JP6979320B2 - Polyvinyl alcohol - Google Patents

Description

The present invention relates to specific polyvinyl alcohols having excellent high speed coatability, water resistance and mechanical strength.

Polyvinyl alcohol (hereinafter, may be abbreviated as PVA) is industrially produced by saponifying polyvinyl acetate obtained by radical polymerization of vinyl acetate. PVA is used in many applications such as paper processing, fiber processing, films, adhesives, binders for various inorganic materials, and emulsion stabilizers. Above all, a method of applying a coating liquid containing PVA to paper to improve the surface characteristics, printing characteristics and the like of the paper is generally performed.

In the above fields, particularly in the field of finely coated paper in which the amount of coating is small, in recent years, it has been required to increase the coating speed for the purpose of improving productivity. As a coating liquid containing PVA, PVA is typically used as an aqueous solution, and it is known that such an aqueous solution of PVA is sheared during coating. However, when the PVA aqueous solution is sheared, when the shear rate is increased, the PVA in the aqueous solution is oriented and crystallized at a certain shear rate, and the viscosity increases. Therefore, if the coating is performed at a shear rate or higher at which an increase in viscosity is observed, it becomes difficult to apply the coating uniformly to the coated surface. Therefore, there is a demand for PVA having excellent high-speed coatability, in which the viscosity does not increase even at a high shear rate when an aqueous solution is used.

As a method for solving such a problem, PVA having excellent high-speed coatability is obtained by lowering the degree of polymerization and saponification of PVA and by containing 1,2-glycol in the side chain in Patent Document 1. It is stated that can be manufactured.

Further, Patent Document 1 describes that PVA containing 1,2-glycol in the side chain and having excellent high-speed coatability can be produced.

Japanese Unexamined Patent Publication No. 2002-241433

However, when the degree of polymerization and the degree of saponification of PVA are lowered, the mechanical strength of the obtained coating film (film) is low, the effect of improving the surface strength of the paper coated with the aqueous solution is small, and water resistance is required. It was difficult to use for the purpose. Further, since the crystallinity of PVA described in Patent Document 1 is lowered by introducing a substituent into the side chain, the mechanical strength and water resistance of the obtained coating film (film) are lowered as described above. As described above, the current situation is that PVA capable of achieving both high-speed coatability, mechanical strength, and water resistance has not yet been obtained. The present invention has been made to solve the above problems, and an object of the present invention is to provide polyvinyl alcohol having excellent high-speed coatability, water resistance, and mechanical strength.

As a result of diligent studies, the present inventors have found that a specific polyvinyl alcohol is excellent in high-speed coating property, water resistance, and mechanical strength, and completed the present invention.

According to the present invention, the above problems are solved.
[1] The number average molecular weight (Mn) is 44,000 to 440,000, the molecular weight distribution (Mw / Mn) is 1.05 to 1.70, and the saponification degree is 80 to 99.99 mol%. Polyvinyl alcohol having a total content of carboxyl groups and lactones of 0.03 mol% or less with respect to all monomer units.
[2] The polyvinyl alcohol of [1] having a carbon-carbon double bond content of 0.1 mol% or less with respect to all the monomers and satisfying the following formula (1).
X · Mn ≤ 1000 (1)
[3] Polyvinyl alcohol according to [1] or [2] having a yellow index (YI) of 50 or less as measured according to ASTM D1925.
[4] The polyvinyl alcohol according to any one of [1] to [3], wherein the total content of the carboxyl group and the lactone is 0.005 mol% or less.
[5] The polyvinyl alcohol according to any one of [1] to [4], which has a 1,2-glycol bond content of 0.7 to 1.5 mol%.
[6] A coating liquid consisting of an aqueous solution containing polyvinyl alcohol according to any one of [1] to [5].
[7] A coated paper obtained by applying the coating liquid of [6] to the surface of a base material.
Is solved by providing.

The polyvinyl alcohol of the present invention has a narrow molecular weight distribution and few low molecular weight components, and therefore has excellent water resistance and mechanical strength. In addition, due to the low total content of carboxyl groups and lactones, the interaction between functional groups is reduced, and even when the number average molecular weight and the degree of saponification are high, the aqueous solution of polyvinyl alcohol has excellent high-speed coatability. Have.

It shows the change in viscosity of the polyvinyl alcohol obtained in Comparative Example 1, Comparative Example 4, and Example 5 with respect to the shear rate.

The polyvinyl alcohol of the present invention has a number average molecular weight (Mn) of 44,000 to 440,000, a molecular weight distribution (Mw / Mn) of 1.05 to 1.70, and a saponification degree of 80 to 99.99 mol%. The total content of the carboxyl group and the lactone is 0.03 mol% or less.

By narrowing the molecular weight distribution and reducing the total content of the carboxyl group and the lactone, it is possible to provide polyvinyl alcohol having excellent high-speed coatability of the aqueous solution and the molded product obtained from the aqueous solution having excellent water resistance and mechanical strength.

A preferred method for producing polyvinyl alcohol of the present invention is a polymerization step of polymerizing a vinyl ester monomer by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex; after the polymerization step, a proton donating polymerization terminator. It has a stopping step of stopping the polymerization to obtain polyvinyl ester by adding the above; and a saponification step of saponifying the polyvinyl ester obtained in the stopping step to obtain polyvinyl alcohol. Hereinafter, the manufacturing method will be described in detail.

First, the polymerization process will be described. In the polymerization step, the vinyl ester monomer is polymerized by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex. Controlled radical polymerization is a polymerization reaction in which the growth radical terminal (active species) is placed in an equilibrium state with a covalent bond species (dormant species) bound to a regulatory agent and the reaction proceeds. In the present invention, an organic cobalt complex is preferably used as a control agent.

Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, trifluorovinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate. , Vinyl benzoate, vinyl versaticate and the like, but vinyl acetate is preferably used from an economical point of view.

