Method for producing polyvinyl alcohol-based particle and polyvinyl alcohol-based particle

Abstract

To provide a production method capable of obtaining polyvinyl alcohol-based particles having adequate water resistance, by heating at a low temperature and / or in a short time compared to those in a conventional production method.SOLUTION: A method for producing polyvinyl alcohol-based particles containing a polyvinyl alcohol-based resin includes a dispersion liquid preparation step, a spraying and drying step, and a heating treatment step, wherein the dispersion liquid preparation step prepares a dispersion liquid containing the polyvinyl alcohol-based resin and water resistance improver polyhydric alcohol, the spraying and drying step sprays and dries the dispersion liquid, and thereby obtains precursor polyvinyl alcohol-based particles, the heating treatment step heats the precursor polyvinyl alcohol-based particles and obtains the polyvinyl alcohol-based particles, when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours, an elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles is lower than an elution rate of the polyvinyl alcohol-based resin in the precursor polyvinyl alcohol-based particles, when the precursor polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyvinyl alcohol particles and polyvinyl alcohol particles. [Background technology]

[0002] Conventionally, particles containing polyvinyl alcohol have been used in a wide range of applications as additives to cosmetics, pharmaceuticals, foods, paints, etc. For example, Patent Document 1 discloses aqueous drug sustained-release microparticles characterized in that a drug to be sustained-released is coated with a polyvinyl alcohol-based polymer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-91716 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional polyvinyl alcohol-based particles need to be heated at a high temperature and / or for a long time to enhance their water resistance to a certain extent, and reducing the number of such heat treatment steps has the problem of causing coloration of the polyvinyl alcohol-based particles and deteriorating other properties of the polyvinyl alcohol-based particles.

[0005] The present invention has been made in view of the above circumstances and provides a production method that can obtain polyvinyl alcohol-based particles having appropriate water resistance by heating at a lower temperature and / or for a shorter time than conventional methods. The present invention also provides a production method that can obtain polyvinyl alcohol-based particles having higher water resistance than conventional methods by heating under similar heating conditions. The present invention provides polyvinyl alcohol-based particles that have appropriate water resistance and exhibit reduced deterioration of properties due to heating. [Means for solving the problem]

[0006] According to the present invention, there is provided a method for producing polyvinyl alcohol-based particles containing a polyvinyl alcohol-based resin, the method comprising a dispersion preparation step, a spray-drying step, and a heat-treatment step, wherein in the dispersion preparation step, a dispersion containing the polyvinyl alcohol-based resin and a polyhydric alcohol is prepared, in the spray-drying step, the dispersion is spray-dried to obtain precursor polyvinyl alcohol-based particles, and in the heat-treatment step, the precursor polyvinyl alcohol-based particles are heated to obtain the polyvinyl alcohol-based particles, and when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours, the elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles is lower than the elution rate of the polyvinyl alcohol-based resin in the precursor polyvinyl alcohol-based particles when the precursor polyvinyl alcohol-based particles are immersed in water at 25°C for 24 hours.

[0007] The present inventors have conducted extensive research and have found that by adding a polyhydric alcohol to polyvinyl alcohol, polyvinyl alcohol-based particles having appropriate water resistance can be obtained by heating at a lower temperature and / or for a shorter time than conventional methods, which has led to the completion of the present invention.

[0008] Various embodiments of the present invention will be described below as examples, and the embodiments shown below can be combined with each other. [1] A method for producing polyvinyl alcohol-based particles containing a polyvinyl alcohol-based resin, comprising a dispersion preparation step, a spray-drying step, and a heat-treatment step, wherein in the dispersion preparation step, a dispersion containing the polyvinyl alcohol-based resin and a polyhydric alcohol is prepared, in the spray-drying step, precursor polyvinyl alcohol-based particles are obtained by spray-drying the dispersion, and in the heat-treatment step, the precursor polyvinyl alcohol-based particles are heated to obtain the polyvinyl alcohol-based particles, and when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours, the elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles is lower than the elution rate of the polyvinyl alcohol-based resin in the precursor polyvinyl alcohol-based particles when the precursor polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours. [2] The manufacturing method according to [1], wherein the difference between the elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours and the elution rate of the polyvinyl alcohol-based resin in the precursor polyvinyl alcohol-based particles when the precursor polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours is 5% by mass or more. [3] The manufacturing method according to [1] or [2], wherein the polyvinyl alcohol-based particles contain 0.1 to 30 parts by mass of the polyhydric alcohol per 100 parts by mass of the polyvinyl alcohol-based resin contained in the polyvinyl alcohol-based particles. [4] A manufacturing method according to any one of [1] to [3], wherein the polyvinyl alcohol-based particles further contain a substance to be sustained-released, and in the dispersion liquid preparation step, the dispersion liquid containing the substance to be sustained-released is prepared. [5] Polyvinyl alcohol-based particles containing a polyvinyl alcohol-based resin and a polyhydric alcohol, wherein when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours, the elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles is 80 mass% or less. [6] Polyvinyl alcohol-based particles according to [5], wherein the polyvinyl alcohol-based particles contain 0.1 to 30 parts by mass of the polyhydric alcohol per 100 parts by mass of the polyvinyl alcohol-based resin contained in the polyvinyl alcohol-based particles. [7] Polyvinyl alcohol-based particles according to [5] or [6], wherein the polyvinyl alcohol-based particles further contain a substance to be sustained-released, and the polyvinyl alcohol-based particles are particles for sustained release that sustainably release the substance to be sustained-released in water. [Effects of the Invention]

