JP2003266013A - Method for forming combined layer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a combined layer coating film capable of forming the combined layer coating film comprising a cation electrodeposition coating film layer and an intermediate coating film layer by one heating/ curing step without generating a problem, i.e., a reduction of rust-resistance. <P>SOLUTION: This method for forming the combined layer coating film comprises a step (1) for coating an object to be coated with a cation electrodeposition coating material and forming an electrodeposition uncured coating film without heating/curing; a step (2) for coating the electrodeposition uncured coating film formed by the step (1) with a water base intermediate coating material to form an intermediate uncured coating film; and a step (3) for simultaneously heating/curing the combined layer uncured coating film formed by the step (1) and the step (2). In the combined layer coating film formed by the above formation method, a temperature T adopting a peak value derived from Tg of the cation electrodeposition coating film among peak values of tanδ measured by a dynamic viscoelasticity measurement is 110°C-140°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for forming a multilayer coating film.

[0002]

2. Description of the Related Art In recent years, in the field of painting, especially in the field of automobile painting, resource saving, cost saving and environmental load (VOC)
And HAPs), it is required to shorten the coating process. As a means of shortening the coating process, a water-based intermediate coating composition is sequentially coated by the wet-on-wet method without performing heat curing treatment after forming an uncured coating film with a cationic electrodeposition coating composition, and these are simultaneously heated. A method of forming a multi-layer coating film by using the above method is under study.

JP-B-56-20073 discloses that an uncured coating film is formed on an uncured coating layer formed by a cationic electrodeposition coating composition with an intermediate coating composition using a blocked isocyanate compound as a curing agent. A coating method by simultaneously heating and curing a cured coating film is described. However, in the multilayer coating film obtained by such a method, a mixed layer of the electrodeposition uncured coating layer and the intermediate coating uncured coating layer occurs, and the components in the intermediate coating uncured coating layer are electrodeposited. When it moves to the uncured coating layer, curing inhibition occurs, and the rust preventive property tends to decrease.

Japanese Patent Laid-Open No. 2000-301062 discloses that
It is described that by blending a tin compound in the electrodeposition coating layer, the cross-linking and curing of the electrodeposition uncured coating film is started earlier than that of the intermediate coating uncured coating film to prevent mixing between the uncured coating films. ing. However, the tin-based compound needs to be used in a large amount of 10 parts by weight or more per 100 parts by weight of the resin solid content, which is contrary to the original purpose of the wet-on-wet multi-layer coating film forming method of cost saving. It was a thing.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, the present invention provides a multilayer coating film comprising a cationic electrodeposition coating film layer and an intermediate coating film layer, which causes a problem of lowering rust prevention. It is an object of the present invention to provide a method for forming a multilayer coating film that can be formed by a single heat curing step.

[0006]

The present invention comprises a step (1) of applying a cationic electrodeposition coating composition onto an object to be coated to form an electrodeposition uncured coating film without heat curing, and the above step (1). (2) applying an aqueous intermediate coating composition on the electrodeposition uncured coating film formed by the method (2) to form an intermediate coating uncured coating film;
And a method for forming a multilayer coating film comprising a step (3) of simultaneously heating and curing the multilayer uncured coating film formed by the above step (1) and the above step (2), wherein the multilayer coating film is Among the peak values of tan δ measured by dynamic viscoelasticity measurement, the temperature T at which the peak value derived from Tg of the cationic electrodeposition coating film is 110 to 140 ° C. Is the way.

In the present invention, the Tg measured by dynamic viscoelasticity of the single-layer cured cationic electrodeposition coating film formed by heating and curing the electrodeposition uncured coating film formed in step (1) is 115. It is preferably ˜140 ° C.
The water-based intermediate coating composition has a Tg of 55 to 110 ° C. measured by dynamic viscoelasticity of the single-layer cured intermediate coating film obtained by applying the water-based intermediate coating composition in a single layer and heat curing.
Is preferred. The water-based intermediate coating composition preferably contains a blocked isocyanate compound as a curing agent. The present invention will be described in detail below.

The multilayer coating film obtained by the method for forming a multilayer coating film of the present invention has a peak value derived from Tg of the cationic electrodeposition coating film among the peak values of tan δ measured by dynamic viscoelasticity. The temperature T is within a temperature range of a lower limit of 110 ° C. and an upper limit of 140 ° C.

The T of the multi-layer coating film is measured by peeling the multi-layer coating film formed on the substrate with mercury and cutting the sample to measure dynamic viscoelasticity. Obtained by In the temperature range from room temperature to 200 ° C., T is a temperature rising rate of 2 ° C. per minute and a frequency of 1
Vibration is applied to the measurement sample at 1 Hz, its viscoelasticity is measured, and the ratio (tan δ) of the loss elastic modulus (E ″) to the storage elastic modulus (E ′) is measured. Is measured as the temperature at which tan δ has the peak value. That is, the peak temperature is T when the above-mentioned measurement sample is measured by the same method as the usual Tg measurement method by viscoelasticity measurement. As an apparatus for performing the dynamic viscoelasticity measurement, for example, RHEOVIBRON MODEL RHEO2
, 3,000 (trade name, manufactured by Orientec Co., Ltd.) and the like.

The coating film formed by the method for forming a multilayer coating film of the present invention is a multilayer coating film comprising a cationic electrodeposition coating film and an intermediate coating film. Therefore, each of the two coating layers has Tg, and in the measurement of the dynamic viscoelasticity of the multilayer coating, it is 2
Of these peaks, the temperature of the peak derived from the electrodeposition coating layer is referred to as T in the present invention.
Which peak is derived from the electrodeposition coating film,
It can be easily predicted from the Tg value measured for each single-layer coating film. That is, T of the electrodeposition single-layer coating film
When g is higher than Tg of the intermediate coating single-layer coating film,
Usually, the peak on the high temperature side is T, and in the opposite case, the peak on the low temperature side is T.

If the above T is less than 110 ° C., it is impossible to sufficiently prevent the deterioration of the rust preventive property, and the obtained coating film has a problem that the peel strength is poor. The above T is 140 ° C
If it exceeds, there is a problem that the resulting coating film has poor impact resistance. The lower limit is more preferably 115 ° C.

