KR20050071168A - The composition of clearcoat for automotive - Google Patents

Abstract

The present invention relates to a transparent coating composition for automotive coatings, and more particularly, to an acrylic resin containing a hydroxy group, a polyfunctional functional epoxy group and an epoxy resin containing a hydroxy group, and a specific curing agent, thereby providing excellent durability, goodness and acid resistance. It relates to a transparent coating composition for automotive top coat having. Transparent coating composition for automotive tops according to the present invention contains the urethane and epoxy properties in the composition has the flexibility and elasticity of the coating film, has the advantage of having excellent hardness and chemical resistance and weather resistance.

Description

The composition of Clearcoat for Automotive

The present invention relates to a transparent coating composition for automotive topcoats, and more particularly, to include a urethane and an epoxy property in the composition to have flexibility and elasticity of a coating film, and to have a high hardness, chemical resistance, and weather resistance. It is about.

Conventionally, acrylic melamine resin type thermosetting solvent type paints have been widely used. However, due to corrosion due to acid rain, acid environment in the industrial area, and poor durability, which are a serious problem worldwide. There are many problems with its use.

Therefore, as a countermeasure, a 2-pack type using polyols such as acrylic polyols or polyester polyols and a polyisocyanate curing agent, or a 1-pack type using a blocky isocyanate curing agent, in order not to use melamine resin which is the main cause of acid resistance weakening. Although some acid resistance, gloss, and durability that have been a problem have been solved by developing automotive transparent paints based on acid and anhydrides, polyisocyanates, which have been commonly used, do not satisfy buyers' needs sufficiently due to disadvantages in physical properties such as weather resistance and yellowing. It is true. In addition, an epoxy / acid curing system may be used as a method for improving acid resistance, but it has poor drawability and poor scratch resistance, which is vulnerable to problems in the coating process and damage to the coating after coating.

Accordingly, the present inventors, while trying to improve the above problems, using a thermosetting acrylic resin containing a hydroxy group and a resin containing a hydroxy group and a polyfunctional epoxy group together, and using a specific curing agent different from the conventional one, the flexibility of the coating film It was possible to obtain a transparent coating composition for automobile top coat having excellent elasticity and excellent acid resistance, hardness, chemical resistance and weather resistance, and the present invention was completed based on this.

Accordingly, an object of the present invention is to solve the problems of the polyisocyanate curing agent used in the past, to have excellent phase clarity and acid resistance, to stabilize the storage property when supplied in one pack with the curing agent, and to tolerate weather resistance, acid resistance and other chemical and mechanical properties. It is to provide an excellent automotive coating transparent coating composition.

In order to achieve the above object, the transparent coating composition for automobile coating of the present invention includes 40-50% by weight of an acrylic resin containing a hydroxy group, 5-20% of an epoxy resin having a polyfunctional epoxy group and a hydroxyl group, diethylmalonate and dimethylpyrazolo. 10 to 20% by weight of blocked hexamethylene diisocyanate curing agent, 20 to 30% by weight of solvent, and 5 to 15% by weight of acid anhydride.

Hereinafter, the present invention will be described in detail.

As described above, in the present invention, there is provided a transparent coating composition for automotive coatings having excellent durability, goodness and acid resistance, comprising an acrylic resin containing a hydroxy group, a polyfunctional epoxy group and an epoxy resin containing a hydroxy group, and a specific curing agent. do.

The transparent coating film for automobile top coats of this invention contains the acrylic resin containing a hydroxyl group, the epoxy resin containing an epoxy group, and a hydroxyl group, a hardening | curing agent, an acid anhydride, and a solvent.

(1) acrylic resin

The acrylic resin used in the present invention is a thermosetting resin containing a hydroxy group, with a solid content of 60 to 80%, a weight average molecular weight of 5,000 to 15,000, a hydroxyl value of 100 to 150, an acid value of 30 or less, and a glass transition temperature (Tg) of 5 to 60 It is between ° C and produced at a reaction temperature of 80 to 180 ° C.

