JPH07216293A - Water-based coating composition and metallic plate coated therewith - Google Patents

Abstract

PURPOSE:To obtain a water-based coating composition excellent in water resistance, processing resistance and coatability, reduced in the organic matter vaporizing when baked, thus useful for home appliances, etc., containing a water-based acrylic resin and a specific methylol-modified amino resin at specified proport ions. CONSTITUTION:This coating composition contains, as the resin components, (A) 20-80wt.% of a water-based acrylic resin and (B) 10-60wt.% of a partially or wholly methylol-modified amino resin partially or wholly etherified with a polyol of the formula (h, i, j and k each is 1-20). It is preferable that the component A be a copolymer of an alpha,beta-monoethylenic unsaturated carboxylic acid and a styrene-based monomer and the component B be such that the polyol be a bisphenol A ethylene oxide adduct and the skeleton of the amino resin be spiroguanamine.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aqueous coating composition which is particularly excellent in water resistance, workability and coatability, and can reduce the amount of organic substances volatilized during baking, and the application thereof. Related to the metal plate.

[0002]

2. Description of the Related Art Paints are applied to metals such as home appliances, automobiles, cans, etc., and contribute to their corrosion resistance and aesthetic appearance. However, recently there is a strong demand for paint performance,
Further improvement in physical properties is required. BACKGROUND ART Acrylic / amino resins or polyester / amino resins have been widely used in fields where aesthetics have been required, because of their excellent transparency. However, at present, it is difficult to balance workability and corrosion resistance.
A large amount of organic substances are volatilized during baking, causing air pollution, which is not preferable from the viewpoint of resource saving. Therefore, the advent of a water-based paint capable of solving these problems has been desired.

There are two types of known water-based paints, water-dispersible and water-soluble. Many water-dispersible resins are usually synthesized by emulsion polymerization using a surfactant, and the surfactant used is Even after the coating film is formed, it remains in the coating film, and there is a drawback that the water resistance is lowered. On the other hand, the water-soluble type needs to have a polar group with strong hydrophilicity in the molecule, and a resin containing a carboxyl group and a hydroxyl group is synthesized to obtain an acid value of 20 or more,
Although those having a hydroxyl value of 20 or more are used, from the viewpoint of water resistance, it is better that the amount of hydrophilic groups in the resin used as the coating film is smaller, and there is a drawback that performance such as water resistance and alkali resistance is poor. there were. In order to improve these drawbacks, a method of blending a large amount of an aqueous amino resin such as hexamethoxymethylmelamine and methylated benzoguanamine has been carried out as one method, but it has a large decrease in processability, water resistance, and processability. It is difficult to balance the
There is a drawback that a part of the amino resin blended in a large amount is volatilized, and it is not a practically satisfactory aqueous paint.

As another method, a method of mixing phosphoric acid- or carboxylic acid-modified epoxy has been carried out. However, since it has poor compatibility with acrylics, it has a problem in storage stability of coating materials and leveling in coating film formation. Is occurring,
This tendency was particularly remarkable when the pigment was dispersed. Further, the conventional water-based paint contains 10% or more of an organic solvent in order to improve the storage stability of the paint and the leveling in forming a coating film, and it is still unsatisfactory in terms of air pollution due to solvent volatilization during baking and resource saving. It was enough. In order to solve the above problems, there is a method of blending a specific polyol having a bisphenol A skeleton as disclosed in JP-A-54-77633. In this method, the amino resin and the polyol itself are volatilized. The problem remains, and it cannot be denied that the polyol, which does not participate in the reaction during baking, has the drawback of reducing the water resistance.

[0005]

Therefore, the present invention provides a water-based coating composition which is excellent in water resistance, workability and paintability, and can reduce the amount of organic substances that volatilize during baking, and a water-based coating composition containing the same. The present invention provides a coated metal plate.

[0006]

The first invention is (a) 20-80% by weight of a water-based acrylic resin as a resin component of a water-based paint, (b) a polyol partially represented by the general formula (I),
Alternatively, it is a water-based coating composition characterized by containing 10 to 60% by weight of a completely etherified partially or completely methylolated amino resin.

[0007]

[Chemical 2]

The second invention is a metal plate coated with the aqueous coating composition of the first invention.