The above temperature T is greatly related to the Tg of each layer forming the multilayer coating film. Therefore, in order to form a multilayer coating film that satisfies the above numerical range of T, in the cationic electrodeposition uncured coating film and the intermediate coating uncured coating film,
It is preferable to select an appropriate paint.

Further, the method for forming a multilayer coating film of the present invention is apt to cause a problem that the above two components are mixed when the intermediate coating and the heat curing are carried out. When the above-mentioned mixed layer occurs, there is a high possibility that curing inhibition will occur due to the presence of the compound derived from another layer in the coating film. Due to the above inhibition of curing, the curing reaction in each coating film does not proceed sufficiently, and the remaining mixed components adversely affect the physical properties of the coating film. When the above curing inhibition occurs, the curing reaction does not proceed sufficiently, so that the above T does not reach the required temperature, and thus the required multilayer coating film physical properties may not be obtained.

Therefore, in order to obtain a multilayer coating film in which T satisfies the necessary temperature range, the composition of the electrodeposition uncured coating film and the intermediate coating uncured coating film is selected, and the uncured coating film layer It is important to prevent mixed layers. In order to achieve these, the compositions of the cationic electrodeposition coating composition and the waterborne intermediate coating composition are important.

In order to set the above T to a required temperature range,
For example, Tg obtained by dynamic viscoelasticity measurement of a single-layer cured cationic electrodeposition coating film formed by heating and curing the electrodeposition uncured coating film formed in the step (1).
Is 115 to 140 ° C., and the aqueous intermediate coating used in the step (2) is a carbon layer-cured intermediate coating obtained by coating the aqueous intermediate coating with a single layer and curing the same. Tg obtained by dynamic viscoelasticity measurement is 55 to
The temperature may be 110 ° C., and the intermediate coating material may contain a blocked isocyanate compound as a curing agent. By using these means or other means alone or in combination, the above T can be adjusted to a required temperature range.

The cationic electrodeposition coating used in the above step (1) contains a cationic substrate resin, a curing agent and necessary additives, and the cationic electrodeposition coating formed in the above step (1). The single-layer cured cationic electrodeposition coating film formed by heat-curing the coating film has a Tg of 115.
It is preferable that the temperature is not lower than 140 ° C. When an electrodeposition coating composition in which the Tg of the cured coating film is less than 115 ° C. is used, the T is less than 110 ° C., and the rust prevention property is often poor. When Tg exceeds 140 ° C., the intermediate coating film becomes a resin having a low elastic modulus, which may result in a coating film having poor impact resistance. The Tg of the single-layer cured cationic electrodeposition coating film is measured by exactly the same method as the T measurement of the multilayer coating film.

The Tg of the above single-layer cured cationic electrodeposition coating film is 1
The range of 15 ° C. or higher and 140 ° C. or lower is achieved by selecting the types and blending amounts of the cationic base resin, the curing agent and the curing catalyst contained in the cationic electrodeposition coating used in the above step (1). be able to. In particular, the Tg of the cationic base resin and the curing agent has a great influence.

The above-mentioned cationic base resin is not particularly limited, and examples thereof include amine-modified epoxy resin systems described in JP-B-54-4978 and JP-B-56-34186, and JP-B-55-115476. Amine-modified polyurethane polyol resin system described in JP-B No. 62-61077 and JP-A No. 63-86766.
Amine-modified polybutadiene resin system described in JP-B No. 63-139909, JP-B-1-60
Examples thereof include amine-modified acrylic resin systems described in JP-A No. 516 and the like, sulfonium group-containing resin systems described in JP-A-6-128351, and the like. In addition to those described in the above-mentioned references, a phosphonium group-containing resin system or the like can be used. Among the above cationic base resins, it is particularly preferable to use an amine-modified epoxy resin system.

In the above-mentioned cationic electrodeposition paint, in addition to the above-mentioned cationic base resin, for example, the amount of the curing catalyst compounded,
The type and blending amount of the curing agent affect the temperature of T in the preferable temperature range. Tg after heat curing is
This is because if the curing reaction rate is increased at the same time as it has a deep relationship with the crosslink density, the mixed layer in the heat curing step can be suppressed.

The curing agent is not particularly limited, but it is preferable to use a blocked isocyanate compound, for example. The blocked isocyanate compound is a compound obtained by blocking the isocyanate compound with a suitable blocking agent. The blocked isocyanate compound that can be incorporated in the above cationic electrodeposition coating composition preferably has two or more isocyanate groups.

The above-mentioned isocyanate compound is not particularly limited, and examples thereof include aliphatic diisocyanate compounds such as hexamethylene diisocyanate (HMDI) and trimethylhexamethylene diisocyanate (TMDI);
Aliphatic diisocyanate compounds such as isophorone diisocyanate (IPDI); aromatic-aliphatic diisocyanate compounds such as xylylene diisocyanate (XDI); aromatic diisocyanates such as tolylene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI) Compounds: dimer acid diisocyanate (DDI), hydrogenated TDI (HTDI), hydrogenated XDI (H6XDI), hydrogenated MDI (H
12 MDI) and the like, diisocyanate compounds such as hydrogenated diisocyanate compounds; and triisocyanate compounds such as trimers of the above diisocyanate compounds.

The blocking agent is not particularly limited, and examples thereof include oximes such as methylethylketoxime, acetoxime and cyclohexanone oxime; phenols such as m-cresol and xylenol; butanol, 2-ethylhexanol, cyclohexanol and ethylene glycol. Alcohols such as monoethyl ether; lactams such as ε-caprolactam; diketones such as diethyl malonate and acetoacetate; mercaptans such as thiophenol; ureas such as thiouric acid; imidazoles; carbamic acids and the like. be able to. Of these, oximes, phenols, alcohols, lactams and diketones are preferable.

The blocked isocyanate compound may be a combination of two or more compounds selected from the above compounds.

