JP2866415B2 - Painting method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coating method, and more particularly, to two kinds of cations having different functions for a coating object having many edges such as an automobile body and an automobile part. After electrodeposition coating twice with electrodeposition paint, apply middle coat or top coat,
The present invention relates to a coating method that achieves both high finish of a general outer panel and high corrosion resistance of an edge.

(Conventional technology and its problems) Conventionally, the edge portion (generally, burr height: 0.03 mm or more)
When the object to be coated is subjected to cationic electrodeposition coating and then baked, a coating film with excellent smoothness is obtained in the general part due to heat flow, but the base material is exposed at the edge part and the uncoated state It becomes easy to rust. Therefore, in order to improve the edge cover properties, various proposals have been made such as an edge cover electrodeposition paint and a two-coat one-bake type double-coat electrodeposition paint. However, it is difficult to achieve both edge corrosion protection and finish, and in practice, It is a situation that has to sacrifice the finish to some extent, and even if a middle coat or a top coat is applied on such a coated surface, it goes without saying that a good finish can not be obtained, edge corrosion protection and finish It has been desired to develop a coating method that can satisfy both performances.

(Means for Solving the Problems) The present inventors have conducted intensive studies in order to achieve both high edge coverability and high finishability. As a result, the first electrodeposition coating has good thermal fluidity. Painted and baked coating, ensure high finish of general parts other than edges,
A second electrodeposition coating is performed on the unpainted portion where the base material such as the edge portion is exposed by baking, using an electrodeposition paint containing a particulate component, and applying an intermediate coating or a top coating in an uncured state. At the same time, it was found that by baking, the edge portion could be sufficiently covered while maintaining high finish, and the present invention was completed.

That is, the present invention applies a cationic electrodeposition coating material (A) having a minimum melt viscosity of 10 ² cps or less at the time of curing of an obtained coating film to an object to be coated having an edge portion, and after baking, applying a cationic electrodeposition coating material. The minimum melt viscosity at the time of curing of the resulting coating film is mainly composed of a conductive resin and a particulate component, and is 10 ³ to 10 ⁸ cp
The present invention relates to a coating method characterized by applying a cationic electrodeposition paint (B) as s, applying an intermediate coat or a top coat in an uncured state, and baking the paint at the same time.

In the present invention, the cationic electrodeposition paint (A) is a paint to be first electrodeposited, and contains a cationic electrodeposition resin as a main component.

As the cationic electrodeposition resin, any of conventionally known epoxy resin, acrylic resin, and polybutadiene resin can be used, and epoxy resin is particularly preferably used.

Such epoxy resin systems include polyamine resins such as amine-added epoxy resins, for example, (i) adducts of polyepoxides with primary mono- and polyamines, secondary polyamines or mixed primary and secondary polyamines (eg, US Pat. No. 3,984,299): (ii) adducts of polyepoxide compounds with ketiminated secondary mono- and polyamines having primary amine groups (see, for example, U.S. Pat. No. 4,017,438); (iii) polyepoxide compounds and ketiminated For example, a reaction product obtained by etherification with a hydroxy compound having a primary amino group (see, for example, JP-A-59-43013) can be used. The polyepoxide compound used in the production of the above polyamine resin has an epoxy group Is a compound having two or more in one molecule, generally those having a number average molecular weight of at least 200, preferably 400 to 4,000, more preferably 800 to 2,000 are suitable, especially the polyphenol compound and epichlorohydrin Those obtained by the reaction are preferred. Examples of the polyphenol compound that can be used for forming the polyepoxide compound include bis (4-hydroxyphenyl) -2,
2-propane, 4,4'-dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-butyl- Phenyl) -2,2-
Propane, bis (2-hydroxynaphthyl) methane, 1,
5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl)
1,1,2,2-ethane, 4,4'-dihydroxyphenyl sulfone, phenol novolak, cresol novolak and the like.

The polyepoxide compound may be partially reacted with a polyol, a polyether polyol, a polyester polyol, a polyamidoamine, a polycarboxylic acid, a polyisocyanate compound, or the like, and further, graft polymerization of ε-caprolactone, an acrylic monomer, or the like. It may be made to be.

The amine-added epoxy resin can be cured, if necessary, using a crosslinking agent such as a polyisocyanate compound blocked with an alcohol or the like or a melamine resin.

