Polyvinyl alcohol-based resin

Abstract

The present invention provides a polyvinyl alcohol-based resin which can control the particle size when made into a polyvinyl acetal resin, prevent the formation of lumps during dissolution, and achieve excellent solubility. The present invention relates to a polyvinyl alcohol-based resin having a methyl acetate content of 0.05 to 3% by weight, a vinyl alcohol unit content of 80 to 99.5 mol%, and an average chain length L A of the vinyl acetate unit is 1 to 4.5, and the average chain length L O of the vinyl alcohol unit is 1 to 30.

Description

Technical Field

[0001] The present invention relates to a polyvinyl alcohol-based resin. Background Art

[0002] Polyvinyl alcohol is a resin used as a raw material for polyvinyl acetal resin. By subjecting it to an acetalization reaction to form a polyvinyl acetal resin, excellent toughness, adhesiveness, crosslinkability, and hygroscopicity can be exhibited (Patent Document 1, Non-Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2019 / 098247

[0006] Non-Patent Documents

[0007] Non-Patent Document 1: Proceedings of the Polymer Society, Vol. 65, No. 1 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Generally, polyvinyl alcohol is produced by saponifying polyvinyl acetate dissolved in methanol with sodium hydroxide or sodium methoxide. However, the polyvinyl alcohol obtained by the conventional method has poor solubility in solvents, and particularly when used in an aqueous solvent, there is a problem that the desired effect cannot be obtained.

[0010] For example, when using an ethylene alcohol-vinyl acetate copolymer produced by the methods described in Patent Document 1 and Non-Patent Document 1 to produce a polyvinyl acetal resin, although the solubility of the polyvinyl alcohol improves, the shape of the resin particles obtained in the case of producing the polyvinyl acetal resin sometimes deforms. Therefore, agglomeration occurs during dissolution, resulting in problems such as a prolonged dissolution time.

[0011] An object of the present invention is to provide a polyvinyl alcohol-based resin that can control the particle size when forming a polyvinyl acetal resin, prevent the generation of agglomeration during dissolution, and achieve excellent solubility.

[0012] Means for Solving the Problems

[0013] The present invention is a polyvinyl alcohol-based resin, wherein the content of methyl acetate is 0.05 to 3% by weight, the content of vinyl alcohol units is 80 to 99.5 mol%, and the average chain length L of vinyl acetate units A is 1 to 4.5, and the average chain length L of vinyl alcohol units O is 1 to 30.

[0014] Hereinafter, the present invention will be described in detail.

[0015] The polyvinyl alcohol-based resin of the present invention has vinyl acetate units (units formed from vinyl acetate) and vinyl alcohol units (units formed from vinyl alcohol).

[0016] In the present invention, the "vinyl alcohol unit" and the "vinyl acetate unit" refer to "vinyl alcohol" and "vinyl acetate" present in the polyvinyl alcohol-based resin.

[0017] The lower limit of the content of methyl acetate in the polyvinyl alcohol-based resin of the present invention is 0.05% by weight, and the upper limit is 3% by weight. By setting it within such a range, when a polyvinyl acetal resin is produced using the polyvinyl alcohol-based resin of the present invention, the particle shape becomes uniform. A more preferable lower limit is 0.06% by weight, a more preferable upper limit is 2% by weight or less, and a further more preferable upper limit is 1.5% by weight or less.

[0018] As a method for measuring the content of methyl acetate contained in the above polyvinyl alcohol-based resin, there is no particular limitation. For example, GC-2010 (manufactured by Shimadzu Corporation) can be used, and using an INNOWAX polar column and a detector FID, a solution prepared by dissolving the obtained polyvinyl alcohol-based resin in dimethyl sulfoxide is measured.

