JPH09271718A - Multilayer coating film forming method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To establish a method for forming a multilayer coating film, which is excellent not only in the appearance of the coating film but also in various properties such as interlayer adhesion, chipping resistance, and weather resistance. SOLUTION: A powder coating obtained by using a polyester resin having a specific structural unit as an essential component is coated, and a coating obtained by baking and curing is further coated with a base coat coating and a top coat coating, By forming a multi-layer coating film, it became possible to develop a coating system with extremely high practicality as described above.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel and useful method for forming a multilayer coating film. More specifically, the present invention relates to a specific polyester resin obtained by using a glycol having an alicyclic structural unit and / or a polybasic acid,
A powder coating obtained from a resin composition containing a curing agent having a functional group capable of reacting with a hydroxyl group in the resin as an essential constituent is applied, and after heating and curing, a base coat coating is applied, and Consists of applying a clear topcoat paint, baking and drying,

Alternatively, after coating the above-mentioned specific powder coating material and curing by heating, a top coat coating material is coated,
The present invention relates to a method for forming a coating film, which comprises baking and drying, and provides a multilayer coating film excellent in appearance, weather resistance, interlayer adhesion and chipping resistance, among others.

The method for forming a multi-layer coating film according to the present invention is capable of obtaining a multi-layer coating film of extremely high practicality, especially when formed on an automobile body.

[0004]

2. Description of the Related Art Powder coating is one form of coating that does not contain organic solvents. In recent years, however, its low pollution has attracted attention from the viewpoint of environmental problems such as air pollution, and the amount used has increased year by year. are doing. Its applications are wide-ranging, including painting of metal products such as home appliances and building materials, but due to the characteristics of powder coatings that solvent that evaporates during coating is virtually non-existent, it can also be used as an automotive coating agent. Examination of application is progressing.

At present, there are various kinds of resin compositions for powder coatings which are practically used. For example, a composition obtained by combining a polyester resin mainly having a hydroxyl group and a block isocyanate compound has a good appearance, mechanical properties and weather resistance, and is widely used. The composition obtained by combining the polyester resin with the epoxy resin is also widely used because the obtained coating film has excellent corrosion resistance and the like.

On the other hand, looking at conventional techniques for coating automobile bodies, at present, an intermediate coating containing an organic solvent is applied to an object to be coated (such as an automobile body) that has been subjected to cationic electrodeposition coating, The mainstream is the coating method in which after baking and drying, the base coat paint containing an organic solvent and the top coat paint containing an organic solvent are sequentially applied and baked and cured. .

However, in such a conventional technique, since the organic solvent is volatilized at the time of coating as described above, such a coating method is problematic in terms of environmental hygiene.

As a method for avoiding the volatilization of the organic solvent, it is possible to use a powder coating material which does not substantially contain an organic solvent, but in the present circumstances, the powder coating material is used as the intermediate coating material. In this case, the powder coating obtained is inferior in smoothness, weather resistance and solvent resistance to conventional organic solvent-based coatings. Even if a so-called multi-layer coating film is formed in the form of applying an organic solvent-based base coat paint or a top coat paint on the intermediate coating film obtained by , Among others, the appearance,
It was inferior in weather resistance and chipping resistance.

[0009]

As described above, as long as the conventional technique is followed, a multilayer coating film excellent in appearance, weather resistance, interlayer adhesion and chipping resistance, among others, is inevitable. It was very difficult to provide a coating film forming method of giving.

Therefore, the present inventors have a very high practicality that the obtained multilayer coating film is particularly excellent in appearance, weather resistance and chipping resistance, and also in interlayer adhesion. In order to provide an innovative method for forming a multilayer coating film, we have earnestly started research.

Therefore, the problem to be solved by the present invention is, in particular, the appearance of the coating film of the top coat,
An object of the present invention is to provide a novel method for forming a multilayer coating film, which has excellent properties such as weather resistance, interlayer adhesion and chipping resistance, and which is extremely highly practical.

[0012]

However, in order to solve the problems of the conventional technique as described above, the present inventors have
In addition, as a result of earnestly and repeatedly focusing on the problem to be solved by the invention as described above, as a result, it has an alicyclic structural unit (1) having a structure as described below, and A powder containing a polyester resin having a hydroxyl value in a specific range and a softening point by a ring and ball method in a specific range, and a curing agent having a functional group capable of reacting with a hydroxyl group in the polyester resin, as essential film-forming components. When the resin composition for paints is used as an intermediate paint or an undercoat paint to form a multilayer coating film, it is of course possible to obtain a very good coating film appearance, In particular, it is found that the weather resistance and the chipping resistance are also significantly improved as compared with the case where the conventional resin composition for powder coating is used. Came to complete.

Alicyclic structural unit (1)

[0014]

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(However, the position of the substituent in the above structural unit formula represents any of the ortho position, the meta position and the para position.)

That is, the present invention basically comprises, as one, respectively, a glycol (a-1) having an alicyclic structural unit as listed above or an alicyclic structural unit as listed above. Having a hydroxyl value of 10 to 350 (mgKOH / g) and a softening point of 80 to 150 by the ring and ball method, which is obtained by using at least one of the polybasic acids (a-2) having A powder coating [I] obtained from a resin composition containing as essential components a polyester resin [A] at 0 ° C. and a curing agent [B] having a functional group capable of reacting with the hydroxyl groups of this polyester resin [A]. To
A method for forming a multilayer coating film, which comprises coating an object to be coated, heat-curing it, then coating a base coat paint [II], further coating a transparent top coat paint [III], and baking and drying. Is what you are trying to

Two, glycols (a-1) having an alicyclic structural unit as listed above or polybasic acids (a-2) having an alicyclic structural unit as listed above.
A hydroxyl value of 10 to 350 (mgKOH / g) obtained by using at least one of the above as an essential component.
And a polyester resin [A] having a softening point of 80 to 150 ° C. according to the ring and ball method, and this polyester resin [A]
After coating a powder coating [I] obtained from a resin composition containing a curing agent [B] having a functional group capable of reacting with the hydroxyl group of (1) as an essential component on an object to be coated and heat curing,
Another object of the present invention is to provide a method for forming a multilayer coating film, which comprises coating a top coat paint [IV], baking and drying.

