JP2002194275A - Intermediate coating composition containing titanium oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate coating composition which can hide the unevenness of a surfacer comprising an electrodeposition coating film, enabling surface flatness to be ensured, and can form a coating film excellent in properties such as resistances to chipping, water, and weather. SOLUTION: This coating composition contains a polyester resin, a melamine resin, and titanium oxide. The polyester resin has a number average mol.wt. of 1,000-4,000, an acid value of 4-15 mgKOH/g, and a hydroxyl value of 50-200. The titanium oxide has a basicity of 1×10-5-12×10-5 mol/g and an acidity of 0.4×10-5-0.8×10-5 mol/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermediate coating composition containing a polyester resin, a melamine resin and titanium oxide, and more particularly, to an intermediate coating composition capable of improving the appearance of an obtained intermediate coating film. About.

[0002]

2. Description of the Related Art Usually, an electrodeposition coating film is formed as an undercoat on an automobile body or parts, and then an intermediate coating film, for example, a base coating film and, if necessary, a clear coating film are sequentially formed. . Among them, the intermediate coating film is to cover the unevenness of the electrodeposition coating film as a base, to secure the surface smoothness, and to impart the coating film properties such as impact resistance, chipping resistance, and weather resistance. It is formed for the purpose.

[0003] An intermediate coating material for forming an intermediate coating film usually contains a coloring pigment and an extender pigment in addition to the film-forming resin, but the coloring pigment is excellent in color concealability and inexpensive. Therefore, titanium oxide is preferably used.

[0004] Titanium oxide is generally produced by a sulfuric acid method or a chlorine method. The sulfuric acid method is a method in which ilmenite as a raw material is digested with sulfuric acid to extract and separate a titanium component, hydrolyzed, and then calcined, pulverized, and surface-treated.The chlorine method is a method in which rutile ore is used as a raw material. This is a method in which chlorination is carried out using chlorine or synthetic rutile with chlorine, separated and oxidized, followed by pulverization and surface treatment. Titanium oxide has different properties such as coloring, gloss, and light resistance depending on whether it is manufactured by using the above sulfuric acid method or chlorine method, and also depending on the surface treatment method, crystal form, specific gravity, particle size, and the like. It is known to

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to conceal unevenness of an electrodeposition coating film as a base, to secure more surface smoothness than a conventional intermediate coating film, and to further improve chipping resistance. An object of the present invention is to provide an intermediate coating composition having excellent coating properties such as water resistance and weather resistance.

[0006]

The present invention is an intermediate coating composition containing a polyester resin, a melamine resin and titanium oxide, wherein the polyester resin has a number average molecular weight of 1,000 to 4,000 and an acid value of 4 to 15 mg KOH. / G,
The titanium oxide has a hydroxyl value of 50 to 200, a basicity of 10 × 10 ^{−5 to} 12 × 10 ⁻⁵ mol / g, and an acidity of 0.4 × 10 ^{−5 to} 0. 8 × 10 ^-5 m
ol / g.

The polyester resin preferably has a number average molecular weight of 1500 to 3000, an acid value of 6 to 10 mg KOH / g, and a hydroxyl value of 90 to 150. The melamine resin is preferably at least one selected from the group consisting of butylated melamine, methyl / butylated melamine, and fully alkylated methylated melamine. Furthermore, the mixing ratio of the polyester resin and the melamine resin is 90/10 to 50 /
Preferably it is 50. Hereinafter, the present invention will be described in detail.

The present inventors have found that the type of titanium oxide generally contained in an intermediate coating composition affects the appearance of an intermediate coating film obtained from the intermediate coating composition. Was found. Then, by using a basic titanium oxide having a specific range of basicity and acidity in combination with a polyester resin and a melamine resin, to improve the base layer concealing property and appearance of the obtained intermediate coating film. The present invention has been found to provide a film having satisfactory coating properties such as chipping resistance, water resistance and weather resistance.

