KR101277446B1 - Water-soluble basecoat paint composition for automobiles and method of forming paint layer using the same - Google Patents

Abstract

PURPOSE: An aqueous paint composition is provided to have excellent exterior appearance, adhesion, impact resistance, flexure resistance, and chipping resistance. CONSTITUTION: An aqueous paint composition comprises: 20-50 wt% of alkali-swelling core-shell resin manufactured by using a urethane aqueous dispersion; 3-10 wt% of hardening mixture; 2-105 wt% of polyester resin; and residual water. The curing mixture comprises 10-30 wt% of butyl cellosolve, 10-30 wt% of isopropylalcohol, 5-15 wt% of N-methyl-2-pyrrolidone, 25-35 wt% of melamine resin, 15-25 wt% of hydrophobic melamine resin, and 2-5 wt% of nonionic surfactant.

Description

WATER-SOLUBLE BASECOAT PAINT COMPOSITION FOR AUTOMOBILES AND METHOD OF FORMING PAINT LAYER USING THE SAME}

The present invention relates to a water-soluble top coating composition for automobiles and a method for forming a coating film using the same, and in particular, the appearance and the water resistance, adhesion, impact resistance, bending resistance and repainting on over-drying coating film, such as gloss and screening The present invention relates to a water-soluble waterborne coating composition for automobiles having excellent mechanical properties such as performance and excellent painting workability related to flow and staining, and a method of forming a coating film using the same.

The automotive paint industry has also changed a lot due to restrictions on the emission of volatile organic compounds (VOCs), which has been an issue for many years in relation to the body painting that forms the central axis with engine and steering parts of the automobile industry. Are going through. In particular, Europe and developed countries are actively restricting the use of VOCs and imposing sanctions on products using them.

In general, since VOC is easily volatilized at room temperature, it is naturally emitted in the atmospheric environment when it is in a gaseous state, which is an important cause of air pollution. In addition, the VOCs have biotoxicity and chemical reactivity, which causes ozone layer destruction, greenhouse effect, and odor generation, thereby seriously destroying the environment.

Therefore, the reduction of VOCs for automobile paints has become very important in terms of environmental preservation and workplace improvement due to the emission control policy for VOC. In order to reduce VOCs in automobile paints, measures to reduce VOCs have been made, such as high solidification of oil-soluble paints, shortening of coating processes for oil-soluble paints, and water-based paints. The most effective countermeasure against VOC is the conversion to water-soluble paint that minimizes the amount of VOC contained in the paint itself. In particular, it is very effective to replace the oil-soluble top coating with a content of 50 to 70% of the organic solvent with a water-soluble top coating. Accordingly, research on water-soluble topcoats has been actively conducted.

In the existing oil-soluble coatings, acrylic resins, melamine resins, polyester resins, polyurethane resins, organic solvents, and the like are mainly used. It is characterized by excellent mechanical properties such as sensibility and adhesion, impact resistance, flex resistance. Alternatively, a hydrophilic melamine resin is used together with a polyester resin, a urethane dispersion, or the like as an auxiliary resin using a water-soluble acrylic resin, a water-soluble microgel resin or an acrylic emulsion as a main resin, or a hydrophobic melamine aqueous dispersion together with the main resin and the auxiliary resin. Has been used. In the case of the water-soluble top coat of such a composition, it tends to be somewhat inferior in workability and water resistance, such as flowability, compared with the existing oil-soluble paint.

As a commonly used water-soluble top coat, acrylic resins and inverted core / shell-type microgel resins are used together, and urethane dispersions and polyester resins are used as auxiliary resins to obtain the effect of improving the orientation of the chipping resistance and the bright pigment. There is.

In particular, acrylic resin may be used as a reaction resin in the production of hydrophobic melamine dispersion. However, the paint of the composition has a disadvantage that the water resistance of the final coating film is lowered due to the anionic reactive emulsifier used in the microgel resin.

In addition, hardeners generally used in conventional water-soluble coatings for automobiles include amino resins, block isocyanate compounds, aziridine compounds, epoxy compounds, and the like. Amino resins usable as curing agents include hydrophilic melamine resins or hydrophobic melamine resins such as methyl etherated melamine having an average of three or more methylol groups per triazine nucleus. In the case of the hydrophilic melamine resin, it can be directly added to the water-soluble coating composition. However, when hydrophobic melamine resin should be used to improve physical properties such as adhesion, there is a restriction that it is used as a curing agent for water-soluble paints by reacting with a melamine resin water dispersion.

 The hydrophobic melamine resin water dispersion is obtained by reacting a specific acrylic resin and a hydrophobic melamine resin. This is because the resin particles having a particle diameter in the range of 20 to 140 nm are dispersed in water and require a reaction time in the range of 1 to 10 hours at a temperature of 70 to 100 ° C. In addition, there is a further need for cooling the obtained reaction product to 50 ° C. or less and dispersing with water. As such a process requires a separate facility and a reaction time of up to 10 hours, it has been noted that the manufacturing efficiency of the water-soluble topcoat due to the application of the hydrophobic melamine resin is reduced.

If only hydrophilic melamine resin is used, there may be a problem in that repainting adhesion is deteriorated on an over baking coating film of a transparent coating (clear coating) coated on the top coating.

