JP2009221461A - Vinyl alcohol-based polymer and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vinyl alcohol-based polymer which has excellent mechanical properties, water resistance, weatherability, colorless and transparent properties, and viscosity stability in an aqueous solution, and can be easily used for preparing a mixed liquid with an inorganic material and effectively used for films, coating films, formed bodies and the like; and to provide a method for producing the same. <P>SOLUTION: As for the vinyl alcohol-based polymer, the viscosity-average polymerization degree is 4,000-8,000; the degree of saponification is 99.50-99.97 mol%; the content of 1,2-glycol bonding unit is 1-1.5 mol%; the time until the viscosity of its aqueous solution having viscosity of 1,000 mPa s increasing to 2,000 mPa s at 10°C is 50-250 min; and the absorbance of its aqueous solution after concentration correction at a wavelength of 280 nm and 320 nm is ≤0.02 L/g as measured at 20°C by using a cell having an optical path length of 30 mm. The method for producing the vinyl alcohol-based polymer is also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vinyl alcohol polymer and a method for producing the same. More specifically, a vinyl alcohol polymer aqueous solution or an inorganic substance-containing vinyl alcohol polymer aqueous solution having a high degree of polymerization, excellent water resistance, weather resistance, transparency, no coloring, and excellent viscosity stability is prepared. The present invention relates to a vinyl alcohol polymer that can be used and a method for producing the same.

  Vinyl alcohol polymers represented by polyvinyl alcohol are known as water-soluble synthetic polymers, and are raw materials for synthetic fiber vinylon, paper and fiber processing agents, adhesives, stabilizers for emulsion polymerization and suspension polymerization. It is widely used in various applications such as inorganic binders and films. Vinyl alcohol polymers are particularly superior in strength properties and film-forming properties compared to other synthetic polymers, and they are used in clear coating agents and pigment coatings to improve the surface properties of paper. It is heavily used as a raw material for producing binders, water-soluble films and optical films.

Various studies have been made for the purpose of further improving the strength characteristics, the binder properties against inorganic substances, and the film-forming properties of vinyl alcohol polymers, and one of them is to increase the degree of polymerization of vinyl alcohol polymers. It has been attempted to do so.
As such a conventional technique, for example, in the polymerization of vinyl ester, while maintaining the pressure in the polymerization system at 500 mmHg or less, the temperature in the polymerization system is set to 50 ° C. or less, and polymerization is performed while boiling the vinyl ester. A method is known in which an ester polymer is produced, and a vinyl ester polymer obtained thereby is saponified to produce polyvinyl alcohol (Patent Document 1). However, when this method is used, it is difficult to obtain a polyvinyl alcohol having a degree of polymerization of 4000 or more, and the obtained polyvinyl alcohol is colored and inferior in colorless transparency or inferior in water resistance. There are problems such as poor viscosity stability when it is made into an aqueous solution.

  As another conventional technique, a vinyl ester polymer is produced by emulsion polymerization under reduced pressure in the presence of an emulsifier to produce a vinyl ester polymer, and the resulting vinyl ester polymer is saponified to produce a vinyl alcohol polymer. There is known a method of manufacturing (Patent Document 2). When this method is used, it is possible to remove the heat of polymerization and prevent the generation of scale during polymerization by emulsion polymerization of vinyl ester in an aqueous medium, but vinyl ester polymer particles produced by emulsion polymerization. In order to perform removal of unreacted vinyl ester and subsequent saponification treatment of vinyl ester polymer, vinyl ester polymer particles were dissolved in alcohol by adding aqueous emulsion containing The production process of the alcohol polymer is likely to be complicated. In addition, when this method is used, there is a risk that the emulsifier used for emulsion polymerization is mixed in the vinyl ester polymer to be produced and the vinyl alcohol polymer obtained by saponifying it, resulting in coloration or quality deterioration. is there. Furthermore, when this method is used, a vinyl alcohol polymer having a degree of polymerization exceeding 10,000, difficult to handle, and having a very high degree of polymerization is generally easily generated. Further, in Patent Document 2, physical properties of a vinyl alcohol polymer obtained by this method (for example, water resistance of a molded product such as a film or film obtained from the vinyl alcohol polymer, presence or absence of coloring, weather resistance, There is no disclosure about the viscosity stability of aqueous solutions prepared from vinyl alcohol polymers.

  From the above points, aqueous solutions and inorganic-containing aqueous solutions having a high degree of polymerization, excellent mechanical properties, excellent handleability, water resistance, weather resistance, transparency, film-forming properties, no coloration, and excellent viscosity stability There is a demand for a vinyl alcohol polymer that can be used to prepare the above and a method for producing the same.

Japanese Patent Publication No.33-3045 Japanese Patent Laid-Open No. 5-117307

The object of the present invention is to prepare an aqueous solution having a high degree of polymerization, excellent mechanical properties, excellent handleability, water resistance, weather resistance, transparency, film-forming property, no coloration, and excellent viscosity stability. It is possible to provide a vinyl alcohol polymer capable of producing a molded body such as a film or film excellent in water resistance and an inorganic mixed film, and a method for producing the same.
Specifically, the present invention has a high degree of polymerization, excellent mechanical properties, water resistance, and weather resistance, and excellent handling properties despite its high degree of polymerization, so that a vinyl alcohol polymer aqueous solution can be smoothly produced. The aqueous solution of vinyl alcohol polymer that can be prepared is excellent in viscosity stability and does not increase in viscosity even when left for a long time. Films, films, etc. obtained from the vinyl alcohol polymer The molded product is not colored, the dissolution rate when the molded product such as a film made of the vinyl alcohol polymer is immersed in water is small, and it is easy to prepare a mixed aqueous solution of the vinyl alcohol polymer and an inorganic material. , Vinyl alcohol polymers having various excellent characteristics such as a molded body such as an inorganic mixed film obtained from the mixed aqueous solution having excellent water resistance, and production thereof It is an object to provide law.

  The present inventors have repeatedly studied to achieve the above object. As a result, the viscosity average polymerization degree (P) is 4000 to 8000, the saponification degree is 99.50 to 99.97 mol%, the content of 1,2-glycol bond units is in a specific range, and the aqueous solution Vinyl alcohol polymers that exhibit specific thickening properties and absorbance when used are excellent in mechanical properties, water resistance, weather resistance, colorless transparency, and in viscosity stability when made into aqueous solutions. The film formed from the vinyl alcohol polymer and other molded articles are not colored, and the dissolution rate when the molded article such as a film formed from the vinyl alcohol polymer is immersed in water is small. The mixture solution of the vinyl alcohol polymer and the inorganic substance can be easily prepared, and the molded body such as a film formed from the mixture solution has a small degree of swelling with respect to water and water resistance. It was found, such as to have an excellent.

  Further, the present inventors have described that the vinyl alcohol polymer having the above-described excellent characteristics includes a vinyl ester monomer mixture obtained by mixing alcohol in a predetermined ratio with a vinyl ester monomer in a polymerization tank. The vinyl ester monomer mixture at a predetermined polymerization rate in a boiling state while maintaining the pressure in the polymerization tank at a reduced pressure at a temperature below the boiling point of the vinyl ester monomer mixture under atmospheric pressure. To produce a vinyl ester polymer, then add a polymerization inhibitor to the reaction product containing the vinyl ester polymer, and replace the vinyl ester monomer remaining in the reaction product with alcohol. And then saponifying the vinyl ester polymer so as to obtain a vinyl alcohol polymer having a predetermined saponification degree in the presence of an alkaline substance. Found that can be produced in smooth, the present invention has been completed based on these findings.

That is, the present invention
(1) A vinyl alcohol polymer that satisfies the following requirements << 1 >> to << 5 >>.
<1> The viscosity average degree of polymerization (P) is 4000 to 8000;
<< 2 >> The degree of saponification is 99.50 to 99.97 mol%;
<3> The content of 1,2-glycol bond units is 1 to 1.5 mol%;
<< 4 >> When the vinyl alcohol polymer is dissolved in water to prepare a vinyl alcohol polymer aqueous solution having a viscosity at 10 ° C. of 10,000 mPa · s, and the aqueous solution is allowed to stand at 10 ° C., the viscosity is The time required to increase to 20000 mPa · s is 50 to 250 minutes; and
<< 5 >> A vinyl alcohol polymer aqueous solution with a concentration of 30 g / L prepared by dissolving the vinyl alcohol polymer in water [in the case of a vinyl alcohol polymer having a viscosity average polymerization degree (P) of less than 6000] or concentration 10 g / L of a vinyl alcohol polymer aqueous solution [in the case of a vinyl alcohol polymer having a viscosity average degree of polymerization (P) of 6000 or more] measured using a cell having an optical path length of 30 mm, at wavelengths of 280 nm and 320 nm. The absorbance after the concentration correction (measurement temperature: 20 ° C.) is 0.02 L / g or less.
And this invention,
(2) The vinyl alcohol polymer according to (1), wherein the content of sodium acetate is 2% by mass or less.

Furthermore, the present invention provides
(3) (i) A vinyl ester monomer mixture containing alcohol at a ratio of 2.5 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester monomer is charged into the polymerization tank, and the vinyl ester monomer The vinyl ester monomer is polymerized at a polymerization rate of 8 to 30% by mass in a boiling state while maintaining the pressure in the polymerization tank at a reduced pressure at a temperature below the boiling point of the monomer mixture at atmospheric pressure. A vinyl ester polymer having a polymerization degree to become a vinyl alcohol polymer having a viscosity average polymerization degree (P) of 4000 to 8000 after conversion, and then (ii) a vinyl ester polymer obtained in the step (i) After adding a polymerization inhibitor to the reaction product containing the polymer and replacing the vinyl ester monomer remaining in the reaction product with alcohol, the vinyl ester polymer is removed in the presence of an alkaline substance. The In the method for producing a vinyl alcohol polymer according to the above (1) or (2), the saponification is carried out under conditions for producing a vinyl alcohol polymer having a saponification degree of 99.50 to 99.97 mol%. is there.

And this invention,
(4) In the polymerization step (i), a vinyl ester monomer mixture containing alcohol at a ratio of 2.5 to 8 parts by mass with respect to 100 parts by mass of the vinyl ester monomer is charged into the polymerization tank. The method for producing a vinyl alcohol polymer according to (3) above, wherein a vinyl ester monomer is produced by polymerizing a vinyl ester monomer at a polymerization rate of 10 to 20% by mass;
(5) The method for producing a vinyl alcohol polymer according to (3) or (4), wherein the polymerization step (i) is performed in the presence of an organic acid that suppresses aldehyde formation due to decomposition of the vinyl ester monomer. ;and,
(6) In the step (ii), the addition amount of the polymerization inhibitor is 1 to 10 mol with respect to 1 mol of undecomposed polymerization initiator remaining in the reaction product. ) Any one of the methods for producing a vinyl alcohol polymer;
It is.

