CN1647862A - Process for forming multi layered coated film and multi layered coated film - Google Patents

Abstract

The present invention provides a method of forming a multilayer coating film with a good finished appearance. The present invention relates to a method for the preparation of a multilayer coating film comprising the steps of electrocoating a substrate with a cationic electroplating coating composition, then heating and curing the coating to form a cured electroplating coating on the substrate film, the intermediate coating composition is applied to the cured electroplating coating film to form an uncured intermediate coating film, and the bottom surface coating composition is applied to the uncured intermediate coating film to form an uncured primer coating film, a clear topcoat composition is applied to an uncured primer coating film to form an uncured clear coating film, and the three uncured coating films are heated and cured simultaneously, wherein the cured electroplated coating film has a specified range Ra and Pa; or a specified range of Tg and crosslink density.

Description

Method for forming multilayer coating film and multilayer coating film

technical field

The present invention relates to a method for forming a multilayer coating film having a good painted appearance.

Background technique

On the surface of the substrate of the automobile body, a multi-layer coating film with various functions is formed to protect the substrate and give the substrate a good appearance. However, in recent years, due to the need for energy saving and cost reduction, a method of forming a multilayer coating film has been used, which includes the steps of: applying the next coating film over the uncured coating film; and simultaneously baking the multiple layers; without the step of baking the uncured coating film after applying each layer.

As an example of this method, a three-coat-bake coating method (three-layer wet coating) is considered the most practical method, which includes the steps of: on the cured electroplated coating film, wet through a wet mask. Coating method, applying intermediate coating, bottom surface coating (base top coating) and clear surface coating (clear topcoat); A schematic flowchart of the coating method.

Disclosed in Japanese Patent Laid-Open No. 277474/1998, a method for forming a multilayer coating film comprises the following steps: on the substrate to be coated, sequentially applying an intermediate coating, a metallic coating and a clear surface coating; and These three layers of the coating film are baked simultaneously. It is described therein that this method can provide coating films with excellent clarity and excellent gloss.

In the three-coat-bake coating process shown in Figure 1, it has been found that the surface condition of the cured electroplated coating has a significant effect on the appearance of the multilayer coating. The reason is considered to be that the number of baking steps is less in this three-coat-bake coating method, as described above. In the above method of forming a multilayer coating film (Japanese Patent Laid-Open No. 277474/1998), there is no description of the surface condition of the plating coating film capable of improving the appearance of the multilayer coating film.

A method for forming a multilayer coating film is disclosed in Japanese Patent Publication 224613/2002, comprising the following steps: forming a cured electroplating coating film on the substrate by a cationic electroplating coating composition; Coating method, applying three layers of coating on the cured electroplated coating film; and simultaneously baking and curing the three layers of uncured coating film; wherein the cured electroplated coating film has a glass transition temperature of not lower than 110°C and not Surface roughness (Ra: centerline average roughness) exceeding 0.3 μm. In this method, only the centerline average roughness (Ra) is used as a parameter for evaluating the appearance of the coating film, and other parameters are not used.

Also, in the three-coat-bake coating method shown in FIG. 1, the composition for the intermediate coating is applied on the cured electroplating coating film. There are cases where the solvent contained in the composition for an intermediate coating is absorbed by the cured plating coating film during application. In the process of baking the above-mentioned laminated coating film, the solvent absorbed in the cured electroplated coating film volatilizes, affects the intermediate coating film, etc., and reduces the finished appearance of the laminated coating film. It has been found that the solvent contained in the uncured intermediate coating applied on top of the cured electroplated coating has a significant effect on the cured electroplated coating due to the low number of baking steps and the In the coating method, uncured coating films laminated into two or more layers are baked simultaneously. In such a method of forming a multilayer coating film as described above (Japanese Patent Laid-Open No. 277474/1998), there is no description of the physical characteristics of the plating coating film which can improve the appearance of the multilayer coating film.

Contents of the invention

The main purpose of the present invention is to provide a method for forming a multi-layer coating film, which has a good finishing appearance in the three-coat-baking coating method capable of saving energy and reducing costs.

In the present invention, a method of obtaining a coating film with a good finished appearance has been found. According to the method of the invention, multilayer coating films with a good finish appearance can be produced even in a three-coat-bake coating process with a reduced number of baking steps. The multilayer coating film includes a plating coating film, an intermediate coating film, a bottom surface coating and a clear surface coating. According to the method of the present invention, it is possible to save the energy required in the baking and curing during the coating process, and to reduce the product cost. The method of the present invention can be suitably used in fields requiring energy saving and good appearance during application.

The above objects, other objects and advantages of the present invention will become clearer to those skilled in the art through the following description with reference to the relevant drawings.

Description of drawings

By the following detailed description in conjunction with the accompanying drawings, the present invention will be more fully understood, but this is only as an explanation, and does not represent that the present invention is limited thereto, and wherein: Fig. 1 illustrates an embodiment of the inventive method flow chart.

Detailed ways

The invention provides a method for forming a multilayer coating film, the method comprising the steps of:

performing electroplating coating on the substrate with a cationic electroplating coating composition, then heating and curing the coating to form a cured electroplating coating film on the substrate,

applying the intermediate coating composition on the cured electroplated coating film to form an uncured intermediate coating film,

The bottom surface coating composition is applied on the uncured intermediate coating film to form an uncured bottom coating film (base coated film),

applying the clear topcoat composition to the uncured primer film to form an uncured clear coated film,

Simultaneously heating and curing the uncured intermediate coating film, the uncured bottom surface coating film and the uncured clear coating film; wherein

The centerline average roughness (Ra) obtained from the roughness curve of the cured electroplated coating film is 0.05-0.25 μm, and the centerline average roughness (Pa) obtained from the profile curve is 0.05-0.30 μm, thereby realizing the above-mentioned purpose of the invention.

The present invention also provides a method for forming a multilayer coating film, the method comprising the above steps, wherein the cured electroplating coating film has a surface energy of 37-43mJ/m ² , and the composition of the intermediate coating is formed on the cured electroplating coating film It has a contact angle of 10-30 degrees, thereby achieving the above-mentioned purpose of the invention.

The present invention also provides a method for forming a multilayer coating film, the method comprising the above steps, wherein the centerline average roughness (Ra) obtained from the roughness curve of the cured electroplated coating film is 0.05-0.25 μm; The centerline average roughness (Pa) obtained on the curve is 0.05-0.30 μm; and the surface energy is 37-43 mJ/m ² , and the composition of the intermediate coating has a contact of 10-30 degrees on the cured electroplated coating film angle, thereby achieving the above-mentioned purpose of the invention.

The present invention also provides a method for forming a multilayer coating film, the method comprising the above steps, wherein the cured electroplating coating film has a glass transition temperature Tg of 100-130°C, a crosslinking density of 1.2-2.6mmol/cc, the above It is measured by dynamic viscoelasticity measurement, thereby achieving the above-mentioned purpose of the invention.

The method for carrying out the present invention will be explained and illustrated in detail below. The inventors have proposed in Japanese Patent Laid-Open No. 224613/2002 a method of evaluating a cured plating coating film by surface roughness (Ra: center line average roughness).

With a single method, it is difficult to evaluate the appearance of a coating film because surface morphology, optical characteristics, and color all visually and complexly affect appearance. In appearance evaluation by using wavelength as a method for evaluating the appearance of a coating film, for example, surface roughness related to gloss and clarity can be evaluated by short wavelengths, and surface roughness related to winding (winding) can be evaluated by long wavelengths. evaluate. In JIS related to surface roughness, it is described that profile curves are divided into profile curves (P), roughness curves (R) and winding curves (Winding curve) (W).

The appearance of the coating film can be evaluated by classifying it into the following items: smoothness, orange peel defects and gloss. In the present invention, it has been found that the Ra value (center line average roughness in the roughness curve) of the cured plated coating film used in the conventional evaluation method correlates with the orange peel defect evaluation item. It has also been found that the Wa value (centerline average roughness in the winding curve) of the cured plated coating film as a parameter related to the winding curve (W) correlates with the smoothness evaluation item in the appearance of the multilayer coating film. In addition, it has also been found that the winding measured by long wavelengths greatly affects the appearance of the obtained multilayer coating film. Moreover, it has now been found that by using the Ra value and the Pa value (centerline average roughness on the profile curve), including the Ra value and the Wa value as parameters to evaluate the cured electroplated coating film, the surface condition is controlled, and the obtained The finishing appearance of the multilayer coating film, thereby realized an embodiment of the present invention.

It is now considered that when the composition of the intermediate coating and the cured electroplated coating film have low wettability, even in the formation of the multilayer coating film in the coating method of three coatings-baking according to the present invention, Controlling the surface condition of the cured electroplated coating film as described above also does not accidentally result in a multilayer coating film with good appearance. These defects greatly affect the appearance of the obtained multilayer coating film, because the number of baking steps in this three-coat-one-bake coating method is less.

In the present invention, it has been found that by adjusting the surface energy of the cured electroplated coating film within a specified range, the wettability of the intermediate coating film can be controlled, and the finishing appearance of the obtained multilayer coating film can be improved, Another embodiment of the present invention is thus achieved.

