Acetoacetyl group-containing polyvinyl alcohol resin, and method for producing the same

Abstract

The present invention provides a resin such as an acetoacetyl group-containing poly(vinyl alcohol)-based resin which has little variation in terms of acetoacetyl group content in different particle size ranges.　A powdered acetoacetyl group-containing poly(vinyl alcohol)-based resin is configured such that the distribution of acetoacetyl group content (highest acetoacetyl group content / lowest acetoacetyl group content) is less than 1.2 in the following particle size ranges: f less than 105 μm, not less than 105 μm but less than 177 μm, not less than 177 μm but less than 600 μm, and not less than 600 μm.

Description

[Technical Field]

[0001] The present invention relates to an acetoacetyl group-containing polyvinyl alcohol resin having a small variation in the content of structural units having an acetoacetyl group according to particle size range, and a method for producing the same. [Background technology]

[0002] Acetoacetyl group-containing polyvinyl alcohol resins, which are acetoacetylated polyvinyl alcohol resins, are known to have excellent water resistance due to their high reactivity with various crosslinking agents (hereinafter, "polyvinyl alcohol resin" may be referred to as "PVA," "acetoacetylated" as "AA-modified," and "acetoacetyl group-containing polyvinyl alcohol resin" as "AA-modified PVA").

[0003] In the past, from the viewpoint of improving the quality of AA PVA, such as its transparency and long-term stability, AA PVA has been proposed, which involves separating AA PVA according to particle size ranges, measuring the content of structural units having acetoacetyl groups for each particle size range (hereinafter, the "content of structural units having acetoacetyl groups" may be referred to as "acetoacetyl group content" or "degree of AA"), and then dividing the highest degree of AA by the lowest degree of AA to yield a value within a specific range (Patent Document 1).

[0004] Furthermore, as a method for producing the above-mentioned AA-PVA, a method has been proposed in which PVA, the swelling degree and elution rate of which have been adjusted to fall within a predetermined range, is swelled with acetic acid, and the swollen PVA is reacted with diketene to produce the desired AA-PVA (Patent Document 1).

[0005] Another method for producing AA-PVA has been proposed, for example, in which PVA is swollen with acetic acid and the swollen PVA is reacted with acetoacetic ester to produce the desired AA-PVA (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-110925 [Patent Document 2] U.S. Patent No. 5,719,231 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been a demand for higher quality AA PVA, and further improvements are required. For example, if the degree of AA in AA PVA varies among particle size ranges, differences in the temperature range at which it dissolves can occur, resulting in problems such as inconsistent uniformity. Also, if the degree of AA in AA PVA varies among particle size ranges, it can be difficult to obtain homogeneous AA PVA when it is separated by particle size during transportation. Therefore, improvements in this variation are required.

[0008] However, the AA PVA disclosed in Patent Documents 1 and 2 does not sufficiently suppress variations in the degree of AA polymerization among particle size ranges, and therefore cannot be said to be sufficiently homogeneous. Moreover, the AA PVA disclosed in Patent Documents 1 and 2 does not sufficiently reduce the amount of fine particles contained in the AA PVA, so there is room for improvement in terms of quality improvement.

[0009] That is, in the production method disclosed in Patent Document 1, in which PVA is swelled with acetic acid and the swollen PVA is reacted with diketene, the reaction rate is so fast that it is not possible to sufficiently suppress the variation in the degree of AA polymerization among particle size ranges, and it is not possible to obtain a sufficiently homogeneous AA PVA, nor is it possible to obtain an AA PVA in which the amount of fine particles is sufficiently reduced. Furthermore, methods using diketene, such as the production method disclosed in Patent Document 1, are highly dangerous due to the acute toxicity inherent to diketene, and there is room for improvement from the viewpoint of safety as well.

[0010] On the other hand, the method disclosed in Patent Document 2 is superior from the viewpoint of safety because it does not use diketene. However, even this method cannot sufficiently suppress the variation in the degree of AA polymerization among particle size ranges, and the reality is that it has not yet been possible to obtain AA PVA with a sufficiently uniform degree of AA polymerization or AA PVA with a sufficiently reduced amount of fine particles. [Means for solving the problem]

[0011] In view of the above circumstances, the present inventors have conducted extensive research and found that the above problems can be solved by an AA PVA in which the distribution of acetoacetyl group content for each particle size range is controlled to a specific range. They also found that the above problems can be solved by a method for producing AA PVA that includes a specific swelling step using acetoacetic ester, and the AA PVA obtained by this production method.

