AU699083B2 - Coating composition - Google Patents

Description

COATING COMPOSITION' BACKGROUND OF THE INVENTION Field of the invention The present invention relates, in general, to a coating composition and, more particularly, an one package type coating composition for automobile, applicable to a top clear coat and superior in appearance, solvent resistance, chemical resistance, thermal resistance and weathering resistance.

Description of the Prior Art There are a variety of coating resins for automobile by their uses. Particularly, as coats for automobile, there have generally been used a polyester resin, an alkyd resin or a thermosetting acrylic resin, in combination with a curing agent of alkoxy methyl melamine resin. By virtue of weathering resistance which is indispensable to clear coat, a composition system of acrylic resin in combination of the S11 curing agent of alkoxy methyl melamine resin has been preferred to other systems of the alkyd or the polyester resin in combination of said curing agent.

Such a coating system as acryl-alkoxy methyl melamine resin is good in clearness, adherence and water resistance but I :25 considerably poor in chemical resistance, especially acid i L _J resistance, relative to urethane resin-based coat for automobile, that is, a curing system consisting of acrylic resin and urethane resin. Particularly, if an H/solid type is adopted for the acryl-alkoxy methyl melamine resin system in order to overcome environment problems and to reinforce clearness, the system may become very vulnerable to acid and weathering.

Poor chemical resistance (acid resistance) of the acrylalkoxy methyl melamine resin system which is now most used for a top coat for automobile is attributed to a fact that the ether bond structure itself produced by reaction of the OH group of the acrylic resin with the alkoxy group of the melamine resin, such as methoxy,' ethoxy, butoxy or i-butoxy, is highly prone to be hydrolyzed by acid, for example, acid rain. Accordingly, this acid hydrolysis is nothing else but etching phenomenon in the acryl-alkoxy methyl melamine resin system. In other words, in at least two chemical mechanisms by which a curing system is accomplished for a coat film, bonds vulnerable to chemicals are always of problem.

."20 Generally, the stability of chemical bond in the coating is; as follows: carbon-carbon>amide>urethane, urea>ether>ester>ether of acryl-melamine. Accordingly, the i conventional art employing the ether bond as main crosslink structure has a drawback in chemical resistance.

2 5 The H/solid type coat which has generally been used for 2 I 2 "i top clear coat for automobile is more easily etched by acid than L/solid type coat, giving rise to increasing the problems of acid resistance and weathering resistance.

To solve the problems, a coat system of polyester resinaliphatic polyisocyanate was suggested. However, this system has difficulty in painting work because the components should be mixed with each other just before use. For the mixing, a general two package coating equipment is necessary, requiring additional facility expense.

In addition, aliphatic isocyanate may cause a yellowing phenomenon after painting work due to decomposition of residual isocyanate group by moisture and formation of primary amine. What is still worse, an isocyanate curing agent, as well known, is harmful to human body.

SUMMARY OF THE INVENTION Therefore, an object of the present invention to overcome the above problems encountered in prior arts and to provide a Sdi 20 coating composition for automobile which is superior in appearance, solvent resistance, chemical resistance, thermal resistance and weathering resistance by harmonizing thermal fluidity of resin, crosslinking reaction rate and resin viscosity therein.

In order to accomplish- the above object, the coating I 3 7 4 composition of the present invention employs an acrylic resin prepared with acrylic monomers which are relatively good in appearance and chemical resistance with the storage stability basically required by a coat, instead of conventional acrylic resin, and a one package type block isocyanate resin. The curing system of blending the acryl resin with the one package type block isocyanate resin produces a coat film superior in chemical resistance and weathering resistance as well as in storage stability.

In accordance with the present invention, the coating composition comprises a blend of acrylic resin and block isocyanate resin in combination with other additives, wherein the acrylic resin is prepared by solution-polymerizing conventional acrylic monomer with acrylic monomer having carboxyl group, hydroxyl group and silane group and the block isocyanate resin is prepared by masking aliphatic isocyanate with a blocking agent and modifying the masked aliphatic iscoyanate with alcohols.