[0009] According to the method for producing polyvinyl alcohol-based particles of the present invention, polyvinyl alcohol-based particles having appropriate water resistance can be obtained by heating at a lower temperature and / or for a shorter time than conventional methods. Furthermore, polyvinyl alcohol-based particles having higher water resistance than conventional methods can be obtained by heating under similar conditions to conventional methods. Furthermore, the polyvinyl alcohol-based particles of the present invention have appropriate water resistance and are less susceptible to deterioration of properties due to heating. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below by illustrating embodiments of the present invention. The present invention is not limited by these descriptions. The features of the embodiments of the present invention described below can be combined with each other. Furthermore, each feature can be an invention independently.

[0011] 1. Method for producing polyvinyl alcohol particles The method for producing polyvinyl alcohol particles according to the present invention comprises a dispersion preparation step, a spray drying step, and a heat treatment step.

[0012] 1.1 Dispersion preparation process In the dispersion preparation step according to the present invention, a dispersion containing a polyvinyl alcohol-based resin and a polyhydric alcohol is prepared. The dispersion contains a polyvinyl alcohol-based resin and a polyhydric alcohol, and may also contain a sustained-release target substance, and preferably contains a solvent. Components that may be contained in the dispersion are described below.

[0013] 1.1.1 Polyvinyl alcohol resin In the present invention, a polyvinyl alcohol-based resin (PVA-based resin) refers to a polymer having a plurality of vinyl alcohol monomer units. A polyvinyl alcohol-based resin according to one embodiment of the present invention preferably contains 60 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more of vinyl alcohol monomer units, when the polyvinyl alcohol-based resin is taken as 100 mol %. A polyvinyl alcohol-based resin according to one embodiment of the present invention may contain vinyl alcohol monomer units and vinyl acetate monomer units, and may also contain monomer units other than vinyl alcohol monomer units and vinyl acetate monomer units. A polyvinyl alcohol-based resin according to one embodiment of the present invention may be composed of vinyl alcohol monomer units and vinyl acetate monomer units.

[0014] The polyvinyl alcohol resin preferably has a degree of saponification of 60 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. The degree of saponification may be, for example, 60, 65, 70, 75, 80, 85, 90, 95, or 100 mol%, or may be within a range between any two of the values ​​exemplified here. By setting the degree of saponification to be equal to or higher than the above lower limit, the polyvinyl alcohol resin can be more appropriately crystallized during heat treatment.

[0015] The degree of polymerization of the polyvinyl alcohol resin can be 400 to 700. The degree of polymerization is, for example, 400, 450, 500, 550, 600, 650, or 700, and may be within a range between any two of the values ​​exemplified here.

[0016] The weight-average molecular weight of the polyvinyl alcohol resin can be 5,000 to 300,000. The weight-average molecular weight of the PVA is, for example, 5,000, 10,000, 50,000, 100,000, or 300,000, and may be within a range between any two of the values ​​exemplified here. When the weight-average molecular weight is within the above range, the dispersion has a viscosity suitable for spray drying, and the shape of the spherical particles in the obtained composite powder becomes closer to a perfect sphere and has fewer irregularities. The degree of saponification and degree of polymerization of the polyvinyl alcohol resin can be determined according to JIS K 6726:1994. The polyvinyl alcohol resins can be used singly or in combination of two or more.

