KR20030087449A - Aqueous top coating composition for automobile - Google Patents

Abstract

PURPOSE: Provided is a water-soluble top-coat composition for cars, which expands a coating temperature/humidity range and is excellent in appearance, mechanical properties, coating workability, storage stability of paint, and color keepability. CONSTITUTION: The water-soluble top-coat composition comprises: 20-50wt% of a polyacryl water-dispersible resin having a hydroxy group of 50-200mgKOH/g and a glass transition temperature of -20 to 10deg.C, which comprises 90-95wt% of a light acryl resin and 5-10wt% of epoxy monomers; 10-40wt% of a reverse core/shell type microgel resin; 0.5-5wt% of a melamine hardener containing a hydrophilic amino group; 5-50wt% of a white or colored pigment water-dispersing solution, or a mixture thereof; 1-15wt% of a co-solvent; 0.5-2wt% of a wet dispersing agent; 0.1-1wt% of an antifoaming agent; 0.01-1wt% of a fluidity-controlling agent; 0.1-2wt% of a wetting agent; and 0.1-1wt% of a neutralizing agent.

Description

Aqueous top coating composition for automobile with expanded coating temperature and humidity

The present invention relates to a water-soluble top coat composition for automobiles in which the coating temperature and humidity region is expanded, and more particularly, the paintable temperature and humidity region (application window) is expanded as compared to the existing water-soluble top coating, and has excellent appearance and mechanical properties. The present invention relates to a water-soluble waterborne coating composition excellent in paintability, paint stability and color retention.

Conventional oil-soluble topcoat is composed of resin type of acrylic / melamine or polyester / melamine type, and has been applied to automotive topcoat until now, but it causes serious environmental problems by discharging a large amount of volatile organic solvents during painting and coating curing. There is a problem. Therefore, in contrast, developed countries have made great efforts to develop new paints that can contribute to reducing the use of organic solvents.As a result, in Western Europe, since the adoption of water-soluble metallic topcoats in automobile paint seal lines in 1985, the adoption rate has rapidly increased. It is increasing, and the trend is spreading in developed countries such as the United States.

In addition, since the conventional water-soluble top coat has a low temperature and humidity range that can be painted, much effort is required to control the temperature and humidity of the coating booth and to secure a good appearance of paint. . In particular, in the case of a solid paint with poor hiding power such as a white color with a high paint film thickness, popping at low humidity and chilling at high humidity have been raised. Attempts are being made to expand.

For example, US Pat. Nos. 4,403,003 and 4,900,774 disclose water-soluble topcoat compositions containing acrylic water dispersions imparted with pseudo-plastic behavior and hydrophilic or hydrophobic melamine as resin components. In the case of the top coat composition according to the patent, the final solid content is very low (15 to 20% by weight), and when the solidification is performed, not only the smoothness of the coating film is significantly lowered, but also the appearance of the coating film is remarkably lowered. By applying the acid alone, there is a disadvantage in that the coating film properties are deteriorated due to the increase in the glass transition temperature of the entire coating film after curing.

On the other hand, core / shell-type acrylic resins using microgels as cores are manufactured by NAD (Non Aqueous Dispersion) method as a means for reducing organic solvent discharge, and are applied to aqueous systems or prepared by emulsion polymerization, in particular for organic solvents. Because of its strong resistance and plasticity, it is mainly applied to aqueous metallic basecoats. The biggest advantage of these resins is that they are not sensitive to changes in humidity during painting, so the temperature / humidity range is wide and the resistance to popping during baking is large, but the greatest point is that a large amount of coarse solvent is required to ensure good fusion during coating film formation. It is known as a disadvantage.

In addition, in the case of water-based paints, unlike the solvent-based paints, most of the volatile components of the paints are composed of water, so that the drying of the volatile components is slower than the solvent-type paints and is sensitively affected by the temperature and relative humidity at the time of coating. Therefore, when the humidity is lower than the critical point or the temperature is higher than the critical point, the drying of the paint proceeds too fast to increase the possibility of dust coating or popping, and vice versa. have.

In order to solve this problem, in order to expand the paintable temperature and humidity range, it is necessary to optimize the arrival NV (Non Volatile) during the balance of the solvent used and the fresh-off process (the process of forcibly drying the water contained in the water-soluble coating). In order to solve the problem of high flow, especially in high humidity, the thixotropic property of the paint should be optimized and designed. The thixotropic property of the paint is used in the storage stability of the paint and the paint transport line (PCS). Filter and transportability, atomization in the coating machine, wetness of the body after arrival, good film formation, and drying of the coating film, and the like.

Therefore, in order to optimize these thixotropic properties, paints generally use a flow control alkylalkyl shellable acrylic emulsion alone, but in this case at all shear rates for paint storage and transportation, painting and drying steps. There is a problem that viscosity optimization cannot be satisfied.

