JP2001009356A - Multilayer coating method - Google Patents

Abstract

(57) [Summary] [Problem] Even when a powder coating is used as an intermediate coating or undercoating to form a multi-layer coating film, it has excellent interlayer adhesion, appearance, weather resistance, chipping resistance, etc. Provided is a method for forming a multilayer coating film from which a multilayer coating film is obtained. SOLUTION: A hydroxyl group-containing polyester resin [A-1]
And an acid group-containing polyester resin [A-2] and a curing agent [B] that reacts with a hydroxyl group, and has a total acid value of 10 to 1
After the powder coating [I] of No. 00 was applied to the object to be coated and cured by heating, a colored basecoat coating [II] and a transparent topcoat coating [II]
I] or a top coat paint [IV], and baking and drying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel and useful method for forming a multilayer coating film. More specifically, the present invention provides
The present invention relates to a method for forming a coating film which gives a multilayer coating film having excellent appearance, weather resistance, interlayer adhesion, chipping resistance, etc. of a top coating film, and particularly a multilayer coating which is extremely practical when formed on an automobile body. The present invention relates to a coating film forming method capable of obtaining a film.

[0002]

2. Description of the Related Art Powder paints are one form of paints that do not contain organic solvents. However, in recent years, from the viewpoint of environmental problems such as air pollution, their low pollution has attracted attention, and their use has been increasing year by year. There are a wide variety of applications, including coatings for metal products such as home appliances and building materials.However, due to the characteristic of powder coatings that there is virtually no solvent that evaporates during coating, application to automotive coatings is being studied. I'm advancing.

There are various resin compositions for powder coatings that are currently in practical use. For example, a polyester resin mainly having a hydroxyl group and a block isocyanate
A composition formed by combining a polyester resin and an epoxy resin, which mainly has a carboxyl group, has a good appearance and mechanical properties, and is widely used because it has weather resistance. It is widely used because the resulting coating has excellent corrosion resistance.

[0004] On the other hand, regarding the prior art of a coating method for an automobile body, at present, an intermediate coating containing an organic solvent is applied to an object (an automobile body or the like) on which cationic electrodeposition has been applied and baked. After drying, a base containing the same organic solvent
The mainstream is a coating method in which a coating for coating and a coating for topcoat containing an organic solvent are successively applied and baked and cured.

[0005]

However, in the prior art, since the organic solvent volatilizes during coating as described above,
Such a coating method has environmental health problems. As a method of avoiding the volatilization of the organic solvent, it is conceivable to use a powder coating substantially not containing an organic solvent. The interlayer adhesion, appearance, weather resistance, chipping resistance and the like of the layer coating film were poor. Japanese Patent Application No. 8-81380 discloses a method for forming a multi-layer coating film using a polyester resin powder coating having a specific composition, which can be improved in appearance and the like. It has a problem of poor interlayer adhesion, and improvement is required.

The problem to be solved by the present invention is that, even when a powder coating is used as an intermediate coating or undercoating to form a multi-layer coating, adhesion between layers, appearance, weather resistance, chipping resistance, etc. It is an object of the present invention to provide a method for forming a multilayer coating film from which a multilayer coating film having excellent resistance can be obtained.

[0007]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of investigations to solve the above-mentioned problems of the prior art, a polyester resin having a hydroxyl value in a specific range and a glass transition temperature in a specific range, and a polyester resin having an acid value and a glass transition temperature in a specific range are described below. And a curing agent having a functional group capable of reacting with a hydroxyl group, and using the resin composition for a powder coating containing an essential component as an intermediate coating or an undercoat, when a multilayer coating film is formed, very good. When the conventional resin composition for powder coating is used, the overcoat resistance, weather resistance and chipping resistance of the multi-layer coating film as well as the excellent coating appearance and interlayer adhesion are obtained. The curing agent [B] used in this case is a block polyisocyanate compound or a uretdione-type self-blocking agent represented by the following structural formula (1). It is preferable to use a block polyisocyanate compound, and the block polyisocyanate compound and the uretdione-type self-block polyisocyanate compound may be used alone or in combination. They found what they could do, and completed the present invention.

That is, the present invention provides: The hydroxyl value is 20 to 200 (mgKOH / g),
Polyester resin having a glass transition temperature of 35 ° C. or higher [A-
1] and a polyester resin having an acid value of 20 to 200 (mg KOH / g) and a glass transition temperature of 35 ° C. or more [A-
2] and a curing agent [B] having a functional group capable of reacting with a hydroxyl group as essential components, and the total acid value of the polyester resins [A-1] and [A-2] is 10 to 100.
The powder coating [I] obtained from the resin composition blended so as to give a coating material is applied to an object to be coated and cured by heating.
A method of forming a multi-layer coating film, which comprises applying a coat paint [II], further applying a transparent top coat paint [III], and baking and drying.

