JPS63235497A - Formation of coated film - Google Patents

Abstract

PURPOSE:To obtain a double coated film having excellent corrosion resistance and filiform corrosion resistance for an automobile body by successively coating a specified cationic paint by a wet-on-wet basis electrodeposition on the lower part of the body, heating and curing the paint, and the applying a barrier coat thereon. CONSTITUTION:A cationic paint I is electrodeposited on only the lower part of an automobile body, and then a cationic electrodeposition paint II is electrodeposited on the whole body surface while the paint I is not curd and heated to simultaneously cure both coated films. Namely, only the lower part of the body is dipped in the bath of the pint I, and electrodeposited. The electrodeposited body is pulled up from the bath, washed with deionized water, dipped in the bath of the paint II and electrodeposited by completely dipping, washed with water, and heated to cure the electrodeposited film. The electrodeposition paint I is composed of a resin binder and >=one kind of pigment B, 5wt.% of which has >=100 oil absorption. The paint II consists essentially of a resin binder C and a pigment D, and is the emulsion type cationic electrodeposition paint with the total oil absorption of the pigment D smaller than that in the paint I.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides excellent corrosion resistance of an automobile body (hereinafter sometimes abbreviated as "vehicle body"), especially edge portion (end surface) corrosion resistance and thread rust resistance, and chipping resistance. (Impact peeling resistance) etc. also relate to a method of forming a good composite coating film.

Electrodeposition coating has traditionally been used as an undercoat for car bodies, and compared to organic solvent-based air spray coatings or electrostatic spray coatings, it has better coverage of the paint on the object being coated, and provides a relatively uniform coating thickness. It has been widely put into practical use because it has the advantage of being easy to obtain. In particular, in recent years, cationic electrodeposition coatings have been replaced by anionic electrodeposition coatings for car bodies where corrosion resistance is important because they form coatings with excellent corrosion resistance.

However, even if cationic electrodeposition coating is applied, the edges of the car body (e.g. corners of cut surfaces, bends, protrusions, etc.) will be affected by heat flow during heating and curing of the formed cationic electrodeposition coating. The disadvantage is that the film cannot be thick enough, resulting in poor edge coverage and poor corrosion protection.

As measures to improve such defects, there are cases in which anti-corrosion steel plates are used for the object to be painted, and there are cases in which the edges are repaired using a roller or brush using an organic solvent-based paint with good anti-corrosion properties called Edge Coat. This method is not necessarily satisfactory in terms of cost and productivity.

In addition, as a method for improving the corrosion resistance and thread rust resistance of edge portions, for example, Japanese Patent Publication No. 60-7716 and Japanese Patent Application Laid-open No. 61-198
No. 195998, etc., proposes applying multiple electrodeposition paints. However, in the former case, since the first layer of electrocoating paint contains conductive powder, uneven coating and skin irritation are likely to occur in the first layer of paint, and even if the second layer of electrocoating paint is repeatedly applied, areas other than the edges will be removed. The anti-corrosion properties and smoothness of the coating film are insufficient for the latter, and on the other hand, the time required for the first electrodeposition coating is as short as 0.5 to 2 seconds, making it extremely difficult to control the coating accurately. It has poor applicability on a practical line, and it is actually difficult to form a coating film only on the edges of a complex-shaped car body by short-time electrodeposition coating, so the coating film is formed on areas other than the edges as well. Therefore, the smoothness of the coating film after the second electrodeposition coating is poor.

In addition, when the outer panel of an automobile is finished by electrocoating as described above and then applying intermediate and top coats, when pebbles, rock salt, etc. thrown up while driving collide with the paint film, the impact energy causes the paint film to deteriorate. Impact peeling (so-called "chipping") may occur.This chipping varies depending on the impact of the pebbles, etc., but it is often caused by not only the top coat or intermediate coat on the impacted area, but also the electrodeposition coating. As a result, the finished appearance and corrosion resistance are significantly reduced.

Therefore, the present inventors conducted extensive research to eliminate the above-mentioned defects (particularly edge coverage, smoothness, yarn rust resistance, chipping resistance, etc.), and as a result, the lower part of the car body was The objective was achieved by applying a wet-on-wet electrodeposition coating (the entire surface was coated with the second electrodeposition), heating and curing, and then applying a barrier coat, thereby completing the present invention. .

That is, the present invention provides a resin binder (A) and at least one
At least 5% by weight of the pigment (B) consists of a pigment with an oil absorption of 100 or more, and the total oil absorption of the pigment (B) is 1 per 100 g of the resin binder (A). Using a cationic electrodeposition paint (I) blended within the range of . Resin binder (C) and pigment (
D) is the main component, and the minimum deposition current density is 0 and 7 t.
sA/cm2 or less and degree of emulsion 80% by weight
An emulsion-type cationic electrodeposition paint (II) having the following F and a total oil absorption amount of pigment (D) smaller than that in the cationic electrodeposition paint (I) is cationically electrodeposited on the entire surface of the automobile body, and then After heating and curing the electrodeposited coating, the electrocoated surface has a static glass transition temperature of 0 to -7.
The present invention relates to a method for forming a coating film, which comprises applying a barrier coat that forms a coating film at a temperature of 5° C., and further coating an intermediate coating and/or top coating as necessary.

