Cellulose particles containing inorganic substances and method for producing the same

Abstract

The present invention provides cellulose particles containing an inorganic substance, wherein the inorganic substance is contained within cellulose particles containing cellulose, the mass ratio of the inorganic substance to the cellulose (inorganic substance / cellulose) being 2 / 8 to 8 / 2, and the average particle size of the cellulose particles containing the inorganic substance being 1 μm to 300 μm. The present invention also provides a method for producing cellulose particles containing an inorganic substance, comprising mixing a cellulose acetate solution containing cellulose acetate dissolved in an organic solvent and the inorganic substance so that the mass ratio of the inorganic substance to the cellulose (inorganic substance / cellulose) is 2 / 8 to 8 / 2 to obtain a resin mixture, suspending the obtained resin mixture in water to prepare a suspension in which the cellulose acetate particles containing the inorganic substance are dispersed in the water, removing the organic solvent from the suspension, and saponifying the cellulose acetate particles to produce the cellulose particles containing the inorganic substance contained within the cellulose particles.

Description

Technical Field

[0001] The invention relates to cellulose particles containing inorganic matter and a method for preparing the same.

[0002] This application claims priority based on Japanese Patent Application No. 2020-083983, filed in Japan on May 12, 2020, the contents of which are incorporated herein by reference. Background Art

[0003] Traditionally, particles such as acrylic beads, polystyrene beads, and polyurethane beads have been used in various products including paints, plastics, adhesives, and cosmetics.

[0004] In recent years, the issue of microplastics in the marine environment has received widespread attention, and as a result, the demand for micron-sized cellulose particles made from natural materials has increased.

[0005] As a method for producing cellulose particles, for example, there is known a method described in Patent Document 1. Patent Document 1 describes the following method (1) and method (2).

[0006] Method (1): A cellulose ester filament produced by a dry spinning method using a solution of cellulose ester in an organic solvent as a stock solution is cut into chips, the chips are heated and melted in a medium to form spherical particles of cellulose ester, and the spherical particles are then saponified. Method (2): A cellulose ester solution in an organic solvent is used as a stock solution, the stock solution is suspended in a medium that is insoluble or slightly soluble in the organic solvent, the medium containing the suspended particles is heated to evaporate the organic solvent, thereby forming spherical particles of cellulose ester, and the spherical particles are then saponified.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Publication No. 55-40618 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, conventional cellulose particles are prone to moisture absorption, leading to issues with their stability over time. Furthermore, when cellulose particles are used in products such as paints, plastics, adhesives, and cosmetics, the moisture in the products can sometimes cause problems.

[0012] An object of the present invention is to provide cellulose particles containing an inorganic substance and having excellent low hygroscopicity, and a method for producing the same.

[0013] Technical means to solve problems

[0014] The present invention includes the following technical solutions.

[0015] [1] A cellulose particle containing an inorganic substance, characterized in that the inorganic substance is contained in the cellulose particle containing cellulose, the mass ratio of the inorganic substance to the cellulose (inorganic substance / cellulose) is 2 / 8 to 8 / 2, and the average particle size of the cellulose particle containing the inorganic substance is 1 μm to 300 μm.

[0016] [2] The inorganic-matter-encapsulating cellulose particles according to [1] above, wherein the cellulose particles have a moisture absorption rate of 3% or less.

[0017] [3] The inorganic-matter-encapsulating cellulose particles according to [1] or [2] above, wherein the inorganic material has a refractive index of 1.43 to 2.00.

[0018] [4] The cellulose particles containing an inorganic substance according to any one of [1] to [3] above, wherein the inorganic substance is surface-treated with at least one of a fatty acid and a silane compound.

[0019] [5] The inorganic-containing cellulose particles according to any one of [1] to [4] above, wherein the mass ratio (inorganic substance / cellulose) is preferably 4 / 6 to 8 / 2, more preferably 6 / 4 to 8 / 2.

[0020] [6] The inorganic-matter-encapsulating cellulose particles according to any one of [1] to [5] above, wherein the average particle size is preferably 1 μm to 150 μm, more preferably 1 μm to 100 μm.

[0021] [7] The cellulose particles containing an inorganic substance according to any one of [1] to [6] above, wherein the inorganic substance is preferably at least one compound selected from calcium carbonate, calcium stearate, barium sulfate, talc, mica, kaolin, silica and alumina, more preferably at least one compound selected from calcium carbonate, calcium stearate, silica and talc, and even more preferably at least one compound selected from calcium carbonate and calcium stearate.

[0022] [8] A method for producing cellulose particles containing an inorganic substance, characterized in that it is the method for producing cellulose particles containing an inorganic substance according to any one of [1] to [7] above, comprising mixing a cellulose acetate solution obtained by dissolving cellulose acetate in an organic solvent and the inorganic substance so that the mass ratio of the inorganic substance to the cellulose (inorganic substance / cellulose) is 2 / 8 to 8 / 2 to obtain a resin mixed solution, suspending the obtained resin mixed solution in water to prepare a suspension in which cellulose acetate particles containing the inorganic substance are dispersed in water, removing the organic solvent from the suspension, and saponifying the cellulose acetate particles to produce cellulose particles containing the inorganic substance in the cellulose particles.

