KR20050077027A - Process for forming multi layered coated film and multi layered coated film - Google Patents

Abstract

The present invention provides a method for producing a multilayer coating film having an excellent finished appearance. The present invention comprises the steps of performing an electrodeposition coating with a cationic electrodeposition coating composition on a substrate, then heating and curing the coating to form a cured electrodeposition coating film on the substrate; Applying an intermediate coating composition on the cured coating film to form an uncured intermediate coating film; Applying a base top coating composition on the uncured intermediate coating film to form an uncured base coating film; Applying a transparent top coating composition on the uncured base coating film to form an uncured transparent coating film; And simultaneously heating and curing the three uncured coating films, wherein the cured electrodeposition coating film has a specific range of Ra and Pa, or a specific range of Tg. And crosslink density.

Description

Manufacturing method and multilayer coating film of a multilayer coating film {PROCESS FOR FORMING MULTI LAYERED COATED FILM AND MULTI LAYERED COATED FILM}

The present invention relates to a method for producing a multilayer coating film having a good finished appearance.

Various layers of coating film having various functions are formed on the substrate surface of the automobile body to protect the substrate and provide a good appearance to the substrate. However, in recent years, due to the need for energy savings and cost reduction, the next coating on the non-hardened coating film by the so-called wet on wet coating, without the step of firing the uncured coating film after applying all the layers Applying a film; A method of making a multilayer coating film has been used, which comprises the step of firing several layers simultaneously.

As an example of the method, the intermediate coating, the basic top coating and the transparent top coating are applied by wet on wet coating on the cured electrodeposition coating film; The three-coating one-baking coating method (3-wet coating) comprising the steps of simultaneously firing and curing three layers of the uncured coating film is considered the most practical method. A process flow diagram of the coating method is shown in FIG. 1.

In Japanese Patent Laid-Open No. 277474/1998, an intermediate coating, a metal coating and a transparent top coating are applied in sequence on a substrate to be coated; Disclosed is a method of making a multilayer coated film comprising simultaneously firing three layers of a coated film. The publication states that the method provides a coating film with excellent sharpness and excellent gloss.

In the 3-coating 1-baking coating method shown in FIG. 1, the surface conditions of the cured electrodeposition coating film were found to have a great influence on the appearance of the multilayer coating film. The reason is believed to be that the three-coating one-baking coating method includes a minimum number of firing steps as described above. In the above method for producing a multilayer coating film (Japanese Patent Laid-Open No. 277474/1998), the surface conditions of the electrodeposited coating film for improving the appearance of the multilayer coating film are not described.

Japanese Patent Laid-Open No. 224613/2002 includes the steps of forming a cured electrodeposited coating film on a substrate from a cationic electrodeposition coating composition; Applying three coating layers onto the electrodeposited coating film cured by the 3-coating 1-baking coating method; And simultaneously firing and curing three layers of the uncured coating film, wherein the cured electrodeposition coated film has a glass transition temperature of at least 110 ° C. and a surface roughness of less than 0.3 μm (Ra: centerline average roughness). A method of making a coating film is disclosed. In this method, only the center line average roughness Ra is used as a parameter for evaluating the appearance of the coating film, and no other parameters are used.

In addition, in the 3-coating 1-baking coating method shown in FIG. 1, the composition for intermediate coating is applied onto the cured electrodeposition coating film. The solvent contained in the intermediate coating composition is sometimes absorbed into the cured electrodeposition coating film during application of the composition. The solvent absorbed in the cured electrodeposition coating film is volatilized during firing of the laminated coating film and affects the intermediate coating film or the like, thereby lowering the finished appearance of the laminated coating film. In the three-coating one-baking coating method, since the number of firing steps is small and the uncured coating film laminated on two or more layers is fired simultaneously, the solvent contained in the uncured intermediate coating film applied on the cured electrodeposition coating film is cured electrodeposition It has been found to have a great effect on the coating film. In the method (Japanese Patent Laid-Open No. 277474/1998) for producing a multilayer coating film, the physical properties of the electrodeposited coating film for improving the appearance of the multilayer coating film are not described.

It is a main object of the present invention to provide a method for producing a multilayer coating film having a good finished appearance with a 3-coated 1-baking coating method which can save energy and reduce cost.

In the present invention, a method for obtaining a coating film having a good finished appearance has been found. According to the method of the present invention, a multilayer coating film having an excellent appearance can be obtained even by a 3-coating 1-baking coating method including fewer firing steps. The multilayer coating film contains an electrodeposition coating film, an intermediate coating film, a base top coating film and a transparent top coating film. According to the method of the present invention, the energy required for firing and curing in the coating step can be saved, and the production cost can be reduced. The method of the present invention can be suitably used in fields where energy saving and good appearance are required in application.

The above and other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.

The invention will be understood in more detail from the following detailed description, and of the accompanying drawings, which are merely exemplary and are not limitative of the invention.

The present invention comprises the steps of performing an electrodeposition coating with a cationic electrodeposition coating composition on a substrate, then heating and curing the coating to form a cured electrodeposition coating film on the substrate; Applying an intermediate coating composition on the cured electrodeposition coating film to form an uncured intermediate coating film; Applying a base top coating composition on the uncured intermediate coating film to form an uncured base coating film; Applying a transparent top coating composition on the uncured base coating film to form an uncured transparent coating film; And simultaneously heating and curing the uncured intermediate coating film, the uncured base top coating film and the uncured transparent coating film, wherein the cured electrodeposition coating film has a centerline average roughness of 0.05 to 0.25 μm obtained from the roughness curve. By providing a method for producing a multilayer coated film having a centerline average roughness (Pa) of 0.05 to 0.30 μm obtained from (Ra) and a profile curve, the above-described object is achieved.

The present invention also provides a multilayer coating comprising the above steps, wherein the cured electrodeposition coating film has a surface energy of 37 to 43 mJ / m ² and the intermediate coating composition has a contact angle of 10 to 30 ° on the cured electrodeposition coating film. The above object is achieved by providing a method for producing a film.

The invention also relates to a centerline average roughness (Ra) of 0.05 to 0.25 μm obtained from a roughness curve, a centerline average roughness (Pa) of 0.05 to 0.30 μm obtained from a profile curve, and 37 to 43 mJ / having a surface energy of the m ^2, in the electro-deposition coating film is a cured intermediate coating composition having a contact angle of 10 to 30 °, achieves the above objects by providing a method of manufacturing a multi-layer coating film comprising the steps:

The present invention also provides a preparation of a multilayer coating film comprising the above step, wherein the cured electrodeposition coating film has a glass transition temperature Tg of 100 to 130 ° C. and a crosslink density of 1.2 to 2.6 mmol / cc obtained by dynamic viscoelasticity measurement. The above object is achieved by providing a method.

The method of carrying out the invention is described in detail. The present inventors have proposed a method of evaluating the electrodeposition coated film cured in Japanese Patent Laid-Open No. 224613/2002 by surface roughness (Ra: centerline average roughness).

It is difficult to evaluate the appearance of the coating film by a single method because the surface morphology, optical properties and color affect the appearance visually in combination. When evaluating the appearance by wavelength as a method of evaluating the appearance of the coating film, for example, roughness related to gloss and clarity can be evaluated by short wavelength, and roughness related to bending can be evaluated by long wavelength. In JIS for surface roughness, it is described that the contour curve can be divided into profile curve P, roughness curve R and bending curve W.

The appearance of the coating film can be evaluated by dividing it into items of smoothness, orange peel and gloss. In the present invention, the Ra value (centerline average roughness in the roughness curve) of the cured electrodeposition coating film used in the conventional evaluation method was found to be correlated with the orange peel. The Wa value (centerline average roughness in the curvature curve) of the cured electrodeposition coating film as a parameter related to the flexure curve (W) was found to correlate with the smoothness in appearance of the multilayer coating film. In addition, the bending measured by the long wavelength was found to have a great influence on the appearance of the resulting multilayer coating film. In addition, the multilayer coating film produced by evaluating the electrodeposition coating film cured using the Ra value and the Pa value (centerline average roughness in the profile curve) including both the Ra and Wa values as parameters for controlling the surface conditions. It has been found to improve the finished appearance of one aspect of the present invention.

Although the surface conditions of the cured electrodeposition coating film as described above are controlled during the manufacture of the multilayer coating film by the 3-coating 1-baking coating method as described herein, the intermediate coating composition is low on the cured electrodeposition coating film. It is sometimes thought that a multilayer coating film with good appearance is not obtained when having wettability. This drawback has a great impact on the appearance of the resulting multilayered coating film, since the three-coating one-baking coating method involves fewer firing steps.

