 100 μm, and hollow particles that passed through the mesh and fell to the bottom were recovered to remove coarse particles, thereby obtaining hollow particles A.

[0323] [Production Example 2 (Hollow Particles B)]

[0324] In Production Example 1, except that the amount of the polymerizable monomer added to the oil phase was changed according to Table 1 in the above-mentioned "(1) Mixed Liquid Preparation Step", the same steps as in Production Example 1 were followed to obtain hollow particles of Production Example 2 (hollow particles B).

[0325] [Production Example 3 (Hollow Particles C)]

[0326] In Production Example 1, hollow particles of Production Example 3 (hollow particles C) were obtained by the same procedures as in Production Example 1 except that the rotation speed of the disperser was changed to 400 rpm in the above-mentioned "(2) Suspension Step".

[0327] [Production Example 4 (Hollow Particles D)]

[0328] In Production Example 1, except that the amount of the polymerizable monomer added to the oil phase was changed according to Table 1 in the above-mentioned "(1) Mixed Liquid Preparation Step", the same steps as in Production Example 1 were followed to obtain hollow particles of Production Example 4 (hollow particles D).

[0329] [Comparative Production Example 1 (Hollow Particles E)]

[0330] In Production Example 1, except that in the above-mentioned "(1) Mixed Liquid Preparation Step", the polymerizable monomer added to the oil phase was changed to only 100 parts of divinylbenzene, the same procedures as in Production Example 1 were followed to obtain hollow particles of Comparative Production Example 1 (hollow particles E).

[0331] [Comparative Production Example 2 (Dense Granules A)]

[0332] In Production Example 1, except that the rotation speed of the disperser was changed to 10 rpm in the above-mentioned "(2) Suspension Step", the same procedures as in Production Example 1 were followed to obtain dense granules of Comparative Production Example 2 (dense granules A).

[0333] [Physical property evaluation of particles]

[0334] The following physical property evaluations were performed on the hollow particles obtained in Production Examples 1 to 4 and Comparative Production Example 1, and the dense particles obtained in Comparative Production Example 2. Furthermore, for the carbon particles used in Comparative Example 3 described below, only the following iodine value and volume average particle size measurements were performed. The results of the particle property evaluations are shown in Table 1.

[0335] 1. Determination of iodine value

[0336] The iodine value of the pellets was measured according to JIS K 0070. The specific measurement method is as follows.

[0337] 0.7-2g of particles (sample) and 10mL of chloroform were added to a 300mL iodine flask, and 25mL of Wei's reagent was further added as a reaction solution. After gentle stirring, the mixture was sealed and allowed to stand in a dark place at 25°C for 30 minutes. Next, 20mL of 100g / L potassium iodide solution and 100mL of purified water were added and stirred. A burette was used to titrate with a titrant (0.1mol / L sodium thiosulfate solution). When the solution turned pale yellow, an indicator (1% starch solution) was added and the titration was continued until the blue color disappeared. In addition to this formal test, a blank test was performed on a solution to which no particles were added, and the iodine value of the particles was calculated by the following formula. In addition, the iodine value is the value obtained by converting the amount of bonded halogen into grams of iodine when 100g of sample was reacted with halogen.

[0338] Iodine value (g / 100g) = {(V0-V1) × f × 1.269} / S

[0339] S: mass of the sample (g)

[0340] V1: Volume of titrant in the formal test (mL)

[0341] V0: Volume of titrant in blank test (mL)

[0342] f: factor of the titrant

[0343] 2. Ratio of particles in a hollow part

[0344] The particles fixed to the carbon tape were rubbed with a cotton swab to intentionally break the particles. The interiors of 100 broken particles were observed using a SEM to determine the number of hollow parts in each particle and calculate the percentage (%) of particles with only one hollow part.

[0345] 3. The proportion of irregular particles

[0346] The measurement sample was prepared by dispersing 0.10-0.12 g of particles in an aqueous solution of sodium linear alkylbenzene sulfonate (concentration 0.3%) using an ultrasonic cleaner for 5 minutes. The circularity of each particle in the measurement sample was measured using a flow particle image analyzer (manufactured by JASCO INTERNATIONAL Co., Ltd., product name: IF-3200) under the following measurement conditions. The mass ratio of particles with a circularity of 0.85 or less was calculated as the proportion of irregular particles.