[0023] [9] The method for producing cellulose particles containing an inorganic substance according to [8] above, wherein the resin mixture is suspended in water in the presence of a suspension stabilizer and a surfactant.

[0024]

[10] The method for producing cellulose particles containing an inorganic substance according to [8] or [9] above, wherein the mass ratio (inorganic substance / cellulose) is preferably 4 / 6 to 8 / 2, more preferably 6 / 4 to 8 / 2.

[0025]

[11] The method for producing cellulose particles containing an inorganic substance according to any one of [8] to

[10] above, wherein the cellulose acetate solution and the inorganic substance are mixed so that the ratio of the inorganic substance to 100 parts by mass of the cellulose acetate is preferably 15 to 240 parts by mass, more preferably 40 to 240 parts by mass, and even more preferably 90 to 240 parts by mass.

[0026]

[12] The method for producing cellulose particles containing an inorganic substance according to any one of [8] to

[11] above, wherein the cellulose acetate is selected from monoacetyl cellulose, diacetyl cellulose and triacetyl cellulose.

[0027]

[13] The method for producing cellulose particles containing an inorganic substance according to any one of [8] to

[12] above, wherein the organic solvent is a solvent having an azeotropic point with water of 100° C. or less at 1013 hPa.

[0028]

[14] The method for producing cellulose particles containing inorganic matter according to any one of [8] to

[13] above, wherein the organic solvent is preferably at least one solvent selected from the following solvents: aromatic compounds such as toluene and benzene; ester compounds such as methyl acetate, ethyl acetate, and butyl acetate; ketone compounds such as acetone and methyl ethyl ketone; and saturated aliphatic hydrocarbons such as n-heptane, n-hexane, and n-octane.

[0029]

[15] A method for producing cellulose particles containing inorganic matter according to any one of [8] to

[14] above, wherein the resin mixture is suspended in water by suspending the resin mixture in an aqueous dispersion medium containing water, a suspension stabilizer and a surfactant.

[0030] Effects of the Invention

[0031] According to the present invention, there are provided cellulose particles containing an inorganic substance and having excellent low hygroscopicity, and a method for producing the same. DETAILED DESCRIPTION

[0032] [Cellulose particles containing inorganic substances]

[0033] The inorganic-encapsulated cellulose particles of the present invention contain cellulose particles containing an inorganic substance. That is, the inorganic-encapsulated cellulose particles contain cellulose and an inorganic substance. The inorganic-encapsulated cellulose particles may further contain other components in addition to the cellulose and inorganic substance, as long as the effects of the present invention are not impaired. Examples of other components include trace amounts of cellulose acetate, suspension stabilizers, surfactants, water, organic fillers, pigments (excluding inorganic substances), and medicinal materials, but the other components are not limited to these examples.

[0034] In the present invention, "containing an inorganic substance" means that the inorganic substance is contained inside the cellulose particles. The inorganic substance may be entirely contained in the cellulose particles or part of the inorganic substance may be exposed on the surface of the cellulose particles.

[0035] The state of "containing inorganic substances" can be confirmed by visual observation of the particle cross section or particle surface using an optical microscope, or by analyzing an image using a scanning electron microscope.

[0036] Furthermore, the "cellulose particles encapsulating an inorganic substance" may be particles in which a plurality of inorganic particles are encapsulated in a single cellulose particle, or particles in which a single inorganic particle is coated with cellulose, or a mixture of particles in these forms.

[0037] It should be noted that even when cellulose particles containing inorganic materials are mixed with a small amount of cellulose particles not containing inorganic materials, as long as the aggregate of particles as a whole meets the requirements of the present invention and can achieve the effects of the present invention, it is included within the scope of the present invention. In this case, the amount of cellulose particles not containing inorganic materials is preferably 8% or less, and more preferably 5% or less.

[0038] The refractive index of the inorganic substance is preferably 1.43 to 2.00, more preferably 1.43 to 1.80, further preferably 1.45 to 1.75, and particularly preferably 1.45 to 1.70. When the refractive index of the inorganic substance is within the above range, the transparency of the cellulose particles containing the inorganic substance can be maintained.

[0039] The refractive index of an inorganic substance is a value measured by irradiating the inorganic substance with sodium D-rays at 25°C using an Abbe refractometer.

[0040] Examples of inorganic substances having a refractive index within the above-mentioned range include calcium carbonate (refractive index: 1.50 to 1.69), calcium stearate (refractive index: 1.47), barium sulfate (refractive index: 1.64), talc (refractive index: 1.54 to 1.59), mica (refractive index: 1.53), kaolin (refractive index: 1.64), silica (refractive index: 1.44 to 1.50), and alumina (refractive index: 1.76). Among these inorganic substances, calcium carbonate, calcium stearate, silica, and talc are preferred, and calcium carbonate and calcium stearate are more preferred, from the viewpoint of easily maintaining the transparency of the cellulose particles encapsulating the inorganic substance.

[0041] The inorganic substances may be used alone or in combination of two or more.

