JP5820560B2 - Coating agent containing vinyl alcohol polymer - Google Patents

Description

  The present invention relates to a coating agent containing a specific vinyl alcohol polymer and a coated product formed using the same, particularly to an ink jet recording material. More specifically, the present invention has high surface strength, excellent durability, water resistance, weather resistance, gloss, ink absorbability, printability, anti-bleeding properties, etc., and high quality printing without cracks. TECHNICAL FIELD The present invention relates to a coating agent for forming a surface (coating layer) and a coated product formed using the same, and the coating agent of the present invention is particularly useful as a coating agent for forming an ink receiving layer in an ink jet recording material. is there.

  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. The vinyl alcohol polymer is particularly excellent in strength characteristics and film-forming properties as compared with other synthetic polymers, and using these characteristics, a coating agent for forming an ink receiving layer for inkjet recording materials, It is used as a clear coating agent for improving the surface properties of paper, a binder in pigment coating, a raw material for producing water-soluble films and optical films, and the like.

The use of vinyl alcohol polymers in ink jet recording materials has already been commercialized. Inkjet recording methods are being applied to facsimiles, various printers, etc. for reasons such as low noise, easy colorization, and high-speed recording. Yes. Recently, methods of using ink jet printers that have attracted particular attention include the creation of color proofs in the printing field where high image quality close to that of photographs is required, and the output of design images in the design field. Of these, gloss-type jet recording materials having gloss on the surface have attracted attention as an alternative to photography.
The properties required for a recording sheet used in such an ink jet recording method include high gloss on the surface of the ink receiving layer, high image density, good color reproducibility, and high ink absorbability. The dot reproducibility is good.

  Examples of conventional techniques related to inkjet recording materials include: an aqueous liquid containing an inorganic fine powder having a refractive index of 1.44 to 1.55, such as glass powder, quartzite powder, colloidal silica, synthetic silica, and a water-soluble binder; Recording paper (see Patent Document 1) formed by coating on a layer, further porous on a layer formed by applying an aqueous liquid containing porous alumina hydrate and a water-soluble binder on a transparent substrate 2. Description of the Related Art A recording sheet (see Patent Document 2) in which a porous fine silica layer is formed by applying an aqueous liquid containing water-soluble fine silica and a water-soluble binder is known. In these conventional techniques, polyvinyl alcohol having an average degree of polymerization of 2000 or less is mainly used as a water-soluble binder. There are problems such as insufficient ink absorbability, and the characteristics required for inkjet recording materials cannot be fully satisfied.

  Also known are ink jet recording materials in which an ink-receiving layer is formed by coating a base material with a coating agent containing a modified vinyl alcohol polymer having a silyl group as a water-soluble binder (Patent Documents 3 and 4 and 5). Although these modified vinyl alcohol polymers used in the prior art are excellent in the ability to bind inorganic pigments in a small amount, the present inventors have investigated that the ink-receiving layer is not cracked and has glossiness. It turned out that there is room for improvement.

  In addition, for the purpose of further improving the strength characteristics, which are the characteristics of vinyl alcohol polymers, binder strength against inorganic substances, film-forming properties and the like, attempts have been made to increase the degree of polymerization of vinyl alcohol polymers from the past. 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. Polyvinyl alcohol produced by producing an ester polymer and saponifying the vinyl ester polymer obtained thereby is known (see Patent Document 6). However, in this prior art, it is difficult to obtain a polyvinyl alcohol having a polymerization degree of 4000 or more, and the obtained polyvinyl alcohol is colored and has poor colorless transparency or poor water resistance. There are problems such as poor viscosity stability when it is made into an aqueous solution, and it does not have a sufficient function as a binder resin for a coating agent, particularly a coating agent used for producing an inkjet recording material.

  Furthermore, as another conventional technique, a vinyl ester polymer produced by emulsion polymerization of a vinyl ester under reduced pressure in the presence of an emulsifier to produce a vinyl ester polymer, and saponifying the resulting vinyl ester polymer. Although a polymer is known (Patent Document 7), it is not disclosed in Patent Document 7 that the vinyl alcohol polymer obtained there is used as a coating agent or an ink jet recording material. Furthermore, the vinyl alcohol polymer according to this prior art is likely to be colored due to the mixing of the emulsifier used in the emulsion polymerization, and the polymerization degree is too high (generally exceeds 10,000). It is difficult to say that it is suitable as a binder resin for a coating agent, particularly a coating agent used in the production of an inkjet recording material.

Japanese Patent Publication No. 61-60793 JP-A-3-215081 JP 2002-67477 A JP 2004-91774 A JP 2004-43817 A Japanese Patent Publication No.33-003045 Japanese Patent Laid-Open No. 5-117307

The object of the present invention is high surface strength, excellent water resistance, durability, weather resistance, gloss, ink absorbability, printability, anti-bleeding properties such as ink, etc. It is providing the coating agent which can form a coating film (coating layer), and the coating material using the same.
Furthermore, the present invention is excellent in various properties such as durability, water resistance, weather resistance, gloss, ink absorbability, printability, etc., and forms high quality printed matter with clear and good color tone without ink bleeding or cracking. An object of the present invention is to provide a coating agent for forming an ink receiving layer in an ink jet recording material, and an ink jet recording material formed using the same.

  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. And when the said vinyl alcohol type polymer was used, the mixed solution with an inorganic substance could be prepared easily, and the film formed from the said mixed solution discovered that the swelling degree with respect to water was small, and was excellent in water resistance.

Therefore, based on the above knowledge, the present inventors prepared a coating agent using the above-mentioned vinyl alcohol polymer as a binder component, and applied the coating agent to a substrate to form a coating film (coating layer). When the film is formed, the coating film has high surface strength, excellent properties such as water resistance, durability, weather resistance, gloss, ink absorbability, printability, and high quality without cracks. I found out.
And when the coating agent containing the said vinyl alcohol-type polymer as a binder component was applied to the base material and the inkjet recording material was manufactured, the inkjet recording material obtained by that was the ink receiving layer formed from the said coating agent Has excellent durability, water resistance, weather resistance, gloss, ink absorbability, printability, no cracks, and excellent durability, water resistance, weather resistance, and gloss when printed with the inkjet recording material. The present inventors have found that a high-quality printed material having a clear and good color tone can be obtained, and the present invention has been completed based on these findings.

That is, the present invention
(1) 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 concentration correction (measurement temperature 20 ° C.) is 0.02 L / g or less in all cases;
It is a coating agent characterized by containing the vinyl alcohol-type polymer which satisfy | fills.

And this invention,
(2) A vinyl alcohol polymer satisfying the above-mentioned requirements << 1 >> to << 5 >>
<< 6 >> The content of sodium acetate is 2% by mass or less;
Further satisfying the requirement << 6 >>, and (1) the coating agent; and
(3) The coating agent according to (1) or (2), which is a coating agent for forming an ink receiving layer in an inkjet recording material;
It is.
Furthermore, the present invention provides
(4) a coated product obtained by applying the coating agent of any one of (1) to (3) to a substrate; and
(5) An inkjet recording material formed by applying the coating agent according to any one of (1) to (3) to a substrate;
It is.

The vinyl alcohol polymer satisfying the above-mentioned requirements << 1 >> to << 5 >> used in the coating agent of the present invention is excellent in mechanical properties, water resistance, weather resistance, and colorless transparency, and is made into an aqueous solution. The viscosity stability at the time is excellent, and furthermore, it is easy to prepare a mixed solution with an inorganic substance, and the film formed from the mixed solution has a small degree of swelling with respect to water and excellent water resistance.
Therefore, the requirement << 1 >> contained in the coating agent by applying the coating agent of the present invention containing the vinyl alcohol polymer satisfying the above-mentioned requirements << 1 >> to << 5 >> to the substrate. The surface strength is increased by impregnating the base material with a vinyl alcohol polymer satisfying <-5> or by forming a coating layer made of the vinyl alcohol polymer on one or both surfaces of the base material. Various coatings that have excellent properties such as durability, water resistance, weather resistance, gloss, ink absorbability, printability, and anti-bleeding properties, and have a coating layer (coating layer) that does not crack and gives a high-quality printed surface. The work can be manufactured smoothly.
In particular, the coating agent of the present invention containing the vinyl alcohol polymer as a binder component is suitable as a coating for forming an ink receiving layer in an ink jet recording material, and has an ink receiving layer formed from the coating agent. The ink jet recording material is excellent in durability, water resistance, weather resistance, gloss, ink absorbability and printability of the ink receiving layer, has no cracks, and is printed with an ink jet method using the ink jet recording material. High quality prints with excellent properties, weather resistance and gloss, clearness and good color tone can be obtained smoothly.

