GB2287469A

GB2287469A - Chipping-resistant paint composition and method for forming chipping-resistant multilayered film

Info

Publication number: GB2287469A
Application number: GB9501375A
Authority: GB
Inventors: Makoto Ozaki; Masuo Kida; Hiroshi Mashima; Mitsuhiro Yoshida; Tadayuki Kawaguchi; Shunji Suizu
Original assignee: Nippon Paint Co Ltd
Current assignee: Nippon Paint Co Ltd
Priority date: 1994-02-17
Filing date: 1995-01-24
Publication date: 1995-09-20
Anticipated expiration: 2015-01-24
Also published as: GB9501375D0; CA2140695A1; GB2287469B; JP3365847B2; JPH07228834A; KR950032539A

Abstract

A chipping-resistant paint comprises as major components (A) a blocked polyisocyanate obtained by mixing (i) an aliphatic or alicyclic polyisocyanate (a) and a cyclic trimerized polyisocyanate polymer (b) obtained from said polyisocyanate (a) with (ii) two or more kinds of polycaprolactone-modified polyols (c) having different number-average molecular weights, reacting ingredient (i) with ingredient (ii) by means of a urethane-forming reaction to yield a modified polyisocyanate compound (d) having a ratio of the molar concentration of isocyanurate groups to that of urethane groups of from 5/5 to 119, and blocking the residual active isocyanate groups of the modified polyisocyanate compound, said blocked polyisocyanate having a content of effective isocyanate groups of from 1 to 10 parts by weight per 100 parts by weight of the blocked polyisocyanate compound on a solid basis, and (B) at least one hydroxyl group-containing compound or resin (e) having two or more hydroxyl groups per molecule. The composition may be used to coat cars in a method comprising electrodeposition, intermediate and top coating steps.

Description

CHIPPING-RESISTANT PAINT COMPOSITION AND METHOD FOR FORMING CHIPPING-RESISTANT MULTILAYERED FILM The present invention relates to a paint composition, preferably for forming a chipping-resistant multilayered film, and a method for forming a chipping-resistant multilayered film.

More preferably this invention relates to a chipping-resistant paint composition for use in the coating of outside plates of automotive body which is capable of preventing damages of film due to small stones sprung by motor traffic and of preventing the substrate plates from rusting due to damages of the film, and to a method for forming a chipping-resistant multilayered film.

When an automobile is runring at a high speed, collisions of small stones or the like against outside plates (strictly speaking, film surfaces) of the automobile are unavoidable. The collisions may form cracks on the film or peel off the film from the substrate such as outside plates or other parts (so-called chipping is generated). If the chipping is generated on the film, water permeates through the resulting flaw to rust the surface of the substrate (outside plate).

In particular, in such regions as the northern part of the U.S., Canada, and northern Europe, where rock salt and sand are scattered in large quantities on roads for the purpose of preventing motorcar slip accidents in the winter season, it is highly important for the films on outside plates of automotive body to have chipping resistance (i.e., impact resistance). Thus, it is desired to obtain a film which, even when small stones collide against it, does not suffer damages (chipping) and protects the substrate (outside plates of automotive body) against rusting.

The coating of outside plates of automotive body is generally conducted by a method in which a steel sheet that has been chemically treated with iron or zinc phosphate is coated successively with an electrodeposition paint (undercoating paint), an intermediate coating paint, and a topcoating paint. In order to improve chipping resistance and rust-preventing properties, various improvements have so far been proposed on electrodeposition paints (undercoating paints), intermediate coating paints, and topcoating paints and on coating methods therefor.

U.S. Patent 4,985,500 (corresponding to JP-A-62169869) discloses a primer composition consisting essentially of (i) at least one resin having a glass transition temperature of not higher than -200C and an elongation at break of not less than 400% at 200C, said resin being selected from the group consisting of a polyolefin resin, a polyacrylic resin, a polyester resin, and a modified resin thereof comprising a linear high molecular weight elastomer; and (ii) at least one cross-linking resin selected from the group consisting of a melamine resin, a urea resin, polyisocyanate, and blocked isocyanate; wherein a weight ratio as a solid resin content of component (i) to component (ii; is (70-99):(30-1). (The term "JP-A" as used herein means an "unexamined published Japanese patent application.") That is, U.S.Patent 4,985,500 discloses a primer composition comprising a combination of a resin such as a polyurethane resin, a polyacrylic resin, a polyvinyl resin, etc. and a hardener such as melamine resin, urea resin, polyisocyanate, etc.

Further, U.S. Patent 4,888,244 (corresponding to JP-A-62-61675) discloses a method which comprises (i) forming a cationic electrodeposited film consisting mainly of a cationic resin having a functional group reactive to isocyanate group, and (ii) subsequently applying thereon an organic solvent-based paint which contains a polyisocyanate compound and forms a film having a static glass transition temperature of 0 to -750C, followed by intermediate coating and topcoating. The preferred examples of the polyisocyanate compound which are enumerated in U.S.Patent 4,888,244 (corresponding to JP-A-62-61675) include a product of reaction between hexamethylene diisocyanate and water, an adduct of xylylene diisocyanate with trimethylolpropane, an adduct of tolylene diisocyanate with hexamethylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate. In this prior-art method, such a polyisocyanate compound is used after being blocked with an ordinary blocking agent such as an oxime. As an example of the cationic resin having a functional group reactive to isocyanate group, a resin obtained by reacting an epoxy resin having a polyphenol with a cationic property-imparting agent is given in the reference.

JP-A-63-43967 discloses a chipping-resistant paint comprising, as major components, (i) a urethane polymer soluble in organic solvents which is an adduct of a diisocyanate compound with a polyol having 2 to 3 hydroxyl groups per molecule on the average and has a number-average molecular weight of 10,000 to 100,000, (ii) a hydroxyl group-containing resin having a specific number-average molecular weight, and (iii) a blocked polyisocyanate compound. In JP-A-63-43967, polyester resins and polyethers are described as preferred examples of the hydroxyl group-containing resin of component (ii).The examples of the blocked polyisocyanate compound (iii) which are enumerated in the reference include diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, and tolylene diisocyanate and adducts of polyol compounds, e.g., polyether polyols and (hydroxyl group-containing) polyester resins, with those diisocyanates. In Examples given in the reference, an oxime-blocked adduct of tolylene diisocyanate with both poly(tetramethylene glycol) and trimethylolpropane or an oxime-blocked adduct of tolylene diisocyanate with trimethylolpropane is used as the blocked polyisocyanate compound (iii).

However, the paint proposed in JP-A-63-43967 has a drawback that since it contains a relatively highmolecular resin component (component (i) has a numberaverage molecular weight of 10,000 to 100,000), the film formed therefrom has insufficient surface smoothness or a solvent should be used in a large amount in order to obtain a smooth finish. Use of a large amount of solvent is disadvantageous from the standpoints of environmental problem, cost, etc.

GB 2268936A (corresponding to JP-A-6-41494) discloses a chipping-resistant paint composition comprising, as major components, (a) a polyisocyanate compound which has a polycaprolactone-modified diol as a bonded component and in which the active isocyanate groups have been blocked and (b) a hydroxyl group-containing resin having two or more hydroxyl groups per molecule, and also discloses a method for forming a chipping-resistant film using the paint composition. However, the polycaprolactone-modified diol used for producing the blocked polyisocyanate compound of component (a) does not comprise polycaprolactone-modified diols having different numberaverage molecular weights, and is the same as the polyisocyanate compounds synthesized in Comparative Synthesis Examples 12 and 13 described later which are used as comparative examples for the present invention.The paint composition proposed in GB 2268936A corresponds to Comparative Examples 12 and 14 described later, and has failed to give a film having sufficient chipping resistance, as compared with the paint compositions according to the present invention.

Furthermore, there is no description in GB 2268936A concerning limitations on the molar concentration of isocyanurate groups in the blocked polyisocyanate compound of component (a) and on the content of effective isocyanate groups therein. According to the present invention, by regulating these properties in respective specific ranges, a paint composition having good chipping resistance is obtained.

JP-A-2-276878 discloses a one-pack type heatcurable polyurethane coating composition comprising components (A), (B), and (C): (A) a blocked polyisocyanate produced by reacting an aliphatic diisocyanate and/or an alicyclic diisocyanate with a polycaprolactone polyol to obtain a polyisocyanate having an isocyanate group at each terminal, and reacting the polyisocyanate with a blocking agent to block the isocyanate groups; (B) a blocked polyisocyanate produced by reacting an aliphatic diisocyanate and/or an alicyclic diisocyanate with a poly(tetramethylene glycol) to obtain a polyisocyanate having an isocyanate group at each terminal, and reacting the polyisocyanate with a blocking agent to block the isocyanate groups; and (C) a polyhydroxy compound having a glass transition temperature of 20 to 1000C and a hydroxyl value of 10 to 150 mgKOH/g-resin, the proportion of component (A) to component (B) being from 100/0 to 0/100 by weight, and the ratio of all the latent NCO groups contained in components (A) and (B) to the OH groups contained in component (C) being from 0.5 to 2 by equivalent.

However, like the composition proposed in GB 2268936A, the composition proposed in JP-A-2-276878 has the following disadvantageous features. That is, only one polycaprolactone polyol is used, and the isocyanates used for producing the blocked isocyanate are limited to diisocyanates and do not contain a cyclic trimerized polyisocyanate polymer, which is different from the present invention. Moreover, there is no description therein concerning limitations on the content of effective isocyanate groups. Because of these, the composition proposed in JP-A-2-276878 is insufficient as a chippingresistant paint.

JP-B-64-10023 discloses a two-pack type stretchable polyurethane paint composition comprising a combination of (i) a bifunctional NCO-terminated prepolymer and/or trifunctional NCO-terminated prepolymer obtained by reacting an aliphatic or alicyclic diisocyanate with a polycaprolactone diol and/or polycaprolactone triol each having a number-average molecular weight of 500 to 1,500 and (ii) an acrylic polyol having a glass transition point of 30 to 1000C and a hydroxyl value of 10 to 150 based on resin amount, component (i) and component (ii) being mixed in such a proportion that the NCO/OH ratio is from 0.5 to 2.0 by equivalent. (The term "JP-B" as used herein means an "examined Japanese patent publication.") However, the composition proposed in JP-B-64-10023 has the following disadvantageous features.That is, the isocyanate used for producing the NCO-terminated prepolymer is limited to diisocyanates, and a cyclic trimerized polyisocyanate polymer is not used therein, which is different from the present invention. Moreover, there is no description therein concerning limitations on the content of effective isocyanate groups. Furthermore, though the composition is 6f the two-pack type, the NCO-terminated prepolymer is not in a blocked form. Because of these, the proposed composition is insufficient as a chipping-resistant paint.

Accordingly, a preferred embodiment of the present invention may provide a chipping-resistant paint composition which not only gives a film having good chipping resistance but also has good suitability for wet-on-wet coating (hereinafter often referred to as "W/W suitability") and can be formilated to have a lower volatile content (lower solvent content), and which enables the cleaning of the piping, coating machine, etc. in the coating line and the removal of films from the equipment to be conducted easily.

In one aspect the present invention concerns a method for forming a multilayered film having good chipping resistance.

In a second aspect the present invention concerns a coated article having a multilayered film formed by coating an outside automotive plate with the excellent chipping-resistant paint composi=ion by the method for forming a film having good chipping resistance.

In a third aspect the present invention provides a chipping-resistant paint composition comprising as major components (A) a blocked polyisocyanate obtained by mixing (i) an aliphatic or alicyclic polyisocyanate (a) and a cyclic trimerized polyisocyanate polymer (b) obtained from said polyisocyanate (a) with (ii) two or more kinds of polycaprolactone-modified polyols (c) having different number average molecular weights, reacting ingredient (i) with ingredient (ii) by means of a urethane-forming reaction to yield a modified polyisocyanate compound (d) having a ratio of the molar concentration of isocyanurate groups to that of urethane groups of from 5/5 to 1/9, and blocking the residual active isocyanate groups of the modified polyisocyanate compound, said blocked polyisocyanate having a content of effective isocyanate groups of from 1 to 10 parts by weight per 100 parts by weight of the blocked polyisocyanate compound on a dry basis (i.e., a solid basis), and (B) at least one hydroxyl group-containing resin (e) having two or more hydroxyl groups per molecule.

In its second aspect the invention provides a method for forming a chipping-resistant multilayered film which comprises applying the chipping-resistant paint composition described above in either (1) a coating process comprising electrodeposition coating, intermediate coating, and topcoating to form at least one film selected from the group consisting of (a) to (e): (a) a film formed between an electrodeposited film and an intermediate coated film, (b) a film formed between an intermediate coated film and a topcoated film, (c) a topcoated film when the topcoated film is of a one-layer type, (d) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type, and (e) an intermediate coated film; or (2) a coating process comprising electrodeposition coating and topcoating to form at least one film selected from the group consisting of (f) to (h): (f) a film formed between an electrodeposited film and a topcoated film, (g) a topcoated film when the topcoated film is of a one-layer type, and (h) a base coated film and/or clear coated film of a topcoated film when the topcoated film is of a two-layer type.

The present invention can further provide an automotive body having a highly chipping-resistant multilayered film formed by using the above-described coating method to apply the chipping-resistant paint composition described above on outside automotive plates to form one layer of the multilayered film.

The chipping-resistant paint composition of the present invention comprises as major components: (A) a blocked polyisocyanate obtained by mixing (i) an aliphatic or alicyclic polyisocyanate (a) and a cyclic trimerized polyisocyanate polymer (b) (hereinafter abbreviated as "trimerized polyisocyanate (b)") obtained from the polyisocyanate (a) with (ii) two or more polycaprolactonemodified polyols (c) having different number-average molecular weights, reacting ingredient (i) with ingredient (ii) by means of a urethane-forming reaction, and blocking the residual active isocyanate groups contained in the reaction product; and (B) a hydroxyl group-containing resin (e) having two or more hydroxyl groups per molecule.

