JPH091048A - Coating material - Google Patents

Abstract

PURPOSE: To obtain a good membrane having excellent shelf stability of a coating material by specifying the contents of alkali metal acetate and acetic acid and the weight ratio between them respectively in a coating material made from a polyvinyl alcohol resin including acetoacetic ester group containing alkali metal acetate and acetic acid. CONSTITUTION: This coating material contains 2wt.% or less of alkali metal acetate, 5wt.% or less of acetic acid, and a polyvinyl alcohol resin (AA- converted PVA) containing an acetoacetic ester with the weight ratio of alkali metal acetate to acetic acid of 0.01-100. The coating material is served practically as an aqueous solution, an emulsion, an aqueous dispersion liquid, etc., with the use of AA-converted PVA but is used conveniently in general in the form of the aqueous solution. Since the AA-converted PVA is crosslinked spontaneously, it can form a good membrane by itself; however, it is mixed advantageously with a crosslinking agent for the purposes of improving the waterproof and mechanical strength of the membrane, the extension of the durable period of membrane formation, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a polyvinyl alcohol resin containing an acetoacetic acid ester group (hereinafter referred to as AA-PVA).
For more details, it is possible to obtain a good film with excellent storage stability, and the degree to which some water is present in the operating environment even when used for provisional film applications. Then, it relates to a water-resistant coating agent capable of sufficiently ensuring the function as a film.

[0002]

2. Description of the Related Art Conventionally, a coating agent using a polyvinyl alcohol resin (hereinafter abbreviated as PVA) has various properties such as antistatic property, antifogging property and water solubility.
Coating films for plastic materials for construction materials and agricultural films, cosmetic packs, and coatings such as temporary coatings for protection of metal surfaces and plastic surfaces for the purpose of antifouling and rustproofing (coating) Widely used for forming applications. From the required performance such as water resistance of the formed film, AA
A film in which various cross-linking agents are used in combination with the modified PVA is also used, and it can also be used as a temporary film by controlling the AA degree of AA-modified PVA (content of acetoacetic ester group) and the cross-linking agent. Has been done.

[0003]

However, a coating agent comprising a conventional PVA aqueous liquid (aqueous solution, emulsion, aqueous dispersion, etc.) using AA-PVA has a stability in leaving the aqueous liquid, for example, long-term stability as an aqueous solution. The stability when stored for a long period of time and the stability when the AA-PVA powder is stored in an aqueous solution after being stored for a long period of time are not yet satisfactory, and there is still room for improvement in the formed film. When used as a temporary coating, it is also observed that the coating partially dissolves due to water such as dew condensation water, which causes problems such as antifouling and rust prevention effects. It also had the drawback that it could not be secured.

[0004]

The inventors of the present invention have made diligent studies to solve the above problems, and as a result, surprisingly, the content of alkali metal acetates of 2% by weight or less and acetic acid of 5% by weight or less was found. In addition, a coating agent using AA-PVA having an alkali metal acetate / acetic acid weight ratio of 0.01 to 100 has excellent leaving stability, and a good coating can be obtained. It has been found that a film capable of sustaining water resistance to the extent that its function is not impaired even when contacted with some amount of moisture even when used for applications is obtained, and the present invention has been completed. Hereinafter, the present invention will be described in detail.

The method for producing the AA-PVA in the present invention is not particularly limited and may be produced by any method, but it is preferably obtained by reacting PVA with diketene. For example, PVA is dispersed in an acetic acid solvent and diketene is added thereto, and PVA is dissolved in a solvent such as dimethylformamide or dioxane in advance and diketene is added thereto. Also,
A method of directly contacting diketene gas or liquid diketene with PVA having absorbed acetic acid or the like to obtain AA-PVA can also be adopted. The PVA used in obtaining the AA-PVA is not particularly limited, but the residual acetic acid group is 0.1 to 20 mol%, the average degree of polymerization is 50 to 6000 (more preferably 300 to 300).
0) and an average saponification degree of 85 to 99.9 mol% are preferable.