[0012] That is, a first gist of the present invention is a powdered acetoacetyl group-containing polyvinyl alcohol resin in which the distribution of acetoacetyl group contents (highest acetoacetyl group content / lowest acetoacetyl group content) for each particle size range of less than 105 μm, 105 μm or more but less than 177 μm, 177 μm or more but less than 600 μm, and 600 μm or more is less than 1.2.

[0013] A second aspect of the present invention is a powdered acetoacetyl group-containing polyvinyl alcohol resin, in which the content of particles having a particle diameter of less than 105 μm is 6% by weight or less of the total particles.

[0014] In the acetoacetyl group-containing polyvinyl alcohol resin of the first aspect, the content of particles having a particle size of less than 105 μm is preferably 6% by weight or less of the total particles.

[0015] A third gist of the present invention is a method for producing a powdered acetoacetyl group-containing polyvinyl alcohol-based resin, the method comprising the steps of swelling the polyvinyl alcohol-based resin with a solvent having an amide group and reacting the swollen polyvinyl alcohol-based resin with an acetoacetic ester.

[0016] A fourth aspect of the present invention is a method for producing a powdered acetoacetyl group-containing polyvinyl alcohol resin, the method comprising the steps of mixing the polyvinyl alcohol resin with a solvent and swelling the polyvinyl alcohol resin to a swelling index of more than 2.5, and reacting the swollen polyvinyl alcohol resin with an acetoacetic ester. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide AA PVA with no bias in the degree of AA polymerization among particle size ranges. Since such AA PVA has a small distribution of the degree of AA polymerization and is homogeneous regardless of particle size, it is expected that AA PVA of stable quality can be safely obtained.

[0018] Furthermore, according to the present invention, it is possible to provide AA PVA with a low content of fine particles, and therefore it is expected that AA PVA with stable quality can be obtained safely. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below. However, the following description is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not deviate from the gist of the present invention.

[0020] An AA PVA according to one embodiment of the present invention is a powdered AA PVA in which the distribution of acetoacetyl group contents (highest acetoacetyl group content / lowest acetoacetyl group content) for each particle size range of less than 105 μm, 105 μm or more but less than 177 μm, 177 μm or more but less than 600 μm, and 600 μm or more is less than 1.2.

[0021] An AA PVA according to another embodiment of the present invention is a powdered AA PVA in which the content of particles having a particle size of less than 105 μm is 6% by weight or less of the total particles.

[0022] (AA PVA) First, the AA-PVA of the present invention will be described. The AA-PVA of the present invention is a PVA obtained by saponifying a polyvinyl ester resin, which is a polymer of a vinyl ester monomer, and into which an acetoacetyl group (AA group) has been introduced, and is a PVA having an AA group in the side chain. The AA-PVA of the present invention has, for example, a structural unit represented by the following formula (1), and in addition to the structural unit having the AA group represented by formula (1), it also has a vinyl alcohol structural unit and a vinyl acetate structural unit, which is an unsaponified portion.

[0023] [ka]

[0024] Examples of the vinyl ester monomers used as raw materials 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 from the standpoint of economy.

[0025] Furthermore, although the vinyl ester monomer is usually used alone, it is also possible to use a saponified copolymer of the vinyl ester monomer with a copolymerizable monomer (comonomer). Examples of such a copolymerizable monomer include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxyl group-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. esters, nitriles such as acrylonitrile and methacrylonitrile; amides such as diacetone acrylamide, acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid and methallylsulfonic acid or salts thereof; vinyl compounds such as alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane and glycerin monoallyl ether; 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.

[0026] Further, examples of the copolymerizable monomer include polyoxyalkylene group-containing monomers such as polyoxyethylene (meth)acrylic ether, polyoxyethylene (meth)acrylamide, polyoxypropylene (meth)acrylamide, polyoxyethylene (meth)acrylate, polyoxypropylene (meth)acrylate, polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, and polyoxypropylene vinylamine, and N-acrylamide. Also included are cationic group-containing monomers such as methyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidopropyltrimethylammonium chloride, 2-acryloxyethyltrimethylammonium chloride, 2-methacryloxyethyltrimethylammonium chloride, 2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, 3-butenetrimethylammonium chloride, dimethyldiallylammonium chloride, and diethyldiallylammonium chloride. In the present invention, (meth)acrylic refers to acrylic or methacrylic, and (meth)acrylate refers to acrylate or methacrylate.