[0019] The lower limit of the content of vinyl alcohol units in the polyvinyl alcohol-based resin of the present invention is 80 mol%, and the upper limit is 99.5 mol%. By setting it within such a range, the function of the hydroxyl group possessed by vinyl alcohol can be imparted to the molecules of the polyvinyl alcohol-based resin, and the solubility in water and solvents can be controlled. If the content of vinyl alcohol units is within the above range, the solubility can be improved in the step of dissolving the polyvinyl alcohol-based resin in an aqueous solution for acetalization. The preferable lower limit of the content of vinyl alcohol units in the polyvinyl alcohol-based resin is 86.0 mol%, and the preferable upper limit is 99.3 mol%. It should be noted that the content of vinyl acetate units and the content of vinyl alcohol units can be measured according to JIS K 6726 Polyvinyl Alcohol Test Method.

[0020] It should be noted that the content of vinyl acetate units in the polyvinyl alcohol-based resin of the present invention is preferably 0.5 to 20 mol%, more preferably 0.5 to 18 mol%, and still more preferably 0.5 to 15 mol%.

[0021] The average chain length L of vinyl acetate units in the polyvinyl alcohol-based resin of the present invention A is 1 to 4.5. By setting the average chain length L of vinyl acetate units A within the above range, the solubility in solvents can be improved. L A is preferably 4 or less, more preferably 3.6 or less, and still more preferably 3.0 or less.

[0022] It should be noted that, in this specification, the average chain length L of the vinyl acetate unit is A " can be calculated using the following formula (1).

[0023] [Mathematical formula 1]

[0024]

[0025] In formula (1), I represents 1 Intensities obtained by H-NMR. In addition, "AAA, AAO, OAO, AOA, AOO, OOO" are as follows.

[0026] First, the polyvinyl alcohol-based resin of the present invention is divided into three chains (Japanese: three chains) (triads) having vinyl alcohol units (hereinafter also abbreviated as O) and / or vinyl acetate units (hereinafter also abbreviated as A). Then, the "three chains centered on vinyl alcohol" are classified as "AOA, AOO, OOO", and the "three chains centered on vinyl acetate" are classified as "AAA, AAO, OAO". Among them, "AOO" and "OOA" are collectively referred to as "AOO", and "AAO" and "OAA" are collectively referred to as "AAO". That is, "I OOO "express" 1 The intensity of OOO measured by H-NMR".

[0027] The average chain length L of the vinyl alcohol unit of the polyvinyl alcohol resin of the present invention is O 1 to 30. By setting the ratio within the above range, the water solubility of the polyvinyl alcohol-based resin is controlled, thereby controlling the particle size when producing the polyvinyl acetal, preventing the occurrence of agglomerates during dissolution, and obtaining excellent solubility.

[0028] It should be noted that, in this specification, the average chain length of the vinyl alcohol unit is L O " can be calculated using the following formula (2). O It is preferably 1 or more, more preferably 3 or more, and even more preferably 7 or more.

[0029] In formula (2), I represents 1 The intensity obtained by H-NMR. OOO " means "through 1 The intensity of OOO measured by H-NMR".

[0030] [Mathematical formula 2]

[0031]

[0032] The polyvinyl alcohol resin of the present invention preferably has an average chain length L of vinyl alcohol units. OGreater than the average chain length L of vinyl acetate units A . In addition, the average chain length L of vinyl acetate units A and the average chain length L of vinyl alcohol units O The sum (L A + L O ) is preferably 2 to 30.

[0033] Preferably, the polyvinyl alcohol-based resin of the present invention is such that, based on the average chain length L O of vinyl alcohol units and the average chain length L A of vinyl acetate units, the randomness value ρ (average persistence ratio, represented by R in the following formula (3)) obtained using the following formula (3) is 0.35 to 1. By setting the randomness value ρ (average persistence ratio) within the above range, the formation of lumps in the polyvinyl acetal resin after acetalization can be suppressed, and a polyvinyl alcohol resin with excellent solubility can be produced.