More particularly, there is provided according to a broad form of the invention a single-package coating composition for a top clear coat for automobiles, comprising an acrylic resin and a blocked isocyanate resin, wherein an acrylic resin is prepared by reacting a mixture comprising 20 to 70% by weight of an alkyl acrylate represented by the following formula I I I CHi 2

=C-COOR

2 6 *6 6 6 66 4 6* ttl wherein R 1 is a hydrogen atom or a methyl group, and R 2 is an alkyl group containing 1 to 14 carbon atoms; to 40% by weight of an aromatic vinyl compound represented by the following formula II

R-CH==CH

II

wherein R is an aromatic group; and 5 to 40% by weight of a reactive monomer having a hydroxyl, carboxyl or silane group with 0.01 to 10.0% by weight of an initiator, and the blocked isocyanate resin is prepared by blocking an aliphati isocyanate with a malonate and modifying the blocked aliph tic isocyanate with diols.

Improvement in chemical resistance by use of block isocyanate resin has been 30 revealed in much literature and many documents, most of which teach that aliphatic itocyanates are blocked in oxime types. However, such arrangements result in deterioration of interlayer adherence and situations where repainting is required, and are disadvantageous in that a yellowing phenomenon occurs upon over-baking.

c i r u*-

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*i i 1 I[N:\BFF0O1705:ssd In an effort to surmount the disadvantages, there is suggested a new process for preparing a block isocyanate resin, ir accordance with the present invention. Following is of the new process.

The block isocyanate resin used in the present invention is prepared.using a non-yellowing type malonate as a blocking agent to mask the NCO group of isocyanate. In detail, an isocyanate mixture consisting of isoporone diisocyanate (hereinafter referred to as "IPDI") and hexamethylene diisocyanate (hereinafter referred to as '"HMDI")-monomer good in appearance and IPDI and HMDI-trimer superior in chemical resistance in a proper ratio is blocked with malonate, modified with alcohol, and then, polymerized, so as to prepare the block isocyanate resin. The use of the monomer/trimer mixture is because the IPDI and HMDI-monomer makes the formed 'coating good in appearance while the IPDI and HMDI-trimer improves chemical resistance. The modification with alcohol provides the isocyanate resin with improvement in flexibility, chipping resistance, interlayer adherence, appearance, 20 chemical resistance, and storing stability.

It is preferred that the malonate used to block the isocyanate mixture is methyl malonate.

Preferred alcohols include tone-polyol, glycol, and polypropylene glycol.

S 25 To improve fluidity and slip property of a coat employing i i T block isocyanate resin and acry'ic resin, the acrylic resin may be prepared by partially modifying acrylic monomer with secondary hydroxyl group and silane group.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a coat composition comprising an acrylic resin and a block isocyanate resin as a curing agent for the acrylic resin.

For preparation of the acrylic resin, the double bonds of acryl monomers are subjected to radical reaction in an aromatic solvent with an initiator. The prepared acrylic resin according to the present invention has an acid value of approximately 5 to approximately 30 mg KOH/g and a hydroxy value of approximately 50 to approximately 200 mg KOH/g with *e a number average molecular weight ranging from approximately 500 to approximately 10,000. The temperature of glass Stransition of the acrylic resin is in a range of approximately -10 to approximately -70 The acrylic resin used in the Spresent invention has a structure of branched chain or graft polymer.

S* 4 i With regard to the block isocyanate resin, a mixture of IPDI and HMDI-monomer and IPDI and HMDI-trimer is masked by ii 5 malonate, a blocking agent and then, modified with alcohols.

S6 00 r c

I

In formulating the coating composition according to the present invcntion, considerable care are taken of the amount of both the blcck isocyanate resin and the acrylic resin because the former serves as a curing agent depending on the hydroxy value of the latter. Since the coating composition of the present invention can be used for a top clear coat for automobile, it is important to select appropriate kind and amount of the block isocyanate resin having great influence on yellowing and weathering resistance. In addition, an excess of acrylic resin causes deterioration in flexibility and mechanical physical properties of the coat. Therefore, in consideration of component resins' respective characteristics, it is demanded that the amounts of the component resins be so appropriately controlled as to valance the characteristics and to reciprocally supplement each other, thereby expressing the best physical properties of the resulting coat.

.o 4.

*Now, a more detailed description will be made for the resins and the coating composition in conjunction with preparation thereof.

