WO2014000983A1 - Aqueous base paint composition and a method of forming a multi-layer paint film using same - Google Patents

Description

Aqueous base paint composition and a method of forming a multi-layer paint film using same [Technical Field]

[0001]

The present invention concerns novel aqueous base paint compositions, and a method of forming multi-layer paint films using said aqueous base paint compositions, which can be used in various fields and especially in the automobile painting field.

[Background Technology]

[0002]

Generally, the method of forming a multi-layer paint film where an automobile body is the object which is to be painted is carried out by forming an electrodeposited paint film on the object which is to be painted and heating and curing the film and then forming a multi-layer paint film comprising a mid-coat paint film, a base paint film and a clear paint film. Furthermore, at the present time aqueous paints are being used for the mid-coat paints and base paints in order to cut back on volatile organic solvents (VOC) . Moreover, in recent years the method of forming a multi-layer paint film with the so-called three coat one bake (3C1B) system in which the mid-coat paint film which has been formed on the electrodeposited paint film is not heated and cured and the base paint film and the clear paint film are formed on the mid-coat paint film which has been subjected to preliminary heating and these three paint film layers are heated and cured at the same time is coming into use from the viewpoint of energy conservation.

[0003]

In the method of forming a multi-layer paint film with the 3C1B system in this way, reducing the water uptake rate and the water elution rate of the mid-coat paint film which is formed from an aqueous mid-coat paint composition and including an acrylic resin emulsion which has a specified glass transition temperature, acid value and hydroxyl group value, a urethane resin emulsion which has a specified acid value and a curing agent has been effective for forming multi-layer paint films in which the mixing of the mid-coat paint film and base paint film phases is prevented effectively and which have excellent water resistance and appearance (see Patent Document 1) . [0004]

Furthermore, in the method of forming a multi-layer paint film in which a first aqueous paint, a second aqueous paint and a clear paint are coated with a 3C1B system the inclusion in specified proportions by mass of an emulsion resin obtained by the emulsion polymerization of specified vinyl monomers, an amide group containing water-soluble acrylic resin, a urethane resin emulsion and a curing agent is effective at the aqueous paint composition for the second aqueous paint for obtaining multi-layer paint films which have excellent water-resistance and appearance (see Patent Document 2) . In Patent Document 2 it is stated that a thixotropic nature can be imparted to the aqueous paint composition by providing the abovementioned emulsion resin with a core/shell structure.

[0005]

Moreover, in the method of forming a multi-layer paint film in which a first aqueous colored paint, a second aqueous colored paint and a clear paint are coated using a 3C1B system, including acrylic resin, curing agent and urethane resin emulsion for the first aqueous colored paint and providing the first colored paint film which is formed with this first aqueous colored paint with a specified water swelling rate and organic solvent swelling rate is effective for forming a multi- layer paint film which has excellent smoothness, gloss and chipping resistance (see Patent Document 3) . In Patent Document 3 it is stated that the abovementioned urethane resin emulsion is produced with a polyisocyanate component and a polyol component as raw materials and that a compound which has a hydrocarbon group which has at least six carbon atoms is preferred for the polyol component raw material.

[0006]

However, in the methods of forming multi-layer paint films with the 3C1B system using the paint compositions described in Patent Documents 1 to 3 layer-mixing occurs between the first paint layer and the second paint layer in those cases where preliminary heating is not carried out after forming the first paint film and a good paint film appearance is not obtained.

[Prior Art Literature]

[Patent Documents]

[0007]

Patent Document 1 : Japanese unexamined patent application laid open

2004-358462

Patent Document 2 :

Japanese unexamined patent application laid open 2007-297545

Patent Document 3 :

WO 2010/082607

[Outline of the Invention]

[Problems to be Resolved by the Invention]

[0008]

Hence, the present invention is intended to provide an aqueous base paint composition with which it is possible to obtain paint films which have an excellent appearance and adherence on the object which has been painted with a method of forming a paint film with the 3C1B system even though preliminary heating is not carried out after forming the first base paint film, and a method of forming a multi-layer paint film in which this aqueous base paint composition is used.

[Means of Resolving These Problems]

[0009]

As a result of thorough research carried out with a view to resolving the abovementioned problems, the inventors have discovered that it is possible to resolve the abovementioned problems with an aqueous base paint composition which includes as the base resin a specified core/shell type emulsion resin of which the core part comprises acrylic resin and the shell part comprises urethane resin, urethane resin and in which said urethane resin includes in specified proportions structural units which are based on dibasic acids and/or dihydric alcohols which have from 10 to 60 carbon atoms, and the invention is based upon this discovery .

[0010]

That is to say, the invention concerns an aqueous base paint composition which includes a core/shell type emulsion resin with the core part comprising acrylic resin and the sheath part comprising polyurethane resin as a base resin which is characterized in that mass content proportions of the core part and the shell part in the aforementioned core/shell type emulsion resin are from 20/80 to 80/20, the hydroxyl group value and the acid value of the aforementioned acrylic resin are from 40 to 140 mgKOH/g and from 0 to 10 mgKOH/g respectively, the hydroxyl group value and the acid value of the aforementioned polyurethane resin are from 20 to 80 mgKOH/g and from 10 to 60 mgKOH/g respectively, and in the aforementioned polyurethane resin the total mass content proportion of structural units based on a dibasic acid and/or dihydric alcohol having from 10 to 60 carbon atoms is from 10 to 50 mass% with respect to the resin solid fraction of the aforementioned polyurethane resin.

[0011]

Moreover, the invention is a method of forming a multilayer paint film in which a first aqueous base paint (A) is coated on the object to be painted and a first paint film is formed and, without carrying out preliminary heating and hot curing after forming said first paint film, a second aqueous base paint (B) is coated on the aforementioned first uncured paint film and a second paint film is formed, a clear paint (C) is coated on the aforementioned uncured second paint film and a clear paint film is formed and the three paint film layers are heated and cured at the same time and in which, moreover, the aforementioned first aqueous base paint (A) and second aqueous base paint (B) are each selected from among the aqueous base paint compositions of this invention. [0012]

Furthermore, the invention concerns the paint films which are obtained with the method of forming a multi^¬ layer paint film described above.

[Effect of the Invention]

[0013]

It is possible by using an aqueous base paint composition of this invention in a method of forming a multi-layer paint film with a 3C1B system to obtain paint films which have excellent paint film appearance and adherence on the object which has been painted without carrying out preliminary heating after forming the first base paint film.

[Embodiment of the Invention]

[0014]

The core/shell type emulsion resin which is included in the base resin of an aqueous base paint composition of this invention is obtained by synthesizing the acrylic resin which forms the core part in a resin aqueous solution or aqueous dispersion of the polyurethane resin which forms the shell part. Here the polyurethane resin has hydrophilic groups and the acrylic resin has no hydrophilic groups and so when these resins form micelles in water the polyurethane resin acts as an emulsifying agent and is located on the outside of the micelles and the acrylic resin is located inside the micelles and the resins form a core/shell structure. Moreover, a core/shell structure is a structure in which two types of resin component which have different resin compositions are present in the same micelle and in which one resin component forms the inner part (core part) and the other component forms an outer shell part (shell part) .

[0015]

The polyurethane resin which forms the shell part of a core/shell type emulsion resin of this invention can be obtained using known methods, such as the method outlined below for example. First of all a resin which forms segments, such as a polyester resin, polyurethane resin or the like, is synthesized and then a carboxyl group-containing diol and polyisocyanate compound are reacted with the segment resin and a urethane pre- polymer which has terminal isocyanate groups is obtained. Then a polyurethane resin which has terminal hydroxyl groups can be obtained by reacting a polyhydric alcohol with this urethane pre-polymer. [0016]

Polyester resin, polyurethane resin and the like can be cited as examples of the abovementioned segment resin, but polyester resin is preferred.

The polyester resin can be obtained with a known method using an esterification reaction with polybasic acids and polyhydric alcohols and raw materials.