In the method of the present invention, by electrocoating only the lower part of the car body with a cationic electrodeposition paint containing as an essential component a pigment with an oil absorption of 100 or more, the corrosion resistance of the edge parts, which are often present in the lower part of the car body, can be improved. By applying an emulsion-type cationic electrodeposition paint having a specific minimum electrodeposition current density to the entire surface of the car body, including the uncured electrodeposition coating surface, only the lower part of the car body is coated. It is possible to improve the coating surface condition (especially smoothness) and thread rust resistance of the first layer of electrocoated film, and to improve chipping resistance by applying a barrier coat after electrocoating the entire surface. Ta.

In the present invention, the cationic electrodeposition paints (I) and (rI) to be applied in the first and second coats are resin binder components (A) and (C), respectively, which are resin binders normally used in electrodeposition paints. agents, such as polyamine resins such as amine-added epoxy resins, such as (1) adducts of polyepoxides with primary mono- and polyamines, 2-edge mono- and polyamines, or 1.2 mixed polyamines (e.g., U.S. Pat. 984,299); (ii) polyepoxide and ketiminated primary amino group-containing 2
G11) Reactants obtained by etherification of polyepoxides with hydroxy compounds having ketiminated primary amino groups (e.g. If the composite cured coating film formed by the present invention is required to have good weather resistance, the resin binder (A) and/or (C ), an amine group-containing or nonionic acrylic resin with excellent weather resistance may be used in combination with the amine-added epoxy resin. The group-containing acrylic resin may be used alone.

The above-mentioned amine-added epoxy resin and amino group-containing acrylic resin can be cured using a polyisocyanate compound blocked with alcohol to form an electrodeposited coating.

In addition, amine-added epoxy resins that can be cured without using blocked isocyanate compounds can also be used, such as resins in which β-hydroxyalkyl carbamate groups are introduced into polyepoxide materials (for example, JP-A-59-155470). ); type of resin that can be cured by transesterification (for example, JP-A-55
-80438) etc. can also be used.

The preparation of a cationic aqueous dispersion using the resin binder described above is usually carried out by neutralizing the resin binder with an insoluble organic acid such as formic acid, acetic acid, or lactic acid.

The cationic electrodeposition paint whose main component is the aqueous dispersion thus obtained further contains a pigment, and in the cationic electrodeposition paint (I) used for electrodeposition coating only the lower part of the car body, the oil absorption amount is increased as the pigment (B). 100 or more, preferably 150
The above pigments are contained in at least 5% by weight, preferably 10% by weight or more, more preferably 2% by weight of the total amount of pigment (B).
It is necessary to contain 0% to 95% by weight.

The blending amount of the pigment (B) with respect to the resin binder (A) is such that the total oil absorption amount of the pigment (B) is t, ooo to 10,000, preferably 1.5 to the resin binder (A) long.
00-9,000. More preferably 3.000 to 7.
The amount is within the range of 000.

Examples of pigments having an oil absorption of 100 or more which are added to the pigment (B) essential to the above-mentioned cationic electrodeposition paint (I) include silicon dioxide pigments such as anhydrous silicon dioxide and hydrated amorphous silicon dioxide, and carbon-based pigments. Examples include pigments, preferably silicon dioxide pigments.

Commercially available silicon dioxide pigments with an oil absorption of lOO or more include, for example, Nippon Aerosil Co., Ltd.'s product name "Erosil 200" (oil absorption amount 143-183), Fuji Davison Chemical Co., Ltd.'s product name "Syroid 161J (oil absorption amount)". 128～
135), “Thyroid 244J (oil absorption 270~
330), "Thyroid 308J (oil absorption 170 ~
220).

"Thyroid 404J (oil absorption 170-230).

"Thyroid 978J (oil absorption: 180-230) can be mentioned, and carbon-based pigments include furnace-type or channel-type carbon black, which is usually used as a black pigment (oil absorption: usually 100-230).
130), such as "Carbon BAGJ" manufactured by Columbian Carbon Company, USA.

In the present invention, if the carbon-based pigment is used alone as a pigment with an oil absorption of 100 or more, since this pigment has conductivity, the coating workability of the cationic electrodeposition paint (1) is somewhat reduced. Preferably, it is blended in combination with a silicon dioxide pigment. In this case, the combined ratio of the silicon dioxide pigment and the carbon pigment is 9515 to 6 by weight.
It can be within the range of 0/40, preferably 90/lo to 70/30.

In addition to the above-mentioned pigments having an oil absorption of 100 or more, the pigments to be added to the cationic electrodeposition paint (I) used in the present invention include pigments commonly used in electrodeposition paints, such as red iron and titanium white. Inorganic coloring pigments; pigments with an oil absorption of less than 100, such as extender pigments such as talc, clay, and calcium carbonate, are combined with the resin binder (pigment CB).
A) Total oil absorption against toog is 1,000 to 10.0
They can be used together as long as they fall within the range of 00.

The oil absorption amount of each pigment in the present invention is JISK 51
It is measured by the following method using 01-78 (pigment test method).

Accurately weigh a specified amount of sample to the nearest 10 mg on parchment paper and transfer it to a frosted glass plate. Calculate the amount of boiled linseed oil required from the expected oil absorption of the sample in advance, and weigh about 90% of it. Take the sample from the microbiulet to the tip of the probe, and immediately use the spatula to thoroughly knead the sample on the frosted glass plate and boiled linseed oil for about 5 minutes.