Means for solving various problems in the conventional technique as described above will be described. The present invention provides the following alicyclic structural unit (1).

[0019]

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(However, the positions of the substituents in the above structural unit formulas represent either the ortho position, the meta position or the para position.)

At least one of the glycols (a-1) having the above or the polybasic acids (a-2) having the alicyclic structural unit (1) as described above is used as an essential raw material component. Each of the obtained hydroxyl values is 10 to 3
A curing agent having a specific polyester resin [A] of 50 (mgKOH / g) and having a softening point of 80 to 150 ° C. by the ring and ball method and a functional group capable of reacting with a hydroxyl group in the polyester resin [A] A powder coating [I] obtained from a resin composition containing [B] as an essential constituent (film-forming component) is applied to an object to be coated and cured by heating, and then a base coat coating [ II], and further, a transparent top coat paint [III] is applied, baked and dried, and a novel method for forming a multilayer coating film is disclosed.

The present invention further relates to glycols (a-1) having the alicyclic structural unit (1) as listed above or polybasic acids having the alicyclic structural unit (1) as listed above. At least one of (a-2) is used as an essential raw material component, and each has a hydroxyl value of 10 to 10.
A specific polyester resin [A] having a softening point of 80 to 150 ° C. according to the ring and ball method of 350 (mgKOH / g) and a curing agent having a functional group capable of reacting with a hydroxyl group in the polyester resin [A] A powder coating [I] obtained from a resin composition containing [B] as an essential constituent (film-forming component) is applied to an object to be coated and cured by heating, and then a top coat coating [ IV] is applied, and a novel method for forming a multilayer coating film, which comprises baking and drying, is also disclosed.

Hardener [B] used in this case
Although various compounds can be used as the compound, a block polyisocyanate compound or the following structural formula (2)

[0024]

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It is desirable to use a so-called self-blocked polyisocyanate compound of the uretdione type represented by: At this time, it is needless to say that the block polyisocyanate compound and the self-block polyisocyanate compound may be used alone or in combination of these two type compounds.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Further, a method for forming a multilayer coating film according to the present invention will be described below, particularly focusing on the constitution of the present invention.

The present invention broadly discloses two types of methods for forming a multilayer coating film. The first method for forming a multilayer coating film comprises applying [1] an object to be coated and [2] a powder coating [I] used in the method for forming a multilayer coating film according to the present invention, followed by baking and curing. And a coating layer formed by [3] base coat coating [II] and [4] coating layer formed by transparent top coat coating [III] And

Specifically, the powder coating [I] used in the present invention is applied onto the article [1] to be coated, and the coating is heated and cured to form the coating layer [2]. Furthermore, after coating the base coat paint [II] and the transparent top coat paint [III] on it, the coating layer [3] and the coating layer [4] are simultaneously dried by heating (curing). Disclosing the method of forming a multilayer coating film is disclosed.

On the other hand, the second method for forming a multilayer coating film is formed by applying [1] an object to be coated and [2] the powder coating [I] used in the present invention, followed by baking and curing. And a coating layer formed from the top coat coating [IV], which is a coating film in the first method for forming a multilayer coating film. By replacing the layers [3] and [4] with the above-mentioned top coat paint [IV], heat-drying (curing), and then forming a coating film layer [5], a multilayer coating film is obtained. The method of forming is disclosed.

The respective constituent elements in the method for forming a multilayer coating film according to the present invention will be described in detail below.

First, a detailed description of the above-mentioned first method for forming a multilayer coating film is as follows.

That is, the first constituent [1] article to be coated refers to a base material to which the paint is applied, and specifically, it is an unpainted steel plate, untreated, Or unpainted metal materials such as aluminum base material that has been subjected to chemical conversion treatment, for base materials used for road vehicles such as automobile bodies and motorcycle bodies, and for automobile parts such as aluminum wheels Examples include base materials used for
Substrates used for road vehicles, such as automobile bodies with electrodeposition coating, are also included. Furthermore, base materials used for home appliances and steel furniture, such as
Electric galvanized steel sheet, hot-dip galvanized steel sheet, etc.
Particularly, it is exemplified as a typical one.

These various base materials may be processed into a shape according to the end use, or a form to which a PCM (pre-coat metal) coating method is applied, that is, a rough plate shape. The cut plate-shaped substrate may be formed by the method of the present invention, after which the multilayer coating film is formed into a predetermined shape according to the purpose. Further, it may be a substrate of the class used in coating systems such as coil coatings, where it is fully post-processed,
Of course.

The powder coating composition [I] used in the present invention [2] which is the second constituent element of the multilayer coating film formed by the method for forming a multilayer coating film according to the present invention. ] And the coating layer obtained by baking and curing is

Of the glycols (a-1) having the alicyclic structural unit (1) as described above or the polybasic acids (a-2) having the alicyclic structural unit (1) as described above, A hydroxyl value of 10 to 350 (mgKOH / g) obtained by using at least one of them as an essential raw material component,
Moreover, a polyester resin [A] having a softening point of 80 to 150 ° C. according to the ring and ball method,

A powder coating obtained from a resin composition containing a curing agent [B] having a functional group capable of reacting with the hydroxyl group in the polyester resin [A] as an essential constituent (film-forming component) [ [I] is referred to as a coating layer in a form obtained by heat curing.