In the above-mentioned cationic electrodeposition coating composition, the mixing ratio of the above-mentioned cationic base resin and the curing agent is not particularly limited, but the lower limit of the base resin is 40 with respect to the total solid mass of these two components. It is preferable that the content is% by mass, the upper limit is 90% by mass, and the balance is a curing agent. The lower limit is 5
It is more preferably 0% by mass, and the upper limit is more preferably 80% by mass. By setting the amount of the curing agent in the above range, it becomes easy to bring the above T into the required temperature range.

When the curing agent is a blocked isocyanate compound, it is preferable to incorporate a curing catalyst in the cationic electrodeposition coating composition. By blending the above curing catalyst, the curing speed of the cation electrodeposition uncured coating film can be increased and the mixed layer at the time of heat curing can be suppressed.
The curing catalyst is not particularly limited, and examples thereof include tin octoate, dibutyltin dilaurate, manganese, cobalt, lead, bismuth stannate, lead stannate, zirconium octoate, zinc octoate, dibutyltin-bis-.
O-phenylphenylene, dibutyltin-S, S-dibutyldithio-carbonate, triphenylantimony dichloride, dibutyltin maleate, dibutyltin diacetate, dibutyltin dilaurate mercaptide, triethylenediamine, bismuth stearate, lead stearate, dimethyltin. Examples thereof include dichloride.
Among the above curing catalysts, it is preferable to use a tin compound, more preferably dibutyltin oxide. The compounding amount of the above curing catalyst is preferably within the range of the lower limit of 0.1 and the upper limit of 10 parts by mass with respect to 100 parts by mass of the total of the cationic base resin and the high molecular weight blocked isocyanate compound.

In addition to the above cationic electrodeposition paints, inorganic pigments such as iron oxide and carbon black may be used according to the purpose of preparing the paints; phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyrimidine yellow, flavanthron yellow and iso. Organic pigments such as indolin yellow, indanthrone blue, quinacridone violet, etc .; titanium dioxide, clay,
Extender pigments such as talc or kaolin; phosphorus molybdenum, which is a salt of phosphomolybdic acid and a divalent or trivalent metal salt of aluminum, ferric iron, titanium, zirconium, manganese, cobalt, nickel, copper, zinc, silicon, etc. Acid salts, aluminum dihydrogen tripolyphosphate, aluminum metaphosphate, ferric pyrophosphate, tripolyphosphoric acid,
A rust preventive pigment such as a salt of metaphosphoric acid, pyrophosphoric acid or the like and the above divalent or trivalent metal salt can be blended.

When the ratio P / V of the weight V of all vehicle components to the total weight P of pigments in the above cationic electrodeposition coating is expressed as P / V, the above-mentioned pigments are preferably in the range of 1/10 to 1/2. With all vehicle components other than the above pigments,
It means all solid components (all resin components including pigment-dispersed resin and curing agent components) that compose a coating material other than pigments. Above P /
If V is less than 1/10, the pigment is insufficient and the barrier property against corrosion factors such as light rays and water against the coating film is excessively lowered, and weather resistance and corrosion resistance at a practical level may not be exhibited.
On the other hand, when P / V is more than 1/2, excess pigment may cause an increase in viscosity at the time of curing, resulting in poor flowability and poor coating film appearance.

Further, in the cationic electrodeposition coating composition of the present invention,
A rust preventive agent such as zinc acetate or cerium acetate can also be added. When the rust preventive agent is added, the addition amount thereof should be in the range of the lower limit of 0.05% by weight and the upper limit of 0.5% by weight based on 100% by weight of the total amount of the base resin and the curing agent in the cationic electrodeposition coating composition. preferable. The lower limit is more preferably 0.1% by mass, and the upper limit is more preferably 0.4% by mass.

The water-based intermediate coating composition used in the above step (2) contains a film-forming resin, a curing agent and necessary additives. The water-based intermediate coating composition has a Tg of 55 ° C. as a lower limit and 110 ° C. as an upper limit as measured by dynamic viscoelasticity of a single-layer cured intermediate coating film obtained by applying a single layer and heating and curing. It is preferably within. More preferably, the lower limit is 65 ° C. and the upper limit is 10
It is more preferably 0 ° C. If the Tg is below the above lower limit, the rust preventive property of the resulting multilayer coating film may not be sufficiently improved. When the Tg is higher than the upper limit, the impact resistance of the coating film may be poor.

The above-mentioned single-layer cured intermediate coating film is applied to the same object to be coated in the case of forming a multilayer coating film under the same film forming conditions as in the case of forming an uncured film. It is formed by applying an intermediate coating and curing by heating. The Tg of the single-layer uncured coating film is measured by the same method as the above T measurement. Regarding the Tg of the intermediate-coating single-layer uncured coating film, a preferable Tg can be realized by the same method as the Tg of the electrodeposition uncured coating film. Examples of the coating film forming resin include water-based polyester resins and water-based acrylic resins, and it is particularly preferable to use water-based polyester resins.

The above-mentioned aqueous polyester resin is, for example, an acid group and / or an acid group obtained by a polymerization reaction of a polybasic acid, a polyhydric alcohol and a compound belonging to both the polybasic acid and the polyhydric alcohol, which are usually used in the field of paints. Alternatively, a polyester resin having a hydroxyl group that is water-soluble or water-dispersed can be used.

The polybasic acid is not particularly limited,
For example, oxalic acid, succinic acid, adipic acid, sebacic acid, phthalic acid, terephthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, tetrachlorophthalic acid, cyclohexanedicarboxylic acid, azelaic acid,
1,10-decanedicarboxylic acid, propanetricarboxylic acid, butanetricarboxylic acid, trimellitic acid, butanetetracarboxylic acid, pyromellitic acid, benzoic acid, and ester-forming derivatives thereof (lower alcohol ester, anhydride, acid halide) Etc. can be mentioned. Among these, isophthalic acid, hexahydrophthalic acid, trimellitic acid and adipic acid are preferable.

The polyhydric alcohol is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5. -Pentanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, 1,9
-Nonanediol, 1,10-decanediol, propylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,
3-propanediol, glycerin, butanetriol, trimethylolethane, trimethylolpropane,
Examples thereof include triethanolamine, sorbitan monooleate, pentaerythritol, dipentaerythritol, ditrimethylolpropane, sorbitol, diglycerin, triglycerin, tripentaerythritol and bisphenol A. Of these, neopentyl glycol, trimethylolpropane and pentaerythritol are preferred.