Examples of the method for polymerizing the vinyl ester monomer include known methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among them, a bulk polymerization method of polymerizing without a solvent or a solution polymerization method of polymerizing in various organic solvents is usually adopted. In order to obtain a polymer having a narrow molecular weight distribution, a massive polymerization method that does not use a solvent or dispersion medium that may cause side reactions such as chain transfer is preferable. On the other hand, solution polymerization may be preferable from the viewpoint of adjusting the viscosity of the reaction solution and controlling the polymerization rate. Examples of the organic solvent used as a solvent in solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene and toluene; lower alcohols such as methanol and ethanol. Of these, esters and aromatic hydrocarbons are preferably used to prevent chain transfer. The amount of the solvent used may be determined in consideration of the viscosity of the reaction solution according to the number average molecular weight of the target polyvinyl alcohol. For example, the mass ratio (solvent / monomer) is selected from the range of 0.01-10. The mass ratio (solvent / monomer) is preferably 0.1 or more, and preferably 5 or less.

As the radical initiator used in the polymerization step, conventionally known azo-based initiators, peroxide-based initiators, redox-based initiators and the like are appropriately selected. Examples of the azo-based initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2'-azobis (4-methoxy-2,4-). Dimethylvaleronitrile) and the like, and examples of the peroxide-based initiator include percarbonate compounds such as diisopropylperoxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethylperoxydicarbonate; t-butyl. Perester compounds such as peroxyneodecaneto, α-cumylperoxyneodecaneate, t-butylperoxyneodecanete; acetylcyclohexylsulfonyl peroxide, diisobutyryl peroxide; 2,4,4-trimethylpentyl-2 -Peroxyphenoxyacetate and the like can be mentioned. Further, the initiator can be obtained by combining potassium persulfate, ammonium persulfate, hydrogen peroxide and the like with the initiator. The redox-based initiator is a combination of the above peroxide (oxidizing agent) and a reducing agent such as N, N-dimethylaniline, sodium bisulfite, sodium hydrogencarbonate, tartaric acid, L-ascorbic acid, and longalit. Things can be mentioned. The amount of the initiator used differs depending on the polymerization catalyst and cannot be unconditionally determined, and is arbitrarily selected according to the polymerization rate.

The organic cobalt complex used as a control agent in the polymerization step may contain a divalent cobalt atom and an organic ligand. Suitable organic cobalt complexes include, for example, cobalt (II) acetylacetonate [Co (acac) ₂ ], cobalt (II) porphyrin complex and the like. Of these, cobalt (II) acetylacetonate is preferable from the viewpoint of manufacturing cost.

In the controlled radical polymerization used in the present invention, first, the radical at the growth end of the short-chain polymer generated by bonding the radical generated by the decomposition of the radical initiator with a small number of vinyl esters is an organic cobalt (II) complex. The organic cobalt (III) complex is covalently bonded to the polymer terminal to form a dormant species. For a certain period after the start of the reaction, a short-chain polymer is produced and only converted into a dormant species, and the degree of polymerization does not substantially increase. This period is called the induction period. After the organic cobalt (II) complex is consumed, the growth phase in which the degree of polymerization increases is entered, and the molecular weight of most of the molecular chains in the reaction system increases in proportion to the polymerization time in the same manner. This makes it possible to obtain a polyvinyl ester having a narrow molecular weight distribution.

As described above, in the controlled radical polymerization of the present invention, theoretically, one polyvinyl ester chain is generated from one molecule of the organic cobalt complex to be added. Therefore, the amount of the organic cobalt complex added to the reaction solution is determined in consideration of the target number average molecular weight and the polymerization rate. Usually, it is preferable to use 0.001 to 1 mol of the organic cobalt complex with respect to 100 mol of the vinyl ester monomer.

If the number of moles of radicals generated is not greater than the number of moles of the organic cobalt complex, the polymerization reaction proceeds only by the mechanism of thermal dissociation of the Co complex from the Dormant species, so the polymerization rate becomes extremely small depending on the reaction temperature. Will end up. Therefore, considering that the radical initiator generates two radicals, the number of moles of the radical initiator used needs to be more than 1/2 times the number of moles of the organic cobalt complex. In general, the amount of active radicals supplied by the initiator depends on the initiator efficiency, so some initiators are not actually used to form the dormant and are inactivated. Therefore, the number of moles of the radical initiator used is preferably 1 times or more, more preferably 1.5 times or more the number of moles of the organic cobalt complex. On the other hand, if the number of moles of the generated radicals is too large to be larger than the number of moles of the organic cobalt complex, the proportion of uncontrolled radical polymerization increases and the molecular weight distribution widens. The number of moles of the radical initiator used is preferably 10 times or less, more preferably 6 times or less, the number of moles of the organic cobalt complex.

The polymerization temperature is preferably, for example, 0 ° C to 80 ° C. If the polymerization temperature is less than 0 ° C., the polymerization rate will be insufficient and the productivity will decrease. From this point, the polymerization temperature is more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher. On the other hand, when the polymerization temperature exceeds 80 ° C., the molecular weight distribution of the obtained polyvinyl ester becomes wide. From this point, the polymerization temperature is more preferably 65 ° C. or lower, and even more preferably 50 ° C. or lower.

When the desired polymerization rate is reached in the polymerization step, the polymerization reaction is stopped by adding a proton-donating polymerization terminator. The hue of polyvinyl alcohol obtained by saponifying the polyvinyl acetate thus obtained is good. The reason is not always clear, but the proton-donating polymerization inhibitor supplies the proton radicals to the radicals generated by the cleavage of the Dormant species, so that they can be hydrogenated while suppressing side reactions. Is considered to be. Then, when the polyvinyl acetate is saponified thereafter, the formation of a conjugated double bond is suppressed, and a polyvinyl alcohol having a small yellow index (YI) and a good hue can be obtained. The time required for the polymerization step is usually 3 to 50 hours including the induction period and the growth period.

The number of moles of the proton-donating polymerization inhibitor added is preferably 1 to 100 times the number of moles of the added organic cobalt complex. If the number of moles of the proton-donating polymerization inhibitor is too small, the radicals at the end of the polymer can be sufficiently captured, and the color tone of the obtained polyvinyl alcohol may be deteriorated. Therefore, the number of moles of the proton-donating polymerization inhibitor is more preferably 5 times or more the number of moles of the organic cobalt complex. On the other hand, if the number of moles of the proton-donating polymerization inhibitor is too large, the production cost may increase. The number of moles of the proton donating polymerization terminator is more preferably 50 times or less the number of moles of the organic cobalt complex.