The chipping-resistant paint composition of the present invention may preferably further contain (C) a caprolactone-modified polyol as a hydroxyl group-containing resin, provided that component (C) is a polyol other than compound (B).

In component (A) of the present invention, it is important that the modified polyisocyanate compound (d) should contain isocyanurate groups therein. This modified polyisocyanate compound (d) of the present invention is obtained by using as essential ingredients an aliphatic or alicyclic polyisocyanate (a) and a trimerized polyisocyanate (b) containing isocyanurate groups and synthesized from the polyisocyanate (a) and reacting these polyisocyanate (a) and trimerized polyisocyanate (b) with polycaprolactone-modified polyols (c).

An important point is that the ratio of the molar concentration of the isocyanurate groups contained in the thus-obtained modified polyisocyanate compound (d) to the molar concentration of the urethane groups contained in the compound (d) is from 5/5 to 1/9.

Another important point is that the content of effective isocyanate groups in the blocked polyisocyanate is from 1 to 10 parts by weight per 100 parts by weight of the blocked polyisocyanate on a dry basis (i.e., a solid basis).

Basically, the isocyanate groups contained in the blocked polyisocyanate have been blocked with a blocking agent. The content of effective isocyanate groups in the blocked polyisocyanate means the amount of isocyanate groups per unit weight of the blocked polyisocyanate.

In synthesizing the blocked polyisocyanate, a dior polyisocyanate in which the isocyanate groups have previously been partly blocked with a blocking agent may be used as a monomer.

It is a matter of course that the blocked isocyanate groups become active at the time of film formation. In the present invention, it is therefore unnecessary in most cases to distinguish such the blocked isocyanate groups from the active isocyanate groups.

Hence, the blocked isocyanate groups are hereinafter referred to simply as isocyanate groups unless this produces especially no misunderstanding.

Examples of the aliphatic or alicyclic polyisocyanate include hexamethylene diisocyanate (hereinafter often referred to as "HDI"), lysine diisocyanate, trimethylhexamethylene diisocyanate, and isophorone diisocyanate (hereinafter often referred to as "IPDI"). Further, polymers of these diisocyanates are also usable. Use of HDI or IPDI is especially preferred.

In synthesizing the trimerized isocyanate (b), such an aliphatic or alicyclic polyisocyanate is used as a starting material.

In the present invention, the modified polyiso cyanate (d) is produced from a mixture of the aliphatic or alicyclic polyisocyanate (a), the trimerized polyisocyanate (b), and two or more polycaprolactone-modified polyols (c) having different number-average molecular weights.

Therefore, a polycaprolactone skeleton is incorporated into the backbone of the modified polyisocyanate to form a soft segment in the molecular chain of the polyisocyanate compound.

As described in "Polyurethane Resin Handbook" (published by Nikkan Kogyo Shinbun-sha), pp.404-406, use of a polyisocyanurate structure is effective in imparting weatherability and durability to films. Containing a polyisocyanurate structure is therefore an essential requirement for topcoated films. In this connection, use of a trimerized polyisocyanate is commonly regarded as undesirable from the standpoint of imparting chipping resistance to coated films because of the presence of a cyclic structure in the trimerized polyisocyanate backbone.

In the present invention, however, a polycaprolactone skeleton is incorporated into the molecular chain of the modified polyisocyanate compound (d) to balance toughness with flexibility. The composition of the present invention is hence characterized in tat despite the use of a trimerized polyisocyanate, the composition is capable of giving a film having excellent chipping resistance.

Since such the blocked polyisocyanate is used as a hardener component (component (A)) to crosslink and cure the resin component (component (B)) comprising the hydroxyl group-containing resin (e) described later, the film obtained can have both of good weatherability and good chipping resistance.

The trimerized polyisocyanate (b) obtained from the aliphatic or alicyclic polyisocyanate (a), in the present invention, is a polyisocyanate having an average functional group number of higher than 2 and preferably having a number-average molecular weight of from 500 to 1,000 (particularly from 500 to 800). This trimerized polyisocyanate preferably has an isocyanate group content of from 16 to 25 parts (particularly from 18 to 22 parts) by weight per 100 parts by weight of the trimerized polyisocyanate on a solid basis.

Examples of the blocking agent for use in blocking the active isocyanate groups of the modified polyisocyanate compound (d) include oximes, lactams such as E-caprolactam, acetoacetic acid esters, phenols such as phenol and xylenol, and alcohols. Of these, oximes, lactams, and acetoacetic acid esters are preferably used as the blocking agent. Specific examples of the blocking agent include MEK oxime, g-caprolactam, and ethyl acetoacetate.

The polycaprolactone-modified polyols (c) used for modification in the present invention are polyols synthesized from a low-molecular polyhydric alcohol and caprolactone.

Examples of usable glycols include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4cyclohexanedimethanol, 2,2-dimethpl-3-hydroxypropyl 2,2dimethyl-3-hydroxypropionate, and polytetramethylene ether glycol. Examples of usable trihydric and higher alcohols include glycerol, sorbitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, and pentaerythritol. These polyhydric alcohols may be used in combination of two or more thereof. Preferred examples of low-molecular polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, glycerol, and sorbitol. Of these, ethylene glycol and propylene glycol are especially preferred.

The two or more polycaprolactone-modified polyols (c) for use in the present invention have different numberaverage molecular weights. Specifically, the polycaprolactone-modified polyols (c) each has a number-average molecular weight of preferably from 200 to 5,000, more preferably from 250 to 3,500. This ingredient (c) is preferably a combination of polycaprolactone-modified polyols in which the difference in number-average molecular weight between the polyol having the highest number-average molecular weight and that having the lowest number-average molecular weight is from 500 to 3,000 (more preferably from 750 to 2,700 and most preferably from 750 to 1,500). If the difference between the maximum and minimum numberaverage molecular weights is smaller than 500, the effect of the soft segment is not produced, resulting in reduced chipping resistance.If that difference exceeds 3,000, the highest-molecular polyol has too high a molecular weight, making a high-solid formulation difficult.

Due to the use of such polycaprolactone-modified polyols having different number-average molecular weights, a film having a balance between flexibility and toughness can be formed. This is because the lower-molecular polycaprolactone-modified polyol serves to impart flexibility to the film due to the increased lactone content thereof, while the higher-molecular polycaprolactone-modified polyol serves to impart toughness to the film due to the reduced lactone content thereof. As a result, a film having both flexibility and toughness can be obtained, which two properties are necessary for attaining good chipping resistance.

The polyol (c) comprises a mixture of diols or a mixture of a diol and a triol. Particularly polycaprolactone polyols such as polycaprolactone diols and polycaprolactone triols may be used as the polyols (c). As compared with polycaprolactone diols, polycaprolactone triols function to enhance the tensile strength of the film to thereby toughen the same.

The blocked polyisocyanate has a content of effective isocyanate groups (which have been blocked with the blocking agent described above but turn into active -NCO groups upon baking) of preferably from 1 to 10% by weight, preferably from 2 to 10% by weight, more preferably from 2 to 8% by weight, most preferably from 3 to 6% by weight, based on the amount of the blocked polyisocyanate on a solid basis. This concentration of effective isocyanate groups can be determined, for example, by heating the blocked polyisocyanate to convert the blocked state into the unblocked state, reacting this polyisocyanate with an excess of an amine, and calculating the isocyanate group concentration from the consumed amine amount.

The modified polyisocyanate compound (d) to which the caprolactone-modified polyols (c) have been bonded has a number-average molecular weight of preferably about from 1,000 to 40,000, more preferably from 2,000 to 20,000.

The hydroxyl group-containing resin using as component (B) for preparing the chipping-resistant pait composition of the present invention is expalained below.

(B) Hydroxyl Group-Containina Resin (e) (Resin Cinponent) In the present invention, a resin having two or more hydroxyl groups per one molecule is used as the hydroxyl group-containing resin (e). Usable examples of the hydroxyl group-containing resin include: (i) a hydroxyl group-containing acrylic resin, (ii) a hydroxyl group-containing polyester resin, (iii) a polyol of an aliphatic hydrocarbon having 2 to 8 carbon atoms and polycaprolactone polyol, (iv) a hydroxyl group-containing epoxy resin, and (v) - a hydroxy group-containing resin used for the coating of outside plates of automotive body.

Of these, a hydroxyl group-containing acrylic resin and a hydroxyl group-containing polyester resin are preferred.

Particularly, a hydroxyl group-containing acrylic resin is preferred.

(i) Hydroxyl Group-Containing Acrylic Resin: As the hydroxyl group-containing acrylic resin, one having a glass transition temperature (Tg) of -50 to OOC is preferably used.

The acrylic resin can be produced from, for example, the following monomers by an ordinary polymerization method.

That is, examples of monomers include: (1) hydroxyl group-containing ethylenic monomers such as hydroxymethyl (meth)acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and N-methylolacrylamide; (2) carboxyl group-containing ethylenic monomers such as acrylic acid, methacrylic acid (MAA), crotonic acid, itaconic acid, fumaric acid, and maleic acid; and (3) alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl acrylate, isopropyl acrylate, isobutyl acrylate, 2ethylhexyl acrylate, lauryl (meth)acrylate, n-octyl acrylate, and n-dodecyl acrylate.

The hydr & yl group-containing acrylic resin can be obtained by copolymerizing at least one o; these compounds by an ordinary method (provided that at least one oç the monomer(s) used should contain a hydroxyl group).

It is also possible to use, besides the above ethylenic monomers (1) to (3), an ethylenic monomer copolymerizable or polymerizable therewith, such as, e.g., styrene or acrylonitrile.

In it the present invention, it is preferred to select at least one monomer from those enumerated above and to determine the amount thereof so that the acrylic resin to be constituted from the selected monomer(s) have a glass transition temperature (Tg) of -50 to OOC.

For example, the acrylic monomers are divided into those whose homopolymers form a coated film having a low glass transition temperature (Tg) of -10 C or lower (hereinafter referred to simply as "low-Tg acrylic monomers") and those whose homopolysners form a coated film having a high glass transition temperature (Tg) (hereinafter referred to simply as "high-Tg acrylic monomers"), and this classification is taken in account when regulating monomer ratio.

The low-Tg acrylic monomers include ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate, 4-hydroxybutyl acrylate, and 2-hydroxyethyl acrylate.

On the other hand, the high-Tg acrylic monomers include acrylic acid, methacrylic acid, alkyl (meth)acrylates such as methyl acrylate, isopropyl acrylate, hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, 2-hydroxyethyl methacrylate, and hydroxypropyl methacrylate, styrene (St), and acrylonitrile.

The content of such high-Tg acrylic monomer(s) in the acrylic resin is preferably 40% by weight or lower. If the content thereof exceeds 40% by weight, the coated film to be obtained has an insufficient elongation. The more preferred range of the content thereof is from 5 to 30% by weight.

Although it is preferred to synthesize an acrylic resin from one or more monomers suitably selected from those enumerated above so as to result in a Tg of -50 to O"C, the monomer selection more'preferably is conducted se as to produce an acrylic resin giving a coated film having a Tg of -40 to -150C.

It is preferable that the number-average molecular weight of the acrylic resin described above be from 2,000 to 8,000. If the number-average molecular weight of the resin is less than 2,000, W/W property is decreased. On the other hand, if the number-average molecular weight thereof exceeds E,00C, a coated film having excellent chipping resistance cannot be obtained and it becomes difficult to formulate a high-sc' id coating composition using the acrylic rest. The number-average molecular weight of the acrylic resin is more preferably from 2,500 to 6,000, with the most preferred range thereof being from 3,000 to 4,000.

The hydroxyl value of the acrylic resin is preferably from 50 to 200. If the hydroxyl value thereof is below 50, low chipping resistance results. On the other hand, if it exceeds 200, the coated film has insufficient flexibility and hence has poor chipping resistance. The more preferred range of the hydroxyl value of the acrylic resin is from 140 to 180.

The acid value of the acrylic resin is preferably from 1 to 10. If the acid value thereof is below 1, the coated film shows poor adhesion. On the other hand, if it exceeds 10, the coating composition has poor storage stability. In the present invention, the units of hydroxyl value and acid value are mgKOH/g.

The acrylic resin described above may be used after being modified with a lactone, which preferably is - caprolactone. It is preferable that this lactone-modified acrylic resin have a number-average molecular weight of 3,G00 to 15,000.

(ii) Hydroxyl Group-Containing Polyester Resin: The polyester resin that can be used in this invention is one having two or more hydroxyl groups per one molecule and generally called a polyester polyol. This polyester resin is usually obtained by the polycondensation (esterification reaction) of a polyhydric alcohol with a polybasic acid or anhydride thereof.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1, 2-butanediol, 1, 3-butanediol, 2,3butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hydrogenated bisphenol A, a hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, 2,2-dimethyl-3- hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 2,2,4trimethyl-l, 3-pentanediol, N, N-bis (2-hydroxyethyl ) dimeth- ylhydantoin, polytetramethylene ether glycol, polycaprolactone polyol, glycerol, sorbitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, and tris (hydroxyethyl ) isocyanate. It is also possible to use a combination of two or more of the above-enumerated polyhydric alcohols.

Examples of the polybasic acid or anhydride thereof include phthalic acid, phthalic acid anhydride, tetrahydrophthalic acid, tetrahydrophthalic acid anhydride, hexahydrophthalic acid, hexahydrophthalic acid anhydride, methyltetrahydrophthalic acid, methy'tetrahydrophthalic acid anhydride, himic acid anhydride, trimellitic acid, trimellitic acid anhydride, pyrom.eD c acid, pyromellitic acid anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic acid anhydride, fumaric acid, itacoric acid, adipic acid, azelaic acid, sebacic acrid, sccinic acid, succinic acid anhydride, lactic acid, dodecenylsuccinic acid, dodecenylsuccinic anhydride, cyclohexane-1,4-di- carboxylic acid, and endic acid anhydride. It is also possible to use a combination of two or more thereof.