[0009] 2. The colored basecoat paint [II] is a paint obtained by combining a vinyl copolymer having a hydroxyl group and at least one compound selected from the group consisting of aminoplasts, polyisocyanates and blocked polyisocyanates. The method for forming a multilayer coating film according to Item 1,

[0010] 3. The hydroxyl value is 20 to 200 (mg KO
H / g), a polyester resin [A-1] having a glass transition temperature of 35 ° C. or more, and an acid value of 20 to 200 (mg KOH).
/ G), a polyester resin [A-2] having a glass transition temperature of 35 ° C. or higher and a curing agent [B] having a functional group capable of reacting with a hydroxyl group as essential components, and a polyester resin [A- 1] and the total acid value of [A-2] is 10 to 10.
A powder coating [I] obtained from a resin composition compounded so as to have a composition of 100 is applied to an object to be coated and cured by heating, and then a topcoat coating [IV] is applied and baked and dried. A multilayer coating film forming method,

4. A colored basecoat paint [IV] comprising at least one resin selected from the group consisting of a hydroxyl group-containing alkyd resin, a hydroxyl group-containing polyester resin and a hydroxyl group-containing vinyl copolymer, and aminoplasts and polyisocyanates 4. The method for forming a multi-layer coating film according to the above 3, which is a paint obtained by combining at least one compound selected from the group consisting of and a blocked polyisocyanate,

5. 5. The method for forming a multilayer coating film according to the above 1, 2, 3, or 4, wherein the curing agent [B] having a functional group capable of reacting with a hydroxyl group is a block isocyanate compound.

6. The above-mentioned 1, 2, 3, or 4, wherein the curing agent [B] having a functional group capable of reacting with a hydroxyl group is a block isocyanate compound having a uretdione bond represented by the following structural formula (1) as a structural unit. A multi-layer coating film forming method, and

[0014]

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[0015] 7. A curing agent [B] having a functional group capable of reacting with a hydroxyl group comprises a block isocyanate compound having a uretdione bond represented by the following structural formula (1) as a structural unit and a block isocyanate compound other than the above. The method for forming a multilayer coating film according to the above 1, 2, 3, or 4, which is a mixture of

[0016]

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Is provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the method for forming a multilayer coating film of the present invention will be described below. The present invention generally discloses two types of multilayer coating film forming methods. The first method for forming a multilayer coating film is a method for applying a coating material, a powder coating layer [I] used in the method for forming a multilayer coating film of the present invention, and baking and curing the powder coating layer. It consists of components of a coating layer consisting of a base coat paint [II] and a coating layer consisting of a transparent top coat paint [III]. After the powder coating [I] according to the present invention is applied and heat-cured to form a coating layer, a colored basecoat coating [II] is further applied, and a transparent topcoat coating [II] is further applied thereon. III], and a method for forming a multilayer coating film by simultaneously heating and drying (curing) the coating film layer and the coating film layer.

On the other hand, the second method for forming a multilayer coating film comprises coating the object to be coated, the powder coating film [I] of the present invention, baking and curing the powder coating layer, and a top coat coating. [I
V], and a top coat paint [IV] is applied in place of the coat layer in the first multilayer paint film forming method and heat-dried (cured). It discloses a method of forming a multi-layer coating film by forming a coating film layer.

Hereinafter, each component of the method for forming a multilayer coating film of the present invention will be described in detail. The object to be coated, which is the first component, refers to a substrate to which a paint is applied, and specifically, an unpainted metal material such as an unpainted steel plate, an untreated or chemically treated aluminum substrate, and the like. And the car body, 2
Examples include base materials used for road vehicles such as wheel bodies, base materials used for automobile parts such as aluminum wheels, and roads such as automobile bodies that have been subjected to electrodeposition coating. Substrates used for vehicles are also included. Further, base materials used for home electric appliances, vending machines, steel furniture and the like, for example, electrogalvanized steel sheets, hot-dip galvanized steel sheets and the like are also exemplified.

These substrates may be processed into a shape suitable for the final use, or may be in a form to which a PCM (pre-coated metal) coating method is applied, that is, a roughly plate-shaped cut plate-shaped substrate. After the multilayer coating film is formed by the method of the present invention, it may be bent into a predetermined shape according to the purpose, or may be completely post-processed such as coil coating. The substrate used in the provided coating system may be used.

The powder coating layer obtained by coating and baking and curing the powder coating [I] of the present invention, which is the second component constituting the multilayer coating film of the present invention, is defined as a hydroxyl value. Is a polyester resin [A-1] having a glass transition temperature of 35 ° C. or higher and an acid value of 2 to 200 (mgKOH / g).
0 to 200 (mgKOH / g) and a glass transition temperature of 3
The polyester resin [A-2] having a temperature of 5 ° C. or higher and a curing agent [B] having a functional group capable of reacting with a hydroxyl group are essential components, and the polyester resin [A-1] and the polyester resin [A-
The powder coating layer obtained by applying a powder coating [I] obtained from a resin composition blended so that the total acid value of 2] is 10 to 100 to an object to be coated and heating and curing the coating is obtained. To tell.

The polyester resins [A-1] and [A-2] used for preparing the powder coating [I] can be prepared by a well-known and usual method. In general, a method of dehydrating and condensing glycols and polybasic acids is simple.

The polyester resins [A-1] and [A-2] used in the method for forming a multilayer coating film of the present invention include various types of glycols used in preparing ordinary polyester resins. Polybasic acids can be used. Typical examples include glycols such as 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, and hydrogenated bisphenol A. Alicyclic glycols such as propylene oxide adduct of ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6-hexanediol, diethylene glycol, dipropylene glycol -Neopentyl glycol, 2-methyl-1,3
-Propylene glycol, 2-ethyl, 2-butylpropanediol, triethylene glycol, bisphenol-
A, an ethylene oxide adduct of bisphenol A,
Propylene oxide adduct of bisphenol A, glycerin, trimethylolpropane, trimethylolethane, trishydroxymethylaminomethane, trishydroxyethylisocyanurate, pentaerythritol
And dipentaerythritol.

