Waterborne clear coat composition

Abstract

The present disclosure relates to a waterborne clear coat composition comprising an acrylic emulsion resin, a silicone-modified polyester resin, a urethane dispersion resin, a melamine resin, and a blocked polyisocyanate, wherein the waterborne clear coat composition of the present disclosure can be diluted with water for use, and can form a coating film having excellent appearance characteristics, gloss, and scratch resistance.

Description

Water-soluble clear coat composition

[0001] The present invention relates to a water-soluble clear coat composition.

[0002] Generally, vehicle body panels must be free from paint film degradation and rust formation, and must possess the durability to maintain the gloss and color of the paint film. Therefore, the vehicle painting process typically involves electrodeposition painting on a pre-treated body, followed by the application of an intermediate (primer) coat to improve adhesion and smoothness, and finally, a base coat applied to the intermediate-coated body to enhance its aesthetics. Afterward, it is common practice to apply a clear coat to protect the base coat's color, enhance its appearance, and shield it from external damage.

[0003] Clear coats typically use utility-based materials, but since these are highly eco-friendly, there is a growing need to replace them with water-soluble alternatives.

[0004] Korean Registered Patent No. 10-1310616 discloses a water-soluble topcoat composition for automobiles applicable to various types of clear coats, but this relates to a water-soluble topcoat composition for automobiles applicable as a base coat.

[0005] Korean Registered Patent No. 10-1881216 discloses a water-based paint composition, but this relates to a water-based paint composition for an automobile body base coat that does not include an intermediate coat and a clear coat.

[0006] Therefore, there is a continuing demand for water-soluble clear coat compositions to switch from the conventional oil-based systems applied to clear coats to eco-friendly water-soluble systems in preparation for environmental regulations and for the purpose of reducing VOCs.

[0007] Meanwhile, coating films obtained using paints crosslinked with isocyanate-based compounds can exhibit excellent abrasion resistance, chemical resistance, and stain resistance. Furthermore, coating films utilizing non-yellowing polyisocyanates derived from aliphatic and alicyclic diisocyanates as isocyanate components demonstrate excellent weather resistance, leading to increasing demand for such products.

[0008] Blocked polyisocyanates have a structure in which at least one isocyanate group is blocked through a chemical reaction with blocking agents. Here, the blocking agents can be dissociated and the isocyanate group can be regenerated by heating, and such blocked polyisocyanates have the advantage of excellent processability.

[0009] However, although block polyisocyanates have become usable in water-soluble paints by introducing hydrophilic functional groups, the chain lengthens as functional groups are added, and the molecular weight increases significantly as the number of added functional groups increases, which is pointed out as a factor that impairs the physical properties of the paint.

[0010] Accordingly, there is a continuing demand for block polyisocyanates that can be used in water-soluble paints without compromising paint properties, and in particular, there is an increasing demand for scratch resistance enhancement technology using block polyisocyanates.

[0011] [Prior Art Literature]

[0012] (Patent Document 1) Republic of Korea Registered Patent No. 10-1310616 (September 13, 2013)

[0013] (Patent Document 2) Republic of Korea Registered Patent No. 10-1881216 (July 17, 2018)

[0014] The present invention aims to provide an eco-friendly water-soluble clear coat composition that has excellent scratch resistance and appearance characteristics of the manufactured coating film, and improved water dispersibility, resulting in a volatile organic compound (VOC) reduction effect.

[0015] The present invention provides a water-soluble clear coat composition comprising an acrylic emulsion resin, a silicone-modified polyester resin, a urethane dispersion resin, a melamine resin, and a blocked polyisocyanate.

[0016] The water-soluble clear coat composition of the present invention can be used by diluting it with water and can form a coating film with excellent appearance characteristics, gloss, and scratch resistance.

[0017] The present invention will be described in detail below.

[0018] In this specification, "weight-average molecular weight (Mw)" and "number-average molecular weight (Mn)" are measured by methods commonly known in the art to which the present invention belongs, and can be measured, for example, by methods such as GPC (gel permeation chromatograph).

[0019] In this specification, "glass transition temperature (Tg)" is measured by a method commonly known in the art to which the present invention belongs, such as differential scanning calorimetry (DSC).

[0020] In this specification, functional groups such as "acid value (Av)" and "hydroxyl value (OHv)" are measured by methods commonly known in the art to which this invention belongs, and may be measured, for example, by methods such as titration.

[0021] The water-soluble clear coat composition according to the present invention comprises an acrylic emulsion resin, a silicone-modified polyester resin, a urethane dispersion resin, a melamine resin, and a blocked polyisocyanate, wherein the acrylic emulsion resin has a hydroxyl value of 100 to 140 mgKOH / g and a weight-average molecular weight of 22,000 to 32,000 g / mol, the silicone-modified polyester resin has a hydroxyl value of 200 to 250 mgKOH / g, and the urethane dispersion resin has a glass transition temperature of -9 to -1℃.

[0022] As described above, when using an acrylic emulsion resin having a specific range of hydroxyl groups and a weight-average molecular weight and a silicone-modified polyester resin having a specific range of hydroxyl groups, the curing reaction rate and crosslinking density of the fast-reactive block polyisocyanate are controlled, thereby improving not only the appearance characteristics of the coating film but also mechanical properties such as impact resistance and water resistance, and having excellent water dispersibility.

[0023] In addition, when using a urethane dispersion resin having a specific range of glass transition temperatures, the surface tension is controlled during the curing reaction of a fast-reactive block polyisocyanate, an acrylic emulsion resin, and a silicone-modified polyester resin, thereby improving the smoothness of the coating film and enabling the formation of a smooth coating film, which has the effect of improving mechanical properties such as chipping resistance and impact resistance of the coating film.

[0024] Acrylic emulsion resin

[0025] Acrylic emulsion resin plays a role in improving the appearance characteristics and mechanical properties of a coating film manufactured from a composition containing it.

[0026] The acrylic emulsion resin may be one that is synthesized directly according to known methods or a commercially available product may be used. For example, the acrylic emulsion resin may contain one or more monomer-derived units selected from the group consisting of allyl methacrylate (AMA), methyl methacrylate (MMA), ethyl acrylate (EA), hydroethyl acrylate (HEA), and methacrylic acid (MAA).

[0027] The acrylic emulsion resin may be prepared from a mixture comprising allyl methacrylate (AMA), methyl methacrylate (MMA), ethyl acrylate (EA), hydroethyl acrylate (HEA), and methacrylic acid (MAA) as monomers. Additionally, the mixture may further include a divalent acrylic monomer. Divalent acrylic monomers are, for example, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,5-pentanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, ethylene glycol diacrylate, ethylene Examples include ethylene glycol dimethacrylate.

[0028] The acrylic emulsion resin may have a solid content (NV) of 35 to 55 weight% or 40 to 50 weight% relative to the total weight of the resin. When the solid content of the acrylic emulsion resin is within the above range, the storage stability of the resin is improved, workability is excellent, and high gloss can be achieved. When the solid content of the acrylic emulsion resin is below the above range, the viscosity becomes excessively low, which causes a problem of insufficient workability in the water-soluble clear coat composition containing it; when it exceeds the above range, the viscosity of the acrylic emulsion resin becomes excessively high, which reduces stability during reaction and causes dispersion stability to deteriorate, which may lead to aggregation over time.

