JP5791415B2 - Process for producing discoloration-resistant polyvinyl alcohol resin cross-linked product - Google Patents

Description

  The present invention relates to a method for producing a crosslinked polyvinyl alcohol-based resin, and more particularly to a method for producing a crosslinked polyvinyl alcohol-based resin with little color change due to ultraviolet rays.

Conventionally, it is known that formation of a crosslinked structure is effective as a method for imparting water resistance to a polyvinyl alcohol resin which is a water-soluble resin.
As a cross-linked product of a polyvinyl alcohol resin, a combination of a polyvinyl alcohol resin containing an acetoacetate group having excellent reactivity and various cross-linking agents is widely used.

  Among them, glyoxylate has been proposed as a cross-linking agent that is capable of obtaining a cross-linked product having excellent viscosity stability of an aqueous solution mixed with acetoacetate group-containing polyvinyl alcohol, excellent water resistance, and small discoloration over time (for example, patents). Reference 1).

JP 2010-77385 A

  However, acetoacetate group-containing polyvinyl alcohol resins (hereinafter abbreviated as AA-PVA resins) and glyoxylate cross-linked products are excellent in water resistance and discoloration resistance. When used, depending on the conditions, it may be gradually discolored by ultraviolet rays.

  An object of the present invention is to provide a cross-linked product composed of an AA-PVA-based resin and a glyoxylate that has little weather discoloration due to ultraviolet rays and excellent weather resistance.

As a result of intensive studies in view of the above circumstances, the present inventors irradiate a cross-linked product of a AA-PVA-based resin with glyoxylate with ultraviolet rays having a wavelength of 300 to 400 nm and an intensity of 50 mW / cm ² or more for 1 hour or more. The inventors have found that the object of the present invention can be achieved, and have completed the present invention. The cross-linked product of the AA-PVA-based resin with glyoxylate is temporarily discolored by the irradiation of the ultraviolet rays, but is discolored by continuing the irradiation, and then is not discolored. This is a phenomenon.

  Since the discoloration-resistant polyvinyl alcohol resin cross-linked product of the present invention has little discoloration over time even in an environment where it receives ultraviolet rays, it is used in applications where it is exposed to sunlight for a long period of time, such as a coating liquid for paper, a floor It is suitable for coating of coating agents, gas barrier coating agents, agricultural sheets, outdoor display films and outdoor equipment.

The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these contents.
Hereinafter, the present invention will be described in detail.

[AA-modified PVA resin]
The AA-PVA resin used in the present invention is a PVA-based resin having an acetoacetate group in the side chain, and the other parts are mainly composed of vinyl alcohol structural units as in general PVA-based resins. It has vinyl acetate structural units according to the degree.
The method for producing the AA-PVA-based resin is not particularly limited. For example, a method of reacting a PVA-based resin with diketene, a method of reacting a PVA-based resin with acetoacetate, and transesterification, acetic acid A method of saponifying a copolymer of vinyl and vinyl acetoacetate can be mentioned, but since the production process is simple and a high-quality AA-PVA-based resin is obtained, the PVA-based resin and diketene are reacted. It is preferable to manufacture by a method.
Hereinafter, this method will be described.

  As the PVA resin used as a raw material, a saponified product of a vinyl ester monomer polymer or a derivative thereof is generally used. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, and valeric acid. Examples include vinyl, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, and vinyl acetate is preferably used from the viewpoint of economy.

Further, a saponified product of a copolymer of a vinyl ester monomer and a monomer copolymerizable with the vinyl ester monomer can be used. Examples of the copolymer monomer include ethylene, propylene, isobutylene, α- Olefins such as octene, α-dodecene, α-octadecene; hydroxy such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 3,4-dihydroxy-1-butene Derivatives such as group-containing α-olefins and acylated products thereof; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, undecylenic acid, salts, monoesters, or dialkyl esters thereof Nitriles such as acrylonitrile and methacrylonitrile; diacetone acrylate Amides such as amide, acrylamide and methacrylamide; Olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid or salts thereof; alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl Vinyl compounds such as ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerol monoallyl ether; substituted vinyl acetates such as isopropenyl acetate and 1-methoxyvinyl acetate; vinylidene chloride, 1, 4-diacetoxy-2-butene, 1,4-dihydroxy-2-butene, vinylene carbonate and the like can be mentioned.
The introduction amount of the copolymerization monomer varies depending on the type of the monomer, and cannot be generally specified. However, it is usually 10 mol% or less, particularly 5 mol% or less of the total structural unit, and if it is too much, the water solubility is impaired. Or compatibility with the cross-linking agent may be reduced.

