阅读说明：本技术 聚乙烯醇树脂的制造方法和聚乙烯醇树脂 (Method for producing polyvinyl alcohol resin and polyvinyl alcohol resin ) 是由 冈本祐治 梅村芳海 于 2019-09-03 设计创作，主要内容包括：提供抑制树脂彼此的融合且有机挥发成分的含量得以降低的聚乙烯醇树脂的制造方法。聚乙烯醇树脂的制造方法,其具有如下清洗工序：利用相对于乙酸甲酯、甲醇和水的合计100质量份以50～98质量份的比例含有乙酸甲酯、以1～49质量份的比例含有甲醇且以1～10质量份的比例含有水的清洗液,清洗将聚乙烯酯皂化而得到的聚乙烯醇。(Provided is a method for producing a polyvinyl alcohol resin, wherein fusion of resins is suppressed and the content of organic volatile components is reduced. A method for producing a polyvinyl alcohol resin, comprising the following cleaning step: a polyvinyl alcohol obtained by saponifying a polyvinyl ester is washed with a washing liquid containing 50 to 98 parts by mass of methyl acetate, 1 to 49 parts by mass of methanol and 1 to 10 parts by mass of water with respect to 100 parts by mass of the total of methyl acetate, methanol and water.)

1. A method for producing a polyvinyl alcohol resin, comprising the following cleaning step: a polyvinyl alcohol obtained by saponifying a polyvinyl ester is washed with a washing liquid containing 50 to 98 parts by mass of methyl acetate, 1 to 49 parts by mass of methanol and 1 to 10 parts by mass of water with respect to 100 parts by mass of the total of methyl acetate, methanol and water.

2. The method for producing a polyvinyl alcohol resin according to claim 1, wherein in the washing step, convection washing is performed at a temperature of 40 to 60 ℃ and a flow rate of 0.1 to 1 mm/s.

3. A polyvinyl alcohol resin obtained by the production method according to claim 1 or 2, wherein the content of methanol in the polyvinyl alcohol resin is less than 1.00 mass%, and the content of methyl acetate in the polyvinyl alcohol resin is less than 2.00 mass%.

Technical Field

The present invention relates to a method for producing a polyvinyl alcohol resin and a polyvinyl alcohol resin.

Background

Polyvinyl alcohol resin is a water-soluble polymer having hydroxyl groups, and is originally mainly used as a raw material of synthetic fibers, vinylon. In recent years, the composition is also used for emulsions, emulsion dispersants, paper, film materials, and thickeners.

The polyvinyl alcohol resin can be produced by, for example, polymerizing a vinyl ester to produce a polyvinyl ester and saponifying the polyvinyl ester. However, even after the drying step, organic volatile components such as methanol and methyl acetate used in the solvent or generated as impurities are contained in the polyvinyl alcohol resin by several percent. In order to reduce such organic volatile components, various attempts have been made to perform humidity-controlling drying, cleaning, and the like (see patent documents 1 and 2).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 9-302024

Patent document 2: japanese patent application laid-open publication No. 2011-178964.

Disclosure of Invention

Problems to be solved by the invention

For example, in the humidity-controlling and drying technique for a polyvinyl alcohol resin described in patent document 1, since steam spreads only over the surface portion of the polyvinyl alcohol resin, the effect of reducing the organic volatile component may be insufficient. Further, in the method of patent document 1, the amount of steam blown increases, and the resins may fuse with each other to form lumps.

In the cleaning with the cleaning liquid described in patent document 2, since the content of methanol is large, the polyvinyl alcohol resin is easily fused when the water content of the cleaning liquid is increased, and the polyvinyl alcohol resin is sometimes adhered to a dryer or aggregates of the polyvinyl alcohol resin are sometimes generated.

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a method for producing a polyvinyl alcohol resin, in which fusion of resins is suppressed and the content of organic volatile components can be easily reduced, and a polyvinyl alcohol resin obtained by the production method.

Means for solving the problems

The above problems are solved by providing a method for producing a polyvinyl alcohol resin, which comprises a step of washing with a washing liquid containing specific amounts of methyl acetate, methanol and water.