In the present invention, it has been found that the solvent resistance of the cured electroplated coating film can be controlled by adjusting the glass transition temperature Tg and the crosslinking density to a specified range. It is obtained by performing dynamic viscoelasticity measurement, and can improve the finished appearance of the obtained multilayer coating film, thereby achieving yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In one embodiment of the present invention, the components contained in the cationic electroplating coating composition and their content are selected so that the cured electroplating coating film formed by electroplating coating has a thickness of 0.05-0.25 μm obtained from the roughness curve. Centerline average roughness (Ra), and centerline average roughness (Pa) of 0.05-0.30 μm obtained from profile curves. The upper limit of the centerline average roughness (Ra) is preferably 0.20 μm. The upper limit of the centerline average roughness (Pa) is preferably 0.25 μm. In the state of the art, it is difficult to obtain a cured electroplated coating film whose centerline average roughness (Ra) and centerline average roughness (Pa) are less than the lower limit of 0.05 µm.

The centerline average roughness (Ra) obtained from the roughness curve and the centerline average roughness (Pa) obtained from the profile curve used here are parameters defined in JIS B0601. The centerline average roughness (Ra) obtained from the roughness curve and the centerline average roughness (Pa) obtained from the profile curve of the cured plated coating film can be measured by the following method, for example, according to JIS B0601, by using Measured by an evaluation surface roughness detector manufactured by Mitutoyo Corporation.

When the Ra value is greater than 0.25 μm, the appearance of the multilayer coating film will be poor, especially the orange peel defect. When the Pa value is greater than 0.30 μm, the appearance of the multilayer coating film will also deteriorate, especially the smoothness.

A cationic plating coating composition is prepared so as to obtain a cured product having a centerline average roughness (Ra) obtained from a roughness curve and a centerline average roughness (Pa) obtained from a profile curve within the above ranges. The method of electroplating coating film includes adjusting the type and content of cationic epoxy resin, blocked isocyanate curing agent and catalyst in the cationic electroplating coating composition. In particular, the type and content of blocked isocyanate curing agent have a great influence on the Ra and Pa values. The smoothness of the coating film can be improved by adjusting the solid content ratio between the cationic epoxy resin and the blocked isocyanate curing agent to increase the fluidity and curing rate of the coating film during film formation (deposited film). The smoothness of the plated coating film can be further improved by using a steel plate whose surface has been treated, which has a small surface roughness.

In another embodiment of the present invention, the cationic electroplating coating composition and the intermediate coating composition used make the formed cured electroplating coating film have a surface energy of 37-43mJ/m ² , and the coated intermediate coating The layer composition has a contact angle of 10-30 degrees on the cured electroplated coating film. When the surface energy of the cured electroplated coating film is in the above-mentioned range, and the contact angle between the cured electroplated coating film and the intermediate coating composition is between 10-30 degrees, the intermediate coating composition is effective for curing The wettability of the electroplated coating film is high, and the finished appearance of the obtained multilayer coating film is excellent.

The lower limit of the surface energy of the cured plated coating film is preferably 38 mJ/m ² , more preferably 39 mJ/m ² , and its upper limit is preferably 42 mJ/m ² , more preferably 41 mJ/m ² . The lower limit of the contact angle between the cured plating coating film and the intermediate coating composition is preferably 10 degrees, and the upper limit is preferably 25 degrees.

When the surface energy is lower than 37 mJ/m ² , the adhesion between the cured plating coating film and the intermediate coating film is weakened. On the other hand, when the surface energy is higher than 43 mJ/m ² , the wettability of the composition of the intermediate coating to the cured plating coating film is weakened. In addition, when the contact angle between the cured plating coating film and the intermediate coating composition is greater than 30 degrees, the wettability of the intermediate coating composition to the cured plating coating film is weakened.

The surface energy of a coating film is the force applied to the free length in the normal direction. In the contact angle method, the surface energy is determined by measuring the contact angle between a coating film and three types of liquids (such as water, diiodomethane, ethylene glycol), which have Force the well-known γ ^LW value, the acidic component γ+ based on the acid-base force and the basic component γ- based on the acid-base force, Equation 1 is derived from the Young-Duprey equation, and the coating film is obtained in the following Equation 1 γ ^LW , γ+ and γ-values; and using Equation 2, calculations are made from these values (see CJ.Van Oss, "J. Protein Chem", Vol. 4, 245, 1985 and CJ. Interface Sci", Vol. 111, 378, 1986).

Equation 1)

2{(γ _i ^LW ·γ _j ^LW ) ^1/2 + (γ _i ⁺ ·γ _j ^- ) ^1/2 +(γ _i ^- ·γ _j ⁺ ) ^1/2 }

＝(1+cosθ){γ _i ^LW +2(γ _i ⁺ ·γ _j ^- ) ^1/2 }

Equation 2) Surface Free Energy

(γ)＝γ _j ^LW +(γ _j ⁺ ·γ _j ^- ) ^1/2

γ _i ^LW : Mathematical term based on the Lifshitz-Van der Waals force for liquids

γ _i ⁺ : acidic component based on the acid-base force of the liquid

γ _i ⁻ : Alkaline component based on the acid-base force of the liquid

θ: contact angle

A method for preparing a cationic electroplating coating composition and an intermediate coating composition from which the surface energy of a cured electroplating coating film and the relationship between the cured electroplating coating film and the intermediate coating composition can be obtained within the above ranges This method includes adjusting the type and content of cationic epoxy resin, blocked isocyanate curing agent, catalyst and surface conditioner contained in the cationic plating coating composition. In particular, the type and content of the surface conditioner have a great influence on the surface energy and the contact angle between the cured plating coating film and the intermediate coating composition. The types of surface conditioners used in the present invention include acryl-based, silicone-based and vinyl-based.

In the process of forming the multilayer coating film of the present invention, it is more preferable that the cured electroplated coating film has a centerline average roughness (Ra) of 0.05-0.25 μm obtained from the roughness curve, and a centerline average roughness (Ra) of 0.05-0.25 μm obtained from the profile curve. The centerline average roughness (Pa) of 0.30 μm, and the contact angle between the cured electroplated coating film and the intermediate coating composition is 10-30 degrees. This is because a multilayer coating film with a better finished appearance can be obtained.

In the present invention, the components contained in the cationic plating coating composition and their contents are selected so that the cured plating coating film formed by plating coating has a glass transition temperature Tg (also expressed herein as " dynamic Tg") and the specified range of crosslink densities obtained by dynamic viscoelasticity measurements.

The dynamic Tg used here is determined by measuring the dynamic glass transition temperature Tg using a sample in the same manner as the conventional method of measuring Tg by dynamic viscoelasticity measurement. Examples of the measuring method used in the present invention include a method in which a sample is prepared by forming a cured plating coating film on a substrate, using a mercury separation coating film, and cutting a coating film, and performing a dynamic test using the prepared sample. Viscoelasticity measurements. In this method, the viscoelasticity of the sample is determined by heating the sample from room temperature to 200°C at a rate of 2°C per minute and vibrating at a frequency of 11 Hz. The ratio (tan δ) of energy storage elasticity (E')/loss elasticity (E") is calculated and their inflection point (temperature at the peak of tan δ) is determined to obtain dynamic Tg. Examples of measuring devices for dynamic viscoelasticity include, for example, Rheovibron model RHEO 2000, 3000 (trade name), manufactured by Orientec Co., Ltd.

In the present invention, the preferred dynamic Tg of the cured plated coating film formed by the plated coating is 100-130°C. The lower limit of dynamic Tg is preferably 110°C, and the upper limit of dynamic Tg is preferably 125°C. When the dynamic Tg of the cured electroplated coating film is lower than 100°C, the electroplated coating film is swollen by the solvent contained in the intermediate coating composition, and the finished appearance of the resulting multilayer coating film becomes poor. On the other hand, when the dynamic Tg is higher than 130 °C, the elastic modulus of the obtained multilayer coating film will decrease, and the impact resistance of the coating film will also decrease.

The dynamic viscoelasticity of the cured plating coating film formed by plating coating was measured in the same manner as the dynamic Tg method, and calculated using the storage energy elasticity (E') obtained in the rubbery region according to the following equation , thus determining the crosslink density:

E'=3nRT

where E' is the storage elasticity; n is the crosslink density; R is the gas constant and T is the absolute temperature.

In the present invention, the crosslinking density of the cured plating coating film formed by plating coating is preferably 1.2 to 2.6 mmol/cc. The lower limit of the crosslink density is more preferably 1.4 mmol/cc, and the upper limit of the crosslink density is more preferably 2.3 mmol/cc. When the crosslinking density of the cured plating coating film is less than 1.2 mmol/cc, the plating coating film is swollen by the solvent contained in the intermediate coating composition, and the finished appearance of the obtained multilayer coating film becomes poor. On the other hand, when the cross-linking density of the cured plated coating film is higher than 2.6 mmol/cc, foaming is likely to occur due to the presence of water, and the corrosion resistance may be lowered.

A method for preparing a cationic electroplating coating composition from which a cured electroplating coating film having a dynamic Tg and a crosslink density within the above-mentioned ranges can be obtained, the method comprising adjusting the composition of the cationic electroplating coating Type and content of cationic epoxy resin, blocked isocyanate curing agent and catalyst. Especially the type and content of cationic epoxy resin and blocked isocyanate curing agent have great influence on dynamic Tg and crosslink density. Examples of cationic epoxy resins include resins obtained by opening epoxy rings of bisphenol A type epoxy resins or bisphenol F type epoxy resins with activated hydrogen compounds into which cationic groups can be introduced group. Examples of blocked isocyanate curing agents include, 1-hexamethylene diisocyanate (including trimer), G-methylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate; alicyclic diisocyanate such as 4,4' - Methylene bis(cyclohexyl isocyanate), aromatic diisocyanates such as toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI) and those blocked with suitable blocking agents 1,6-Hexanediisocyanate (HDI). In addition, dynamic Tg and crosslink density can also be adjusted by selecting the ratio of blocked isocyanate curing agent to cationic epoxy resin, or the baking temperature of the electroplated coating film.