[0017]

Usually polycarboxylic acids are used for the polybasic acids, and monobasic aliphatic acids can be used conjointly, as required. Examples of the polycarboxylic acids include phthalic acid, isophthalic acid, tetrahydrophthalic acid, tetrahydroisophthalic acid, hexahydrophthalic acid, hexahydroterephthalic acid, trimellitic acid, adipic acid, sebacic acid, succinic acid, azeleic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid and the like, and the anhydrides of these acids. One of these polybasic acids can be used individually or a combination of two more or types can be used.

[0018]

Glycols and polyhydric alcohols with three or more hydroxyl groups can be cited as polyhydric alcohols. Actual examples of the glycols include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexylene glycol, 1 , 3-butanediol , 1,4- butanediol, 1 , 5-pentanediol , 1 , 6-hexanediol , 2-butyl-2- ethyl-1, 3-propanediol, methylpropanediol, cyclohexane- dimethanol, 3, 3-diethyl-l, 5-pentanediol and the like. Furthermore, examples of polyhydric alcohols which have three or more hydroxyl groups include glycerol, trimethylolethane, trimethylolpropane, pentaerythritol , dipentaerythritol and the like. One of these polyhydric alcohols can be used individually or a combination of two or more types can be used.

The number average molecular weight of the resin segments is preferably from 1,000 to 5,000, and actual ideal number average molecular weights include 1,000, 1,500, 2,000, 2,500, 3,000, 3,500, 4,000, 4,500, 5,000 and the like but it may be within the range between any two of the numerical values shown.

[0019]

Next a urethane pre-polymer which has terminal isocyanate groups is obtained by reacting a carboxyl- group containing diol and a polyisocyanate compound with the segment resin which has been obtained in this way .

Examples of the carboxyl group-containing diols which are reacted with the segment resin include dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolheptanoic acid, dimethyloloctanoic acid, dimethylolnonanoic acid and the like. From among these dimethylolpropionic acid and dimethylolbutanoic acid are preferred from the viewpoints of obtaining an excellent paint film, industrial cost and the like.

One of these carboxyl group-containing diols can be used individually or a combination of two or more types can be used.

[0020]

Furthermore, examples of the polyisocyanate compounds which are reacted with the segment resin include aromatic diisocyanates such as 4 , 4 ' -diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate, 1,5- naphthalene diisocyanate, p- or m-phenylene diisocyanate, and the like, alicyclic diisocyanates such as isophorone diisocyanate, 4,4'-di- cyclohexylmethane diisocyanate, 1 , 4-cyclohexylene diisocyanate, hydrogenates of tolylene diisocyanate and the like, aliphatic diisocyanates such as hexamethylene diisocyanate and the like, xylylene diisocyanate, m-tetramethylxylylene diisocyanate and the like. From among these the alicyclic diisocyanates are preferred from the viewpoint of yellowing resistance and the like. One of these polyisocyanate compounds can be used individually or a combination of two or more types can be used.

[0021]

Finally a polyurethane resin which has terminal hydroxyl groups can be obtained by reacting the urethane pre-polymer obtained in this way with a polyhydric alcohol.

Examples of the polyhydric alcohols which react with the urethane pre-polymer include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1, 4-butanediol, 1 , 6-hexanediol , diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, hydrogenated bisphenol A, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol , dipentaerythritol and the like. One of these polyhydric alcohols can be used individually or a combination of two or more types can be used.

[0022]

In this invention it is possible to obtain paint films which have excellent paint film appearance by introducing in a specified proportion monobasic acid and/or polyhydric alcohol which has from 10 to 60 carbon atoms. The dibasic acid and/or polyhydric alcohol which has from 10 to 60 carbon atoms may be introduced into the abovementioned polyester segments or into some other part, but it is possible to obtain paint films which have even better paint film appearance by using dibasic acid and/or dihydric alcohol which has from 10 to 60 carbon atoms as a raw material from which the abovementioned resin segments are synthesized.

[0023]

From the viewpoint of the paint film appearance the dibasic acid and/or dihydric alcohol preferably has from 30 to 40, and more desirably from 34 to 38, carbon atoms. If the dibasic acid and/or dihydric alcohol has less than 10 carbon atoms then layer-mixing occurs between the first aqueous base paint and the second aqueous base paint as a result of the raised polarity of the urethane resin of the shell part and there are cases where the appearance of the paint film declines, and if it exceeds 60 then the water-solubility of the polyurethane resin of the shell part is reduced and so there are cases where the acrylic resin which should form the core part and the polyurethane resin which should form the shell part do not form a core/shell structure .

[0024]

Examples of the abovementioned dibasic acids which have from 10 to 60 carbon atoms include sebacic acid, 1,9- nonanedicarboxylic acid, 1, 10-decanedicarboxylic acid, 1, 11-undecanedicarboxylic acid, 1 , 12-dodecane- dicarboxylic acid, 1 , 13-tridecanedicarboxylic acid,

1 , 14-tetradecanedicarboxylic acid, 1 , 15-pentadecane- dicarboxylic acid, 1 , 16-hexadecanedicarboxylic acid, 2-hexadecylmalonic acid, 1, 18-octadecanedicarboxylic acid, dimer acid, hydrogenated dimer acid and the like. From among these dimer acid is preferred from the viewpoint of providing a further improvement in the paint film appearance. One of these dibasic acids which has from 10 to 60 carbon atoms can be used individually or a combination of two or more types can be used.

[0025]

Examples of the abovementioned dihydric alcohols which have from 10 to 60 carbon atoms include 1, 10-decandiol, 1, 2-decandiol, 3, 6-dimethyl-3, 6-octanediol, 2,2- dibutylpropane-1, 3-diol, 1, 12-dodecanediol, 1,2- dodecanediol , 1, 13-tridecanediol, 2 , 2-diisoamyl-l , 3- propanediol, 1, 14-tetradecanediol, 1, 2-tetradecanediol, 1, 15-pentadecanediol, 1, 16-hexadecanediol , 1, 2-hexadecanediol, 1, 2-heptadecanediol,

1, 12-octadecanediol, 2, 2-di-n-octyl-l , 3-propanediol ,

1, 20-eicosanediol, dimer diol, and the like. From among these dimer diol is preferred from the viewpoint of even better paint film appearance. One of these dihydric alcohols which has from 10 to 60 carbon atoms can be used individually or a combination of two or more types can be used.

[0026]

The total mass content proportion of structural units based on dibasic acid and/or dihydric alcohol which has from 10 to 60 carbon atoms is from 10 to 50 mass% with respect to the resin solid fraction of the polyurethane resin which forms the shell part and, from the viewpoint of the paint film appearance the total mass content proportion is preferably from 20 to 40 m.cL S S "6 and more desirably from 30 to 35 mass"6. If the total mass content proportion of dibasic acid and/or dihydric diol is less than 10 mas s"6 then layer-mixing of the first aqueous base paint and the second aqueous base paint occurs due to the raised polarity of the polyurethane resin and there are cases where the paint film appearance declines, and if it exceeds 50 massti then satisfactory flow properties cannot be obtained because the drying properties are too pronounced and there are cases where the paint film appearance declines .

[0027]

The polyurethane resin which forms the shell part has a sufficient number of hydrophilic groups for achieving water-solubility or water-dispersibility and functional groups for reacting with the curing agent. In more practical terms the carboxyl group, amino group, methylol group and the like can be cited as examples of hydrophilic groups.

The hydroxyl group value of the polyurethane resin which forms the shell part is from 20 to 80 mgKOH/g and, from the viewpoint of adherence on the object which has been painted, it is preferably from 30 to 70 mgKOH/g and more desirably from 35 to 45 mgKOH/g. If the hydroxyl group value is less than 20 mgKOH/g then there are cases where the adherence on the object which has been painted is reduced, and if it exceeds 80 mgKOH/g then layer-mixing of the first aqueous base paint and the second aqueous base paint occurs and there are cases where the paint film appearance declines .

[0028]

Furthermore, the acid value of the polyurethane resin which forms the shell part is from 10 to 60 mgKOH/g and, from the viewpoint of the paint film appearance, it is preferably from 30 to 40 mgKOH/g. If the acid value is less than 10 mgKOH/g then there are cases where the paint film appearance declines as a result of a lowering of the emulsification stability of the polyurethane resin in the aqueous medium, and if it exceeds 60 mgKOH/g then there are cases where the water-solubility of the polyurethane resin becomes too great, layer mixing of the first aqueous paint and second aqueous paint arises and the paint appearance declines .