[0347] In addition, although the number of particles contained in the measurement sample increases as the particle size decreases, the number of particles contained in each of the production examples and the comparative production examples is within the range of 1,000 to 3,000.

[0348] (Measurement conditions)

[0349] Flow cell spacer thickness: 50 μm

[0350] Telecentric zoom lens magnification: 4.5x

[0351] Total magnification: 9.0 times

[0352] Measurement volume: 0.5mL

[0353] Image resolution: 0.185 μm / pixel

[0354] Detection algorithm: Ghost detection

[0355] Threshold: 15%

[0356] 4. Residual volatile content

[0357] The residual volatile content contained in the pellets was determined by the purge and trap / gas chromatography (P&T / GC) method described below.

[0358] 0.1 g of pellets were added to a purge container. Helium was introduced as a carrier gas at a flow rate of 50 ml / min. The container was heated from room temperature at a rate of 10°C / min and maintained at 200°C for 30 minutes. The generated volatile components were trapped in a collection tube at -130°C. The trapped residual volatile components were quantified to determine the residual volatile content in the pellets.

[0359] The measuring apparatus was an Agilent gas chromatograph 6890 (FID method), the analytical instrument was a Shimadzu C-R7A chromatography data processor, the purge and trap injector was an Agilent TDS, and the chromatographic column used was a J&W DB-5 (L=30 m, ID=0.32 mm, Film=0.25 μm). The measurement was performed under the following conditions:

[0360] Column temperature: 50°C (hold for 2 minutes) ~ 270°C (10°C / min heating)

[0361] Injection temperature: 280°C

[0362] Detection temperature: 280℃

[0363] Carrier gas: helium, flow rate: 1ml / min

[0364] 5. Particle size and particle size distribution

[0365] The particle size of the particles was measured using a particle size distribution analyzer using the Coulter counter method (product name: Multisizer 4e, manufactured by Beckman Coulter). The number average and volume average values ​​were calculated to determine the number average particle size (Dp) and volume average particle size (Dv). Furthermore, the particle size distribution (Dv / Dp) was determined by dividing the volume average particle size by the number average particle size.

[0366] The measurement conditions were: pore size: 50 μm, dispersion medium: ISOTON II (product name), concentration: 10%, and number of particles measured: 100,000. Specifically, 0.2 g of a particle sample was placed in a beaker, and an aqueous surfactant solution (product name: DRIWEL, manufactured by Fujifilm Corporation) was added as a dispersant. 2 ml of the dispersion medium was then added to wet the particles, and then 10 ml of the dispersion medium was added. The particles were dispersed using an ultrasonic disperser for 1 minute, and then measured using the aforementioned particle size distribution analyzer.

[0367] 6. Porosity

[0368] 6-1. Determination of apparent density of hollow particles

[0369] First, in a volume of 100cm 3 Fill the volumetric flask to about 30 cm 3The mass of the hollow particles was accurately weighed. Next, the volumetric flask filled with the hollow particles was filled with isopropyl alcohol to the mark while taking care not to introduce air bubbles. The mass of the isopropyl alcohol added to the volumetric flask was accurately weighed, and the apparent density D1 (g / cm 3 ).

[0370] Formula (I)

[0371] Apparent density D1 = [mass of hollow particles] / (100-[mass of isopropyl alcohol] / [specific gravity of isopropyl alcohol at the measurement temperature])

[0372] 6-2. Determination of True Density of Hollow Particles

[0373] After the hollow particles are crushed in advance, the volume is 100cm 3 A volumetric flask is filled with about 10 g of hollow particle fragments, and the mass of the filled fragments is accurately weighed.

[0374] Then, isopropyl alcohol was added to the volumetric flask in the same manner as in the above-mentioned apparent density measurement, and the mass of isopropyl alcohol was accurately weighed. The true density D0 (g / cm2) of the hollow particles was calculated based on the following formula (II): 3 ).