[0006] The degree of AA conversion of AA-modified PVA is 0.1.
20 mol%, more preferably 0.5 to 15 mol%. AA-PVA having a degree of AA of less than 0.1 mol% has poor crosslinkability and film-forming property, and conversely has a degree of AA of 20 mol%.
If the PVA exceeds AA, the viscosity of the aqueous liquid (aqueous solution, emulsion, aqueous dispersion, etc.) becomes unstable, which is not preferable. In the present invention, 2% by weight or less (preferably 0.5% by weight or less) of acetic acid salts of alkali metals (sodium, potassium, etc.) and 5% by weight or less (preferably 2% by weight) of acetic acid are added to the conventional AA-PVA. (% By weight or less), and the weight ratio of the alkali metal acetate and acetic acid (alkali metal acetate / acetic acid) is 0.01 to 100 (preferably 0.0).
The greatest feature is the use of AA-PVA controlled in the range of 1 to 10). When the alkali metal acetate exceeds 2% by weight, an aqueous liquid (aqueous solution, emulsion, aqueous dispersion, etc.) is obtained. Viscosity becomes unstable and acetic acid becomes 5
If it exceeds 5% by weight, the crosslinking property and the film-forming property are poor and the performance as a coating agent is not sufficiently exhibited.

When the weight ratio of the alkali metal acetate / acetic acid is less than 0.01, the rate of crosslinking (film formation) is slow. On the contrary, when the weight ratio exceeds 100, an aqueous liquid (aqueous solution, emulsion) is obtained. However, the viscosity of the aqueous dispersion) becomes unstable, which is not preferable. The amount of the alkali metal acetate is quantified by an atomic absorption method for a solution obtained by ashing the AA-PVA and then dissolving the ash in a hydrochloric acid aqueous solution under heating. As a method for quantifying acetic acid, a sample is used as an aqueous solution and determined by gas chromatography / mass spectrometry (GC / MS method).

In the present invention, the amounts of the alkali metal acetate and acetic acid contained in the AA-PVA used may be controlled as described above, and the controlling method is arbitrary. For example, the amount of alkali catalyst at the time of saponification at the time of producing bulk PVA is adjusted,
It is optional to add or remove the alkali metal acetate after the production. Regarding the amount of acetic acid, acetic acid may be added after PVA production, or PVA containing a large amount of acetic acid may be washed and dried. In addition to bulk powder treatment, AA-ized P
Control may be carried out by adding or removing an alkali metal acetate or removing or adding acetic acid during or after the production of VA. Industrially, it is practical to remove the alkali metal acetate and acetic acid after the production of AA-PVA, and to remove the alkali metal acetate,
Specifically, alcohol cleaning is adopted, and examples of the alcohol include methanol, ethanol, n-propanol, isopropanol and the like, but methanol is preferably used. This alcohol cleaning is usually performed using 1 to 15 times the weight of PVA as alcohol, and cleaning is performed 1 to 3 times under the conditions of 5 to 60 ° C. and 0.5 to 2 hours.

Further, in order to remove acetic acid, it is possible to remove it by a method such as distillation under reduced pressure, washing with methanol, drying treatment, filtration and centrifugation.
Examples thereof include a method of treating A-PVA, and these treatments may be performed simultaneously or separately, but a drying treatment is preferably adopted. The conditions of the drying treatment differ depending on the device and cannot be generally stated, but it may be carried out at 30 to 80 ° C. for about 10 hours, preferably at 40 to 70 ° C. for about 6 hours. In the present invention, by adjusting the pH of such a 4% by weight aqueous solution of AA-PVA to 3 to 6.5, preferably 4 to 5, the stability of the aqueous liquid is further improved and a good film is obtained. It becomes possible.

The method for adjusting the pH is not particularly limited, and for example, the amount of the alkali catalyst at the time of saponification at the time of producing the bulk powder PVA is adjusted, or acetic acid is added after the production of PVA, Any of them may be removed. If necessary, mineral acids such as hydrochloric acid, sulfuric acid and phosphoric acid, organic acids such as propionic acid and maleic acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, primary amines, secondary amines and tertiary amines. The pH may be adjusted by adding a quaternary ammonium salt or the like. In addition to the raw powder treatment, the above-mentioned pH adjustment may be performed during or after the production of AA-modified PVA. Industrially, the method of removing acetic acid after the production of AA-modified PVA is practical. Is. Next, the coating agent using the obtained AA-PVA will be described.