[0029] Meanwhile, acrylic emulsion resin may be in the form of an emulsion dispersed in a solvent such as deionized water. When the acrylic emulsion resin is in the form of an emulsion dispersed in deionized water, it has the effect of reducing the volatile organic compound (VOC) content of the paint.

[0030] The acrylic emulsion resin may have a glass transition temperature (Tg) of 25 to 45°C or 30 to 40°C. When the glass transition temperature of the acrylic emulsion resin is within the above range, the hardness and solvent resistance of the coating film produced from a composition containing it are improved. When the glass transition temperature of the acrylic emulsion resin is below the above range, the drying speed and crosslinking density of the coating film decrease, resulting in a problem where the hardness and solvent resistance of the produced coating film are insufficient. When it exceeds the above range, the coating film becomes brittle, which may result in a lack of appearance characteristics and chipping resistance of the produced coating film.

[0031] The acrylic emulsion resin may have a viscosity of 10 to 500 cps or 50 to 300 cps at 25°C. When the viscosity of the acrylic emulsion resin at 25°C is within the above range, the viscosity of the composition containing it is appropriate, and thus workability, high appearance, and durability are improved. When the viscosity of the acrylic emulsion resin at 25°C is below the above range, the viscosity of the composition is too low, resulting in a problem where the paint flowability, adhesion, and scratch resistance are reduced due to the failure to form a manufactured coating film. When it exceeds the above range, the workability of the composition is insufficient, which may result in a problem where the appearance characteristics of the manufactured coating film are reduced.

[0032] The acrylic emulsion resin may have an acid value (Av) of 5 to 20 mgKOH / g or 10 to 15 mgKOH / g. When the acid value of the acrylic emulsion resin is within the above range, the reactivity of the composition containing it can be controlled to improve the appearance characteristics of the coating film produced therefrom, and the leveling (long wave) of the paint can be improved. When the acid value of the acrylic emulsion resin is below the above range, the resin stability is reduced, causing a problem of reduced storage stability of the prepared paint composition. When it exceeds the above range, the viscosity of the composition increases due to increased resin cohesion, causing a problem of reduced workability and water resistance of the coating film.

[0033] The acrylic emulsion resin may have a hydroxyl group (OHv) of 100 to 140 mgKOH / g or 110 to 130 mgKOH / g. When the hydroxyl group of the acrylic emulsion resin is within the above range, the reactivity of the composition containing it is controlled to improve the appearance characteristics of the coating film produced therefrom and to improve the orange peel effect of the paint. When the hydroxyl group of the acrylic emulsion resin is below the above range, the resin stability is reduced, causing a problem of reduced storage stability of the prepared paint composition. When it exceeds the above range, the viscosity of the composition increases due to increased resin cohesion, which may cause a problem of reduced workability and water resistance of the coating film.

[0034] The acrylic emulsion resin may have a weight-average molecular weight (Mw) of 22,000 to 32,000 g / mol or 25,000 to 30,000 g / mol. When the weight-average molecular weight of the acrylic emulsion resin is within the above range, the long-term physical properties of the manufactured coating film, such as durability, adhesion, hardness, and weather resistance, are excellent, and the leveling properties of the paint may be improved. When the weight-average molecular weight of the acrylic emulsion resin is below the above range, the water resistance, impact resistance, and cold chipping resistance of the manufactured coating film are insufficient due to the low molecular weight, and when it exceeds the above range, the flowability decreases due to the increase in molecular weight, resulting in poor workability of the water-soluble clear coat composition containing it and poor surface smoothness, which may cause problems in making it difficult to manufacture a coating film with an excellent appearance.

[0035] Acrylic emulsion resin may be included in the composition in an amount of 10 to 30 weight% or 15 to 25 weight% based on the total weight of the water-soluble clear coat composition. When acrylic emulsion resin is included within the above content range, there is an effect of improving appearance characteristics and gloss. If the content of acrylic emulsion resin is below the above range, drying performance is reduced, which may result in a decrease in the adhesion, gloss, hardness, and durability of the coating film; if it exceeds the above range, drying proceeds too quickly, which may result in a lack of paint workability and paint flowability of the composition, leading to a decrease in the appearance and scratch resistance of the coating film.

[0036] silicone-modified polyester resin

[0037] The silicone-modified polyester resin plays a role in forming the appearance characteristics and physical properties of the coating film manufactured from a composition containing it.

[0038] Silicone-modified polyester resins can be prepared by reacting a carboxylic acid compound, a diol compound, and a silicone intermediate. For example, the silicone-modified polyester resin comprises: one or more carboxylic acid compounds selected from the group consisting of adipic acid (AA), isophthalic acid (IPA), trimaletic anhydride (TMA), cycloaliphatic acids, phthalic anhydrides, isophthalic acid, terephthalic acid, succinic acid, adipic acid, fumaric acid, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and derivatives thereof; and one or more diol compounds selected from the group consisting of 1,6-hexanediol (1,6-HD), neopentyl glycol (NPG), trimethylolpropane (TMP), ethylene glycol, propylene glycol, diethylene glycol, butanediol, 1,4-hexanediol, and 3-methylpentanediol. It can be prepared by reacting a silicone intermediate, which is a polysiloxane resin having reactive groups such as siloxane groups or methoxy groups within the molecule.

[0039] The silicone-modified polyester resin may have a solid content (NV) of 80 to 90 weight% or 82 to 88 weight% relative to the total weight of the resin. When the solid content of the silicone-modified polyester resin is within the above range, the storage stability of the resin is improved, workability is excellent, and there is an effect of improving gloss and curing reactivity. When the solid content of the silicone-modified polyester resin is below the above range, the viscosity becomes excessively low, which causes a problem of insufficient workability in the water-soluble clear coat composition containing it, and when it exceeds the above range, the viscosity of the silicone-modified polyester resin becomes excessively high, which may result in reduced stability during the reaction.

[0040] The silicone-modified polyester resin may have a glass transition temperature (Tg) of 1 to 8°C or 2 to 6°C. When the glass transition temperature of the silicone-modified polyester resin is within the above range, the hardness and solvent resistance of the coating film produced from a composition containing the same are improved. When the glass transition temperature of the silicone-modified polyester resin is below the above range, the drying speed and crosslinking density of the coating film decrease, resulting in a problem where the hardness and solvent resistance of the produced coating film are insufficient. When it exceeds the above range, the coating film becomes brittle, which may result in a lack of appearance characteristics and chipping resistance of the produced coating film.

[0041] The silicone-modified polyester resin may have a viscosity of 8,500 to 11,000 cps or 9,000 to 10,500 cps at 25°C. When the viscosity of the silicone-modified polyester resin at 25°C is within the above range, the viscosity of the water-soluble clear coat composition is appropriate, which improves workability and increases the solid content, thereby improving the Solid Volume Ratio (SVR) of the paint. When the viscosity of the silicone-modified polyester resin at 25°C is below the above range, the viscosity of the composition is too low, resulting in a problem where the paint flowability, adhesion, and scratch resistance are reduced due to the failure to form a manufactured coating film. When it exceeds the above range, the workability of the composition is insufficient, which may result in a problem where the appearance characteristics of the manufactured coating film are reduced.

[0042] The silicone-modified polyester resin may have an acid value (Av) of 15 to 25 mgKOH / g or 18 to 22 mgKOH / g. When the acid value of the silicone-modified polyester resin is within the above range, there is an effect of improving the crosslinking density and curing reactivity of the composition containing it. If the acid value of the silicone-modified polyester resin is below the above range, the resin stability is reduced, causing a problem of reduced storage stability of the manufactured paint composition; if it exceeds the above range, the viscosity of the composition increases due to increased resin cohesion, which may cause a problem of reduced workability and water resistance of the coating film.