The water-based acrylic resin used in the present invention is
Α / β monoethylenically unsaturated carboxylic acid monomers such as acrylic acid and fumaric acid, acrylic acid acrylic esters such as methyl acrylate and ethyl acrylate, styrene-based monomers such as styrene and vinyltoluene, hydroxyethyl acrylate and hydroxy acrylate Produced by appropriately selecting and copolymerizing a hydroxy group-containing monomer such as propyl, or obtained by partially or completely esterifying and ether modifying the resulting acrylic resin with a carboxyl group- or hydroxyl group-containing resin or monomer A wide range of things can be used. This aqueous acrylic resin is used in an amount of 20 to 80% by weight based on the resin solid content of the entire coating composition. If it is less than 20 parts by weight, the adhesion to the base material is lowered, the water dispersibility is poor, the storage stability of the coating is poor, and the pigment dispersibility is poor when the pigment is added. On the other hand, when it is 80% by weight or more, the hardness is lowered and the water resistance is poor.

The amino resin used in the present invention is an amino resin that can be dissolved or dispersed in an aqueous medium, and is a bisphenol A ethylene oxide and propylene oxide adduct represented by the following general formula partially or completely. It is a partially or completely methylolated melamine resin, benzoguanamine resin, or spiroguanamine resin etherified with a polyol represented by the general formula (I), and the remaining methylol group when partially etherified with a specific polyol is methanol. It can be etherified with other alcohols such as ethanol. In addition, these amino resins can be used alone or as a mixture, or in some cases, condensed.

[0011]

[Chemical 3]

Particularly, as the specific polyol, a bisphenol A ethylene oxide adduct of h, i = 2 is preferable from the viewpoint of water solubility, and its etherification is melamine, benzoguanamine, or spiroguanamine, and an average of 0.1 to 0 per molecule. It is preferably 0.5. If it is 0.1 or less, it is difficult to reduce the amount of volatile components, and if it is 0.5 or more, it is not preferable because the viscosity of the coating composition becomes high. The type of skeleton of the amino resin is preferable in that spiroguanamine generates less tar-like low-molecular substances generated during baking of the coating material as compared with melamine or benzoguanamine.

The aqueous amino resin is used in an amount of 15 to 60% by weight based on the resin solid content of all paint components. Below 10% by weight,
The hardness and water resistance are insufficient, and if it exceeds 60% by weight, the processability of the coating film is deteriorated.

The resin used in the present invention can be partially or completely neutralized with an acidic group in the resin component, and it is dissolved or dispersed in an aqueous medium. The basic substance may be any substance capable of enjoying a proton of an acidic group, and is preferably an organic amine having a primary and / or secondary and / or tertiary amino group,
Examples thereof include ammonia, monoethanolamine, diethanolamine, diethylamine, triethylamine, triethanolamine and the like, and these are used alone or as a mixture of two or more kinds.

The above-mentioned aqueous medium is water or a mixture of water and a hydrophilic solvent, or a mixture of water and a hydrophilic resin. The hydrophilic solvent may be one having water solubility, preferably glycols and / or alcohols, and examples thereof include ethylene glycol, ethyl cellosolve, diethylene glycol monoethyl ether, ethanol and butanol. Are used alone or as a mixture of two or more. The hydrophilic resin may be any one that has water solubility, and is preferably an aqueous acrylic resin and / or a polyol. For example, as the constituent components of the aqueous acrylic resin, acrylic acid 15% by weight, styrene 10% by weight, It is 75% by weight of methyl acrylate, and examples of the polyol include polyethylene glycol. These are used as one kind or as a mixture of two or more kinds.

In the coating composition of the present invention, an amine-blocked acid catalyst such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid or dinonylnaphthalene disulfonic acid is used as a curing aid, if necessary, in a resin solid content of 100% by weight. 0.1 to 5 parts by weight is added to each part to form a paint. It is also possible to mix water-soluble resins and water-dispersible resins, which are generally used as resins for water-based paints, such as water-soluble polyester resins, maleated fatty acids and polyols. Further, similarly, additives such as a leveling agent, a defoaming agent, and a lubricant can be added. Further, pigments such as titanium oxide and quinacridone, and other fillers can be added. In order to mix pigments, fillers, etc., it is preferable to knead with a solution of an aqueous acrylic resin to prepare a dispersion paste and then to make it into a paint.

As the method for coating the aqueous coating composition of the present invention, known means such as roll coating, spraying and brush coating can be used.

