JPS6244578B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aqueous resin composition, and more specifically, to a coating composition for baking on metals such as untreated steel sheets, treated steel sheets, galvanized iron sheets, and tin plates, to form a film with particularly excellent anticorrosion properties. The present invention relates to an aqueous resin composition that can be used. Conventionally, it has been desired to shift to water-based binders for anticorrosive paints from the viewpoint of resource saving, energy saving, and environmental pollution. As with the solvent-based type, epoxy resin-based ones have been mainly studied in water-based systems, and various methods have been proposed for dispersing epoxy resins in water. For example, there are two methods for dispersing epoxy resin in water using a surfactant: one using an anionic surfactant and the other using a nonionic surfactant. , the oxirane ring opens during the emulsification process and storage, resulting in decreased reactivity and poor performance of the formed coating, and sometimes problems with thickening and gelation during storage. On the other hand, in the latter case, from the viewpoint of dispersibility and storage stability, the system contains a considerably large amount of surfactant, which tends to adversely affect the chemical and mechanical properties of the formed coating film. . As a solution to this problem, various self-emulsifying epoxy resin emulsions have recently been proposed. This method modifies the epoxy resin with other compounds,
A self-emulsifying epoxy resin dispersion with emulsifying segments introduced into the molecule. For example, US Pat. No. 3,301,804 states that an adduct of an epoxy resin with a boric acid ester forms a self-emulsifying emulsion. That is, epoxidized cresol formaldehyde novolak resin and 2-(P-dimethylaminoethoxy)-
A stable dispersion has been obtained when water is added dropwise to the conjugate adduct with 4-methyl-1,3,2-dioxaborinane and mixed. However, this product alone does not have sufficient crosslinking, so it does not provide sufficient coating performance, and when combined with a curing agent such as tetramethylene diamine or tetraethylene pentamine, the desired coating performance can be achieved, but storage Poor stability and workability problems. Additionally, US Pat. No. 4,021,396 discloses that an acrylic polymer obtained by copolymerizing 0.5 to 10% of an unsaturated carboxylic acid with other specified monomers and an epoxy resin are combined with a base such as ammonium or an amine. Aqueous coating compositions neutralized with a neutral substance are shown. However, according to research conducted by the present inventors, the aqueous coating composition described above lacks storage stability, especially at high temperatures (about 50°C), and has problems such as gelation and differences in baking temperature. There are still other problems that need to be resolved, such as the problem with the printing process that causes variations in the physical properties of the film. The present inventors have conducted extensive research into how to improve the above-mentioned problems in a well-balanced manner, such as the dispersibility, storage stability, and coating performance of epoxy resins. We have developed a new aqueous resin composition that has particularly excellent corrosion resistance and is suitable for spray coating such as air spray, airless spray, and electrostatic spray, and completed the present invention. That is, the present invention contains 30 to 50% by weight (however, excluding 30% by weight) of a monobasic carboxylic acid monomer selected from acrylic acid or methacrylic acid, and contains an acrylic acid alkyl ester type, a methacrylic acid alkyl ester type, Number average molecular weight obtained by copolymerizing a copolymerizable monomer mixture consisting of one or more selected styrene monomers.
5,000 to 80,000 alkali-neutralized acrylic resin (A) and an aromatic epoxy resin (B) having a number average molecular weight of 1,400 or more and having an average of 1.1 to 2.0 epoxy groups in one molecule in the alkali. Partial reaction of an epoxy resin with an excess of carboxyl groups and an acrylic resin in which the solid content ratio of the Japanese-type acrylic resin (A) and the aromatic epoxy resin (B) is in the range of 1:1 to 1:5. The present invention relates to an aqueous resin dispersion in which a compound is dispersed in an aqueous medium in the presence of ammonia or amine in an amount such that the pH thereof becomes 4 to 11. The characteristics of the aqueous resin composition according to the present invention are as follows. That is, the high molecular weight epoxy resin and the acrylic resin, which have poor compatibility, are chemically bonded, and the carboxyl group becomes an epoxy resin/acrylic resin partial reactant with excessive self-emulsifying properties, so that phase separation does not occur. Since a high molecular weight epoxy resin is used, the viscosity of the paint does not increase or gelation occurs easily due to the chemical reaction of the epoxy group in the aqueous medium during storage. It has self-crosslinking properties due to the high content of epoxy resin compared to acrylic resin and the presence of epoxy groups remaining at the ends.In addition, the film-forming ability of acrylic resin provides excellent corrosion resistance and chemical resistance. A coating film is formed that exhibits physical properties such as hardness and solvent resistance. Acid content 30-50
