KR20200096365A - Coat composition for primer - Google Patents

Abstract

The present invention relates to a middle coating composition comprising a urethane-modified polyester resin, a polyester resin, an acrylic resin, a melamine resin, and an isocyanate resin. The middle coating composition is suitable as a paint for coating vehicle components and vehicle bodies.

Description

Medium coating composition {COAT COMPOSITION FOR PRIMER}

The present invention relates to a coating composition for intermediate use.

Background of the Invention [0002] It is common for the vehicle body to perform electrodeposition coating, intermediate coating, base coating and clear coating to protect the surface from external and external environments. For example, the electrodeposition coating is applied to the vehicle body, followed by curing, and the intermediate coating is applied and then cured. Subsequently, it is a common automotive coating system to continuously coat the base coat and the clear coat on the intermediate coating layer and then cure. In addition, the automotive coating process as described above is typically a first coating after a middle coating, and a base coat and a clear coat coating, and a second coating (3C2B) coating method for secondary curing.

However, in order to reduce costs such as equipment investment cost, equipment management cost and coating cost of the coating process, and to improve the eco-friendliness of the coating, a 3 coat 1 bake (3C1B) coating method, a mid-delete coating method, and the like have been proposed. 3 coat 1 bake coating method consists of electrodeposition, middle coat, base coat and clear coat, and coats the middle coat but coats the base coat and clear coat with wet on wet without first curing after mid coat to be. In addition, the intermediate eradication type coating method is composed of electrodeposition, base and clear coat, and is a coating method that deletes the intermediate coating itself and implements the intermediate function in the base coating film.

In this regard, Korean Patent Registration No. 1,806,580 (Patent Document 1) includes epoxy modified polyesters, acrylate polymers or polyurethane polymers, polymer microparticles, polymers having isocyanate or amino groups, pigments, organic solvents and additives containing additives A multicoat paint system is disclosed that includes a composition and a functional layer made therefrom. In addition, the paint system uses a wet-on-wet 3-coat 1 bake coating method. However, as shown in Patent Document 1, the conventional 3 coat 1 bake coating method of the intermediate coating composition has a limitation to be applied as a coating for a vehicle body due to insufficient mechanical properties of the prepared coating film.

Therefore, the appearance of the manufactured coating film is excellent, it can be cured at a low temperature of 140°C or less, and due to the effect of reducing volatile organic compounds (VOC) through high solidification, a study on an eco-friendly and economical coating composition for intermediate use It is in need of development.

Korean Patent Registration No. 1,806,580 (published on October 10, 2012)

Accordingly, the present invention has excellent appearance characteristics of the manufactured coating film, can be cured at a low temperature of 140° C. or lower, and is eco-friendly and economical due to the effect of reducing volatile organic compounds (VOC) through high solidification. Want to provide.

The present invention provides a coating composition for intermediate use, comprising a urethane-modified polyester resin, a polyester resin, an acrylic resin, a melamine resin and an isocyanate resin.

The coating composition for intermediate use according to the present invention can be cured at a low temperature of 140° C. or less, and can produce a coating film having excellent appearance characteristics and mechanical properties, and is suitable as a coating material for automobile parts and body coatings. Furthermore, the coating composition is eco-friendly and economical due to a high content of solids and a VOC reduction effect.

Hereinafter, the present invention will be described in detail.

The coating composition for intermediate use according to the present invention includes a urethane-modified polyester resin, a polyester resin, an acrylic resin, a melamine resin and an isocyanate resin.

Urethane modified polyester resin

The urethane-modified polyester resin is the main resin of the composition containing the same and serves to form the appearance characteristics and mechanical properties of the coating film produced through chemical bonding with melamine resin and isocyanate resin.

The urethane-modified polyester resin has a hydroxyl value (OHV) of 70 to 100 mgKOH/g, an acid value (AV) of 1 to 10 mgKOH/g, and a solid content (NV) of 50 to 70% by weight based on the total weight of the resin. , And the viscosity at 25°C may be 850 to 1,290 cps. In another example, the urethane-modified polyester resin has a hydroxyl value of 70 to 95 mgKOH/g, or 75 to 95 mgKOH/g, an acid value of 1 to 8 mgKOH/g, or 2 to 4 mgKOH/g, and a solid content of 55 to 65% by weight, or 58 to 62% by weight relative to the total weight of the resin, the viscosity at 25 ℃ may be 870 to 1,250 cps, or 885 to 1,200 cps.

