Aqueous one-coat coating compositions, one-coat coating films, and processes for forming coating films

Abstract

Problem: To offer aqueous one-coat coating compositions which form coating films with outstanding adhesion after a water-resistance test, and high lightness value, and cured one-coat coating films obtained from such aqueous one-coat coating compositions. Solution: Aqueous one-coat coating compositions containing an acrylic resin having hydroxy groups (A), a hardener (B), a coloured pigment (C), wherein the acrylic resin having hydroxy groups (A) is an acrylic resin with a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g, a Hansen solubility parameter (HSP) of 9.8-10.8, a mass-average molecular weight of 10,000-100,000, and a glass transition temperature of 0-40ºC, and when formed on an undercoat film with a lightness value L*45 of 40 to give a dry film thickness of 30 µm, the 60º gloss value of a cured one-coat coating film formed from an aforementioned aqueous one-coat coating composition is ≥85, lightness 20 value L*45 is 60-95, and infrared solar reflectance (IRSR) is ≥60%.

Description

Document : Speci ficationTitle of the invention Aqueous one-coat coating compositions , one-coat coating films , and processes for forming coating filmsTechnical field

[0001] The present invention relates to aqueous one-coat coating compositions , one-coat coating films , and processes for forming coating films .Background Art

[0002] For automobile outer panel components , a coating process involving coating with an undercoat coating such as a cationic electrodeposition coating composition, and a middle-coat coating, and then f inishing by coating a topcoat coating such as a solid type on top of this coating film, and a coating process finished by coating a topcoat coating directly on top of a coating film of undercoat coating such as a cationic electrodeposition coating composition, are already known . These processes form a topcoat coating film as a single coat ; therefore , there are the advantages that there are few steps , productivity is high, and energy can be saved .

[0003] For example , in Patent Document 1 it is disclosed that coating films with outstanding recoat adhesion can be formed by means of white coating material for an aqueous one-coat topcoat characteri zed in that it contains (A) a polyester having a speci fied hydroxyl value and acid value , (B ) an aqueous melamine resin, and ( C ) a white coloured pigment .

[0004] In addition for example , it is disclosed by Patent Document 2 that coating films with outstanding recoat adhesion, water resistance , weather resistance and chipping resistance can be formed by an aqueous one-coattopcoat coating composition characteri zed in that it contains (A) a polyester resin with a speci fied acid value , hydroxyl value , and benzene ring concentration, (B ) a hardener, ( C ) a coloured pigment , and ( D) an acrylic resin for pigment dispersion, obtained by copolymeri zing speci fied polymeri zable unsaturated monomers .Prior art documents[Patent documents ]

[0005] [Patent Document 1 ] JP 2003-206439 A[Patent Document 2 ] JP 2003-292884 ASynopsis of the inventionProblem which the invention is intended to solve

[0006] However, when coating films with a high lightness value are needed, a topcoat coating film which has the feature of being able to hide the colour of the underlying coating film is needed . Especially when a one-coat topcoat coating such as those described in Patent Document 1 and Patent Document 2 above is used, in order to hide the colour of the underlying coating film the quantity of pigments in the coating composition, especially white pigments , needs to be increased .However, when the pigment content in the coating compositions in either of Patent Document 1 or Patent Document 2 is increased, the adhesion of the resulting coating film after a water-resistance test may be lowered .

[0007] Accordingly, the obj ect of the present invention is to of fer aqueous one-coat coating compositions which can form coating films with outstanding adhesion after a water-resistance test , and high lightness value , and one- coat coating films obtained from such aqueous one-coat coating compositions . A further obj ect of the present invention is to of fer processes for forming coating film by using such aqueous one-coat coating compositions .Means for solving the problem

[0008] As the result of intensive studies to solve the aforementioned problem, the present inventors have perfected this invention with the discovery that the problem above can be solved by aqueous one-coat coating compositions which contain an acrylic resin containing hydroxyl groups, which has a specified hydroxyl value, acid value, Hansen solubility parameter (HSP) , massaverage molecular weight, and glass transition temperature (A) , and a hardener (B) and coloured pigment (C) , which are aqueous one-coat coating compositions which give a one-coat coating film with a specified 60° gloss value, lightness value L*45, and infrared solar reflectance (IRSR) when formed on an underlying coating film having a specified lightness value L*45 to give a specified dry film thickness.

[0009] Thus, the problem above addressed by the present invention is solved by aqueous one-coat coating compositions which are aqueous one-coat coating compositions containing an acrylic resin having hydroxy groups (A) , a hardener (B) , and a coloured pigment (C) , wherein the acrylic resin having hydroxy groups (A) is an acrylic resin with a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g, a Hansen solubility parameter (HSP) of 9.8-10.8, a mass-average molecular weight of 10,000-100,000, and a glass transition temperature of 0-40°C; and when formed to give a dry film thickness of 30 pm on an underlying coating film having a lightness value L*45 of 40, the 60° gloss value of the cured one-coat coating film is >85, lightness value L*45 is 60-95, and infrared solar reflectance (IRSR) is >60%.