At this time, when the solid content in the acrylic resin is less than 60%, appearance deterioration and physical properties such as acid resistance, scratch resistance, solvent resistance, and the like appear, and when it exceeds 80%, there is a problem in appearance deterioration and painting workability after coating.

In addition, when the weight average molecular weight of the acrylic resin is less than 5,000, physical properties such as acid resistance and scratch resistance are lowered, and when it exceeds 15,000, there is a problem that the appearance after coating is lowered.

When the hydroxyl value of the acrylic resin is less than 100, the amount of unreacted NCO on the paint increases, so that physical properties such as acid resistance and appearance deterioration appear, and when it exceeds 150, water resistance and acid resistance due to a large amount of OH groups are poor. In addition, when the acid value exceeds 30, there is a problem that the reaction is delayed.

On the other hand, the amount of the acrylic resin in the total coating composition is preferably 40 to 50% by weight, when the amount is less than 40% by weight unreacted NCO remains on the paint, causing problems in acid resistance and water resistance, 50% by weight If exceeded, unreacted OH groups remain on the paint, causing physical problems such as acid resistance.

(2) epoxy resin

The epoxy resin used in the present invention is a multifunctional epoxy resin containing at least one hydroxy group and 1 to 4 epoxy groups, and serves as an auxiliary resin, and the hydroxy group and the acid anhydride in the epoxy resin react to form an ester group. The resulting ester groups can react with the ring-opened epoxy ring possessed by the epoxy resin to improve appearance and acid resistance, hardness, overbaking adhesion and scratch resistance, which are most important in coating properties. The epoxy resin has a solid content of 100%, an epoxy equivalent of 100 to 200, a hydroxyl value of 150 to 300, and a specific gravity of about 1.2 to 1.5.

On the other hand, the amount of the epoxy resin used in the total composition is preferably 5 to 20% by weight, when the amount is less than 5% by weight acid-epoxy reaction proceeds in a small amount may cause the degradation of acid resistance may appear, 20% by weight If it exceeds, the content ratio of the urethane composition in the composition is lowered may cause a physical property degradation of the coating film such as chipping resistance and scratch resistance. In addition, it is most preferable from the viewpoint of reactivity that the equivalence ratio of the epoxy group in the said epoxy resin and the acid group of an acid anhydride is 1: 0.5-0.5: 1.

(3) curing agent

The hardening agent, which is the biggest feature of the paint composition of the present invention, is hexamethylene diisocyanate blocked with dimethylpyrazole and diethylmalonate, and the acid resistance is equivalent to that of the new curing system and compared with the conventional acrylic melamine curing system paints. It is excellent and scratch resistance is also superior to the new curing system, and improves the appearance, such as the selectivity of the coating film.

The isocyanate group content in the curing agent used in the present invention is 8 to 10%, the solid content is 68 to 72%, the equivalent temperature of the isocyanate group 400 to 500, the temperature at which the block of the isocyanate is broken is 110 to 120 ℃.

In the present invention, the hexamethylene diisocyanate trimer may be used as the main curing agent, and a small amount of melamine resin may be added as the auxiliary curing agent if necessary.

Resin obtained by blocking dimethylpyrazole and diethyl malonate in a hybrid type on the basis of the hexamethylene diisocyanate trimer is obtained by blocking dimethylpyrazole alone or diethylmalonate alone. Compared to the block isocyanate, there is an advantage of good reactivity and acid resistance.

On the other hand, in the coating composition of the present invention, the hydroxyl group in the acrylic resin and the isocyanate in the curing agent are preferably added in an equivalent ratio of 1.5: 1 to 1: 1, and when the equivalent ratio is out of the above range, the hydroxyl group or isocyanate in the coating composition The group remains, causing problems such as water resistance of the coating film.

It is preferable that the usage-amount in the whole coating composition of the said hardening | curing agent is 10-20 weight%, and when the usage-amount is less than 10 weight%, water resistance is bad by unreacted OH group, and when it exceeds 20 weight%, acid resistance etc. by unreacted NCO group is carried out. The physical properties of may be lowered.