[0034] The above randomness value ρ serves as a criterion for confirming whether the entire polymer chain is a block structure or a random structure. When the randomness value ρ is 0, it can be said that the entire polymer chain is a block structure, and when the randomness value ρ is 1, it can be said that the entire polymer chain is a random structure.

[0035] In addition, when the randomness value ρ is 2, it can be said that the vinyl alcohol units and vinyl acetate units coexist alternately in one molecule.

[0036] The preferred upper limit of the above randomness value ρ is 0.95, more preferably 0.9 or less. The preferred lower limit is 0.4, more preferably 0.45, and even more preferably 0.5 or more. By setting it within this range, the formation of lumps in the polyvinyl acetal resin after acetalization is suppressed, and the solubility is improved.

[0037] [Mathematical formula 3]

[0038]

[0039] Preferably, the degree of polymerization (viscosity-average degree of polymerization) of the polyvinyl alcohol-based resin of the present invention is 1000 to 4000. By setting it within the above range, good physical properties of the film can be exhibited.

[0040] The degree of polymerization can be measured according to JIS K 6726 Polyvinyl Alcohol Test Methods.

[0041] In addition, the melting point of the polyvinyl alcohol-based resin of the present invention is preferably 30 to 240 °C. It should be noted that the above melting point can be measured using a differential scanning calorimeter.

[0042] The polyvinyl alcohol-based resin of the present invention may also have units formed from other monomers.

[0043] The above-mentioned other monomers are not particularly limited, and are preferably monomers having at least one functional group selected from carboxyl group, hydroxyl group, amide group, amino group, epoxy group, and ether group and one olefinic double bond in the molecule. Examples of such monomers include crotonic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, allyl alcohol, vinyl ether, allylamine, etc.

[0044] These functional groups can be introduced by copolymerization during the polymerization of vinyl acetate, or can be introduced after saponification to form polyvinyl alcohol.

[0045] The content of the units formed by other monomers contained in the polyvinyl alcohol-based resin of the present invention is designed according to the use, and thus is not particularly limited. It is preferably 20 mol% or less, more preferably 10 mol% or less, further preferably 5 mol% or less, and usually 0 mol% or more, for example, 1 mol% or more, relative to the entire polyvinyl alcohol-based resin.

[0046] There is no particular limitation on the shape of the polyvinyl alcohol-based resin, and a particle shape or a powder shape is preferred.

[0047] As a method for producing the polyvinyl alcohol-based resin of the present invention, there is no particular limitation. For example, it can be obtained by polymerizing vinyl acetate by solution polymerization method, bulk polymerization method, suspension polymerization method, emulsion polymerization method, etc. to obtain polyvinyl acetate, and then saponifying, that is, hydrolyzing the polyvinyl acetate.

[0048] As the temperature during the polymerization of the above polyvinyl acetate, there is no particular limitation, and it is preferably 0 to 180 °C, more preferably 20 to 120 °C, and further preferably 40 to 90 °C.

[0049] Regarding the measurement of the degree of polymerization of the above polyvinyl acetate, it can be measured according to the polyvinyl alcohol test method of JIS K 6726 after saponification.

[0050] The catalyst for the above saponification usually uses an alkali or an acid, and an alkali is particularly preferably used.

[0051] As the above alkali (saponification catalyst), a compound having an alkali metal, especially a compound having a sodium atom or a potassium atom, is particularly preferred. Examples of the compound having a sodium atom include sodium hydroxide, sodium methoxide, etc.

[0052] Examples of the compound having a potassium atom include potassium tert-butoxide (BuOK), etc.

[0053] In addition, as the above alkali, tetrabutylammonium hydroxide (TBAH) is preferably used.

[0054] Among them, BuOK and TBAH are more preferably used.

[0055] It should be noted that the above-mentioned alkali addition amount is preferably 0.001 to 0.5 mol, more preferably 0.002 to 0.4 mol, and still more preferably 0.003 to 0.2 mol, based on the molar ratio relative to the vinyl acetate units in the vinyl acetate polymer.