.20 A. Preparation of acrylic resin SThe acrylic resin used in the coating composition of the present invention has one or two carboxyl groups at its ends 5 and has preferably an acid value of approximately 5 to 30 mg 7 Ki_ KOH/g and a hydroxy value of approximately 50 to approximately 200 mg KOH/g. For example, if the acid value is below 5, the resulting coat may be problematic in curing and adherence strength. On the other hand, the acid value exceeding 30 may drive an adduct reaction upon reacting with the block isocyanate resin, which deleteriously affects storing stability.

As previously mentioned, the hydroxy value of the acrylic resin is preferably in a range of approximately 50 to approximately 200 mg KOH/g. For example, if an acrylic resin with too less hydroxy value is used, the crosslink density of the resulting coat is lowered, which reduces chemical resistance and corrosion resistance of coating. On the other hand, the hydroxy value exceeding 200 increases the crosslink density too much, deteriorating yellowing, crack resistance and chipping resistance of coating film.

9* S, To improve slip property and scratch resistance, silane group may be introduced into the acrylic resin.

The acrylic monomers used to prepare the acrylic resin of 20 the present invention essentially consist of: Si: an alkyl acrylate represented by the following formula I: S i !I

CH

2

C-COOR

2 I wherein R, is a hydrogen atom or a methyl group, and

R

2 is an alkyl group containing 1 to 14 carbon atoms; an aromatic vinyl compound represented by the following formula II: R-CH= CH 2 I wherein R is an aromatic group; and a reactive monomer.

The acrylic monomer of the formula I includes methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-methylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobuty.

methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, 0 lauryl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, and cellosolve methacrylate. Of them, methyl a* acrylate, ethyl acrylate, cyclohexyl acrylate, methyl Amethacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, cellosolve methacrylate and lauryl methacrylate are preferred and may be used alone or in combination.

9 The acrylic monomer of formula I is preferably contained S in an amount of 20 to 70 by weight based on the total weight of the acrylic resin and, more preferably, 30 to 50 by weight. For example, if too little alkyl acrylate is used.

the coat has a weak adherence strength with regard to base material and cannot exhibit basic physical properties of acrylic group itself. On the other hand, if the amount of the acrylic monomer of formula I exceeds 70 by weight, the coating is in lack of flexibility and thus, becomes inordinately hardened as well as is problematic in chipping.

That is, in order to express the characteristic properties of the acrylic monomer of formula I, it is required that its amount along with its glass transition temperature be selected so properly as to improve flexibility, hardness and appearance of the resulting coating film.

Another acrylic monomer used in the acrylic resin of the present invention, represented by the formula II, includes Ct styrene, a-methyl styrene, benzyl(meth)acrylate, phenyl(meth)acrylate, and vinyl toluene, and they may be used alone or in combination.

.I In the acrylic resin, the acrylic monomer of formula II preferably amounts to 10 to 40 by weight based on the total weight of the acrylic resin and, more preferably, 10 to 30 by weight. It is used to control the physical properties of the acrylic resin and to adjust the total price of the coat.

1 However, excessive amount of more than 40 by weight decreases weathering resistance.

As the reactive monomer constituting the acrylic resin, there are exemplified methacrylic acid hydroxyl methyl, methacrylic acid hydroxyl ethyl, methacrylic acid hydroxyl propyl, methacrylic acid hydroxyl butyl, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, vinyl trichloro silane, vinyl tri(2-methoxy-ethoxy)silane, vinyl triethoxy silane, vinyl trimethoxy silane, 3methacryloxypropyl trimethoxy silane, allyl trimethoxy silane, 1-(3-methacryloxypropyl)-1,1,3,3,3-pentamethyl disiloxane, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, t-butyl-aminoethyl acrylate, iso-butoxymethyl acrylainide, n-butoxymethyl acrylamide and acrylamide. The reactive monomer brings about an effect of improving pigment dispersion when preparing the coat. At least one species selected from the exemplary reactive monomers is used in an amount of 5 to 40 by weight based on the total weight of the acrylic resin.

There are various processes for preparing the acrylic S"r resin. Herein, a solution polymerization process which is one of the most typical processes is employed and believed to be 2 m ost appropriate.