The polyester resin for use in the present invention can be obtained by reacting such a polyhydric alcohol as those enumerated above with such a polybasic acid or anhydride thereof as those enumerated above in such a proportion that the molar ratio of the hydroxyl groups of the former to the carboxyl groups of the latter is from 1.2 to 1.8, and it has two or more residual hydroxyl groups per one molecule as described above.

It is preferable that the number-average molecular weight of te hydroxyl group-containing polyester resin be from 500 to 10,000. The hydroxyl value of the resin is preferably from 40 to 200 and particularly preferably from 70 to 180, while the acid value thereof is preferably from 2 to 40.

The hydroxyl group-containing polyester resin may be used after being modified with a lactone, an oil or fat or a fatty acid, a melamine resin, an epoxy resin, a urethane resin, etc.

- Examples of the oil-modified polyester resin include those obtained by modifying the above-described polyester resin with oils or fats, e.g., castor oil, dehydrated castor oil, palm oil, corn oil, cottonseed oil, linseed oil, perilla oil, poppy seed oil, safflower oil, soybean oil, and tung oil, or with fatty acids extracted from these fats and oils.

The preferred range of the number-average molecular weight of the oil-modified polyester resin (oil-, fat-, or fatty acid-modified polyester resin) is from 500 to 15,000, while that of the hydroxyl value thereof is preferably from 40 to 200 and particularly preferably from 70 to 160.

In producing the oil-modified polyester resin, it is preferred to add such an oil or fat and/or fatty acid as those enumerated above to a polyester resin in a total amount of up to 30 parts by weight per 100 parts by weight of polyester resin.

(iii) Polyol Having 2-8 Carbon Atoms and Polycaprolactone diol: An aliphatic polyol having 2 to 8 carbon atoms can be used as component (B) in the present invention.

Examples thereof include ethylene glycol, propylene glycol, butylene glycol, 1,5-pentanediol, 1,6-hexanediol, 2-ethyl1,3-hexanediol, and neopentyl glycol. In addition, polycaprolactonediol and polycaprolactonepolyol such as polycaprolactonetriol can be used.

In the case of using polycaprolactonepolyol, the preferred range of the number-average molecular weight thereof is from 200 to 5,000.

(iv) Hydroxyl Group-Containing Epoxy Resin: Examples of the epoxy resin having two or more hydroxyl groups include various kinds of bisphenol epoxy resins.

The preferred range of the number-average molecular weight of the hydroxyl group-containing epoxy resin is from 300 to 5,000, while that of the hydroxyl value thereof is preferably from 50 to 200 and particularly preferably from 70 to 160.

Such epoxy resins may also be used after being modified with a lactone. In the case of modifying an epoxy resin with a lactone, it is preferred to add the lactone in an amount of 5 to 50 parts by weight per 100 parts by weight of the hydroxy arollp-containing epoxy resin.

It is preferred for obtaining an excellent cured film that a mixing ratio of a blocked polyisocyanate as component (A) and a hydroxyl group-containing resin as component (B), that is, a mole ratio of an isocyanate group (-NCO) in component (A) and a hydroxyl group (-OH) in component (B) (i.e., -NCO/-OH ratio) is (30 to 70)/(70 to 30) and particularly (40 to 60)/(60 to 40).

The chipping-resistant paint composition of the present invention may further contain a caprolactonemodified polyol (C) in an amount of 25 to 80 parts by weight per 100 parts by weight of the total of components (A) and (B).

Examples of the caprolactone-modified polyol which is preferably used as component (C) include a hydroxyl group-containing lactone-modified polyester resin as described above, a polyol having 2 to 8 carbon atoms as described above, polycaprolactone diol and polycaprolactone triol.

The chipping-resistant paint composition of the present invention may contain a pigment and various additives described below in addition to the essential components described above.

Usable examples of the pigment include various kinds of organic pigments; inorganic pigments such as carbon black, titanium dioxide, and iron oxide; extender pigments such as barium sulfate. and talc, and flaky pigments such as aluminium or graphite.

It is also possible to add a surface modifier of the acrylic or polyoxyethylene type (e.g., Liponox NC-60, manufactured by Lion Fat & Oil Co., Japan) for the purpose of improving spray dust affinity.

In the present invention, it is desirable that a catalyst such as an organotin compound be added as a curing reaction accelerator to the coating corposition. Examples of the tin compound include dimethyltin dilaurate, dibutyltin dilaurate, dimethyltin chloride, dbuty1tin chloride, and di-n-octyltin dilaurate. zif com?ounS and tertiary amine catalyst may be used in combination with such a tin compound catalyst.

A known anti-settling agent may be incorporated, such as one of the polyethylene or polyamide type or other type.

It is possible to use an amino resin in place of a part of component (A), which is a hardener component.

The amounts of the above-described various additives to be incorporated are preferably as follows; the amount of a pigment is from 5 to 30 parts be weight, that of a catalyst is from 0.5 to 3 parts by weight, and that of an anti-settling agent is 1 part by weight or less, per 100 parts by weight of the total amount (solid amount) of the above-described essential components (A) and (B).

- Theref3xe, the representativo example of mixing ratio for the chipping-resistant paint composition containing the additives described abcve is shown below.

Component (A) 20 to 80 parts by weight Component (B) 80 to 20 Component (A) and (B) 100 parts by weight in total (solid amount) Component (C)* 25 to 80 Pigments* 5 to 30 Catalyst* 0.5 to 3 Other additives 0.2 to 5 (Organic) solvent 50 to 200 * These additives are added, if necessary.

The chipping-resistant paint composition of the present invention is dissolved or dispersed in an organic solvent or water to obtain a chipping-resistant topcoating paint, a chipping-resistant intermediate coating paint and a paint composition which is generally called "chipping primer".

In the case where the chipping-resistant paint composition of the present invention is to be used as an organic soXvent-based paint, examples of the usable solvent include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as mineral spirit, esters such as ethyl acetate and butyl acetate, and ketones such as methyl ethyl ketone. One or more solvents may be suitably selected from those and sed alone or as a mixture.

Besides being used as an organic solvent-based paint, the chipping-resistant paint composition of this invention can also be used as a water-based paint of the aqueous dispersion type. In this case, water or any of various hydrophilic organic solvents can be used as a solvent.

The chipping-resistant paint composition of the present invention may be applied in either (1) a coating process comprising electrodeposition coating, intermediate coating, and topcoating to form at least one film selected fro the group consisting of (a) to (e): (a) a film formed between an electrodeposited film and an intermediate coated film, (b) a film formed between an intermediate coated film and a topcoated film, (c) a topcoated film when the topcoated film is of a one-layer type, (d) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type, and (e) an intermediate coated film; or (2) a coating process comprising electrodeposition coating and topcoating to form at least one film selected from the group consisting of (f) to (h): (f) a film formed between an electrodeposited film an' a .topcoated film, (g) a topcoated film when the topcoated film is of a one-layer type, and (h) a base coated film and/or clear coated film of a topcoated film when the topcoated film is of a two-layer type.

As a result, the multi-layered coated article (i.e., the coated article having a multi-layered film) of the present invention which has a chipping-resistant film can be obtained.

The coating processes employing the chipping resistant paint composition of the present invention will be explained below in detail.

(1) Application in Coating Process Comprising Electro deposition Coating, Intermediate Coating, and Top coating: First, the steel substrate is subjected to electrodeposition coating. As the electrodeposition paint, any of the conventional ones of the anionic resin type and cationic resin type can be used.

It is usually preferred that the electrodeposition coating be conducted so as to deposit a film having a thickness of 10 to 40 Rm after baking. The other conditions for the electrodeposition coating may be the same as those for conventional electrodeposition coating processes.

It is aso preierred tat the ordinary ch.eraical conversion be conducted prior to the electrodeposition coating.

In the case of (a) above, a paint obtained from the coating composition of the present invention is applied on an electrodeposited film.

For dissolving the chipping-resistant paint composition of this invention in a suitable solvent to give a paint, it is necessary to well disperse and mix the components. This can be attained by using a mixing device for use in producing ordinary paint, such as a paint shaker, dissolver, ball mill, sand grinding mill, or the like.

The chipping-resistant paint composition of the present invention is diluted with a solvent to a proper viscosity, and is applied by spraying, coating, or other technique. The viscosity (according to JIS K-5400) of the chipping-resistant paint composition is measured with 4 Ford cup. The viscosity of the composition for a spray coating method is adjusted to 10 to 30 seconds/200C with $4 Ford cup.

Preferred examples of the coating machine include those of the atomizer type such as an air spray, an airless spray, and an electrostatic coating machine.

It is preferable that the chipping-resistant film obtained from the composition of the present invention have a thicknes of 2 to < 0 pm on a dry basis. If the thickness of the chipping-resistant film is less than 2 pm, the film has poor chipping-resistance. If the thickness thereof exceeds 60 pm, a poor appearance results because of compatibility between an overlying coated film and the underlying coated chipping-resistant film in wet-on-wet coating. The more preferred range of the thickness of the chipping-resistant film is from 5 to 40 Wm.

Intermediate coating is then conducted. This intermediate coating for applying an intermediate coated film on the film obtained from the chipping-resistant paint composition of this invention may be carried out by the socalled wet-on-wet method or by a combination thereof with the semi-bake (preheating) flash off a solvent from wet film] method.

As the intermediate coating paint, a paint of the alkyd resin, polyester resin, or acrylic resin type may be used. The intermediate coating may be applied by an ordinary method, e.g., electrostatic coating. Baking may also be performed in an ordinary manner. The thickness of the intermediate coated film is preferably from 20 to 60 pm on a dry basis.

A "colored intermediate coating paint" containing a coloring pigment may b used as the intermediate coating paint so as to give an attractive finish when combined with a topcoating paint.

Examples of the tcpcoatir.g paint include paints of the acrylic resin, polyester resin, and fluororesin types. These may be any of the organic solvent-based type, water-based type, and powder type.

The conditions for topcoating may be the same as those for the conventional topcoating of automotive bodies.

In the case of (b) above, electrodeposition coating and baking are first conducted, followed by intermediate coating on the electrodeposited film and baking. Subsequently, a paint obtained from the chippingresistant paint composition of the present invention is applied on the intermediate coated film, and the topcoating is then conducted by the wet-on-wet method or by a combination thereof with the semi-bake (preheating) method.

In this case, it is preferred that the thickness of the film formed from the chipping-resistant paint composition of this invention be about 2 to 60 zm on a dry basis. The conditions for each of the electrodeposition coating, intermediate coating, and topcoating may be the same as those in the case of (a) described above.

In the case of (c) above, the chipping-resistant paint composition of the present invention is used as a one-layer type topcoating paint (so-called solid topcoating paint). After electrodeposition coating/baking and intermediate coating/baking have been conducted in the same manner as in the case of (a) described above, a paint obtained from the paint composition of this invention is applied on the intermediate coated film.

When the chipping-resistant paint composition of this invention is to be used as a solid topcoating paint, in addition to a hydroxyl group-containing acrylic resin of the kind described hereinabove, a suitable hydroxyl groupcontaining resin such as an oil-modified polyester resin may be employed as component (B).

In the case of forming a topcoated film consisting of abase coated film and a clear coated film (in the case of (d) above), the chipping-resistant paint composition of the present invention may be used for forming either coated film (base coated film or clear coated film) or may be used for forming both (base coated film and clear coated film).

When the chipping-resistant paint composition of the present invention is to be used as a topcoating paint, a hydroxyl group-containing acrylic resin is preferred as component (B). In particular, use of a fluororesinmodified hydroxyl group-containing acrylic resin or a cellulose ester-modified hydroxyl group-containing acrylic resin is preferable. A preferred example of the fluororesin-modified hydroxyl group-containing acrylic resin is the fluoroolefin-Inodified acrylic resin as described in JP A-2-245067.

Examples. of the cellulose ester-modified hydroxyl grou-conta'.ning acrylic resin include those obtained by modifying hydroxyl group-containing acrylic resins of the kind described hereinabove with cellulose nitrate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose acetate propionate, o mixtures thereof. The amount of such a cellulose ester is preferably about from 2 to 50% by weight, more preferably from 5 to 20% by weight, based on the solid amount of the hydroxyl group-containing acrylic resin.

When the coating composition of the present invention is to be used as the base coating paint of a topcoating paint, it is especially preferred to select a cellulose ester-modified hydroxyl group-containing acrylic resin as component (B). The thickness of the base coated film in this case is preferably from 15 to 20 zm on a dry basis.

When the chipping-resistant paint composition of the present invention is to be used as the clear coating paint of a topcoating paint, it is especially preferred to select a fluororesin-modified hydroxyl group-containing acrylic resin as component (B). The thickness of the clear coated film in this case is preferably from 30 to 50 pm on a dry basis.

The paint composition of the present invention can also be used as an intermediate coating paint as in the case of (e) above. In this case, it is preferred to select a hydro;yl groip-containing polyester resin of the kind.

described hereinabove (including various modified polyester resins, i.e., epoxy-modified, oil-modified, melaminemodified, and urethane-modified polyester resins) as the resin of component (B) in the paint composition of this invention. The thickness of the intermediate coated film in this case is preferably from 30 to 50 zm on a dry basis.

(2) Application in Coating Process Comprising Electro deposition Coating and Topcoating: On the other hand, in the case of (f) above, electrodeposition coating is conducted as described above, and a paint obtained from the chipping-resistant composition of the present invention is applied on the electrodeposited film. In this case, it is preferred to use a hydroxyl group-containing polyester resin as component (B) in the coating composition of this invention.

Especially preferred as component (B) is a hydroxyl groupcontaining lactone-modified polyester resin. The thickness of the film is preferably from 5 to 40 zm on a dry basis.