The present invention is described in detail below.
As described above, the coating agent of the present invention has the following requirements << 1 >> to << 5 >>, that is,
<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;
It contains a vinyl alcohol polymer that satisfies the five requirements.

The vinyl alcohol polymer used in 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 used in the present invention is excellent in the ease of preparation of the coating agent, the stability of the coating agent, and the coating film formed from the coating agent has surface strength, It is possible to form an ink-receiving layer that is excellent in durability, glossiness, printability, has no cracks, does not bleed when printed, and gives a high-quality printed product with a clear and excellent color tone.
When the viscosity average polymerization degree (P) of the vinyl alcohol polymer is less than 4000, the coating film formed from the coating agent easily swells in water, and the water resistance decreases. Further, when the viscosity average polymerization degree (P) of the vinyl alcohol polymer is less than 4000, the viscosity stability of the coating agent may be lowered, and the viscosity increase with time may be increased. On the other hand, when the viscosity average degree of polymerization (P) of the vinyl alcohol polymer exceeds 8000, the viscosity of the coating agent becomes too high and the handling property becomes inferior, and the filler contains together with the vinyl alcohol polymer. The coating agent is likely to be difficult to prepare.
The vinyl alcohol polymer used in the present invention is a coating agent handling property, viscosity stability, ease of mixing a vinyl alcohol polymer and a filler when preparing the coating agent, coating strength, durability. From the viewpoints of weather resistance, crack prevention, gloss, printability, and the like, the viscosity average polymerization degree (P) is preferably from 4200 to 7500, and more preferably from 4500 to 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 in water. 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 used in the present invention needs to satisfy the requirement << 2 >> that the saponification degree is 99.50 to 99.97 mol%, and the requirement << 2 >> is satisfied. When satisfied, the coating agent can be easily prepared, and a coating film having excellent water resistance, crack resistance, printability, ink absorbability and the like 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 coating film formed from the coating agent containing the vinyl alcohol polymer. The water swell degree increases, and the water resistance decreases. In addition, if the saponification degree of the vinyl alcohol polymer is less than 99.50 mol%, the ink droplet dots blot on the ink jet recording material formed using the coating agent containing the vinyl alcohol polymer. May increase and print quality may deteriorate.
On the other hand, when the saponification degree of the vinyl alcohol polymer exceeds 99.97 mol%, it becomes difficult to prepare a coating agent, and the viscosity of the coating agent increases with time, resulting in poor stability and handling. easy. Further, when the saponification degree of the vinyl alcohol polymer exceeds 99.97 mol%, the surface of the ink jet recording material formed using the coating agent containing the vinyl alcohol polymer is cracked or printed. Print quality may be reduced.
The saponification degree of the vinyl alcohol polymer used in the present invention is preferably 99.58 to 99.96 mol%, and more preferably 99.65 to 99.95 mol%.

The vinyl alcohol polymer used in 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%". When the vinyl alcohol polymer satisfies the requirement << 3 >>, a coating agent having excellent viscosity stability can be easily prepared, and the water resistance, crack resistance, printability, and ink absorption of the coating film can be easily prepared. Etc. will be good.
When the content of the 1,2-glycol bond unit in the vinyl alcohol polymer is less than 1 mol%, it is difficult to prepare the coating agent, and the stability of the coating agent tends to be lowered. 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, crack resistance, printability, ink absorbability, etc. of the coating film are reduced. Easy to be.
The vinyl alcohol polymer used in the present invention has a 1,2-glycol bond unit in a proportion 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 to have.

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 described later, a vinyl alcohol polymer having a 1,2-glycol bond unit content in the range of 1 to 1.5 mol% can be produced smoothly. Also, when producing a vinyl alcohol polymer according to the following production method, a small amount of ethylene carbonate may be copolymerized with the vinyl ester monomer or the polymerization temperature may be changed during the production of the vinyl ester polymer. Also, the content of 1,2-glycol bond units can be further adjusted.

The vinyl alcohol polymer used in the present invention is “a vinyl alcohol polymer aqueous solution having a viscosity of 10,000 mPa · s at 10 ° C. by dissolving the vinyl alcohol polymer in water, and the aqueous solution is 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 is 50 to 250 minutes. When the vinyl alcohol polymer satisfies the requirement << 4 >>, it is possible to prepare a coating agent that has little viscosity increase over a long period of time and that is excellent in viscosity stability and handleability, and is a coating film formed from the coating agent. Is excellent in water resistance, bleed resistance, printability and ink absorbability.
When using 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. is less than 50 minutes, an inorganic filler or the like is added. When the coating agent is prepared, gelation occurs at an early stage, and a stable coating agent cannot be prepared. On the other hand, when a vinyl alcohol polymer having a viscosity of 10000 mPa · s, the time required for the viscosity of the vinyl alcohol polymer aqueous solution to increase to 20000 mPa · s at 10 ° C. exceeds 250 minutes, the water resistance of the coating film is lowered. When the ink jet recording material is formed, the dots of ink droplets become more blurred and printability is deteriorated.
The vinyl alcohol polymer used in 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. The time required for the viscosity to increase to 20000 mPa · s when allowed to stand is preferably 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 used in the present invention, the content of sodium acetate is not particularly limited as long as the requirement << 4 >> is satisfied, but the content of sodium acetate is 2 based on the mass of the vinyl alcohol polymer. By setting the content to 1% by mass or less, further 1% by mass or less, and particularly 0.5% by mass or less, it is possible to more smoothly obtain a vinyl alcohol polymer having an aqueous solution behavior that satisfies the above requirement << 4 >>.

  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 referred to simply as “degree of polymerization”), it can be prepared 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 used in the present invention is “a vinyl alcohol polymer aqueous solution having a concentration of 30 g / L prepared by dissolving the vinyl alcohol polymer in water [vinyl having a viscosity average polymerization degree (P) of less than 6000”. In the case of an alcohol 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. Thus, 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 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.)” is 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 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 coating film that is not colored and excellent in color tone, excellent in weather resistance, and has no discoloration.
If the concentration-corrected absorbance (cell optical path length 30 mm) at a wavelength of 280 nm and 320 nm of the aqueous vinyl alcohol polymer solution having the above concentration exceeds 0.02 L / g, the coating film is colored or the weather resistance is lowered.
In the vinyl alcohol polymer used in the present invention, the concentration-corrected absorbance (cell optical path length 30 mm) at wavelengths of 280 nm and 320 nm of the aqueous solution of the vinyl alcohol polymer 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 of the vinyl alcohol polymer aqueous solution at wavelengths of 280 nm and 320 nm (cell optical path length: 30 mm) is not particularly limited. 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 described later, the vinyl alcohol-based polymer in which the absorbance (cell optical path length 30 mm) after concentration correction at wavelengths of 280 nm and 320 nm of the aqueous vinyl alcohol-based polymer solution having the above concentration is 0.02 L / g or less. A polymer can be produced smoothly.

  As long as the vinyl alcohol polymer used in the present invention is within the range not impairing the object and effect of the present invention, one or more structural units derived from other copolymerizable monomers as necessary. You may have. The proportion of structural units derived from other copolymerizable monomers that the vinyl alcohol polymer used in the present invention may have is the type of structural units derived from other monomers, the vinyl alcohol weight. Generally, it is preferably 20 mol% or less, more preferably 10 mol% or less, based on all structural units constituting the vinyl alcohol polymer, although it may vary depending on the use of the coalescence. More preferably, it is 5 mol% or less.