The materials to be coated, the cationic plating coating composition, the intermediate coating composition, the bottom surface coating composition and the clear surface coating composition used in the process of forming the multilayer coating film of the present invention and their application methods will be described below explained in the text.

substrate to be coated

The substrate to be coated used in the process of forming the multilayer coating film of the present invention may be any substrate capable of electroplating coating. Examples of substrates include metals such as iron, steel, aluminum, tin, zinc, etc., and alloys thereof, plated parts thereof, or deposited parts thereof. Specific examples thereof include passenger cars, delivery trucks, motorcycles, buses, etc., manufactured using metal components. Moreover, plastics obtained by conductively treated resins such as polyethylene resins, polypropylene resins, ethylene-vinyl acetate copolymer resins, polyamide resins, acrylic resins, vinylidene chloride, polycarbonate resins, etc. can also be used as substrates. Ester resin, polyurethane resin, epoxy resin and various FRP.

In forming the multilayer coating film of the present invention, the substrate may be used as it is or after pretreatment such as degreasing treatment or chemical conversion treatment before plating the coating film.

Cationic Plating Coating Composition

The cationic electroplating coating composition used in the present invention comprises a binder resin with an aqueous solvent, a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in an aqueous solvent; an acid for neutralization; Organic solvents. The cationic electroplating coating composition may also contain pigments.

cationic epoxy resin

The cationic epoxy resins used in the present invention include amine-modified epoxy resins. Cationic epoxy resins are known resins, and they are described in Japanese Patent Laid-Open Nos. 4978/1979, 34186/1981 and the like.

Cationic epoxy resins are generally made by opening all epoxy rings in bisphenol-type epoxy resins with activated hydrogen compounds, which can introduce cationic groups into activated hydrogen compounds; or by opening part of the rings with other activated hydrogen compounds Oxygen rings are made by opening the remaining epoxy rings with activated hydrogen compounds, and cationic groups can be introduced into activated hydrogen compounds.

Specific examples of bisphenol type epoxy resins include bisphenol A type epoxy resins and bisphenol F type epoxy resins. Examples of bisphenol A type epoxy resins include Epikote 828 (epoxy equivalent: 180-190), Epikote 1001 (epoxy equivalent: 450-500), Epikote 1010 (epoxy Equivalent: 3000-4000), etc. Examples of the bisphenol F type epoxy resin include Epikote 807 (epoxy equivalent: 170) commercially available from Yuka Shell Epoxy Co., Ltd., and the like.

Epoxy resins containing oxazolidinone rings having the formula:

Formula 1

Wherein R represents a residue obtained by removing a glycidyl group from a diglycidyl epoxy compound, R' represents a residue obtained by removing an isocyanate group from a diisocyanate compound, and n represents a positive integer,

It can be used in cationic epoxy resins because it can produce coating films with excellent heat resistance and corrosion resistance. This is because a coating film having excellent solvent resistance (solvent swelling resistance) can be obtained.

A method for introducing an oxazolidinone ring into an epoxy resin comprises the steps of heating a blocked isocyanate curing agent and a polyepoxide under an alkaline catalyst and maintaining a constant temperature, and the above-mentioned curing agent is blocked with a lower alcohol such as methanol, And lower alcohols are distilled out from the system as by-products.

A particularly preferred epoxy resin is an oxazolidone ring-containing resin. This is because a coating film excellent in solvent resistance (solvent swelling resistance), heat resistance, corrosion resistance and impact resistance can be obtained.

It is well known that an epoxy resin containing an oxazolidinone ring can be obtained by reacting a difunctional epoxy resin with a monohydric alcohol-terminated diisocyanate (ie bisurethane). Specific examples of oxazolidinone ring-containing epoxy resins and their production methods are disclosed in paragraphs [0012] to [0047] of Japanese Patent Laid-Open No. 128959/2000, which are well known.

Epoxy resins can be modified with suitable resins, such as polyester polyols, polyether polyols, and monofunctional alkylphenols. In addition, epoxy resins can be chain extended by reacting epoxy groups with diols or dicarboxylic acids.

It is desirable to ring-open epoxy resins with activated hydrogen compounds so that they have an amine equivalent weight after ring opening of 0.3-4.0 meq/g, especially 5-50% of which are primary amino groups.

Examples of activated hydrogen compounds, into which cationic groups can be introduced, include acid salts, sulfides, and acid mixtures of primary, secondary, and tertiary amines. In order to prepare epoxy resins containing primary, secondary and/or tertiary amines, acid salts of primary, secondary and tertiary amines are used as activated hydrogen compounds into which cationic groups can be introduced.

Its specific examples include: butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, acid salt of triethylamine, acid salt of N,N-dimethylethanolamine, diethylamine Disulfide-acetic acid mixtures and secondary amines obtained by capping primary amines, such as the ketimine of aminoethylethanolamine, the ketimine of diethylenetriamine. These amines may be used in combination.

Blocked isocyanate curing agent

The polyisocyanate used in the preparation of the blocked isocyanate curing agent in the present invention is a compound having at least 2 isocyanate groups in the molecule. The polyisocyanates may be aliphatic, cycloaliphatic, aromatic or araliphatic polyisocyanates.

Examples of polyisocyanates include: aromatic diisocyanates such as toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate and naphthalene diisocyanate; aliphatic diisocyanates having 3 to 12 carbon atoms, Such as 1,6-hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate and lysine diisocyanate; alicyclic diisocyanates with 5-18 carbon atoms, such as 1,4 -Cyclohexane diisocyanate, isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isomylidene dicyclohexyl- 4,4'-diisocyanate and 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis(isocyanatomethyl)-bicyclohexane [2.2.1] Heptane (=norbornane diisocyanate); aliphatic diisocyanates with aromatic rings, such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI) ; its modified compounds (urethane compounds, carbodiimide, urethodion, urethonimine, biuret and/or isocyanurate modified compounds) and the like. Polyisocyanates may be used alone or in combination of two or more.

The addition compound or prepolymer obtained by reacting polyisocyanate and polyol with a NCO/OH ratio of not less than 2 can be used as a blocked isocyanate curing agent, such as ethylene glycol, propylene glycol, trimethylol propane and hexanetriol.

A blocking agent is added to the polyisocyanate group, the blocking agent is stable at room temperature, but the free cyanate group can be regenerated when heated at a temperature not lower than the dissociation temperature.

pigment

The cationic electroplating coating composition used in the method of the present invention may contain pigments, which are pigments typically used in coatings. Examples of pigments include: inorganic pigments such as colored pigments such as titanium dioxide, carbon black, and iron oxide; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, and clay; antirust pigments such as zinc phosphate, iron phosphate, phosphoric acid Aluminum, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate.

When a pigment is used as a component of an electroplating coating, the pigment is generally pre-dispersed in a high concentration in an aqueous solvent in the form of a slurry (pigment-dispersed slurry). This is because it is difficult to uniformly disperse powdered pigments at low concentrations in one step. Slurry is generally also referred to as pigment dispersion slurry.

The pigment dispersion paste is prepared by dispersing a pigment together with a pigment-dispersing resin varnish in an aqueous medium. As the pigment-dispersing resin, a cationic or nonionic low-molecular-weight surfactant, or a cationic polymer such as a modified epoxy resin having a quaternary ammonium group and/or a tertiary sulfonium group can be used. As the aqueous medium, deionized water or water containing a small amount of alcohol can be used. The resin for dispersing the pigment is generally used at a solid content of 20-100 parts by mass, based on 100 parts by mass of the total amount of the coating film. The pigment dispersion slurry can be obtained by mixing the pigment dispersing resin varnish with the pigment, and then dispersing the pigment using a suitable dispersing device such as a ball mill or a sand mill.

Cationic plating coating compositions may optionally contain dissociation catalysts, organotin compounds such as dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide; amines such as N-methylmorpholine, lead acetate; strontium, Metal salts of cobalt and copper; the purpose is to dissociate blocking agents other than the above components. The amount of the dissociation catalyst is 0.1-6 parts by mass, based on 100 parts by mass of the total solid content of the cationic epoxy resin and the blocked isocyanate curing agent in the cationic electroplating coating composition.

Preparation and Application of Cationic Plating Coating Composition

The cationic electroplating coating composition of the present invention is prepared by dispersing the above-mentioned catalyst, cationic epoxy resin, blocked isocyanate curing agent and pigment dispersion slurry in an aqueous solvent. In addition, the aqueous medium may contain a neutralizing acid for the purpose of neutralizing the cationic epoxy resin to improve the dispersibility of the binder resin emulsion. Examples of neutralizing acids include inorganic or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid.