[0017] 1.1.2 Polyhydric alcohols In the method for producing polyvinyl alcohol-based particles according to the present invention, by using a polyvinyl alcohol-based resin in combination with a polyhydric alcohol as a raw material, it is possible to impart appropriate water resistance to the polyvinyl alcohol-based particles by heating at a lower temperature and / or for a shorter time than conventional methods. The mechanism by which the use of a polyhydric alcohol makes it easier to control water resistance is unclear, but it is believed that the polyhydric alcohol has the function of promoting crystallization of the polyvinyl alcohol-based resin, which has rapidly dried from a water-dissolved state into an amorphous state, upon heat treatment. It is also speculated that hydrogen bonding between the polyvinyl alcohol-based resin and the polyhydric alcohol may improve water resistance. It is also speculated that promoting crystallization, etc., has the effect of suppressing deterioration of the polyvinyl alcohol-based resin's properties, such as coloration.

[0018] In the present invention, a polyhydric alcohol refers to an alcohol having two or more hydroxyl groups in the molecule. The valence of the polyhydric alcohol may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and may be within a range between any two of the values ​​exemplified herein. Examples of polyhydric alcohols include ethylene glycol, glycerol, propylene glycol, 1,3-butylene glycol, 1,4-butanediol, 1,2-hexanediol, 1,6-hexanediol, pentylene glycol, hexylene glycol, polyglycerin, polyethylene glycol, dipropylene glycol, and cyclodextrin. The polyhydric alcohol may not contain polyvinyl alcohol. A polyhydric alcohol according to one embodiment of the present invention preferably contains at least one selected from these groups. A polyhydric alcohol according to one embodiment of the present invention preferably has little coloration and a high boiling point. A polyhydric alcohol according to one embodiment of the present invention preferably contains at least one selected from glycerol and ethylene glycol. The polyhydric alcohols may be used alone or in combination of two or more.

[0019] 1.1.3 Substances subject to sustained release The polyvinyl alcohol-based particles according to one embodiment of the present invention have suitable water resistance and gradually dissolve in a solvent such as water, and therefore can be used as particles for sustained release that sustainably release a substance to be sustained-released in water. The dispersion according to one embodiment of the present invention can contain the substance to be sustained-released.

[0020] The controlled-release target substance according to one embodiment of the present invention is not particularly limited, and examples thereof include pesticides, medicines, fragrances, dyes, oxygen, etc. The controlled-release target substance can be used alone or in combination of two or more. The controlled-release target substance can be added to the dispersion liquid as is, or can be supported on a carrier such as fine particles, and the carrier can be added to the dispersion liquid. The carrier can be inorganic porous fine particles such as silicon dioxide, calcium silicate, or zeolite, or organic porous fine particles such as acrylic, polyurethane, cellulose, phenolic resin, or epoxy resin.

[0021] 1.1.4 Content of each component in the dispersion A dispersion according to one embodiment of the present invention can be a dispersion in which a polyvinyl alcohol resin, a polyhydric alcohol, and other components added as needed are dispersed in a solvent. Examples of the solvent for the dispersion include water, organic solvents, and mixed solvents of water and organic solvents. Among these, it is preferable to contain water, and water is preferred. Examples of water include natural water, purified water, distilled water, ion-exchanged water, and pure water. Among these, ion-exchanged water is preferred. Examples of organic solvents include aliphatic monohydric alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, and aromatic compounds such as toluene and xylene. For example, the solvent may be a mixed solvent of water and an organic solvent.

[0022] A dispersion according to one embodiment of the present invention may contain 0.1 to 30 parts by mass of polyhydric alcohol, preferably 0.5 to 20 parts by mass, more preferably 5 to 15 parts by mass, and even more preferably 8 to 15 parts by mass, of polyhydric alcohol, based on 100 parts by mass of polyvinyl alcohol-based resin contained in the dispersion. The content of polyhydric alcohol, based on 100 parts by mass of polyvinyl alcohol-based resin contained in the dispersion, may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, or 30 parts by mass, or may be within a range between any two of the values ​​exemplified here.

[0023] A dispersion according to one embodiment of the present invention may contain 0.1 to 30 parts by mass of a substance to be sustained-released, based on 100 parts by mass of the polyvinyl alcohol-based resin contained in the dispersion. The content of the substance to be sustained-released, based on 100 parts by mass of the polyvinyl alcohol-based resin contained in the dispersion, may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, or 30 parts by mass, or may be within a range between any two of the values ​​exemplified here.

[0024] The polyvinyl alcohol resin concentration in the dispersion according to one embodiment of the present invention can be 1 to 30% by mass, for example, 1, 2, 3, 4, 5, 10, 15, 20, 25, or 30% by mass, and may be within a range between any two of the values ​​exemplified here.

