Polyvinyl alcohol resin powder

Abstract

To provide a polyvinyl alcohol resin powder with uniform distribution of impurities.SOLUTION: There is provided a polyvinyl alcohol resin powder having a content of sodium acetate of a polyvinyl alcohol resin with a particle diameter of 500 to 1000 μm (wt.%) / a content of sodium acetate of the polyvinyl alcohol resin with a particle diameter of 100 to 300 μm (wt.%) of 0.9 to 1.1. The polyvinyl alcohol resin power is unmodified polyvinyl alcohol consisting of only a vinyl alcohol structural unit and a vinyl ester structural unit.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a polyvinyl alcohol-based resin powder, and more particularly to a polyvinyl alcohol-based resin powder for use in medicines and cosmetics. [Background technology]

[0002] Polyvinyl alcohol resins (hereinafter referred to as PVA resins) are known as water-soluble resins, and are used for various purposes. Applications in which the compound is used as an aqueous solution include, for example, adhesives, emulsifiers, suspending agents, and coating agents, and applications in which the compound is used as a molded product (mainly, films) include, for example, polarizing films, water-soluble films, gas barrier films, seed tapes, and fibers. They are used in a wide range of fields, including papermaking, agriculture, electricity, medicine, cosmetics, food additives, and food packaging materials.

[0003] In particular, when they are used in pharmaceuticals, cosmetics, and food, strict control is required even for trace amounts of impurities. Therefore, the PVA-based resin after saponification is washed several times with a solvent such as methanol. Furthermore, it has been disclosed that various effects can be obtained by controlling the washing and crushing processes (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 013675 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the PVA resin described in Patent Document 1, the distribution of impurities in the aggregate of PVA resin powder is uneven, and the particle size distribution of the PVA resin powder is classified during transportation, etc., which causes unevenness in the components and content of impurities adhering to and contained in the PVA resin powder, affecting the binding power, film-forming properties, barrier properties, and solubility, resulting in unstable quality. There is a demand for a PVA resin powder with less distribution of impurities by particle size. [Means for solving the problem]

[0006] However, in light of the above circumstances, the present inventors conducted extensive research and discovered that the above-mentioned problems can be solved by using a PVA-based resin powder having a constant distribution of sodium acetate content for each particle size, thereby completing the present invention.

[0007] That is, the gist of the present invention is a polyvinyl alcohol-based resin powder characterized in that the sodium acetate content (wt %) of the polyvinyl alcohol-based resin having a particle size of 500 to 1000 μm / the sodium acetate content (wt %) of the polyvinyl alcohol-based resin having a particle size of 100 to 300 μm is 0.9 to 1.1. Effect of the Invention

[0008] The PVA resin powder of the present invention has a uniform distribution of sodium acetate, and even when the PVA resin is used for relatively small sized molded products, for example, solid preparations such as tablets and granules, or non-solid preparations such as eye drops and ointments, preparations with uniform performance can be obtained.

[0009] That is, in the PVA resin of the present invention, impurities are distributed uniformly, so there is no influence due to classification during production, and the content uniformity is maintained, eliminating variation between preparations. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in detail below. In this specification, all percentages and parts expressed by mass are equivalent to percentages and parts expressed by weight.

[0011] [PVA resin powder] The PVA resin powder of the present invention has vinyl alcohol structural units corresponding to a degree of saponification and vinyl ester structural units which are unsaponified portions, and the ratio of the sodium acetate content (wt%) of the PVA resin having a particle size of 500 to 1000 μm to the sodium acetate content (wt%) of the PVA resin having a particle size of 100 to 300 μm is 0.9 to 1.1.

[0012] The content (wt%) of sodium acetate in the present invention is measured in accordance with JIS K 6726 (1994), 3.6.1 titration method.