[0043] The silicone-modified polyester resin may have a hydroxyl group (OHv) of 200 to 250 mgKOH / g or 210 to 240 mgKOH / g. When the hydroxyl group of the silicone-modified polyester resin is within the above range, the composition containing it has the effect of improving low-temperature curing and crosslinking density. When the hydroxyl group of the silicone-modified polyester resin is below the above range, the resin stability is reduced, causing a problem of reduced storage stability of the manufactured paint composition. When it exceeds the above range, the viscosity of the composition increases due to increased resin cohesion, which may cause a problem of reduced workability and water resistance of the coating film.

[0044] The silicone-modified polyester resin may have a weight-average molecular weight of 2,500 to 4,500 g / mol or 3,000 to 4,000 g / mol. When the weight-average molecular weight of the silicone-modified polyester resin is within the above range, the solid content increases, which has the effect of improving the Solid Volume Ratio (SVR) of the paint. When the weight-average molecular weight of the silicone-modified polyester resin is below the above range, the water resistance, weather resistance, and scratch resistance of the manufactured coating film are insufficient due to the low molecular weight. When it exceeds the above range, the flowability decreases due to the increase in molecular weight, resulting in poor workability of the water-soluble clear coat composition containing it and poor surface smoothness, which may cause problems in manufacturing a coating film with an excellent appearance.

[0045] The silicone-modified polyester resin may have a number average molecular weight of 800 to 1,600 g / mol or 1,000 to 1,400 g / mol. When the weight average molecular weight of the silicone-modified polyester resin is within the above range, the solid content increases, which has the effect of improving the Solid Volume Ratio (SVR) of the paint. When the weight average molecular weight of the silicone-modified polyester resin is below the above range, the water resistance, weather resistance, and scratch resistance of the manufactured coating film are insufficient due to the low molecular weight; when it exceeds the above range, the flowability decreases due to the increase in molecular weight, resulting in poor workability of the water-soluble clear coat composition containing it and poor surface smoothness, which may cause problems in manufacturing a coating film with an excellent appearance.

[0046] Silicone-modified polyester resin may be included in the composition in an amount of 5 to 15 weight% or 7 to 13 weight% based on the total weight of the water-soluble clear coat composition. When the silicone-modified polyester resin is included within the above content range, high gloss of the paint can be achieved, and impact resistance and chipping resistance are improved. If the content of the silicone-modified polyester resin is below the above range, drying performance is reduced, which may result in a decrease in the adhesion, gloss, hardness, and durability of the coating film; if it exceeds the above range, drying proceeds too quickly, which may result in insufficient paint workability and paint flowability of the composition, leading to a decrease in the appearance and scratch resistance of the coating film.

[0047] Urethane dispersion resin

[0048] The urethane dispersion resin improves the drying properties of a water-soluble clear coat composition containing it and improves the flexibility of the coating film produced from the composition.

[0049] The urethane dispersion resin may be a urethane dispersion resin derived from polyester-polycarbonate. For example, the urethane dispersion resin may be a urethane dispersion resin derived from polyester-polycarbonate diol.

[0050] The solid content (NV) of the urethane dispersion resin may be 30 to 40 weight% or 32 to 38 weight% with respect to the total weight of the resin. When the solid content of the urethane dispersion resin is within the above range, the storage stability of the resin and the storage stability of the water-soluble clear coat composition may be improved, and workability may be excellent. When the solid content of the urethane dispersion resin is below the above range, the viscosity becomes excessively low, resulting in a problem of insufficient workability of the water-soluble clear coat composition containing it; when it exceeds the above range, the viscosity of the urethane dispersion resin becomes excessively high, resulting in reduced stability during reaction and poor dispersion stability, which may cause aggregation over time.

[0051] The urethane dispersion resin may be in the form in which the urethane resin is dispersed in a solvent. The aqueous medium for dispersing the urethane resin may be a water solvent or a mixed medium of water and a hydrophilic organic solvent. For example, the water solvent may be tap water, ion-exchanged water, distilled water, ultrapure water, etc. In particular, ion-exchanged water may be used to prevent the particles from becoming unstable due to ease of availability or the influence of salts. In addition, the hydrophilic organic solvent may be a lower monohydric alcohol such as methanol, ethanol, or propanol, a polyhydric alcohol such as ethylene glycol or glycerin, or an aprotic hydrophilic organic solvent such as N-methylmorpholine, dimethyl sulfoxide, or dimethylformamide.

[0052] The urethane dispersion resin may have a glass transition temperature (Tg) of -9 to -1°C or -8 to -2°C. When the glass transition temperature of the acrylic emulsion resin is within the above range, the hardness and solvent resistance of the coating film produced from the composition containing it are improved. When the glass transition temperature of the acrylic emulsion resin is below the above range, the drying speed and crosslinking density of the coating film decrease, resulting in a problem where the hardness and solvent resistance of the produced coating film are insufficient. When it exceeds the above range, the coating film becomes brittle, which may result in a lack of appearance characteristics and chipping resistance of the produced coating film.

[0053] The urethane dispersion resin may have a viscosity of 5 to 50 cps or 10 to 40 cps at 25°C. When the viscosity of the urethane dispersion resin at 25°C is within the above range, the viscosity of the water-soluble clear coat composition is appropriate, which has the effect of improving workability. When the viscosity of the urethane dispersion resin at 25°C is below the above range, the viscosity of the composition is too low, resulting in a problem where the paint flowability, adhesion, and scratch resistance are reduced due to the failure to form a manufactured coating film. When it exceeds the above range, the workability of the composition is insufficient, which may result in a problem where the appearance characteristics of the manufactured coating film are reduced.

[0054] The urethane dispersion resin may have a weight-average molecular weight of 21,000 to 25,000 g / mol, or 22,000 to 24,000 g / mol. When the weight-average molecular weight of the urethane dispersion resin is within the above range, the water-soluble clear coat composition has excellent drying properties, cold chipping properties, and impact resistance. When the weight-average molecular weight of the urethane dispersion resin is below the above range, there is a problem that the mechanical properties of the manufactured coating film are degraded due to the low molecular weight, and when it exceeds the above range, the flowability decreases due to the increase in molecular weight, causing the coating film to become brittle, resulting in reduced smoothness and reduced scratch resistance.

[0055] Urethane dispersion resin may be included in the composition in an amount of 5 to 15 weight% or 7 to 13 weight% based on the total weight of the water-soluble clear coat composition. When the urethane dispersion resin is included within the above content range, there is an effect of improving tensile strength, flexibility, elongation, adhesion, abrasion resistance, scratch resistance, and film smoothness. If the content of the urethane dispersion resin in the composition is less than the above range, flexibility is reduced, which may cause problems such as reduced tensile strength and scratch resistance; if it exceeds the above range, the viscosity of the composition becomes excessively high, which may cause problems such as reduced workability and drying properties, and reduced appearance and mechanical properties.

[0056] Melamine resin

[0057] Melamine resin acts as a curing agent, cross-linking with each component of the water-soluble clear coat composition to cure the composition and improve the hardness of the manufactured coating film.

[0058] The melamine resin may be an alkylated melamine resin, and may be one synthesized directly according to known methods or a commercially available product.