The vinyl alcohol polymer of the present invention that satisfies the above requirements << 1 >> to << 5 >> has excellent mechanical properties, water resistance, weather resistance, colorless transparency, and excellent viscosity stability when made into an aqueous solution. ing. Therefore, the film, coating film, molded product, etc. formed from the vinyl alcohol polymer of the present invention are not colored, have excellent colorless transparency, are not easily discolored even after a long time, and are immersed in water. In this case, the elution rate and the degree of swelling are small, the water resistance is further improved, the scratches are hard to be damaged, and the scratch resistance is excellent.
Furthermore, the vinyl alcohol polymer of the present invention forms a stable mixed solution with an inorganic substance, and can smoothly produce a film or the like from the mixed solution. The resulting film or the like has a low degree of swelling with respect to water. Excellent water resistance. Therefore, the vinyl alcohol polymer of the present invention exhibits excellent performance when used as a coating agent in combination with an inorganic substance.
Further, by preparing a coating agent using the vinyl alcohol polymer of the present invention and applying it to a substrate, an ink jet recording material excellent in various performances such as ink absorbability and glossiness can be obtained. .
By the production method of the present invention, the vinyl alcohol polymer of the present invention having the above-described excellent characteristics can be produced smoothly.

The present invention is described in detail below.
As described above, the vinyl alcohol polymer of the present invention is as follows.
<1> The viscosity average degree of polymerization (P) is 4000 to 8000;
<< 2 >> The degree of saponification is 99.50 to 99.97 mol%;
<3> The content of 1,2-glycol bond units is 1 to 1.5 mol%;
<< 4 >> When the vinyl alcohol polymer is dissolved in water to prepare a vinyl alcohol polymer aqueous solution having a viscosity at 10 ° C. of 10,000 mPa · s, and the aqueous solution is allowed to stand at 10 ° C., the viscosity is The time required to increase to 20000 mPa · s is 50 to 250 minutes; and
<< 5 >> A vinyl alcohol polymer aqueous solution with a concentration of 30 g / L prepared by dissolving the vinyl alcohol polymer in water [in the case of a vinyl alcohol polymer having a viscosity average polymerization degree (P) of less than 6000] or concentration 10 g / L of a vinyl alcohol polymer aqueous solution [in the case of a vinyl alcohol polymer having a viscosity average degree of polymerization (P) of 6000 or more] measured using a cell having an optical path length of 30 mm, at wavelengths of 280 nm and 320 nm. The absorbance after concentration correction (measurement temperature 20 ° C.) is 0.02 L / g or less in all cases;
The vinyl alcohol polymer satisfying the five requirements << 1 >> to << 5 >>.

The vinyl alcohol polymer of the present invention is required to satisfy the above-mentioned requirement << 1 >> that "viscosity average degree of polymerization (P) is 4000 to 8000". By satisfying the requirement << 1 >>, the vinyl alcohol polymer of the present invention is excellent in water resistance, heat resistance, and handleability. Further, the vinyl alcohol polymer aqueous solution is easy to prepare, and the vinyl alcohol polymer aqueous solution. It has excellent viscosity stability, ease of preparation of mixed aqueous solutions with inorganic substances, and the like.
When the viscosity average polymerization degree (P) of the vinyl alcohol polymer is less than 4000, a film or a film formed by containing an inorganic substance in the vinyl alcohol polymer easily swells in water, resulting in a decrease in water resistance. To do. Moreover, when the viscosity average polymerization degree (P) of the vinyl alcohol polymer is less than 4000, the viscosity stability of the vinyl alcohol polymer aqueous solution may be lowered, and the viscosity increase with time may be increased. On the other hand, if the viscosity average degree of polymerization (P) of the vinyl alcohol polymer exceeds 8000, the aqueous solution viscosity of the vinyl alcohol polymer becomes too high, resulting in poor handling, and the vinyl alcohol polymer and the inorganic substance. It tends to be difficult to prepare a mixed aqueous solution.
The vinyl alcohol polymer of the present invention has a viscosity average degree of polymerization in terms of water resistance, handleability, viscosity stability when made into an aqueous solution, ease of preparation of a mixed aqueous solution of a vinyl alcohol polymer and an inorganic substance, and the like. (P) is preferably 4200-7500, more preferably 4500-7000.

Here, the viscosity average degree of polymerization (P) of the vinyl alcohol polymer in this specification is a viscosity average degree of polymerization measured according to JIS-K6726. That is, the viscosity average polymerization degree (P) of the vinyl alcohol polymer is determined by re-saponifying the vinyl alcohol polymer to a saponification degree of 99.5 mol% or more, purifying it, and then using the aqueous solution at 30 ° C. It is calculated | required according to the following numerical formula (I) from intrinsic viscosity [(eta)] measured by (1).

Viscosity average degree of polymerization (P) = ([η] × 1000 / 8.29) ^{(1 / 0.62)} (I)

The vinyl alcohol polymer of the present invention is required to satisfy the above requirement << 2 >> that “the degree of saponification is 99.50 to 99.97 mol%”, and satisfies the requirement << 2 >>. Therefore, it is easy to prepare an aqueous vinyl alcohol polymer solution or a mixed aqueous solution of a vinyl alcohol polymer and an inorganic substance, and from these aqueous solutions, a film, a film, a molded article having excellent water resistance can be obtained. It is formed.
When the saponification degree of the vinyl alcohol polymer is less than 99.50 mol%, the vinyl alcohol polymer is dissolved in water to prepare a vinyl alcohol polymer aqueous solution having a viscosity at 10 ° C. of 10,000 mPa · s. When the aqueous solution is allowed to stand at 10 ° C., the time required for the viscosity to increase to 20000 mPa · s exceeds 250 minutes, and the film, coating, and molding formed from the vinyl alcohol polymer aqueous solution. The water swell degree of the body or a film or film formed from a mixed aqueous solution of vinyl alcohol polymer and inorganic substance increases, and the water resistance decreases. On the other hand, if the saponification degree of the vinyl alcohol polymer exceeds 99.97 mol%, it becomes difficult to prepare an aqueous solution of the vinyl alcohol polymer or a mixed aqueous solution containing the vinyl alcohol polymer and an inorganic substance. When an aqueous solution is used, the viscosity increases with time, and the stability and handleability of the aqueous solution become poor.
The saponification degree of the vinyl alcohol polymer of the present invention is water resistance, ease of preparation of a vinyl alcohol polymer aqueous solution or a mixed aqueous solution of a vinyl alcohol polymer and an inorganic material, viscosity stability of the vinyl alcohol polymer aqueous solution. From the viewpoints of properties and handling properties, it is preferably 99.58 to 99.96 mol%, more preferably 99.65 to 99.95 mol%.

The vinyl alcohol polymer of the present invention needs to satisfy the above-mentioned requirement << 3 >> that "the content of 1,2-glycol bond units is 1 to 1.5 mol%". By satisfying the requirement << 3 >>, the vinyl alcohol polymer is excellent in water resistance, easy to prepare a vinyl alcohol polymer aqueous solution, easy to prepare a mixed aqueous solution of a vinyl alcohol polymer and an inorganic substance, In addition, the viscosity stability of the vinyl alcohol aqueous solution is excellent.
When the content of 1,2-glycol bond units in the vinyl alcohol polymer is less than 1 mol%, the viscosity stability of the aqueous solution prepared using the vinyl alcohol polymer is lowered, and the viscosity increases with time. In addition, it is difficult to prepare a mixed aqueous solution of a vinyl alcohol polymer and an inorganic substance. On the other hand, when the content of 1,2-glycol bond units in the vinyl alcohol polymer exceeds 1.5 mol%, the water resistance of a molded article (film, film, inorganic material-containing film, etc.) made of the vinyl alcohol polymer. Tends to be lowered.
The vinyl alcohol polymer of the present invention is water resistant, easy to prepare a vinyl alcohol polymer aqueous solution, viscosity stability of an aqueous solution prepared from the vinyl alcohol polymer, and a mixed aqueous solution of a vinyl alcohol polymer and an inorganic substance. From the point of easiness of preparation, etc., the 1,2-glycol bond unit has a ratio of 1.2 to 1.5 mol% based on the total number of moles of all structural units constituting the vinyl alcohol polymer. It is preferable.

The “content of 1,2-glycol bond unit” in the present specification means the ratio (mol%) of “1,2-glycol bond unit” to “total vinyl alcohol unit” in the vinyl alcohol polymer. .
The content of 1,2-glycol bond units can be determined using NMR as described in the examples below.

  By adopting the production method of the present invention described later, the vinyl alcohol polymer of the present invention in which the content of 1,2-glycol bond units is in the range of 1 to 1.5 mol% can be produced smoothly. it can. Further, when producing a vinyl alcohol polymer according to the method of the present invention, a small amount of ethylene carbonate is copolymerized with the vinyl ester monomer or the polymerization temperature is changed during the production of the vinyl ester polymer. The content of 1,2-glycol bonding units can be further adjusted.

The vinyl alcohol polymer of the present invention is prepared by “dissolving the vinyl alcohol polymer in water to prepare a vinyl alcohol polymer aqueous solution having a viscosity of 10,000 mPa · s at 10 ° C., and the aqueous solution at 10 ° C. It is necessary to satisfy the above-mentioned requirement << 4 >> that the time required for the viscosity to increase to 20000 mPa · s when standing is 50 to 250 minutes. When the vinyl alcohol polymer satisfies the requirement << 4 >>, a vinyl alcohol polymer aqueous solution that is less thickened over a long period of time and has excellent viscosity stability and handleability, and a mixture of an inorganic substance and a vinyl alcohol polymer An aqueous solution can be prepared, and a film, a film, a molded body, a mixed film with an inorganic material, and the like excellent in water resistance can be formed.
When the viscosity of a vinyl alcohol polymer aqueous solution having a viscosity of 10,000 mPa · s is less than 50 minutes for the viscosity of the aqueous solution of vinyl alcohol polymer to increase to 20000 mPa · s at 10 ° C., when preparing a mixed aqueous solution with an inorganic substance, Gelation occurs early and a stable mixed aqueous solution cannot be prepared. On the other hand, a vinyl alcohol polymer in which the time required for the viscosity of a vinyl alcohol polymer aqueous solution having a viscosity of 10,000 mPa · s to increase to 20000 mPa · s at 10 ° C. exceeds 250 minutes is a mixture of an inorganic substance and a vinyl alcohol polymer. A film formed using an aqueous solution easily swells in water and has poor water resistance.
The vinyl alcohol polymer of the present invention is prepared by dissolving the vinyl alcohol polymer in water to prepare a vinyl alcohol polymer aqueous solution having a viscosity at 10 ° C. of 10,000 mPa · s. When it is placed, it is preferable that the time required for the viscosity to increase to 20000 mPa · s is 60 to 240 minutes.

