JPH0598209A - Water-based intercoating composition and method of forming coating film - Google Patents

Abstract

PURPOSE:To obtain a water-based intercoating composition which shows excellent curing properties to give a satisfactory intercoat film excellent in chipping resistance and other performances. CONSTITUTION:The title composition comprises as essential ingredients a polyester resin containing a hydroxy group and an acid radical, an amino resin, an alicyclic epoxy compound, a neutralizing agent, a pigment, and water. The title method comprises applying the composition on the surface of a coating film formed by cationic electrodeposition, heating the applied composition to form a cured intercoat film, and then forming a cured topcoat film on the intercoat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous intermediate coating material and a method for forming a coating film.

[0002]

2. Description of the Related Art In general, outer panels of automobiles are subjected to undercoating, intermediate coating and topcoating. Currently, the mainstream paints used for these coatings are cationic electrodeposition paints (undercoats), polyester-melamine-curable organic solvent type paints (intermediate coats), and acrylic-melamine-curable (topcoats) paints.

However, since the intermediate coating composition generates a large amount of organic solvent during coating and baking, it is problematic in terms of environmental pollution and safety. Currently, the development of water-based coating composition in which the amount of organic solvent generation is small is an automobile. Is desired in such fields.

Further, as an aqueous paint, an aqueous solution of a cured resin composition prepared by blending a neutralized product obtained by neutralizing a resin containing a hydroxyl group and a carboxyl group with an amine and an amino resin has been proposed. The coating film of an aqueous coating composition obtained by coating the surface of a cationic electrodeposition coating film and baking it has the drawback that the curability is poor and the performance required as an intermediate coating film (for example, chipping property) is not exhibited.

[0005]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors for the purpose of solving the above-mentioned drawbacks, as a result, an aqueous solution containing a hydroxyl group- and acid group-containing polyester resin and an amino resin as a curable resin component has been developed. The inventors have found that a coating containing an alicyclic epoxy compound in the coating can provide a coating having satisfactory performance as an intermediate coating, and have completed the present invention.

That is, the present invention is a water-based intermediate coating composition containing a hydroxyl group- and acid group-containing polyester resin, an amino resin, an alicyclic epoxy compound, a neutralizing agent, a pigment and water as essential components, and After the aqueous intermediate coating composition is applied to the surface of the cationic electrodeposition coating film, heating is performed to form an intermediate coating cured coating film, and then an overcoat cured coating film is formed on the cured coating film surface. The present invention relates to a coating film forming method.

The water-based intermediate coating composition of the present invention will be described below.

The hydroxyl group- and acid group-containing resin used in the aqueous intermediate coating composition is a component constituting the base resin of the coating composition and has a number average molecular weight of about 1,000 to 100,000, preferably about 2,000 to 20, 000, an acid value of about 10 to 200, preferably about 15 to 90, and a hydroxyl value of about 10 to 200, preferably about 20 to 150 are preferred.
When the number average molecular weight is less than about 1,000, the mechanical properties of the coating film are deteriorated, while the number average molecular weight is about 100,000.
If it exceeds the range, the coating workability and finish are deteriorated, which is not preferable. When the acid value is less than about 10, the water dispersibility becomes poor, while when the acid value exceeds about 200, the storage stability of the coating composition is deteriorated, which is not preferable. Further, when the hydroxyl value is less than about 10, the physicochemical properties of the coating film deteriorate, while when the hydroxyl value exceeds about 200, the water resistance of the coating film decreases, which is not preferable. The acid group is preferably a carboxyl group.

Examples of the polyester resin include polybasic acids (for example, (anhydrous) phthalic acid, isophthalic acid, terephthalic acid, (anhydrous) maleic acid, (anhydrous) pyromellitic acid,
2-4 carboxylic groups in one molecule such as (anhydrous) trimellitic acid, (anhydrous) succinic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dimethyl isophthalate, dimethyl terephthalate, cyclohexyldicarboxylic acid, adipic acid Or a compound having a carboxylic acid methyl ester group) and a polyhydric alcohol such as ethylene glycol, polyethylene glycol, propylene glycol,
Neopentyl glycol, 1,6-hexanediol,
Those produced by esterification reaction or transesterification reaction with trimethylolpropane, pentaerythritol, glycerin, tricyclodecanedimethanol, alcohol having 2 to 6 hydroxyl groups in one molecule such as cyclohexyldimethylol can be used. .. Further, in addition to the above-mentioned ones, a monobasic acid (for example, soybean oil, safflower oil, coconut oil, castor oil, benzoic acid) can be used if necessary.