[0042] The particle size of the inorganic substance is not particularly limited as long as the average particle size of the cellulose particles encapsulating the inorganic substance is within the following range.

[0043] The inorganic material is preferably surface-treated with at least one of a fatty acid and a silane compound (hereinafter, the fatty acid and the silane compound are collectively referred to as the "surface treatment agent"). When the inorganic material is surface-treated with a surface treatment agent, the hydrophobicity of the inorganic material surface is enhanced, making it easier to be internalized in the cellulose acetate particles described below.

[0044] It should be noted that, in the present invention, "surface treatment" means coating the surface of an inorganic substance with a surface treatment agent.

[0045] Examples of the surface treatment agent include fatty acids and silane compounds. Fatty acids are preferred from the viewpoint of easily encapsulating the inorganic substance in the cellulose acetate particles.

[0046] The surface treatment agents may be used alone or in combination of two or more.

[0047] The amount of the surface treatment agent added is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass, relative to 100 parts by mass of the inorganic substance.

[0048] Examples of fatty acids include saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and isostearic acid, or their salts; and unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, arachidonic acid, and ricinoleic acid, or their salts. Salts of saturated and unsaturated fatty acids include alkali metal salts such as potassium salts and sodium salts, and ammonium salts.

[0049] Among these fatty acids, from the viewpoint of easier inclusion of inorganic substances in cellulose acetate particles, saturated fatty acids are preferred, and stearic acid is more preferred.

[0050] The fatty acids may be used alone or in combination of two or more.

[0051] Examples of the silane compound include vinyl trimethoxysilane, vinyl triethoxysilane, and other vinyl-containing silane coupling agents; 3-(meth)acryloyloxypropyl trimethoxysilane, 3-(meth)acryloyloxypropyl triethoxysilane, 3-(meth)acryloyloxypropyl methyl dimethoxysilane, 3-(meth)acryloyloxypropyl methyl diethoxysilane, and other (meth)acryloyl group-containing silane coupling agents; 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, N-2-(aminoethyl)-3-(meth)acryloyloxypropyl methyl diethoxysilane, and other (meth)acryloyl group-containing silane coupling agents. Silane coupling agents containing amino groups such as -aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane; silane coupling agents containing epoxy groups such as 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc.

[0052] The silane compounds may be used alone or in combination of two or more.

[0053] The mass ratio of the inorganic substance to the cellulose (inorganic substance / cellulose) is 2 / 8 to 8 / 2, preferably 4 / 6 to 8 / 2, and more preferably 6 / 4 to 8 / 2. When the mass ratio is at least the lower limit, the low hygroscopicity of the cellulose particles containing the inorganic substance is improved. When the mass ratio is at least the lower limit, the properties of the cellulose particles (excluding hygroscopicity) are more easily maintained.

[0054] Cellulose particles containing inorganic substances are usually spherical.

[0055] The average particle size of the inorganic-containing cellulose particles is 1 to 300 μm, preferably 1 to 150 μm, and more preferably 1 to 100 μm. When the average particle size of the inorganic-containing cellulose particles is within this range, spherical inorganic-containing cellulose particles tend to be easily produced.

[0056] The average particle size of the inorganic-containing cellulose particles is a volume-based average particle size (volume average particle size) measured using a laser diffraction particle size distribution analyzer.

[0057] The inorganic-matter-encapsulating cellulose particles of the present invention preferably have a moisture absorption rate of 3% or less, more preferably 2.5% or less, further preferably 2% or less, and particularly preferably 1.5% or less, from the perspective of achieving excellent low hygroscopicity. The lower the moisture absorption rate, the more preferred, and 0% is also possible.

[0058] The moisture absorption rate of the inorganic-matter-encapsulating cellulose particles can be determined as follows.

[0059] Cellulose particles containing inorganic matter (for example, 1 g or more) were dried at 110°C for 15 hours and then placed in an environment with a humidity of 100% and a temperature of 85°C to allow the cellulose particles containing inorganic matter to absorb moisture. After 2 hours from the start of the placement, the cellulose particles containing inorganic matter were collected and the mass of the cellulose particles containing inorganic matter after moisture absorption (W) was measured. 11 The cellulose particles containing inorganic matter, the mass of which was measured, were dried at 110° C. for 2 hours, and the mass of the cellulose particles containing inorganic matter after drying was measured (W 12 ), the non-volatile content (N1) after 2 hours of moisture absorption was calculated according to the following formula (i). Similarly, the cellulose particles containing inorganic matter were collected at the moment of 168 hours from the start of placement, and the mass of the cellulose particles containing inorganic matter after moisture absorption (W 21 The cellulose particles containing inorganic matter, the mass of which was measured, were dried at 110° C. for 2 hours, and the mass of the cellulose particles containing inorganic matter after drying was measured (W 22 ), the non-volatile content (N2) after 168 hours of moisture absorption was determined by the following formula (ii). The moisture absorption rate of the cellulose particles containing inorganic substances was determined by the following formula (iii).