(4) solvent

In the coating composition of the present invention, the solvent may be an aromatic hydrocarbon type such as xylene; Ketones such as methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, ethyl propyl ketone, methyl isobutyl ketone and the like; Esters such as methyl acetate, ethyl acetate, normal propyl acetate, isopropyl acetate, butyl acetate, methyl cellosolve acetate, cellosolve acetate, butyl cellosolve acetate and carbitol acetate; One or more selected from alcohol solvents such as ethyl alcohol, normal propanol, isopropanol, normal butanol, isobutanol and tertiary butanol can be used.

Such solvents are used in 20 to 30% by weight based on the total coating composition, when the amount is less than 20% by weight, the appearance of the paint is lowered, and when the amount exceeds 30% by weight, the flowability during vertical coating, the solid content of the paint is reduced The castle is considerably degraded.

(5) acid anhydride

In order to produce an acid-epoxy reactant in the coating composition according to the present invention, it is preferable to use an acid anhydride capable of reacting with an epoxy group. Aromatic acid anhydrides, such as phthalic anhydride, have a significant adverse effect on the phase clarity of the cured coating film or on the haze problem of the resin due to poor compatibility with acrylic resins as well as weather resistance problems when used in excess. It is preferable to use the cycloaliphatic acid anhydride and aliphatic acid anhydride as appropriate as a countermeasure thereof, so that it is possible to induce a skeleton that satisfies the flexibility and weather resistance of the polyester segment simultaneously.

Examples of preferred alicyclic acid anhydrides and aliphatic acid anhydrides may include raw materials such as maleic hydride, methyltetrahydro phthalic hydride, hexahydrogenphthalic hydride, methyl hexahydrogenphthalic hydride, and the like. Here, there is also a method of imparting a reactive unsaturated double bond in the resin skeleton by using fatty acids having a long aliphatic unsaturated double bond with an alkyl group, but it is not preferable in view of excellent durability and weather resistance.

At this time, the amount of the acid anhydride is preferably 5 to 15% by weight based on the total coating composition of the present invention, if the amount is less than 5% by weight, the acid epoxy reaction does not occur completely, the unreacted epoxy is present, 15% by weight If exceeded, unreacted acid anhydride is present, which is undesirable in terms of acid resistance and weather resistance.

(6) Other additives

In addition, the coating composition according to the present invention may further optionally add an appearance control agent, a UV absorber, etc., if necessary, may be blended with a melamine resin and an amino group resin as a modifier for improving the hardness and supplementing the physical properties of the paint. It is also possible to adjust the viscosity of the paint by using an aromatic and aliphatic hydrocarbon solvent for thinners. In addition, when necessary, a curing catalyst may be used for the purpose of controlling the baking temperature during curing, wherein the curing catalyst uses a catalyst such as a tin catalyst or bismuth to activate the reaction of the hydroxyl group with the isocyanate group.

A basic catalyst is mainly used as the catalyst for opening the epoxy group, and in the case of the ammonium salt, it is preferable because it acts as a catalyst for the ring opening of the epoxy group. Quaternary ammonium salts that can be used include tetramethylammonium bromide, trimethylbenzylammonium hydroxide, 2-hydroxypyridine, trimethylbenzylammonium methoxide, phenyltrimethylammonium chloride, phenyltrimethylammonium bromide, phenyltrimethylammonium hydroxide, phenyl Trimethylammonium iodide, phenyltrimethylammoniumtribromide, stearylammonium bromide, tetra-n-butylammonium bromide, tetra-n-butylammonium hydroxide, tetraethylammonium hydroxide and the like.

At this time, the appropriate amount of the catalyst for curing the paint is preferably from 0.01% to 5% by weight based on the total coating composition.

The transparent coating composition according to the present invention is applied on an oil-soluble top coat (base coat), and the top coat refers to a paint made by using an acrylic melamine resin-based, polyester melamine-based metal pigment and colorant, which are usually applied to automobile paints.

As described above, the transparent coating composition according to the present invention is excellent in flexibility and elasticity of the coating film by the urethane bond produced by the reaction of the acrylic resin and the curing agent, thereby improving the chipping resistance, and the conventional melamine ether by the acid / epoxy reaction. Acid resistance by bonding is improved, and hardness, chemical resistance and weather resistance are excellent, and it has excellent durability to be equipped as a clear for automotive top coat.

