JP2003253211A - Aqueous intermediate coating composition and method for forming film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous intermediate coating composition capable of affording a film having excellent chipping resistance. <P>SOLUTION: The aqueous intermediate coating composition comprises a film-forming resin, a curing agent, a color pigment, talc and a silane coupling agent. The content of the talc is 1-20 mass% based on the solid content of the aqueous intermediate coating composition. The content of the silane coupling agent is 0.1-5.0 mass% based on the solid content of the talc. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aqueous intermediate coating composition, a method for forming a coating film, and a coated product.

[0002]

2. Description of the Related Art A coating, which is applied to the outer panel of a car body, may have a phenomenon called chipping in which pebbles or the like collide with each other when the vehicle is running, which causes cracks or peeling of the coating. Are known. When such chipping occurs, water or the like intrudes from this portion, and rust occurs on the front surface of the vehicle body outer plate.

Particularly in cold regions, a large amount of rock salt and sand are sprayed on the road surface due to snow melting in winter,
There is a demand for a coating film which is easily chipped against pebbles and the like and has excellent chipping resistance.

[0004] A coating film that is usually applied to an automobile is provided with an intermediate coating film for imparting chipping resistance to the coating film. It is known that the inclusion of talc in the intermediate coating composition forming this coating film can improve the chipping resistance and suppress the scratching of the base material on the outer panel of the automobile.

However, in recent years, environmental load (VOC
Etc.) The use of water-based paints is required to solve the problem of reduction, and it is also desired to improve chipping resistance in water-based intermediate coatings. , The talc is a flat pigment, the surface is hydrophobic, etc., so that there is a problem that the dispersibility is particularly low in an aqueous paint and the storage stability and the water resistance of the coating film are reduced. .

[0006]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide an aqueous intermediate coating composition capable of obtaining a coating film having excellent chipping resistance.

[0007]

The present invention is an aqueous intermediate coating composition comprising a film-forming resin, a curing agent, a coloring pigment, talc and a silane coupling agent, wherein the content of talc is It is 1 to 20 mass% with respect to the solid content of the water-based intermediate coating composition, and the content of the silane coupling agent is 0.1 to the solid content of the talc.
The water-based intermediate coating composition is 5.0% by mass.

The talc is preferably surface-treated with the silane coupling agent in advance. The silane coupling agent is preferably a trialkoxysilane compound having a functional group having a high affinity with the coating film forming resin or the curing agent. The functional group having a high affinity for the coating film-forming resin or the curing agent is preferably an amino group.

The present invention is a method for forming an intermediate coating film, which comprises the step of applying the above-mentioned aqueous intermediate coating composition to an object to be coated. The present invention is also a coated product having an intermediate coating film obtained by the above intermediate coating film forming method. Hereinafter, the present invention will be described in more detail.

The aqueous intermediate coating composition of the present invention comprises a film forming resin, a curing agent, a coloring pigment, talc and a silane coupling agent. The aqueous intermediate coating composition of the present invention contains talc and a silane coupling agent. That is, it is possible to improve the chipping resistance of the coating film obtained by including talc in the coating, but the dispersibility of talc in the aqueous intermediate coating composition is low, and the storage stability of the coating composition is stable. In some cases, the water resistance of the resulting coating film decreases, and the water resistance of the resulting coating film decreases.

However, since the aqueous intermediate coating composition of the present invention further contains a silane coupling agent, the group represented by SiOR in the silane coupling agent reacts with water to form SiOH. Group represented by R
OH (alcohol) is generated, and the generated group represented by SiOH and the OH group on the surface of talc react with each other, and the silane coupling agent and talc are bonded by a Si-O- bond, whereby the surface of talc is treated. It is speculated that this can improve the stability of talc in the waterborne intermediate coating composition. Therefore,
The water-based intermediate coating composition of the present invention has excellent talc dispersibility and storage stability, and since it contains talc, the resulting coating film has excellent chipping resistance. is there. Further, by containing the silane coupling agent, the affinity between the resin component and the pigment component is increased, and the water resistance of the resulting coating film can be improved.

The above talc has the effect of improving the chipping resistance of the resulting coating film. The talc is not particularly limited, and examples thereof include known ones such as S talc and PS talc, and commercially available products can also be used.

The content of talc is 1% by mass as the lower limit and 20% by mass as the upper limit based on the solid content of the aqueous intermediate coating composition. If it is less than 1% by mass, the chipping resistance may be insufficient, and if it exceeds 20% by mass, the appearance of the obtained coating film may be deteriorated. More preferably, the lower limit is 2% by mass and the upper limit is 15% by mass.