Next, add 1-2 drops of boiled linseed oil to the spatula and mix evenly. The process of adding 1-2 drops of oil to the boiled flax and kneading it is repeated, and the end point is when the whole sample becomes a hard, uniform, putty-like mass for the first time, and the boiled flax has been added to the boiled flax until then. Reduce the amount of oil to 0. Read up to OlwJ.

Next, the oil absorption amount is calculated using the following formula.

Here, A: Oil absorption amount S: Mass of sample (g) L: Amount of boiled linseed oil used (g) Also, the total oil absorption amount is calculated by adding the amount of each pigment (g) to 100 g of resin using the above formula. It is calculated as the sum of the values obtained by multiplying the oil absorption values of each pigment. It is a value.

Among the pigments (B) used in the present invention, when the amount of the pigment with an oil absorption of 100 or more is less than 5% by weight of the total amount of the pigment (B), the coating film of the cationic electrodeposition paint (II) is There is a tendency for precipitation to become difficult.

Further, in the present invention, if the total oil absorption amount of the pigment (B) in the cationic electrodeposition paint (1) used for electrodeposition coating only on the lower part of the car body is less than t, ooo, the edge On the other hand, to, oo
If it exceeds 0, pigment aggregation tends to occur, resulting in filter clogging and paint surface abnormalities due to pigment agglomerates.
Problems such as skin irritation (such as skin irritation) may occur.

In the present invention, after the electrodeposition coating is applied only to the lower part of the car body, it is not necessarily necessary to wash the electrodeposition coating with water, but it is usually preferable to wash it with water (washing with shower water or immersion). Although it is preferable to use ionized water or reverse osmosis, it is more preferable to use a liquid or the like because the corrosion resistance of the edge portion is further improved and an electrodeposited coating film with substantially no pinhole defects is formed.

Next, the cationic electrodeposition paint (■) used for electrodeposition coating the entire surface of the car body contains a resin binder (C) and a pigment (D) as main components, and has a minimum electrodeposition current density of 0.7 A/A. C@2 or less, preferably 0.5 mA/cm2 or less, more preferably 0.3 mA/cm2 or less, and emulsification degree of 80% by weight or more, preferably 85% by weight or more,
More preferably, it is 90% by weight or more, and the pigment (D
Electrodeposition paint of any composition without particular limitation as long as the total oil absorption per 100g of resin binder (C) is smaller than that of cationic electrodeposition paint (I), more preferably less than 1.000. can be used.

The minimum electrodeposition current density of the cationic electrodeposition paint (II) described above is a value measured by the following method.

A platinum plate with a surface area of 1 cm 2 and an insulated back side was used as an object to be coated and a counter electrode, respectively, and placed in an electrodeposition paint bath at a distance of 15 cm so that their surfaces faced each other. 2
At 8℃, a constant current was applied without stirring, and the time and voltage were recorded.The current density was changed every 0.05 taA/am2, and the sudden increase in voltage due to the increase in resistance due to electrodeposition of the paint was measured by 3. The current density that occurs in the vicinity of 3 minutes or more than 3 minutes is defined as the minimum deposition current density.

Furthermore, the degree of emulsion of the cationic electrodeposition paint (If) described above is an index representing the proportion (% by weight) of particles truly suspended as particles in the electrodeposition paint, and is determined by the following procedure. .

First, a clear emulsion with a solid content of 15 to 20% by weight that does not contain pigments or other ingredients, about 35 c.
Put c in a cell and seal it to 28.0OOR, P, at 6
Centrifuge for 0 minutes. Pipette 2 cc of the supernatant of the separated sample and dry it at 120°C for 1 hour to remove the non-volatile content.
Measure l (%).

Next, turn the cell upside down and drain off the supernatant.

Invert for an additional 10 minutes and remove the supernatant layer. After homogenizing the remaining sediment layer with a glass rod, 1.5 to 2.0 g was accurately weighed, dried at 120° C. for 1 hour, and the nonvolatile content N2 (%) was measured.

Next, approximately 2 cc of the clear emulsion was accurately weighed, dried at 120°C for 1 hour, and the nonvolatile content No. (%) was measured. The degree of emulsification is a value determined by the following formula.

In the present invention, if the minimum electrodeposition current density of the cationic electrodeposition paint (II) exceeds 0.7 mA/cm2, it becomes difficult to ensure a film thickness that provides coating surface smoothness.

Furthermore, if the degree of emulsion is less than 80% by weight, the second layer of electrodeposition coating will mix with the first layer of electrodeposition coating in the lower part of the car body, resulting in poor edge corrosion resistance and coating surface smoothness. There is a tendency to decrease.

The automobile body in the coating method of the present invention is a passenger car, bus, truck, motorcycle, microbus, etc.
The lower part has many edges and is often exposed to a harsh corrosive environment.

In the present invention, both electrodeposition paints were applied by electrodepositing only the lower part of the body with the cationic paint (I), and then electrodepositing the entire surface of the body with the cationic paint (II) without curing. Thereafter, both coating films are cured simultaneously by heating. That is, only the lower part of the car body is immersed in a bath of cationic electrodeposition paint (I), and the body is coated with cationic electrodeposition, then taken out of the bath, washed with deionized water, etc., and then air-dried as necessary. Thereafter, the automobile body is completely immersed in a bath of cationic electrodeposition paint (n) to be coated with cationic electrodeposition, followed by washing with water and heating to harden the electrodeposition coating.