This may be because an aqueous resin dispersion in which a large amount of acrylic resin is reacted with a high molecular weight epoxy resin in an amount equal to or more than the acrylic resin component exhibits (pseudo) plastic flow when spray-painted. It has good atomization properties, little dripping, and excellent spray painting properties. Number average molecular weight 1400 to 5000
Aromatic epoxy resin having two epoxy groups in the molecule Number average molecular weight having 1.1 to 2.0 epoxy groups in one molecule obtained by heat treatment in the presence or absence of an epoxy group modifier
Aqueous coating resin compositions using aromatic epoxy resins of 2,000 to 10,000 have industrially advantageous properties in that there is little variation in coating film performance even with variations in baking temperature during coating film formation. Also in other coating properties, it is superior to coatings obtained from aqueous coating resin compositions using aromatic epoxy resins that are not heat treated. The alkali-neutralized acrylic resin (A) used in the present invention contains 30 to 50% by weight of a monobasic carboxylic acid monomer such as acrylic acid or methacrylic acid.
Copolymerizable momano mixture containing, boiling point 70 ~ 230
℃ in a hydrophilic organic solvent such as ethylene glycol monoethyl ether or ethylene glycol monobutyl ether using a radical polymerization initiator such as azobisisobutyronitrile or peroxide.
It can be obtained by copolymerization at a temperature of 80°C to 150°C. In this case, if the monobasic carboxylic acid monomer is used in an amount exceeding 50% by weight, the viscosity of the resulting composition will be extremely high, making it difficult to manufacture, and since it must be used with a low solids composition, it will be difficult to dry the composition. It is also disadvantageous in terms of energy conservation. Monomers other than the unsaturated carboxylic acid monomer used in the present invention include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, Acrylic acid alkyl esters such as n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, decyl acrylate, dodecyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate , methacrylic acid alkyl esters such as isobutyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, dodecyl methacrylate, styrene, vinyltoluene, 2 - One or more styrenic monomers such as methylstyrene, t-butylstyrene, and chlorostyrene are used, and if necessary, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate,
Hydroxy group-containing monomers such as hydroxypropyl methacrylate, N-substituted (meth)acrylic monomers such as N-methylol (meth)acrylamide and N-butoxymethyl (meth)acrylamide, and epoxy groups such as glycidyl acrylate and glycidyl methacrylate. Containing monomers, acrylonitrile, etc. can also be blended. The above alkali-neutralized acrylic resin (A) has a number average molecular weight of 5,000 to 80,000, preferably 20,000 to 20,000.
Something in the 40000 range is good. In addition, an acid value of 190 to 310 in terms of solid content is suitable. An average of 1.1 per molecule used in the present invention
Examples of aromatic epoxy resins having a number average molecular weight of 1,400 or more and having 1 to 2.0 epoxy groups include epichlorohydrin/bisphenol type epoxy resins, such as Epicote 1004 and Epicote 1007, commercially available from Ciel Chemical Co., Ltd. , Epicort 1009, or Epiclon 4050, Epiclon 4050, commercially available from Dainippon Ink Chemical Co., Ltd.
7050 etc. have two epoxy groups in one molecule,
It is used as an aromatic epoxy resin with a number average molecular weight of 1,400 to 5,000. In the present invention, the unmodified aromatic epoxy resin as described above is further heat-treated in the presence or absence of an epoxy group modifier to modify it into a higher molecular weight aromatic epoxy resin. The resulting aqueous resin composition can form a coating film with superior corrosion resistance, chemical resistance, and the like. Examples of the above-mentioned epoxy group modifier include bisphenols such as bisphenol A and bisphenol B, dehydrated castor oil, soybean oil fatty acid, cottonseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, linseed oil fatty acid, castor oil fatty acid, Vegetable oil fatty acids such as coconut oil fatty acids and palm oil fatty acids, or mixtures thereof are mainly used, but aromatic carboxylic acids such as benzoic acid and paratertiary butylbenzoic acid may be used in combination, if necessary. Theoretically, the amount of these epoxy group modifiers should be 45 equivalent% or less of the epoxy groups in the unmodified aromatic epoxy resin, but in general, this modification reaction requires heating, so aromatic epoxy The resin self-condenses. For this reason, in practice, 0.5 to 10
By using about equivalent percent, a modified aromatic epoxy resin having 1.1 to less than 2.0 epoxy groups in one molecule and a number average molecular weight of 2,000 to 10,000 can be obtained. When bisphenols are used as the conditions for heating and reacting the unmodified aromatic epoxy resin and the epoxy group modifier, a predetermined amount of epoxy resin and bisphenols are placed in a nitrogen gas purge container equipped with a stirrer. It can be prepared by cooking in the absence of a solvent or in a hydrophilic organic solvent such as ethylene glycol monobutyl ether at a temperature range of 150 to 170°C for about 5 hours. When using a fatty acid, similarly to the above, a predetermined amount of epoxy resin, fatty acid, and if necessary a small amount of sodium carbonate as an alkali catalyst are placed in a nitrogen gas purge container equipped with a stirrer, and this is also carried out in a solvent-free solution or with ethylene. It can be prepared by cooking in a hydrophilic organic agent such as glycol monobutyl ether at 140 to 170°C for about 5 hours. In addition, the conditions for heat treatment in the absence of an epoxy group modifying agent are the same, such as in the absence of a solvent or in a hydrophilic organic solvent such as ethylene glycol monobutyl ether, or in some cases with the addition of a catalyst such as soda carbonate. hand
