JP2002126622A - Method for forming multilayered coating film and multilayered coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a multilayered coating film by which a multilayered coating film having excellent weather resistance, solvent resistance, corrosion resistance and chipping resistance can be formed in a three-wet one-bake method to reduce the coating process, cost and load on the environment. SOLUTION: In the method for forming a multilayered coating film, an electrodeposition coating material consisting of an anionic polyester resin and a cationic epoxy resin is applied on the objective body to be coated and then hardened by heating to form an electrodeposition coating film. Then a water- based intermediate coating material containing a polyester resin having 20 to 100 mgKOH/g acid value of the solid content and a polyester resin having <20 mgKOH/g acid value of the solid content, a water-based base coating material and a clear coating material are successively applied. The unhardened intermediate coating film, base coating film and clear coating film are heated to harden at a time to form a multilayered coating film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multilayer coating film, and more particularly, to a method for forming an electrodeposition coating film and then applying an intermediate coating material, a base coating material and a clear coating material on a wet basis. The present invention relates to a method for forming a multilayer coating film using a three-wet, one-bake coating system in which three unhardened layers are heated and cured at one time.

[0002]

2. Description of the Related Art In recent years, in the field of paints, especially in the field of automotive coatings, resource saving, cost saving and environmental burden (VOC and HOC) have been observed.
(APs etc.) In order to solve the problem of reduction, there is a strong demand for shortening the coating process. That is, in the conventional automobile coating finishing procedure, the electrodeposition coating, the intermediate coating, and the topcoat have been performed by a three-coat three-bake coating method in which each coating is baked after each coating. After baking the electrodeposition coating film, three coating processes of intermediate coating, base coating and clear coating are performed on the wet coating on a wet basis, and a three-wet coating system for baking these wet coating films collectively is performed. It is required to reduce the number of baking steps and to maintain the same appearance, corrosion resistance and impact resistance (chipping resistance) as a three-coat film obtained by a conventional three-coat three-bake coating method.

[0003] With respect to the above-mentioned impact resistance, particularly the so-called chipping resistance due to the collision of obstacles such as pebbles on the vehicle body during running, the conventional three-coat three-bake coating method requires a unique intermediate coating having chipping resistance. By providing a coating film, etc., the chipping resistance was able to be secured. However, when the conventional intermediate coating material was used in the above-described three-wet coating system, problems such as adaptation to the obtained coating film and inversion occurred. It can not be used because it will be inferior in appearance and the coating film obtained by the 3 wet coating system is
There is a drawback that impact resistance and chipping resistance are low.

Japanese Patent Application Laid-Open No. 62-65765 discloses that a resin layer (so-called chipping-resistant primer layer) having an ability to absorb impact on a coating film is formed during the formation of a multilayer film, especially between an electrodeposition coating film and an intermediate coating film. Is disclosed. However, further incorporation of such a step into the painting process of an automobile body does not meet the market needs for the above-mentioned step saving and cost saving.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a three-wet, one-bake coating method aiming at shortening the coating process, reducing costs and reducing environmental burden, and has excellent weather resistance and solvent resistance comparable to conventional three-coat films. An object of the present invention is to provide a method for forming a multilayer coating film capable of forming a multilayer coating film having not only resistance and corrosion resistance but also excellent chipping resistance.

[0006]

According to the present invention, there is provided a step (1) of forming an electrodeposition coating film by applying an electrodeposition coating material on an object to be coated and then heating and curing the same to form an electrodeposition coating film. (2) forming an uncured intermediate coating film by applying an aqueous intermediate coating material to the substrate, and forming an uncured base coating film by applying an aqueous base coating on the intermediate coating film Step (3), and
A step (4) of applying a clear paint thereon to form an uncured clear coating, and simultaneously heating and curing the intermediate coating, the base coating and the clear coating to form a multilayer coating. A method for forming a multilayer coating film comprising a step (5) of obtaining a film, wherein the electrodeposition paint has a solubility parameter of δ.
a) containing particles A containing the resin (a) and resin (b) having a solubility parameter of δb and particles B containing a curing agent, wherein (i) the value of (δb−δa) Is
1.0 or more; (ii) the resin (a) is an anionic polyester resin; (iii) the resin (b) is a cationic epoxy resin; Acid value is 20-100mgKOH / g
Polyester resin (I) having a solid content of 2
Polyester resin (II) less than 0 mgKOH / g
And a method for forming a multilayer coating film. The present invention is also a multilayer coating formed by the above-described method for forming a multilayer coating. Hereinafter, the present invention will be described in more detail.

[0007] The applicant of the present invention states that the solubility parameter is δ.
An electrodeposition paint comprising particles A containing a resin (a) as a, and a resin (b) having a solubility parameter δb and particles B containing a curing agent, wherein (1) (δb−δa) The electrodeposition paint having a value of 1.0 or more, (2) resin (a) being an anionic polyester resin, and (3) resin (b) being a cationic epoxy resin, was prepared by applying Japanese Patent Application No. 11-32811.
A patent application has already been filed as the first publication. This technique is capable of obtaining an electrodeposition coating film having a multilayer structure having excellent appearance, solvent resistance, weather resistance and corrosion resistance comparable to conventional three-coat films.

However, since this upper layer has a low acid value,
When the polarity is low and a normal intermediate coating film is applied, the adhesion between the multi-layer electrodeposition coating film and the intermediate coating film may be reduced in the obtained multilayer coating film. There is a problem that the coating film itself is peeled off by collision of an object. When an intermediate coat containing the same polyester resin as the low acid value polyester resin contained in the upper layer of the multilayer electrodeposition coating is applied, the multi-layer electrodeposition coating and the intermediate coating Although the adhesion is improved, there arises a problem that the curability of the intermediate coating film becomes insufficient and the adhesion to the top coating film is poor.

The present invention relates to the above-mentioned Japanese Patent Application No. 11-328111.
JP-A No. 2000-209, on a polyester resin similar to the low acid value polyester resin contained in the upper layer of the multilayer electrodeposition coating film, further has a solid content acid value of 20 to 100 mg
When a water-based intermediate coating which is a combination of a polyester resin (I) of KOH / g is applied, and a base coating and a clear coating are further applied thereon by wet-on-wet, it is comparable to a conventional three-coat film. A multilayer coating film having not only excellent weather resistance and corrosion resistance but also excellent impact resistance (chipping resistance) can be formed.

The method for forming a multilayer coating film according to the present invention comprises the steps of: (a) coating an electrodeposition coating material on an object to be coated, and then heating and curing to form an electrodeposition coating film; (2) forming an uncured intermediate coating film by applying an aqueous intermediate coating material to the substrate, and forming an uncured base coating film by applying an aqueous base coating on the intermediate coating film Step (3), and
A step (4) of applying a clear paint thereon to form an uncured clear coating, and simultaneously heating and curing the intermediate coating, the base coating and the clear coating to form a multilayer coating. Step (5) for obtaining a film is included.

[0011]Process (1)  In the above step (1), the electrodeposition paint is coated on the object to be coated.
After coating, it is cured by heating to form an electrodeposition coating film.Electrodeposition paint  The electrodeposition paint is a resin having a solubility parameter of δa.
(A) and the solubility parameter is δb.
Containing resin (b) and particles B containing a curing agent
Where (i) the value of (δb−δa) is 1.0 or more and
(Ii) the resin (a) is an anionic polyester
(Iii) the resin (b) is
Epoxy resin.

In the present specification, the particles A and the particles B are prepared as separate emulsions, and both emulsions are mixed in the preparation of the electrodeposition paint, but are fused to each other in the paint. Without separate particles. Particle A above
And an electrodeposition coating containing particles B, to form a multi-layer electrodeposition coating film, of which the layer directly in contact with air is formed of particles A, and the layer directly in contact with the object to be coated is particles B. The electrodeposited coating film having a multilayer structure formed from the above-mentioned electrodeposition paint has a layer in direct contact with air having weather resistance, and a layer in direct contact with an object to be coated having anticorrosion properties. And a high degree of weather resistance.

In the above electrodeposition paint, the particles A are
When the particle B contains a resin (a) having a solubility parameter of δb and the particle B contains a resin (b) having a solubility parameter of δb, (δb−δa)
Is 1.0 or more. An electrodeposited coating film having a multilayer structure can be formed by selecting two types of resin components incompatible or hardly compatible with each other, in which the value of (δb−δa) is 1.0 or more. .