The proton donating polymerization inhibitor used in the termination step is a polymerization inhibitor capable of providing a proton radical to the radical at the end of the polyvinyl acetate chain, and has a chain transfer constant of 0.1 or more with respect to vinyl acetate at 60 ° C. Is preferable. Suitable proton-donating polymerization inhibitors include, for example, sorbic acid used in Examples described later. Further, an organometallic compound having a metal-hydrogen bond or the like can also be used.

The temperature of the reaction solution in the termination step may be any temperature as long as the proton donating polymerization inhibitor can provide a proton radical to the radical at the end of the polyvinyl acetate chain, and is preferably 0 ° C to 80 ° C. If the temperature of the reaction solution is less than 0 ° C., the stopping step takes too much time and the productivity is lowered. From this point, the temperature is more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher. On the other hand, if the temperature of the reaction solution exceeds 80 ° C., unnecessary polymerization of vinyl acetate may proceed and the molecular weight distribution (Mw / Mn) may increase. From this point, the temperature is more preferably 70 ° C. or lower, and even more preferably 60 ° C. or lower. The time required for the stop process is 10 minutes to 5 hours.

After the stopping step, it is preferable to carry out an extraction step of contacting the obtained polyvinyl ester solution with an aqueous solution containing a water-soluble ligand to extract and remove the cobalt complex from the polyvinyl ester solution. As described above, by performing the saponification step after removing the cobalt complex contained in the polyvinyl ester solution in advance, polyvinyl alcohol having a good hue and difficult to gel can be obtained. Specifically, the aqueous solution and the polyvinyl ester solution, which are insoluble in each other, are vigorously stirred so that the area of the interface between the two is large, and then allowed to stand, separated into an oil layer and an aqueous layer, and then the aqueous layer is formed. Perform the operation except. This operation may be repeated a plurality of times.

After the stopping step, it is preferable to carry out an extraction step of contacting the obtained polyvinyl ester solution with an aqueous solution containing a water-soluble ligand to extract and remove the cobalt complex from the polyvinyl ester solution. As described above, by performing the saponification step after removing the cobalt complex contained in the polyvinyl ester solution in advance, polyvinyl alcohol having a good hue and difficult to gel can be obtained. Specifically, the aqueous solution and the polyvinyl ester solution, which are insoluble in each other, are vigorously stirred so that the area of the interface between the two is large, and then allowed to stand, separated into an oil layer and an aqueous layer, and then the aqueous layer is formed. Perform the operation except. This operation may be repeated a plurality of times.

The water-soluble ligand used in the extraction step is preferably an acid having a pKa of 0 to 12 at 25 ° C. When a strong acid having a pKa of less than 0 is used, it is difficult to efficiently extract the cobalt complex, and the pKa is preferably 2 or more. Further, it is difficult to efficiently extract the cobalt complex even when a weak acid having a pKa of more than 12 is used, and the pKa is preferably 7 or less. When the acid is a polyvalent acid, the first dissociation constant (pKa1) needs to be in the above range. The acid having a pKa of 0 to 12 is preferably a carboxylic acid, and particularly preferably acetic acid (pKa 4.76).

The pH of the aqueous solution containing the water-soluble ligand is preferably 0 to 5. The pH is more preferably 1 or more, and even more preferably 1.5 or more. The pH is more preferably 4 or less, still more preferably 3 or less.

In the saponification step, the polyvinyl ester obtained in the stopping step is saponified to obtain polyvinyl alcohol. At this time, the extraction step may be performed after the stop step, and then the saponification step may be performed.

In the saponification step, the polyvinyl ester produced by the above method is saponified in a state of being dissolved in alcohol or hydrous alcohol to obtain polyvinyl alcohol. Examples of the alcohol used in the saponification reaction include lower alcohols such as methanol and ethanol, and methanol is particularly preferably used. The alcohol used in the saponification reaction may contain acetone, an ester such as methyl acetate or ethyl acetate, or a solvent such as toluene. Examples of the catalyst used for the saponification reaction include hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide, alkaline catalysts such as sodium methylate, and acid catalysts such as mineral acid. For the temperature of the saponification reaction, for example, the range of 20 to 60 ° C. is appropriate. If a gel-like product precipitates as the saponification reaction progresses, polyvinyl alcohol can be obtained by pulverizing the product at that time, washing the product, and then drying the product.

The saponification degree of the polyvinyl alcohol of the present invention is 80 to 99.99 mol%. When the degree of saponification is less than 80 mol%, the crystallinity of polyvinyl alcohol is remarkably lowered, and the physical properties such as the mechanical strength of the molded product are lowered. The degree of saponification is preferably 85 mol% or more, and more preferably 90 mol% or more. On the other hand, if the saponification degree exceeds 99.99 mol%, it becomes difficult to produce polyvinyl alcohol, and the moldability tends to be inferior. From the viewpoint of excellent high-speed coatability of the aqueous solution, the saponification degree is preferably 99.95 mol% or less, more preferably 95.0 mol% or less, and further preferably 92.0 mol% or less.

The number average molecular weight (Mn) of polyvinyl alcohol of the present invention is 44,000 to 440,000. By using an organic cobalt complex as a control agent, polyvinyl alcohol having a narrow molecular weight distribution and a high number average molecular weight (Mn) can be obtained. The number average molecular weight (Mn) is preferably 11,000 or more, and more preferably 22,000 or more, from the viewpoint of obtaining a molded product having excellent water resistance and mechanical strength. On the other hand, if the number average molecular weight (Mn) is too high, the viscosity of the solution may become too high and handling may be difficult, or the dissolution rate may decrease. Therefore, the number average molecular weight (Mn) is 220,000 or less. It is preferably 190,000 or less, and more preferably 190,000 or less. The number average molecular weight (Mn) and the weight average molecular weight (Mw) in the present invention are values measured by a gel permeation chromatography (GPC) method using polymethylmethacrylate as a standard substance and using an HFIP-based column. The measuring method is as described in the examples.

The molecular weight distribution (Mw / Mn) of polyvinyl alcohol of the present invention is 1.05 to 1.70. Polyvinyl alcohol having a narrow molecular weight distribution can be obtained by polymerizing by controlled radical polymerization. The molecular weight distribution is preferably 1.60 or less, and more preferably 1.55 or less. When the molecular weight distribution is in the above range, the amount of the low molecular weight component of the obtained polyvinyl alcohol is reduced, and the molded product is excellent in water resistance. Further, when the molecular weight distribution is in the above range and the number average molecular weight is in the above range, a molded product having excellent mechanical strength can be obtained.