Thereafter, topcoating is conducted on the film formed from the paint composition of the present invention, in the same manner as in (a) above.

In the case of (g) above, electrodeposition coating is conducted in the same manner as described above, and a solid topcating paint obtained from the chipping resistant 'paint compositlon of the present invention is then Rrclied in the same manner as in (c) above.

In the case of (h) above, a base coated film and a clear coated film are formed as a topcoated film on an electrodeposited film in the same manner as in (d) above.

Preferred embodiments of the present invention are as follows.

(l) In the chipping-resistant paint composition of the present invention, the molar ratio of the isocyanate groups contained in the modified polyisocyanate compound (d) to the hydroxyl groups contained in the hydroxyl groupcontaining resin (e) of component (B) is from 3/7 to 7/3.

(2) In the chipping-resistant paint composition of the present invention, the molar ratio of the isocyanate groups contained in the modified polyisocyanate compound (d) to the hydroxyl groups contained in the hydroxyl groupcontaining resin (e) of component (B) is preferably from 4/6 to 6/4.

(3) In the chipping-resistant paint composition of the present invention, the proportion of the aliphatic or alicyclic polyisocyanate (a) to the cyclic trimerized polyisocyanate (b) obtained from the polyisocyanate (a) is from 0.5/1 to 25/1 by weight.

(4) In the chipping-resistant paint composition of the present invention, the proportion of the aliphatic or alicyclic polyisocyanate (a) to the cyclic trimerized polyisocyanate (b) obtained from the polyisocyanat? (a) is preferably from 1.5/1 to 7/1 by weigh;.

(5) In the chipping-resistant paint composition of the present invention, the molar ratio of the sum of the aliphatic or alicyclic polyisocyanate (a) and the cyclic trimerized pclyisocyanate (b) obtained from the polyisocyanate (a) to the polycaprolactone-modified polyols (c) is from 1.5/1 to 6 (6) In the chipping-resistant paint composition of the present invention, the molar ratio of the sum of the aliphatic or alicyclic polyisocyanate (a) and the cyclic trimerized polyisocyanate (b) obtained from the polyisocyanate (a) to the polycaprolactone-modified polyols (c) is preferably from 2/1 to 4/1.

(7) In the chipping-resistant paint composition of the present invention, two or more kinds of the polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) each has a numberaverage molecular weight of from 250 to 3,500.

(8) In the chipping-resistant paint composition of the present invention, two or more kinds of the polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) satisfy the following equation Mn MAX - Mn MIN = 750 to 2,700 where Mn MAX is the number-average molecular weight of the .polìol component cf -the polyols (c) which has the hiahert n'Le-average molecular weight and ML EN is the number- average molecular weight of the polyol component of the polyols (^) which has the lowest number-average molecular weight.

(9) In the chipping-resistant paint composition of the present invention, two or more kinds of the polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) comprise a mixture of diols or a mixture of a triol and a diol.

(10) In the chipping-resistant paint composition of the present invention, two or more kinds of the polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) comprise a mixture of a polycaprolactone triol and a polycaprolactone diol in a weight ratio of from 0/1 to 10/1.

(11) In the chipping-resistant paint composition of the present invention, the hydroxyl group-containing resin (e) of component (B) having two or more kinds of hydroxyl groups per molecule is an acrylic polyol or a polyester polyol.

(12) In the chipping-resistant paint composition of the present inv.ntion, the hydroxyl group-containing resin (e) of component (B) having two or more kinds of hydroxyl groups per molecule is a lactone-modified acrylic polyol or a lactone-modified polyester polyol, preferably a lactone-modified acrylic polyol.

(13) In the chipping-i~esista3t. paint composi-:on of the present invention, the hydroxyl group-containing resin (e) of component (B) having two or more kinds of hydroxyl groups per molecule is a combination of an acrylic polyol or a polyester polyol with a polycaprolactone diol or triol, preferably a polycaprolactone tiol.

(14) In the chipping-resistant paint composition of the present invention, the modified polyisocyanate compound (d) in component (A) has a ratio of the molar concentration of isocyanurate groups to that of urethane groups of from 4/6 to 2/8.

(15) In the chipping-resistant paint composition of the present invention, the blocked polyisocyanate compound as component (A) has a content of effective isocyanate groups of from 2 to 10 parts by weight per 100 parts by weight of the blocked polyisocyanate compound on a dry basis (i.e., a solid basis).

(16) In the chipping-resistant paint composition of the present invention, the blocked polyisocyanate compound as component (A) has a content of effective isocyanate groups of from 2 to 8 parts by weight per 100 parts by weight of the blocked po2.yisocyanate compound on a dry basis (i.e., a solid basis).

(17) In the chipping-resistant paint composition of the present invention, the blocked polyisocyanate compound as compor.ent (A) has a content of effective isocyanate. groups of-from 3 to 6 parts by weight per i^DQ parts by weight of the blocked polyisocyanate compound on a dry basis (i.e., a solid basis).

(18) In the chipping-resistant paint composition of the present invention, the aliphatic or alicyclic polyisocyanate (a) used for synthesizing the modified polyisocyanate compound (d) comprises at least either of hexamethylene diisocyanate and isophorone diisocyanate.

(19) In the chipping-resistant paint composition of the present invention, the cyclic trimerized polyisocyanate (b) obtained from the aliphatic or alicyclic polyisocyanate (a) is an isocyanurate obtained from at least either of hexamethylene diisocyanate and isophorone diisocyanate.

(20) In the chipping-resistant paint composition of the present invention, a blocking agent is used for synthesizing component (A), and said blocking agent is at least one member selected from the group consisting of MEK oxime, caprolactam, and ethyl acetoacetate.

(21) A coated article having a chipping resistant multilayered film formed by a method comprising applying the chipping-resistant paint composition of the present invention (particularly preferably on an automotive body) in either (1) a coating process comprising electro 'deposition coating, intermediate coating, and topcoating to form at least one film selected croir. the group ccnristln of (a) to (e):: (a) a film formed between an electrodeposited film and an intermediate coated film, (b) a film formed between an intermediate coated film and a topcoated film, (c) a topcoated film when the topcoated film is of a one-layer type, (d) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type, and (e) an intermediate coated film; or (2) a coating process comprising electrodeposition coating and topcoating to form at least one film selected from the group consisting of (f) to (h): (f) a film formed between an electrodeposited film and a topcoated film, (g) a topcoated film when the topcoated film is of a one-layer type, and (h) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type.

...XAhPLE The present invention is explained below in more detail by reference to the following Synthesis Exampltzs and Examples, but the invention should not be construed as being limited thereto.

Synthesis F.xanles: In the following Synthesis Examples for the present Invention, all "parts" and "percents" are by weight.

(Synthesis of HbI-Trimerized Polyisocyanate A) HDI was introduced into a four-necked flask equipped with a stirrer, thermometer, and reflux condenser.

Potassium 2-ethylhexanoate was added thereto, and the mixture was heated at 50 to 600 to allow a reaction for forming a cyclic trimer to proceed. t the time when the NCO content had reached a desire value of 2.05, phosphoric acid was added to stop the reaction. Thus, a pale-yellow liquid reaction product was obtained. The unreacted HDI was removed therefrom by thin-film distillation at 120 to 1400C and 0.01 to 0.05 Torr to obtain the desired compound, which had an NCO content of 21.3%, a free HDI content of 0.3%, and a viscosity of 2,400 cP at 250C.

(Synthesis of Blocked Polyisocyanate) SYNTHESIS EXAMPLES I TO 9 AND COMPAKkTIvE SYNTHESIS EXAMPLES 10 TO 17 Into a four-necked flask equipped with a stirrer, thermometer, and reflux condenser were introduced the ingredients shown in Tables 1 to 4.

That is, the polyisocyanate and the trimerized polyisocyanate were dissolved into the solvent in the four .necked flask. The polyol was then introduced to conduct a urethane-forming reaction at 70 to 80 C. The reaction was allowed to proceed until the NCO content reached a desired value. Thereafter, the blocking agent was introduced in an amount corresponding to that value of NCO content to conduct the blocking reaction until the NCO content reached 0. Thus, a blocked polyisocyanate was obtained.

The ingredients used in Synthesis Examples 1 to 9 and Comparative Synthesis Examples 10 to 17 and the properties of the blocked polyisocyanates obtained are shown in-Tables 1 to 4.

TABLE 1 ..SYnthesis Example 1 2 3 4 5 (Polyol) PCL- 300 36.1 19.6 14.3 PCL- 500 - - - 30.1 185.9 PCb-1250 150.2 163.7 224.1 - 123.6 t*u-2000 - 261. 43.8 301.8 90.7 PCL-3000 360.6 - - (Polyisocyanate) RDI 56.9 144.0 239.3 164.b 153.3 IPDI - - - - - (Trimerized Polyisocyanate) HDI iso- 102.7 52.0 10.8 55.2 87.7 cyanurate A VESTANAT T - - - - - 1890/100 (Blocking Agent) MEK oxime 43.6 108.9 217.8 - 108.9 Caprolactam - - - - 198.1 Ethyl aceto- - - - - acetate (Solvent) Toluene 250 250 250 250 250 Butyl acetate - - - - Effective NCO 2.0 5.0 10.0 7.0 5.0 Content (wt%) Solid Content (wt%) 75 75 75 75 75 Viscosity (cP/25 C) 6200 2100 650 1200 2000 Isocyanurate group 0.97 0.45 0.14 0.66 0.56 concentration/ urethane group concentration (molar ratio) Mn MAX-Mn MIN 2700 1700 1700 1500 1500 TABLE 2 Synthesis Example 6 7 8 9 (Polyol) PCL- 300 PCL- 500 24.0 - - 205.6 PCL-1250 - - 54.0 136.7 PCL-2000 - 218.3 - PCL-3000 540.8 130.6 487.6 (Polyisocyanate) HDI - - 107.5 166.9 IPDI 104.1 241.7 - (Trimerized Pciyisocyanate) HDI isocyanurate A 46.2 - - 95.5 VESTANAT T 1890/100 - 35.2 20.7 (Blocking Agent) MEK oxime - 174.2 - Caprolactam 84.9 - - Ethyl acetoacetate - - 130.2 195.3 (Solvent?) Toluene Butyl acetate 200 200 200 200 Effective NCO Content 3.0 8.0 4.0 6.0 (wt%) Solid Content (wt%) 80 80 80 80 Viscosity (cP/25 C) 4600 600 3500 800 Isocyanurate group 0.69 0.41 0.24 0.63 concentration/urethane group concentration (molar ratio) Mn MAX-Mn MIN 2500 1000 1750 750 TABLE 3 ComDarative Synthesis Example 10 11 12 13 (Polyol) PCL- 300 16.0 - 303.s - PCL- 500 PCL-1250 133.1 - - PCL-2000 2@@.9 - - 291.4 PCL-3000 (Polyisocyanate) HDI 213.9 - .8 234.C IPDI (Trimerized Polyisocyanate) HDI isocyanurate A - 512.4 125.9 6.9 VESTANAT.T 1890/100 - - - (Blocking Agent) MEK oxime 174.2 237.6 108.9 217.8 Caprolactam Ethyl acetoacetate - - - - (Solvent) Toluene 250 250 250 250 Butyl acetate - - - Effective NCO Content 8.0 10.9 5.0 10.0 (wt%) Solid Content (wt%) 75 75 75 75 Viscosity (cP/250C) 1200 960 1500 510 Isocyanurate group - - 0.43 0.11 concentration/urethane group concentration (molar ratio) Mn MAX-Mn MIN 1700 - - - TABLE 4 Comparative Synthesis Example 14 15 16 17 (Polyol) PCL- 300 PCL- 500 13.0 203.0 - 181.0 PCL-1250 - 135.0 - 120.4 P':L-2000 - 99.1 122.8 PC--3Gû0 293.2 - 73.5 (Polyisocyanate) HDI - 195.3 - 118.3 IPDI 170.2 - 310.8 (Trimerized Polyisocyanate) HDI isocyanurate A 75.5 8.8 - 185.0 VESTANAT T 1890/100 - - 42.4 - (Blocking Agent) MEK oxime - 108.9 250.4 Caprolactam 198.1 - - Ethyl acetoacetate - - - 195.3 (Solvent) Toluene 250 250 - Butyl acetate - - 200 200 Effective NCO Content 7.0 5.0 11.5 6.0 (wt%) Solid Content (wt%) 75 75 80 80 Viscosity (cP/250C) 1300 2400 440 1070 Isocyanurate group 2.08 0.05 0.89 1.38 concentration/urethane group concentration (molar ratio) Mn MAX-Mn MIN 2500 1500 1000 750 The properties of the five kinds polyols and a kind of trimerized polyisocyanate which were used above in the syntheses of blocked polyisocyanates are shown in Table 5 togetler with the manufacturers thereof.

TABLE 5

Number of Trade name Manufacturer Mn OHV group NV (%) (%) PCL- 300 < 1 > 300 374 2 100 PCL- 500 < 1 > 500 224 2 " PCL-1250 Placcel 212 Daicel 1250 90 2 " Chemical Industries, Ltd.

PCL-2000 Placcel 320 " 2000 84 3 " PCL-3000 Placcel 230 " 3000 37 2 " Trade Manufacturer Mn NCO NV (%) (%) VSTANAT T 1890/100 Daicel-Huels Ltd. about 800 17.3 lOG Note < 1 > : Sample product available from Nippon Polyurethane - Industry Co., Ltd. Of the polyols used in Synthesis Examples 1 to 9 and Comparative Synthesis Examples 10 to 17 and and specified in Table 5, the synthetis examples of PCL-300 and PCL-500 are shown below.