  Examples of structural units derived from other copolymerizable monomers that the vinyl alcohol polymer used in the present invention can have as necessary include ethylene, propylene, 1-butene, isobutene, 1-hexene, and the like. Α-olefins of carboxylic acids such as fumaric acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride or derivatives thereof; acrylic acid or salts thereof, methyl acrylate, ethyl acrylate, n-propyl acrylate, Acrylic esters such as isopropyl acrylate; methacrylic acid or salts thereof, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, etc .; acrylamide, N-methyl acrylamide, N-ethyl Acrylic such as acrylamide Methacrylamide derivatives; 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, 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; Body; isopropenyl acetate, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octene- Hydroxyl group-containing α-olefins such as 1-ol, 9-decen-1-ol, 3-methyl-3-buten-1-ol; ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-acrylamide- Monomers having a sulfonic acid group such as 2-methylpropanesulfonic acid; vinyloxyethyltrimethylammonium chloride, vinyloxybutyltrimethylammonium chloride, vinyloxyethyldimethylamine, vinyloxymethyldiethylamine, N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidodimethylamine, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, dimethylallylamine Monomers having cationic groups such as ethylene and allylethylamine; vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3- (meth) Examples include structural units derived from monomers having a silyl group such as acrylamide-propyltrimethoxysilane and 3- (meth) acrylamide-propyltriethoxysilane. The vinyl alcohol polymer used in the present invention may have one or more structural units derived from the aforementioned monomers.

The vinyl alcohol polymer used in the present invention may be obtained by any production method as long as the vinyl alcohol polymer satisfies the above five requirements << 1 >> to << 5 >>.
Among them, the vinyl alcohol polymer used in the present invention is (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. It is charged in a polymerization tank, and the vinyl ester monomer mixture is in a boiling state while maintaining the pressure in the polymerization tank at a temperature below the boiling point under atmospheric pressure, with a polymerization rate of 8 to 30% by mass. Ester monomers are polymerized to produce a vinyl ester polymer having a degree of polymerization that becomes a vinyl alcohol polymer having a viscosity average polymerization degree (P) of 4000 to 8000 after saponification, and then (ii) After adding a polymerization inhibitor to the reaction product containing the vinyl ester polymer obtained in the step (i) and replacing the vinyl ester monomer remaining in the reaction product with alcohol, In the presence of alkaline substances, the polyvinyl ester, is smoothly produced by the method of saponifying under conditions to produce vinyl alcohol polymer with a degree of saponification 99.50 to 99.97 mol%.

  As a polymerization method of the vinyl ester monomer, a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method and the like are known, and the polymerization step (i) [hereinafter referred to as “polymerization step (i In some cases, a solution polymerization method using 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 (solution polymerization method) First, a vinyl ester polymer is produced by a method similar to the above. The polymerization step (i) for producing the vinyl ester polymer and the subsequent step (ii) may be carried out batchwise (batch type) or continuously, but the production efficiency From the viewpoint of the above, the continuous type is preferably employed.

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 the both is within the above-described range, and the polymerization tank and the polymerization degree are set in the polymerization tank for a predetermined time so that the above-described polymerization rate and degree of polymerization are obtained. Polymerization is performed while retaining to form a vinyl ester polymer of a predetermined polymerization degree, and after the reaction product containing the vinyl ester polymer is continuously removed from the polymerization tank, polymerization is prohibited on the reaction product. After removing the vinyl ester monomer remaining in the reaction product with alcohol, the vinyl ester polymer is adjusted to a predetermined degree of saponification in the presence of an alkaline substance. To emissions reduction.
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 copolymerization monomers that the vinyl alcohol polymer used in the present invention may have as necessary. Examples of the monomer constituting the structural unit derived from the body include those exemplified in the above paragraph 0027, 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 thereof include an initiator, 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 >>. In the present invention, the vinyl alcohol polymer may be used as the vinyl alcohol polymer.

  The vinyl ester monomer mixture (vinyl ester monomer mixture in the polymerization tank) used in the polymerization step (i) is a high vinyl alcohol polymer that satisfies the above requirements << 1 >> to << 5 >>. In order to obtain smoothly with production efficiency, it is preferable to contain alcohol in a ratio of 2.5 to 10 parts by mass, particularly 2.5 to 8 parts by mass with respect to 100 parts by mass of the vinyl ester monomer.

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. It is preferable to polymerize the vinyl ester monomer in a boiling state while keeping the pressure in the polymerization tank in a reduced pressure state 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 tends to be difficult to obtain a vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >>.
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) at a wavelength of 280 nm and 320 nm of the vinyl alcohol polymer aqueous solution (cell optical path length: 30 mm) (measurement temperature: 20 ° C.) may both exceed 0.02 L / g. It is difficult to obtain a vinyl alcohol polymer satisfying 1 >> to << 5 >>.

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 may be polymerized in the polymerization tank while maintaining the mass% range.
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), and 1-5 mol It is more preferable that it is 1 to 3 mol.

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.
Depending on the type of polymerization initiator used in the polymerization step (i), one or more of the polymerization inhibitors described above can be used. Among these, as the polymerization inhibitor, sorbic acid, sorbic acid ester, and sorbate are preferably used from the viewpoint of the weather resistance of the film.

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, a vinyl alcohol polymer satisfying the above requirements << 1 >> to << 5 >> is obtained.
The coating agent of the present invention containing a vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >> is a coating agent for producing an inkjet recording material, a coating agent for glass fiber, a metal surface coating agent, and an antifogging agent. It can be effectively used as various coating agents such as coating agents. Among them, the coating agent of the present invention is suitable for the production of ink jet recording materials due to the above-mentioned properties such as excellent water resistance, durability, weather resistance, gloss, ink absorbability, printability, bleeding resistance, and crack resistance. It is suitable as a coating agent, that is, a coating agent for forming an ink receiving layer in an ink jet recording material.

  The coating agent of the present invention may consist of a solution in which only a vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >> is dissolved in a solvent, depending on the application and usage form of the coating agent. (For example, for clear coat) or a solution in which a vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >> is dissolved in a solvent satisfies other components such as the requirements << 1 >> to << 5 >> A solution containing one or more of water-soluble polymers other than vinyl alcohol polymers, water-insoluble polymers, inorganic fillers, organic fillers, inorganic pigments, organic pigments, organic dyes, dispersion stabilizers, etc. Or you may consist of a dispersion liquid.

In preparing the coating agent of the present invention, the solvent used to dissolve the vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >> is water-soluble such as water, dimethyl sulfoxide, dimethylformamide, hexafluoroisopropanol. An organic solvent, a mixed solvent in which two or more of the above-mentioned solvents are mixed, and the like can be mentioned. Among them, as a solvent, water alone or an aqueous solvent obtained by mixing water and a water-soluble organic solvent, particularly water, is easy to prepare a coating agent, handleability, quality of a coating film obtained from the coating agent, environment It is preferably used from the viewpoint of safety and cost.
The content of the vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >> in the coating agent may vary depending on the use of the coating agent, the type and content of other components contained in the coating agent, and the like. In general, the content is preferably 1 to 80% by mass, and more preferably 2 to 50% by mass based on the total mass of the coating agent.
In a solution in which a vinyl alcohol polymer is dissolved in water or other solvent, an acid, a base, a salt, or the like may be dissolved and contained as necessary.