[0010] Moreover, the aqueous one-coat coating composition of the present invention is preferably an aqueous one-coat coating composition in which the content of acrylic resinhaving hydroxy groups (A) is 50-90 parts by mass in 100 parts by mass of total resin solids.

[0011] Moreover, the aqueous one-coat coating compositions of the present invention is preferably an aqueous one-coat coating composition in which the hardener (B) is a melamine resin.

[0012] Moreover, the aqueous one-coat coating composition of the present invention is preferably an aqueous one-coat coating composition in which the coloured pigment (C) is a white pigment, which can be further combined with a coloured pigment selected from a set comprising red pigments, orange pigments, yellow pigments, green pigments, blue pigments, purple pigments and black pigments .

[0013] In addition the problem addressed by this invention is also solved by a cured one-coat coating film which is a cured coating film obtained from an aqueous one-coat coating composition containing an acrylic resin having hydroxy groups (A) , with a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g a Hansen solubility parameter (HSP) of 9.8-10.8, a mass-average molecular weight of 10,000-100,000, and a glass transition temperature of 0-40°C, a hardener (B) , and a coloured pigment (C) , and has a 60° gloss value of >85, a lightness value L*45 of 60-95, and infrared solar reflectance (IRSR) of >60%Moreover, the problem addressed by this invention is also solved by a process for forming a cured one-coat coating film in which a cured electrodeposited coating film is formed by coating an electrodeposited coating composition on a metallic substrate for coating and curing, and then the aqueous one-coat coating composition above is coated directly onto this and cured.Effects of the invention

[0015] With aqueous one-coat coating compositions of the present invention it is possible to form coating films with outstanding adhesion after a water-resistance test , and a high lightness value . Moreover, coating films obtained with aqueous one-coat coating compositions of the present invention also have outstanding heat shielding properties . or Carrying Out the InventionAqueous one-coat coating compositions of the present invention contain an acrylic resin having hydroxy groups (A) , a hardener (B ) and a coloured pigment ( C ) . In the present invention, "aqueous" means that the resin, hardener, etc . , which contains , form a stably dissolved or dispersible state in water or in a mixture of water and organic solvents

[0017] The acrylic resin having hydroxy groups (A) employed in the present invention is a water-soluble or water- dispersible acrylic resin, which can be obtained from free-radical polymeri zable monomer as starting constituents by a known process employing free-radical ri zation .Free-radical polymeri zable monomers include , for example , (meth) acrylic acid, methyl (meth) acrylate , ethyl (meth) acrylate , n-propyl (meth) acrylate , isopropyl (meth) acrylate , n-butyl (meth) acrylate , isobutyl (meth) acrylate , sec-butyl (meth) acrylate , tert-butyl (meth) acrylate , hexyl (meth) acrylate , 2-ethylhexyl (meth) acrylate , octyl (meth) acrylate , lauryl (meth) acrylate , stearyl (meth) acrylate , allyl alcohol ,2 -hydroxyethyl methacrylate, 2 -hydroxypropyl (meth) acrylate,3-hydroxypropyl (meth) acrylate , 4-hydroxybutyl (meth) - acrylate , styrene , cyclohexyl (meth) acrylate , 4-tert- butylcyclohexyl (meth) acrylate , and (meth) acrylonitrile .These free-radical polymeri zable monomers can be used individually, or used in combinations of two or more .

[0019] A hydroxyl value of the acrylic resin having hydroxy groups (A) employed in the present invention is preferably 60- 100 mgKOH / g; 65- 95 mgKOH / g is more preferable , and 70- 90 mgKOH / g is particularly preferable . By making the hydroxyl value of the acrylic resin having hydroxy groups (A) 60- 100 mgKOH / g, it is possible to obtain coating films with an adequate crosslinking density, which also show outstanding adhesion after a water-resistance test .

[0020] In this invention, the hydroxyl value of the acrylic resin having hydroxy groups (A) , which is the number of milligrams of potassium hydroxide equivalent to the hydroxy groups in 1 g of sample , is calculated from the monomer formulation of the acrylic resin .

[0021] In addition, an acid value of the acrylic resin having hydroxy groups (A) employed in the present invention is preferably 10-30 mgKOH / g; 13-27 mgKOH / g is more preferable , and 15-25 mgKOH / g is particularly preferable . By making the acid value of the acrylic resin having hydroxy groups (A) 10-30 mgKOH / g, the acrylic resin having hydroxy groups (A) shows a stability in water which is not problematic . In addition, the resulting coating film shows outstanding adhesion after a waterresistance test .

[0022] In this invention, the acid value of the acrylic resin having hydroxy groups (A) , which is the number of milligrams of potassium hydroxide needed to neutrali ze the free acid in 1 g of sample , is calculated from the monomer formulation of the acrylic resin .