(Syntheses of PCL-300 and PCL-500) 1. Synthesis Example for PCL-300 Into a four-necked flask equipped with a stirrer, thermometer, and reflux condenser were introduced 793.1 g of dehydrated and purified caprolactone, 206.9 g of ethylene glycol, and 0.02 g of tetrabutyl titanate as a catalyst. Reaction was conducted at 1800C first at ordinary pressure for 6 hours and then at a reduced pressure of 10 Torr for 2 hours to obtain the desired reaction product, which had an OH value of 374.

2. Synthesis Exa..gLe for PCL-500 into a four-necked flask equipped with a stirrer, thermS"etcr nreflux condenser were introduced 875.9 g of dehydrated and purified caprolactone, 124.1 g of ethylene glycol, cnd 0.G2 g cf tetrabutyl titanate as a catalyst. Reaction was conducted at 1800C first at ordinary pressure for 7 hours and then at a reduced pressure of 10 Torr for 2 hours to obtain the desired reaction product, which had an OH value of 224.

The examples of the present invention and the comparative examples are explained below.

EXAMPLES 1 TO 2 AND COMPARATIVE EXAMPLES 1 TO 3 A cationic electrodeposition paint (Power Top U226E, manufactured by Nippon Paint Co., Ltd.) was applied by electrodeposition-coating on a dull steel sheet which had dimensions of 7 cm x 15 cm x 0.8 mm and had undergone zinc phosphate treatment, at a thickness of about 20 m on a dry basis. The film was then baked under conditions of 165 C and 30 minutes.

Subsequently, the blocked polyisocyanate (A) synthesized in Synthesis Example 5 (hereinafter component (A) will be also referred to as "hardener component") was mixed with a hydroxylated acrylic resin (B) (trade name "Dianal HR-2024"; manuractured by Mitsubishi Rayon Co., Ltd., Japan) having a hydroxyl value of 160, a numberaverage molecular weight of about 3,500, and a nonvolatile content of 50% in such a proporton that the NCO/OH ratio was 50/50 by mole. This mixture was further missed with other ingredients according to *..< the fol2owin formulation to prepare a chipping-resistant paint composition. (Component (B) is also referred to as "resin component.") Formulation for Chipping-Resistant Paint Composition Components (A) and (B) : 100 parts by weight in total (solid amount) Titanium dioxide : 5 parts by weight Carbon black : 0.5 part by weight Liponox NC-60 : 1 part by weight (surface modifier) Dibutyltin dilaurate : 1.5 parts by weight Solventsl) : 210 parts by weight Note (1): Solvent consisting of a 1/1 (by weight) mixture of butyl acetate and xylene.

As a thinner solvent for dilution, a 1:1 (by weight) mixture of butyl acetate and toluene was employed.

The chipping-resistant paint composition obtained above was dissolved in this solvent so that the viscosity of the resulting paint as measured with a =4 Ford cup was adjusted at 11 seconds. This paint was applied by air spray at a thickness of about 10 m on a dry basis.

After the paint applied was allowed to set for about 2 minutes, an intermediate coating paint ("Orga P-611 Gray", manufactured by Nippon Paint Co., Ltd.; polyester/ melamine rein paint) was applied by air spray coating at a thicess of abcut 35 m on a dry basis (by the wet-on-wet method), and was @aked ex 's0 C for 25 minutes.

Thereafter, an acrylic/melamine resin-type base topcoating paint ("Superlac h-80 Metallic Base", manufactured by Nippon Paint Co., Ltd.) was applied at a thickness of about 15 m on a dry basis, and the resulting coating was allowed to set for 3 minutes. A clear paint ("Superlac 0-130 Clear", manufactured by Nippon Paint Co., Ltd.) was then applied at a thickness of about 30 jim on a dry basis, and the resulting coating was allowed to set for about 10~minutes. Baking was then conducted at 140 C for 25 minutes to obtain a test piece (Example 1).

Another chipping-resistant paint composition was prepared by mixing a hardener component with a resin component in an NCO/OH ratio of 50/50 by mole and adding other ingredients thereto in the same manner as in Example 1, except that the blocked polyisocyanate synthesized in Synthesis Example 9 was used as the hardener component in place of the blocked polyisocyanate synthesized in Synthesis Example 5, and as the resin component, a blend of 85 parts of a hydroxyl group-containing lactone-modified acrylic resin (trade name "Placcel DC-2209"; manufactured by Daicel Chemical Industries, Ltd., Japan) having a hydroxyl value of 12.5, a number-average molecular weight of about 11,000, and nonvolatile content of 508 and 15 parts of a polycaprolactone triol (trade name "Placcel L320AL"; manufactured by Daicel chemical Industries, Ltd.) having a hydroxyl value of 84, , numb .verge molecular weight of 2,000, and a nonvolatile content of 100% was used.

A paint prepared from the thus-obtained chippingresistant paint composition was applied on an electrodeposition-coated steel sheet in the same manner as in Example 1 to form a chipping-resistant film. Intermediate coating and topcoating were conducted thereon in the same manner as in Example 1 to obtain a test piece (Example 2).

Another test piece (Comparative Example 1) was prepared without using a chipping-resistant paint composition of the present invention, by coating an electrodeposition-coated steel sheet with a conventional solvent-based chipping primer in place of the chippingresistant paint composition of Example 1 at a thickness of 5 jim on a dry basis and then conducting intermediate coating and topcoating on the chipping primer film in the same manner as in Example 1.

Still another test piece (Comparative Example 2) was prepared in the same manner as in Examples 1 and 2 and Comparative Example 1, except that the chipping-resistant paint composition used was the same as in Example 1 except that a melamine resin was employed as a hardener component and the above-described "Dianal HR-2040" (manufactured by Mitsabishi Rayon Co., Ltd.) was employed as a resin component. A further test piece (Comparative Exmle 3) was prepared with @@ cating process consisting of ele:.o- deposition coating, intermediate coating, and topcoating in which neither a chipping-resistant coating composition of the present invention nor a chipping primer was used.

The test pieces obtained were evaluated with respect to chipping resistance by the method described below. Further, each chipping-resistance coating composition was evaluated with respect to washability by the method shown below. The results obtained are shown in Table 6. - (1) Chipping Resistance Test was conducted using a Graverro tester (manufactured by Suga Shikenki K.K., Japan) under the following conditions.

Stone size : &num;7 crushed stone (according to JIS-A-5001) Stone amount : 50 g Distance : 35 cm Air pressure : 4.0 kg/cm2 Angle : 450 Test temperature : -20 C After the chipping resistance test, the resulting samples were visually examined and the degrees of chipping resistance were evaluated in the following five grades, with the chipping resistance O-L the test sample having no chipping primt.T layer (Comparative Example 3) being taken a. "B".

E : Excellent (no peelings were entirely observed) G : Good (few peelings were observed) M : Standard (peelings of 1 mmb or smaller were scatteringly observed) P : Poor (peelings were considerably observed) B : Bad (peelings were extremely considerablv observed) (2) washability Each of the chipping-resistant paints (and the conventional chipping primer) used in the Examples and Comparative Examples was applied alone on a tinplate and allowed to stand at 20 C for 5 minutes. The coated tinplate was then immersed in a xylene/butyl acetate (8/2 by weight) mixed solvent for 5 minutes and taken out, and each film was then scrubbed lightly with a brush. The dissolved states of the resulting films were visually examined and evaluated.

G : The film was entirely dissolved away, leaving no film.

B : The film remained almost undissolved.

TLLBLE Hardener Resin Chipping Wash Example No. component component resistance abi'.- F . 1 Synthesis B < 2 > E Ex. 5 Ex. 2 Synthesis B < 3 > E G Ex. 9 COD. Er. 1 ï:one B < 4 > G 3 Comp. Ex. 2 Melamine B < 2 > P G resin A < 6 > Comp. Ex. 3 no chipping primer B As is apparent from the results in Table 6, the application of the chipping-resistant paint compositions of the present invention on an electrodeposition-coated steel sheet is effective for improving the chipping resistance, and the chipping-resistant paint compositions of the present invention have improved washability.

Notes to Table 6: B < 2 > : "Dianal HR-2024" (manufactured by Mitsubishi Rayon Co., Ltd.) B < 3 > : 85/15 Mixture of "Placcel DC-2209" and "Placcel L-320AL" (both manufactured by Daicel Chemical Industries, Ltd.) B < 4 > : Solvent-based chipping primer of the "modified polyolefin type" A < 6 > :Melamine resin "Uvan 20N-60" (manufactured by Mitsui Toatsu Chemicals, Inc., Japan) EXAMPLES 1 AND 3 TO 6 AND COMPARATIVE EXAMPLES 4 TO 7 For examining the effect on chipping resistance of OH group/NCO group ratio in the chipping-resistant paint composition of the present invention, the following test pieces were produced and examined with respect to chipping resista:.ce; - Th2*same steel sheets as in Example 1 were coated to obtain the test pieces in the same manner as in Example 1, except thaw the -OH/-NCO molar ratio was changed as shown in Table 7 by changing the proportion of the hardener component (component (A)) to the resin component (component (B)).

The test pieces were evaluated w th respect to chipping resistance in the same manner as in Example 1.

The results are shown in Table 7.

TABLE 7 Chipping Example No. -OM/-NCO resistance Ex. 1 50/50 E Ex. 3 60/40 G Ex. 4 55/45 E Ex. 5 45/55 E Ex. 6 40/60 G Comp. Ex. 4 75/25 M Comp. Ex. 5 25/75 M Comp. Ex. 6 100/0 P Comp. Ex. 7 0/100 P As is apparent from the results in Table 7, the chipping-resistant paint compositions having an OH group/NCO group molar ratio o: from 60/40 to 40/60 provide a satisfactory effect.

EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLES 8 AND 9 For examining the effect on chipping resistance of the Dresence or absence of the trimerized polyisocyanate (b) in the chipping-resistant pain@ composition of the present invention, particularly in the hardener component, tet piees were produced and evaluated as follows. That is, a test piece of Comparative Example 8 was produced using a chipping-resistant paint composition obtained in the same manner as in Example 1, except that the trimerized-polyisocyanate-free blocked polyi socyanate synthesized in Synthesis Example 10 was used as a hardener component in place of the trimerized-polyisocyanatecontaining blocked polyisocyanate (Synthesis Example 5) used in Example 1. Further, a test piece of Comparative Example 9 was produced using a chipping-resistant paint composition obtained in the same manner as in Example 2, except that the trimerized-polyisocyanate-free blocked polyisocyanate synthesized in Synthesis Example 10 was used as a hardener component in place of the trimerizedpolyisocyanate-containing blocked polyisocyanate (Synthesis Example 9). These comparative test pieces and the test pieces produced in Examples 1 and 2 were evaluated with respect to chipping resistance. The results are shown in Table 8.

TABLE 8 Hardener Resin Chipping component :o: comDonent comDonent resistance À. ; Synthesis Ex. 5 B < 2 > E Ex. 2 Synthesis Ex. 9 B < 3 > E Comp. Ex. 2 Synthesis Ex. 10 B < 2 > M Comp Ex. r9 Synthesis Ex. 10 B < 3 > M As is apparent from the results in Table 8, the presence--of a trimerized polyisocyanate in chippingresistant paint compositions was essential.

Notes to Tables 8 to 11: B < 2 > : "Dianal HR-2024" (manufactured by Mitsubishi Rayon Co., Ltd.) B < 3 > : 85/15 Mixture of "Placcel DC-2209" and "Placcel L-320AL" (both manufactured by Daicel Chemical Industries, Ltd.) EXAMPLES 1 AND 2 MD COMPARATIVE EXAMPLES 10 TO 15 For examining the effect on chipping resistance of the molecular structures of the polycaprolactonemodified polyols used for synthesizing the hardener component of the chipping-resistant paint composition of the present invention, test pieces were produced as follows using plural polycaprolactone-modified polyols having different number-average molecular weights and tested with respect to chipping resistance.

That is, each of the same steel sheets as in Example 1 was coated in the same manner as in Example 1 using a chipping-resistant paint composition produced, as shown in Table 9, using one of the hardener components synthesized in Synthesis Examples 11 to 1:?. for blocked polyisocyanate synthesis and using either of ha hydroxyl cYroup-containing resins used in Examples 1 and 2 as a resin component. The thus-obtaine@ test pieces and the test pieces obtained in Examples 1 and 2 were evaluated with respect to chipping resistance in the same manner as in Example 1. The results are shown in Table 9.

TABLE 9 Hardener Resin Chipping Example No. - component component resistance Ex. 1 Synthesis Ex. 5 B < 2 > E Ex. 2 Synthesis Ex. 9 B < 3 > E Comp. Ex. 10 Synthesis Ex. 11 B < 2 > P Comp. Ex. 11 Synthesis Ex. 11 B < 3 > M Comp. Ex. 12 Synthesis Ex. 12 B < 2 > M Comp. Ex. 13 Synthesis Ex. 12 B < 3 > M Comp. Ex. 14 Synthesis Ex. 13 B < 2 > M Comp. Ex. 15 Synthesis Ex. 13 B < 3 > M As is apparent from the results in Table 9, it is essential that the blocked polyisocyanate should contain as components thereof two or more polycaprolactone-modified polyols having different number-average molecular weights.

EXAMPLES 1, 2, AND 7 TO 10 AND COMPARATIVE EXAMPLES 16 TO 21 For examining the effect on chipping resistance of isocyanurate group/urethane group molar ratio in the hardener component of the chipping-resistant paint composition of the present invention, the following test was conducted. Hardener components in which the ratio o -the molar concentration of-isocyanurate groups in the blocked polyisocyanate to that of urethane groups there ; s i. the range of from 5/5 to 1/9 and which had @e@@ synthesized using different kinds of trimerized no'yisocyan,tes in different amounts were used to produce test pieces by the method described below.On the other hand, hardener components synthesized so as to have an isocyanurate group/urethane group ratio outside the above range were also used to produce test pieces. These test pieces were tested with respect to chipping resistance.