It is generally considered that if the difference in solubility parameter between resins is 0.5 or more, the resin loses compatibility and the coating film exhibits a separated structure. However, in the present invention, it is necessary to form a coating film structure in which the layers are clearly separated from each other. When it is less than 1.0, when electrodeposition coating is performed, a coating film structure in which layers are distinctly separated is not formed, and a coating film having excellent corrosion resistance and weather resistance cannot be obtained.

The above-mentioned solubility parameter δ is generally S
It is also called P (solubility parameter) and is a scale indicating the degree of hydrophilicity or hydrophobicity of the resin, and is also an important scale in judging the compatibility between resins. The solubility parameters are numerically quantified based on turbidity measurement methods known to those skilled in the art (KW Suh, DH Clarke, J. Pol).
ymer. Sci. , A-1,5,1671 (196
7)).

Regarding the resin (a) and the resin (b), those having a large solubility parameter, that is, the resin (b) has a higher affinity for a conductive substrate surface such as a metal having a high surface polarity. Since it is high, the electrodeposition coating film formed from the particles B containing the resin (b) is formed on the side in contact with the conductive substrate made of a metal material or the like during heating and curing. On the other hand, the particles A containing the resin (a) move to the air layer side to form a resin layer. Thus, the difference between the solubility parameters of the two resins is considered to be the driving force that causes the separation of the resin layers.

In the above electrodeposition paint, the resin (a)
Is an anionic polyester resin. The polyester resin is generally obtained by dehydrating and condensing a polybasic acid and a polyol. The anionic polyester resin means a polyester resin having an acid group. The amount of this acid group is 3 to 20 mgKOH /
g, preferably in the range of 5 to 15 mg KOH / g. If it is less than 3 mgKOH / g, the adhesion to the overcoat may be poor. If it exceeds 20 mgKOH / g, there is a possibility that poor curing or difficulty in forming a pigment paste when using blocked polyisocyanate as a curing agent may occur.

The anionic polyester resin preferably has a hydroxyl value in the range of 50 to 150. 50
If it is less than 1, it causes poor curing of the coating film, and if it exceeds 150,
As a result of excessive hydroxyl groups remaining in the coating film after curing, the water resistance may decrease. Further, the number average molecular weight is 1000
The range of ~ 30000 is preferred. If it is less than 1,000, physical properties such as solvent resistance of the cured coating film are inferior. If it exceeds 30,000, the viscosity of the resin solution is high, so that not only handling is difficult in operation such as emulsification and dispersion of the obtained resin, but also the film appearance of the obtained electrodeposition coating film may be significantly reduced. . More preferably, it is 1,000 to 10,000. The above-mentioned anionic polyester resin can be used alone, but in order to balance the coating film performance, 2 is used.
Species or more can also be used.

The above-mentioned anionic polyester resin comprises, in addition to a polyol component, a polybasic acid component and / or an anhydride thereof, lactones such as δ-butyrolactone and ε-caprolactone, if necessary, and coconut as a modifier. Various fatty acids such as oil fatty acids, tung oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, and the like,
It can be produced by dehydrating and condensing an epoxy compound such as di- or triglyceride, Cardular E-10 (monoepoxide having a branched alkyl group having 10 carbon atoms, manufactured by Shell Chemical Co., Ltd.) according to a conventional method.

Examples of the polyol component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 2,2-diethyl-1. , 3-propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanediol, neopentyl glycol hydroxypivalate, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl -1,5-pentanediol,
Diols such as 2,2,4-trimethylpentanediol and hydrogenated bisphenol A; trivalent or higher polyol components such as trimethylolpropane, trimethylolethane, glycerin and pentaerythritol; 2,2-dimethylolpropionic acid; And hydroxycarboxylic acid components such as 2,2-dimethylolbutanoic acid, 2,2-dimethylolpentanoic acid, 2,2-dimethylolhexanoic acid, and 2,2-dimethyloloctanoic acid.

The polybasic acid components and their anhydrides include aromatic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrabromophthalic anhydride, tetrachlorophthalic anhydride, and pyromellitic anhydride. Polycarboxylic acids and acid anhydrides; hexahydrophthalic anhydride, tetrahydrophthalic anhydride, 1,4- and 1,3-
Alicyclic polycarboxylic acids and anhydrides such as cyclohexanedicarboxylic acid; and aliphatic polycarboxylic acids and anhydrides such as maleic anhydride, fumaric acid, succinic anhydride, adipic acid, sebacic acid, and azelaic acid. Can be. The components used when synthesizing the anionic polyester resin such as the polyol component, the polybasic acid component and their anhydrides may be used alone or in combination of two or more.

The anionic polyester resin may contain a suitable amount of urethane bonds. The introduction of such a urethane bond is carried out, for example, by adding 4,4′- to both ends of a polyester polyol such as polyδ-butyrolactone or polyε-caprolactone having hydroxyl groups at both ends of the molecular chain.
The diisocyanate such as diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and the like can be urethane-bonded, partially chain-extended, and used as a part of the polyol component.

Further, the anionic polyester resin preferably has a tertiary carboxyl group in the molecule. A tertiary carboxyl group is one in which no hydrogen is bonded to the carbon atom to which the carboxyl group is directly bonded. The tertiary carboxyl group has a low activity as an acid group, and the SP value can be easily adjusted by introducing it into an anionic polyester resin. In addition, since the anionic polyester resin has a tertiary carboxyl group in the molecule, the interaction between acidic groups in the resin is reduced and the heat flow property of the coating film is improved. Even in this case, the film smoothness is ensured at the time of heat curing, and the appearance can be improved. Furthermore, when a melamine resin is used as a curing agent, it is expected to act as a catalyst in the curing reaction of the melamine resin. Examples of the anionic polyester resin having a tertiary carboxyl group in the molecule include a method using the hydroxycarboxylic acid component.

The anionic polyester resin is subjected to an addition reaction with a half-block diisocyanate compound or a partial cocondensation of a melamine resin, if necessary.
A self-crosslinking resin can also be used. Since the self-crosslinking type is excellent in curing reactivity, it is suitably used in the present invention.

The resin (b) used in the above electrodeposition paint is a cation-modified epoxy resin. this is,
It exhibits rust-preventive properties to the conductive substrate. The cation-modified epoxy resin has a hydroxyl value of 50 to 250.
Is preferably within the range. If it is less than 50, poor curing of the coating film will be caused, and if it exceeds 250, excessive hydroxyl groups will remain in the coating film after curing, and as a result, the water resistance may decrease. Number average molecular weight of the cation-modified epoxy resin,
The range of 1500 to 5000 is preferred. If it is less than 1500, physical properties such as solvent resistance and corrosion resistance of the cured film may be poor. When it exceeds 5,000, not only the viscosity of the resin solution is difficult to control and the synthesis is difficult, but also the viscosity of the obtained resin becomes high, and the handling such as emulsification and dispersion sometimes becomes difficult. Furthermore, the flow property during heating and curing is poor, and the appearance of the coating film may be significantly impaired. Further, it is desirable to use a resin having a softening point of 80 ° C. or higher, preferably 100 ° C. or higher for achieving the object of the present invention. The resin softening point can be determined based on JISK5665.

The above cation-modified epoxy resin generally has a primary amine, a primary amine,
It is produced by ring opening by reaction with an amine such as a secondary amine or a tertiary amine salt. A typical example of the starting material resin is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak and epichlorohydrin. Examples of other starting material resins include oxazolidone ring-containing epoxy resins described in JP-A-5-306327.
This epoxy resin is obtained by reacting a diisocyanate compound or a bisurethane compound obtained by blocking the NCO group of a diisocyanate compound with a lower alcohol such as methanol or ethanol, and epichlorohydrin.

The starting material resin can be used after a chain extension with a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like before the ring-opening reaction of the epoxy ring with amines. . Also, before the ring opening reaction of the epoxy ring with amines, for the purpose of adjusting the molecular weight or amine equivalent, improving the heat flow property, etc., 2-epoxyhexanol, nonylphenol, ethylene glycol Monohydroxy compounds such as -2-ethylhexyl ether and propylene glycol mono-2-ethylhexyl ether can also be used.