The total content of the carboxyl group and the lactone with respect to all the monomer units of the polyvinyl alcohol of the present invention is 0.03 mol% or less. The total content of carboxyl groups and lactones is preferably 0.005 or less. When the total content of the carboxyl group and the lactone is in the above range, the interaction between the functional groups is reduced, and the aqueous solution of polyvinyl alcohol has excellent high-speed coatability even when the number average molecular weight and the degree of saponification are high.

The content (X) of the carbon-carbon double bond with respect to all the monomer units of the polyvinyl alcohol of the present invention is preferably 0.1 mol% or less. The carbon-carbon double bond content (X) is more preferably 0.03 mol% or less, further preferably 0.01 mol% or less, and particularly preferably 0.001 mol% or less.

Further, the polyvinyl alcohol of the present invention preferably satisfies the following formula (1). The left side (X · Mn) of the formula (1) is the content (X) (mol%) of the carbon-carbon double bond with respect to all the monomer units of polyvinyl alcohol multiplied by the number average molecular weight (Mn). be. Here, since the number average molecular weight (Mn) is a value inversely proportional to the number of polymer terminals per unit weight, the fact that X · Mn is below a certain value means that carbon-carbon double with respect to the number of polymer molecule terminals. It means that the ratio of the content (X) of the double bond is below a certain level. In the case of coloring derived from the terminal structure, the higher the number average molecular weight (Mn), the smaller the terminal ratio, so that a polymer having a high whiteness can be easily obtained, and the lower the number average molecular weight (Mn), the terminal ratio. Therefore, it is difficult to obtain a polymer having a high whiteness. The formula (1) shows that when polyvinyl alcohols having the same molecular weight are compared with each other, polyvinyl alcohol having a higher whiteness than the conventional one can be obtained. X · Mn is more preferably 700 or less, and even more preferably 400 or less.
X · Mn ≤ 1000 (1)

The polyvinyl alcohol of the present invention preferably has a yellow index (YI) of 50 or less as measured according to ASTM D1925.

By using polyvinyl alcohol having a low carbon-carbon double bond content (X), polyvinyl alcohol having a small hue with a small YI can be obtained. YI is more preferably 40 or less, further preferably 30 or less, and particularly preferably 20 or less. Here, YI uses a spectrophotometer (D65 light source, CM-A120 white calibration plate, specular reflection measurement SCE) to spread polyvinyl alcohol resin powder on a petri dish without pressing the powder. Is measured and obtained. Specifically, it is a value measured according to the method described in the example.

The content of the 1,2-glycol bond of the polyvinyl alcohol of the present invention is preferably 0.7 to 1.5 mol%. When the content of 1,2-glycol bond is 1.5 mol% or less, polyvinyl alcohol can have high crystallinity. In addition to having a low molecular weight distribution (Mw / Mn), it has higher crystallinity, and the molded product obtained from the aqueous solution of polyvinyl alcohol has excellent mechanical strength. The content of the 1,2-glycol bond is more preferably 1.4 mol% or less, further preferably 1.3 mol% or less. On the other hand, when the content of the 1,2-glycol bond is less than 1 mol%, the water solubility is deteriorated and the handleability is deteriorated. The content of the 1,2-glycol bond is more preferably 0.9 mol% or more, further preferably 1.1 mol% or more.

The method for molding polyvinyl alcohol of the present invention includes, for example, a method of molding from the form of a solution such as water or dimethylsulfoxide, a method of plasticizing and molding polyvinyl alcohol by heating, for example, an extrusion molding method, an injection molding method, or an inflation molding method. , Press molding method, blow molding method and the like. By these methods, molded products having an arbitrary shape such as a film, a sheet, a tube, and a bottle can be obtained.

The polyvinyl alcohol of the present invention can be used for various purposes by utilizing its characteristics. For example, coating liquids, coating agents for paper, surfactants, internal additives for paper, pigment binders, adhesives, non-woven binders, paints, textile processing agents, fiber pastes, coated papers, films, sheets, bottles, etc. It can be used for fibers, thickeners, flocculants, soil modifiers, etc.

When the polyvinyl alcohol of the present invention is used as a coating liquid, it is preferable to use polyvinyl alcohol as an aqueous solution.

When the polyvinyl alcohol of the present invention is used for coating paper, it is preferable that the coating liquid is applied to the surface of the base material. As the base material, for example, a paper base material and a film base material are used.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited to these Examples. The methods for measuring and evaluating polyvinyl alcohol obtained in each Example and Comparative Example are as follows.

[Induction period and growth period]
The "induction period" in the present invention means the period from the start of heating of the reaction solution to the start of consumption of vinyl acetate, and the "growth period" means the period from the start of consumption of vinyl acetate. It means the period from to reach the target conversion rate. During these periods, for example, sampling is performed at an arbitrary time after the consumption of vinyl acetate is started, the consumption rate of vinyl acetate is calculated from the solid content concentration, and the time-vinyl acetate consumption rate correlation is plotted. It can be calculated by setting the time when the vinyl acetate consumption rate becomes 0% when an approximate straight line is drawn at at least three points as the boundary between the "induction period" and the "growth period".