The intermediate coating composition of the present invention contains a polyester resin and a melamine resin as a film-forming resin. The polyester resin is a basic resin component that imparts chipping resistance, hiding of the base, surface smoothness, and the like, which are the essential functions of the intermediate coating composition. The polyester resin has a number average molecular weight of 1,000 to 4,000.
It is. When it is less than 1,000, the coating film performance such as chipping resistance and water resistance is deteriorated. If it exceeds 4,000, the appearance (skin) of the obtained coating film may be reduced, and the viscosity at the time of application may be too high. Preferably, 1500
~ 3000. In the present specification, the number average molecular weight is a value in terms of polystyrene measured by gel permeation chromatography.

The above polyester resin has an acid value of 4 to 15.
mg KOH / g. If it is less than 4 mgKOH / g, the curability will be poor, and if it exceeds 15 mgKOH / g, the water resistance will decrease. Preferably, 6 to 10 mg KO
H / g. The polyester resin has a hydroxyl value of 5
0 to 200. If it is less than 50, the curability will be poor, and if it exceeds 200, the water resistance will decrease. Preferably, it is 90 to 150.

The above polyester resin can be produced by polycondensing a polyhydric carboxylic acid and / or acid anhydride as an essential component with a polyhydric alcohol. The polyvalent carboxylic acid and / or acid anhydride is not particularly limited. For example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid , Methyltetrahydrophthalic anhydride, hymic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid,
Itaconic acid, adipic acid, azelaic acid, sebacic acid,
Succinic acid, succinic anhydride, dodecenylsuccinic acid, dodecenylsuccinic anhydride and the like.

The polyhydric alcohol is not particularly restricted but includes, for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol,
Dipropylene glycol, polypropylene glycol,
Neopentyl glycol, 1,2-butanediol,
1,3-butanediol, 1,4-butanediol,
2,3-butanediol, 1,5-pentanediol,
1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl-
2,2-dimethyl-3-hydroxypropionate,
2,2,4-trimethyl-1,3-pentanediol,
Examples include polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol and the like.

As a reaction component other than the above-mentioned polycarboxylic acid and / or acid anhydride and polyhydric alcohol, monocarboxylic acid, hydroxycarboxylic acid and the like may be contained. It may also contain a drying oil, an anti-drying oil and their fatty acids. Others include, for example, Kajura E
It is also possible to contain a monoepoxide compound such as (manufactured by Shell Chemical Company) or a lactone. The lactone is capable of forming a graft chain by ring-opening addition of a polyhydric carboxylic acid and a polyhydric alcohol to polyesters,
For example, β-propiolaclone, dimethylpropiolactone, butyllactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprylolactone, crotlactone, δ-valerolactone, δ-caprolactone, and the like. However, ε-caprolactone is particularly preferred. The above-mentioned polycarboxylic acids and / or acid anhydrides, polyhydric alcohols, other lactones, etc. may be used alone or in combination of two or more.

The above polyester resin is preferably blended in the solid content of the intermediate coating composition at a ratio of 20 to 50% by weight. If it is less than 20% by weight, the dispersion becomes poor and the gloss is reduced, and if it exceeds 50% by weight, the concealing property of the base becomes insufficient. More preferably, it is 30 to 40% by weight.

In the present invention, the above-mentioned melamine resin is not particularly limited, and may be used as long as it is generally used as a curing agent in paints. Butylated melamine, methyl / butylated melamine and full alkyl It is preferably at least one selected from the group consisting of methylated melamine.

Above all, an average of less than 5 bound formaldehyde, an average of 1.0 to 3.5 methyl ether groups, an average of 0.5 to 3.0 butyl ether groups and an average of 1.0 per melamine nucleus. ~ 3.0 imino groups, average 1.0
Methyl / butylated melamine having less than one methylol group and having an average degree of polymerization of the melamine nucleus of 1.5 to 3.5 is effectively used. The reason for this is that the methyl / butylated melamine has a low degree of condensation and a low rate of reaction initiation, which increases the degree of flow during heating and enhances surface smoothness. This is because the coating rate is low and the coating film performance is excellent. Therefore, if any one of the number of bonded formaldehyde, methyl ether group, butyl ether group, imino group and methylol group and the average degree of polymerization is less than the above range, the curability of the coating film becomes poor, and if it exceeds the above range, the coating film becomes hard. The film becomes hard and brittle,
Chipping resistance is reduced.