[0029] No particular limitation is imposed upon the number average molecular weight of the polyurethane resin which forms the shell part but, for example, it may be from 500 to 50,000, and in more practical terms it may be, for example, 500, 1,500, 2,500, 3,500, 4,500, 5,500, 6,500, 7,500, 10,000, 15,000, 20,000, 30,000, 40,000 or 50,000 and it may be within the range between any two of the numerical values shown. Moreover, the number average molecular weight referred to in this specification is the value obtained by gel permeation chromatography (GPC) with polystyrene as the standard substance .

[0030]

The acrylic resin which forms the core can be obtained with a known method using a radical polymerization reaction with radically polymerizable monomers as the raw material components, and it is synthesized in an aqueous resin solution or aqueous dispersion of the polyurethane resin which forms the shell part.

Examples of the radically polymerizable monomers include (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, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, allyl alcohol, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, styrene, (meth) acrylonitrile, (meth) acrylamide and the like. One of these radically polymeri zable monomers can be used individually or a combination of two or more types can be used.

[0031]

A radical polymerization initiator may be compounded when synthesizing the acrylic resin. Examples of the radical polymerization initiators include azo compounds such as 2 , 2 ' -azobisisobutyronitrile, 2 , 2 ' -azobis-2 , 4- dimethylvaleronitrile, 4 , 4 ' -azobis-4-cyanovaleric acid, 1-azobis-l-cyclohexanecarbonitrile, dimethyl-2, 2 ' - azobisisobutyrate and the like and organic peroxides such as methyl ethyl ketone peroxide, cyclohexanone peroxide, 3 , 5 , 5-trimethylhexanone peroxide, l,l-bis(t- butylperoxy) -3, 3, 5-trimethylcyclohexane, 1, 1-bis (t- butylperoxy) cyclohexane, 2, 2-bis (t-butylperoxy) octane, t-butyl hydroperoxiode, diisopropylbenzene hydroperoxide, dicumyl peroxide, t-butyl cumyl peroxide, isobutyl peroxide, lauroyl peroxide, benzoin peroxide, diisopropylperoxydicarbonate, t-butylperoxy 2-ethylhexanoate, t-butylperoxy neodecanate, t-butyl- peroxy laurate, t-butylperoxy benzoate, t-butyl- peroxyisopropylcarbonate and the like. One of these radical polymerization initiators may be used individually or a combination of two or more types may be used.

[0032]

The hydroxyl group value of the acrylic resin which forms the core part is from 40 to 140 mgKOH/g and, from the viewpoint of the paint film appearance and adherence on the object which has been painted it is preferably from 60 to 120 mgKOH/g, and more desirably from 75 to 85 mgKOH/g. If the hydroxyl group value is less than 40 mgKOH/g then there are cases where adherence on the object which has been painted is poor, and if it exceeds 140 mgKOH/g then the polarity of the core part is too high and so the acrylic resin which should form the core part and the polyurethane resin which should form the sheath part do not form a core/shell structure and there are cases where the paint film appearance declines.

[0033]

The acid value of the acrylic resin which forms the core part is from 0 to 10 mgKOH/g and, from the viewpoint of the paint film appearance it is preferably from 0 to 5 mgKOH/g, and more desirably from 0 to 3 mgKOH/g. If the acid value exceeds 10 mgKOH/g then there are cases where the acrylic resin which should form the core part and the polyurethane resin which should form the sheath part do not form a core/shell structure .

No particular limitation is imposed upon the glass transition temperature (Tg) of the acrylic resin which forms the core part and, for example, is from 20 to 60°C, and in more practical terms it is, for example, 20, 25, 30, 35, 40, 45, 50, 55, or 60°C or it may be within the range between any two of the numerical values shown.

[0034]

The acrylic resin which forms the core part is synthesized in a resin aqueous solution or aqueous dispersion of the polyurethane resin which forms the sheath part and so it is difficult to measure its number average molecular weight precisely. The number average molecular weight of the acrylic resin can be varied in the main by means of the reaction temperature when it is being synthesized and the amount of radical polymerization initiator which is used in the synthesis. The reaction temperature during synthesis is, for example, from 60 to 110°C, and in more practical terms it is, for example, 60, 70, 80, 90, 100 or 110°C, or it may be within the range between any two of the numerical values shown. Furthermore, the amount of radical polymerization initiator used in the synthesis is, for example, from 0.1 to 3.0 parts by mass per 100 parts by mass of radically polymerizable monomer, and in more practical terms it is, for example, 0.1, 0.5, 1.0, 1.5, 2.0, 2.5 or 3.0 parts by mass, or it may be within the range between any two of the numerical values shown.

[0035]

The mass content proportions of the core part and the shell part in a core/shell type emulsion resin which is included in an aqueous base paint composition of this invention are from 20/80 to 80/20 and, from the viewpoint of the paint film appearance, they are preferably from 35/65 to 65/35, and more desirably from 45/55 to 55/45. If the mass content proportion of the core part is less than 20 then the water-solubility of the core/shell type emulsion resin is raised, layer mixing of the first aqueous base paint and the second aqueous base paint occurs and there are cases where the paint film appearance declines. On the other hand if the mass content proportion of the core part exceeds 80 then the granularity of the acrylic resin of the core part is strengthened and there are cases where the paint film appearance declines.

[0036]

Some or all of the carboxyl groups of the aforementioned core/shell type emulsion resin are preferably neutralized with a basic substance to impart auto-emulsification properties so that the core/shell type emulsion polymer is present in a stable manner in an aqueous base paint composition of this invention. Examples of the basic substances which can be used for neutralization include ammonia, morpholine,

N-alkylmorpholine, monoisopropanolamine, methylethanol- amine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine, methylamine, ethylamine, propylamine, butylamine, 2-ethylhexylamine, dimethylamine, diethylamine, dipropylamine, dibutyl- amine, trimethylamine, triethylamine, triisopropyl- amine, tributylamine and the like. One of these basic substances may be used individually or a combination of two or more may be used.

[0037]

From the viewpoint of the paint film appearance the mass content proportion of the abovementioned core/shell type emulsion resin with respect to the whole of the resin solid fraction of the base resin in an aqueous base paint composition of this invention is preferably from 5 to 80 m sS # and more desirably from 10 to 40 mass%.

[0038]

An aqueous base paint composition of this invention preferably includes a known aqueous resin as well as the abovementioned core/shell type emulsion resin as a base resin. At least one type of resin selected from among the polyurethane resins or acrylic resins is preferred for the known aqueous resin.

[0039]

The hydroxyl group value of an aqueous polyurethane resin is, for example, preferably from 10 to 140 mgKOH/g and the acid value of the aqueous resin is, for example, preferably from 3 to 80 mgKOH/g.

The number average molecular weight of an aqueous polyurethane resin is, for example, preferably from 1,000 to 100,000. In more practical terms the number average molecular weight is, for example, 1,000, 5,000, 10,000, 20,000, 40,000, 60,000 80,000 or 100,000, or it may be within the range between any two of the numerical values shown.

[0040]

The hydroxyl group value of an aqueous acrylic resin is, for example, preferably from 10 to 200 mgKOH/g, the acid value of an aqueous acrylic resin is, for example, preferably from 0 to 20 mgKOH/g and the glass transition temperature of an aqueous acrylic resin is, for example, preferably from -40 toD80°C. Moreover, the value of the glass transition temperature referred to in this specification is the value of the transition start temperature in DSC (differential scanning calorimetry) .

The number average molecular weight of an aqueous acrylic resin is, for example, preferably from 1,000 to more practical terms the number average molecular weight is, for example, 1,000, 5,000, 10,000, 50,000, 100,000, 200,000 400,000, 600,000, 800,000 or 1, 000, 000, or it may be within the range between any two of the numerical values shown.

