JP2667884B2 - Method for forming highly durable anion electrodeposition coating film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a novel highly durable anion electrodeposition coating film.

(Prior art and its problems) Conventionally, as an example of an electrodeposition paint provided for coating an aluminum material, an acrylic-melamine-based water-soluble or water-dispersible paint is exemplified. For example, acrylic acid or methacrylic acid and another acrylic A water-soluble or water-dispersible resin obtained by neutralizing a polycarboxylic acid resin obtained by copolymerizing a system unsaturated monomer or an ethylenically unsaturated monomer with ammonia or an organic amine, and melamine as a crosslinking agent. A mixture of resins is used. This acrylic-melamine-based electrodeposition paint is widely used for painting building materials such as aluminum sashes used in ordinary houses and high-rise buildings because of its excellent corrosion resistance and weather resistance.

However, the weather resistance of the acrylic-melamine-based electrodeposition paint is sufficiently high when it is used for general houses, but recently it is only a few when it is used for building materials. Since a long-term durability of ten years has been required, the above-mentioned requirements cannot be satisfied with the electrodeposition paint at all.

However, even in the past, electrodeposition paints for forming highly durable coating films have been disclosed in JP-A-61-87765 and JP-A-62-59676.
JP-A No. 62-127362 and the like.

These electrodeposition coatings form a coating film having excellent durability because the water-dispersible fluorine-containing resin is used as a vehicle component.However, since the fluorine-containing resin is expensive, the price of the obtained product is high, There is a disadvantage that it is economically disadvantageous and not practical. Further, when the content of the fluorine component is large, the paint has a disadvantage in that the adhesion to the object to be coated is deteriorated and the durability is inferior.

An object of the present invention is to provide a method for forming a coating film excellent in durability that has solved the above-mentioned problems.

(Means for Solving the Problems) The present invention has conducted various researches on a method for overcoming the above-mentioned drawbacks, and as a result, after the electrodeposition coating of the acrylic resin electrodeposition coating as the first step on the surface to be coated, the second step It has been found that when a fluororesin electrodeposition coating having a specific electrodeposition coating polarization value is electrodeposited, an acrylic resin electrodeposition coating and a fluororesin electrodeposition coating are sequentially formed on the surface to be coated. Was completed.

That is, according to the present invention, (A)
An anionic acrylic resin electrodeposition coating material (I) having an electrodeposition coating polarization value (kΩ · cm ² , the same unit is hereinafter referred to) of 200 to 2500 is electrodeposited to form a coating film. As the stage, (B) the electrodeposited coating polarization value (kΩ · cm ² ) is (A)
Same or less as the conductive析塗membrane polarization value (kΩ · cm ^2),
In the case of small, the difference is up to 1500, electrodeposition coating of anionic type fluorine resin electrodeposition paint (II)
Next, the present invention relates to a method for forming a highly durable anion electrodeposition coating film characterized by heating.

The electrodeposition paint (I) to be electrodeposited in the first step of the method of the present invention is obtained by dispersing a resin containing a carboxyl group-containing water-dispersible acrylic resin and a crosslinking agent as a vehicle component with a neutralizing agent in water. A conventionally known anionic acrylic resin paint can be used.

The carboxyl group-containing acrylic resin is α, β-
It is obtained by copolymerizing an ethylenically unsaturated carboxylic acid with an acrylic weight such as alkyl acrylate or alkyl methacrylate and an ethylenically unsaturated monomer copolymerizable therewith.

Typical examples of the α, β-ethylenically unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid and itaconic acid. Typical examples of the acrylic monomer include hydroxyl-containing acrylic monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate; Acrylic ester-based monomers such as methyl, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate , N-propyl methacrylate,
Isopropyl methacrylate, n-butyl methacrylate,
Methacrylate monomers such as isobutyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, glycidyl methacrylate, acrylamide, N-methylol acrylamide, methacrylamide, N-methylol methacrylamide, Examples include acrylamide or methacrylamide monomers such as acetone acrylamide, diacetone methacrylamide, and methylolated diacetone acrylamide. Examples of the ethylenically unsaturated monomer include styrene, aromatic monomers such as vinyltoluene, vinyl acetate, carboxylic acid vinyl esters such as vinyl propionate, acrylonitrile, methacrylonitrile, and the like. And unsaturated nitriles.