In the present invention, the wettability of the intermediate coating film can be controlled by adjusting the surface energy of the cured electrodeposition coating film to a specific range and the finished appearance of the resulting multilayer coating film can be improved to carry out another aspect of the present invention. It turned out.

In the present invention, the solvent resistance of the cured electrodeposition coating film can be improved by adjusting the glass transition temperature Tg and the crosslink density obtained from the dynamic viscoelasticity measurement of the cured electrodeposition coating film to a specific range and the completion of the resulting multilayer coating film It has been found that the appearance can be improved to carry out another aspect of the present invention.

In one embodiment of the present invention, the components contained in the cationic electrodeposition coating composition and their contents are such that the centerline average roughness (Ra) and profile of 0.05 to 0.25 μm of the cured electrodeposition coating film formed by the electrodeposition coating is obtained from the roughness curve. It is selected to have a centerline average roughness (Pa) of 0.05 to 0.30 μm obtained from the curve. Preferably the upper limit of center line average roughness Ra is 0.20 micrometer. Preferably the upper limit of center line average roughness Pa is 0.25 micrometer. It is difficult to obtain a cured electrodeposition coating film having a centerline average roughness Ra and a centerline average roughness Pa less than the lower limit of 0.05 μm at the current state of the art.

Centerline average roughness (Ra) obtained from the roughness curve as used herein and centerline average roughness (Pa) obtained from the profile curve are the parameters defined in JIS B 0601. Centerline average roughness (Ra) obtained from the roughness curve of the cured electrodeposition coating film and centerline average roughness (Pa) obtained from the profile curve are produced, for example, by Mitutoyo Corp. according to JIS B 0601. It can be measured using one evaluation surface roughness tester.

When the Ra value is larger than 0.25 μm, the appearance of the multilayer coating film, in particular the orange peel, is lowered. If the Pa value is larger than 0.30 mu m, the appearance, in particular, the smoothness of the multilayer coating film is lowered.

The method for preparing a cationic electrodeposition coating composition for obtaining a cured electrodeposition coating film having a centerline average roughness Ra obtained from the roughness curve within the above range and a centerline average roughness Pa obtained from the profile curve is cationic. Methods of adjusting the type and content of cationic epoxy resins, blocked isocyanate curing agents and catalysts in electrodeposition coating compositions. In particular, the type and content of blocked isocyanate curing agent has a great influence on the Ra and Pa values. The smoothness of the coating film is improved by adjusting the solids content ratio between the cationic epoxy resin and the blocked isocyanate curing agent by improving the flowability and curing rate of the coating film during the manufacture of the film (electrodeposit film). The smoothness of the electrodeposition coated film can be further improved by using a surface treated steel sheet having a smaller surface roughness.

In another aspect of the invention, the cationic electrodeposition coating composition and the intermediate coating composition are formed on the electrodeposition coating film wherein the cured electrodeposition coating film formed has a surface energy of 37 to 43 mJ / m ² and the coated intermediate coating composition is cured. It is used to have a contact angle of 10 to 30 degrees. When the surface energy of the cured electrodeposition coating film is within the above range and the contact angle between the cured electrodeposition coating film and the intermediate coating composition is within the range of 10 to 30 °, the wettability of the intermediate coating composition to the cured electrodeposition coating film is high. The finished appearance of the resulting multilayer coating film is good.

The surface energy of the cured electrodeposition coating film preferably has a lower limit of 38 mJ / m ² , more preferably 39 mJ / m ² , preferably 42 mJ / m ² , more preferably 41 mJ / m ^2. Has an upper limit of. The contact angle between the cured electrodeposition coating film and the intermediate coating composition preferably has a lower limit of 10 ° and preferably an upper limit of 25 °.

If the surface energy is lower than 37 mJ / m ² , the adhesion between the cured electrodeposition coating film and the intermediate coating film is lowered. On the other hand, if the surface energy is higher than 43 mJ / m ² , the wettability of the intermediate coating composition on the cured electrodeposition coating film is lowered. In addition, when the contact angle between the cured electrodeposition coating film and the intermediate coating composition is greater than 30 °, the wettability of the intermediate coating composition relative to the cured electrodeposition coating film is lowered.

The surface energy of the coating film is the force applied in the direction perpendicular to the free length. Surface energy is based on the Lifshitz-van der Waals force in the contact angle process, the ^LW value, the acidic component γ ⁺ based on the acid-base force, and the basicity based on the acid-base force. component γ ^- known three kinds of liquid (e.g., water, methylene iodide and ethylene glycol) and measuring the contact angle between the coating film; Γ ^LW , γ ⁺ and γ ⁻ values of the coating films were obtained from Equation 1 below derived from the Young-Dupre equation; These values are determined by calculation using Equation 2 below (CJ Van Oss, J. Protein Chem ., Vol. 4 , 245, 1985; and CJ Van Oss, J. Colloid Interface Sci ., Vol. 111 , 378, 1986).

^{_{2 [(γ i LW · γ}} j LW) 1/2 + (γ i + · γ j -) 1/2 + (γ i - · γ j +) 1/2] = (1 + cosθ) [γ j _{^{LW + 2 (γ i + ·}} γ j -) 1/2]

The surface free energy ^{_{(γ) = γ j LW +}} (γ j + · γ j -) 1/2

In the above,

γ _i ^LW is a term based on the leafscheet-van der Waals forces of the liquid;

γ _i ⁺ is an acidic component based on the acid-base force of the liquid;

γ _i ^- is a basic component based on the acid-base force of the liquid;

θ is the contact angle.

As a method of producing a cationic electrodeposition coating composition and an intermediate coating composition from which the surface energy of the cured electrodeposition coating film within the above range and the contact angle between the cured electrodeposition coating film and the intermediate coating composition can be obtained, Methods for adjusting the type and content of cationic epoxy resins, blocked isocyanate curing agents, catalysts and surface conditioners contained in the 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 electrodeposition coating film and the intermediate coating composition. Types of surface conditioners used in the present invention include acrylic type, silicone type and vinyl type.

In the method for producing the multilayer coating film of the present invention, the cured electrodeposition coating film has a centerline average roughness Ra of 0.05 to 0.25 탆 obtained from the roughness curve and a centerline average roughness of 0.05 to 0.30 탆 obtained from the profile curve. It is more preferred that the contact angle between the cured electrodeposition coating film and the intermediate coating composition is within the range of 10 to 30 degrees. This is because a multilayer coated film can be obtained with a better finished appearance.

In the present invention, the components contained in the cationic electrodeposition coating composition and their contents are determined in a specific range of glass transition temperature Tg (herein referred to as "dynamic Tg"), in which the cured electrodeposition coating film formed by electrodeposition coating is obtained by dynamic viscoelasticity measurement. And also to a particular range of crosslink densities.

Dynamic Tg as used herein is determined by measuring the dynamic glass transition temperature Tg using a sample in the same manner as the general Tg measurement method by dynamic viscoelasticity measurement. Examples of the measuring method used in the present invention include a method of forming a cured electrodeposited coating film on a substrate, separating the coating film using mercury and cutting the film to perform dynamic viscoelasticity measurements. . In this method, the sample was heated from room temperature to 200 ° C. at a rate of temperature rise of 2 ° C. per minute and vibrated at a frequency of 11 Hz to measure its viscoelasticity. The ratio (tanδ) of storage elasticity (E ') / lossy elasticity (E ") was calculated and its inflection point (temperature at the peak of tanδ) was obtained to obtain a dynamic Tg. As an example of a dynamic viscoelasticity measuring device, Examples include Rheovibron model RHEO 2000, 3000 (trade name) manufactured by Orientec Co., Ltd.

In the present invention, the cured electrodeposition coated film formed by electrodeposition coating preferably has a dynamic Tg of 100 to 130 ° C. The lower limit of the dynamic Tg is preferably 110 ° C and the upper limit of the dynamic Tg is preferably 125 ° C. When the dynamic Tg of the cured electrodeposition coating film is lower than 100 ° C., the electrodeposition coating film swells with a solvent contained in the intermediate coating composition, and the finished appearance of the resulting multilayer coating film is lowered. On the other hand, if the dynamic Tg is higher than 130 ° C., the elastic modulus of the resulting multilayer coating film is low and the impact resistance of the coating film is lowered.