[Measurement of number average molecular weight (Mn) and molecular weight distribution (Mw / Mn)]
The number average molecular weight (Mn) and the molecular weight distribution (Mw / Mn) were measured using a size exclusion high-speed liquid chromatography device "HLC-8320GPC" manufactured by Toso Co., Ltd. The measurement conditions are as follows.
Column: HFIP-based column "GMHR-H (S)" manufactured by Tosoh Corporation, connected in series Standard sample: Polymethylmethacrylate Solvent and mobile phase: Sodium trifluoroacetate-HFIP solution (concentration 20 mM)
Flow rate: 0.2 mL / min
Temperature: 40 ° C
Sample solution concentration: 0.1 wt% (filtered with a 0.45 μm opening diameter filter)
Injection volume: 10 μL
Detector: RI

[Measurement of total content of carboxyl group and lactone]
¹ H-NMR measurement of polyvinyl alcohol was performed at 80 ° C. using a nuclear magnetic resonance apparatus "LAMDA 500" manufactured by JEOL Ltd. Heavy water was used as the solvent. The total content (mol%) of the carboxyl group and the lactone with respect to the total body unit of polyvinyl alcohol was calculated as follows. When the total integral value (4.15-4.06 ppm) of the peak derived from the known polyvinyl alcohol methine proton (-CH ₂ CH (OH) _{-or -CH 2} CH (OCOCH _{3)-) is set to 100.} The integral value of the peak of the methine proton (-CH _2- COONa) adjacent to the carboxyl group detected in the range of 2.33-2.21 ppm and the methine of the lactone detected in the range of 2.76-2.71 ppm. It was calculated by halving the sum of the values at the integration sites of the proton (-CHCH ₂ CH _{2 COOCH-) peaks.}

[Measurement of carbon-carbon double bond content (X) (mol%)]
¹ H-NMR measurement of polyvinyl alcohol was performed at 40 ° C. and 95 ° C. using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by JEOL Ltd. DMSO-d ₆ was used as the solvent. The content (X) (mol%) of the carbon-carbon double bond with respect to all the monomer units of polyvinyl alcohol was calculated as follows. Known polyvinyl alcohol methine _{(-CH 2 C H (OH)} - or _{-CH 2 C H (OCOCH 3)} -) total integrated value of peak derived from (3.3ppm, 3.4ppm, 3.5ppm, 3.6 ppm, 3.9 ppm and 4.8 ppm; of these, for the four peaks of 3.3 to 3.6 ppm, each integrated value was calculated from the comparison of the measured values at 40 ° C / 95 ° C) as 100. In this case, the integrated value of all peaks detected in the range of 5.5 to 7.5 ppm was calculated, and 1/2 of the value was defined as X (mol%). When calculating the integrated value of 5.5 to 7.5 ppm, if a slope was found at the baseline, the area value of each peak was calculated in consideration of the slope.

[Measurement of 1,2-glycol bond amount (mol%)]
Polyvinyl alcohol Been 90 ° C. vacuum dried for 2 days, then dissolved in DMSO-d _6, was subjected to Samples were prepared measurement plus a few drops of trifluoroacetic acid. ¹ H-NMR measurement was performed at 80 ° C. using a nuclear magnetic resonance apparatus "LAMBDA 500" manufactured by JEOL Ltd. At this time, in the case of a sample having a saponification degree of less than 99.9 mol%, the sample was saponified to 99.9 mol% or more and then subjected to measurement. The peak derived from methine of vinyl alcohol unit is assigned to 3.2 to 4.0 ppm (integral value A), and the peak derived from one methine of 1,2-glycol bond is assigned to 3.25 ppm (integral value B). The 1,2-glycol bond content can be calculated with.
1,2-Glycol binding amount (mol%) = (B / A) x 100

[Evaluation of hue (YI)]
The obtained polyvinyl alcohol powder YI (ASTM D1925) was measured using a spectrophotometer "CM-8500d" manufactured by Konica Minolta Co., Ltd. (light source: D65, CM-A120 white calibration plate, CM-A126 Petri dish). Set use, specular reflection measurement SCE, measurement diameter φ30 mm). 5 g of the sample was added to the petri dish, and the powder was lightly tapped on the side surface without pressing the powder to shake it, and the powder was spread evenly and evenly. In this state, a total of 10 measurements were performed (each time the petri dish was shaken once and then remeasured), and the average value was obtained as the YI of the resin.

[Evaluation of high-speed coatability]
An aqueous solution having a concentration of 10% by mass was prepared using the obtained polyvinyl alcohol. Using a high-grade flow tester "301 type" manufactured by Shimadzu Corporation, this aqueous solution was used with a die diameter of 0.2 mm, a die length of 5 mm, a temperature of 30 ° C., a preheating time of 5 minutes, and a shear rate of 1 × 10 ^{3 to} 5. The solution viscosity was measured within the range of × 10 ^{6 / s.} The evaluation of high-speed coatability was judged according to the following criteria.
◯: Shear rate at which the shear viscosity is maximum is 7.32 × 10 ⁵ / s or more Δ: Shear rate at which the shear viscosity is maximum is 2.20 × 10 ⁵ / s or more and ^{less than 7.32 × 10 5} / s × : shear rate shear viscosity reaches a maximum is less than 2.20 × ¹⁰ 5 / s

[Water resistance evaluation]
An aqueous polyvinyl alcohol solution having a concentration of 10% by mass was prepared, poured into a PET mold, and allowed to stand and dry in a room adjusted to 23 ° C. and 53% RH for one week.
The obtained film was removed from the mold, the film thickness at the center was measured with a thickness gauge, and a film having a film thickness of 100 to 200 μm was used as an evaluation target. The obtained film was immersed in water at 20 ° C. for 20 hours, and the elution rate [mass%] was calculated from the weight change before and after the immersion. The evaluation of water resistance was judged according to the following criteria.
◯: Elution rate less than 10% Δ: Elution rate 10% or more and less than 40% ×: Elution rate 40% or more

[Evaluation of mechanical strength]
A polyvinyl alcohol aqueous solution having a concentration of 10% by mass was prepared, poured into a PET mold, and allowed to stand for one week in a room adjusted to 23 ° C. and 90% RH. Using the autograph "AG-IS" manufactured by Shimadzu, strong elongation was measured under the conditions of a chuck distance of 50 mm and a tensile speed of 500 mm / min, and the maximum stress [kgf / mm ^{2] was measured under the conditions of 23 ° C. and 90% RH.} ] Was asked. The measurement was performed 5 times for each sample, and the average value was calculated. The evaluation of mechanical strength was judged according to the following criteria.
○: maximum stress 6.7kgf / mm ² or more △: maximum stress 3.5 kgf / mm ² or more, 6.7kgf / mm ² less ×: maximum stress 3.5 kgf / mm less than ²

[Evaluation of high-speed coatability of coating liquid]
An aqueous solution (coating liquid) having a concentration of 8% by mass was prepared using the obtained polyvinyl alcohol. This coating liquid was applied to high- ^{quality paper (basis weight 65 g / m 2} ) with a blade coater at a coating temperature of 30 ° C., a coating speed of 1200 m / min, and a gap of 0.004 mm between the paper and the blade. The shear rate applied to the coating liquid at this time is 5 × 10 ⁶ / s. After coating, it was dried in a drum dryer at 80 ° C. for 5 minutes. To evaluate whether the coating liquid is evenly applied to the obtained coated paper, apply colored toluene to the coated surface of the coated paper with a brush, observe the colored toluene coming out from the back surface, and use the following criteria. evaluated.
◯: Colored toluene is not strike-through and there is no uneven coloring on the coated surface. ×: Colored toluene is severely strike-through and there is uneven coloring on the coated surface.