The silane coupling agent has the effect of improving the dispersibility of the talc in the coating composition and improving the water resistance of the resulting coating film. The silane coupling agent is not particularly limited and includes, for example, the following general formula (1) R ¹ —Si— (R ² ) _n (OR ² ) _3-n (1) (wherein R ¹ is an organic group. An alkyl group having 1 to 6 carbon atoms substituted or unsubstituted with, an epoxyalkyl group having 1 to 11 carbon atoms, an aryl group, an alkenyl group having 1 to 11 carbon atoms, an aminoalkyl group having 1 to 5 carbon atoms, Carbon number 1
5 represents a mercaptoalkyl group having 5 or a halogenoalkyl group having 1 to 5 carbon atoms. R ² represents an alkyl group having 1 to 6 carbon atoms. n is 0, 1 or 2. ) Can be mentioned.

Examples of the silane coupling agent include trimethylmethoxysilane, trimethylethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, n-propyltrimethoxysilane, isobutyltrimethoxysilane, n-decyltrimethoxysilane and n. -Hexadecyltrimethoxysilane, 1,6-bis (trimethoxysilyl) hexane, γ-ureidopropyltriethoxysilane, γ-dibutylaminopropyltrimethoxysilane, nonafluorobutylethyltrimethoxysilane, γ-glycidoxypropyl Methyldimethoxysilane, γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxy Orchid, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane, cyclohexylmethyldimethoxy Examples thereof include silane, vinyltrimethoxysilane, dimethyldimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride and the like. These may be used alone or in combination of two or more.

The silane coupling agent is preferably a trialkoxysilane compound having a functional group having a high affinity with the coating film-forming resin or the curing agent. That is, when R ¹ in the general formula (1) is a functional group having a high affinity for the coating film-forming resin or the curing agent and n is 0,
Since not only a Si—O— bond is formed between the silane coupling agent and talc, but also the functional group having high affinity has affinity for the film-forming resin or curing agent, Affinity of talc with the film-forming resin or curing agent in the intermediate coating composition is increased, and the talc dispersibility in the coating composition and the storage stability of the coating composition are further improved. be able to. Further, since it has three groups represented by OR ² , more Si—O— bonds will be formed between the silane coupling agent and talc, and the dispersibility and storage stability of talc will be improved. It is presumed that the sex can be further improved.

The functional group having a high affinity with the coating film-forming resin or the curing agent means a functional group which causes an interaction with the coating film-forming resin or the curing agent. It means a functional group having a high affinity with the hydrophilic group present in the forming resin or the curing agent.

The functional group having a high affinity with the coating film forming resin or the curing agent depends on the kind of the coating film forming resin or the curing agent, but the coating film forming resin or the curing agent is a carboxyl group. When it has a group, examples thereof include an amino group. That is, since the dispersibility and storage stability of talc can be improved by the affinity between the carboxyl group and the amino group, it has a high affinity with the hydrophilic group present in the coating film-forming resin or the curing agent. The functional group is preferably an amino group.

Affinity with the above film forming resin or the above curing agent
And a trialkoxysilane compound having a highly functional group
Is not particularly limited, and for example, NH_TwoC_ThreeH₆Si
(OC_TwoH₅)_Three, NH_TwoC_TwoH_FourNHC_ThreeH₆Si
(OCH_Three)_Three, NH_TwoCONHC _ThreeH₆Si (OC_Two
H₅)_ThreeEtc. can be mentioned. Among them, talc
From the viewpoint of dispersibility, storage stability, and water resistance of the coating film, NH_TwoC
_ThreeH₆Si (OC_TwoH₅)_ThreeIs preferred.

Commercially available products can be used as the trialkoxysilane compound having a functional group having a high affinity with the coating film-forming resin or the curing agent, for example, A-11.
00, A-1120, A-1160 (trade name, manufactured by Nippon Unicar Co., Ltd.) and the like. Among them, A-1
100 is preferred.

The above talc is preferably surface-treated in advance with a silane coupling agent. That is, in this case, the aqueous intermediate coating composition of the present invention is prepared by mixing talc, which has been surface-treated with a silane coupling agent in advance, with a film-forming resin, a curing agent and a color pigment. Since the surface of the talc has already been subjected to a surface treatment with a silane coupling agent, it is possible to further improve the coating compared to the case where the surface treatment is carried out by incorporating the talc and the silane coupling agent into the coating composition. The dispersibility of talc in the composition and the storage stability of the coating composition can be improved.