The acid value of the acrylic resin is 20 to 150, preferably 3
It is in the range of 0-100. When the acid value is less than 20, the polarization value of the electrodeposited coating film formed becomes high, so that it is difficult to form a second coating film on the coating film, which is not preferable.
If it is larger than 150, the water resistance of the coating film is undesirably deteriorated.

The hydroxyl value of the acrylic resin is 20 to 100, preferably 30
It is in the range of ~ 80. If the hydroxyl value of the resin is less than 20, the physical properties of the resulting coating film are poor. On the other hand, if the hydroxyl value exceeds 100, the water resistance of the coating film is inferior.

Conventionally known amino resins and blocked polyisocyanates are used as needed as the crosslinking agent. As the amino resin, a formaldehyde adduct of melamine, urea, benzoguanamine, acetoguanamine or a mixture thereof and an alcohol ether thereof are used, and the amino resin does not need to be water-soluble. Blocked polyisocyanate is a polyisocyanate compound with a blocking agent (eg, alcohol, phenol, etc.)
And isocyanate compounds such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, metaxylylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, and 4,4'-methylene bis (cyclohexyl isocyanate). And methylcyclohexane 2,4 (2,6) diisocyanate, 1,3- (isocyanatomethyl) cyclohexane, isophorone diisocyanate, trimethylhexamethylene diisocyanate, and the like.

The above-mentioned amino resin and blocked polyisocyanate may be used alone or in combination. Its use amount is 50% by weight or less in terms of resin solid content.

Ammonia, dimesylamine, ammonia and organic amines used as neutralizing agents for water-solubilization
Trimethylamine, diethylamine, triethylamine, diisopropylamine, butylamine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-methylethanolamine, N-aminoethylethanolamine, N
-Methyldiethanolamine, polyglycolamine and the like. These neutralizing agents are used in the range of 0.3 to 1.2 equivalents based on the carboxyl groups of the polycarboxylic acid resin.

In addition, hydrophilic organic solvents such as alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and butyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether to assist in solubilizing and dispersing the resin in water. Cellosolve solvents, propylene glycol ethers, diethylene glycol ethers and the like can be used. The amount of these solvents is used in the range of 0 to 10% by weight in the coating material (I).

The solid content of the coating material (I) thus obtained is about 3 to 20% by weight, preferably about 5 to 15% by weight, based on the solid content of the electrodeposition coating.

The coating (I) to be electrodeposited in the first step of the method of the present invention comprises (A) a polarization value of the electrodeposited coating film of 200 to 2500, preferably 300 to 2000.
It is. (A) When the electrodeposition coating polarization value is smaller than 200, the electrodeposition coating applied in the second step enters the electrodeposition coating applied in the first step, and a coating film separated into two layers cannot be obtained. , (A)
If the electrodeposition coating polarization value is greater than 2500, the paint applied in the second step is not preferable because it becomes difficult to form an electrodeposition coating film of a sufficient thickness on the electrodeposition coating film applied in the first step .

Further, the paint (I) is (C) the minimum electrodeposition current density (mA
The same unit is shown for / cm ² or less. ) It can have a value between 0.01 and 0.7, preferably between 0.05 and 0.6. (C) If the minimum electrodeposition current density is smaller than 0.01, the electrodeposition coating applied in the second step enters the electrodeposition coating applied in the first step, and a coating film separated into two layers is not formed. When the properties such as finishability and durability are inferior, on the other hand, when the (C) minimum electrodeposition current density is larger than 0.7, the paint applied in the second step is not sufficiently deposited on the electrodeposition coating film applied in the first step. It is not preferable because it is difficult to form an electrodeposited coating film having a large thickness.