By adjusting the degree of polymerization, the degree of saponification, and the content of 1,2-glycol bonding units within the range specified in the present invention, a vinyl alcohol-based polymer having an aqueous solution viscosity behavior satisfying the above requirement << 4 >>. Can be combined.
Moreover, the vinyl alcohol polymer which shows aqueous solution viscosity behavior which satisfies said requirements << 4 >> can be obtained also by adjusting content, such as sodium acetate, in a vinyl alcohol polymer. That is, when the content of sodium acetate is large, the thickening rate of the aqueous vinyl alcohol polymer solution increases, whereas when the content of sodium acetate is low, the thickening rate of the aqueous vinyl alcohol polymer solution decreases. Therefore, in the vinyl alcohol polymer of the present invention, the content of sodium acetate is not particularly limited as long as the requirement << 4 >> is satisfied, but the sodium acetate content is 2 mass based on the mass of the vinyl alcohol polymer. % Or less, further 1% by mass or less, particularly 0.5% by mass or less, a vinyl alcohol polymer having an aqueous solution behavior that satisfies the above requirement << 4 >> can be obtained more smoothly.

  The “vinyl alcohol polymer aqueous solution whose viscosity at 10 ° C. is 10000 mPa · s” for investigating whether the vinyl alcohol polymer satisfies the requirement << 4 >> is the viscosity of the vinyl alcohol polymer. Depending on the average degree of polymerization (P) (hereinafter sometimes simply referred to as “degree of polymerization”), it can be obtained by adjusting the concentration of the vinyl alcohol polymer during preparation of the aqueous solution of the vinyl alcohol polymer. For example, if the degree of polymerization of the vinyl alcohol polymer is 2400, the concentration is about 11% by mass. If the degree of polymerization is 4000, the concentration is about 8% by mass. If the degree of polymerization is 5000, about 7% by mass. If the degree of polymerization is 6000, the concentration is about 6% by mass, and if the degree of polymerization is 8000, the concentration is about 4% by mass, so that the vinyl alcohol system has a viscosity at 10 ° C. of 10,000 mPa · s. An aqueous polymer solution can be prepared. However, fine adjustment is necessary.

The vinyl alcohol polymer of the present invention is “a vinyl alcohol polymer aqueous solution with a concentration of 30 g / L prepared by dissolving the vinyl alcohol polymer in water [vinyl alcohol having a viscosity average polymerization degree (P) of less than 6000”. In the case of a system polymer] or a vinyl alcohol polymer aqueous solution having a concentration of 10 g / L (in the case of a vinyl alcohol polymer having a viscosity average polymerization degree (P) of 6000 or more), using a cell having an optical path length of 30 mm It is necessary to satisfy the above-mentioned requirement << 5 >> that the absorbance after the concentration correction at the wavelengths of 280 nm and 320 nm (measurement temperature: 20 ° C. is both 0.02 L / g or less).
As used herein, “vinyl alcohol polymer aqueous solution having a concentration of 30 g / L prepared by dissolving a vinyl alcohol polymer in water [vinyl alcohol heavy polymer having a viscosity average degree of polymerization (P) of less than 6000”. In the case of coalescence] or a vinyl alcohol polymer aqueous solution having a concentration of 10 g / L [in the case of a vinyl alcohol polymer having a viscosity average polymerization degree (P) of 6000 or more], measured using a cell having an optical path length of 30 mm. , “Absorbance after concentration correction at wavelengths of 280 nm and 320 nm (measurement temperature 20 ° C.)” refers to the absorbance of the aqueous vinyl alcohol polymer solution having a concentration of 30 g / L or 10 g / L as described above using a cell with an optical path length of 30 mm. The values of absorbance at a wavelength of 280 nm and absorbance at a wavelength of 320 nm obtained by measurement are measured with the vinyl alcohol used in the measurement. It refers to a value obtained by dividing (unit L / g) Le system concentration of the polymer solution (Unit g / L).
Hereinafter, the absorbance after concentration correction may be described as “absorbance after concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length: 30 mm)”.

When the vinyl alcohol polymer satisfies the requirement << 5 >>, it is possible to form a film, a film, a molded body, etc. that are not colored and excellent in color tone, and also excellent in weather resistance and not discolored.
When the absorbance (cell optical path length 30 mm) after concentration correction at a wavelength of 280 nm and 320 nm of a vinyl alcohol polymer aqueous solution having the above concentration exceeds 0.02 L / g, a film, a coating film, or a molded body made of a vinyl alcohol polymer Coloring may occur, and weather resistance may be reduced.
In the vinyl alcohol polymer of the present invention, the concentration-corrected absorbance (cell optical path length 30 mm) at wavelengths of 280 nm and 320 nm of the vinyl alcohol polymer aqueous solution having the above concentration prepared by dissolving the vinyl alcohol polymer in water. ) (Measurement temperature 20 ° C.) is preferably 0.018 L / g or less.
The lower limit of the absorbance after correction of the concentration (cell optical path length 30 mm) at wavelengths of 280 nm and 320 nm of the aqueous vinyl alcohol polymer solution is not particularly limited, but the absorbance is less than 0.008 L / g. Since it takes time and cost to remove impurities generated during the manufacturing process, it is practical that the absorbance is 0.008 L / g or more.
By adopting the production method of the present invention described later, the absorbance (cell optical path length 30 mm) (measurement temperature 20 ° C.) after concentration correction at wavelengths of 280 nm and 320 nm of the aqueous vinyl alcohol polymer solution having the above concentration is 0 at all. The vinyl alcohol polymer of the present invention that is 0.02 L / g or less can be produced smoothly.

  As long as the vinyl alcohol polymer of the present invention is within a range that does not impair the object and effect of the present invention, one or more structural units derived from other copolymerizable monomers are optionally included. You may have. The proportion of structural units derived from other copolymerizable monomers that the vinyl alcohol polymer of the present invention may have is the type of structural units derived from other monomers, vinyl alcohol polymers. In general, it is preferably 20 mol% or less, more preferably 10 mol% or less, based on all structural units constituting the vinyl alcohol polymer. More preferably, it is 5 mol% or less.

  Examples of structural units derived from other copolymerizable monomers that the vinyl alcohol polymer of the present invention can have as necessary include ethylene, propylene, 1-butene, isobutene, and 1-hexene. α-olefins; carboxylic acids or derivatives thereof such as fumaric acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride; acrylic acid or salts thereof, methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic Acrylic esters such as isopropyl acid; Methacrylic acid or salts thereof, Methyl methacrylate, Ethyl methacrylate, n-propyl methacrylate, Methacrylic acid esters such as isopropyl methacrylate; Acrylamide, N-methylacrylamide, N-ethylacrylamide Such as acrylamide Conductors; Methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether; ethylene glycol vinyl ether, 1 Hydroxy group-containing vinyl ethers such as 1,3-propanediol vinyl ether and 1,4-butanediol vinyl ether; allyl ethers such as allyl acetate, propyl allyl ether, butyl allyl ether, and hexyl allyl ether; monomers having an oxyalkylene group Isopropenyl acetate, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol Hydroxyl group-containing α-olefins such as ethylene, 9-decene-1-ol, 3-methyl-3-buten-1-ol; ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-acrylamide-2 A monomer having a sulfonic acid group such as methylpropanesulfonic acid; vinyloxyethyltrimethylammonium chloride, vinyloxybutyltrimethylammonium chloride, vinyloxyethyldimethylamine, vinyloxymethyldiethylamine, N-acrylamidomethyltrimethylammonium chloride, N -Acrylamidoethyltrimethylammonium chloride, N-acrylamidodimethylamine, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, dimethylallylamine, Monomers having a cationic group such as rilethylamine; vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3- (meth) acrylamide- Examples include structural units derived from monomers having a silyl group such as propyltrimethoxysilane and 3- (meth) acrylamide-propyltriethoxysilane. The vinyl alcohol polymer of the present invention can have one or more structural units derived from the aforementioned monomers.

The vinyl alcohol polymer of the present invention may be produced by any method as long as it satisfies the above five requirements << 1 >> to << 5 >>.
Among them, the vinyl alcohol polymer of the present invention polymerizes a vinyl ester monomer mixture containing (i) 2.5 to 10 parts by mass of alcohol with respect to 100 parts by mass of vinyl ester monomer. The vinyl ester was charged in a tank and the polymerization rate was 8 to 30% by mass in a boiling state while maintaining the pressure in the polymerization tank at a reduced pressure at a temperature below the boiling point of the vinyl ester monomer mixture under atmospheric pressure. A vinyl ester polymer having a polymerization degree which becomes a vinyl alcohol polymer having a viscosity average polymerization degree (P) of 4000 to 8000 after saponification, and then (ii) the above ( A polymerization inhibitor is added to the reaction product containing the vinyl ester polymer obtained in step i), and the vinyl ester monomer remaining in the reaction product is removed by substitution with alcohol. In the presence of the active substance, the vinyl ester polymer is saponified smoothly under the conditions of producing a vinyl alcohol polymer at a saponification degree of 99.50 to 99.97 mol% by the production method of the present invention. Can be manufactured.

  As a polymerization method of a vinyl ester monomer, a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method and the like are known. In the production method of the present invention, the polymerization step (i) above is performed. [Hereinafter referred to as “polymerization step (i)”], a vinyl ester monomer mixture containing a small amount of alcohol of 2.5 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester monomer is used. First, a vinyl ester polymer is produced by a solution polymerization method (a method according to a solution polymerization method). The polymerization step (i) for producing the vinyl ester polymer and the subsequent step (ii) may be carried out by a batch method (batch method) or a continuous method. Among these, it is preferable to carry out continuously from the viewpoint of production efficiency.

When performing polymerization step (i) (production of vinyl ester polymer) and step (ii) (polymerization inhibition treatment of residual monomer and subsequent saponification treatment of vinyl ester polymer) in a continuous manner The vinyl ester monomer and the alcohol are continuously supplied to the polymerization tank so that the mass ratio of both is within the range specified by the present invention, and the polymerization is performed so that the polymerization rate and degree of polymerization specified by the present invention are achieved. The polymerization is carried out while retaining in the tank for a predetermined time to form a vinyl ester polymer having a predetermined polymerization degree, and the reaction product containing the vinyl ester polymer is continuously taken out from the polymerization tank. After adding a polymerization inhibitor to the reaction product and replacing the vinyl ester monomer remaining in the reaction product with alcohol, the vinyl ester polymer is removed in the presence of an alkaline substance. Saponification of the constant of the degree of saponification.
At that time, the amount of monomer and alcohol mainly composed of vinyl ester monomer to the polymerization tank and the amount of reaction product taken out from the polymerization tank (the amount supplied and taken out per unit time), polymerization The residence time in the tank is adjusted according to the mass ratio of the vinyl ester monomer and the alcohol, the polymerization temperature, the polymerization rate, the scale of the polymerization tank, the polymerization rate, and the like. In order to bring the polymerization rate into the range of 8 to 30% by mass, the residence time in the polymerization tank is generally 1 to 12 hours, particularly preferably 2 to 6 hours.