  In addition, by increasing the polymerization temperature when polymerizing and copolymerizing vinyl ester monomers and other monomers, the amount of heterogeneous bonds produced mainly with respect to 1,3-bonds produced is increased, and 1 in the PVA main chain is increased. , 2-diol bond having a content of about 1.6 to 3.5 mol% can be used.

  The introduction of acetoacetyl groups by the reaction of PVA resin obtained by saponifying the polymer and copolymer of the above vinyl ester monomer and diketene involves direct reaction of PVA resin with gaseous or liquid diketene. Alternatively, after adsorbing and occluding an organic acid in a PVA resin in advance, a gaseous or liquid diketene is sprayed and reacted in an inert gas atmosphere, or a mixture of an organic acid and a liquid diketene is applied to the PVA resin. Methods such as spraying and reacting are used.

  As a reaction apparatus for carrying out the above reaction, an apparatus that can be heated and has a stirrer is sufficient. For example, a kneader, a Henschel mixer, a ribbon blender, other various blenders, and a stirring and drying apparatus can be used.

  The average polymerization degree of the AA-PVA-based resin thus obtained may be appropriately selected depending on the use, but is usually 300 to 4000, and particularly 400 to 3500, and more preferably 500 to 3000 are preferably used. If the average degree of polymerization is too small, sufficient water resistance may not be obtained or a sufficient crosslinking rate may not be obtained. On the other hand, if it is too large, the viscosity becomes too high when used as an aqueous solution. Application to various processes tends to be difficult, for example, coating on a substrate becomes difficult.

  The saponification degree of the AA-PVA-based resin used in the present invention is usually 80 mol% or more, more preferably 85 mol% or more, and particularly preferably 90 mol% or more. When the degree of saponification is low, it tends to be difficult to obtain an aqueous solution, the stability of the aqueous solution is lowered, or the water resistance of the resulting crosslinked polymer tends to be insufficient. The average degree of polymerization and the degree of saponification are measured according to JIS K6726.

  Further, the content of acetoacetyl groups in the AA-PVA-based resin (hereinafter abbreviated as AA degree) is usually 0.1 to 20 mol%, further 0.2 to 15 mol%, especially What is 0.3-10 mol% is generally used widely. If the content is too small, the water resistance tends to be insufficient or a sufficient crosslinking rate may not be obtained. Conversely, if the content is too large, the water solubility tends to decrease or the stability of the aqueous solution tends to decrease. There is.

[Glyoxylate]
Next, the glyoxylate of the present invention will be described.
Examples of the glyoxylate include metal salts and amine salts of glyoxylic acid. Examples of the metal salt include alkali metals such as lithium, sodium and potassium, alkaline earth metals such as magnesium and calcium, titanium, zirconium, Transition metals such as chromium, manganese, iron, cobalt, nickel, copper, other metals such as zinc and aluminum and metal salts of glyoxylic acid, and amine salts include amines such as ammonia, monomethylamine, dimethylamine, and trimethylamine And salts of glyoxylic acid.
In particular, metal salts, particularly alkali metal and alkaline earth metal salts, are preferably used from the viewpoint of obtaining a crosslinked polymer having excellent water resistance.

  In addition, it is considered that the hydrophilicity of the carboxylate group introduced into the crosslinked structure is small compared to the carboxylic acid group, which contributes to the improvement of the water resistance of the crosslinked polymer. Glyoxylate having a lower solubility in water is preferable. Specifically, the solubility in water at 23 ° C. is 0.01 to 100%, particularly 0.1 to 50%, and further 0.5 to 20%. Is preferably used. For example, the solubility of sodium glyoxylate is about 17% and the solubility of calcium glyoxylate is about 0.7%.

  As a method for producing glyoxylate, a known method can be used. For example, (1) a method based on a neutralization reaction of glyoxylic acid, (2) a salt of glyoxylic acid with an acid dissociation constant larger than glyoxylic acid, And (3) a method by alkaline hydrolysis of glyoxylic acid ester (see, for example, JP-A-2003-300996). In particular, when the alkaline compound used for the neutralization reaction with glyoxylic acid is highly water-soluble, the method of (1) is a salt of an acid whose glyoxylate salt is low in water solubility and has an acid dissociation constant greater than glyoxylic acid. When the water solubility of is high, the method (2) is preferably used.

The method (1) is usually carried out using water as a medium, glyoxylic acid and an alkaline compound, for example, various metal hydroxides or amine compounds are reacted in water, and the precipitated glyoxylate is filtered off. It can be produced by drying.
The method (2) is also generally carried out in water, and glyoxylate can be obtained in the same manner as the method (1). Examples of the acid salt having a larger dissociation constant than glyoxylic acid used in the method (2) include, for example, alkali metal or alkaline earth metal salts of aliphatic carboxylic acids such as sodium acetate, calcium acetate, and calcium propionate. Can be mentioned.