However, when there is a possibility of baking at a low temperature, the above-mentioned methyl / butylated melamine alone may not provide sufficient coating film performance.
It is preferable that butylated melamine and / or melamine having an imino group and a methylol group content higher than the above ranges are partially blended and used.

The above-mentioned butylated melamine, methyl / butylated melamine and fully alkylated methylated melamine can usually be used in combination with an acid catalyst. The acid catalyst is not particularly limited, for example, p-toluenesulfonic acid,
Dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid and the like can be mentioned.

In the melamine resin, the mixing ratio of the polyester resin and the melamine resin is 90% by weight based on the solid content.
/ 10 to 50/50. If the amount of the melamine resin is too small, the curability will be insufficient, and the hardness and water resistance of the resulting coating film will be poor. If the amount of the melamine resin is too large, the formed coating film will be hard and brittle, and the chipping resistance and the adhesion will decrease. More preferably, it is 80/20 to 60/40.

The mixing ratio of the melamine resin intermediate coating composition to the solid content is preferably 5 to 30% by weight. If it is less than 5% by weight, the curability becomes insufficient, and if it exceeds 30% by weight, the formed coating film becomes hard and brittle. More preferably, it is 15 to 25% by weight. The polyester resin and the melamine resin may be used alone or in combination of two or more.

The intermediate coating composition of the present invention contains titanium oxide. In the present invention, the titanium oxide has a basicity of 10 × 10 ^{−5 to} 12 × 10 ⁻⁵ mol / g.
And an acidity of 0.4 × 10 ^{−5 to} 0.8 × 10 ⁻⁵ mo
Use what is 1 / g. By using titanium oxide having the basicity and acidity in the above range, the basicity of the titanium oxide surface is increased, so in the intermediate coating composition combining the titanium oxide and a polyester resin and a melamine resin, It is considered that the curing speed is slowed and the flow property is generated at the time of heating, so that it is possible to improve the smoothness of the surface of the obtained coating film and the concealing property of the base. Therefore, if the basicity and the acidity are out of these ranges, the base coat concealing property for the electrodeposition coating film and the surface smoothness of the obtained coating film will be poor.

In the present specification, the above basicity means the amount of a base present on the surface of titanium oxide.
According to the following method using perchloric acid as an acid and potassium methoxide as a base, the amount of a base present on a unit amount of titanium oxide is determined by a back titration method.

That is, 2 g of titanium oxide and 30 ml of a solution of 10 ^-2 M perchloric acid in methyl isobutyl ketone (MIBK)
Into a Erlenmeyer flask, stopper tightly, and cool at 20 ℃
In an ultrasonic cleaner controlled for 1 hour. Supernatant liquid 1 obtained by centrifuging titanium oxide from this dispersion liquid
0 ml is diluted with a 4: 1 mixture of MIBK and methanol and titrated (back titration) with a 10 ^-2 M potassium methoxide solution. From the amount of perchloric acid consumed by the base on the titanium oxide surface, the basicity per gram of titanium oxide is determined.

In the present specification, the above-mentioned acidity means the amount of acid present on the surface of titanium oxide. According to the following method using perchloric acid as an acid and dimethylethanolamine (DMEA) as a base, The amount of acid present on a unit amount of titanium oxide surface is determined by a back titration method.

That is, 2 g of titanium oxide and 10 ^-2 MDME
30 ml of the MIBK solution of A is placed in an Erlenmeyer flask, sealed, and then subjected to ultrasonic dispersion for 1 hour in an ultrasonic cleaner controlled in a thermostat at 20 ° C. 10 ml of the supernatant obtained by centrifuging titanium oxide from this dispersion was diluted with MIBK and titrated with a 10 ⁻² M perchloric acid in MIBK (back titration).
I do. DMEA consumed by acid on titanium oxide surface
The acidity per 1 g of titanium oxide is determined from the amount of

As the above-mentioned titanium oxide, for example, commercially available products such as titanium dioxide R-61N manufactured by Sakai Chemical Industry Co., Ltd. can be used. The method for producing the titanium oxide is not particularly limited as long as it is a method capable of obtaining titanium oxide having the above basicity and the above acidity, and examples thereof include a chlorine method and a sulfuric acid method.