That is, each of the same steel sheets as in Example 1 was coated to obtain test pieces in the same manner as in Example 1 using a chipping-resistant paint composition produced, as shown in Table 10, using one of the hardener components synthesized in Synthesis Examples 1, 3, 14, 15, and 17 for synthesis of blocked polyisocyanate and using either of the hydroxyl group-containing resins used in Examples 1 and 2 as a resin component.

The thus-obtained test pieces and the test pieces obtained in Examples 1 and 2 were evaluated with respect to chipping resistance in the same manner as in Example 1.

The results are shown in Table 10.

TABLE 10 Example H.rdener Resign wature/urethane Chipping No. component component ratio resistance Ex. 1 Synthesis B < 2 > 0.56 (36/64) E Ex. 5 Ex. 2 Synthesis B < 3 > 0.63 (39/61) E Ex. 9 Rx . 7 Synthesis B < 2 > 0.97 (49/51) M Ex. 1 Ex. 8 Synthesis Dj > 0.97 (49/51) G Ex. 1 Ex. 9 Synthesis B < 2 > 0.1 (12/88) G Ex. 3 Ex. 10 Synthesis B < 3 > 0.14 (12/88) G Ex. 3 Comp. Synthesis B < 2 > 1.38 P Ex. 16 Ex. 17 Comp. Synthesis B < 3 > 1.38 M Ex. 17 Ex. 17 Comp. Synthesis B < 2 > 2.08 P Ex. 18 Ex. 14 Comp. Synthesis B < 3 > 2.08 M Ex. 19 - Ex. 14 Comp. Synthesis B < 2 > 0.05 M Ex. 20 Ex. 15 Comp.Synthesis B < 3 > 0.05 P Ex. 21 Ex. 15 As is apparent from the results in Table 10, the blocked-polyisocyanate hardener components in which the ratio of the molar concentration of the isocyanurate groups to that of the urethane groups was in the range of from 5/5 to 1/9 were effective for obtaining good chipping resistance.

EXAMPLES 1, 2, AND 9 TO 16 AND COMPARATIVE EXAMPLES 22 AND 23 For examining the effect on chipping resistance of the content o effective isocyanate groups in -the blocked polyisocyanate as the hardener component of the chipplr:g-resistant paint composition of the present invention, test pieces were produced.es follow r.' tested with respect to chipping resistance.

That is, each of the same steel sheets as in Example 1 was coated to obtain test pieces in the same manner as i Example 1 using a chipping-resistant paint composition produced, as shown in Table 11, using one of the blocked-polyisocyanates used in Examples 1 and 2 and one of other blocked polyisocyanates synthesized in Synthesis Examples shown in Table 11 and using either of the hydroxyl group-containing resins used in Examples 1 and 2 as a resin component.

The thus-obtained test pieces were evaluated with respect to chipping resistance in the same manner as in Example 1. The results are shown in Table 11.

TABLE 11 Hardener Resin Chipping Example No. component component NCO ratio resistance (%) Ex. 1 Synthesis B < 2 > 5.0 E Ex. 5 Ex. 2 Synthesis B < 3 > 6.0 E Ex. 9 Ex. 9 Synthesis B < 2 > 10.0 G Ex. 3 Ex. 10 Synthesis B < 3 > 10.0 G Ex. 3 Ex. 11 Synthesis B < 3 > 5.0 E Ex. 5 Ex. 12 Synthesis B < 2 > 6.0 E Ex. 9 Ex. 13 Synthesis B < 2 > 8.0 G Ex. 7 Ex. 14 Synthesis B < 3 > 8.0 G Ex. 7 Ex. 15 Synthesis B < 2 > 3.0 E Ex. 6 Ex. 16 - Synthesis -B < 3 > 3.0 E Ex. 6 Comp. Ex. 22 Synthesis B < 2 > 11.5 P Ex. 16 Comp. Ex. 23 Synthesis B < 3 > 11.5 M Ex. 16 As is apparent from the results in Table 11, the blocked-polyisocyanate hardener components having an effective isocyanate group content of from 2.0 to 10.0% were effective for obtaining good chipping resistance.

EXAMPLES 15 TO 22 For examining whether the performance of the chipping-resistant paint composition of the present invention is influenced by the kinds of the trimerized polyisocyanate and blocking agent used as raw materials for synthesizing the blocked polyisocyanate as the hardener component of the composition, the various trimerized polyisocyanates and blocking agents shown in the Remarks given below were used to produce chipping-resistant paint compositions, and test pieces were produced using these compositions and tested with respect to chipping resistance.

That is, each of the same steel sheets as in Example 1 was coated to obtain test pieces in the same manner as in Example 1 using a chipping-resistant paint composition produced, as shown in Table 12, using as a hardener component one of the blocked polyisocyanates synthesized in Synthesis Examples shown in Table 12 (specifically the blocked polyisocyanates each synthesized from the raw materials shown in the Remarks for Table 12) and using either of the hydroxylated resins used in Examples 1 and 2 as a resin component.

The thus-obtained test pieces were evaluated with respect to chipping resistance in the same manner as in Example 1. The results are shown in Table 12. Details of the hardener components used are shown in Table 12 (Remarks).

TABLE 12 Hardener Resin Chipping Example No. component component resistance Ex. 15 Synthesis Ex. 6 B < 2 > E Ex. 16 Synthesis Ex. 6 3 < 3 > E Ex. 17 Synthesis Ex. 2 B < 2 > E Ex. 18 Synthesis Ex. 2 B < 3 > E Ex. 19 Synthesis Ex. 4 B < 2 > E Ex. 20 Synthesis Ex. 4 B < 3 > E Ex. 21 Synthesis Ex. 8 B < 2 > E Ex. 22 Synthesis Ex. 8 B < 3 > E TABLE 12 (Remarks) Example Trimerized Blocking No.Monomer polyisocyanate ~ agent Ex. 15 IPDI HDI-trimerized caprolactam polyisocyanate A < 7 > Ex. 16 IPDI HDI-trimerized caprolactam polyisocyanate A < 7 > Ex. 17 HDI HDI-trimerized MEK oxime polyisocyanate A < 7 > Ex. 18 HDI HDI-trimerized MEK oxime polyisocyanate A < 7 > Ex. 19 HDI HDI-trimerized caprolactam polyisocyanate A < 7 > Ex. 20 HDI HDI-trimerized caprolactam polyisocyanate A < 7 > Ex. 21 HDI IPDI-trimerized ethyl polyisocyanate < 8 > acetoacetate Ex. 22 HDI IPDI-trimerized ethyl polyisocyanate < 8 > acetoacetate < 7 > HDI-trimerized polyisocyanate A is described in the Synthesis Example given hereinabove.

< 8 > IPDI-trimerized polyisocyanate is "VESTANAT T1890/100." As is apparent from the results in Table 12, chipping resistance was not influence by the kinds of the raw materials (monomer, trimerized polyisocyanate, and blocking agent) used for synthesizing the blocked polyisocyanates as hardener components.

EXAMPLES 1, 2, AND 23 TO 26 AND COMPARATIVE EXAMPLES 3, 24, AND 25 For examining the effect on chipping resistance of the kind of topcoated film, test pieces were produced as follows by coating on an electrodeposition-coated sheet a multilayered film containing a film formed from a chippingresistant paint composition of the present invention, and were tested with respect to chipping resistance.

That is, each of the same electrodepositioncoated steel sheets as in Example 1 was coated with either of the chipping-resistant paint compositions used in Examples 1 and 2 in the same manner as in Example 1, and then subjected to intermediate coating in the same manner as in Example 1 to obtain intermediate test pieces (i). On the other hand, intermediate test pieces (ii) were prepared by directly subjecting the same electrodeposition-coated steel sheets to intermediate coating in the same manner without forming a chipping-resistant film. Each of the intermediate test pieces (i) and (ii) was coated successively with two paints (1) and (2) as the components of the following three kinds of topcoating paints ((i), (ii), and (iii)) as shown in Table 13. Thus, test pieces were obtained. The results are shown in Table 13.

Topcoating paint (i): acrylic/melamine resin type coating paint (solvent-based) (1) "Superlac M-80 Metallic Base" (manufactured by Nippon Paint Co., Ltd.) (2) "Superlac 0-130 Clear" (manufactured by Nippon Paint Co. Ltd.) Topcoating paint (ii): acrylic/melamine resin type paint (basecoat aqueous solution or dispersion, i.e., waterbased) (1) "Orga TO-H900 Metallic Base" (water-based) (manufactured by Nippon Paint Co., Ltd.) (2) "Orga TO-561 Clear" (solvent-based) (manufactured by Nippon Paint Co., Ltd.) Topcoating paint (iii): paint formulated for protecting the acid rain (1) "Orga TO-H500 Metallic Base" (solvent-based) (manufactured by Nippon Paint Co., Ltd.) (2) "Orga TO-H580 Clear" (solvent-based) (manufactured by Nippon Paint Co., Ltd.) TABLE 13 Chipping protective Topcoating Chipping Example No. primer paint resistance Ex. 1 Ex. 1 (i) E Ex. 2 Ex. 2 (i) E Ex. 23 Ex. 1 (ii) E Ex. 24 Ex. 2 (ii) E Ex. 25 Ex. 1 (iii) E Ex. 26 Ex. 2 (iii) E Comp. Ex. 3 no primer (i) B Comp. Ex. 24 no primer (li) B Comp. Ex. 25 no primer (iii) B As is apparent from the results in Table 13, the chipping resistance of the test pieces was not influenced by the topcoating paints.

EXAMPLES 1, 2, AND 27 TO 34 AND COMPARATIVE EXAMPLE 3 For examining the effect on chipping resistance of the resin component (i.e., the hydroxyl group-containing resin) for preparing the chipping-resistant paint composition of the present invention, test pieces were prepared using various kinds of resin components and tested with respect to chipping resistance.

That is, each of the same steel sheets as in Example 1 was coated to obtain test pieces in the same manner as in Example 1, except that in producing the chipping-resistant paint composition, one of the resin components shown in Table 14 was used in combination with either the hardener component synthesized in Synthesis Example 5 from a blocked polyisocyanate and apolycaprolactone polyol, as in Example 1, or the hardener component synthesized in Synthesis Example 9 from a blocked polyisocyanate and a polycaprolactone polyol, as in Example 2. Further, a test piece for Comparative Example 3 was produced without applying a chipping-resistant primer. The results are shown in Table 14.

TABLE 14 Example Hardener Chipping No. component Resin component resistance Ex. 1 Synthesis Ex. 5 HR 2024 E Ex. 2 Synthesis Ex. 9 < 6 > / < 9 > =85/15 E Ex. 27 Synthesis Ex.- 5 polyester resin < 1 > E Ex. 28 Synthesis Ex. 5 lactone-modified E polyester resin < 2 > Ex. 29 Synthesis Ex. 5 palm oil-modified E polyester resin < 3 > Ex. 30 Synthesis Ex. 5 melamine-modified E polyester resin < 4 > Ex. 31 Synthesis Ex:: 5 lactone-modified E acrylic resin A < 5 > Ex. 32 Synthesis Ex. 5 2-ethyl-1,3- E hexanediol < 7 > Ex. 33 Synthesis Ex. 5 polycaprolactone E diol < 8 > Ex. 34 Synthesis Ex. 9 < 6 > / < 8 > =85/15 E Comp. no primer B Ex. 3 As is apparent from the results in Table 14, the chipping resistance of the test pieces was not influenced by differences in kind of the resin components (i.e., hydroxyl group-containing resins) used for preparing the chipping-resistant paint compositions applied.

Notes to Table 14: < 1 > : Espel 1690 (manufactured b Hitachi Chemical Co., Ltd., Japan); nonvolatile content: 64.8%; hydroxyl value: 120; number-average molecular weight: 2,700.

< 2 > : Lactone-modified polyester resin in which a lactone backbone has been incorporated in both the main chain and side chains. Placcel CDE-9P (manufactured by Daicel Chemical Industries, Ltd.); nonvolatile content: 80%; hydroxyl value: 90; number-average molecular weight: 3,500.

< 3 > : BS 57-851-65 (manufactured by Dainippon Ink & BR< Chemicals, Inc., Japan); nonvolatile content: - 65%; hydroxyl value: 100; ns..ber-average molecular weight: 2,100.

< 4 > : BL BF-115-65X (manufactured by Dainippon Ink & BR< Chemicals, Inc.); nonvolatile content: 65%; hydroxyl value: 130; number-average molecular weight: 2,900.

< 5 > : EPA-5860 (manufactured by Daicel Chemical Industries, Ltd.); nonvolatile content: 60%; hydroxyl value: 30; number-average molecular weight: 5,000.

< 6 > : Placcel DC-2209 (manufactured by Daicel Chemical Industries, Ltd.); nonvolatile content: 50%; hydroxyl value: 12.5 (on solid basis); number average molecular weight: 11,000.

< 7 > : EHD (manufactured by Chisso Petrochemical Corp., Japan); nonvolatile content: 100%; hydroxyl value: 73; number-average molecular weight: 146.

< 8 > : Placcel 205 (manufactured by Daicel Chemical Industries, Ltd.); nonvolatile content: 100%; hydroxyl value: 212; number-average molecular weight: 530.

< 9 > : Placcel L-320AL (manufactured by Daicel Chemical Industries, Ltd.); nonvolatile content: 100%; hydroxyl value: 84; number-average molecular weight: 2,000.

EXAMPLES 1, 2, AND 35 TO 38 AND COMPARATIVE EXAMPLES 3 AND 26 Besides the test pieces of Examples 1 and 2, in which a chipping-resistant paint composition (CP) of the present invention was applied between an electrodeposited film and an intermediate coated film to form a multilayered film, four kinds of test pieces having a multilayered film were prepared by a method in which the chipping-resistant paint composition was not applied between an electrodeposited film and an intermediate coated film but was applied in accordance with the respective sequences of coating shown in the Notes to Table 15.Further, as comparative test pieces having a multilayered film, a test piece for Comparative Example 3 was prepared in the same manner as in Example 1 except that no chipping-resistant primer was applied, while a test piece having neither a chipping-resistant primer layer nor an intermediate coated film was produced in Comparative Example 26.