Therefore, in the present invention, as a result of various studies to solve the problems as described above, by applying a reverse-phase core / shell microgel and a complex flow control agent to expand the narrow coating temperature and humidity region and at the same time excellent in appearance and mechanical properties It was possible to obtain a water-soluble waterborne coating composition for automobiles excellent in painting workability and paint storage stability and color retention ability, and the present invention was completed based on this.

Accordingly, an object of the present invention is not only to expand the paintable temperature and humidity range, but also to show a water-soluble top coat composition for automobiles having excellent mechanical properties such as glossiness and sunscreen resistance and cold resistance chipping resistance, impact resistance, bending resistance, and repaint adhesion. To provide.

It is another object of the present invention to provide a water-soluble top coating composition for automobiles having excellent paintability such as spreadability with a base material, compatibility with transparent paints applied on top coats, dust stability during coating, and storage stability and color retention of paints. .

The composition of the present invention for achieving the above and other objects is 20 to 50% by weight of a polyacrylic water dispersion resin having a hydroxyl group of 50 to 200 mgKOH / g and a glass transition temperature of -20 to 10 ℃, reverse phase core / shell type 10 to 40% by weight of microgel resin, 0.5 to 5% by weight of hydrophilic imino group-containing melamine curing agent, 5 to 50% by weight of white or colored pigment aqueous dispersion, or mixtures thereof, 1 to 15% by weight of solvent, 0.5 to 2 wet dispersant It consists of a weight%, an antifoamer 0.1-1 weight%, a fluidity regulator 0.01-1 weight%, a wetting agent 0.1-2 weight%, and a neutralizing agent 0.1-1 weight%.

Hereinafter, the present invention will be described in more detail.

According to the present invention, a polymer particle having a two-layer structure having a particle size of about 0.1 micron, and the shell portion of the polymer is applied to a microgel containing a carboxyl group partially or completely neutralized with an amine, thereby improving plasticity at low solids content. It is possible to provide a water-soluble coating composition for automobiles which can not only control the flowability during formation of the coating film but also help fusion of the polymer particles during the coating film formation and express good coating performance.

In addition, in the present invention, by applying a separate fluidity regulator to the water-soluble coating composition for automobiles can improve the flow affecting the vertical appearance defects after drying or after transparent coating.

The water-soluble coating composition for automobiles of the present invention is 20 to 50% by weight of a polyacrylic water dispersion resin having a hydroxyl group of 50 to 200 mgKOH / g and a glass transition temperature of -20 to 10 ° C, and a reversed phase core / shell type microgel resin 10 to 40% by weight, 0.5-5% by weight of hydrophilic imino group-containing melamine curing agent, 5-50% by weight of white or colored pigment aqueous dispersion, or mixtures thereof, 1-15% by weight of coarse solvent, 0.5-2% by weight of wet dispersion, antifoaming agent 0.1 It consists of -1 weight%, a fluidity regulator 0.01-1 weight%, a wetting agent 0.1-2 weight%, and a neutralizing agent 0.1-1 weight%.

The components of each of the automotive water-soluble coating composition of the present invention will be described in more detail as follows.

(1) polyacrylic water dispersion resin

According to the present invention, the polyacrylic water-dispersible resin may have various physical properties depending on the type of monomer, solvent used, initiator and specific additives used as the main resin of the water-soluble topcoat composition for automobiles.

The polyacrylic water-dispersible resin of the present invention is prepared by copolymerizing an acrylic monomer while controlling the molecular weight to the initiator content in the presence of a solvent. On the other hand, in the case of general polyacrylic water-dispersion resin, since the hardening of the coating film promotes, the polyacrylic water-dispersion resin of the present invention improves softness, tensile strength and adhesion to 90-95% by weight of hard acrylic resin. It is prepared by introducing 5 to 10% by weight of an epoxy monomer. On the other hand, as the epoxy monomer usable in the present invention, Kadura E-10 (shell company) containing an epoxy group is particularly preferable. The copolymer thus prepared is subjected to water removal by removing the solvent through reduced pressure, neutralizing with trivalent amine, and then adding water.

The polyacrylic water-dispersion resin prepared as described above has a solid content of 40% by weight, an acid value of 30 to 80 mgKOH / g, a hydroxyl group of 50 to 200 mgKOH / g, a glass transition temperature of -20 to 10 ° C, a molecular weight of 5000 to 15000, and It is a water dispersion resin which is stable at pH 7.5-8.5.