The above-mentioned chlorine method can be carried out in accordance with a conventionally known method. However, natural rutile or synthetic rutile as a raw material is chlorinated in a high-temperature reduction state, and titanium is converted to TiCl _4.
In addition, impurities such as iron are converted into chlorides such as FeCl ₂ , and impurities such as iron chloride which are solidified by cooling are converted into liquid TiCl
_After being separated from _4, and further purified by rectification, a nucleating agent is added and instantaneously reacted with oxygen at a temperature of 1000 ° C. or higher to obtain rutile titanium oxide. Thereafter, finishing operations such as pulverization, sizing, and surface treatment are performed to obtain titanium oxide as a pigment.

In the above sulfuric acid method, raw ore is distilled with sulfuric acid, and T
i, Fe, etc. are extracted as sulfates, iron sulfate is removed by crystallization and separation, and the remaining titanyl sulfate solution is filtered and purified, then subjected to thermal hydrolysis, and the precipitated hydrous titanium oxide is filtered off to remove impurities. After removing by washing and adding a particle size adjusting agent, etc., 800
By firing at ~ 1000 ° C, crude titanium oxide can be obtained. Thereafter, it can be obtained by performing the same finishing operation as described above. In the present invention, titanium oxide having a specific basicity and acidity can be selected from the titanium oxides produced by the above-mentioned production methods and the like.
The titanium oxide may be used alone or in combination of two or more.

The titanium oxide is preferably contained in an amount of 10 to 55% by weight based on the weight of the solid content of the intermediate coating composition.
If the amount is less than 10% by weight, the resulting coating film may be inferior in base concealing property and surface smoothness. If it exceeds 55% by weight, the pigment becomes excessive and the physical properties of the coating film may be poor. More preferably, it is 15 to 45% by weight.

The above-mentioned titanium oxide is contained in the solid content weight of all the pigments of the coloring pigment, the extender pigment and the bright pigment in the amount of 2%.
It is preferable to contain 5% by weight or more. If the amount is less than 25% by weight, the resulting coating film may be inferior in base concealing property and surface smoothness. More preferably, it is 40 to 70% by weight.

In the intermediate coating composition of the present invention, in addition to the titanium oxide having the specific basicity and acidity described above, a titanium oxide having a basicity and acidity outside the above ranges may be used in combination. . Color pigments such as carbon black, barium sulfate, chromium oxide, iron oxide, phthalocyanine, and quinacridone; extenders such as talc, calcined kaolin, calcium carbonate, and magnesium silicate; aluminum foil, mica, tin foil, gold foil, and metal titanium foil And other pigments such as bright pigments such as nickel foil.

The total amount of the pigment is preferably 25 to 55% by weight based on the weight of the solid content of the intermediate coating composition.
If the amount is less than 25% by weight, the base concealing property cannot be sufficiently ensured, and if it exceeds 55% by weight, the surface smoothness of the obtained coating film is reduced. More preferably, it is 30 to 50% by weight in the solid component.

The intermediate coating composition of the present invention may be a gray intermediate coating composition containing the above-mentioned titanium oxide and carbon black as main pigments, or a top coating color and lightness. And a so-called color intermediate coating composition having the same hue and the like.

The intermediate coating composition of the present invention comprises, in addition to the above-mentioned polyester resin, the above-mentioned melamine resin, the above-mentioned titanium oxide and other optional pigments, crosslinked resin particles as a thickener, organic bentonite, and fatty acid polyamide. , Polyethylene wax, etc .; aromatic hydrocarbon-based, aliphatic hydrocarbon-based, ester-based, alcohol-based solvents, etc. as organic solvents; acid catalysts, ultraviolet absorbers, hindered amine light stabilizers, antioxidants, surfaces as other additives Adjusters, leveling agents, pigment dispersants, plasticizers, defoamers and the like may be used.

