JP2000239576A - Cationic electrodeposition coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the amount of a generated gas at the time of electrodeposition, efficiently carry out a cationic electrodeposition coating and obtain a high-quality automotive body, etc., by coating a material to coated with a cationic electrodeposition coating material, baking the coating material, then coating a cationic electrodeposition coating material and baking the coating material. SOLUTION: A material which is to be coated and has a complicated shape such as an automotive part is coated with (A) a cationic electrodeposition coating material prepared by including a nonionic surfactant having 5-25 mg equivalents(MEQ) and 5-20 hydrophile-lipophile balance(HLB) such as a polyoxyethylene alkyl ether in an amount of 0.1-10 wt.%, preferably 0.2-5 wt.% in the solid matter of the electrodeposition coating material and the formed coating film is then baked. The resultant coated material is subsequently coated with (B) a cationic electrodeposition coating material and the resultant coating film is further baked to conduct the cationic electrodeposition coating. A substrate resin component used in the cationic electrodeposition coating material (B) is preferably good in compatibility with the substrate resin of the cationic electrodeposition coating material (A).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cationic electrodeposition coating method, and more particularly, to a method for applying two types of cationic electrodeposition coatings having different functions to an object having a complicated shape such as an automobile body or an automobile part. The present invention relates to a cationic electrodeposition coating method capable of achieving both high finish of a general outer plate portion and high corrosion resistance of an inner plate portion and an edge portion by performing two coats and two baking.

[0002]

2. Description of the Related Art Cationic electrodeposition is usually performed by
Although a coating film with excellent smoothness is obtained due to the heat flow of the wet film in the baking process, even at the edge portion or the bag portion, even if the coating film is formed by concentration of current in the state of the wet film before baking, There was a problem that the base material was exposed at the edge portion and the like due to the heat flow in the baking stage, so that it was unpainted and rust easily. Therefore, conventionally, the edge coverage has been improved by adopting an edge-cover electrodeposition paint or a two-coat one-bake type double-coat electrodeposition paint, but it is difficult to achieve both edge coverage and finish. Actually, however, the finish was somewhat sacrificed.

In order to solve the above-mentioned problem, the applicant of the present invention has made two coats and two bake using two kinds of cationic electrodeposition paints including an electrodeposition paint having excellent edge coverage, so that a general outer plate portion is formed. We have proposed a cationic electrodeposition coating method that can achieve both high finish and high corrosion resistance at the edge (Japanese Patent Laid-Open No.
223496, JP-A-6-57496). However, in recent years, there has been an increasing demand for a specification in which the intermediate coating is omitted and the topcoat is directly applied to the electrodeposition coating film surface, and further improvement in finishability has been desired.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, in two coats and two bake, the MEQ was lowered and a specific amount of a nonionic surfactant was blended. The present inventors have found that the use of the resulting cationic electrodeposition coating for the first electrodeposition coating can ensure a high finish of the general outer panel portion corresponding to the intermediate coating less, and have reached the present invention.

That is, according to the present invention, an object to be coated has an MEQ of 5
25 to 25, and 0.1 to 10% by weight of a nonionic surfactant contained in the solid content of the electrodeposition coating composition. An object of the present invention is to provide a cationic electrodeposition coating method characterized by coating and baking a paint (B).

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a cationic electrodeposition coating (A) is a coating to be firstly electrodeposited, has a MEQ of 5 to 25, preferably 10 to 15, and has a nonionic surfactant. The agent is contained in the solid content of the electrodeposition coating in an amount of 0.1 to 10% by weight, preferably 0.2 to 5% by weight.

[0007] Here, the MEQ is mg equivalent.
is an abbreviation of "ent" and is a mg equivalent of a neutralizing agent (acid) per 100 g of solid content of the coating material. Usually, about 10 g of an electrodeposition coating material is precisely weighed and dissolved in 50 ml of a solvent (THF).
It is calculated by potentiometric titration using a 0N NaOH alcohol solution to quantify the amount of acid contained. The ME
When Q is less than 5, the running stability of the diluted paint is reduced. On the other hand, when Q is more than 25, the amount of gas generated at the time of electrodeposition coating increases, and high finishability is not obtained, which is not preferable.

[0008] The nonionic surfactant is HLB.
Are preferably in the range of 5 to 20, specifically, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl allyl ether, and polyoxyethylene alkyl amine ether. -Ter, polyoxyethylene polyoxypropylene block polymer and the like. When the amount of the nonionic surfactant is less than 0.1% by weight, the running stability of the diluted paint is reduced. On the other hand, when it exceeds 10% by weight, various properties of the obtained electrodeposition coating film are undesirably reduced.