[0025] The polyhydric alcohol concentration in the dispersion according to one embodiment of the present invention can be 0.05 to 10% by mass. The polyvinyl alcohol resin concentration in the dispersion is, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% by mass, and may be within a range between any two of the values ​​exemplified here.

[0026] The concentration of the sustained-release target substance in the dispersion according to one embodiment of the present invention can be 0.05 to 10% by mass. The polyvinyl alcohol resin concentration in the dispersion is, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% by mass, and may be within a range between any two of the values ​​exemplified here. Note that the dispersion according to one embodiment of the present invention does not necessarily contain the sustained-release target substance.

[0027] The dispersion can be prepared by stirring with a known stirrer, such as a disper mixer, a homomixer, a high-pressure homogenizer, etc. The dispersion may contain known components within the range that does not impair the effects of the present invention.

[0028] The viscosity of the dispersion is preferably 1000 mPa·s or less at 25°C. The viscosity may be 0.5, 1, 5, 10, 20, 50, 100, 200, 500, or 1000 mPa·s, or may be within a range between any two of the values ​​exemplified here. By adjusting the viscosity in this range, polyvinyl alcohol particles with an appropriate shape and / or structure can be obtained. The viscosity of the dispersion can be measured using a tuning fork vibrating viscometer SV-1A (manufactured by A&D). In the dispersion preparation process, treatments to adjust the viscosity and rheological properties of the dispersion may be performed as needed. Examples include treatments to reduce the viscosity, particularly the dynamic viscosity under high shear, and treatments to impart pseudoplasticity or thixotropy. These treatments can be performed by adding a dispersant or by reducing the molecular weight of the organic material.

[0029] 1.2 Spray drying process In the spray drying step, the above-mentioned dispersion is spray dried to obtain precursor polyvinyl alcohol particles. In the spray drying step, the dispersion liquid is supplied to a spray dryer adjusted to a predetermined temperature, and sprayed to obtain precursor polyvinyl alcohol particles. The spray dryer is not particularly limited as long as it is a spray dryer used in the production of ordinary granules. The spray dryer is - Raw material tank for storing dispersion liquid, A raw material supply pump for supplying the dispersion liquid, Nozzles (four-fluid nozzles, two-fluid nozzles, or one-fluid nozzles) or rotating disks that turn the dispersion into fine droplets, A drying chamber for drying and granulating the droplets; Blowers, filters, heaters for blowing dried and heated air or inert gas into the drying chamber, and A collector that collects composite powder precursors using a two-point collection method, cyclone method, bag filter method, etc. (These may be heatable collectors.) etc. can be provided. By adjusting the droplet formation conditions and drying conditions in the spray drying step, the shape, structure, and physical properties of the resulting precursor polyvinyl alcohol particles can be adjusted.

[0030] In the spray drying step, the outlet temperature of the spray dryer can be set to 70 to 250°C. The outlet temperature is, for example, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, or 250°C, and may be within a range between any two of the values ​​exemplified here. In the spray drying step, some of the resulting precursor polyvinyl alcohol particles may crystallize. The spray drying step can also serve as a heat treatment step, which will be described later, by, for example, adjusting the drying conditions after granulation or by providing the spray dryer with a heating function or a heating chamber capable of heating and maintaining the temperature for a certain period of time.

[0031] 1.3 Heat treatment process In the heat treatment step, precursor polyvinyl alcohol particles are heated to obtain polyvinyl alcohol particles. It has been known that heating promotes crystallization of polyvinyl alcohol resins, improving their water resistance. As described above, in the method for producing polyvinyl alcohol particles according to the present invention, by using a polyvinyl alcohol resin in combination with a polyhydric alcohol as a raw material, it is possible to impart appropriate water resistance to the polyvinyl alcohol particles by heating at a lower temperature and / or for a shorter time than conventional methods. This is presumably because the polyhydric alcohol has the function of promoting crystallization of the polyvinyl alcohol resin upon heat treatment, and also because hydrogen bonding between the polyvinyl alcohol resin and the polyhydric alcohol may improve water resistance.

[0032] Here, when the heated polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours, the elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles is lower than the elution rate of the polyvinyl alcohol-based resin in the precursor polyvinyl alcohol-based particles when the unheated precursor polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours. The difference in the dissolution rate can be 5% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more. The difference in the dissolution rate between the heated polyvinyl alcohol-based resin when immersed in water at 25°C for 72 hours and the unheated polyvinyl alcohol-based resin when immersed in water at 25°C for 72 hours is, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85% by mass, and may be within a range between any two of the values ​​exemplified here.