[0041]

Various pigments such as coloring pigments, glitter pigments, true pigments and the like can be included in an aqueous base paint composition of this invention. Examples of the coloring pigments include inorganic pigments such as chrome yellow, yellow iron oxide, iron oxide, carbon black, titanium dioxide and the like and organic pigments such as azochelate-based pigments, insoluble azo-based pigments, condensed azo-based pigments, phthalocyanine-based pigments, indigo pigments, perinone-based pigments, perylene-based pigments, dioxane-based pigments, quinacridone-based pigments, isoindolinone-based pigments, metal complex pigments and the like. Furthermore, the glitter pigments include aluminum flake pigments, alumina flake pigments, mica pigments, silica flake pigments, glass flake pigments and the like. Moreover examples of the true pigments include calcium carbonate, baryta, precipitated barium sulfate, clay, talc and the like. One of these pigments may be used individually or a combination of two or more types may be used.

[0042]

The mass content proportion when a pigment is included in an aqueous base paint composition of this invention is, for example, from 3 to 200 mass% with respect to the whole of the resin solid fraction of the base resin, and in more practical terms it is, for example, 3, 5, 15, 30, 50, 70, 90, 110, 130, 150, 175 or 200 m.cL S S "6 or it may be within the range between any two of the numerical values shown.

One or more of various additives such as surface controlling agents, anti-foaming agents, surfactants, film-forming promoters, antifungal agents, ultraviolet absorbers, light-stabilizers, antioxidants and the like, various rheology-controlling agents and various organic solvents can be included in an aqueous base paint composition of this invention.

An aqueous base paint composition of this invention includes water as the medium, but the paint can be supplied for painting after dilution to the ideal viscosity using water and, depending on the particular case, a small quantity of organic solvent or amine, as required .

[0043]

An aqueous base paint composition of this invention can be used as the first aqueous base paint (A) and as the second aqueous base paint (B) in the method for forming a multi-layer film in which a first aqueous base paint (A) is coated on an object which is to be painted and a first paint film is formed, a second aqueous base paint (B) is coated over the uncured aforementioned first paint film and a second paint film is formed, a clear paint (C) is coated over the uncured aforementioned second paint film and a clear paint film is formed and these three paint film layers are heated and cured at the same time.

In those cases where, in the method of forming a multi^¬ layer paint film of this invention, an aqueous base paint composition of this invention is used for the first aqueous base paint (A) and the second aqueous base paint (B) adherence on the object which has been painted can be assured even if no curing agent is included in the second aqueous base paint (B) . [0044]

Amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, polycarbodiimide compounds and the like can be cited as examples of curing agents for the aqueous base paint compositions of this invention. From among these the polyisocyanate compounds and polycarbodiimide compounds are preferred from the viewpoint of the paint film appearance. Furthermore, one of these curing agents may be used individually or a combination of two or more types may be used.

[0045]

Amino resin is a general term signifying resins where formaldehyde has been added to a compound which includes amino groups and condensed, and in more practical terms examples of these include melamine resins, urea resins, guanamine resins and the like. From among these the melamine resins are preferred. Moreover, some or all of the methylol groups of said amino resins may be etherified with one type, or two or more types, of alcohol selected from among the monohydric alcohols such as methanol, ethanol, propanol, butanol and the like to provide alkyl- etherified amino resins and the like.

In those cases where an amino resin is used as a curing agent the solid fraction mass ratio represented by (base resin/amino resin) is preferably from 0.65 to 4.0, and more desirably from 1.8 to 3.0, from the viewpoints of the adherence on the object which has been painted, water resistance and chipping resistance.

[0046]

Examples of the polyisocyanate compounds include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate and the like, and also alicyclic diisocyanates such as isophorone diisocyanate, xylylene diisocyanate (XDI), m-xylylene diisocyanate, hydrogenated XDI and the like, aromatic diisocyanates such as tolylene diisocyanate (TDI ) , 4,4- diphenylmethane diisocyanate (MDI), hydrogenated TDI, hydrogenated MDI and the like, and adducts, biuret forms and isocyanurate forms of these.

[0047]

Examples of the blocked polyisocyanate compounds include those which have been blocked with, for example, alcohols such as butanol or the like, oximes such as methyl ethyl ketone oxime, lactams such as ε-caprolactam and the like, diketones such as acetoacetic acid diesters and the like, imidazoles such as imidazole, 2-ethylimidazole and the like or phenols such as m-cresol and the like.

In those cases where isocyanate compounds and blocked isocyanate compounds are used as curing agents the NCO/OH mole ratio in the aqueous base paint composition is preferably from 0.5 to 1.5, and more desirably from 0.8 to 1.2, from the viewpoints of the adherence on the object which has been painted and the paint film appearance .

[0048]

Hydrophilic carbodiimide compounds are preferred as carbodiimide compounds. Those obtained by reacting an agent for providing hydrophilicity which has active hydrogen and hydrophilic parts with the reaction product obtained by reacting a polycarbodiimide compound which has at least two isocyanate groups in the molecule and a polyol which has terminal hydroxyl groups in such a way that the NCO/OH mole ratio exceeds 1, for example, can be cited as hydrophilic carbodiimides . In those cases where a carbodiimide compound is used as a curing agent in this invention the NCN/COOH mole ratio in the aqueous base paint composition is preferably from 0.5 to 2.0, and more desirably from 0.8 to 1.5, from the viewpoints of the adherence on the object which has been painted and the paint film appearance .

[0049]

No particular limitation is imposed upon the form of an aqueous base paint composition of this invention provided that it is an aqueous paint and, for example, it may take the form of an aqueous solution, an aqueous dispersion, an aqueous emulsion or the like.

Any organic solvent paint, aqueous paint or powder paint can be used for the clear paint (C) which is used in the method of forming a multi-layer paint film of this invention. Examples of the base resins of the clear paint include acrylic resins, polyester resins, alkyd resins and the like, and the curing system can be a melamine curing, acid/epoxy curing, isocyanate curing or such like curing system, but from the viewpoint of the paint film appearance a clear paint of the acrylic resin/melamine curing type, acrylic resin/isocyanate curing type or acid/epoxy curing type is preferred.

[0050]

The methods which are being used generally in the automobile industry, such as air-spray painting, air- atomization type electrostatic painting, bell-rotation atomization type electrostatic painting and the like can be used as the method of painting each of the paints in the method of forming a multi-layer paint film of this invention.

The preferred painting conditions for the aqueous base paint compositions in the method of forming a multi^¬ layer paint film of this invention are temperature from 10 to 40°C and relative humidity from 65 to 85%.

[0051]

In the method of forming a multi-layer paint film of this invention preliminary heating may be carried out after coating the first aqueous base paint (A) and after coating the second aqueous base paint (B) , but in those cases where aqueous base paint compositions of this invention are being used an excellent paint film appearance can be obtained without carrying out preliminary heating after coating the first aqueous base paint (A) . Moreover, the temperature when preliminary heating is carried out is preferably from 30 to 100°C and the time is preferably from 3 to 10 minutes.

In the method of forming a multi-layer paint film of this invention the heating and curing temperature of the multi-layer paint film is preferably from 60°C to 170°C and the heating and curing time is preferably from 20 to 40 minutes.

[0052]

In those cases where in the method of forming a multi^¬ layer paint film of this invention the curing agent of the first aqueous base paint (A) and the second aqueous base paint (B) is a polyisocyanate compound and/or blocked polyisocyanate compound or in cases where the curing agent of the first aqueous base paint (A) is a polyisocyanate compound and/or blocked polyisocyanate compound and no polyisocyanate compound and/or blocked polyisocyanate compound is included in the second aqueous base paint (B) the heating and curing temperature can be set to from 60°C to 100 °C by using a clear paint (C) of the isocyanate curing type.

[0053] Moreover, the objects to be painted with the method of forming a multi-layer paint film of this invention may be objects where an electrodeposited paint film has been formed on a metal, objects where a mid-coat paint film has been formed over an electrodeposited paint film, plastics and the like, but objects where an electrodeposited paint film has been formed on a metal are preferred.

In the method of forming a multi-layer paint film of this invention a coating process with a chipping primer or undercoat primer or the like carried out with the usual three coat two bake coating process may be included before coating the first aqueous base paint (A) .

[Illustrative Examples]

[0054]

The invention is described in more detail below by means of illustrative examples, but the invention is not limited by these illustrative examples. Moreover, in the absence of any indication to the contrary the terms "parts", "%" and "ratio" signify "parts by mass", "mass i " and "ratio by mass" respectively.