Hereinafter, the present invention will be described in more detail with reference to the following Examples, but the present invention is not limited thereto.

Examples 1-6 and Comparative Example 1

Next, 0.5L tin cans were prepared using the composition shown in Table 1 (content unit: g), and an acrylic resin and melamine, a flow regulator, a curing agent, and ethyl alcohol were prepared using an electronic balance, and a dissolver was used. Mix for 5 minutes. Then, after about 5 minutes, the acid neutralizing agent, the buffer, the leveling agent, and the tin catalyst are added, followed by secondary stirring. Finally, a UV absorber, a light stabilizer and the remaining solvent are added and stirred for about 10 minutes to prepare a paint.

Then, a conventional base coat (Ebony Black E, manufactured by KCC, Inc.) was applied to the substrate (0.8 mm thick electrodeposited and intermediate coated specimens) with a thickness of 20 μm, and left at room temperature for about 1 minute, followed by a wet on wet method. The clear coat is applied to a thickness of about 45 μm and left at room temperature for about 10 minutes. The applied coating is then thermally cured for about 25 minutes in a 150 ° C. oven.

Physical properties of the coating film were evaluated as follows, and the results are shown in Table 2 below.

(1) Appearance: The numerical value of the horizontal coating film measured by QMS. The lower the value, the better the appearance.

(2) Water resistance: The presence or absence of abnormality after the coating film was deposited for 96 hours in warm water at 40 ° C was visually observed.

(3) Acid resistance: After dropping 2 cc of sulfuric acid pH 1,2 and phosphoric acid pH 1,2 solutions onto the coating film, the solution was maintained at 50, 60 and 70 ° C for 30 minutes, and then the degree of damage to the coating was visually determined.

(4) Chipping resistance: The chipping test was performed after being left for 2 hours at -40 ° C. The lower the value, the better the chipping resistance.

(5) Solvent resistance: The presence of abnormality was visually observed through xylene spot test.

(6) Scratch resistance: Scratch resistance is measured by ANTEK's CAR WASHIER EQUIPMENT after measuring 10 gloss retention rate after 10 round trips to express gloss before test / gloss after test as a percentage.

(7) resistance to gasoline; The gasoline spot was observed visually for 1 hour immersion test.

(8) impact resistance; The coating film breaking height of the coating film after falling at 20, 30, 40, and 50 cm using 50g weight was measured using the Dupont gauge.

(9) Oven baking adhesion: After cutting the specimen, the presence or absence of adhesion to the coating film was visually observed.

(10) brake oil resistance; Observation was observed visually for 1 hour immersion experiment with automobile brake oil spot.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 A. CSR-2A-30 74.61 74.61 - - - - 74.61 (One) B. CSR-2A-31 - - 74.61 74.61 - - - A. CSR-2A-32 - - - - 74.61 74.61 - (2) A. EJ-190 17.46 8.73 - - 4.36 8.73 - B. EJ-300 - - 17.46 8.73 4.36 8.73 - (6) Melamine resin - - - - - - 3.61 (3) Hardener 21.17 28.44 21.17 28.44 22.25 16.40 - Diethylmalonate non-yellowing block isocyanate - - - - - - 36.47 Solvent (Ethyl Alcohol) 9.79 9.79 9.79 9.79 9.79 9.79 9.79 Leveling agent (BYK 333-10%) 0.49 0.49 0.49 0.49 0.49 0.49 0.49 Leveling agent (BYK 358-10%) 0.97 0.97 0.97 0.97 0.97 0.97 0.97 UV absorber (T-384, CIBA-GEIGY) 1.64 1.64 1.64 1.64 1.64 1.64 1.64 Light stabilizer (T-123, CIBA-GEIGY) 0.82 0.82 0.82 0.82 0.82 0.82 0.82 (4) Acid anhydride 18 18 18 18 18 18 18 (5) Acid catalyst - - - - - - One Solves # 100 4.91 4.91 4.91 4.91 4.91 4.91 4.91 Tin catalyst 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Basic catalyst (tetramethylammonium bromide) 0.1 0.1 0.1 0.1 0.1 0.1 - Solves # 150 18.8 18.8 18.8 18.8 18.8 18.8 18.8 Isocyanate: hydroxyl equivalent ratio 1: 1.3 1: 1.3 1: 1.3 1: 1.3 1: 1.3 1: 1.3 1: 1.3 Epoxy addition ratio 5% 10% 5% 10% 10% 20%