In the present invention, cationic electrodeposition paint (I) and (I
As a method and apparatus for applying electrodeposition coating to a car body using I), methods and apparatus known per se that have been conventionally employed in cationic electrodeposition coating can be used,
It is desirable to use the vehicle body as a cathode and a carbon plate as an anode.

The electrodeposition coating conditions that can be used are not particularly limited, but generally, bath temperature: 20 to 30°C, voltage: 100°C.
~400V (preferably 150~350V), current density: 0,01~3A/dm2, current application time: 30 seconds ~
It is preferable to electrodeposit with stirring, electrode area ratio (A/C): 6/1-1/6, distance between electrodes = 10 to 100 cm.

The film thickness (dry state S) of the first electrodeposition coating film formed only on the lower part of the car body using the above electrodeposition coating method is 5 to 30-1.
It is preferably within the range of 1O to 25-, and the thickness of the second electrodeposited coating (dry state) that is then formed on the entire surface of the car body.
is 5-70. , preferably in the range 1O to 50 #uII.

In the present invention, the second electrodeposition coating is performed with the first electrodeposition coating formed only on the lower part of the car body uncured, which is useful for forming a composite coating and also for improving adhesion. Although preferred and a necessary condition, the first electrodeposited coating may be heated, for example, at 120° C. for about 10 minutes, or heated to the extent that moisture is removed using hot air. Therefore, it should be understood that the term "uncured state" in the present invention includes a semi-cured state.

The electrodeposited coating formed on the car body has a coating thickness of about 150~ after being washed with water.
It is hardened by baking at about 180°C. The total electrodeposited coating thickness at the lower part of the car body is determined by the above-mentioned first self-adhesive coating thickness and second coating thickness.
The total thickness of the electrodeposited coating can be the total thickness of the electrodeposited coating, but from the viewpoint of economy etc., the total coating thickness of the electrodeposited coating is generally 15 to 80I.
It is desirable that it be within the range of tIM.

In the present invention, after the electrodeposition paint is applied as described above, a barrier coat is further applied.

Although the term "barrier coat" is not commonly used,
In the present invention, the solvent or dispersion medium is water and/or an organic solvent that has specific physical property values and is capable of forming a coating film that achieves the objectives of the present invention such as improving chipping resistance. It is a composition.

Specifically, the aqueous barrier coat to be applied to the second electrodeposited surface is an aqueous barrier coat that uses water as the main solvent or dispersion medium and has a static glass transition temperature of 0 to -75°C. A composition is used.

The composition has an aqueous vehicle and water as main components, and can further contain a viscosity imparting agent, an organic solvent, a coloring pigment, an extender pigment, an anticorrosive pigment, etc., as necessary.

As the aqueous vehicle, it is preferable to use thermoplastic resins that have excellent adhesion to the above-mentioned electrodeposited coating film and the middle (top) coating film described below, and have a static glass transition temperature within the above range. Things can be mentioned.

■Modified polyolefin resin: For example, propylene-ethylene copolymer (in molar ratio, 4
0 to 80: preferably 60 to 20) and 1 to 50 parts by weight, preferably 10 to 20 parts by weight of a chlorinated polyolefin (for example, polypropylene with a chlorination rate of about 1 to 60% by weight) (both of which are based on the copolymer). or 0.1 to 50 parts by weight, preferably 0.3 to 2.0 parts by weight of maleic acid or anhydride per 100 parts by weight of the propylene-ethylene copolymer. Examples include graft polymers obtained by graft polymerization. It is generally preferred that the number average molecular weight of these copolymers, chlorinated polyolefins and graft polymers range from about 5.000 to about 300,000.

When making the modified polyolefin resin water-based, the propylene-ethylene copolymer can be made water-based by anionic, cationic or nonionic emulsion polymerization, which is known per se, and the graft polymer has a carboxyl group. The chlorinated polyolefin can be water-solubilized or water-dispersed by neutralizing it, and the chlorinated polyolefin can be water-dispersed, for example, in the presence of an emulsifier.

■Styrene-butadiene copolymer: Styrene content is approximately 1 to 80% by weight, preferably 10% by weight.
An aqueous dispersion of the copolymer is obtained by copolymerizing styrene and butadiene in the presence of a polymerization modifier, catalyst, soap, and water.

The polymerization temperature is preferably 100°C or less, and the number average molecular weight of the copolymer is about to, ooo to about 1.000,00
It is preferably within the range of 0.

(2) Butadiene resin: This is an aqueous dispersion composition obtained by polymerizing in (1) above without using styrene.

(2) Acrylonitrile-butadiene copolymer: Acrylonitrile content is 1 to 50% by weight.

Preferably, it is a 10 to 40% by weight copolymer, comprising acrylonitrile and butadiene, optionally containing functional monomers such as acrylic acid and methacrylic acid, and the presence of a polymerization catalyst, molecular weight regulator, surfactant, etc. The copolymerization temperature obtained by nibbledion polymerization in water is preferably 100° C. or less, and the number average molecular weight of the copolymer is suitably within the range of about 10.000 to about 1.000,000.