In addition, the polyacrylic water-dispersion resin of the present invention is cold-resistant chipping resistance, impact resistance and bending resistance reduction due to the hardening of the coating film, which is a problem that the conventional polyacrylic water-dispersion resin when applied as a main resin of automotive water-soluble coating composition The phenomenon can be improved, and compatibility with the reversed phase core / shell type microgel applied as the secondary resin of the present invention is also very good. At this time, the amount of the water-dispersible resin is preferably 20 to 50% by weight. If the amount of the water-dispersible resin is less than 20% by weight, there is a problem in that repainting adhesion of the coating film is significantly lowered. There is a problem that the cold resistance chipping resistance, impact resistance and bending resistance of the coating film is lowered.

(2) Reversed-phase Core / Shell Microgel Resin

According to the present invention, the reversed-phase core / shell-type microgel is crosslinked with a central core, and graft polymerized around the core to stabilize the shell. As a method of preparing the reversed phase core / shell-type microgel, an emulsion method of transferring particles obtained by non-aqueous dispersion into water is usually used, but recently, a method obtained by emulsion method in water is also used. Since the shell portion of the reversed-phase core / shell type microgel of the present invention contains a carboxyl group partially or completely neutralized with an amine, it not only contributes to the stabilization of particles but also forms a weak network by mutual attraction with adjacent particle shells, thereby increasing viscosity. Cause. In addition, these mutual forces are reversible and destroyed during atomization under high shear stress and then restored at low shear rates after arrival. Therefore, the coating material including the microgel of the present invention has a plasticity property even at a low solid content, and can control the flowability of the coating film when forming the coating film. On the other hand, the shell assists the fusion of the polymer particles during coating film formation and crosslinks the carboxyl group and the hydroxyl group with the melamine resin to impart good coating performance.

The process for producing a reversed phase core / shell microgel resin of the present invention comprises 5 to 40% by weight of a monomer containing a carboxylic acid group, 50 to 90% by weight of a non-crosslinkable monomer containing one olefin in a molecule, and 0.1 to anionic reactive emulsifier. A first step of obtaining a core particulate polymer by adding 0.5 to 1.2 equivalents of a neutralizing agent to 1 equivalent of carboxylic acid of the polymer is added to the core emulsion polymer prepared by adding 3.0% by weight and 0.2 to 1.5% by weight of the radical polymerization initiator. Include.

In the first step of obtaining the core particulate polymer is prepared a polymer by a conventional emulsion polymerization method. In the polymer production method, the monomer having a carboxylic acid group is used in an amount sufficient to serve as a stabilizer of the polymer particles in the subsequent shell polymerization of the second stage and to cause phase inversion, wherein the non-crosslinkable monomer is A small amount of anionic reactive emulsifier and radical polymerization initiator are used in the added hydrophilic monomer composition to obtain a core emulsion polymer. Next, a neutralizing agent is added to the polymer to obtain a pseudo water-soluble resin.

On the other hand, as a monomer used to prepare the core emulsion of the first step, as a non-crosslinkable monomer containing one olefin in the molecule, alkyl or cycloalkyl acrylic acid, methacrylic acid ester, alkoxy alkyl acrylic acid or mecha having 1 to 18 carbon atoms Acrylic esters, alkoxy alkyl acrylic or methacrylic esters, hydroxy alkyl acrylic or methacrylic esters of 2 to 8 carbon atoms, vinyl aromatic compounds, conjugate dienes of 4 to 9 carbon atoms, and acrylonitrile or methacrylonitrile, acrylamide , Methacrylamide, and the like. At this time, the amount of the non-crosslinking monomer is preferably 50 to 90% by weight.

Examples of the monomer containing a carboxylic acid group include a monomer containing a single carboxylic acid group consisting of acrylic acid, methacrylic acid, vinylbenzene acid and isopentylbenzene acid, and two carbons consisting of itacic acid, maleic acid, phthalic acid and acid anhydride thereof. It is preferable to select one or two or more from the group consisting of monomers containing an acid group, and the amount thereof is preferably 5 to 40% by weight. If the amount of the monomer containing the carboxylic acid group is 5% by weight or less, the degree of water solubility during neutralization is low, so that it does not play a role as an emulsifier in the subsequent shell manufacturing process. This progresses the disadvantage that the particle growth and the stability of the reaction is lowered.

According to the present invention, an anionic reactive emulsifier having a vinyl group which can be polymerized by radicals is added to further reduce the content of the low molecular weight emulsifier in the core component and to give polarity to the surface of the core particle to facilitate phase inversion. The anionic reactive emulsifier acts as an emulsifier as a kind of monomer, and in particular, anion may cause anion of the surface of the polymer to be produced. At this time, the amount of the anionic reactive emulsifier is preferably 0.1 to 3.0% by weight, and if the amount of the emulsifier is less than 0.1% by weight, the reaction stability is lowered due to lack of emulsifier. When new particles are produced, the water resistance of the final coating is lowered.