The (A) electrodeposition coating polarization value and the (C) minimum electrodeposition current density of the paint (I) are determined by the above-mentioned carboxyl group-containing acrylic resin composition (for example, α, β-ethylenically unsaturated carboxylic acid content). Etc.), the cross-linking agent content, the type of neutralizing agent, the neutralization equivalent, the type of organic solvent, the amount of organic solvent, the solid content of the resin, etc., can be adjusted to fall within the above range.

As the electrodeposition paint (II) to be electrodeposited in the second step of the method of the present invention, a conventionally known anion-type fluororesin paint can be used. Specifically, for example, (1) tetrafluoroethylene, hexafluoropropene, chlorotrifluoroethylene,
An electrodeposition coating composition containing a resin obtained by mixing a homopolymer or a copolymer of a fluoroolefin such as vinylidene fluoride and vinyl fluoride as a vehicle component (for example, Japanese Patent Application Laid-Open No.
No. 87765), (2) an electrodeposition coating composition containing a carboxyl group-containing fluoropolymer as a vehicle component (for example, JP-A-62-59676, JP-A-62-127362, etc.), ( 3) Monomers having a perfluoroalkyl group or a perfluoroalkenyl group at one end and having an ethylenic double bond at the other end (eg, perfluorooctylethyl methacrylate, perfluoroisononylethyl methacrylate, etc.) 56-167139), said α, β
-An electrodeposition coating composition containing a copolymer containing an ethylenically unsaturated carboxylic acid and the above-mentioned hydroxyl group-containing acrylic monomer as an essential monomer component as a vehicle component can be suitably used. In the composition, a cross-linking agent such as the amino resin and the blocked isocyanate described above can be used.

The paint (II) to be electrodeposited in the second step of the method of the present invention is:
(B) The polarization value of the electrodeposited coating film is the same as or smaller than the polarization value of the (A) electrodeposition coating film.
Preferably it is 600. (B) Electrodeposition coating polarization value is (A)
If the electrodeposition coating film polarization value is larger than the electrodeposition coating film applied in the second step, the electrodeposition coating film applied in the first step enters the electrodeposition coating film applied in the first step, and a coating film separated into two layers cannot be obtained. (A)
If the difference from the electrodeposition coating polarization value is greater than 1500, the paint applied in the second step is difficult to form an electrodeposition coating film of sufficient thickness on the electrodeposition coating applied in the first step It is not preferable.

The paint (II) is the same as or smaller than the (C) minimum electrodeposition current density.
It is advantageous to have a (D) minimum electrodeposition current density of 0.6, preferably up to 0.4. (D) When the minimum electrodeposition current density is larger than the above (C) minimum electrodeposition current density, the electrodeposition coating film applied in the second stage enters the electrodeposition coating film applied in the first stage and is separated into two layers. Since no film is formed, the properties such as finishability and durability of the coating film are inferior. On the other hand, if the difference between the minimum electrodeposition current density (D) and the minimum electrodeposition current density (C) is larger than 0.6, the two-step The paint applied to the eyes is not preferable because it becomes difficult to form an electrodeposited film having a sufficient thickness on the electrodeposited film applied to the first step.

The (B) electrodeposited coating polarization value and the (D) minimum electrodeposition current density of the paint (II) are the carboxyl group-containing acrylic resin composition, a neutralizing agent type, a neutralization equivalent, an organic solvent type,
It can be adjusted so as to be within the above range depending on the fluctuation factors such as the amount of the organic solvent and the solid content of the resin. However, it generally depends on the type of the above-mentioned anionic fluororesin paint (1) to (3). However, fluorine resin acid value 20-150, preferably 30-100, neutralization equivalent 0.3-1.5, preferably 0.6-1.
2. The amount of the organic solvent (for example, the hydrophilic organic solvent) is 0 to 10% by weight, preferably 2 to 8% by weight, and the resin solid content is 3 to 20% by weight, preferably 5 to 15% by weight.