[Example 1]
Add 0.037 parts by mass of cobalt (II) acetylacetonate to a reactor equipped with a stirrer, a reflux condenser, and an initiator addition port, evacuate the inside of the reactor, and then introduce nitrogen into the inert gas substitution. Was performed 3 times. After that, 100 parts by mass of vinyl acetate purified by simple distillation was added, 0.09 part by mass of N, N-dimethylaniline (hereinafter abbreviated as DMA) was added as a reducing agent, and then the reactor was immersed in a water bath. The mixture was heated and stirred so that the temperature became 30 ° C. After that, a toluene solution (concentration: 1% by mass) of diisopropylperoxydicarbonate (hereinafter abbreviated as IPP) was added as an oxidizing agent to 1.6 parts by mass per unit time until 1.5 hours after the start of addition, and then 0. It was added in 3 parts by mass (total amount of IPP added 0.033 parts by mass). Sampling was performed as appropriate, and the progress of polymerization was confirmed from the solid content concentration. When the conversion rate of vinyl acetate reached 20%, the water bath was replaced with ice water, and the internal temperature was rapidly cooled to 10 ° C. or lower. To this, 2.3 parts by mass of a methanol solution of sorbic acid (concentration: 10% by mass, 0.23 parts by mass as sorbic acid) was added as a polymerization inhibitor. The chain transfer constant of sorbic acid with respect to the vinyl acetate monomer at 60 ° C. exceeds 0.1. The induction period in the polymerization reaction was 2 hours, and the growth period was 2.5 hours.

After adding the polymerization inhibitor, the mixture was connected to a vacuum line and the remaining vinyl acetate was distilled off under reduced pressure at 15 ° C. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol. Then, the mixture was heated to 30 ° C., and methanol was distilled off under reduced pressure at 35 ° C. while adding ethyl acetate to obtain an ethyl acetate solution of polyvinyl acetate. To this, 94 parts by mass of an acetic acid aqueous solution (pH 2.0) having a concentration of 25% by mass was added, and the mixture was stirred for 5 minutes and then allowed to stand for 30 minutes to separate into two layers. After the aqueous layer was withdrawn with a syringe, it was connected to the vacuum line again, and the residual ethyl acetate was distilled off under reduced pressure at 30 ° C. When ethyl acetate was distilled off, methanol was added to dissolve polyvinyl acetate, and the solution was added dropwise to deionized water to precipitate polyvinyl acetate. Polyvinyl acetate was recovered by a filtration operation and dried in a vacuum dryer at 40 ° C. for 24 hours to obtain polyvinyl acetate. The details of the above polymerization steps are shown in Table 1.

Next, 100 parts by mass of the obtained polyvinyl acetate and 233 parts by mass of methanol were added and dissolved in the same reactor as above (concentration: 30% by mass), and then the water bath was heated to bring the internal temperature to 40 ° C. Was heated and stirred until. To this, 33.2 parts by mass of a methanol solution of sodium hydroxide (concentration: 14% by mass) was added, and saponification was carried out at 40 ° C. (4.6 parts by mass as sodium hydroxide). The produced gelled product was pulverized with a pulverizer and left at 40 ° C. for 1 hour to proceed with saponification. To the obtained saponified product, 33.2 parts by mass of a methanol solution of sodium hydroxide (concentration: 14% by mass) was further added, and the saponification reaction was driven for another 1 hour under heating and refluxing at 65 ° C. Then, 200 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming that the neutralization was completed using the phenolphthalein indicator, a solid was obtained by filtration, and 500 parts by mass of methanol was added thereto and the mixture was heated under reflux for 1 hour. Then, the solid obtained by centrifugal dehydration was dried in a vacuum dryer at 40 ° C. for 24 hours to obtain polyvinyl alcohol. The details of the above saponification process are shown in Table 2.

Various physical properties of the obtained polyvinyl alcohol were measured and the performance was evaluated. The degree of saponification was 99.9 mol%, the number average molecular weight (Mn) was 74,800, and the molecular weight distribution (Mw / Mn) was 1.30. The content of the lactone ring and the carboxyl group was less than the measurement limit of 0.005 mol%. The carbon-carbon double bond content (X) was 0.0018 mol%. The content of 1,2-glycol bond was 1.3 mol%. Hue (YI) is 15.0, the evaluation of high-speed coatability is 7.33 × 10 5 ^{/ s,} the water resistance evaluation is ○, evaluation of the mechanical strength was ○. The above results are summarized in Table 3. The high-speed coatability of the coating solution consisting of the obtained aqueous solution of polyvinyl alcohol was evaluated as ◯.

[Example 2]
0.037 parts by mass of cobalt (II) acetylacetonate was added to the same reactor as in Example 1, the inside of the reactor was evacuated, and then the inert gas substitution was carried out three times to introduce nitrogen. After that, 100 parts by mass of vinyl acetate purified by simple distillation was added, 100 parts by mass of methyl acetate obtained by simple distillation was added, 0.09 part by mass of DMA was added as a reducing agent, and then the reactor was immersed in a water bath to provide an internal temperature. Was heated to 30 ° C. and stirred. After that, a toluene solution of IPP (concentration 1% by mass) was added as an oxidizing agent in an amount of 1.6 parts by mass per unit time until 1.5 hours after the start of addition, and then 0.3 parts by mass per unit time (total amount of IPP added). 0.044 parts by mass). When the conversion of vinyl acetate reached 30%, the water bath was replaced with ice water, and the internal temperature was rapidly cooled to 10 ° C. or lower. Subsequent operations were the same as those described in Example 1 to obtain polyvinyl acetate. The induction period in the polymerization reaction was 2 hours, and the growth period was 6 hours. The details of the above polymerization steps are shown in Table 1.