As the radical polymerization initiator of the present invention, both an initiator which generates a radical by thermal dissociation at a high temperature and an initiator which generates a radical by a redox reaction at a low temperature can be used, but a thermal dissociation initiator is particularly preferable. As the thermal dissociation initiator, for example, ammonium, potassium, sodium persulfate, cyclohexyl hydroperoxide, cumene hydroperoxide, n-octyl hydroperoxide, t-butyl hydroperoxide, sec-butyl Water-soluble thermal dissociation initiators such as hydroperoxide, 1-phenyl-2-methylpropyl 1-hydroperoxide and the like are preferred. In this case, the amount of the radical polymerization initiator is preferably 0.2 to 1.5% by weight, and when the amount of the polymerization initiator is 0.2% by weight or less, there is a disadvantage in that the polymerization time is long. There is this.

On the other hand, the core emulsion sufficiently containing the carboxylic acid prepared by the addition of the respective components is neutralized with a neutralizing agent consisting of a base for use as a polymer dispersant in the second step of obtaining the next shell emulsion polymer. At this time, the core emulsion polymer is competitively swelling and dissolution behavior, the factors that affect the competitive behavior decisively include the kind of neutralizing agent, the appropriate neutralization degree, the hydrophilicity of the core composition and the core particle structure.

The neutralizing agents usable in the present invention include inorganic bases such as ammonia, sodium hydroxide and potassium hydroxide, and organic bases such as primary, secondary and tertiary amines such as dimethylethanol amine and triethylamine. 0.5-1.2 equivalent is preferable with respect to 1 equivalent of carboxylic acid of the said core emulsion polymer. At this time, if the amount of the emulsifier is less than 0.5 equivalent, the degree of solubilization during neutralization is low, so that it cannot act as an emulsifier in the subsequent shell process. Can't play a role. On the other hand, the degree of neutralization is the most important factor in the swelling / melting behavior of the core emulsion polymer. As the degree of neutralization increases, the dissolution behavior becomes stronger, so that the solubility of the core particles is promoted, but the degree of neutralization is too high. It does not give stability of emulsion polymerization. Therefore, in order to impart stability of the second stage emulsion polymerization, an appropriate degree of neutralization is required, and according to the present invention, a degree of neutralization of 10 to 50% is suitable for the total amount of carboxylic acid groups of the core polymer.

In addition, the method for producing a reversed-phase core / shell microgel resin of the present invention is a shell by reacting 88 to 99.9% by weight of a non-crosslinkable monomer containing one olefin and 0.1 to 12% by weight of a crosslinking monomer containing two or more olefins. A second step of obtaining an emulsion polymer is included.

According to the present invention, in the second step of obtaining the shell emulsion polymer, a phase hydrophobic monomer composition is prepared by using a non-crosslinkable monomer and a crosslinking monomer in the shell monomer composition so that phase inversion occurs.

On the other hand, the monomer used to prepare the shell emulsion of the second step is a non-crosslinkable monomer containing one olefin in the molecule, alkyl or cycloalkyl acrylic acid or methacrylic acid ester of 1 to 18 carbon atoms, alkoxy alkyl acrylic acid or Methacrylic acid ester, alkoxy alkyl acrylic acid or methacrylic acid ester, hydroxy alkyl acrylic acid or methacrylic acid ester having 2 to 8 carbon atoms, vinyl aromatic compound, conjugate diene having 4 to 9 carbon atoms, acrylonitrile or methacrylonitrile.

In addition, as the crosslinkable monomer usable in the present invention, monomers containing two or more olefins in the molecule to increase the graft reaction with the shell component include divinylbenzene, 1.4-divinylbenzene arylacrylate, and arylmethacryl. Rate, 1.6-hexanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, butanediol diacrylate, diaryl phthalate, diaryl One or more selected from the group consisting of phthalate, tripropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and the like may be mixed and used, and the amount of use thereof is sufficiently smaller than that of the non-crosslinked monomer to enable phase inversion. Therefore, the amount of the crosslinking monomer used is preferably 0.1 to 12% by weight, when the amount of the crosslinking monomer used is less than 0.1% by weight, the crosslinking effect is lowered, and when the amount of the crosslinking monomer is more than 12% by weight, it is difficult to reverse phase.

On the other hand, the weight ratio of the polyacrylic water dispersion resin of the present invention and the core / shell-type microgel resin is preferably 60:40 ~ 90:10, when the weight ratio is out of the above range, the re-coating adhesion of the coating film is lowered There are disadvantages.

In the case of using the prepared reversed phase core / shell type microgel resin in an automotive water-based paint, it has the advantages of the paint using a conventional microgel emulsion polymer and at the same time can be enhanced in water resistance, alkali resistance, rust resistance and adhesion. In addition, when the resin is prepared by blending the resin with a polyacrylic water-dispersible resin, the crosslinking density of the coating film is higher than that of the non-microgel, so that the stain resistance and the denseness of the coating film are improved, and the plasticity is excellent, thereby providing a beautiful appearance and high gloss. The paint which has is obtained.