[0056] As the solvent used in the above saponification, methanol or a mixed solvent containing methanol and water is preferably used.

[0057] When saponifying polyvinyl acetate, the concentration of the polyvinyl acetate solution (after alkali addition) is preferably 3 to 40% by weight, more preferably 5 to 35% by weight, still more preferably 8 to 30% by weight, and even more preferably 10 to 25% by weight. If the concentration of the polyvinyl acetate solution during saponification is within this range, it is easy to control the average chain length L of the vinyl acetate units A and the average chain length L of the vinyl alcohol units O , and thus the formation of agglomerates of the polyvinyl alcohol acetal resin after acetalization is inhibited.

[0058] When using sodium methoxide or potassium tert-butoxide as the above-mentioned alkali, the solvent used in the saponification is preferably methanol.

[0059] When using sodium hydroxide as the above-mentioned alkali, the solvent used in the saponification is preferably a mixed solvent of methanol and water. It should be noted that the content ratio of methanol to water in the above-mentioned mixed solvent is preferably methanol / water = 99 / 1 to 70 / 30 by weight. The upper limit of the weight ratio of methanol is preferably 95% by weight or less, and more preferably 90% by weight or less.

[0060] It should be noted that the above-mentioned solvent may contain alcohols such as ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene.

[0061] As the reaction temperature in the above saponification (the temperature at which alkali is added to the polyvinyl acetate solution for reaction), there is no particular limitation, and it can be selected from the range of 0 to 100 °C. It is preferably 5 to 50 °C, more preferably 10 to 48 °C, and even more preferably 15 to 45 °C. By setting it within this range, it is easy to control the average chain length L of the vinyl acetate units A and the average chain length L of the vinyl alcohol units O . Therefore, the formation of agglomerates of the polyvinyl alcohol acetal resin after acetalization is inhibited.

[0062] In addition, the saponification time (the time from the addition of the base to the polyvinyl acetate solution until the reaction ends) is preferably 15 to 170 minutes. More preferably, it is 20 to 150 minutes, and even more preferably, it is 25 minutes to 130 minutes. If the saponification time is above the above lower limit, the compositional distribution of polyvinyl alcohol can be suppressed from broadening. On the other hand, if the saponification time is below the above upper limit, the generation of highly saponified portions can be suppressed, and the generation of insoluble resins when dissolved in the solvent can be suppressed.

[0063] In addition, after performing the above saponification, a cleaning step is preferably provided.

[0064] The above cleaning step is a step of cleaning polyvinyl alcohol with a mixed cleaning liquid. The mixed cleaning liquid here contains, for example, methanol, water, acetic acid, etc. It is preferably to change the ratio of methanol and other solvents according to the saponification degree and the values of L A and L O Moreover, the above cleaning step is preferably performed more than twice, and the ratio of the cleaning liquid can be changed after the first and second times. The solid content concentration of polyvinyl alcohol in the cleaning step is not particularly limited, and is preferably 1 to 25% by weight. In addition, the amount of the solvent in the above cleaning step is preferably set to 1 times or more, more preferably 2 times or more, of the object to be cleaned.

[0065] A drying step can be provided as needed after the cleaning step. The temperature and time in the drying step are not particularly limited, and are preferably 30 to 150 °C, 1 to 24 hours, and more preferably 40 to 120 °C, 1.5 to 10 hours. In addition, the number of drying times in the drying step is preferably 2 times or more, and more preferably 3 times or more. By drying under such conditions, it is easy to control the methyl acetate content.