Accordingly, the technical problem of the present invention is a water-soluble coating composition having a new composition having excellent mechanical properties such as adhesion, impact resistance, bending resistance, chipping resistance, and repainting adhesion on over-drying coatings, as well as appearance such as gloss and lightness. To provide.

Another object of the present invention is to provide a method for forming a coating film using the above water-soluble coating composition.

The water-soluble coating composition for realizing the above object of the present invention is 20 to 50% by weight of an alkali swellable core shell resin prepared by using a urethane water dispersion as an emulsifier based on the total amount of the coating composition; 10-30 weight% butyl cellosolve, 10-30 weight% isopropyl alcohol, 5-15 weight% N-methyl-2-pyrrolidone, 25-35 weight% hydrophilic melamine resin based on the total amount of the curing agent mixture 3 to 10 weight percent of a curing agent mixture comprising 15 to 25 weight percent of a hydrophobic melamine resin and 2 to 5 weight percent of a nonionic surfactant; 2 to 10 wt% polyester resin; And excess water.

In one embodiment, the urethane water dispersion is a bifunctional isocyanate compound having a polycarbonate polyol having a molecular weight of 1,500 ~ 2,500 and two or more hydroxyl groups and reacting a compound having a monofunctional carboxylic acid having an isocyanate functional group at the terminal It can be obtained by preparing a prepolymer, dispersing it in an aqueous amine solution and then chain extension.

In one embodiment, the bifunctional isocyanate compound may be at least one selected from the group consisting of 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4-bis isocyanato cyclohexyl methane.

In one embodiment, the compound having two or more hydroxyl groups and a monofunctional carboxylic acid may be at least one of dimethylol propionic acid and dimethylol butanoic acid.

In one embodiment, the alkali swellable core shell resin may include a core formed by emulsion polymerization of the emulsifier and the first monomer mixture and a shell portion formed of a second monomer mixture on the outside of the core. In this case, the mixing ratio of the first monomer mixture and the second monomer mixture is 65 to 85: 15 to 35 by weight, and the emulsifier is 5 to 30% by weight based on the total amount of the first monomer mixture and the second monomer mixture. Range.

In one embodiment, the first monomer mixture comprises 75-90 mol% of (cyclo) alkyl (meth) acrylates containing 4-12 carbon atoms and 10-25 mol% of copolymerizable mono alkylenically unsaturated monomers. In addition, the second monomer mixture may include 20 to 40 mol% of (meth) acrylic acid and 60 to 80 mol% of a copolymerizable monoalkylene unsaturated monomer.

In one embodiment, the urethane dispersion is an acid value of 90 ~ 100 mgKOH / g, the solid content may be 28 to 34%.

In one embodiment, the coating composition is a metal pigment 1 to 3% by weight; Pigment aqueous dispersion 5-50 wt%; Coarse solvent 3-6 wt%; 0.1 to 2 wt% wetting agent; 0.1 to 2 wt% dispersant; Antifoam 0.1-1.5 wt%; 0.1 to 1.0 wt% thickener and 0.1 to 3 wt% neutralizing agent may be further included.

Another object of the present invention described above is 20 to 50% by weight of an alkali swellable coreshell resin prepared by using a urethane water dispersion as an emulsifier, based on the total amount of the coating composition; 10-30 weight% butyl cellosolve, 10-30 weight% isopropyl alcohol, 5-15 weight% N-methyl-2-pyrrolidone, 25-35 weight% hydrophilic melamine resin based on the total amount of the curing agent mixture 3 to 10 weight percent of a curing agent mixture comprising 15 to 25 weight percent of a hydrophobic melamine resin and 2 to 5 weight percent of a nonionic surfactant; 2 to 10 wt% polyester resin; And coating the water-soluble coating composition comprising excess water on the substrate; And it is achieved by a method for forming a coating film comprising the step of drying.

In one embodiment, the coating film may have a thickness of 10 ~ 25㎛ automotive top coat film.

In one embodiment, the painting may be performed by any one of spray coating and electrostatic painting.

In one embodiment, the step of coating and curing the transparent paint on top of the coating film may be further performed.

The water-soluble topcoat composition for automobiles is prevented from flowing or staining after painting, and the water resistance of the dry coating film and the orientation of the metallic particles are improved. Moreover, even if an auxiliary resin is not used, a coating film excellent in chipping resistance can be formed.

Hereinafter, the present invention will be described in more detail. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are further described in the text. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

In this application, the terms "comprises" or "having" are intended to indicate that there is a feature, ingredient, step, process, composition, or combination thereof described on the specification, one or more other features or ingredients, It is to be understood that it does not preclude the presence or possibility of addition of steps, processes, compositions or combinations thereof.

Also, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, the present invention will be described in detail.

The coating composition according to the present invention comprises 20 to 50% by weight of an alkali swellable core shell resin prepared by using a urethane water dispersion as an emulsifier based on the total amount of the coating composition as a main component; 10-30 weight% butyl cellosolve, 10-30 weight% isopropyl alcohol, 5-15 weight% N-methyl-2-pyrrolidone, 25-35 weight% hydrophilic melamine resin based on the total amount of the curing agent mixture 3 to 10 weight percent of a curing agent mixture comprising 15 to 25 weight percent of a hydrophobic melamine resin and 2 to 5 weight percent of a nonionic surfactant; 2 to 10 wt% polyester resin; And excess water.

Referring to each component of the coating composition according to an embodiment of the present invention in detail as follows.