  In addition, when performing the polymerization step (i) (production of vinyl ester polymer) and the above step (ii) (stopping polymerization and saponification of vinyl ester polymer) in batch (batch) method, Both the polymerization of the ester monomer and the saponification of the vinyl ester polymer produced by the polymerization may be carried out in the same polymerization tank, or after the vinyl ester monomer is polymerized in the polymerization tank The reaction product containing the ester polymer may be taken out from the polymerization tank, and the vinyl ester polymer may be saponified outside the polymerization tank. At that time, the supply amount of the monomer and alcohol mainly composed of vinyl ester monomer to the polymerization tank, the polymerization time in the polymerization tank, the mass ratio of the vinyl ester monomer and alcohol, the polymerization The temperature is adjusted according to the polymerization rate, polymerization tank scale, polymerization rate, and the like. In order to bring the polymerization rate into the range of 8 to 30% by mass, the polymerization time in the polymerization tank is generally 1 to 12 hours, and particularly preferably 2 to 6 hours.

  As the vinyl ester monomer used in the polymerization step (i), any of the vinyl ester monomers conventionally known to be usable for the production of vinyl ester polymers can be used. Can include vinyl acetate, vinyl formate, vinyl propionate, vinyl valenate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, etc. Species or two or more can be used. Among these, as the vinyl ester monomer, vinyl acetate is preferably used from the viewpoints of versatility and handleability.

The vinyl ester monomer mixture used in the polymerization step (i) may contain other copolymerizable monomers as necessary as long as the object and effect of the present invention are not impaired. In the case of containing other copolymerizable monomers, it is preferably 20 mol% or less with respect to the total number of moles of all monomers contained in the vinyl ester monomer mixture. More preferably, it is more preferably 5 mol% or less.
Examples of other copolymerizable monomers that can be contained in the vinyl ester monomer mixture include other copolymerizable monomers that the vinyl alcohol polymer of the present invention may have as necessary. Examples of the monomer constituting the structural unit derived from can include those exemplified in the above paragraph 0026, and one or more of them can be used.

  As the alcohol used in the polymerization step (i), lower alcohols such as methanol (methyl alcohol), ethanol (ethyl alcohol), and propanol (propyl alcohol) are preferably used from the viewpoint of handleability. Among them, methanol is versatile. It is more preferably used from the viewpoint.

As the polymerization initiator used in the polymerization step (i), any of the polymerization initiators conventionally known to be usable for the polymerization of vinyl ester monomers can be used. '-Azobisisobutyronitrile, 2,2'-azobis (2,4-dimethyl-valeronitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), other azo series Examples include initiators, benzoyl peroxide, n-propyl peroxydicarbonate, and other peroxide-based initiators. Among them, as polymerization initiators, 2,2′-azobis (2,4-dimethyl-valeronitrile) and 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) have high low-temperature activity. It is preferably used from the viewpoint.
The use amount of the polymerization initiator is generally 0.0001 to 0.02 mass% (1 to 200 mass ppm) based on the total mass of all polymerizable monomers including the vinyl ester monomer, In particular, it is preferable that the content be about 0.0005 to 0.01 mass% (5 to 100 mass ppm) from the viewpoint that a vinyl alcohol polymer satisfying the above requirements << 1 >> to << 5 >> can be obtained smoothly.

  Further, the polymerization step (i) is carried out in the presence of a thiol compound such as 2-mercaptoethanol, n-dodecyl mercaptan, mercaptoacetic acid, 3-mercaptopropionic acid in the vinyl ester monomer mixture, and thus obtained. When the vinyl ester polymer is saponified in the step (ii) above, a vinyl alcohol polymer in which a functional group derived from a thiol compound is introduced at the end, satisfying the above requirements << 1 >> to << 5 >>. The present invention also includes the vinyl alcohol polymer in the scope of the present invention.

The vinyl ester monomer mixture (vinyl ester monomer mixture in the polymerization tank) used in the polymerization step (i) is the vinyl alcohol heavy polymer of the present invention satisfying the above requirements << 1 >> to << 5 >>. In order to obtain a coalescence smoothly with high production efficiency, it is necessary to contain alcohol in a ratio of 2.5 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester monomer, It is preferable to contain in the ratio of 8 mass parts.
When the content ratio of the alcohol in the vinyl ester monomer mixture is less than 2.5 parts by mass with respect to 100 parts by mass of the vinyl ester monomer, the aqueous solution absorbance specified in the above requirement << 5 >> A satisfactory vinyl alcohol polymer cannot be obtained, and the resulting vinyl alcohol polymer is colored, resulting in poor color tone and poor weather resistance. On the other hand, when the alcohol content exceeds 10 parts by mass with respect to 100 parts by mass of the vinyl ester monomer, the production efficiency of the vinyl ester polymer, and thus the production efficiency of the vinyl alcohol polymer, greatly decreases. A film, a film, or the like formed from a mixed aqueous solution of a vinyl alcohol polymer and an inorganic substance easily swells in water, and water resistance decreases.

In the polymerization step (i), in order to smoothly obtain a vinyl alcohol polymer satisfying the above requirements << 1 >> to << 5 >>, a vinyl ester monomer mixture (a mixture of a vinyl ester monomer and an alcohol) is used. The vinyl ester monomer is polymerized in a boiling state while maintaining the pressure in the polymerization tank at a reduced pressure at a temperature equal to or lower than the boiling point of the liquid) under atmospheric pressure.
If the vinyl ester monomer is polymerized at a temperature higher than the boiling point of the vinyl ester monomer mixture at atmospheric pressure, the vinyl alcohol polymer contains 1,2-glycol bonding units. The amount exceeds 1.5 mol%, and it becomes difficult to obtain a vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >>. In addition, a film, a film, or the like formed from a mixed aqueous solution of the vinyl alcohol polymer and the inorganic substance obtained thereby easily swells in water, resulting in poor water resistance.
Even if the temperature of the polymerization of the vinyl ester monomer is lower than the boiling point of the vinyl ester monomer mixture under atmospheric pressure, the polymerization is carried out without causing a reduced pressure (no boiling). In this case, the absorbance (cell optical path length 30 mm) after concentration correction at a wavelength of 280 nm and 320 nm (measurement temperature 20 ° C.) of the aqueous vinyl alcohol polymer solution may exceed 0.02 L / g. It becomes difficult to obtain a vinyl alcohol polymer satisfying << 1 >> to << 5 >>. As a result, the weather resistance of the film formed from the vinyl alcohol polymer is lowered.

The temperature in the polymerization tank (polymerization temperature) in the polymerization step (i) is preferably 5 to 60 ° C, more preferably 20 to 50 ° C, and further preferably 30 to 50 ° C.
In order to bring the vinyl ester monomer mixture in the polymerization tank to the boiling state at the above-described temperature, the pressure (absolute pressure) in the polymerization tank is preferably 1 to 100 KPa, particularly preferably 20 to 90 KPa.
Since the boiling point of vinyl acetate under atmospheric pressure is 73 ° C. and the boiling point of methanol under atmospheric pressure is 64 ° C., a polymerization step (using vinyl acetate as the vinyl ester monomer and methanol as the alcohol) When a vinyl ester polymer is produced in i), the temperature in the polymerization tank (polymerization temperature) in the polymerization step (i) is 5 to 60 ° C., particularly 20 to 50 ° C., and the pressure in the polymerization tank It is preferable to produce a vinyl ester polymer by setting (absolute pressure) to 1 to 100 KPa, particularly 30 to 90 KPa.

Furthermore, in the polymerization step (i), in order to obtain a vinyl alcohol polymer satisfying the above requirements << 1 >> to << 5 >> smoothly with high production efficiency, the polymerization rate of the vinyl ester monomer is set to 8-30. The vinyl ester monomer is polymerized in the polymerization tank while maintaining the mass% range.
In the polymerization step (i), when the polymerization rate of the vinyl ester monomer is less than 8% by mass, the production efficiency is lowered, whereas when the polymerization rate of the vinyl ester monomer exceeds 30% by mass, it is obtained. The degree of polymerization of the resulting vinyl alcohol polymer is less than 4000, or the content of 1,2-glycol bond units exceeds 1.5 mol%, and the aqueous solution absorbs the above requirement << 5 >>. It may be difficult to obtain a vinyl alcohol polymer, or the water resistance of a film formed from a mixed aqueous solution of a vinyl alcohol polymer and an inorganic substance may be lowered.
In the polymerization step (i), the polymerization is preferably performed so that the polymerization rate of the vinyl ester monomer is in the range of 10 to 20% by mass.

In addition, in the polymerization step (i), when organic acids such as lactic acid and tartaric acid are added to the vinyl ester monomer mixture in order to suppress aldehyde formation due to decomposition of the vinyl ester monomer, wavelengths of 280 nm and 320 nm. Thus, a vinyl alcohol polymer can be obtained which has a lower absorbance (cell optical path length: 30 mm) and gives a less colored vinyl alcohol polymer aqueous solution.
When organic acids such as lactic acid and tartaric acid are added to the vinyl ester monomer mixture, the addition amount of the organic acids is 0.0001 to 0.02 mass based on the mass of the vinyl ester monomer. % (1 to 200 mass ppm), more preferably 0.0001 to 0.01 mass% (1 to 100 mass ppm).

  After producing the vinyl ester polymer in the polymerization step (i), in the step (ii) above (hereinafter sometimes referred to as “step (ii)”), the vinyl ester type obtained in the polymerization step (i) After the polymerization inhibitor is added to the reaction product containing the polymer to inhibit or inhibit the subsequent polymerization, the vinyl ester monomer remaining in the reaction product in that state is removed by replacing with alcohol, A vinyl alcohol polymer is produced by saponifying a vinyl ester polymer in the presence of an alkaline substance.

  The aqueous solution absorbance of the vinyl alcohol polymer obtained after saponification is affected by the type and addition amount of the polymerization inhibitor. It is preferable that the addition amount of a polymerization inhibitor is 1-10 mol with respect to 1 mol of undecomposed polymerization initiators generally contained in the reaction product obtained by polymerization process (i), It is more preferable that it is 1 to 3 mol. When the addition amount of the polymerization inhibitor is too large, the weather resistance of the vinyl alcohol polymer is easily lowered and the absorbance of the aqueous solution of the vinyl alcohol polymer is likely to increase. On the other hand, when the addition amount of the polymerization inhibitor is small, the polymerization of the vinyl ester polymer contained in the reaction product obtained in the polymerization step (i) further proceeds and the degree of polymerization may not be as intended. is there.