[0066] Various physical properties of the polyvinyl alcohol-based resin of the present invention can be controlled by the degree of polymerization, concentration of the polyvinyl acetate used as a raw material, temperature and time of the saponification reaction, type of base used in saponification, base concentration, type of solvent, addition amount, cleaning degree of the cleaning step, operations in the drying step, etc. In particular, after performing the above saponification, it can be controlled by changing the time and temperature of immersing the pulverized gel in the cleaning liquid, increasing the number of cleaning times, increasing the amount of the solvent used in cleaning, changing the drying temperature and drying time after cleaning, etc. By the method as described above, for example, the content of methyl acetate generated as a by-product during the saponification of polyvinyl acetate can be controlled.

[0067] In addition, after performing the above saponification, a cleaning step and a drying step are performed, and methyl acetate is further added, whereby various physical properties of the polyvinyl alcohol-based resin of the present invention can also be controlled. The timing of adding the above methyl acetate is preferably after the cleaning step and the drying step have been performed.

[0068] At this time, the addition amount of the above methyl acetate is preferably 0.05 to 3% by weight based on the polyvinyl alcohol resin.

[0069] The polyvinyl alcohol resin of the present invention can be used, for example, in applications such as viscosity regulators for aqueous solutions, gas barrier coating agents, suspending agents, emulsifying agents, polarizing plates, water-soluble films, dispersing agents, and raw materials for various resins. It can also be used in the form of a polyvinyl alcohol resin composition containing the polyvinyl alcohol resin of the present invention.

[0070] In addition, when the polyvinyl alcohol acetal resin is produced using the polyvinyl alcohol resin of the present invention, the particle size of the obtained resin particles becomes uniform, the generation of agglomeration during dissolution in a solvent can be prevented, and the dissolution time can be shortened.

[0071] Advantages of the Invention

[0072] According to the present invention, a polyvinyl alcohol resin can be obtained that can control the particle size when forming a polyvinyl alcohol acetal resin, prevent the generation of agglomeration during dissolution, and achieve excellent solubility. Detailed Embodiments

[0073] Hereinafter, examples are given to more specifically illustrate the embodiments of the present invention, but the present invention is not limited to these examples.

[0074] (Example 1)

[0075] Methanol was added to a polyvinyl acetate copolymer having a viscosity-average degree of polymerization of 1000 as a raw material and stirred to dissolve, to prepare a polyvinyl acetate solution (saponification raw material solution, polyvinyl acetate concentration: 20% by weight). After adding a methanol solution (concentration: 3%) of potassium tert-butoxide (BuOK) as a saponification catalyst (alkali) solution so that the molar ratio of the alkali to the vinyl acetate unit in the above polyvinyl acetate copolymer became 0.0035 (the concentration of the polyvinyl acetate solution after alkali addition was 19.4% by weight), stirring was carried out to obtain a mixture. The obtained mixture was maintained at 40°C for 120 minutes to carry out a saponification reaction.

[0076] The gel obtained by the saponification reaction was pulverized, immersed in a cleaning liquid containing methanol and acetic acid at 40°C for 1 hour, and then dewatered using a centrifugal dewatering machine. The obtained pulverized gel was immersed again in a methanol cleaning liquid, and then most of the liquid was removed using a centrifuge, dried at 100°C for 1 hour, then dried at 80°C for 1 hour, and then dried at 40°C for 15 hours. It should be noted that the amount of the cleaning liquid was set to 2 times the amount of the pulverized gel after dewatering.

[0077] In addition, the obtained product was put into a glass bottle, and 0.06% by weight of methyl acetate was added relative to the obtained product, and then mixed with a mixing rotor in the glass bottle for 1 hour, thereby obtaining the target product (polyvinyl alcohol-based resin). The viscosity-average degree of polymerization of the obtained polyvinyl alcohol-based resin was 1000, the content of vinyl acetate units was 13.2 mol%, the average chain length L A of vinyl acetate units was 2.01, the content of vinyl alcohol units was 86.8 mol%, and the average chain length L O of vinyl alcohol units was 8.8, and the content of methyl acetate was 0.06% by weight.