[0060] N1 (mass %) = W 12 / W 11 ×100···(i)

[0061] N2 (mass %) = W 22 / W 21 ×100···(ii)

[0062] Moisture absorption rate (%) = (N1-N2) / N2×100···(iii)

[0063] <Method for producing cellulose particles containing inorganic substances>

[0064] Hereinafter, an example of the method for producing the inorganic-matter-encapsulating cellulose particles of the present invention will be described.

[0065] In the method for producing inorganic-encapsulating cellulose particles according to this embodiment, a cellulose acetate solution containing cellulose acetate dissolved in an organic solvent and an inorganic substance are mixed so that the mass ratio of the inorganic substance to the cellulose (inorganic substance / cellulose) is 2 / 8 to 8 / 2 to obtain a resin mixture. The obtained resin mixture is suspended in water to prepare a suspension in which cellulose acetate particles containing the inorganic substance are dispersed in the water. The organic solvent is removed from the suspension, and the cellulose acetate particles are saponified to produce inorganic-encapsulating cellulose particles containing the inorganic substance. After the cellulose acetate particles are saponified to produce the inorganic-encapsulating cellulose particles, the water can be removed by solid-liquid separation, and the inorganic-encapsulating cellulose particles can be dried.

[0066] It can be said that the method for producing inorganic-matter-encapsulating cellulose particles of this embodiment includes the following steps (a) to (d), or it can be said that it further includes the following step (e) in addition to the steps (a) to (d).

[0067] Step (a): A step of mixing a cellulose acetate solution obtained by dissolving cellulose acetate in an organic solvent with an inorganic substance to prepare a resin mixed solution.

[0068] Step (b): A step of suspending the resin mixed solution in water to prepare a suspension in which cellulose acetate particles containing an inorganic substance are dispersed in water.

[0069] Step (c): a step of removing the organic solvent from the suspension.

[0070] Step (d): a step of saponifying the cellulose acetate particles to prepare inorganic-encapsulated cellulose particles containing an inorganic substance.

[0071] Step (e): A step of removing water from the saponified aqueous dispersion obtained in step (d) to dry the cellulose particles containing the inorganic substance.

[0072] In step (a), the cellulose acetate solution and the inorganic substance are mixed so that the mass ratio of the inorganic substance to the cellulose (inorganic substance / cellulose) is 2 / 8 to 8 / 2, preferably 4 / 6 to 8 / 2, more preferably 6 / 4 to 8 / 2.

[0073] The cellulose acetate solution and the inorganic substance are preferably mixed so that the ratio of the inorganic substance to 100 parts by mass of the cellulose acetate is 15 to 240 parts by mass. The ratio of the inorganic substance to 100 parts by mass of the cellulose acetate is more preferably 40 to 240 parts by mass, and even more preferably 90 to 240 parts by mass.

[0074] In step (b), the resin mixture obtained in step (a) is suspended in water to prepare a suspension in which cellulose acetate particles containing an inorganic substance are dispersed in water. Since cellulose acetate is dissolved in an organic solvent in the resin mixture, when the resin mixture is suspended in water, the resin mixture becomes an oily component and disperses in the water to form oil droplets, thereby obtaining a suspension in which cellulose acetate particles containing an inorganic substance are dispersed in water.

[0075] In cellulose acetate, the degree of substitution of acetyl groups, the acetylation rate, and the like are not particularly limited.

[0076] Examples of cellulose acetate include monoacetyl cellulose, diacetyl cellulose, and triacetyl cellulose.

[0077] The viscosity of the cellulose acetate solution is not particularly limited, but is preferably 500 to 300,000 mPa·s, and more preferably 2,000 to 100,000 mPa·s. The viscosity is a value measured at 25°C using a BL type rotational viscometer (e.g., "RB-85L" manufactured by Toki Sangyo Co., Ltd.).

[0078] Cellulose acetate may be used alone or in combination of two or more.

[0079] The organic solvent used in step (a) is not particularly limited as long as it is a compound that can dissolve cellulose acetate. However, the organic solvent is preferably one with low solubility in water. Furthermore, the organic solvent is preferably one having an azeotropic point with water of 100°C or lower at 1013 hPa.

[0080] Examples of organic solvents having an azeotropic point with water of 100° C. or lower at 1013 hPa include aromatic compounds such as toluene and benzene; ester compounds such as methyl acetate, ethyl acetate, and butyl acetate; ketone compounds such as acetone and ethyl methyl ester; and saturated aliphatic hydrocarbons such as n-heptane, n-hexane, and n-octane.

[0081] The organic solvent may be used alone or in combination of two or more.

[0082] The concentration of the cellulose acetate solution is not particularly limited, but is preferably 4% by mass to 40% by mass, and more preferably 8% by mass to 16% by mass.

[0083] In the method for producing inorganic-encapsulating cellulose particles of this embodiment, the resin mixture is preferably suspended in water in the presence of a suspension stabilizer. The suspension stabilizer can be pre-added to the water serving as the dispersion medium, for example. If the water serving as the dispersion medium further contains a suspension stabilizer, the suspension state tends to be stabilized, allowing for simpler production of inorganic-encapsulating cellulose particles.