The metal plate used in the present invention has a plate thickness of 0.0.
1 ~ 2.0mm cold rolled steel plate, stainless steel plate,
An aluminum alloy plate or the like. In some cases, the surface of these metal plates is plated, vapor-deposited, coated or further coated with an inorganic metal such as chromium, tin, zinc or nickel, or an alloy or composite of one or more organic substances such as acrylic resin. , Alumite, phosphoric acid treatment, etc. Further, a metal plate obtained by laminating a resin film such as polyethylene terephthalate or polybutylene terephthalate on these plates can also be used.

[0019]

EXAMPLES The present invention will be described below with reference to examples. In the examples, “part” means “part by weight”, “%” means “% by weight”, and “solid content” means 20
Represents the residue after baking for 3 minutes at 0 ° C. Production Example 1 Production of Aqueous Acrylic Resin Solution A1 A four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank, and a nitrogen gas blowing tube was charged with 100 parts of n-butanol, while stirring while introducing nitrogen gas. Temperature 10
Keep at 5 ° C., add 5 parts of benzoyl peroxide to 100 parts of a mixture of styrene 30%, ethyl acrylate 20%, butyl acrylate 10%, 2-hydroxyethyl acrylate 20%, methyl methacrylate 10%, acrylic acid 10% from a dropping tank. The dissolved product was added dropwise over 3 hours. Thereafter, the mixture was kept at 105 ° C. and reacted for 1 hour, 0.5 part of benzoyl peroxide was added, and the reaction was further continued for 1 hour to complete the reaction. The n-butanol was distilled off under reduced pressure at 80 ° C. until the nonvolatile content became 83%, then 14.6 parts of dimethylethanolamine and water were added, and the solid content was 50%.
Transparent and viscous water-based acrylic resin A1 containing 10% butanol
Got

Production Example 2 Production of Aqueous Acrylic Resin Solution A2 According to Production Example 1, styrene 20%, ethyl acrylate 15%, 2-hydroxyethyl acrylate 20%,
Polymerization was performed in the same manner with a monomer composition of 30% methyl methacrylate and 15% methacrylic acid to obtain an aqueous acrylic resin solution A2.

Production Example 3 Production of Aqueous Amino Resin Solution B1 Benzoguanamine 42.7 was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank and a nitrogen gas blowing tube.
, 20.5 parts of paraformaldehyde, 25%
After adding 0.7 part of sodium hydroxide, the mixture was heated at 60 ° C. for 3 hours. Next, 36.1 parts of bisphenol A ethylene glycol diether was charged. Then, 60% nitric acid was charged until the solution had a pH of 3.5, and the reaction was continued at 70 ° C. for 4 hours. After completion of the reaction, the mixture was neutralized with 25% sodium hydroxide, methanol water was removed under reduced pressure at 70 ° C. or lower, and filtered under reduced pressure to take out. Then, the solid content was adjusted to 75% with butyl cellosolve.

Production Example 4 Production of Aqueous Amino Resin Solution B2 Benzoguanamine 37.4 was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank and a nitrogen gas blowing tube.
Parts, 18.0 parts of paraformaldehyde and 1 part of methanol
2.4 parts were charged, 0.6 part of 25% sodium hydroxide was added, and the mixture was heated at 60 ° C. for 3 hours. Next, 31.6 parts of bisphenol A ethylene glycol diether was charged. Then, 60% nitric acid was charged until the pH of the solution became 3.5, and the reaction was continued at 70 ° C. for 6 hours. After completion of the reaction, the mixture was neutralized with 25% sodium hydroxide, methanol water was removed under reduced pressure at 70 ° C. or lower, and filtered under reduced pressure to take out. Then, the solid content was adjusted to 75% with butyl cellosolve.

Production Example 5 Production of Aqueous Amino Resin Solution B3 Benzoguanamine 52.3 was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank and a nitrogen gas blowing tube.
Part, paraformaldehyde 25.2 parts and methanol 2
After adding 1.7 parts of the mixture and adding 0.6 parts of 25% sodium hydroxide, the mixture was heated at 60 ° C. for 3 hours. Next, 60% nitric acid was charged until the solution reached pH 3.5, and the reaction was continued at 70 ° C. for 6 hours. After completion of the reaction, the mixture was neutralized with 25% sodium hydroxide, methanol water was removed under reduced pressure at 70 ° C. or lower, and filtered under reduced pressure to take out. Then, the solid content was adjusted to 75% with butyl cellosolve.