In the above cationic electrodeposition paint (A), usually,
As the base resin, cationic resins such as an epoxy resin, an acrylic resin, and a polyurethane resin are mainly used. Among them, a polyamine resin represented by, for example, an amine-added epoxy resin is preferable from the viewpoint of anticorrosion properties.

Examples of the amine-added epoxy resin include (i) an adduct of an epoxy resin with a primary mono- and polyamine, a secondary mono- and polyamine, or a mixed primary and secondary polyamine (for example, US Pat. , 984,29
(Ii) adducts of epoxide resins with secondary mono- and polyamines having ketiminated primary amino groups (see, for example, US Pat. No. 4,017,438).
(Iii) a reaction product obtained by etherification of an epoxide resin with a ketiminated hydroxy compound having a primary amino group (for example, see JP-A-59-1984).
No. 43013).

The epoxy resin used for producing the amine-added epoxy resin is a compound having two or more epoxy groups in one molecule, and is generally at least 200, preferably 400 to 4000, more preferably 800 to 20.
Suitable are those having a number average molecular weight in the range of 00, particularly those obtained by reacting a polyphenol compound with epichlorohydrin, or those obtained by reacting an adduct of a polyphenol compound with an alkylene oxide with epichlorohydrin. Are preferred. Examples of the polyphenol compound that can be used for forming the epoxy resin 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, tetra (4-hydroxyphenyl) -1,1,2,2
Examples thereof include 2-ethane, 4,4-dihydroxydiphenyl sulfone, phenol novolak, and cresol novolak.

The epoxy resin is a polyol, a polyether,
Terpolymers, polyester polyols, polyamidoamines, polycarboxylic acids, polyisocyanate compounds and the like may be partially reacted with each other.
-Caprolactone, acrylic monomer, or the like may be graft-polymerized. Further epoxy resins other than those described above include a reaction product of polyol and epichlorohydrin and a reaction product of the reaction product and a polyphenol compound,
Alternatively, it may be obtained by oxidizing an unsaturated compound with peracetic acid.

The above-mentioned base resin may be any of an external cross-linking type and an internal (or self-cross-linking) type, and a curing agent used in combination with an external cross-linking type resin is conventionally known. And a block polyisocyanate compound is particularly preferable, but tris (alkoxycarbonylamino) triazine and the like can also be used.
In addition, as the internally crosslinked resin, block isocyanate
Those in which a thio group is introduced are preferred.

The block polyisocyanate compound which can be used in the above externally crosslinked type can be an addition reaction product of a stoichiometric amount of a polyisocyanate compound with an isocyanate blocking agent. Examples of the polyisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, and phenylenedi isocyanate.
Aromatic, alicyclic or aliphatic such as bis (isocyanatemethyl) cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, isophorone diisocyanate Diisocyanate compounds and isocyanurate compounds thereof, and excessive amounts of these isocyanate compounds are mixed with low molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, trimethylolpropane, and hexanetriol. Examples thereof include a terminal isocyanate-containing compound obtained by the reaction.

On the other hand, the isocyanate blocking agent is one that blocks by adding to the isocyanate group of the polyisocyanate compound, and the blocked polyisocyanate compound formed by the addition is stable at room temperature and about 100%. When heated to 200 ° C., it is desirable that the blocking agent be dissociated to regenerate a free isocyanate group. Examples of the blocking agent satisfying such requirements include lactam compounds such as ε-caprolactam and γ-butyrolactam; oxime compounds such as methylethylketoxime and cyclohexanone oxime; phenol, para-t-butylphenol, and cresol. Phenolic compounds such as n-butanol;
Aliphatic alcohols such as ethylhexanol; aromatic alkyl alcohols such as phenylcarbinol and methylphenylcarbinol; ether alcohol compounds such as ethylene glycol monobutyl ether; Can be mentioned. Of these, oxime-based and lactam-based blocking agents are dissociable at relatively low temperatures, and are particularly suitable from the viewpoint of curability of the electrodeposition coating composition.

The block isocyanate group can be introduced into the base resin in the self-crosslinking type having a block isocyanate group in the base resin molecule by a conventionally known method. It can be introduced by reacting a free isocyanate group in the partially blocked polyisocyanate compound with an active hydrogen-containing portion in the base resin.

In the case of a cationic resin, the resin is usually neutralized and made water-soluble by neutralizing the resin with an aliphatic carboxylic acid, particularly a water-soluble organic acid such as acetic acid and / or formic acid. This is performed by dispersing in water. It is preferable to use acetic acid and / or formic acid as the neutralizing agent because they are excellent in finishing properties and throwing power. The amount of the neutralizing agent used is appropriately selected so as to obtain a desired MEQ.