The test pieces obtained were evaluated with respect to chipping resistance in the same manner as in Example 1. The results are shown in Table 15.

TABLE 15 Sequence of CP Chipping Example No. CP primer acDlication resistance Ex. 1 Ex. 1 < 1 > E Ex. 2 Ex. 2 < 1 > E Ex. 35 Ex. 1 < 2 > E Ex. 36 Ex. 2 < 2 > E Ex. 37 Ex. 1 - < 3 > E Ex. 38 Ex. 2 < 3 > E Comp. Ex. 3 no primer < 4 > B Comp. Ex. 26 no primer < 5 > P Notes to Table 15: Sequence of CP application is as follows.

< 1 > : electrodeposition coating // CP coating / intermediate coating // topcoating < 2 > : electrodeposition coating // intermediate coating // CP coating / topcoating < 3 > : electrodeposition coating // CP coating / topcoating < * > < 4 > : electrodeposition coating // intermediate coating // top coating < 5 > : electrodeposition coating // topcoating < * > (Symbol "//" means "dry-on-wet" and symbol "/" means "weton-wet"; the same applied hereinafter.) Topcoating < * > is coating with a solid type polyester resin topcoating paint ("Orga G-75 White," manufactured by Nippon Paint Co., Ltd.) The chipping resistance of all of the test pieces of Examples 1, 2, and 35 to 38 was evaluated as "E".

In contrast, the test pieces of Comparative Examples 1 and 26, which applied no CP coating, showed poor chipping resistance.

In the following Examples 39 to 41, a chippingresistant paint composition (CP) of the present invention or a chipping-resistant paint composition for intermediate coating prepared using a hardener component of the present invention was applied to form a multilayered film to examine the effect on chipping resistance of the position of the chipping-resistant primer in the multilayered film.

Embodiments are explained respectively in the following Examples.

EXAMPLE 39 A dull steel sheet was subjected to electrodeposition coating in the same manner as in Example 1.

A chipping-resistant paint composition for intermediate coating (intermediate CP coating paint) to be applied on the electrodeposited film was then -prepared as follows.

That is, the blocked polyisocyanate synthesized in Synthesis Example 5 given hereinabove was mixed as a hardener component (hereinafter referred to as "component (A)") with a polyester resin ("Espel 1690"; manufactured by Hitachi Chemical Co., Ltd.) having a nonvolatile content of 64.8%, a hydroxyl value of 120, and a number-average molecular weight of 2,700 as a resin component (hereinafter referred to as "component (B)"). This mixture was further mixed with other ingredients according to the following formulation to prepare the intermediate CP coating paint.

In this intermediate CP coating paint, the molar ratio of the isocyanate groups (-23) contained in the hardener~component to the hydroxyl groups !-OS) contained in component (B) was 1:1.

Formulation for Intermediate CP Coating Paint: Components (A) and (B): 100 parts by weight in total (solid amount) Titanium dioxide : 55 parts by weight Carbon black : 2 parts by weight Anti-settling agent : 2 parts by weight Surface modifier : 1 part by weight Dibutyltin dilaurate : 1.5 parts by weight Solvent : 65 parts by weight Composition of the solvent: Solvesso 150 (manufactured by Exxon Chemical Co.)/ xylene/butyl acetate = 1/2/1 (by weight) The thus-obtained intermediate coating composition was diluted with a 1/1 (by weight) mixture of Solvesso 150 and butyl acetate as a thinner. This paint was applied on the electrodeposited film by air spraying at a thickness of 35 jim on a dry basis, and baked at 1400C for 25 minutes.

Topcoating was conducted on the intermediate CP coated film to prepare a test piece. Hence, the sequence of coating in this Example was: electrodepositioncoating // intermediate CP coating // topcoating.

The topcoating paint used above was topcoating paint (i) described hereinabove.

EXAMPLE 40 A dull steel sheet was subjected to electrodeposition coating in the same manner as in Example 1.

Subsequently, the same chipping-resistant paint composition as in Example 1 was prepared and applied on the electrodeposited film in the same manner as in Example 1 to form a CP coated film having a thickness of 10 jim on a dry basis. This CP coated film was coated, at a thickness of 25 jim on a dry basis, with a chipping-resistant paint composition for intermediate coating obtained in the same manner as in Example 39 except that the resin component was changed to a lactone-modified hydroxyl group-containing polyester resin having lactone backbone in both the main chain and side chains thereof ("Placcel CDE-9P"; manufactured by Daicel Chemical Industries, Ltd.) having a nonvolatile content of 80%, a hydroxyl value of 90, and a number-åveraae molecular weight of 3,500.Topcoating was then conducted on the intermediate CP coated film in the same manner as in Example 39 to obtain a test piece.

Hence, the sequence of coating in this Example was: electrodeposition coating // CP coating / inter mediate CP coating // topcoating.

EXAMPLE 41 A dull steel sheet was subjected to electrodeposition coating in the same manner as in Example 1.

Subsequently, the same chipping-resistant paint composition for intermediate coating as in Example 40 was applied on the electrodeposited film at a thickness of 25 Rm on a dry basis. A chipping-resistant paint composition of the present invention was applied thereon in the same manner as in Example 1 to form a CP coated film having a thickness of 10 zm on a dry basis. Topcoating was then conducted on the CP coated film in the same manner as in Example 39 to produce a test piece. Hence, the sequence of coating in this Example was: electrodeposition coating // intermediate CP coating // CP coating / topcoating.

The test pieces obtained in Examples 39 to 41 given above were evaluated with respect to chipping resistance in the same manner as in Example 1. As a result, the chipping resistance of the test pieces were evaluated as "E".

In the following Examples 42 to 44, the intermediate coating paint used in Example 1 given hereinabove ["Orga P-61-1 Gray" (polyester/melamine resin paint manufactured by Nippon Paint Co., Ltd.] was applied on an electrodeposition-coated substrate at a thickness of about 35 zm, and the thus-obtained intermediate test piece was further coated with a multi- or single-layer chippingresistant topcoated film as described below to form a multilayered film. This test piece was examined with respect to the effect on chipping resistance of the topcoated film. Embodiments are described respectively in the following Examples.

EXAMPLE 42 A dull steel sheet was subjected to electrodeposition coating in the same manner as in Example 1, and the intermediate coating paint used in Example 1 was applied thereon to form an intermediate coated film.

(Preparation of Chipping-Resistance Base Topcoating Composition) The blocked polyisocyanate synthesized in Synthesis Example 5 given hereinabove was mixed as component (A) with an acrylic resin modified with cellulose acetate butyrate (a modified acrylic resin obtained by reacting 16 parts by weight of cellulose acetate butyrate with 100 parts by weight of a styrene/methyl methacrylate/ethyl methacrylate/ethyl acrylate/2-hexylethyl methacrylate/ methyl acrylate copolymer) having nonvolatile content of 40.5%, hydroxyl value of 45 and number-average molecular weight of 11,100 as component (B), and further with other ingredients according to the following formulation to prepare a chipping-resistant base topcoating composition (hereinafter referred to as "base topcoat CP coating paint").In this base topcoat OP coating paint, the molar ratio of the isocyanate groups (-NOO) contained in component (A) to the hydroxyl groups (-OH) contained in component (B) was 1:1.

Formulation for Base Topcoat CP Coating Paint: Components (A) and (B): 100 parts by weight in total (solid amount) Titanium dioxide : 60 parts by weight Carbon black : 1 part by weight Anti-settling agent : 2 parts by weight Surface modifier : 1 part by weight Dibutyltin dilaurate : 1.5 parts by weight Solvent : 160 parts by weight Composition of the solvent: xylene/methyl isobutyl ketone/ethyl acetate = 7/2/1 (by weight) The thus-obtained base topcoat CP coating paint was diluted with a 1/1 (by weight) mixture of ethyl acetate and xylene as a thinner to give a base topcoating paint.

Topcoating was conducted in the same manner as in Example 1 using this base topcoating paint and using "Superlac 0-130" (manufactured by Nippon Paint Co., Ltd.) as a clear topcoating paint. The base topcoating paint was applied at a thickness of 15 Rm on a dry basis. The sequence of coating in this Example was: electrodeposition coating // intermediate coating // base topcoat CP coating / clear topcoat coating.

The test piece obtained was evaluated with respect to chipping resistance in the same manner as in Example 1. As a result, the dipping resistance of the test pieces was evaluated as "G".

EXAMPLE 43 A dull steel sheet was subjected to electrodeposition coating in the same manner as in Example 1, and the intermediate coating paint used in Example 1 was applied thereon to form an intermediate coated film.

(Preparation of Chipping-Resistance Clear Topcoating Paint) The blocked polyisocyanate synthesized in Synthesis Example 5 given hereinabove was mixed as component (A) with fluorine-containing resin ("Lumiflon LF9201" manufactured by Asahi Glass Co., Ltd., Japan) having nonvolatile content of 65.5%, hydroxyl value of the varnish of 52.4 and number-average molecular weight of about 7,000) component (B), and further with other ingredients according to the following formulation to prepare a chipping-resistant clear topcoating composition (referred to as "clear topcoat CP coating paint"). In this clear topcoat CP coating paint, the molar ratio of -NCO/-OH was 1:1.

Formulation for Clear Topcoat CP Coating Paint: Components (A) and (B): 100 parts by weight in total (solid amount) Surface modifier . 2 parts by weight Ultraviolet absorber : 1 part by weight Antioxidant : 1 part by weight Dibutyltin dilaurate : 1.5 parts by weight Solvent : 95 parts by weight Composition of the solvent: Solvesso 150/xylene = 1/2 (by weight) Topcoating was conducted in the same manner as in Example 42 using "Superlac M-80 Metallic Base" (manufactured by Nippon Paint Co., Ltd.) as a base topcoating paint and using the above-described clear topcoat CP coating paint as a clear topcoating paint. The clear topcoat CP coating paint was applied at a thickness of 35 zm on a dry basis.

The sequence of coating in this Example was: electrodeposition coating // intermediate coating // base topcoat coating / clear topcoat CP coating.

The test piece obtained was evaluated with respect to chipping resistance in the same manner as in Example 1. As a result, the chipping resistance of the test pieces was evaluated as "G".

EXAMPLE 44 A dull steel sheet was subjected to electrodeposition coating in the same manner as in Example 1, and the intermediate coating paint used in Example 1 was applied thereon to form an intermediate coated film.

(Preparation of Chipping-Resistant Solid Topcoating Paint) The blocked polyisocyanate synthesized in Synthesis Example 5 given hereinabove was mixed as component (A) with a palm oil-modified hydroxyl groupcontaining polyester resin ("BS 57-1086N," manufactured by Dainippon Ink & Chemicals, Inc.) having nonvolatile content of 65%, hydroxyl value of 130 and number-average molecular weight of 3,179 as component (B), and further with other ingredients according to the following formulation to prepare a chipping-resistant solid topcoating composition (referred to as "topcoat CP coating paint"). In this topcoat CP coating paint, the molar ratio of -NCO/-OH was 1:1.

Formulation for Topcoat CP Coating Paint: Components (A) and (B): 100 parts by weight in total (solid amount) Titanium dioxide : 50 parts by weight Carbon black : 1 part by weight Anti-settling agent : 2 parts by weight Surface modifier : 1 part by weight Dibutyltin dilaurate : 1.5 parts by weight Solvent : 80 parts by weight Composition of the solvent: Solves so 150/xylene/methyl isobutyl ketone = 2/5/1 (by weight) The topcoat CP coating pant described above was applied on the intermediate coated film formed above, and was then baked. The topcoat CP coating paint was applied at a thickness of 35 zm on a dry basis. Hence, the sequence of coating in this Example was: electrodeposition coating // intermediate coating // topcoat CP coating.

EXAMPLE 45 The same dull steel sheet as in Example 1 was subjected to electrodeposition coating and baking in the same manner as in Example 1.

The same chipping-resistance coating paint (CP) as in Example 1 was applied on the electrodeposited film at a thickness of 5 zm on a dry basis.

After the paint applied wa allowed to set for about 2 minutes, an intermediate coating paint ("Orga P-611 Gray," manufactured by Nippon Paint Co., Ltd.; polyester/melamine resin coating paint) was applied by air spray coating at a thickness of about 35 Fm on a dry basis (by the wet-on-wet method), and was baked at 1400C for 25 minutes.

The same chipping-resistant solid topcoating paint (topcoat CP coating paint) as in Example 44 was applied on the intermediate coated film at a thickness of about 35 zm on a dry basis.

The sequence of coating in this Example was: electrodeposition coating // CP coating / intermediate coating // topcoat CP coating.

The test piece obtained was evaluated with respect to chipping resistance in the same manner as in Example 1. As a result, the chipping resistance of the test pieces was evaluated as "E".

EXAMPLE 46 A test piece was produced in the same manner as in Example 45, except that the chipping-resistant coating paint (CP) and intermediate coating paint both used in Example 1 were applied in the reversed order. The test piece obtained was evaluated with respect to chipping resistance in the same manner as in Example 1. As a result, the chipping resistance of the test pieces was evaluated as "E".

The sequence of coating in this Example was: electrodeposition coating // intermediate coating // CP coating / topcoat CP coating.

COMPARATIVE EXAMPLE 27 An electrodeposition-coated dull steel sheet was coated, in the same manner as in Exale 42, with the intermediate coating paint used in Example 7 to obtain an intermediate test piece having an inte=eiate coated film.

This intermediate test piece was topcoated, under the same conditions as in Example 1, first with the same base topcoating paint as in Example 43, i.e., "Superlac M-80 Metallic Base" (manufactured by Nippon Paint Co., Ltd.), in place of the chipping-resistant base topcoating composition used in Example 42, and then with the same clear topcoating paint as in Example 42, i.e., "Superlac 0-130" (manufactured by Nippon Paint Co., Ltd.). The base topcoating paint was applied at a thickness of 15 zm on a dry basis.