The compounds belonging to both the polybasic acid and the polyhydric alcohol are not particularly limited, and for example, ε-
Examples thereof include lactones such as caprolactone and γ-butyrolactone, and aromatic oxymonocarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid.

The above polyester resin can be produced by charging a predetermined amount of the above polybasic acid and the above polyhydric alcohol into a reaction vessel and subjecting them to a condensation reaction by a conventional method.

The acid value of the above polyester resin is, from the viewpoint of water dispersion or water solubilization and the paint recyclability,
It is preferable that the lower limit is 20 and the upper limit is 80. The lower limit is more preferably 30, and the upper limit is more preferably 60. When the acid value is less than 20, the dispersibility in water or the water solubility is lowered and the stability is impaired, and the recyclability of the coating material is sometimes lowered accordingly. on the other hand,
When the acid value exceeds 80, the hydrophilicity of the resin becomes too high, and the water resistance and weather resistance of the coating film may deteriorate.

The hydroxyl value of the polyester resin is preferably in the range of 50 as the lower limit and 200 as the upper limit. The lower limit is more preferably 100. When the hydroxyl value is less than 50, the water solubility or water dispersibility is reduced, the stability is impaired, the recyclability of the paint using this resin may be lowered, and the curability of the paint is insufficient. May be When the hydroxyl value exceeds 200, the water resistance and weather resistance of the coating film of the coating material obtained by using this resin may deteriorate.

Further, the number average molecular weight of the above polyester resin is preferably within the range of the lower limit of 1000 and the upper limit of 10,000. It is more preferable that the upper limit is 5000. When the number average molecular weight is less than 1000, the water resistance and weather resistance of the coating film of the coating material may decrease, and when the number average molecular weight exceeds 10,000, the viscosity of the coating material becomes too high and the coating workability deteriorates. There is a case.

The above-mentioned polyester resin is made water-based by
For example, it can be carried out by neutralizing the acid group of the polyester resin with a neutralizing base and then dissolving or dispersing it in water. The neutralizing base is not particularly limited, for example, monomethylamine, dimethylamine, trimethylamine, monoethylamine, triethylamine,
Monoisopropylamine, diethylenetriamine, triethylenetriamine, triethylenetetramine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, dimethylethanolamine, 2-aminomethylpropanol, morpholine, methylmorpholine, piperazine, ammonia , Sodium hydroxide, potassium hydroxide, lithium hydroxide and the like.

The above-mentioned waterborne intermediate coating composition preferably uses a blocked isocyanate compound as a curing agent.
The blocked isocyanate compound is preferable in that it hardly causes a mixed layer at the time of heat curing and causes a curing reaction with the cationic electrodeposition resin even when the mixed layer is generated, so that the problem of curing inhibition is less likely to occur. Other curing agents may be used in combination with the blocked diisocyanate compound, but it is preferable that the curing agents do not substantially contain a melamine resin. The melamine resin is liable to form a mixed layer, and when mixed in a cation electrodeposition uncured coating film, it does not cause a reaction with the cation electrodeposition uncured coating resin, and thus tends to cause curing inhibition. When such inhibition of curing occurs, T of the uncured coating film obtained may not fall within the above range, and the rust preventive property may decrease.

The blocked isocyanate compound is not particularly limited, and for example, the blocked isocyanate compound used in the cationic electrodeposition coating composition can be used. The blocking agent is not particularly limited,
The blocking agent described in the blocked isocyanate compound that can be incorporated in the above cationic electrodeposition coating composition can be used. Of these, oximes, phenols, alcohols, lactams and diketones are preferable. As the blocked isocyanate compound, two or more compounds selected from the above compounds may be used in combination.

The blocked isocyanate compound may be a combination of two or more compounds selected from the above compounds. In particular, it is preferable that the blocked isophorone diisocyanate is contained in an amount of 90% by mass or more.

In the above intermediate coating composition, the compounding ratio of the coating film forming resin and the curing agent is not particularly limited, but the lower limit of the base resin is 40% by mass with respect to the total solid weight of these two components. The upper limit is 90% by mass, and the balance is preferably a curing agent. The lower limit is more preferably 50% by mass, and the upper limit is more preferably 80% by mass. By setting the amount of the curing agent in the above range, it becomes easy to bring the above T into the required temperature range.

When the above curing agent is a blocked polyisocyanate compound, it is preferable to incorporate a curing catalyst into the aqueous intermediate coating composition. By blending the above curing catalyst, the curing rate of the uncured intermediate coating film can be increased, and the mixed layer at the time of heat curing can be suppressed. The curing catalyst is not particularly limited, and examples thereof include tin octoate, dibutyltin dilaurate, manganese, cobalt, lead, bismuth stannate, lead stannate, zirconium octoate, zinc octoate, dibutyltin-bis-O.
-Phenylphenylene, dibutyltin-S, S-dibutyldithio-carbonate, triphenylantimony dichloride, dibutyltin maleate, dibutyltin diacetate, dibutyltin dilaurate mercaptide, triethylenediamine, bismuth stearate, lead stearate, dimethyltin dichloride Etc. can be mentioned.
Among the above curing catalysts, it is preferable to use a tin compound, more preferably dibutyltin oxide.

The amount of the above-mentioned curing catalyst compounded varies depending on the kind of the curing agent used, but the above tin-containing compound is used as the tin metal amount of the above tin-containing compound and the solid content of the coating film,
It is preferable that the lower limit is 0% by mass and the upper limit is 10.0% by mass.

In addition to the above-mentioned components, the above-mentioned intermediate coating composition may contain an inorganic pigment, an organic pigment, an extender pigment, a coloring pigment, a surface conditioner, etc. within a range not impairing the effects of the present invention. As the inorganic pigments, organic pigments, extender pigments, and coloring pigments, those exemplified in the above cationic electrodeposition coating composition can be used in the same manner.