The surface treatment method is not particularly limited, and a conventionally known method can be used.
It can be carried out by adding a mixture of a silane coupling agent and a solvent such as water to talc with stirring, mixing and further drying. As a result, the group represented by SiOH formed in the silane coupling agent reacts with the OH group on the surface of talc, the silane coupling agent and talc are linked by a Si—O— bond, and further dried to obtain water. It is presumed that the surface treatment of talc will be carried out by removing the alcohol generated by liberation from or SiOR.

The drying is not particularly limited as long as talc surface-treated with a silane coupling agent can be obtained, but the drying temperature is 90 to 150 ° C. and the drying time is 3
It is preferably 0 minutes to 2 hours. By performing the above-mentioned drying, water and alcohol generated during the surface treatment can be removed. If the drying temperature and the drying time are less than the lower limits, water and generated alcohol remain. It is also possible to use a commercially available product as the talc which has been surface-treated with the silane coupling agent in advance.

When a trialkoxysilane compound having a functional group having a high affinity for a film-forming resin or a curing agent is used as a silane coupling agent used when preparing the above-mentioned surface-treated talc, a silane cup is used. Since the affinity of the ring agent for talc and the affinity for the coating film-forming resin or curing agent are further enhanced, the affinity between the coating film-forming resin or curing agent and talc is further enhanced.
This is more preferable because the dispersibility of talc in the aqueous intermediate coating composition and the storage stability of the coating composition are excellent.

The content of the silane coupling agent is 0.1% by mass as the lower limit and 5.0% by mass as the upper limit with respect to the solid content of talc. If it is less than 0.1% by mass, the dispersibility of talc, storage stability, and water resistance may be poor,
If it exceeds 5.0% by mass, it may not be economical.
The upper limit is more preferably 2.0% by mass.

The coating film-forming resin is not particularly limited, and examples thereof include acrylic resin, polyester resin, alkyd resin, epoxy resin, urethane resin and the like.
The coating film-forming resin can be used in a stable manner in the waterborne intermediate coating composition by using a water-soluble resin or by emulsifying and dispersing it by applying a dispersing resin, a surfactant or the like dispersing agent. be able to.

When the above-mentioned coating film-forming resin has a carboxylic acid group, the acid value has a lower limit of 10 (mgKO).
H / g resin), and the upper limit is preferably 100 (mgKOH / g resin). When it is less than 10, the coating film adhesion may be poor and curing may be poor, and when it exceeds 100, the hydrophilicity may be too high and the water resistance of the coating film may be deteriorated. More preferably, the lower limit is 20 and the upper limit is 80.

When the above-mentioned coating film-forming resin has a hydroxyl group, the hydroxyl value has a lower limit of 30 and an upper limit of 150.
Is preferred. If it is less than 30, curing failure may occur, and if it exceeds 150, excess hydroxyl groups may remain in the coating film after curing, resulting in poor water resistance. More preferably, the lower limit is 50 and the upper limit is 150.

The coating film-forming resin preferably has a number average molecular weight obtained by gel permeation chromatography (GPC) of 1,000 as a lower limit and 30,000 as an upper limit. When it is less than 1,000, the physical properties such as solvent resistance of the cured coating film may be poor, and when it exceeds 30,000, the viscosity of the resin solution is high, and thus it is difficult to handle the obtained resin in terms of operation such as emulsion dispersion. In addition, the appearance of the obtained coating film may be significantly deteriorated. More preferably, the lower limit is 1500 and the upper limit is 20000.

The method for producing the above-mentioned coating film-forming resin is not particularly limited and can be appropriately selected depending on the kind and properties of the above-mentioned coating-film forming resin, for example, melt polymerization method, ester. Conventionally known production methods such as an exchange method, an interfacial polymerization method, a solution polymerization method and the like can be used.

As the above-mentioned curing agent, a curing agent well known by those skilled in the art can be appropriately selected according to the kind of the above-mentioned coating film-forming resin. Generally, from the viewpoint of pigment dispersibility and coating workability, the coating film-forming resin is a polyester resin and / or an acrylic resin having a hydroxyl group, and the curing agent is a polyisocyanate and / or a melamine resin. It is preferable. The polyisocyanate has an isocyanate group such as butyl cellosolve and alcohols such as 2-ethylhexanol and oximes such as methyl ethyl ketoxime, from the viewpoint of storage stability.
It is preferably blocked by a blocking agent known to those skilled in the art.