In the solution polymerization process, a radical reaction is executed with an initiator. As this initiator, *1 i *hh I there may be employed an azo compound, such as azobisisobutyronitrile and azobisdimethylvaleronitrile, or a peroxide compound, such as benzoyl peroxide, tertiary-butyl hydroperoxide, tertiary-butyl peroxibenzoate, ditertiary-butyl peroxide, cumene hydroperoxide, dicumene peroxide and laurodiperoxide. The initiator is used in an amount of 0.01 to 10 by weight based on the total weight of the acrylic resin.

As a solvent for the solution polymerization process, an aliphatic or aromatic hydrocarbon solvent is used. Preferred organic solvents include hydrocarbon solvents, such as heptane, toluene and xylene, ester solvents, such as ethyl acetate, n-butyl acetate, isobutyl acetate and methylcellosolve acetate, ketone solvents, such as methylethyl ketone, methylisobutyl ketone and methylamyl ketone, alcohol t solvents, su'h as ethanol, isopropyl alcohol, n-butanol, s- 4 t 6; «t butanol and asobutyl alcohol, and ether solvents, such as n- "I butyl ether and ethylene glycol monoethylether. These S* solvents may be used alone or in combination.

,*20 Solution polymerization is usually carried out within a reflux temperature range of a solvent employed, and the reaction time is generally in a range of 5 to 15 hours. In thg< present invention, a mercaptan-based polymerization i modifier is used to prevent the acrylic resin from having an OI W- S 45 excessive molecular weight. Preferred polymerization modifier I 12 12 awn_ includes n-buityl-mercaptan, n-acrylmercaptan, n-dodecyl mercaptan, t-butyl mercaptan, 3-ethoxy-propyl-mercaptan and noctyl-mercaptan, and its amount is not more than 1.0 by Weight.

B. Preparation of Block Isocyanate Resin .4 4*

I.

Sr As mentioned hereinbefore, the coating composition comprises an acrylic resin and a block isocyanate resin which is used as a curing agent for the acrylic resin.

In accordance with the present invention, the block isocyanate resin is prepared by masking isocyanate with a blocking agent, modifying the masked isocyanate with an alcohol and polymerizing the alcohol-modified isocyanate.

Existing block isocyanate resins have been used for prior deposition and middle coating owing to such reasons as previously mentioned rather than for a c.ear coating. On the contrary, the block isocyanate resin of the present invention S can be in harmony with a top clear coatinc for automobile.

.20 Also, it is significantly improved in chemical resistance and crack resistance without affecting appearance of the resulting coating film.

r The polyisocyanate to be used as a curing agent for the acrylic resin consists mainly of non-yellowing type with A5 supegior weathering resistance, in accordance with the present II S 13 S S. j t 'St r Li_ i i s 1Ty i invention. In addition, the polyisocyanate has a number average molecular weight of approximately 500 to approximately 3,000 with NCO moiety amounting to 5 to 50 and 1 to isocyanate groups at its terminal. For preparing the polyisocyanate, such aliphatic isocyanate as hexamethylene diisocyanate monomer, hexamethylene diisocyanate trimer (buret type), hexamethylene diisocyanate trimer (cycle type), isoporone diisocyanate monomer and isoporone diisocyanate trimer may be used.

As the blocking agent to modify the isocyanate, it is preferred to use malonates which are of one package type, superior in storing stability at ordinary temperatures and "C and can be dissociated at low temperatures, and more preferred to use diethyl malonate.

Like the acrylic resin, the block isocyante resin is prepared in a solution polymerization process. In the solution pblymerization process, there is employed a solvent, such as aromatic solvent, ether solvent, ketone solvent and the mixture thereof.

At early time of the process, the isocyanate is masked with the blocking agent. Usually, this reaction is executed at a temperature of about 30 to about 100 Masking ratio of the isocyanate with the blocking agent is preferably in a range of 50 to 90 For example, if the masking ratio is less than 50 too little isocyanate is dissociated, lowering 14 J. Y crosslink density of the resulting coating film which may finally be disadvantageous in chemical resistance and hardness. On the other hand, if the masking ratio is more than 90 there is little effect of introducing intermediate, which leads to depressing leveling and gloss of the coat film.