The above-mentioned polyester resin [A] which can be used when preparing such a powder coating [I] can be prepared by various known and commonly used methods, but is generally used. For this, a method of dehydration-condensing glycols and polybasic acids is recommended because it is simple and easy.

The polyester resin [A] used in the method for forming a multilayer coating film according to the present invention means the glycols (a- having the alicyclic structural unit (1) as described above.
1) or at least one of the polybasic acids (a-2) having the alicyclic structural unit (1) as described above is used as an essential raw material component to designate a resin in such a form. .

Here, only typical examples of glycols (a-1) having an alicyclic structural unit that can be used as an essential raw material component are 1,4-cyclohexane. Various alicyclic glycols represented by dimethanol, hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, propylene oxide adduct of hydrogenated bisphenol A, and the like.

Similarly, only the representative examples of the polybasic acids (a-2) having an alicyclic structural unit which can be used as an essential raw material component are given as follows: And various cycloaliphatic carboxylic acids represented by 4-cyclohexanedicarboxylic acid or 1,3-cyclohexanedicarboxylic acid,
Alternatively, it is an acid anhydride of various alicyclic groups represented by hexahydrophthalic anhydride. Of course, each of the glycols (a-1) and the polybasic acids (a-2) having these alicyclic structural units may be used alone or in combination.

Further, in addition to each of these essential raw material components, it is used when preparing the polyester resin.
Various glycols and various polybasic acids can also be used together.

Of these, only typical ones are exemplified, ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6.
-Hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, bisphenol A, and the like, and further, bisphenol A ethylene oxide adduct or bisphenol A propylene oxide adduct, glycerin, trimethylolpropane, Examples include trishydroxymethylaminomethane, trishydroxyethyl isocyanurate, pentaerythritol, and dipentaerythritol.

Further, to list only particularly representative polybasic acids, phthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic anhydride, Tetrabrom phthalic anhydride, tetrachlorophthalic anhydride, hettic anhydride, hymic acid anhydride [this "hymic acid"
Is a registered trademark of Hitachi Chemical Co., Ltd. ], Maleic anhydride, fumaric acid, itaconic acid, trimellitic anhydride, methylcyclohexene tricarboxylic acid anhydride or pyromellitic anhydride.

In addition to these polyhydric alcohols and polybasic acids, various monohydric alcohols such as methanol, propanol, butanol or benzyl alcohol, benzoic acid or p-tert-butylbenzoic acid, etc. Various monobasic acids, castor oil fatty acid,
Various fatty acids such as coconut oil fatty acid or soybean oil fatty acid, and further various forms such as dimethylolpropionic acid or hydroxypivalyl pivalate having both a hydroxyl group and a carboxyl group in one molecule. Compound or epoxy resin, "Cardura E10"
Various epoxy group-containing compounds such as (trade name of glycidyl ester of branched fatty acid, manufactured by Shell Co., Netherlands) can also be used.

The hydroxyl value of the polyester resin [A], which is one essential constituent component (one film forming component) used in the method for forming a multilayer coating film according to the present invention, is 10 to 35.
The range of 0 (mgKOH / g) is suitable, and the range of 50 to 350 (mgKOH / g) is preferable.

When the hydroxyl value is less than 10, the coating layer [2] is liable to have insufficient solvent resistance, and the appearance of the resulting multilayer coating film may be poor. The resulting multilayer coating film tends to be inferior, and in particular, the chipping resistance and the like are also inferior. In any case, the layer coating film tends to be inferior in smoothness and the like, which is not preferable.

In addition, the polyester resin [A]
The softening point according to the ring and ball method is appropriately in the range of 80 to 150 ° C. When the softening point is lower than 80 ° C, the powder coating [I] is apt to be inferior in blocking resistance, and when the softening point is higher than 150 ° C. In particular, the resulting multilayer coating film tends to have insufficient smoothness, which is not preferable in any case.

Next, a hydroxyl group in the polyester resin [A] as described above, which is an essential component (film forming component) of the powder coating [I] used in the method for forming a multilayer coating film according to the present invention, is added. The curing agent [B] having a functional group capable of reacting refers to a compound having a functional group capable of reacting with a hydroxyl group. Of these, only typical ones are exemplified. Aminoplast,
Examples thereof include polyisocyanate compounds or block polyisocyanate compounds.

First, only representative examples of aminoplasts are given, and various amino group-containing compounds such as melamine, urea, acetoguanamine, benzoguanamine, steroguanamine or spiroguanamine, and formaldehyde and para. Formaldehyde, acetaldehyde or glyoxal, and various aldehyde compound components, by various known and conventional methods, such as a condensate in the form obtained by reacting, or each of these condensates, Compounds in the form obtained by etherification with alcohols, etc., of course, any compound can be used as long as it is usually used for paints. Is.

Among them, it is particularly preferable to use a partially or completely etherified form of the C ₁ -C ₄ alcohols, and only a particularly representative form of such aminoplasts is preferable. Hexamethyl etherified methylol melamine,
Examples thereof include hexabutyl etherified methylol melamine, methylbutyl mixed etherified methylol melamine, methyl etherified methylol melamine, butyl etherified methylol melamine, and isobutyl etherified methylol melamine, and condensates thereof.