  In addition, after synthesizing glyoxylate, it is possible to carry out the above reaction (1) or (2) in the system without isolating the glyoxylate and use the produced glyoxylate as it is.

  The glyoxylate of the present invention may contain raw materials used in the production of glyoxylate, impurities contained in the raw material, by-products during production, etc., for example, glyoxylic acid, metal hydroxide Products, amine compounds, aliphatic carboxylates, glyoxal, oxalic acid, oxalate, glycolic acid or glycolate may be contained.

  In particular, when glyoxylic acid is used as a raw material, glyoxal, which is a by-product at the time of production thereof, may be contained in the crosslinking agent, and the content of such glyoxal is most desirably 0% by weight. Is preferably 5% by weight or less, particularly 2% by weight or less, and more preferably 1% by weight or less. When the content of glyoxal is large, the stability of the aqueous solution mixed with the AA-PVA resin decreases, the pot life is shortened, and the resulting cross-linked product of the AA-PVA resin discolors over time depending on the storage conditions. There is a case.

  In addition, the glyoxylate in the present invention is acetalized with an alcohol having 3 or less carbon atoms such as methanol and ethanol, a diol having 3 or less carbon atoms such as ethylene glycol and propylene glycol, and hemiacetal. Including the compound. Such an acetal group and a hemiacetal group easily desorb alcohol in water or at a high temperature and take an equilibrium state with the aldehyde group. It functions as.

[Crosslinked product]
The color-change-resistant PVA resin cross-linked product of the present invention is obtained by irradiating a cross-linked product obtained by cross-linking the above-mentioned AA-PVA resin with glyoxylate with ultraviolet rays.
Hereinafter, the cross-linked product of the AA-PVA-based resin with glyoxylate will be described.
In such a cross-linked product, the blending ratio of the AA-PVA resin and the glyoxylate is not particularly limited, but usually 0.1 to 30 weights of glyoxylate per 100 parts by weight of the AA-PVA resin. Parts, more preferably 1 to 20 parts by weight, particularly 2 to 15 parts by weight. If the blending ratio of the AA-PVA-based resin is too large, crosslinking between the polymers is not sufficiently performed, and there is a tendency that a crosslinking effect cannot be obtained. If too small, the crosslinking density of the crosslinked product is lowered and sufficient crosslinking is performed. There is a tendency not to be effective.

The reaction between the acetoacetyl group and the glyoxylate in AA-modified PVA occurs when an active methylene sandwiched between two carbonyl groups of the acetoacetyl group attacks the aldehyde carbon in the glyoxylate by nucleophilic attack. The cross-linked structure portion is assumed to be shown in the following structural formula.
In addition, X in the formula represents a metal element, and the case where the glyoxylate is a salt of a monovalent metal such as an alkali metal is typically exemplified, but a polyvalent metal such as an alkaline earth metal is exemplified. In some cases, the metal may be shared with other cross-linked structures or free glyoxylic acid.

Such a cross-linked product is usually obtained by forming a resin composition aqueous solution containing an AA-PVA-based resin and glyoxylate, and then forming a film or sheet, or coating on a substrate, etc., and cross-linking by drying and heat treatment. It is done.
Such an aqueous resin composition is (i) a method in which a mixture of AA-PVA resin and glyoxylate is added to water and dissolved, (ii) AA-PVA resin and glyoxylate previously dissolved separately (Iii) A method in which glyoxylate is added to an aqueous solution of an AA-PVA-based resin and mixed, and the like. In addition, when glyoxylate is produced in the system as described above and used without isolation, it is possible to perform such a reaction in the presence of an AA-PVA-based resin. For example, glyoxylic acid is alkaline. When neutralizing with a compound to obtain a glyoxylate, a method of adding an alkaline compound to a mixed aqueous solution of an AA-PVA-based resin and glyoxylic acid can also be used.

  In the above aqueous solution, additives such as antifoaming agents, antifungal agents, preservatives, leveling agents, various emulsions, polyester ionomer-type urethane resins (for example, Dainippon) are used within the range not impairing the characteristics of the present invention. "Hydran AP-20" and "Hydran APX-101H" "manufactured by Ink Chemical Industry Co., Ltd.), various polymer dispersions typified by polyurethane dispersion and polyester dispersion, polyhydroxyethyl methacrylate, polyhydroxyethyl acrylate Further, a water-soluble resin such as polyacrylic acid, a compound having a glycidyloxy group, a metal colloid such as aluminum (for example, “Alumina sol-10A” manufactured by Kawaken Fine Chemical Co., Ltd.), and the like may be blended.