As the kind of the polymerization inhibitor, a compound having a conjugated double bond with a molecular weight of 1000 or less, an aromatic compound, or the like that stabilizes radicals and inhibits the polymerization reaction is preferably used.
Specific examples of the compound having a conjugated double bond that can be used as a polymerization inhibitor include isoprene, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, and 2-t-butyl. -1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3,4-dimethyl-1,3-pentadiene, 3 -Ethyl-1,3-pentadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 1,3-hexadiene, 2,4-hexadiene 2,5-dimethyl-2,4-hexadiene, 1,3-octadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1-methoxy-1,3-butadiene, -Methoxy-1,3-butadiene, 1-ethoxy-1,3-butadiene, 2-ethoxy-1,3-butadiene, 2-nitro-1,3-butadiene, chloroprene, 1-chloro-1,3-butadiene 1-bromo-1,3-butadiene, 2-bromo-1,3-butadiene, fulvene, tropone, osymene, ferrandlene, myrcene, farnesene, semblene, sorbic acid, sorbic acid ester, sorbic acid salt, abietic acid, etc. Conjugated dienes consisting of a conjugated structure of two carbon-carbon double bonds: 1,3,5-hexatriene, 2,4,6-octatriene-1-carboxylic acid, eleostearic acid, tung oil, cholecalciferol Conjugated triene consisting of a conjugated structure of three carbon-carbon double bonds such as cyclooctatetraene, 2,4,6,8-decate Such as conjugated polyene and the like made of carbon double bonds 4 or more conjugated structure - Raen-1-carboxylic acid, retinol, carbon such retinoic acid. Any of those having a plurality of stereoisomers such as 1,3-pentadiene, myrcene, and farnesene may be used.

Specific examples of aromatic compounds that can be used as a polymerization inhibitor include p-benzoquinone, hydroquinone, hydroquinone monomethyl ether, 2-phenyl-1-propene, 2-phenyl-1-butene, and 2,4-diphenyl-4. -Methyl-1-pentene, 3,5-diphenyl-5-methyl-2-heptene, 2,4,6-triphenyl-4,6-dimethyl-1-heptene, 3,5,7-triphenyl-5 -Ethyl-7-methyl-2-nonene, 1,3-diphenyl-1-butene, 2,4-diphenyl-4-methyl-2-pentene, 3,5-diphenyl-5-methyl-3-heptene, 1 , 3,5-triphenyl-1-hexene, 2,4,6-triphenyl-4,6-dimethyl-2-heptene, 3,5,7-triphenyl-5-ethyl-7-methyl-3- Nene, 1,3 1-phenyl-butadiene, aromatic compounds such as 1,4-diphenyl-1,3-butadiene.
In the present invention, one or more of the above-described polymerization inhibitors can be used depending on the type of polymerization initiator used in the polymerization step (i).
Among them, in the present invention, as the polymerization inhibitor, sorbic acid, sorbic acid ester, and sorbate are preferably used from the viewpoint of the weather resistance of the vinyl alcohol polymer.

After adding a polymerization inhibitor to the reaction product, unreacted vinyl ester monomers and other copolymerizable monomers contained in the reaction product (hereinafter collectively referred to as “unreacted vinyl ester”). (Sometimes referred to as "system monomers") is substituted with alcohol and discharged out of the reaction product to obtain an alcohol solution of a vinyl ester polymer. If unreacted vinyl ester monomers are mixed in the alcohol solution of the vinyl ester polymer, the monomers are decomposed during the next saponification treatment to produce aldehydes, etc. This causes an increase in the absorbance of the aqueous solution of the coalescence. Therefore, the removal rate of unreacted vinyl ester monomers from the reaction product is preferably 99% or more, more preferably 99.5% or more, and 99.8% or more. Is more preferable.
As a method for removing unreacted vinyl ester monomers contained in the reaction product to which a polymerization inhibitor has been added by replacing with alcohol, (1) a method of bringing the reaction product into contact with alcohol vapor, (2) A method of adding alcohol to the reaction product and azeotropically reacting the unreacted vinyl ester monomer with the added alcohol by depressurization, (3) unreacted vinyl ester monomer contained in the reaction product And the like, and the like, and the like. Among these, the method (1) is preferably employed from the viewpoints of economy and operability.

An alkaline substance is added to the alcohol solution of the vinyl ester polymer obtained by the above-described substitution treatment with alcohol, and the vinyl ester polymer is saponified in the presence of the alkaline substance, so that the saponification degree is 99.50 to 99.99. A 97 mol% vinyl alcohol polymer is produced.
As an alkaline substance that is a catalyst for saponification of a vinyl ester polymer, any of alkaline substances conventionally known as a saponification catalyst for vinyl ester polymers can be used, and among them, potassium hydroxide, One or more of alkali metal hydroxides such as sodium hydroxide and alkali metal alkoxides such as sodium methoxide are preferably used. In particular, sodium hydroxide is more preferably used from the viewpoint of versatility and handleability. .
The amount of the alkaline substance used as a saponification catalyst is preferably in the range of 0.005 to 0.2 mol per mol of vinyl ester monomer units in the vinyl ester polymer. More preferably, it is in the range of 0.007 to 0.1 mol. Alkaline substances that are saponification catalysts may be added all at the beginning of the saponification reaction, or a portion may be added at the beginning of the saponification reaction and the rest added during the saponification reaction. It may be added.

  The saponification reaction is preferably carried out in an alcohol solvent, particularly methanol, but if necessary, it may be carried out in an organic solvent other than alcohol such as methyl acetate, dimethyl sulfoxide, diethyl sulfoxide, dimethylformamide, or alcohol. And an organic solvent other than the alcohol described above. In the saponification of the vinyl ester polymer, the water content of the organic solvent (especially alcohol, particularly methanol) is preferably 0.001 to 1% by mass in order to facilitate the saponification reaction. It is more preferable that it is 003-0.9 mass%, and it is still more preferable that it is 0.005-0.8 mass%.

The temperature of the saponification treatment is preferably 5 to 80 ° C., particularly 20 to 70 ° C., and the time of the saponification treatment is preferably 5 minutes to 10 hours, particularly preferably 10 minutes to 5 hours.
In order to obtain a vinyl alcohol polymer having a saponification degree of 99.50 to 99.97 mol%, the polymerization degree of the vinyl ester polymer used for the saponification treatment, the vinyl ester polymer in the saponification treatment solution Suitable for obtaining a vinyl alcohol polymer having a saponification degree of 99.50 to 99.97 mol% from the above-mentioned range of the concentration, temperature and treatment time of the alkaline substance depending on the concentration, water content, etc. Adopt conditions.
Among the above conditions, the concentration of the alkaline substance (particularly sodium hydroxide) is 0.007 to 0.100 mol, particularly 0.010 to 0.050 mol, with respect to 1 mol of the vinyl ester monomer, When the saponification treatment is carried out at a saponification treatment time of 10 minutes to 5 hours, particularly 20 minutes to 4 hours, the saponification degree is 99.50 to 99.97. A mol% vinyl alcohol polymer can be produced smoothly.
After completion of the saponification treatment, the remaining saponification catalyst (alkaline substance) may be neutralized as necessary. Examples of usable neutralizing agents include organic acids such as acetic acid and lactic acid, and methyl acetate. The ester compound can be mentioned.

By the series of steps described above, the vinyl alcohol polymer of the present invention satisfying the above-mentioned requirements << 1 >> to << 5 >> is obtained.
The vinyl alcohol polymer of the present invention satisfies the above requirements << 1 >> to << 5 >>, so that it has excellent water resistance, weather resistance, mechanical properties, no coloration and excellent colorless transparency, vinyl Since the viscosity increase with time of the alcoholic polymer aqueous solution is in an appropriate range, it is easy to handle and forms an inorganic substance-containing film that has high affinity with inorganic substances and excellent water resistance. Can be used effectively.
Examples of the use of the vinyl alcohol polymer of the present invention include, for example, a binder for an ink receiving layer in an ink jet recording material, a paper internal sizing agent, a fiber processing agent, a dye, a glass fiber coating agent, a metal surface coating agent, Coating agents such as anti-fogging agents, adhesives such as wood, paper, aluminum foil, plastics, nonwoven fabric binders, fibrous binders, binders for building materials such as gypsum board and fiberboard, thickeners for various emulsion adhesives, urea Resin-based adhesive additives, cement and mortar additives, hot-melt adhesives, pressure-sensitive adhesives, and other ethylene-based unsaturated monomers such as ethylene, vinyl acetate, and vinyl chloride Polymeric dispersants, stabilizers for pigment dispersion in paints, adhesives, etc., vinyl chloride, vinylidene chloride, styrene, (meth) acrylic acid Dispersion stabilizers for suspension polymerization of various ethylenically unsaturated monomers such as vinyl acetate, molded products such as fibers, films, sheets, pipes, tubes, water-soluble fibers, hydrophilicity imparting agents for hydrophobic resins, composites Examples thereof include compounding agents for synthetic resins such as fibers, films and other additives for molded articles, soil condition improvers, soil stabilizers, and the like.
The vinyl acetal polymer obtained by acetalizing the vinyl alcohol polymer of the present invention with an aldehyde compound such as acetaldehyde or butyraldehyde is a safety glass interlayer film, ceramic binder, ink dispersant, photosensitive material. It is useful for such applications.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.
In the following examples, the polymerization rate, the removal rate of unreacted vinyl acetate monomer from the reaction product (purge rate), the polymerization degree of vinyl alcohol polymer (polyvinyl alcohol) (viscosity average polymerization degree), saponification Degree, 1,2-glycol bond unit content and sodium acetate content, viscosity stability of vinyl alcohol polymer aqueous solution (polyvinyl alcohol aqueous solution), wavelength 280 nm of vinyl alcohol polymer aqueous solution (polyvinyl alcohol aqueous solution) and Absorbance after concentration correction at 320 nm (cell optical path length 30 mm), water resistance (water elution rate) and weather resistance of vinyl alcohol polymer film (polyvinyl alcohol film), and inorganic substance-containing vinyl alcohol polymer film (inorganic substance-containing polyvinyl) The water resistance (water swelling degree) of the alcohol film is calculated as follows: Or it was evaluated (hereinafter the "polyvinyl alcohol" may be referred to as "PVA").

(1) Calculation method of polymerization rate and operation method for calculation:
1-2 g of the reaction product containing polyvinyl acetate taken out from the polymerization tank is collected, and its mass (A) (g) is accurately measured. After the measurement, 1 ml of a 0.25 mass% methanol solution of hydroquinone as a polymerization inhibitor is added and dried in a dryer at 160 to 170 ° C. for 30 minutes to remove unreacted vinyl acetate and methanol, and the residue after drying The mass (B) (g) of (polyvinyl acetate) is measured, and the polymerization rate is determined from the following mathematical formula (II).