[0013] The method for measuring the amount of sodium acetate (wt%) per particle size is as follows: (1) The PVA resin powder is sieved using sieves having mesh sizes of 100 μm, 300 μm, 500 μm, and 1000 μm. (2) The PVA-based resin powder on a sieve with a mesh size of 500 μm and the PVA-based resin powder on a sieve with a mesh size of 1000 μm are mixed to obtain a PVA-based resin powder having a particle size of 500 to 1000 μm. The PVA-based resin powder that is on a sieve with an opening of 100 μm and below a sieve with an opening of 300 μm is defined as the PVA-based resin powder having a particle size of 100 to 300 μm. (3) The amount of sodium acetate in each of the PVA-based resin powders having a particle size of 500 to 1000 μm and the PVA-based resin powders having a particle size of 100 to 300 μm is determined by the above-mentioned titration method.

[0014] The method for producing the PVA resin powder of the present invention will now be described in more detail. The PVA resin powder can be obtained, for example, by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl ester monomer. Examples of such vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl versatate, with vinyl acetate being preferred for practical purposes.

[0015] In addition, saponified copolymers of the vinyl ester monomers and monomers copolymerizable with the vinyl ester monomers can also be used to the extent that the effects of the present invention are not impaired. Examples of such copolymerizable monomers include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxyl-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, and 3,4-dihydroxy-1-butene; and derivatives thereof such as acylated products; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, and undecylenic acid; salts thereof, monoesters thereof, and dialkyl esters thereof. Examples of the copolymerizable monomer include nitriles such as acrylonitrile, methacrylonitrile, and the like, amides such as diacetone acrylamide, acrylamide, and methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, and their salts, alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, and glycerin monoallyl ether, and other vinyl compounds, substituted vinyl acetates such as isopropenyl acetate and 1-methoxyvinyl acetate, vinylidene chloride, 1,4-diacetoxy-2-butene, 1,4-dihydroxy-2-butene, and vinylene carbonate, etc. The content of such copolymerizable monomers is usually 10 mol % or less, preferably 5 mol % or less, and particularly preferably 1 mol % or less, based on the total amount of the polymer. In the present invention, unmodified PVA consisting of only vinyl alcohol structural units and vinyl ester structural units of unsaponified portions is preferred.

[0016] There is no particular limitation on the polymerization of the vinyl ester monomer and copolymerizable monomer, and any known method such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be used, but solution polymerization is usually carried out.

[0017] Solvents used in such polymerization usually include aliphatic alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, isopropyl alcohol, n-propanol, and butanol, and ketones, such as acetone and methyl ethyl ketone, and methanol is preferably used industrially. The polymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, or any of various known low-temperature active catalysts. The reaction temperature is selected from the range of 35° C. to the boiling point.

[0018] The obtained PVA resin powder is then saponified in a continuous or batch manner. Either alkali saponification or acid saponification can be used for the saponification, but industrially, the polymer is dissolved in alcohol and the saponification is carried out in the presence of an alkali catalyst. Examples of such alcohol include methanol, ethanol, and butanol. The concentration of the polymer in the alcohol is selected from the range of 20 to 60% by mass. If necessary, water of about 0.3 to 10% by mass may be added, and further, various esters such as methyl acetate, and various solvents such as benzene, hexane, and DMSO (dimethyl sulfoxide) may be added.

[0019] Specific examples of the saponification catalyst include alkali catalysts such as hydroxides and alcoholates of alkali metals, such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, and potassium methylate. The amount of such catalyst used is preferably 1 to 100 millimole equivalents relative to the monomer.

[0020] After saponification, the resulting polyvinyl ester polymer is washed with a washing liquid, such as an alcohol such as methanol, ethanol, isopropyl alcohol, or butanol, or a mixture of the above alcohol and water, with methanol being preferred from the viewpoints of washing efficiency and drying efficiency.

[0021] Examples of the washing method include: (i) a method in which the PVA-based resin is mixed with a washing liquid, followed by stirring for a certain period of time (pool washing), followed by solid-liquid separation by filtration, centrifugation, decantation, or the like; (ii) a method in which the PVA-based resin is mixed with a washing liquid, followed by solid-liquid separation while further adding washing liquid and simultaneously carrying out solid-liquid separation (shower washing); and (iii) a method in which methods (i) and (ii) are combined. Among these, method (iii) is preferred since it is easier to obtain the effects of the present invention.