The coating material of the present invention is put to practical use as an aqueous solution such as an aqueous solution, emulsion, or aqueous dispersion using the AA-PVA, but generally, an aqueous solution is simple and mainly used. Will be explained in detail. The aqueous solution is AA-PVA
1 to 50% by weight, preferably 2 to 30% by weight (the same applies to emulsions, aqueous dispersions, etc.). Further, in the coating agent of the present invention, alcohols such as methanol, ethanol, isopropyl alcohol and n-propyl alcohol, dioxane and DM can be used as a solvent in addition to water.
F, DMSO and the like may be contained in an amount of 0.1 to 99% by weight, and as other additives, plasticizers (polyhydric alcohols such as ethylene glycol, glycerin and propylene glycol and their higher fatty acid esters) You may contain about 1-80 weight%.

Since the AA-PVA has a self-crosslinking property,
It is possible to form a good film with only the AA-PVA without using any other cross-linking agent. However, the water resistance and mechanical strength of the film are further improved, and the film formation duration is newly extended. It is also useful to blend a crosslinking agent for the purpose of
Examples of the cross-linking agent include dialdehyde compounds such as glyoxal and glutanaldehyde, amine compounds such as melamine, acetoguanamine, benzoguanamine and urea, phenolic resin initial condensates, polyepoxy compounds and isocyanate compounds. Although the compounding amount of the agent varies somewhat depending on the purpose and type, it is usually AA P
The amount is 0.5 to 50 parts by weight, preferably 1 to 25 parts by weight, and particularly preferably 2 to 15 parts by weight, based on 100 parts by weight of VA. Further, as a method for imparting mechanical strength, durability and the like to the film, crosslinking by irradiation with radiation can be mentioned, and as the radiation, electron beam, ultraviolet ray, X-ray, γ-ray or the like can be used.

The aqueous solution has been mainly described as the form of the coating material of the present invention.
A known PVA AA known method (method of emulsion polymerization of vinyl monomers using the AA PVA as an emulsifier or protective colloid, a method of post-emulsifying a solution or melt of a synthetic resin in the presence of the AA PVA, It is of course possible to use the synthetic resin emulsion obtained by any method as an emulsion or an aqueous dispersion by adding the AA-PVA to a more stable emulsion.

In coating the coating material, a known method can be adopted. Specifically, a gravure coater, a reverse roll coater, an air knife coater,
Examples thereof include a method of coating the surface of plastic, metal or the like by spraying, dipping, brush coating, or the like. The film obtained by such a method is excellent in film-forming property, and it is a coating film for building materials or packaging plastic materials for the purpose of preventing static electricity, antifogging, etc., or a film for agricultural use, etc.
It is very useful for coating applications such as temporary coatings for surface protection of metal materials and various substrates such as automobiles for the purpose of antifouling and rust prevention.

[0015]

[Operation] Since the coating material of the present invention uses a specific AA-PVA, the coating material is excellent in leaving stability and a good film can be obtained. A film with excellent durability can be obtained, and a film for coating such as a plastic material for building materials or packaging or a film for agriculture, a temporary film for protecting the surface of various base materials such as metal materials and plastics, etc. Very useful for the purpose.

[0016]

The present invention will be specifically described below with reference to examples. In the examples, “%” and “part” mean on a weight basis unless otherwise specified. (Production of AA-PVA) AA-P P is prepared by the following method.
VA (PVA-I-VIII) was produced. [PVA-I] PV containing 0.3% sodium acetate
100 parts of A powder (saponification degree 99.4%, degree of polymerization 1200, average particle size 100 mesh) was charged into a kneader, and 60 parts of acetic acid was added to the kneader to swell, and the mixture was stirred at 20 rpm to 60 ° C. After heating, 25 parts of diketene and acetic acid 2
Part of the mixed solution was added dropwise over 4 hours, and the reaction was continued for another 30 minutes. After completion of the reaction, the reaction dispersion was washed with 500 parts of methanol and then dried at 70 ° C. for 6 hours to contain 0.05% sodium acetate and 0.1% acetic acid (sodium acetate / acetic acid weight ratio = 0.5) AA-PVA having an AA-degree of 6.0 mol% was obtained. Also, such AA-PVA
The pH of the 4% aqueous solution was 4.5.