  The concentration of the aqueous solution in the method for preparing the aqueous resin composition solution is preferably 1 to 30% by weight, more preferably 2 to 20% by weight, and particularly preferably 3 to 15% by weight. If the concentration of the aqueous resin composition solution is too large, the viscosity of the aqueous solution is increased, and various workability may be lowered, or a uniform film thickness may be difficult to obtain at the time of coating or the like. In addition, when the concentration is too small, when applying an aqueous solution, the film thickness obtained by a single application becomes small, and it may be necessary to apply a plurality of times in order to obtain a desired film pressure. Absent.

  The aqueous solution of the resin composition thus prepared is applied to various uses by a known method such as coating, casting, and dipping, and then a crosslinking reaction is performed by drying and heat treatment.

The temperature of the crosslinking reaction is usually 10 to 180 ° C, more preferably 15 to 150 ° C, and particularly preferably 20 to 120 ° C. If the temperature is too high, the polyvinyl alcohol resin is decomposed and coloring may occur, which is not preferable. On the other hand, if the temperature is too low, the crosslinking reaction takes time and the productivity is not good, which is not preferable.
The crosslinking reaction time is usually 1 to 1000 minutes, more preferably 2 to 100 minutes, and particularly preferably 3 to 10 minutes. If the time is too long, the productivity is not good, and if it is too short, a sufficiently cross-linked reaction product cannot be obtained, and the cross-linking becomes insufficient.

  Although the color-change-resistant PVA resin cross-linked product of the present invention can be applied to various uses of a coating agent, a film, a sheet, an adhesive layer, and a binder, the thickness when used as a film is usually 1-1000 μm, and further 5 It is preferable that it is -500 micrometers, especially 10-200 micrometers. If the thickness is too large, the film is not preferred because a difference in dimensional change in the thickness direction due to moisture absorption or the like may occur and warp may occur. Moreover, when too small, the film strength of the discoloration-resistant PVA resin cross-linked product is lowered and the cross-linked film is easily broken, which is not preferable.

[Discoloration-resistant PVA resin cross-linked product]
The cross-linked product of the AA-PVA-based resin thus obtained with glyoxylate is then irradiated with ultraviolet rays to obtain the discoloration-resistant PVA-based resin cross-linked product of the present invention.
As the ultraviolet irradiation method, irradiation may be performed using a xenon lamp, an excimer lamp, a metal halide lamp, a hydrogen discharge tube, a rare gas discharge tube, or the like that emits light in a wavelength range of 300 to 400 nm. The intensity of the ultraviolet rays to be irradiated needs to be 50 mW / cm ² or more as an integrated value of a wavelength of 300 to 400 nm, more preferably 100 to 500 mW / cm ² , particularly preferably 150 to 300 mW / cm ^2. . If the intensity of the ultraviolet ray is too strong, the crosslinked product may be decomposed, and if it is too weak, the effect of ultraviolet irradiation may not be sufficiently obtained.

  Further, the irradiation distance in the case of irradiation with ultraviolet rays is usually 1 to 3000 mm, more preferably 10 to 1000 mm, and particularly preferably 100 to 500 mm. If the irradiation distance is too long, the effect of ultraviolet irradiation may not be sufficiently obtained, and if it is too close, ultraviolet irradiation may be difficult when the film has irregularities, which is not preferable. Furthermore, the time for irradiating such ultraviolet rays needs to be 1 hour or longer, and is usually 4 to 100 hours, more preferably 6 to 50 hours, and particularly preferably 9 to 30 hours. If the irradiation time is too long, the crosslinked product may be decomposed, which is not preferable. Moreover, when too short, the effect of ultraviolet irradiation may not be obtained sufficiently, which is not preferable.

  The temperature of the atmosphere for ultraviolet irradiation is usually 0 to 120 ° C., more preferably 10 to 100 ° C., and particularly preferably 20 to 80 ° C., and the humidity is usually 80% RH or less, more preferably 70% RH or less, particularly Is preferably 60% RH or less. If the temperature is too high, discoloration of the cross-linked product may be promoted, and if it is too low, the effect of ultraviolet irradiation may not be sufficiently obtained. Moreover, since it may be easy to color a crosslinked material when this humidity is too high, it is unpreferable.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the description of the examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Example 1
<Manufacture of AA-PVA-based resin>
In a ribbon blender with temperature control, 3600 parts of unmodified PVA resin (average polymerization degree 1200, saponification degree 99.2 mol%) was added, and 1000 parts of acetic acid was added thereto to swell, while stirring at a rotation speed of 20 rpm, After raising the temperature to 60 ° C., 550 parts of diketene was added dropwise over 3 hours, and the reaction was further continued for 1 hour. After completion of the reaction, it was washed with methanol and then dried at 70 ° C. for 6 hours to obtain AA-modified PVA.
The obtained AA-modified PVA had an AA degree of 5.3 mol%, a saponification degree of 98.9 mol%, and an average degree of polymerization of 1200.