First, an alkali swellable core shell resin prepared by using a urethane water dispersion as an emulsifier is a resin obtained by dropping a monomer mixture containing a hydrophilic vinyl monomer into a core formed through emulsion polymerization as a main resin to form a hydrophilic shell portion.

By using the alkali swellable core shell resin as a main resin, the carboxyl group of the shell portion of the core shell resin may be neutralized with an amine to implement excellent workability such as flowability using structural viscosity expressed by expansion and expansion of the shell. In addition, it is possible to improve the orientation of the particles during coating to form a coating film having an excellent appearance and graininess.

The urethane aqueous dispersion reacts a bifunctional isocyanate compound with a polycarbonate polyol having a molecular weight of 1,500 to 2,500 and a compound having two or more hydroxyl groups and a monofunctional carboxylic acid to prepare a prepolymer having an isocyanate functional group at the terminal, and receiving an amine It can be prepared by water-dispersed in the liquid phase and then chain extended.

The bifunctional isocyanate compound used in the preparation of the urethane water dispersion may be at least one selected from the group consisting of 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4-bis isocyanato cyclohexyl methane. have.

The compound having two or more hydroxy groups and monofunctional carboxylic acid used in preparing the urethane aqueous dispersion may be at least one of dimethylol propionic acid and dimethylol butanoic acid.

Examples of the neutralizer for water dispersion of the prepolymer include triethylamine and ammonia.

When preparing an alkali swelling type coreshell resin using the urethane water dispersion as an emulsifier, 5-30% by weight of the urethane water dispersion is used as an emulsifier and preferably emulsified using 10-20% by weight. The polymerization is carried out. The urethane aqueous dispersion is preferably an acid value of 90 ~ 100 mgKOH / g, a solid content of 28 ~ 34%.

The alkali swellable coreshell resin is a copolymer prepared in at least two steps. First, a first monomer mixture consisting of 75 to 90 mol% of (cyclo) alkyl (meth) acrylate containing 4 to 12 carbon atoms and 10 to 25 mol% of other copolymerizable mono alkylenically unsaturated monomers is prepared. Manufacture. In this case, the sum of the two components should be 100 mol%.

A second monomer mixture is then prepared, consisting of 20-40 mol% (meth) acrylic acid and 60-80 mol% of other copolymerizable monoalkylene unsaturated monomers. In this case, the sum of the two components should be 100 mol%.

65 to 85% by weight of the first monomer mixture and 15 to 35% by weight of the second monomer mixture are copolymerized in a continuous step to obtain an alkali swelling coreshell resin. It includes carboxylic acid groups derived from at least some ionized (meth) acrylic acid.

Examples of the (cyclo) alkyl (meth) acrylate in which the (cyclo) alkyl group used for the preparation of the first monomer mixture contain 4 to 12 carbon atoms include butyl acrylate, butyl methacrylate, octyl acrylate and iso Boryl acrylate, 2-ethylhexyl acrylate, isobornyl methacrylate, 2-ethylhexyl methacrylate, dodecyl acrylate, dodecyl methacrylate, mixtures thereof, and the like can be given. Of these, butyl acrylate, butyl methacrylate and mixtures thereof are preferred monomers.

In addition, the copolymerizable mono alkylene unsaturated monomers used for the preparation of the first monomer mixture include methyl methacrylate, methyl acrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl. Acrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 3-methoxypropyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxy Propyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, mixtures of the above compounds, and the like. Of these, methyl methacrylate, ethyl acrylate, ethyl methacrylate, mixtures thereof can be preferably used, and 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate , 2-hydroxypropyl methacrylate, mixtures thereof can also be preferably used.

The copolymerizable monoalkylene unsaturated monomers used in the preparation of the second monomer mixture include styrene, vinyl toluene, acrylonitrile, methacrylonitrile, methyl methacrylate, methyl acrylate, ethyl acrylate and ethyl methacrylate. , Propyl acrylate, propyl methacrylate, isopropyl acrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2- Hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, these And mixtures thereof.

Ammonium persulfate, sodium persulfate, potassium persulfate and the like can be used as the radical initiator in the emulsion copolymerization. Copolymerization of the monomer mixture can be carried out under temperature conditions of about 70-80 ° C. and nitrogen filled atmospheric pressure. The derived carboxylic acid groups are neutralized by 80-100% by the addition of neutralizing agents such as ammonia and amines. Specific examples of the neutralizing agent may include triethyl amine, N, N-dimethylethanol amine, N, N-diethyl ethanol amine, and the like.

The alkali swellable core shell resin is to be used in the range of 20 to 50% by weight based on the total amount of the water-soluble coating composition. If the amount is less than 20% by weight, the viscosity of the paint is insufficient, the paint workability is lowered and the water resistance is lowered. If the amount is more than 50% by weight, the re-coating adhesion of the coating film may be lowered. .

When the alkali swellable core shell resin prepared according to the above-described method is used in the production of water-soluble topcoat for automobiles, the thixotropy of the water-soluble paint can be controlled to achieve good workability without flow and stain. By using this, it is possible to manufacture a paint having excellent appearance and adhesion, impact resistance and flex resistance, and increase water resistance which is lowered when using a general emulsifier. In addition, although the adhesiveness of a coating film and the orientation of a metallic pigment can be improved, it can further improve especially when it mixes with the water-soluble polyester resin mentioned later. Due to the influence of the urethane water dispersion used as an emulsifier, an excellent chipping resistance coating film can be obtained even when a urethane dispersion is not used in the coating composition that has been used for improving chipping resistance.