When the hydroxyl value of the urethane-modified polyester resin is within the above range, low-temperature curing is possible, and the adhesion and impact properties of the prepared coating film are improved, and when the acid value is within the above range, the appearance and adhesion are excellent, and the solid content is When it is within the above range, appearance characteristics, in particular, gloss, durability, elasticity and hardening density are improved, and when the viscosity at 25°C is within the above range, the solid content increases and the solid volume ratio (SVR) of the paint There is an improvement effect.

In addition, the urethane-modified polyester resin may have a weight average molecular weight (Mw) of 1,000 to 2,500 g/mol. As another example, the urethane-modified polyester resin may have a weight average molecular weight of 1,200 to 2,000 g/mol. When the weight average molecular weight of the first urethane-modified polyester resin is within the above range, the appearance and gloss may be excellent.

In addition, the urethane-modified polyester resin may be included in the composition in an amount of 10 to 20 parts by weight based on 5 to 15 parts by weight of the polyester resin. As another example, the urethane-modified polyester resin may be included in the composition in an amount of 12 to 18 parts by weight, or 12 to 16 parts by weight based on 5 to 15 parts by weight of the polyester resin. When the content of the urethane-modified polyester resin is within the above range, there is an effect of improving appearance characteristics, impact resistance, and chipping resistance.

Polyester resin

The polyester resin serves to form the appearance properties and physical properties of the coating film prepared from the composition containing the same.

The polyester resin has a hydroxyl value (OHV) of 100 to 170 mgKOH/g, an acid value (AV) of 0.1 to 8 mgKOH/g, and a solid content (NV) of 70 to 85% by weight based on the total weight of the resin, The viscosity at 25°C can be 500 to 4,000 cps. In another example, the polyester resin has a hydroxyl value of 110 to 160 mgKOH/g, or 120 to 150 mgKOH/g, an acid value of 0.2 to 5 mgKOH/g, or 0.5 to 3 mgKOH/g, and a solid content of the total resin. It is 70 to 80% by weight, or 72 to 75% by weight, and the viscosity at 25°C may be 1,000 to 4,000 cps, or 1,100 to 3,500 cps.

When the hydroxyl value of the polyester resin is within the above range, low temperature curing and crosslinking density are improved, and when the acid value is within the above range, there is an effect of improving crosslinking density and curing reactivity, and when the solid content is within the above range, gloss and curing There is an effect of improving reactivity, and when the viscosity at 25°C is within the above range, the solid content increases, thereby improving the SVR (Solid Volume Ratio) of the paint.

In addition, the polyester resin may have a weight average molecular weight (Mw) of 800 to 2,000 g/mol. As another example, the polyester resin may have a weight average molecular weight of 1,000 to 1,800 g/mol, or 1,100 to 1,500 g/mol. When the weight average molecular weight of the polyester resin is within the above range, the solid content increases, thereby improving the SVR (Solid Volume Ratio) of the paint.

Further, the polyester resin may be included in the composition in an amount of 5 to 15 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. As another example, the polyester resin may be included in the composition in an amount of 7 to 13 parts by weight, or 8 to 12 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. When the content of the polyester resin is within the above range, high gloss of the paint can be realized, and impact resistance and chipping resistance are improved.

Acrylic resin

The acrylic resin serves to improve the appearance properties and mechanical properties of the coating film prepared from the composition comprising the same.

The acrylic resin has a hydroxyl value (OHV) of 50 to 100 mgKOH/g, an acid value (AV) of 1 to 30 mgKOH/g, and a solid content (NV) of 15 to 35% by weight relative to the total weight of the resin, 25 The viscosity at ℃ may be 50 to 250 cps. As another example, the acrylic resin has a hydroxyl value of 60 to 80 mgKOH/g, or 65 to 75 mgKOH/g, an acid value of 5 to 20 mgKOH/g, or 7 to 15 mgKOH/g, and a solid content of the total resin weight With respect to 20 to 30% by weight, or 24 to 28% by weight, at 25 ℃ viscosity may be 80 to 220 cps, or 100 to 200 cps.

When the hydroxyl value of the acrylic resin is within the above range, there is an effect of improving the orange peel of the paint, and when the acid value is within the above range, the leveling (long wave) of the paint is improved, and the solid content is within the above range. In this case, it is possible to realize high gloss, and when the viscosity is within the above range at 25°C, there is an effect of improving high appearance and durability.