In the water-based intermediate coating composition of the present invention, the solid content mass ratio of the coating film-forming resin and the curing agent is 8
It is preferably 5/15 to 50/50. If the ratio exceeds 85/15, the curability may decrease, and if it is less than 50/50, various properties of the obtained coating film may decrease.

The above-mentioned coloring pigment is not particularly limited as long as it improves weather resistance and secures hiding property, but titanium dioxide is particularly excellent in white color hiding property and is inexpensive, preferable.

Examples of pigments other than titanium dioxide include azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments. , Organic color pigments such as isoindolinone pigments and metal complex pigments; yellow lead, yellow iron oxide, red iron oxide,
Inorganic color pigments such as carbon black can be used. Further, in the present invention, an extender pigment such as calcium carbonate, barium sulfate or clay may be used as the pigment.

As the above-mentioned coloring pigment, a standard gray-based intermediate coating composition containing carbon black and titanium dioxide as main pigments may be used, or a set gray or various coloring pigments in which the top coating composition and brightness or hue are combined. A combination of so-called color intermediate coating materials can also be used.
These pigments may be used alone or in combination of two or more.

The above-mentioned pigments (talc, coloring pigment and extender pigment) are pigments and resin solids (talc, coloring pigment, extender pigment, resin solids in the film-forming resin and Ratio of the mass of the above pigment to the total mass of the resin solid content in the curing agent) (PWC)
Is preferably 10 to 60% by mass. If it is less than 10% by mass, the hiding property may be deteriorated due to lack of pigment. If it exceeds 60% by mass, the excess pigment may cause an increase in viscosity at the time of curing, resulting in poor flowability and poor coating film appearance.

The above-mentioned talc is the total mass of the pigment and resin solids (talc, coloring pigment, extender pigment, resin solids in the film-forming resin and resin solids in the curing agent) in the above-mentioned waterborne intermediate coating composition. The ratio (PWC) of the mass of talc to the total mass of () is preferably 1 to 15 mass%. If it is less than 1% by mass, the chipping resistance may be insufficient, and if it exceeds 15% by mass, the appearance of the obtained coating film may be deteriorated.

In addition to the above-mentioned components, the aqueous intermediate coating composition of the present invention may further contain, if necessary, an organic solvent, a curing catalyst, a surface conditioner, a defoaming agent, a plasticizer, a film-forming aid, an ultraviolet absorber, Antioxidants and the like can be contained. These are not particularly limited, and those well known by those skilled in the art can be used.

The method for obtaining the aqueous intermediate coating composition of the present invention is not particularly limited, and the compound of the film forming resin, the curing agent, the pigment and the like is kneaded by using a kneader or a roll. All methods well known to those skilled in the art such as dispersion using a sand grind mill or a disperser can be used.

The method of forming an intermediate coating film of the present invention comprises the step of coating the above-mentioned aqueous intermediate coating composition on an article to be coated. As a preferred form of the intermediate coating film forming method, for example, on an object to be coated on which an electrodeposition coating film is formed,
Step (1) of forming an intermediate coating film by heating and curing after applying an aqueous intermediate coating composition, and applying an overcoat composition on the intermediate coating film obtained in the above step (1) and uncuring A method for forming a multilayer coating film comprising the step (2) of forming a top coating film, and the step (3) of curing the uncured top coating film obtained in the above step (2) to obtain a multilayer coating film. Among these, the water-based intermediate coating composition may be the above-mentioned water-based intermediate coating composition.

The electrodeposition coating composition for forming the above-mentioned electrodeposition coating film is not particularly limited and may be either a cation type or an anion type, but from the viewpoint of corrosion resistance and rust resistance, it must be a cation type. Is preferred.

The article to be coated is not particularly limited, and examples thereof include iron, steel, aluminum, tin, zinc and the like, and alloys and castings containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles and buses. These metals are preferably surface-treated in advance before electrodeposition coating is performed.

The first step in the above-mentioned method for forming a multilayer coating film is to form an intermediate coating film by applying an aqueous intermediate coating composition on an object to be coated on which an electrodeposition coating film has been formed and then heat curing. In the step (1), the water-based intermediate coating composition is the above-mentioned water-based intermediate coating composition.

The above water-based intermediate coating composition is usually applied so that the dry film thickness is 10 to 60 μm. 10 μm
If it is less than 60 μm, the hiding of the undercoat may be insufficient. If it exceeds 60 μm, sagging during coating, cracking during heat curing, or the appearance of the resulting intermediate coating film may deteriorate. .