That is, the present invention includes the following aspects.

[1] A method for producing a polyvinyl alcohol resin, comprising the following cleaning step: a polyvinyl alcohol obtained by saponifying a polyvinyl ester is washed with a washing liquid containing 50 to 98 parts by mass of methyl acetate, 1 to 49 parts by mass of methanol and 1 to 10 parts by mass of water with respect to 100 parts by mass of the total of methyl acetate, methanol and water.

[2] The method for producing a polyvinyl alcohol resin according to the above [1], wherein in the washing step, convection washing is performed at a temperature of 40 to 60 ℃ and a flow rate of 0.1 to 1 mm/s.

[3] A polyvinyl alcohol resin obtained by the production method according to the above [1] or [2], wherein the polyvinyl alcohol resin has a methanol content of less than 1.00 mass% and a methyl acetate content of less than 2.00 mass%.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the production method of the present invention, a polyvinyl alcohol resin in which fusion of resins is suppressed and the content of organic volatile components is reduced can be easily obtained. The polyvinyl alcohol resin obtained by the production method of the present invention contains a small amount of methanol and methyl acetate, and is therefore particularly suitable for use in foods, cosmetics, and pharmaceuticals in which reduction of organic volatile components is desired.

Detailed Description

The present invention relates to a method for producing a polyvinyl alcohol resin (hereinafter, may be abbreviated as "PVA resin"), which comprises the following cleaning steps: a polyvinyl alcohol obtained by saponifying a polyvinyl ester is washed with a washing liquid containing 50 to 98 parts by mass of methyl acetate, 1 to 49 parts by mass of methanol and 1 to 10 parts by mass of water with respect to 100 parts by mass of the total of methyl acetate, methanol and water.

In the production of the PVA resin, as described later, a production method using a vinyl ester as a raw material and having a polymerization step, a saponification step, a washing step, and a drying step is suitably used. However, methanol and methyl acetate, which are generally used as solvents in production, remain in the PVA resin even after undergoing a drying process. The content of organic volatile components such as methanol and methyl acetate in the PVA resin can be adjusted by changing, for example, cleaning conditions and drying conditions. However, since the volatile organic components that have entered the resin are not easily volatilized, it is difficult to sufficiently reduce the volatile organic components by the conventional production method. The detailed reason why the organic volatile component in the PVA resin can be reduced by having the step of washing with a washing liquid containing specific amounts of methyl acetate, methanol and water as in the production method of the present invention is not clear, but it is presumed that: this is probably because water molecules enter the polyvinyl alcohol further inside to cause plasticization, and as a result, organic volatile components such as methanol and methyl acetate can be easily reduced during drying.

< method for producing PVA resin >

The method for producing a PVA resin of the present invention comprises the following cleaning step: a polyvinyl alcohol obtained by saponifying a polyvinyl ester is washed with a washing liquid containing 50 to 98 parts by mass of methyl acetate, 1 to 49 parts by mass of methanol and 1 to 10 parts by mass of water with respect to 100 parts by mass of the total of methyl acetate, methanol and water. The production method is preferably a production method comprising a polymerization step of polymerizing a vinyl ester to obtain a polyvinyl ester, a saponification step of saponifying the polyvinyl ester, the above-mentioned washing step and the drying step.

[ polymerization Process ]

The polyvinyl ester can be produced by polymerizing a vinyl ester by a conventionally known method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, and dispersion polymerization. The solution polymerization method is preferably a method of polymerizing in a lower alcohol as a solvent. The lower alcohol is not particularly limited, but is preferably an alcohol having 3 or less carbon atoms such as methanol, ethanol, propanol, and isopropanol, and more preferably methanol. The polymerization may be carried out by any of a batch method, a semi-batch method and a continuous method.