[0023] A Hansen solubility parameter (HSP) of the acrylic resin having hydroxy groups (A) employed in the presentinvention is preferably 9.8-10.8; 9.9-10.7 is more preferable, and 10.0-10.6 is particularly preferable. By making the Hansen solubility parameter (HSP) of the acrylic resin having hydroxy groups (A) 9.8-10.8, it is possible to obtain outstanding pigment dispersability, and possible to obtain coating films with an outstanding gloss value.

[0024] The Hansen solubility parameter (HSP) was developed by C. M. Hansen, and is a parameter for indicating the solubility of substances (C. M. Hansen, Hansen Solubility Parameters: A User's Handbook, 1999) . In this invention, the Hansen solubility parameter (HSP) was estimated by using the group-contribution method proposed by D. W. van Krevelen and P. J. Hoftyzer (D. W. van Krevelen, P. J. Hoftyzer, Properties of Polymers 2nd Edition, 1976) .

[0025] A mass-average molecular weight of the acrylic resin having hydroxy groups (A) employed in the present invention is preferably 10,000-100,000; 15,000-80,000 is more preferable, and 20,000-60,000 is particularly preferable. Making the mass-average molecular weight of the acrylic resin having hydroxy groups (A) 10,000-100,000 means that the coating composition can be coated without any problems. The resulting coating film also shows outstanding adhesion after a water-resistance test .

[0026] In this invention, the mass-average molecular weight was found as the value calculated from data measured by gel permeation chromatography (GPC) using tetrahydrofuran (THE) as an eluent, at a temperature of 40°C and flow rate of 1 ml / minute, using the mass-average molecular weight of polystyrene as a standard. In this gel permeation chromatography (GPC) , combinations of TSKgel G2000HXL, G3000HXL, G4000HXL, and G5000HXL (proprietary name, Tosoh Corp.) were used as columns.

[0027] In addition, a glass transition temperature of the acrylic resin having hydroxy groups (A) employed in the present invention is preferably 0-40°C; 5-35°C is more preferable, and 10-30°C is particularly preferable. Making the glass transition temperature of the acrylic resin having hydroxy groups (A) 0-40°C, means that the coating composition can be coated without any problems. The resulting coating film shows outstanding adhesion after a water-resistance test.In this invention, the glass transition temperature was found from the monomer formulation of the acrylic resin by the equation below.1 / Tg = £(Wi / Tgi)Tg: glass transition temperature of the copolymer (absolute temperature)Wi : mass! of monomer constituent iTgi : glass transition temperature (absolute temperature) of a homopolymer of monomer constituent i.In the aqueous one-coat coating composition of the present invention, the content of acrylic resin having hydroxy groups (A) is preferably 50-90 parts by mass in 100 parts by mass of total resin solids in the composition; 55-85 parts by mass is more preferable, and 60-80 parts by mass is particularly preferable. By making the content of acrylic resin having hydroxy groups (A) 50-90 parts by mass, it is possible to obtained coating films with an adequate crosslinking density, and they also show outstanding adhesion after a water-resistance test .

[0030] As the acrylic resin having hydroxy groups (A) employed in the present invention, a single resin can be used, or ination of two or more can be used.In addition, hardeners (B) which can be employed in the present invention, include, for example, amino resins,polyisocyanate compounds, blocked polyisocyanate compounds, polycarbodiimide compounds, etc. In these hardeners, amino resins are particularly preferred. These hardeners (B) can be used singly, or a combination of two or more can be used

[0032] Amino resin is a collective term for resins formed by condensation of formaldehyde with a compound containing an amino group. Amino resins include, for example, melamine resins, urea resins, guanamine resins, etc. In these amino resins, melamine resins are particularly preferred .

[0033] Melamine resins include, for example, partially or completely methylolated melamine resins obtained by reacting melamine with formaldehyde, partially or completely alkyl etherified melamine resins obtained by partial or complete etherification by means of an alcohol constituent and methylol groups of a methylolated melamine resin, imino group-containing melamine resins, mixed melamine resins which are mixtures of two or more of these melamine resins, etc. Alkyl etherified melamine resins include, for example, methylated melamine resin, butylated melamine resin, methyl / butyl mixed alkyl etherified melamine resins, etc.

[0034] Polyisocyanate compounds include, for example, aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, etc., aromatic diisocyanates such as xylene diisocyanate (XDI) , trilene diisocyanate (TDI) , 4,4'- diphenylmethane diisocyanate (MDI) , etc., alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI hydrogenated MDI, etc., and diisocyanate dimers, trimers, or compounds comprising more diisocyanates such as urethdione structures, allophanate structures, adduct structures, biuret structures, isocyanurate structures,iminooxadiazindione structures, etc. Moreover, some of these isocyanate groups can be modified by an amino group-containing silane coupling agent, etc.

[0035] Blocked polyisocyanate compounds, include polyisocyanate compounds above with the isocyanate groups blocked, for example, by an alcohol such as butanol, etc., an oxime such as butyl ethyl ketoxime, etc., a lactam such as s- caprolactam, etc., an active methylene compound such as a malonic acid diester, an acetoacetic acid ester, etc., a pyrazole such as 3, 5-dimethylpyrazole, etc., an imidazole such as imidazole, 2-ethylimidazole, etc., or a phenol such as m-cresol etc.