The crosslink density is determined by measuring the dynamic viscoelasticity of the cured electrodeposited coating film formed by electrodeposition coating in the same manner as the method of measuring the dynamic Tg, and calculated by using the storage elasticity (E ') obtained in the rubber region from the equation do:

E '= 3 nRT

In the above, E 'is storage elastic; n is the crosslink density; R is a gas constant; T is the absolute temperature.

In the present invention, the crosslink density of the cured electrodeposition coating film formed by the electrodeposition coating is preferably within the range of 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 is more preferably 2.3 mmol / cc. When the crosslinking density of the cured electrodeposition coating film is lower than 1.2 mmol / cc, the electrodeposition coating film swells with a solvent contained in the intermediate coating composition, and the finished appearance of the resulting multilayer coating film is lowered. On the other hand, when the crosslink density is higher than 2.6 mmol / cc, containing water easily causes foaming and lowers corrosion resistance.

As a method of preparing a cationic electrodeposition coating composition for obtaining a cured electrodeposition coating film having a dynamic Tg and crosslink density within the above range, cationic epoxy resin in the cationic electrodeposition coating composition, blocked isocyanate curing agent And a method of adjusting the type and content of the catalyst. In particular, the type and content of cationic epoxy resins and blocked isocyanate curing agents have a great influence on the dynamic Tg and crosslink density. Examples of the cationic epoxy resin include a resin obtained by ring opening an epoxy ring of a bisphenol A type epoxy resin or a bisphenol F type epoxy resin with an activated hydrogen compound into which a cationic group can be introduced. Examples of blocked isocyanate curing agents include hexamethylene diisocyanate (including trimers), tetramethylene diisocyanate and trimethylhexamethylene diisocyanate blocked with suitable blocking agents; Alicyclic diisocyanates such as 4,4'-methylene bis (cyclohexylisocyanate); Aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI) and hexamethylene diisocyanate Cyanate (HDI). In addition, the dynamic Tg and crosslink density can also be adjusted by selecting the ratio of blocked isocyanate curing agent to cationic epoxy resin or firing temperature of the electrodeposition coating film.

The materials to be coated, the cationic electrodeposition coating composition, the intermediate coating composition, the basic top coating composition and the transparent top coating composition, and methods of applying the same, which are used in the production method of the multilayer coating film of the present invention, are described below.

Substrate to be coated

The substrate to be coated used in the method for producing the multilayer coating film of the present invention may be any substrate that can be electrodeposition coated. Examples of such substrates include metals such as iron, steel, aluminum, tin, zinc, and the like, and alloys thereof, and plated products thereof or electrodeposition products thereof. Specific examples thereof include passenger cars, vans, motorcycles, buses, and the like, manufactured using metal components. Also obtained by conducting conductive treatment of resins such as polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, polyamide resin, acrylic resin, vinylidene chloride, polycarbonate resin, polyurethane resin, epoxy resin and various FRP Plastic materials can be used as the substrate.

In the method for producing the multilayer coating film of the present invention, the substrate can be used as tolerated conditions or after pretreatment such as degreasing treatment or chemical conversion treatment prior to electrodeposition coating.

Cationic Electrodeposition Coating Composition

Cationic electrodeposition coating compositions used in the present invention include a binder resin containing an aqueous solvent, a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in an aqueous solvent; Neutralizing acid; And organic solvents. The cationic electrodeposition coating composition may also contain pigments.

Cationic epoxy resin

Cationic epoxy resins used in the present invention include amine-modified epoxy resins. The cationic epoxy resin may be a known resin described in Japanese Patent Laid-Open No. 4978/1979, 34186/1981 and the like.

Cationic epoxy resins typically ring-open all epoxy rings of bisphenol type epoxy resins with activated hydrogen compounds into which cationic groups can be introduced; Or by opening a portion of an epoxy ring with another activated hydrogen compound and ringing the remaining epoxy ring with an activated hydrogen compound into which a cationic group can be introduced.

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

An oxazolidone ring-containing epoxy resin having the following formula (1) may be used in the cationic epoxy resin for the reason that a coating film having excellent heat resistance and corrosion resistance is obtained:

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 is a quantity Represents an integer.

This is because a coating film having excellent solvent resistance (solvent swelling resistance) can be obtained.

The method of introducing the oxazolidone ring into the epoxy resin involves heating a lower alcohol such as methanol and a polyepoxide blocked isocyanate curing agent under a basic catalyst, keeping the temperature constant, and lower alcohol from the system as a byproduct. Included are methods comprising distillation.

Particularly preferred epoxy resins are oxazolidone ring containing resins. 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 known to obtain an epoxy resin containing an oxazolidone ring by reaction of a difunctional epoxy resin with a monoalcohol blocked diisocyanate (ie bisurethane). Specific examples of oxazolidone ring-containing epoxy resins and methods for producing the same are disclosed in paragraphs [0012] to [0047] of Japanese Patent Laid-Open Publication No. 128959/2000, which are known.

Epoxy resins may be modified with suitable resins such as polyesterpolyols, polyetherpolyols, and monofunctional alkylphenols. Epoxy resins can also be chain-extended by reaction of epoxy groups with diols or dicarboxylic acids.

The epoxy resin is preferably ring-opened with an activated hydrogen compound so as to have an amine equivalent value of 0.3 to 4.0 meq / g after ring opening, in particular so that 5 to 50% thereof is a primary amine group.

Examples of activated hydrogen compounds to which cationic groups can be introduced include acid, sulfide and acid mixtures of primary amines, secondary amines, and tertiary amines. To prepare primary amine, secondary amine and / or tertiary amine containing epoxy resins, acid salts of primary amine, secondary amine, and tertiary amine are used as activating hydrogen compounds into which a cationic group can be introduced.

Specific examples thereof include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, acid salts of triethylamine, acid salts of N, N-dimethylethanolamine, diethyl disulfide-acetic acid mixture, and primary Secondary amines obtained by blocking amines, such as ketimines of aminoethylethanolamine, ketimines of diethylenetriamine. Amines can be used in mixtures.

Blocked isocyanate curing agent

Polyisocyanates used in the preparation of the blocked isocyanate curing agents of the present invention are compounds having two or more isocyanate groups in the molecule. The polyisocyanates can be aliphatic, cycloaliphatic, aromatic or aromatic-alicyclic.

Examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate Anate and naphthalene diisocyanate; Aliphatic diisocyanates having 3 to 12 carbon atoms such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate and lysine diisocyanate Nate; Alicyclic diisocyanates having from 5 to 18 carbon atoms, for example 1,4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), 4,4'-dicyclo Hexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate and 1,3-diisocyanato Methylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanate methyl) -bicyclo [2.2.1] heptane (= norbornene diisocyanate) ; Aliphatic diisocyanates having aromatic rings such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); Modified compounds thereof (urethane compounds, carbodiimide, uretodione, uretonimine, biuret and / or isocyanurate modified compounds); Etc. are included. Polyisocyanates may be used alone or in mixture of two or more.

Blocking isocyanates from adducts or prepolymers obtained by reacting polyisocyanates with polyalcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at a NCO / OH ratio of at least 2 It can be used as an anate curing agent.

The blocking agent is added to the polyisocyanate group and stable at room temperature, but free isocyanate groups can be regenerated by heating at temperatures above the dissociation temperature.

Pigment

The cationic electrodeposition coating composition used in the process of the invention may contain pigments that have conventionally been used for coating. Examples of pigments include inorganic pigments such as colored pigments such as titanium dioxide, carbon black and coalcotar; Extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; Antirust pigments such as zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphorate, zinc molybdate, aluminum molybdate, calcium molybdate , Aluminum phosphomolybdate and aluminum zinc phosphomolybdate.

In the case of using the pigment as a component of the electrodeposition coating, the pigment is generally predispersed in a high concentration in an aqueous solvent in the form of a paste (pigment dispersed paste). This is because it is difficult to uniformly disperse powdery pigments at low concentration in one step. Pastes are commonly referred to as pigment dispersion pastes.

Pigment dispersion pastes are prepared by dispersing the pigment together with the pigment dispersion resin varnish in an aqueous medium. As the pigment dispersion resin, it is possible to use cationic or non-ionic low molecular weight surfactants or modified epoxy resins having cationic polymers such as quaternary ammonium groups and / or tertiary sulfonium groups. As the aqueous medium, deionized water or water containing a small amount of alcohol can be used. Pigment dispersion resins are generally used in solids content of 20 to 100 parts by mass, based on 100 parts by mass of coating. The pigment dispersion paste can be obtained by mixing the pigment dispersion resin varnish with the pigment and dispersing the pigment using a suitable dispersing apparatus such as a ball mill or a sand grinding mill.