Examples of amines that can be used when opening the epoxy ring and introducing an amino group include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, and N-methyl. Primary, secondary or tertiary amine salts such as ethanolamine, triethylamine salt and N, N-dimethylethanolamine salt can be mentioned. Also, secondary amines having a ketimine block primary amino group such as aminoethylethanolamine methyl isobutyl ketimine can be used. These amines need to be reacted in at least an equivalent amount to the epoxy ring in order to open all the epoxy rings.

Further, as a method for introducing cationicity into the epoxy resin, it is preferable to modify the epoxy ring to a sulfonium salt according to the production method described in JP-A-11-209663.

The mixing ratio of the resin (a) and the resin (b) incompatible therewith in the electrodeposition paint is preferably 70/30 to 30/70, more preferably 60/40 by weight.
４０40/60. If it is out of this range, the resulting coating film does not have a multi-layer structure, and the resin with a higher blending ratio forms a continuous phase, and the lower resin forms a dispersed phase with a sea-island structure (or microdomain). Structure). Further, even in the case of a layered structure, one of the multilayer structures has an extremely thin layer thickness, so that either weather resistance or corrosion resistance may be remarkably inferior.

The curing agent contained in the electrodeposition paint may be of any type as long as it can cure the respective resin components during heating, but is preferably a blocked agent suitable as a curing agent for the electrodeposition resin. Polyisocyanates are used. In the above electrodeposition paint, there are a case where only a blocked polyisocyanate is used as a curing agent and a case where a blocked polyisocyanate and a melamine resin are used. That is, there are cases where both the particles A and the particles B use a blocked polyisocyanate, and cases where the particles A use a melamine resin and the particles B use a blocked polyisocyanate.

When only the blocked polyisocyanate is used as the curing agent, the solubility parameter δi of the blocked polyisocyanate contained in the particles A is used.
Is between the solubility parameter δa of the resin (a) and the solubility parameter δb of the resin (b), that is, δ
It is preferable that a <δi <δb. By setting the solubility parameter of the blocked polyisocyanate in this way, it is possible to partition and dissolve the blocked polyisocyanate in each layer after the two-layer separation, and the resin (a)
And the simultaneous curing of the layer containing the resin (b) can be compatible.

When using a blocked polyisocyanate and a melamine resin as the curing agent, the following conditions for the solubility parameter must be satisfied. That is, the respective solubility parameters of the blocked polyisocyanate and the melamine resin are different, and the difference between the solubility parameter δm of the melamine resin and the solubility parameter δa of the resin (a) is less than 0.5, and , The solubility parameter δi ′ of the blocked polyisocyanate and the solubility parameter δ of the resin (b)
The difference from b is preferably less than 0.5.

Here, if the difference between the solubility parameters is 0.5 or more, the amount of the curing agent transferred to the resin layer formed by each resin component during the heating and curing of the multilayer electrodeposition coating film is reduced. Insufficient curing may result in poor curing.

When only the blocked polyisocyanate is used, the amount of the curing agent in the electrodeposition paint is determined by considering the total properties of the resins (a) and (b) in consideration of the physical properties of the coating film and the compatibility with the top coat. The range is preferably from 15 to 40% by weight based on the amount. On the other hand, when a blocked polyisocyanate and a melamine resin are used, the mixing ratio of the melamine resin to the solid weight of the resin (a) and the mixing ratio of the blocked polyisocyanate to the solid weight of the resin (b) are determined. Preferably, the ratios are both in the range of 15 to 40% by weight.

When the amount of the curing agent is less than 15% by weight, the coating film may be hardly cured, resulting in poor physical properties such as mechanical strength. It may cause poor appearance such as erosion. If it exceeds 40% by weight, on the contrary, it becomes excessively hardened,
Poor coating properties such as impact resistance may be caused.

As the above blocked polyisocyanate, those obtained by blocking polyisocyanate with a suitable sealing agent can be used. It is desired that the blocked polyisocyanate is blocked in advance by using one or a plurality of sealing agents. If there is no purpose to react with the resin (a) or the resin (b), the blocking ratio is preferably set to 100% in order to secure the storage stability of the paint.

Examples of the above polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and 4,4'-methylenebis (cyclohexyl isocyanate). Isocyanate, 4,4 '
-Aromatic diisocyanates such as diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate, and multimers thereof.
Examples of the sealing agent include monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenolcarbinol, and methylphenylcarbinol; ethylene glycol Cellosolves such as monohexyl ether and ethylene glycol mono 2-ethylhexyl ether; phenol, para-t-butylphenol,
Phenols such as cresol; dimethyl ketoxime,
Oximes such as methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, cyclohexanone oxime; and ε-caprolactam, γ
-Lactams represented by butyrolactam are preferably used. Since oximes and lactams dissociate at a low temperature, they are suitable from the viewpoint of resin curability. The above-mentioned blocked polyisocyanate may be used in combination of two or more kinds depending on circumstances such as adjustment of physical properties of the coating film and degree of curing.

Specific examples of the melamine resin include those obtained by condensation or co-condensation of melamine, benzoguanamine, urea or the like with formaldehyde, or
Further, those obtained by etherification with a lower monohydric alcohol such as methanol or butanol can be used. These are paint hardeners well known to those skilled in the art. The solubility parameter δm of the melamine resin can be selected in consideration of the fact that the solubility parameter δm changes depending on the degree of methylolation with respect to the melamine skeleton and the type and amount of alcohol used for etherification.

The pigment contained in the electrodeposition paint is not particularly limited as long as it is commonly used in paints, but is preferably a colored pigment from the viewpoint of improving weather resistance and securing concealing properties. . Titanium dioxide is particularly suitable for the present invention because it is excellent in white color hiding and inexpensive. By controlling the distribution of titanium dioxide particularly on the resin layer side of the composite electrodeposited film which is in direct contact with air, the ability to block light rays inside the film can be significantly improved. As a result, the weather resistance of the composite coating film can be improved.

As the above pigment, besides titanium dioxide,
Inorganic pigments such as iron oxide, carbon black, etc. according to the purpose of paint preparation; such as phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyrimidine yellow, flavanthrone yellow, isoindoline yellow, indanthrone blue, quinacridone violet, etc. An appropriate amount of an organic pigment; and, if necessary, an extender such as clay, talc, kaolin, barium sulfate, and the like.

In the electrodeposition coating composition, the pigment is a ratio P / P of the weight V of all the vehicle components to the total weight P of the pigment.
When represented by V, it is preferably in the range of 1/10 to 1/2. The term "all vehicle components other than pigments" as used herein means all solid components (main resin components incompatible with each other, respective curing agents, pigment-dispersed resins, etc.) constituting the coating material other than pigments. If the above P / V is less than 1/10, the shortage of pigments causes the coating film to have an excessively low ability to block corrosion factors such as light rays and moisture, and may not be able to exhibit weatherability and corrosion resistance at a practical level. On the other hand, when P / V is more than 過, the viscosity at the time of curing is increased due to an excessive amount of the pigment, so that the flowability is reduced and the appearance of the coating film is sometimes reduced.

The above-mentioned electrodeposition coating composition can be obtained by mixing and dispersing the above-mentioned components using a method well known to those skilled in the art, but is preferably produced by the following method. That is, the pigment dispersion obtained by dispersing the pigment using the resin (a) is further dispersed in an aqueous medium containing a cationic dispersion resin to obtain an aqueous pigment dispersion paste. It is preferably obtained by mixing the paste, the resin (b) and the curing agent.

As the cationic dispersing resin, those generally used as a dispersing resin for a cationic electrodeposition paint can be used.
Is the solubility parameter δa of the resin (a) and the resin (b)
Is preferably in the middle of the solubility parameter δb. By setting to this value, at the time of forming the aqueous pigment dispersed paste, the pigment and the resin (a) coated on the pigment surface can be stably dispersed in water by adsorbing to the resin (a) serving as the dispersing resin. However, it is presumed that at the time of coating film formation, particularly at the time of baking, the film migrates to the vicinity of the interlayer, or a part thereof is distributed to both layers.