[0036] As polycarbodiimide compounds, hydrophilic carbodiimide compounds are preferred. Hydrophilic carbodiimide compounds include, for example, compounds obtained by reacting a polycarbodiimide compound having at least two isocyanate groups in a molecule, with a polyol having terminal hydroxy groups, in a proportion giving an NCO / OH mol ratio in excess of 1, and then reacting a hydrophilization agent having active hydrogen and a hydrophilic moiety with the reaction product.In the aqueous one-coat coating composition of the present invention, the content of the hardener (B) is preferably 10-50 parts by mass in 100 parts by mass of total resin solids in the composition; 15-45 parts by mass is more preferable, and 20-40 parts by mass is particularly preferable. By making the content of the hardener (B) 10-50 parts by mass, it is possible to obtained coating films with an adequate crosslinking density, and they also show outstanding adhesion after a water-resistance test.

[0037] The coloured pigment (C) employed in the present invention is preferably at least one coloured pigment selected from a set comprising white pigments, red pigments, orange pigments, yellow pigments, greenpigments, blue pigments, purple pigments, and black pigments .

[0038] This coloured pigment (C) is particularly preferably a white pigment; only one white pigment can be used, or a white pigment combined with a further coloured pigment selected from a set comprising red pigments, orange pigments, yellow pigments, green pigments, blue pigments, purple pigments, and black pigments can be used.White pigments as a coloured pigment (C) employed in the present invention include, for example, titanium oxide, etc .

[0040] Red pigments as a coloured pigment (C) employed in the present invention include, for example, azo pigments, ansanthrone pigments, anthraquinone pigments, perylene pigments, quinacridone pigments, diketopyrrolopyrrole pigments, iron oxide pigments, etc.Orange pigments as a coloured pigment (C) employed in the present invention include, for example, azo pigments, anthraquinone pigments, perinone pigments, quinacridone pigments, composite oxide pigments, etc.Yellow pigments as a coloured pigment (C) employed in the present invention include, for example, isoindoline pigments, azomethine pigments, anthrone pigments, benzimidazolone pigments, quinoxalindione pigments, isoindolinone pigments, iron oxide pigments, composite oxide pigments, etc.

[0043] Green pigments as a coloured pigment (C) employed in the present invention include, for example, phthalocyanine pigments, azomethine pigments, composite oxide pigments, etc .

[0044] Blue pigments as a coloured pigment (C) employed in the present invention include, for example, phthalocyanine pigments, threne pigments, indigo pigments, composite oxide pigments, etc.Purple pigments as a coloured pigment (C) employed in the present invention include, for example, dioxazine pigments, perylene pigments, quinacridone pigments, composite oxide pigments, etc.Black pigments as a coloured pigment (C) employed in the present invention include, for example, carbon black, azo pigments, perylene pigments, composite oxide pigments, etc. It should be noted that employment of carbon black is a fall-back option, and employment of black pigments such as azo pigments, perylene pigments, composite oxide pigments, etc., are more preferred, because when these are employed the resulting multilayer coating films show an outstanding heat shielding effect.There is no particular restriction as to the total content of coloured pigment (s) (C) in the aqueous one- coat coating composition of the present invention, but is preferably 10-200 parts by mass in 100 parts by mass of total resin solids in the composition; 35-160 parts by mass is more preferable, and 60-120 parts by mass is particularly preferable.

[0048] The aqueous one-coat coating compositions of the present invention can further include luminescent pigments. Luminescent pigments include, for example, uncoloured or coloured aluminium pigments, vapour deposited metal flake pigments, interference pigments of a transparent or semitransparent base material coated with a metal oxide, etc. A single such luminescent pigment can be used, or a combination of two or more can be used.

[0049] There is no particular restriction as to the total content of luminescent pigment (s) in the aqueous one-coat coating composition of the present invention, but is preferably 0-2.0 parts by mass in 100 parts by mass of total resin solids in the composition; 0-1.0 parts by mass is more preferable, and 0-0.5 parts by mass is particularly preferable.