The method of applying the above-mentioned water-based intermediate coating composition is not particularly limited, and examples thereof include a spray coating method and an electrostatic coating method. Industrially, for example, an air electrostatic spray coating machine commonly called "react gun" or a rotary atomization type electrostatic coating machine commonly called "micro-microbell", "microbell", "metallic bell", etc. is used. A method can be mentioned. A method using a rotary atomization type electrostatic coating machine is preferable.

After the above-mentioned water-based intermediate coating material is applied, it is heated and cured to obtain an intermediate coating film. The conditions for the heat curing are not particularly limited, and are appropriately determined depending on the type of the water-based intermediate coating composition. As conditions for the above-mentioned heat curing, for example, the lower limit is 110 ° C and the upper limit is 200 ° C, more preferably the lower limit is 120 ° C and the upper limit is 180 ° C, and the heating time is the lower limit of 10 minutes and the upper limit of 60 minutes.

The second step in the method for forming a multilayer coating film is a step of applying an overcoating composition on the intermediate coating film obtained in the above step (1) to obtain an uncured topcoating film. .
The above-mentioned top-coat paint imparts aesthetics and protection to the object to be coated.

The top coating material is not particularly limited,
For example, there may be mentioned a film-forming resin, a curing agent, a bright pigment, a pigment such as a color pigment and an extender pigment, and various additives. Examples of the coating film-forming resin, the curing agent, the color pigment, and the various additives include those described in the above aqueous intermediate coating composition. From the viewpoint of pigment dispersibility and workability, a combination of an acrylic resin and / or a polyester resin and a melamine resin is preferable.
Further, as the method for preparing the top coating composition, the method exemplified for the above water-based intermediate coating composition can be mentioned.

The bright pigment is not particularly limited,
Examples thereof include uncolored or colored metallic luster pigments such as metals or alloys and mixtures thereof, interference mica powder, colored mica powder, white mica powder, graphite or colorless colored flat pigments. A non-colored or colored metallic glitter material such as a metal or an alloy and a mixture thereof are preferable because they can form a coating film having excellent dispersibility and high transparency. Specific examples of the metal include aluminum, aluminum oxide, copper, zinc, iron, nickel and tin.

The shape of the bright pigment is not particularly limited,
Further, although it may be colored, for example, the average particle size (D5
0) has a lower limit of 2 μm and an upper limit of 50 μm, and a scale-like one having a lower limit of 0.1 μm and an upper limit of 5 μm is preferable. The average particle size is more preferably the lower limit of 10 μm and the upper limit of 35 μm, because it is excellent in brilliance.

The above-mentioned pigments may be used alone or in combination of two or more, and one or more of them may be combined from coloring pigments and extender pigments and, if necessary, flat pigments and luster pigments. Can be used.

The total pigment concentration (PWC) contained in the top coating is generally 0.1% by mass for the lower limit and 5% for the upper limit.
0% by mass, more preferably, the lower limit is 0.5% by mass,
The upper limit is 40% by mass, more preferably the lower limit is 1% by mass and the upper limit is 30% by mass. If the pigment concentration is less than 0.1% by mass, the effect of the pigment cannot be obtained, and if it exceeds 50% by mass, the appearance of the obtained coating film may be deteriorated.

The form of the top coat is not particularly limited, and may be an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion) or a non-water-dispersed type. The above-mentioned top-coat paint usually has a dry film thickness of 15 to 70 μm.
It is painted to be. If the dry film thickness is less than 15 μm, the hiding of the base may be insufficient or color unevenness may occur. If the dry film thickness exceeds 70 μm, sagging may occur during coating or armpits may occur during heat curing. There is.

Examples of the method of applying the above-mentioned topcoat paint include the methods exemplified when applying the above-mentioned waterborne intermediate paint. In the case of coating the above-mentioned top coating on an automobile body or the like, in order to improve the design, multi-stage coating by the above-mentioned air electrostatic spray coating, preferably two-stage coating, or the above-mentioned air electrostatic coating is carried out. It is preferable to perform the coating method by combining spray coating and the rotary atomization type electrostatic coating.

The uncured top coating film may be composed of a base coating film and an uncured clear coating film.
In this case, the step (2) is, for example, a step of applying a base paint to obtain a base coating film, and then applying a clear paint to obtain an uncured clear coating film. Examples of the base coating material include the top coating material.

The above base paint is usually applied so as to have a dry film thickness of 5 to 35 μm. If the dry film thickness is less than 5 μm, the hiding of the base may be insufficient or color unevenness may occur. If it exceeds 35 μm, sagging during coating or cracking during heat curing may occur. May occur. Examples of the method of applying the base paint include the same methods as the methods of applying the topcoat paint.