In the present invention, the `` minimum electrodeposition current density '' is the surface area 1c
cathode platinum plate insulated back surface of m ^2, also using a coated article as an anode, placed in electrodeposition coating bath at a distance of 15cm to both surfaces of facing. When a constant current is applied at 22 ° C without stirring and the time and voltage are recorded, the current density is changed, and a sharp increase in voltage due to resistance increase due to electro-deposition of the paint occurs in 3 minutes or in the vicinity of more than 3 minutes. The current density (mA / cm ² ).

The “electrodeposited coating polarization value” is a stainless steel plate (area 100c
m ² ) as the cathode and the object to be coated (area 200 cm ² ) as the anode,
It is placed in the electrodeposition coating bath at a distance of 15 cm so that both surfaces face each other. Electrodeposition coating thickness (dry) at 22 ℃ without stirring
This is a value obtained by conducting a current for 3 minutes at a constant voltage so as to be 10 μm, calculating a current value for 3 minutes, and calculating a polarization value of an electrodeposited coating film based on the following equation.

The object used in the above-mentioned "minimum electrodeposition current density" and "polarization value of electrodeposition coating film" was a JIS A-60635 aluminum alloy plate which was anodized (alumite film thickness 10 µm). When a material other than the above (for example, a zinc phosphate-treated steel plate) is used as the object to be coated, the numerical values described in the present invention slightly change. Therefore, in the case of representing the "minimum electrodeposition current density" and "electrodeposition coating polarization value" in the coated object other than the above, the anodized plate and the other coated object are measured by the above-described measuring method. It can be expressed (converted) by measuring.

In the present invention, a coloring pigment, an extender pigment or the like can be added to the anionic acrylic resin electrodeposition paint (I) and the anion type fluorine resin electrodeposition paint (II) as needed. When the pigment is added, the minimum electrodeposition current density and electrodeposition coating polarization value of the electrodeposition paint (I) and the electrodeposition paint (II) containing the pigment must be within the above-mentioned ranges. . The amount of the extender pigment can be used without any particular limitation, but the extender pigment in the electrodeposition paint (II) is the same as the electrodeposition paint (I).
It is preferable to use the same amount as or less than the extender pigment. The blending amount of the extender pigment in the electrodeposition paint (I) is preferably 100 g of the resin component in the electrodeposition paint (I) because the finally formed composite coating film has excellent smoothness and durability. The total oil absorption (JIS K5101-78) of the pigment is about 1,000 or less.

As the article to be used in the method of the present invention, a material having conductivity, for example, iron, steel, copper, aluminum, a steel plate, a plated steel plate plated with zinc, tin, chromium, aluminum or the like, a steel surface having chrome Metal materials and the like which are chemically or electrolytically treated with an acid, phosphoric acid, or the like can be given. Among them, anodized aluminum articles having various shapes (for example, plate, rod, enamel, etc.) are preferred.

In the present invention, as a method and an apparatus for electrodepositing an object to be coated using an anionic acrylic resin electrodeposition paint (I) and an anion type fluorine resin electrodeposition paint (II), anodic electrodeposition coating has conventionally been used. The methods and devices known per se used in the above can be used. Adhesive coating conditions that can be used are generally a bath temperature of 20 to 30 ° C and a voltage of 100 to 400V.
(Preferably 100 to 300 V), and it is preferable to perform electrodeposition in a current supply time of 30 seconds to 10 minutes.

The film thickness (dry state) of the first-stage electrodeposition coating film formed by using the above-mentioned electrodeposition coating method is 5 to 50 μm, preferably 7 to 30 μm.
μ, and the thickness (dry state) of the second electrodeposition coating film formed thereon is 0.5 to 30 μm, preferably 2 to 20 μm.
It is better to be in the range of μ.

Further, the coating film formed by the first electrodeposition coating can be subjected to the second electrodeposition coating without washing, but the first electrodeposition coating bath is used in the second electrodeposition coating bath. Since the electrodeposition paint may be mixed, it is preferable to perform the second-stage electrodeposition coating after washing the first-stage electrodeposition coating film.