[0050] Optionally, the coating film performance of the aqueous one-coat coating compositions of the present invention can be adjusted by adding (an) other resin (s) . Other resins include, for example, polyester resins, polyurethane resins, polyurea resins, acrylic-urethane resins, polyurethane-polyurea resins, polyolefin resins (including chlorinated and / or modified resins) , epoxy resins, etc. Moreover, other resins can be partially crosslinked particles, or can be core / shell particles comprising an inside (core) and an outside (shell) . Particulate base polymers include, for example, polyurethane-polyurea particles, urethane core / acrylic shell particles, acrylic core / urethane shell particles, etc. It should be noted that in the case of partially crosslinked resin particles, this portion isinsoluble in organic solvents (gel portion) , and therefore, the gel fraction, which indicates the proportion of gel in the resin particle solids, can be measured. In addition, other resins preferably have hydroxy groups and / or carboxy groups as a functional group. Other resins can be used individually, or used in combinations of two orThe aqueous one-coat coating compositions of the present invention can also optionally include suitable solvents such as water and / or organic solvents, various coating additives such as rheology control agents, pigment dispersants, antisettling agents, curing catalysts, defoaming agents, antioxidants, UV absorbing agents, extender pigments, etc. Organic solvents include, forexample aromatic hydrocarbons such as toluene, xylene, aromatic naphtha, etc., ketones such as acetone, methyl ethyl ketone, methyl amyl ketone, etc., esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, ethyl ethoxypropionate, etc., alcohols such as isopropanol, butanol, 2-butoxyethanol , 2-ethyl- hexanol, etc., ether, aliphatic hydrocarbons including chlorinated hydrocarbons, or mixtures thereof. Organic solvents can be used individually, or used in ations of two or more.Although there is no particular restriction as to the content of non-volatile constituents in the aqueous one- coat coating compositions of the present invention at the time of coating, it is preferably 30-70 mass%; 40-60 mass% is preferable, and 45-55 mass% is particularly preferred. Making the content of non-volatile constituents 30-70 mass% means that the coating composition can be coated without any problems.By coating the aqueous one-coat coating composition of this invention onto a substrate, and then baking (heating) , a cured one-coat coating film can be obtained.

[0054] There is no particular restriction as to substrates to which the aqueous one-coat coating compositions of the present invention can be applied; examples include members made of a metal such as iron, zinc, aluminium, magnesium, etc., members made from alloys of these metals, members with these metals plated or vapour deposited thereon, members made of glass, plastic, foams of various materials, etc. In these examples, metal and plastic substrates constituting automobile bodies are preferred. Optionally, these member can have been given a suitable treatment such as degreasing, surface treatment, etc.

[0055] In addition, substrates to which the aqueous one-coat coating compositions of the present invention can be applied include aforementioned members with an undercoat coating film formed thereon. The undercoat coating film is applied to the surface of the members because it can hide the surface of the member, and confer corrosion resistance, rust prevention, adhesion, etc. on the member; it can be formed by coating a undercoat coating material, and curing or drying. There are no particular restrictions as to this undercoat coating material, which in itself can be known; for example, an electrodeposition coating composition, a solvent-based primer, a waterbased primer, etc., can be used. In these undercoat coating material, cationic electrodeposition coating compositions which form a cured electrodeposition coating film by coating on metallic substrates and curing are preferred. Moreover, particularly preferably this cured cationic electrodeposition coating film has a lightness value L*45 of at least 40.The aqueous one-coat coating compositions of the present invention can be coated by electrostatic coating, air spraying, airless spraying, etc.

[0057] Although there are no particular restrictions as to a dry film thickness of the cured one-coat coating film, it is preferably 10-50 pm, more preferably 20-40 pm, and even more preferably 25-35 pm.

[0058] In the present invention, baking (heating) can be carried out by known means, for example, a drying oven such as a hot air oven, an electric oven, an infrared induction heating oven, etc., can be employed. Although there is no particular restriction as to a curing temperature, it is preferably 100-160°C; 120-155°C is more preferable, and 130-150°C is particularly preferable. By making the curing temperature 100-160°C, the curing reaction can be adequately promoted. In addition, although there is noparticular restriction as to a heating time, it is preferably 10-50 minutes; 15-45 minutes is more preferable, and 20-40 minutes is particularly preferable.

[0059] A 60° gloss value of the hardened one-coat coating film of the aqueous one-coat coating composition of the present invention is preferably >85, >87 is more preferable, and >90 is particularly preferable. In this invention, the 60° gloss value is the value measured by using a Micro-tri-gloss Glossmeter (proprietary name, BYK-Gardner GmbH) .

[0060] On an undercoat film with a lightness value L*45 of 40, the lightness value L*45 of the cured one-coat coating film of the aqueous one-coat coating composition of the present invention formed to give a dry film thickness of 30 pm is preferably 60-95; 65-92 is more preferable, and 70-90 is particularly preferable. Making the lightness value L*45 of the cured one-coat coating film 60-95 means that the cured one-coat coating film shows an outstanding heat shielding effect. Here, lightness value L*45 is a lightness value in the CIE LAB colour system, based on the spectral reflectance of light illuminated at an angle of 45° with respect to a perpendicular line to the the coating film layer and received at an angle of 45° deviated from the specular reflection light to the incident light direction. It should be noted that the CIE LAB colour system was defined by the International Commission on Illumination (CIE) in 1976, and is the colour system adopted by JIS Z 8781-4:2013. In this invention, the lightness values L*45 are values measured using a BYK mac i Multiangle Spectrophotometer (proprietary name, BYK-Gardner GmbH) .

[0061] In addition, an infrared solar reflectance (IRSR) of the cured one-coat coating film obtained from the aqueous one-coat coating composition above is preferably >60%; >63% is more preferable, and >65% is particularlypreferable. Making the infrared solar reflectance (IRSR) of the cured one-coat coating film >60% means that the cured one-coat coating film shows an outstanding heat shielding effect. It should be noted that, in this invention, infrared solar reflectance (IRSR) values were measured using a UV-3600 UV / visible / near-IR Spectrophotometer (proprietary name, Shimadzu Corp.) .