Polymerization rate (mass%) = {B / A (100-C)} × 100 (II)

[In the formula, C represents the amount of methanol (mass%) contained in the reaction product. ]

(2) Calculation method of unreacted vinyl acetate removal rate (purge rate) and operation method for calculation:
(I) After adding sorbic acid to the reaction product taken out from the polymerization tank to stop the polymerization reaction, a process for removing unreacted vinyl acetate by contacting countercurrent with methanol vapor (purge process) 4 to 6 g of a methanol solution of polyvinyl acetate obtained by performing is collected, and its mass (D) (g) is measured. After the measurement, methanol is added and dissolved, 5 ml of a 1.7% by mass acetic acid solution of bromine is added, and 10 ml of a 5% by mass aqueous solution of potassium iodide is further added. Add 2 to 4 ml of a 0.5% by weight aqueous starch solution as an indicator, and titrate with 0.1N aqueous sodium thiosulfate solution until it becomes colorless to give a titer of (E ₁ ). Separately, the same operation is performed using only methanol, and the titration amount until it becomes colorless with 0.1N sodium thiosulfate aqueous solution at that time is defined as (E ₀ ) (ml). According to the following formula (III), vinyl acetate [F] (mass%) remaining in the methanol solution of polyvinyl acetate is determined.

Content of vinyl acetate (F) (mass%) = 0.0043 × (E ₀ −E ₁ ) × 100 / D (III)

(Ii) In order to determine the content of polyvinyl acetate using the methanol solution of polyvinyl acetate after the expelling treatment in the same manner as in (i), 1 to 2 g of the methanol solution was sampled and its mass (G) (G) is measured. Dry in a dryer at 160-170 ° C. for 30 minutes. The mass (H) (g) after drying is measured, and polyvinyl acetate [P] (mass%) is obtained according to the following formula (IV).

Polyvinyl acetate [P] (mass%) = (H / G) × 100 (IV)

(Iii) Using the vinyl acetate content (F) and polyvinyl acetate (P) obtained from the above (i) and (ii), the expulsion rate is determined according to the following formula (V).

Expulsion rate (%) = {P / (P + F)} × 100 (V)

(3) Degree of polymerization of PVA (viscosity average degree of polymerization):
According to JIS-K6726, the degree of polymerization [viscosity average degree of polymerization (P)] of PVA obtained in the following examples and comparative examples was determined by the above-described mathematical formula (I).

(4) Saponification degree of PVA:
According to the method described in JIS-K6726, the degree of saponification (mol%) of PVA obtained in the following Examples and Comparative Examples was determined.

(5) Content of 1,2-glycol bond unit of PVA:
(I) To the PVA obtained in the following examples or comparative examples, a methanol solution of sodium hydroxide is added in an amount such that the amount of sodium hydroxide is 0.1 mol with respect to 1 mol of vinyl alcohol units in PVA. The purified PVA having a saponification degree of 99.9 mol% or more is obtained by re-saponification at 60 ° C. for 5 hours and Soxhlet extraction of the obtained PVA with methanol for 1 week.
(Ii) The purified PVA having a saponification degree of 99.9 mol% or more obtained in (i) above was dried under reduced pressure at 90 ° C. for 2 days to completely remove methanol, and then dimethyl sulfoxide-d6 (DMSO-d6) Dissolve in 0.1 wt% solution, add a few drops (about 0.1 ml) of trifluoroacetic acid to the solution, and use a nuclear magnetic resonance apparatus (“AL-400” manufactured by JEOL Ltd.) at 80 ° C. Then, the proton NMR was measured.
The content of 1,2-glycol bond units contained in PVA (PVA) is a peak (integral value α) of 3.2 to 4.0 ppm derived from methine of vinyl alcohol units, and 1,2-glycol bond units. From the 3.25 ppm peak (integral value β) derived from one methine of (2), it is calculated according to the following formula (V).

Content of 1,2-glycol bond unit of PVA (mol%) = 100 × β / α (VI)

(6) Content of sodium acetate in PVA:
The content of sodium acetate in PVA was determined according to the dissolution conduction method described in JIS-K6726.

(7) Viscosity stability of PVA aqueous solution:
Using each of the PVA obtained in the following Examples and Comparative Examples, the concentration was adjusted and the viscosity of the aqueous solution at 10 ° C. was 10,000 mPa in a B-type viscometer (“B-type viscometer” manufactured by Tokyo Keiki Co., Ltd.). Each of the PVA aqueous solutions that are s was prepared, and the PVA aqueous solution was left in a thermostatic bath at 10 ° C., and the viscosity of the PVA aqueous solution was measured with a B-type viscometer every predetermined time. Viscosity was plotted on the vertical axis, and the time when the viscosity of the aqueous PVA solution reached 20000 mPa · s at 10 ° C. was determined from the graph obtained thereby to evaluate the viscosity stability. The measurement of the viscosity of the PVA aqueous solution was performed up to 360 minutes.
Specifically, the PVA aqueous solution of one Example or Comparative Example prepared above was evenly dispensed into 13 tall beakers (capacity 300 ml), and all the 13 tall beakers were placed in a 10 ° C. constant temperature water bath. The viscosity of the PVA aqueous solution in the first beaker is measured at the start of measurement while the sample is allowed to stand at the same time, and the viscosity of the PVA aqueous solution in the second beaker is measured 30 minutes after the start of measurement. The viscosity of the PVA aqueous solution was measured 60 minutes after the start of measurement, the viscosity of the PVA aqueous solution in the fourth beaker was measured 90 minutes after the start of measurement, and thereafter every 30 minutes for the PVA aqueous solution in the 5th to 13th beakers. The time was plotted on the horizontal axis and the viscosity was plotted on the vertical axis, and the time when the viscosity reached 20000 mPa · s was determined from the graph obtained thereby.
In addition, when the viscosity of the aqueous PVA solution in the beaker reached 20000 mPa · s before 360 minutes passed from the start of measurement, the measurement of the viscosity was terminated at that time.

(8) Absorbance after concentration correction at a wavelength of 280 nm and 320 nm of the PVA aqueous solution (cell optical path length: 30 mm):
(I) Using each of the PVA obtained in the following Examples and Comparative Examples, an aqueous PVA solution was prepared, and a spectrophotometer described in JIS-K0115 (“UV-1700” manufactured by Shimadzu Corporation) was used. Using a quartz cell with an optical path length of 30 mm (“S10-UV30” manufactured by Shimadzu Corporation), the absorbance in the ultraviolet region of a wavelength of 190 to 400 nm was measured at a temperature of 20 ° C., and the absorbance at a wavelength of 280 nm (Aa ₂₈₀ ) and a wavelength of 320 nm. Absorbance (Aa ₃₂₀ ) was determined.
The concentration of the PVA aqueous solution used for the measurement of absorbance (Aa ₂₈₀ ) and absorbance (Aa ₃₂₀ ) was 30 g / L for PVA having a polymerization degree of less than 6000, and 10 g / L for PVA having a polymerization degree of 6000 or more. . At that time, the concentration of the PVA aqueous solution was measured by the method described in JIS-K6726.
(Ii) Using the same spectrophotometer and quartz cell as in (i) above, measure the absorbance in the ultraviolet region of the wavelength of 190 to 400 nm of water used for the preparation of the PVA aqueous solution at a temperature of 20 ° C. The absorbance of water at 280 nm (Ab ₂₈₀ ) and the absorbance of water at a wavelength of 320 nm (Ab ₃₂₀ ) were determined.
(Iii) From the following mathematical formulas (VII-1) and (VII-2), the water quality corrected absorbance (A ₂₈₀ ) and absorbance (A ₃₂₀ ) of the PVA aqueous solution at wavelengths of 280 nm and 320 nm were determined.

Absorbance (A ₂₈₀ ) corrected for water quality = Absorbance (Aa ₂₈₀ ) −Absorbance (Ab ₂₈₀ ) (VII-1)
Absorbance (A ₃₂₀ ) corrected for water quality = Absorbance (Aa ₃₂₀ ) −Absorbance (Ab ₃₂₀ ) (VII-2)

(Iv) The water-absorbed absorbance (A ₂₈₀ ) obtained by the above formula (VII-1) was divided by the concentration (C) (g / L) of the PVA aqueous solution used for the measurement, and thereby obtained The value [absorbance (A ₂₈₀ ) / C] (L / g) was defined as “absorbance after concentration correction at a wavelength of 280 nm of the PVA aqueous solution (cell optical path length 30 mm)” in the present invention.
Also, the water quality corrected absorbance (A ₃₂₀ ) obtained by the above formula (VII-2) is divided by the concentration (C) (g / L) of the PVA aqueous solution used for the measurement, and the value obtained thereby [Absorbance (A ₃₂₀ ) / C] (L / g) was defined as “absorbance after concentration correction at a wavelength of 320 nm of the PVA aqueous solution (cell optical path length 30 mm)” in the present invention.

(9) Water resistance of PVA film (water elution rate of PVA film):
(I) A 2% by mass aqueous solution of PVA was prepared using distilled water, and this aqueous solution was cast into a film at 20 ° C., and then dried at 20 ° C. for 1 week to produce a PVA film having a thickness of 40 μm. The PVA film thus obtained was heat-treated at 120 ° C. for 10 minutes, then cut into a size of length × width = 10 cm × 10 cm to produce a test piece, and its mass (W ₀ ) was measured.
(Ii) After immersing the test piece prepared in (i) above in distilled water at 20 ° C. for 24 hours, taking out (collecting), wiping off moisture adhering to the surface with gauze, and drying at 105 ° C. for 16 hours, The mass (W ₁ ) at the time of drying is measured, the water elution rate (% by mass) of the PVA film is obtained from the following formula (VIII), and the water resistance of the PVA film is evaluated according to the evaluation criteria shown in Table 1 below. did.

Water elution rate of PVA film (mass%) = {(W ₀ −W ₁ ) / W ₀ } × 100 (VIII)

(10) Weather resistance of PVA coating:
(I) A 2% by mass aqueous solution of PVA was prepared using distilled water, and this aqueous solution was cast into a film at 20 ° C., and then dried at 20 ° C. for 1 week to produce a 150 μm thick PVA film. The PVA film thus obtained was heat-treated at 120 ° C. for 10 minutes, and then cut into a size of length × width = 20 cm × 20 cm to prepare a test piece.
(Ii) Using the test piece prepared in (i) above, using a sunshine weather meter (“S80” manufactured by Suga Test Instruments Co., Ltd.), the sample is left for 2000 hours at a black panel temperature of 63 ° C. and a humidity of 50%. The amount of change in the b value before and after (Δb) was determined and the weather resistance was evaluated.
In addition, b value was measured with SM color computer (made by Suga Test Instruments). It shows that it is easy to yellow and it is inferior to a weather resistance, so that the value of change ((DELTA) b) of b value is large.