The clear coating film obtained from the above clear coating composition smoothes unevenness, flicker, etc. of the base coating film due to the bright pigment when a metallic base coating composition containing the bright pigment is used as the base coating material. It is formed to protect the base coating film. The clear coating material is not particularly limited, and examples thereof include a coating film-forming resin, a curing agent, and other additives.

The coating film-forming resin is not particularly limited, and examples thereof include acrylic resin, polyester resin, epoxy resin, urethane resin and the like, which are combined with a curing agent such as amino resin and / or blocked isocyanate resin. Used. From the viewpoint of transparency or acid etching resistance, a combination of an acrylic resin and / or polyester resin with an amino resin, or a carboxylic acid
It is preferable to use an acrylic resin and / or polyester resin having an epoxy curing system.

As the clear paint, a viscosity control agent is added as an additive in order to apply the above-mentioned base paint in an uncured state after coating, and to prevent familiarity between layers, reversal, or sagging. It is preferable. The addition amount of the viscosity control agent is 0.01 parts by mass as the lower limit and 10 parts by mass as the upper limit, and preferably 0.02 parts by mass as the lower limit and 8 parts by mass as the upper limit, relative to 100 parts by mass of the resin solid content of the clear paint. ,
More preferably, the lower limit is 0.03 parts by mass and the upper limit is 6 parts by mass. When it exceeds 10 parts by mass, the appearance is deteriorated, and when it is less than 0.1 parts by mass, the viscosity control effect cannot be obtained, which causes problems such as sagging.

The clear coating composition may be of any of organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), non-aqueous dispersion type and powder type, and if necessary, a curing catalyst and a surface. A regulator or the like can be used.

The clear coating composition can be prepared and coated by a conventional method. The dry film thickness of the clear coating film varies depending on the application, but is 1
It is 0 to 70 μm. If this dry film thickness exceeds the upper limit,
If the image quality is lower than the lower limit, the appearance may be deteriorated.

The base coating film may be an uncured base coating film or a cured base coating film. The above-mentioned uncured base coating film is a concept including the state after the preheating treatment. As the preheat treatment,
For example, heat treatment at room temperature to about 100 ° C. for 1 to 10 minutes. Further, the coating film after curing is the above-mentioned uncured base coating film which is cured by heating. The heat curing conditions are not particularly limited and can be appropriately set depending on the type of the base coating used, for example, 110 to 18
It is 10 to 60 minutes at 0 degreeC. From the viewpoint of energy saving and process shortening, it is preferable that the base coating film is not a cured base coating film but an uncured base coating film. Such a method is called wet-on-wet painting.

The third step in the method for forming a multilayer coating film is to obtain a multilayer coating film by heat-curing the uncured topcoat coating film obtained in the step (2). When the uncured top coating film is composed of the uncured base coating film and the uncured clear coating film, the third step is to perform the uncured base coating film and the uncured coating film. A clear coating film and a clear coating film are simultaneously cured.

The lower limit of the temperature for heating and curing is 1
It is preferable that the temperature is 10 ° C. and the upper limit is 180 ° C., and the lower limit is 12
It is more preferable that the temperature is 0 ° C. and the upper limit is 160 ° C. Thereby, a cured coating film having a high degree of crosslinking can be obtained. If the temperature is lower than 110 ° C, curing will be insufficient and
If it exceeds 80 ° C, the obtained coating film may be hard and brittle. The heating and curing time can be appropriately set according to the above temperature, but when the temperature is 120 to 160 ° C., it is, for example, 10 to 60 minutes.

The thickness of the multilayer coating film obtained by the above steps (1), (2) and (3) is usually preferably 30 μm as a lower limit and 300 μm as an upper limit, and 50 μm as a lower limit and 250 μm as an upper limit. More preferable. If it is less than 30 μm, the film strength of the obtained multilayer coating film may be lowered, and if it exceeds 300 μm, the physical properties of the film may be lowered,
There may be a problem in coating performance.

Since the coated product having the intermediate coating film obtained by the above intermediate coating film forming method is obtained by using the above-mentioned aqueous intermediate coating composition, it is excellent in chipping resistance. Is. Such a coated product is also part of the present invention.