[0078] (Examples 2 to 8, Comparative Example 2)

[0079] The degree of polymerization of polyvinyl acetate as the raw material, the concentration of the polyvinyl acetate solution, the type of solvent, the type of saponification catalyst, the addition amount, the saponification temperature, the saponification time, and the addition amount of methyl acetate were changed as shown in Table 1. Except for this, the operation was the same as in Example 1, and a polyvinyl alcohol-based resin was produced.

[0080] "TBAH" in Table 1 is "tetrabutylammonium hydroxide".

[0081] (Comparative Example 1)

[0082] After the reaction was stopped, only washing was carried out, and no methyl acetate was added. Except for this, the operation was the same as in Example 1, and a polyvinyl alcohol-based resin was produced.

[0083] (Comparative Examples 3 and 4)

[0084] The degree of polymerization of polyvinyl acetate as the raw material, the concentration of the polyvinyl acetate solution, the type of saponification catalyst, and the addition amount were changed as shown in Table 1. Then, after the reaction was stopped, it was impregnated in a cleaning liquid containing methanol at 25°C for 1 hour, dewatered using a centrifugal dewatering machine, and after most of the dewatering using a centrifuge, it was dried at 105°C for 3 hours. After drying, no methyl acetate was added. Except for this, a polyvinyl alcohol-based resin was produced in the same manner as in Example 1.

[0085] (Evaluation method)

[0086] The polyvinyl alcohol-based resin obtained above was evaluated by the following method. The results are shown in Table 1.

[0087] (1-1) Average chain lengths (L A , L O ) of vinyl acetate units and vinyl alcohol units

[0088] By subjecting the obtained polyvinyl alcohol-based resin to 1H-NMR measurement was carried out to determine the composition ratio (vinyl acetate unit content, vinyl alcohol unit content) of the polyvinyl alcohol-based resin. It should be noted that in 1 the H-NMR measurement, JEOL JNM-ECX500 was used, and the measurement was carried out at 150 °C using a DMSO-d6 solution (1 wt / vol%). In the analysis, the presaturation method was used to make the peak of water disappear. By using the presaturation method, the peak from the hydroxyl group disappeared, and the analysis accuracy could be improved. In the analysis of the triple chain using NMR, the NMR analysis software DELTA V re.5 manufactured by JEOL RESONANCE was used.

[0089] In addition, the triple-chain content ratios of the triple chains centered on vinyl alcohol (AOA, AOO, OOO) and the triple chains centered on vinyl acetate (AAA, AAO, OAO) were calculated from the area values obtained by fitting the peaks in three forms for each chain. The assignment of each peak referred to the literature (Macromolecules 1982, 15, 1071). It should be noted that the peak may be split at the front due to the influence of the three-dimensional structure, etc., but it was regarded as one peak for fitting.

[0090] It should be noted that "AOO" and "OOA" were collectively set as "AOO", and "AAO" and "OAA" were collectively set as "AAO".

[0091] In addition, the average chain lengths (L A , L O ) of the vinyl acetate unit and the vinyl alcohol unit were calculated.

[0092] In addition, the randomness value ρ was calculated based on L A , L O .

[0093] (1-2) Methyl acetate content determination

[0094] To about 10 mg of the obtained polyvinyl alcohol-based resin, 2 ml of dimethyl sulfoxide was added, and it was heated and dissolved on a hot plate at 70 °C. The prepared solution was filtered through a 0.2 μm filter, and then using GC-2010 (manufactured by Shimadzu Corporation), 1.0 μL was injected for measurement under the conditions of an INNOWAX polar column, a helium flow rate of 1 ml / min, a column temperature of 50 °C → 250 °C, and an FID detector.