The cationic electrodeposition paint (A) can contain pigments and paint additives as required. The pigments are not particularly limited as long as they are pigments usually used in electrodeposition paints. Any pigment can be used, for example, titanium oxide, car
Coloring pigments such as Bon Black and Bengala; extenders such as clay, mica, barita, talc, calcium carbonate and silica; and rust preventing pigments such as aluminum phosphomolybdate and aluminum tripolyphosphate. Examples of the coating additive include an organic solvent, a coating surface adjusting agent, and a curing catalyst such as a metal salt.

The above cationic electrodeposition paint (A) can be applied to a desired metal material surface by electrodeposition coating.
Electrodeposition coating generally has a solid concentration of about 5 to 40% by weight.
An electrodeposition bath made of an electrodeposition paint diluted with deionized water or the like so as to have a pH of 5.0 to 9.0, usually adjusted to a bath temperature of 15 to 35 ° C, Load voltage 1
It can be performed under the condition of 00 to 400V. The cationic efficiency of the cationic electrodeposition paint (A) is 40 to 80 mg /
c, preferably 45 to 75 mg / c.

The coating film formed by using the cationic electrodeposition coating material (A) is washed with deionized water or the like, and then washed for about 100 to 200.
It can be baked and cured in the range of ° C. The thickness of the electrodeposition coating film is not particularly limited, but is generally 1 to 50 μm, preferably 2 to 50 μm based on the cured coating film.
It is preferably in the range of 5 to 45 μm. Further, the obtained coating film preferably has a surface roughness of 0.15 μm or less in Ra value.

In the present invention, the cationic electrodeposition paint (B)
Is a paint to be electrodeposition-coated the second time, and is a paint for forming an electrodeposition coating film on an unpainted portion (an inner plate portion or an edge portion) of the object exposed after the first baking.

Therefore, as the cationic electrodeposition coating (B),
Conventionally known paints can be used without any particular limitation, but paints having excellent edge coverage are suitable, and examples thereof include paints containing a base resin component and a particulate component such as gelled polymer fine particles or pigment as main components. . As the base resin component, one or more kinds can be selected from those listed in the description of the base resin of the cationic electrodeposition coating composition (A). Further, it is desirable that the base resin component used in the cationic electrodeposition paint (B) has good compatibility with the base resin of the cationic electrodeposition paint (A).

As the gelled polymer fine particles which can be used in the above-mentioned cationic electrodeposition coating material (B), conventionally known ones can be widely applied, and those having a cationic electrodeposition property may be used. Polymerized fine particles obtained by dispersing an acrylic copolymer containing a hydroxyl group and a cationic group in water and cross-linking the particles, and gelling by mixing a cationic acidic colloidal silica with the acrylic copolymer and dispersing in water. Polymer fine particles, gelled polymer fine particles obtained by emulsion polymerization of a monomer mixture containing a polymerizable monomer having two or more unsaturated groups in one molecule using a cationic reactive emulsifier, a cationic reactive emulsifier Gelled polymer fine particles having a core-shell structure obtained by emulsion polymerization using an epoxy resin amine adduct containing a hydrolyzable alkoxysilane group. Such decentralized was allowed crosslinked in particle gelled polymer particles can be exemplified (Japanese Patent Laid-Open 2-47107
JP-A-2-269164, JP-A-3-62860
JP-A-3-128979, JP-A-6-16818
And JP-A-6-287267). It is desirable that such gelled polymer fine particles are blended in an amount of 3 to 50% by weight, preferably 7 to 35% by weight, based on the total resin solid content including the base resin component.

When using the gelled polymer fine particles,
If necessary, other particulate components such as the pigments listed in the description of the pigments of the cationic electrodeposition paint (A) can be used in combination.

When only the pigment is used without using the gelled polymer fine particles as the particulate component, for example, a pigment having an oil absorption of 100 or more, such as a silicon dioxide type or a carbon type, is used in 5% of the total pigment content. It is preferable to mix it by weight% or more.

The electrodeposition coating using the above-mentioned cationic electrodeposition paint (B) can be carried out in the same manner as in the case of the above-mentioned cationic electrodeposition paint (A). One of the time required for paint (A)
Even in the range of ４ to ２, a coating film can be sufficiently formed on an unpainted portion of the object to be coated.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited by this. “Parts” and “%” are “parts by weight” and “% by weight”
Is shown.

Preparation of cationic electrodeposition paints Cationic electrodeposition resins, pigments, and the like are blended in the composition shown in Table 1 and each of the cationic electrodeposition paints (A-1) to (A-
7) and (B-1) to (B-3) were obtained. Table 1 shows the solid content, and (Note 1) to (Note 5) in the table are as follows.