In the polymerization, other monomers than the vinyl ester may be copolymerized within a range not to impair the gist of the present invention. Examples of the other monomers include α -olefins such as ethylene, propylene, n-butene and isobutylene; (meth) acrylic acid and salts thereof; (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and octadecyl (meth) acrylate; (meth) acrylamide compounds such as (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamidopropanesulfonic acid and salts thereof, (meth) acrylamidopropyldimethylamine and salts thereof or quaternary ammonium salts thereof, and N-methylol (meth) acrylamide and derivatives thereof; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and salts or esters thereof; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate, and the like. These may be used alone or in combination of 2 or more. The copolymerization amount of the other monomer is usually 10 mol% or less. In the present specification, "(meth) acrylic" refers to a generic name of methacrylic and acrylic.

The polymerization temperature is not particularly limited, but is preferably 0 to 180 ℃, more preferably 20 to 160 ℃, and still more preferably 30 to 150 ℃. When the polymerization is carried out at a boiling point of the solvent used in the polymerization step or less, a boiling polymerization under reduced pressure in which the polymerization is carried out while boiling the solvent under reduced pressure, or a non-boiling polymerization under atmospheric pressure in which the polymerization is carried out under conditions in which the solvent is not boiled under atmospheric pressure can be selected. In addition, when the polymerization is carried out in the presence of a solvent having a boiling point or higher used in the polymerization step, a pressure non-boiling polymerization in which the polymerization is carried out under a condition that the solvent is not boiled under pressure, or a pressure boiling polymerization in which the polymerization is carried out while the solvent is boiled after the pressure is applied, can be selected.

[ saponification step ]

In the saponification step, the solution containing polyvinyl ester obtained in the polymerization step may be subjected to alcoholysis-hydrolysis reaction in the presence of a saponification catalyst. The saponification catalyst may be an alkali catalyst or an acid catalyst, and among them, an alkali metal catalyst, particularly a catalyst having a sodium atom, is particularly preferable. Examples of the catalyst having a sodium atom include sodium hydroxide and sodium methoxide. The amount of the saponification catalyst to be used is preferably 0.001 to 0.5 in terms of a molar ratio to a vinyl ester unit in the polyvinyl ester, more preferably 0.002 to 0.4, and still more preferably 0.004 to 0.3. The solvent used in the saponification step is preferably a solution containing methanol. 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 are contained in an amount of usually less than 10 mass% based on methanol in the saponification system.

[ cleaning Process ]

The important point of the manufacturing method is that the method comprises the following cleaning steps: a polyvinyl alcohol obtained by saponifying a polyvinyl ester is washed with a washing liquid containing 50 to 98 parts by mass of methyl acetate, 1 to 49 parts by mass of methanol and 1 to 10 parts by mass of water with respect to 100 parts by mass of the total of methyl acetate, methanol and water. From the viewpoint of further reducing the organic volatile content in the PVA resin to be obtained, the content of methyl acetate may be preferably 56 to 90 parts by mass, more preferably 58 to 80 parts by mass, and still more preferably 60 to 70 parts by mass, based on 100 parts by mass of the total of methyl acetate, methanol, and water in the cleaning liquid. The content of methanol is preferably 9 to 40 parts by mass, more preferably 18.5 to 40 parts by mass, and still more preferably 20 to 38 parts by mass, based on 100 parts by mass of the total of methyl acetate, methanol, and water in the cleaning liquid. The content of methanol is preferably 30 to 40 parts by mass in some cases. The content of water is preferably 1 to 5 parts by mass, more preferably 1.5 to 4 parts by mass, and still more preferably 1.5 to 3 parts by mass, based on 100 parts by mass of the total of methyl acetate, methanol, and water in the cleaning solution. The content of water is preferably 2 to 5 parts by mass in some cases. The inventors of the present invention found that: by adding a certain amount of water to the cleaning liquid, the content of organic volatile components in the PVA resins can be reduced, but there is a problem that the PVA resins fuse with each other. Thus, it has been clarified that: by making the content of methyl acetate in the cleaning liquid larger than the content of methanol, fusion of PVA resins with each other can be suppressed, and more water can be contained in the cleaning liquid. It can be presumed that: when the above-mentioned cleaning liquid is used, water in the cleaning liquid enters into the interior of the polyvinyl alcohol (plasticization by water), and as a result, intramolecular and intermolecular interactions of the polyvinyl alcohol are weakened, and methanol and methyl acetate can be easily reduced in a drying step described later.