The above-mentioned pigment has a total pigment concentration represented by [total pigment mass / (total pigment mass + total resin solid content mass)] × 100 of 20 to 60% by mass in the aqueous intermediate coating composition. Is preferred. If the above concentration is less than 20% by mass, the color design of the paint may become difficult, and 6
If it exceeds 0% by mass, the undercoating hiding property may decrease. More preferably, it is 30 to 55 mass%.

The method for forming a multilayer coating film of the present invention comprises a step (1) of applying the above-mentioned cationic electrodeposition coating composition onto an object to be coated to form an electrodeposition uncured coating film without heating and curing, A step (2) of applying the aqueous intermediate coating composition on the electrodeposition uncured coating film formed in (1) to form an intermediate coating uncured coating film, and the step (1) and the step ( It is a method of forming a multilayer coating film by the step (3) of simultaneously heating and curing the multilayer uncured coating film formed in 2).

The method of electrodeposition coating in the step (1) is not particularly limited, and a usual coating method can be used. The cationic electrodeposition coating used in the step (1) can be obtained by dispersing the above components in an aqueous medium containing a water-soluble organic acid or an inorganic acid as a neutralizing agent. Examples of the water-soluble organic acid include, for example, formic acid, acetic acid, propionic acid, lactic acid, citric acid, malic acid, tartaric acid, acrylic acid, and the like.
Examples thereof include hydrochloric acid, phosphoric acid, sulfamic acid and the like.

The pH of the electrodeposition coating solution during electrodeposition coating is preferably within the range of 5.7 as the lower limit and 6.7 as the upper limit. p
When H is less than 5.7, the Coulombic efficiency of the electrodeposition coating is reduced and the throwing power is reduced. If the pH exceeds 6.7, the metal catalyst in the electrodeposition coating bath becomes unstable and easily precipitates, and the effective catalytic function deteriorates. More preferable above pH
Has a lower limit of 5.8, and a more preferable upper limit of pH is 6.5.

The conditions for the electrodeposition coating in this step are as follows: the coating voltage is within the lower limit of 100 V and the upper limit of 400 V, the coating time is within the lower limit of 1 minute and the upper limit of 5 minutes, and the lower limit of the electrodeposition liquid temperature is set. It is preferable that the solid content of the electrodeposition liquid be within the range of 15 ° C. and the upper limit of 35 ° C. and the lower limit of 5% by mass and the upper limit of 40% by mass. The dry film thickness of the electrodeposition uncured coating film is preferably in the range of the lower limit of 10 μm and the upper limit of 40 μm, and the lower limit is 15 μm.
More preferably, the upper limit is 25 μm.

In the method for forming a multilayer coating film of the present invention, after the cationic electrodeposition coating is formed by the above steps, the coating with the aqueous intermediate coating material is performed without performing the heat curing step. It is preferable to perform preheating before applying the aqueous intermediate coating composition. By performing preheating, water in the uncured coating film is removed, and at the same time pores on the surface of the uncured coating film generated during electrodeposition are closed, so that the resulting multilayer coating film has a good finished appearance. Is preferred.

The above-mentioned preheating is carried out at a lower limit of room temperature and an upper limit of 100.
It is preferably carried out under the condition of a temperature range of ° C. When preheating is performed at a temperature higher than 100 ° C., the heating and curing conditions of the uncured coating film are approached, and thus the cost reduction due to the omission of steps may not be sufficiently achieved.
The lower limit of the preheat temperature is more preferably 50 ° C, and the upper limit of the preheat temperature is more preferably 9 ° C.
It is 0 ° C. The preheating is preferably performed for 1 to 10 minutes. If the preheating time is less than 1 minute, the effect of preheating is not sufficiently obtained, and if the preheating time is more than 10 minutes, the effect of cost reduction due to omission of steps may not be sufficiently achieved.

The coating of the above-mentioned aqueous intermediate coating composition is not particularly limited, and examples thereof include air electrostatic spray commonly referred to as “react gun”, commonly referred to as “micro-microbell (μμbell)”, and “microbell (μbell). ) ”,“ Metallic Bell ”and the like, which can be performed by using a rotary atomization type electrostatic coating machine or the like. After coating, it is preferable to perform preheating as in the case of the above electrodeposition coating. When preheating is performed, preferable preheating conditions are the same as the preheating conditions for the above electrodeposition uncured coating film.

The film thickness of the uncured coating film formed by the above water-based intermediate coating composition is not particularly limited and can be set according to the application. The lower limit of the film thickness is 5 μm
Is more preferable, 10 μm is more preferable, and 15 μm is still more preferable. The upper limit of the film thickness is 50 μm
Is more preferable, 40 μm is more preferable, and 35 μm is still more preferable.

In the method for forming a multilayer coating film of the present invention, the multilayer uncured coating film formed in the above step (1) and step (2) as the step (3) after the formation of the intermediate coating uncured coating film. Are simultaneously cured by heating. Heat curing is 100 to 2
It is preferable to carry out the treatment at a temperature of 50 ° C. for 5 to 60 minutes.

The article to be coated by the method of the present invention is
There is no particular limitation as long as it is a metal product that can be subjected to cationic electrodeposition coating. Examples include iron, copper, aluminum, tin, zinc and alloys containing these metals, as well as plated or vapor deposited products with these metals.

Further, on the multilayer coating film formed by the method for forming a multilayer coating film of the present invention, a coating film may be formed with a base paint, a clear paint or the like. The above base paint,
The clear paint is not particularly limited, and a known paint can be used.

The coating film obtained by the above-mentioned method for forming a multilayer coating film has excellent appearance characteristics, and the above method is a two-wet coating method. Is possible.

[0060]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, when simply describing “%” in this example, it means “mass%”.

Preparation Example 1 Preparation of electrodeposition coating composition 1- (1) Preparation of blocked isocyanate curing agent (A) In a reaction vessel equipped with a stirrer, a nitrogen introducing tube, a cooling tube and a thermometer, 222 parts by mass of isophorone diisocyanate and methyl isobutyl. After adding 99 parts by mass of ketone (MIBK) and mixing, add 0.2 parts by mass of butyltin laurate,
The temperature was raised to 50 ° C. Methyl ethyl ketoxime 1
74 parts by mass was dropped. During the dropping, the temperature and dropping rate were adjusted so that the contents did not exceed 70 ° C. 7 after dropping
The reaction was carried out at 0 ° C for 1 hour. The infrared absorption spectrum of the reaction product confirmed that the absorption derived from the isocyanate groups had disappeared, and a blocked isocyanate curing agent (A) having a solid content of 80% was obtained.