[0062] The aqueous one-coat coating compositions of this invention and process for forming coating films using the same are efficacious for vehicle bodies, parts and components for passenger vehicles, trucks, motorcycles, busses, etc., and especially for metallic automobile bodies . esThis invention is described more specifically below by means of practical examples; however, this invention is not restricted to these examples. In addition, unless stated otherwise, in the examples "parts" means "parts by mass"; and in relation to contents, "%" means "mass%".

[0064] <Production Example. 1-1: Production of acrylic resin aqueous dispersion AC-1> Deionized water 94 parts was loaded into a flask provided with two dropping devices, a reflux condenser, a thermometer, a stirring device, and a nitrogen gas introduction tube, and the temperature was raised to 80°C under an atmosphere of nitrogen. Then a free-radical polymerizable monomer mixture comprising styrene 13.68 parts, 2-hydroxyethyl methacrylate 18.52 parts, n-butyl acrylate 16.03 parts, n-butyl methacrylate 49.21 parts and acrylic acid 2.56 parts, n-dodecyl mercaptan 4.0 parts as an emulsion polymerization regulator, and a mixed emulsifier solution comprising a reactive anionic emulsifier Eleminol RS-3000 (proprietary name, Sanyo Chemical Industries, Ltd., sodium methacryloyloxy polyoxypropylene sulfate) 2.0 parts, a reactive non-ionicemulsifier ADEKA REASOAP NE20 (proprietary name, ADEKA Corp.) 1.0 part, and deionized water 15 parts, were added dropwise using one dropping device at an even rate over 3 hours, and simultaneously with dropwise addition using the dropping device above, a polymerization initiator solution comprising ammonium persulphate 0.30 part in deionized water 15 parts was added dropwise at an even rate over 3 hours by using the another dropping device. After completing dropwise addition, stirring was continued for 1 hour, followed by cooling to 40°C, to give acrylic resin aqueous dispersion AC-1 having the property values shown in Table 1.

[0065] <Production Examples 1-2 to 1-19: Production of acrylic resin aqueous dispersions AC-2 to AC-19>Acrylic resin aqueous dispersions AC-2 to AC-19 having the property values shown in Table 1 and Table 2 were obtained by the same process as in Production example 1- 1, following the formulations shown in Table 1.Table 1 . Formulation and property values of aqueous acrylic resin dispersions AC-1 to AC-10Table 2. Formulation and property values of aqueous acrylic resin dispersions AC-11 to AC-19

[0068] (Note 1) emulsion polymerization regulator: n-dodecyl mercaptan(Note 2) reactive anionic emulsifier Eleminol RS-3000 (proprietary name, Sanyo Chemical Industries, Ltd., sodium methacryloyloxy polyoxypropylene sulfate) (Note 3) reactive non-ionic emulsifier: ADEKA REASOAP NE20 (proprietary name, ADEKA Corp.)

[0069] <Production Example 2: Production of aqueous acrylic-urethane resin dispersion AU-1> 2-1 Production of polyester polyol PE-1 Adipic acid 49.9 parts, 1 , 6-hexanediol 18.5 parts, neopentyl glycol 31.6 parts were loaded, under a stream of nitrogen gas, into a flask provided with a reflux condenser fitted with a separating tube for reaction water, a thermometer, a stirring device, and a nitrogen gas introduction tube, and stirred while the temperature was raised to 160°C. After holding at 160°C for 1 hour, the temperature was raised to 230°C over 5 hours. Acid value was measured at regular intervals while holding at 230°C, and when the acid value became 3.5 mgKOH / g, the mixture was cooled to <80°C. Finally, methyl ethyl ketone 21.9 parts was added, to give polyester polyol PE-1. The property values of polyester polyol PE-1 were acid value of 3.5 mgKOH / g, hydroxyl value 155 mgKOH / g, and resin solids 80 mass%.

[0070] 2-2 Production of aqueous acrylic-urethane resin dispersion AU-1>Polyester polyol PE-1 obtained in Production example 2-1 420.0 parts, neopentyl glycol 31.0 parts, trimethylolpropane monoallyl ether 27.8 parts, dibutyltin dilaurate 0.5 part, and methyl ethyl ketone 195.7 parts were loaded, under a stream of nitrogen gas, into a flask provided with two dropping devices, a reflux condenser, a thermometer, a stirring device, and a nitrogen gas introduction tube, and stirred to give a uniform mixture.

[0071] Then isophorone diisocyanate 259.9 parts was added to the resulting solution. After the exothermal reaction subsided, the reaction mixture was gradually heated to 80°C, with stirring, and stirring was continued at this temperature until isocyanate content became 2.2 mass%. Then, trimethylolpropane 66.7 parts was added, followed by stirring at 80°C until free isocyanate groups in the solution were not detected any more. Then, methyl ethyl ketone 248.9 parts was added to the resulting polyurethane solution.