[0055]

Example of Production 1-1 Production of Polyester Resin Varnish Al

Dimer acid (trade name Empol 1008, produced by the Cognis Co., carbon number 36, 54.0 parts), 8.0 parts of neopentyl glycol, 17.8 parts of isophthalic acid, 19.4 parts of 1 , 6-hexanediol and 0.8 part of trimethylolpropane were introduced into a reaction vessel which had been furnished with a reflux condenser which was fitted with a water separating tube for the reaction water, nitrogen gas delivery apparatus, a thermometer and stirring apparatus, the temperature was raised to 120°C and after the raw materials had dissolved the temperature was raised to 160°C, with stirring. After being maintained at 160°C for 1 hour the temperature was gradually raised to 230°C over a period of 5 hours. The temperature was maintained at 230°C and the reaction continued and when the resin acid value reached 4 mgKOH/g the mixture was cooled to 80°C or below and then 31.6 parts of methyl ethyl ketone were added and the polyester resin varnish Al which had the property values shown in Table 1 was obtained .

[0056]

Examples of Production 1-2 to 1-4 Production of Polyester Resin Varnishes A2 to A4

The polyester resin varnishes A2 to A4 which had the property values shown in Table 1 were obtained with the same method as in Example of Production 1-1 on the basis of the formulations shown in Table 1.

[0057]

Table 1

Polyester Resin Varnish Carbon Al A2 A3 A4

Number

Dimer Acid (*1) 36 54.0

1,10-Decane Dicarboxylic Acid 12 54.0

Adipic Acid 6 21.0

Suberic Acid 8 54.0

Neopentyl Glycol 5 8.0 8.0 21.6 8.0

Isophthalic Acid 8 17.8 8.3 35.0 3.1

1, 6-Hexanediol 6 19.4 29.0 21.6 34.1

Trimethylolpropane 6 0.8 0.8 0.8 0.8 (Amount of Water Removed) ^— 7.2 10.1 12.7 11.7

Methyl Ethyl Ketone ^— 31.5 30.6 29.7 30.0

TOTAL ^— 124.4 120.5 117.0 118.3

Resin Solid Fraction ^— 74.6% 74.6% 74.6% 74.6%

Number Average Molecular Weight ^— 1800 1800 1800 1800

Hydroxyl Group Value (mgKOH/g) ^— 62 62 62 62

Resin Acid Value (mgKOH/g) ^— 4 4 4 4

[0058]

Details of each of the compounded components shown in Table 1 are indicated below.

*1: Trade name Empol 1008, produced by the Cognis Co., carbon number 36

[0059]

Example of Production 2-1 Production of Polyurethane Resin Bl

The polyester resin solution Al (78.3 parts), 7.8 parts of dimethylolpropionic acid, 1.4 parts of neopentyl glycol and 40.0 parts of methyl ethyl ketone were introduced into a reaction vessel which had been furnished with nitrogen gas delivery apparatus, a thermometer and stirring apparatus and, after raising the temperature to 80°C, with stirring, 27.6 parts of isophorone diisocyanate were introduced and the components were reacted while maintaining the temperature at 80°C. Trimethylolpropane (4.8 parts) was added when the isocyanate value reached 0.43 meq/g and the reaction was continued at 80°C. Then, when the isocyanate value reached 0.01 meq/g, 33.3 parts of butyl cellosolve were added and the reaction was terminated. Subsequently the temperature was raised to 100°C and the methyl ethyl ketone was removed under reduced pressure. Then the temperature was lowered to 50°C. 4.4 parts of dimethylethanolamine were added and the acid groups were neutralized, and then 147.9 parts of deionized water were added and the polyurethane resin Bl which had the property values shown in Table 2 was obtained.

[0060]

Examples of Production 2-2 to 2-13 Production of Polyurethane Resins B2 to B13

The polyurethane resins B2 to B13 which had the property values shown in Table 2 were obtained with the same method as Example of Production 2-1 based on the formulations shown in Table 2. Moreover, B2 and B7 were produced using neopentyl glycol instead of the trimethylolpropane used when producing Bl .

The higher dibasic acid/dihydric alcohol content ratio in Table 2 and in Tables 8 to 10 signifies the overall mass content ratio of structural units based on dibasic acid and/or dihydric alcohol which has from 10 to 60 carbon atoms with respect to the resin solid fraction of the polyurethane resin.

[0061]

BASF Coatings GmbH

- 42 -

Table 2

Aqueous Polyurethane Resin Carbon Bl B2 B3 B4 B5 B6 B7 B8 B9 B10 Bll B12 Β1Ξ

Number

Polyester Resin Al 78.3 78.9 80.3 32.0 79.3 79.9 79.6 58.4 18.1 23.

Varnish A2 29.8 78.3

(*1) A3 26.1 39.7

A4 78.3

Dimer Diol (*2) 36 35.4 42.

Dimethylolpropionic Acid 5 7.8 7.8 2.3 13.3 2.7 7.8 7.8 5.9 0.9 15.2 7.8 8.0 2.7

Isophorone Diisocyanate 27.6 27.8 25.7 35.6 31.2 27.6 28.0 25.0 28.2 36.0 27.6 37.5 31.

Neopentyl Glycol (Added Initially) 5 1.4 1.5 1.3 0.0 0.0 1.4 1.5 0.0 5.4 0.0 1.4 5.2

Methyl Ethyl Ketone (*3) 40.0 40.0 40.0 40.0 70.0 40.0 40.0 40.0 70.0 40.0 40.0 70.0 70.0

Trimethylolpropane 6 4.8 10.7 9.4 6.8 4.8 9.6 6.1 5.2 4.8 6.2 6.0

Neopentyl Glycol (Added Subsequently) 5 4.0 3.5

Butyl Cellosolve 33.3 33.3 33.3 33.3 66.7 33.3 33.3 33.3 66.7 33.3 33.3 66.7 66.7

Dimethylethanolamine (*4) 4.4 4.4 1.5 7.2 1.5 4.4 4.4 3.4 0.8 8.2 4.4 4.4 1.5

Deionized Water 147.9 147.9 150.9 145.2 165.1 147.9 147.9 148.9 166.1 144.0 147.9 162.2 165.1

BASF Coatings GmbH

- 43 -

TOTAL - 285.7 285.7 285.7 285.7 324.3 285.7 285.6 285.6 333.5 285.5 285.7 333.3 333.

Resin Solid Fraction 35.0% 35.0% 35.0% 35.0% 30.0% 35.0% 35.0% 35.0% 30.0% 35.0% 35.0% 30.0% 30. C

Hydroxyl Group Value (mgKOH/g) 40 23 78 78 40 40 17 82 40 40 40 40 40

Acid Value (mgKOH/g) 35 35 12 57 12 35 35 27 6 65 35 35 12

Number Average Molecular Weight - 4880 4330 3100 2680 7300 4880 5550 2430 6280 5240 4880 6650 628

Higher Dibasic Acid/Dihydric Alcohol 32% 32% 32% 12% 48% 32% 32% 32% 32% 24% 0% 7% 52%

Content Ratio

[0062]

Details of each of the compounded components shown in Table 2 are indicated below.

(*1) : The solvent included in the polyester varnish was removed under reduced pressure and so it is not included in the TOTAL in Table 2.

(*2) : Trade name Pripol 2023, produced by the Croda Co., carbon number 36.

(*3) : Since it was removed under reduced pressure this is not included in the TOTAL in Table 2.

(*4) : This was used as a neutralizing agent and it is not included in the resin solid fraction in Table 2.