When the content of methyl acetate in the cleaning liquid is less than 50 parts by mass, the PVA resin is easily fused, and adhesion to the dryer is observed, and aggregates of the PVA resin are generated. On the other hand, if the content of methyl acetate exceeds 98 parts by mass, plasticization by water becomes insufficient. Further, if the content of methanol in the cleaning liquid is less than 1 part by mass, plasticization by water becomes insufficient. On the other hand, if the content of methanol exceeds 50 parts by mass, the PVA resins are easily fused with each other, and adhesion to a dryer is observed, and aggregates of the PVA resins are generated. Further, if the content of water in the cleaning liquid is less than 1 part by mass, the amount of water taken into the polyvinyl alcohol is small, and therefore, plasticization becomes insufficient, and the content of organic volatile components does not sufficiently decrease. On the other hand, when the water content exceeds 10 parts by mass, the PVA resins are easily fused with each other, and adhesion to a dryer is observed, and aggregates of the PVA resins are generated.

The cleaning solution may consist essentially of methyl acetate, methanol and water. The total content of methyl acetate, methanol and water in the cleaning liquid is preferably 90% by mass or more, more preferably 99% by mass or more, and may be 100% by mass.

The solid content concentration of the polyvinyl alcohol in the washing step is not particularly limited, and is preferably 1 to 30% by mass. In the washing step, the form of the polyvinyl alcohol is not particularly limited, and may be a slurry or a powder. In the case of a powder, the powder preferably has an average particle diameter of 50 to 2000 μm. The solid content concentration of polyvinyl alcohol in the cleaning step generally refers to a content ratio of polyvinyl alcohol to a mixed liquid including polyvinyl alcohol in a cleaning state and a cleaning liquid (for example, a mixed liquid including polyvinyl alcohol and a cleaning liquid in a cleaning tank).

The cleaning temperature is not particularly limited, and is usually 20 ℃ to the boiling point of the solvent, preferably 40 to 60 ℃. When the washing temperature is not lower than the lower limit, the amount of water taken into the polyvinyl alcohol increases, and the organic volatile components are easily reduced. On the other hand, when the washing temperature exceeds 60 ℃, methanol in the washing liquid starts to boil.

The method for washing polyvinyl alcohol is not particularly limited, and examples thereof include a method in which polyvinyl alcohol obtained in the saponification step and a washing liquid are put into a washing tank and stirred, or the washing liquid is dispersed in polyvinyl alcohol obtained in the saponification step, or the polyvinyl alcohol obtained in the saponification step and the washing liquid are brought into contact with each other in a convection manner.

Among the above, the polyvinyl alcohol washing method is preferably convective washing in which the polyvinyl alcohol obtained in the saponification step is brought into contact with a washing liquid in a convective manner. The convection cleaning is as follows: a method of supplying the polyvinyl alcohol obtained in the saponification step to the washing tank and simultaneously circulating the cleaning liquid in a direction opposite to the direction of the polyvinyl alcohol in the washing tank, i.e., in a direction forming a convection flow path. By flowing the cleaning liquid in the convection direction, the cleaning efficiency is improved as compared with the case where the cleaning liquid is flowed in the same direction as the flow direction of the polyvinyl alcohol, that is, in the direction of cocurrent flow, or is flowed in the direction perpendicular to the flow path of the polyvinyl alcohol. The cleaning liquid may be continuously or intermittently circulated, and the supply position of the cleaning liquid is not particularly limited as long as the polyvinyl alcohol flow and the convection flow path are formed.

Specifically, in the cleaning step, the polyvinyl alcohol and the cleaning liquid are preferably cleaned by convection at a flow rate of 0.1 to 1 mm/s. The flow velocity is a velocity at which the fluid moves, and can be determined from the flow rate of the cleaning solution and the aperture of the cleaning tank. When the flow rate is less than 0.1mm/s, the cleaning efficiency tends to be lowered, and when it exceeds 1mm/s, the polyvinyl alcohol tends to float and overflow from the cleaning tank. In any of the convection cleaning and other cleaning methods, the flow rate of the cleaning liquid is set to the flow rate in the cleaning step. The cleaning time is not particularly limited, and is preferably about 30 minutes to 10 hours.