The amount of the neutralizing acid is preferably 10 mg equivalent to 25 mg equivalent, based on 100 g of the binder resin containing the cationic epoxy resin and the blocked isocyanate curing agent. The lower limit of the amount of neutralizing acid is more preferably 15 mg equivalent, and the upper limit of the amount of neutralizing acid is more preferably 20 mg equivalent. When the amount of the neutralizing acid is less than 10 mg equivalent, the miscibility with water cannot be sufficiently obtained, and dispersion in water is difficult, or the stability is greatly reduced. On the other hand, when the amount of the neutralizing acid is higher than 25 mg equivalent, the electric power required for deposition increases, and the deposition of the solid content of the coating film decreases, thereby reducing the spreading ability.

The cationic electroplating coating composition is prepared by dispersing a cationic epoxy resin and a blocked isocyanate curing agent in an aqueous solvent. It is hoped that in the curing process, the amount of blocked isocyanate curing agent that reacts with activated hydrogen compounds containing functional groups such as primary amino groups, secondary amino groups, and hydroxyl groups is sufficient to obtain a good cured coating film. The amount of blocked isocyanate curing agent is represented by the ratio (cationic epoxy resin/curing agent) of the solid content of cationic epoxy resin and blocked isocyanate curing agent, and it is preferably 90/10-50/50, more preferably 80 /20-60/40, most preferably 80/20-65/35. The fluidity and curing rate of the coating film at the time of film formation (deposited film) can be improved by adjusting this ratio, and the smoothness of the coating film is also improved. The smoothness of the plated coating film can be further improved by using a surface-treated steel sheet having a lower roughness. In addition, by adjusting the amount of the blocked isocyanate curing agent to the above range, or selecting the baking temperature, it is easy to give the cured electroplating coating the required dynamic Tg and crosslinking density.

When synthesizing resin components such as cationic epoxy resins, blocked isocyanate curing agents, resins for dispersing pigments, organic solvents may be used as the solvents. A complex process for complete solvent removal is necessary. The fluidity of the coating film at the time of film formation can be improved by including a solvent in the binder resin, and the smoothness of the film is also improved.

Examples of organic solvents used in cationic plating coating compositions include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, propylene glycol monobutyl ether, Phenyl ether and so on.

The cationic plating coating composition can contain coating additives such as plasticizers, surfactants, antioxidants and ultraviolet absorbers in addition to the above components. The cationic plating coating composition may also include amino group-containing acrylic resins, amino group-containing polyester resins, and the like.

The electroplating coating is carried out by applying a voltage between the substrate as the cathode and the anode, and the voltage is generally 50-450V. When the applied voltage is lower than 50V, plating becomes insufficient. On the other hand, when the applied voltage is higher than 450V, the coating film is cracked and its appearance is deformed. The temperature of the electroplating bath is generally controlled at 10-45°C.

The electroplating process comprises the steps of immersing the substrate to be coated in the electroplating coating composition and applying a voltage between the substrate as cathode and anode to deposit the coating. Also, the time to apply the voltage is generally 2-4 minutes, although it varies with plating conditions.

The thickness of the plated coating film is preferably 5 to 25 μm, more preferably 20 μm. When the thickness is less than 5 µm, rust resistance cannot be effectively obtained. On the other hand, when the thickness is greater than 25 µm, it leads to waste of the coating composition.

The electroplating coating film obtained by the method described above is baked at 120-260 ° C, preferably 140-220 ° C for 10-30 minutes, so as to be directly cured, or after the electroplating process is completed, it is washed with water and then cured to form a cured electroplating coating. membrane.

Intermediate coating composition

The intermediate coating composition used in the present invention contains an intermediate coating resin component, a pigment, an aqueous medium and/or an organic solvent. The mid-coat resin component comprises a mid-coat resin and optionally a mid-coat curing agent. The same aqueous media and organic solvents as in the cationic plating coating composition can be used.

Examples of intermediate coating resins include acrylic resins, polyester resins, polyurethane resins, alkyd resins, fluororesins, epoxy resins, polyether resins, and the like. Preferred are acrylic resins, polyester resins and polyurethane resins. The intermediate coating resins may be used alone or in combination of two or more.

Examples of acrylic resins include copolymers of acrylic monomers and other ethylenically unsaturated monomers. Examples of acrylic monomers used in copolymers include methyl, ethyl, propyl, n-butyl, isobutyl, tert-butyl, 2-ethylhexyl, lauryl, benzene 2-hydroxyethyl acrylate, benzyl and 2-hydroxypropyl esters; ring-opening addition products of caprolactone to 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate; glycidyl acrylate, methacrylate Glycerides, acrylamides, methacrylamides and N-methylolacrylamides, (meth)acrylates of polyols, etc. Other ethylenically unsaturated monomers that can be copolymerized with the above monomers include styrene, α-methylstyrene, itaconic acid, maleic acid, vinyl acetate, and the like.

Examples of polyester resins include saturated polyester resins and unsaturated polyester resins such as condensates obtained by condensing polybasic acids and polyhydric alcohols by applying heat. Examples of polybasic acids include saturated polybasic acids and unsaturated polybasic acids. Examples of saturated polybasic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, hexahydrophthalic acid, and 1,4-cyclohexanedicarboxylic acid. Examples of unsaturated polybasic acids include maleic acid, maleic anhydride, fumaric acid, phthalic anhydride, terephthalic acid, and isophthalic acid. Examples of polyols include diols and triols. Examples of dihydric alcohols include ethylene glycol, diethylene glycol, neopentyl glycol, 1,5-pentanediol and 1,6-hexanediol. Examples of triols include glycerol and trimethylolpropane.

Examples of polyurethane resins include resins having urethane bonds obtained from polyol components such as acrylic, polyester, polyether, polycarbonate, and polyisocyanate compounds. Examples of polyisocyanate compounds include 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI) and mixtures thereof (TDI), diphenylmethane-4,4 '-diisocyanate (4,4'-MDI), diphenylmethane-2,4'-diisocyanate (2,4'-MDI) and its (MDI) mixture, naphthalene-1,5-diisocyanate (NDI ), 3,3'-dimethyl-4,4'-diphenyl diisocyanate (TODI), xylylene diisocyanate (XDI), dicyclohexylmethane diisocyanate (hydrogenated MDI), isofor ketone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), hydrogenated xylylene diisocyanate (HXDI), etc.

Examples of alkyd resins include alkyd resins obtained by reacting polybasic acids and polyhydric alcohols with modifiers, such as fats and oils or fatty acids thereof (such as soybean oil, linseed oil, coconut oil, stearic acid, etc.), natural Resins (such as rosin, amber, etc.).

Examples of fluorine-containing resins include vinylidene fluoride resins, tetrafluoroethylene resins, or mixtures thereof, fluorine-based copolymers obtained by copolymerizing fluoroolefins and monomers containing hydroxyl compounds and other copolymerizable vinyl groups compound.

Examples of epoxy resins include resins obtained by reacting bisphenol and epichlorohydrin, and the like. Examples of bisphenols include bisphenol A and bisphenol F. Examples of bisphenol type epoxy resins include Epikote 828, Epikote 1001, Epikote 1004, Epikote 1007, Epikote 1009 (commercially available from Shell Chemical Co.). Additionally, these resins can be chain extended by a suitable chain extender.

Examples of polyether resins, that is, polymers or copolymers having ether linkages include polyoxyethylene-based polyethers, polyoxypropylene-based polyethers or polyoxybutylene-based polyethers, or polyoxyethylene-based polyethers having at least two hydroxyl groups in one molecule. Ether resins, such as polyethers derived from aromatic polyols, such as bisphenol A and bisphenol F. In addition, examples also include carboxyl-containing polyether resins obtained by reacting spiro ether resins with reactive derivatives, such as polycarboxylic acids including succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, Terephthalic acid and trimellitic acid or their anhydrides.

It is desirable that the acid value of the intermediate coating resin be 3-200, the hydroxyl number be 30-200, and the number average molecular weight be 500-50000. Preferred resins are especially acrylic resins with an acid value of 3-200, a hydroxyl number of 30-200, and a number-average molecular weight of 2,000-50,000, and an acid value of 3-200, a hydroxyl number of 30-200, and a number-average molecular weight of 500 -20000 polyester resin. In the case of preparing an intermediate coating composition as an aqueous solution or an aqueous dispersion, it is desirable that the intermediate coating resin has an acid value of 10-200 and a hydroxyl number of 30-200.

Among intermediate coating resins, there are generally curable and varnish resins. Curable resins are preferred. If a curable type resin is used, an intermediate coating curing agent such as blocked isocyanate compound, oxazolidinone compound, carbodiimide compound and melamine compound is used in combination with the intermediate coating resin. The curing reaction of the mid-coat resin component containing the mid-coat curing agent can be performed under heating or at room temperature. Additionally, combinations of curable and non-curable midcoat resins can also be used.

If an intermediate coating curing agent is included, in the solid content of the coating, the weight ratio of the intermediate coating resin to the intermediate coating curing agent is preferably 90/10-50/50, more preferably 85/15-60/40. When the ratio is more than 90/10 and the amount of the intermediate coating curing agent is less than 10% by weight, the crosslinking density of the coating cannot be sufficiently obtained. On the other hand, when the ratio is less than 50/50 and the amount of the intermediate coating curing agent is more than 50% by weight, the storage stability of the coating composition decreases, the curing rate becomes large, and the appearance of the coating film decreases.