Further, only representative examples of polyisocyanate compounds are exemplified, various aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; xylylene diisocyanate or isophorone diisocyanate, Various cycloaliphatic (alicyclic) diisocyanates; or various organic diisocyanates typified by various aromatic diisocyanates such as tolylene diisocyanate or 4,4′-diphenylmethane diisocyanate;

Further, there are adducts of these various organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins (polyester polyols), water, and the like. Examples include polymers of organic diisocyanates (including isocyanurate type polyisocyanate compounds) and isocyanate biuret.

Furthermore, only by exemplifying only typical examples of the block polyisocyanate compound, various polyisocyanate compounds as mentioned above are blocked with various known and commonly used blocking agents. Such as those obtained by incarnation,

To give a list of only typical commercial products of this type, "VESTANAT B
1358/100 "or" VESTAGON B10
65 or B1530 "(both are trade names of block polyisocyanates manufactured by Hüls, Germany)
Or "Kureran UI or TPLS2122" [trade name of block polyisocyanate manufactured by Sumitomo Bayer Urethane Co., Ltd.].

Further, as the polyisocyanate compound, in particular, in the molecule, the following structural formula (2)

[0056]

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It is also possible to use compounds of the so-called self-blocking type polyisocyanates having a uretdione bond represented by:

As only typical examples of such self-blocking type polyisocyanates, "VESTAGON BF1540 or EP-BF1300" (both manufactured by Hüls, Germany, containing uretdione bond) are given. (Trade name of self-blocking type block polyisocyanate compound) and “Clelan TPLS2147” [Sumitomo Bayer Urethane Co., Ltd.'s self-blocking type block polyisocyanate compound containing uretdione bond] Product name].

To prepare the powder coating [I] used in carrying out the method for forming a multilayer coating film of the present invention from the polyester resin [A] and the curing agent [B], respectively, it is known and commonly used. Although various methods of can be adopted,
Generally, the polyester resin [A] and the curing agent [B] are further mixed with various additive components such as a pigment, a curing accelerator and / or a surface modifier, and melt kneaded. The so-called mechanical crushing method of crushing after crushing is further recommended because it is simple and convenient.

The powder coating [I] thus obtained is electrostatically powder-coated on the substrate to be coated by various known and conventional methods, and then baked to obtain the desired cured coating film. Will be formed on the substrate to be coated.

Subsequently, the coating layer [3] formed of the above-mentioned base coat coating [II], which is one component of the multilayer coating film according to the present invention, will be described in detail.

The base coat paint [II] used for forming the coating layer [3] is a paint obtained by using water or an organic solvent as a medium. is there.

First of all, only representative examples of water-based paints will be given. As an example, a water-based resin binder and a dispersion (water dispersion) type resin binder will be used. And a form using an emulsion polymer as a binder.

As the paints belonging to the above type,
For example, an acrylic resin containing an acid group by copolymerization with a vinyl monomer containing a carboxyl group, and further neutralizing with an amine to form an aqueous solution of a polymer completely solubilized. And so on,
Examples of the paints belonging to the above-mentioned type include those composed of a water-dispersible polyurethane resin having an anion-forming group as disclosed in Japanese Patent Publication No. 3-45755. Examples of paints belonging to JP-A-56-157358
And the like, which are composed of an emulsion polymer aqueous solution containing cross-linkable polymer fine particles.

If only representative examples of paints using an organic solvent as a medium are given as examples, polymer compounds soluble in various organic solvents such as toluene or xylene, for example, hydroxyl groups. A composition in the form of a combination of an organic solvent solution of a vinyl copolymer having the following and a polymer compound capable of reacting with, for example, aminoplast, polyisocyanates or block polyisocyanates.

These base coat paints [II] in a form obtained by using water or an organic solvent as a medium are, in addition to these resin components, various known inorganic pigments such as titanium oxide; extender pigments. Organic pigments; or various commonly used glittering (metallic) pigments such as aluminum flakes and mica flakes; curing accelerators; or various additives typified by leveling agents Can be included.

Next, the coating layer [4] formed of the above-mentioned transparent top coat coating [III], which is one component of the multilayer coating film according to the present invention, will be described in detail.

The transparent topcoat paint [III] used for forming the coating layer [4] is mainly a powder in a form obtained by using water or an organic solvent as a medium. It is possible to use the resin composition for paints, and it is also possible to use the resin composition for powder paints which is substantially free of water, organic solvent and the like.

The top coat paint used in this case is for forming a transparent coating film, and needless to say, may be colored as long as it is transparent.

As described above, each coating layer [3]
And the coating layer [4] is coated in this order on the various substrates to be coated as described above, and then simultaneously baked and dried, so that the coating layer [2],
This means that a so-called multi-layer coating film in which each layer [3] and [4] is laminated is formed. However, after coating the coating layer [3], before coating the coating layer [4], the coating layer [3] is baked and dried, that is, the so-called 2C2B ( It is also possible to adopt a 2 coat 2 bake) system, a so-called 2C1B (2 coat 1 bake) system in which such a baking step is not performed, and further, the coating layer [3] is It is also possible to take a preliminary step of drying in a temperature range from room temperature to about 100 ° C.

Next, the other one of the methods for forming a multilayer coating film according to the present invention, that is, the second method for forming a multilayer coating film, will be described in detail.

The other method for forming a multilayer coating film according to the present invention is obtained by applying [1] an object to be coated and [2] the powder coating material [I] used in the present invention and baking and curing. A coating layer and a coating layer formed from the [5] topcoat coating composition [IV], which are referred to as a method for forming a multilayer coating film comprising each coating layer,
Regarding the article to be coated [1] and the coating layer [2], the constituent elements and the usage are the same as in the case of the first method for forming a multilayer coating film as described above.