Further, a self-crosslinking type amine-added epoxy resin which can be cured without using the above-mentioned crosslinking agent can also be used. For example, a resin in which a β-hydroxyalkyl carbamate group is introduced into a polyepoxide substance (for example, Japanese Patent Application Laid-Open No. JP-A-155470); a resin which can be cured by a transesterification reaction (for example, see JP-A-55-80436); a resin in which a blocked isocyanate group is introduced into a base resin, and the like can also be used.

One or more of the amine-added epoxy resins listed above can be selected and used as the cationic electrodeposition resin, and when weather resistance is required, an amino group-containing acrylic resin having excellent weather resistance or A nonionic acrylic resin can be used in combination with the above amine-added epoxy resin.

In the present invention, the cationic electrodeposition coating composition (A) may contain, if necessary, a usual coating additive, for example, a coloring pigment such as carbon black, titanium white, and red bean;
An extender pigment such as calcium carbonate; a rust-preventive pigment such as strontium chromate, lead chromate or lead silicate; or other additives may be added. Other additives include, for example, dispersing aids (nonionic surfactants); anti-cissing agents (acrylic resin, fluororesin, silicon resin, etc.) on the coated surface; curing accelerators (eg, lead, bismuth, tin, etc.) Metal salt) and the like.

The cationic electrodeposition coating composition (A) can be appropriately diluted with deionized water so that the solid content concentration is about 5 to 25% by weight and the pH is about 55 to 8. In the present invention, as a method and an apparatus for performing electrodeposition coating on an object to be coated using the cationic electrodeposition coating (A), a known method and apparatus conventionally used in cationic electrodeposition coating are used. be able to. At this time, it is desirable to use a coating object as a cathode and use stainless steel # 316, preferably ferrite metal, as an anode. Electrodeposition conditions that can be used are not particularly limited, but generally, bath temperature: 15 to 35 ° C (preferably 20 to 30 ° C), voltage: 100 to 400V
(Preferably 200 to 300 V), current density: 0.01 to 3 A / dm ² , energization time: 30 seconds to 10 minutes, pole area ratio (A / C): 6/1 to 1/6, distance between poles: 10 to It is desirable to perform electrodeposition under a stirring condition of 100 cm.

The electrodeposition coating film formed on the object to be coated can be cured by baking at about 100 to 200 ° C., preferably 100 to 180 ° C. after washing with deionized water or the like.

The thickness (dry state) of the electrodeposition coating film formed by the cationic electrodeposition coating material (A) is preferably in the range of 5 to 30 μm, and more preferably 10 to 25 μm.

In the present invention, the cationic electrodeposition coating material (A) needs to have good thermal fluidity, and the minimum melt viscosity of the coating film obtained from the coating material upon curing is 10 ² cps or less.
The coating film thus obtained has good smoothness due to heat flow at the time of baking, and the baking exposes a base material at an edge portion or the like.

In the present invention, the cationic electrodeposition paint (B) is a paint to be electrodeposited for the second time, and contains a cationic electrodeposition resin and a particulate component as main components. In the second electrodeposition coating, in the first electrodeposition coating, an electrodeposition coating film is selectively formed on an unpainted portion such as an edge portion where the substrate is exposed due to heat flow during baking due to a difference in electric resistance.

As the cationic electrodeposition resin that can be used for the cationic electrodeposition paint (B), any of conventionally known epoxy resin systems, acrylic resin systems, and polybutadiene resin systems can be used, and epoxy resin systems are particularly preferable. used.
As such an epoxy resin, one or more types can be selected from the amine-added epoxy resins listed in the description of the cationic electrodeposition resin of the cationic electrodeposition paint (A).

In the present invention, it is desirable that the cationic electrodeposition resin used for the cationic electrodeposition coating material (B) has good compatibility with the cationic electrodeposition resin used for the cationic electrodeposition coating material (A). As a result, the boundary portion between the first and second electrodeposition coating films is sufficiently covered, which contributes to the improvement of the corrosion resistance.