■Polybutene: Mainly inbutylene, mixed with normal butylene as necessary, polybutene obtained by low-temperature polymerization is heated to 50-70℃ in the presence of an emulsifier, water is added, and stirred uniformly and thoroughly. obtained by The number average molecular weight of the resin is preferably within the range of about 1.000 to about 500,000.

■Acrylic resin The main component is diacrylic acid ester and/or methacrylic acid ester, and if necessary, functional additives such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, etc.
or) It can be obtained by emulsion polymerizing a vinyl monomer component mixed with other polymerizable unsaturated monomers to form an aqueous dispersion; or by solution polymerizing and then converting it into an aqueous solution or aqueous dispersion. Examples of the acrylic esters include ethyl acrylate, propyl acrylate, n-butyl acrylate, 1so-butyl acrylate, 3-pentyl acrylate, hexyl acrylate, 2-hebutyl acrylate, octyl acrylate, 2-octyl acrylate, nonyl acrylate, lauryl Acrylate, 2-ethylhexyl acrylate, 2-ethylbutyl acrylate, etc. are particularly suitable, and examples of the methacrylic acid ester include pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate, stearyl methacrylate, etc. is particularly preferred.

The static glass transition temperature of the homopolymers derived from these acrylic esters and methacrylic esters exemplified here is all 0°C or lower, and one or more types selected from these seven polymers are used. Acrylic esters and methacrylic esters are suitable as monomers for forming the above-mentioned acrylic resin.

The acrylic resin has a number average molecular weight of about s, ooo to 1.0.
Preferably, it is in the range of 00,000.

■In addition to these, we also have natural rubber latex, methyl methacrylate-butadiene copolymer emulsion, etc. Lichloroprene emulsions, polyvinylidene chloride emulsions, and the like can also be used as aqueous vehicles.

The organic solvent-based barrier coat to be applied to the electrodeposited film surface uses an organic solvent as a main solvent or dispersion medium whose static glass transition temperature of the formed film is O to -75°C, specifically an organic solvent and a dispersion medium. The main component is a vehicle component.

Examples of the vehicle component include those exemplified for the aqueous barrier coat described above, and vehicles obtained by removing parent wood groups (or neutralizing groups) from these can also be used.

Suitable organic solvents are those that can dissolve or disperse these vehicles, such as aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane, heptane, octane, and decane; trichloroethylene; , chlorinated hydrocarbons such as perchlorethylene, dichloroethylene, dichloroethane, dichlorobenzene;
It is also possible to add ketone solvents such as methyl ethyl ketone and diacetoalcohol; alcohol solvents such as ethanol, propatool and butamele; and cellosolve solvents such as methyl cellosolve, butyl cellosolve and cellosolve acetate.

The coating film formed by the barrier coat has a static glass transition temperature (Tg) of O to -75°C, preferably -30 to -
It is important that the Tg is within the range of 60°C, particularly preferably -40 to -55°C; if the Tg is higher than 0°C, the chipping resistance, corrosion resistance, physical performance, etc. of the final composite coating will not be improved; On the other hand, if the temperature is lower than -75°C, the water resistance, adhesion, etc. of the final composite coating will deteriorate, which is not preferable.

In the present invention, if these vehicles themselves have a static glass transition temperature within the above range, they can be used as a barrier coating by themselves, but if the vehicle deviates from the above range or even within the range, the static glass transition temperature cannot be used. When it is desired to finely adjust the glass transition temperature, a viscosity imparting agent can be added as necessary. The viscosity-imparting agent may be a resin having good compatibility with the vehicle, such as rosin or petroleum resin (
coumaron resin), ester gum, epoxy-modified polybutadiene, low-molecular weight aliphatic epoxy resin, low-molecular weight aliphatic bisphenol type epoxy resin, polyoxytetramethylene glycol, vinyl acetate-modified polyethylene, etc., or emulsified dispersions thereof. The blending amount is 1 to 50 parts per 100 parts by weight of the vehicle (solid content).
It is preferably within the range of parts by weight (as solid content).

In addition, extender pigments, color pigments, anticorrosion pigments, etc. may be added to the barrier coat.
It is preferably within the range of 150 parts by weight.

In particular, by incorporating an anti-corrosion pigment into the barrier coat, the anti-corrosion properties can be significantly improved compared to when the anti-corrosion pigment is included in the electrodeposition coating.

Regarding the coating film forming the barrier coat, it is essential that the static glass transition temperature is within the above range. ,oo.

%, especially 300 to 700%, whereby the object of the present invention can be achieved even more markedly.

In the present invention, these barrier coats are applied to the cured electrodeposition coating surface, but the coating method is not limited, and examples include spray coating, spacing coating, dipping coating, melt coating, electrostatic coating, etc. The thickness of the coating film is preferably 1 to 20 IL, particularly 5 to 10K, based on the dry coating film.

The static glass transition temperature of the formed coating film of the barrier coat used in the present invention was measured using a differential scanning calorimeter (DSC-1 manufactured by Daini Seikokin Co., Ltd.).
o type), and the tensile strength elongation at break is measured using a universal tensile tester with a constant temperature bath (Shimabara Autograph S-D).
This is the value measured using a mold), and the length of the sample is 20-■
The tensile speed was 201/min. The samples used for these measurements were coated with the barrier coat on a tin plate so that there were 25 tiles based on the formed coating film, and heated at 120°C for 3
After baking for 0 minutes, it was isolated by the mercury amalgam method and used.