Following completion of the masking of isocyanate with the blocking agent, modification step is undertaken by use of alcohol, such as polyglycol and the like, in accordance with the present invention. At the moment, the modification ratio is preferably in a range of approximately 10 to approximately and more preferably approximately 15 to approximately For' example, if too little modified, flexibility, interlayer adherence and chemical resistance are problematic.

On the other hand, if too much modified, the coat film becomes 15 too much hardened.

jg C. Preparation of Coating Composition for Automobile Using the acrylic resin and the curing agent of the block isocyanate resin prepared, a coating composition for Sautomobile is prepared in a usual manner. The curing agent is added preferably in an amount of approximately 0.9 to

K

approximately 1.5 equivalent based on the unit equivalent of the acrylic resin, and ibre preferably approximately 1.0 to approximately 1.2 equivalent, in accordance with the present

_I

invention. For example, if too little curing agent is used, the curing of the acrylic resin is so insufficient as to make mechanical physical properties and solvent resistance of the coat film poor. On the other hand, if too much curing agent is used, not only poor is surface appearance of the resulting coat film, but spray work with the coating composition is difficult.

In addition to the acrylic resin and the curing agent of the block isocyanate resin, the coating composition for automobile may comprise inorganic and organic pigment in combination with other additives, such as flowing agent, leveling agent, UV absorbent, stabilizer and the like. In this case, it may be prepared in a usual process for the H o preparation of coating composition for automobile.

15 The following are of the properties of the coating g composition for automobile according to the present invention.

First, since the curing temperature of the coating composition of the present invention is lower than that of existing acryl-melamine resin, the former which was subjected to curing reaction even under the condition of 130 'C x min. exhibits similar mechanical physical properties, such as B, appearance, impact resistance and flexibility, and superior S° t thermal resistance, weathering resistance and acid resistance, V to those of the latter.

NExt, a coating composition which is prepared by blending 16 \1\1 linear acryl and graft acryl resins with the block isocyanate copolymer in such an amount that the equivalent ratio of the block isocyanate copolymer to the acryl resins is in a range of 0.9 to 1.5 is similar to the existing acryl-melamine resin in storing stability at temperatures ranging from 50 to 60 °C and superior to the existing one in thermal fluidity and leveling and gloss of coat film.

Finally, although a coat film of the coating composition which is cured in the above curing system is harder relative to that of the conventional one, it is superior to the conventional paint film in chipping resistance, slip property and scratch resistance as well as exhibits better yellowing upon over-baking, interlayer adherence, appearance and repaintability than existing block isocyanate articles do.

1 ^5 The preferred embodiments of the present invention will now be further described with reference to specific examples.

EXPERIMENTAL PART PREPARATION EXAMPLE 1 Preparation of Acrylic Resin (A-l) l I *140 g of methyl methacrylate, 140 g of n-butyl I e methacrylate, 140 g of styrene, 70 g of ethylhexyl acrylate, S 25 21 g of acrylic acid, 189 g of hydroxylpropyl methacrylate, i17 a and 50 g of vinyl trichloro silane were mixed with one another and then, added with 35 g of di-tertiary-butyl peroxide, an initiator and with 2.4 g of N-octyl-mercaptan, a polymerization modifier. This reaction mixture was subjected to dropping reaction in 280 g of SOLVESSO 100 for 3 hours.

Thereafter, reflux was executed for 2 hours. 1 g of ditertiary-butyl peroxide was added in 35 g of SOLVESSO 100 and polymerization reaction further proceeded for 2 hours, to obtain an acrylic resin which had a number average molecular weight of about 6,000.

PREPARATION EXAMPLE 2 Preparation of Acrylic Resin (A-2) :15 99 *9 Sr 9 9*.999 210 g of styrene, 175 g of n-butyl methacrylate, 70 g of lauryl methacrylate, 21 g of methacrylic acid, 224 g of hydroxylethyl methacrylate, and 30 g of diethylaminoethyl methacrylate. were mixed. To this mixture, 42 g of ditertiary-butyl peroxide as an initiator were added.

Using the same kind and amount of solvent as Preparation Example 1, the resulting reaction mixture was subjected to polymerization in the same manner with that of Preparation Example 1.