[0095] (2) Shape of polyvinyl butyral resin particles

[0096] (2-1) Preparation of polyvinyl acetal resin particles (polyvinyl butyral resin particles)

[0097] To 250 g of the obtained polyvinyl alcohol resin, 2700 g of pure water was added, and it was stirred at 90 °C for about 2 hours to dissolve it. The solution was cooled to 40 °C, and after adding 100 g of hydrochloric acid with a concentration of 35% by weight and 115 g of butyraldehyde thereto in stages, the liquid temperature was maintained at 40 °C for 3 hours to carry out an acetalization reaction, and neutralization and washing were carried out by a conventional method to obtain polyvinyl butyral resin particles.

[0098] (2-2) Shape evaluation

[0099] The shape of the obtained polyvinyl butyral resin particles was visually observed and evaluated according to the following criteria.

[0100] ○: The shapes are consistent

[0101] △: Resin particles containing deformed shapes

[0102] ×: The shapes are inconsistent or cannot be evaluated

[0103] (2-3) Solubility evaluation

[0104] 10 g of the obtained polyvinyl butyral resin was added to 100 g of a mixed solvent of ethanol and toluene (weight mixing ratio 1:1), shaken at room temperature for 2 hours and then left to stand, and observed visually. The case where there was no resin undissolved in the solvent was evaluated as "○", the case where a little resin undissolved in the solvent was observed was evaluated as "△", and the case where there was a large amount of resin undissolved in the solvent was evaluated as "×".

[0105] (2-4) Evaluation of the amount of undissolved resin

[0106] The polyvinyl butyral resin prepared using the polyvinyl alcohol resin obtained in Example 8 and Comparative Example 4 was dissolved such that the ethanol-toluene mixed solution with a weight ratio of 1:1 became 0.2% by weight. The particle size distribution of 10 ml of the obtained solution was measured using a particle counter (manufactured by RION Co., Ltd., KS-42C), and the number of particles with a diameter of 0.5 to 1.0 μm per 1 ml was measured. As a result, it was 10,000 or less in Example 8, whereas it was more than 10,000 in Comparative Example 4.

[0107] From this result, it was found that a polyvinyl butyral resin containing the polyvinyl alcohol resin of Example 8 could produce a solution in a state where there were extremely few minute undissolved resin particles.

[0108] [Table 1]

[0109]

[0110] Industrial availability

[0111] According to the present invention, it is possible to provide a polyvinyl alcohol-based resin that can control the particle size when producing a polyvinyl acetal resin, prevent the generation of agglomeration during dissolution, and achieve excellent solubility.

Claims

1. A polyvinyl alcohol-based resin, wherein, The content of methyl acetate is 0.05% by weight to 3% by weight, the content of vinyl alcohol units is 80 mol% to 99.5 mol%, and the average chain length L of vinyl acetate units represented by the following formula (1) A is 1 to 4.5, and the average chain length L of vinyl alcohol units represented by the following formula (2) O is 1 to 30, and the randomness value ρ represented by R in the following formula (3) is 0.5 or more and 0.9 or less. In the formula (1) and the formula (2), I represents the intensity obtained by 1 1H-NMR. In addition, with respect to "AOA, AOO, OOO, AAA, AAO, OAO", the polyvinyl alcohol-based resin is divided into three chains, i.e., three-unit groups, having vinyl alcohol units O and / or vinyl acetate units A. The "three chains centered on vinyl alcohol" are classified as "AOA, AOO, OOO", the "three chains centered on vinyl acetate" are classified as "AAA, AAO, OAO", "AOO" and "OOA" are collectively referred to as "AOO", and "AAO" and "OAA" are collectively referred to as "AAO". 。 2. The polyvinyl alcohol resin according to claim 1, having a viscosity-average degree of polymerization of 1,000 to 4,000.

3. The polyvinyl alcohol-based resin according to claim 1 or 2, wherein, The content of vinyl alcohol units is 86.0 mol% to 99.3 mol%.

4. Use of the polyvinyl alcohol resin according to any one of claims 1 to 3 in the production of a polyvinyl acetal resin.

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