The cationic electrodeposition coating composition may optionally contain, in addition to the above components, a separation catalyst, an organotin compound, such as dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, to separate the blocker; Amines such as N-methyl morpholine; Lead acetate; Metal salts of strontium, cobalt and copper. The amount of separation catalyst is 0.1 to 6 parts by mass based on 100 parts by mass of the total solids content of the cationic epoxy resin and the blocked isocyanate curing agent in the cationic electrodeposition coating composition.

Preparation and Application of Cationic Electrodeposition Coating Compositions

The cationic electrodeposition coating composition of the present invention is prepared by dispersing the catalyst, cationic epoxy resin, blocked isocyanate curing agent and pigment dispersion paste in an aqueous solvent. The aqueous medium may also contain a neutralizing acid to neutralize 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 neutralizing acid is preferably 10 to 25 mg equivalents based on 100 g of binder resin containing cationic epoxy resin and blocked isocyanate curing agent. The lower limit of the amount of neutralizing acid is more preferably 15 mg equivalent, and the upper limit is more preferably 20 mg equivalent. If the amount of neutralizing acid is less than 10 mg equivalent, sufficient miscibility with water is not obtained and it is difficult to disperse in water or the stability is considerably lowered. On the other hand, if the amount of neutralizing acid is more than 25 mg equivalent, the power required for electrodeposition is increased and deposition of the solid component of the coating is lowered, resulting in lower uniform electrodeposition.

Cationic electrodeposition coating compositions can be prepared by dispersing a cationic epoxy resin and blocked isocyanate curing agent in an aqueous solvent. The amount of blocked isocyanate curing agent is preferably sufficient to react with activated hydrogen containing functional groups such as primary amino groups, secondary amino groups and hydroxyl groups upon curing to provide a good cured coating film. The amount of blocked isocyanate curing agent represented by the solids content ratio (cationic epoxy resin / curing agent) of cationic epoxy resin to blocked isocyanate curing agent is preferably 90/10 to 50/50, more preferably 80/20 to 60/40, most preferably within the range of 80/20 to 65/35. The flowability and curing rate of the coated film (electrodeposited film) in forming the film is improved by adjusting the ratio, and the smoothness of the coated film is also improved. The smoothness of the electrodeposited coating film is further improved by using surface treated steel sheets with smaller roughness. It is also easy to provide the desired dynamic Tg and crosslink density to the cured electrodeposition coating film by adjusting the amount of blocked isocyanate curing agent to the above range or by selecting the firing temperature.

When synthesizing resin components such as cationic epoxy resins, blocked isocyanate curing agents, pigment dispersion resins, organic solvents are used as solvents. Complex procedures are necessary to completely remove the solvent. The flowability of the coating film upon film formation is improved by the inclusion of an organic solvent in the binder resin, and the smoothness of the coating film is also improved.

Examples of organic solvents used in the cationic electrodeposition coating composition include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol Chol monobutyl ether, propylene glycol monophenyl ether, and the like.

In addition to the above components, the cationic electrodeposition coating composition may contain additives for coating, such as plasticizers, surfactants, antioxidants and ultraviolet absorbers. The cationic electrodeposition coating composition may contain an amino group-containing acrylic resin, an amino group-containing polyester resin, and the like.

Electrodeposition coating is carried out by applying a voltage of typically 50 to 450 V between the substrate serving as the cathode and the anode. If the applied voltage is lower than 50 V, electrodeposition becomes insufficient. On the other hand, if the applied voltage is higher than 450 V, the coated film is broken and its appearance becomes strange. Electrodeposition bath temperature is normally adjusted to 10-45 degreeC.

The electrodeposition process includes immersing the substrate to be coated in the electrodeposition coating composition and applying a voltage between the substrate as a cathode and an anode to cause deposition of the coated film. In addition, the time for applying the voltage depends on the electrodeposition conditions, but may generally be 2 to 4 minutes.

The thickness of the electrodeposition coated film is preferably 5 to 25 µm, more preferably 20 µm. If the thickness is smaller than 5 mu m, rust resistance is not sufficiently obtained. On the other hand, if the thickness is larger than 25 μm, the coating composition is wasted.

The electrodeposited coating film obtained in the manner as described above is cured immediately by firing at a temperature of 120 to 260 ° C., preferably 140 to 220 ° C. for 10 to 30 minutes, or by washing with water and then curing after completion of the electrodeposition process. A cured electrodeposition coating film is formed.

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 intermediate coating resin component comprises an intermediate coating resin and optionally an intermediate coating curing agent. The aqueous medium and the organic solvent can be the same as used in the cationic electrodeposition coating composition.

Examples of the intermediate coating resin include acrylic resins, polyester resins, polyurethane resins, alkyd resins, fluorine resins, epoxy resins, polyether resins, and the like. Acrylic resins, polyester resins and polyurethane resins are preferred. The intermediate coating resins can be used alone or in mixture with two or more.

Examples of acrylic resins include copolymers of acrylic monomers and other ethylenically unsaturated monomers. Examples of acrylic monomers that can be used in the copolymer include methyl esters of acrylic acid or methacrylic acid, ethyl esters, propyl esters, n-butyl esters i-butyl esters, t-butyl esters, 2-ethylhexyl esters, lauryl esters, Phenyl esters, benzyl esters and 2-hydroxypropyl esters; Ring-opening addition products of caprolactone of 2-hydroxyethyl acrylate or methacrylate; Glycidyl acrylate, glycidyl methacrylate, acrylamide, methacrylamide and N-methylol acrylamide, (meth) acrylic esters of polyalcohols and the like. Examples of other ethylenically unsaturated monomers that can be copolymerized with the monomers include styrene, α-methylstyrene, itaconic acid, maleic acid, vinyl acetate, and the like.

Examples of polyester resins include condensates obtained by condensation of saturated polyester resins or unsaturated polyester resins such as polyhydric acids and polyalcohols by heat. Examples of polyvalent acids include saturated polyvalent acids and unsaturated polyvalent acids. Examples of saturated polyvalent acids include succinic acid, adipic acid, azelaic acid, sebacic acid, hexahydrophthalic acid and 1,4-cyclohexane dicarboxylic acid. Examples of unsaturated polyhydric acids include maleic acid, maleic anhydride, fumaric acid, phthalic anhydride, terephthalic acid and isophthalic acid. Examples of polyalcohols include dihydric alcohols and trihydric alcohols. Examples of dihydric alcohols include ethylene glycol, diethylene glycol, neopentyl glycol, 1,5-pentanediol and 1,6-hexanediol. Examples of trihydric alcohols include glycerin and trimethylolpropane.

Examples of polyurethane resins include polyol components such as acrylics, polyesters, polyethers, polycarbonates, and resins having urethane bonds obtained from polyisocyanate compounds. Examples of polyisocyanate compounds include 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI) and mixtures thereof ( TDI), diphenylmethane-4,4'-diisocyanate (4,4'-MDI), diphenylmethane-2,4'-diisocyanate (2,4'-MDI) And mixtures thereof (MDI), naphthalene-1,5-diisocyanate (NDI), 3,3'-dimethyl-4,4'-biphenylene diisocyanate (TODI), xylylene dia Isocyanate (XDI), dicyclohexylmethane diisocyanate (hydrogenated MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hydrogenated xylene diiso Cyanate (HXDI) and the like.

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

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

Examples of epoxy resins include resins obtained by the reaction of bisphenol and epichlorohydrin and the like. Examples of bisphenols include bisphenol A and bisphenol F. Examples of bisphenol type epoxy resins include Epikote 828, Epicoat 1001, Epicoat 1004, Epicoat 1007, Epicoat 1009 (commercially available from Shell Chemical Co.). In addition, the resin may be chain-extended with a suitable chain extender.

Examples of polyether resins that are polymers or copolymers having ether bonds include polyoxyethylene-based polyethers, polyoxypropylene-based polyethers or polyoxybutylene polyethers, or two or more hydroxyl groups in a molecule. Polyether resins such as bisphenol A or bisphenol F, such as polyethers derived from aromatic polyhydroxy compounds. Further examples include carboxyl group-containing polyether resins obtained by the reaction of polyether resins with reactive derivatives such as succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid and trimellis. Polycarboxylic acids or their anhydrides are also included, including butyric acid.