[0027] The amount of the copolymerizable monomer introduced is set appropriately depending on the type of monomer, but is usually 10 mol % or less, particularly 5 mol % or less. If the amount introduced is too large, water solubility and chemical resistance may be impaired, which is not preferable.

[0028] In addition, in the case of ordinary PVA, the main chain bonding mode 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 PVA with a content of 1.7 to 3.5 mol % by increasing the polymerization temperature when polymerizing vinyl ester monomers.

[0029] The content of structural units having AA groups in the AA-PVA (degree of AA conversion) is usually 0.1 to 20 mol%, more preferably 0.3 to 15 mol%, even more preferably 1 to 10 mol%, and particularly preferably 3 to 8 mol%. If the content of structural units having AA groups is too low, water resistance tends to decrease, while if the content is too high, the AA groups tend to react with each other to form crosslinked structures during long-term storage under high-temperature and high-humidity conditions, resulting in a decrease in water solubility.

[0030] The degree of AA can be determined by, for example, nuclear magnetic resonance spectroscopy. Specifically, the method is not limited to the following, but may be, for example, 1 It can be calculated from the ratio of the peak area derived from the acetoacetyl group appearing at 2.2 ppm in H-NMR to the peak area derived from the CH2 unit of PVA.

[0031] In the present invention, the distribution of acetoacetyl group content by particle size range (AA degree distribution) means the value obtained by dividing the highest AA degree by the lowest AA degree when measuring the AA degree of each AA PVA sorted according to particle size range (highest acetoacetyl group content / lowest acetoacetyl group content). In one embodiment of the present invention, the AA degree distribution is less than 1.2. Specifically, sieving is performed using sieves with openings of 105 μm, 177 μm, and 600 μm, and the AA degree distribution is calculated based on the AA degrees of each sieved AA-PVA. The value is less than 1.2, preferably less than 1.15, and more preferably less than 1.13. There is no particular restriction on the lower limit, but a value closer to 1 is preferable because the effects of the present invention can be obtained more effectively.

[0032] More specifically, the AA PVA has a first particle group consisting of particles with a particle size of less than 105 μm, a second particle group consisting of particles with a particle size of 105 μm or more and less than 177 μm, a third particle group consisting of particles with a particle size of 177 μm or more and less than 600 μm, and a fourth particle group consisting of particles with a particle size of 600 μm or more. The acetoacetyl group content (A 1) [mol %], the acetoacetyl group content of the second particle group (A 2 ) [mol %], the acetoacetyl group content of the third particle group (A 3 ) [mol %], and the acetoacetyl group content (A 4 ) [mol %], the lowest acetoacetyl group content (A L ) [mol %] to the highest acetoacetyl group content (A H ) [mol%] content ratio (A H / A L ) is less than 1.2 [A H / A L <1.2]. The particle group refers to an aggregate of multiple particles.

[0033] In addition, the acetoacetyl group content (A 1 ) [mol %] and the acetoacetyl group content (A 4 ) [mol %], the ratio of the relatively high acetoacetyl group content to the relatively low acetoacetyl group content (relatively high acetoacetyl group content / relatively low acetoacetyl group content) is preferably less than 1.15, more preferably less than 1.13, particularly preferably less than 1.1, and especially preferably less than 1.08. The lower limit is not particularly limited, but is 1.

[0034] In addition, the acetoacetyl group content (A 3 ) [mol %] and the acetoacetyl group content (A 4 ) [mol %], the ratio of the relatively high acetoacetyl group content to the relatively low acetoacetyl group content (relatively high acetoacetyl group content / relatively low acetoacetyl group content) is preferably less than 1.15, more preferably less than 1.13, particularly preferably less than 1.1, and especially preferably less than 1.08. The lower limit is not particularly limited, but is 1.

[0035] In the present invention, separation by particle size means sieving using sieves with mesh sizes of 105 μm, 177 μm, and 600 μm into the following: 105 μm pass; 177 μm pass and 105 μm on; 600 μm pass and 177 μm on; and 600 μm on.