The remaining coating layer [5] is formed on the coating layer [2] after the coating layer [2] as described above is formed by the baking and curing reaction, and thus formed. The top coat coating [IV] used in this case refers to a coating layer, and the transparent top coating [III] used when forming the coating layer [4] as described above. However, in the other method for forming a multilayer coating film of the present invention, unlike the case of the coating layer [4] as described above, the coating layer [5] can be used.
As such, it may be transparent or opaque.

As only a typical resin composition which can be used as the top coat paint [IV], only the representative ones are listed in the above-mentioned various organic solvents such as toluene or xylene. A soluble polymer compound, for example, an organic solvent solution of a vinyl copolymer having a hydroxyl group, and an aminoplast, a polyisocyanate or a block polyisocyanate capable of reacting with the hydroxyl group of the polymer compound, respectively. A resin composition for powder coating in a combined form, etc.
As described above, it is also possible to use a resin composition for powder coating in the form of water as a medium, water, an organic solvent, etc.,
Substantially, it is a resin composition for powder coating in the form of not containing, such various resin compositions, such as titanium oxide and carbon black, has a hiding property,
Various pigments can be included.

Each of the thus obtained polyester resins [A] and a curing agent [B] having a functional group capable of reacting with the hydroxyl group of the polyester resin [A] are obtained from a resin composition as essential components. The powder coating [I] is applied to an object to be coated, heated and cured, then the base coat coating [II] is coated, and further the transparent top coat coating [III] is coated, baked and dried.

Alternatively, a powder coating obtained from a resin composition comprising a polyester resin [A] and a curing agent [B] having a functional group capable of reacting with the hydroxyl groups of the polyester resin [A] as essential components [ I] is applied to an object to be coated, heat-cured, and then topcoat paint [IV] is applied, followed by baking and drying, whereby the method for forming a multilayer coating film according to the present invention is successfully achieved. It is that.

That is, the 2C2B (2 coat 2 bake) system and the 2C1B (2 coat 1 bake) system are used, and further, the coating layer [3] described above is preliminarily subjected to a temperature of from room temperature to about 100 ° C. It is said that the method of the present invention can be successfully achieved by adopting various methods in which the drying is performed within the range.

[0078]

EXAMPLES Next, the present invention will be explained more specifically with reference to Reference Examples, Examples and Comparative Examples, but the present invention is by no means limited to these Examples. Absent. In the following, all parts and percentages are by weight unless otherwise specified.

Reference Example 1 [Preparation example of polyester resin [A] used in the method for forming a multilayer coating film of the present invention]

A reaction vessel equipped with a stirrer, a thermometer, a rectification column and a nitrogen gas inlet was charged with 127 g of ethylene glycol.
, 293 parts of 1,4-cyclohexanedimethanol and 46 parts of trimethylolpropane were charged, and the temperature was raised to 150 ° C. under a nitrogen atmosphere while continuing stirring.

To this, 683 parts of terephthalic acid and 0.5 part of dibutyltin oxide were added, the temperature was raised to 240 ° C., and the dehydration condensation reaction was continued at the same temperature to give a hydroxyl value of 55 mgKOH / The target polyester resin [A] having a weight of g and a softening point by the ring and ball method of 110 ° C. was obtained. Hereinafter, this is abbreviated as polyester resin [A-1].

Reference Example 2 (same as above) A reaction vessel equipped with a stirrer, a thermometer, a rectification column and a nitrogen gas inlet was charged with 229 parts of ethylene glycol and 165 parts of trimethylolpropane, and under a nitrogen atmosphere, While continuing stirring, the temperature was raised to 150 ° C.

Here, 378 parts of terephthalic acid, 1,4
-By adding 392 parts of cyclohexanedicarboxylic acid and 0.5 part of dibutyltin oxide and heating up to 240 ° C. and continuing the dehydration condensation reaction at the same temperature, the hydroxyl value is 110 mgKOH / g, and A desired polyester resin having a softening point of 90 ° C. according to the ring and ball method was obtained. Hereinafter, this is a polyester resin [A-2]
Abbreviated.

Reference Example 3 (same as above) In a reaction vessel equipped with a stirrer, thermometer, rectification column and nitrogen gas inlet, 21 parts of neopentyl glycol, 1, 4
30 parts of cyclohexanedimethanol and 410 parts of glycerin were charged, and the temperature was raised to 150 ° C. under a nitrogen atmosphere while continuing stirring.

Here, 620 parts of isophthalic acid, 1,4
-By adding 71 parts of cyclohexanedicarboxylic acid and 0.5 part of dibutyltin oxide and raising the temperature to 240 ° C and continuing the dehydration condensation reaction at the same temperature, the hydroxyl value is 320 mgKOH / g, and A desired polyester resin having a softening point of 110 ° C. by the ring and ball method was obtained. Hereinafter, this is a polyester resin [A-3]
Abbreviated.

Reference Example 4 (same as above) A reaction vessel equipped with a stirrer, a thermometer, a rectification column and a nitrogen gas inlet was charged with 222 parts of ethylene glycol, 94 parts of hydrogenated bisphenol A and 140 parts of trimethylolpropane. After charging, the temperature was raised to 150 ° C. under a nitrogen atmosphere while continuing stirring.

Here, 620 parts of isophthalic acid, 1,4
-71 parts of cyclohexanedicarboxylic acid and 0.5 parts of dibutyltin oxide were added, and the temperature was raised to 240 ° C. By continuing the dehydration condensation reaction at the same temperature, a target polyester resin having a hydroxyl value of 150 mgKOH / g and a softening point of 120 ° C. according to the ring and ball method was obtained. Hereinafter, this is a polyester resin [A-4]
Abbreviated.