Representative examples of polybasic acids include phthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic anhydride, tetrabromophthalic anhydride, Tetrachloro phthalic anhydride, heptic anhydride, hymic anhydride, maleic anhydride, fumaric acid, itaconic acid, trimellitic anhydride, methylcyclohexentricarboxylic anhydride, pyromellitic anhydride and 1,4-cyclohexanedicarboxylic acid, There are alicyclic carboxylic acids such as 1,3-cyclohexanedicarboxylic acid, and alicyclic acid anhydrides such as hexahydrophthalic anhydride.

In addition to these polyhydric alcohols and polybasic acids, monohydric alcohols such as methanol, propanol, butanol and benzyl alcohol, benzoic acid, p-te
Monobasic acids such as rt-butylbenzoic acid, fatty acids such as castor oil fatty acid, coconut oil fatty acid and soybean oil fatty acid, and one molecule such as dimethylolpropionic acid and hydroxypivalyl pivalate. Compounds having both a hydroxyl group and a carboxyl group, epoxy resins, cardura E ₁₀
Compounds having an epoxy group such as (glycidyl ester of a branched fatty acid manufactured by Shell, Netherlands) can also be used.

The hydroxyl value of the polyester resin [A-1], which is an essential component used in the method for forming a multilayer coating film of the present invention, must be in the range of 20 to 200 (mgKOH / g). , Especially 50-100 (mg KOH /
It is desirably within the range of g). Hydroxyl value is 20
If it is smaller than (mgKOH / g), the solvent resistance of the coating layer is insufficient, so that the appearance of the obtained multilayer coating film is inferior, and conversely, the hydroxyl value is larger than 200 (mgKOH / g). Then, the chipping resistance of the obtained multilayer coating film becomes inferior.

Next, the acid value of the polyester resin [A-2] needs to be 20 to 200 (mg KOH / g), and preferably 50 to 100 (mg KOH / g). If the acid value is less than 20 (mgKOH / g), the interlayer adhesion during overbaking of the multilayer coating film will be poor, and if it exceeds 200 (mgKOH / g), the appearance will deteriorate and the coating film will be discolored. It is not preferable.

The polyester resins [A-1] and [A-2]
In order to maintain the interlaminar adhesion of the multilayer coating film, it is extremely necessary to adjust the acid value of the polyester resin component to 10 to 100 (mg KOH / g) as a whole. As the method for adjusting the acid value of the polyester resin [A-2], the charge ratio of the polybasic acid and the glycol may be considered in advance when synthesizing the polyester resin, or after synthesizing the hydroxyl group-containing polyester resin, phthalic anhydride, A method of adding an acid anhydride such as succinic acid or trimellitic anhydride may be used.

Next, the polyester resins [A-1] and [A-2], which are essential components used in the method for forming a multilayer coating film of the present invention, need to have a glass transition temperature of 35 ° C. or higher. In particular, the temperature is preferably in the range of 40 to 70 ° C. If the glass transition temperature is lower than 35 ° C., the blocking resistance of the powder coating [I] becomes extremely poor.

The glass transition temperature Tg of the polyester resin can be measured by a differential scanning calorimetry method.
At a heating rate of ° C., a glass transition temperature Tg is obtained at the first inflection point.

Further, the curing agent [B] having a functional group capable of reacting with a hydroxyl group, which is an essential component used in the method for forming a multilayer coating film of the present invention, refers to a compound having a functional group reactive with a hydroxyl group. , Typical examples are aminoplasts,
There are block polyisocyanates and the like. Representative examples of aminoplasts include amino group-containing compounds such as melamine, urea, acetoguanamine, benzoguanamine, steroganamin, and spiroguanamine, and aldehyde-based compound components such as formaldehyde, paraformaldehyde, acetaldehyde, and glyoxal. Condensates obtained by reacting according to a conventional method or those obtained by etherifying each of these condensates with alcohols, and the like, are usually used as long as they are used for paints. Of course, it can be used. Among them, those partially or completely etherified with alcohols having 1 to 4 carbon atoms are preferable. Specific examples of such aminoplasts include hexamethyletherified methylolmelamine, hexabutyletherified methylolmelamine, Methyl butyl mixed etherified methylol melamine, methyl etherified methylol melamine, butyl etherified methylol melamine, isobutyl etherified methylol melamine, condensates thereof, and the like.

Further, when only typical representative examples are given as the blocked polyisocyanate compounds, there may be mentioned aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as xylylene diisocyanate and isophorone diisocyanate; Organic diisocyanates such as aromatic diisocyanates such as diisocyanate and 4,4'-diphenylmethane diisocyanate, or adducts of these organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins (polyester polyols), water, etc. And polymers of organic diisocyanates (including isocyanurate-type polyisocyanate compounds) and isocyanates as described above. Various blocking agent of polyisocyanate compounds conventionally known, lactams such as Uretto body,
There are products obtained by blocking with an oxime or the like. Examples of commercially available products include VESTANAT B13
58/100, VESTAGON B1065, B
1530 (all block polyisocyanates manufactured by Huls, Germany), Cleran UI, Cleran TPLS
2122 (block polyisocyanate manufactured by Sumitomo Bayer Urethane Co.).

Further, as the polyisocyanate compound,
A so-called self-block type compound having a uretdione bond represented by the following structural formula (1) in the molecule can also be used.