(1) Acrylic resin A has a hydroxyl value of 90, a solid content of 70%, a weight average molecular weight of 10000, acrylic resin B has a hydroxyl value of 120, a solid content of 70%, a weight average molecular weight of 12000, and acrylic resin C is It has a hydroxyl value of 150, a solid content of 70% and a weight average molecular weight of 15000.

(2) Epoxy resin A has 4 epoxy groups and 2 hydroxy groups having an equivalent weight of 175 and a hydroxyl group of 250, epoxy resin B having 3 epoxy groups and 1 hydroxyl group having an equivalent weight of 148 and a hydroxyl group of 200.

(3) The curing agent is diethylmalonate and dimethylpyrazole block hexamethylene diisocyanate.

(4) The acid anhydride is methyl hexa hydrophthalic anhydride.

(5) The acid catalyst is King Nacure5543.

(6) Melamine is L167 from DIC Corporation.

Evaluation item Example Example Example Example Example Example Comparative example One 2 3 4 5 6 One Exterior 70 68 70 66 67 63 75 Water resistance Good Good Good Good Good Good Good Acid resistance Good Great Good Great Good Great usually Chipping resistance 7- 7- 7- 7 7 7 7+ Solvent resistance Good Good Good Good Good Good Good Scratch Resistance (%) 65 63 65 63 68 60 60 Petty Good Good Good Good Good Good Good Impact resistance (cm) 40 40 40 40 40 40 35 Of Baking Adhesion Good Good Good Good Good Good Good Brake oil resistance Good Good Good Good Good Good Good

From the results of Table 2, the coating composition according to the present invention is slightly lower in appearance than the conventional acrylic-melamine cured coating composition, it can be seen that the acid resistance and scratch resistance is equivalent or more. In addition, it can be seen that the acid resistance is improved as the content is increased in the composition containing both a urethane group and an acid / epoxy.

As described above, the transparent coating composition for automotive top coating according to the present invention has a flexibility and elasticity of the coating film by forming a urethane bond and an acid-epoxy bond during thermosetting, and simultaneously provides excellent hardness, chemical resistance, and weather resistance to the automotive phase. It can provide the excellent durability, lightness, and acid resistance which are related to the environment of the coating film which should be equipped as a coating clear.

Claims (6)

40-50% by weight of an acrylic resin containing a hydroxy group, 5 to 20% of an epoxy resin containing a polyfunctional epoxy group and a hydroxyl group, 10-20% by weight of hexamethylene diisocyanate curing agent blocked with diethylmalonate and dimethylpyrazole, Solvent 20-30% by weight, and 5-15 wt% of acid anhydride Transparent coating composition for automotive tops comprising a. According to claim 1, wherein the acrylic resin containing a hydroxyl group has a solid content of 60 to 80%, a hydroxyl value of 100 to 150, an acid value of 30 or less, a glass transition temperature (Tg) of 5 to 60 ℃ and a weight average molecular weight of 5,000 to 15,000. Transparent coating composition for automotive tops, characterized in that. The transparent coating composition for automobile coating according to claim 1, wherein the epoxy resin has 1 to 4 epoxy groups and at least one hydroxy group. The transparent coating composition for automobile coating according to claim 1, wherein the equivalent ratio of the hydroxy group in the acrylic resin and the isocyanate group in the curing agent is 1.5: 1 to 1: 1. The transparent coating composition for automobile coating according to claim 1, wherein the equivalent ratio of the epoxy group and the acid group of the acid anhydride in the multifunctional epoxy resin is 1: 0.5 to 0.5: 1. The transparent coating composition of claim 1, wherein the acid anhydride is an alicyclic acid anhydride, an aliphatic acid anhydride, or a mixture thereof.