1- (2) Preparation of Blocked Isocyanate Curing Agent (B) Hexamethylene diisocyanate trimer 19 is placed in a reaction vessel equipped with a stirrer, nitrogen introducing tube, cooling tube and thermometer.
After 9 parts by mass and 73 parts by mass of methyl isobutyl ketone (MIBK) were added and mixed, 0.2 parts by mass of butyltin laurate was added and the temperature was raised to 50 ° C. To this, 44 parts by mass of methyl ethyl ketoxime and 87 parts by mass of ethylene glycol mono-2-ethylhexyl ether were added dropwise. During the dropping, the temperature and dropping rate were adjusted so that the contents did not exceed 70 ° C. After dropping, the reaction was carried out at 70 ° C. for 1 hour. The infrared absorption spectrum of the reaction product confirmed that the absorption derived from the isocyanate group had disappeared. After the reaction, n
-By diluting with 10 parts by weight of butanol, a blocked isocyanate curing agent (B) having a solid content of 80% was obtained.

1- (3) Preparation of Block Polyisocyanate Curing Agent (C) 250 parts by mass of didiphenylmethane diisocyanate and 78 parts by mass of methyl isobutyl ketone (MIBK) in a reaction vessel equipped with a stirrer, a nitrogen introducing tube, a cooling tube and a thermometer. After mixing and mixing, 0.2 part by mass of butyltin laurate was added and the temperature was raised to 50 ° C. To this, 53 parts by mass of propylene glycol and 49 parts by mass of butyl diglycol were dropped. During the dropping, the temperature and dropping rate were adjusted so that the contents did not exceed 70 ° C. After dropping, the reaction was carried out at 70 ° C. for 1 hour. The infrared absorption spectrum of the reaction product confirmed that the absorption derived from the isocyanate group had disappeared. After the reaction, the blocked isocyanate curing agent (C) having a solid content of 80% was obtained by diluting with 10 parts by mass of n-butanol.

1- (4) Preparation of cationic epoxy resin Stirrer, decanter, nitrogen introduction tube, thermometer and dropping roe
Epoxy equivalent of 188
Enol A type epoxy resin (trade name DER-331J,
Dow Chemical Co., Ltd.) 2400 parts by mass, methanol 141
Parts by mass, MIBK168 parts by mass and dibutyrate dibutylate
Add 0.5 parts by weight of tin and stir at 40 ° C to dissolve evenly.
Let 2,4 / 2,6-tolylene diisocyanate was added to the above solution.
30 parts by weight of nate (80/20 mass ratio mixture)
Dropped in minutes. The temperature of the reaction solution rises due to dripping
Then, the solution became 70 ° C. N, N- was added to the above reaction mixture.
Add 5 parts by mass of dimethylbenzylamine and increase the temperature to 120.
The temperature was raised to ℃ and the reaction was carried out for 3 hours while distilling off methanol.
It was The epoxy equivalent at the end of the reaction was 500. the above
The reaction mixture further contains 341 parts by mass of bisphenol A, 2-
413 parts by mass of ethylhexanoic acid and 664 parts by mass of MIBK
Part, and the reaction was carried out for 3 hours while maintaining the temperature at 120 ° C.
It was The epoxy equivalent after the reaction was 1070. Up
After cooling the reaction mixture to 110 ° C., diethylenetri
Amine diketimine solid content 73% MIBK solution 241 quality
And 192 parts by mass of N-methylethanolamine
By adding the product and reacting at 110 ° C for 1 hour.
An on epoxy resin was obtained. The number average molecular weight of the above resin is
The hydroxyl value was 2100 and 160. Also the infrared of the resin
From measurements such as spectrum measurement, oxazoline was found in the resin.
Ring (absorption wavelength 1750 cm ^-1) Is sure to have
It has been certified.

1- (5) Preparation of Cationic Epoxy Resin Emulsion (E1) 1834 parts by mass of a curing agent (A) (cation-modified epoxy resin) in the cationic epoxy resin obtained in Preparation Example 1- (4) above. 38% by mass of the blocked isocyanate compound relative to 100 parts by mass), 90 parts by mass of acetic acid, 2 parts by mass of zinc acetate and 2 parts by mass of cerium acetate as a rust preventive agent were added, and then diluted with ion-exchanged water to a nonvolatile content of 32%. rear,
The nonvolatile content was concentrated to 36% under reduced pressure to obtain a cationic epoxy resin emulsion (E1).

1- (6) Preparation of Cationic Epoxy Resin Emulsion (E2) Into the cationic epoxy resin obtained in Preparation Example 1- (4) above, 550 parts by mass of the curing agent (B) and the curing agent (C ) 12
84 parts by mass (compounding ratio of blocked isocyanate compound to 38 parts by mass of cation-modified epoxy resin 38
%), 90 parts by mass of acetic acid, 2 parts by mass of zinc acetate as a rust preventive and 2 parts by mass of cerium acetate, and then diluted with ion-exchanged water to a nonvolatile content of 32%, and then a nonvolatile content of 36% under reduced pressure.
% To obtain a cationic epoxy resin emulsion (E2).

1- (7) Preparation of Resin for Dispersing Pigment 1- (7) -1 Preparation of Resin A bisphenol A type epoxy resin having an epoxy equivalent of 198 was added to a reaction vessel equipped with a stirrer, a nitrogen introducing tube, a cooling tube and a thermometer. (Product name Epon 829, manufactured by Shell Chemical Co., Ltd.) 710 parts by mass and bisphenol A 289.6 parts by mass were added, and the reaction was carried out at 150 to 260 ° C. for 1 hour under a nitrogen atmosphere. Then, after cooling to 120 ° C., 406.4 parts by mass of a solution of 2-ethylhexanolated half-block tolylene diisocyanate in MIBK solution (solid content 95%) was added. The reaction mixture was reacted at 110 to 120 ° C. for 1 hour, and then 1584.1 parts by mass of ethylene glycol mono n-butyl ether was added. The above reaction product was cooled to 85 to 95 ° C. and homogenized.