[0035]

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Vestagon BF15 is an example of such a self-block type polyisocyanate.
EP-BF1300 (a self-block type block polyisocyanate having a uretdione bond manufactured by Huls, Germany) and Cleran
TPLS2147 (self-block type block polyisocyanate having a uretdione bond manufactured by Sumitomo Bayer Urethane Co., Ltd.) and the like. It is also preferable to add an epoxy resin such as a bisphenol A diglycidyl ether type epoxy resin in order to improve corrosion resistance and adhesion. Representative examples of epoxy resins include Epicron 3050, Epicron 4050, and Epicron 70.
50 [all epoxy resins manufactured by Dainippon Ink and Chemicals, Inc.] and the like.

These polyester resins [A-1],
In order to prepare the powder coating [I] used in the method for forming a multilayer coating film of the present invention from [A-2] and the curing agent [B], a well-known conventional method can be employed. The polyester resins [A-1] and [A-2] and the curing agent [B] may be further used, if necessary, with pigments such as titanium oxide and carbon black, curing accelerators such as dibutyltin laurate, benzoin, and flow agents. It is convenient to use a so-called mechanical pulverization method in which components such as a surface conditioner are mixed by a high-speed mixer, melt-kneaded using a single-screw or twin-screw kneader, and then finely pulverized.

The powder coating [I] thus obtained is adjusted in particle size by means of a sieve or the like, and then applied to an object by a well-known and usual method, and then baked to form a cured coating film on the object. You.

Next, a coating layer composed of a colored basecoat paint [II], which is a component of the multilayer coating film according to the present invention, will be described. The colored basecoat paint [II] used for forming the coating film layer is a paint mainly using water or an organic solvent as a medium. Typical examples of those using water as a medium include (1) an aqueous resin as a binder, (2) a dispersion (water dispersion) type resin as a binder, and (3) an emulsion. And those using a polymer as a binder. (1)
Examples of the (2) type include those obtained by copolymerizing a carboxyl group-containing vinyl monomer to obtain an acid group-containing acrylic resin, and further neutralizing with an amine to make the resin completely water-soluble. Are water-dispersible polyurethane resins having an anion-forming group (JP-B-3-45755).
No. 6,086,045. And the type (3) includes those comprising an aqueous solution of an emulsion polymer (disclosed in JP-A-56-157358) containing crosslinkable polymer fine particles.

Typical examples of paints using an organic solvent as a medium include a polymer soluble in an organic solvent such as toluene and xylene, for example, an organic solvent solution of a vinyl resin having a hydroxyl group, and a vinyl copolymer. Coatings formed by combining aminoplasts, polyisocyanates, blocked polyisocyanates, and the like that react with the hydroxyl groups in the coalescence are exemplified.

Among these pigmented basecoat paints [II], a vinyl copolymer having a hydroxyl group mainly using water or an organic solvent as a medium, an aminoplast or a polyether which reacts with the hydroxyl group in the vinyl copolymer. A coating comprising a combination of an isocyanate and a blocked polyisocyanate is preferable. Since the effect of improving the adhesion to the cured coating film composed of the powder coating [I] is remarkable, a vinyl copolymer having a hydroxyl group and an aminoplast are used. Is particularly preferred.

These colored basecoat paints [II] using water or an organic solvent as a medium may be used in addition to these resin components, inorganic pigments such as titanium oxide, extenders, organic pigments, aluminum flakes and mica flakes. And other additives such as a glittering (metallic) pigment such as a black pigment, a curing accelerator, and a leveling agent.

Next, the coating layer obtained from the transparent top coat paint [III], which is a component of the multilayer coating according to the present invention, will be described. The transparent top coat paint [III] used for forming the coating film layer which is a component of the multilayer coating film forming method of the present invention includes a colored base coat paint [I].
The resin composition using water or an organic solvent as a medium described in the description of [I] can be used, and a resin composition for powder coating substantially containing no water or an organic solvent can also be used. .

Top coat paint [III] used at that time
Forms a transparent coating film, and may be colored as long as it is transparent. The coating layer and the coating layer are applied to the object in this order, and then baked and dried at the same time.As a result, a multilayer coating film in which the coating layer and the respective layers are laminated is formed. Become. However, a so-called 2C2B step of baking and drying the coating layer after the coating layer is applied and before the coating layer is applied.
(2 coat 2 bake) method, so-called 2C1B (2 coat 1 bake) method which does not take such a baking step, and further, a coating film A step of preliminarily drying the layer in a temperature range from room temperature to about 100 ° C. may be taken.

Next, the second method for forming a multilayer coating film of the present invention will be described. The second method for forming a multi-layer coating film of the present invention comprises a coating material, a powder coating layer obtained by applying and baking and curing the powder coating material [I] of the present invention, and a top coat coating material [IV]. The coating elements and coating layers are the same as those of the first multilayer coating film forming method described above. The coating layer is a coating layer formed by applying a baking curing reaction to a coating layer after the coating layer is formed thereon.
As the paint [IV], a transparent top coat paint [III] used in forming the above-mentioned coating film layer can also be used. However, in the second multilayer coating film forming method, Unlike the case of a coating layer, the coating layer may be transparent or opaque.

Representative examples of the resin composition that can be used as the top coat paint [IV] include the aforementioned toluene,
Polymers soluble in organic solvents such as xylene, for example, an alkyd resin or polyester resin having a hydroxyl group, an organic solvent solution of a vinyl copolymer having a hydroxyl group, and an aminoplast or polyamine that reacts with the hydroxyl group of these polymers. Isocyanates, a composition obtained by combining a blocked polyisocyanate, an organic solvent solution of a vinyl copolymer having a carboxylic acid group, and an epoxy group-containing compound that reacts with the carboxylic acid group of the polymer. And the like. In addition, the above-described resin composition using water as a medium can be used, and a resin composition for powder coating which does not substantially contain water or an organic solvent can be exemplified. May contain opaque pigments such as titanium oxide and carbon black.