[0084] Examples of the suspension stabilizer include water-soluble cellulose resins (methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, etc.), polyvinyl alcohol, polyacrylates, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide, triphosphates, etc. It should be noted that when a water-soluble cellulose resin is used as the suspension stabilizer, it is removed along with the water in step (e) and therefore does not affect the inorganic / cellulose ratio of the ultimately obtained inorganic-containing cellulose particles.

[0085] The suspension stabilizers may be used alone or in combination of two or more.

[0086] In the method for producing inorganic-encapsulating cellulose particles of this embodiment, the resin mixture is preferably suspended in water in the presence of a surfactant. The surfactant can be pre-added to the water serving as the dispersion medium, for example. If the water serving as the dispersion medium further contains a surfactant, the suspension state tends to be stabilized, allowing for simpler production of inorganic-encapsulating cellulose particles.

[0087] The surfactant is not particularly limited, and known anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants and the like can be used.

[0088] The surfactant may be used alone or in combination of two or more.

[0089] In step (b), it is preferred to prepare an aqueous dispersion medium solution in advance, suspend the resin mixture in the aqueous dispersion medium solution, and obtain a suspension in which cellulose acetate particles containing an inorganic substance are dispersed in water. The aqueous dispersion medium solution and the resin mixture can be stirred, for example, using a stirrer.

[0090] The aqueous dispersion medium preferably contains water, the above-mentioned suspension stabilizer, and the above-mentioned surfactant.

[0091] The content of the suspension stabilizer in the aqueous dispersion medium solution is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 8 parts by mass, even more preferably 0.3 to 7 parts by mass, and particularly preferably 0.4 to 5 parts by mass, relative to 100 parts by mass of water. When the content of the suspension stabilizer is at least the lower limit, the suspended state of the cellulose acetate particles and the inorganic material during the production process is easily stabilized, allowing for simpler production of cellulose particles containing inorganic materials. When the content of the suspension stabilizer is at most the upper limit, the viscosity of the suspension does not become excessively high, preventing problems such as the suspension tangling with the shafts of the production equipment, and facilitating granulation.

[0092] The content of the surfactant in the aqueous dispersion medium solution is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, even more preferably 0.02 to 1.5 parts by mass, and particularly preferably 0.03 to 0.5 parts by mass, relative to 100 parts by mass of water. When the content of the surfactant in the aqueous dispersion medium solution is at least the lower limit, the suspended state of the cellulose acetate particles during the production process is easily stabilized, allowing for simpler production of inorganic-encapsulating cellulose particles. When the content of the surfactant in the aqueous dispersion medium solution is at most the upper limit, foaming of the suspension due to stirring is less likely to occur, making it easier to produce inorganic-encapsulating cellulose particles.

[0093] In step (c), the organic solvent is removed from the suspension. It is believed that the cellulose acetate particles containing inorganic substances and the organic solvent in the suspension are dispersed in water as an oily component. Therefore, by removing the organic solvent from the suspension in step (c), an aqueous dispersion in which the cellulose acetate particles containing inorganic substances are dispersed in water can be obtained.

[0094] In step (c), the organic solvent is preferably removed by heating the suspension containing the cellulose acetate particles containing the inorganic substance to a temperature above the azeotropic point of the organic solvent and water. Heating the suspension to a temperature above the azeotropic point of the organic solvent and water in step (c) allows for sufficient removal of the organic solvent, minimizing the amount of organic solvent remaining in the cellulose particles. The heating temperature is preferably 100°C or lower at 1013 hPa. The cellulose acetate particles containing the inorganic substance are dispersed in water in a slurry. If the heating temperature of the cellulose acetate particles exceeds 100°C, water will also be volatilized and removed along with the organic solvent, potentially causing the cellulose acetate particles to fuse together.

[0095] In step (d), the inorganic-encapsulating cellulose acetate particles are saponified to produce inorganic-encapsulating cellulose particles containing the inorganic substance. The saponification reaction can be carried out, for example, by mixing an aqueous dispersion of the inorganic-encapsulating cellulose acetate particles in water with an alkaline compound, and optionally heating the mixture.

[0096] The alkaline compound used for saponification is not particularly limited, and examples thereof include sodium hydroxide, potassium hydroxide, ammonia, and triethylamine.

[0097] The basic compound may be used alone or in combination of two or more.

[0098] The reaction time for the saponification reaction is preferably 1.5 to 4 hours, more preferably 2 to 3 hours. When the reaction time for the saponification reaction is at least the lower limit, deacetylation is more likely to proceed adequately, and the acetic acid odor of the inorganic-encapsulated cellulose particles is more likely to be reduced. When the reaction time for the saponification reaction is at most the upper limit, the time required for a single production step can be shortened, thereby improving production efficiency.

[0099] The reaction temperature of the saponification reaction is preferably 90°C to 100°C, more preferably 93°C to 98°C. When the reaction temperature of the saponification reaction is at least the lower limit, deacetylation is likely to proceed sufficiently, and the acetic acid odor of the cellulose particles containing the inorganic substance is likely to be reduced. When the reaction temperature of the saponification reaction is at most the upper limit, excessive heating of the reaction solution (the aqueous dispersion of the cellulose acetate particles containing the inorganic substance) tends to be unnecessary, allowing the production of the cellulose particles containing the inorganic substance to be simpler and at lower cost.