(3) hydrophilic melamine resin

The hydrophilic melamine resin of the present invention is applied for crosslinking reaction upon curing with a polyacrylic water-dispersible resin and a microgel resin prepared according to the above-described method, and in the present invention, the water-dispersible resin described above at 140 to 150 ° C under a catalyst. 0.5 to 5% by weight of an imino group-containing hydrophilic melamine resin is applied so that the hydroxyl group and the methoxy group and the imino group of the hydrophilic melamine resin can crosslink. At this time, when the amount of the melamine resin used is less than 0.5% by weight, the uncrosslinked hydroxyl group remains in the coating film, and in particular, the recoating adhesion of the coating film is lowered. When the amount of the melamine resin is used, the self-polymerization of the unreacted hydrophilic melamine resin in the coating film is exceeded. As a result, a tendency of the coating film to crumble occurs, and in particular, the cold resistance chipping resistance, impact resistance and bending resistance of the coating film are lowered.

On the other hand, the product applicable to the hydrophilic melamine resin of the present invention, for example, Cytec's Cymel-325, Cymel-327, Cymel-385 and Solusia's Regimen HM-2608, Regimen-718, Reji Men-717.

As described above, when the coating composition is applied by applying the resin of the present invention, the hydroxyl structure of the main resin and the methoxy group and imino group of the hydrophilic melamine resin are crosslinked at 140 to 150 ° C. so that the molecular structure of the resin is completed. Is designed.

(4) White or colored pigment water dispersion

The aqueous dispersion of white or colored pigments may be used alone, or a mixture thereof may be used, and the amount thereof is preferably 5 to 50% by weight.

(5) solvent

Cosolvents usable in the present invention include high boiling point solvents such as butyl glycol, butyl carbitol, N-methyl-2-pyrrolidone, 2-ethylhexanol, hexyl cellosolve; And low boiling point solvents such as n-propyl alcohol, isopropyl alcohol, butanol, and the like, and the component ratio of the co-solvent has a great influence on the antipopping and smoothing of the coating film, lowers the minimum film forming temperature, and the paint is atomized during painting. Not only does it smooth the atomization, it also contributes greatly to the volatilization of water, the main solvent. At this time, the amount of the solvent is preferably used in an amount of 1 to 15% by weight, and if the amount is less than 1% by weight, the surface of the paint cannot be wrapped, and thus the smoothness of the coating film is increased due to an increase in the surface tension of the paint. In addition, if the content exceeds 15% by weight, the atomization of the paint or the smoothness of the coating may be improved, but the volatile organic solvent content may be out of the standard to contaminate the air.

(6) wetting dispersant

As the wet dispersant of the present invention, a water-soluble dispersant is used to disperse the pigment in a uniform and stable state in the preparation of the aqueous dispersion of the white pigment and the pigment pigment to particles of 5 microns or less, and the water-soluble dispersant is an interface containing ionic groups. Polymers, such as an aromatic, aliphatic ethoxylate, and polyacrylate which consist of an active agent and a nonionic group, are contained. For example, the water-soluble dispersant includes D180 and D-190 of BYK, W-22 and W-28 of Daniel, Solsper 20000 and 27000 of Avecia, FX-504 and FN-360 of Servo Delden. At this time, the amount of the wet dispersant is preferably applied in 3 to 20% by weight depending on the type of pigment applied, which corresponds to 0.5 to 2% by weight of the total coating composition. When the amount of the wet dispersant is less than 0.5% by weight of the total coating composition, it is difficult to disperse the pigment to a desired particle size during pigment dispersion. When the amount of the wet dispersant exceeds 2% by weight, the pigment dispersibility is improved, but the adhesion and water resistance of the coating film are inhibited. It becomes a factor.

(7) antifoam

The antifoaming agent of the present invention is applied to suppress the generation of bubbles generated during the aqueous dispersion of the pigment and the paint and to suppress and eliminate the phenomenon such as pinhole or popping caused during the formation of the coating film. The antifoaming agent is first added half of the total amount used in the preparation of the aqueous component dispersion, the other half is added during the manufacture of the paint, the amount is preferably 0.1 to 1.0% by weight. At this time, if the amount of the antifoaming agent is less than 0.1% by weight, there is no defoaming effect, so that a large amount of bubbles are generated during pigment dispersion and paint production, and it does not turn off easily. Of course, there is a problem of inhibiting the adhesion of the coating film. On the other hand, examples of the product applicable as the antifoaming agent include BYK-011 manufactured by BYK, DF-21 manufactured by Air Products, and Foamaster-324 manufactured by Sanofco.