[0059] Melamine resin may include one or more selected from the group consisting of, for example, methoxymethyl melamine, methyl melamine, butyl melamine, isobutoxy melamine, butoxy melamine, hexamethylol melamine, hexamethoxymethyl melamine, hexabutoxymethyl melamine, hexamethoxybutoxymethyl melamine, aminomethoxymethyl melamine, and imino group-containing alkylated melamine.

[0060] Commercially available melamine resins include, for example, CYTEC’s CYMEL-325, CYMEL-303, CYMEL-1161, CYMEL-1168, BASF’s LUWIPAL 012, LUWIPAL 072, and NUPLEX’s SETAMINE US-138.

[0061] The melamine resin may have a solid content (NV) of 60 to 80 weight% or 65 to 75 weight% relative to the total weight of the resin. When the solid content of the melamine resin is within the above range, the workability of the water-soluble clear coat composition is improved. If the solid content of the melamine resin is below the above range, the viscosity becomes excessively low, resulting in reduced flowability and a problem of insufficient workability of the base coat composition containing it. If it exceeds the above range, the viscosity becomes excessively high, resulting in reduced stability during reaction and poor dispersion stability, which may cause aggregates to form within the base coat composition over time.

[0062] The viscosity of the melamine resin at 25°C may be 1,000 to 1,800 cps or 1,100 to 1,700 cps. When the viscosity of the melamine resin at 25°C is within the above range, it has excellent gloss and appearance. When the viscosity of the melamine resin at 25°C is below the above range, the low viscosity results in a failure to form a coating film, which causes problems such as reduced adhesion and scratch resistance of the coating film; when it exceeds the above range, the workability of the composition is poor, which may result in a lack of appearance characteristics of the manufactured coating film.

[0063] In addition, the melamine resin may have an acid value (Av) of 0.1 to 3 mgKOH / g or 0.1 to 2 mgKOH / g. If the acid value of the melamine resin is below the above range, the curing reaction rate decreases, which may cause problems with reduced hardness and appearance characteristics of the manufactured coating film, and if it exceeds the above range, water resistance may decrease as hydrophilicity improves.

[0064] Melamine resin may be included in the composition in an amount of 10 to 20 weight% or 12 to 15 weight% based on the total weight of the water-soluble clear coat composition. When the content of melamine resin is within the above range, it has the effect of improving the adhesion and hardness of the manufactured coating film by improving the crosslinking density. If the content of melamine resin is below the above range, there is a problem of reduced hardness and appearance characteristics due to reduced curability, and if it exceeds the above range, the coating film may become brittle due to excessive curability, resulting in reduced adhesion, impact resistance, and scratch resistance.

[0065] Block polyisocyanate

[0066] The block polyisocyanate of the present invention is obtained from a polyisocyanate compound and a blocking agent.

[0067] The block polyisocyanate of the present invention may contain a first block isocyanate group in which the isocyanate group is blocked by a silane-based blocking agent, a second block isocyanate group in which the isocyanate group is blocked by a polyalkylene polyol blocking agent, and a third block isocyanate group in which the isocyanate group is blocked by a pyrazol-based blocking agent.

[0068] The above configurations are described in detail below.

[0069] polyisocyanate compounds

[0070] Polyisocyanate compounds are a general term for compounds containing one or more isocyanate groups. Polyisocyanate compounds may include, for example, aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, aromatic polyisocyanate compounds, etc., but are not limited thereto. Preferably, polyisocyanate trimers may be used.

[0071] Aliphatic polyisocyanate compounds include, for example, trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate (tetramethylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate), 1,5-pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HMDI), 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanate methylcapate, etc., but are not limited thereto.

[0072] As alicyclic polyisocyanate compounds, examples include 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, cyclohexane diisocyanate (1,3- or 1,4-cyclohexane diisocyanate), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI), methylenebis(cyclohexyl isocyanate) (4,4'-, 2,4'- or 2,2'-methylenebis(cyclohexyl isocyanate), their trans, trans-body, trans, cis-body, cis, cis-body, or mixtures thereof) (H12MDI), methylcyclohexane diisocyanate (methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane Diisocyanate), norbornene diisocyanate (NBDI), bis(isocyanatomethyl)cyclohexane (1,3- or 1,4-bis(isocyanatomethyl)cyclohexane or a mixture thereof) (H6XDI), etc., but are not limited thereto.

[0073] Aromatic polyisocyanate compounds include, for example, tolylene diisocyanate (2,4- or 2,6- tolylene diisocyanate or a mixture thereof) (TDI), phenylene diisocyanate (m-, p-phenylene diisocyanate or a mixture thereof), 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate (NDI), diphenylmethane diisocyanate (4,4'-, 2,4'- or 2,2'-diphenylmethane diisocyanate or a mixture thereof) (MDI), 4,4'-toluidine diisocyanate (TODI), 4,4'-diphenyl ether diisocyanate, xylylene diisocyanate (1,3- or 1,4-xylylene diisocyanate or a mixture thereof) (XDI), and tetramethylxylylene Diisocyanate (1,3- or 1,4-tetramethylxylylene diisocyanate or a mixture thereof) (TMXDI), ω,ω'-diisocyanate-1,4-diethylbenzene, etc., but are not limited thereto.

[0074] As for the polyisocyanate compound, a single compound may be used or two or more may be used in combination, but are not limited thereto.

[0075] In one embodiment, the polyisocyanate compound may be preferred as an aliphatic polyisocyanate compound and a cycloaliphatic polyisocyanate compound because they have excellent weather resistance.

[0076] In addition, among the aliphatic polyisocyanate compounds, it is preferable that the aliphatic polyisocyanate compound is derived from an aliphatic diisocyanate. More specifically, regarding the aliphatic diisocyanate, 1,6-hexamethylene diisocyanate trimer may be preferred in terms of weather resistance and industrial availability, but is not limited thereto.

[0077] In addition, by using a blocked polyisocyanate in which isocyanate groups are blocked by a blocking agent, a water-soluble clear coat composition can be provided that exhibits excellent physical properties such as appearance, water dispersibility, and scratch resistance.

[0078] The polyisocyanate compound may be included in an amount of 30 to 60 weight% or 38 to 50 weight% based on the total weight of the composition for manufacturing the block polyisocyanate. By using a water-soluble clear coat composition containing a block polyisocyanate in which the content of the polyisocyanate compound is within the above range, a coating film with excellent physical properties such as wear resistance, chemical resistance, stain resistance, and scratch resistance can be formed. In addition, a water-soluble clear coat composition that exhibits excellent water dispersibility by being blocked by a blocking agent can be provided.

[0079] blocking agents

[0080] The blocking agent used in the present invention forms a new bond with the isocyanate (NCO) within the polyisocyanate compound, thereby blocking the isocyanate group from reacting with other compounds, such as the resin part. In addition, the block isocyanate thus formed contains a blocked isocyanate group in that the blocking agent can be dissociated through reactions such as heating, thereby allowing the isocyanate group to participate in the curing reaction again.

[0081] Here, the block polyisocyanate may be obtained from 30 to 60 parts by weight of a polyisocyanate compound and 15 to 60 parts by weight of a blocking agent, or 38 to 50 parts by weight of a polyisocyanate compound and 18 to 55 parts by weight of a blocking agent, but is not limited thereto.