[ drying Process ]

After the washing step, a drying step may be provided as necessary. The temperature and time in the drying step are not particularly limited, but are preferably 40 to 130 ℃ for 1 to 20 hours, more preferably 80 to 120 ℃ for 1.5 to 6 hours. By performing drying under such conditions, a PVA resin with reduced contents of methanol and methyl acetate can be easily obtained.

< PVA resins >

The PVA resin obtained by the production method of the present invention is a resin containing polyvinyl alcohol as a main component. The content of the polyvinyl alcohol in the PVA resin is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. The content of polyvinyl alcohol in the PVA resin may be 99.9 mass% or less, or may be 99 mass% or less. Examples of the component other than polyvinyl alcohol which may be contained in the PVA resin include methanol, methyl acetate, and water.

Among the PVA resins obtained by the production method of the present invention, preferred are: the content of methanol was less than 1.00 mass%, and the content of methyl acetate was less than 2.00 mass%. The content of methanol in the PVA resin is preferably less than 0.95% by mass, more preferably less than 0.90% by mass. Further, the content of methyl acetate in the PVA resin is preferably less than 1.80 mass%, more preferably less than 1.70 mass%. When the content of methanol and methyl acetate in the PVA resin is within the above range, the PVA resin can be suitably used in particular for food, cosmetics, and pharmaceutical applications in which reduction of organic volatile components is desired. The content of methanol and methyl acetate in the PVA resin can be measured by headspace gas chromatography as shown in examples described later. Furthermore, the content of methanol is preferably less than the content of methyl acetate. From the viewpoint of productivity and the like, the lower limit of the content of methanol in the PVA resin may be, for example, 0.1 mass%, or may be 0.3 mass% or 0.5 mass%. From the viewpoint of productivity and the like, the lower limit of the content of methyl acetate in the PVA resin may be, for example, 0.1 mass%, or may be 0.3 mass% or 0.5 mass%.

The viscosity average degree of polymerization of the polyvinyl alcohol contained in the PVA resin is not particularly limited, but is preferably 100 to 5000, and more preferably 200 to 4000. It is difficult to produce polyvinyl alcohol having a viscosity average degree of polymerization of less than 100 and exceeding 5000. The viscosity average degree of polymerization is a value measured in accordance with JIS-K6726 (1994). Specifically, when the saponification degree is less than 99.5 mol%, the viscosity average degree of polymerization (P) is determined by the following formula using the intrinsic viscosity [ η ] (liter/g) measured at 30 ℃ in water for polyvinyl alcohol saponified to a saponification degree of 99.5 mol% or more.

P＝（[η]×10⁴/8.29）^（1/0.62）

The saponification degree of the polyvinyl alcohol contained in the PVA resin is not particularly limited, but is preferably 70 to 99.9 mol%, and more preferably 78 to 95 mol%. When the saponification degree is less than 70 mol%, the solubility in water tends to decrease, while it is difficult to produce polyvinyl alcohol having a saponification degree of more than 99.9 mol%. The degree of saponification was measured in accordance with JIS-K6726 (1994).

The shape of the PVA resin is not particularly limited, but is preferably a powder having an average particle diameter of 50 to 2000. mu.m. The average particle diameter of the powdery PVA resin was determined in accordance with JIS-K6726 (1994).

Examples

The present invention will be described in more detail below with reference to examples. In the following examples and comparative examples, "part" and "%" represent part by mass and% by mass, respectively, unless otherwise specified.

[ viscosity average polymerization degree of polyvinyl alcohol ]

The degree of viscosity average polymerization was measured in accordance with JIS-K6726 (1994). Specifically, when the degree of saponification is less than 99.5 mol%, the viscosity average degree of polymerization (P) is determined by the following formula using the intrinsic viscosity [ η ] (liter/g) measured at 30 ℃ in water for the PVA resin saponified to a degree of saponification of 99.5 mol% or more.