(11) Water resistance of inorganic substance-containing PVA coating:
(I) A 2% by mass aqueous solution of PVA was prepared using distilled water, and colloidal silica (“Snowtex ST-manufactured by Nissan Chemical Industries, Ltd.” was prepared so that the mass ratio of PVA: colloidal silica was 100: 50. O ") 20% by mass aqueous dispersion was added to prepare a PVA / colloidal silica mixture, and the PVA / colloidal silica mixture was cast into a film at 20 ° C and then dried at 20 ° C for 1 week. Thus, an inorganic substance-containing PVA film having a thickness of 40 μm was produced. The inorganic substance-containing PVA film thus obtained was heat-treated at 120 ° C. for 10 minutes, and then cut into a size of length × width = 10 cm × 10 cm to prepare a test piece.
(Ii) The test piece prepared in (i) above was immersed in distilled water at 20 ° C. for 24 hours, then taken out (collected), the moisture adhering to the surface was wiped off with gauze, and the mass at the time of water swelling (W ₂ ) Was measured. The specimen mass was measured at the time of water-swollen and dried 16 hours at 105 ° C., dry the mass (W ₃₎ was measured, the water swelling degree of the inorganic-containing PVA film from the formula (IX) following the (times) The water resistance of the inorganic substance-containing PVA coating was evaluated according to the evaluation criteria shown in Table 2 below.

Water swelling degree of inorganic-containing PVA film (times) = W ₂ / W ₃ (IX)

Example 1 [Production of “PVA-1a”]
(1) A polymer tank equipped with a stirrer, thermometer, hot water jacket and water-cooled condenser with an internal volume of 6600 liters, a height of 3 m, and a tower diameter (inner diameter) of 1.8 m was charged with 679.5 kg / kg of predeoxygenated vinyl acetate. 22.9 kg / hr of methanol, 7.0 kg / hr of 0.5% methanol solution of 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), and tartaric acid to vinyl acetate A 0.3% by mass methanol solution of tartaric acid is continuously charged so that the added amount is 20 ppm (4.5 kg / hour), and the residence time in the polymerization tank is 4.5 hours in the polymerization tank. While maintaining the polymerization, vinyl acetate was polymerized, and the content (reaction product) in the polymerization tank was continuously removed from the polymerization tank by a gear pump. The total amount of methanol in the polymerization tank at this time was 5.06 parts by mass with respect to 100 parts by mass of vinyl acetate.
At that time, if the contents are boiled while keeping the inside of the polymerization tank and the condenser at a reduced pressure of 36 ± 1 KPa (absolute pressure), the temperature of the contents is maintained at 40 ± 0.5 ° C. and taken out from the polymerization tank. The polymerization rate of vinyl acetate in the contents (reaction product) was 12% by mass.
(2) A 0.26 mass% methanol solution of sorbic acid was added to the reaction product taken out from the polymerization tank at a rate of 7.0 kg / hour to stop the polymerization reaction, and the reaction product was equipped with a tray. From the top of the tower at normal pressure and at a rate of 716.8 kg / hour, while blowing methanol vapor at a temperature of 90 ° C. and a pressure (gauge pressure) of 190 KPa from the bottom of the tower in an amount of 600 kg / hour, Unreacted vinyl acetate contained in the reaction product is driven countercurrently from the reaction product [removal rate of unreacted vinyl acetate (purge rate) 99.9%], and polyvinyl acetate is removed from the bottom of the tower. Was recovered in a proportion of 21% by mass.

(3) A 6 mass% methanol solution of sodium hydroxide in the methanol solution of polyvinyl acetate obtained in (2) above so that the molar ratio of sodium hydroxide to vinyl acetate units of polyvinyl acetate is 0.023. Was added with stirring to initiate the saponification reaction at 30 ° C. As the saponification reaction progressed, a gelled product was formed. When 50 minutes had elapsed from the start of the saponification reaction, the gelled product was pulverized to obtain PVA swollen with methanol. The PVA was washed with 5 times its mass of methanol and then dried at 55 ° C. for 1 hour and at 100 ° C. for 2 hours to obtain PVA (referred to as “PVA-1a”).
(4) The degree of polymerization of “PVA-1a” obtained in (3) above is 5500, the degree of saponification is 99.51 mol%, the content of 1,2-glycol bond units is 1.4 mol%, acetic acid The sodium content was 0.4% by mass.
In addition, viscosity stability of the aqueous solution of “PVA-1a” obtained in (3) above, absorbance after concentration correction at a wavelength of 280 nm and 320 nm (cell optical path length 30 mm), and water resistance of the film formed from “PVA-1a” The properties (water elution rate) and weather resistance, and the water resistance (water swelling degree) of the inorganic substance-containing PVA film formed from “PVA-1a” were measured or evaluated by the methods described above, and as shown in Table 3 below. there were.

<< Examples 2 to 6 >> [Production of "PVA-2a" to "PVA-6a"]
(1) “PVA-2a” to “PVA-6a” were produced in the same manner as in Example 1 except that the conditions shown in Table 3 below were adopted. In addition, in the vinyl acetate polymerization step for producing “PVA-2a” to “PVA-6a”, in the same manner as in Example 1, the tartaric acid was added to the vinyl acetate in an amount of 20 ppm so that the amount of tartaric acid was 20 ppm. A 3% by mass methanol solution was continuously charged into the polymerization tank.
(2) The polymerization degree, saponification degree, 1,2-glycol bond unit content and sodium acetate content of “PVA-2a” to “PVA-6a” obtained in (1) above are shown in the table below. As shown in FIG.
Further, viscosity stability of aqueous solutions of “PVA-2a” to “PVA-6a” obtained in (1) above, absorbance after concentration correction at a wavelength of 280 nm and 320 nm (cell optical path length 30 mm), [PVA-2a] ~ Water resistance (water elution rate) and weather resistance of the film obtained from "PVA-6a" and water resistance (water swelling degree) of the inorganic substance-containing PVA film obtained from "PVA-2a" to "PVA-6a" ) Was measured or evaluated by the method described above, and the results were as shown in Table 3 below.

<< Examples 7 to 12 >> [Production of "PVA-7a" to "PVA-12a"]
(1) “PVA-7a” to “PVA-12a” were produced in the same manner as in Example 1 except that the conditions shown in Table 4 below were adopted. In addition, in the polymerization step of vinyl acetate for producing “PVA-7a” to “PVA-12a”, in the same manner as in Example 1, the tartaric acid was added in an amount of 0. A 3% by mass methanol solution was continuously charged into the polymerization tank.
(2) The polymerization degree, saponification degree, 1,2-glycol bond unit content and sodium acetate content of “PVA-7a” to “PVA-12a” obtained in (1) above are shown in the table below. As shown in FIG.
In addition, viscosity stability of aqueous solutions of “PVA-7a” to “PVA-12a” obtained in (1) above, absorbance after correction for concentrations at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), [PVA-7a] ~ Water resistance (water elution rate) and weather resistance of the film obtained from "PVA-12a" and water resistance (water swelling degree) of the inorganic substance-containing PVA film obtained from "PVA-7a" to "PVA-12a" ) Was measured or evaluated by the method described above, and the results were as shown in Table 4 below.

<< Comparative Examples 1 to 7 >> [Production of "PVA-1b" to "PVA-7b"]
(1) “PVA-1b” to “PVA-7b” were produced in the same manner as in Example 1 except that the conditions shown in Table 5 below were adopted. In the vinyl acetate polymerization step for producing “PVA-1b” to “PVA-7b”, in the same manner as in Example 1, the tartaric acid was added in an amount of 0. A 3% by mass methanol solution was continuously charged into the polymerization tank.
(2) The polymerization degree, saponification degree, 1,2-glycol bond unit content and sodium acetate content of “PVA-1b” to “PVA-7b” obtained in (1) above are shown in the table below. As shown in FIG.
Also, viscosity stability of aqueous solutions of “PVA-1b” to “PVA-7b” obtained in (1) above, absorbance after concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), [PVA-1b] ~ Water resistance (water elution rate) and weather resistance of the film obtained from "PVA-7b" and water resistance (water swelling degree) of the inorganic substance-containing PVA film obtained from "PVA-1b" to "PVA-7b" ) Was measured or evaluated by the method described above, and the results were as shown in Table 5 below.
As shown in Table 5 below, in Comparative Example 2 (PVA-2b), Comparative Example 4 (PVA-4b), Comparative Example 6 (PVA-6b) and Comparative Example 7 (PVA-7b), an aqueous PVA solution When an aqueous dispersion of colloidal silica was mixed to prepare a PVA / colloidal silica mixture, gelation occurred and a film could not be obtained.

<< Comparative Examples 8 to 13 >> [Production of "PVA-8b" to "PVA-13b"]
(1) “PVA-8b” to “PVA-13b” were produced in the same manner as in Example 1 except that the conditions shown in Table 6 below were adopted. In addition, in the polymerization step of vinyl acetate for producing “PVA-8b” to “PVA-13b”, in the same manner as in Example 1, the tartaric acid was added in an amount of 0. A 3% by mass methanol solution was continuously charged into the polymerization tank.
(2) The polymerization degree, saponification degree, 1,2-glycol bond unit content and sodium acetate content of “PVA-8b” to “PVA-13b” obtained in (1) above are shown in the table below. As shown in FIG.
Also, viscosity stability of aqueous solutions of “PVA-8b” to “PVA-13b” obtained in (1) above, absorbance after concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), [PVA-8b] ~ Water resistance (water elution rate) and weather resistance of the film obtained from "PVA-13b" and water resistance (water swelling degree) of the inorganic substance-containing PVA film obtained from "PVA-13b" to "PVA-13b" ) Was measured or evaluated by the method described above, and the results were as shown in Table 6 below.

<< Comparative Example 14 >> [Production of “PVA-14b”]
(1) PVA (PVA-14b) was produced in the same manner as in Example 1 of Patent Document 2 (Japanese Patent Laid-Open No. 5-117307).
That is, 100 parts by mass of ion-exchanged water, 1000 parts by mass of vinyl acetate, polyoxyethylene [POE (40)] nonylphenyl ether (Sanyo Kasei) were installed in a reactor equipped with a stirrer, a thermometer, a nitrogen introduction pipe and a dry ice cooling pipe. “Nonipol 400” manufactured by Co., Ltd.) 40 parts by mass, 1.25 parts by mass of Rongalite and 0.12 parts by mass of FeSO ₄ .7H ₂ O were added, boiled for 30 minutes, and then introduced to 5 ° C. while introducing nitrogen. Decompressing degree (absolute pressure) 35 Torr (4.7 KPa) while continuously adding 0.07% by mass of hydrogen peroxide aqueous solution prepared using ion-exchanged water that has been cooled and degassed uniformly at 10 parts by mass / hour The polymerization was started. During the polymerization, vinyl acetate was constantly refluxed. When the polymerization rate reached 64.7% by mass (4.1 hours after the start of polymerization), the addition of hydrogen peroxide was stopped to stop the polymerization.
(2) The polyvinyl acetate emulsion obtained in (1) above was charged into a solution of 15,000 parts hydroquinone monomethyl ether in 25,000 parts by mass of methanol at room temperature and dissolved while stirring. While adding methanol under reduced pressure, unreacted vinyl acetate was removed to obtain a methanol solution of polyvinyl acetate.
(3) The methanol solution of polyvinyl acetate obtained in the above (2) was subjected to Ken under the conditions of a concentration of 6% by mass, [NaOH] / [vinyl acetate unit] (molar ratio) = 0.15 and a temperature of 40 ° C. To PVA. As the saponification reaction progressed, a gelled product was formed, and when 60 minutes had elapsed from the start of the saponification reaction, the gelled product was pulverized to obtain PVA swollen with methanol. The PVA was washed with 5 times its mass of methanol and then dried at 55 ° C. for 1 hour and at 100 ° C. for 2 hours to obtain PVA (referred to as “PVA-14b”).