The particulate component that can be used in the cationic electrodeposition coating composition (B) in the present invention is not particularly limited as long as it controls the decrease in the viscosity of the molten coating film during baking. It is preferable to select one or more. Examples of the gelled polymer fine particles that can be used in the cationic electrodeposition coating composition (B) in the present invention include (i) a vinyl double bond as proposed in Japanese Patent Application No. 63-54965 or the like. A polymerizable unsaturated vinylsilane monomer containing a hydrolyzable alkoxysilane group, and (b) a polymerizable unsaturated monomer containing a vinylic double bond and a cationic group as essential monomer components, and Accordingly, an acrylic resin obtained by copolymerizing (c) a polymerizable unsaturated monomer containing a vinylic double bond and a hydroxyl group, and / or (d) a monomer mixture containing a polymerizable unsaturated monomer other than the above. Gelled polymer microparticles obtained by dispersing the copolymer in water and cross-linking within the particles; (ii) as proposed in Japanese Patent Application No. 63-213661, etc.
Gelled polymer microparticles obtained by mixing the acrylic copolymer with cationic acidic colloidal silica and dispersing in water; (iii) as proposed in Japanese Patent Application No. 63-19970.
In the above unsaturated monomers (a) to (d), instead of (b), a polymerizable monomer containing at least two radically polymerizable unsaturated groups in a molecule is used, and the unsaturated monomers are Gelled polymer fine particles obtained by emulsion polymerization using a cationic reactive emulsifier containing an allyl group in the molecule are exemplified.

In the present invention, when any of the above gelled polymer fine particles is blended in the cationic electrodeposition coating composition (B), the blending amount of the gel polymer fine particles is based on the total resin solid content including the cationic electrodepositable resin. 1 to 50% by weight, further 3 to 35% by weight
It is preferred that When the content of the gelled polymer fine particles in the cationic electrodeposition paint (B) is less than 1% by weight based on the total resin solid content, the effect of controlling the thermal fluidity during baking of the electrodeposition coating film is obtained. If it is small, the edge coverage of the electrodeposition coating film tends to be insufficient, while if it exceeds 50% by weight,
It is not preferable because the workability of the electrodeposition coating is somewhat reduced.

When using the gelled polymer fine particles, if necessary, coloring pigments such as titanium white, carbon black, red iron, and graphite as other particulate components; volume pigments such as takul, calcium carbonate, mica, clay, and silica; Rust preventing pigments such as strontium chromate, lead chromate and lead silicate may be used in combination.

When only a pigment is selected as the particulate component of the cationic electrodeposition paint (B), the amount of the pigment usually used in the electrodeposition paint can be larger than the usual compounding amount.
It is preferable to blend the above pigments, for example, silicon dioxide pigments such as anhydrous silicon dioxide and water-containing amorphous silicon dioxide, and carbon-based pigments in an amount of 5% by weight or more based on the total pigment content. In that case, the total oil absorption of all the pigments used is 1,
More preferably, it is in the range of 0000 to 10,000.

Thus, the cationic electrodeposition paint (B) obtained from the cationic electrodeposition resin and the particulate component has a minimum melt viscosity of 10 ³ to 1 when the coating film obtained from the paint is cured.
0 ⁸ , preferably in the range of 10 ⁴ to 10 ⁸ cps, is indispensable from the viewpoint of edge coverage. In the present invention, the minimum melt viscosity refers to the minimum value when the viscosity of the coating film once becomes lower than the initial value in the process of curing the coating film by baking, and the viscosity of the coating film rapidly increases thereafter. To go. Such a minimum melt viscosity is determined from the heat-fluid appearance of a scratch mark in comparison with a paste having a known viscosity in accordance with the ball rolling type viscosity measurement method described in JIS-Z-0237.

The cationic electrodeposition paint (B) consumes less than the cationic electrodeposition paint (A) although it depends on the shape of the object to be coated.
Since the electrodeposition bath will be used for a long time, the bath concentration is preferably lower than usual. Therefore, the cationic electrodeposition paint (B) is appropriately diluted with deionized water so that the solid content concentration is about 3 to 20% by weight, preferably 5 to 18% by weight, and the pH is in the range of about 5.5 to 8. It is appropriate to adjust.

In the present invention, a method and an apparatus for performing electrodeposition coating using a cationic electrodeposition paint (B) on an unpainted edge portion of an object on which an electrodeposition coating film has already been formed by the cationic electrodeposition paint (A). Can be used in the same manner as in the method and apparatus used in the cationic electrodeposition paint (A). Among them, the energization time may be the same as the time required in the cationic electrodeposition paint (A).
Even with 1/4 to 1/2, the cationic electrodeposition paint (B) can be sufficiently applied to the unpainted portion of the object to be coated.