Barrier Coat When applying an intermediate coat (or top coat) on the paint surface, it is preferable to bake the barrier coat in advance, but it is also possible to apply the intermediate coat (or top coat) paint wet-on-wet without baking. The baking temperature of the barrier coat is 8.
0-160°C, especially 80-130°C are suitable.

Intermediate paint: A paint that is applied to the above-mentioned barrier coated surface as necessary, and is a well-known intermediate paint that has excellent adhesion, smoothness, sharpness, overpaint resistance, weather resistance, etc. can be used. Specifically, examples include thermosetting intermediate coatings whose main components are a short oil having an oil length of 30% or less, an ultra-short oil alkyd resin, or an oil-free polyester resin and an amino resin. These alkyd resins and polyester resins preferably have a hydroxyl value of 60 to 140, an acid value of 5 to 200, and use unsaturated oil or unsaturated fatty acid as the modified oil. ) Etherified melamine resin, urea resin, benzoguanamine resin, etc. are suitable. These compounding ratios are 65 to 85% of alkyd resin and/or oil-free polyester resin based on solid content weight.
%, especially 70 to 80%, amino resin 35 to 15%, especially preferably 30 to 20%. Furthermore, at least a part of the above amino resin can be replaced with a polyisocyanate compound or a blocked polyisocyanate compound. .

The form of the intermediate coating is most preferably an organic solution type, but
In the present invention, the hardness (pencil hardness) of the intermediate coating film is 3B.
It is preferably within the range of 20°C or more, and
The intermediate paint may contain extender pigments, coloring pigments, other paint additives, and the like, as required.

In the present invention, the intermediate coating paint can be applied to the barrier coat surface by the same method as the barrier coat, and the coating film thickness is preferably in the range of 10 to 50 IL based on the cured film. The curing temperature varies depending on the vehicle component, and when curing by heating, it is preferably heated at a temperature of 80 to 170°C, particularly 120 to 150°C.

Top coat: A paint that is applied to the barrier coated surface or the intermediate coated surface as necessary, and is used to impart cosmetic properties to the vehicle body. Specifically, the finished appearance (image clarity,
It is already known in itself to form a coating film with excellent properties such as smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance, and hardening properties. Paints can be used, including paints whose vehicle main component is an ami/acrylic resin system, an amino alkyd resin system, an amino polyester resin system, or the like. The form of these paints is not particularly limited, and may include organic solution type, non-aqueous dispersion type,
Can be used in aqueous (dispersed) liquid type, powder type, high solid type, etc. Drying φ curing of the coating film is carried out by drying at room temperature, heating drying, irradiation with active energy, etc. In the present invention, the coating film formed by these top coatings has a pencil hardness within the range of 2B to 9H (20°C). It is desirable to have this.

The top coating paints that can be used in the present invention are classified into enamel paints that contain metallic pigments and/or coloring pigments in paints that use the above-mentioned vehicle main component, and clear paints that contain no or little of these pigments. . 1) Bake using these top coats,
Topcoat finishing can be done by methods such as 2-coat 1-bake, 2-coat 2-bake, 3-coat 1-bake, 3:1-to 2-bake, and 3-coat 3-bake.

The performance of the composite coating film formed by applying cationic electrodeposition paint to the car body as described above (two coats applied only to the lower part of the car body) - barrier coating = (intermediate coating) - coating, is as follows: It has excellent appearance (e.g. smoothness, gloss, sharpness, etc.), water resistance, weather resistance, etc., and has particularly improved chipping resistance, corrosion resistance of steel edges, physical properties, etc. It is.

In particular, as mentioned above, the first and second electrodeposition coatings are performed wet-on-wet on the lower part of the car body, so the second electrodeposition coating coats the surface of the first electrodeposition coating. The first electrodeposited layer and the second electrodeposited layer form a multilayer coating. That is, the first electrodeposited coating containing a highly oil-absorbing pigment covers the edges, and the second electrodeposition coating takes care of the smoothness of the coated surface and the uniform film formation of the coating. As a result, the multilayer electrodeposited coating on the lower part of the car body has excellent corrosion resistance at the edges and is also in excellent coating surface condition with no pinhole defects. Furthermore, since a barrier coat is applied to the surface of the electrodeposited film and then an intermediate coat or top coat is applied, the chipping resistance and physical performance of the composite film are significantly improved.

According to the method of the present invention, the corrosion resistance of the edges of the lower part of the car body, which was a serious defect of conventional cationic electrodeposition coatings, is significantly improved, and the coating surface is also excellent in smoothness, and is resistant to chipping. It also has good properties and physical properties, making it the most effective coating system for automobile bodies.

The present invention will be specifically explained below with reference to Examples and Comparative Examples. In principle, 0 parts and % mean parts by weight and % by weight.

Engineering Sample (1) Object to be coated: Car body (size: 300 x 90 x 0.8 cm) chemically treated with Bonderite #3004 (manufactured by Nippon Barker Rising, zinc phosphate system).

(2) Cationic electrodeposition paint (I) (I-A) Water-soluble heat-formable poxy-based boria 100 (parts) Mino
Fat 1) Carbon black (Zero 2) [40] 3 Graphite [40] 5 Refined clay [43] 15 Thyroid 244 (
Request 3) [300] 26 Resin: Pigment (solid content weight ratio) = 100:49 Total oil absorption 8,765 (Book 1) Kansai Paint Company Nireclone No. 9000
A corresponding water-soluble epoxy polyamino resin, which is obtained by making an epoxy polyamino resin with a resin base value of 80 water-soluble with acetic acid at a neutralization equivalent of 0.55 (contains a curing agent).