[0063]

Example of Production 3-1 Production of Core/Shell Type Emulsion CI

Polyurethane resin Bl (46.4 parts) and 33.1 parts of deionized water were introduced into a reaction vessel which had been furnished with nitrogen gas delivery apparatus, a thermometer, a dropping funnel and stirring apparatus and, after raising the temperature to 85°C, with stirring, a homogeneous liquid mixture of 4.9 parts of styrene, 4.5 parts of methyl methacrylate, 3.9 parts of n-butyl acrylate, 3.0 parts of 2- hydroxyethyl methacrylate, 3.8 parts of propylene glycol mono-methyl ether and 0.24 part of t-butyl- peroxy-2-ethylhexanoate which is a polymerization initiator as a drip-feed component was drip fed at a constant rate over a period of 3.5 hours using the dropping funnel. After the drip feed had been completed the temperature was maintained at 85°C for 1 hour and then a polymerization initiator solution where 0.03 part of t-butylperoxy-2-ethylhexanoate, which is a polymerization initiator, had been dissolved in 0.14 part of propylene glycol mono-methyl ether was added as supplementary catalyst and the reaction was terminated when the temperature had been maintained at 85°C for 1 hour and the core/shell type emulsion resin CI was obtained .

[0064]

Examples of Production 3-2 to 3-23 Production of Core/Shell Type Emulsions C2 to C23

Core/shell type emulsions C2 to C23 which had the property values shown in Tables 3 and 4 were obtained with the same method as Example of Production 3-1 based on the formulations shown in Tables 3 and 4.

[0065] BASF Coatings GmbH

- 46 -

Table 3

Core/Shell Type Emulsion Resin CI C2 C3 C4 C5 C6 C7 C8 C9 CIO Cll

Bl 46.4 71.5 20.4 46.4 46.4 46.4

Aqueous B2 46.4

Introduced Polyurethane B3 46.4

Initially Resin B4 46.4

(Shell Part) B5 54.2

B6 46.4

Deionized Water 33.1 19.3 48.3 33.0 33.1 33.1 33.1 33.1 25.3 33.1 33.1

Styrene 4.9 2.2 7.6 4.9 4.9 4.9 4.9 4.9 4.9 4.9 4.9

Acrylic Methyl 4.5 2.1 7.0 2.8 5.5 5.5 2.8 2.8 4.5 4.5 4.3

Drip-feed Resin Methacrylate

Component (Core Part) n-Butyl Acrylate 3.9 1.8 6.1 3.5 4.2 4.2 3.5 3.5 3.9 3.9 3.9

2-Hydroxyethyl 3.0 1.4 4.7 5.1 1.6 1.6 5.1 5.1 3.0 3.0 3.0 Methacrylate

Acrylic Acid 0.2 t-Butylperoxy-2-ethylhexanoate 0.2 0.1 0.4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Propylene Glycol Mono-methyl 3.8 1.5 5.2 3.9 3.9 3.9 3.9 3.9 3.8 3.8 3.9

BASF Coatings GmbH

- 47 -

Ether

Supplementary t-Butylperoxy-2-ethylhexanoate 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Catalyst Propylene Glycol Mono-methyl 0.14 0.09 0.31 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14

Ether

TOTAL 100 100 100 100 100 100 100 100 100 100 100

Hydroxyl Group Value of the Acrylic Resin 80 80 80 135 43 43 135 135 80 80 80

(mgKOH/g)

Acid Value of the Acrylic Resin (mgKOH/g) 0 0 0 0 0 0 0 0 0 0 9

Core Part/Shell Part Mass Ratio 50/50 23/77 78/2 50/50 50/50 50/50 50/50 50/50 50/50 50/50 50/50

2

Resin Solid Fraction (mass%) 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5

BASF Coatings GmbH

- 48 -

Table 4

Core/Shell Type Emulsion Resin C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23

Bl 46.4 46.4 76.1 15.8 46.4

Aqueous B7 46.4

Introduced Polyurethane B8 46.4

Initially Resin B9 54.2

(Shell Part) BIO 46.4

Bll 46.4

B12 54.2

B13 46.4

Deionized Water 33.0 33.0 16.6 51.0 33.0 33.0 25.3 33.0 33.0 25.3 33.0 33.0

Styrene 4.9 4.9 1.8 8.1 4.9 4.9 4.9 4.9 4.9 4.9 4.9 4.9

Acrylic Methyl 5.7 2.5 1.6 7.4 5.7 5.7 5.7 5.7 5.7 5.7 5.7 4.2

Drip-feed Resin Methacrylate

Component (Core Part) n-Butyl Acrylate 4.3 3.4 1.4 6.5 4.3 4.3 4.3 4.3 4.3 4.3 4.3 3.9

2-Hydroxyethyl 1.4 5.4 1.1 5.0 1.4 1.4 1.4 1.4 1.4 1.4 1.4 3.0 Methacrylate

BASF Coatings GmbH

- 49 -

Acrylic Acid 0.3 t-Butylperoxy-2-ethylhexanoate 0.2 0.2 0.1 0.4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Propylene Glycol Mono-methyl 3.9 3.9 1.2 5.5 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9

Ether

Supplementary t-Butylperoxy-2-ethylhexanoate 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Catalyst Propylene Glycol Mono-methyl 0.14 0.14 0.07 0.33 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14

Ether

TOTAL 100 100 100 100 100 100 100 100 100 100 100 100

Hydroxyl Group Value of the Acrylic Resin 37 144 80 80 80 80 80 80 80 80 80 80

(mgKOH/g)

Acid Value of the Acrylic Resin (mgKOH/g) 0 0 0 0 0 0 0 0 0 0 0 12

Core Part/Shell Part Mass Ratio 50/50 50/50 18/82 83/17 50/50 50/50 50/50 50/50 50/50 50/50 50/50 50/5(

Resin Solid Fraction (mass%) 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5

[0067]

Example of Production 4-1 Production of First Aqueous Base Paint Dl

Titanium dioxide (trade name Ti-Pure R706, produced by the DuPont Co., 39.1 parts) and 0.4 part of carbon black (trade name MA-100, produced by the Mitsubishi Kagaku Co.) were dispersed using the aqueous polyurethane resin Bl as dispersing resin in a mortar mill to produce a pigment paste.

Next 25.5 parts of the core/shell type emulsion CI, the aqueous polyurethane resin Bl and 5.9 parts of aqueous acrylic resin (trade name Setaqua 6511, produced by the Nuplex Resin Co., acid value 8 mgKOH/g, hydroxyl group value 138 mgKOH/g, glass transition temperature 12°C, resin solid fraction 47%) were mixed together in a dissolver to prepare a resin base and then the pigment paste produced earlier was added and admixed. Finally 13.2 parts of melamine resin (trade name Cymel 327, produced by the Cytec Industries Co., resin solid fraction 90%) were added and admixed and the first aqueous base paint Dl was obtained. Moreover, the aqueous polyurethane Bl content of the first aqueous base paint Dl was set to 47.4 parts. [0068]

Examples of Production 4-2 to 4-32 Production of First Aqueous Base Paints D2 to D32

The first aqueous base paints D2 to D32 were obtained with the same method as Example of Production 4-1 on the basis of the formulations shown in Tables 5 and 6.

In Tables 5 to 7 P/B represents the pigment/resin solid fraction mass ratio.

[0069]

BASF Coatings GmbH

Table 5

First Aqueous Dl D2 D3 D4 D5 D6 D7 D8 D9 D10 Dll D12 D13 D14 D15 D16 Base Paint

CI 25.5 8.5 42.5 68.1 85.1

C2 25.5

C3 25.5

Core/Shell C4 25.5

Type C5 25.5

Emulsion C6 25.5

C7 25.5

C8 25.5

C9 25.5

CIO 25.5

Cll 25.5

Aqueous Polyurethane Resin 47.4 63.2 31.6 7.9 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 4

Bl

Aqueous Acrylic Resin 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9

Melamine Resin (*1) 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2

BASF Coatings GmbH

- 53 -

[0070]

BASF Coatings GmbH

- 54 -

Table 6

First Aqueous D18 D19 D20 D21 D22 D23 D24 D25 D26 D27 D28 D29 D30 D31 Base Paint

C12 25.5 25.5

cl3 25.5

C14 25.5

Core/Shell C15 25.5

Type C16 25.5

Emulsion C17 25.5

C18 25.5

C19 25.5

C20 25.5

C21 25.5

C22 25.5 c23 2

Aqueous Polyurethane Resin Bl 71.1 71.1 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 4

Aqueous Acrylic Resin 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9

BASF Coatings GmbH

- 55 -

[0071]

Example of Production 5-1 Production of Second Aqueous Base Paint El

Carbon black (trade name MA-100, produced by the Mitsubishi Kagaku Co., 2.1 parts) was dispersed using the aqueous polyurethane resin Bl as dispersing resin in a mortar mill to produce a pigment paste.