In the present invention, the second-stage electrodeposition coating is performed in an uncured state of the first-stage electrodeposition coating, but the first-stage electrodeposition coating film is heated at, for example, 100 ° C. for about 10 minutes, or heated with hot air. It may be carried out in an uncured state by heating to such an extent that is removed.

The electrodeposited coating film formed on the workpiece is
Bake at 20 ° C, preferably 160-200 ° C. The overall electrodeposited coating thickness is generally about 5 to 80μ, preferably about 7 to 70μ.
Is desirably within the range.

(Effects and Effects of the Present Invention) When the first and second electrodeposition coatings are performed based on the method of the present invention, the surface of the electrodeposition coating film coated in the first step is changed to the surface of the electrodeposition coating film coated in the second step. The coating film is deposited on the upper surface, and the first electrodeposition layer and the second electrodeposition layer are formed in a multi-layer state. Furthermore, in the formation of the baked coating film of the multilayer coating film, the coating film is formed in a form separated from the first electrodeposition layer because the second electrodeposition layer contains a fluororesin component. from these things,
The first-stage electrodeposition coating film has excellent adhesion to an object to be coated, and the second-stage electrodeposition coating film has excellent weather resistance and coating surface smoothness.

(Example) The present invention will be described more specifically. In the examples, “parts” and “%” are based on weight.

(Preparation of Anionic Acrylic Resin Electrodeposition Paint (I)) Commercially available acrylic-melamine-based electrodeposition paint clear stock solution (trade name, “Elecron AG100” manufactured by Kansai Paint Co., Ltd., resin solid content 30%) and deionized water 100 And 200 parts by weight, to obtain an electrodeposition paint having a resin solid content of 10%, a neutralization equivalent of 0.8, and an organic solvent amount of 5%.

(Preparation of anion type fluororesin electrodeposition paint (II)) In an autoclave (withstand pressure of 50 kg / cm ² ), 106 parts of hydroxybutyl vinyl ether (hereinafter referred to as HBVE), 60 parts of diglyme, 180 parts of i-propanol and N-dimethyl After 1 ml of benzylamine was charged and the space was replaced with nitrogen, 116 parts of chlorotrifluoroethylene was added, and the mixture was heated to 65 ° C.

Next, a mixture 4 of diglyme / i-propanol (1/1 by weight) in which 2.5 parts of azobisisobutyronitrile was dissolved was used.
0 parts were added to initiate the polymerization. While stirring, bring the temperature to 20
Time kept. 475 parts of a varnish having a solid content of 42% were obtained.

The solvent was removed by reducing the pressure while heating the varnish to 60 to 80 ° C.

Next, 109 parts of 1,2-cyclohexanedicarboxylic anhydride (100 μm) of zirconium naphthenate was added to the varnish while stirring, and the mixture was reacted for 5 hours while heating and refluxing acetone.

Further, after the obtained reaction product was cooled to room temperature, a mixture of 70 parts of triethylamine (neutralizing agent) and butyl cellosolve was added dropwise over 1 hour with stirring, to obtain a varnish containing a fluorine-containing copolymer. .

400 parts of deionized water is added to the obtained varnish, the solid content temperature is adjusted to 40%, and the hydroxyl value and acid value of the fluorinated copolymer are determined by JI.
When measured by the method described in S K 0070, 2 each
5 and 100.

Next, 7.4 parts by weight of 80% methylmethylolated melamine resin (manufactured by Hitachi Chemical Co., Ltd., Melan 620, solid content 70%) was added to 100 parts of the varnish, and mixed well so as to be uniform. 269 g of deionized water was added to the mixture to adjust the solid content to 12% (butyl cellosolve 0.5%) to prepare a composition to be subjected to electrodeposition coating.

Example 1 In the electrodeposition paint (I) bath, alumite treatment was performed.
63S aluminum alloy plate (alumite film thickness 10μm)
Was used as an object to be coated (anode), a current was applied at a bath temperature of 22 ° C. and a voltage of 150 V for 3 minutes to form a coating film of electrodeposition paint (I) on the object to be coated, and the first-stage electrodeposition coating was performed.