(Request 2) Manufactured by Asahi Carbon Co., Ltd., product name “Carbon ASMJ (
Attack 3) Manufactured by Fuji Davison Co., Ltd., hydrated amorphous silicon dioxide pigment [The number in 1 indicates the oil absorption amount of the pigment (the same applies hereinafter) (I-B) Water-soluble Saithermal-type epoxy boria 100 (parts) Mino
Low-fat carbon silk (Kyo 2) 3 Refined clay (43) 10 Thyroid 244 (Kyo 3) 1O Resin: Pigment = 100-:23 (solid content weight ratio) Total oil absorption: 3,550 (I-C) Carbon black (Zero 2) 2 Thyroid 244 (Book 3) 15 Resin: Pigment = 100: 17 (Solid content weight ratio) Total oil absorption: 4,580 (*4) Kansai paint using water-soluble epoxy polyamide resin■ Manufactured by Nirekuron No. 9000J (product name)
Equivalent cationic electrodeposition paint made of epoxy polyamino resin with a resin base value of 80 and water-solubilized with formic acid at a neutralization equivalent of 0.55 (contains curing agent).

(ID) Aqueous wire thermosetting epoxy boria too (part) Mino
Fat 5) Titanium oxide [22] 20 Talc [4
3] 5 Purified Clay [43]
10 Thyroid 244 (Zero 3) l
O Resin: Pigment = 100:45 Total oil absorption: 4,085 (Equivalent to Nireclone 9400J manufactured by Kansai Paint using Zero 51 water-soluble epoxy polyamino resin,
An epoxy polyamino resin with a resin base value of 80 is water-solubilized with hydroxyacetic acid at a neutralization equivalent of 0.6 (contains curing agent).

(I-E) Carbon black (Book 2) 2 Titanium white [22] 8 Thyroid 244 (Book 3) 2 Total oil absorption = 856 (3) Cationic electrodeposition paint (n) (II-A) Titanium oxide white [22 ] 10 Purified clay [43] 7 Carbon black (Attack 2) 1 Minimum electrodeposition type flow density: 0
．． Epoxy polyamino resin with a base value of 80 is water-dispersed with acetic acid at a neutralization equivalent of 0.24, and the degree of emulsion is 90% by weight.
Contains hardening agent).

(II-B) Titanium oxide [22] 10 Refined clay [43] 7 Carbon plaque (
Book 2) 30 Total oil absorption: 641 Minimum deposition current density: 0.20 Intestinal A/c layer 2 (Attack 7) Kansai paint using epoxy resin containing acrylic resin ■
Product name of cationic electrodeposition paint manufactured by Nireclone #960 OJ
A corresponding water-soluble acrylic-modified epoxy resin with a resin base value of 45 was water-dispersed with acetic acid at a neutralization equivalent of 0.2, and the degree of emulsion was 92% by weight (contains a curing agent).

(II-C) Water-dispersed bran-heated epoxy poly 100 (parts) Amino Fat 0 8) Titanium oxide [22] 20 Carbon black [40] 1 Total oil absorption = 480 Electrodeposition current density: 0.29 ■ A/am2 (08) An epoxy polyamine resin having a resin base value of 80 was water-dispersed with hydroxyacetic acid at a neutralization equivalent of 0.15, and the degree of emulsion was 95% by weight (contains a curing agent).

(II-D) The epoxy resin of (II-B) above is water-dispersed with acetic acid at a neutralization equivalent of 0.5, and the degree of emulsion is 75.
It was produced in the same manner as (T1-B) except that the weight percent was used. The deposition current density was 0.9 mA/c+m''.

(4) Barrier coat (A): Propylene-ethylene copolymer (molar ratio, 60
:40) Organic liquid of a resin graft-polymerized with 11 parts by weight of maleic acid per too parts by weight (static glass transition temperature -43°C, tensile strength elongation at -20°C 410%).

(B): Propylene-ethylene copolymer (mole ratio 60:
40) Organic liquid of a composition containing 15 parts by weight of chlorinated polyolefin (chlorination rate 30%) per 100 parts by weight (static glass transition temperature -48°C, tensile strength elongation at -20°C 650%) ).

(5) Intermediate coating paint Near Mirac N-2 Sealer (manufactured by Kansai Paint Co., Ltd., amino polyester resin intermediate coating paint) (6) Top coating paint (A) Near Mirac White (manufactured by Kansai Paint Co., Ltd., amino alkyd resin based top coating paint, l Coat l baking white paint, pencil hardness H) ■ Examples and comparative examples The above electrodeposition paints (I), (II), barrier coat, intermediate coat paint, and top coat paint were applied according to the steps shown in Table 1. .

(1) First 0 electrodeposition coating conditions Only the lower part of the car body was immersed in a bath in which the electrodeposition paint (1) was adjusted to a solid content of 20% with deionized water, and the voltage was 150~
Cationic electrodeposition coating was performed under the following conditions: 250V Current application time: 2 minutes Bath temperature: 28°C Film thickness: 20#L (as a dry coating film).