The total solid content of the intermediate coating composition of the present invention at the time of coating is preferably 40 to 70% by weight. 4
If the amount is less than 0% by weight, the viscosity is too low to cause poor appearance such as adaptation or unevenness. If the amount is more than 70% by weight, the viscosity is too high and the appearance of the coating film may be deteriorated. Preferably,
50 to 60% by weight.

The process for producing the intermediate coating composition of the present invention can be carried out in accordance with the coating form of the intermediate coating composition, and includes, for example, a pigment, a film-forming resin, a solvent and, if desired, a pigment dispersion. A method known to those skilled in the art can be used, such as mixing a compound such as an agent to obtain a pigment dispersion paste and then mixing with a curing agent.

The substrate to which the intermediate coating composition of the present invention obtained as described above is applied is not particularly limited, and examples thereof include metals, plastics, foams and the like. Is advantageously used, and a metal product capable of cationic electrodeposition coating is particularly preferably used.
The metal product is not particularly limited, for example, iron,
Simple metals such as copper, aluminum, tin, and zinc, and
Alloys and castings containing these metals alone are included.
Specifically, the vehicle body and parts of automobiles such as passenger cars, trucks, motorcycles, and buses are exemplified. The above metal products are
Those which have been previously subjected to a chemical conversion treatment with a phosphate, a chromate or the like are particularly preferable.

It is preferable that an electrodeposition coating film is formed on the base material on the steel sheet which has been subjected to the chemical conversion treatment, for the purpose of imparting corrosion resistance and rust resistance. As the electrodeposition paint for forming the above electrodeposition coating film, a cationic or anion type electrodeposition coating material can be used, but a cationic type electrodeposition coating material is preferable because it gives a laminated coating film having excellent anticorrosion properties.

The method for applying the intermediate coating composition of the present invention to the above-mentioned substrate is not particularly limited, and includes, for example, an air electrostatic spray so-called “react gun”; a so-called “micro-micro (μμ) bell”. , "Micro (μ) bell", "meta bell" or the like, using a rotary atomizing electrostatic coating machine or the like.

The dry film thickness of the coating film formed from the intermediate coating composition varies depending on the application, but is preferably from 5 to 70 μm. If it exceeds 70 μm, inconveniences such as flow and armpit may occur, and if it is less than 5 μm,
Unevenness of the base cannot be concealed, resulting in film breakage.

The intermediate coating composition of the present invention is a so-called three-coat coating composition in which a base coating is applied after heating and curing the intermediate coating, and the base coating is cured or uncured and a clear coating is applied. It can be used for 3 bake coating system or 3 coat 2 bake coating system. Also, without curing the intermediate coating film, apply base paint, apply clear paint on it and then heat 3 layers at once It can also be used in a so-called three-coat one-bake coating system for curing. Furthermore, it is also possible to apply a solid base paint after applying the intermediate coating composition and use it in a two-coat one-bake coating system or a two-coat two-bake coating system without using a clear coating.
The method for preparing the electrodeposition coating material, the base coating material and the clear coating material, the dry film thickness, the curing temperature, and the like are not particularly limited, and can be performed, for example, by a conventionally known method.

The intermediate coating composition of the present invention has a basicity of 10 × 10 ^{−5 to} 12 × 10 ⁻⁵ mol / g and an acidity of 0.4 × 10 ^{−5 to} 0.8 × 10 ^{5. Since -5} mol / g of titanium oxide is contained, in the intermediate coating composition in which a specific polyester resin and a melamine resin are combined,
In the heat curing process, the curing speed is slowed down, and the flow property is generated, so that the unevenness of the electrodeposition coating film can be hidden,
A coating film having a smooth surface can be obtained. Further, it is possible to obtain a coating film excellent in performance such as chipping resistance, water resistance and weather resistance. Therefore, the intermediate coating composition of the present invention can be suitably used particularly for the body and parts of automobiles.