Next, after washing the painted material obtained in the first painting with water,
The coated product was used as an anode, and a current was applied at a voltage of 140 V for 3 minutes in an electrodeposition coating (II) bath (22 ° C.) to perform second-stage electrodeposition coating, followed by washing with water.

Example 2 In Example 1, the melamine resin of the electrodeposition paint (II) was used.
The first step was conducted in the same manner as in Example 1 except that the minimum electrodeposition current density (mA / cm ² ) and the electrodeposited coating film polarization value (kΩ · cm ² ) shown in Table 1 were changed from 7.4 parts to 3.7 parts. And the second stage electrodeposition coating was performed.

Example 3 In Example 1, the melamine resin of the electrodeposition paint (II) was used.
The first and second electrodeposition coatings were carried out in the same manner as in Example 1 except that 7.4 parts was changed to 11.1 parts and the minimum electrodeposition current density and electrodeposition coating film polarization value shown in Table 1 were used.

Example 4 In the same manner as in Example 1 except that the butyl cellosolve content of electrodeposition coating (II) was set to 0.5% and the minimum electrodeposition current density and electrodeposition coating film polarization value shown in Table 1 were set to 0%. The first and second electrodeposition coatings were performed.

Comparative Example 1 In Example 1, the electrodeposition coating (II) was used as the first electrodeposition coating instead of the electrodeposition coating (I), and the electrodeposition coating (II) was used as the second electrodeposition coating instead of the electrodeposition coating (II). The first and second electrodeposition coatings were performed in the same manner as in Example 1 except that the paint (I) was used instead.

After the electrodeposition coating films obtained in Examples and Comparative Examples were baked at 180 ° C. for 30 minutes, the coating surface was tested for smoothness, gloss, pencil hardness, glutinous adhesiveness, alkali resistance, weather resistance and the like.
These results are summarized in Table 1.

Coating surface smoothness: The appearance of the coating film after coating was observed with the naked eye, and the peeled skin, pinholes, irregularities, and appearance were examined.

Gloss: Specular reflectance (unit:%) was measured using a gloss meter (VG-2PD manufactured by Nippon Denshoku Industries Co., Ltd.).

Adhesiveness on squares: 1 square 1 mm square on the coating with a cutter knife
00 cuts were made and a peel test was performed 10 times with a cellophane adhesive tape to determine the number of remaining meshes.

Alkali resistance: 72% in 3% by weight aqueous sodium hydroxide solution
The appearance of the coating film after immersion for a period of time was visually observed, and the presence or absence of blister generation was examined.

Weather resistance: Accelerated weather resistance test was conducted for 240 hours using a weather meter (manufactured by Suga Test Instruments Co., Ltd., Dew cycle, irradiation 60 minutes / dark 60 minutes, black panel temperature 63 ° C), and gloss retention (unit:%) and The appearance was measured.

Claims (3)

(57) [Claims] 1. An electrodeposition coating of an anionic acrylic resin (I) having a polarization value (kΩ.cm ² ) of 200 to 2500 as an electrodeposition coating film on a surface to be coated as a first step. After forming the film by the second step, (B) the electrodeposition coating polarization value (kΩ ·
When the cm ² ) is the same as or smaller than (A) the electrodeposition coating polarization value (kΩ · cm ² ), the difference is up to 1500. A method for forming a highly durable anion electrodeposition coating film, comprising coating, coating and then heating. 2. An anionic acrylic resin electrodeposition paint (I)
The method according to claim 1, wherein (C) has a minimum electrodeposition current density (mA / cm ² ) of 0.01 to 0.7. 3. An anionic fluororesin electrodeposition paint (II)
Is the same or smaller than (C) the minimum electrodeposition current density (mA / cm ² ), and when it is small, the difference is up to 0.6 (D)
^{2. The} method according to claim 1, having a minimum electrodeposition current density (mA / cm ² ).