When the coating agent of the present invention contains other water-soluble polymer and / or water-insoluble polymer together with the vinyl alcohol polymer that satisfies the requirements << 1 >> to << 5 >>, other water-soluble polymers that may be contained For example, albumin, gelatin, casein, starch, cationized starch, arabic rubber, polyamide resin, melamine resin, poly (meth) acrylamide, polyvinylpyrrolidone, sodium poly (meth) acrylate, sodium alginate, water-soluble polyester , Cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose (CMC), anion-modified polyvinyl alcohol, and vinyl alcohol polymers other than vinyl alcohol polymers satisfying other requirements << 1 >> to << 5 >> It can be. Examples of water-insoluble polymers (such as water-insoluble polymer dispersions) that can be contained include SBR latex, NBR latex, vinyl acetate emulsion, ethylene / vinyl acetate copolymer emulsion, (meth) acrylic ester emulsion, and chloride. A vinyl emulsion can be mentioned.
The coating agent of the present invention can contain one or more of the aforementioned polymers.

  When the coating agent of the present invention contains the above-mentioned other water-soluble polymer and / or water-insoluble polymer together with the vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >>, The content of the polymer (when two or more other polymers are contained, the total content thereof) is 200 with respect to 100 parts by mass of the vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >>. It is preferably no greater than 100 parts by mass, more preferably no greater than 100 parts by mass, and even more preferably no greater than 50 parts by mass. When there is too much content of another polymer, it may become difficult to exhibit the above-mentioned outstanding characteristic of the vinyl alcohol-type polymer which satisfy | fills requirements << 1 >>-<< 5 >>.

When the coating agent of the present invention contains a filler, examples of the filler that can be contained include precipitated silica, gel silica, vapor phase silica, colloidal silica, colloidal alumina, aluminum oxide, pseudoboehmite, clay, Examples thereof include talc, diatomaceous earth, zeolite, calcium carbonate, alumina, zinc oxide, satin white, organic pigments, and the like, and one or more of these can be contained.
In particular, when the coating agent of the present invention is used as a coating agent for forming an ink receiving layer of an ink jet recording material, one or more of the above-mentioned fillers, among them, one of colloidal silica, colloidal alumina, and aluminum oxide. Or it is preferable to contain 2 or more types from points, such as surface strength of an ink receiving layer, crack resistance, ink absorptivity, and glossiness.
When the filler is included in the coating agent of the present invention, the mass ratio of vinyl alcohol polymer: filler satisfying the requirements << 1 >> to << 5 >> is in the range of 5: 100 to 100: 100. It is preferable that it is within the range of 7: 100 to 80: 100, more preferably within the range of 10: 100 to 60: 100.

  Further, when the coating agent of the present invention is a coating agent for forming an ink receiving layer of an ink jet recording material, an ink fixing agent can be contained as necessary. Examples of the ink fixing agent include monomers, oligomers, and polymers having primary to tertiary amino groups or quaternary ammonium bases that dissociate and exhibit cationic properties when dissolved in water, and among them, oligomers and / or polymers. Specific examples include dimethylamine / epichlorohydrin polycondensate, acrylamide / diallylamine copolymer, polyvinylamine copolymer, dimethyldiallylammonium chloride polymer, polyethyleneimine, and the like.

  The kind of the substrate for applying the coating agent of the present invention is not limited, and any substrate may be used as long as it is a conventionally known transparent or opaque support substrate. Although not limited, examples of the transparent support substrate on which the coating agent of the present invention can be applied include polyester, polystyrene, polyvinyl chloride, polymethyl methacrylate, cellulose acetate, polycarbonate, polyimide, cellophane, and celluloid. Transparent films, sheets, transparent plastic moldings, highly transparent paper, and the like. Examples of the opaque support substrate to which the coating agent of the present invention can be applied include, for example, general paper, pigment-coated paper, fabric, wood, metal plate, synthetic paper, synthetic resin film or sheet subjected to opacification treatment, Other opaque polymer molded bodies can be mentioned. Any of the transparent support substrate and the opaque support substrate exemplified above can be used as a support substrate for inkjet recording materials and a support substrate for other coated materials.

The coating method in particular when applying the coating agent of this invention to a base material is not restrict | limited, Any of the coating methods of the coating agent known conventionally can be employ | adopted, for example, a size press, an air knife coater Examples thereof include a method of coating a substrate using a roll coater, a bar coater, a blade coater, a curtain coater, a cast coater and the like.
The coating agent of the present invention is applied to a base material, and the base material is impregnated with a vinyl alcohol polymer satisfying the requirements << 1 >> to << 5 >> contained in the coating agent, or the vinyl alcohol type By forming a coating layer made of a polymer on one or both sides of the substrate, the surface strength is high, and durability, water resistance, weather resistance, gloss, ink absorbability, printability, anti-bleeding properties, etc. An ink jet recording material and other coated materials having a coating film (coating layer, particularly an ink receiving layer) that gives an excellent, crack-free and high-quality printing surface can be obtained smoothly.

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 The absorbance after the concentration correction at 320 nm (cell optical path length 30 mm) and the weather resistance of the vinyl alcohol polymer film (polyvinyl alcohol film) were calculated or evaluated as follows (hereinafter, “polyvinyl alcohol” is referred to as “PVA”). Sometimes).
Furthermore, regarding the surface hardness, crack, ink absorbency, ink bleed degree, print quality and gloss of the ink receiving layer (coating layer, coating layer) in the inkjet recording paper formed using the coating agent containing PVA, Measurement or evaluation was performed by the following method.

(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):
In accordance with JIS-K6726, the degree of polymerization [viscosity average degree of polymerization (P)] of PVA obtained in the following production examples and comparative production 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 Production Examples and Comparative Production Examples was determined.

(5) Content of 1,2-glycol bond unit of PVA:
(I) In a PVA obtained in the following production examples or comparative production 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. In addition, re-saponification was performed at 60 ° C. for 5 hours, and the obtained PVA was subjected to Soxhlet extraction with methanol for 1 week to obtain purified PVA having a saponification degree of 99.9 mol% or more.
(Ii) 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 production examples and comparative production examples, the concentration was adjusted and the viscosity of the aqueous solution at 10 ° C. was measured with a B-type viscometer (“B-type viscometer” manufactured by Tokyo Keiki Co., Ltd.) Each PVA aqueous solution of 10,000 mPa · 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. The viscosity was plotted on the vertical axis, and the time when the viscosity of the PVA aqueous 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 production example or comparative production example prepared above was equally dispensed into 13 tall beakers (capacity 300 ml), and all the 13 tall beakers were kept at a constant temperature of 10 ° C. The viscosity of the PVA aqueous solution in the first beaker was measured at the start of measurement while being left in the water tank at the same time, and the viscosity of the PVA aqueous solution in the second beaker was measured 30 minutes after the start of measurement. The viscosity of the PVA aqueous solution in the beaker 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 30 for the PVA aqueous solution in the 5th to 13th beakers. Measurement was performed every minute, time was plotted on the horizontal axis, and 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) A PVA aqueous solution was prepared using each of the PVA obtained in the following production examples and comparative production examples, and a spectrophotometer described in JIS-K0115 (“UV-1700” manufactured by Shimadzu Corporation) was used. Then, using a quartz cell having 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 is measured at a temperature of 20 ° C., and the absorbance (Aa ₂₈₀ ) and wavelength at a wavelength of 280 nm are measured. Absorbance at 320 nm (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) 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 = 10 cm × 10 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 variation | change_quantity ((DELTA) b) of b value is large.

(10) Surface strength of ink receiving layer:
Adhesive tape [manufactured by Nichiban: Cello Tape (registered trademark)] was applied to the surface of the ink receiving layer (coating layer) of the ink jet recording paper produced in the following Examples and Comparative Examples, and a pressure of 0.5 kg / cm ² was applied. And then left to stand at 25 ° C. and 60% RH for 24 hours. Thereafter, the pressure-sensitive adhesive tape was peeled off at an angle of 180 degrees, and the amount of desorbed material from the ink receiving layer adhering to the pressure-sensitive adhesive layer surface of the pressure-sensitive adhesive tape was visually observed and evaluated according to the following evaluation criteria.
[Evaluation criteria for surface strength of ink receiving layer]
A: No detachment from the ink receiving layer is observed on the surface of the adhesive tape.
B: A very small amount of detachment from the ink receiving layer was observed on the surface of the adhesive tape.
C: Desorption from the ink receiving layer was partially observed on the surface of the adhesive tape.
D: Detachment from the ink receiving layer was observed on the entire surface of the adhesive tape.