[0036] The average particle size of the powdered AA PVA obtained by the present invention is usually 50 to 2000 μm, preferably 100 to 1700 μm, more preferably 200 to 1500 μm, and particularly preferably 400 to 1000 μm. If the average particle size is too small, the powder tends to become lumpy when dissolved, while if it is too large, it tends to take a long time to dissolve. The average particle size is the particle size at which the cumulative value of the powder particle size distribution calculated from the weight of each sieve is 50% by weight when powdered AA PVA is sieved using sieves with openings of 105 μm, 177 μm, and 600 μm, respectively: 105 μm pass; 177 μm pass and 105 μm on; 600 μm pass and 177 μm on; and 600 μm on.

[0037] In the AA PVA according to one embodiment of the present invention, the content of particles having a particle size of less than 105 μm is preferably 6% by weight or less, more preferably 5% by weight or less, and particularly preferably 3% by weight or less of the total particles. There is no particular lower limit, but the closer to 0% by weight it is, the better.

[0038] In another embodiment of the present invention, the AA PVA has a content of particles having a particle size of less than 105 μm of 6% by weight or less. That is, in the powdered AA PVA, the content of particles having a particle size of less than 105 μm is 6% by weight or less relative to the total content (100% by weight: total particles) of particles having a particle size of less than 105 μm and particles having a particle size of 105 μm or more. The content of particles having a particle size of less than 105 μm is preferably 5% by weight or less, more preferably 4% by weight or less. There is no particular lower limit, but the closer to 0% by weight it is, the better.

[0039] In another embodiment of the present invention, the content of particles having a particle size of less than 177 μm in the AA PVA is not particularly limited, but is preferably 18% by weight or less, more preferably 15% by weight or less, and particularly preferably 12% by weight or less. The lower limit is not particularly limited, but the closer to 0% by weight the better.

[0040] The degree of saponification of the AA PVA of the present invention is the same as the degree of saponification of the raw material PVA described below.

[0041] The average degree of polymerization of the AA PVA of the present invention (according to JIS K6726) is usually 300 to 4000, particularly preferably 400 to 2000, and further preferably 500 to 1500. If the average degree of polymerization is too low, the water resistance tends to decrease, and if it is too high, the viscosity tends to increase, making it difficult to handle.

[0042] (Manufacturing method of AA PVA) The method for producing the AA PVA of the present invention is not particularly limited, but from the viewpoint of obtaining an AA PVA with a low content of fine particles and an AA degree distribution in the preferred range as described above, a production method including a step of subjecting the raw material PVA (hereinafter sometimes referred to as "raw material PVA") in a swollen state to an ester exchange reaction with acetoacetic ester is preferred. Specifically, the method for producing the AA PVA of the present invention preferably comprises the steps of swelling the raw material PVA with a solvent, using acetoacetic ester as a substrate, and further carrying out an ester exchange reaction using a catalyst.

[0043] The saponification degree (according to JIS K6726) of the raw material PVA used in the present invention is usually 75 to 99.9 mol%, more preferably 80 to 99.5 mol%, and particularly preferably 85 to 99.3 mol%. If the saponification degree is too low, the solubility in water tends to decrease, which is undesirable.

[0044] The average degree of polymerization (according to JIS K6726) of the raw material PVA 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 low, water resistance tends to decrease, and if it is too high, viscosity tends to increase, making it difficult to handle.

[0045] The viscosity of a 4 wt % aqueous solution of the raw material PVA used in the present invention at 20°C (based on JIS K6726) is usually 1.5 to 100 mPa·s, preferably 4 to 80 mPa·s, and more preferably 5 to 70 mPa·s. If the viscosity of the 4 wt % aqueous solution is too high, the viscosity increases and tends to become difficult to handle, whereas if the viscosity of the 4 wt % aqueous solution is too low, the water resistance tends to decrease.

[0046] The solvent used in the step of swelling the starting PVA of the present invention is not particularly limited as long as it dissolves the acetoacetic ester used in the transesterification reaction with PVA and is capable of swelling the PVA. Examples include organic acids having at least one carboxy group and compounds having an amide group (solvents having an amide group). Specific examples include carboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid; lactam compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone (NMP), N-methyl-2-piperidone, N-methylcaprolactam, N-acetylpyrrolidine, and N-ethyl-2-pyrrolidone; urea derivatives such as 1,3-dimethyl-2-imidazolidinone (DMI), tetramethylurea, N,N-dimethylethyleneurea, and N,N'-dimethylpropyleneurea (DMPU); and amide compounds such as hexamethylphosphoramide, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N,N',N'-tetramethylmalonamide, N,N-diethylacetamide, N,N-dimethylpropionic acid amide, N,N-dimethylisobutylamide, and N-methylformamide. Among these, compounds having an amide group (solvents having an amide group) are preferred, more preferably 2-pyrrolidone, N-methyl-2-pyrrolidone, and N,N'-dimethylpropyleneurea, and particularly preferably N-methyl-2-pyrrolidone. These solvents can be used alone or in any combination and ratio of two or more.