Reference Example 5 [Preparation Example of Control Polyester Resin Used in Comparative Symmetrical Multilayer Coating Forming Method]

137 of ethylene glycol was placed in a reaction vessel equipped with a stirrer, a thermometer, a rectification column and a nitrogen gas inlet.
Parts, 230 parts of neopentyl glycol and 43 parts of trimethylolpropane were charged, and the temperature was raised to 150 ° C. in a nitrogen atmosphere while continuing stirring.

753 parts of terephthalic acid and 0.5 part of dibutyltin oxide were added thereto, the temperature was raised to 240 ° C., and the dehydration condensation reaction was continued at the same temperature to give a hydroxyl value of 40 mgKOH / The objective polyester resin having a softening point of 115 ° C. by the ring and ball method was obtained. Hereinafter, this is abbreviated as a control polyester resin [A ′].

Reference Examples 6 to 12 [Preparation examples of powder coating [I] used in the method for forming a multilayer coating film according to the present invention and the method for forming a reference multilayer coating film]

Tables 1 and 2 listed below, respectively
The resin composition for powder coating was blended in the proportions shown in the table, and the blend thus obtained was used as a co-kneader PR-46 type "(manufactured by Buss in Switzerland, uniaxial kneader). After melt-kneading using the product name),
By finely pulverizing and further classifying with a wire mesh of 150 mesh, the average particle size is 30 to 40 micro
Various powder coatings of meters (μm) were prepared.

After that, each powder coating was
As shown in the table and Table 2, [I-1] to [I-
7].

[0094]

[Table 1]

<< Footnotes in Table 1 >> 1) Manufactured by Huls in Germany: Trade name of block polyisocyanate obtained by blocking the nurate of isophorone diisocyanate with ε-caprolactam

2) Product name of block polyisocyanate manufactured by Huls in Germany: Isophorone diisocyanate is self-blocked by uretdione bond.

[0097]

[Table 2]

<< Footnotes in Table 2 >> 3) Trade name of bisphenol A polyglycidyl ether type epoxy resin manufactured by Dainippon Ink and Chemicals, Inc.

4) Trade name of surface conditioner manufactured by BASF, Germany

5) Trade name of rutile type titanium oxide manufactured by Ishihara Sangyo Co., Ltd.

6) Trade name of carbon black manufactured by Mitsubishi Chemical Corporation

[0102]

[Table 3]

[0103]

[Table 4]

Reference Example 13 [Preparation example of water-based resin [W] used as a component of base coat paint [II] used in the method for forming a multilayer coating film according to the present invention]

A reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen gas inlet was charged with 680 deionized water.
Parts, 2 parts of ammonium persulfate, and “Triton
15 parts of "x-200" (Note) was added, and the temperature was raised to 95 ° C.

An aqueous emulsion of an acrylic monomer component as shown below was added dropwise to this reaction system at 95 ° C. over 4 hours, and after the completion of the addition, it was held for 3 hours. Then, the reaction solution was cooled and 5 parts of dimethylethanolamine and 40 parts of deionized water were added.

Thus, stable, solid content of 45%,
A target milky white dispersion of an aqueous acrylic resin was obtained. Hereinafter, this is abbreviated as an aqueous resin [WA].

Acrylic monomer component

Methyl methacrylate 450 parts Ethyl acrylate 350 parts 2-Hydroxyethyl methacrylate 150 parts Acrylic acid 20 parts Ethylene glycol dimethacrylate 30 parts

N-octyl mercaptan 5 parts ammonium persulfate 4 parts “Triton X-200” 15 parts “Emulgen 840s” (note) 10 parts deionized water 530 parts

[0111]

[Footnote] Rohm and Haas (Rohm & H)
Product name of anionic surfactant manufactured by aas)

Trade name of nonionic surfactant manufactured by Kao Atlas Co., Ltd.

Reference Example 14 [Preparation Example of Thickener] 64 parts of “Acrysol ASE-60” (trade name of thickener manufactured by Rohm and Haas Co .; solid content = 28%) was added to dimethyl ethanol. Addition of 6 parts of amine and 530 parts of deionized water gave the desired thickener with 3% solids. Hereinafter, this is abbreviated as [AD].

Reference Example 15 [Example of preparation of base coat paint [II] used in the method for forming a multilayer coating film according to the present invention]

Reference Example 1 was added to 100 parts of the aqueous resin [WA].
10 parts of the thickener [AD] obtained in No. 4, "Cymel 30
0 "[trade name of hexamethoxymethylated melamine manufactured by Mitsui Cyanamid], 1.0 part of paratoluenesulfonic acid (p-toluenesulfonic acid), and" aluminum paste dispersion # 4919 ". Mix 12 parts of isopropanol with 3 parts of [trade name of aluminum paste manufactured by Toyo Aluminum Co., Ltd.] and 1.5 parts of "aluminum paste dispersion liquid # 55-519" (product of the same company). Ford with deionized water at 20 ° C
Cup No. The viscosity according to No. 4 was adjusted to 16 seconds. Hereinafter, this is abbreviated as base coat paint [II].

Reference Example 16 [Preparation example of transparent top coat paint [III] used in the method for forming a multilayer coating film according to the present invention]

A reaction vessel similar to that of Reference Example 13 was charged with 500 parts of xylene and heated to 120 ° C. Then 150 parts of styrene, 15 parts of methyl methacrylate
0 part, 75 parts of n-butyl acrylate and 125 parts of 2-hydroxyethyl methacrylate, 3 parts of azobisisobutyronitrile and 3 parts of tert-butyl peroctoate (hereinafter abbreviated as TBPO). The mixture consisting of is added dropwise over 4 hours, and the temperature is kept at the same temperature for 10 hours even after the completion of the addition, so that the nonvolatile content is 50.5% and the hydroxyl value on the solution basis is A solution of 53 (mg KOH / g) of the desired resin for use in the preparation of the top coat paint [III] was obtained. Hereinafter, this resin solution is abbreviated as a resin [T-1] for top coat paint.