In addition, the acrylic resin may have a weight average molecular weight (Mw) of 1,500 to 3,500 g/mol. As another example, the acrylic resin may have a weight average molecular weight of 2,000 to 3,200 g/mol, or 2,500 to 3,000 g/mol. When the weight average molecular weight of the acrylic resin is within the above range, the leveling property of the paint may be improved.

Further, the acrylic resin may be included in the composition in an amount of 10 to 30 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. As another example, the acrylic resin may be included in the composition in an amount of 12 to 28 parts by weight, or 12 to 20 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. When the content of the acrylic resin is within the above range, there is an effect of improving appearance characteristics and gloss.

Melamine resin

The melamine resin serves to cure the composition by reacting with the components in the composition containing it.

The melamine resin may include at least one selected from the group consisting of butoxy-methoxy mixed melamine resin and methylate melamine resin. As another example, the melamine resin may include butoxy-methoxy mixed melamine resin and methylate melamine resin.

In addition, the butoxy-methoxy mixed melamine resin may have a weight average molecular weight (Mw) of 300 to 1,000 g/mol, and a viscosity at 25°C of 2,000 to 4,000 cps. As another example, the butoxy-methoxy mixed melamine resin may have a weight average molecular weight of 500 to 900 g/mol, or 600 to 750 g/mol, and a viscosity at 25° C. of 2,200 to 3,900 cps, or 2,400 to 3,800 cps. have.

When the weight average molecular weight of the butoxy-methoxy mixed melamine resin is within the above range, the coating film has an excellent effect on hardness, impact resistance and chipping resistance, and when the viscosity at 25°C is within the above range, the solid content increases. It has the effect of improving the solid volume ratio (SVR) of the paint. In addition, commercially available products of the butoxy-methoxy mixed resin include CYTEC's CYMEL-254, CYMEL-235, CYMEL-1168, CYMEL-1156 and CYMEL-1170, SOLUTIA's RESIMINE-751 and RESIMINE755.

Furthermore, the methylate melamine resin has a weight average molecular weight (Mw) of 500 to 2,000 g/mol, a solid content (NV) of 80 to 90% by weight based on the total weight of the resin, and a viscosity of 2,000 to 6,500 at 25°C. can be cps. In another example, the methylate melamine resin has a weight average molecular weight of 800 to 1,800 g/mol, or 1,000 to 1,500 g/mol, and a solid content of 81 to 88% by weight, or 82 to 86% by weight based on the total weight of the resin. , Viscosity at 25 ℃ may be 2,700 to 6,000 cps, or 3,000 to 5,000 cps.

When the weight average molecular weight of the methylate melamine resin is within the above range, it has an excellent effect on hardness, impact resistance and chipping resistance of the coating film, and when the solid content is within the above range, it has an effect of improving low temperature curing property and at 25°C. When the viscosity is within the above range, the solid content rises, and there is an effect of improving the solid volume ratio (SVR) of the paint.

In addition, commercially available products of the methylate melamine resin include CYMEL-303, CYMEL-327 and CYMEL-370 from CYTEC, BE-370 and BE3717 from BIP, RESIMINE-717, RESIMINE-730, RESIMINE-747, and RESIMINE-7550 from SOLUTIA. And so on.

In addition, the melamine resin may be included in the composition in an amount of 1 to 15 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. As another example, the melamine resin may be included in the composition in an amount of 2 to 12 parts by weight, or 3 to 10 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. When the content of the melamine resin is within the above range, there is an effect of improving storage stability, impact resistance, and chipping resistance of the paint.

In another example, the intermediate coating composition is 1 to 5 parts by weight, or 1 to 3 parts by weight of butoxy-methoxy mixed melamine resin and 1 to 10 parts by weight, or 2 parts based on 10 to 20 parts by weight of the urethane-modified polyester resin. It may contain to 9 parts by weight of methylate melamine resin. When the content of the butoxy-methoxy melamine resin is within the above range, there is an effect of improving curing reactivity, and when the content of the methylate melamine resin is within the above range, there is an effect of improving appearance and storage stability.

Isocyanate resin

The isocyanate resin serves to cure the composition by crosslinking with other components in the composition containing the same. As another example, the isocyanate group of the isocyanate resin reacts with hydroxyl groups of other components in the paint composition to form urethane bonds, thereby curing the paint composition.