[0047] The solvent is typically used in an amount of 10 to 300 parts by weight, preferably 40 to 250 parts by weight, and particularly preferably 70 to 200 parts by weight, per 100 parts by weight of the starting PVA. If the amount of solvent used is too large, the PVA tends to dissolve, requiring a reprecipitation step. If the amount of solvent used is too small, the PVA tends to swell insufficiently, resulting in a slower reaction rate and uneven reaction.

[0048] The swelling degree of the raw PVA is preferably evaluated by the volumetric swelling degree (the rate of increase in volume before and after swelling). For example, the swelling degree of the raw PVA is expressed as the volume ratio [(B) / (A)] of the volume of the PVA before swelling (A) to the volume of the PVA after swelling (B). More specifically, for example, 200 g of PVA with a known volume (A) is added to a reaction apparatus described below, followed by dropwise addition of 200 g of solvent (S), and the mixture is uniformly heated and stirred at 91°C for 1 hour. The volume (B) of the PVA is measured, and the swelling degree [(B) / (A)] is calculated. When N-methyl-2-pyrrolidone (NMP) is used as the solvent (S), the swelling degree [(B) / (A)] is 3.45, and when acetic acid is used as the solvent (S), the swelling degree [(B) / (A)] is 2.5. The method for measuring the volumes (A) and (B) is not particularly limited, but a measuring instrument such as a measuring cylinder can usually be used. Note that the swollen state means a state in which the swelling ratio [(B) / (A)] is greater than 1.0.

[0049] In the present invention, the swelling degree [(B) / (A)] in the step of swelling the starting PVA is preferably greater than 2.5 and less than 10, more preferably 2.8 to 7.5, and particularly preferably 3.0 to 5.0. If the swelling degree is too high, the PVA tends to dissolve, which is undesirable because a reprecipitation step is required. If the swelling degree is too low, the swelling degree of the PVA becomes insufficient, which tends to cause a decrease in the reaction rate and unevenness in the reaction, and also undesirably causes self-crosslinking between AA groups.

[0050] In the present invention, examples of acetoacetates used in the step of reacting swollen PVA with an acetoacetate include methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, s-butyl acetoacetate, t-butyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, stearyl acetoacetate, benzyl acetoacetate, and phenyl acetoacetate. The alkyl group of the acetoacetate preferably has 1 to 10 carbon atoms, more preferably 1 to 5. Among these, methyl acetoacetate and t-butyl acetoacetate are particularly preferred. These may be used alone or in any combination and ratio of two or more.

[0051] The acetoacetic ester is typically used in an amount of 0.1 to 100 parts by weight, preferably 0.5 to 85 parts by weight, and particularly preferably 1 to 75 parts by weight, per 100 parts by weight of the raw material PVA. If the amount of acetoacetic ester used is too large, it tends to inhibit the swelling of the PVA, causing a decrease in the reaction rate and unevenness of the reaction. If the amount is too small, the chemical equilibrium tends to shift toward the reactant, causing a decrease in the reaction rate.

[0052] In the present invention, the catalyst used in the step of reacting the swollen PVA with the acetoacetic ester is not particularly limited as long as it is a catalyst commonly used in transesterification reactions, such as a Brønsted organic acid, a Brønsted inorganic acid, a Lewis inorganic acid, a Lewis organic base, or a combination thereof. Specific examples of Bronsted organic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, benzoic acid, phthalic acid, gallic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, malic acid, citric acid, and aconitic acid; Bronsted inorganic acids include sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, and partial esters thereof; Lewis inorganic acids include sodium acetate, potassium acetate, magnesium acetate, calcium acetate, zinc acetate, lithium triflate, magnesium triflate, zinc triflate, ytterbium triflate, bisacetylacetonatozinc, tetrakisacetylacetonatozirconium, tin dioctylate, and tetrabutoxytitanium; and Lewis organic bases include primary amines, secondary amines, tertiary amines, pyridine, primary phosphines, secondary phosphines, and tertiary phosphines.