Next, 100 parts by mass of the obtained polyvinyl acetate and 400 parts by mass of methanol were added and dissolved in the same reactor as above (concentration 20% by mass), and a methanol solution of sodium hydroxide (concentration 14% by mass) was added. ) A saponification reaction was carried out in two steps in the same manner as in Example 1 except that 45.7 parts by mass was added (6.4 parts by mass as sodium hydroxide) to obtain polyvinyl alcohol. The details of the above saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are summarized in Table 3.

[Example 3]
Add 0.019 parts by mass of cobalt (II) acetylacetonate, add 0.04 parts by mass of DMA as a reducing agent, and add a toluene solution of IPP (concentration 1% by mass) as an oxidizing agent until 1.5 hours after the start of addition. The polymerization reaction of vinyl acetate was carried out under the same conditions as in Example 1 except that the mixture was added in an amount of 0.8 parts by mass per unit time and then 0.15 parts by mass per unit time (total amount of IPP added: 0.017 parts by mass). rice field. When the conversion of vinyl acetate reached 25%, the water bath was replaced with ice water, and the internal temperature was rapidly cooled to 10 ° C. or lower. Here, 1.2 parts by mass of a methanol solution of sorbic acid (chain transfer constant with respect to vinyl acetate monomer at 60 ° C. exceeds 0.1) as a polymerization inhibitor (concentration: 10% by mass, 0.12% by mass as sorbic acid). Part) was added. Subsequent operations were the same as those described in Example 1 to obtain polyvinyl acetate. The induction period in the polymerization reaction was 2 hours, and the growth period was 3.1 hours. The details of the above polymerization steps are shown in Table 1.

Next, 100 parts by mass of the obtained polyvinyl acetate and 900 parts by mass of methanol were added and dissolved in the same reactor as above (concentration: 10% by mass), and then the water bath was heated to bring the internal temperature to 40 ° C. Was heated and stirred until. 77 parts by mass of a methanol solution of sodium hydroxide (concentration: 10% by mass) was added thereto, and saponification was carried out at 40 ° C. (7.7 parts by mass as sodium hydroxide). The produced gelled product was pulverized with a pulverizer, left at 40 ° C. for 1 hour, and then saponified for 1 hour, and then 200 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming that the neutralization was completed using the phenolphthalein indicator, a solid was obtained by filtration, and 500 parts by mass of methanol was added thereto and the mixture was heated under reflux for 1 hour. Then, the solid obtained by centrifugal dehydration was dried in a vacuum dryer at 40 ° C. for 24 hours to obtain polyvinyl alcohol. The details of the saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are summarized in Table 3. The details of the above saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are summarized in Table 3.

[Example 4]
Polyvinyl acetate was obtained under the same conditions as in Example 1. The induction period in the polymerization reaction was 2 hours, and the growth period was 2.5 hours. The details of the above polymerization steps are shown in Table 1.

Next, 100 parts by mass of the obtained polyvinyl acetate and 233 parts by mass of methanol were added and dissolved in the same reactor as above (concentration: 30% by mass), and then the water bath was heated to bring the internal temperature to 40 ° C. Was heated and stirred until. Described in Example 3 except that 5.0 parts by mass of a methanol solution of sodium hydroxide (concentration: 14% by mass) was added and saponification was performed at 40 ° C. (0.70 parts by mass as sodium hydroxide). A saponification reaction was carried out in one step in the same manner as in the method to obtain polyvinyl alcohol. The details of the saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are summarized in Table 3.

[Example 5]
0.037 parts by mass of cobalt (II) acetylacetonate in a reactor equipped with a stirrer, a reflux cooling tube, and an initiator addition port, and 2,2'-azobis (4-methoxy-2,4-) as an initiator. 0.13 parts by mass of dimethylvaleronitrile (hereinafter abbreviated as V-70) was added, the inside of the reactor was evacuated, and then the inert gas substitution to introduce nitrogen was performed three times. Then, 100 parts by mass of vinyl acetate purified by simple distillation was added, and then the reactor was immersed in a water bath, heated and stirred so that the internal temperature became 30 ° C. Sampling was performed as appropriate, and the progress of polymerization was confirmed from the solid content concentration. When the conversion rate of vinyl acetate reached 20%, the water bath was replaced with ice water, and the internal temperature was rapidly cooled to 10 ° C. or lower. To this, 2.3 parts by mass of a methanol solution of sorbic acid (concentration: 10% by mass, 0.23 parts by mass as sorbic acid) was added as a polymerization inhibitor. The induction period in the polymerization reaction was 6 hours, and the growth period was 2.5 hours. The details of the above polymerization steps are shown in Table 1.

After adding the polymerization inhibitor, the mixture was connected to a vacuum line and the remaining vinyl acetate was distilled off under reduced pressure at 15 ° C. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol, and the internal temperature was further raised to 50 ° C. and heated and stirred for 1 hour. Then it was cooled to 30 ° C. Subsequent operations were the same as those described in Example 1 to obtain polyvinyl acetate. The details of the above polymerization steps are shown in Table 1.

Further, in the saponification step, the same method as described in Example 1 was carried out except that 36.4 parts by mass (5.1% by mass as sodium hydroxide) of a methanol solution of sodium hydroxide (concentration 14% by mass) was added. The saponification reaction was carried out in two steps to obtain polyvinyl alcohol. The details of the saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are shown in Table 3, and the evaluation results of mechanical strength are shown in FIG.

[Example 6]
The polymerization reaction of vinyl acetate was carried out under the same conditions as in Example 1. When the conversion of vinyl acetate reached 18%, the water bath was replaced with ice water, and the internal temperature was rapidly cooled to 10 ° C. or lower. Subsequent operations were the same as those described in Example 1 to obtain polyvinyl acetate. The induction period in the polymerization reaction was 2 hours, and the growth period was 2.3 hours. The details of the above polymerization steps are shown in Table 1.

Next, 100 parts by mass of the obtained polyvinyl acetate and 233 parts by mass of methanol were added and dissolved in the same reactor as above (concentration: 30% by mass), and then the water bath was heated to bring the internal temperature to 40 ° C. Was heated and stirred until. Described in Example 3 except that 182.9 parts by mass of a methanol solution of sodium hydroxide (concentration: 14% by mass) was added and saponification was performed at 40 ° C. (25.6 parts by mass as sodium hydroxide). A saponification reaction was carried out in one step in the same manner as in the method to obtain polyvinyl alcohol. The details of the saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are summarized in Table 3.