The isocyanate resin may be used without particular limitation as long as it is a conventional isocyanate resin that can be used for a curing agent for a paint. For example, the isocyanate resin may be a hexamethylene diisocyanate (HMDI) system having excellent yellowing resistance and weather resistance. Commercial products of the HMDI-based isocyanate resin include DESMODUR PL 350 (BAYER), DURANATE K-6000, and the like.

On the other hand, the isocyanate resin may be a block isocyanate resin in which the terminal isocyanate group is sealed.

In addition, the isocyanate resin may have a viscosity of 1,500 to 7,500 cps at 25° C., and a solid content of 70 to 80% by weight based on the total weight of the resin. As another example, the isocyanate resin has a viscosity at 25°C of 2,000 to 6,500 cps, or 2,500 to 5,000 cps, and the solid content may be 72 to 78% by weight based on the total weight of the resin. When the viscosity of the isocyanate resin at 25°C is within the above range, there is an effect of improving the leveling and wetting of the paint, and when the solid content is within the above range, the impact resistance and chipping resistance of the produced coating film And there is an effect of improving the flexibility.

Further, the isocyanate resin may be included in the composition in an amount of 1 to 5 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. As another example, the isocyanate resin may be included in the composition in an amount of 1 to 4 parts by weight, or 2 to 4 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. When the content of the isocyanate resin is within the above range, there is an effect of improving appearance properties, particularly gloss, and mechanical properties of the prepared coating film.

solvent

The intermediate coating composition may further include a solvent. At this time, the solvent serves to improve the workability of the composition by adjusting the viscosity of the composition.

For example, the solvent is an aromatic hydrocarbon-based solvent such as toluene and xylene; Ketone solvents such as methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, and ethyl propyl ketone; Ester solvents such as methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, propylene glycol methyl ether acetate, and ethyl ethoxypropionate; And alcohol solvents such as 2-ethyl hexanol, iso-butanol, n-butanol, propanol, and 1-methoxy-2-propanol; and the like. In addition, it can be appropriately selected and used depending on the properties and volatilization rate of the resin contained in the composition. Further, commercially available products of the aromatic hydrocarbon-based solvent include cocosol #100 and cocosol #150.

In addition, the intermediate coating composition may contain 10 to 40 parts by weight of a solvent relative to 10 to 20 parts by weight of a urethane-modified polyester resin. For example, the intermediate coating composition may include 12 to 38 parts by weight, or 15 to 35 parts by weight of a solvent based on 10 to 20 parts by weight of the urethane-modified polyester resin. When the solvent content in the composition is within the above range, there is an effect of improving the coating workability.

Pigment

The intermediate coating composition may further include a pigment. At this time, the pigment serves to impart color to the prepared coating film.

For example, the pigment is not particularly limited as long as it is a pigment commonly used in coating compositions, and for example, inorganic pigments and organic pigments can be used. As another example, the pigment may include metal oxides such as titanium dioxide, carbon black, zinc oxide, ultramarine, and red iron oxide; Sulfides of lithopone, lead, cadmium, iron, cobalt, aluminum and hydrochloride or sulfates thereof; Azo pigments; And copper phthalocyanine pigments.

The intermediate coating composition may include 10 to 30 parts by weight of pigment with respect to 10 to 20 parts by weight of the urethane-modified polyester resin. For example, the intermediate coating composition may include 15 to 25 parts by weight of pigment with respect to 10 to 20 parts by weight of the urethane-modified polyester resin. When the pigment content in the intermediate coating composition is within the above range, problems such as insufficient concealment power of the prepared film and degradation of stability of the composition and deterioration of dispersibility of the pigment can be prevented.

additive

The intermediate coating composition may further include at least one additive selected from the group consisting of a curing catalyst, a surface modifier, and a dispersant.

The additive may be included in an amount of 1 to 20 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin. For example, the additive may be included in an amount of 1 to 15 parts by weight, or 2 to 10 parts by weight based on 10 to 20 parts by weight of the urethane-modified polyester resin.

The curing catalyst serves to control the curing reaction rate of the composition containing the same. For example, the curing catalyst may be an acid catalyst, and commercially available products include King Industries' Nacure 2547, Nacure 3327, Nacure 3325, XP-221, Nacure 4167, and the like.

The surface adjuster serves to control the smoothness of the coating film prepared by adjusting the surface tension after application of the coating composition, and can be used without particular limitation, as long as it is a common one that can be used in the coating composition. For example, the surface modifier may be a polyacrylate-based or silicone-based surface modifier.