Then, 100 parts of the resin solution of this resin [T-1] was added to "Super Beckamine L-117-6.
0 ”[trade name of butyl etherified melamine formaldehyde resin manufactured by Dainippon Ink and Chemicals, Inc.] 3
5.7 parts was added and "Solvesso 100" (trade name of aromatic hydrocarbon organic solvent manufactured by Exxon Chemical Co., Ltd.) was used.
Ford Cup No. at 20 ° C. The viscosity according to No. 4 was adjusted to 24 seconds. Hereinafter, this is abbreviated as transparent top coat paint [III-1].

Reference Example 17 [Preparation example of transparent top coat coating composition [III] used in the method for forming a multilayer coating film according to the present invention]

400 parts of xylene was charged into a reaction vessel similar to that of Reference Example 16, and the temperature was raised to 135 ° C. Then 90 parts of styrene, 240 parts of methyl methacrylate
Part, 30 parts of 2-ethylhexyl acrylate and 240 parts of glycidyl methacrylate and 24 parts of TBPO
The mixture consisting of 1 part and 6 parts was added dropwise at the same temperature over 6 hours.

After the dropping was completed, the reaction was continued at the same temperature for 8 hours. After the completion of the polymerization reaction, the solution of the copolymer thus obtained is kept under a reduced pressure of about 30 Torr, and xylene is distilled off to obtain a nonvolatile content of 99.5% and a softening point by a ring and ball method of 117 ° C.
Thus, a solid product of the target copolymer having an epoxy equivalent of 380 and a number average molecular weight of 4,700 was obtained. Hereinafter, this is abbreviated as a resin for top coat paint [T-2].

Then, the resin for the top coat paint [T
-2] to 76 parts of 24 parts, 24 parts of dodecanedioic acid (hereinafter abbreviated as DDA) is added, and further 1 of "Modaflow" (trade name of flow regulator manufactured by Monsanto, USA) After adding 0.0 part, powdery topcoat clear paints that can be used as transparent topcoat paints [III] were obtained in the same manner as in Reference Examples 6 to 12. Hereinafter, this is abbreviated as a transparent top coat paint [III-2].

Reference Example 18 [Preparation example of top coat paint [IV] used in the method for forming a multilayer coating film according to the present invention]

To 100 parts of the resin [T-1] for topcoat paint obtained in Reference Example 16, 27 parts of titanium oxide was added.
Parts were added and the pigment and resin were dispersed using a sand mill.

Then, 35.7 parts of "Super Beckamine L-117-60" was added to this dispersion, and the mixture was kept at 20 ° C.
Ford Cup No. Viscosity of 4 is 24
Diluted with "Solvesso 100" to give a topcoat paint containing pigment. Hereinafter, this is abbreviated as top coat paint [IV].

Examples 1 to 8 and Comparative Examples 1 to 4 According to various methods for forming a multilayer coating film as shown below,
Various coating films as shown in Tables 3 to 5 were prepared, and then comparative study tests of coating film performances were conducted. The results are summarized in each table.

Powder coatings prepared in Reference Examples 6 to 12 [I-
1] to [I-7], the base coat paint [II] prepared in Reference Example 15, and the top coat paints [III-1], [III-2] and [I] prepared in Reference Examples 16 to 18.
V] and the multilayer coating film of the present invention and the control,
It was prepared by the method described below.

First, as the base material used as the article [1] to be coated, a base material subjected to the following pretreatment was used.

That is, "Bondelight # 3030"
[Product name of mild steel plate manufactured by Nippon Parkerizing Co., Ltd., which was treated with a zinc phosphate-based treating agent], which was electrodeposited with an epoxy resin-based cationic electrodeposition coating was used.

Next, the powder coating [I-1] or the like is electrostatically powder coated onto the article [1] to be coated so that the film thickness after baking is about 50 μm, and then 180 ° C. Baking was performed under the condition of / 20 minutes. After cooling the coated object coated with the powder coating material to room temperature, the base coating material [II] is dried in a coating atmosphere having a temperature of 25 ° C. and a relative humidity of 65 to 70%. Film thickness is 20
The coating was applied twice each so that the thickness became μm. A setting for 2 minutes was performed between these two coatings.

At the time of the first coating, the air pressure of the spray gun was 5 kg / cm ^2, and the flow rate of the coating was 400 m.
/ Min and the flow rate of the paint is 200 during the second coating.
m / min, the distance between the object to be coated and the spray gun is 40 cm
I did it. The substrate for coating was held such that the coated surface on the substrate for coating was always perpendicular to the ejection direction.

After such two times of coating, the coated object is
After air-drying at a temperature of 0 ° C. for 5 minutes and further cooling to room temperature, a transparent top coat paint [III-1]
I painted it.

At this time, when the top coat paints were [III-1] and [IV], the coating was carried out by an ordinary spray coating method, and the baking temperature was 14
It was carried out at 0 ° C./20 minutes. When the top coat paint is [III-2], electrostatic powder coating
Apply it so that the dry film thickness is 60 μm, and 150 ℃
/ 20 minutes of baking was performed.

Each of the cured coating films thus obtained was evaluated for various properties. The results are collectively shown in Tables 3 to 5.

[0135]

[Table 5]

<< Footnote >> The evaluation judgment procedure is as follows.

Smoothness ……………………………………………………………………………………………………………………………………………………………………………………………………………………………… The criteria for evaluation judgment are as follows.