[0022] Method (iii) is explained in detail below. First, the PVA-based resin is mixed with the cleaning solution, and the ratio (by weight) of the cleaning solution to the PVA-based resin is preferably cleaning solution / PVA-based resin from 1 to 20, and particularly preferably from 3 to 10. If this ratio is too small, the cleaning efficiency tends to decrease, and if it is too large, the cleaning tends to be insufficient.

[0023] Next, the temperature of the cleaning solution during stirring for a certain period of time (during reservoir cleaning) is usually 10 to 80°C, and particularly preferably 20 to 70°C. If the temperature is too high, the amount of evaporation of the cleaning solution increases, and reflux equipment tends to be required. If the temperature is too low, the cleaning efficiency tends to decrease. The cleaning time is usually 5 minutes to 12 hours, and particularly preferably 30 minutes to 4 hours. If the cleaning time is too long, the production efficiency tends to decrease, and if the cleaning time is too short, the cleaning tends to be insufficient. The number of times of cleaning is usually 1 to 10, and particularly preferably 1 to 5. If the number of times of cleaning is too large, the productivity tends to decrease and the cost tends to increase.

[0024] Next, the solid (mainly PVA-based resin) and liquid (mainly cleaning liquid) are separated by filtration, centrifugation, decantation, etc. Filtration can be performed by natural filtration (normal pressure filtration), reduced pressure filtration, pressure filtration, centrifugal filtration, suction filtration, etc.

[0025] When adding the washing liquid and performing solid-liquid separation simultaneously (in the case of shower washing), it is preferable to gradually add a small amount of the washing liquid in such a case. The amount of the washing liquid from the start to the end of washing, in terms of the ratio (by weight) of the washing liquid to the PVA-based resin, is preferably 1 to 20, and particularly preferably 3 to 10. The temperature of the cleaning solution is usually 10 to 80°C, and preferably 20 to 70°C. If the temperature is too high, the amount of evaporation of the cleaning solution increases, and reflux equipment tends to be required. If the temperature is too low, the cleaning efficiency tends to decrease. The cleaning time is usually 5 minutes to 12 hours, and preferably 30 minutes to 4 hours. If the cleaning time is too long, the production efficiency tends to decrease, and if the cleaning time is too short, the cleaning tends to be insufficient.

[0026] The washed PVA resin powder is dried with hot air or the like in a continuous or batch manner to obtain a PVA resin. The drying temperature is usually 50 to 150°C, particularly 60 to 130°C, and especially 70 to 110°C. If the drying temperature is too high, the PVA resin powder tends to deteriorate due to heat, and if the drying temperature is too low, drying tends to take a long time. The drying time is usually 1 to 48 hours, and particularly 2 to 36 hours is preferred. If the drying time is too long, the PVA resin powder tends to deteriorate due to heat, and if the drying time is too short, drying tends to be insufficient or high-temperature drying is required.

[0027] The content of the solvent in the dried PVA resin powder is usually 0 to 10% by mass, particularly preferably 0.1 to 5% by mass, and even more preferably 0.1 to 1% by mass.

[0028] The average degree of polymerization of the PVA resin powder used in the present invention is preferably 200 to 4000, more preferably 400 to 3500, and even more preferably 500 to 3000. If the average degree of polymerization is too small, sufficient binding strength and sustained release may not be obtained when the tablet is made, and if the average degree of polymerization is too large, the mixing with the active ingredient and excipients may deteriorate, and the moldability may deteriorate. In the present invention, the average degree of polymerization is determined by a method according to JIS K6726.