The dispersant improves the dispersibility of various components in the composition and serves to increase the stability of the coating composition. In addition, the dispersant may be used without particular limitation as long as it is a conventional dispersant or dispersion stabilizer that can be used in the coating composition. For example, commercially available products of the dispersant include BYK's DISPERBYK-103, DISPERBYK-110, and DISPERBYK-161.

The intermediate coating composition may have a viscosity of 15 to 30 seconds and an electrical resistance of 0.3 to 4.0 MΩ based on Pod Cup No. 4 at 25°C. As another example, the intermediate coating composition may have a viscosity of 18 to 23 seconds and an electrical resistance of 0.3 to 3.0 MΩ based on Pod Cup 4 at 25°C. When the viscosity at 25°C of the intermediate coating composition is within the above range, atomization is possible when the coating is applied, and when the electrical resistance is within the above range, there is an effect of improving the arrival efficiency of the coating.

The intermediate coating composition according to the present invention as described above can be cured at a low temperature of 140° C. or less, or 120 to 140° C., including melamine resin and isocyanate resin. In addition, the coating composition can produce a coating film having excellent appearance characteristics and mechanical properties of a drafted coating film including a urethane-modified polyester resin, and is suitable as a coating material for automobile parts and vehicle body coating. Furthermore, the coating composition is eco-friendly and economical due to a high content of solids and a VOC reduction effect.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for the understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

In the present invention, functional groups such as'acid value' and'hydroxyl value' of the resin may be measured by a method well known in the art, and may be, for example, a value measured by a titration method.

In addition, the'weight average molecular weight' of the resin may be measured by a method well known in the art, for example, may represent a value measured by a method of gel permeation chromatograph (GPC).

[Example]

Examples 1 to 8 and Comparative Examples 1 to 3. Preparation of intermediate coating composition

By mixing the ingredients in the composition (parts by weight) as described in Table 1, the viscosity of the Ford Cup #4 at 25°C based on Pod Cup No. 4 was adjusted to about 20 seconds to prepare a middle coating composition.

Urethane modified polyester resin Polyester resin Acrylic resin Melamine resin Isocyanate resin Pigment additive solvent Total amount One 2 Dispersant surface
Regulator Curing catalyst practice
Example 1 14 10 17 2 5 3 20 One 1.5 0.5 26 100 Example 2 18 10 17 2 5 3 20 One 1.5 0.5 22 100 Example 3 14 13 17 2 5 3 20 One 1.5 0.5 23 100 Example 4 14 10 10 2 5 3 20 One 1.5 0.5 33 100 Example 5 9 10 17 2 5 3 20 One 1.5 0.5 31 100 Example 6 14 3 17 2 5 3 20 One 1.5 0.5 33 100 Example 7 14 10 9 2 5 3 20 One 1.5 0.5 34 100 Example 8 14 10 17 7 5 3 20 One 1.5 0.5 21 100 Comparative Example 1 - 11 19 2 5 3 20 One 1.5 0.5 37 100 Comparative Example 2 15 - 18 2 5 3 20 One 1.5 0.5 34 100 Comparative Example 3 16 12 - 2 5 3 20 One 1.5 0.5 39 100

Hereinafter, the manufacturer and product name of each component used in Comparative Examples and Examples are shown in Table 2.

ingredient Remark Urethane modified polyester resin OHV: 80 mgKOH/g, AV: 4 mgKOH/g, Mw: 1,600 g/mol, solid content: 60% by weight, viscosity at 25°C: 890 cps Polyester resin OHV: 130 mgKOH/g, AV: 1 mgKOH/g, Mw: 1,360 g/mol,
Solid content: 73% by weight, viscosity at 25°C: 1,830 cps Acrylic resin OHV: 70 mgKOH/g, AV: 9 mgKOH/g, Mw: 2,700 g/mol, solid content: 26% by weight, viscosity at 25°C: 160 cps Melamine-1 Butoxy-methoxy mixed type
Melamine resin Mw: 650 g/mol, viscosity at 25°C: 2,853 cps Melamine-2 Methylate melamine resin Mw: 1,300 g/mol, viscosity at 25°C: 4,200 cps Isocyanate resin Solid content: 75% by weight, viscosity at 25°C: 2,700 cps Pigment White Pigment (TiO ₂ (Titanium Dioxide)) Dispersant DISPERBYK-161, BYK Surface modifier BYK-331, BYK Curing catalyst NACURE XP-221, King Industries solvent Aromatic hydrocarbon type (KOCOSOL #100, GS CALTEX)

Test Example: Evaluation of properties of the prepared coating film

After applying the intermediate coating composition of Examples 1 to 8 and Comparative Examples 1 to 3 on the electrodeposition-coated specimen, it was dried at room temperature for 15 minutes to form an intermediate coating film having a thickness of 20 μm. Subsequently, a base coat (manufacturer: KCC, dry film thickness: 35 μm) and a clear coat (manufacturer: KCC, dry film thickness: 40 μm) were coated, dried and cured at 140° C. for 20 minutes to prepare a final coating film.