Next, the curing agent mixture will be described.

In water-soluble paints, there is no problem in directly adding the hydrophilic melamine resin to the water-soluble paint. However, when the hydrophobic melamine resin is directly added to the water-soluble paint and water, aggregation of the resin occurs. This can lead to deterioration of the appearance of the coating film, mechanical properties, and adhesion performance. According to the embodiment of the present invention, by using a curing agent mixture in which a nonionic surfactant is added to the hydrophilic melamine resin and the hydrophobic melamine resin, compatibility with the alkaline swellable core shell resin and water can be maximized. Thereby, the coating film excellent in the repaint adhesion in an external appearance and an overdrying coating film can be obtained.

Solvents usable for the preparation of the curing agent mixture include butyl cellosolve, isopropyl alcohol, N-methyl-2-pyrrolidone and the like. The curing agent mixture is based on the total amount of curing agent mixture 10-30% by weight of butyl cellosolve, 10-30% by weight of isopropyl alcohol, 5-15% by weight of N-methyl-2-pyrrolidone, hydrophilic melamine resin 25 35 wt%, hydrophobic melamine resin 15-25 wt% and surfactant 2-5 wt%.

If the amount of butyl cellosolve is less than 10% by weight, sufficient dissolution of the melamine resin does not occur, resulting in deterioration of appearance and physical properties. If the amount of the butyl cellosolve exceeds 30% by weight, the painting workability is deteriorated due to the decrease of the paint TI. . Therefore, the amount of the butyl cellosolve is to be in the range of 10 to 30% by weight based on the total amount of the curing agent mixture.

The amount of isopropyl alcohol is to be in the range of 10 to 30% by weight based on the total amount of the curing agent mixture. If the amount is less than 10% by weight of the paint storage property is lowered, if it exceeds 30% by weight may cause pinholes and boiling phenomenon when the coating film is dried.

N-methyl-2-pyrrolidone functions to improve the dissolution of the melamine resin and paint shelf life. Its usage amount is in the range of 5 to 15% by weight, based on the total amount of the curing agent mixture. If the amount is less than 5% by weight, the improvement of paint storage is reduced. If the amount is more than 15% by weight, the paint TI (lower thixotrophy index) is lowered and the film boils due to poor flow and dryness during painting. This is because the phenomenon occurs.

 Cymel-202, Cymel-325, Cymel-327, Cymel-370, Cymel-385 and Cymel-254, BASF's Rubypal-052, etc. can be used as said hydrophilic melamine resin.

Hydrophobic melamine resins include, for example, M3-1280 and M3-1286 Newplex's Cetamine-146 and Cetamine-138, Cytec's Cymel-683, Cymel-1158 and Cymel-1156. have.

The mixing ratio of the hydrophilic melamine resin and the hydrophobic melamine resin is preferably in the range of 50:50 to 70:30 by weight. If the proportion of the hydrophilic melamine resin is increased from the weight ratio, the repainting adhesion on the over-drying transparent coating film is lowered. On the contrary, if the proportion of the hydrophobic melamine resin is increased, the appearance quality of the water-soluble topcoat may be degraded.

The surfactant used in the curing agent mixture is a nonionic surfactant so that the amount thereof is in the range of 2 to 5% by weight based on the total amount of the curing agent mixture. If the amount is less than 2% by weight, the compatibility of the curing agent mixture into the water-soluble topcoat may be lowered. If the amount is more than 5% by weight, the water resistance may decrease with the price of the coating composition. This is because the cruttering phenomenon may be caused by a decrease in the surface tension of the paint. The surfactant may include, for example, Sufinol-420, Sufinol-440, Sufinol-465, etc. of AirFredder.

Next, the polyester resin contained as an auxiliary resin in the coating composition of the present invention will be described.

The polyester resin is a dispersed phase resin having a particle size of about 50 nm, and the amount thereof is in the range of 2 to 10% by weight based on the total amount of the coating composition. If the amount thereof is less than 2% by weight, the adhesion and orientation of the particles are lowered. If the amount is more than 10% by weight, the physical properties such as impact resistance and flex resistance may be reduced. Examples of applicable polyester resins include Norroster's Noorster 8210.

It is preferable that the metal pigment contained in the water-soluble top coat composition for automobiles of this invention is 5-40 micrometers in average particle diameter (D50). Also preferred are pigments that have been surface treated to suit aqueous paints. Specific examples include non-colored or colored aluminum pastes of metals such as aluminum and aluminum oxide. Representative examples include aluminum paste products of the Eckart hydrane series. Its amount is appropriately adjusted as necessary, but is suitably in the range of 1 to 3% by weight based on the total amount of the coating composition.

The pigment aqueous dispersion contained in the water-soluble top coat composition of the present invention may be an inorganic pigment, an organic pigment or the like as a pigment. Its amount is preferably in the range of 5 to 50% by weight based on the total amount of the coating composition. If the amount thereof is less than 5% by weight can lower the hiding power of the lower layer of the coating film, if it exceeds 50% by weight it is because the paint stability and pigment dispersibility may be lowered.