[Comparative Example 1]
A reactor equipped with a stirrer, a reflux condenser, an argon introduction tube, and an initiator addition port was charged with 100 parts by mass of vinyl acetate and 40 parts by mass of methanol, and the inside of the reactor was replaced with an inert gas for 30 minutes while nitrogen bubbling. did. The temperature of the reactor was started by heating the water bath, and when the internal temperature reached 60 ° C., 0.025 parts by mass of azobisisobutyronitrile (AIBN) was added as an initiator to start the polymerization. Sampling was appropriately performed, the progress of the polymerization was confirmed from the solid content concentration, and when the conversion of vinyl acetate reached 30%, the mixture was cooled to 30 ° C. to terminate the polymerization. It was connected to a vacuum line and the residual vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain a methanol solution of polyvinyl acetate. The induction period in the polymerization reaction was 0.2 hours, and the growth period was 2.7 hours. The details of the above polymerization steps are shown in Table 1.

Saponification reaction in the same manner as in Example 4 except that methanol was added to the obtained polyvinyl acetate methanol solution (150 parts by mass as polyvinyl acetate) to adjust the concentration of polyvinyl acetate to 30% by mass. Was carried out to obtain polyvinyl alcohol. The details of the saponification process are shown in Table 2. Table 3 shows the results of measurement and evaluation of the obtained polyvinyl alcohol, and FIG. 1 shows the evaluation results of mechanical strength. The evaluation of the high-speed coatability of the coating solution composed of the obtained aqueous solution of polyvinyl alcohol was x.

[Comparative Example 2]
Polymerization of vinyl acetate was carried out under the same conditions as in Comparative Example 1. The induction period in the polymerization reaction was 0.2 hours, and the growth period was 2.7 hours. The details of the above polymerization steps are shown in Table 1.

Methanol was added to the obtained polyvinyl acetate methanol solution (150 parts by mass as polyvinyl acetate) to adjust the concentration of polyvinyl acetate to 30% by mass, and the methanol solution of sodium hydroxide (concentration 14% by mass). A saponification reaction was carried out in one step in the same manner as in Example 3 except that 65.7 parts by mass (9.2 parts by mass of sodium hydroxide) was added to obtain polyvinyl alcohol. The details of the saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are summarized in Table 3.

[Comparative Example 3]
Add 0.15 parts by mass of cobalt (II) acetylacetonate, add 0.70 parts by mass of DMA as a reducing agent, and add a toluene solution of IPP (concentration 5% by mass) as an oxidizing agent until 1.7 hours after the start of addition. The polymerization reaction of vinyl acetate was carried out under the same conditions as in Example 1 except that it was added in an amount of 3.8 parts by mass per unit time and then 0.96 parts by mass per unit time (total amount of IPP added 0.52 parts by mass). rice field. When the conversion of vinyl acetate reached 16%, the water bath was replaced with ice water, and the internal temperature was rapidly cooled to 10 ° C. or lower. To this, 9.4 parts by mass (concentration: 10% by mass, 0.94 parts by mass as sorbic acid) of a methanol solution of sorbic acid was added as a polymerization inhibitor. The induction period in the polymerization reaction was 2.5 hours, and the growth period was 3.2 hours. Subsequent operations were the same as those described in Example 1 to obtain polyvinyl acetate. The details of the above polymerization steps are shown in Table 1.

Next, 100 parts by mass of the obtained polyvinyl acetate and 150 parts by mass of methanol were added and dissolved in the same reactor as above (concentration 40% by mass), and a methanol solution of sodium hydroxide (concentration 14% by mass) was added. ) A saponification reaction was carried out in two steps in the same manner as in Example 1 except that 21.8 parts by mass (3.05 parts by mass as sodium hydroxide) was added to obtain polyvinyl alcohol. The details of the above saponification process are shown in Table 2. The results of measurement and evaluation of the obtained polyvinyl alcohol are summarized in Table 3.

[Comparative Example 4]
Vinyl acetate was polymerized under the same conditions as in Comparative Example 1 except that 4.8 parts by mass of methanol and 0.003 parts by mass of AIBN as an initiator were added. The induction period in the polymerization reaction was 0.2 hours, and the growth period was 2.7 hours. The details of the above polymerization steps are shown in Table 1.

Methanol was added to the obtained polyvinyl acetate methanol solution (150 parts by mass as polyvinyl acetate) to adjust the concentration of polyvinyl acetate to 10% by mass, and the methanol solution of sodium hydroxide (concentration 14% by mass). A saponification reaction was carried out in two steps in the same manner as in Example 1 except that 42.1 parts by mass (5.9 parts by mass of sodium hydroxide) was added to obtain polyvinyl alcohol. The details of the saponification process are shown in Table 2. Table 3 shows the results of measurement and evaluation of the obtained polyvinyl alcohol, and FIG. 1 shows the evaluation results of mechanical strength.

Claims (7)

The number average molecular weight (Mn) is 44,000 to 440,000, the molecular weight distribution (Mw / Mn) is 1.05 to 1.60 , the saponification degree is 80 to 99.99 mol%, and the total unit weight is Polyvinyl alcohol having a total content of carboxyl groups and lactones of 0.03 mol% or less per body unit. The polyvinyl alcohol according to claim 1, wherein the content (X) of the carbon-carbon double bond with respect to all the monomer units is 0.1 mol% or less, and the following formula (1) is satisfied.
X · Mn ≤ 1000 (1) The polyvinyl alcohol according to claim 1 or 2, wherein the yellow index (YI) measured according to ASTM D1925 is 50 or less. The polyvinyl alcohol according to any one of claims 1 to 3, wherein the total content of the carboxyl group and the lactone is 0.005 mol% or less. The polyvinyl alcohol according to any one of claims 1 to 4, wherein the content of 1,2-glycol bond is 0.7 to 1.5 mol%. A coating liquid comprising an aqueous solution containing polyvinyl alcohol according to any one of claims 1 to 5. A coating paper obtained by applying the coating liquid according to claim 6 to the surface of a base material.

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