It can be produced by heating at 140 to 170°C for several hours. The above-mentioned modification reaction of unmodified aromatic epoxy resins has been described, for example, by B. Dobinson and W. Hofmann.
It can be controlled by measuring the percent reduction in oxirane by the ``hydrobromide/acetic acid method'' described in ``Determination of epoxide groups'', co-authored by BP Stark and BP Stark. In the present invention, in order to react the alkali-neutralized acrylic resin (A) and the aromatic epoxy resin (B) to produce an epoxy resin/acrylic resin partial reaction product having an excess of carboxyl groups, ethylene glycol The mixture may be stirred in a hydrophilic organic solvent such as monobutyl ether in the presence of ammonia or amine as described below at 60°C to 170°C for about 10 minutes to 2 hours. Control of the reaction can be checked by measuring the percentage of oxirane, measuring the increase in viscosity, or charting the molecular weight distribution by gel vermiaction chromatography (GPC) as detailed in Example 1 below. In the present invention, the weight ratio of alkali-neutralized acrylic resin (A) and aromatic epoxy resin (B) is
The ratio of (A) to (B) is preferably from 1:1 to 1:5.
If the usage ratio of component (A) exceeds this range, the corrosion resistance of the resulting coating film tends to deteriorate, and (B)
When the amount increases, problems tend to arise in the dispersibility and storage stability of the aqueous resin composition in an aqueous medium. The aqueous resin composition according to the present invention is prepared by adding ammonia or amine in an amount such that the final coating composition has a pH of 5 to 11 and dispersing it in an aqueous medium. Bye. As the amine, for example, alkylamines such as trimethylamine, triethylamine, and butylamine, alcohol amines such as 2-dimethylaminoethanol, diethanolamine, triethanolamine, and aminomethylpropanol, and morpholine are used. Polyvalent amines such as ethylenediamine and diethylenetriamine can also be used. In the present invention, the aqueous medium means water alone or a mixture with a hydrophilic organic solvent in which at least 10% by weight is water. Examples of the hydrophilic organic solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, Alkyl alcohols such as sec-butanol, tert-butanol, isobutanol, ether alcohols such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, methyl carbitol, ethyl carbitol, ethers such as methyl cellosolve acetate, ethyl cellosolve acetate, etc. Esters, dioxane, dimethylformamide, diacetone alcohol, etc. are used. The aqueous resin composition of the present invention can be used by adding appropriate fillers such as a rust preventive agent, a hardening agent, a pigment, and an antifoaming agent, depending on the intended use. As the rust preventive agent, barium metaborate, styrotium chromate, zinc fluorate, zinc molybdate, aluminum silicate, etc. can be used. As the curing agent, an aqueous aminoplast resin is preferable, and for example, hexamethoxymethylmelamine, methylolated melamine resin, methylolated benzoguanamine resin, methylolated urea resin, etc. can be used. As pigments, inorganic pigments such as titanium oxide, iron oxide, and phthalocyanine, and organic pigments with good weather resistance can be used. As antifoaming agents, silicone-based ones are useful, such as Paintacl-M manufactured by Fuji Polymer Co., Ltd., which is effective. The aqueous resin composition according to the present invention can be used for metal plates such as untreated steel plates, treated steel plates, galvanized iron plates, and tin plates, and is particularly useful as a rust-preventing primer and anti-corrosion coating for adhesion to metals, corrosion resistance, and chemical resistance. Excellent coating performance such as properties. As for the coating method, spray coating such as air spray, airless spray, and electrostatic spray is most suitable, but dipping coating, roll coater coating, electrodeposition coating, etc. are also possible. As for other uses, by selecting the type of acrylic resin and the type and content of epoxy resin, it is possible to apply it to can inner surface paint, adhesive, fiber processing agent, etc. The present invention will be specifically explained below using Examples. In the examples, parts indicate parts by weight. Example 1 (A) Production of carboxyl group-containing acrylic resin Styrene 200 parts Ethyl acrylate 200 Methacrylic acid 200 Ethylene glycol monobutyl ether 388 Benzoyl peroxide 12 A four-necked flask in which 1/4 of the mixture with the above composition was replaced with nitrogen gas Heat it to 80-90℃, then gradually drop the remaining 3/4 over 2 hours while keeping it at that temperature.
Stir for an hour and then cool, acid value 215 (solid content equivalent, same below), solid content 59.7%, viscosity Z ₁ ~ _{Z 2}
(Gardner bubble viscometer, 25℃, below viscosity is
Measured values are shown at 25°C. ) was obtained. (B) Production of epoxy resin solution Epicote 1009 500 parts Ethylene glycol monobutyl ether
333.3 Pour the entire amount into a 4-necked flask purged with nitrogen gas, gradually heat to raise the internal temperature to 100℃, and
After stirring for a period of time to completely dissolve the mixture, the mixture was cooled to 80°C to obtain an epoxy resin solution with a solid content of 60% by weight. (C) Preparation of aqueous coating composition