(11) Cracking of ink receiving layer:
The surface of the ink receiving layer (coating layer) of the inkjet recording paper produced in the following Examples and Comparative Examples was observed with an optical microscope (enlarged 100 times) and evaluated according to the following evaluation criteria.
[Evaluation criteria for cracks in ink receiving layer]
A: No cracks are observed on the surface.
B: Cracks are partially generated on the surface.
C: Cracks occur on the entire surface

(12) Ink absorbability of ink receiving layer:
Using an inkjet printer [“PM2000C” manufactured by Seiko Epson Corporation] on the ink receiving layer (coating layer) surface of the inkjet recording paper produced in the following examples and comparative examples, printing is performed with black ink and printing. Immediately after that, after 3 seconds, 5 seconds, 8 seconds, 10 seconds, and then rub the print surface with a finger at intervals of 5 seconds, observe the blur, and the ink is completely absorbed by the ink receiving layer. The time until no longer occurred was measured and evaluated according to the following evaluation criteria.
[Evaluation criteria for ink absorbency of ink receiving layer]
A: Fading does not occur in less than 5 seconds, and ink absorbency is good.
B: No fading occurs in 5 seconds or more and less than 10 seconds, and the ink absorbability is slightly poor.
C: Fading does not occur in 10 seconds to less than 30 seconds, and ink absorbency is poor.
D: It takes 30 seconds or more until no blur occurs, and the ink absorbability is extremely poor.

(13) The degree of ink bleeding in the ink receiving layer:
Using an ink jet printer [“PM2000C” manufactured by Seiko Epson Corporation] on the ink receiving layer (coating layer) surface of the ink jet recording paper produced in the following examples and comparative examples, only one dot with black ink is used. Print alone, measure the diameter of the black ink print dot with a stereo microscope ("VH-7000" manufactured by KEYENCE, 100x magnification), and measure how many times the ink droplet (diameter 30 µm). This was used as an index of the degree of ink bleeding. The diameter of the ink droplet was measured using a slide glass with a scale.

(14) Print quality:
Using an ink jet printer [“PM-970C” manufactured by Seiko Epson Corporation] on the ink receiving layer (coating layer) surface of the ink jet recording paper produced in the following Examples and Comparative Examples, an image is printed with black ink. Printing was performed, the printed surface was visually observed, and the printing quality was evaluated according to the following evaluation criteria.
[Print quality evaluation criteria]
A: The recording density was uniform throughout the printed area, and a good image was obtained.
B: Spots of recording density were observed only slightly, but the image was not greatly affected.
C: Recording density spots were partially generated, and the image quality was impaired.
D: Recording density spots were generated as a whole, and the quality of the image was significantly impaired.

(15) Glossiness of printed surface:
Black, yellow, magenta and cyan were used on the ink receiving layer (coating layer) surface of the ink jet recording paper produced in the following examples and comparative examples using an ink jet printer ["PM2000C" manufactured by Seiko Epson Corporation]. The ink was then color-printed, and the glossiness of the printed surface was measured with a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method of JIS-Z-8714 (mirror glossiness at an incident angle of 60 degrees). The measurement was performed 5 times and the average was taken.

<< Production 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, when 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 room temperature and at a rate of 716.8 kg / hour, while methanol vapor at a temperature of 90 ° C. and a pressure (gauge pressure) of 190 KPa was blown from the bottom of the tower at a rate of 600 kg / hour to react. Unreacted vinyl acetate contained in the product was driven countercurrently from the reaction product [removal rate of unreacted vinyl acetate (purge rate) 99.9%], and polyvinyl acetate was removed from the bottom of the tower. A methanol solution containing 21% by mass was recovered.

(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, the viscosity stability of the aqueous solution of “PVA-1a” obtained in (3) above, the absorbance after correction of the concentration at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), and the film formed from “PVA-1a” When the weather resistance was measured or evaluated by the method described above, it was as shown in Table 1 below.

<< Production 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 Production Example 1 except that the conditions shown in Table 1 below were adopted. In the vinyl acetate polymerization step for producing “PVA-2a” to “PVA-6a”, in the same manner as in Production 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-2a” to “PVA-6a” obtained in (1) above are shown in the table below. 1 as shown.
Further, the viscosity stability of the aqueous solutions of “PVA-2a” to “PVA-6a” obtained in the above (1), the absorbance after the concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), and [PVA-2a When the weather resistance of the film obtained from “PVA-6a” was measured or evaluated by the method described above, it was as shown in Table 1 below.

<< Production 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 Production Example 1 except that the conditions shown in Table 3 below were adopted. In the vinyl acetate polymerization step for producing “PVA-7a” to “PVA-12a”, in the same manner as in Production 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. 2 as shown.
Further, the viscosity stability of the aqueous solutions of “PVA-7a” to “PVA-12a” obtained in the above (1), the absorbance after the concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), and [PVA-7a] When the weather resistance of the film obtained from “PVA-12a” was measured or evaluated by the method described above, it was as shown in Table 2 below.

<< Comparative Production Examples 1 to 8 >> [Production of "PVA-1b" to "PVA-8b"]
(1) “PVA-1b” to “PVA-8b” were produced in the same manner as in Production Example 1 except that the conditions shown in Table 3 below were adopted. In the vinyl acetate polymerization step for producing “PVA-1b” to “PVA-8b”, in the same manner as in Production Example 1, the tartaric acid was added to the vinyl acetate 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-8b” obtained in (1) above are shown in the table below. As shown in FIG.
Further, the viscosity stability of the aqueous solutions of “PVA-1b” to “PVA-8b” obtained in the above (1), the absorbance after the concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), and [PVA-1b] When the weather resistance of the film obtained from “PVA-8b” was measured or evaluated by the method described above, it was as shown in Table 3 below.

<< Comparative Production Examples 9 to 13 >> [Production of "PVA-9b" to "PVA-13b"]
(1) “PVA-9b” to “PVA-13b” were produced in the same manner as in Production Example 1 except that the conditions shown in Table 4 below were adopted. In the vinyl acetate polymerization step for producing “PVA-9b” to “PVA-13b”, in the same manner as in Production 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-9b” to “PVA-13b” obtained in the above (1) are as follows. As shown in FIG.
Further, the viscosity stability of the aqueous solutions of “PVA-9b” to “PVA-13b” obtained in (1) above, the absorbance after correction of the concentration at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), and “PVA-9b” When the weather resistance of the film obtained from “PVB-13b” was measured or evaluated by the method described above, it was as shown in Table 4 below.

<< Comparative Production Example 14 >> [Production of “PVA-14b”]
(1) PVA (PVA-14b) was produced in the same manner as in Production Example 1 of Patent Document 7 (JP-A-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. Decompression degree 35 Torr (absolute pressure) (4.7 KPa) while continuously adding 10 parts by mass / hour of hydrogen peroxide water of 0.07% by mass prepared by using ion-exchanged water that has been cooled and degassed separately 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. The gelled product generated as the saponification reaction progressed 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-13b”).

(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
Also, viscosity stability of the aqueous solution of “PVA-14b” obtained in (3) above, absorbance after concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length 30 mm), and weather resistance of the film formed from “PVA-14b” The properties were measured or evaluated by the methods described above, and the results were as shown in Table 4 below.