Next 25.5 parts of the core/shell type emulsion CI, the aqueous polyurethane resin Bl and 5.9 parts of aqueous acrylic resin (trade name Setaqua 6511, produced by the Nuplex Resin Co., acid value 8 mgKOH/g, hydroxyl group value 138 mgKOH/g, glass transition temperature 12°C, resin solid fraction 47%) were mixed together in a dissolver to prepare a resin base and then the pigment paste produced earlier was added and admixed and the second aqueous base paint El was obtained. Moreover, the aqueous polyurethane Bl content of the second aqueous base paint El was set to 47.4 parts.

[0072]

Example of Production 5-2 Production of Second Aqueous Base Paint E2

Carbon black (trade name MA-100, produced by the Mitsubishi Kagaku Co., 2.9 parts) was dispersed using the aqueous polyurethane resin Bl as dispersing resin in a mortar mill to produce a pigment paste.

Next 25.5 parts of the core/shell type emulsion CI, the aqueous polyurethane resin Bl and 5.9 parts of aqueous acrylic resin (trade name Setaqua 6511, produced by the Nuplex Resin Co., acid value 8 mgKOH/g, hydroxyl group value 138 mgKOH/g, glass transition temperature 12°C, resin solid fraction 47%) were mixed together in a dissolver to prepare a resin base and then the pigment paste produced earlier was added and admixed. Finally 13.2 parts of melamine resin (trade name Cymel 327, produced by the Cytec Industries Co., resin solid fraction 90%) were added and admixed and the second aqueous base paint E2 was obtained. Moreover, the aqueous polyurethane Bl content of the second aqueous base paint E2 was set to 47.4 parts.

[0073]

Examples of Production 5-3 to 5-18 Production of Second Aqueous Base Paints E2 to El8

The second aqueous base paints E2 to E18 were obtained with the same method as Example of Production 5-2 on the basis of the formulations shown in Table 7.

[0074] BASF Coatings GmbH

- 58

Second Aqueous El E2 E3 E4 E5 E6 E7 E8 E9 E10 Ell E12 E13 E14 E15 E16 El^" Base Paint

CI 25.5 25.5 25.5 25.5 8.5 42.5 68.1 85.1

C2 25.5

C3 25.5

Core/Shell C4 25.5

Type C5 25.5

Emulsion C6 25.5

C7 25.5

C8 25.5

C9 25.5

CIO 25.5

Cll

Aqueous Polyurethane Resin Bl 47.4 47.4 47.4 47.4 63.2 31.6 7.9 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4 47.4

Aqueous Acrylic Resin 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9

Melamine Resin (*1) 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2 13.2

BASF Coatings GmbH

- 59 -

[0075]

Details of each of the compounded components shown in Tables 5 to 7 are indicated below.

(*1) : Melamine resin (trade name Cymel 327, produced by the Cytec Industries Co., resin solid fraction 90%)

(*2): Polyisocyanate (trade name Baihidure 3100, produced by the Sumika Beyer Co.)

(*3): Polycarbodiimide (trade name Carbodilite V-02-L2, produced by the Hiseibo Chemical Co.)

(*4) : Titanium Dioxide (trade name Ti-Pure R706, produced by the DuPont Co.)

(5*) : Carbon Black (trade name MA-100, produced by the Mitsubishi Kagaku Co.)

[0076]

Example 1

Cationic electro-deposition paint (trade name CathoGuard No.500, produced by the BASF Coatings Co., Ltd.) was electro-deposition coated in such a way as to provide a dry film thickness of 20 μιη on a zinc phosphate treated mild steel sheet and baked for 25 minutes at 175°C to form an electrodeposited paint filmed sheet (referred to hereinafter as an electrodeposited sheet) which was used for evaluation purposes . Next an assessment sheet was produced in the way outlined below under coating conditions of 25°C and 75% (relative humidity) using a rotary atomization type bell painting machine (trade name Metallic Bell Gl- COPES Bell produced by the ABB Co.). Moreover, in the formation of a multi-layer paint film described below the first aqueous base paint and second aqueous base paint were applied after dilution with deionized water so that the Ford Cup #4 viscosity was 40 seconds (20°C) .

[0077]

The first aqueous base paint Dl was coated on an electrodeposited sheet in such a way as to provide a dry film thickness of 20 μιη. After this the sheet was left to stand for 5 minutes at room temperature and the second aqueous base paint El was coated in such a way as to provide a dry film thickness of 12 μιη. After coating, the sheet was left to stand for 5 minutes at room temperature and preliminary heating to 80°C was carried out for 3 minutes. After cooling to room temperature clear paint (trade name Belcoat No.7300, produced by the BASF Coatings Japan Co., Ltd.) was coated in such a way as to provide a dry film thickness of 30 μιη. After coating, the sheet was left to stand for 10 minutes at room temperature, baked at 140°C for

30 minutes and an assessment sheet was obtained.

[0078]

The assessment sheet obtained was subjected to paint film performance evaluation as indicated below.

[0079]

(1) Paint Film Appearance

The paint film appearance of the assessment sheet obtained was assessed by visual observation on the basis of the following criteria:

®: When a fluorescent lamp was reflected by the paint film the fluorescent lamp was reflected quite distinctly.

0+: When a fluorescent lamp was reflected by the paint film the fluorescent lamp was reflected distinctly.

O: When a fluorescent lamp was reflected by the paint film the fluorescent lamp was reflected with some distinction.

O-: When a fluorescent lamp was reflected by the paint film the range (profile) of the fluorescent lamp was rather blurred.

X: When a fluorescent lamp was reflected by the paint film the region (profile) of the fluorescent lamp was markedly blurred.

[0080]

(2) Adherence on the Painted Object

A pattern of one hundred 2 mm x 2 mm squares was established in the paint film on an assessment sheet using a cutter knife, cellophane tape was stuck firmly over the patterned part and peeled away in one pull with the end of the tape at an angle of 45° and the state of the pattern was observed and an assessment was may made in the following way.

O: No peeling of the paint film was seen.

X: Peeling of the paint film was seen.

Examples 2 to 24 and Comparative Examples 1 to 15

Assessment sheets were prepared in the same way as in Example 1 using the combinations of first aqueous base paint, second aqueous base paint and clear paint described in Tables 8 to 10 and paint film performance evaluations were carried out. The results of the paint film performance evaluations are summarized in Tables 8 to 10.

[0081] BASF Coatings GmbH

- 64 -

Table 8

Example 1 2 3 4 5 6 7 8 9 10 11

First Aqueous Base Paint Dl Dl Dl Dl D2 D3 D4 D5 D6 D7 D8

Core/Shell Type Emulsion CI CI CI CI CI CI CI CI C2 C3 C4

Aqueous Polyurethane Resin Bl Bl Bl Bl Bl Bl Bl Bl Bl Bl Bl

Core Part/Shell Part Mass 50/50 50/50 50/50 50/50 50/50 50/50 50/50 50/50 23/77 78/22 50/50

Ratio

Acrylic Hydroxyl 80 80 80 80 80 80 80 80 80 80 135

Resin (Core Group Value

Part) (mgKOH/g)

Core/Shell Acid Value 0 0 0 0 0 0 0 0 0 0 0

Type (mgKOH/g)

Emulsion Hydroxyl 40 40 40 40 40 40 40 40 40 40 40

Aqueous Group Value

Polyurethane (mgKOH/g)

BASF Coatings GmbH

- 65 -

Resin (Shell Acid Value 35 35 35 35 35 35 35 35 35 35 35 Part) (mgKOH/g)

Higher 32% 32% 32% 32% 32% 32% 32% 32% 32% 32% 32% Dibasic

Acid/Dihydric

Alcohol Ratio

(Core/Shell Type Emulsion) /Base Resin 30% 30% 30% 30% 10% 50% 80% 100% 30% 30% 30% Solid Fraction Mass Ratio