The acrylic resin prepared had a number average molecular weight of about 5,000.

i 9 :1 1fl-* N: PREPARATION EXAMPLE 3 Preparation of Acrylic Resin (A-3) A mixture of 210 g of methyl methacrylate, 140 g of butyl acrylate, 140 g of ethylhexyl acrylate, 250 g of styrene, 100 g of vinyl trichlorosilane, 14 g of acrylic acid, and 196 g of hydroxylpropyl acrylate was added with 60 g of di-tertiarybutyl peroxide as an initiator and 2.4 g of n-butyl mercaptan as a polymerization modifier.

0 Using the same kind and amount of solvent as Preparation Example 1, the resulting reaction mixture was subjected to polymerization in the same manner with that of Preparation Example 1.

The acrylic resin prepared had a number average molecular 5 weight of about 6,000.

to 0 06 000* *ai 400060

S,

00 0 6 0 O 0 06 4 00 PREPARATION EXAMPLE 4 Preparation of Acrylic Resin (A-4) 175 g of styrene, 196 g of n-butyl methacrylate, 140 g of butyl acrylate, 14 g of acrylic acid, 80 g of 3methacryloxypropyl trimethoxysila'e, and 175 g of hydroxylpropyl acrylate were mixed. To this mixture, 70 g of azobisisobutyronitrile as an initiator were added.

Using the same kind and amount of solvent as Preparation Using the same kind and amount of solvent as Preparation iU ~t ii 1~ Example 1, the resulting reaction mixture was subjected to polymerization in the same manner with that of Preparation Example 1.

The acrylic resin prepared had a number average molecular weight of about 3,500.

PREPARATION EXAMPLE Preparation of Acrylic Resin 35 g of methyl methacrylate, 140 g of styrene, 210 g of n-butyl methacrylate, 70 g of ethyl acrylate, 14 g of methacrylic acid, and 245 g of hydroxylethyl methacrylate were mixed. To the mixture, 20 g of di-tertiary-butyl peroxide as an initiator and 2.4 g of n-dodecyl mercaptan as a polymerization modifier were added.

Using the same kind and amount of solvent S Preparation Example 1, the resulting reaction mixture was subjected to polymerization in the same manner with th-t of Preparation Example 1.

-The acrylic resin prepared had a nuim'er average molecular weight of about 6,200.

PREPARATION EXAMPLE 6 0* Preparation of Block Isocyanate Resin (B-1) i 1

V'

500 g of isoporone diisocyanate monomer/trimer, 500 g of malonate, and 30 g of polypropylene glycol (PP-400) were added and reacted with one another until the isocyanate groups completely vanished.

The block isocyanate resin prepared had a number average molecular weight of approximately 1,000 to approximately 2,000.

PREPARATION EXAMPLE 7 Preparation of Block Isocyanate Resin (B-2) 400 g of hexamethylene diisocyanate monomer/trimer, 350 g of malonate, and 15 g of diethylene glycol were added and reacted with one another until the isocyanate groups 15 completely vanished.

SThe block isocyanate resin prepared had a number average molecular weight of approximately 2,000 to approximately 3,000.

9.

COMPARATIVE EXAMPLE 1 S' Preparation of Acrylic Resin (C-i) 168 g of methyl methacrylate, 175 g of n-butyl acrylate, 1"40 g of 2-hydroxylethyl methacrylate, 21 g of methacrylic S 25 acid, and 56 g of styrene were mixed with one another. To 21

L:

this mixture, 7 g of benzyl peroxide as an initiator was added. This reaction mixture was added dropwise in a solvent mixture of 510 g of SOLVESSO 100 and 140 g of n-butanol over 3 hours. Thereafter, reflux was executed for 2 hours. 1 g of benzyl peroxide was added dropwise in 50 g of SOLVESSO 100 and polymerization reaction further proceeded for 2 hours, to obtain an acrylic resin.

COMPARATIVE EXAMPLE 2 Preparation of Acrylic Resin (C-2) 140 g of styrene, 70 g of n-butyl acrylate, 210 g of i methyl methacrylate, 70 g of ethylhexyl acrylate, 196 g of hydroxylethyl acrylate, and 14 g of acrylic acid were mixed *4 1 5 with one another. To this mixture, 70 g of cumene hydrc peroxide as an initiator was added. This reaction

I

mixture was added dropwise in 330 g of SOLVESSO 100 over 4 hours. Polymerization reaction further proceeded for 2 hours, i I' to obtain an acrylic resin.