<< Comparative Production Example 15 >> [Production of “PVA-15b”]
(1) PVA (PVA-15b) was produced in the same manner as in Production Example 1 of “PVA1” described in paragraph 0061 of Patent Document 4 (Japanese Patent Application Laid-Open No. 2004-91774).
That is, a methanol solution containing 2450 parts by mass of vinyl acetate, 315 parts by mass of methanol, and 1% by mass of vinyltrimethoxysilane in a 6-liter separable flask equipped with a stirrer, a temperature sensor, a dropping funnel and a reflux condenser. 735 parts by mass were charged, and the inside of the system was purged with nitrogen under stirring, and then the internal temperature was raised to 60 ° C. To this system, 20 parts by mass of methanol containing 0.8 part by mass of 2,2′-azobisisobutyronitrile was added to initiate the polymerization reaction. A polymerization reaction was carried out for 4 hours while adding 55% by mass of methanol containing vinyltrimethoxysilane at a concentration of 1% by mass from the start of the polymerization, and the polymerization reaction was stopped at that point. The solid content concentration in the system when the polymerization reaction was stopped was 34.6% by mass. Next, methanol vapor was introduced into the system to drive off unreacted vinyl acetate monomer, thereby obtaining a methanol solution containing a vinyl ester polymer in a proportion of 40% by mass.

(2) The molar ratio of sodium hydroxide to vinyl acetate units in the vinyl ester polymer relative to the methanol solution of the vinyl ester polymer obtained in (1) above is 0.02, Methanol and a methanol solution containing sodium hydroxide at a concentration of 10% by mass were added with stirring in this order so that the solid content concentration was 30% by mass, and a saponification reaction was started at 40 ° C. Immediately after the saponification reaction progresses, a gelled product is formed and removed from the reaction system and pulverized. Then, when 1 hour has elapsed from the start of the saponification reaction, methyl acetate is added to the pulverized product. The PVA neutralized by addition and swollen with methanol was obtained. To the PVA swollen with methanol, 6 times the amount of methanol (6 times the bath ratio) of methanol was added, washed under reflux for 1 hour, and then dried at 65 ° C. for 16 hours to obtain PVA (“PVA-14b” Got.
(3) The content of structural units derived from vinyltrimethylsilane in “PVA-15b” obtained in (2) above is 0.20 mol%, and the content of 1,2-glycol bond units is 1.56 mol. %, The degree of polymerization was 1700, and the degree of saponification was 98.5 mol%.
Also, viscosity stability of the aqueous solution of “PVA-15b” obtained in (2) above, absorbance after concentration correction at wavelengths of 280 nm and 320 nm (cell optical path length: 30 mm), and weather resistance of the film formed from “PVA-15b” The properties were measured or evaluated by the methods described above, and the results were as shown in Table 4 below.

<< Comparative Production Example 16 >> [Production of “PVA-16b”]
(1) In (2) of Comparative Production Example 15, the saponification conditions were changed so that the molar ratio of sodium hydroxide to vinyl acetate units in the vinyl ester polymer was 0.007. PVA (“PVA-16b”) was produced in the same manner as in Comparative Production Example 14 except that a saponification reaction was performed by adding a 10 mass% methanol solution.
(2) The content of the structural unit derived from vinyltrimethoxysilane in “PVA-16b” obtained in (1) above is 0.20 mol%, the degree of polymerization is 1700, the degree of saponification is 88.11 mol%, The content of 1,2-glycol bonding units was 1.6 mol%.
In addition, viscosity stability of the aqueous solution of “PVA-16b” obtained in (2) above, absorbance after concentration correction at a wavelength of 280 nm and 320 nm (cell optical path length 30 mm), and weather resistance of the film formed from “PVA-16b” The properties were measured or evaluated by the methods described above, and the results were as shown in Table 4 below.

Example 1 [Production of coating agent and inkjet recording paper]
(1) Preparation of dispersion of aluminum oxide fine particles:
Ion-exchanged water in which 600 g of aluminum oxide powder [“Aerosil Al ₂ O ₃ .C” manufactured by Nippon Aerosil Co., Ltd., γ-type crystal, average particle diameter of primary particles of 20 nm or less] and acetic acid 12 g as a dispersion stabilizer are dissolved. An aqueous dispersion of aluminum oxide powder (concentration of aluminum oxide powder of 20% by mass) prepared by mixing 2400 g and stirring and dispersing with a stirrer was prepared. This aqueous dispersion was pulverized by applying a pressure of 700 kg / cm ² with a high-pressure homogenizer [“Gorin homogenizer 15MR-8TA type” manufactured by Doei Shoji Co., Ltd.] to give a milky white slurry-like viscous dispersion. (Solid content concentration 20% by mass) was prepared. The average particle diameter of the aluminum oxide fine particles dispersed in this aqueous dispersion was 95 nm. In addition, the average particle diameter of the aluminum oxide fine particles was measured using a laser diffraction / scattering particle size distribution measuring apparatus [“LA-910” manufactured by Horiba, Ltd.].

(2) Production of coating agent (coating agent for forming an ink receiving layer in ink jet recording paper):
“PVA-1a” produced in Production Example 1 above was dissolved in ion-exchanged water to prepare an aqueous solution having a concentration of 4.2% by mass of “PVA-1a”. To 476.2 g, 1000 g of the aqueous dispersion of aluminum oxide fine particles prepared in the above (1) (concentration of aluminum oxide fine particles of 20% by mass) was added and well mixed and stirred to form an ink receiving layer on an ink jet recording paper. A coating agent (aqueous dispersion) was produced.
The content of the aluminum oxide fine particles in the coating agent thus obtained is 200 g, the content of PVA is 20 g (aluminum oxide fine particles: PVA mass ratio = 10: 1), and the solid content concentration (aluminum oxide with respect to the total mass of the coating agent). The ratio of the total content of fine particles and PVA) was 14.90% by mass.
Moreover, it was 110 mPa * s (20 degreeC) when the viscosity in the temperature of 20 degreeC of this coating agent was measured using the B-type viscosity meter (made by Tokyo Keiki Co., Ltd.).

(3) Apply the coating agent obtained in (2) above to the surface of the laminated paper using a Mayer bar at room temperature so that the coating amount (at the time of drying) is 10 g / m ^2, and dry with hot air The ink-jet recording paper was manufactured by drying at 100 ° C. for 3 minutes in a machine.
In addition, as the laminated paper, polyethylene is applied to the surface of the coated layer of commercially available coated paper (“OK Coat” manufactured by Oji Paper Co., Ltd., basis weight = 127.9 g / m ² ) by a thickness of 50 μm by the extrusion laminating method. A laminate was used.
(4) For the ink jet recording paper obtained in (3) above, the surface strength of the ink receiving layer, the crack of the ink receiving layer, the ink absorbency of the ink receiving layer, the degree of ink bleeding of the ink receiving layer, the print quality and the printing When the glossiness of the surface was measured or evaluated by the method described above, it was as shown in Table 5 below.

<< Examples 2 to 6 >>
(1) Each of “PVA-2a” to “PVA-6a” produced in Production Examples 2 to 6 is dissolved in ion-exchanged water, and an aqueous solution having a PVA concentration of 4.2 mass% (Example 2). To 4) or an aqueous solution (Examples 5 to 6) having a PVA concentration of 3.2% by mass, respectively, and 476.2 g (Examples 2 to 4) or 625.0 g of the aqueous solution of PVA thus obtained. To (Examples 5 to 6), 1000 g of the same aqueous dispersion of aluminum oxide fine particles as prepared in (1) of Example 1 (concentration of aluminum oxide fine particles of 20% by mass) was added, and well mixed and stirred. A coating agent (aqueous dispersion) for forming an ink receiving layer in an inkjet recording paper was produced.
The content of the aluminum oxide fine particles in the coating agent thus obtained is 200 g, the content of PVA is 20 g (aluminum oxide fine particles: PVA mass ratio = 10: 1), and the solid content concentration (aluminum oxide with respect to the total mass of the coating agent). The ratio of the total content of the fine particles and PVA) was 14.90% by mass (Examples 2 to 4) or 13.54% by mass (Examples 5 to 6).
The viscosities at a temperature of 20 ° C. of these coating agents were measured in the same manner as in Example 1 and were as shown in Table 5 below.
(2) Inkjet recording paper was produced in the same manner as (3) of Example 1 using each coating agent obtained in (1) above.
(3) About each ink jet recording paper obtained in the above (2), the surface strength of the ink receiving layer, the crack of the ink receiving layer, the ink absorbency of the ink receiving layer, the degree of ink bleeding of the ink receiving layer, the print quality Further, when the glossiness of the printed surface was measured or evaluated by the method described above, it was as shown in Table 5 below.