Since the aqueous intermediate coating composition of the present invention contains talc and a silane coupling agent, the dispersibility of talc in the coating composition, the storage stability of the coating composition, and the obtained The water resistance of the coating film is excellent.
In particular, when the silane coupling agent is a trialkoxysilane compound having an amino group and talc which has been surface-treated with this compound is used, in the coating composition, a coating film-forming resin or a curing agent is used. Since the affinity with talc is further enhanced, the above-mentioned effects can be more exerted. As a result, the above-mentioned waterborne intermediate coating composition is suitably used in the field of automobile coating where excellent chipping resistance is required.

[0068]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" unless otherwise specified.

Production Example 1 Production of Aqueous Polyester In a reaction vessel equipped with a nitrogen inlet tube, a stirrer, a temperature controller, a cooling tube and a decanter, 176 parts of phthalic anhydride, 197 parts of isophthalic acid, 87 parts of adipic acid, trimethylolpropane. 102 parts, 272 parts of neopentyl glycol, 0.8 part of dibutyltin oxide, and 17 parts of xylene were charged, and the temperature was raised to 200 ° C. over 2 hours after the reflux of xylene was started. Meanwhile, water generated by the reaction was azeotropically removed with xylene. When the acid value of the carboxylic acid reached 8, it was cooled to 150 ° C, 49 parts of trimellitic anhydride was added, and then cooled to 60 ° C, and 46 parts of dimethylethanolamine was added and mixed. 1137 parts of ion-exchanged water was added, and the number average molecular weight measured by gel permeation chromatography was 20.
00, solid content 40%, solid content acid value 40, hydroxyl value 100
A water-based polyester resin of

Production Example 2 Production of Talc Treated with Silane Coupling Agent 100 parts of PK50 (trade name, manufactured by Fuji Talc Co.) was placed in a Henschel mixer and premixed A-1100.
6 parts of a mixture having a mass ratio of (trade name, manufactured by Nippon Unicar Co., Ltd.) and ion-exchanged water of 1: 5 was gradually added while stirring,
Mix for an additional 10 minutes. Then take it out to the tray, 15
It was dried at 0 ° C. for 1 hour to obtain a silane coupling agent-treated talc.

Example 1 (Preparation of aqueous intermediate coating composition 1) 33 parts of the aqueous polyester resin obtained in Production Example 1 and 24.5 parts of CR-97 (trade name, titanium dioxide manufactured by Ishihara Sangyo Co., Ltd.) , B-34
(Trade name, Sakai Chemical Co., Ltd. sedimentary barium sulfate) 12 parts, M
A-100 (trade name, carbon black manufactured by Mitsubishi Chemical Corporation)
0.5 parts, 3 parts of the silane coupling agent-treated talc obtained in Production Example 2 and 5 parts of ion-exchanged water were premixed,
A glass bead medium was added in a paint conditioner, and the mixture was mixed and dispersed at room temperature for 1 hour to obtain a pigment paste 1 for intermediate coat paint having a particle size of 10 μm or less. To 78 parts of this paste, 72 parts of water-based polyester resin, CYMEL 235
(Product name, Mitsui Cytec melamine resin, solid content 1
100 parts by mass) and 0.5 part of Surfynol 104E (trade name, a surface conditioner manufactured by Air Products Japan Co., Ltd.) are mixed and stirred with a disper for 10 minutes to obtain an aqueous intermediate coating composition 1. It was

(Coating film forming method) 15 treated with zinc phosphate
Power Top U-50 (trade name, cationic electrodeposition paint manufactured by Nippon Paint Co., Ltd.) is electro-deposited on a 0 x 70 x 0.7 mm hot-dip galvanized steel plate so that the dry film thickness is 20 µm.
It was baked and cured at 160 ° C. for 30 minutes to obtain an electrodeposited substrate.
The resulting aqueous intermediate coating composition 1 was applied onto this electrodeposited substrate by air spraying so that the dry film thickness would be 25 μm, and baked and cured at 160 ° C. for 30 minutes. Furthermore, A
R-2000 (trade name, water-based base paint manufactured by Nippon Paint Co., Ltd., coating color: silver) is spray-coated in two stages to a dry film thickness of 15 μm, followed by a preheating step at 80 ° C. for 5 minutes and then at room temperature It is cooled until it becomes, and Macflow O-1801w (trade name, an organic solvent type clear paint manufactured by Nippon Paint Co., Ltd.) is spray-coated to a dry film thickness of 35 μm, and then baked and cured at 140 ° C. for 30 minutes to obtain a test plate. Got

Example 2 B-34 (trade name, precipitating barium sulfate manufactured by Sakai Chemical Co., Ltd.) 1
5.5 parts of B-34 (trade name, precipitated barium sulfate manufactured by Sakai Chemical Industry Co., Ltd.) instead of 2 parts, silane coupling agent-treated talc instead of 3 parts of silane coupling agent-treated talc 9.
A pigment paste 2 for an intermediate coating composition, an aqueous intermediate coating composition 2 and a test plate were obtained in the same manner as in Example 1 except that 5 parts were used.