[0053] The catalyst is typically used in an amount of 0.01 parts by weight or more, preferably 0.05 parts by weight or more, and more preferably 0.1 parts by weight or more, per 100 parts by weight of the raw material PVA. If the amount of catalyst used is 0.01 parts by weight or less, the reaction tends to proceed slowly. Preferably, the amount used is 10 parts by weight or less, more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less. If the amount of catalyst used exceeds 10 parts by weight, it is economically disadvantageous and tends to make catalyst removal difficult, which is undesirable.

[0054] The reaction apparatus used in the transesterification reaction of the present invention is preferably a heatable apparatus equipped with a stirrer, and examples of such apparatus include kneaders, Henschel mixers, ribbon blenders, and various other blenders.

[0055] Furthermore, in the step of swelling the raw material PVA, the solvent may be added dropwise. The dropwise addition time is optional and depends on the reaction scale and the capacity of the cooling equipment, but the lower limit is preferably 0.1 hours or more, more preferably 0.5 hours or more, and particularly preferably 1.0 hour or more. If the dropwise addition time is 0.1 hours or more, the swelling of the PVA tends to be more uniform. The upper limit is preferably 6 hours or less, more preferably 3 hours or less, and particularly preferably 2 hours or less. A dropwise addition time of 6 hours or less is preferable from the viewpoint of productivity, and the application of excess heat can be suppressed.

[0056] Furthermore, the temperature at which the swollen PVA and acetoacetic acid ester are reacted in the above-mentioned reactor is not particularly limited, but the lower limit is preferably 60°C or higher, more preferably 70°C or higher, and particularly preferably 80°C or higher. A temperature of 60°C or higher tends to increase the reaction rate, which is preferable from the viewpoint of productivity. The upper limit is preferably 120°C or lower, more preferably 100°C or lower, and particularly preferably 95°C or lower. A temperature of 120°C or lower is preferable because it tends to more easily suppress self-crosslinking between AA groups.

[0057] Furthermore, in the present invention, in the step of reacting swollen PVA with acetoacetic acid ester, the acetoacetic acid ester may be added dropwise. The dropwise addition time of the acetoacetic acid ester is optional and depends on the reaction scale and the capacity of the cooling equipment, but the lower limit is preferably 0.5 hours or more, more preferably 1 hour or more, and particularly preferably 2.0 hours or more. A dropwise addition time of 0.5 hours or more is preferred because it allows the reaction to proceed while maintaining the swelling degree of the PVA. The upper limit is preferably 8 hours or less, more preferably 6 hours or less, and particularly preferably 5 hours or less. A dropwise addition time of 8 hours or less is preferred from the viewpoint of productivity.

[0058] The reaction time in the transesterification reaction step is not particularly limited, but the lower limit is preferably 1 hour or more, more preferably 2 hours or more, and the upper limit is preferably 10 hours or less, more preferably 6 hours or less.

[0059] After the transesterification reaction, the solvent is removed through a washing step in which washing is performed with a washing solvent of an alcohol having 1 to 3 carbon atoms, and a drying step. Specific examples of the alcohol having 1 to 3 carbon atoms used in the washing step include ethanol, methanol, and n-butyl alcohol. These may be used alone or in any combination and ratio of two or more. Among these, methanol is preferably used because it has a low boiling point and requires little energy for removal. The drying time in the drying step is selected appropriately taking into consideration the temperature and pressure conditions, the weight of the object to be treated, etc., but is usually preferably set within the range of 0.5 to 10 hours. The temperature of the drying treatment is also selected appropriately, but is usually preferably set within the range of 20 to 80°C.

[0060] The AA PVA of the present invention thus obtained can be used in a variety of applications, including, for example, the following applications (1) to (10).