The intermediate coating resin preferably has an acid value of 3 to 200, a hydroxyl value of 30 to 200, and a number average molecular weight of 500 to 500,000. Preferred resins are, in particular, an acrylic resin having an acid value of 3 to 200, a hydroxyl value of 30 to 200, a number average molecular weight of 2,000 to 50,000, and an acid value of 3 to 200, a hydroxyl value of 30 to 200 and a number average. It is a polyester resin with a molecular weight of 500-20,000. When preparing the intermediate coating composition as an aqueous solution or an aqueous dispersion, it is preferred that the intermediate coating resin has an acid value of 10 to 200 and a hydroxyl value of 30 to 200.

The intermediate coating resins generally include curable and lacquer resins. Hardening type is preferable. When using a curable type, an intermediate coating curing agent such as blocked isocyanate compound, oxazolidone compound, carbodiimide compound and melamine compound is used with the intermediate coating resin. The curing reaction of the intermediate coating resin component containing the intermediate coating curing agent may proceed under heating or at room temperature. In addition, mixtures of curable and non-curable intermediate coating resins may also be used.

In the case of containing the intermediate coating curing agent, the weight ratio of the intermediate coating resin to the intermediate coating curing agent in the coating solid component is preferably 90/10 to 50/50, more preferably 85/15 to 60/40. If the ratio is greater than 90/10 and the amount of the intermediate coating curing agent is less than 10% by weight, sufficient crosslinking is not obtained in the coated film. On the other hand, when the ratio is smaller than 50/50 and the amount of the intermediate coating curing agent is larger than 50% by weight, the storage stability of the coating composition is lowered, the curing speed is high, and the appearance of the coating film is lowered.

The intermediate coating composition of the present invention contains a pigment. Examples of pigments include extender pigments such as barita powder, precipitated sulfate, barium carbonate, gypsum, clay, silica, talc, magnesium carbonate, alumina white and the like, and colored pigments. Examples of colored pigments include organic pigments such as azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophtharone pigments, dioxazine pigments, quinacridone pigments and isoindori. Paddy pigments, metal complex pigments, carbon black; Or inorganic pigments such as yellow lead, yellow iron oxide, coalcotar, titanium dioxide. The amount of pigment may optionally be selected according to the desired performance and color tone. Pigments may be used alone or in admixture with two or more.

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

The solids content of the intermediate coating composition is preferably in the range of 35 to 65% by weight. The lower limit is more preferably 40% by weight, and the upper limit is more preferably 60% by weight. If the lower limit of the solids content is less than 35% by weight, sag occurs during coating application and the finished appearance is degraded. On the other hand, if the upper limit is higher than 65% by weight, the fluidity during coating application is reduced and the finished appearance is lowered.

The intermediate coating composition may include, in addition to the above components, polyamide waxes, which are lubricant dispersions of aliphatic amides, polyethylene waxes, which are colloidal dispersions based on polyethylene oxide, curing catalysts, ultraviolet absorbers, antioxidants, leveling agents, surface conditioners. Silicone and organic polymers, anti-sag agents, thickeners, defoamers, lubricants, crosslinkable polymer powders (microgels) and the like. The performance of the coating composition and the coated film can be improved by blending the additive in an amount of up to 15 parts by mass (based on solids content) based on 100 parts by mass of the intermediate coating resin.

Preparation and Application of Intermediate Coating Compositions

The 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 intermediate coating resin component, but 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 hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate, cellosolve acetate and butyl cellosolve, alcohols and the like. If the use of an organic solvent is restricted from the viewpoint of the environment, it is preferable to use water. In such cases, an appropriate amount of hydrophilic organic solvent may be contained therein.

Upon application of the intermediate coating composition the viscosity is preferably adjusted to 10 to 30 seconds (pod cup # 4/20 ° C.) using organic solvents and / or water and mixtures thereof. If the viscosity is lower than the above range, the intermediate coating film is mixed with the base top coating film formed in the subsequent application step. On the other hand, if the viscosity is higher than the above range, it is difficult to handle the coating composition and the coated film is initially solidified, and in the subsequent coating step, surface planarization occurs to a level that is coated and unrecoverable by the coated film.

The intermediate coating film is obtained by applying the intermediate coating composition onto the cured electrodeposition coating film. Forming the intermediate coating film provides the opacity and impact resistance of the electrodeposition coating film. In addition, the adhesion to the base top coating film applied on the intermediate coating film in the subsequent step is also improved.

The method of applying the intermediate coating is not limited, but includes an air electrostatic spray coating machine called a "react-gun"; So-called "micro micro bells", "micro bells" and "meta bells" using a rotary spray electrostatic coating machine and the like. Preference is given to a method by means of a rotary spray electrostatic coater.

The intermediate coating film preferably has a dry thickness of 5 to 80 μm, preferably 10 to 50 μm. After the intermediate coating film is formed, a step of forming a basic top coating film without heating and curing is performed. The intermediate coating film may be preheated at a temperature below the heating and curing (baking) treatment temperature before forming the base top coating film.

Base top coating composition

The base top coating composition used in the present invention is a brilliant coating composition or solid coating composition containing a base top coating resin component, a brilliant pigment and / or colored pigment, a extender pigment and a solvent. The base top coating composition is either water based with water dispersion or organic solvent based with organic solvent-dispersed.

The base top coating resin component contained in the base top coating composition comprises a base top coating resin and optionally a base top coating curing agent. The base top coating resin component (base top coating resin and base top coating curing agent), color pigments, extender pigments, various additives and solvents contained in the base top coating composition may be the same as described in the intermediate coating. Using the base top coating resin component, the brilliant pigment and optionally the colored pigment are dispersed in the brilliant base top coating composition, and the colored pigment is dispersed in the solid base top coating composition.

Examples of the basic top coating resin used include one or more of coating film forming resins selected from the group consisting of acrylic resins, polyester resins, fluorine resins, epoxy resins, polyurethane resins, polyether resins and modified resins thereof. Can be. Examples of basic top coating curing agents include intermediate coating curing agents as described above. Melamine resins, in particular etherified melamine resins, are preferred. Etherified melamine resins are obtained by etherifying melamine with alcohols such as methanol and butanol. Preferred combinations of the base top coating resin and the base top coating curing agent as the base top coating resin component include an acrylic resin-melamine system. In the above system, the acrylic resin preferably has an acid value of 10 to 200, a hydroxyl value of 30 to 200, and a number average molecular weight of 2,000 to 50,000.

Examples of brilliant pigments as pigments contained in the base top coating composition include aluminum flake pigments, colored aluminum flake pigments, interference mica pigments, colored mica pigments, metal oxide coated glass flake pigments, metal plated glass flake pigments, metal oxide coated Silica flake pigments, metal titanium flake pigments, graphite pigments, stainless steel flake pigments, plate iron oxide pigments, phthalocyanine flake pigments and hologram pigments. When using brilliant pigments and / or colored pigments, the weight content (PWC) of all pigments is preferably within the range of 1 to 50%, more preferably 5 to 30%. If the PWC is less than 1%, it is not enough to add a design to the coating film. On the other hand, when the PWC is larger than 50%, the appearance of the coating film is lowered.

Preparation and Application of Base Top Coating Compositions

Base top coating compositions are 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 base top coating resin component, but may be an organic solvent and / or water. Examples of organic solvents include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate, cellosolve acetate and butyl cellosolve, alcohols and the like.

The viscosity of the base top coating composition is preferably adjusted to 10 to 30 seconds (pod cup # 4/20 ° C.) using a suitable diluent. If the viscosity is lower than the above range, the base top coating film is blended with the transparent top coating film formed in the subsequent application step. On the other hand, if the viscosity is higher than the above range, it is difficult to handle the coating composition and the coated film is initially solidified, and in the subsequent coating step, surface planarization occurs to a level that is coated and unrecoverable by the coated film.

The base top coating film is obtained by applying the base top coating composition on the intermediate coating film. The base top coating composition is applied on the uncured intermediate coating film by wet on wet coating. The method of applying the base top coating composition is not limited and includes the method described as the method of applying the intermediate coating composition. When the base top coating composition is applied to a vehicle body, the application is carried out by a two stage coating using an air electrostatic spray coater to provide high quality to the multi stage coating, preferably the coating film. The method of application may also be a combination of an air electrostatic spray coater and a rotary spray type electrostatic coater.

The formation of the base top coating film allows the design to be added to the coating film, ensuring adhesion to the intermediate coating film formed in the preceding step and securing adhesion to the base top coating film coated in the subsequent step.