In the present invention, after applying the cationic electrodeposition coating (B), an intermediate coating or a top coating is applied in a state where the coating is uncured. Here, after applying the cationic electrodeposition coating (B), the coating may be washed with water, and the portion may be heated for a short time at a temperature of, for example, 100 ° C. or less, or may be heated to remove moisture with hot air. It should be understood that the “uncured state” in the present invention includes a semi-cured state.

In the present invention, the intermediate coating or the top coating is an acrylic resin, a polyester resin, an alkyd resin as a base resin,
Conventional resins using one or more conventionally known resins such as epoxy resins and silicone resins can be applied.
As a curing agent for curing the base resin, an amino resin (melamine / formaldehyde resin, urea / formaldehyde resin, etc.), polyisocyanate, or the like is used.

In the present invention, the intermediate coating or the top coating is coated on the substrate on which the electrodeposition coating film is formed, by a known method such as an air spray method, an airless spray method, and an electrostatic coating method, and then baked. It is baked simultaneously with the coated portion of the cationic electrodeposition paint (B) such as an edge portion. When the intermediate coating is applied on the electrodeposition coating film, the above-mentioned upper coating is applied thereon.

According to the method of the present invention, the electrodeposition coating film formed by the first electrodeposition coating obtains good smoothness due to the heat flow at the time of baking, while an unpainted portion occurs at an edge portion or the like, and the uncoated portion is formed. By forming an electrodeposition coating film on the painted part by the second electrodeposition coating, the finish (smoothness) of the general part other than the edge part is kept at a high level, and the corrosion resistance of the edge part and the like is secured. In addition, in the state where the electrodeposition coating film formed by the second electrodeposition coating is in an uncured state, an intermediate coating or a top coating is applied repeatedly,
Simultaneous baking enabled simplification of the process and further edge coverage due to curing of the applied layer, as well as finishability. Accordingly, the method of the present invention can be widely applied as a coating method in the field of industrial coatings, such as automobiles and electric equipment, where both finishability and corrosion resistance are highly required.

(Examples) Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. In the present invention and Comparative Examples, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively.

Examples 1-4 and Comparative Examples 1-3 Electrodeposition paints A-1 and B- obtained with the formulations shown in Table-1.
Electrodeposition coating was performed according to the conditions in Table 2 with the combinations of Tables 1 to B-4 in Table 3, and the intermediate coating and the top coating were further coated in Table 3
The test plate was obtained by spray coating as shown in Table 1. The coating results and coating film performance are also shown in Table-3. Table-
The amount of 1 is a solid content.

In the table,-and (* 1) to (* 4) are as follows.

Kansai Paint Co., Ltd. Electron HB-2000L clear (water-based epoxy polyamide resin, block polyisocyanate compound) Kansai Paint Co., Ltd. Electron No. 9400 clear (water-based epoxy polyamine resin, block polyisocyanate compound) Kansai Paint Co., Ltd. ) Elecron LT-100 clear (aqueous epoxy polyamine resin, block polyisocyanate compound) Internally crosslinked gelled polymer fine particle dispersion: The production method is shown below.

In a flask equipped with a stirrer, thermometer, cooling tube and heating mantle, put 320 parts of isopropyl alcohol,
While stirring, the temperature was raised to the reflux temperature, and styrene 272 was added thereto.
Parts, n-butyl acrylate 224 parts, 2-hydroxyethyl acrylate 80 parts, dimethylaminoethyl methacrylate 144 parts, KBM-503 ^** 80 parts, azobisisobutyronitrile 24 parts and a mixture of a polymerization initiator at a reflux temperature. For about 2 hours. Then after stirring for another 30 minutes,
A solution prepared by dissolving 8 parts of azobisdimethylvaleronitrile in 120 parts of isopropyl alcohol was added dropwise. After stirring, 320 parts of isopropyl alcohol was added and cooled to obtain an acrylic copolymer varnish. 780 parts of this acrylic copolymer varnish and 6.4 parts of acetic acid were added to two flasks, and stirred at about 30 ° C. for 5 minutes.
Drop over a minute, heat to 75-80 ° C and stir for about 3 hours,
A dispersion of gelled polymer fine particles having a solid content of 20% and crosslinked in the particles was obtained.