The midcoat composition of the present invention contains pigments. Examples of pigments include extender pigments such as barium oxide powder, deposited sulfate, barium carbonate, gypsum, clay, silica, talc, magnesium carbonate, alumina white, etc., and colored pigments. Examples of colored pigments include organic pigments such as azo lake-based pigments, phthalocyanine-based pigments, indigo-based pigments, perylene-based pigments, quinophtharone-based pigments, dioxazine-based pigments, quinacridone-based pigments, isoindolinone pigments, metal complex pigments, carbon black; or inorganic pigments such as lead oxide, yellow iron oxide, red iron, titanium dioxide. The amount of pigment is chosen arbitrarily depending on the desired properties and shades. Pigments can be used alone or in combination of two or more.

The pigment concentration (PWC) is preferably 10-50% by weight, based on the coating solids content of the midcoat composition. The upper limit of the concentration is more preferably 30% by weight.

The solids content of the midcoat composition is preferably 35-65% by weight. The lower limit is more preferably 40% by weight, and the upper limit is more preferably 60% by weight. When the lower limit of the solid content is less than 35% by weight, sagging may occur during application of the coating, and the appearance of the finish may be lowered. On the other hand, when the upper limit of the solid content is higher than 65% by weight, the fluidity during the application of the coating is lowered, and the finished appearance may be lowered.

The midcoat composition may comprise, in addition to the above-mentioned ingredients, polyamide waxes, which are lubricious dispersions of aliphatic amides, polyethylene waxes, which are colloidal dispersions based on polyethylene oxide, curing catalysts, UV-absorbing agents, antioxidants, leveling agents, surface conditioners such as silicones and organic polymers, anti-sagging agents, thickeners, defoamers, lubricants, cross-linkable polymer powders (microgels), etc. By mixing the aforementioned additives in an amount of not more than 15 parts by mass (based on solid content), based on 100 parts by mass of the total amount of the intermediate coating resin, the properties of the coating composition and the coating film can be improved.

Preparation and Application of Intermediate Coating Compositions

An intermediate coating composition can be prepared by dissolving or dispersing the above components in a solvent. The solvent is not limited as long as it can dissolve and disperse the mid-coat resin component, but the solvent may be an organic solvent and/or water. The organic solvent may be one commonly used in the field of coating compositions. Examples of organic solvents include hydrocarbon solvents such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate, acetate cellosolve and butyl cellosolve, alcohol, and the like. If the use of organic solvents is limited for environmental reasons, water is ideal. If so, a suitable amount of a hydrophilic organic solvent may be included therein.

During application, the viscosity of the midcoat composition is preferably adjusted to the range of 10-30 seconds (Ford Cup #4/20° C.) using organic solvents and/or water and mixtures thereof. When the viscosity is lower than the above range, the intermediate coating film is easily miscible with the bottom surface coating film formed in the subsequent coating step. On the other hand, when the viscosity is higher than the above range, it is difficult to control the coating composition, and the coating film is cured prematurely, and the uniformity of the surface appears at a level that cannot be coated and repaired by the coating film in the subsequent coating step .

The intermediate coating film can be obtained by applying the intermediate coating composition on the cured plating coating film. Due to the formation of the intermediate coating film, the electroplating coating film has the properties of opacity and anti-shattering performance. In addition, the adhesive force of the bottom surface coating film applied on the intermediate coating film in a subsequent step is also improved.

The method of applying the intermediate coating is not limited, by using an air electrostatic sprayer, also known as a "reaction gun"; a rotating electrostatic sprayer, also known as a "micro micro(μμ) bell", "micro(μ) bell", and "meta bell"; etc., can implement this method. The preferred method is to utilize a rotating electrostatic sprayer.

The ideal dry thickness of the intermediate coating film is 5-80 μm, preferably 10-50 μm. After the intermediate coating film is formed, the bottom surface coating film forming step is performed without heating and curing. The intermediate coating film is preheated at a temperature lower than its heating and curing (baking) treatment temperature before forming the bottom surface coating film.

Bottom surface coating composition

The base coating composition used in the present invention is a gloss coating composition or a solid coating composition comprising a base coating resin component, a gloss pigment and/or a color pigment, an extender pigment and a solvent. The bottom surface coating composition is a water-based or organic solvent-based composition, including a water-dispersed or organic solvent-dispersed composition.

The base coat resin component contained in the base coat composition includes a base coat resin and optionally a base coat curing agent. The undercoat resin components (undercoat resin and undercoat curing agent), coloring pigments, extender pigments, various additives and solvents contained in the undercoat composition are the same as those described in the midcoat. same. By using the base coat resin component, both the gloss pigment and the optional color pigment can be dispersed in the gloss base coat composition, and the color pigment is dispersed in the solid base coat composition.

Examples of the undercoating resin used include at least one resin capable of forming a coating film selected from acrylic resins, polyester resins, fluorine resins, epoxy resins, polyurethane resins, polyether resins and modified resins thereof. Examples of the bottom surface coating curing agent include the above-mentioned curing agents for the intermediate coating layer. Preference is given to melamine compounds, especially etherified melamine resins. Etherified melamine resins can be obtained by etherifying melamine with alcohols such as methanol and butanol. A preferred combination of the base coat resin and the base coat curing agent as the base coat resin component includes an acrylic resin-melamine resin system. In this system, it is desirable that the acrylic resin has an acid value of 10-200, a hydroxyl number of 30-200, and a number average molecular weight of 2,000-50,000.

Examples of gloss pigments as pigments contained in the undersurface coating composition include flake pigments, colored flake pigments, interference mica pigments, colored mica pigments, glass flake pigments coated with metal oxides, coated with Metallic glass flake pigments, silica flake pigments coated with metal oxides, metallic titanium flake pigments, graphite pigments, stainless steel flake pigments, iron oxide flake pigments, phthalocyanine flake pigments and holographic pigments. If gloss pigments and/or colored pigments are used, the total pigment weight content (PWC) is preferably 1-50%, more preferably 5-30%. When the PWC is less than 1%, it is insufficient to add a pattern in the coating film. On the other hand, when PWC exceeds 50%, the appearance of a coating film will deteriorate.

Preparation and Application of Undersurface Coating Compositions

The bottom surface coating composition is prepared by dissolving or dispersing the above components in a solvent. The solvent is not limited as long as it can dissolve and disperse the undercoat resin component, but may be an organic solvent and/or water. Examples of the organic solvent include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate, acetate cellosolve and butyl cellosolve, alcohol, and the like.

The viscosity of the bottom surface coating composition is preferably adjusted to the range of 10-30 seconds (Ford cup #4/20°C) with a suitable diluent. When the viscosity is lower than the above range, the bottom surface coating film is easily miscible with the transparent surface coating film formed in the subsequent application step. On the other hand, when the viscosity is higher than the above range, it is difficult to control the coating composition, and the coating film is cured prematurely, and the uniformity of the surface appears at a level that cannot be coated and repaired by the coating film in the subsequent coating step .

The bottom surface coating film can be obtained by applying the bottom surface coating composition on the intermediate coating film. The bottom surface coating composition is applied over the uncured intermediate coating film by wet-on-wet coating. The method of applying the bottom surface coating composition is not limited, but includes the methods described above for applying the midcoat composition. When the bottom surface coating composition is applied to the vehicle body, it is carried out by multi-stage coating, preferably with an air electrostatic sprayer for secondary coating, the purpose of which is to make the coating more aesthetically pleasing. Application method can also combine air electrostatic sprayer and rotary electrostatic sprayer.

Formation of the bottom surface coating film allows adding a pattern in the coating film while ensuring adhesion to the intermediate coating film formed in the previous step and adhesion to the bottom surface coating film applied in the subsequent step.

Desirably, the thickness of each coating layer after drying of the bottom surface coating film is 5-50 µm, preferably 10-30 µm. After the bottom surface coating film is formed, the subsequent step of forming a transparent surface coating film is performed without heating and curing. Before the transparent surface coating film is formed, the bottom surface coating film is preheated at a temperature lower than its heating and curing (baking) temperature.

clear surface coating composition

The clear top coat composition consists of a clear coat composition comprising a clear top coat resin component, various additives and solvents. The clear topcoat compositions are water-based and organic solvent-based, including water-dispersed and organic solvent-dispersed compositions.

The clear topcoat resin component included in the clear topcoat composition includes a clear topcoat resin and optionally a clear topcoat curing agent. The clear top coat resin components (clear top coat resin and clear top coat curing agent), various additives and solvents contained in the clear top coat resin composition are the same as those described for the intermediate coat.

A preferred combination of the clear top coat resin and the clear top coat curing agent as the clear top coat resin component includes an acrylic resin-melamine resin system. In this system, it is desirable that the acrylic resin has an acid value of 10-200, a hydroxyl number of 30-200 and a number average molecular weight of 2000-50000.

As the clear surface coating composition, there can be used a clear coating composition comprising a carboxyl group-containing polymer and an epoxy group-containing polymer disclosed in Japanese Patent Publication No. 19315/1996 for wet-on-wet coating In this method, by increasing the solubility difference with the bottom surface coating film, acid rain resistance is ensured and the orientation of glossy pigments in the bottom surface coating film is maintained. The clear topcoat composition may optionally contain additives such as coloring pigments, extenders, modifiers, UV absorbers, leveling agents, dispersants and defoamers.

Preparation and application of clear surface coating composition

The clear topcoat composition is prepared by dissolving or dispersing the above components in a solvent. Any of the solvents mentioned above can be used. The clear topcoat composition is applied on the bottom topcoat film to obtain a clear topcoat film. The clear topcoat composition is applied to an uncured bottom surfacecoat film by wet-on-wet coating.