The amino resin used in the water-based intermediate coating composition is for reacting with the resin to form a three-dimensionally cross-linked and cured intermediate coating film, and specifically, a melamine resin,
Benzoguanamine resins, urea resins and their methylol compounds, alkyl ether compounds and the like are included. Among the amino resins, it is preferable to use melamine formaldehyde resin as a main component from the viewpoint of curability. It is usually desirable to add the amino resin in an amount of about 10 to 50% by weight based on the total solid weight of the resin.

The alicyclic epoxy compound used in the water-based intermediate coating composition is for improving the curability of the coating film, and contains an epoxy group and an alicyclic hydrocarbon ring on the alicyclic hydrocarbon ring. It has at least two or more epoxy groups in one molecule selected from the epoxy groups directly bonded to the carbon atoms to be formed. The alicyclic hydrocarbon ring may be a 3-membered small-membered ring to a 7-membered ring or more, and the ring may be a monocyclic ring or a polycyclic ring. It may constitute a hydrocarbon ring.
Examples of the epoxy group on the alicyclic hydrocarbon ring include those represented by the formula:

[0012]

[Chemical 1]

Examples of the epoxy group which includes a group represented by: and which is directly bonded to a carbon atom forming an alicyclic hydrocarbon ring include, for example, the formula:

[0014]

[Chemical 2]

Examples include groups represented by:

If a compound having two or more aliphatic glycidyl groups (for example, diglycidyl ether, bisphenol A-epichlorohydrin type) is used in place of the alicyclic epoxy compound, the storage stability of the paint and the performance of the coating film are deteriorated. Therefore, it is particularly important to use an alicyclic epoxy compound in the present invention.

As the alicyclic epoxy compound, industrially available ones can be used, and specific examples of such an alicyclic epoxy compound include the following.

[0018]

[Chemical 3]

General formula

[0020]

[Chemical 4]

A compound represented by the formula (wherein k is an integer of 0 to 15).

A compound having the following unit formula (1), (2) or (3)

[0023]

[Chemical 5]

(In the formula, R ₁ is an organic residue having active hydrogen, and p is 2 to 100.)

[0025]

[Chemical 6]

(In the formula, p has the same meaning as described above.)

[0027]

[Chemical 7]

(Wherein Y is an alicyclic epoxy residue,
X is

[0029]

[Chemical 8]

R ₂ is a C _1-18 alkyl group or a cycloalkyl group, R ₃ is a C _1-6 alkylene group, n is 0 to 100, and m is 5 to 100. )
Such.

Y in the unit formula (3) is

[0032]

[Chemical 9]

An organic group having an alicyclic epoxy group such as

Examples of the compounds having the above unit formulas (1) to (3) include those described in Japanese Patent Application No. 1-209667, for example, the following compounds.

The compound having the unit formula (1) is a polycyclohexene having a vinyl group side chain obtained by ring-opening polymerization of 4-vinylcyclohexene-1-oxide with an organic compound having active hydrogen as an initiator. A product produced by epoxidizing an oxide ring-opening polymer with an oxidizing agent such as peracid or hydroperoxide can be used.

As the organic compound having the active hydrogen,
Monohydric alcohols such as methanol, ethanol, propanol, pentanol, hexanol, benzyl alcohol, cyclohexanol, ethylene glycol,
Alcohols such as polyhydric alcohols such as diethylene glycol, triethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, neopentyl glycol, glycerin, trimethylolpropane, pentaerythritol, dipentaerythritol; phenol, cresol, bisphenol A Phenols such as bisphenol F; carboxylic acids such as formic acid, acetic acid, maleic acid, adipic acid, dodecane diacid, trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid and the like.

The ring-opening polymerization is usually carried out with ethylamine,
Propylamine, caustic potash, pyridine and other bases, formic acid, acetic acid, sulfuric acid, hydrochloric acid and other acids, sodium methylate and other alkali metal alcoholates, boron trifluoride, zinc chloride, aluminum chloride and other Lewis acids or their complexes , In the presence of a catalyst such as an organic metal such as triethylaluminum, generally about -70 ° C to about 20 ° C.
It can be carried out at 0 ° C, preferably in the range of about -30 ° C to about 100 ° C.

Examples of the compound having the unit formula (1) include EHPE-3150, EHPE-3100 and EHP.
E-1150 (above, trade name of Daicel Chemical Industries, Ltd.) and the like can be mentioned.