(8) fluidity regulator

As the fluidity regulator of the present invention, an alkali shellable acrylic emulsion and hectorite clay are used together, and its amount is preferably 0.01 to 1% by weight. At this time, if the amount of use is less than 0.01% by weight, it causes the flow in high humidity at the time of coating, and when it exceeds 1% by weight, the viscosity of the paint is too high, the pigment dispersibility is poor, and the atomization of the paint is difficult. On the other hand, examples of the product applicable as the hectorite clay rheology control agent include Liax Benton AD and ED, Sudchem's Optigel CK and SK, Lafort's Laponite RD and RDS.

(9) wetting agent

According to the present invention, in order to improve the wettability of the coating material and smoothness of the coating film, a wetting agent or an acetylene alcohol type wetting agent of a polyether-modified polysiloxane system is added during the preparation of the paint. At this time, the amount of the wetting agent is preferably 0.1 to 2% by weight, if the amount of the wetting agent is less than 0.1% by weight of the paint has a problem in that the paint does not adhere well to the material during painting, 2 Exceeding the weight% may cause a cost increase of the paint, as well as a reduction in the surface tension of the paint, which may cause a cracking phenomenon on the surface of the substrate during coating, and also cause a problem that adhesion of the coating film is impaired. On the other hand, examples of the product that can be applied to the wetting agent include BYK- BYK-345 and BYK-348, Air Products' Surfynol-104BC and Surfynol-61, Taego's Wet 510 and Wet 505.

(10) neutralizer

According to the present invention, the neutralizing agent of the amines is used to control the storage stability and pH of the aqueous dispersion and the final coating, and the pH of the aqueous dispersion and the coating is measured and adjusted to about 7.5 to 9.5. At this time, the amount of the neutralizing agent is preferably 0.1 to 1% by weight, and when the amount of the neutralizing agent is less than 0.1% by weight, the pH of the paint decreases, thereby affecting the storage stability, thereby causing the precipitation and reaggregation of pigments. When the weight% is exceeded, the paint is alkalized, and there is a problem in that the alkali resistance of the coating film is significantly lowered. On the other hand, amines applicable as the neutralizing agent include ammonia, triethylamine, dimethylethanol aman and Angus' AMP-95 and the like.

The water-soluble topcoat composition for automobiles of the present invention prepared as described above may be coated by conventional methods, including brushing, dipping, pro-coating, etc., in particular, in the case of automobile coating, such as bell and gun automatic coating and manual It is preferably carried out by spray coating, and the paint according to the invention can also be applied on various substrates such as wood, metal, glass, fiber, plastics and steel.

As described above, the present invention not only enlarges the paintable temperature and humidity range, but also has excellent appearance such as gloss and lightness, and water-soluble topcoat for automobiles having excellent mechanical properties such as cold resistance chipping resistance, impact resistance, bending resistance, and repaint adhesion. A composition can be provided. In addition, the present invention can provide a water-soluble top coating composition for automobiles excellent in coating workability such as spreadability with the base material, compatibility with the transparent coating applied to the top coating and dust stability during coating and storage stability and color retention of the coating. .

Hereinafter, the present invention will be described in detail with reference to comparative examples and examples, but the scope of the present invention is not limited to the following examples.

Preparation Example 1

Preparation of Polyacrylic Water Dispersion Resin

According to the composition of Table 1 below, an initiator, xylene, butanol were mixed and injected into a glomerular glass flask to adjust the temperature to 120 to 130 ° C. Then, Kadura E10 and acrylic monomers were mixed and added dropwise to the flask for 3 hours. After holding for 2 hours, n-methyl-2-pyrrolidone was added and reduced in pressure to remove xylene and butanol. The temperature was then lowered to 80 ° C., then dimethylethanolamine was added and held for 30 minutes. Distilled water was slowly added thereto, dispersed in water, and filtered with # 400. The polyacrylic water dispersion thus prepared was a stable aqueous dispersion having a solid content of 40 wt%, an acid value of 65 mg KOH / g, a hydroxyl group of 126 mg KOH / g, a weight average molecular weight of 9000, a glass transition temperature of 5 ° C., and a pH of 8.

Furtherance Parts by weight Azobisisobutyronitrile 1.0 Zyren 135 Butanol 15 Kadura E-10 110 Acrylic acid 50 Methyl methacrylate 60 Butyl acrylate 200 Styrene monomer 60 2-hydroxyethyl methacrylate 120 n-methyl-2-pyrrolidone 30 Dimethylethanolamine 7 Distilled water 862 Sum 1650

Preparation Example 2

Preparation of Reversed-Phase Core / Shell Microgels

In a 5-liter four-necked flask equipped with a thermometer, 2000 g of distilled water, 2 g of sulfated ammonium salt of alkylphenoxypoly (5 mole of ethyleneoxy) ethanol, and 31 g of monomer MMA were added and the temperature was raised to 80 ° C. When the temperature was maintained at 80 ℃ was injected nitrogen for 5 minutes to remove the nitrogen after the reaction part in a nitrogen atmosphere. 0.7 g of sodium persulfate was dissolved in 10 g of distilled water, and then charged into a reactor and aged for 30 minutes.