<Manufacture of glyoxylate>
To 456 g (3.10 mol) of 50% aqueous glyoxylic acid solution in a 2 L two-necked reaction vessel, 645 g (3.22 mol) of 20% aqueous sodium hydroxide solution was added, and the resulting white crystals were washed with filtered water, and then cooled to 50 ° C. And dried for 1 hour to obtain 210 g (1.84 mol, yield 59.5%) of sodium glyoxylate.

<Production of cross-linked product>
To 100 parts by weight of the obtained 10% aqueous solution of AA-PVA, 1 part by weight of the obtained sodium glyoxylate (10% by weight with respect to AA-PVA) is added and mixed by stirring. The film was allowed to stand for 72 hours under conditions of 23 ° C. and 50% RH to obtain a film having a thickness of 100 μm.
The YI value (color difference meter, “SZ-Σ90” manufactured by Nippon Denshoku Industries Co., Ltd., transmission method) of the obtained film was 0.7.

<Production of discoloration-resistant crosslinked product>
The obtained film was irradiated with ultraviolet rays under the following conditions.
Apparatus: “SUV-W23” manufactured by Iwasaki Electric Co., Ltd.
Lamp: Metal halide lamp ("M08-PL21 / SUB" manufactured by Iwasaki Electric Co., Ltd.)
Intensity (300 to 400 nm): 160 mW / cm ²
Irradiation distance: 240mm
Atmosphere: 63 ° C, 50% RH
Irradiation time: 15 hours

<Evaluation of UV discoloration resistance>
The treated film was irradiated with ultraviolet rays under the following conditions, and the YI values at the initial stage and after 3 hours were measured. The results are shown in Table 1.
Equipment: “SZ-Σ90” manufactured by Nippon Denshoku Industries Co., Ltd.
Atmosphere: 23 ° C, 50% RH

Example 2
In Example 1, a film was produced in the same manner as in Example 1 except that the amount of sodium glyoxylate used was 0.5 parts by weight (5% by weight based on AA-PVA), and ultraviolet irradiation was performed for 6 hours. The same evaluation was performed.

Example 3
In Example 1, a film was produced in the same manner as in Example 1 except that calcium glyoxylate was used in place of sodium glyoxylate, and ultraviolet irradiation was performed for 6 hours.

Comparative Example 1
In Example 1, the same evaluation was performed for those not subjected to the ultraviolet irradiation treatment.

※対ＡＡ化ＰＶＡ

* PVA against AA

  As is clear from these results, the cross-linked product containing AA-PVA and glyoxylate is irradiated with ultraviolet rays under specific conditions, and there is less discoloration over time than when no ultraviolet irradiation treatment was performed. Thus, a cross-linked product excellent in discoloration resistance was obtained.

The resin cross-linked product of the present invention is excellent in water resistance and further has no characteristic of discoloration over time, and is a paper coating solution, floor coating agent, gas barrier coating agent, agricultural sheet, outdoor It is useful when used in a place exposed to ultraviolet rays for a long period of time, such as a film for display and a coating for outdoor use equipment.

Claims (4)

Discoloration-resistant polyvinyl alcohol resin that irradiates ultraviolet rays having a wavelength of 300 to 400 nm with an intensity of 50 mW / cm ² or more for 1 hour or more to a crosslinked product obtained by crosslinking an acetoacetate group-containing polyvinyl alcohol resin with glyoxylate. A method for producing a crosslinked product. The method for producing a cross-linked color-change resistant polyvinyl alcohol resin according to claim 1, wherein the acetoacetate group content in the acetoacetate group-containing polyvinyl alcohol resin is 0.1 to 20 mol%. The method for producing a discoloration-resistant polyvinyl alcohol resin frame according to claim 1 or 2, wherein the glyoxylate is at least one glyoxylate selected from alkali metal salts and alkaline earth metal salts of glyoxylic acid. The method for producing a cross-linked color-change resistant polyvinyl alcohol resin according to any one of claims 1 to 3, wherein the content ratio of the acetoacetate group-containing polyvinyl alcohol resin and glyoxylate is 100 / 0.1 to 100/30.