[0375] Formula (II)

[0376] True density D0 = [mass of hollow particle fragments] / (100 - [mass of isopropyl alcohol] / [specific gravity of isopropyl alcohol at the measurement temperature])

[0377] 6-3. Calculation of porosity

[0378] The porosity of the hollow particles was calculated based on the following formula (III) from the apparent density D1 and true density D0 of the hollow particles.

[0379] Formula (III)

[0380] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0381] [Table 1]

[0382]

[0383] [Production of Elastomer Composition and Production of Elastomer Cross-linked Molded Article]

[0384] [Example 1]

[0385] 100 parts by mass of ethylene-propylene-diene terpolymer (EPDM) (product name: Nordel IP 4725, manufactured by The Dow Chemical Company, Mooney viscosity at 100°C (JIS K6300): 25) as a base elastomer was placed in a twin-roll kneader (model name: DY6-15, roll diameter: 6 inches, roll spacing: 0.5 mm, manufactured by Daihan Co., Ltd.) maintained at 80°C. The kneader rotor speed was set at 10 to 35 rpm, and after the base elastomer was wound around the rolls, 25 parts by mass of the hollow particles A obtained in Production Example 1 were placed in the kneader. Subsequently, 3 parts of dicumyl peroxide (10-hour half-life temperature: 116°C, 1-minute half-life temperature: 175°C) was added as a crosslinking agent to obtain a mixture. The resulting mixture was kneaded for 15 minutes to obtain the elastomer composition of Example 1.

[0386] The obtained elastomer composition was press-molded in a hot press at 160° C. and a pressure of 10 MPa for 15 minutes to obtain a cylindrical elastomer cross-linked molded body having a diameter of 29±0.5 mm and a height of 12.5±0.5 mm.

[0387] The obtained elastomer cross-linked molded product was used as a test piece for the compression set measurement (JIS K 6262) described below.

[0388] [Examples 2-3]

[0389] In Example 1, except that the addition amount of the hollow particles A obtained in Production Example 1 was changed according to Table 2, the elastomer compositions and elastomer cross-linked molded products of Examples 2 and 3 were obtained in the same manner as in Example 1.

[0390] [Examples 4 to 6]

[0391] In Example 1, except that the hollow particles B obtained in Preparation Example 2, the hollow particles C obtained in Preparation Example 3, or the hollow particles D obtained in Preparation Example 4 were used in place of the hollow particles A obtained in Preparation Example 1 according to Table 2, the elastomer compositions and elastomer cross-linked molded articles of Examples 4 to 6 were obtained in the same manner as in Example 1.

[0392] [Examples 7-8]

[0393] In Example 1, except that NBR (acrylonitrile butadiene rubber, product name: Nipol (registered trademark) DN4050, manufactured by Zeon Corporation of Japan, bound acrylonitrile content: 40.0%, Mooney viscosity: 50.0) or HNBR (hydrogenated acrylonitrile butadiene rubber, product name: Zetpol (registered trademark) 2010L, manufactured by Zeon Corporation of Japan, iodine value: 11.00 g / 100 g, bound acrylonitrile content: 36.2%, Mooney viscosity: 57.5) was used instead of the ethylene-propylene-diene terpolymer (EPDM) according to Table 2, the elastomer compositions and elastomer cross-linked molded products of Examples 7 and 8 were obtained in the same manner as in Example 1.

[0394] [Comparative Example 1]

[0395] In Example 1, the elastomer composition and elastomer cross-linked molded article of Comparative Example 1 were obtained in the same manner as in Example 1, except that the hollow particles E obtained in Comparative Preparation Example 1 were used instead of the hollow particles A obtained in Preparation Example 1.

[0396] [Comparative Example 2]

[0397] In Example 1, except that the dense particles A obtained in Comparative Preparation Example 2 were used instead of the hollow particles A obtained in Preparation Example 1, the elastomer composition and elastomer cross-linked molded article of Comparative Example 2 were obtained in the same manner as in Example 1.