As a specific example of the cationic dispersion resin, a cation-modified novolak type epoxy resin is preferable. This cation-modified novolak type epoxy resin, for example, all or part of the epoxy group of the cresol novolak type epoxy resin or phenol novolak type epoxy resin, by a well-known onium conversion method,
It can be obtained by changing to a tertiary sulfonium salt, a quaternary ammonium salt or a quaternary phosphate. These cation-modified resins can be dissolved or dispersed in an aqueous medium as they are. It can also be obtained by forming a tertiary amino group by an addition reaction between the epoxy group and a secondary amine, and then forming a neutralized salt using an appropriate acid.

The cation-modified novolak-type epoxy resin has a primary hydroxyl group for imparting curing reactivity and a stearyl group, dodecyl group, octyl group, etc. for improving the adsorptivity to the anionic polyester resin. Introduction of a long-chain alkyl group may be performed. These are carried out by reacting a part of the epoxy groups present in the cation-modified novolak epoxy resin with a secondary amine having a hydroxy group or a secondary amine having a long-chain alkyl group.

In addition to the above-mentioned cation-modified novolak-type epoxy resin, a graft resin of the cation-modified epoxy resin of the resin (b) and a polyester resin or a polyether resin can be used as the cationic dispersion resin. These are, for example, alkoxy-modified poly ε-caprolactone having a hydroxyl group at one end of a molecular chain as a polyester resin, alkoxy-modified poly δ-valerolactone, etc., and alkoxy-modified polypropylene having a hydroxyl group at one end of a molecular chain as a polyether resin. Diisocyanates such as 4'-diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like, which are half-blocked via urethane bonds, can be obtained by reacting with hydroxyl groups in a cation-modified epoxy resin.

The number average molecular weight of the cationic dispersion resin is preferably in the range of 1,000 to 10,000. If it is less than 1,000, the adsorbability to the resin (a) is poor, so that the dispersion stability in an aqueous medium may be reduced. When it exceeds 10,000, not only is the handling of the obtained resin emulsified and dispersed difficult due to the high viscosity of the resin solution, but also the appearance of the obtained electrodeposition coating film may be adversely affected. . Furthermore, due to the high viscosity, the layer separation between the resin (a) and the resin (b) at the time of heat curing may be reduced.

The above-mentioned cationic dispersion resin is dissolved or dispersed in an aqueous medium, and the resulting mixture is stirred by, for example, a homomixer or a disper, and the pigment dispersion obtained from the pigment and the resin (a) is dropped. To obtain an aqueous pigment-dispersed paste. At this time, if necessary, a cationic surfactant or 1
An appropriate amount of a dihydric alcohol or the like may be added.

On the other hand, the resin (b) is emulsified and dispersed in water as it is as an emulsion, or is neutralized using a neutralizing agent in an amount capable of neutralizing the amino group in each resin, thereby obtaining a cationized emulsion. Is preferably emulsified and dispersed in water.

When a blocked polyisocyanate and a melamine resin are used as the curing agent,
It is preferable that the pigment is dispersed in a mixture of the resin (a) and the melamine resin, the blocked polyisocyanate is previously mixed with the resin (b), and the mixture is emulsified.

Examples of the neutralizing agent include inorganic acids such as hydrochloric acid, nitric acid and phosphoric acid; and organic acids such as formic acid, acetic acid, lactic acid, sulfamic acid and acetylglycinic acid. When the resin (b) is emulsified, an appropriate amount of a rust inhibitor may be added inside the resin. As the rust preventive agent, zinc and / or organic acid salts of rare earth metals such as cerium, neodymium, praseodymium and the like are water-soluble and easy to use because of recent market demand for eliminating harmful heavy metals such as lead. Recommended. For example, zinc acetate, cerium acetate, cerium carbonate, neodymium acetate and the like can be added at the time of emulsification or later.

The aqueous pigment-dispersed paste thus obtained, an emulsion of the resin (b), a curing agent and an ultraviolet absorber, an antioxidant, a surfactant, a coating film surface smoothing agent, a curing accelerator (organotin compound ) Can be obtained by mixing additive components such as Note that, as described above, the curing agent is desirably included in at least one of the aqueous pigment-dispersed paste and the emulsion.

The above-mentioned electrodeposition paint has a solid concentration of 15 to 25.
It is preferable to adjust so as to be in the range of% by weight. Aqueous medium for adjusting the solid content concentration, for example, water alone, or
This is performed using a mixture of water and a hydrophilic organic solvent.

[0055]Electrodeposition coating method  The electrodeposition paint is one that is electrodeposited on an object to be coated.
You. The object to be coated is not particularly limited, for example,
Iron, copper, aluminum, tin, zinc, etc .; these metals
Alloys and castings. Specifically, riding
Automobile bodies and parts such as cars, trucks, motorcycles, and buses
Goods. These metals are electrodeposited
Previously, a chemical conversion treatment with phosphate, chromate, etc.
Is particularly preferred.

The above electrodeposition coating method is preferably a cationic electrodeposition coating performed by connecting an object to be coated to a cathode terminal. Specifically, a cathode electrode terminal is connected to a conductive base material to be coated, and a dry film is formed under the conditions of a bath temperature of 15 to 35 ° C. and a load voltage of 100 to 400 V of a bath filled with the electrodeposition paint. 10 to 50 μm in thickness, preferably 20 to 40 μm
The electrodepositing of the amount of coating film corresponding to m is performed. Then 140-20
Bake at 0C, preferably 160-180C for 10-30 minutes. For this baking, there are a method in which the coating is put into a heating facility that has been adjusted to the target temperature from the beginning, and a method in which the temperature is raised after putting the coating.

By the heating, the resin (a) and the resin (b) and the pigment-dispersed resin contained in the electrodeposited electrodeposition paint are coated on the air side and the conductive group in accordance with the solubility parameter inherent to each resin. It is distributed to the material side. When the coating film is cured, the resin (a) is on the side directly in contact with air, the resin (b) is on the side directly in contact with the conductive substrate, and the pigment is mainly present in the layer containing the resin (a). It becomes an electrodeposition cured film having a multilayer structure.

In order to confirm the separation state of the resin layer, a method of observing the cross section of the electrodeposition coating film with a video microscope visually or with a scanning electron microscope (SEM observation) can be mentioned. Further, in order to identify the resin component constituting each resin layer, for example, a total reflection type Fourier transform infrared photometer (FTIR-ATR) can be used. Furthermore, SEM-EDX analysis is effective for determining the presence of a specific pigment such as titanium dioxide in each layer and the difference in interlayer concentration.

[0059]Step (2)  The step (2) is performed on the electrodeposited coating film formed as described above.
On top, apply an aqueous intermediate coating to form an uncured intermediate coating.
Form.Waterborne intermediate coating  The aqueous intermediate coating has a solid content acid value of 20 to 100 mg.
KOH / g polyester resin (I) and solid
Polyester tree having an acid value of less than 20 mgKOH / g
Fat (II). High acid value polyester
By blending the resin (I) with the aqueous intermediate coating,
As a result, the adhesion to the top coat can be improved. Obedience
Thus, if the amount is less than 20 mgKOH / g,
Is inferior in adhesion. If it exceeds 100 mgKOH / g,
The resulting coating film has poor water resistance. Preferably, 30 to 80 m
gKOH / g. The acid value is calculated based on the polyester resin
It is derived from a carboxyl group in the fat (I).

The polyester resin (I) preferably has a hydroxyl value in the range of 50 to 150. If it is less than 50, it causes poor curing of the coating film, and if it exceeds 150,
As a result of excessive hydroxyl groups remaining in the coating film after curing, the water resistance may decrease. Furthermore, the number average molecular weight is 1000-
A range of 30,000 is preferred. If it is less than 1,000, physical properties such as solvent resistance of the cured coating film are inferior. If it exceeds 30,000, the viscosity of the resin solution is high, so that not only is it difficult to handle the obtained resin in operation such as emulsification and dispersion, but also the film appearance of the obtained intermediate coating film may be significantly reduced. . Preferably, it is 2000 to 20000. The polyester resin (I) may be used alone, but two or more kinds may be used in order to balance the coating film performance.

Examples of the method for producing the polyester resin (I) include the methods described for the anionic polyester resin as the resin (a) in the above electrodeposition coating composition. It is preferable to react with the components and their anhydrides, whereby the high acid value polyester resin (I) used in the above-mentioned aqueous intermediate coating can be obtained.