Among these top coat paints [IV],
Mainly using water or an organic solvent as a medium, an alkyd resin having a hydroxyl group, a polyester resin or a vinyl copolymer, respectively, and a combination of an aminoplast, a polyisocyanate, and a blocked polyisocyanate which react with a hydroxyl group in these resins. Coatings are preferred, and since the effect of improving the adhesion to the cured coating film composed of the powder coating [I] is remarkable, alkyd resins each having a hydroxyl group,
Particularly preferred are paints comprising a combination of a polyester resin, a vinyl copolymer and an aminoplast.

[0048]

Next, the present invention will be described in more detail with reference to Reference Examples, Examples and Comparative Examples. In the following, all parts and percentages are by weight unless otherwise specified.

Reference Example 1 [Preparation of Polyester Resin [A-1]] In a reaction vessel equipped with a stirrer, thermometer, rectification tower and nitrogen gas inlet, 283 parts of neopentyl glycol, 1,4
-97.9 parts of cyclohexanedimethanol and 122.5 parts of trimethylolpropane were charged, and the mixture was heated to 150 ° C while stirring under a nitrogen atmosphere, and 632.9 parts of isophthalic acid and 0.5 parts of dibutyltin oxide were added. The temperature was raised to 240 ° C. The dehydration condensation reaction was continued at the same temperature to obtain a polyester resin having a hydroxyl value of 110 mgKOH / g, an acid value of 3.0 mg / KOH / g, and a glass transition temperature (Tg) of 50 ° C. by differential scanning calorimetry. This is abbreviated as polyester resin [A-1-1].

Reference Example 2 (Same as above) 389 parts of neopentyl glycol and 100.9 parts of trishydroxyethyl isocyanurate were charged into a reaction vessel equipped with a stirrer, a thermometer, a rectification tower, and a nitrogen gas inlet. The temperature was raised to 150 ° C. while stirring under an atmosphere, and 649.3 parts of isophthalic acid and 0.5 part of dibutyltin oxide were further added, and the temperature was raised to 240 ° C.
The dehydration condensation reaction is continued at the same temperature, and the hydroxyl value is 50 mg KO.
A polyester resin having an H / g of 5.0 mg / KOH / g and a Tg of 58 ° C. by differential scanning calorimetry was obtained. This is abbreviated as polyester resin [A-1-2].

Reference Example 3 (same as above) In a reaction vessel equipped with a stirrer, a thermometer, a rectification tower and a nitrogen gas inlet, 50.9 parts of ethylene glycol, 341.9 parts of neopentyl glycol and trimethylolpropane were added. 5 parts were charged and heated to 150 ° C. while stirring under a nitrogen atmosphere, and terephthalic acid 663.6 was added.
, 30.8 parts of adipic acid and 0.5 part of dibutyltin oxide, and the mixture was heated to 240 ° C. The dehydration condensation reaction is continued at the same temperature, and the hydroxyl value is 80 mgKOH / g.
A polyester resin having an acid value of 3.0 mg / KOH / g and a Tg of 52 ° C. by differential scanning calorimetry was obtained. This is abbreviated as polyester resin [A-1-3].

Reference Example 4 [Preparation of Polyester Resin [A-2]] Polyester resin [A-1-1] 1 prepared in Reference Example 1
The reaction was carried out by charging 14.1 parts of phthalic anhydride to 00 parts at 180 ° C. and having a hydroxyl value of 50 mg KOH / g and an acid value of 50.
A polyester resin having a mgKOH / g and a Tg of 54 ° C. was obtained. This is abbreviated as polyester resin [A-2-1].

REFERENCE EXAMPLE 5 (Same as above) 292.4 parts of neopentyl glycol and 84.1 parts of trimethylolpropane were charged into a reaction vessel equipped with a stirrer, a thermometer, a rectification tower and a nitrogen gas inlet. The temperature was raised to 150 ° C. while continuing stirring under an atmosphere, and 755.2 parts of isophthalic acid and 0.1 ml of dibutyltin oxide were added.
5 parts were further added, and the temperature was raised to 240 ° C. The dehydration condensation reaction is continued at the same temperature, and the hydroxyl value is 10 mgKOH / g,
A polyester resin having an acid value of 100 mgKOH / g and a Tg of 55 ° C. was obtained. The polyester resin [A-
2-2].

Reference Example 6 (Preparation of polyester resin for comparison) In a reaction vessel equipped with a stirrer, a thermometer, a rectifying tower and a nitrogen gas inlet, 137 parts of ethylene glycol and 230 parts of neopentyl glycol were added. And trimethylolpropane 4
Charge 3 parts and continue stirring under a nitrogen atmosphere for 15 minutes.
The temperature was raised to 0 ° C., 753 parts of terephthalic acid and 0.5 part of dibutyltin oxide were further added, and the temperature was raised to 240 ° C. The dehydration condensation reaction is continued at the same temperature, and the hydroxyl value is 40 m.
A polyester resin having an acid value of 3 mgKOH / g, a Tg of 68 ° C., and a gKOH / g was obtained. This is abbreviated as a comparative polyester resin [A '].