[Table] Pour the entire amount into a 4-necked flask and add with stirring to neutralize the carboxyl groups by approximately 40 mol%, then raise the internal temperature to 80°C and keep at this temperature for 30 minutes. After continued stirring, the mixture was cooled to room temperature. The reduction rate of oxirane% is
The viscosity was 43.8%, and the viscosity was 1.7 times higher after shoeing than before shoeing. In addition, as shown in Figure 1, the chart of molecular weight distribution by GPC before packing shows two types of acrylic resin with high molecular weight and epoxy resin with low molecular weight.
However, after cutting, the peak of the low molecular weight epoxy resin disappears as shown in FIG. 2, confirming that the epoxy resin is pendant to the acrylic resin. After the above-mentioned cooking, the mixture was gradually added little by little while stirring to obtain a milky white dispersion having a solid content of 19.6% by weight and a viscosity of 240 cps. The obtained dispersion was stored at 50°C for one month, but no abnormality was observed. Example 2 (B) Production of fatty acid modified epoxy resin

[Table] -tel
Pour the entire amount of the mixture into a 4-necked flask purged with nitrogen gas, raise the internal temperature to 160℃, and
After baking for ~5 hours, the percentage decrease in oxirane was measured to be 14%. Thereafter, the mixture was cooled to 80° C. and added to obtain a modified epoxy resin solution with a solid content of 60% by weight. (C) Preparation of aqueous resin composition