The co-solvents applicable to the present invention include 2-ethylhexanol, 2-ethylhexyl glycol, butyl carbitol, isopropyl alcohol, butanol and the like. The amount of the co-solvent is 3 to 6 wt% based on the total amount of the coating composition. It is good to be. If the amount thereof is less than 3% by weight, the smoothness of the coating film is lowered. If the amount thereof is more than 6% by weight, the smoothness is improved, but the content of volatile organic solvents is increased, which may pollute the air. The co-solvent is used separately from the solvent contained in the curing agent mixture.

The wetting agent included in the water-soluble topcoat composition may be a wetting agent of a polyether siloxane copolymer type, a wetting agent of a nonionic organic surfactant type, or the like. The wetting agent is suitably used in the range of 0.1 to 2% by weight based on the total amount of the composition. If the amount thereof is less than 0.1% by weight, the wettability may decrease during coating, and when the amount thereof exceeds 2% by weight, the water resistance and the cratering resistance of the coating may decrease. Examples of usable examples of the wetting agent include TEGO Wet-260, TEGO Wet-265, TEGO Wet-270, TEGO Wet-280, TEGO Wet-500, and the like.

The dispersant included in the water-soluble topcoat composition may include an alkylol ammonium salt of a block copolymer having an acidic group or a block copolymer of a polymer having a pigment affinity group or a solution thereof. Applying such a water-soluble dispersant can stably disperse the particles in a uniform size in the production of the pigment aqueous dispersion and also prevent the re-agglomeration of the surface-treated metal pigment. Applicable examples of the dispersant include BYPER's DISPERBYK-180, DISPERBYK-182, DISPERBYK-190, DISPERBYK-192, DISPERBYK-2012, and the like. Its amount is preferably in the range of 0.1 to 2% by weight based on the total amount of the coating composition. If the amount thereof is less than 0.1% by weight, the particle size of the dispersion may not be uniform, and the shelf life of the dispersion may be deteriorated. If the amount thereof is more than 2% by weight, the water resistance of the coating film may be reduced.

 The antifoaming agent used in the coating composition of the present invention serves to suppress the generation of bubbles in the composition and at the same time to suppress the pinhole phenomenon generated when the coating film is dried. Antifoaming agent may be added to the entire amount during the manufacture of the paint, but a part may be applied first in the pigment aqueous dispersion manufacturing process in order to remove bubbles generated during the production of the pigment aqueous dispersion. The amount of the antifoaming agent is appropriate to be in the range of 0.1 to 1.5% by weight based on the total amount of the coating composition. If the amount thereof is less than 0.1% by weight, the ability to suppress bubbles in the paint may be deteriorated, and a pinhole may occur in the coating layer. If the amount is more than 1.5% by weight, it may cause a decrease in water resistance. Examples of the antifoaming agent include DF-110D from Air Products, SN-DEFORMER 1320 from Sanofko, and BYK-028 from BYK.

The water-soluble topcoat composition of the present invention may comprise a thickener. The coating composition exhibits structural viscosity through expansion and expansion of the shell due to amine neutralization, but in some cases, the viscosity control technique of the resin is insufficient. Thickeners are used to compensate for this. The acrylic alkali thickening emulsion and the urethane-modified polyether-based thickener can be used in combination to provide excellent thixotropy and improve particle orientation through high atomization to obtain a good coating appearance. Particularly, in the case of an acrylic alkali thickening emulsion, excellent coating workability can be realized by providing thixotropic viscosity. Specific examples include NOPALL-642, NOPALL UT-666, SN-THICKENER 617, SN-THICKENER AM-1, NOPALL 700N, and the like.

The amount of thickener used is preferably in the range of 0.1 to 1.0% by weight based on the total amount of the composition. If its amount is less than 0.1% by weight, workability defects such as chilling may occur under high humidity of the paint booth.If its amount exceeds 1.0% by weight, poor paint storage property, poor atomization and water resistance due to viscosity increase This is because whitening may occur.

The neutralizing agent is used to adjust the pH of the water-soluble topcoat composition according to the present invention, which is preferably in the range of 0.1 to 3% by weight based on the total amount of the composition. If the amount thereof is less than 0.1% by weight, the particle orientation may be lowered and the shelf life of the paint may be deteriorated, thereby causing reaggregation and precipitation of the pigment. If the amount is more than 3% by weight, solvent resistance, particularly alkali resistance may be reduced. have. It is preferable to maintain pH of coating composition about 7.5-8.5. As the neutralizing agent, an amine is preferably used and examples thereof include AMIETOL M21, a product of 2-dimethylaminoethanol from TAMINCO, ammonia, triethylamine and the like.

Water included in the water-soluble topcoat composition for automobiles according to the present invention serves to provide an environmentally friendly water-soluble paint as a main solvent to replace the organic solvent. As water, deionized water, pure water and the like can be used without exception.

It is to form a coating film using the water-soluble topcoat composition for automobiles of the present invention manufactured as described above.

Painting may be carried out by a method such as air spray coating, electrostatic coating or the like. The thickness of the coating film is preferably to be in the range of about 10 ~ 25㎛ based on the cured coating film when applied as a base coat for automobiles. When applied as a top coat for automobiles, the water-soluble coating composition is coated, and then water-dried for about 2 to 5 minutes at about 80 ° C., then a transparent paint (clear paint) is applied and about 20 at a temperature of 140 to 150 ° C. It is preferable to crosslink and cure both coating layers at once by heating for ˜40 minutes. This prevents flow and stains, improves the water resistance of the dry coating and the orientation of the metallic particles, and improves the appearance such as gloss and clarity, as well as adhesion, impact resistance, bending resistance, chipping resistance, and repainting adhesion on over-drying coatings. This excellent coating film can be formed.