Cationic acidic colloidal silica-containing gelled polymer fine particle dispersion: acrylic copolymer varnish 48 obtained above
Add 0 parts to 2 flasks, and stir with stirring cationic acidic colloidal silica dispersion "Adelite CT-300"
(Asahi Denka Kogyo Co., Ltd., solid content 20%) 196 parts and acetic acid
Add 4.0 parts and stir at about 30 ° C for 5 minutes.
The mixture was added dropwise over about 30 minutes under strong stirring, the temperature was raised to 75 to 80 ° C., and the mixture was stirred for about 3 hours to obtain a dispersion of gelled polymer fine particles having a solid content of 20%.

Gel Polymer Fine Particle Dispersion Using Cationic Reactive Emulsifier: The production method is shown below.

In a flask equipped with a stirrer, thermometer, cooling tube and heating mantle, 3,507.5 parts of deionized water and latemul K
80 parts of -180 (manufactured by Kao Corporation, 25% aqueous solution) was added, and the temperature was raised to 90 ° C with stirring. In addition to this, the polymerization initiator VA
−086 (Wako Pure Chemical Industries, Ltd.) 12.5 parts deionized water 500
20% of the aqueous solution mixture dissolved in the part was added. After 15 minutes,
Styrene 430 parts, n-butyl acrylate 440 parts, 1,6-
5% of a mixture of 40 parts of hexanediol diacrylate, 40 parts of 2-hydroxyethyl acrylate and 50 parts of KBM-503 ^** were added. Then, after stirring for further 30 minutes, the remaining monomer mixture and the aqueous polymerization initiator solution were added dropwise, and after the addition was completed, 30 minutes.
After maintaining at 90 ° C. for 90 minutes, the mixture was cooled to room temperature to obtain a dispersion of gelled polymer fine particles having a solid content of 20%.

** KBM-503: γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.) (* 1) When using the resin, the cationic electrodepositable resin is dispersed in water with acetic acid at a neutralization equivalent of 0.55. The base number of each of the cationic electrodepositable resins is 80.

(* 2) Scaly graphite made by Chuetsu Graphite Company.

(* 3) A product made by Fuji Devison, trade name, water-containing amorphous silicon dioxide pigment (oil absorption 300).

(* 4) Product name, basic lead silicate, manufactured by Kikuchi Pigment Industry Co., Ltd.

In the table, (Note 1) to (Note 8) are as follows.

(Note 1) Luga Bake KPX-36: manufactured by Kansai Paint Co., Ltd.
Intermediate coating (polyester / melamine / formaldehyde resin) (Note 2) Amirac sealer: manufactured by Kansai Paint Co., Ltd.
Intermediate coating (alkyd / melamine / formaldehyde resin) (Note 3) Lugave B-326: manufactured by Kansai Paint Co., Ltd.
Topcoat (polyester / melamine / formaldehyde resin) (Note 4) Amirac # 002: Kansai Paint Co., Ltd. Topcoat (alkyd / melamine / formaldehyde resin) (Note 5) Asukabake MG-500: Kansai Paint Co., Ltd. ),
Water-based topcoat (acrylic emulsion / water-based melamine ・
(Formaldehyde resin type) (Note 6) The melt viscosity of the electrodeposition coating (B) is JIS-
According to the rolling ball type viscosity measurement method described in Z-0237, it was measured from the appearance of heat fluidity of a scratch mark in comparison with a paste having a known viscosity. The numerical value of the melt viscosity was indicated by the lowest viscosity, cps.

(Note 7) Finishability: The finish of the general part other than the punched part of the painted plate is measured by a PGD meter (Portable Gloss and Distinctness).
The angle was fixed at 90 ° and the measurement was performed.

(Note 8) Edge corrosion protection: A salt water spray test was carried out on a coated plate having a punched part by electrodeposition coating according to JIS-Z-2371, and the number of chain points generated in the punched burr part after 240 hours was measured. And the number was evaluated.

Claims (1)

(57) [Claims] An object having an edge portion is coated with a cationic electrodeposition coating material (A) having a minimum melt viscosity of 10 ² cps or less when the obtained coating film is cured, and after baking, a cationic electrodeposition coating is applied. as main components rESIN and particulate components, and the minimum melt viscosity at the time of curing the resulting coating film is painted a cationic electrodeposition paint (B) is 10 ³ to 10 ⁸ cps, paint is uncured A coating method, wherein an intermediate coating or a top coating is applied and baked simultaneously.