The above-mentioned polyester resin (I) can also be made into a self-crosslinking resin by performing an addition reaction with a half-block diisocyanate compound or a partial co-condensation of a melamine resin, if necessary. Since the self-crosslinking type is excellent in curing reactivity, it is suitably used in the present invention.

In the aqueous intermediate coating composition, an acid value of 20 mg was used in addition to the high acid value polyester resin (I).
A polyester resin (II) less than KOH / g is used in combination. By using together the polyester resin (II) having an acid value of less than 20 mgKOH / g, the curability and the physical properties of the obtained coating film can be adjusted. Further, when coated on the electrodeposition coating film of the multilayer structure, since the same type of polyester resin contained in the upper layer of the multilayer electrodeposition coating film, the electrodeposition coating film Adhesion with the intermediate coating film is also improved. As a result, the adhesiveness of the obtained coating film as a whole is significantly improved, and the chipping resistance of the obtained multilayer coating film is also improved.

As the polyester resin (II),
Examples of the electrodeposition paint include those described for the anionic polyester resin of the resin (a). The polyester resin (II) may be used alone or in combination of two or more.

In the above-mentioned aqueous intermediate coating composition, the weight ratio of the polyester resin (I) having an acid value of the solid content of 20 to 100 mgKOH / g to the polyester resin (II) is 1/1 based on the solid content. 9 to 9/1. When the compounding amount of the polyester resin (I) having an acid value of the solid content of 20 to 100 mgKOH / g exceeds the above range, the curability may decrease, and the physical properties of the obtained coating film may be balanced. It will also be difficult. If the amount of the polyester resin (II) exceeds the above range, the amount of the polyester resin (I) having a high acid value will decrease, resulting in poor adhesion to the top coat.

The above-mentioned aqueous intermediate coating composition usually contains a curing agent. The curing agent may be of any type as long as each resin component can be cured at the time of heating, but a melamine resin is preferred from the viewpoint of pigment dispersibility and workability.

Considering the physical properties of the coating film and the compatibility with the top coat, the amount of the curing agent is set to 100 parts by weight of the resin solid content, that is, the total solid content of the polyester resin (I) and the polyester resin (II). On the other hand, the range of 10 to 100 parts by weight is preferable. If the compounding ratio is less than 10 parts by weight,
As a result of inadequate curing of the coating film, the physical properties of the coating film such as mechanical strength may be reduced, and the appearance of the coating film may be impaired, for example, the coating film may be attacked by the paint thinner during top coating. If it exceeds 100 parts by weight, on the contrary, it becomes excessively hardened,
Poor coating properties such as impact resistance may be caused. The above-mentioned curing agents may be used in combination of two or more depending on the properties of the coating film and the degree of curing. Examples of the melamine resin include those described above.

The above-mentioned waterborne intermediate coating usually contains a pigment. Examples of the pigment include those exemplified for the electrodeposition paint. The water-based intermediate coating is preferably a color pigment from the viewpoint of improving weather resistance and securing concealment. In particular, titanium dioxide is more preferable since it is excellent in white color hiding properties and is inexpensive. As the above pigment, it is possible to use a standard gray-based water-based intermediate paint having carbon black and titanium dioxide as main pigments, or a so-called combination of set gray or various color pigments combining lightness or hue with an overcoat paint. It can also be a color aqueous intermediate coating.

The above-mentioned pigment is preferably in the range of 1/10 to 2/1 when expressed as a ratio P / V of the weight V of all the vehicle components to the total weight P of the pigment in the aqueous intermediate coating composition. Here, all vehicle components other than pigments are:
It means all solid components (main resin components incompatible with each other, respective curing agents, pigment-dispersed resins, etc.) constituting the paint other than the pigment. If the P / V is less than 1/10, the concealing properties may be reduced due to insufficient pigment. On the other hand, when P / V exceeds 2/1, an excessive amount of the pigment causes an increase in viscosity at the time of curing, so that the flowability is reduced and the appearance of the coating film may be reduced.

The aqueous intermediate coating composition can be obtained by mixing and dispersing the above components using a method well known to those skilled in the art. For example, a method of dispersing using a surfactant, a method of dispersing a resin, And the like and the like. From the viewpoint of dispersion stability of the obtained aqueous intermediate coating composition, a pigment dispersion obtained by dispersing using the polyester resin (I), the polyester resin (II), a curing agent and a pigment is dispersed in an aqueous solution containing a dispersing resin. It is preferred to further disperse in the medium. Further, ultraviolet absorbers; antioxidants;
By mixing additive components such as an antifoaming agent, a surface conditioner, and an anti-bake agent, an aqueous intermediate coating can be obtained.

Examples of the dispersion resin include those exemplified as the cationic dispersion resin. The compounding amount of the above-mentioned dispersing resin is preferably in the range of 5 to 30 parts by weight in terms of solids based on 100 parts by weight of solids of polyester resin (I), polyester resin (II), curing agent and pigment. When the amount is less than 5 parts by weight, the dispersion stability of the emulsion is poor, and when it exceeds 30 parts by weight, not only the water resistance of the coating film is deteriorated, but also the characteristics such as the top coat adhesion based on the polyester resin (I) are sufficiently exhibited. It becomes difficult.

[0072]Intermediate coating film formation method  The above-mentioned waterborne intermediate coating is the object to which
To form an uncured intermediate coating film. Up
The coating method is not particularly limited.
Air gun spray called "act gun";
Micro micro (μμ) bell ”,“ micro (μ)
Rotary atomization type electrostatic coating called "Ru", "Metabell" etc.
It can be performed by using a machine or the like. Preferably
Is a method using a rotary atomization type electrostatic coating machine or the like.

The dry film thickness of the intermediate coating film varies depending on the application, but is preferably 5 to 50 μm. If the amount exceeds the upper limit, the sharpness may be reduced, or sagging may occur during coating or baking may occur. If the amount is below the lower limit, the appearance may be reduced.

In the present invention, to form an uncured coating film for the aqueous intermediate coating, the aqueous base coating, and the clear coating means that the intermediate coating, the base coating, and the clear coating are applied in this order by wet-on-wet. It means to do. In the present specification, uncured means
For example, the concept includes a state after performing preheating. As the above preheat, after coating, for example,
This is a step of leaving or heating at room temperature to less than 100 ° C. for 1 to 10 minutes. For the purpose of obtaining a good finished appearance, it is preferable to perform preheating after applying the aqueous intermediate coating and after applying the aqueous base coating.

[0075]Step (3)  The step (3) is performed in the uncured state formed as described above.
Apply an aqueous base paint on top of the uncoated
A base coat is formed.Water-based paint  In the present invention, the aqueous base paint is not particularly limited.
For example, film-forming resins, curing agents, pigments and others
Can be mentioned. The above coating
The formable resin is not particularly limited, for example, acrylic
Resin, polyester resin, alkyd resin, epoxy tree
Fats, urethane resins, etc., which are amino resins and
And / or hardener such as blocked isocyanate resin
Used together. In terms of pigment dispersibility and workability,
Krill resin and / or polyester resin and melamine resin
Is preferred.

The above-mentioned aqueous base paint may be used as a metallic base paint by adding a glittering pigment, or may be blended with a coloring pigment such as red, blue or black and / or an extender pigment without blending the glittering pigment. It can also be used as a solid base paint. The brilliant pigment is not particularly limited. For example, an uncolored or colored metallic brilliant such as a metal or an alloy and a mixture thereof, interference mica powder, colored mica powder, white mica powder, graphite or a colorless colored flat pigment And the like. A non-colored or colored metallic brilliant material such as a metal or an alloy, and a mixture thereof are preferable since a coating film having excellent dispersibility and high transparency can be formed. Specific examples of the metal include aluminum, aluminum oxide, copper, zinc, iron, nickel, and tin.

The shape of the glitter pigment is not particularly limited.
Further, it may be colored, but for example, has an average particle size (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm
Is preferable. Average particle size 10-35μ
Those having a range of m are excellent in glitter and are more preferable. The pigment concentration (PWC) of the glitter pigment in the base paint is generally 23% by weight or less. When the content exceeds 23% by weight, the appearance of the coating film is deteriorated. Preferably, it is 0.01 to 20% by weight, more preferably 0.01 to 18% by weight.