<< Examples 7 to 12 >>
(1) Each of “PVA-7a” to “PVA-12a” produced in the above Production Examples 7 to 12 was dissolved in ion-exchanged water, and an aqueous solution having a PVA concentration of 3.2 mass% (Example 7) ) 5.2% by weight aqueous solution (Examples 8-9), 4.6% by weight aqueous solution (Example 10), 5.7% by weight aqueous solution (Example 11) or 4.2% by weight aqueous solution. (Example 12) were prepared, and 625.0 g (Example 7), 384.6 g (Examples 8 to 9), 434.8 g (Example 10), and 350. of the aqueous solution of PVA thus obtained. To 9 g (Example 11) or 476.2 g (Example 12), 1000 g of the same aqueous dispersion of aluminum oxide fine particles (concentration of aluminum oxide fine particles 20 mass%) as prepared in (1) of Example 1 was added. In addition, mix well and stir to make inkjet recording. A coating agent (aqueous dispersion) for forming an ink receiving layer on a recording paper was produced.
The content of the aluminum oxide fine particles in the coating agent thus obtained is 200 g, the content of PVA is 20 g (aluminum oxide fine particles: PVA mass ratio = 10: 1), and the solid content concentration (aluminum oxide with respect to the total mass of the coating agent). The ratio of the total content of fine particles and PVA) was 13.54% by mass (Example 7), 15.89% by mass (Examples 8 to 9), 15.33% by mass (Example 10), and 16.29% by mass. % (Example 11) or 14.90 mass% (Example 12).
The viscosities at a temperature of 20 ° C. of these coating agents were measured in the same manner as in Example 1 and were as shown in Table 6 below.
(2) Inkjet recording paper was produced in the same manner as (3) of Example 1 using each coating agent obtained in (1) above.
(3) About each ink jet recording paper obtained in the above (2), the surface strength of the ink receiving layer, the crack of the ink receiving layer, the ink absorbency of the ink receiving layer, the degree of ink bleeding of the ink receiving layer, the print quality Further, when the glossiness of the printed surface was measured or evaluated by the method described above, it was as shown in Table 6 below.

<< Comparative Examples 1-8 >>
(1) Each of “PVA-1b” to “PVA-7b” produced in Comparative Production Examples 1 to 7 is dissolved in ion-exchanged water, and an aqueous solution having a PVA concentration of 4.2 mass% (Comparative Example). 1-2) 3.2% by weight aqueous solution (Comparative Examples 3-4), 5.2% by weight aqueous solution (Comparative Examples 5-6), 5.7% by weight aqueous solution (Comparative Example 7) and 6. A 6 mass% aqueous solution (Comparative Example 8) was prepared, respectively, and 476.2 g (Comparative Examples 1 to 2), 625.0 g (Comparative Examples 3 to 4), and 384.6 g of the aqueous solution of PVA thus obtained ( Comparative Examples 5 to 6), 350.9 g (Comparative Example 7) or 303.0 g (Comparative Example 8), the same aqueous dispersion of aluminum oxide fine particles as prepared in (1) of Example 1 (aluminum oxide fine particles) Of 20% by mass), and mix and stir well. A coating agent (aqueous dispersion) for forming an ink receiving layer on a recording paper was produced.
The content of the aluminum oxide fine particles in the coating agent thus obtained is 200 g, the content of PVA is 20 g (aluminum oxide fine particles: PVA mass ratio = 10: 1), and the solid content concentration (aluminum oxide with respect to the total mass of the coating agent). The ratio of the total content of fine particles and PVA) was as shown in Table 7 below.
Further, the viscosities at a temperature of 20 ° C. of these coating agents were measured in the same manner as in Example 1. The results were as shown in Table 7 below.
(2) Inkjet recording paper was produced in the same manner as (3) of Example 1 using each coating agent obtained in (1) above.
(3) About each ink jet recording paper obtained in the above (2), the surface strength of the ink receiving layer, the crack of the ink receiving layer, the ink absorbency of the ink receiving layer, the degree of ink bleeding of the ink receiving layer, the print quality Further, when the glossiness of the printed surface was measured or evaluated by the method described above, it was as shown in Table 7 below.

<< Comparative Examples 9-16 >>
(1) Each of “PVA-9b” to “PVA-16b” produced in Comparative Production Examples 9 to 16 is dissolved in ion-exchanged water, and an aqueous solution having a PVA concentration of 6.6% by mass (Comparative Example) 9), 8.3% by mass aqueous solution (Comparative Example 10), 5.2% by mass aqueous solution (Comparative Example 11), 3.2% by mass aqueous solution (Comparative Example 12), 4.2% by mass aqueous solution ( Comparative Example 13), 1.2% by weight aqueous solution (Comparative Example 14), 10.1% by weight aqueous solution (Comparative Example 15) or 10.8% by weight aqueous solution (Comparative Example 16) were prepared, respectively. 303.0 g (Comparative Example 9), 241.0 g (Comparative Example 10), 384.6 g (Comparative Example 11), 625.0 g (Comparative Example 12), 476.2 g (Comparative Example 13) of the obtained aqueous solution of PVA ), 1666.7 g (Comparative Example 14), 198.0 g (Comparative Example 15) Alternatively, to 185.2 g (Comparative Example 16), 1000 g of the same aqueous dispersion of aluminum oxide fine particles (concentration of aluminum oxide fine particles of 20% by mass) as prepared in Example 1 (1) was added and mixed well. Thus, a coating agent (aqueous dispersion) for forming an ink receiving layer in an inkjet recording paper was produced.
The content of the aluminum oxide fine particles in the coating agent thus obtained is 200 g, the content of PVA is 20 g (aluminum oxide fine particles: PVA mass ratio = 10: 1), and the solid content concentration (aluminum oxide with respect to the total mass of the coating agent). The ratio of the total content of fine particles and PVA) was as shown in Table 8 below.
Moreover, when the viscosity at the temperature of 20 degreeC of these coating agents was measured like Example 1, it was as showing in following Table 8.
In Comparative Example 14, gelation occurred during mixing of the aqueous solution of “PVA-14b” and the aqueous dispersion of aluminum oxide fine particles, so that a coating agent could not be prepared. Therefore, inkjet recording in the following (2) Paper could not be produced.
(2) Inkjet recording paper was produced in the same manner as (3) of Example 1 using each coating agent obtained in (1) above.
(3) About each ink jet recording paper obtained in the above (2), the surface strength of the ink receiving layer, the crack of the ink receiving layer, the ink absorbency of the ink receiving layer, the degree of ink bleeding of the ink receiving layer, the print quality Further, when the glossiness of the printed surface was measured or evaluated by the method described above, it was as shown in Table 8 below.

  As seen in the results of Tables 5 to 8, the coating agents of Examples 1 to 11 satisfy the above requirements << 1 >> to << 5 >> and the content of sodium acetate is 2% by mass or less. Contains PVA. Therefore, the ink jet recording papers of Examples 1 to 11 in which the ink-receiving layer is formed by applying the coating agent on the base material have the surface strength of the ink-receiving layer, the crack of the ink-receiving layer, and the ink absorbability of the ink-receiving layer. In addition, all of the print quality is A rank, and the above-mentioned characteristics are extremely excellent. In addition, the ink receiving layer has a high ink bleed value of 1.3 or less, no ink bleed during printing, and a high glossiness of 49-58.