Production Example 6 Production of Aqueous Amino Resin Solution B4 Benzoguanamine 63.2 was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank and a nitrogen gas blowing tube.
Parts, paraformaldehyde 30.4 parts and methanol 5.
Two parts were charged, 1.1 parts of 25% sodium hydroxide was added, and the mixture was heated at 60 ° C. for 3 hours. Next, 60% nitric acid was charged until the pH of the solution became 3.5, and then the mixture was kept at 70 ° C. for 6 hours.
Reacted for hours. After completion of the reaction, the mixture was neutralized with 25% sodium hydroxide, methanol water was removed under reduced pressure at 70 ° C. or lower, and filtered under reduced pressure to take out. Then, the solid content was adjusted to 75% with butyl cellosolve.

The amino resin, B, obtained as described above
Table 1 shows the analysis results of the average bound formaldehyde number, the average bound methanol number, and the average bound bisphenol A ethylene glycol diether number per 1 molecule of benzoguanamine of 1 to B4.

Examples 1 to 4 Comparative Examples 1 to 2 The compositions in Table 2 show the amounts of each component in parts by weight. After mixing the components according to the composition of Table 2,
Add butyl cellosolve to reduce the amount of organic solvent in the paint to 1
0 parts by weight, to which 0.3 parts by weight of amine salt of p-toluenesulfonic acid, 0.3 parts by weight of a silicone-based leveling agent were added, and the rest was adjusted by adding water to prepare an aqueous coating composition. Obtained. The test results of the paints prepared in Examples and Comparative Examples are shown in the test results of Table 2. Each test method is as follows.

◎ Volatility test; electroplated tin plate having a plate thickness of 0.23 mm is dried by roll coating, and the film thickness is 7 μm.
And paint in a gas oven at ambient temperature 19
300 cm of painted panels baked at 0 ° C for 3 minutes
Cut into ² and weigh. Further, the coated plate was baked in a gas oven at an ambient temperature of 190 ° C. for 20 minutes, and the weight thereof was measured to evaluate the change rate of the weight. ○ ・ ・ ・ 0% to 3% △ ・ ・ ・ 3% to 7% × ・ ・ ・ 7% or more Coating film physical property test Electroplated tin plate having a plate thickness of 0.23 mm is dried by roll coating to a coating film thickness of 7 μm. The coating was applied as described above, and baked in a gas oven at an ambient temperature of 190 ° C. for 10 minutes to prepare a painted panel.

Adhesion test: A cross-cut peeling test was performed, and the peeled area was visually evaluated. ○ ・ ・ ・ 0% to 5% △ ・ ・ ・ 5% to 39% × ・ ・ ・ 40% or more

Water resistance test: The coated panel was immersed in water, heat-treated at 100 ° C. for 30 minutes, and then subjected to an adhesion test. ○ ・ ・ ・ 0% to 5% △ ・ ・ ・ 5% to 39% × ・ ・ ・ 40% or more ◎ Coating hardness: JIS standard “pencil scratch test” (JIS
NO. It was performed according to the method registered in K5400). ◎ Workability test; Erichsen test: JIS Z-2247
According to, the state of the coating film was evaluated after extrusion processing to the point where the underlying metal started to crack.

○: No change △: Some cracking ×: Cracking overall

[0031]

[Table 1]

[0032]

[Table 2]

The composition values in the table indicate parts by weight of the solid content of the resin.

[0034]

Industrial Applicability According to the present invention, it is possible to form a coating film which is particularly excellent in water resistance, workability and coatability, and further it is possible to reduce the amount of organic substances volatilized during baking. According to Z-2247, the state of the coating film was evaluated after extrusion processing to the point where the underlying metal started to crack. ○ ・ ・ ・ No change △ ・ ・ ・ Slightly cracked × ・ ・ ・ Overall cracked

[0035]

Claims (2)

[Claims] 1. As a resin component of an aqueous paint, (a) 20 to 80% by weight of an aqueous acrylic resin, (b) a partially or completely etherified partly or completely methylol with a polyol represented by the general formula (I). Amino resin 10-60
%, And a water-based coating composition. [Chemical 1] 2. A metal plate coated with the aqueous coating composition according to claim 1.