[0061] (1) Molded products: Fibers, films, sheets, pipes, tubes, leak-proof membranes, temporary coatings, chemical lace, water-soluble fibers, etc. (2) Adhesives: Adhesives for wood, paper, aluminum foil, plastics, etc., pressure-sensitive adhesives, rewetting agents, binders for nonwoven fabrics, binders for various building materials such as gypsum board and fiberboard, binders for various powder granulations, additives for cement and mortar, hot-melt adhesives, pressure-sensitive adhesives, fixing agents for anionic paints, etc. (3) Coating agents: clear coating agents for paper, pigment coating agents for paper, internal sizing agents for paper, sizing agents for textile products, warp sizing agents, textile processing agents, leather finishing agents, paints, anti-fogging agents, metal corrosion inhibitors, brighteners for zinc plating, antistatic agents, conductive agents, temporary paints, etc. (4) Blending agents for hydrophobic resins: antistatic agents for hydrophobic resins, hydrophilic agents, additives for composite fibers, films and other molded products, etc. (5) Suspension and dispersion stabilizers: Pigment dispersion stabilizers for paints, ink, water-based colors, adhesives, etc.; dispersion stabilizers for suspension polymerization of various vinyl compounds such as vinyl chloride, vinylidene chloride, styrene, (meth)acrylate, and vinyl acetate. (6) Emulsion dispersion stabilizers: emulsifiers for emulsion polymerization of various acrylic monomers, ethylenically unsaturated compounds, butadiene compounds, post-emulsifiers for hydrophobic resins such as polyolefins and polyester resins, epoxy resins, paraffins, bitumen, etc. (7) Thickeners: Thickeners for various aqueous solutions, emulsions, and oil drilling fluids. (8) Flocculants: Flocculants for suspended and dissolved matter in water, drainage of pulp and slurry, etc. (9) Exchange resins, etc.: ion exchange resins, chelating exchange resins, ion exchange membranes, etc. (10) Others: soil conditioners, photosensitizers, photosensitive resist resins, etc. [Example]

[0062] The present invention will be described in more detail below with reference to examples and comparative examples. The following examples are presented to explain the present invention in detail, and the present invention is not limited to the following examples unless it is contrary to the spirit of the present invention. In the examples, "parts" means by weight. Example 1 200 parts of raw PVA (saponification degree 99.1 mol%, viscosity of 4 wt% aqueous solution at 20 °C 13.3 mPa·s, average degree of polymerization 1200) and 0.83 parts of sodium acetate as a reaction catalyst were charged into a kneader heated to 91 °C. 200 parts of N-methyl-2-pyrrolidone (NMP) were added dropwise over 1 hour while stirring at 20 rpm to swell the raw PVA (volume swelling degree 3.45). Subsequently, 142 parts of t-butyl acetoacetate (t-BAA) were added dropwise over 3 hours while maintaining the same rotation speed and temperature, and the reaction was continued for another 4 hours. After the reaction was completed, the mixture was washed with methanol and dried under vacuum at 40 °C for 3 hours to obtain powdered AA-PVA1 (average degree of polymerization 1200, AA degree 4.7 mol%, average particle size 437 μm).

[0063] (Comparative Example 1) 100 parts of raw PVA (saponification degree 99.1 mol%, viscosity of 4 wt% aqueous solution at 20 °C 13.3 mPa·s, average degree of polymerization 1200) and 0.83 parts of sodium acetate as a reaction catalyst were charged into a kneader heated to 91 °C. 30 parts of acetic acid were added and the raw PVA was swelled under stirring at 20 rpm (volume swelling degree 1.85). 5 parts of diketene were then added dropwise over 3 hours at 20 rpm and 60 °C, and the reaction was continued for another 1 hour. After the reaction was completed, the mixture was washed with methanol and dried under vacuum at 70 °C for 12 hours to obtain powdered AA-PVA2 (average degree of polymerization 1200, AA degree 5.2 mol%, average particle size 231 μm).

[0064] (Comparative Example 2) 200 parts of raw PVA (saponification degree 99.1 mol%, viscosity of 4 wt% aqueous solution at 20°C 13.3 mPa·s, average degree of polymerization 1200) and 0.83 parts of sodium acetate as a reaction catalyst were charged into a kneader heated to 91°C. 200 parts of acetic acid were added and the raw PVA was swollen (volume swelling degree 2.5) under stirring at 20 rpm. 142 parts of t-butyl acetoacetate were then added dropwise over 3 hours at 20 rpm and 91°C, and the reaction was continued for an additional 4 hours. After the reaction was completed, the mixture was washed with methanol and dried under vacuum at 40°C for 3 hours to obtain powdered AA-PVA3 (average degree of polymerization 1200, AA degree 2.7 mol%, average particle size 306 μm).