As the pigments other than the above-mentioned brilliant pigments, the coloring pigments and extenders described in the electrodeposition paints can be used. As the pigment, one or a combination of two or more of a brilliant pigment, a coloring pigment, and an extender can be used. Pigment concentration (PWC) in base paint including the above-mentioned brilliant pigments and all other pigments
Is generally 0.1 to 50% by weight, preferably 0.5 to 40% by weight, and more preferably 1 to 30% by weight. If it exceeds 50% by weight, the appearance of the coating film will be reduced. Examples of the base paint include other additives to be used, and examples of the method of preparing the base paint include those exemplified for the aqueous intermediate paint.

[0079]Base coating film formation method  The base paint is the uncured material formed as described above.
Apply to form an uncured base coating on top of the coating
You. As the above coating method, apply an aqueous intermediate coating
The method exemplified at that time can be mentioned. Base coating
When applying paint to automobile bodies, etc.,
Multistage coating with air electrostatic spray
Coating, preferably in two stages, or air
Combine the electrostatic spray with the above-mentioned rotary atomizing type electrostatic coating machine.
It is preferable to carry out by a combined coating method.

The dry film thickness of the base coating varies depending on the application, but is preferably from 5 to 35 μm. Exceeding the upper limit may result in poor clarity and / or inconveniences such as unevenness and flow during coating. Below the lower limit, color unevenness may occur.

[0081]Step (4)  In the step (4), the uncured base formed as described above is used.
Apply a clear paint on the uncoated
To form a coating film.Clear paint  The clear coating film contains a glitter pigment as a base paint.
Due to glitter pigments when using tallic base paint
Smoothes the unevenness and flicker of the base coating film.
It is also formed to protect the base coating.
You. There is no particular limitation on the clear paint, for example,
For example, from film-forming resins, curing agents and other additives.
Can be mentioned.

The film-forming resin is not particularly restricted but includes, for example, acrylic resins, polyester resins, epoxy resins, urethane resins, etc., which are combined with a curing agent such as an amino resin and / or a blocked isocyanate resin. Used. From the viewpoint of transparency or acid etching resistance, etc., a combination of an acrylic resin and / or a polyester resin and an amino resin, or a carboxylic acid.
It is preferable to use an acrylic resin and / or a polyester resin having an epoxy curing system.

The clear paint contains a viscosity control agent as an additive in order to apply it in an uncured state after the above-mentioned base paint is applied, and to prevent break-in, reversal or sagging between layers. Is preferred. The amount of the viscosity control agent to be added is 0.01 to 10 parts by weight, preferably 0.1 to 100 parts by weight, based on 100 parts by weight of the resin solid content of the clear paint.
The amount is from 02 to 8 parts by weight, more preferably from 0.03 to 6 parts by weight. If the amount is more than 10 parts by weight, the appearance deteriorates. If the amount is less than 0.1 part by weight, the effect of controlling the viscosity cannot be obtained, which causes problems such as sagging.

The form of the clear coating composition may be any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), a non-aqueous dispersion type, and a powder type. An adjusting agent or the like can be used.

[0085]Clear coating film forming method  The preparation method and coating method of the above clear paint are as follows.
It can be done according to the following method. Above clear coating
The dry film thickness varies depending on the application, but is 10 to 70 μm
It is. When the dry film thickness exceeds the upper limit, the sharpness deteriorates.
Troubles such as unevenness and flow during painting
Yes, if it is below the lower limit, the appearance may be reduced.

[0086]Step (5)  In the step (5), the intermediate coating film, the base
Heat-curing simultaneously the clear coating film and the clear coating film,
Obtain a multilayer coating. The temperature for heat curing is 1
Perform at 10 to 180 ° C, preferably 120 to 160 ° C
By doing so, it is possible to obtain a cured coating film with a high degree of crosslinking.
You. When the temperature exceeds 180 ° C., the coating film becomes hard and brittle,
If the temperature is lower than ℃, curing is not sufficient. Curing time depends on curing temperature
It changes more, but it takes 10-60 minutes at 120-160 ° C
Appropriate.

The thickness of the multilayer coating film obtained by the coating film forming method of the present invention is usually 30 to 300 μm, preferably 5 to 300 μm.
0 to 250 μm. If it exceeds 300 μm, the physical properties of the film such as a thermal cycle decrease, and if it is less than 30 μm, the strength of the film itself decreases.

Among the multilayer coating films obtained by the multilayer coating forming method of the present invention, the electrodeposition coating film forms a resin layer in which an anionic polyester resin is in direct contact with air, and a cationic epoxy resin is in contact with a substrate. Since it has a two-layer separation structure for forming a resin layer, a coating film having excellent corrosion resistance and weather resistance can be obtained. Since the intermediate coating containing the polyester resin (I) and the polyester resin (II) is applied on the electrodeposited coating film, the intermediate coating paint containing the resin layer which is in direct contact with the air of the electrodeposition coating film is formed. The same type of polyester resin (II) is included in the intermediate coating film, so that the adhesion between the intermediate coating film and the electrodeposition coating film is improved, and the adhesion between the intermediate coating film and the top coating film is excellent. is there. As a result, a multilayer coating film having extremely excellent adhesion can be obtained as a whole, and thus the chipping resistance can be improved by the anchor effect. Further, the three-wet one-bake coating method of the present invention can omit the baking step of the intermediate coating paint as compared with the conventional three-coat two-bake method, so that the process can be shortened, the cost can be reduced, and the energy consumption can be reduced. A new coating system aiming at reduction and environmental load reduction can be constructed.

[0089]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Parts and% mean parts by weight and% by weight, respectively. Production Example 1 Production of polyester resin (II) In a reaction vessel equipped with a stirrer, a cooler, a decanter, a nitrogen inlet tube, a thermometer and a dropping funnel, 21.6 parts of neopentyl glycol, 95.2 parts of trimethylolpropane.
Parts, phthalic anhydride 328.5 parts, isophthalic acid 157.
8 parts, 2,2 parts of 2,2'-dimethylolbutanoic acid, 0.6 parts of dibutyltin oxide as a reaction catalyst and 60 parts of xylene as a reflux solvent were charged at 150 ° C. under a nitrogen atmosphere.
And kept heated. Further, 598.5 parts of Cardura E-10 (manufactured by Shell Chemical Co., Ltd., monoepoxide having a branched alkyl (C10) group) was dropped from the dropping funnel over 30 minutes, and then the temperature was raised to 210 to 230 ° C. to dehydrate. The condensation reaction was performed for 5 hours. Thereafter, 240 parts of methyl isobutyl ketone was added as a diluting solvent. The obtained polyester resin (II) has a solid content of 80%, a number average molecular weight by GPC (gel permeation chromatography) of 1600 (in terms of polystyrene), and an acid value of 8 mgKOH /
g, hydroxyl value was 70, and solubility parameter of the resin was 10.0.

Production Example 2 Production of Polyester Resin (I) As in Production Example 1, 200.0% of isophthalic acid was placed in a reaction vessel.
Parts, 179.0 parts of phthalic anhydride, 150.0 parts of trimethylolpropane, 295.0 parts of neopentyl glycol
And 2 parts of dibutyltin oxide, and heated in a stream of nitrogen to melt the raw materials.
The temperature was gradually raised to ° C. After that, it takes 22 hours for 3 hours.
While the temperature was raised to 0 ° C., dehydration transesterification was performed. When the acid value became 10 mgKOH / g, it was cooled to 150 ° C. Further, 110.0 parts of hexahydrophthalic acid was added and reacted for 1 hour to complete the reaction. Then 100
After cooling to ℃, 112.0 parts of butyl cellosolve was added to obtain a polyester resin (I). The obtained polyester resin has a solid content of 80% and an acid value of solid content of 50 mg.
The polymer had a KOH / g, a hydroxyl value of 65, and a number average molecular weight by GPC of 10,000 (in terms of polystyrene).