(* 1) Cationic electrodepositable resin: amine-added epoxy resin / block polyisocyanate compound having a resin base number of 80 (* 2) "CF Bowsei C-100": trade name, manufactured by Kikuchi Pigment Industry Co., Ltd. , Basic lead silicate (Note 3) Surfactant: “KP-152K”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name, polyoxyethylene octylphenyl ether, HLB: 15 (Note 4) Gelling polymer Fine particles: gelled polymer fine particles obtained by dispersing an acrylic copolymer containing a hydrolyzable alkoxysilane group and a cationic group in water and cross-linking the particles. (Note 5) MEQ: Approximately weigh 10 g of the electrodeposition paint, 50 ml
1 / 10N NaOH after dissolving in a solvent (THF)
Potentiometric titration was performed using an alcohol solution, and the content of acid was determined and calculated.

[0030]

[Table 1]

Examples and Comparative Examples Table 2 was obtained by combining each of the above-mentioned cationic electrodeposition paints with the combination of Table 3.
Electrodeposition coating was performed according to the above coating conditions to obtain each electrodeposition coated plate. These were subjected to the following performance tests. The results of coating and the performance of the coating film are shown in Table 3.

(Performance test) (* 1) Stability of diluted paint: 3 liters of paint of a predetermined nonvolatile content, which was previously filtered through a 400 mesh wire mesh, was circulated for a predetermined time by a laboratory pump ("IWAKIMAGNETPUNP MD-30R") (normally 1 hour). ), And the condition of the filtration residue (400 mesh filtration) after circulation was visually evaluated. During circulation, paint temperature is 2
The temperature was kept at 8 to 30 ° C., and care was taken not to foam. In addition, the residue of the filtration included the aggregation of the pumping portion.

○: No filtration residue △: Filtration residue is slightly recognized ×: Filtration residue is considerably large (* 2) Finishing property: The surface roughness of each electrodeposited coating film is measured by a surface roughness meter “Surtest 301” (Mitsutoyo Co., Ltd.) (measurement conditions λc = 0.8 mm, × 5)
000 times). Numerical values were indicated by Ra value: μm.

(* 3) Edge anticorrosion: Each electrodeposited plate is J
Perform salt spray test according to IS Z 2371, 2
After 40 hours, the number of rust points generated in the punched burrs was measured, and the number was evaluated.

(* 4) Chipping resistance: Each electrodeposition coated plate is further overcoated (dry thickness: 30-40 μm, 140 ° C.)
The coated plate was kept at -20 ° C, and 100 g of No. 7 crushed stone was sprayed onto the coated plate at an angle of 30 ° at a pressure of 3 kgf / cm ² . From the peeled area of the coating film at that time, evaluation was made by comparison with a rating reference plate (5 levels).

：: Rating 4, 5 Δ: Rating 3 ×: Rating 1, 2 (* 5) Water-resistant secondary adhesion: Each electrodeposited plate was immersed in hot water at 40 ° C. for 240 hours, and then ground with an NT cutter. 1m to reach
Make 11 vertical and 11 horizontal cuts at m intervals, for a total of 10
Make 0 Goban eyes, stick cellophane tape tightly,
One end of the cellophane tape was held, and the cellophane tape was quickly peeled off in the direction perpendicular to the coated plate, and the peeled area ratio (%) was evaluated as follows.

：: No peeling X: Peeling area is 50% or more

[0038]

According to the method of the present invention, by suppressing the MEQ in the cationic electrodeposition coating composition (A), the cron efficiency increases, and the amount of gas generated during electrodeposition can be suppressed.
Therefore, the volume shrinkage of the coating film at the time of baking is reduced, and high finishability is obtained. In addition, an increase in the cron efficiency allows a thicker film to be formed than in the prior art, allows the application of an intermediate coating function, and allows direct overcoating on the electrodeposited surface. On the other hand, the stability of the base resin emulsion, which is impaired by keeping the MEQ low, can be sufficiently compensated for by adding a specific amount of the nonionic surfactant.

[0039]

[Table 2]

[0040]

[Table 3]

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshiyuki Kawamata 33-1, Kanzakicho, Amagasaki-shi, Hyogo Kansai Paint Co., Ltd. F-term (Reference) 4D075 AE03 BB28Z BB89 DC12 EC35 4J038 EA011 EA012 KA09 PA04 PA07 PA19

Claims (2)

[Claims] An MEA having an MEQ of 5 to 25 and a nonionic surfactant in a solid content of an electrodeposition coating material of 0.1 to 0.1%.
Cationic electrodeposition paint (A) containing 10 to 10% by weight
Coating and baking, and then applying and baking a cationic electrodeposition paint (B). 2. The method according to claim 1, wherein the nonionic surfactant is HLB5 to HLB2.
The cationic electrodeposition coating method according to claim 1, wherein the value is 0.