The method of forming the transparent surface coating film is not limited, but preferred methods include spray coating method, roll coating method and the like. Ideally, the thickness of each layer of the transparent surface coating film after drying is 20-50 μm, preferably 25-40 μm.

The formation of the transparent surface coating film can protect the bottom surface coating film and impart a feeling of depth to the obtained multilayer coating film.

to bake

After the clear surface coating film is formed, the uncured three-layer coating film of the middle coating film, the bottom surface coating film and the clear surface coating film is baked and cured at 120-160° C. for a given time to obtain a multilayer coating film. In the method of the present invention, the intermediate coating composition, the bottom surface coating composition and the clear coating composition are applied sequentially, respectively, by means of wet-on-wet coating. That is, an uncured coating film is formed in the above order. The term "uncured" here refers to a state where the coating film is not completely cured, and also includes a state where the coating film is preheated. The term "preheating" as used herein refers to keeping or heating the coating film at room temperature to 100°C for 1-10 minutes, which is lower than the heating and curing (baking) treatment temperature of the coating film. A coating film having a better finish appearance can be obtained by preheating the coating film after the intermediate coating film and the bottom surface coating film are respectively formed.

Example

The present invention will be explained in further detail based on the following examples, but the present invention is not limited to these examples. In these examples, "parts" means parts by weight unless otherwise specified.

Preparation Example 1

Preparation of Amine Modified Epoxy Resin

92 parts of 2,4-/2,6-toluene diisocyanate (weight ratio=8/2), 95 parts of methyl isobutyl ketone (hereinafter referred to as MIBK) and 0.5 part of dibutyltin dilaurate were put into a Stirrer, cooling tube, nitrogen input tube, thermometer and dropping funnel in the flask. While stirring the reaction mixture, 21 parts of methanol were added. Starting at room temperature, the temperature of the reaction mixture was raised to 60° C. by exotherm, the reaction was maintained for 30 minutes, and then 50 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise using a dropping funnel. Furthermore, 53 parts of bisphenol A-propylene oxide 5 molar adduct were added. The reaction is mainly carried out at a temperature of 60-65° C. and is continued until the absorption based on isocyanate groups disappears in IR spectroscopy.

Next, 365 parts of epoxy resin with an epoxy equivalent of 188 were added to the reaction mixture and heated to 125°C, wherein the epoxy resin with an epoxy equivalent of 188 was synthesized from bisphenol A and epichlorohydrin according to known methods . Then, 1.0 part of benzyldimethylamine was added and reacted at 130°C until the epoxy equivalent became 410.

Thereafter, 61 parts of bisphenol A and 33 parts of octanoic acid were added, and reacted at 120° C. to make the epoxy equivalent 1190. Thereafter, the reactant was cooled, 11 parts of diethanolamine, 24 parts of N-ethylethanolamine, and 25 parts of a 79% by weight ketiminated aminoethylethanolamine MIBK solution were added, and the mixture was reacted at 110° C. for 2 hours. Then, the reaction mixture was diluted with MIBK until the non-volatile solid content became 80%, thereby obtaining an amine-modified epoxy resin (resin solid content: 80%) having a glass transition temperature of 2°C.

Preparation Example 2

Preparation of blocked polyisocyanate curing agent (1)

Put 1250 parts of diphenylmethane diisocyanate and 266.4 parts of MIBK into the reactor, add 2.5 parts of dibutyltin laurate after heating to 80°C. Then, at 80° C., 226 parts of ε-caprolactam solution dissolved in 944 parts of butyl cellosolve was dropped over 2 hours. The reaction was maintained at 100° C. for 4 hours, and after confirming that the absorption due to the isocyanate group disappeared in the IR spectrum measurement, the reactant was left to cool. 336.1 parts of MIBK were added to obtain a blocked polyisocyanate curing agent having a glass transition temperature of 0°C.

Preparation Example 3

Preparation of Pigment Dispersion Resin

Put 222.0 parts of isophorone diisocyanate (hereinafter referred to as IPDI) into a reactor equipped with a stirrer, a cooling pipe, a nitrogen gas inlet pipe and a thermometer, and after diluting with 39.1 parts of MIBK, add 0.2 parts of dilauric acid diisocyanate Butyl tin. Then, the reaction mixture was heated to 50° C., and 131.5 parts of 2-ethylhexanol were added dropwise over 2 hours while stirring under a dry nitrogen atmosphere. The reaction temperature was maintained at 50°C with cooling if necessary. Finally, 2-ethylhexanol semi-blocked IPDI (resin solid content: 90.0%) was obtained.

Add 87.2 parts of dimethylethanolamine, 117.6 parts of 75% lactic acid aqueous solution and 39.2 parts of ethylene glycol monobutyl ether into a suitable reaction vessel, and stir the reaction mixture for half an hour at 65° C. to prepare a quaternizing agent.

Subsequently, 710.0 parts of EPON829 (bisphenol A type epoxy resin manufactured by Shell Chemical Company, epoxy equivalent weight 193-203) and 289.6 parts of bisphenol A were charged into the reactor. Under a nitrogen atmosphere, the reaction mixture was heated to 150-160°C for an initially exothermic reaction. Heating was continued at 150-160° C. for about 1 hour, then the reaction mixture was cooled to 120° C., and 498.8 parts of the prepared 2-ethylhexanol semi-blocked IPDI (MIBK solution) were added.

The reaction mixture was kept at 110-120°C for about 1 hour, 463.4 parts of ethylene glycol monobutyl ether was added, and the mixture was cooled to 85-95°C. After homogenization, 196.7 parts of quaternizing agent were added. The reaction mixture was kept at 85-95°C until the acid value became 1, and 964 parts of deionized water was added to terminate the quaternization of the epoxy-bisphenol A resin to obtain a pigment dispersion resin with quaternary ammonium salt moieties (Resin Tg=5°C, resin solid content: 50%).

Preparation Example 4

Preparation of Pigment Dispersion Slurry

120 parts of pigment dispersion resins obtained in Preparation Example 3, 2.0 parts of carbon black, 100 parts of kaolin, 80.0 parts of titanium dioxide, 18.0 parts of aluminum phosphomolybdate and 221.7 parts of ion-exchanged water were put into a sand mill, and dispersed in The particle diameter is not more than 10 μm to obtain a pigment dispersion slurry (solid content: 48%).

Example 1

Preparation of cationic electroplating coating composition and formation of electroplating coating film

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked polyisocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 80/20. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. MIBK was removed under reduced pressure to obtain an emulsion with a solid content of 36%.

1500 parts of this emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of a 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20.0% by weight cationic plating coating composition. The Tg of the plated coating film (deposited film) was determined to be 15° C. based on the Tg calculation of each resin of all the resin components in the plated coating composition. The volatile organic substance concentration (VOC) contained in the electroplating coating composition in the coating was 0.5%, and the milliequivalent value MEQ(A) of acid based on 100 g of resin solid content was 24.2. At an electroplating bath temperature of 30° C., the surface-treated steel plate is electroplated with a coating composition to obtain a cationic electroplating coating (A-1), and the electroplating coating has a dry coating thickness of 15 μm after baking, The surface roughness of the steel plate used was Ra=0.90 μm (cutoff value: 2.5 mm).

Formation of cured plating coating film

The obtained cationic plating coating (A-1) was baked at 170° C. for 20 minutes to obtain a cured plating coating as a substrate.

Formation of intermediate coating film

A polyester-melamine curing type intermediate coating composition ("OTO H-880", manufactured by Nippon Paint Co., Ltd.) was applied to the substrate using an electrostatic sprayer of rotary gasification type , so that the thickness of the dry coating is 20 μm. After application, preheat at room temperature for 8 minutes to form an uncured intermediate coating film.

Formation of bottom surface coating film and clear surface coating film

An acryl-melamine curing type bottom surface coating composition ("OTO H-600", produced by Nippon Paint Co., Ltd.) was applied on the intermediate coating film so that the thickness of the dried coating was 10 μm, and after application Thereafter, it was preheated at room temperature for 7 minutes to form an uncured bottom surface coating film. Then, an acrylic-epoxy resin curing type clear surface coating composition ("MA O-1600", produced by Nippon Paint Co., Ltd.) was applied on the bottom surface coating film so that the thickness of the dry coating was 35 μm. The applied intermediate coating film, base surface coating film, and clear surface coating film were baked at 140° C. for 30 minutes to obtain a multilayer coating film.

The centerline average roughness Ra) of the roughness curve and the centerline average roughness of the profile curve (Pa) Determination

According to JIS-B 0601, the Ra and Pa values of the cured electroplated coating film obtained from the electroplated coating composition were measured using an evaluation type surface roughness tester manufactured by Mitutoyo Corporation. Using a cut-off value with a width of 2.5mm as a sample, the measurement was repeated 7 times, and Ra and Pa were determined by removing the average value obtained by the highest and lowest values. The results are shown in Table 1.

Determination of Surface Energy

After the solvent droplet was dropped for 30 seconds, the cured electroplated coating film and DIW (deionized water ), the contact angle between ethylene glycol and diiodomethane. The surface energy of the cured plated coating film was determined by calculation from the measured values obtained using the above equation.

Determination of contact angle

After the droplet of the intermediate coating composition fell for 30 seconds, the cured plating coatings of Examples and Comparative Examples were measured with an automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., model PD-X) The contact angle between the composition and the intermediate coating composition ("OTO H-880").