The compound having the unit formula (2) can be produced by radical polymerization reaction of vinyl 3,4 epoxycyclohexyl. The radical polymerization reaction can be carried out using the same method and conditions as those for a polymerization reaction based on a polymerizable unsaturated bond such as an ordinary acrylic resin or vinyl resin. As an example of such a polymerization reaction, there can be shown a method in which each monomer component is dissolved or dispersed in an organic solvent and heated in the presence of a radical polymerization initiator at a temperature of about 60 to 180 ° C. with stirring. .. The reaction time can be usually about 1 to 10 hours. Also,
As the organic solvent, an alcohol solvent, an ether solvent, an ester solvent, a hydrocarbon solvent or the like can be used.
When a hydrocarbon solvent is used, it is preferable to use another solvent in combination from the viewpoint of solubility. Further, any of those usually used as a radical initiator can be used, and specific examples thereof include peroxides such as benzoyl peroxide and t-butylperoxy-2-ethylhexanoate; azoisobutyrate. Examples thereof include azo compounds such as ronitrile and azobisdimethylvaleronitrile.

Examples of the compound having the unit formula (3) include 3,4-epoxycyclohexyl methyl acrylate and 3,4-epoxy cyclohexyl acrylate, and commercially available products such as METHB and AETHB (both trade names, manufactured by Daicel Chemical Industries, Ltd.). Examples of the polymerizable epoxy monomer include those obtained by performing a radical polymerization reaction alone or with another radical polymerizable monomer.

The alicyclic epoxy compound preferably has a number average molecular weight of about 100,000 or less, preferably about 50,000 or less, and an average number of alicyclic epoxy groups of about 2 to 400. When the number average molecular weight exceeds about 100,000, the smoothness of the intermediate coating film deteriorates. On the other hand, if the average number of epoxy groups is less than about 2, the curability of the intermediate coating film decreases, while if the number of epoxy groups is more than about 400, the storage stability of the coating material and the adhesion to the top coating film decrease. Not preferable.

The alicyclic epoxy compound is used in an amount of about 1 to 20 parts by weight, preferably about 2 to 10 parts by weight, based on 100 parts by weight of the total amount (solid content) of the hydroxyl group- and acid group-containing polyester resin and amino resin. It is desirable to mix them. If the blending amount is less than about 1 part by weight, the adhesion between the intermediate coating film and the cationic electrodeposition coating film is deteriorated. On the other hand, if the blending amount is more than about 20 parts by weight, the storage stability of the coating composition and the top coating film It is not preferable because the adhesiveness is deteriorated.

The neutralizing agent used in the water-based intermediate coating composition is one which makes water-soluble by neutralizing the acid groups in the above-mentioned hydroxyl group- and acid group-containing polyester resin to form a salt. Examples include ammonia, trimethylamine, triethylamine, dimethylethanolamine, triethanolamine, and tetraethylammonium hydroxide. The neutralizing agent, with respect to the acid groups in the resin,
Usually, it is preferable to mix about 0.2 to 1.5 equivalents.

As the pigment used in the aqueous intermediate coating composition, conventionally known pigments such as coloring pigments (eg titanium white, carbon black etc.) and extender pigments (eg barium sulfate, calcium carbonate etc.) can be used.

In addition to the above, an organic solvent, an anti-settling agent, an antifoaming agent and the like can be added to the water-based intermediate coating material, if necessary.

Next, a method for forming a coating film using the intermediate coating composition of the present invention will be described below.

According to the method of the present invention, the intermediate coating composition is applied to the surface of the cationic electrodeposition coating film, heated to form an intermediate coating cured coating film, and then the top coating composition is applied to the obtained coating film surface. Can be implemented.

The cationic electrodeposition coating film is preferably a cured coating film formed by using an epoxy cationic electrodeposition coating composition. The intermediate coating can be performed by a usual coating method, for example, electrostatic coating or non-electrostatic coating. The coating film thickness is usually about 20 to 50 μm as a cured coating film. The heating conditions for the intermediate coating are generally about 120 to 16
Heat at 0 ° C. for about 10-40 minutes. The top coating material applied to the intermediate coating film can be appropriately selected and used from conventional ones without particular limitation. Specifically, an acrylic resin, a silicone resin, a fluororesin and a modified resin thereof are used as a base resin component, and a (block) polyisocyanate compound, a melamine resin, a metal chelate, and an alkoxysilane compound are contained as a crosslinking agent (or catalyst). Examples include water-based, organic solvent-based or non-water-dispersed coatings. Further, the top coating composition can be finished by 1 coat 1 bake, and a metallic / clear system can be finished by 2 coat 1 bake or 2 coat 2 bake system. The top coating film is usually a cured coating film and is applied in an amount of about 10 to 100 μm.