Reference Examples 7 to 12 [Preparation of Powder Coating [I] Used in Examples and Comparative Examples] Resin compositions for powder coatings were blended in the ratios shown in Table 1 below, and After melt-kneading using a Nieder-PR-46 type (uniaxial kneader manufactured by Buss, Switzerland), finely pulverized, and further classified with a 150-mesh wire netting, the average particle size is 30 to 40 μm. Was prepared. These powder coatings were used as shown in Table 1 [I-1] to [I-
6].

[0056]

[Table 1] Table 1

Footnotes in Table 1 1): Block polyisocyanate produced by Hüls, Germany, in which the nucleate of isophorone diisocyanate is blocked with ε-caprolactam 2): Isophorone, manufactured by Hüls, Germany Diisocyanate
Block polyisocyanate obtained by self-blocking a uretdione bond 3): a polyglycidyl ether type epoxy resin of bisphenol A manufactured by Dainippon Ink and Chemicals, Inc. 4): BASF, Germany 5): Ishihara Sangyo Co., Ltd., rutile type titanium oxide 6): Mitsubishi Chemical Co., Ltd., carbon black

Reference Example 13 [Colored basecoat paint [II]
Preparation of Aqueous Resin [A] Used for Preparation] To a reaction vessel equipped with a stirrer, a thermometer, a condenser, and a nitrogen gas inlet, 680 parts of deionized water, 2 parts of ammonium persulfate, and Triton X-20015 parts were added. Heated to 95 ° C. An aqueous emulsion of the following acrylic monomer component was added dropwise to the reaction system at 95 ° C. over 4 hours, and the mixture was kept for 3 hours after the completion of the addition. Thereafter, the reaction solution was cooled, and 5 parts of dimethylethanolamine and 40 parts of deionized water were added. Thus, a stable milky white dispersion of an aqueous acrylic resin having a solid content of 45% was obtained. This is abbreviated as aqueous resin [A].

Acrylic monomer component: Methyl methacrylate 450 parts Ethyl acrylate 350 parts 2-hydroxyethyl methacrylate 150 parts Acrylic acid 20 parts Ethylene glycol di-methacrylate 30 parts n-octyl mercaptan 5 parts Ammonium persulfate 4 parts Triton X-200 15 parts (anionic surfactant manufactured by Rohm & Haas) Emulgen 840s 10 parts (nonionic surfactant manufactured by Kao Atlas) 530 parts of deionized water

Reference Example 14 (Preparation of thickener) "Acryzole ASE-60" (Rome and
6 parts of dimethylethanolamine and 530 parts of deionized water were added to 64 parts of a thickener manufactured by Haas Co., Ltd. (solid content: 28%) to obtain a target product having a solid content of 3%. This thickener is abbreviated as [AD].

Reference Example 15 [Colored basecoat paint [II]
Preparation of aqueous resin [A] 10 parts, thickener [AD] 10 parts obtained in Reference Example 3, Cymel 300 (hexamethoxymethylated melamine manufactured by Mitsui Cyanamid Co., Ltd.) 5 parts, and paratoluenesulfonic acid 1 part in 100 parts of aqueous resin [A]. , Aluminum paste dispersion # 491
9 (Toyo Aluminum Co., Ltd. product aluminum paste) 3
Part, aluminum paste dispersion # 55-519 (manufactured by the company)
1.5 parts was mixed with 12 parts of isopropanol and adjusted to a viscosity of 16 seconds (Ford Cup No. 4/20 ° C.) with deionized water. This is abbreviated as colored basecoat paint [II].

Reference Example 16 [Transparent topcoat paint [II
Preparation of I] Using the same reactor as that used in Reference Example 13,
500 parts of xylene was charged into a reaction vessel, and the temperature was raised to 120 ° C. Subsequently, 150 parts of styrene, 150 parts of methyl methacrylate, 75 parts of n-butyl acrylate, 125 parts of 2-hydroxyethyl methacrylate, 3 parts of azobisisobutyronitrile, and t-butyl peroctoate (hereinafter referred to as TBPO) Abbreviated.) 4 parts mixture
After the dropping, the temperature is maintained at the same temperature for 10 hours. The topcoat paint having a nonvolatile content of 50.5% and a hydroxyl value of 53 (mgKOH / g) based on a solution [ III] to obtain a resin solution. This resin solution is abbreviated as Topcoat paint resin [T-1].

Next, the resin for topcoat paint [T
-1] 100 parts of Super-Beckamine L-117-60
[Butyl etherified melamine formaldehyde resin manufactured by Dainippon Ink and Chemicals, Inc.] 35.7 parts was added, and the viscosity was adjusted to 24 seconds using Solvesso 100 (an aromatic hydrocarbon organic solvent manufactured by Exxon) (Ford Cup). No4 / 2
0 ° C). Use this as a transparent topcoat paint [III
-1].

Reference Example 17 (same as above) 400 parts of xylene was charged into the same reaction vessel as used in Reference Example 16, and the temperature was raised to 135 ° C. Then, a mixture of 90 parts of styrene, 240 parts of methyl methacrylate, 30 parts of 2-ethylhexyl acrylate, 240 parts of glycidyl methacrylate and 24 parts of TBPO was added dropwise at the same temperature over 6 hours. . After the completion of the dropwise addition, the reaction was continued at the same temperature for another 8 hours. After the completion of the polymerization reaction, the resin solution was kept under a reduced pressure of 30 Torr, xylene was distilled off, and the nonvolatile content was 99.5%, the softening point by the ring and ball method was 117 ° C., the epoxy equivalent was 380, and A copolymer solid having a number average molecular weight of 4,700 was obtained. Hereinafter, this is abbreviated as Topcoat paint resin [T-2].