Moreover, although the coating agent of Example 12 satisfies the requirements << 1 >> to << 5 >> for the PVA in the coating agent, the sodium acetate content is 2.5% by mass and is somewhat high. Ink jet recording paper of Example 12 in which the ink receiving layer was formed by coating the base material on the base material had a surface strength of the ink receiving layer, cracks in the ink receiving layer, and a print quality evaluation result rank B. Although their quality is a little lower than those of Examples 1 to 11, there is no practical problem. In the ink jet recording paper of Example 12, the ink absorption evaluation of the ink receiving layer is A rank, the ink bleeding value is as small as 1.2, the glossiness is as high as 52, and the bleeding resistance and Excellent in terms of gloss.
In Example 11, the glossiness of the ink receiving layer is somewhat lower than in the other examples. This is because the degree of polymerization of PVA is close to the lower limit of the range of 4000 to 8000 defined in the present invention. It seems to do.

  On the other hand, in the coating agents of Comparative Examples 1 to 13, 15 and 16, the PVA contained in the coating agent does not satisfy one or more of the above requirements << 1 >> to << 5 >>. According to at least one of the surface strength of the ink receiving layer, the crack of the ink receiving layer, the ink absorbability of the ink receiving layer, and the print quality in the inkjet recording paper produced by applying the coating agent to the base material, The evaluation result is C rank or D rank, the ink bleed value is as high as 1.6 or more, and ink bleed easily occurs during printing, or the gloss value is as low as 47 or less, glossiness. Compared with the ink jet recording paper obtained in Examples 1 to 12, the quality is greatly inferior.

  Specifically, in the ink jet recording paper obtained in Comparative Examples 1, 3, and 5, the saponification degree of PVA contained in the coating agent used for forming the ink receiving layer is 99.40 mol% or 99.30. It is a mol% and does not satisfy the above requirement << 2 >> (the degree of saponification is smaller than the lower limit specified in the present invention), and the PVA aqueous solution having a viscosity of 10,000 mPa · s is 10 ° C. Since the time until the viscosity is increased to 20000 mPa · s is 300 minutes or 280 minutes and the above requirement << 4 >> is not satisfied (the thickening time exceeds the upper limit in the present invention), the ink The numerical value of the degree of blur is as large as 1.6 or more, and all the other physical properties are rank B and there is no rank A.

  Further, in the inkjet recording paper obtained in Comparative Examples 2, 4, 6 and 7, the saponification degree of PVA contained in the coating agent used for forming the ink receiving layer was 99.99 mol%. The above requirement << 2 >> is not satisfied (the degree of saponification exceeds the upper limit defined in the present invention), and the PVA solution is a PVA aqueous solution having a viscosity of 10,000 mPa · s at 10 ° C. and a viscosity of 20000 mPa The time until it increases to s is 5 minutes, 30 minutes, 20 minutes, or 15 minutes and does not satisfy the above requirement << 4 >> (thickening time is lower than the lower limit specified in the present invention) In other words, the crack of the ink receiving layer and the rank of the print quality are both inferior in C, and in Comparative Example 7, the surface strength and the turbidity of the ink receiving layer are greatly inferior.

In the ink jet recording paper obtained in Comparative Examples 8 to 10, the content of 1,2-glycol bond unit of PVA contained in the coating agent used for forming the ink receiving layer is 1.6 mol% or 1.7. And the above requirement << 3 >> is not satisfied (the 1,2-glycol bond unit exceeds the upper limit defined in the present invention), and the polymerization degree of PVA is 3500 or 2400 and does not satisfy the requirement << 1 >> (the degree of polymerization is smaller than the lower limit specified in the present invention), the surface strength of the ink receiving layer, the crack of the ink receiving layer, the ink absorption All of the evaluation results of the printability and the print quality are inferior to rank C or D, and the ink has a high degree of bleeding (particularly Comparative Examples 9 to 11), and further has a low glossiness of 32 to 42, and the quality is greatly inferior. Have .
Further, in the ink jet recording paper obtained in Comparative Example 11, the content of 1,2-glycol bond unit of PVA contained in the coating agent used for forming the ink receiving layer is 1.6 mol% or 1.7. Since it is mol% and does not satisfy the requirement << 3 >> (the 1,2-glycol bond unit exceeds the upper limit defined in the present invention), the ink bleed degree is 1. The quality is inferior because it is as high as 6 and the glossiness is as low as 42.

In the ink jet recording paper obtained in Comparative Examples 12 and 13, the PVA in the coating agent used for forming the ink receiving layer was measured for the concentration-corrected absorbance at the wavelengths of 280 nm and 320 nm of the aqueous solution (cell optical path length 30 mm) (measurement). (Temperature of 20 ° C.) exceeded 0.02 L / g and did not satisfy the above requirement << 5 >>. Therefore, the glossiness was as low as 41 or 40 and the glossiness was poor.
In Comparative Example 14, the degree of polymerization was too high as 19800 and did not satisfy the requirement << 1 >>. The content of 1,2-glycol bond units was 0.5 mol% and the requirement << 3 >> and PVA having an absorbance after adjustment of the concentration at a wavelength of 280 nm and 320 nm (cell optical path length 30 mm) (measurement temperature 20 ° C.) of the PVA aqueous solution exceeds 0.02 L / g. Since the coating agent was used to prepare the coating agent, as described above, gelation occurs during the preparation of the coating agent and the coating agent cannot be obtained.
Furthermore, in the ink jet recording paper obtained in Comparative Examples 15 and 16, the polymerization degree of PVA having a structural unit derived from vinyl methoxysilane in the coating agent used for forming the ink receiving layer was 1700. The above requirement << 1 >> is not satisfied, the saponification degree is 98.50 mol% or 88.11 mol%, the above condition << 2 >> is not satisfied, and the viscosity is 10000 mPa · s. The time required for the PVA aqueous solution to increase to a viscosity of 20000 mPa · s at 10 ° C. is 360 minutes or more and does not satisfy the above requirement << 4 >>, so that the ink bleed degree is large and the ink bleeds. It is easy, and the numerical value of glossiness is small and the glossiness is inferior.

  The coating agent of the present invention is easy to prepare, has little change in viscosity over time, has excellent storage stability, and has high surface strength, durability, water resistance, weather resistance, gloss, ink absorbability, and printability. Forms a high-quality printing surface (coating layer) with excellent properties such as anti-bleeding properties and no cracks. Therefore, the coating agent of the present invention can be effectively used for various applications, and is particularly useful as a coating agent for forming an ink receiving layer in an inkjet recording material. The ink jet recording material formed using the coating agent of the present invention is excellent in durability, water resistance, weather resistance, gloss, ink absorbability and printability of the ink receiving layer, and has no cracks. By using the ink jet printing method, it is possible to smoothly obtain a high-quality printed matter that is excellent in durability, water resistance, weather resistance, and gloss, is clear and has a good color tone.

Claims (5)

Vinyl alcohol homopolymer 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 >> The vinyl alcohol homopolymer is dissolved in water to prepare a vinyl alcohol homopolymer 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 viscosity is 20000 mPa · s. the time required to increase to s is 50-250 minutes; and
"5" [When a viscosity average polymerization degree (P) is less than 6000 vinyl alcohol homopolymers] The vinyl alcohol homopolymer of a vinyl alcohol homopolymer aqueous solution having a concentration 30 g / L, prepared by dissolving in water or the concentration 10 g / L vinyl alcohol homopolymers solution [viscosity average polymerization degree (P) is the case of 6000 or more vinyl alcohol homopolymers], and becomes measured using a cell having a light path length of 30 mm, the absorbance after the density correction at wavelengths 280nm and 320nm (Measuring temperature 20 ° C.) are both 0.02 L / g or less;
A coating agent comprising: A vinyl alcohol homopolymer satisfying the above-mentioned requirements << 1 >> to << 5 >>
<< 6 >> The content of sodium acetate is 2% by mass or less;
The coating agent according to claim 1, further satisfying the requirement <6>.   The coating agent according to claim 1 or 2, which is a coating agent for forming an ink receiving layer in an inkjet recording material.   The coated material formed by apply | coating the coating agent of any one of Claims 1-3 to a base material.   The inkjet recording material formed by apply | coating the coating agent of any one of Claims 1-3 to a base material.