P＝（[η]×10⁴/8.29）^（1/0.62）

[ degree of saponification of polyvinyl alcohol ]

The degree of saponification was measured in accordance with JIS-K6726 (1994).

[ contents of methanol and methyl acetate in the PVA resin ]

< preparation of Standard Curve >

Using isopropanol as an internal standard, 3 kinds of aqueous solutions having a known methanol content and 3 kinds of aqueous solutions having a known methyl acetate content were prepared, and measured by using a gas chromatograph (GC-2010, shimadzu corporation) equipped with a headspace sampler (Turbo Matrix HS40, Parkin Elmer corporation), and a calibration curve was prepared.

< measurement of methanol and methyl acetate content >

Distilled water was collected on the marked line of a 1000mL volumetric flask, and 0.1mL of isopropyl alcohol as an internal standard solution was added to the volumetric flask through a measuring tube and sufficiently stirred. This liquid was referred to as "solution". Subsequently, 500mg of the PVA resin was weighed into a vial for headspace gas chromatography, a stirrer was put in the vial, and 10mL of the solution was measured with a full-volume pipette and put in the vial. The vial was capped and screwed down to lock, and then the vial was carried on a heated stirrer and heated to dissolve the PVA resin. After the PVA resin was confirmed to be completely dissolved by visual observation, the content of methanol and the content of methyl acetate in the PVA resin were determined from the calibration curves prepared as described above by headspace gas chromatography measurement.

[ evaluation of fusion State in PVA resin ]

The fusion state in the PVA resin was observed by visual observation, and evaluated according to the following criteria.

A. No change in resin was observed.

B. The resin that is fused and connected is dispersed in a very small amount.

C. The resin fused and connected is much.

D. Fusion occurs and the resin is integrated.

[ example 1]

Sodium hydroxide was added as a saponification catalyst in a molar ratio of 0.01 relative to a vinyl acetate unit in polyvinyl acetate at 40 ℃ in a 30% methanol solution of polyvinyl acetate having a viscosity average polymerization degree of 1700, and a saponification reaction was carried out for 1 hour. After the saponification, the obtained polyvinyl alcohol (degree of saponification: 93 mol%) was coarsely pulverized by a pulverizer to obtain a powder passed through a mesh vessel of 5mm phi. The obtained polyvinyl alcohol powder was subjected to convection washing at 50 ℃ for 1 hour and at a flow rate of 0.44mm/s using a washing liquid containing methyl acetate in an amount of 64.05 parts by mass, methanol in an amount of 34.13 parts by mass, and water in an amount of 1.82 parts by mass. In the washing step, the solid content concentration of polyvinyl alcohol was 30 mass%. Then, most of the solvent (cleaning solution) was removed by centrifugal separation, and the resulting mixture was dried at 105 ℃ for 3 hours to obtain a powdery PVA resin having a viscosity average polymerization degree of 1700, a saponification degree of 93 mol% of the polyvinyl alcohol, a methanol content of 0.89 mass%, and a methyl acetate content of 1.32 mass%. The results are shown in table 1.

Examples 2 to 8 and comparative examples 1 to 4

A powdery PVA resin was obtained in the same manner as in example 1, except that the saponification degree of polyvinyl alcohol to be subjected to the cleaning step and the composition of the cleaning liquid were changed as shown in table 1. The viscosity average polymerization degree of polyvinyl alcohol, the saponification degree of polyvinyl alcohol, the methanol content and the methyl acetate content in the obtained PVA resin are shown in table 1.

[ Table 1]

In all examples, little fusion of the resulting PVA resin was observed, which was good. Further, in all examples, the methanol content in the resulting PVA resin was less than 1.00 mass%, and the methyl acetate content was less than 2.00 mass%. On the other hand, in comparative examples 1 and 2, the content of organic volatile components in the obtained PVA resins was large. In addition, in comparative examples 3 and 4, fusion of the obtained PVA resins was observed.

Industrial applicability

According to the method for producing a PVA resin of the present invention, a PVA resin having a reduced content of organic volatile matter can be easily obtained, and therefore, the obtained PVA resin is useful as a constituent material or a packaging material for foods, cosmetics, medicines, and the like.