[0043]

EXAMPLES The present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples. Parts and% are parts by weight and% by weight, respectively.
Means Synthesis Example Synthesis of Polyester Resin 415 parts of isophthalic acid, 90 parts of adipic acid, 100 parts of trimethylolpropane, 100 parts of neopentyl glycol in a reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen inlet pipe, a water separator and a rectification tower. 200 parts, 195 parts of 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, and 2 parts of dibutyltin oxide were charged and heated to 210 ° C. However, 16
From 0 ° C to 210 ° C, the temperature was raised at a constant rate over 3 hours. The generated condensed water was distilled out of the system. 21
When the temperature reached 0 ° C., the temperature was maintained. After 1 hour, 30 parts of xylene was gradually added as a reflux solvent into the reaction vessel, and the reaction was switched to condensation in the presence of a solvent to continue the reaction. When the resin acid value reaches 8.5 mg KOH / g (solid content), the
After cooling to 0 ° C, 200 parts of ε-caprolactone was added and
After keeping the temperature at 50 ° C for 2 hours, it was cooled to 100 ° C. Further, 430 parts of xylene was added, the number average molecular weight was 2700, the acid value was 7 mgKOH / g (solid content), and the hydroxyl value was 93 mgKO.
Non-volatile content 7 containing H / g (solid content) polyester resin
0% varnish was obtained.

Example 1 70 parts of xylene and 2 parts of titanium dioxide R-61N manufactured by Sakai Chemical Industry Co., Ltd. were added to 480 parts of the polyester resin obtained in the above synthesis example.
50 parts, 135 barium sulfate B-34 manufactured by Sakai Chemical Industry Co., Ltd.
Parts, 5 parts of carbon black MA-100 manufactured by Mitsubishi Chemical Co., Ltd., and after premixing, a glass bead medium was added in a paint conditioner, and mixed and dispersed at room temperature for 1 hour to give a particle size of 5 μm or less and a nonvolatile content of 77%. A pigment dispersion paste was obtained. 96 parts of the pigment dispersion paste described above were mixed with 18 parts of Cymel 202 (80% non-volatile content; methyl / butyl mixed alkyl etherified melamine) manufactured by Mitsui Cytec, and 0.1 part of Resimix RL-4 manufactured by Mitsui Petrochemical Industries, Ltd. Thus, an intermediate coating composition was obtained.

On a 0.8 mm-thick phosphoric acid-treated steel sheet, a cationic electrodeposition paint (Powertop U-5 manufactured by Nippon Paint Co., Ltd.) was applied.
0) is applied to a dry film thickness of about 25 μm,
Bake at 0 ° C. for 30 minutes. Using the above intermediate coating composition as a thinner (butyl acetate / xylene = 1/4 (weight ratio))
And diluted to 23 seconds / 20 ° C. (# 4 Ford cup), and coated with an air spray gun to a dry film thickness of about 40 μm.
After setting for 7 to 10 minutes, baking was performed at 140 ° C. for 30 minutes.

The measurement and evaluation were performed as follows. The results are shown in Table 1. (1-1) Measurement of Acidity of Titanium Oxide 2 g of titanium oxide pigment and 30 ml of 10 ^-2 MDMEA / MIBK solution were placed in a Erlenmeyer flask, sealed, and then placed in an ultrasonic cleaner with a thermostat controlled at 20 ° C. Ultrasonic dispersion was performed for 1 hour. 10 ml of the supernatant obtained by centrifuging the pigment from this dispersion was diluted with 100 ml of MIBK, and 10 ⁻² M
It was titrated (back titration) with a MIBK solution of perchloric acid. The acidity per mol of pigment (mol / g) was determined from the amount of DMEA consumed by the acid on the titanium oxide pigment surface. An automatic titrator (Hiranuma COM-900) was used for the titration, and a glass electrode was used as the indicator electrode, and a silver-silver chloride electrode was used as the reference electrode. The perchloric acid solution was prepared by diluting a 10 ^-1 M perchloric acid-dioxane solution 10-fold with MIBK.