[0049]

ACTION AND EFFECTS OF THE INVENTION It is known that the surface of the cationic electrodeposition coating film is basic due to its own properties, and that the basic compound is volatilized from the cured coating film by baking. .. When a normal amino resin curable paint is applied to this product and heated, the basic atmosphere slows down the curing of the amino resin curable paint (especially the interface between both paint films) and is satisfactory as an intermediate coating film. You can't get the performance you can.

In the present invention, by incorporating an alicyclic epoxy compound in a usual paint, the epoxy group in the epoxy compound captures the basic substance and the usual curing reaction between the amino group and the hydroxyl group proceeds. It is presumed that, as a result, the curability of the coating film was excellent, and the performance excellent in chipping resistance and the like, which was satisfactory as the intermediate coating film, could be exhibited.

Further, the epoxy compound itself undergoes a similar reaction or a reaction with a hydroxyl group in a basic atmosphere, and exhibits satisfactory performance as an intermediate coating film as described above.

Further, the alicyclic epoxy group of the epoxy compound used in the coating composition of the present invention has a reaction with the epoxy group or other functional group (particularly carboxyl group) in an aqueous system as compared with the aliphatic epoxy group. Since it is slow, it has the effect of not deteriorating the storage stability of the paint.

[0053]

EXAMPLES Next, the present invention will be specifically described with reference to examples.

[0054]

Example 1 The coating material of Example 1 was prepared with the following composition.

(* 1) Polyester resin 1000 g (* 2) Amino resin 230 g (* 3) EHPE-3150 100 g (* 4) Pigment titanium white 800 g Carbon black 3 g Diethylaminoethanol 38 g Deionized water 430 g (* 1) Polyester: Was added to a reaction vessel and reacted at 200 ° C. for 5 hours, 0.05 mol of phthalic anhydride was added, and the mixture was further reacted at 130 ° C. for 1 hour to obtain a polyester resin having a number average molecular weight of 4800, an acid value of 30, and a hydroxyl value of 55. Obtained.

(* 2) Amino resin: manufactured by Mitsui Cyanamide Co., Ltd., Cymel 370 (* 3) EHPE-3150: Daicel Chemical Industries, Ltd.
Product name, epoxidized polyvinyl cyclohexene oxide, epoxy equivalent 190, average molecular weight 1500 (* 4) titanium white: JR-602 (trade name) manufactured by Teikoku Kako Co., Ltd. carbon black: Mitsubishi carbon black manufactured by Mitsubishi Kasei Co., Ltd. M-100

[0057]

Example 2 The coating material of Example 2 was prepared with the following composition.

(* 1) Polyester resin 1000 g (* 2) Amino resin 230 g 3,4-Epoxycyclohexylcarboxymethylcyclohexene oxide 100 g (* 4) Pigment titanium white 800 g Carbon black 3 g Dimethylaminoethanol 38 g Deionized water 360 g ( * 1), (* 2), and (* 4) were the same as above.

[0059]

Example 3 In Example 2, (* 3) EHPE-3
Example 3 was prepared in the same composition as in Example 2 except that 100 g of 150 was changed to 62 g.

[0060]

Example 4 Example 4 was prepared in the same manner as in Example 3, except that the amount of 3,4-epoxycyclohexylcarboxymethylcyclohexene oxide was changed from 100 g to 200 g.

Comparative Example 1 In Example 1, the same solid content as in Example 1 was prepared without adding (* 3) EHPE-3150.

Comparative Example 2 In Example 1, (* 3) EHPE-3150 was replaced with (*
5) The same as in Example 1 was prepared except that the aliphatic epoxy resin Denacol EX-313 was completely replaced.

(* 5) Aliphatic epoxy resin Denacol EX-313: manufactured by Nagase Kasei Kogyo Co., Ltd. Mainly composed of the following structures

[0064]

[Chemical 10]

Table 1 shows the results of the storage stability test of Examples and Comparative Examples.

[0066]

[Table 1]

Storage stability test The test method is as follows.

The paints obtained in the Examples and Comparative Examples were treated with Ford Cup No. 4 (measurement temperature 20 ℃)
After diluting it for 40 seconds, it was stored at 40 ° C. for 10 days, and the change in viscosity of the paint was evaluated based on the following criteria.