Production Example 3 Production of Dispersed Resin In a reaction vessel equipped with a stirrer, a cooling pipe, a nitrogen introducing pipe, and a thermometer, a gresol novolak type epoxy resin having an epoxy equivalent of 203 (Epototo YDCN-703, manufactured by Toto Kasei Co., Ltd.) 122 parts, 10 parts of diethanolamine, 74 parts of Farmin D86 (mixture of dialkylamines having 14 to 18 carbon atoms, manufactured by Kao Corporation) and 52 parts of methyl isobutyl ketone
The reaction was carried out at 120 ° C. for 1 hour in a nitrogen atmosphere. Next, after cooling to 70 ° C., SHP-100 (1-
48 parts of (2-hydroxyethylthio) -2,3-propanediol, manufactured by Sanyo Chemical Industries, 32 parts of glacial acetic acid and 80 parts of deionized water were added. The reaction mixture was kept at 70 to 75 ° C. for 6 hours to carry out the reaction. The obtained dispersed resin had a resin solid content of 60%, a number average molecular weight by GPC of 5000 (in terms of polystyrene), and a solubility parameter of 10.8.

Production Example 4 Production of Dispersion Paste 1 A pigment dispersion having the following composition was prepared using a sand mill. 61.3 parts of polyester resin varnish (II) of Production Example 1 26.3 parts of polyester resin varnish (I) of Production Example 2 melamine resin curing agent (Uban 20N60, manufactured by Mitsui Chemicals, resin solid content 60% by weight) 0 parts Titanium dioxide 100.0 parts

Production Example 5 Production of Dispersion Paste 2 A pigment dispersion having the following composition was prepared using a sand mill. 43.8 parts of polyester resin varnish (II) of Production Example 1 43.8 parts of polyester resin varnish (I) of Production Example 2 50.0 parts of melamine resin curing agent (Uban 20N60) 100.0 parts of titanium dioxide

Production Example 6 Preparation of aqueous base paint Dipropylene glycol methyl ether 2 was placed in a reaction vessel.
3.9 parts and propylene glycol methyl ether 1
6.1 parts were added and mixed and stirred in a nitrogen stream for 120 minutes.
The temperature was raised to ° C. Then, 54.5 parts of ethyl acrylate,
A mixed solution of 12.5 parts of methyl methacrylate, 14.7 parts of 2-hydroxyethyl acrylate, 10.0 parts of styrene, 8.5 parts of methacrylic acid and 10.0 parts of dipropylene glycol methyl ether, t-butyl peroxy -2-ethylhexanoate, 2.0 parts of an initiator solution
It was dropped into the reaction vessel in parallel over time. After completion of the dropping, aging was performed at the same temperature for 0.5 hour. Further, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 parts of t-butylperoxy-2-ethylhexanoate was dropped into the reaction vessel over 0.5 hour. After completion of dropping, aging was performed at the same temperature for 1 hour. Then, the solvent is removed under reduced pressure (70 Torr) 110
After distilling off 16.1 parts of the solvent at ℃, dimethylethanolamine and ion-exchanged water were added to obtain a water-soluble acrylic resin having a nonvolatile content of 31%, an acid value of 56 mgKOH / g and a hydroxyl value of 70.

100.0 parts of the above water-soluble acrylic resin,
After premixing 28.9 parts of ion-exchanged water, 0.3 parts of dimethylaminoethanol, and 5.1 parts of Degussa Carbon FW-285 (manufactured by Degussa AG), a glass bead medium was added in a paint conditioner, and room temperature was added. For 1 hour to obtain a color pigment paste having a particle size of 5 μm or less.
134.3 parts of the coloring paste, 118.8 parts of a water-soluble acrylic resin, 29.1 parts of a melamine resin (Cymel 204, manufactured by Mitsui Cytec), and 161.
The aqueous base paint was prepared by blending to be 3 parts.

Production Example 7 Preparation of Electrodeposition Paint for Forming Two-Layer Separated Coating Film (1) Production of Blocked Polyisocyanate Curing Agent 222 parts of isophorone diisocyanate was placed in a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a cooling tube and a thermometer. It was placed,
After diluting with 56 parts of methyl isobutyl ketone, 0.2 parts of butyltin laurate was added. After the temperature was raised to 50 ° C., 17 parts of methyl ethyl ketoxime was added so that the content temperature did not exceed 70 ° C. Then, the mixture was kept at 70 ° C. for 1 hour until the absorption of isocyanate residues substantially disappeared according to the infrared absorption spectrum, and then diluted with 43 parts of n-butanol to obtain the objective blocked polyisocyanate (solid solubility: 70%). Parameter = 11.8) was obtained.

(2) Production of Cation-Modified Epoxy Emulsion A reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel was charged with a bisphenol A type epoxy resin having an epoxy equivalent of 188 (DER-331J, Dow Chemical Company). 2400 parts, 141 parts of methanol, 168 parts of methyl isobutyl ketone, and 0.5 part of dibutyltin dilaurate were stirred and uniformly dissolved at 40 ° C., followed by 2,4- / 2,6-tolylene diisocyanate (8
(0/20 weight ratio mixture) 320 parts was dropped over 30 minutes, and heat was generated and the temperature rose to 70 ° C. N, N
5 parts of dimethylbenzylamine were added and the temperature in the system was raised to 1
The temperature was raised to 30 ° C., and the reaction was continued at 130 ° C. for 3 hours until the epoxy equivalent reached 232 while distilling off methanol. Further, 644 parts of methyl isobutyl ketone and 341 parts of bisphenol A were added, the temperature in the system was maintained at 130 ° C., and the reaction was performed until the epoxy equivalent reached 840.
The system was cooled until the temperature in the system reached 110 ° C. Then, 241 parts of diethylenetriaminediketimine (73% solid solution of methyl isobutyl ketone), 300 parts of N-methylethanolamine and di (2-ethylhexyl) amine 3
By adding 46 parts of the mixture and reacting at 120 ° C. for 1 hour, a cation-modified epoxy resin was obtained. The number average molecular weight of this resin was 1,800, the hydroxyl value was 160, and the resin softening point was 130 ° C. as measured according to JIS-K-5665. From the measurement of the infrared absorption spectrum and the like, it was found that the oxazolidone ring (absorption wave number: 1750c
m ^-1 ). The solubility parameter was 11.4.

To the cation-modified epoxy resin thus obtained, 1834 parts of the above-prepared blocked polyisocyanate curing agent, 90 parts of acetic acid, and 2 parts of zinc acetate and 2 parts of cerium acetate as rust inhibitors were added. After diluting to 32% of the non-volatile content with ion-exchanged water, the solution was concentrated to 36% of the non-volatile content under reduced pressure to obtain an aqueous emulsion mainly composed of a cation-modified epoxy resin.

(3) Production of Aqueous Pigment Dispersion Paste Using a sand mill, a pigment dispersion containing the polyester resin (II) obtained in Production Example 1 and having the following composition was prepared.
The solubility parameter of Uban 20N60 = 1
0.0. 87.5 parts of polyester resin (II) of Production Example 1 30.0 parts of melamine resin curing agent (Uban 20N60) 100.0 parts of titanium dioxide

After previously dispersing 25 parts of the dispersion resin solution obtained in Production Example 3 and 2 parts of ethylene glycol mono-n-hexyl cellosolve in 230 parts of ion-exchanged water, 114 parts of the above pigment dispersion was dropped with stirring. Thus, a dispersion having a nonvolatile content of 32% was obtained, and further concentrated under reduced pressure to a nonvolatile content of 36% to obtain an aqueous pigment dispersion paste.

(4) Preparation of electrodeposition paint Aqueous paint (solid content: 20%) using the above-mentioned aqueous emulsion, the above-mentioned aqueous pigment dispersion paste and deionized water
Was prepared. In the paint, an emulsified emulsion paste of dibutyltin oxide was blended as a curing accelerator so that the tin content was 1.5% of the paint solid content. The mixing ratio of the aqueous emulsion and the aqueous pigment-dispersed paste (resin solids ratio, calculated not including the weight of the curing agent) is 50.
/ 50, pigment / resin vehicle (total vehicle weight,
(Including the weight of the curing agent) is 1/10.

Example 1 (1) Preparation of aqueous intermediate coating composition 25 parts of the dispersion resin solution obtained in Production Example 3 and 2 parts of ethylene glycol mono-n-hexyl cellosolp were previously dispersed in 230 parts of ion-exchanged water. Thereafter, 134 parts of the dispersion paste 1 obtained in Production Example 4 was dropped under stirring to prepare an aqueous intermediate coating composition P-1.