[0072] Then, the temperature was adjusted to 82°C, and a free- radical polymerizable monomer mixture comprising n-butyl acrylate 312.5 parts, methyl methacrylate 312.5 parts, 2-hydroxypropyl methacrylate 74.7 parts, and acrylic acid. 58.4 parts was added dropwise using one dropping device at an even rate over 3 hours. And simultaneously with dropwise addition using the dropping device above, a polymerization initiator solution comprising 2,2'- azobis (methylbutyronitrile ) 22.8 parts and methyl ethyl ketone 152.3 parts was added dropwise at an even rate over 3.5 hours by using the another dropping device.

[0073] After completing dropwise addition of the monomer mixture and the polymerization initiating solution, the resulting reaction mixture was stirred at 82°C for a further 2.5 hours, and dimethylethanolamine 56.9 parts, and deionized water 2242 parts were added. Then, a separating tube was fitted to a reflux condenser , and the solvent was removed under decreased pressure at 45°C until resin solids in the dispersion became 40 mass%, to give aqueous acrylic- urethane resin dispersion AU-1. The resulting aqueous acrylic-urethane resin dispersion AU-1 had an acid value mgKOH / g, hydroxyl value 57 mgKOH / g, and pH was 8.1.<Production Example 3: Production of black pigment paste P-l>Aqueous acrylic-urethane resin dispersion AU-1 100.0 parts as a dispersing resin, the perylene black pigment Spectrasense Black L0086 (proprietary name, Sun Chemical Colors & Effects GmbH) 40.0 parts, and deionized water 60.0 parts were mixed, and then dispersed by a motor mill to obtain black pigment paste P-1.

[0075] <Production Example 4: Production of blue pigment paste P-2>Aqueous acrylic-urethane resin dispersion AU-1 100.0 parts as a dispersing resin, Cobalt Blue Pigment HEUCODUR Blue 2R (proprietary name, HEUBACH GmbH) 40.0 parts, and deionized water 60.0 parts were mixed, and then dispersed by a motor mill to obtain blue pigment paste P-2.

[0076] <Production Example 5: Production of red pigment paste P-3>Aqueous acrylic-urethane resin dispersion AU-1 100.0 parts as a dispersing resin, red iron oxide pigment 100ED (proprietary name, Toda Kogyo Corp.) 40.0 parts, and deionized water 60.0 parts were mixed, and then dispersed by a motor mill to obtain red pigment paste P-3.

[0077] <Production Example 6-1: Production of aqueous one- coat coating composition WB-1>Aqueous acrylic resin dispersion AC-1 55.30 parts was employed as the dispersing resin, and titanium oxide pigment TI-PURE R-706 (proprietary name, The Chemours Company) 84.92 parts, together with 2-butoxyethanol 8.50 parts and deionized water 21.20 parts to adjust the viscosity, were added to this and dispersed by a motor mill, to obtain a pigment paste.Then 169.92 parts of the pigment paste above was stirred with a dissolver, and aqueous acrylic resin dispersion AC-1 113.30 parts, melamine resin solution CYMEL 325 (proprietary name, ALLNEX GmbH, non-volatile content 80mass%) 12.50 parts, melamine resin solution CYMEL 203 (proprietary name, ALLNEX GmbH, non-volatile content 72 mass%) 20.80 parts, black pigment paste P-1 1.26 parts, blue pigment paste P-2 6.30 parts, red pigment paste P-3 3.15 parts, UV absorbing agent TINUVIN 384-2 (proprietary name, BASF Japan, Ltd.) 2.00 parts, photostabilizer TINUVIN 292 (proprietary name, BASF Japan, Ltd.) 2.00 parts, thickener RHEOVIS HS 1152 (proprietary name, BASF Japan, Ltd.) 2.00 parts, surface regulating agent BYK- 346 (proprietary name, BYK-Chemie GmbH) 1.00 parts, and deionized water 10.00 parts were added in this order, and mixed .Finally, this was diluted with deionized water to give a viscosity of 120 mPa.s at 20°C and a shear rate of 1000s-x, using a R180 portable rotational viscometer (proprietary name, porRheo GmbH) , to obtain aqueous one- coat coating composition WB-1 with the formulation shown in Table 3.

[0078] <Production Examples 6-2 to 6-22: Production of aqueous one-coat coating composition WB-2 to WB-22> Aqueous one-coat coating compositions WB-2 to WB-22 were obtained by the same process as in Production Example 6-1 with the formulations shown in Table 3-5.Table 3. Formulation of WB-1 to WB-8Table 4. Formulation of WB-8 to WB-16Table 5. Formulation of WB-17 to WB-22