[PVA-II] sodium acetate 0.3%
PVA powder contained (saponification degree 88 mol%, degree of polymerization 13
00, average particle size 200 mesh) was charged in a kneader in an amount of 100 parts, and 15 parts of liquid diketene was added by spraying at room temperature for 30 minutes while stirring at a rotation speed of 60 rpm.
The temperature was raised to 60 ° C. and the reaction was carried out for 3 hours. After the reaction, the reaction mixture was washed 3 times with 50 parts of methanol, and then sodium acetate was added to 0.
After adding 05 parts, it was dried at 60 ° C. for 8 hours, and contained 0.05% sodium acetate and 0.01% acetic acid (weight ratio of sodium acetate / acetic acid = 5), AA degree of 3.3 mol%.
A PVA composition of AA was obtained. In addition, such AA PV
The pH of the 4% aqueous solution of A was 4.8.

[PVA-III] sodium acetate 0.3%
% PVA powder (saponification degree 88 mol%, degree of polymerization 1
300, average particle size 100 mesh) in a kneader 100
8 parts of diketene gas generated in the evaporator was allowed to flow into the reactor while the temperature was raised to 90 ° C. over 1 hour while stirring the parts and stirring at a rotation speed of 20 rpm. After heating to 90 ° C., stirring for another 30 minutes, 5 parts of water and 10 parts of acetic acid were sprayed and mixed, and dried under reduced pressure (100 mmHg) at 60 ° C. for 8 hours to obtain 0.1% sodium acetate and 2 parts acetic acid. % (Sodium acetate / acetic acid weight ratio = 0.05) A
AA-PVA having a degree of A conversion of 3.1 mol% was obtained. The pH of a 4% aqueous solution of such AA-PVA was 3.5.

[PVA-IV] In the above production of PVA-I, washing with 500 parts of methanol was further added once, and the drying conditions were changed to 70 hours at 70 ° C. under reduced pressure (100 mmHg), and the same manner was applied. Manufacture and add sodium acetate to 0.
AA-modified PVA containing 0075% and acetic acid 0.001% (sodium acetate / acetic acid weight ratio = 7.5) and having a degree of AA conversion of 3.1 mol% was obtained. Also, 4% of such AA-PVA
The pH of the aqueous solution was 5.8. [PVA-V] In the above production of PVA-I, the same procedure was performed except that the amount of methanol was changed to 100 parts and the drying condition was changed to 40 ° C. for 6 hours, and sodium acetate 0.2
%, Acetic acid 5.3% (sodium acetate / acetic acid weight ratio = 0.04), AA conversion degree 6.0 mol%, 4% AA-modified PVA having a pH of 2.8 was obtained.

[PVA-VI] In the production of the above-mentioned PVA-I AA-PVA, the drying condition is a reduced pressure (100 mm).
Hg) The same procedure was repeated except that the temperature was changed to 70 ° C. for 6 hours.
AA-PV which contains 0.2% of sodium acetate and 0.001% of acetic acid (sodium acetate / acetic acid weight ratio = 200) and has a degree of AA of 6.0 mol% and a pH of 4% aqueous solution of 5.8.
A was obtained. [PVA-VII] In the production of AA-modified PVA of PVA-I described above, sodium acetate 1.
7 parts was added and stirred, and the drying conditions thereafter were reduced pressure (10
0 mmHg) The same procedure was repeated except that the temperature was changed to 70 ° C. for 4 hours, and the mixture contained 2.2% sodium acetate and 0.25% acetic acid (sodium acetate / acetic acid weight ratio = 8.8). 0 mol%, 4% AA-ized P whose pH is 5.3
VA was obtained.