An initiator solution of 0.5 g of sodium persulfate dissolved in 25 g of distilled water was added dropwise for 10 minutes, followed by 106 g of monomer mixture BA (Butyl Acrylate), 50 g of MMA (Methyl Metacrylate), 96 g of BMA (Butyl Methacrylate), 36 g of MAA (Methacrylic Acid), and CO- An emulsifier solution in which 3.2 g of 436 (sulfated ammonium of alkylphenoxypolyethanol: Rhodia) was dissolved in 324 g of distilled water was added dropwise at the same time for 1 hour and 30 minutes, and then maintained for 1 hour. The neutralizer solution in which 2.6 g of NaOH was dissolved in 165.4 g of distilled water was added thereto for 20 minutes, and then maintained for 20 minutes.

A mixture of 1.34 g of 1,6-HDDA (Hexanediol Dicacrylate), 0.31 g of Ethyleneglycol Dimethacrylate (EGDMA) and 22.6 g of 2-Hydroxy Ethyl Methacrylate (2-HEMA), 175 g of Butyl Acrylate (BA), 235 g of Methyl (Methyl Metacrylate), BMA (Butyl Methacrylate) A mixture of 208 g of the mixture and an initiator solution of 3.3 g of sodium sulfate dissolved in 283 g of distilled water were added dropwise at the same time for 2 hours and then aged for 1 hour. The reactor was cooled to 40 ° C. and a pH of 8.0-8.5 was adjusted by dropping 10% aqueous solution of dimethyl ethanol amine (DMEA). Filtration was removed by filtration with a 200 mesh filter, and left for 1 day after packing. Solid content of the finally prepared emulsion was 26 parts by weight based on the total emulsion components, the pH was 8.3, the particle size was 110nm.

Preparation Example 3

Preparation of White Pigment Dispersions

Each component shown in Table 2 was mixed and then dispersed to 5 microns or less with a disperser to prepare a white pigment dispersion.

Furtherance weight% Distilled water 21 Butyl Carbitol 5 Wet Dispersant 2.5 Antifoam 0.5 10% Dimethyl Ethanol Amine (DMEA) One Polyurethane Dispersion 20 Titanium dioxide 50 system 100

Example 1 and Comparative Examples 1-3

A water-soluble top coat composition for automobiles was prepared by mixing the respective components shown in Table 3 in the order of 50 seconds with Pood Cup # 4. The water-soluble topcoat composition for automobiles prepared as described above was bell-painted so as to be 15 to 25 microns in a dry coating film on the middle (coating condition: 20 ° C, relative humidity 70% / 25 ° C, relative humidity 75% / 25 ° C, relative Humidity 85%), infrared oven at 80 ℃ for 2 minutes and hot air for 2 minutes to evaporate the remaining water in the paint to paint a useful transparent topcoat and at 140 ~ 150 ℃ for 20-30 minutes in general oven. After heating and curing to form a final coating film, their physical properties were measured and the results are shown in Table 4 below.

Furtherance Example 1 (parts by weight) Comparative Example 1 (parts by weight) Comparative Example 2 (parts by weight) Comparative Example 3 (parts by weight) Preparation Example 3 40 40 40 40 Laponite RD 0.25 0.25 - 0.25 Byketol WS (BYK Corporation) One One One - Preparation Example 1 33 42 33 33 Preparation Example 2 12 - 12 12 2-ethylhexanol One One One One Butyl Cellosolve 4.5 4.5 4.5 4.5 Hexyl cellosolve 5.5 5.5 5.5 5.5 BYK-345 ¹ 0.5 0.5 0.5 0.5 Cymel 325 ² 2 2 2 2 10% DMEA 2 2 2 2 Foamaster 324 ³ 0.5 0.5 0.5 0.5 Colorant One One One One Alkali Shellable Acrylic Emulsion 0.5 0.5 0.5 - Distilled water - 3 - - system 103.75 102.75 103.5 103