(2) Coating method The electrodeposited paint for forming a two-layered separated coating film of Production Example 7 was electrodeposited on a dull steel plate treated with zinc phosphate so that the dry coating film had a thickness of 20 μm. A plate baked for 30 minutes was made. Apply the above intermediate paint to the board by air spray coating.
After coating with 0 μm and drying at 80 ° C. for 5 minutes, the above Production Example 6
18 of the aqueous base paint obtained in
μm was applied and dried at 80 ° C. for 5 minutes. Further, a clear paint was applied to the coated plate by air spray coating at 35 μm, and then baked at 140 ° C. for 30 minutes.

(3) Evaluation method of electrodeposited coating film The electrodeposited coating material for forming a two-layer separated coating film of Production Example 7 was electrodeposited on a dull steel plate treated with zinc phosphate so that the dry coating film had a thickness of 20 μm. Evaluation was performed using a plate baked at 30 ° C. for 30 minutes. The results are shown in Table 1. 1. Layer separation state of electrodeposition coating film The cross section was visually observed with a video microscope. In the case of a multi-layer separation membrane, the main resin constituting each layer is FTIR
-Identified by ATR analysis. Here, FTIR-AT
In the R analysis, the ester layer (absorption wave number: 1720, 1280 and 1070) derived from the resin (a) was added to the surface layer of the cured coating film sample, that is, the resin layer directly in contact with air.
cm ^-1 ), and an oxazolidone ring derived from the resin (b) (absorption wave number: 1750 cm ^-1 )
Almost no absorption is found, while the lower layer of the sample, that is, the resin layer directly in contact with the conductive substrate,
When characteristic absorption (same wave number as above) characteristic of oxazolidone ring derived from resin (b) is confirmed, and absorption (same wave number as above) attributed to ester bond derived from resin (a) is hardly found. Was determined to be two-layer separation.

2. Relative pigment concentration relationship in each layer of electrodeposition coating film Relative pigment concentration relationship in each layer of titanium dioxide
Judgment was made from the distribution of titanium atoms by SEM-EDX (X-ray fluorescence analysis using a scanning electron microscope). 3. Attach SWH1000H coated plate to Sunshine Weatherometer
After irradiation for 00 hours, the gloss was measured at 60 degrees, and the retention ratio with respect to the initial value was determined. If delamination occurred during the test, the state was recorded.

4. A cross cut reaching the substrate was put on the SDT coated plate with a knife, a salt spray test (5% saline, 55 ° C.) was performed for 480 hours, and the maximum width of the peeled portion peeled off from both sides of the cut portion with an adhesive tape was shown. 5. Electrodeposition coating surface roughness Using Handy Surf E-30A (Tokyo Seimitsu Co., Ltd.)
According to JIS B 0601, the surface roughness R of the electrodeposition coating film
a was measured (cut-off 0.8 mm).

[0107]

[Table 1]

(5) Evaluation method of multilayer coating film Chipping resistance evaluation method Stepping stone tester (manufactured by Suga Test Instruments Co., Ltd.)
A coated plate cooled to −30 ° C. is attached so that the stone enters at an angle of 90 °, and 100 g of No. 7 crushed stone is jetted at an air pressure of 3 kg / cm ² to cause the crushed stone to collide with the coated plate. The degree of peeling (number, size, location of destruction) at that time is evaluated on a five-point scale. 1: peeling on the entire surface, peeling off from the substrate 2: peeling on the entire surface, no peeling off from the substrate 3: partly peeling, peeling off from the substrate 4: partly peeling No peeling from the substrate 5: Almost no destruction The results are shown in Table 2.

[0109]

[Table 2]

Example 2 An aqueous intermediate coating composition P-2 was prepared in the same manner as in Example 1, except that Dispersion Paste 1 was replaced by Dispersion Paste 2 obtained in Production Example 5. Using the obtained intermediate coating, a coated plate was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1 A coated plate was prepared and evaluated in the same manner as in Example 1 except that Powertop U-50 (a cationic electrodeposition paint manufactured by Nippon Paint) was used as the electrodeposition paint. Table 1 shows the evaluation of the electrodeposition coating film, and Table 2 shows the evaluation of the multilayer coating film.

From the examples and comparative examples, it was found that 2
Examples 1 and 2 using an electrodeposition coating material for forming a layer separation coating film and using an aqueous intermediate coating material containing a high acid value polyester resin (I) and a polyester resin (II) as the intermediate coating material are obtained. The multilayer coating had excellent chipping resistance. It seems that Comparative Example 1 using a normal electrodeposition paint had poor chipping resistance due to poor adhesion between the electrodeposition coating film and the intermediate coating film.

[0113]

According to the method for forming a multilayer coating film of the present invention, a resin layer in which an anionic polyester resin is in direct contact with air and a resin layer in which a cationic epoxy resin is in contact with a substrate are formed as electrodeposition coating films. Since it has a two-layer separation structure and uses an aqueous intermediate coating containing the polyester resin (I) and the polyester resin (II), a multilayer coating film is formed by a three-wet one-bake method. When formed, the interlayer adhesion is improved, and a multilayer coating film having excellent chipping resistance can be formed by the anchor effect.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B05D 7/24 302 B05D 7/24 302V 302U C09D 5/00 C09D 5/00 Z D 5/44 5/44 Z 163/00 163/00 167/00 167/00 C25D 13/00 307 C25D 13/00 307D 308 308C 13/06 13/06 BE // C09D 175/04 C09D 175/04 F term (reference) 4D075 AE06 BB26Z DB02 DC12 EA06 EA43 EB33 EB35 EB54 EB55 4J038 DA162 DA172 DB061 DB071 DB161 DB391 DD041 DD121 DD231 DG111 DG161 DG301 GA01 GA08 KA03 MA14 NA03 NA04 NA11 NA27 PA04 PA19

Claims (8)

[Claims] After coating an electrodeposition paint on an object to be coated,
A step (1) of forming an electrodeposition coating film by heat curing, a step (2) of applying an aqueous intermediate coating composition on the electrodeposition coating film to form an uncured intermediate coating film, A step (3) of applying an aqueous base paint on the paint film to form an uncured base coat, and a step of applying a clear paint thereon to form an uncured clear coat (4), and
A method for forming a multi-layer coating film comprising a step (5) of simultaneously heating and curing the intermediate coating film, the base coating film, and the clear coating film to obtain a multi-layer coating film, wherein the electrodeposition coating material is soluble. Particle A containing resin (a) whose parameter is δa
And a resin (b) having a solubility parameter of δb and particles B containing a curing agent, wherein (i)
The value of (δb−δa) is 1.0 or more, and (ii) the resin (a) is an anionic polyester resin,
(Iii) The resin (b) is a cationic epoxy resin, and the aqueous intermediate coating composition has an acid value of solid content of 20 to 1
A method for forming a multilayer coating film, comprising: a polyester resin (I) having an amount of 00 mg KOH / g; and a polyester resin (II) having an acid value of less than 20 mg KOH / g. 2. The particles A contained in the electrodeposition paint contain a curing agent, and have a solubility parameter δ of the curing agent.
2. The method according to claim 1, wherein i is δb>δi> δa. 3. The weight ratio of the resin (a) to the resin (b) based on the solid content of the electrodeposition paint is 30/70 to 70/70.
The method for forming a multilayer coating film according to claim 1, wherein the number is 30. 4. The method according to claim 1, wherein the anionic polyester resin contained in the electrodeposition paint has a tertiary carboxyl group in the molecule. 5. The method according to claim 1, wherein the polyester resin (I) contained in the aqueous intermediate coating composition has a number average molecular weight of 1,000 to 30,000. 6. The polyester resin (II) contained in the aqueous intermediate coating composition has a number average molecular weight of 1,000 to 30,000.
The method for forming a multilayer coating film according to claim 1, 2, 3, 4, or 5. 7. The weight ratio of the solid content of the polyester resin (I) and the polyester resin (II) contained in the aqueous intermediate coating composition is from 1/9 to 9/1. 5
Or the method for forming a multilayer coating film according to item 6. 8. A multilayer coating film formed by the multilayer coating forming method according to claim 1, 2, 3, 4, 5, 6, or 7.