[0398] [Comparative Example 3]

[0399] In Example 1, except that 45 parts of carbon particles (product name: DIABLACK (registered trademark) H, manufactured by Mitsubishi Chemical Corporation) were used instead of the hollow particles A (25 parts) obtained in Production Example 1, the elastomer composition and elastomer cross-linked molded product of Comparative Example 3 were obtained in the same manner as in Example 1.

[0400] [Reference Example 1]

[0401] In Example 1, except that the hollow particles A obtained in Production Example 1 were not added, the elastomer composition and elastomer cross-linked molded article of Reference Example 1 were obtained in the same manner as in Example 1.

[0402] [Evaluation of physical properties of cross-linked elastomer molded products]

[0403] 1. Lightweight rate

[0404] The specific gravity of the cross-linked elastomer molded product was measured by a water displacement method in accordance with JIS K 7112:1999 using a sample cut into 1 cm square and 2 mm thick.

[0405] The weight reduction ratio (%) was calculated by the following formula (1) based on the specific gravity of the elastomer cross-linked molded product measured above and the specific gravity of the base elastic body used in the elastomer cross-linked molded product.

[0406] Formula (1):

[0407] Weight reduction ratio (%) = {(specific gravity of base elastomer - specific gravity of elastomer cross-linked molded body) / specific gravity of base elastomer} × 100

[0408] In addition, the following value was used as the specific gravity of the base elastic body.

[0409] Specific gravity of EPDM: 0.9

[0410] Specific gravity of NBR: 1.0

[0411] Specific gravity of HNBR: 1.0

[0412] 2. Compression set

[0413] In accordance with the room temperature test of JIS K 6262:2013, a cylindrical cross-linked elastomer molded article having a diameter of 29±0.5 mm and a height of 12.5±0.5 mm was used as a test piece. The compression set (%) of the cross-linked elastomer molded article was measured under the following conditions: a standard temperature of 23±2°C, a test temperature of 30°C, a test time of 168 hours, and a ratio of compression test pieces set to 25%. Evaluation was performed based on the following evaluation criteria.

[0414] (Compression set evaluation criteria)

[0415] A: Compression set less than 40%

[0416] B: Compression set is 40% or more and less than 60%

[0417] C: Compression set is more than 60%

[0418] More specifically, the compression set is measured by the following steps. First, the thickness of the central part of the test piece is measured at a standard temperature. The test piece is placed on a compression plate (smooth stainless steel plate), a spacer (thickness 9.3 mm) is clamped on the outside of the test piece, and then compressed until the compression plate and the spacer are tightly fitted. The device for compressing the test piece is kept in a constant temperature bath at the test temperature for the test time. After the test time, the device is taken out, the test piece is immediately released from the compressed state, and after being placed at a standard temperature for 30 minutes, the thickness of the central part of the test piece is measured. Based on the thickness of the test piece before and after compression and the thickness of the spacer, the compression set (%) is calculated by the following formula (2).

[0419] [Mathematical formula 1]

[0420] Formula (2):

[0421]

[0422] CS: Compression set (%)

[0423] t0: Original thickness of the test piece (mm)

[0424] t1: thickness of the spacer (mm)

[0425] t2: Thickness of the test piece 30 minutes after being removed from the compression device (mm)

[0426] [Table 2]

[0427]

[0428] [Investigation]

[0429] The crosslinked elastomer molded products obtained in Examples 1 to 8 contain hollow particles having an iodine value of 10 g / 100 g or more and 50 g / 100 g or less, and are therefore lighter and have smaller compression set than the crosslinked elastomer molded product of Reference Example 1 containing no hollow particles.

[0430] The reason why the compression set in Example 1 was smaller than that in Examples 2 and 3 is considered to be that the amount of hollow particles contained in the elastomer cross-linked molded product in Example 1 was larger.

[0431] It is inferred that the compression set in Example 1 is smaller than that in Example 4 because the iodine value of the hollow particles in Example 1 is appropriately low, thereby suppressing the aggregation of the hollow particles and resulting in uniform dispersion. Furthermore, in Example 1, the content of residual volatile components in the hollow particles is low, so the reactivity of the hollow particles with the base elastomer is good. As a result, the hollow particles can uniformly suppress the plastic deformation of the elastomer cross-linked molded body.