[0029] The viscosity of a 4% by mass aqueous solution of the PVA resin powder at 20°C is preferably 1.5 to 100 mPa·s, more preferably 4 to 80 mPa·s, and even more preferably 5 to 70 mPa·s. If the viscosity of the 4% by mass aqueous solution is too high, the solvent used during production may cause gelation, resulting in poor mixability and poor moldability, whereas if the viscosity of the 4% by mass aqueous solution is too low, sufficient binding strength and sustained release properties may not be obtained. In the present invention, the viscosity of the 4% by mass aqueous solution at 20°C is a viscosity measured by a method conforming to JIS K6726.

[0030] The saponification degree of the PVA resin powder used in the present invention is preferably 70 to 100 mol%, more preferably 80 to 95 mol%, and even more preferably 85 to 90%. If the saponification degree is too low, sustained release properties cannot be maintained, and if the saponification degree is too high, the binding strength is insufficient and the powder may disintegrate immediately. In the present invention, the saponification degree is measured by a method in accordance with JIS K6726.

[0031] In the case of a typical PVA resin powder, the bonding mode of the main chain is mainly 1,3-diol bonds, and the content of 1,2-diol bonds is about 1.5 to 1.7 mol %, but it is also possible to use one in which the content is 1.7 to 3.5 mol % by increasing the polymerization temperature when polymerizing the vinyl ester monomer.

[0032] In the present invention, the 50% particle size of the PVA resin powder is preferably 50 to 2000 μm, more preferably 60 to 1500 μm, and further preferably 70 to 1000 μm. If the 50% particle size of the unmodified PVA powder is too small, it may be difficult to handle it during washing, pulverization, etc., while if it is too large, the efficiency of washing and pulverization may decrease. The 50% particle size is the diameter at which the integrated value (cumulative distribution) is 50% when the volume distribution by particle size is measured by laser diffraction.

[0033] The PVA resin powder of the present invention obtained as described above can be suitably used as an additive for pharmaceutical tablets, a pharmaceutical binder, or for cosmetics and food products. EXAMPLES

[0034] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention. In the examples, "parts" refer to parts by mass.

[0035] In the following examples, the degree of saponification and the viscosity of a 4% by mass aqueous solution were measured by a method in accordance with JIS K6726 as described below.

[0036] Example 1 [Preparation of PVA resin powder] A reactor equipped with a reflux condenser, a dropping funnel, and a stirrer was charged with 28 parts of vinyl acetate, 30 parts of methanol, and 0.06 mol% of acetyl peroxide (relative to the charged vinyl acetate), and the temperature was raised while stirring under a nitrogen stream to initiate polymerization. 0.4 hours after the start of polymerization, 72 parts of vinyl acetate were added at a constant rate over 9.5 hours. When the polymerization rate of vinyl acetate reached 92%, a specified amount of hydroquinone monomethyl ether was added to terminate the polymerization, and then the unreacted vinyl acetate monomer was removed from the system by distillation while blowing in methanol vapor, yielding a methanol solution of vinyl acetate polymer. Next, the above methanol solution was further diluted with methanol to adjust the concentration to 50% and charged into a kneader. While maintaining the solution temperature at 35°C, a 2% sodium content methanol solution of sodium hydroxide was added at a ratio of 6.0 mmol per mol of vinyl acetate structural unit in the polymer to perform saponification. As the saponification proceeded, the saponified product precipitated, and when it became granular, it was diluted with methanol, centrifuged, and dried to obtain a PVA-based resin dry powder.

[0037] The degree of saponification of the obtained solid, dried powder of PVA resin was analyzed based on the amount of alkali consumed for the hydrolysis of the remaining vinyl acetate and was found to be 88 mol %. The viscosity of a 4 mass % aqueous solution was 5.0 mPa s and the average degree of polymerization was 500.

[0038] [Cleaning PVA resin powder] The PVA resin powder obtained above was poured into methanol (at room temperature) having a bath ratio of 4 times, and washed by stirring for 2 hours, followed by solid-liquid separation. Further, methanol (at room temperature) was gradually added to the PVA resin powder, and the added methanol was brought into contact with the PVA resin powder and then subjected to solid-liquid separation by a rotary shaker. Next, fresh methanol was gradually added, and solid-liquid separation was performed by shaking off, and this process was repeated (a total of 6 times (by weight) of methanol was used as a bath ratio).