Hereinafter, the present invention will be described in detail through production examples, examples, comparative examples, and the like.

  ≪ Preparation Example 1 &

Preparation of Alkali Swelling Core Shell Resin

23 parts by weight of a polycarbonate polyol having a molecular weight of 2,000, 64 parts by weight of dimethylol propionic acid, 190 parts by weight of N-methylpyrrolidone and 0.3 part by weight of dibutyltin laurate were placed in a reaction vessel, and the temperature was raised to 65 ° C. 220 parts by weight of 4,4-bis isocyanato cyclohexyl methane was slowly added thereto. After heating up to 80 ℃ to maintain the NCO equivalent to reach 970 to prepare a prepolymer. 400 parts by weight of ion-exchanged water and 50 parts by weight of triethylamine were mixed, and the prepolymer was added over 20 minutes while stirring at high speed at 25 to 35 ° C. to form an aqueous dispersion. Thereafter, a mixture of 40 parts by weight of ion-exchanged water and 9.0 parts by weight of 80% hydrazine hydrate was added for chain extension to prepare a self-emulsifying urethane dispersion having an acid value of 95 mgKOH / g and a solid content of 31%.

10 g of the prepared urethane water dispersion was added to 170 g of ion-exchanged water whose temperature was adjusted to 80 ° C. while stirring, 23 g of methyl methacrylate, 20 g of n-butyl methacrylate, 22 g of n-butyl acrylate, and 2-hydroxyethyl acryl 43 g of monomer preemulsions prepared by adding 4 g of acrylate and 1 g of methacrylic acid were added to the flask as a seed. After 10 minutes, ammonium persulfate 10% solution (solvent: deionized water) was added and stirred. After about 10 minutes, the monomer preemulsion was added dropwise over 4 hours, and a mixed solution of 17 g of methyl methacrylate, 5 g of methacrylic acid, and 10 g of 2-hydroxyethyl acrylate was added dropwise over 3 hours. After 2 hours, the mixture was neutralized with 60 g of a 10% solution of dimethylethanolamine at a temperature of 40 to 50 ° C. to prepare an alkali swellable core shell resin having a solid content of 24.6%, pH 6.5, and an average particle size of 150 nm.

≪ Preparation Example 2 &

Preparation of Curing Agent Mixture 1

244 g of butyl cellosolve, 127 g of isopropyl alcohol, and 114 g of N-methyl-2-pyrrolidone were added to the vessel, and 220 g of cymel 327, a hydrophilic melamine resin, was added while stirring. After stirring for 10 minutes 220g of hydrophobic melamine resin setamine-146 was added and stirred for 20 minutes at 25 ~ 30 ℃ temperature conditions. After stirring, 36.9 g of Sufinol-440 was added as a surfactant to prepare a curing agent mixture 1.

≪ Preparation Example 3 &

Preparation of Curing Agent Mixture 2

244 g of butyl cellosolve, 127 g of isopropyl alcohol, and 114 g of N-methyl-2-pyrrolidone were added to the vessel, and 176 g of Cymel 327, a hydrophilic melamine resin, was added while stirring. After stirring for 10 minutes, 246 g of hydrophobic melamine resin, setamine-146, was added thereto, and stirred for 20 minutes at a temperature of 25 to 30 ° C. After stirring, 36.9 g of Sufinol-440 was added as a surfactant to prepare a curing agent mixture 2.

≪ Preparation Example 4 &

Preparation of Curing Agent Mixture 3

244 g of butyl cellosolve, 127 g of isopropyl alcohol, and 114 g of N-methyl-2-pyrrolidone were added to the container, and 352 g of Cymel 327, a hydrophilic melamine resin, was added while stirring. After stirring for 10 minutes 88g of hydrophobic melamine resin setamine-146 was added and stirred for 20 minutes at 25 ~ 30 ℃ temperature conditions. After stirring, 36.9 g of Sufinol-440 was added as a surfactant to prepare a curing agent mixture 3.

≪ Production Example 5 &

Preparation of Pigment Aqueous Dispersion

In order to prepare a blue pigment aqueous dispersion, 380 g of deionized water, 100 g of DISPERBYK-2012 as a dispersant, and 10 g of DF-110D as an antifoam were added and stirred in a container. 300 g of blue pigment G-314 was added and premixed for about 1 hour. After dispersing to a particle size of about 5 microns or less using a sand mill, 18 g of 10% solution of dimethylethanolamine and 72 g of deionized water were added to prepare a blue pigment aqueous dispersion.

≪ Example 1 >

35 g of alkaline swellable core shell resin prepared in Preparation Example 1 and 10 g of deionized water were added to the vessel-1, followed by stirring for 10 minutes, and then 1, 7 g of the curing agent mixture prepared in Preparation Example 2 was slowly added thereto. After stirring for 20 minutes, the particle size was confirmed to be about 5㎛ or less. 6 g of NOROSTER-8210 (manufacturer: NORO HOLDINGS), a polyester resin, was added and stirred for 20 minutes.