∘: very smooth and smooth coated surface ∘: large round is recognized x: fine dust skin is recognized

60-degree gloss: Numerical evaluation judgment based on 60-degree specular reflectance (%).

Metallic feeling ……………… [ALCOPE
Numerical evaluation was performed according to the IV value obtained by measurement with "LMR-100" [trade name of metallic feeling measuring device manufactured by Kansai Paint Co., Ltd.]. The correspondence with the visual evaluation judgment at that time is as follows.

Excellent: When it exceeds 250, that is, the arrangement of the aluminum flakes is good and the appearance is very beautiful,
In addition, depending on the viewing angle, the metallic coating can provide the depth feeling peculiarly. Good ... In the range of 200 or more and less than 250, that is, the arrangement of the aluminum flakes is generally , If the brightness of the coating film is slightly inferior although it is good, it is inferior. If it is less than 200, that is, the arrangement of the aluminum flakes is disturbed and the coating film is black. If

DuPont Impact: An evaluation judgment test (1/2 inch) using the DuPont impact tester. When a load of 500 g is dropped, the coating film is displayed at a height (cm) at which defects such as cracks do not occur in the coating film, and the larger this value is, the better the impact resistance is. .

Erichsen: Evaluation and judgment test by Erichsen tester. This test was carried out in accordance with a conventional method, and the extrusion distance (mm) when a defect such as cracking or peeling occurred was displayed.

The larger this value, the better the flexibility of the coating film.

Chipping resistance: A test plate cooled to −20 ° C. was measured at an angle of 90 °, at 5 atm. The peeling state of the coating film when 200 g of crushed stone No. 7 was applied was evaluated by visual observation. The evaluation criteria in that case are as follows.

◯: Almost no peeling was observed Δ: Peeling of the coating layer was recognized to some extent ×: Large peeling was observed in the powder coating layer and, moreover, the bottom electrodeposition coating film Also damaged and exposed metal surface

Interphase Adhesion …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… .

The criteria for evaluation judgment are as follows.

◯: No peeling was observed between any of the coating layers or between the coating and the coating layer. Δ: Between any of the coating layers or the coating. When partial peeling is observed between the object and the coating layer x ... When delamination is entirely observed

Water resistance: Test plate at 40 ° C
Evaluation was made on the basis of the gloss retention rate after immersion in warm water for 10 days. The criteria for evaluation judgment are as follows.

⊚: When the gloss retention rate exceeds 80% ◯: When the gloss retention rate is in the range of 60% or more and less than 80% ×: When the gloss retention rate is less than 60%

Weather resistance ………………………………………………………………………………………………………………………………………………………… Sunshine Weather Meter [trade name of Suga Test Instruments Co., Ltd.] However, the higher the value, the better the weather resistance.

[0153]

[Table 6]

[0154]

[Table 7]

[0155]

As is apparent from the above,
The coating film obtained by the method for forming a multilayer coating film according to the present invention is particularly excellent in various physical properties such as the coating film appearance of the top coat, interlayer adhesion, and chipping resistance. The method for forming a layer coating film is extremely practical in that it gives a cured coating film having excellent physical properties as described above.

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Claims (5)

[Claims] 1. An alicyclic structural unit as follows: (However, the positions of the substituents in the above structural unit formulas shall represent any positions of the ortho position, the meta position or the para position.) Glycols (a-1) or the following: Alicyclic structural unit (However, the positions of the substituents in the above structural unit formulas represent any of the ortho, meta, and para positions.) Of the polybasic acids (a-2) A polyester resin [A] having a hydroxyl value of 10 to 350 (mgKOH / g) and a softening point of 80 to 150 ° C. according to the ring and ball method, which is obtained by using at least one of them as an essential component, and the polyester resin [A]. Powder coating [I] obtained from a resin composition comprising a curing agent [B] having a functional group capable of reacting with the hydroxyl group of A] as an essential component
Is applied to an object to be coated, heat-cured, and then coated with a base coat paint [II], further with a transparent top coat paint [III], and baked and dried. Forming method. 2. An alicyclic structural unit such as: (However, the positions of the substituents in the above structural unit formulas shall represent any positions of the ortho position, the meta position or the para position.) Glycols (a-1) or the following: Alicyclic structural unit (However, the positions of the substituents in the above structural unit formulas represent any of the ortho, meta, and para positions.) Of the polybasic acids (a-2) A polyester resin [A] having a hydroxyl value of 10 to 350 (mgKOH / g) and a softening point of 80 to 150 ° C. according to the ring and ball method, which is obtained by using at least one as an essential component, and the polyester resin [A]. Powder coating [I] obtained from a resin composition comprising a curing agent [B] having a functional group capable of reacting with the hydroxyl group of A] as an essential component
Is applied to an object to be coated, heat-cured, and then topcoat paint [IV] is applied, followed by baking and drying. 3. The multilayer coating film formation according to claim 1, wherein the curing agent [B] having a functional group capable of reacting with the hydroxyl group of the polyester resin [A] is a block polyisocyanate compound. Method. 4. The above-mentioned curing agent [B] having a functional group capable of reacting with the hydroxyl group of the polyester resin [A] has the following structural formula: The method for forming a multilayer coating film according to claim 1 or 2, which is a so-called self-blocking polyisocyanate compound having a uretdione bond represented by as a structural unit. 5. The above-mentioned curing agent [B] having a functional group capable of reacting with the hydroxyl group of the polyester resin [A] has the following structural formula: The multilayer coating film formation according to claim 1 or 2, which is a mixture of a so-called self-blocking polyisocyanate compound having a uretdione bond represented by the formula as a structural unit and a block polyisocyanate compound. Method.