[Table] Pour the entire amount into a 4-necked flask, add with stirring to neutralize the carboxyl groups by 60 mol%, raise the internal temperature to 100°C, and keep at this temperature for 60 minutes. I went shoe-king. The rate of decrease in oxirane percentage at this time was calculated to be 59.2%. When this was gradually added little by little while stirring, the solid content was 19.5% by weight, and the viscosity was 19.5% by weight.
A milky white dispersion of 170 cps was obtained. The obtained dispersion was stored at 50°C for one month, but no abnormality was observed. Examples 3 to 4 and Comparative Examples 1 to 3 (A) Production of carboxyl group-containing acrylic resins Each carboxyl group-containing acrylic resin solution was prepared using the same procedure as in Example 1 according to the formulation shown in Table 1 below. Manufactured.

[Table] The meanings of the symbols representing monomers, solvents and catalysts in Table 1 are as follows. St: Styrene MMA: Methyl methacrylate 2EHA: 2-ethylhexyl acrylate EA: Ethyl acrylate MAA: β-methacrylate HEMA: β-hydroxyethyl methacrylate EGMBE: Ethylene glycol monobutyl ether BPO: Benzoyl peroxide (B) Epoxy resin solution and Manufacturing method of modified epoxy resin solution The modified epoxy resin solution was manufactured according to the recipe shown in the table below. However, the operating method is to charge all the raw materials other than ethylene glycol monobutyl ether for dilution into a 4-necked flask, raise the temperature to a specified temperature, stir, and cook for a specified period of time.
After cooling to 0.degree. C., diluent ethylene glycol monobutyl ether was added.

[Table] (C) Preparation of aqueous resin composition A water-based resin composition was prepared in the same manner as in Example 1 using the formulation shown in the table below. However, in Comparative Example 2, shoeing was not performed.

[Table] The results of the storage stability test for the aqueous resin compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 3. Dry coating thickness is 10~15μ on treated steel plate
A test panel was created by painting with an airless spray paint machine so as to cover the front and back, and baking and drying at 200℃ for 5 minutes. Regarding spray suitability, Examples 1 to 4
It atomized well and formed a good coating film with almost no sagging. However, both Comparative Example 2 and Comparative Example 3 had insufficient atomization, and Comparative Example 3 in particular had a low solids content, so when applied to a predetermined film thickness,
Severe sagging occurred and a good coating film could not be obtained. Next, test panels were tested for corrosion resistance using JIS, Z-
2371, Examples 1 to 4 and Comparative Example 3
It showed good results, withstanding a 100 hour resistance test. Comparative Example 2 showed severe initial rusting and was poor. Furthermore, this Example 1~
Regarding No. 4, 15 to 20% by weight of strontium chromate was added to the resin content as a rust-preventing pigment, and a similar test was conducted, and it withstood a 500-hour durability test.

[Brief explanation of the drawing]

Figure 1 is a chart showing the molecular weight distribution by GPC immediately after mixing (A) carboxyl group-containing acrylic resin and (B) epoxy resin solution at room temperature in Example 1, and Figure 2 shows the molecular weight distribution at 80°C. This is a chat after 1 hour of shoeing.

Claims (1)

[Scope of Claims] 1 Contains 30 to 50% by weight (excluding 30% by weight) of a monobasic carboxylic acid monomer selected from acrylic acid or methacrylic acid, and contains an acrylic acid alkyl ester type or a methacrylic acid alkyl ester type. , an alkali-neutralized acrylic resin (A) having a number average molecular weight of 5,000 to 80,000 and an alkali-neutralized acrylic resin (A) copolymerized with a copolymerizable monomer mixture consisting of one or more types selected from styrenic monomers, and an average of 1.1 to 80,000 per molecule. An aromatic epoxy resin (B) having a number average molecular weight of 1400 or more and having 2.0 epoxy groups,
An acrylic resin with an excess of carboxyl groups, which is obtained by reacting the alkali-neutralized acrylic resin (A) and the aromatic epoxy resin (B) at a solid content ratio of 1:1 to 1:5. The pH of the resin partial reactant is 4.
An aqueous resin dispersion, which is dispersed in an aqueous medium in the presence of ammonia or amine in an amount of 1 to 11. 2. The aqueous resin dispersion according to claim 1, characterized in that an alkali-neutralized acrylic resin having a number average molecular weight of 20,000 to 40,000 is used. 3 2 in one molecule with a number average molecular weight of 1400 to 5000
An aromatic epoxy resin having 1.1 to less than 2.0 epoxy groups in one molecule and having a number average molecular weight of 2,000 to 2,000, obtained by heat-treating an aromatic epoxy resin having 2,000 epoxy groups in the presence or absence of an epoxy group modifier.
3. The aqueous resin dispersion according to claim 1 or 2, characterized in that an aromatic epoxy resin of 10,000 is used. 4. The aqueous resin dispersion according to claim 3, wherein the epoxy group modifier is a bisphenol or a monovalent fatty acid.