(4) The polymerization degree of “PVA-14b” obtained in the above (3) was 19800, the saponification degree was 99.75 mol%, the 1,2-glycol content was 0.5 mol%, and the sodium acetate content Was 1.5% by mass. In addition, the said polymerization degree of "PVA-14b" is the value calculated | required from the intrinsic viscosity which measured the acetone solution of the polyvinyl acetate obtained by re-acetylating PVA-14b obtained by said (3) at 30 degreeC. In order to calculate the viscosity average polymerization degree (P) from the intrinsic viscosity, the formula of P = ([η] × 1000 / 7.94) ^{(1 / 0.62)} was adopted (the intrinsic viscosity of polyvinyl acetate The degree of polymerization was calculated from
In addition, viscosity stability of the aqueous solution of “PVA-14b” obtained in (3) above, absorbance after concentration correction at a wavelength of 280 nm and 320 nm (cell optical path length 30 mm), and water resistance of the film formed from “PVA-14b” The properties (dissolution rate) and weather resistance were measured or evaluated by the methods described above, and the results were as shown in Table 6 below.
As shown in Table 6 below, in Comparative Example 14 (PVA-14b), when an aqueous dispersion of colloidal silica was mixed into an aqueous PVA solution to prepare a PVA / colloidal silica mixed solution, A film could not be obtained.

As can be seen from the results in Tables 3 to 6, the PVA obtained in Examples 1 to 12 satisfied the above requirements << 1 >> to << 5 >>. The absorbance after cell concentration correction (cell optical path length: 30 mm) is low, there is no coloration, and the color tone (colorless transparency) is excellent.
Moreover, the PVA film formed from the PVA of Examples 1 to 12 satisfying the above requirements << 1 >> to << 5 >> has a low water elution rate and excellent water resistance, Δb is small and excellent weather resistance, and An inorganic substance-containing PVA film can be produced smoothly without causing gelation using the PVA, and the resulting inorganic substance-containing PVA film has a small degree of water swelling and is excellent in water resistance.

  On the other hand, the PVA of Comparative Examples 1, 3 and 5 has a saponification degree of 99.40 mol% or 99.30 mol% and does not satisfy the requirement << 2 >> (the saponification degree is Smaller than the lower limit in the present invention), and the time required for the PVA aqueous solution having a viscosity of 10,000 mPa · s to increase to a viscosity of 20000 mPa · s at 10 ° C. is 300 minutes or 280 minutes, and also satisfies the above requirement << 4 >> If it is not done (thickening time exceeds the upper limit in the present invention), the water-swelling degree of the inorganic substance-containing PVA film formed using the PVA is high and the water resistance is poor.

  The PVA of Comparative Examples 2, 4, 6 and 7 had a saponification degree of 99.99 mol% and did not satisfy the above requirement << 2 >> (the saponification degree was the upper limit in the present invention). The time required for the PVA aqueous solution having a viscosity of 10,000 mPa · s to increase to a viscosity of 20000 mPa · s at 10 ° C. is 5 minutes, 30 minutes, 20 minutes or 15 minutes, and the above requirement << 4 >> Is not satisfied (thickening time is shorter than the lower limit in the present invention), so that when the PVA film is used to produce an inorganic substance-containing PVA film, gelation occurs and an inorganic substance-containing PVA film is produced. Can not do it. Moreover, the film formed from the PVA of Comparative Example 4 has a large Δb value and is inferior in weather resistance.

  The PVA of Comparative Examples 8 to 11 has a 1,2-glycol bond unit content of 1.6 mol% or 1.7 mol%, and does not satisfy the requirement << 3 >> (1, 2-glycol bonding unit exceeds the upper limit in the present invention), and among these PVA of Comparative Examples, PVA of Comparative Examples 8 to 10 has a polymerization degree of 3500 or 2400, and the above requirement << 1 >> Is not satisfied (the degree of polymerization is smaller than the lower limit in the present invention), the water elution rate of the film formed from the PVA is high and the water resistance is poor.

In the PVA of Comparative Examples 12 and 13, the absorbance (cell optical path length 30 mm) (measurement temperature 20 ° C.) after concentration correction at wavelengths of 280 nm and 320 nm of the aqueous solution of the PVA both exceeds 0.02 L / g. Therefore, the Δb value of the film formed from the PVA is large and the weather resistance is inferior.
In addition, the PVA of Comparative Example 14 has a polymerization degree as high as 19800 and does not satisfy the requirement << 1 >>, and the content of 1,2-glycol bond units is 0.5 mol% and the above requirement is satisfied. << 3 >> is not satisfied, and the concentration-corrected absorbance (cell optical path length 30 mm) at a wavelength of 280 nm and 320 nm of the PVA aqueous solution (measurement temperature: 20 ° C.) both exceeds 0.02 L / g. For this reason, the Δb value of the film formed from the PVA is large and inferior in weather resistance, and when an inorganic substance-containing PVA film is produced using the PVA, gelation occurs and an inorganic substance-containing PVA film is produced. Can not do it.

Furthermore, as can be seen from the results in Tables 3 to 6, in Examples 1 to 12, the requirements << 1 >> to << 5 >> are satisfied by adopting the production method of the present invention to produce PVA. Satisfactory PVA is obtained.
In contrast, in Comparative Examples 1 to 7, no saponification treatment was performed so that the degree of saponification was in the range of 99.50 to 99.97 mol%. In Comparative Examples 8 to 10, vinyl acetate and methanol were not used. Vinyl acetate is polymerized at the boiling point of the mixture at atmospheric pressure (not polymerized under reduced pressure), and also in Comparative Example 11, vinyl acetate is polymerized at the boiling point of vinyl acetate and methanol mixture at atmospheric pressure. (Not polymerized under reduced pressure) and the amount of alcohol during polymerization of vinyl acetate is less than the range of the present invention. In Comparative Example 12, polymerization was performed under reduced pressure at a temperature below the boiling point of the vinyl acetate and methanol mixture at atmospheric pressure. However, the amount of alcohol during polymerization of vinyl acetate is less than the range of the present invention. In Comparative Example 13, the amount of polymerized at a temperature below the boiling point of the vinyl acetate and methanol mixture at atmospheric pressure is reduced. To unpolymerized below, the "1" to "5" have not satisfactory PVA is simultaneously obtained.

The vinyl alcohol polymer of the present invention is excellent in mechanical properties, water resistance and weather resistance, excellent in color tone without coloration, excellent in viscosity stability when made into an aqueous solution, and easily prepared as a mixture with an inorganic substance. It is possible to form films, coatings, molded products, etc. that are excellent in water resistance, weather resistance, and color tone, and various applications including various coating agents and ink jet recording materials, taking advantage of these properties. Can be used effectively.
By the production method of the present invention, the vinyl alcohol polymer of the present invention having the above-described excellent characteristics can be produced smoothly.

Claims (6)

A vinyl alcohol polymer characterized by satisfying the following requirements << 1 >> to << 5 >>.
<1> The viscosity average degree of polymerization (P) is 4000 to 8000;
<< 2 >> The degree of saponification is 99.50 to 99.97 mol%;
<3> The content of 1,2-glycol bond units is 1 to 1.5 mol%;
<< 4 >> When the vinyl alcohol polymer is dissolved in water to prepare a vinyl alcohol polymer aqueous solution having a viscosity at 10 ° C. of 10,000 mPa · s, and the aqueous solution is allowed to stand at 10 ° C., the viscosity is The time required to increase to 20000 mPa · s is 50 to 250 minutes; and
<< 5 >> A vinyl alcohol polymer aqueous solution with a concentration of 30 g / L prepared by dissolving the vinyl alcohol polymer in water [in the case of a vinyl alcohol polymer having a viscosity average polymerization degree (P) of less than 6000] or concentration 10 g / L of a vinyl alcohol polymer aqueous solution [in the case of a vinyl alcohol polymer having a viscosity average degree of polymerization (P) of 6000 or more] measured using a cell having an optical path length of 30 mm, at wavelengths of 280 nm and 320 nm. The absorbance after the concentration correction (measurement temperature: 20 ° C.) is 0.02 L / g or less.   The vinyl alcohol polymer according to claim 1, wherein the content of sodium acetate is 2% by mass or less.   (I) A vinyl ester monomer mixture containing alcohol in a proportion of 2.5 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester monomer is charged into the polymerization tank, and the vinyl ester monomer mixture is prepared. Viscosity is obtained by polymerizing a vinyl ester monomer at a polymerization rate of 8 to 30% by mass in a boiling state while maintaining the pressure in the polymerization tank at a reduced pressure at a temperature equal to or lower than the boiling point under atmospheric pressure. Producing a vinyl ester polymer having a polymerization degree that becomes a vinyl alcohol polymer having an average polymerization degree (P) of 4000 to 8000, and then (ii) a vinyl ester polymer obtained in the step (i). A polymerization inhibitor is added to the reaction product, and the vinyl ester monomer remaining in the reaction product is removed by replacement with alcohol, and then the vinyl ester polymer is removed in the presence of an alkaline substance. Method for producing a vinyl alcohol polymer according to claim 1 or 2, characterized in that saponification under conditions to produce a degree 99.50 to 99.97 mole% of the vinyl alcohol polymer.   In the polymerization step (i), a vinyl ester monomer mixture containing alcohol at a ratio of 2.5 to 8 parts by mass with respect to 100 parts by mass of the vinyl ester monomer is charged into the polymerization tank, and the polymerization rate The method for producing a vinyl alcohol polymer according to claim 3, wherein a vinyl ester polymer is produced by polymerizing a vinyl ester monomer at 10 to 20% by mass.   The method for producing a vinyl alcohol polymer according to claim 3 or 4, wherein the polymerization step (i) is performed in the presence of an organic acid that suppresses aldehyde formation due to decomposition of the vinyl ester monomer.   6. The process according to claim 3, wherein in the step (ii), the addition amount of the polymerization inhibitor is 1 to 10 mol with respect to 1 mol of the undecomposed polymerization initiator remaining in the reaction product. The manufacturing method of the vinyl alcohol-type polymer of description.