[0039] [Drying PVA resin powder] Next, the mixture was vacuum dried at 90° C. until the volatile content was reduced to 1% or less, to obtain the PVA resin powder of the present invention.

[0040] [Evaluation of PVA resin powder] The uniformity of the PVA-based resin powder was evaluated as follows. The obtained PVA resin powder was sieved and dissolved in water, and the sodium acetate content was determined according to JIS K 6726. The ratio of the sodium acetate content by particle size was calculated for the following particle size ranges. The results are shown in Table 1. ○: The content (weight%) of sodium acetate having a particle size of 500 to 1000 μm / a particle size of 100 to 300 μm is 0.9 to 1.1 ×: The content (wt%) of sodium acetate having a particle size of 500 to 1000 μm / a particle size of 100 to 300 μm is less than 0.9 or more than 1.1

[0041] Comparative Example 1 In the [Washing of PVA resin powder] of Example 1, the PVA resin powder was put into a 4-fold bath ratio of methanol (at room temperature), stirred and washed for 2 hours, and then solid-liquid separation was performed, and the resulting PVA powder was put into a 6-fold bath ratio of methanol (at room temperature), stirred and washed for 2 hours, but the sodium acetate content was measured in the same manner as in Example 1. The results are shown in Table 1.

[0042] Comparative Example 2 The sodium acetate content was measured in the same manner as in Example 1 [Washing of PVA-based resin powder], except that the PVA-based resin powder was washed by putting it into a 10-fold bath of methanol (at room temperature) and stirring for 3 hours. The results are shown in Table 1.

[0043] [Table 1]

[0044] The PVA resin powder of the present invention had a uniform distribution of sodium acetate, whereas Comparative Examples 1 and 2 had a non-uniform distribution of sodium acetate, with more sodium acetate present on the larger particle size side.

[0045] When the PVA resin powder of the present invention is used, even if the particle size distribution of the PVA resin powder is classified due to transportation or the like, there is no unevenness in the components and content of impurities adhering to or contained in the PVA resin powder, and the quality is stable. [Industrial Applicability]

[0046] When the PVA resin powder of the present invention is used, even if the particle size distribution of the PVA resin powder is classified due to transportation or the like, the components and contents of impurities adhering to or contained in the PVA resin powder do not become uneven, and the quality is stable. Therefore, the PVA resin powder is useful because it provides stable quality for small-sized molded products such as tablets and granules, and products to which a small amount of PVA resin is added, such as eye drops and ointments.

Claims

1. A polyvinyl alcohol-based resin powder having a volume distribution 50% particle size of 50 to 1000 μm as measured by laser diffraction, A polyvinyl alcohol-based resin powder characterized in that the sodium acetate content (wt%) of the polyvinyl alcohol-based resin having a particle size of 500 to 1000 μm / the sodium acetate content (wt%) of the polyvinyl alcohol-based resin having a particle size of 100 to 300 μm is 0.9 to 1.1, and the sodium acetate content of each of the polyvinyl alcohol-based resin having a particle size of 500 to 1000 μm and the polyvinyl alcohol-based resin having a particle size of 100 to 300 μm is 0.07 wt% or less.

2. 2. The polyvinyl alcohol-based resin powder according to claim 1, wherein the polyvinyl alcohol-based resin powder is an unmodified polyvinyl alcohol consisting only of vinyl alcohol structural units and vinyl ester structural units.

3. 3. The polyvinyl alcohol-based resin powder according to claim 1, wherein the polyvinyl alcohol-based resin powder has a degree of saponification of 80 to 95 mol %.

4. 4. The polyvinyl alcohol-based resin powder according to claim 1, wherein the polyvinyl alcohol-based resin powder has an average degree of polymerization of 200 to 4,000.

5. A pharmaceutical binder comprising the polyvinyl alcohol resin powder according to any one of claims 1 to 4.

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