This resin for topcoat paint [T-2] 7
To 6 parts, 24 parts of dodecanedioic acid (hereinafter abbreviated as DDA) was added, and 1 part of Modafuro (a flow modifier manufactured by Monsanto Co.) was added. Then, as in Reference Examples 7 to 12, A powdery topcoat clear paint which can be used as a transparent topcoat paint [III] was obtained. This is abbreviated as transparent top coat paint [III-2].

Reference Example 18 [Preparation of Topcoat Paint [IV]] The resin for topcoat paint [T-
1] 27 parts of titanium oxide were added to 100 parts, and the pigment and resin were dispersed using a sand mill. To this dispersion, 35.7 parts of Super-Beckamine L-117-60 (butyl ether melamine formaldehyde resin manufactured by Dainippon Ink and Chemicals, Inc.) was added, and the viscosity was changed to 24 seconds (Food Cup No. 1). 4/20 ° C)
00 (Exxon aromatic hydrocarbon solvent)
A top coat paint containing a pigment was obtained. This is the top
Abbreviated as paint [IV-1].

Reference Example 19 (same as above) To 58.3 parts of Veccosol J-524-IM-60 [alkyd resin manufactured by Dainippon Ink and Chemicals, Inc.], 50 parts of titanium oxide was added, and a sand mill was used. To disperse the pigment and the resin. Super Beckamine L-117-60 [butyl ether melamine formaldehyde resin manufactured by Dainippon Ink and Chemicals, Inc.] 25
Part, and the viscosity is 24 seconds (Forecup No. 4/2)
(0 ° C.) with Solvesso 100 (an aromatic hydrocarbon solvent manufactured by Exxon Co.) to obtain a topcoat paint containing a pigment. This is abbreviated as Topcoat paint [IV-2].

Reference Example 20 (same as above) 84.5 parts of Finedick A-224S [glycidyl group-containing acrylic resin manufactured by Dainippon Ink and Chemicals, Inc.]
A colored powder coating was prepared in the same manner as in Reference Example 7, except that 15.5 parts of DDA, 0.5 part of Acronal 4F, 0.5 part of benzoin, and 50 parts of titanium oxide were used. This is abbreviated as Topcoat paint [IV-3].

Examples 1 to 9 and Comparative Examples 1 to 4 The coating films shown in Tables 2 to 5 were prepared according to the method for forming a multilayer coating film shown below, and the coating film performance test was carried out. The results are shown in Tables 2 to 5.

The powder coatings prepared in Reference Examples 7 to 12 [I-
1] to [I-6], the colored basecoat paint [II] prepared in Reference Example 15, the topcoat paints [III-1], [III-2], and [IV-1] prepared in Reference Examples 16 to 20. ] To [IV
-3], and multilayer coating films of the present invention and comparative examples were prepared by the following method.

First, the substrate used as the object to be coated is
"Bonderite # 3030" [mild steel sheet treated with a zinc phosphate treating agent manufactured by Nippon Parkerizing Co., Ltd.]
An epoxy resin-based cationic electrodeposition paint was applied by electrodeposition.

Next, a powder paint [I-1] or the like is applied to the object by electrostatic powder coating so that the film thickness after baking becomes 50 μm, and then baking is performed at 180 ° C. for 20 minutes. Was done. After the object to be cooled is cooled to room temperature, the colored basecoat paint [II] is heated at a temperature of 25 ° C and a relative humidity of 6 ° C.
Under a coating atmosphere of 5 to 70%, the coating was performed twice so that the dry film thickness became 20 μm. The setting was performed for 2 minutes between these two coatings. 1
The air pressure of the spray gun at the time of the second coating is 5 (Kg / c
m ² ), the flow rate of the paint was 400 (m / min), and at the time of the second coating, the flow rate of the paint was 200 (m / min), and the distance between the object to be coated and the spray gun was 40 cm. The object was held such that the application surface on the object was always perpendicular to the discharge direction.

After the two coatings, the object to be coated was air-dried at a temperature of 30 ° C. for 5 minutes and further cooled to room temperature, and then the top coat paints [III-1], [III-2],
[IV-1] to [IV-3] were coated. In this case, the top coat paint is [III-1] and [IV-1], [IV-
In the case of [2], coating was carried out by a normal spray coating method, and the baking temperature was 140 ° C./20 minutes. When the top coat paint is [III-2] or [IV-3], it is applied by electrostatic powder coating so that the dry film thickness becomes 60 μm, and baked at 150 ° C. for 20 minutes. Was. Various performances were evaluated for each cured coating film thus obtained. The results are summarized in Tables 2 to 5.

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[Table 2] Table 2

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[Table 3] Table 3

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[Table 4] Table 4

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[Table 5] Table 5

The procedure for evaluation judgment was as follows. Smoothness: Judged visually. The criteria are as follows. ◎ ・ ・ The coating film is very smooth and smooth ○ ・ ・ There is a large round in the coating film × ・ ・ There is fine dust on the coating film

60 degree gloss: 60 degree specular reflectance (%)
Numerical evaluation by.

Metallic feeling: [ALCOPE LMR
-100 ”(a metallic feeling measuring device manufactured by Kansai Paint Co., Ltd.) and numerically evaluated according to the IV value obtained. The correspondence with the visual evaluation is as follows. Excellent: Exceeding 250: The arrangement of the aluminum flakes is good and the appearance is very beautiful, and the depth feeling unique to the metallic coating film can be sufficiently exhibited depending on the viewing angle. Good: 200 or more and less than 250: The arrangement of aluminum flakes is generally good, but the brightness of the coating film is slightly inferior. Poor: Less than 200: The arrangement of the aluminum flakes was disordered, and the coating film was blackened.