3 g of metal pigment (STAPA IL Hydrolan 9157) in a separate container-2, 6 g of water dispersion pigment dispersion prepared according to Preparation Example 5, 4 g of crude solvent 1 (2-ethylhexanol), 1 g of crude solvent 2 (2-ethylhexyl glycol) 1.1 g of a dispersant (DISPERBYK-192) and 0.9 g of a wetting agent (TEGO Wet 500) were sequentially added and stirred for 10 minutes.

Into the vessel-1, the mixture of vessel-2 was stirred for 10 minutes, followed by 0.2 g of thickener 1 (NOPALL 642), 0.4 g of thickener 2 (NOPALL UT-666), and 2 g of a 10% solution of dimethylethanolamine as a neutralizing agent. Charged and stirred for 20 minutes. Subsequently, the final viscosity was adjusted to 55 seconds with a Pod Cup # 4 to prepare a water-soluble waterborne coating composition for automobiles according to the present invention.

≪ Examples 2 to 3 >

Performed in the same manner as in Example 1, but according to the composition and content shown in Table 1 to prepare a water-soluble top coating composition according to the present invention.

≪ Comparative Examples 1 to 4 >

Performed in the same manner as in Example 1, but according to the composition and the content shown in Table 1 to prepare a water-soluble top coating composition according to the comparative example.

In the above Table 1, 1) represents Noruster-8210 manufactured by Norru Holdings as a water-soluble polyester resin, and 2) represents STAPA IL Hydrolan 9157 manufactured by ECKART (AL PASTE) as a metal pigment for water-based coatings. 3) is 2-ethylhexanol and 4) is 2-ethylhexyl glycol. 5) represents BYPER's DISPERBYK-192 as a block copolymer of a polymer having a pigment affinity group, 6) represents TEGO Wet 500 of TEGO as a wetting agent of a nonionic organic surfactant type, and 7) represents a nonionic ratio Air product DF-110D as silicone type surfactant is shown. 8) shows NOPALL 642 of Sanofko Corporation as an acrylic alkali thickening emulsion, 9) shows NOPALL UT-666 of Sanofko Corporation as a urethane-modified polyether-based thickener, and 10) shows a 10% solution of dimethylethanolamine. Indicates.

Physical property evaluation

In order to perform physical property experiments, water-soluble coating compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were prepared. In order to form a lower coating on the paint test specimen for automotive paints, a cationic electrodeposition paint (KED-2000 Gray from Nohold Holdings) was applied and cured for about 25 minutes at a temperature of about 150 ° C. and a relative humidity of 70%. Then, a water-soluble intermediate coating material (DWP-3000 from Nohold Holdings, Inc.) was coated on the formed lower coating film and cured for about 30 minutes at a temperature of about 140 ° C. and a relative humidity of 70% to form a middle coating film.

Thereafter, the water-soluble topcoats prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were coated as a base coat. Curing was performed at about 80 ° C. for about 3 minutes. Thereafter, a transparent coating material (DS-3000, manufactured by NORO HOLDINGS CO., LTD.) Was coated to form a top coat.

For the experiment, the intermediate coating layer was coated to have a thickness of about 30 to 40 μm, a top coat base of about 10 to 25 μm, and a top coat transparent coating of about 30 to 50 μm.

Various physical properties were measured and the results are shown in Table 2 below.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Paint stability ○ ○ ○ ○ ○ × ◎ Chill flow ○ ◎ ◎ × ○ ○ ○ stain ○ ◎ ◎ × ○ ○ ○ Polish ◎ ◎ ◎ ○ ○ △ ◎ Appearance ◎ ◎ ◎ ○ ○ × ◎ Particle orientation ◎ ◎ ◎ △ ◎ ○ ○ Water resistance ◎ ◎ ◎ △ △ ○ ○ Adhesion ◎ ○ ◎ ○ △ ◎ △ Impact resistance ○ ○ ○ ○ △ △ ○ Flexibility ○ ○ ○ ○ △ △ ○ Chipping resistance ○ ○ ○ ○ △ ○ △ Overdrying film re-adhesiveness ◎ ○ ◎ ○ × ◎ ×

Each physical property in Table 2 was tested and confirmed in the following manner.

Paint Stability: Stored at 40 ° C. for 5 days using Pod Cup # 4. Viscosity changes before and after storage were measured. It was confirmed that the change in viscosity was in the range of about -20% to + 20%.

Chill Flow: The degree of flow of the coating surface was visually observed during the painting operation.

Stains: The staining degree was visually observed on the painted surface during and after painting.

Gloss: It confirmed that it became 90 or more at 60 degree | times.

Appearance (Spilarity): The size and appearance quality of the surface curvature were measured by analyzing the structure spectrum of the painted surface using a wave-scan DOI.

Particle orientation: The flip-flop state of the metal pigment of the coating surface was visually confirmed.

Water resistance: After the specimen was immersed for about 10 days in hot water of about 40 ~ 50 ℃ it was visually confirmed whether the coating film.

Adhesiveness: About 100 2mm cross cuts were produced and peeled off using a tape, and there existed the peeling surface.

Impact resistance: Using a Dupont (Dupont) impact machine using a weight of about 300g, the impact degree was measured by applying a shock at a height of about 40cm or more.