Next, the electrodeposited surface was sprayed with deionized water, washed, dried at room temperature for 10 minutes, and then subjected to a second self-adhesive coating.

(2) Second self-deposition coating conditions The above car body was completely immersed in a bath in which the electrodeposition paint (n) was adjusted to a solids content of 20% with deionized water, and the voltage was 250.
Cationic electrodeposition coating was performed under the following conditions: ~350V Current application time: 2 minutes Bath temperature: 28°C Film thickness: 20 to 25 IL (as a dry coating film).

The painted surface is then sprayed with deionized water and washed, and then
Both electrodeposited coatings were cured by baking at 180° C. for 30 minutes.

(3) Barrier coat coating: Apply the coating on the electrodeposited surface using an air spray machine and heat it for 30 minutes at 120℃.
I baked it separately. The thickness of the film is 6 mm, including the dry coating film.

(4) Both the middle and top coats are spray-painted using an electrostatic coating machine, and the film thickness is 2
5 pots, 35 wins for the topcoat (all based on cured coatings), and 140 for both coatings.

It was cured by baking at ℃ for 3θ minutes.

■ Performance test results The test results are also listed in Table 1.

The test method is as follows.

(1) Thread rust resistance 0 based on ASTM-02803-697 thread rust test
Using a single-edged safety razor, make a diagonal X-shaped cut on the specimen that reaches the substrate, and place it in a salt spray tester for 36 hours. After salt water spray WI, wash thoroughly with deionized water, and before drying the specimen, place it in a constant temperature and humidity chamber at a temperature of 50 ± 2 °C and a humidity of 85.
The test was continued for 840 hours while maintaining the temperature at ±2% RH. Intermediate checks were made at 240 hours, 480 hours and 720 hours during the test to determine whether yarn rust was occurring.

O: Not generated at all Δ: A little bit of thread rust with a length of 3 ram or less. X: A lot of thread rust. The test was continued for up to 840 hours. Intermediate checks were made at 240 hours and 480 hours during the test to determine whether black rust had formed on the bent portions.

O: No abnormality Δ: Slight rust occurrence ×: Significant rust occurs (3) - Crotch corrosion resistance According to JIS Z 2371 salt spray test.

Check for black rust and blisters on the paint film in general areas where no cuts are made. It lasted up to 2,000 hours.

Intermediate checks were performed for 1,000 hours to check for black rust and blisters.

0: No abnormality Δ: Slight rust (4) Chipping resistance: (1) Test equipment: Q-G-R Gravelometer (product of Q Panel Company) (2) Stone to be sprayed: Approximately 15 to 20 squares in diameter / Crushed stones of the intestine (3) Capacity of the stone to be sprayed: Approximately 500 J (4) Air pressure for spraying approximately 4 kg/ crm2 (5) Temperature during test: approximately 20°C Mount the test piece on the test piece holder , about 4 kg/ct
In the spraying of s2, approximately 500-sized crushed stone particles were shot onto the test piece using air pressure, and then the coated surface condition and salt water spray resistance were evaluated.

The condition of the painted surface was visually observed and evaluated using the following criteria. Salt water spray resistance was determined by testing the test piece according to JIS Z2371.
After conducting the salt spray test for 0 hours, an adhesive cellophane tape was attached to the painted surface and rapidly peeled off, and the presence or absence of rust from the impacted area, peeling of the paint film, and corrosion state were observed.

■ Coated surface condition O: Only a few scratches due to impact were observed on a portion of the top coat, and no peeling of the electrodeposited coating was observed.

Δ: Many scratches due to impact were observed on the top coat and intermediate coat, and peeling of the electrodeposition film was also observed here and there.

×: Most of the top coat and intermediate coat are peeled off, and the impact area including the impact area and its surroundings is damaged! The electrodeposited coating peeled off in some areas.

■ Corrosion resistance @: Almost no rust, corrosion, paint peeling, etc. are observed.

0: Slight peeling of the top coat or intermediate coat is observed.

Δ: Slightly more rust, corrosion, and paint peeling are observed.

X: Significant rust, corrosion, and peeling of the paint film occurred.

(5) Painted surface condition Visual judgment O: Good Δ: Slight unevenness occurs

Claims (1)

[Scope of Claims] Consisting of a resin binder (A) and at least one pigment (B), at least 5% by weight of the pigment (B) consists of a pigment with an oil absorption of 100 or more, and the pigment (B)
The total oil absorption amount is 1,00 per 100g of resin binder (A).
Cationic electrodeposition coating is applied only to the lower part of the car body using a cationic electrodeposition paint (I) formulated to have a molecular weight within the range of 0 to 10,000, and then a resin binder is applied in an uncured state. (C) and a pigment (D) as the main components, the minimum electrodeposition current density is 0.7 mA/cm^2 or less, the degree of emulsion is 80% by weight or more, and the pigment (
An emulsion type cationic electrodeposition paint (II) in which the total oil absorption amount of D) is smaller than that in the cationic electrodeposition paint (I).
After applying cationic electrodeposition coating to the entire surface of the automobile body, and then curing the electrodeposition coating film by heating, a coating film having a static glass transition temperature of 0 to -75°C is formed on the electrodeposition coating surface. A coating film forming method characterized by applying a barrier coat to areas requiring improved chipping resistance, and further applying an intermediate coat and/or top coat as necessary.