[0432] It is inferred that the compression set in Example 1 is smaller than that in Example 5 because the particle size of the hollow particles in Example 1 is moderately small, thereby increasing the interface between the hollow particles and the base elastomer and forming more crosslinks between the hollow particles and the base elastomer.

[0433] It is inferred that the compression set in Example 1 is smaller than that in Example 6 because the hollow particles in Example 1 have a higher iodine value, thereby forming more cross-linking bonds between the hollow particles and the base elastomer.

[0434] It is speculated that the compression set in Example 1 is smaller than that in Examples 7 and 8 because the iodine value of the base elastomer in Example 1 is higher, resulting in more crosslinks formed between the hollow particles and the base elastomer. Furthermore, the compression set value in Example 7 is smaller than that in Example 8. It is speculated that this is because the iodine value of the base elastomer in Example 7 is higher than that in Example 8.

[0435] On the other hand, the cross-linked elastomer molded article obtained in Comparative Example 1 contained hollow particles having an iodine value of greater than 50 g / 100 g. Therefore, although the cross-linked elastomer molded article was lighter than the cross-linked elastomer molded article of Reference Example 1, which did not contain hollow particles, it was inferior in reducing compression set compared to the cross-linked elastomer molded articles obtained in Examples. This is presumably because the hollow particles used in Comparative Example 1 were easily aggregated, resulting in the hollow particles not being uniformly dispersed within the cross-linked elastomer molded article.

[0436] Since the cross-linked elastomer molded article obtained in Comparative Example 2 contained dense particles instead of hollow particles, it was not lighter than the cross-linked elastomer molded article of Reference Example 1, which did not contain hollow particles. Furthermore, it is inferred that the cross-linked elastomer molded article obtained in Comparative Example 2 had a small compression set because the iodine value of the dense particles used in Comparative Example 2 was within the range of 10 g / 100 g to 50 g / 100 g, thereby forming cross-links between the dense particles and the base elastomer.

[0437] The cross-linked elastomer molded article obtained in Comparative Example 3 contained carbon particles instead of hollow particles, and therefore was not as lightweight as the cross-linked elastomer molded article of Reference Example 1, which did not contain hollow particles. Furthermore, the cross-linked elastomer molded article was inferior in reducing compression set compared to the cross-linked elastomer molded articles obtained in Examples. It is speculated that the poor compression set-reducing effect in the cross-linked elastomer molded article obtained in Comparative Example 3 is due to the fact that the iodine value of the carbon particles was less than 10 g / 100 g, resulting in insufficient cross-linking between the carbon particles and the base elastomer.

[0438] Description of Reference Numerals

[0439] 1: Water-based medium;

[0440] 2: Low polarity materials;

[0441] 4a: hydrophobic solvent;

[0442] 4b: Materials other than hydrophobic solvents;

[0443] 6: Shell;

[0444] 7: hollow part;

[0445] 8: droplet;

[0446] 9: precursor particles;

[0447] 10: Hollow particles whose hollow parts are filled with gas.

Claims

Hollow particles comprising a shell made of a resin and a hollow portion surrounded by the shell, wherein the iodine value measured according to JIS K 0070 is 10 g / 100 g or more and 50 g / 100 g or less.

2. The hollow particles according to claim 1, wherein The proportion of hollow particles having a circularity of 0.85 or less is less than 15% by mass.

3. The hollow particles according to claim 1 or 2, wherein The content of residual volatile components in the hollow particles is less than 100 ppm.

4. The hollow particles according to claim 1 or 2, wherein The hollow particles contain a polymer including 50% by mass or more of a cross-linkable monomer unit as the resin.

5. The hollow particles according to claim 1 or 2, wherein The hollow particles have a volume average particle size of 0.1 μm or more and 100 μm or less. 6 . An elastomer composition comprising the hollow particles according to claim 1 and a base elastomer.

7. The elastomer composition according to claim 6, wherein The content of the hollow particles is 10 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the base elastic body.

8. A cross-linked elastomer molded product, which is obtained by cross-linking and molding the elastomer composition according to claim 6.

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