[0082] Some isocyanate groups in the blocked polyisocyanate may be included without being blocked. More specifically, based on the total isocyanate groups in the polyisocyanate compound, the content of unblocked isocyanate groups may be 5 NCO% or less, for example, 1 NCO% or less, 0.5 NCO% or less, or 0 NCO% (i.e., not included).

[0083] When the content of the polyisocyanate compound and the blocking agent is within the above range, a desired water-soluble clear coat composition can be provided; when it is below the above range, the degree of improvement in water dispersibility is negligible, and when it exceeds the above range, a problem may arise in which the physical properties of the formed film deteriorate.

[0084] Blocking agents may include silane-based blocking agents, polyalkylene polyol blocking agents, and pyrazole-based blocking agents. Blocked polyisocyanate groups can be obtained by reacting each of these three types of blocking agents with an isocyanate trimer. By using these three types of blocking agents in combination, the water dispersibility of a water-soluble clear coat composition containing blocked polyisocyanates can be improved, and the physical properties of the coating film formed using this composition can be enhanced. The three types of blocking agents described above will be explained in detail below.

[0085] Silane-based blocking agents

[0086] Silane-based blocking agents increase the curing density of block polyisocyanates and improve the scratch resistance of coating films formed with water-soluble clear coat compositions containing them.

[0087] Silane-based blocking agents are -Si(OR) capable of reacting with isocyanates n It is a compound having a group. Silane-based blocking agents can combine with one of the isocyanate trimers to form a first block isocyanate group. -Si(OR) bonded to isocyanate nThe gas can form an -Si-O-Si- structure by undergoing hydrolysis and self-condensation reactions, or form organic chemical bonds of the -Si-O- structure by heat.

[0088] Silane-based blocking agents may have epoxy groups, amino groups, or a combination thereof, but are not limited thereto.

[0089] Silane-based blocking agents consist of gamma-aminopropyltrimethoxysilane (Silquest A-1100), bis(trimethoxysilylpropyl)amine (Silquest A-1170), bis(triethoxysilylpropyl)amine (Silquest Y-11699), organoalkoxysilane (Silquest Y-96699), 3-glycidoxypropyl trimethoxysilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, bis-gamma-trimethoxysilylpropylamine, bis-gamma-triethoxysilylpropylamine, and aminopropyltriethoxysilane. It may include one or more types selected from the military.

[0090] A silane-based blocking agent may be included in an amount of 2 to 15 weight% or 6 to 10 weight% based on the total weight of the composition for manufacturing the block polyisocyanate. When the silane-based blocking agent is included within the above content range, it has the effect of improving the adhesion and durability of the coating film by creating appropriate siloxane bonds. If the content of the silane-based blocking agent is below the above range, the number of siloxane bonds is small, resulting in a decrease in crosslinking density and a problem of reduced adhesion, gloss, and durability of the coating film. If it exceeds the above range, the storage stability of the paint is reduced due to hydrolysis caused by increased reactivity with moisture resulting from the increase in the molecular weight of the silane, and consequently, the appearance and scratch resistance of the coating film may be reduced.

[0091] Polyalkylene polyol blocking agent

[0092] Polyalkylene polyol blocking agents play a role in controlling the hydrophilicity of polyisocyanates.

[0093] The polyalkylene polyol blocking agent can combine with one of the isocyanate trimers to form a second block isocyanate group.

[0094] As a polyalkylene polyol blocking agent, for example, one or more selected from the group consisting of polyols containing polyoxyethylene groups, more specifically polyethylene glycol (PEG), polytetramethylene oxide (PTMO), polypropylene oxide (PPO), monoalkoxypolyethylene glycol, polyethylenetriol, polypropylenetriol alone, or copolymers thereof may be included. As a polyalkylene polyol blocking agent, it may be preferable to use polyethylene glycol in terms of controlling the hydrophilicity and chain extension of the blocked isocyanate. In particular, it may be more preferable to use methoxypolyethylene glycol in terms of being able to block the isocyanate from the side and increasing the number of hydrophilic groups per molecule.

[0095] Polyalkylene polyol blocking agents may be used alone or in combination of two or more types of polyalkylene polyols, and the copolymer of the polyalkylene polyol may be a block copolymer, graft copolymer, star copolymer, or alternating copolymer.

[0096] Polyalkylene polyol blocking agents may be used having a number average molecular weight of 200 to 800, for example, 300 to 700, or 400 to 600.

[0097] When the number average molecular weight of the polyalkylene polyol blocking agent is within the above range, the efficiency of polyisocyanate blocking can be improved. In addition, by maintaining appropriate hydrophilicity, excellent water dispersibility of the blocked polyisocyanate can be exhibited.

[0098] If the number average molecular weight of the polyalkylene polyol blocking agent is below the aforementioned range, hydrophilicity is reduced, thereby reducing the compatibility of the resin composition; if it exceeds the aforementioned range, hydrophilicity increases with increasing molecular weight, thereby reducing water resistance and consequently reducing appearance and scratch resistance.

[0099] The polyalkylene polyol blocking agent may be included in an amount of 5 to 17 weight% or 8 to 13 weight% based on the total weight of the composition for manufacturing the block polyisocyanate. When the polyalkylene polyol blocking agent is included within the above content range, it has the effect of improving storage stability and mechanical properties by generating an appropriate number of hydrophilic groups. If the content of the polyalkylene polyol blocking agent is below the above range, there is a problem that the compatibility of the resin composition is reduced due to the small number of hydrophilic groups, and if it exceeds the above range, the water resistance of the coating film is reduced due to moisture absorption resulting from increased hydrophilicity, and consequently, the appearance, gloss, and scratch resistance of the coating film may be reduced.

[0100] Pyrazol-based blocking agents

[0101] Pyrazol-based blocking agents improve the storage stability of block polyisocyanates and improve the appearance of the coating film formed by a water-soluble clear coat composition containing them.

[0102] Pyrazol-based blocking agents can combine with one of the isocyanate trimers to form a third block isocyanate group.

[0103] As a pyrazole-based blocking agent, one or more selected from the group consisting of, for example, pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole may be included. In one example, a blocked polyisocyanate was prepared using 3,5-dimethylpyrazole as a pyrazole-based blocking agent.

[0104] A pyrazol-based blocking agent may be included in an amount of 11 to 23 weight% or 14 to 21 weight% based on the total weight of the composition for manufacturing block polyisocyanate. When the pyrazol-based blocking agent is included within the above content range, storage stability is excellent, and when reacting with the resin, the shrinkage of the coating film due to addition reactions is minimal, which has the effect of improving the appearance of the coating film. If the content of the pyrazol-based blocking agent is below the above range, the isocyanate content after dissociation is low, resulting in reduced reactivity and insufficient crosslinking density, which may lower the durability and weather resistance of the manufactured coating film. If it exceeds the above range, the content of the silane-based blocking agent and polyalkylene polyol blocking agent is relatively reduced, which lowers compatibility with the resin composition and insufficient crosslinking density, which may consequently lower the impact resistance, chipping resistance, and scratch resistance of the coating film.

[0105] For example, the weight ratio of a silane-based blocking agent, a polyalkylene polyol blocking agent, and a pyrazole-based blocking agent may be 1:0.3 to 7:0.7 to 10 or 1:0.5 to 5:1 to 8. By using these three types of blocking agents in the above weight ratios, an appropriate crosslinking density is maintained with the resin composition due to increased reactivity, thereby providing a water-soluble clear coat composition that has excellent physical properties such as appearance, gloss, adhesion, impact resistance, and scratch resistance, as well as water dispersibility.