[0100] When the basic compound has hydroxyl groups, the amount of hydroxyl groups in the basic compound relative to 100 mol% of the acetyl groups in the cellulose acetate is preferably 90 mol% to 100 mol%, more preferably 95 mol% to 100 mol%, and even more preferably 98 mol% to 100 mol%. When the amount of hydroxyl groups in the basic compound is at least the lower limit, deacetylation is readily performed, and the acetic acid odor of the inorganic-encapsulating cellulose particles is readily reduced. When the amount of hydroxyl groups in the basic compound is at most the upper limit, the use of an excessive amount of the basic compound tends to be unnecessary, allowing for simpler and more cost-effective production of inorganic-encapsulating cellulose acetate particles.

[0101] In step (e), water is removed from the saponified aqueous dispersion obtained in step (d), and the inorganic-encapsulating cellulose particles are dried. The method for removing water from the saponified aqueous dispersion is not particularly limited, but for example, solid-liquid separation is preferred. The time and temperature for solid-liquid separation can be appropriately set depending on the intended use of the inorganic-encapsulating cellulose particles.

[0102] The details and preferred embodiments of the inorganic-containing cellulose particles obtained by the method for producing inorganic-containing cellulose particles of this embodiment may be the same as those described in the above section "Inorganic-containing cellulose particles".

[0103] <Effects>

[0104] The inorganic-matter-encapsulating cellulose particles of the present invention described above contain an inorganic material within the cellulose particles and are excellent in low hygroscopicity.

[0105] Furthermore, according to the method for producing inorganic-matter-encapsulating cellulose particles of the present invention, inorganic-matter-encapsulating cellulose particles having excellent low hygroscopicity can be produced simply.

[0106] <Purpose>

[0107] The inorganic-substance-encapsulating cellulose particles of the present invention can be used as microbeads for use as fillers in coatings, plastics, adhesives, cosmetics, paper coating materials, fiber processing materials, writing instruments, markers, and the like.

[0108] Example

[0109] Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the following description.

[0110] [Measurement method]

[0111] <Measurement of Refractive Index>

[0112] The refractive index of the inorganic substance was measured by irradiating the inorganic substance with sodium D-rays at 25° C. using an Abbe refractometer (“Model 1T” manufactured by ATAGO CO., LTD.).

[0113] <Measurement of Volume Average Particle Size>

[0114] The volume average particle size of the inorganic-substance-encapsulating cellulose particles was measured using a laser diffraction particle size distribution analyzer (“SALD2100” manufactured by Shimadzu Corporation).

[0115] <Measurement of Moisture Absorption Rate>

[0116] The moisture absorption rate of the inorganic-matter-encapsulating cellulose particles can be determined as follows.

[0117] After drying the cellulose particles containing inorganic matter at 110°C for 15 hours, the particles were placed in an environment with a humidity of 100% and a temperature of 85°C to allow the particles to absorb moisture. After 2 hours from the start of the placement, the particles containing inorganic matter were collected and the weight of the particles containing inorganic matter after moisture absorption (W) was measured. 11 The cellulose particles containing inorganic matter, the mass of which was measured, were dried at 110° C. for 2 hours, and the mass of the cellulose particles containing inorganic matter after drying was measured (W 12 ), the non-volatile content (N1) after 2 hours of moisture absorption was calculated according to the following formula (i). Similarly, the cellulose particles containing inorganic matter were collected at the moment of 168 hours from the start of placement, and the mass of the cellulose particles containing inorganic matter after moisture absorption (W 21 The cellulose particles containing inorganic matter, the mass of which was measured, were dried at 110° C. for 2 hours, and the mass of the cellulose particles containing inorganic matter after drying was measured (W 22 ), the non-volatile content (N2) after 168 hours of moisture absorption was determined by the following formula (ii). The moisture absorption rate of the cellulose particles containing inorganic substances was determined by the following formula (iii).

[0118] N1 (mass %) = W 12 / W 11 ×100···(i)

[0119] N2 (mass %) = W 22 / W 21 ×100···(ii)

[0120] Moisture absorption rate (%) = (N1-N2) / N2×100···(iii)

[0121] [Example 1]

[0122] 500 g of water was added to a 2 L separable flask equipped with a stirrer, and 12 g of hydroxypropyl methylcellulose (equivalent to 2.4 parts by mass per 100 parts by mass of water) and 0.5 g of sodium lauryl sulfate (equivalent to 0.1 parts by mass per 100 parts by mass of water) were dissolved therein to prepare an aqueous dispersion medium solution.

[0123] Separately, 600 g of ethyl acetate was added to a 2 L separable flask equipped with a stirrer, and 90 g of cellulose acetate (acetylation ratio 55%) was dissolved therein to prepare a cellulose acetate solution. 690 g of the resulting cellulose acetate solution was mixed with 200 g of calcium carbonate ("AFF-STF" manufactured by Fimatec Ltd., refractive index: approximately 1.7) surface-treated with stearic acid as an inorganic substance (equivalent to 222.2 parts by mass per 100 parts by mass of cellulose acetate) to prepare a resin mixture.