Appearance Quality Evaluation of Multilayer Coating Films

After the multilayer coatings were baked and cured, their finished appearance was determined by Wave-Scan DOI (BYK-Gardner Co.). Among the measured values, the "Wa" value is related to the gloss evaluation item of the multilayer coating film, the "Wc" value is related to the orange peel defect evaluation item of the multilayer coating film, and the "Wd" value is related to the smoothness of the multilayer coating film. related to degree evaluation items. Wa, Wc and Wd values were used for the above evaluation. The smaller the value, the better the appearance quality.

Example 2

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 3 were uniformly mixed at a solid content ratio of 70/30. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 35, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solids content of 36%.

Mix 1500 parts of the above-mentioned emulsion, 280 parts of the pigment dispersion resin obtained in Preparation Example 4, 1560 parts of ion-exchanged water, 20 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide to obtain a cation with a solid content of 20% by weight. Electroplating coating composition. The Tg of the plated coating film (deposited film) was determined to be 14°C based on the Tg calculation of each resin of all the resin components in this plated coating composition. The volatile organic content (VOC) contained in the electroplating coating composition in the coating is 0.5%, and the milliequivalent value MEQ(A) of acid based on 100 g of resin solid content is 25.5. Under the electroplating bath temperature 30 ℃, carry out electroplating coating with coating composition on the steel plate of surface treatment, in order to obtain cationic plating film (A-2), the surface roughness of used steel plate is Ra=0.90 μ m (cutoff Value: 2.5mm).

As described in Example 1, except for preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The obtained multilayer coating films were also evaluated by the method described in Example 1. The results are shown in Table 1.

Example 3

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 70/30. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

Mix 1500 parts of the above-mentioned emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide to obtain a cation with a solid content of 20% by weight. Electroplating coating composition. The Tg of the plated coating film (deposited film) was determined to be 10° C. based on the Tg calculation of each resin of all the resin components in this plated coating composition. The volatile organic content (VOC) contained in the coating of the electroplating coating composition was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Under the electroplating bath temperature 30 ℃, carry out electroplating coating on the steel plate that surface treatment has been carried out with coating composition, so that obtain cationic plating film (A-3), the surface roughness of used steel plate is Ra=0.60 μ m (cutoff Value: 2.5mm).

As described in Example 1, except for preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 1. The results are shown in Table 1.

Example 4

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 80/20. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

Mix 1500 parts of the above-mentioned emulsion, 280 parts of the pigment dispersion resin obtained in Preparation Example 4, 1560 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide to obtain a cation with a solid content of 20% by weight. Electroplating coating composition. The Tg of the plated coating film (deposited film) was determined to be 15° C. based on the Tg calculation of each resin of all the resin components in this plated coating composition. The volatile organic content (VOC) of the electroplating coating composition contained in the coating was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Under the electroplating bath temperature 30 ℃, carry out electroplating coating with coating composition on the steel plate of surface treatment, in order to obtain cationic plating film (A-4), the surface roughness of used steel plate is Ra=0.20 μ m (cutoff Value: 2.5mm).

As described in Example 1, except for preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 1. The results are shown in Table 1.

Example 5

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 60/40. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

Mix 1500 parts of the above-mentioned emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide to obtain a cation with a solid content of 20% by weight. Electroplating coating composition. The Tg of the plating coating film (deposited film) was determined to be 4°C by calculating the Tg of each resin of all the resin components in this plating coating composition. The volatile organic content (VOC) contained in the coating film of the electroplating coating composition was 0.5%, and the milliequivalent value MEQ(A) of acid based on 100 g of resin solid content was 24.2. Under electroplating bath temperature 30 ℃, carry out electroplating coating with coating composition on the steel plate of surface treatment, in order to obtain cationic plating film (A-5), the surface roughness of used steel plate is Ra=0.60 μ m (cutoff Value: 2.5mm).

As described in Example 1, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 1. The results are shown in Table 1.

Comparative Example 1

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 70/30. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

1500 parts of the above emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. Cationic plating coating composition. The Tg of the plating coating film (deposited film) was determined to be 10°C by calculating the Tg of each resin of all the resin components in this plating coating composition. The volatile organic substance concentration (VOC) contained in the coating film of the electroplating coating composition was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Under the electroplating bath temperature 30 ℃, carry out electroplating coating with coating composition on the steel plate of surface treatment, in order to obtain cationic plating film (B-1), the surface roughness of used steel plate is Ra=0.90 μ m (cutoff Value: 2.5mm).

As described in Example 1, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 1. The results are shown in Table 1.

Comparative Example 2

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 70/30. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

Mix 1500 parts of the above-mentioned emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide to obtain a cation with a solid content of 20% by weight. Electroplating coating composition. The Tg of the plating coating film (deposited film) was determined to be 10°C by calculating the Tg of each resin of all the resin components in this plating coating composition. The volatile organic content (VOC) contained in the coating film of the electroplating coating composition was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Under the electroplating bath temperature 30 ℃, carry out electroplating coating with coating composition on the steel plate of surface treatment, in order to obtain cationic plating film (B-2), the surface roughness of used steel plate is Ra=1.20 μ m (cutoff Value: 2.5mm).

As described in Example 1, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 1. The results are shown in Table 1.

Example 6

Preparation of cationic electroplating coating composition and formation of electroplating coating film

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 70/30. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

Mix 1500 parts of the above-mentioned emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide to obtain a cation with a solid content of 20% by weight. Electroplating coating composition. The volatile organic content (VOC) contained in the coating film of the electroplating coating composition was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Electroplating was performed using the obtained cationic plating coating composition at a plating bath temperature of 30° C. to obtain a cationic plating coating film. Baking the obtained electroplated coating film at 160° C. for 20 minutes can obtain a cured electroplated coating film (A-6), and the electroplated coating film can be used as a substrate.

Formation of intermediate coating film

A polyester-melamine curing type intermediate coating composition ("OTO H-880", manufactured by Nippon Paint Co., Ltd.) was applied on the substrate using an electrostatic sprayer of rotary gasification type, so that the thickness of the dry coating is 20 μm. After application, an uncured intermediate coating film was formed by preheating at room temperature for 8 minutes.

Formation of bottom surface coating and clear surface coating film

An acryl-melamine curing type bottom surface coating composition ("OTO H-600", produced by Nippon Paint Co., Ltd.) was applied on the intermediate coating film so that the thickness of the dried coating was 10 μm, and after application Thereafter, an uncured bottom surface coating was formed by preheating at room temperature for 7 minutes. Then, an acrylic-epoxy resin curing type clear surface coating composition ("MA O-1600", produced by Nippon Paint Co., Ltd.) was applied on the bottom surface coating film so that the thickness of the dry coating was 35 μm. The applied intermediate coating film, bottom surface coating film, and clear surface coating film were baked at 140° C. for 30 minutes to obtain a multilayer coating film.

Determination of dynamic Tg of cured electroplated coating film

The electroplating coating compositions prepared in Examples and Comparative Examples were electroplated on a tin plate for dynamic viscoelasticity measurement to obtain an electroplating coating film. Then, the plating coating film was baked at 170° C. for 20 minutes to obtain a cured plating coating film. The obtained coating film was separated from the tin plate with mercury, and it was chipped to prepare a sample for measurement. The sample was heated from room temperature to 200° C. at a rate of 2° C. per minute while vibrating at a frequency of 10 Hz, and the viscoelasticity was measured with a Rheovibron model RHEO 2000, 3000 (trade name) manufactured by Orientec Co., Ltd.. The ratio (tan δ) of the storage elasticity (E') and loss elasticity (E") is calculated to determine the inflection point (temperature at the peak of tan δ) to obtain the dynamic Tg.

Determination of crosslink density of cured electroplated coatings

The crosslink density was determined by calculation from the storage elasticity (E') obtained in the dynamic Tg measurement by the equation described above.

Appearance Quality Evaluation of Multilayer Coating Films

The finish appearance of the baked and cured multilayer coating films was determined by wave scanning DOI (BYK-Gardner Co.). Among the measured values, the "Wa" value is related to the gloss evaluation item of the multilayer coating film, the "Wc" value is related to the orange peel defect evaluation item of the multilayer coating film, and the "Wd" value is related to the smoothness of the multilayer coating film. related to degree evaluation items. Wa, Wc and Wd values were used for the above evaluation. The smaller the value, the better the appearance quality.

Example 7

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 3 were uniformly mixed at a solid content ratio of 80/20. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 35, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

1500 parts of the above-mentioned emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 20 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. Cationic plating coating composition. The electroplating coating composition contained in the coating had a volatile organic content (VOC) of 0.5%, and an acid milliequivalent value (MEQ(A)) based on 100 g of resin solid content of 25.5. Electroplating was performed using the obtained cationic plating coating composition at a plating bath temperature of 30° C. to obtain a cationic plating coating film. Baking the deposited coating film obtained at 160° C. for 20 minutes can obtain a cured electroplating coating film (A-7), and the electroplating coating film can be used as a substrate.

As described in Example 6, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 6. The results are shown in Table 2.

Example 8

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 80/20. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

1500 parts of the above emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. Cationic plating coating composition. The volatile organic content (VOC) contained in the coating of the electroplating coating composition was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Electroplating was performed using the obtained cationic plating coating composition at a plating bath temperature of 30° C. to obtain a cationic plating coating film. Baking the obtained electroplated coating film at 180° C. for 20 minutes can obtain a cured electroplated coating film (A-8), and the electroplated coating film can be used as a substrate.