1: BYK wetting agent

2: melamine curing agent from Cytec

3: antifoaming agent

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Painting condition 20 ℃, relative humidity 70% 25 ℃, relative humidity 75% 25 ℃, relative humidity 85% 20 ℃, relative humidity 70% 25 ℃, relative humidity 75% 25 ℃, relative humidity 85% 20 ℃, relative humidity 70% 25 ℃, relative humidity 75% 25 ℃, relative humidity 85% 20 ℃, relative humidity 70% 25 ℃, relative humidity 75% 25 ℃, relative humidity 85% Storage stability O O O O O O O O O △ △ △ Painting workability ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Coating appearance O ◎ ◎ △ X X △ △ X △ X X Polish ◎ ◎ ◎ △ X X △ △ X X X X Flex resistance O O O O O O O O O O O O Repaint adhesion ◎ ◎ ◎ O O O ◎ ◎ ◎ O O O Impact resistance O O O O O O O O O O O O Chipping resistance O O O O O O O O O O O O Chilsung Castle ◎ ◎ O △ X X △ △ X X X X ◎: Very good O: Good △: Normal X: Poor

Storage stability: After standing at 45 ° C. for 5 days, within 15% of the viscosity change when measuring viscosity at room temperature, and in the container of paint, there is no dust, foreign matter, hard mass, and it is dispersed uniformly.

Paintability: Good spraying condition when discharging paint, good wettability

Gloss: Should be above 90 at 60 degrees.

Coating appearance: After bell coating in each condition, there should be no phenomena such as crater, pinhole and popping in the coating after curing.

Cold resistance chipping resistance: After holding at -40 ℃ for 3 hours, impact with Honda Stone at 4bar pressure to make 10 or less peeling parts between 1 and 2m, and 1 or more for 2mm or more.

Impact resistance: There should be no crack and peeling on the coating film when the weight of 500g is dropped from the height of 20cm.

Flex resistance: No cracks or peeling on the coating film when the body is bent in a round steel of 3/16 inch circumference.

Re-coating Adhesion: After final coating curing at 150 ℃ for 20 minutes, over-baking at 160 ℃ for 60 minutes, repainting and curing of top coat and transparent topcoat, and adhesion test should be more than 90/100. .

Chilling property: There shall be no paint flow or gloss decrease when observed after curing the electrodeposited and intermediate coated specimens vertically and coating the top coat under each condition.

As shown in Table 4, the water-soluble top coat according to the embodiment of the present invention is capable of coating a temperature-humidity region, such as extending the coating work conditions compared to the existing water-soluble topcoat to exhibit a good appearance and flowability at low or high humidity. In addition to the enlargement, it was found that the mechanical properties such as appearance and cold resistance chipping resistance, impact resistance, bending resistance and re-coating adhesion, such as gloss and lightness, were excellent.

As described above, the water-soluble topcoat composition for automobiles of the present invention has excellent appearance such as gloss and stiffness, as well as cold resistance chipping resistance, compatibility with transparent coatings applied on top coats, dust stability, etc. It is expected to be very useful industrially because of its excellent workability, storage stability and color retention of paint and wider range of temperature and humidity available for coating than recently introduced waterborne topcoat.

Claims (5)

20-50% by weight of polyacrylic water-dispersible resin having a hydroxyl group of 50-200 mgKOH / g and a glass transition temperature of -20-10 ° C, 10-40% by weight of a reversed phase core / shell-type microgel resin, melamine containing hydrophilic imino group 0.5 to 5% by weight of curing agent, 5 to 50% by weight of white or colored pigment aqueous dispersion, or mixtures thereof, 1 to 15% by weight of coarse solvent, 0.5 to 2% by weight of dispersant, 0.1 to 1% by weight of antifoaming agent, and 0.01 to 1% of fluidity regulator A water-soluble top coat composition for automobiles, comprising 1% by weight, 0.1 to 2% by weight of the wetting agent, and 0.1 to 1% by weight of the neutralizing agent. The water-soluble topcoat composition for automobiles according to claim 1, wherein the polyacrylic water-dispersible resin is made of 90 to 95% by weight of hard acrylic resin and 5 to 10% by weight of epoxy monomer. The method of claim 1, wherein the reversed phase core / shell microgel resin is: 5 to 40% by weight of monomer containing carboxylic acid group, 50 to 90% by weight of non-crosslinkable monomer containing one olefin, 0.1 to 3.0% by weight of anionic reactive emulsifier, and 0.2 to 1.5% by weight of radical polymerization initiator A core polymer prepared by adding 0.5 to 1.2 equivalents of a neutralizing agent based on 1 equivalent of the carboxylic acid of the polymer to the core emulsion polymer prepared by the method; And Water-soluble waterborne coating composition for automobiles, comprising a shell emulsion polymer prepared by reacting 88 to 99.9% by weight of a non-crosslinking monomer containing one olefin and 0.1 to 12% by weight of a crosslinking monomer containing two or more olefins. . The water-soluble top coat composition for automobiles according to claim 1, wherein the weight ratio of the polyacrylic water-dispersible resin and the reversed phase core / shell-type microgel resin is 60:40 to 90:10. The water-soluble topcoat composition for automobiles according to claim 1, wherein the flow control agent is an alkali shellable acrylic emulsion and hectorite clay.