[0033] It is preferable that the elution rate of the polyvinyl alcohol-based resin from the polyvinyl alcohol-based particles after heating when the particles are immersed in water at 25°C for 1 hour is lower than the elution rate of the polyvinyl alcohol-based resin from the precursor polyvinyl alcohol-based particles before heating when the particles are immersed in water at 25°C for 1 hour. The difference in dissolution rate can be 15% by mass or more, preferably 20% by mass or more, and more preferably 25% by mass or more. The difference in dissolution rate between the heated polyvinyl alcohol-based resin when immersed in water at 25°C for 1 hour and the unheated polyvinyl alcohol-based resin when immersed in water at 25°C for 1 hour is, for example, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, or 75% by mass, and may be within a range between any two of the values ​​exemplified here.

[0034] It is preferable that the elution rate of the polyvinyl alcohol-based resin from the polyvinyl alcohol-based particles after heating when the particles are immersed in water at 25°C for 24 hours is lower than the elution rate of the polyvinyl alcohol-based resin from the precursor polyvinyl alcohol-based particles before heating when the particles are immersed in water at 25°C for 24 hours. The difference in dissolution rate when the heated polyvinyl alcohol particles are immersed in water at 25° C. for 24 hours can be 10% by mass or more, preferably 15% by mass or more, and preferably 20% by mass or more. The difference in dissolution rate when the heated polyvinyl alcohol resin is immersed in water at 25° C. for 24 hours and the unheated polyvinyl alcohol resin is immersed in water at 25° C. for 24 hours is, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80% by mass, and may be within a range between any two of the values ​​exemplified here.

[0035] The elution rate of the polyvinyl alcohol-based resin can be evaluated by the method described in the Examples. The elution rate of the polyvinyl alcohol-based resin can be controlled by adjusting the type and amount of the compound in the dispersion, specifically the type and amount of polyvinyl alcohol or polyhydric alcohol, and the conditions of the spray drying step and the heat treatment step.

[0036] In the heat treatment step, the heat treatment is preferably carried out at a temperature of 90°C or higher and lower than 200°C, more preferably 100 to 160°C, and even more preferably 120 to 150°C. The heat treatment temperature is, for example, less than 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, or 200°C, and may be within a range between any two of the values ​​exemplified here.

[0037] The heat treatment time is, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 hours, and may be within a range between any two of the values ​​exemplified here.

[0038] 2. Polyvinyl alcohol particles The polyvinyl alcohol-based particles according to the present invention can be polyvinyl alcohol-based particles obtained by the above-mentioned production method. Furthermore, the polyvinyl alcohol-based particles according to one embodiment of the present invention are polyvinyl alcohol-based particles containing a polyvinyl alcohol-based resin and a polyhydric alcohol, and when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours, the elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles is 80 mass% or less.

[0039] The polyvinyl alcohol-based particles according to one embodiment of the present invention can be spherical particles. Spherical particles include nearly spherical particles and refer to particles with a rounded shape. The maximum diameter / minimum diameter ratio of the spherical particles is preferably 0.5 to 1.5, more preferably 0.8 to 1.2. The spherical particles may also include partially crushed or truncated spherical shapes, such as hemispherical (lens-like, etc.) particles, but it is preferable that at least half of the particles have a maximum diameter / minimum diameter ratio within the above numerical range. Furthermore, the spherical particles can have few depressions or wrinkles on the surface, making them smooth.

[0040] The average particle size of the spherical particles can be 10 μm or less. The average particle size can be 0.1 to 10 μm, for example, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 μm, and may be within a range between any two of the values ​​exemplified here. The average particle size of the spherical particles can be measured by SEM observation. The average particle size can be determined by measuring the particle size of each spherical particle and averaging the results.

[0041] The polyvinyl alcohol-based particles according to one embodiment of the present invention contain a polyvinyl alcohol-based resin and a polyhydric alcohol. The polyvinyl alcohol-based particles according to one embodiment of the present invention may also contain a polyvinyl alcohol-based resin, a polyhydric alcohol, and a sustained-release target substance, and may further contain a known drug as needed. The aspects of the polyvinyl alcohol-based resin, the polyhydric alcohol, and the sustained-release target substance are as described above.

[0042] The polyvinyl alcohol particles according to one embodiment of the present invention preferably contain 0.1 to 30 parts by mass of polyhydric alcohol per 100 parts by mass of the polyvinyl alcohol resin contained in the polyvinyl alcohol particles, preferably 0.5 to 20 parts by mass, more preferably 5 to 15 parts by mass, and even more preferably 8 to 15 parts by mass. The content of the polyhydric alcohol is, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, or 30 parts by mass, and may be within a range between any two of the values ​​exemplified here.