(Evaluation) O (Good): Viscosity increase of 20 seconds or less as compared with the initial one.

Δ (Slightly bad): Viscosity increase more than 20 seconds compared to the initial one.

X (Poor): Gelation occurred.

Preparation of coated plate Epoxy resin-based cationic electrodeposition paint (Electron # 9800, Kansai Paint Co., Ltd.) on a dull steel plate (zinc phosphate treated)
Manufactured, trade name) (25 μm) and heat-cured at 170 ° C. for 30 minutes, and then as an intermediate coating, the coating materials of the above Examples and Comparative Examples are spray-coated to a dry film thickness of 30 μm. An intermediate coating film was prepared by baking at 30 ° C. for 30 minutes.

Next, a metallic base paint (* 6) was spray-coated on the intermediate coating film so that the dry film thickness was about 15 to 20 μm, and then it was left for 3 minutes for immediate clear top coating. Approximately 35-35 dry paint film
Spray coating was performed so as to have a thickness of 45 μm. Then, it was left at room temperature for 10 minutes and baked at 140 ° C. for 30 minutes. The coating performance and appearance are shown in Table 2.

(* 6) Base coating: acrylic resin (methyl methacrylate / ethyl acrylate / 2-hydroxyethyl methacrylate / acrylic acid = 30/56 /
12/2 (g), average molecular weight 40,000 70 g, Uban 28-60 (Mitsui Toatsu Chemicals, Inc., trade name, melamine resin) 30 g, Alpaste N-519 (Toyo Aluminum Industry Co., Ltd.) , Trade name) 12 g (the compounding amount is represented by solid content, respectively).

(* 7) Paint for clear top coat: acrylic resin (styrene / butyl methacrylate / 2-hydroxyethyl methacrylate / acrylic acid = 30/4
8/20/2 (g), average molecular weight 15,000) 70
g, Uban 20SE (Mitsui Toatsu Chemicals, Inc., trade name, melamine resin) 30 g (above solid content) xylol solvent solution.

[0076]

[Table 2]

Interlayer adhesion (cationic electrodeposition coating / intermediate coating): A cutter knife is used to reach the substrate, and 11 mm of vertical and horizontal parallel lines are formed in the center of the test piece at 1 mm.
Draw it at intervals of 1 cm ² to make 100 squares in 1 cm ² and make a scratch on the surface, stick adhesive cellophane tape on the coated surface, and peel it off sharply The face was evaluated. O indicates that no peeling of the coating film was observed, Δ indicates that a small amount of peeling was observed between the layers, and x indicates that a large amount of interlayer peeling was observed.

Water resistance: After the test plate was immersed in warm water at 40 ° C. for 10 days, the interlaminar adhesion (tested and evaluated in the same manner as above) was examined.

Chipping resistance: The test method is as follows.

(1) Test equipment: QGR GRAVELOMETER (product of Q panel company) (2) Stone to be sprayed: JIS A 5001 No. 7 crushed stone (3) Weight of stone to be sprayed: about 100 g (4) Spraying air pressure: about 0.39 MPa (5) Temperature at the time of test: -20 ° C Attach the test piece to the test piece holder, and then about 4.5 kg / cm ²
Approximately 100 g of crushed stone was fired on the test piece with the blowing air pressure. The state of the coated surface is visually observed and evaluated according to the following criteria.

(Evaluation) O (Good): Slight scratches are observed between the electrodeposition coating film and the intermediate coating film.

Δ (Slightly bad): A scratch is observed between the electrodeposition coating film and the intermediate coating film.

X (Poor): Many large scratches are observed between the electrodeposition coating film and the intermediate coating film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location C09D 167/02 PLB 8933-4J (72) Inventor Hiroshi Inoue 4-17-1, Higashihachiman, Hiratsuka-shi, Kanagawa No. Kansai Paint Co., Ltd.

Claims (2)

[Claims] 1. A hydroxyl group- and acid group-containing polyester resin,
An aqueous intermediate coating composition comprising an amino resin, an alicyclic epoxy compound, a neutralizing agent, a pigment and water as essential components. 2. An aqueous intermediate coating composition according to claim 1 is applied to the surface of a kaolin electrodeposition coating film, followed by heating to form an intermediate coating cured coating film, and then the top coating cured on the cured coating film surface. A method for forming a coating film, which comprises forming a coating film.