1- (7) -2 Preparation of quaternizing agent In parallel with the preparation of the above reaction product, a quaternizing agent is prepared separately. In a separate reaction container, dimethylethanolamine 1 was added to 384 parts by mass of a 2-ethylhexanolated half-block tolylene diisocyanate MIBK solution (solid content: 95%).
What added 04.6 mass part was stirred at 80 degreeC for 1 hour. Next, 141.1 parts by mass of 75% lactic acid water was added to the above reaction vessel, and then 47.0 parts by mass of ethylene glycol mono-n-butyl ether were mixed and stirred for 30 minutes, and 4
A grader was obtained.

1- (7) -3 Reaction of resin with quaternizing agent 620.46 parts by mass of the quaternizing agent is added to the total amount of the resin obtained by the reaction, and the mixture is heated at 85 ° C to 95 ° C. ℃
The resin varnish for pigment dispersion (resin solid content 56%, number average molecular weight 2200) was obtained by keeping the acid value at 1.

1- (8) Preparation of Pigment Dispersion Paste Using a sand mill, a pigment paste having the following formulation containing the pigment dispersion resin prepared in Preparation Example 1- (7) above was prepared.

[0071] (Pigment dispersion paste formulation) Preparation Example 1- (7) Pigment dispersion resin varnish 53.6 parts by mass Titanium dioxide CR-90 (manufactured by Ishihara Sangyo Co., Ltd.) 88.0 parts by mass Carbon black MA-100 (manufactured by Mitsubishi Chemical Corporation) 2.0 parts by mass Aluminum phosphomolybdate 10.0 parts by mass

1- (9) Preparation of Electrodeposition Coating (D-1) Cationic Epoxy Resin Emulsion (E1) Obtained in Preparation Example 1- (5), Pigment Obtained in Preparation Example 1- (8) Dispersion paste and deionized water are used to
An electrodeposition paint having a solid content of 20% was prepared so that the mass ratio P / V of all vehicle components was 1/4. An emulsified emulsion paste of dibutyltin oxide as a curing accelerator was added to the above-mentioned electrodeposition paint so that the tin metal content was 6.5% of the solid mass of the paint, and the electrodeposition paint (D-1) was prepared. Prepared.

1- (10) Preparation of Electrodeposition Paint (D-2) Cationic Epoxy Resin Emulsion (E2) Obtained in Preparation Example 1- (6), Pigment Obtained in Preparation Example 1- (8) Dispersion paste and deionized water are used to
An electrodeposition paint having a solid content of 20% was prepared so that the mass ratio P / V of all vehicle components was 1/4. An emulsified emulsion paste of dibutyltin oxide as a curing accelerator was added to the above electrodeposition coating composition so that the tin metal content was 1.5% of the solid content of the coating composition, and an electrodeposition coating composition (D-2) was prepared. Prepared.

1- (11) Preparation of Electrodeposition Paint (D-3) An emulsion emulsion paste of dibutyltin oxide was added to the electrodeposition paint to obtain a tin metal content of 1.5% of the solid mass of the paint.
An electrodeposition coating material (D-3) was prepared in the same manner as in Preparation Example 1- (9) except that the composition was blended as described below.

1- (12) Preparation of Electrodeposition Paint (D-4) An emulsified emulsion paste of dibutyltin oxide was added to the electrodeposition paint so that the tin metal content was 0.5% of the solid content of the paint. An electrodeposition coating composition (D-4) was prepared in the same manner as in Preparation Example 1- (10) except that the above was carried out.

Preparation Example 2 (Preparation of Waterborne Intermediate Coating Material) 2- (2) Preparation of Waterborne Polyester Resin (F) 200 parts by mass of isophthalic acid was placed in a reaction vessel equipped with a stirrer, nitrogen inlet tube, cooling tube and thermometer. 179 parts by mass of phthalic anhydride, 176 parts by mass of adipic acid, 150 parts by mass of trimethylolpropane, 295 parts by mass of neopentyl glycol, 2 parts by mass of dibutyltin oxide were added, and the mixture was heated in a nitrogen stream to melt the raw materials and then mixed and stirred. While 17
The temperature was gradually raised to 0 ° C. After that, 2 more hours
The dehydration transesterification reaction was carried out while the temperature was raised to 20 ° C.
When the acid value reached 10, it was cooled to 150 ° C. Hexahydrophthalic acid (114.0 parts) was added for 1 hour 1 hour.
The reaction was completed at 50 ° C. The obtained polyester resin had a solid content acid value of 50, a hydroxyl value of 65, and a number average molecular weight of 10,000 obtained by gel permeation chromatography (GPC). The resin obtained by the above reaction was cooled to 60 ° C., 80 parts by mass of dimethylethanolamine and ion-exchanged water were added to obtain an aqueous polyester resin (F) solution having a nonvolatile content of 50%.

2- (3) Preparation of Color Pigment Paste After pre-mixing the following raw materials containing the aqueous polyester resin (F) solution prepared by the above Preparation Example 2- (2), the glass bead medium was added in the paint conditioner. ,
The mixture was mixed and dispersed at room temperature for 1 hour to prepare a color pigment paste having a particle size of 5 μm or less.

[0078] (Color pigment paste prescription) Preparation Example 2- (2) Aqueous polyester resin (F) solution 50.0 parts by mass Ion-exchanged water 17.9 parts by mass Titanium dioxide CR-97 (manufactured by Ishihara Sangyo Co., Ltd.) 34.5 parts by mass Barium sulfate B-34 (manufactured by Sakai Chemical Industry Co., Ltd.) 34.4 parts by mass Talc LMR-100 (manufactured by Fuji Talc) 6.0 parts by mass Carbon black MA-100 (manufactured by Mitsubishi Chemical Corporation) 0.1 part by mass

2- (4) Preparation of Water-based Intermediate Coating Paint Coloring pigment paste, water-based polyester resin (F), and blocked isocyanate compound (A) in the following compounding ratios:
Was blended to prepare an aqueous intermediate coating composition.