[0043] The polyvinyl alcohol-based particles according to one embodiment of the present invention may contain 0.1 to 30 parts by mass of a substance to be sustained-released relative to 100 parts by mass of the polyvinyl alcohol-based resin contained in the polyvinyl alcohol-based particles. The content of the substance to be sustained-released may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, or 30 parts by mass, or may be within a range between any two of the values ​​exemplified here.

[0044] In the polyvinyl alcohol particles according to one embodiment of the present invention, when the polyvinyl alcohol particles are immersed in water at 25° C. for one hour, the elution rate of the polyvinyl alcohol resin from the polyvinyl alcohol particles is preferably 60% by mass or less, and more preferably 40% by mass or less. When the polyvinyl alcohol particles are immersed in water at 25° C. for one hour, the elution rate of the polyvinyl alcohol resin from the polyvinyl alcohol particles is, for example, 5, 10, 15, 20, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 40, 45, 50, 55, or 60% by mass, and may be within a range between any two of the values ​​exemplified here.

[0045] In the polyvinyl alcohol particles according to one embodiment of the present invention, when the polyvinyl alcohol particles are immersed in water at 25° C. for 24 hours, the elution rate of the polyvinyl alcohol resin from the polyvinyl alcohol particles is preferably 65% ​​by mass or less, and more preferably 50% by mass or less. When the polyvinyl alcohol particles are immersed in water at 25° C. for 24 hours, the elution rate of the polyvinyl alcohol resin from the polyvinyl alcohol particles is, for example, 5, 10, 15, 20, 25, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 45, 50, 55, 60, or 65% by mass, and may be within a range between any two of the values ​​exemplified here.

[0046] In the polyvinyl alcohol particles according to one embodiment of the present invention, when the polyvinyl alcohol particles are immersed in water at 25° C. for 72 hours, the elution rate of the polyvinyl alcohol resin from the polyvinyl alcohol particles is preferably 80% by mass or less, and more preferably 70% by mass or less. When the polyvinyl alcohol particles are immersed in water at 25° C. for 72 hours, the elution rate of the polyvinyl alcohol resin from the polyvinyl alcohol particles is, for example, 15, 20, 25, 30, 35, 40, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 60, 65, 70, 75, or 80% by mass, and may be within a range between any two of the values ​​exemplified here. In a polyvinyl alcohol-based resin according to one embodiment of the present invention, the 72-hour elution rate, the 24-hour elution rate, and / or the 1-hour elution rate are preferably within the above-mentioned numerical ranges when the polyvinyl alcohol-based particles are immersed in water at 25° C. In a polyvinyl alcohol-based resin according to one embodiment of the present invention, the 72-hour elution rate, the 24-hour elution rate, and the 1-hour elution rate are preferably at least two within the above-mentioned numerical ranges when the polyvinyl alcohol-based particles are immersed in water at 25° C., and more preferably all of the 72-hour elution rate, the 24-hour elution rate, and the 1-hour elution rate are all within the above-mentioned numerical ranges.

[0047] The elution rate of the polyvinyl alcohol-based resin can be evaluated by the method described in the Examples. The elution rate of the polyvinyl alcohol-based resin can be controlled by adjusting the type and amount of the compound in the dispersion, specifically the type and amount of polyvinyl alcohol or polyhydric alcohol, and the conditions of the spray drying step and the heat treatment step.

[0048] When the polyvinyl alcohol-based particles according to one embodiment of the present invention contain a substance to be sustained-released, the amount of the substance to be sustained-released released from the polyvinyl alcohol-based particles when the polyvinyl alcohol-based particles are immersed in water at 25° C. for one hour can be 3 to 40% by mass. When the polyvinyl alcohol-based particles are immersed in water at 25° C. for one hour, the amount of the substance to be sustained-released released from the polyvinyl alcohol-based particles can be, for example, 3, 5, 10, 15, 20, 25, 30, 35, or 40% by mass, and may be within a range between any two of the values ​​exemplified here.

[0049] When the polyvinyl alcohol-based particles according to one embodiment of the present invention contain a substance to be sustained-released, the amount of the substance to be sustained-released released from the polyvinyl alcohol-based particles when the polyvinyl alcohol-based particles are immersed in water at 25° C. for 24 hours can be 5 to 60% by mass. When the polyvinyl alcohol-based particles are immersed in water at 25° C. for 24 hours, the amount of the substance to be sustained-released released from the polyvinyl alcohol-based particles can be, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60% by mass, and may be within a range between any two of the values ​​exemplified here.