The base top coating film preferably has a dry thickness of 5 to 50 μm, preferably 10 to 30 μm, per one coating. After formation of the base top coating film, the subsequent steps of forming the transparent top coating film are carried out without heating and curing. The base top coat film may be preheated at a temperature below the heating and curing (baking) treatment temperature prior to forming the transparent top coat film.

Clear top coating composition

The clear top coating composition is made from a clear coating composition containing a clear top coating resin component, various additives and a solvent. The transparent top coating composition is water based, including water-dispersed or organic solvent-containing, including organic solvent-dispersed.

The transparent top coating resin component contained in the transparent top coating composition comprises a transparent top coating resin and optionally a transparent top coating curing agent. The transparent top coating resin component (transparent top coating resin and transparent top coating curing agent), various additives and solvents contained in the transparent top coating composition may be the same as described in the intermediate coating.

Preferred combinations of the transparent top coating resin and the transparent top coating curing agent as the transparent top coating resin component include an acrylic resin-melamine system. In the above system, the acrylic resin preferably has an acid value of 10 to 200, a hydroxyl value of 30 to 200, and a number average molecular weight of 2,000 to 50,000.

In order to ensure acid rain resistance of the brilliant pigment in the base top coating film and to maintain the orientation of the pigment by increasing the solubility difference with the base top coating film in the wet on wet coating, Japanese Patent Publication No. 19315 / Transparent coating compositions comprising carboxyl group-containing polymers and epoxy group-containing polymers disclosed in 1996 can be suitably used. The transparent top coating composition may optionally contain additives such as color pigments, extender pigments, modifiers, ultraviolet absorbers, levelers, dispersants, and antifoaming agents.

Preparation and Application of Transparent Top Coating Compositions

Transparent top coating compositions are prepared by dissolving or dispersing the above components in a solvent. Any solvent described above can be used. The transparent top coating film is obtained by providing a transparent top coating composition to the base top coating film. The clear top coating composition is applied over the uncured base top coating film by wet on wet coating.

The method of forming the transparent top coating film is not limited, but preferably includes a spray method, a roll coater method, and the like. The transparent top coating film preferably has a dry thickness of 20-50 μm, preferably 25-40 μm, per one coating.

The formation of the transparent top coat film allows the base top coat film to be protected and adds depth to the resulting multilayer coating film.

Firing

After formation of the transparent top coating film, three coating film layers of uncured intermediate coating film, base top coating film and transparent top coating film are baked and cured at 120 to 160 ° C. for a given time to obtain a multilayer coating film. In the process of the invention, the intermediate coating composition, the basic top coating composition and the transparent top coating composition are each applied in sequence by wet and wet coating. That is, the uncured coating films are formed in the order of execution. As used herein, the term "uncured" refers to a state in which the coating film is not fully cured and includes a preheated coating film state. As used herein, the term “preheat” refers to leaving or heating the coating film at a temperature from room temperature to 100 ° C. at a temperature below the heating and curing (firing) treatment temperature for 1 to 10 minutes. Coating films having a better finished appearance can be obtained by preheating the coating film after the formation of the intermediate coating film and the formation of the basic top coating film, respectively.

Example

The invention is explained in more detail according to the following examples, although the invention is not limited to these examples. In the examples, “parts” are based on weight unless otherwise indicated.

Preparation Example 1

Preparation of Amine Modified Epoxy Resins

92 parts 2,4- / 2,6-tolylenediisocyanate (weight ratio = 8/2), 95 parts methyl isobutyl ketone (hereinafter referred to as MIBK) and 0.5 parts dibutyltin dilaurate Was charged to a flask equipped with a stirrer, cooling tube, nitrogen introduction tube, thermometer, and dropping funnel. 21 parts of methanol was added while stirring the reaction mixture. Starting at room temperature, the reaction mixture was raised to 60 ° C by exotherm, the reaction was held for 30 minutes, and 50 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise from the dropping funnel. In addition, 5 mole adducts of 53 parts of bisphenol A-propylene oxide were added. The reaction was carried out mainly in the temperature range of 60-65 ° C. and continued until no absorption appeared based on isocyanate groups in the IR spectral measurement.

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

61 parts of bisphenol A and 33 parts of octylic acid were then added and reacted at 120 ° C. to achieve an epoxy equivalent of 1190. Thereafter, the reaction mixture was cooled down, and 25 parts of a 79 wt% solution in MIBK of 11 parts of diethanolamine, 24 parts of N-ethylethanolamine and ketimated aminoethyl ethanolamine were added and reacted at 110 ° C for 2 hours. The reaction mixture was then diluted with MIBK until the non-volatile solids content was 80%, yielding an amine modified epoxy resin (resin solids content: 80%) with a glass transition temperature of 2 ° C.

Preparation Example 2

Preparation of Block Polyisocyanate Curing Agent (1)

1250 parts of diphenylmethane diisocyanate and 266.4 parts of MIBK were fed to the reaction vessel, heated to 80 ° C, and 2.5 parts of dibutyltin dilaurate was added. A solution of 226 parts of ε-caprolactam dissolved in 944 parts of butylcellosolve was added dropwise to the mixture at 80 ° C. for 2 hours. The reaction was maintained at 100 ° C. for 4 hours and cooled down after confirming no absorption in IR spectral measurements based on isocyanate groups. 336.1 parts of MIBK were added, thereby obtaining a blocked isocyanate curing agent having a glass transition temperature of 0 ° C.

Preparation Example 3

Preparation of Pigment Dispersion Resin

222.0 parts of isophorone diisocyanate (hereinafter referred to as IPDI) are fed to a reaction vessel equipped with a stirrer, cooling tube, nitrogen inlet tube and thermometer, diluted with 39.1 parts of MIBK and then 0.2 parts of dibutyltin dilau Rate was added. The reaction mixture was then heated to 50 ° C. and 131.5 parts of 2-ethyl hexanol was added dropwise for 2 hours under stirring under anhydrous nitrogen atmosphere. The reaction temperature was cooled as needed and kept at 50 ° C. As a result, IPDI (resin solids content: 90.0%) half-blocked with 2-ethyl hexanol was obtained.

87.2 parts of dimethylethanolamine, 117.6 parts of 75% lactic acid aqueous solution and 39.2 parts of ethylene glycol monobutyl ether were added to a suitable reaction vessel, and the reaction mixture was stirred at 65 ° C. for 30 minutes to prepare a quaternizing agent.

Subsequently, 710.0 parts of EPON 829 (epoxy equivalent 193 to 203, bisphenol A epoxy resin produced by Shell Chemical Company) and 289.6 parts of bisphenol A were fed to the reaction vessel. When the reaction mixture was heated to 150 to 160 ° C. under a nitrogen atmosphere, an initial exothermic reaction occurred. The 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 IPDI (MIBK solution) half blocked with the prepared 2-ethyl hexanol were added.

The reaction mixture was maintained at 110-120 ° C. for about 1 hour, 463.4 parts of ethylene glycol monobutyl ether were added, the mixture was cooled to 85-95 ° C. and homogenized and 196.7 parts of the above prepared quaternizing agent was added. The reaction mixture was maintained at 85 to 95 ° C. until the acid value was 1, and 964 parts of deionized water were added to complete quaternization of the epoxy-bisphenol A resin and to have a pigment dispersion resin having a quaternary ammonium salt residue (resin Tg = 5 ° C.). , Resin solids content: 50%) was obtained.

Preparation Example 4

Preparation of Pigment Dispersion Paste

120 parts of pigment dispersion resin obtained in Preparation Example 3, 2.0 parts of carbon black, 100.0 parts of kaolin, 80.0 parts of titanium dioxide, 18.0 parts of aluminum phosphomolybdate and 221.7 parts of ion-exchanged water were fed to a sand grinding mill, Was dispersed until it became 10 mu m or less to obtain a pigment dispersion paste (solid content: 48%).

Example 1

Preparation of Cationic Electrodeposition Coating Composition and Formation of Electrodeposition 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 in a solids content ratio of 80/20. Glacial acetic acid was added to the mixture so that the mg equivalent of the acid was 30 based on 100 g of the binder resin solids content MEQ (A), and the mixture was diluted by gradually adding ion exchanged water. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

Cation having 1500 parts of the above emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate solution and 10 parts of dibutyltin oxide, and having a solids content of 20.0% by weight An electrodeposition coating composition was obtained. The Tg of the electrodeposition coated film (electrodeposit film) determined by calculating from the respective resin Tg of all the resin components in the electrodeposition coating composition was 15 ° C. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. The electrodeposition coating was applied using a coating composition on a surface-treated steel sheet having a surface roughness Ra of 0.90 μm (cutoff value: 2.5 mm) at an electrodeposition bath temperature of 30 ° C. so that the electrodeposited coating film after firing had a dry thickness of 15 μm. This was carried out to obtain a cationic electrodeposition coating film (A-1).