[0106] Formation of block polyisocyanates

[0107] The block polyisocyanate of the present invention can be prepared, for example, by mixing a polyisocyanate compound and a pyrazole-based blocking agent in a solvent to carry out a first reaction, adding a silane-based blocking agent to carry out a second reaction, and then adding a polyalkylene polyol blocking agent to carry out a third reaction. The first reaction between the polyisocyanate compound and the pyrazole-based blocking agent can be carried out at 40 to 85°C, for example, 80°C, and the second and third reactions can be carried out at 60 to 85°C, for example, 80°C.

[0108] If the above reaction is performed within the above range, the polyisocyanate compound can be blocked by each blocking agent in the desired amount. On the other hand, if the above reaction is performed below the above range, the unblocked polyisocyanate may be included in excess, for example, 5 NCO% or more based on the total isocyanate groups, and if performed beyond the above range, the dissociation reaction of the formed blocked polyisocyanate may be performed.

[0109] The solvent may be any commonly used solvent without limitation, but ketone-based solvents such as methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, ethyl propyl ketone, methyl isobutyl ketone, methyl aryl ketone, and diisobutyl ketone, acetate-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, methyl cellosolve acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, and propylene glycol methyl ether acetate (PMA), alcohol-based solvents such as butyl cellosolve, or mixtures thereof may be used, which do not react with the polyisocyanate compound and affect the water-soluble paint.

[0110] The block polyisocyanate according to the present invention may contain organic chemical bonds of a -Si-O-Si- structure or a -Si-O- structure by a silane-based blocking agent, may contain urethane groups by a polyalkylene polyol blocking agent, and may contain urea groups by a pyrazole-based blocking agent. The block polyisocyanate of the present invention has a technical feature in improving water dispersibility and the physical properties of the coating film formed by the water-soluble clear coat composition used by the three types of blocking agents and their content ratios.

[0111] In addition, the block polyisocyanate may have a weight-average molecular weight (Mw) of 500 to 5,000, for example, 1,000 to 3,000.

[0112] When the weight-average molecular weight of the block polyisocyanate is within the above range, it maintains an appropriate reaction rate to improve reactivity with the resin, thereby increasing the crosslinking density of the coating film and having the effect of improving mechanical properties, appearance, and chemical resistance.

[0113] If the weight-average molecular weight of the above-mentioned block polyisocyanate is below the aforementioned range, reactivity is reduced, and the compatibility and appearance of the resin composition are reduced; if it exceeds the aforementioned range, side reactions of the isocyanate functional group increase due to the increase in molecular weight, and consequently, the appearance and scratch resistance are reduced.

[0114] When forming a block polyisocyanate, the block polyisocyanate may be obtained in a mixed state with an unblocked polyisocyanate compound and / or three types of blocking agents remaining after being used for isocyanate blocking. At this time, the resulting mixture may have a solid content of 70 to 90 weight% or 75 to 85 weight% in the composition. In one example, a mixture with a solid content of 80% was prepared.

[0115] Block polyisocyanates are in-si(OR 1 The )3 content may be 1 to 11%, or 2 to 10%. Here, R 1 It is an alkyl group having 1 to 2 carbon atoms.

[0116] Meanwhile, Si(OR 1 The )3 content can be calculated using the following formula.

[0117] Si(OR 1 )3% = Silane monomer equivalent × Si(OR 1 )3 Molecular Weight × F / Total Content × 100

[0118] Here, F = Si within the polymer (OR 1 )3 items

[0119] Si(OR) of block polyisocyanate 1 When the content of )3 is within the above range, it creates appropriate siloxane bonds, resulting in excellent storage stability and improved reactivity with the resin, which increases the crosslinking density of the coating film and has the effect of improving mechanical properties, appearance, and weather resistance.

[0120] Si(OR) of the above block polyisocyanate 1If the content is less than the aforementioned range, the number of siloxane bonds is small, which lowers the crosslinking density of the coating film and reduces weather resistance; if it exceeds the aforementioned range, the storage stability of the paint is reduced due to hydrolysis caused by reaction with moisture resulting from the increase in the molecular weight of the silane, and consequently, the appearance, gloss, and scratch resistance are reduced.

[0121] Block polyisocyanates are in-situ alkoxides (R 2 O) The content may be 5 to 15%, or 7 to 12%. Here, R 2 is an alkyl group having 1 to 4 carbon atoms.

[0122] Meanwhile, alkoxide (R 2 O) The content can be calculated using the following formula.

[0123] Alkoxide (R 2 O) Content = Polyalkylene polyol equivalent × R 2 O Molecular weight × F / Total content × 100

[0124] Here, F = R 2 Number of repetition units

[0125] Alkoxide of block polyisocyanate ((R 2 When the content is within the above range, it generates an appropriate number of hydrophilic groups, resulting in excellent storage stability and improved reactivity with the resin, which increases the crosslinking density of the coating film and has the effect of improving mechanical properties, appearance, and weather resistance.

[0126] The alkoxide of the above-mentioned block polyisocyanate ((R 2 If the content is below the aforementioned range, the number of hydrophilic groups is small, which reduces reactivity and lowers the compatibility of the resin composition; if it exceeds the aforementioned range, the water resistance is reduced due to moisture absorption resulting from increased hydrophilicity, and consequently, the appearance, gloss, and scratch resistance are reduced.

[0127] Solid content of block polyisocyanate, Si(OR 1 )3 content, and alkoxide ((R 2If the content is within the above range, it may be desirable in terms of the resin part and the block polyisocyanate crosslink.

[0128] The block polyisocyanate according to the present invention can be used as a curing agent in paint compositions, adhesive compositions, adhesive compositions, mold compositions, etc.

[0129] Block polyisocyanate may be included in the composition in an amount of 10 to 20 weight% or 12 to 18 weight% based on the total weight of the water-soluble clear coat composition. When the content of block polyisocyanate is within the above range, it has the effect of improving the adhesion and hardness of the prepared coating film by improving the crosslinking density. If the content of block polyisocyanate is below the above range, there is a problem of reduced hardness and appearance characteristics due to reduced curability, and if it exceeds the above range, the coating film may become brittle due to excessive curability, resulting in reduced adhesion, impact resistance, and scratch resistance.

[0130] additives

[0131] The water-soluble clear coat composition according to the present invention may further include conventional components included in water-based paint compositions to the extent that it does not impede the purpose of the present invention.

[0132] The additive may be included in the composition in an amount of 1 to 10 weight% or 3 to 8 weight% based on the total weight of the water-soluble clear coat composition.

[0133] The water-soluble clear coat composition according to the present invention may include, as additives, a rheology modifier added to adjust the rheological behavior of the composition (e.g., RM12W, DOW), a light stabilizer for absorbing ultraviolet rays and suppressing radical chain reactions caused by ultraviolet rays (e.g., Tinuvin 1130 / Tinuvin 123 = 2 / 1), an acid catalyst for promoting the reaction and controlling the curing speed (e.g., dodecylbenzenesulfonic acid type acid catalyst, NACURE 5225, King Industries), an antifoaming agent for suppressing bubble generation (e.g., BYKETOL AQ, BYK), and a wetting agent for improving wettability (e.g., BYK-348, BYK).

[0134] solvent

[0135] The water-soluble clear coat composition according to the present invention may include an organic solvent within a range that does not degrade the physical properties during paint manufacturing, and may include, for example, butyl carbitol, dipropylene glycol n-butyl ether, butyl cellosolve, etc.