[0124] The resin mixture was added to the aqueous dispersion medium to prepare a suspension. The suspension was then heated to 90°C while stirring at 300 rpm in a stirrer. The mixture was heated at 90°C for 2 hours to volatilize the ethyl acetate from the suspension. The temperature was then raised to 95°C, 35 g of sodium hydroxide was added, and the temperature was maintained at 90°C for 1.5 hours to remove the acetyl groups from the cellulose acetate particles. This yielded cellulose particles containing inorganic substances encapsulated within the cellulose particles. This produced a slurry in which the inorganic substances were dispersed in water.

[0125] Next, the slurry was cooled to room temperature and filtered to separate the solid and liquid. The recovered solid matter was thoroughly washed with water and then dried at 70° C. for 20 hours to obtain spherical inorganic-containing cellulose particles.

[0126] The volume average particle size and moisture absorption rate of the obtained inorganic-containing cellulose particles were measured. The results are shown in Table 1. Table 1 also shows the mass ratio of the inorganic substance to the cellulose in the inorganic-containing cellulose particles (inorganic substance / cellulose).

[0127] [Example 2]

[0128] In the same manner as in Example 1, a dispersion medium aqueous solution was prepared.

[0129] Separately, 700 g of ethyl acetate was added to a 2 L separable flask equipped with a stirrer, and 90 g of cellulose acetate (acetylation ratio 55%) was dissolved therein to prepare a cellulose acetate solution. 790 g of the resulting cellulose acetate solution was mixed with 90 g of calcium carbonate ("AFF-STF" manufactured by Fimatec Ltd., refractive index: approximately 1.7) surface-treated with stearic acid as an inorganic substance (equivalent to 100 parts by mass per 100 parts by mass of cellulose acetate) to prepare a resin mixed solution.

[0130] Spherical inorganic-matter-containing cellulose particles were obtained in the same manner as in Example 1 except that the obtained dispersion medium aqueous solution and resin mixed solution were used.

[0131] The volume average particle size and moisture absorption rate of the obtained inorganic-containing cellulose particles were measured. The results are shown in Table 1. Table 1 also shows the mass ratio of the inorganic substance to the cellulose in the inorganic-containing cellulose particles (inorganic substance / cellulose).

[0132] [Example 3]

[0133] In the same manner as in Example 1, a dispersion medium aqueous solution was prepared.

[0134] Separately, 750 g of ethyl acetate was added to a 2 L separable flask equipped with a stirrer, and 90 g of cellulose acetate (acetylation ratio 55%) was dissolved therein to prepare a cellulose acetate solution. 840 g of the resulting cellulose acetate solution was mixed with 40 g of calcium carbonate ("AFF-STF" manufactured by Fimatec Ltd., refractive index: approximately 1.7) surface-treated with stearic acid as an inorganic substance (equivalent to 44.4 parts by mass per 100 parts by mass of cellulose acetate) to prepare a resin mixed solution.

[0135] Spherical inorganic-matter-containing cellulose particles were obtained in the same manner as in Example 1 except that the obtained dispersion medium aqueous solution and resin mixed solution were used.

[0136] The volume average particle size and moisture absorption rate of the obtained inorganic-containing cellulose particles were measured. The results are shown in Table 1. Table 1 also shows the mass ratio of the inorganic substance to the cellulose in the inorganic-containing cellulose particles (inorganic substance / cellulose).

[0137] [Example 4]

[0138] 500 g of water was added to a 2 L separable flask equipped with a stirrer, and 6 g of polyvinyl alcohol (equivalent to 1.2 parts by mass per 100 parts by mass of water) and 0.5 g of sodium lauryl sulfate (equivalent to 0.1 parts by mass per 100 parts by mass of water) were dissolved therein to prepare an aqueous dispersion medium solution.

[0139] Separately, the same operation as in Example 1 was carried out to prepare a resin mixed liquid.

[0140] Spherical inorganic-matter-containing cellulose particles were obtained in the same manner as in Example 1 except that the obtained dispersion medium aqueous solution and resin mixed solution were used.

[0141] The volume average particle size and moisture absorption rate of the obtained inorganic-containing cellulose particles were measured. The results are shown in Table 1. Table 1 also shows the mass ratio of the inorganic substance to the cellulose in the inorganic-containing cellulose particles (inorganic substance / cellulose).

[0142] [Example 5]

[0143] 500 g of water was added to a 2 L separable flask equipped with a stirrer, and 3 g of hydroxypropyl methylcellulose (equivalent to 0.6 parts by mass per 100 parts by mass of water) and 0.2 g of sodium lauryl sulfate (equivalent to 0.04 parts by mass per 100 parts by mass of water) were dissolved therein to prepare an aqueous dispersion medium solution.

[0144] Separately, the same operation as in Example 1 was carried out to prepare a resin mixed liquid.

[0145] Spherical inorganic-matter-containing cellulose particles were obtained in the same manner as in Example 1 except that the obtained dispersion medium aqueous solution and resin mixed solution were used.