Formation of Cured Electrodeposited Film

The resulting cationic electrodeposition coating film (A-1) was calcined at 170 ° C. for 20 minutes to obtain a cured electrodeposition coating film as a substrate.

Formation of intermediate coating film

Rotational vaporization of a polyester-melamine curable intermediate coating composition ("OTO H-880", commercially available from Nippon Paint Co., Ltd.) to a dry thickness of 20 μm It was applied onto the substrate using a type electrostatic coating apparatus, and after application, it was preheated at room temperature for 8 minutes to form an uncured intermediate coating film.

Formation of base top coat film and transparent top coat film

An acrylic-melamine curable base top coating composition ("Auto H-600", commercially available from Nippon Paint Company, Limited) is applied over the intermediate coating film to a dry thickness of 10 μm and applied for 7 minutes at room temperature. Preheated to form an uncured base top coating film. An acrylic acid-epoxy curable transparent top coating film ("MAC O-1600", commercially available from Nippon Paint Company, Limited) was then applied over the base top coating film to a dry thickness of 35 μm. The applied intermediate coating film, base top coating film and transparent top coating film were calcined at 140 ° C. for 30 minutes to obtain a multilayer coating film.

Centerline average roughness (Ra) of roughness curve and centerline average roughness (Pa) of profile curve

The Ra and Pa values of the cured electrodeposition coated film obtained from the electrodeposition coating composition were measured using an evaluation surface roughness tester manufactured by Mitutoyo Corp. according to JIS-B 0601. The measurement was carried out seven times using a sample containing a 2.5 mm wide cutoff, and the Ra and Pa values were determined from the average obtained by excluding the upper and lower limits. The results are shown in Table 1.

Surface energy measurement

The contact angle between the cured electrodeposited coating films of Examples and Comparative Examples and DIW (deionized water), ethylene glycol and methylene iodide 30 seconds after dropping the solvent droplets, automatic contact angle meter (PD-X type, car It was measured using Iowa Interface Science Co., Ltd. (manufactured by Kyowa Interface Science Co., Ltd.). The surface energy of the cured electrodeposited coating film was determined by calculation using the above equation from the resulting measurements.

Contact angle measurement

The contact angle between the cured electrodeposition coating films of the Examples and Comparative Examples and the intermediate coating composition ("Auto H-880") was 30 seconds after the dropping of the intermediate coating composition was dropped. Automatic contact angle meter (PD-X type, Kaiowa Measured using Interface Science Co., Ltd.).

Appearance Evaluation of Multilayer Coating Film

The finished appearance of the multilayer coating film after firing and curing was measured using a Wave-scan DOI (BYK-Gardner Co.). Among the measured values, in the appearance of the multilayer coating film, the "Wa" value is a correction value converted into gloss, the "Wc" value is a correction value converted into orange peel, and "Wd" is a correction value converted to smoothness. Evaluation was performed from Wa, Wc and Wd values. The smaller the value, the better the appearance.

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 in a solids content ratio of 70/30. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 35 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 280 parts of pigment dispersion resin obtained in Preparation Example 4, 1560 parts of ion-exchanged water, 20 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, having a solids content of 20% by weight An electrodeposition coating composition was obtained. The Tg of the electrodeposition coated film (electrodeposit film) determined by calculating from the respective resin Tg of all the resin components in the electrodeposition coating composition was 14 ° C. The electrodeposition coating composition had an acid mg equivalent value of 25.5 based on the volatile organics content (VOC) of 0.5% in the coating, and the resin solids content (MEQ (A)) of 100 g. Electrodeposition coating was carried out using a coating composition on a surface-treated steel sheet having a surface roughness Ra of 0.90 μm (cutoff value: 2.5 mm) at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film (A-2). It was.

A multilayer coating film was obtained as described in Example 1 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 70/30. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The Tg of the electrodeposition coating film (electrodeposition film) determined by calculating from the respective resin Tg of all the resin components in the electrodeposition coating composition was 10 ° C. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was carried out using a coating composition on a surface-treated steel sheet having a surface roughness Ra of 0.60 μm (cutoff value: 2.5 mm) at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film (A-3). It was.

A multilayer coating film was obtained as described in Example 1 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 80/20. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 280 parts of pigment dispersion resin obtained in Preparation Example 4, 1560 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, having a solids content of 20% by weight An electrodeposition coating composition was obtained. The Tg of the electrodeposition coated film (electrodeposit film) determined by calculating from the respective resin Tg of all the resin components in the electrodeposition coating composition was 15 ° C. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was carried out using a coating composition on a surface-treated steel sheet having a surface roughness Ra of 0.20 μm (cutoff value: 2.5 mm) at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film (A-4). It was.

A multilayer coating film was obtained as described in Example 1 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 60/40. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The Tg of the electrodeposition coated film (electrodeposit film) determined by calculating from the respective resin Tg of all the resin components in the electrodeposition coating composition was 4 ° C. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was carried out using a coating composition on a surface-treated steel sheet having a surface roughness Ra of 0.60 μm (cutoff value: 2.5 mm) at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film (A-5). It was.

A multilayer coating film was obtained as described in Example 1 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 70/30. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The Tg of the electrodeposition coating film (electrodeposition film) determined by calculating from the respective resin Tg of all the resin components in the electrodeposition coating composition was 10 ° C. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was carried out using a coating composition on a surface-treated steel sheet having a surface roughness Ra of 0.90 μm (cutoff value: 2.5 mm) at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film (B-1). It was.

A multilayer coating film was obtained as described in Example 1 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 70/30. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The Tg of the electrodeposition coating film (electrodeposition film) determined by calculating from the respective resin Tg of all the resin components in the electrodeposition coating composition was 10 ° C. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was carried out using a coating composition on a surface-treated steel sheet having a surface roughness Ra of 1.20 μm (cutoff value: 2.5 mm) at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film (B-2). It was.

A multilayer coating film was obtained as described in Example 1 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as described in Example 1. The results are shown in Table 1.

Example 6

Preparation of Cationic Electrodeposition Coating Composition and Formation of Electrodeposition 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 in a solids content ratio of 70/30. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20.0% by weight An electrodeposition coating composition was obtained. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was performed using the cationic electrodeposition coating composition produced at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film. The resulting electrodeposition coated film was baked at 160 ° C. for 20 minutes to obtain a cured electrodeposition coating film (A-6) as a substrate.

Formation of intermediate coating film

A polyester-melamine curable intermediate coating composition ("Auto H-880", commercially available from Nippon Paint Company, Limited) was applied onto the substrate using a rotary vaporized electrostatic coating device to a dry thickness of 20 μm, After application it was preheated for 8 minutes at room temperature to form an uncured intermediate coating film.

Formation of base top coat film and transparent top coat film

An acrylic-melamine curable base top coating composition ("Auto H-600", commercially available from Nippon Paint Company, Limited) is applied over the intermediate coating film to a dry thickness of 10 μm and applied for 7 minutes at room temperature. Preheated to form an uncured base top coating film. An acrylic acid-epoxy curable transparent top coat film (commercially available from "Mac O-1600", Nippon Paint Company, Limited) was then applied over the base top coat film to a dry thickness of 35 μm. The applied intermediate coating film, base top coating film and transparent top coating film were calcined at 140 ° C. for 30 minutes to obtain a multilayer coating film.

Dynamic Tg Measurement of Cured Electrodeposited Film

Electrodeposited coating compositions prepared in Examples and Comparative Examples were electrodeposited coated on a tin plate for dynamic viscoelasticity measurement to obtain an electrodeposited coated film. The electrodeposited coating film was then baked at 170 ° C. for 20 minutes to obtain a cured electrodeposition coating film. The resulting coating film was separated from the tin plate using mercury and cut to prepare a sample for measurement. The sample was heated from room temperature to 200 ° C. at a rate of temperature rise of 2 ° C. per minute and vibrated at a frequency of 10 Hz to produce a rheovibron model Leo manufactured by Orientec Co., Ltd. Viscoelasticity was measured using (RHEO) 2000, 3000 (trade name). The ratio (tanδ) of storage elasticity (E ') to loss elasticity (E ") was calculated and its inflection point (peak temperature of tanδ) was measured to obtain a dynamic Tg.