0 t EXAMPLES 1 THROUGH 7 i Coating compositions for automobile were prepared with the resins polymerized in Preparation Examples 1 through 7 and other additives. The paint compositions had such composition 22

II:

'j ratios as listed in the following Table 1.

Table 1 20 V,be.

a. ti '2 0 q

CI.

2 a a unit: wt. parts Example No.

1 2 3 4 5 6 7 C.1 C.2 A-1 A-2 A-3 A-4 A-5 A-1 A-i Component B-1 B-2 B-i B-2 B-I B-2 B-2 C-I C-1 Acrylic resin 500 500 500 500 500 500 500 500 500 Block Isocyanate 80 70 80 70 80 70 Melamine resin 1 214 Melamine resin 2 190 Acid Curing Catalyst 3 i Flowing Agent 5 5 5 5 5 5 5 5 UV Absorbent 4 20 20 20 20 20 20 20 20 Solvent 400 400 400 400 400 400 400 400 400 note: Butoxy melamine, made by K.C.C Company 2 CYNEL 303, made by Cyanamide Company 3 10 paratoluene sulfonic acid in xylene 4 Tivurin 440, Sandover 3206, made by Ciba geigy Company With the paint compositions formulated as given in Table 1, samples which had been subjected to electrodeposition and middle coating were upper-coated. Thereafter, the clear paint compositions were made to have a spray viscosity of 20 to sec in a ford cup at 25 "C and then were sprayed into the

I

a ,"30 *l a 'a a

A

samples which were, in turn, cured under the condition of 130 °C x 30 min., so as to prepare coated samples with a film thickness of 50?5 pm.

These paint films according to Examples and Comparative Examples were tested for physical properties and the results are given as shown in the following Table 2.

In the test, appearance was measured with naked eye at the photographs of the coated samples, using a tension meter.

Acid resistance was evaluated by dropping a 26 H 2

SO

4 solution and a 36 H 2

S

4 solution on 0.5 ML samples, leaving them at 50 60 and 70 °C for 1 hour, and detecting damage and expressed as 1 for "good", 2 for "fine trace", 3 for "color maintenance", and 4 for "corrosion".

Gloss was checked at 60 "C using a glossmeter (trade name "Hicho-Tri-Gloss Meter", commercially available from BYK p company).

In storing stability test, the samples were left at 60 'C for 3 days and then, it was determined whether change in viscosity was not more than 10 sec.

Water resistance test was carried out in such a way that the samples were left at 40 °C for 10 days and then, change therein was checked.

Coid chipping resistance was measured by checking the samples at negative 40 "C after left under the condition of negative 40 °C x 3 hours.

24 i#

;R

For weathering resistance, a Q.U.V test was carried out with W-O-M.

Table 2 Example No.

1 2 3 4 5 6 7 C.1 C.2 Test A-1 A-2 A-3 A-4 A-5 A-1 A-1 Item B-1 B-2 B-1 B-2 B-1 B-2 B-2 C-1 C-1 Appearance 16-17 15-16 16 16 16 16 15-16 14-15 16 Gloss 92 89 91 90 89 90 92 89 91 Storing Stability 0 0 0 0 0 0 0 0 Acid Resistance 26% H 2 SO4 1 1 1 1 1 1 1 2-3 3-4 36%H 2

SO

4 1-2 1 1 1 1 1 1 Water Resistance good good good good good good good decolor bubble Cold Chipping Resistance 8+ 7+ 8 7+ 8 7 8 7 7 Weathering Resistance 1000 HRS good good good good good good good good choking 2000 HRS good good good good good good good good crack Key: 0 very good a A normal Other features, advantages and embodiments of the invention disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing disclosures. In this regard, while specific embodiments of .9 *t a *1*

I

ft I

I

*114 4 P IC

CI

I 4 1 1

I

4144 ii

S-,

IN lIBFi07005:sd the invention have been described in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as described and claimed.

it 26

Claims (8)