[0080] (Water-based intermediate coating formulation) Coloring pigment paste 95.27 parts by mass Aqueous polyester resin (F) solution 48.01 parts by mass Blocked diisocyanate curing agent (A) 18.07 parts by mass

Example 1 Using the electrodeposition coating composition (D-1) obtained in Preparation Example 1- (9), a voltage of 200 was applied to a zinc phosphate-treated dull steel sheet.
Electrodeposition coating with V to a dry film thickness of 20 μm, 80
Preheated at 0 ° C for 10 minutes. The plate was coated with the aqueous intermediate coating composition obtained in Preparation Example 2 by air spray coating to a thickness of 30 μm.
It was painted, dried at 60 ° C. for 3 minutes, and then heat-cured at 160 ° C. for 20 minutes. The evaluation results are shown in Table 1.

(Evaluation method) Dynamic viscoelasticity measurement An electrodeposited single film and a multilayer coating film applied on a tin plate in the same manner as in the above examples were peeled and cut with mercury to obtain a measurement sample. Prepared and RHEOVIBRON MODEL
Using RHEO 2000, 3000 (trade name, manufactured by Orientec Co., Ltd.), from room temperature to 200 ° C, 2 ° C per minute
The sample was vibrated at a temperature rising rate of 11 Hz and a frequency of 11 Hz to measure its viscoelasticity, and the ratio (tan δ) of the loss elastic modulus (E ″) to the storage elastic modulus (E ′) was calculated to obtain the peak value. The respective T and dynamic Tg were determined by determining the temperature at which The electrodeposition single film and the multilayer coating film were cured by baking at 160 ° C. for 20 minutes.

Measurement of viscoelasticity of intermediate coating film The above aqueous intermediate coating composition was air-sprayed onto a polypropylene test plate of 10 × 30 × 2 mm to give a dry film thickness of 40 μm.
And the coating film obtained by baking and curing at 160 ° C. for 20 minutes was peeled off and cut into a size of 10 × 70 mm to obtain a test piece. The test piece was subjected to viscoelasticity measurement by the same method as that for the electrodeposition single film and the multilayer coating film to measure Tg of the intermediate coating film.

Anticorrosion Test (SDT) A coated plate was cut with a knife to reach the substrate, and a salt water immersion test (5% saline solution, 55 ° C.) was performed for 240 hours. The maximum width was evaluated, and less than 10 mm was passed (◯) and 10 mm or more was rejected (x).

Example 2 Coating was carried out in the same manner as in Example 1 except that the electrodeposition coating material (D-2) obtained in Example 1- (10) was used. The evaluation results are shown in Table 1.

Comparative Example 1 Coating was carried out in the same manner as in Example 1 except that the electrodeposition coating material (D-3) obtained in Preparation Example 1- (11) was used. The evaluation results are shown in Table 1.

Comparative Example 2 Coating was carried out in the same manner as in Example 1 except that the electrodeposition coating material (D-4) obtained in Preparation Example 1- (12) was used. The evaluation results are shown in Table 1.

Comparative Example 3 As in Example 1, after electrodeposition coating, heat curing was carried out at 160 ° C. for 20 minutes. The water-based intermediate coating composition obtained in Preparation Example 2 was applied to the plate by air spray coating at 30 μm.
It was dried at 0 ° C. for 3 minutes and further heat-cured at 160 ° C. for 20 minutes. The evaluation results are shown in Table 1.

Comparative Example 4 After electrodeposition coating as in Example 2, coating and heat curing as in Comparative Example 3 were carried out. The evaluation results are shown in Table 1.

Comparative Example 5 After electrodeposition coating as in Comparative Example 1, the same coating and heat curing as in Comparative Example 3 were carried out. The evaluation results are shown in Table 1.

Comparative Example 6 After electrodeposition coating as in Comparative Example 2, coating and heat curing were carried out as in Comparative Example 3. The evaluation results are shown in Table 1.

[0092]

[Table 1]

From the above results, the multilayer coating films of Examples 1 and 2 formed by the method for forming a multilayer coating film of the present invention are superior to the multilayer coating films of Comparative Examples 1 and 2 in rust prevention. It is clear that

[0094]

According to the method for forming a multilayer coating film of the present invention, it is possible to obtain a multilayer coating film in which the steps of the wet-on-wet method are simplified without causing the problem of deterioration of rust prevention.

Continued front page    (72) Inventor Hitoshi Yoshida             19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan             Into Inc. (72) Inventor Seiji Yokoi             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. F-term (reference) 4D075 AE03 AE06 AE16 BB26Z                       BB89X BB93Z DA23 DC12                       EA06 EB12 EB22 EB33 EB35                       EB38 EB43 EB45

Claims (4)

[Claims] 1. A step (1) of applying a cationic electrodeposition coating composition onto an object to be coated to form an electrodeposition uncured coating film without heat curing, and the electrodeposition formed by the step (1). Step (2) of applying an aqueous intermediate coating composition on the uncured coating film to form an intermediate coating uncured coating film, and the multilayer uncured coating formed by the steps (1) and (2) A method for forming a multilayer coating film comprising the step (3) of simultaneously heating and curing the film, wherein the multilayer coating film is a cationic electrodeposition coating film among tan δ peak values measured by dynamic viscoelasticity measurement. Of the peak value derived from Tg of
A method for forming a multilayer coating film, which is 0 ° C. 2. A Tg measured by dynamic viscoelasticity of a single-layer cured cationic electrodeposition coating film formed by heating and curing the electrodeposition uncured coating film formed in the step (1) is 1.
The method for forming a multilayer coating film according to claim 1, which has a temperature of 15 to 140 ° C. 3. The water-based intermediate coating composition has a Tg of 55 as measured by dynamic viscoelasticity of a single-layer cured intermediate coating film obtained by coating the water-based intermediate coating composition in a single layer and heat curing.
The method for forming a multilayer coating film according to claim 1 or 2, wherein the temperature is from 110 ° C. 4. The method for forming a multilayer coating film according to claim 1, wherein the water-based intermediate coating material contains a blocked isocyanate compound as a curing agent.