The sequence of coating in this Example was: electrodeposition coating // intermediate coating // base topcoat coating / clear topcoat coating.

The test piece obtained was evaluated with respect to chipping resistance in the same manner as tit Example 1. As a xesalt,-tilQ chipping resistance of the test pieces was evaluated as "B".

COMPARATIVE EXAMPLE 28 The same dull steel sheet as in Example 1 was subjected to electrodeposition coating and baking in the same manner as in Example 1, and then coated with a solid type polyester resin topcoating paint ("Orga G-75 White," manufactured by Nippon Paint Co., Ltd.) to obtain a test piece. This test piece was evaluated with respect to chipping resistance in the same manner as in Example 1. As a result, the chipping resistance of the test piece was evaluated as "P".

The results of Examples 39 to 46 and Comparative Examples 27 and 28 are shown in Table 16 below.

TABLE 16 Example Hardener Resin Sequence Chipping No. component component of coating resistance Ex. 39 Synthesis < 1 > < 5 > E Ex. 5 Ex. 40 Synthesis < 1 > < 6 > E Ex. 5 Ex. 41 Synthesis < 1 > < 7 > E Ex. 5 Ex. 42 Synthesis < 2 > < 8 > G Ex. 5 E;. 43 Synthesis < 3 > < 9 > G Ex. 5 Ex. 44 Synthesis < 4 > < 10 > G Ex. 5 Ex. 45 Synthesis < 4 > < 11 > E Ex. 5 Ex. 46 Synthesis < 4 > < 12 > E Ex. 5 Comp. Ex. 27 no primer < 13 > B Comp.Ex. 28 no primer < 14 > P Notes td-Table 16: [Resin Component] < 1 > : Espel 1690 (manufactured by Hitachi Chemical Co., Ltd.) < 2 > : Modified acrylic resin obtained by reacting cellulose acetate butyrate with a methacrylate copolymer < 3 > : Lumiflon LF9201 (fluorine-containing resin manufactured by Asahi Glass Co., Ltd.) < 4 > : Palm oil-modified hydroxyl group-containing polyester resin "BS 57-1086N" (manufactured by Dainippon Ink & Chemicals, Inc.) [Sequence of Coating] < 5 > : Electrodeposition coating // intermediate CP coating // tooating < 6 > : Electrodeposition coating // CP coating / intermediate CP coating // topcoating < 7 > : Electrodeposition coating // intermediate CP coating // CP coating / topcoating < 8 > :Electrodeposition coating // intermediate coating // base topcoat CP topcoating / clear topcoat coating < 9 > : Electrodeposition coating // intermediate coating // base topcoat coating / clear topcoat CP coating < 10 > : Electrodeposition coating // intermediate coating ~ // topcoat CP coating < 11 > : Electrodeposition coating // CP coating / intermediate coating // topcoat CP coating < 12 > : Electrodeposition coating // intermediate coating // CP coating / topcoat CP coating < 13 > : Electrodeposition coating // intermediate coating // base topcoat coating / clear topcoat coating < 14 > :Electrodeposition coating // white topcoat (one coat solid type) coating As is apparent from the results of chipping resistance evaluation shown in Tables 15 and 16, the CP coated films formed from the chipping-resistant paint compositions of the present invention were effective for improving chipping resistance regardless of the positions where the CP coated films had been formed.

As described above, the hardener component of the chipping-resistant paint composition cE the present invention contains a modified polsrisocyanate compound (d3 which has polycaprolactone skeleton incorporated in the molecular chain thereof, because the polyisocyanate compound (d) has been obtained by the urethane-forming reaction of a mixture of two or more polycaprolactonemodified polyols (c) having different number average molecular weights with a mixture of two essential ingredients, i.e., an aliphatic or alicyclic polyisocyanate (a) and a cyclic trimerized isocyanate (b) obtained from the po1ysocyanate (a).

The hardener compound can be used in combination with any of a wide range of hydroxyl group-containing resins to constitute a chipping-resistant paint composition, which provides a highly flexible film.

Consequently, the chipping-resistant paint composition of the present invention, when used for forming a constituent film of a multilayered film applied on outside plates of automobile, not only imparts satisfactory chipping resistance to the multilayered film, but also enables wet-on-wet coating and gives a satisfactory film appearance.

As compared with conventional chipping primers, the chipping-resistant paint composition of the present invention can be formulated to have a low solvent content, in which formulation is advantageous from the standpoint of coping with the VOC regulations.

The composition of 'he present invention has another advantage that it facilitates coating operations and the maintenance of the coating line.

Further, it is possible to attain reduction of a solvent amount by using the chipping-resistant composition of the present invention in combination with a water-based paint. Furthermore, when used in combination with a paint formulated for protection against acid rain, the composition of the present invention enables the formation of a film having satisfactory durability.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

1. A chipping-resistant paint composition comprising as major components (A) a blocked polyisocyanate obtained by mixing (i) an aliphatic or alicyclic polyisocyanate (a) and a cyclic trimerized polyisocyanate polymer (b) obtained from said polyisocyanate (a) with (ii) two or more kinds of polycaprolactone-modified polyols (c) having different number-average molecular weights, reacting ingredient (i) with ingredient (ii) by means of a urethane-forming reaction to yield a modified polyisocyanate compound (d) having a ratio of the molar concentration of isocyanurate groups to that of urethane groups of from 5/5 to 1/9, and blocking the residual active isocyanate groups of the modified polyisocyanate compound, said blocked polyisocyanate having a content of effective isocyanate groups of from 1 to 10 parts by weight per 100 parts by weight of the blocked polyisocyanate compound on a solid basis, and (B) at least one hydroxylated resin (e) having two or more hydroxyl groups per molecule.

2. The chipping-resistant paint composition as claimed in claim 1, wherein the two or more kinds of polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) each has a numberaverage molecular weight of from 250 to 3,500.

3. The chipping-resistant paint composition as claimed in claim 1, wherein the two or more kinds of polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) satisfy the following equation ; MAX - Mn uN = 750 to 2,700 where Mi is the number-average molecular weight of the polyol component of the polyols (c) which has the highest number-average molecular weight and M,nw is the number- average molecular weight of the polyol component of the polyols (c) which has the lowest number-average molecular weight.

4. The chipping-resistant paint composition as claimed in any preceding claim wherein the two or more kinds of polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) comprise a mixture of diols or a mixture of a triol and a dull.

5. The chipping-resistant paint composition as claimed in claim 1, 2 or 3 wherein the two or more kinds of polycaprolactone-modified polyols (c) used for synthesizing the modified polyisocyanate compound (d) comprise a mixture of a polycaprolactone triol and a polycaprolactone diol in a weight ratio of from 0/1 to 10/1.

6. The chipping-resistant paint composition as claimed in any preceding claim wherein the molar ratio of the sum of the aliphatic or alicyclic polyisocyanate (a) and the cyclic trimerized polyisocyanate (b) obtained from the polyisocyanate (a) to the polycaprolactone-modified polyols (c) is from 1.5/1 to 6/l.

7. The chipping-resistant paint composition as claimed in any preceding claim, wherein the molar ratio of the sum of the aliphatic or alicyclic polyisocyanate (a) and the cyclic trimerized polyisocyanate (b) obtained from the polyisocyanate (a) to the polycaprolactone-modified polyols (c) is from 2/1 to 4/1.

8. The chipping-resistant paint composition as claimed in any preceding claim wherein the modified polyisocyanate compound (d) in component (A) has a ratio of the molar concentration of isocyanurate groups to that of urethane groups of from 4/6 to 2/8.

9. The chippng-resstant paint composition as claimed in any preceding claim wherein the blocked polyisocyanate compound as component (A) has a content of effective isocyanate groups of from 2 to 8 parts by weight per 100 parts by weight of the blocked polyisocyanate compound on a solid basis.

10. The chipping-resistant paint composition as claimed in any preceding claim wherein the proportion of the aliphatic or alicyclic polyisocyanate (a) to the cyclic trimerized polyisocyanate (b) obtained from the polyisocyanate (a) is from 0.5/1 to 25/1 by weight.

11. The cffipping-resistant paint composition as claimed in any preceding claim wherein the proportion of the aliphatic or alicyclic polyisocyanate (a) to the cyclic trimerized polyisocyanate (b) obtained from the polyisocyanate (a) is from 1.5/1 to 7/1 by weight.

12. The chipping-resistant paint composition as claimed in any preceding claim wherein the aliphatic or alicyclic polyisocyanate (a) used for synthesizing the modified polyisocyanate compound (d) comprises at least either of hexamethylene diisocyanate and isophorone diisocyanate.

13. The chipping-resistant paint composition as claimed in any preceding claim wherein the cyclic trimerized polyisocyanate (b) obtained from the aliphatic or alicyclic polyisocyanate (a) is an isocyanurate obtained from at least either of hexamethylene diisocyanate and isophorone diisocyanate.

14. The chipping-resistant paint composition as claimed in any preceding claim wherein a blocking agent is used for synthesizing component (A) and said blocking agent is at least one member selected from the group consisting of MEK oxime, lactam, and ethyl acetoacetate.

15. The chipping-resistant paint composition as claimed in any preceding claim wherein the molar ratio of the isocyanate groups contained in the modified polyisocyanate compound (d) to the hydroxyl groups contained in the hydroxyl group-containing resin (e) of component (B) is from 3/7 to 7/3.

16. The chipping-resistant paint composition as claimed in any preceding claim wherein the hydroxyl group-containing resin (e) of component (B) having two or more kinds of hydroxyl groups per molecule is an acrylic polyol or a polyester polyol or a lactone-modified polyester polyol.

17. The chipping-resistant paint composition as claimed in any of claims 1-15 wherein the hydroxyl group-containing resin (e) of component (B) having two or more kinds of hydroxyl groups per molecule is a lactone-modified acrylic polyol.

18. The chipping-resistant paint composition as claimed in any of claims 1-15 wherein the hydroxyl group-containing resin (e) of component (B) having two or more kinds of hydroxyl groups per molecule is a combination of an acrylic polyol or a polyester polyol with a polycaprolactone diol or triol.

19. A method for forming a chipping-resistant multilayered film which comprises applying a chippingresistant paint composition comprising as major components (A) a blocked polyisocyanate obtained by mixing (i) an aliphatic or alicyclic polyisocyanate (a) and a cyclic trimerized polyisocyanate polymer (b) obtained from said polyisocyanate (a) with (ii) two or more kinds of polycaprolactone-modified polyols (c) having different number-average molecular weights, reacting ingredient (i) with ingredient (ii) by means of a urethane-forming reaction to yield a modified polyisocyanate compound (d) having a ratio of the molar concentration of isocyanurate groups to that of urethane groups of from 5/5 to 1/9, and blocking the residual active isocyanate groups of the modified polyisocyanate compound, said blocked polyisocyanate having a content of effective isocyanate groups of from 1 to 10 parts by weight per 100 parts by weight of the blocked polyisocyanate compound on a solid basis, and (B) at least one hydroxylated resin (e) having two or more hydroxyl groups per molecule; in either (1) a coating process comprising electrodeposition coating, intermediate coating, and topcoating to form at least one film selected from the group consisting of (a) to (e): (a) a film formed between an electrodeposited film and an intermediate coated film, (b) a film formed between an intermediate coated film and a topcoated film, (c) a topcoated film when the topcoated film is of a one-layer type, (d) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type, and (e) an intermediate coated film; or (2) a coating process comprising electrodeposition coating and topcoating to form at least one film selected from the group consisting of (f) to (h): (f) a film formed between an electrodeposited film and a topcoated film, (g) a topcoated film when the topcoated film is of a one-layer type, and (h) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type.

20. A coated article having a chipping-resistant multilayered film formed by a method comprising applying the chipping-resistant paint composition comprising as major components (A) a blocked polyisocyanate obtained by mixing (i) an aliphatic or alicyclic polyisocyanate (a) and a cyclic trimerized polyisocyanate polymer (b) obtained from said polyisocyanate (a) with (ii) two or more kinds of polycaprolactone-modified polyols (c) having different number-average molecular weights, reacting ingredient (i) with ingredient (ii) by means of a urethane-forming reaction to yield a modified polyisocyanate compound (d) having a ratio of the molar concentration of isocyanurate groups to that of urethane groups of from 5/5 to 1/9, and blocking the residual active isocyanate groups of the modified polyisocyanate compound, said blocked polyisocyanate having a content of effective isocyanate groups of from 1 to 10 parts by weight per 100 parts by weight of the blocked polyisocyanate compound on a solid basis, and (B) at least one hydroxylated resin (e) having two or more hydroxyl groups per molecule; on an automotive body in either (1) a coating process comprising electrodeposition coating, intermediate coating, and topcoating to form at least one film selected from the group consisting of (a) to (e): (a) a film formed between an electrodeposited film and an intermediate coated film, (b) a film formed between an intermediate coated film and a topcoated film, (c) a topcoated film when the topcoated film is of a one-layer type, (d) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type, and (e) an intermediate coated film; or (2) a coating process comprising electrodeposition coating and topcoating to form at least one film selected from the group consisting of (f) to (h): (f) a film formed between an electrodeposited film and a topcoated film, (g) a topcoated film when the topcoated film is of a one-layer type, and (h) a base coated film and/or clear coated film of a topcoating when the topcoated film is of a two-layer type.

21. A method according to claim 19 wherein the chippingresistant paint composition is according to any of claims 1-18.

22. A coated article according to claim 20 wherein the chipping-resistant paint composition is according to any of claims 1-18.

23. A chipping resistant paint composition, a method for forming a chipping-resistant multilayered film or a coated article, wherein said composition, said method, or the coating on said article is substantially as any herein described with reference to and as exemplified in examples 1 to 46.