1. A single-package coating composition for a top clear coat for automobiles, comprising an acrylic resin and a blocked isocyanate resin, wherein an acrylic resin is prepared by reacting a mixture comprising 20 to 70% by weight of an alkyl acrylate represented by the following formula I I I CH 2 COOR 2 wherein R 1 is a hydrogen atom or a methyl group, and R 2 is an alkyl group containing 1 to 14 carbon atoms; to 40% by weight of an aromatic vinyl compound represented by the following o1 formula II R-CH-CH 2 wherein R is an aromatic group; and to 40% by weight of a reactive monomer having a hydroxyl, carboxyl or silane group with 0.01 to 10.0% by weight of an initiator, and the blocked isocyanate resin is 1i prepared by blocking an aliphatic isocyanate with a ralonate and modifying the blocked aliphatic isocyanate with diols.

2. A single-package coating composition for a top clear coat for automobiles according to claim 1, wherein the alkyl acrylate of formula I is selected from a group consisting of methyl acrylate, ethyl acryiate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-methylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t- butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, cellosolve methacrylate, and mixtures thereof.

3. A single-package coating composition for a top clear coat for automobiles S 25 according to claim 1 or claim 2, wherein the aromatic vinyl compound of formula II is selected from a group consisting of styrene, ac-methyl styrene, benzyl(meth)acrylate, phenyl(meth)acrylate, vinyl toluene, and mixtures thereof.

4. A single-package coating composition for a top clear coat for automobiles I .according to any one of claims 1 to 3, wherein the reactive monomer is selected from a 30 group consisting of methacrylic acid hydroxyl methyl, methacrylic acid hydroxyl ethyl, methacrylic acid hydroxyl propyl, methacrylic acid hydroxyl butyl, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, vinyl trichloro silane, vinyl tri(2- Smethoxy-ethoxy)silane, vinyl triethoxy silane, vinyl trimethoxy silane, 3- methacryloxypropyl trimethoxy silane, allyl trimethoxy silane, 1-(3-methacryloxypropyl)- s 1,1,3,3,3-pentamethyl disiloxane, dimethylaminoethyl methacrylate, diethylaminoethyl SN:\LIBFF101705ssd s I, Crr k )L II"-- 28 methacrylate, t-butyl-aminoethyl acrylate, iso-butoxymethyl acrylamide, n-butoxymethyl acrylamide and acrylamide.

A single-package coating composition for a top clear coat for automobiles according to any one of claims 1 to 4, wherein the aliphatic isocyanate is blocked with to 90% by weight of malonate.

6. A single-package coating composition for a top clear coat for automobiles according to claim 5, wherein the aliphatic isocyanate is selected from a group consisting of hexamethylene diisocyanate monomer, hexamethylene diisocyanate trimer (burit type), hexamethylene diisocyanate trimer (cycle type), isoporone diisocyanate monomer and isoporone diisocyanate trimer.

7. A single-package coating composition for a top clear coat for automobiles according to claim 6, wherein the blocked aliphatic isocyanate with malonate is modified with polyglycol in an amount of 10 to

8. A single-package coating composition for a top clear coat for automobiles, comprising an acrylic resin and a blocked isocyanate resin, which composition is substantially as hereini described with reference to any one of Examples 1 to 7, excluding the comparative examples. Dated 8 October, 1998 Korea Chemical Co., Ltd. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON (VL( .4 CL I C C I I C .41(4( C t (4O (1 4 IO E 4 1 1 ill- -u Sr" rjr 'I IH, l tRnFli317tl1,r 41 V Coating Composition ABSTRACT There is disclosed a coating composition for automobile, comprising an acrylic resin and a block isocyanate resin as a curing agent for the acrylic resin, in combination of other additives. The acrylic resin is prepared by solution-polymerizing conventional acrylic monomer with acrylic monomer having carboxyl group., hydroxyl group and silane group and the block isocyanate resin is prepared by masking aliphatic isocyanate with a blocking agent and modifying the masked aliphatic isocyanate with alcohols. Applicable to a top clear coating for automobile, the coating composition wherein thermal fluidity, crosslinking reaction rate and viscosity valance with one another is superior in appearance, solvent resistance, chemical resistance, thermal resistance and weathering resistance. w