Comparative Example 1 PK5 was used in place of 3 parts of talc treated with a silane coupling agent.
A pigment paste 3 for an intermediate coating composition, an aqueous intermediate coating composition 3 and a test plate were obtained in the same manner as in Example 1 except that 0 (trade name, talc manufactured by Fuji Talc Co.) was used.

Comparative Example 2 B-34 (trade name, precipitated barium sulfate manufactured by Sakai Chemical Co., Ltd.) 1
5.5 parts of B-34 (trade name, precipitating barium sulfate manufactured by Sakai Chemical Co., Ltd.) instead of 2 parts, PK50 (trade name, talc manufactured by Fuji Talc Co., Ltd.) instead of 3 parts of silane coupling agent-treated talc 9. A pigment paste 4 for intermediate coating composition, an aqueous intermediate coating composition 4 and a test plate were obtained in the same manner as in Example 1 except that 5 parts were used.

Evaluation method <Pigment dispersibility> Before and after the dispersion step in Examples and Comparative Examples, that is, before and after the step of adding a glass bead medium in a paint conditioner and mixing and dispersing at room temperature for 1 hour, using a Stormer viscometer at 20 ° C. The change in viscosity was used as an index of dispersibility. The obtained results are shown in Table 1. Passes were those in which the increase in viscosity after the dispersion step was +10 Ku or less compared to the viscosity before the dispersion step.

<Paint Storage Stability> The aqueous intermediate coating compositions obtained in Examples and Comparative Examples were treated with ion-exchanged water to obtain N.
o. 4 Ford cup diluted at 20 ℃ for 30 seconds as a sample, 150 ml in 200 ml inner coated round can
It was put in cc and stored in a furan vessel at 40 ° C. for 10 days. The viscosity after storage was also set to No. 4 with Ford Cup 2
It was measured at 0 ° C., and the increase / decrease in the number of seconds was used as an index of storage stability. The obtained results are shown in Table 1.

<Water resistance> The test plates obtained in Examples and Comparative Examples were immersed in warm water of 40 ° C for 10 days, and the appearance after 1 hour of washing was visually observed. The obtained results are shown in Table 1. The evaluation criteria are as follows. There was no problem with the adhesion. ◯: No blemishes Δ: There are blemishes ×: There are blemishes, and the gloss is reduced.

[0079]

[Table 1]

The aqueous intermediate coating compositions obtained in the examples showed no increase in viscosity after dispersion and were excellent in storage stability of the coating. In addition, the test plates obtained in the examples were free from tingling and were excellent in water resistance.

[0081]

EFFECTS OF THE INVENTION Since the aqueous intermediate coating composition of the present invention has the above-mentioned constitution, a coating film having excellent chipping resistance can be obtained by using the above aqueous intermediate coating composition. is there. Therefore, the intermediate coating film forming method comprising the step of coating the above-mentioned water-based intermediate coating composition on an object to be coated is particularly advantageous because the resulting coating film is excellent in chipping resistance and impact resistance. It can be suitably applied to vehicle painting such as.

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Claims (6)

[Claims] 1. An aqueous intermediate coating composition comprising a film-forming resin, a curing agent, a color pigment, talc and a silane coupling agent, wherein the content of the talc is in the aqueous intermediate coating composition. It is 1 to 20 mass% with respect to the solid content, and the content of the silane coupling agent is 0.1 to 5.0 mass% with respect to the solid content of the talc. Intermediate coating composition. 2. The aqueous intermediate coating composition according to claim 1, wherein the talc is surface-treated with a silane coupling agent in advance. 3. The aqueous intermediate coating composition according to claim 1 or 2, wherein the silane coupling agent is a trialkoxysilane compound having a functional group having a high affinity with the film-forming resin or the curing agent. 4. The aqueous intermediate coating composition according to claim 3, wherein the functional group having a high affinity for the film-forming resin or the curing agent is an amino group. 5. A method for forming an intermediate coating film, which comprises the step of applying the aqueous intermediate coating composition according to claim 1, 2, 3 or 4 to an object to be coated. 6. A coated product having an intermediate coating film obtained by the method for forming an intermediate coating film according to claim 5.