[0136] In addition, the water-soluble clear coat composition according to the present invention may include one or more types of water selected from the group consisting of deionized water (DIW), pure water, ultrapure water, and distilled water as an aqueous solvent.

[0137] The solvent may be included in the composition in an amount of 5 to 35 weight% or 8 to 33 weight% based on the total weight of the water-soluble clear coat composition. When the solvent content in the composition is within the above range, problems such as reduced water dispersibility of the resins in the composition, reduced environmental friendliness which is an advantage of water-based paints, and film defects such as pinholes and stains on the final film caused by insufficient evaporation of water can be prevented.

[0138] The present invention will be explained in more detail below through examples.

[0139] However, these examples are intended only to aid in understanding the invention and do not limit the scope of the invention in any way to these examples.

[0140] [Examples and Comparative Examples]

[0141] 1. Manufacture of Block Polyisocyanate

[0142] Block polyisocyanate was prepared by the following method.

[0143] HMDI trimer was added to a 4-neck flask equipped with a stirrer, thermometer, condenser, and nitrogen inlet tube in the amounts listed in Table 1, and the temperature was raised to 40°C. Dimethylpyrazole (DMP) was added to this, and the temperature was slowly raised. The temperature was raised and maintained up to 80°C while controlling the exothermic reaction until the primary NCO% reached 2.4 to 2.7%. When the primary NCO% reached 2.4 to 2.7%, a silane-based blocking agent (Iquest A-1170) was added, and the temperature was maintained at 80°C. When the secondary NCO% reached 0.9 to 1.2%, methoxypolyethylene glycol was added, and the temperature was maintained at 80°C. When the NCO% reached 0%, the solvents propylene glycol methyl ether acetate (PMA) and butyl cellosolve were added, the reaction was terminated, and the mixture was cooled.

[0144]

[0145] Reaction result: Solid content 80%, Si(OR 1 )3 content 5 wt%, alkoxide ((R 2 A block polyisocyanate with a content of 9 wt% was prepared.

[0146] The measurement of NCO% was performed using the following method.

[0147] Weigh the sample containing isocyanate groups into a 250 mL beaker. Then, add 25 mL of 0.1 N di-n-butylamine solution using a pipette. Add 25 mL of 1,4-dioxane (if the polymer does not dissolve, add 10 mL of reagent-grade acetone) and stopper the flask. Then, stir mechanically for 15 minutes to dissolve the prepolymer. Add 4 to 6 drops of bromphenol blue indicator solution and rinse the walls of the beaker with 50 mL of isopropyl alcohol. Titrate with 0.1 N hydrochloric acid until a yellow endpoint is reached. Perform a blank test using all the above reagents under conditions without the sample.

[0148] The isocyanate group content is calculated as follows.

[0149] Solution : NCO content (%) = {(BV)×N×0.4202} / W(g)}

[0150] Here,

[0151] B: mL of hydrochloric acid consumed in the blank test

[0152] V: mL of hydrochloric acid consumed in sample titration

[0153] 0.4202 : Milliequivalent weight of isocyanate group

[0154] W: Weight of the sample

[0155] 2. Preparation of a water-soluble clear coat composition

[0156] A water-soluble clear coat composition was prepared by mixing manufactured block polyisocyanate, acrylic emulsion resin, silicone-modified polyester resin, urethane dispersion resin, melamine resin, additives, and a solvent.

[0157] Table 2 presents the physical properties of the ingredients used, or the manufacturer and product name.

[0158]

[0159] A water-soluble clear paint composition for automobiles was prepared by mixing the components in the order shown in Table 2 and adjusting the final viscosity to Ford Cup #4 in 50 seconds.

[0160] The content of acrylic emulsion resin, silicone-modified polyester resin, urethane dispersion resin, melamine resin, additives, solvents, and blocked polyisocyanates is presented in Tables 3 to 5 below.

[0161]

[0162]

[0163]

[0164] 3. Evaluation of Physical Properties of the Coating

[0165] A primer paint was applied to an electrodeposited steel plate specimen and cured at 140°C for 20 minutes to form a primer film with a thickness of 30 to 50 μm. Subsequently, a base coat was bell-sprayed onto the primer film, and hot air was blown at 80°C for 3 minutes to evaporate the water remaining in the paint, thereby forming a base film with a thickness of 15 μm. Subsequently, the water-soluble clear coat composition prepared in the examples and comparative examples was applied onto the base film and cured at 140°C for 20 minutes to form a clear film with a thickness of 40 μm, thereby producing the final film.

[0166] The appearance characteristics and physical properties of the final coating were measured in the following manner, and the results are shown in Tables 6 to 8.

[0167] (1) Appearance

[0168] Gloss (LU), sharpness (SH), and orange peel (OP) were measured on the manufactured final coating using the Wave Scan DOI (BYK Gardner), an automotive exterior measuring instrument, and the overall appearance evaluation value (CF) was calculated using the following Equation 1 using the measured properties.

[0169] [Mathematical Formula 1]

[0170] CF = LU × 0.15 + SH × 0.35 + OP × 0.5

[0171] CF was measured and calculated horizontally and vertically. Based on the horizontal / vertical values ​​of CF, CF was evaluated as excellent (◎) if CF was 79 / 74 or higher, good (○) if 75 / 70 or higher but less than 79 / 74, average (△) if 72 / 67 or higher but less than 75 / 70, and poor (×) if less than 72 / 67.

[0172] (2) Scratch resistance

[0173] The resistance to scratching of the finished paint film was measured using an automotive scratch resistance tester (AMTEC-KISTER). The 20-degree gloss of the paint film surface before and after the test was measured, and the gloss retention rate (%) was calculated and evaluated. Based on the measurement results, the gloss retention rate (%) was evaluated as excellent (◎) if it was 70% or higher, good (○) if it was 60% or higher but less than 70%, average (△) if it was 50% or higher but less than 60%, and poor (×) if it was less than 50%.

[0174] (3) Gloss

[0175] To measure the gloss (GLOSS, %) reflected from the coating film, a polisher (BYK Gardner) was applied to 20 of the final coating film o Gloss was measured. Based on the measurement results, gloss was evaluated as excellent (◎) if 91% or more, good (○) if 89% or more but less than 91%, average (△) if 87% or more but less than 89%, and poor (×) if less than 87%.

[0176] (4) Chipping

[0177] After leaving the final film at -20℃ for 3 hours, a 50g chipping stone (4mm diameter) is applied at a pressure of 5 bar for 45 oIt was struck at an angle. Afterwards, foreign substances such as peeled film remaining on the final coating were removed. Regarding the damaged areas of the final coating, it was evaluated as excellent (◎) if there were 10 or fewer damages of 1 mm or less, good (○) if there were 10 or fewer damages of more than 1 mm and less than 2 mm, average (△) if there were 10 or fewer damages of 2 mm or more and less than 3 mm, and poor (×) if there were more than 10 damages of 2 mm or more and less than 3 mm.

[0178] (5) Hardness

[0179] The hardness of the clear film was measured using the pencil hardness method. Specifically, the maximum hardness that does not damage the clear film was measured using 2B, B, HB, F, H, and 2H pencils, respectively.

[0180] The measurement results were evaluated as Excellent (◎) if HB or higher, Good (○) if B, and Poor (×) if B or lower.