[0065] (Separation method) AA-PVA1 was fractionated by particle size range using sieves with mesh sizes of 105 μm, 177 μm, and 600 μm as specified in JIS Z8815. Specifically, AA-PVA1 was fractionated using these sieves into AA-PVA consisting of particles with a particle size of less than 105 μm, AA-PVA consisting of particles with a particle size of 105 μm or more but less than 177 μm, AA-PVA consisting of particles with a particle size of 177 μm or more but less than 600 μm, and AA-PVA consisting of particles with a particle size of 600 μm or more. AA-PVA2 and 3 were fractionated in the same manner.

[0066] (AA degree measurement by particle size range) The degree of AA of each AA-PVA fractionated according to particle size range was measured using a Bruker Ascend 400 (400 MHz), AVANCE III 400, Cryo-probe nuclear magnetic resonance spectrometer. Specifically, each AA-PVA was dissolved in DMSO-d6 (dimethyl sulfoxide-D6) (concentration 4%) and measured at 50°C for 16 cycles. 1 The degree of AA was calculated from the ratio of the peak area of ​​the acetoacetyl group at 2.2 ppm in H-NMR to the peak area of ​​the PVA CH2 unit, and the AA degree distribution was calculated from the calculated degree of AA. The results are shown in Table 1.

[0067] (Measurement of average particle size) The powder was sieved using sieves with openings of 105 μm, 177 μm, and 600 μm, with the following sieves: 105 μm pass; 177 μm pass and 105 μm on; 600 μm pass and 177 μm on; and 600 μm on. The particle size at which the cumulative value of the powder particle size distribution calculated from the weight of each sieve was 50% by weight was determined using exponential approximation to calculate the average particle size.

[0068] As shown in Table 1, in Example 1, the AA degree of the AA PVA fractionated to a particle size of less than 105 μm was the highest, and the AA degree of the AA PVA fractionated to a particle size of 177 μm or more and less than 600 μm was the lowest, and the AA degree distribution was 1.09. On the other hand, in Comparative Example 1, the AA degree of the AA PVA fractionated to particle sizes less than 105 μm was the highest, and the AA degree of the AA PVA fractionated to particle sizes 600 μm or more was the lowest, and the AA degree distribution was 1.53. In addition, in Comparative Example 2, the AA degree of the AA PVA fractionated to particle sizes less than 105 μm was the highest, and the AA degree of the AA PVA fractionated to particle sizes 600 μm or more was the lowest, and the AA degree distribution was 1.4.

[0069] [Table 1]

[0070] The weight of the AA PVA for each particle size range was measured, and the particle size distribution (wt%) was calculated by taking the total weight of each particle size range as 100 wt%. The results are shown in Table 2.

[0071] [Table 2]

[0072] As shown in Table 2, in Example 1, the content of particles separated into particles with a particle size of less than 105 μm was sufficiently reduced, whereas in Comparative Examples 1 and 2, the content of particles separated into particles with a particle size of less than 105 μm was not sufficiently reduced.

[0073] According to the present invention, AA PVA can be safely produced without using diketene, and AA PVA produced using acetoacetic ester has a uniform AA degree distribution according to particle size range, so that AA PVA of stable quality can be obtained.

[0074] According to the present invention, AA PVA can be safely produced by not using diketene, and AA PVA produced using acetoacetic ester has a low content of fine particles less than 105 μm, so that AA PVA of excellent quality can be obtained.

[0075] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

Claims

1. The powdered acetoacetyl group-containing polyvinyl alcohol resin has an acetoacetyl group content distribution (highest acetoacetyl group content / lowest acetoacetyl group content) of less than 1.2 for each particle size range of less than 105 μm in particle size, between 105 μm and 177 μm in particle size, between 177 μm and 600 μm in particle size, and at least 600 μm in particle size, and the content of particles less than 105 μm in particle size is 6 wt % or less of the total particles, and the amount of monomer copolymerizable with vinyl ester monomers introduced is 5 mol % or less of the acetoacetyl group-containing polyvinyl alcohol resin.

2. 2. A method for producing the powdered acetoacetyl group-containing polyvinyl alcohol resin according to claim 1, comprising the steps of: swelling the polyvinyl alcohol resin with a solvent having an amide group; and reacting the swollen polyvinyl alcohol resin with an acetoacetic ester.

3. 2. A method for producing the powdered acetoacetyl group-containing polyvinyl alcohol resin according to claim 1, comprising the steps of: mixing the polyvinyl alcohol resin with a solvent to swell the polyvinyl alcohol resin to a swelling degree of greater than 2.5; and reacting the swollen polyvinyl alcohol resin with an acetoacetic ester.

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