[0050] When polyvinyl alcohol-based particles according to one embodiment of the present invention contain a controlled-release substance, the amount of the controlled-release substance released from the polyvinyl alcohol-based particles when immersed in water at 25° C. for 72 hours can be 10 to 80% by mass, more preferably 40 to 70% by mass, or, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80% by mass, and may be within a range between any two of the values ​​exemplified here.

[0051] The release amount of the sustained-release target substance can be evaluated by the method described in the Examples. The release amount of the sustained-release target substance can be controlled by adjusting the type and amount of the components in the dispersion, specifically the type and amount of polyvinyl alcohol, polyhydric alcohol, and sustained-release target substance, as well as the conditions for the spray-drying and heat-treatment steps. The release amount of the sustained-release target substance can be adjusted so that a desired amount of the sustained-release target substance is released in a desired time, depending on the application, etc.

[0052] The polyvinyl alcohol-based particles according to one embodiment of the present invention preferably have a color difference ΔE of 0 to 20. ΔE can be a value relative to a reference white in the L*a*b* color space. The color difference ΔE is, for example, 0, 1, 2, 3, 4, 5, 10, 15, or 20, and may be within a range between any two of the values ​​exemplified here. The color difference ΔE can be controlled by adjusting the production conditions during production of the polyvinyl alcohol-based particles (the types and amounts of polyvinyl alcohol and polyhydric alcohol blended in the dispersion, and the heat treatment temperature and time), particularly the heat treatment temperature and time.

[0053] The polyvinyl alcohol-based particles according to one embodiment of the present invention may contain a substance to be released slowly, and the polyvinyl alcohol-based particles may be used as particles for sustained release that slowly release the substance to be released slowly in water. The polyvinyl alcohol-based particles according to one embodiment of the present invention have moderate water resistance, and therefore can gradually release a substance to be released into water. Furthermore, the polyvinyl alcohol-based particles according to one embodiment of the present invention allow for easy and highly adjustable resin elution amounts and release amounts of the substance to be released, making it possible to prepare polyvinyl alcohol-based particles with a desired release amount of the substance to be released. The applications of the polyvinyl alcohol-based particles according to one embodiment of the present invention are not particularly limited, and they can be used for the sustained release of drugs that require sustained release in agriculture, forestry, fisheries, medicine, and other fields. [Example]

[0054] The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited to these examples.

[0055] Example 1 <Dispersion liquid preparation process> Polyvinyl alcohol (JMR-10HH, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., saponification degree 98.5% or more, polymerization degree 240, molecular weight approximately 10,000) and glycerol as a polyhydric alcohol were added to ion-exchanged water to prepare a dispersion with a polyvinyl alcohol concentration of 15% by mass and a glycerol concentration of 0.3% by mass.

[0056] <Spray drying process> The resulting dispersion was spray-dried to obtain precursor polyvinyl alcohol particles. The spray drying was performed using a two-fluid nozzle laboratory spray dryer, and the inlet temperature of the spray dryer was set to 200°C. When the inlet temperature of the spray dryer was set to 200°C, the outlet temperature was 70 to 120°C.

[0057] <Heat treatment process> The obtained precursor polyvinyl alcohol particles were heated at 100°C for 8 hours in an air atmosphere to obtain polyvinyl alcohol particles. When the shape of the obtained polyvinyl alcohol particles was observed by SEM, it was confirmed that spherical particles with a particle diameter of 0.1 to 10 μm were formed.

[0058] (Examples 2 to 12, Comparative Examples 1 to 3) Polyvinyl alcohol particles were produced in the same manner as in Example 1, except that in the dispersion preparation step, the formulation of the dispersion, and the presence or absence, temperature, and time of a heat treatment step were as shown in Tables 1 and 3. In Examples 9 to 12 and Comparative Example 3, benzoic acid was used as the sustained-release target substance.

[0059] (Examples 13 to 24, Comparative Examples 4 to 6) Polyvinyl alcohol particles were produced in the same manner as in Example 1, except that in the dispersion preparation step, the formulation of the dispersion, and the presence or absence, temperature, and time of a heat treatment step were as shown in Tables 2 and 3. In Examples 13 to 24 and Comparative Examples 4 to 6, ethylene glycol was used as the polyhydric alcohol.

[0060] (Comparative Examples 7 to 16) Polyvinyl alcohol particles were produced in the same manner as in Example 1, except that in the dispersion preparation step, the formulation of the dispersion, and the presence or absence, temperature, and time of a heat treatment step were as shown in Table 4. In Comparative Examples 7 to 16, no polyhydric alcohol was used. In Comparative Example 17, no polyvinyl alcohol was used, and starch (hydroxypropylated starch, Purecoat B790, manufactured by Sansho Co., Ltd.) was used instead.