Second Aqueous Base Paint El E2 E3 E4 E5 E6 E7 E8 E9 E10 Ell

Core/Shell Type Emulsion CI CI CI CI CI CI CI CI C2 C3 C4

Clear Paint (*1) IK IK IK IK IK IK IK IK IK IK IK

Paint Film Appearance o+ o+ o+ o+ o+ O O o- O- O- O-

Adherence on the Painted Object o o o o o o o o o o o

BASF Coatings

- 66 -

[0082] Table 9

Example 13 14 15 16 17 18 19 20 21 22 23

First Aqueous Base Paint D10 Dll D12 D13 D14 D15 D16 D17 Dl D16 D17

Core/Shell Type Emulsion C6 C7 C8 C9 CIO Cll CI CI CI CI CI

Aqueous Polyurethane Resin B2 B3 B4 B5 B6 Bl Bl Bl Bl Bl Bl

Core Part/Shell Part Mass 50/50 50/50 50/50 50/50 50/50 50/50 50/50 50/50 50/50 50/50 50/50

Ratio

Acrylic Hydroxyl 43 135 135 80 80 80 80 80 80 80 80

Resin (Core Group Value

Part) (mgKOH/g)

Core/Shell Acid Value 0 0 0 0 0 9 0 0 0 0 0

Type (mgKOH/g)

Emulsion Hydroxyl 23 78 78 40 40 40 40 40 40 40 40

Aqueous Group Value

Polyurethane (mgKOH/g)

BASF Coatings GmbH

- 67 -

Resin (Shell Acid Value 35 12 57 12 35 35 35 35 35 35 35

Part) (mgKOH/g)

Higher 32% 32% 12% 48% 32% 32% 32% 32% 32% 32% 32%

Dibasic

Acid/Dihydric

Alcohol Ratio

(Core/Shell Type Emulsion) /Base Resin 30% 30% 30% 30% 30% 30% 30% 30% 30% 30% 30%

Solid Fraction Mass Ratio

Second Aqueous Base Paint E13 E14 E15 E16 E17 E18 E2 E2 E2 E2 E2

Core/Shell Type Emulsion C6 C7 C8 C9 CIO Cll CI CI CI CI CI

Clear Paint (*1) IK IK IK IK IK IK IK IK 2K 2K 2K

Paint Film Appearance O- O- O- O- o- O- o+ o+ o+ o+ o+

Adherence on the Painted Object o o o o o o o o o o o

BASF Coatings GmbH

[0083]

Table 10

Comparative Example 1 2 3 4 5 6 7 8 9 10 11 12 13

First Aqueous Base Paint D18 D19 D20 D21 D22 D23 D24 D25 D26 D27 D28 D29 D30

Core/Shell Type Emulsion C12 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21

Aqueous Polyurethane Resin Bl Bl Bl Bl Bl B7 B8 B9 B10 Bll B12

Core Part/Shell Part Mass Ratio 50/50 50/50 50/50 18/82 83/17 50/50 50/50 50/50 50/50 50/50 50/50

Acrylic Resin Hydroxyl Group Value 37 37 144 80 80 80 80 80 80 80 80 (Core Part) (mqKOH/q)

Core/Shell Acid Value (mqKOH/q) 0 0 0 0 0 0 0 0 0 0 0 Type Hydroxyl Group Value 40 40 40 40 40 17 82 40 40 40 40 Emulsion Aqueous (mqKOH/q)

Polyurethane Resin Acid Value (mqKOH/q) 35 35 35 35 35 35 27 6 65 35 35 (Shell Part) Hiqher Dibasic 32% 32% 32% 32% 32% 32% 32% 32% 24% 0% 7%

Acid/Dihydric

Alcohol Ratio

(Core/Shell Type Emulsion) /Base Resin Solid Fraction 30% 30% 30% 30% 30% 30% 30% 30% 30% 30% 30%

BASF Coatings GmbH

- 69 -

Mass Ratio

Second Aqueous Base Paint E3 E3 E3 E3 E3 E3 E3 E3 E3 E3 E3 E3 E3

Core/Shell Type Emulsion CI CI CI CI CI CI CI CI CI CI CI CI CI

Clear Paint (*1) 2K 2K 2K 2K 2K 2K 2K 2K 2K 2K 2K 2K 2K

Paint Film Appearance o o o

Adherence on the Painted Object o o o o o o o o o o

[0084]

Details of each of each compounded component shown in Tables 8 to 10 are indicated below.

(*1) :

IK: Acrylic resin/melamine curing type clear paint, trade name Belcoat No.7300, produced by the BASF

Coatings Japan Co., Ltd.

2K: Acrylic resin/isocyanate curing type clear paint, trade name Evergloss, produced by the BASF Coatings Japan Co . , Ltd .

[0085]

Consideration

In all of the examples good results were obtained for the paint film appearance and the adherence on the base material while on the other hand in all of the comparative examples either the paint film appearance or the adherence on the base material was poor. On looking at Examples 4 to 8 it is clear that the (core/shell type emulsion) /base resin solid fraction mass ratio is preferably less than 100% and more desirably less than 50%. Furthermore, on comparing Example 1 and Example 17 the evaluation results for Example 1 where the carbon number of the higher dibasic acid/dihydric alcohol was 36 were better than those of Example 17 where the carbon number was 12.

Claims

Patent Claims

[Claim 1]

Aqueous base paint composition which includes a core/shell type emulsion resin with the core part comprising acrylic resin and the sheath part comprising polyurethane resin as a base resin, characterized in that mass content proportions of the core part and the shell part in the aforementioned core/shell type emulsion resin are from 20/80 to 80/20, the hydroxyl group value and the acid value of the aforementioned acrylic resin are from 40 to 140 mgKOH/g and from 0 to 10 mgKOH/g respectively, the hydroxyl group value and the acid value of the aforementioned polyurethane resin are from 20 to 80 mgKOH/g and from 10 to 60 mgKOH/g respectively, and in the aforementioned polyurethane resin the total mass content proportion of structural units based on a dibasic acid and/or dihydric alcohol having from 10 to 60 carbon atoms is from 10 to 50 mass% with respect to the resin solid fraction of the aforementioned polyurethane resin.

[Claim 2]

Aqueous base paint composition, according to Claim 1, in which the mass content proportions of the core parts and shell parts in said core/shell type emulsion resin are from 45/55 to 55/45, the acid value of the aforementioned urethane resin is from 30 to 40 mgKOH/g and in the aforementioned polyurethane resin the total mass content proportion of structural units based on a dibasic acid and/or dihydric alcohol having from 34 to 38 carbon atoms is from 30 to 35 mass% with respect to the resin solid fraction of the aforementioned polyurethane resin.

[Claim 3]

Aqueous base paint composition, according to Claim 1 or Claim 2, in which the mass content proportion of the aforementioned core/shell type emulsion resin is from 5 to 80 mass% with respect to the whole of the resin solid fraction of the base resin.

[Claim 4]

Aqueous base paint composition, according to any one of Claims 1 to 3, in which the mass content proportion of the aforementioned core/shell type emulsion resin is from 10 to 40 mass% with respect to the whole of the resin solid fraction of the base resin.

[Claim 5]

Method of forming a multi-layer paint film in which a first aqueous base paint (A) is coated on the object to be painted and a first paint film is formed and, without carrying out preliminary heating and hot curing after forming said first paint film, a second aqueous base paint (B) is coated on the aforementioned first uncured paint film and a second paint film is formed, a clear paint (C) is coated on the aforementioned uncured second paint film and a clear paint film is formed and the three layers of the paint film are heated and cured at the same time, and in which the aforementioned first aqueous base paint (A) and second aqueous base paint (B) are each selected from among the aqueous base paint compositions described in any one of Claims 1 to 4.

[Claim 6]

Method of forming a multi-layer paint film, according to Claim 5, in which the aforementioned first aqueous base paint (A) and second aqueous base paint (B) include a polyisocyanate compound and/or polycarbodiimide compound as a curing agent.

[Claim 7]

Method of forming a multi-layer paint film, according to Claim 5 or Claim 6, in which the aforementioned clear paint (C) includes a hydroxyl group-containing acrylic resin and a polyisocyanate compound.

[Claim 8]

Paint film which has been obtained with the method of forming a multi-layer paint film described in any one of Claims 5 to 7.