As described in Example 6, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 6. The results are shown in Table 2.

Example 9

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 60/40. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIRK was removed to obtain an emulsion with a solids content of 36%.

1500 parts of the above emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. Cationic plating coating composition. The volatile organic content (VOC) contained in the electroplating coating composition in the coating is 0.5%, and the milliequivalent value MEQ(A) of acid based on 100 g of resin solid content is 24.2. Electroplating was performed using the obtained cationic plating coating composition at a plating bath temperature of 30° C. to obtain a cationic plating coating film. Baking the obtained electroplated coating film at 180° C. for 20 minutes can obtain a cured electroplated coating film (A-9), and the electroplated coating film can be used as a substrate.

As described in Example 6, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 6. The results are shown in Table 2.

Comparative Example 3

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 90/10. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

1500 parts of the above emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. Cationic plating coating composition. The volatile organic content (VOC) contained in the electroplating coating composition in the coating is 0.5%, and the milliequivalent value MEQ(A) of acid based on 100 g of resin solid content is 24.2. Electroplating was performed using the obtained cationic plating coating composition at a plating bath temperature of 30° C. to obtain a cationic plating coating film. Baking the obtained deposited coating film at 160° C. for 20 minutes can obtain a cured electroplated coating film (B-3), and the electroplated coating film can be used as a substrate.

As described in Example 6, except that the cationic plating coating composition was prepared and the plating coating was formed as described above, a multilayer coating was also obtained. The obtained multilayer coatings were evaluated using the method described in Example 6. The results are shown in Table 2.

Comparative Example 4

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 80/20. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

1500 parts of the above emulsion, 540 parts of the pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. Cationic plating coating composition. The volatile organic content (VOC) contained in the coating film of the electroplating coating composition was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Electroplating was performed using the obtained cationic plating coating composition at a plating bath temperature of 30° C. to obtain a cationic plating coating film. Baking the deposited coating film obtained at 150° C. for 20 minutes can obtain a cured electroplating coating film (B-4), which can be used as a substrate.

As described in Example 6, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 6. The results are shown in Table 2.

Comparative Example 5

The amine-modified epoxy resin obtained in Preparation Example 1 and the blocked isocyanate curing agent obtained in Preparation Example 2 were uniformly mixed at a solid content ratio of 70/30. Glacial acetic acid was added to the mixture so that the milliequivalent value MEQ(A) of the acid based on 100 g of the solid content of the binder resin was 30, and ion-exchanged water was slowly added for dilution. Under reduced pressure, MIBK was removed to obtain an emulsion with a solid content of 36%.

1500 parts of the above-mentioned emulsion, 280 parts of the pigment dispersion resin obtained in Preparation Example 4, 1560 parts of ion-exchanged water, 40 parts of 10% aqueous solution of cerium acetate and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. Cationic plating coating composition. The volatile organic content (VOC) contained in the coating of the electroplating coating composition was 0.5%, and the milliequivalent value of acid (MEQ(A)) based on 100 g of resin solid content was 24.2. Electroplating was performed using the obtained cationic plating coating composition at a plating bath temperature of 30° C. to obtain a cationic plating coating film. Baking the deposited coating film obtained at 180° C. for 20 minutes can obtain a cured electroplating coating film (B-5), and the electroplating coating can be used as a substrate.

As described in Example 6, in addition to preparing a cationic plating coating composition and forming a plating coating film as described above, a multilayer coating film was also obtained. The multilayer coating films obtained were evaluated by the method described in Example 6. The results are shown in Table 2.

The measurement results

Table 1 Example number Comparative Example No. 1 2 3 4 5 1 2 A-1 A-2 A-3 A-4 A-5 B-1 B-2 Evaluation of Cured Plated Coating Films Ra(μm)(cut-off value 2.5) 0.25 0.23 0.23 0.05 0.19 025 0.3 Pa(μm)(cut-off value 2.5) 0.3 0.24 0.28 0.05 0.21 0.34 0.44 Surface energy (mJ/m ² ) 37 39 41 37 44 41 42 Contact angle with intermediate coating composition (degrees) 17 20 25 17 36 32 33 Appearance Evaluation of Multilayer Coating Films Wa 8 9 8 7 10 12 15 wc 14 16 16 12 20 twenty three 27 Wd 14 16 17 11 17 20 twenty three

Table 2 Example number Comparative Example No. 6 7 8 9 3 4 5 A-6 A-7 A-8 A-9 B-3 B-4 B-5 Evaluation of Cured Plated Coating Films Cross-link density (mmol/cc) 1.42 1.20 1.62 2.51 0.91 1.10 1.99 Dynamic Tg(℃) 108 100 110 130 110 101 90 Appearance Evaluation of Multilayer Coating Films Wa O(8) O(9) O(8) O(8) X(12) X(12) X(15) wc O(18) O(17) O(17) O(17) X(21) X(21) X(24) Wd O(16) O(16) O(16) O(17) X(22) X(21) X(22)

Wa O: no more than 10, X: no less than 11

Wc O: no more than 20, X: no less than 21

Wd O: no more than 20, X: no less than 21

From the results shown in Table 1, it can be clearly concluded that the cured electroplating coating films involved in Examples 1-5 of the present invention have good surface conditions. A multilayer coating film having good appearance without revealing defects from the electroplating coating film was obtained on the cured electroplating coating film by the three-coat-bake method. In contrast, in Comparative Example 1-2, since the plating coating film had appearance defects, a multilayer coating film having a good appearance was not obtained.

From the results shown in Table 2, it is evident that the multilayer coating films obtained by the three-coat-bake method on the cured electroplated coating films of Examples 6-9 of the present invention have good appearance. In contrast, in Comparative Examples 3-5, a multilayer coating film having a good appearance was not obtained.

Claims (5)

1. A method for forming a multilayer coating film, characterized in that the method may further comprise the steps: Carrying out electroplating coating on the substrate with a cationic electroplating coating composition, then heating and curing the coating to form a cured electroplating coating film on the substrate, applying the intermediate coating composition on the cured electroplated coating film to form an uncured intermediate coating film, Applying the bottom surface coating composition to the uncured intermediate coating film to form an uncured primer coating film applying a clear topcoat composition to the uncured primer film to form an uncured clear coat film, and Simultaneously heating and curing the uncured intermediate coating film, the uncured bottom surface coating film and the uncured clear coating film; The centerline average roughness (Ra) obtained from the roughness curve of the cured electroplated coating film is 0.05-0.25 μm, and the centerline average roughness (Pa) obtained from the profile curve is 0.05-0.30 μm. 2. A method for forming a multilayer coating film, characterized in that the method may further comprise the steps: performing electroplating coating on the substrate with a cationic electroplating coating composition, then heating and curing the coating to form a cured electroplating coating film on the substrate, applying the intermediate coating composition on the cured electroplated coating film to form an uncured intermediate coating film, Applying the bottom surface coating composition to the uncured intermediate coating film to form an uncured primer coating film applying a clear topcoat composition to the uncured primer film to form an uncured clear coat film, and Simultaneously heating and curing the uncured intermediate coating film, the uncured bottom surface coating film and the uncured clear coating film; The surface energy of the cured electroplating coating film is 37-43 mJ/m ² , and the contact angle of the intermediate coating composition on the cured electroplating coating film is 10-30 degrees. 3. A method for forming a multilayer coating film, characterized in that the method may further comprise the steps: performing electroplating coating on the substrate with a cationic electroplating coating composition, then heating and curing the coating to form a cured electroplating coating film on the substrate, applying the intermediate coating composition on the cured electroplated coating film to form an uncured intermediate coating film, Applying the bottom surface coating composition to the uncured intermediate coating film to form an uncured primer coating film applying a clear topcoat composition to the uncured primer film to form an uncured clear coat film, and Simultaneously heating and curing the uncured intermediate coating film, the uncured bottom surface coating film and the uncured clear coating film; The centerline average roughness (Ra) obtained from the roughness curve of the cured electroplated coating film is 0.05-0.25 μm, the centerline average roughness (Pa) obtained from the profile curve is 0.05-0.30 μm, and the surface energy is 37 -43 mJ/m ² , and the contact angle of the intermediate coating composition on the cured electroplated coating film is 10-30 degrees. 4. A method for forming a multilayer coating film, characterized in that the method may further comprise the steps: performing electroplating coating on the substrate with a cationic electroplating coating composition, then heating and curing the coating to form a cured electroplating coating film on the substrate, applying the intermediate coating composition on the cured electroplated coating film to form an uncured intermediate coating film, Applying the bottom surface coating composition to the uncured intermediate coating film to form an uncured primer coating film applying a clear topcoat composition to the uncured primer film to form an uncured clear coat film, and Simultaneously heating and curing the uncured intermediate coating film, the uncured bottom surface coating film and the uncured clear coating film; The cured electroplating coating film has a glass transition temperature Tg of 100-130° C. obtained by a dynamic viscoelasticity measurement method, and a crosslinking density of 1.2-2.6 mmol/cc. 5. The method for forming a multilayer coating film as claimed in any one of claims 1-4, wherein the intermediate coating composition comprises: Intermediate coating resins, including at least one selected from acrylic resins, polyester resins and polyurethane resins, An intermediate coating curing agent comprising at least one selected from blocked isocyanate compounds, oxazoline compounds, carbodiimide compounds and melamine compounds, and pigment.