Determination of Crosslink Density of Cured Electrodeposited Coating Film

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

Appearance Evaluation of Multilayer Coating Film

The finished appearance of the multilayer coated film after firing and curing was measured using a Wave-scan DOI (BWK-Gardner Company). Among the measured values, in the appearance of the multilayer coating film, the "Wa" value is a correction value converted into gloss, the "Wc" value is a correction value converted into orange peel, and "Wd" is a correction value converted to smoothness. Evaluation was performed from Wa, Wc and Wd values. The smaller the value, the better the appearance.

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 in a solids content ratio of 80/20. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 35 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 20 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The electrodeposition coating composition had an acid mg equivalent value of 25.5 based on the volatile organics content (VOC) of 0.5% in the coating, and the resin solids content (MEQ (A)) of 100 g. Electrodeposition coating was performed using the cationic electrodeposition coating composition produced at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film. The resulting electrodeposition coated film was baked at 160 ° C. for 20 minutes to obtain a cured electrodeposition coating film (A-7) as a substrate.

A multilayer coating film was obtained as described in Example 6 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 80/20. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was performed using the cationic electrodeposition coating composition produced at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film. The resulting electrodeposition coated film was baked at 180 ° C. for 20 minutes to obtain a cured electrodeposition coating film (A-8) as a substrate.

A multilayer coating film was obtained as described in Example 6 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 60/40. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was performed using the cationic electrodeposition coating composition produced at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film. The resulting electrodeposition coated film was baked at 180 ° C. for 20 minutes to obtain a cured electrodeposition coating film (A-9) as a substrate.

A multilayer coating film was obtained as described in Example 6 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solid content ratio of 90/10. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was performed using the cationic electrodeposition coating composition produced at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film. The resulting electrodeposition coated film was baked at 160 ° C. for 20 minutes to obtain a cured electrodeposition coating film (B-3) as a substrate.

A multilayer coating film was obtained as described in Example 6 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 80/20. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 540 parts of pigment dispersion resin obtained in Preparation Example 4, 1920 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, and having a solids content of 20% by weight An electrodeposition coating composition was obtained. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was performed using the cationic electrodeposition coating composition produced at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film. The resulting electrodeposition coated film was baked at 150 ° C. for 20 minutes to obtain a cured electrodeposition coating film (B-4) as a substrate.

A multilayer coating film was obtained as described in Example 6 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as 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 in a solids content ratio of 70/30. Glacial acetic acid was added to the mixture so that the mg equivalent of acid was 30 based on 100 g of binder resin solids content MEQ (A) and ion exchanged water was added slowly to dilute. MIBK was removed under reduced pressure to yield an emulsion having a solids content of 36%.

A cation having 1500 parts of said emulsion, 280 parts of pigment dispersion resin obtained in Preparation Example 4, 1560 parts of ion-exchanged water, 40 parts of 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide, having a solids content of 20% by weight An electrodeposition coating composition was obtained. The electrodeposition coating composition had an acid mg equivalent value of 24.2 based on the volatile organics content (VOC) of 0.5% and the resin solids content (MEQ (A)) of 100 g in the coating. Electrodeposition coating was performed using the cationic electrodeposition coating composition produced at an electrodeposition bath temperature of 30 ° C. to obtain a cationic electrodeposition coating film. The resulting electrodeposition coated film was baked at 180 ° C. for 20 minutes to obtain a cured electrodeposition coating film (B-5) as a substrate.

A multilayer coating film was obtained as described in Example 6 except for the preparation of the cationic electrodeposition coating composition and the formation of the electrodeposition coating film described above. The resulting multilayered coating film was evaluated as described in Example 6. The results are shown in Table 2.

Test result

As is apparent from the results shown in Table 1, the cured electrodeposition coating films of the present inventions of Examples 1 to 5 had excellent surface conditions. The 3-coated 1-baking coating on the cured electrodeposition coating film gave a multilayer coating film having a good appearance without appearance defects from the electrodeposition coating film. On the other hand, in Comparative Examples 1 to 2, since the electrodeposition coating film had appearance defects therefrom, a multilayer coating film having excellent appearance was not obtained.

As is apparent from the results shown in Table 2, the multilayer coating film obtained by 3-coating 1-baking coating on the cured electrodeposition coating film of the present invention of Examples 6 to 9 had a good appearance. On the other hand, in Comparative Examples 3 to 5, no multilayer coated film with good appearance was obtained.

According to the present invention there is provided a method comprising the steps of applying an intermediate coating, a base top coating and a transparent top coating by wet on wet coating on a cured electrodeposition coating film; And by firing and curing three layers of the uncured coating film at the same time, the energy required for firing and curing in the coating step is saved, including fewer firing steps. The production cost can be reduced and a multilayer coating film having a good finished appearance without appearance defects can be obtained.

1 is a flow diagram illustrating one aspect according to the method of the present invention.

Claims (5)

Performing electrodeposition coating with a cationic electrodeposition coating composition on the substrate, then heating and curing the coating to form a cured electrodeposition coating film on the substrate; Applying an intermediate coating composition on the cured electrodeposition coating film to form an uncured intermediate coating film; Applying a base top coating composition on the uncured intermediate coating film to form an uncured base coating film; Applying a transparent top coating composition on the uncured base coating film to form an uncured transparent coating film; And Simultaneously heating and curing the uncured intermediate coating film, the uncured base top coating film and the uncured transparent coating film, The cured electrodeposition coating film has a centerline average roughness (Ra) of 0.05 to 0.25 μm obtained from the roughness curve and a centerline average roughness (Pa) of 0.05 to 0.30 μm obtained from the profile curve. Performing electrodeposition coating with a cationic electrodeposition coating composition on the substrate, then heating and curing the coating to form a cured electrodeposition coating film on the substrate; Applying an intermediate coating composition on the cured electrodeposition coating film to form an uncured intermediate coating film; Applying a base top coating composition on the uncured intermediate coating film to form an uncured base coating film; Applying a transparent top coating composition on the uncured base coating film to form an uncured transparent coating film; And Simultaneously heating and curing the uncured intermediate coating film, the uncured base top coating film and the uncured transparent coating film, The cured electrodeposition coating film has a surface energy of 37 to 43 mJ / m ² , and the intermediate coating composition has a contact angle of 10 to 30 ° on the cured electrodeposition coating film. Performing electrodeposition coating with a cationic electrodeposition coating composition on the substrate, then heating and curing the coating to form a cured electrodeposition coating film on the substrate; Applying an intermediate coating composition on the cured electrodeposition coating film to form an uncured intermediate coating film; Applying a base top coating composition on the uncured intermediate coating film to form an uncured base coating film; Applying a transparent top coating composition on the uncured base coating film to form an uncured transparent coating film; And Simultaneously heating and curing the uncured intermediate coating film, the uncured base top coating film and the uncured transparent coating film, Centerline average roughness (Ra) of 0.05 to 0.25 μm obtained from the roughness curve, centerline average roughness (Pa) of 0.05 to 0.30 μm obtained from the profile curve, and the surface of 37 to 43 mJ / m ^{2, wherein} the cured electrodeposition coating film was cured 10. A method of making a multilayer coating film having energy, and wherein the intermediate coating composition has a contact angle of 10 to 30 degrees on the cured electrodeposition coating film. Performing electrodeposition coating with a cationic electrodeposition coating composition on the substrate, then heating and curing the coating to form a cured electrodeposition coating film on the substrate; Applying an intermediate coating composition on the cured electrodeposition coating film to form an uncured intermediate coating film; Applying a base top coating composition on the uncured intermediate coating film to form an uncured base coating film; Applying a transparent top coating composition on the uncured base coating film to form an uncured transparent coating film; And Simultaneously heating and curing the uncured intermediate coating film, the uncured base top coating film and the uncured transparent coating film, The cured electrodeposition coating film has a glass transition temperature (Tg) of 100 to 130 ° C. and a crosslink density of 1.2 to 2.6 mmol / cc obtained by dynamic viscoelasticity measurement. The method according to any one of claims 1 to 4, Intermediate coating composition, Intermediate coating resin containing at least one selected from the group consisting of acrylic resin, polyester resin and polyurethane resin; An intermediate coating curing agent comprising at least one selected from the group consisting of blocked isocyanate compounds, oxazoline compounds, carbodiimide and melamine compounds; And a pigment.