[PVA-VIII] sodium acetate 0.1%
% PVA powder (saponification degree 99.5%, degree of polymerization 1
200, average particle size 200 mesh) 100 in a kneader
30 parts of acetic acid, 30 parts of methyl acetoacetate and 2 parts of sulfuric acid were added to the mixture, and the mixture was reacted at 80 ° C. for 8 hours while stirring.
Dry for hours and contain sodium acetate 0.02%, acetic acid 4% (sodium acetate / acetic acid weight ratio = 0.005) AA
AA-PVA having a degree of conversion of 6.0 mol% and a pH of a 4% aqueous solution of 2.5 was obtained.

Example 1 After preparing an aqueous solution for a coating agent consisting of 100 parts of PVA-I described above, 1 part of glyoxal and 900 parts of water, in order to examine the storage stability of the aqueous solution, the viscosity (a) at 25 ° C.
Brookfield type viscometer [rotor (No. 2)
Rotation speed of 20 rpm] and the aqueous solution at room temperature for 24 hours.
After standing for a time, the viscosity (b) of the aqueous solution is measured again,
The viscosity ratio of (b) / (a) was determined. Furthermore, the above PVA
After leaving the -I powder in a thermostatic chamber at 60 ° C and 65% RH for 3 months, an aqueous solution for a coating agent was similarly prepared using the powder, and the viscosity (c) of the aqueous solution was measured in the same manner as above. (C) /
The viscosity ratio of (a) was determined.

Further, the aqueous solution for coating agent before and after the above-mentioned standing treatment is dried on the surface of the glass plate to a dry thickness of about 1
The coating film was applied so as to have a thickness of 00 μm, left standing at 20 ° C. and 65% RH for 48 hours, and the state of the formed film was visually observed to evaluate the film forming property as follows. ○ −−− No abnormalities × −−− Abnormalities such as wrinkles and thickness unevenness are recognized. Furthermore, a film alone obtained by using the aqueous solution for a coating agent before the above-mentioned standing treatment (drying condition; 40 ° C., 24 hours) 25 ℃
After 7 days of immersion in water, the film state was visually observed, and the water resistance was evaluated as follows. ○ −−− No abnormalities Δ −−− Swelling of the film is observed, but the original shape is maintained. × −−− Partial elution, etc. is observed, and the original shape is impaired. The chemical solution was applied to the surface of the cold-rolled steel sheet so that the dry thickness was about 20 μm.
After drying at 0 ° C for 2 hours to form a film, a 5 mm square cross cut is applied to the film surface with a cutter knife,
A 5% saline solution was sprayed for 7 days in an atmosphere of 50 ° C. to examine the rust generation state.

Examples 2 to 4 and Comparative Examples 1 to 4 Using the AA-modified PVA shown in Table 1, the viscosity ratio, film-forming property, water resistance and rust occurrence were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0025]

Table 1 Types of viscosity storage stability of AA-PVA (a) (cps) (b) / (a) Viscosity ratio of (c) / (a) Viscosity ratio Example 1 PVA-I 250 2.2 1.0 〃 2 PVA-II 280 1.5 1.1 〃 3 PVA-III 270 1.3 1.1 1.1 〃 4 PVA-IV 275 1.5 1.0 Comparative Example 1 PVA-V 240 ＊＊＊ 〃 2 PVA-VI 250 *** 〃 3 PVA-VII 240 *** 〃 4 PVA-VIII 230 1.8 *** (b) was not measured because the aqueous solution gelled after standing at room temperature for 24 hours. ** (c) was not measured because the powder after standing for 3 months at 60 ° C, 65% RH was not completely dissolved in water.

[0026]

[Table 2] Film formation Water resistance Rust generation status Before leaving treatment Before leaving treatment A Leaving treatment B Example 1 ○ ○ ○ ○ Not generated 〃 2 ○ ○ ○ ○ Not generated 〃 3 ○ ○ ○ ○ Not generated 〃 4 ○ ○ ○ ○ No occurrence Comparative Example 1 × × × × Rust generation 2 × × × × 〃 〃 3 × × × × 〃 〃 4 × ○ × △ 〃 Note) The neglected treatment A and neglected treatment B are It means a treatment for 24 hours at room temperature and a treatment for 3 months at 60 ° C.