[0181] (6) Impact resistance

[0182] Impact resistance of the final coating was evaluated according to ASTM D2794. A DuPont impact tester was used, and the appearance of the coating was observed when a 500g weight was dropped onto the specimen while varying the drop height from 30 cm to 50 cm.

[0183] As a result of observation, the coating was evaluated as excellent (◎) if no cracking or peeling occurred at a drop height of 50 cm or more, good (○) if cracking or peeling occurred at 30 cm or more but less than 50 cm, average (△) if cracking or peeling occurred at 20 cm or more but less than 30 cm, and poor (×) if cracking or peeling occurred at less than 20 cm.

[0184] (7) Water resistance

[0185] The final film was immersed in a 40℃ constant temperature water bath for 240 hours and left at room temperature for 1 hour, after which adhesion was evaluated using the checkerboard method and discoloration was visually checked.

[0186] Specifically, the checkerboard method is a method of measuring adhesion by making 100 squares of 2 mm by 2 mm on the surface of a clear coating with a knife and then peeling off the squares using tape. The adhesion was evaluated as excellent (◎) if 100% of the remaining squares among the 100 squares were fully attached, good (○) if 70% or more but less than 100%, average (△) if 50% or more but less than 70%, and poor (×) if less than 50%.

[0187] (8) Content

[0188] After placing a cotton cloth sufficiently soaked in xylene solvent on the surface of the final coating, the time taken for the base coating surface to appear was measured by scratching it four times with a fingernail at 1 minute with a force of 2 kgf.

[0189] The measurement results were evaluated as excellent (◎) if 10 minutes or more, good (○) if 7 minutes or more but less than 10 minutes, average (△) if 5 minutes or more but less than 7 minutes, and poor (×) if 5 minutes or less.

[0190] (9) Weather resistance

[0191] Gloss retention rate (20) before and after 1,000 hours of exposure of the final coating to WOM, an accelerated weathering tester. ㅇ Gloss), adhesion, and color difference (X-Rite MA98) tests were conducted.

[0192] Specifically, adhesion was evaluated using the checkerboard method of item (7), and was evaluated as excellent (◎) if the remaining squares were 100%, the gloss retention rate was 95% or more, and the color difference value (△E) was 1.0 or less; good (○) if the remaining squares were 100%, the gloss retention rate was 90% or more and less than 95%, and the color difference value (△E) was 1.0 or less; and poor (×) if the remaining squares were less than 90%, the gloss retention rate was less than 90%, and the color difference value (△E) was greater than 1.0.

[0193]

[0194]

[0195]

[0196] As can be seen in Tables 6 to 8, Examples 1 to 21 showed average in some evaluation items and excellent or good in most evaluation items. On the other hand, Comparative Examples 1 to 11 showed poor in many evaluation items.

[0197] Although the present invention has been described in detail above only with respect to the described embodiments, it is obvious to those skilled in the art that various modifications and variations are possible within the scope of the technical spirit of the present invention, and it is natural that such modifications and variations fall within the scope of the appended claims.

[0198] Various embodiments of the present invention are described below.

[0199] Specific Example 1. A water-soluble clear coat composition comprising an acrylic emulsion resin, a silicone-modified polyester resin, a urethane dispersion resin, a melamine resin, and a blocked polyisocyanate, wherein the acrylic emulsion resin has a hydroxyl value of 100 to 140 mgKOH / g and a weight-average molecular weight of 22,000 to 32,000 g / mol, the silicone-modified polyester resin has a hydroxyl value of 200 to 250 mgKOH / g, and the urethane dispersion resin has a glass transition temperature of -9 to -1°C.

[0200] Example 2. The water-soluble clear coat composition of Example 1, wherein the acrylic emulsion resin has an acid value of 5 to 20 mgKOH / g, a glass transition temperature of 25 to 45°C, and a viscosity of 10 to 500 cps at 25°C.

[0201] Example 3. The water-soluble clear coat composition of Example 1, wherein the silicone-modified polyester resin has an acid value of 15 to 25 mgKOH / g, a glass transition temperature of 1 to 8°C, a viscosity of 8,500 to 11,000 cps at 25°C, a weight-average molecular weight of 2,500 to 4,500 g / mol, and a number-average molecular weight of 800 to 1,600 g / mol.

[0202] Example 4. The water-soluble clear coat composition of Example 1, wherein the urethane dispersion resin has a weight-average molecular weight of 21,000 to 25,000 g / mol and a viscosity of 5 to 50 cps at 25°C.

[0203] Example 5. In Example 1, the block polyisocyanate has a solid content (NV) of 70 to 90 weight% based on the total weight, and Si (OR in the system 1 The )3 content is 1 to 11 weight%, and the alkoxide (R 2 O) The content is 5 to 15 weight%, and R 1 is an alkyl group having 1 to 2 carbon atoms, and R 2 A water-soluble clear coat composition having an alkyl group having 1 to 4 carbon atoms.

[0204] Example 6. The water-soluble clear coat composition of Example 1, comprising, based on the total weight of the water-soluble clear coat composition, 10 to 30 weight% of an acrylic emulsion resin, 5 to 15 weight% of a silicone-modified polyester resin, 5 to 15 weight% of a urethane dispersion resin, 10 to 20 weight% of a melamine resin, and 10 to 20 weight% of a blocked polyisocyanate.

Claims

1. Includes acrylic emulsion resin, silicone-modified polyester resin, urethane dispersion resin, melamine resin, and blocked polyisocyanate, The acrylic emulsion resin has a hydroxyl value of 100 to 140 mgKOH / g and a weight-average molecular weight of 22,000 to 32,000 g / mol, and The silicone-modified polyester resin has a hydroxyl value of 200 to 250 mgKOH / g, and A water-soluble clear coat composition in which the urethane dispersion resin has a glass transition temperature of -9 to -1°C.

2. In Claim 1, A water-soluble clear coat composition having an acrylic emulsion resin having an acid value of 5 to 20 mgKOH / g, a glass transition temperature of 25 to 45℃, and a viscosity of 10 to 500 cps at 25℃.

3. In Claim 1, A water-soluble clear coat composition in which a silicone-modified polyester resin has an acid value of 15 to 25 mgKOH / g, a glass transition temperature of 1 to 8°C, a viscosity of 8,500 to 11,000 cps at 25°C, a weight-average molecular weight of 2,500 to 4,500 g / mol, and a number-average molecular weight of 800 to 1,600 g / mol.

4. In Claim 1, A water-soluble clear coat composition having a urethane dispersion resin, a weight-average molecular weight of 21,000 to 25,000 g / mol, and a viscosity of 5 to 50 cps at 25°C.

5. In Claim 1, The blocked polyisocyanate has a solid content (NV) of 70 to 90 weight% based on total weight, and Si (OR in the system) 1 The )3 content is 1 to 11 weight%, and the alkoxide (R 2 O) The content is 5 to 15 weight%, and R 1 is an alkyl group having 1 to 2 carbon atoms, and R 2 A water-soluble clear coat composition having an alkyl group having 1 to 4 carbon atoms.

6. In Claim 1, A water-soluble clear coat composition comprising, based on the total weight of the water-soluble clear coat composition, 10 to 30 weight% of an acrylic emulsion resin, 5 to 15 weight% of a silicone-modified polyester resin, 5 to 15 weight% of a urethane dispersion resin, 10 to 20 weight% of a melamine resin, and 10 to 20 weight% of a blocked polyisocyanate.

Images