[0061] The obtained polyvinyl alcohol particles were evaluated as follows.

[0062] (Elution rate of polyvinyl alcohol resin) The resulting particles were immersed in water, and the amount of resin (polyvinyl alcohol or starch) eluted into the water after 1 hour, 24 hours, and 72 hours was evaluated. The amount of polyvinyl alcohol (starch) in the water was determined as follows: First, 1 g of sample was immersed in 10 g of ion-exchanged water at 25°C for a predetermined time. The mixture was then suction-filtered through a glass fiber filter, and the residue captured on the filter was dried in a dryer at 100°C for 2 hours, and the mass of the residue was calculated. The mass of the sample before immersion was Ag and the mass of the residue was Bg, and the elution rate of each sample was calculated using the following formula. [Elution rate (mass%)]=(AB) / A×100 The dissolution rate indicates the amount of polyvinyl alcohol (starch) dissolved into water when polyvinyl alcohol particles (or particles containing starch) are immersed in water for a certain period of time, relative to 100% by mass of polyvinyl alcohol (starch) contained in the particles.

[0063] (Amount of sustained release target substance released) 1 g of the resulting particles was immersed in 10 g of ion-exchanged water at 25°C, and the amount of the sustained-release target substance released after 1 hour, 24 hours, and 72 hours was evaluated. The amount of the sustained-release target substance (benzoic acid) in the water was determined by quantifying the benzoic acid concentration in the water from the absorption peak of the aromatic ring using an absorptiometer. The amount of the sustained-release target substance released indicates the amount of the sustained-release target substance (benzoic acid) released into water when immersed in water for a certain period of time, relative to 100% by mass of the sustained-release target substance (benzoic acid) contained in the polyvinyl alcohol-based particles (or particles containing starch).

[0064] (color difference) The color tone of the obtained particles was measured in the L*a*b* color space using a Color Reader CR-13 (Konica Minolta), and the color difference ΔE from a reference white (L=100, a=b=0) was calculated.

[0065] [Table 1]

[0066] [Table 2]

[0067] [Table 3]

[0068] [Table 4]

Claims

1. A method for producing polyvinyl alcohol-based particles containing a polyvinyl alcohol-based resin, comprising: The method comprises a dispersion preparation step, a spray drying step, and a heat treatment step, In the dispersion preparation step, a dispersion containing the polyvinyl alcohol-based resin and a polyhydric alcohol is prepared, In the spray-drying step, the dispersion is spray-dried to obtain precursor polyvinyl alcohol particles, In the heat treatment step, the precursor polyvinyl alcohol-based particles are heated to obtain the polyvinyl alcohol-based particles, a leaching rate of the polyvinyl alcohol-based resin from the polyvinyl alcohol-based particles when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours is lower than a leaching rate of the polyvinyl alcohol-based resin from the precursor polyvinyl alcohol-based particles when the precursor polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours.

2. 2. The manufacturing method according to claim 1, wherein a difference between a dissolution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours and a dissolution rate of the polyvinyl alcohol-based resin in the precursor polyvinyl alcohol-based particles when the precursor polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours is 5% by mass or more.

3. 3. The manufacturing method according to claim 1, wherein the polyvinyl alcohol-based particles contain 0.1 to 30 parts by mass of the polyhydric alcohol per 100 parts by mass of the polyvinyl alcohol-based resin contained in the polyvinyl alcohol-based particles.

4. 3. The method according to claim 1, wherein the polyvinyl alcohol-based particles further contain a sustained-release target substance, In the dispersion preparation step, the dispersion containing the substance to be sustained-released is prepared.

5. Polyvinyl alcohol-based particles containing a polyvinyl alcohol-based resin and a polyhydric alcohol, Polyvinyl alcohol-based particles, wherein when the polyvinyl alcohol-based particles are immersed in water at 25°C for 72 hours, the elution rate of the polyvinyl alcohol-based resin in the polyvinyl alcohol-based particles is 80 mass% or less.

6. 6. The polyvinyl alcohol-based particles according to claim 5, wherein the polyvinyl alcohol-based particles contain 0.1 to 30 parts by mass of the polyhydric alcohol per 100 parts by mass of the polyvinyl alcohol-based resin contained in the polyvinyl alcohol-based particles.

7. 7. The polyvinyl alcohol-based particles according to claim 5 or 6, wherein the polyvinyl alcohol-based particles further contain a sustained-release target substance, The polyvinyl alcohol-based particles are particles for sustained release that sustainably release the target substance for sustained release in water.

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