Flex resistance: When the base was bent in a round steel having a circumference of 3/16 inch, it was confirmed that the coating film was free of cracks and peeling.

Chipping resistance: After maintaining at -40 ℃ for 4 hours, the impact was applied to the Honda Stone at a pressure of 4bar to determine whether 10 or less peeling parts between 1 and 2mm, peeling parts of 2mm or more.

Over baking coating re-adhesiveness: After coating and normal drying the water-soluble top coat and the clear paint on the middle coat and overdrying again at 150 ℃ for 1 hour, then the top coat and the clear paint are repainted and returned to normal conditions. After curing, the adhesion test was carried out to determine whether it was 90/100 or more.

As for evaluation criteria, ◎ was excellent, ○ was good, △ was moderate, and × was evaluated as poor.

 As can be seen from the results shown in Table 2, the water-soluble coating composition according to the embodiment of the present invention generally shows good physical properties. Comparing the composition according to the embodiment it can be seen that the difference in physical properties such as appearance and paint storage properties, coating workability, particle orientation, water resistance, depending on the content of the alkali swelling core shell resin.

According to the present invention as described above it is possible to prevent a decrease in water resistance by applying an alkali swelling-type core shell resin using a urethane water dispersion as an emulsifier, and the structural viscosity expressed through swelling and expansion of the resin shell by amine neutralization Due to this, it is possible to prepare a water-soluble coating composition having good coating flow and staining property and excellent paint workability. In addition, it can be seen that the repainting adhesion is excellent even on the over-drying coating film while maintaining excellent screening properties.

After all, as a coating composition according to the invention automotive water-soluble top coating using a reverse-phase core / shell-type microgel resin and urethane dispersion paint composition, automotive water-soluble top coating using a melamine water dispersion produced by the reaction of acrylic resin and hydrophobic melamine resin It is possible to form a coating film having excellent quality by replacing an existing composition including a coating composition and the like.

Although described above with reference to the embodiments, those skilled in the art can be variously modified and changed within the scope of the present invention without departing from the spirit and scope of the invention described in the claims below. I can understand.

Claims (12)

20 to 50% by weight of an alkali swellable core shell resin prepared by using the urethane water dispersion as an emulsifier based on the total amount of the water-soluble coating composition;
10-30 weight% butyl cellosolve, 10-30 weight% isopropyl alcohol, 5-15 weight% N-methyl-2-pyrrolidone, 25-35 weight% hydrophilic melamine resin based on the total amount of the curing agent mixture 3 to 10 weight percent of a curing agent mixture comprising 15 to 25 weight percent of a hydrophobic melamine resin and 2 to 5 weight percent of a nonionic surfactant;
2 to 10 wt% polyester resin; And
Water-soluble coating composition containing excess water. According to claim 1, wherein the urethane water dispersion is a bifunctional isocyanate compound having a molecular weight of 1,500 ~ 2,500 polycarbonate polyol and a compound having two or more hydroxyl groups having a monofunctional carboxylic acid having a isocyanate functional group at the terminal A water-soluble coating composition prepared by producing a prepolymer, water dispersion on an aqueous amine solution, and then chain extension. 3. The bifunctional isocyanate compound according to claim 2, wherein the bifunctional isocyanate compound is at least one selected from the group consisting of 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4-bis isocyanato cyclohexyl methane. Water-soluble coating composition. The water-soluble coating composition according to claim 2, wherein the compound having at least two hydroxyl groups and having a monofunctional carboxylic acid is at least one of dimethylol propionic acid and dimethylol butanoic acid. According to claim 1, The alkali swellable core shell resin comprises a core formed by emulsion polymerization of the emulsifier and the first monomer mixture and a shell portion formed of a second monomer mixture on the outside of the core,
Mixing ratio of the first monomer mixture and the second monomer mixture is 65 to 85: 15 to 35 by weight, and the emulsifier is 5 to 30% by weight relative to the total amount of the first monomer mixture and the second monomer mixture. A water-soluble coating composition characterized in. 6. The composition of claim 5, wherein the first monomer mixture comprises 75-90 mol% of (cyclo) alkyl (meth) acrylates containing 4-12 carbon atoms and 10-25 mol% of copolymerizable mono alkylene unsaturated monomers. Wherein the second monomer mixture comprises 20 to 40 mol% of (meth) acrylic acid and 60 to 80 mol% of copolymerizable monoalkylene unsaturated monomers. The water-soluble coating composition according to claim 1, wherein the urethane water dispersion has an acid value of 90 to 100 mgKOH / g and a solid content of 28 to 34%. According to claim 1, wherein the coating composition is a metal pigment 1 to 3% by weight; Pigment aqueous dispersion 5-50 wt%; Coarse solvent 3-6 wt%; 0.1 to 2 wt% wetting agent; 0.1 to 2 wt% dispersant; Antifoam 0.1-1.5 wt%; Water-soluble coating composition further comprises 0.1 to 1.0% by weight thickener and 0.1 to 3% by weight neutralizer. Painting a water-soluble coating composition according to claim 1 on a substrate; And
Method of forming a coating film comprising the step of drying. The method for forming a coating film according to claim 9, wherein the coating film is a top coat film for automobiles having a thickness of 10 to 25 µm. 10. The method of claim 9, wherein the painting is performed by any one of spray painting and electrostatic painting. 10. The method of claim 9, further comprising coating and curing the transparent coating on top of the coating film.