[0146] The volume average particle size and moisture absorption rate of the obtained inorganic-containing cellulose particles were measured. The results are shown in Table 1. Table 1 also shows the mass ratio of the inorganic substance to the cellulose in the inorganic-containing cellulose particles (inorganic substance / cellulose).

[0147] [Example 6]

[0148] In the same manner as in Example 1, a dispersion medium aqueous solution was prepared.

[0149] Separately, 750 g of ethyl acetate was added to a 2 L separable flask equipped with a stirrer, and 90 g of cellulose acetate (acetylation ratio 55%) was dissolved therein to prepare a cellulose acetate solution. 840 g of the resulting cellulose acetate solution was mixed with 30 g (equivalent to 33.3 parts by mass per 100 parts by mass of cellulose acetate) of calcium stearate surface-treated with stearic acid ("Calcium Stearate" manufactured by Tamnan Chemical Industry Co., Ltd., refractive index: approximately 1.5) as an inorganic substance to prepare a resin mixed solution.

[0150] Spherical inorganic-matter-containing cellulose particles were obtained in the same manner as in Example 1 except that the obtained dispersion medium aqueous solution and resin mixed solution were used.

[0151] The volume average particle size and moisture absorption rate of the obtained inorganic-containing cellulose particles were measured. The results are shown in Table 1. Table 1 also shows the mass ratio of the inorganic substance to the cellulose in the inorganic-containing cellulose particles (inorganic substance / cellulose).

[0152] [Comparative Example 1]

[0153] 500 g of water was added to a 2 L separable flask equipped with a stirrer, and 10 g of hydroxypropyl methylcellulose (equivalent to 2 parts by mass per 100 parts by mass of water) and 2 g of sodium lauryl sulfate (equivalent to 0.4 parts by mass per 100 parts by mass of water) were dissolved therein to prepare an aqueous dispersion medium solution.

[0154] Separately, 1000 g of ethyl acetate was placed in a 2 L separable flask equipped with a stirrer, and 250 g of cellulose acetate (acetylation rate 55%) was dissolved therein to prepare a cellulose acetate solution. The obtained cellulose acetate solution is also referred to as a resin mixed solution in Comparative Example 1.

[0155] The aqueous dispersion medium solution was added to the cellulose acetate solution to prepare a suspension. The suspension was then heated to 90°C while stirring at 300 rpm in a stirrer. The suspension was heated at 90°C for 2 hours to volatilize the ethyl acetate from the suspension. The temperature was then raised to 95°C, and 95 g of sodium hydroxide was added. The mixture was held at this temperature for 1.5 hours to remove the acetyl groups from the cellulose acetate particles, yielding cellulose particles. This yielded a slurry containing cellulose particles dispersed in water.

[0156] The slurry was then cooled to room temperature and filtered to separate the solid and liquid. The recovered solid matter was thoroughly washed with water and then dried at 70° C. for 20 hours to obtain spherical cellulose particles.

[0157] The volume average particle size and moisture absorption rate of the obtained cellulose particles were measured. The results are shown in Table 1.

[0158] [Table 1]

[0159]

[0160] The abbreviations in Table 1 are as follows.

[0161] HPMC: Hydroxypropyl methylcellulose.

[0162] PVA: polyvinyl alcohol.

[0163] As can be seen from Table 1, the inorganic-matter-encapsulating cellulose particles obtained in each example have a low moisture absorption rate and are excellent in low hygroscopicity.

[0164] On the other hand, the cellulose particles not containing an inorganic substance had a high moisture absorption rate and were inferior in low moisture absorption to the cellulose particles containing an inorganic substance obtained in each example.

Claims

1. A cellulose particle containing an inorganic substance, characterized in that: It contains inorganic substances enclosed in cellulose particles containing cellulose. The mass ratio of the inorganic substance to the cellulose, i.e., inorganic substance / cellulose, is 2 / 8 to 8 / 2. The inorganic substance is surface treated with fatty acid, The average particle size of the cellulose particles containing inorganic substances is 1 μm to 300 μm.

2. The cellulose particles containing an inorganic substance according to claim 1, wherein the cellulose particles have a moisture absorption rate of 3% or less.

3. The cellulose particles containing inorganic matter according to claim 1 or 2, wherein The refractive index of the inorganic substance is 1.43 to 2.

00.

4. A method for producing cellulose particles containing inorganic substances, characterized in that: The method for producing cellulose particles containing an inorganic substance according to any one of claims 1 to 3, A cellulose acetate solution obtained by dissolving cellulose acetate in an organic solvent and the inorganic substance are mixed so that the mass ratio of the inorganic substance to the cellulose, i.e., inorganic substance / cellulose, is 2 / 8 to 8 / 2 to obtain a resin mixed solution. The obtained resin mixed solution is suspended in water to prepare a suspension in which cellulose acetate particles containing the inorganic substance are dispersed in water. removing the organic solvent from the suspension, The cellulose acetate particles are saponified to prepare inorganic-encapsulated cellulose particles containing the inorganic substance encapsulated in the cellulose particles.

5. The method for producing cellulose particles containing inorganic matter according to claim 4, wherein: The resin mixture is suspended in water in the presence of a suspension stabilizer and a surfactant.

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