(1-2) Measurement of Basicity of Titanium Oxide 2 g of titanium oxide pigment and 10^-2M perchloric acid methyl iso
30 ml of butyl ketone (MIBK) solution and triangular frus
Ultrasonic with a thermostat controlled at 20 ° C after sealing
Ultrasonic dispersion was performed in a wave washer for 1 hour. Face from this dispersion
10 ml of the supernatant obtained by centrifuging the material was mixed with MIBK.
Dilute with a 4: 1 mixture of methanol and add 10 ^-2M potassium
Titration with methoxide solution. Base on titanium oxide pigment surface
Per g of pigment from the amount of perchloric acid consumed by
Was determined for its basicity (mol / g). 10^-2M Caliu
Mumethoxide solution for non-aqueous titration^-1M potassium met
The benzene / methanol solution of oxide was mixed with MIBK and methano
And a 10-fold dilution with a 4: 1 mixture of

(2-1) Evaluation of Appearance (Skin) of Coated Plate Obtained The appearance of the coated plate obtained above was evaluated according to the following evaluation criteria. ：: Very smooth. Δ: Yuzu skin is slightly observed. X: Yuzu skin is remarkable.

(2-2) Evaluation of base opacity of the obtained coated plate The base concealment of the coated plate obtained above was evaluated according to the following evaluation criteria. ：: Almost no unevenness of the electrodeposition coating film was observed. C: The unevenness of the electrodeposition coating film is somewhat hidden. X: The unevenness of the electrodeposition coating film appears almost as it is.

(2-3) Evaluation of Appearance of Obtained Coated Plate The appearance of the coated plate obtained above was evaluated by the SW value of Wavescan manufactured by Big Chemie. The smaller the value, the better the appearance was obtained.

[0051]

[Table 1]

Comparative Examples 1 to 3 Instead of titanium dioxide R-61N manufactured by Sakai Chemical Industry Co., Ltd. in Example 1, titanium dioxides R820, CR92 and CR95 were used.
The acidity and basicity of titanium dioxide were measured in the same manner as in Example 1, except that each of them was manufactured by Sakai Chemical Industry Co., Ltd. Further, a coated plate was prepared and evaluated. The results are shown in Table 1.

From Table 1, it can be seen that Comparative Example 1 using titanium dioxide having both acidity and basicity outside the range of the present invention, and comparison using titanium dioxide having basicity outside the range of the present invention. In Example 2, Comparative Example 3 using titanium dioxide whose acidity was out of the range of the present invention, all were inferior in the base material hiding property and the surface smoothness. on the other hand,
In Example 1, a material excellent in base layer concealing property and surface smoothness was obtained, and a value of 20 or less, which is a pass value, was also obtained in the SW value of the wave scan, and the finished appearance was good.

[0054]

The intermediate coating composition of the present invention has a basicity of 10 × 10 ^{−5 to} 12 × 10 ⁻⁵ mol / g and an acidity of 0.4 × 10 ^{−5 to} 0.8. Since it contains titanium oxide of ^10-5 mol / g, flowability occurs during the heating and curing process in the intermediate coating composition in which a specific polyester resin and a melamine resin are combined. The coating can be concealed and a coating film having a smooth surface can be obtained. Further, the coating film performance such as chipping resistance, water resistance and weather resistance can be improved. Therefore, the intermediate coating composition of the present invention can be suitably used for vehicle bodies and parts of automobiles.

Claims (4)

[Claims] 1. An intermediate coating composition comprising a polyester resin, a melamine resin and titanium oxide, wherein the polyester resin has a number average molecular weight of 1,000 to 4,000, an acid value of 4 to 15 mg KOH / g, and a hydroxyl value of 50 to 200. Wherein the titanium oxide has a basicity of 10 × 10 ^{−5 to} 12
× 10 ⁻⁵ mol / g and acidity of 0.4 ×
An intermediate coating composition having a content of 10 ^{−5 to} 0.8 × 10 ⁻⁵ mol / g. 2. The polyester resin has a number average molecular weight of 1
The intermediate coating composition according to claim 1, wherein the composition has an acid value of 500 to 3000, an acid value of 6 to 10 mgKOH / g, and a hydroxyl value of 90 to 150. 3. The intermediate coating composition according to claim 1, wherein the melamine resin is at least one selected from the group consisting of butylated melamine, methyl / butylated melamine and fully alkylated methylated melamine. 4. The compounding ratio of the polyester resin and the melamine resin is 90/10 to 50/50 based on the weight of the solid content.
The intermediate coating composition according to claim 1, 2, or 3.