[0081] (Note 4) Titanium oxide pigment: TI-PURE R-706 (proprietary name, The Chemours Company)(Note 5) Melamine resin solution: CYMEL 325 (proprietary name, ALLNEX GmbH, non-volatile content 80 mass% )(Note 6) Melamine resin solution: CYMEL 203 (proprietary name, ALLNEX GmbH, non-volatile content 72 mass% )(Note 7) UV absorbing agent: TINUVIN 384-2 (proprietary name, BASF Japan, Ltd.)(Note 8) Photostabilizer: TINUVIN 292 (proprietary name, BASF Japan, Ltd.)(Note 9) Thickener: RHEOVIS HS 1152 (proprietary name, BASF Japan, Ltd.)(Note 10) Surface regulating agent: BYK-346 (proprietary name, BYK-Chemie GmbH)

[0082] <Examples 1-14 and Comparative Examples l-8>(1) Production of test sheets and evaluation of appearanceUsing cationic electrodeposition coating Cathogard 500 (proprietary name, BASF Japan, Ltd.) , zinc phosphate- treated soft steel sheets were electrodeposition coated to give a dry film thickness of 20 pm, and cured at 175°C for 25 minutes to obtain electrodeposition coated sheets. The lightness value L*45 of the resulting electrodeposition coating film, measured using a BYK mac i Multiangle Spectrophotometer (proprietary name, BYK- Gardner GmbH) , was 40.Then aqueous one-coat coating compositions WB-l-WB-22 were spray coated onto the electrodeposition coated sheets to give a dry film thickness of 30 pm, and after standing for 3 minutes at room temperature, they were heated at 140°C for 30 minutes to produce cured one-coat coating film test sheets. The appearance of the resulting coating films was evaluated visually using the criteria below, and the results are shown in Table 6 and Table 7.O: no abnormalities in the coating filmX : small foam swellings or holes in the coating film (pinholes )

[0084] (2) Evaluation of cured one-coat coating filmsCured one-coat coating film test sheets evaluated as O in the evaluation of appearance above (Examples 1- 14, Comparative Examples 1, 3 and 5-8) were subjected to the measurements and evaluations in (2)-l to (2) -4 below, e results are shown in Table 6 and Table 7.(2) — 1 60° gloss valueA 60° gloss value was measured by using a Micro-trigloss Glossmeter (proprietary name, BYK-Gardner GmbH) .(2) -2 Measurement of lightness value L*45A lightness value L*45 was measured using a BYK mac i Multiangle Spectrophotometer (proprietary name, BYK- Gardner GmbH) .(2) -3 Measurement of infrared solar reflectance (IRSR)An infrared solar reflectance (IRSR) was measured using a UV-3600 UV / visible / near-IR Spectrophotometer ietary name, Shimadzu Corp.) .(2) -4 Measurement of adhesion after a waterresistance testThe test sheets were immersed for 10 days in warm water at 40°C, and then taken out and dried. They were then evaluated for adhesion in accordance with JIS K5400-8.5 (cross-cut test) . Thus, lines were cut with a cutter in the surface of the coating films of the test sheets down to the underlying material to give 100 squares at size of 2mm x 2mm; Sellotape® was then pasted over this surface and, at 20°C, detached suddenly at 45°. The evaluation was carried out according to the following criteria based on the number of squares remaining on the coating film.: number of squares of the remaining coating film was 100 (no detachment )X : number of squares of the remaining coating film was 99 or lessTable 6. Evaluation of the hardened one-coat coating films of Example 1 to Example 14Table 7 Evaluation of the hardened one-coat coating films of Comparative Example 1 to Comparative Example 8

Claims

Document: Claims

1. An aqueous one-coat coating composition containing an acrylic resin having hydroxy groups (A) , a hardener (B) , and a coloured pigment (C) , wherein the acrylic resin having hydroxy groups (A) is an acrylic resin with a hydroxyl value of 60-100 mgKOH / g, an acid value of 10-30 mgKOH / g, a Hansen solubility parameter (HSP) of 9.8-10.8, a mass-average molecular weight of 10,000-100,000, and a glass transition temperature of 0-40°C, and when formed on an undercoat film with a lightness value L*45 of 40 to give a dry film thickness of 30 pm, the 60° gloss value of a cured one-coat coating film formed from an aforementioned aqueous one-coat coating composition is >85, lightness value L*45 is 60- 95, and infrared solar reflectance (IRSR) is >60%.

2. The aqueous one-coat coating composition according to claim 1 wherein the content of the acrylic resin having hydroxy groups (A) is 50-90 parts by mass in 100 parts by mass of total resin solids.

3. The aqueous one-coat coating composition according to claim 1 or 2 wherein the aforementioned hardener (B) is a melamine resin.

4. The aqueous one-coat coating composition according to claim 1 or 2 wherein the aforementioned coloured pigment (C) is a white pigment, and can further be combined with a coloured pigment selected from a set comprising red pigments, orange pigments, yellow pigments, green pigments, blue pigments, purple pigments, and black pigments

5. A one-coat coating film obtained from the aqueous one- coat coating composition according to claim 1 or 2.

6. A process for forming a cured one-coat coating f ilm, in which a cured electrodeposition coating film is formed by coating a cationic electrodeposition coating composition on a metallic substrate for coating and curing, and then the aqueous one-coat coating composition according to claim 1 or 2 is coated directly onto this and cured .

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