DuPont impact: Evaluation by a DuPont impact tester (1/2 inch). Indicated by a height (cm) at which no defects such as cracks occur in the coating film when a load of 500 g is dropped. The higher the value, the better the impact resistance.

Erichsen: Evaluation with an Erichsen tester. The larger the value, the better the flexibility of the coating film.

Chipping resistance: A test plate cooled to -20 ° C. was placed at a 90 ° angle at 5 atm. 200g using the pressure of
The peeling state of the coating film when the No. 7 crushed stone was applied was visually evaluated. The evaluation criteria are as follows.・: Almost no peeling is observed. Δ: Some peeling of the coating layer is observed. X: Large peeling of the powder coating layer was observed, and the lowermost electrodeposition coating film was also damaged, and the metal surface was exposed.

Overbake interphase adhesion: A coated plate in which the curing temperature of the powder coating was changed to 220 ° C./30 minutes was immersed in warm water of 40 ° C. for 10 days, and a cross cut was made 30 minutes after lifting. A peel test using an adhesive tape was performed. The evaluation criteria are as follows.・: No peeling was observed between any of the coating layers or between the object to be coated and the coating layer. Δ: Partial peeling was observed between any of the coating layers or between the object to be coated and the coating layer. ×: Delamination is observed on the entire surface.

Water resistance: The gloss retention after the test plate was immersed in warm water at 40 ° C. for 10 days was evaluated. The evaluation criteria are as follows. A: The gloss retention exceeds 80%.・: Gloss retention is less than 60% to less than 80%. X: The gloss retention was less than 60%.

Weather resistance: Expressed as a gloss retention (%) after 1000 hours by Sunshine Weather Meter [Suga Test Instruments Co., Ltd.]. The higher this value, the better the weather resistance.

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The coating film obtained by the method for forming a multilayer coating film of the present invention is a cured coating film which is excellent in various physical properties such as a topcoat coating appearance, adhesion between overbaked layers and chipping resistance. give.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B05D 7/24 302 B05D 7/24 302T C09D 5/03 C09D 5/03 157/00 157/00 167/00 167/00 175/04 175/04 F-term (Reference) 4D075 AA09 AA82 BB26Y BB26Z BB89X CA04 CA13 CA32 DA06 DB05 DC12 EA02 EB15 EB35 EB38 EB55 EC02 EC11 EC37 4J038 CG141 DA132 DD001 DD002 DD041 DD042 DG03 MA03 DG001 MA03 PA02 PA07 PA19 PB07 PC02

Claims (7)

[Claims] A hydroxyl value of 20 to 200 (mg KOH /
g), a polyester resin [A-1] having a glass transition temperature of 35 ° C. or more, and an acid value of 20 to 200 (mgKOH /
g), a polyester resin [A-2] having a glass transition temperature of 35 ° C. or higher and a curing agent [B] having a functional group capable of reacting with a hydroxyl group as essential components, and a polyester resin [A-1] ] And [A-2] have a total acid value of 10 to 1
After the powder coating [I] obtained from the resin composition blended so as to give a coating composition having a viscosity of 00 and applied to the object to be cured by heating, a colored basecoat coating [II] is applied, and a transparent top coat is further applied. -A method for forming a multilayer coating film, which comprises applying a paint [III] and baking and drying. 2. A colored basecoat paint [II] comprising a vinyl copolymer having a hydroxyl group and one or more compounds selected from the group consisting of aminoplasts, polyisocyanates and blocked polyisocyanates. The method for forming a multilayer coating film according to claim 1, wherein the coating material is a combination of the coating materials. 3. A compound having a hydroxyl value of 20 to 200 (mg KOH /
g), a polyester resin [A-1] having a glass transition temperature of 35 ° C. or more, and an acid value of 20 to 200 (mgKOH /
g), a polyester resin [A-2] having a glass transition temperature of 35 ° C. or higher and a curing agent [B] having a functional group capable of reacting with a hydroxyl group as essential components, and the polyester resin [A-1] ] And [A-2] have a total acid value of 10 to 1
The composition is characterized in that a powder coating [I] obtained from a resin composition blended to give 00 is applied to an object to be coated and cured by heating, and then a topcoat coating [IV] is applied and baked and dried. Method for forming a multilayer coating film. 4. A colored basecoat paint [IV] comprising an alkyd resin having a hydroxyl group, a polyester resin having a hydroxyl group or a vinyl copolymer having a hydroxyl group, and aminoplasts, polyisocyanates and block polyisocyanates. The method for forming a multilayer coating film according to claim 3, wherein the coating material is a paint obtained by combining at least one compound selected from the group consisting of: 5. The method according to claim 1, wherein the curing agent [B] having a functional group capable of reacting with a hydroxyl group is a block isocyanate compound. 6. The curing agent [B] having a functional group capable of reacting with a hydroxyl group is a block isocyanate compound having a uretdione bond represented by the following structural formula (1) as a structural unit. 5. The method for forming a multilayer coating film according to 2, 3 or 4. Embedded image 7. A curing agent [B] having a functional group capable of reacting with a hydroxyl group comprises a block isocyanate compound having a uretdione bond represented by the following structural formula (1) as a structural unit, and another block isocyanate: 5. The method for forming a multilayer coating film according to claim 1, which is a mixture with a net compound. Embedded image