Example 5 After preparing an aqueous solution for a coating agent for a temporary coating consisting of 100 parts of PVA-I described above, 10 parts of hydroxyethyl cellulose and 900 parts of water, in order to examine the storage stability of the aqueous solution, the viscosity at 25 ° C. After measuring (a) with a Brookfield viscometer [rotor speed 10 rpm of rotor (No. 2)], the aqueous solution was left at 40 ° C. for 2 weeks, and the viscosity (b) of the aqueous solution was measured again. The viscosity ratio of (b) / (a) was determined. Further, the above PVA-I powder was added at 60 ° C. and 65
After standing for 3 months in a thermostatic chamber at% RH, an aqueous solution for a coating agent was prepared in the same manner using the powder, and the viscosity (c) of the aqueous solution was measured in the same manner as described above to obtain (c) / (a). The viscosity ratio was determined.

Further, the aqueous solution before and after the above-mentioned standing treatment is applied to the surface of the cold-rolled steel sheet to a dry thickness of about 20.
It was applied so as to have a thickness of μm, and dried at 80 ° C. for 2 hours to form a temporary film. In order to examine the water resistance durability of the obtained provisional coating in a humidified state, the above provisional coating was treated at 40 ° C.
The surface state of the coating film after standing at 90% RH for 24 hours was visually observed and evaluated as follows. ○ −−− No abnormalities △ −−− Floating is observed in the film × −−− Dissolution is observed in a part of the film In addition, in order to examine the removal property of the temporary film, 4 kg / High-pressure water washing was performed at a pressure of m ² for about 10 minutes, and the evaluation was performed as follows. ○ −−− Most of the temporary film was removed Δ −−− Some of the temporary film remained × −−− Almost no temporary film was removed

Examples 6 to 8 and Comparative Examples 5 to 8 Using the AA-modified PVA shown in Table 3, the viscosity ratio, water resistance and removability were evaluated in the same manner as in Example 5. The evaluation results are shown in Tables 3 and 4.

[0030]

Table 3 Types of viscosity storage stability of AA-PVA (a) (cps) (b) / (a) Viscosity ratio of (c) / (a) Viscosity ratio Example 5 PVA-I 350 4.3 1.1 〃 6 PVA-II 300 3.2 1.3 〃 7 PVA-III 320 3.0 1.1 〃 8 PVA-IV 300 3.8 1.2 Comparative Example 5 PVA-V 350 8.3 * 〃 6 PVA-VI 340 10.5 * 〃 7 PVA-VII 350 11.3 * 〃 8 PVA-VIII 350 8.9 * * 60 ℃, 65% RH, powder after 3 months storage is completely complete in water Since it did not dissolve, (c) was not measured.

[0031]

[Table 4] Water resistance / sustainability removal Treatment A Treatment B Treatment C Treatment A Treatment B Treatment C Example 5 ○ ○ ○ ○ ○ ○ 〃 6 ○ ○ ○ ○ ○ ○ 〃 7 ○ ○ ○ ○ ○ ○ 〃 8 ○ ○ ○ ○ ○ ○ Comparative Example 5 △ △ × △ × × 〃 6 △ × × ○ △ × 〃 7 △ × × ○ △ × 〃 8 △ △ × △ × × Note Note: Treatment A is before standing treatment, Treatment B is Treatment at 60 ° C. for 1 month, treatment C means treatment at 60 ° C. and 65% RH for 3 months.

[0032]

The coating material of the present invention is a specific AA-PVA.
Since the coating agent is used, the leaving stability of the coating agent is excellent, a good film can be obtained, and even when it is used for a provisional film, it is possible to obtain a film having excellent water resistance persistence. It is very useful for film forming applications such as coating films for packaging plastic materials and agricultural films, and temporary films for surface protection of various substrates such as metal materials and plastics.

Claims (1)

[Claims] 1. An alkali metal acetate of 2% by weight or less,
A coating agent comprising 5% by weight or less of acetic acid and a polyvinyl alcohol-based resin containing an acetoacetate ester group having an alkali metal acetate / acetic acid weight ratio of 0.01 to 100.