Thereafter, the dispersibility and storage stability of the coating composition for intermediate use, the appearance properties and physical properties of the final coating film were measured in the following manner, and the results are shown in Table 3.

(1) Viscosity

The viscosity was measured based on the Ford Cup No. 4 at 25° C. for the intermediate coating composition.

(2) Dispersibility

After the intermediate coating composition was stirred at 1,500 rpm, the particle size of the coating composition was checked with a particle size meter to evaluate whether the composition was uniformly dispersed without lumps.

Specifically, if the average particle size is 3 μm or less, it is evaluated as excellent (◎), if it is more than 3 μm and less than 5 μm, it is good (○), if it is more than 5 μm and less than 7 μm, it is evaluated as normal (△), and if it is more than 7 μm, it is evaluated as poor (×). I did.

(3) storage stability

After storing the intermediate coating composition at 50° C. for 120 hours, the increase in viscosity was compared with that before storage to evaluate storage stability. At this time, if the increase rate was 10% or less, it was evaluated as excellent (◎), if it was more than 10% and less than 30%, it was good (○), if it was more than 30% and less than 40%, it was evaluated as normal (△), and if it was more than 50%, it was evaluated as bad (×).

(4) Gloss

The 60° gloss of the final coating was measured.

(5) Adhesion

The final coating was drawn into 100 squares (1 mm wide x 1 mm long) each with a knife blade, and the number of squares remaining after removing the squares with a tape was measured to evaluate adhesion.

At this time, if 100 squares are 100% completely attached, it is excellent (◎), if the remaining squares are 70% or more and less than 100%, good (○), if 50% or more and less than 70%, normal (△), 30% or more and less than 50% The case was evaluated as defective (×).

(6) Hardness

The hardness of the intermediate coating film was measured by the pencil hardness method. Specifically, 3B, 2B, B, HB, F, H, 2H and 3H were used to measure the maximum hardness without damaging the intermediate coating film (3B, 2B, B, HB, F, H, 2H) , 3H: thirteen ⇔ excellent).

(7) Impact resistance

When the weight of 500 g was dropped on the final coating film while changing the drop height of the weight from 20 cm to 50 cm, the final coating film was observed to measure the maximum drop height at which the cracks and peeling phenomenon did not occur in the final coating film, and the impact resistance was evaluated.

Specifically, when the maximum fall height was 40cm or more, it was evaluated as excellent (◎), when it was 30cm or more and less than 40cm, good (○), when it was 20cm or more and less than 30cm, it was evaluated as normal (△), and when it was less than 20cm, it was evaluated as bad (×).

(8) Chipping resistance

After leaving the final coating film at -20°C for 3 hours, 50 g of chipping stone was pushed out at a pressure of 4 bar to strike the surface of the final coating film. At this time, if the damaged part of the final coating film was less than 1mm, it was evaluated as excellent (◎), if it was more than 1mm and less than 2mm, it was good (○), if it was more than 2mm and less than 3mm, it was evaluated as normal (△), and if it was more than 3mm, it was evaluated as bad (×).

25℃ Pod Cup Viscosity(sec) Dispersibility Storage stability Polish(%) Adherence Hardness Impact resistance Chipping resistance Example 1 19 ◎ ◎ 90 ◎ HB ◎ ◎ Example 2 19 ◎ ◎ 88 ◎ F ○ ○ Example 3 19 ◎ ◎ 90 ◎ HB ○ ○ Example 4 19 ◎ ◎ 87 ○ HB ○ ◎ Example 5 19 ◎ ◎ 90 ◎ HB △ △ Example 6 18 ◎ ◎ 84 ◎ HB △ △ Example 7 19 ◎ ◎ 88 △ B △ ◎ Example 8 18 ◎ △ 82 ◎ HB △ △ Comparative Example 1 20 ○ ○ 70 ○ B X X Comparative Example 2 25 ○ ○ 74 △ 2B △ X Comparative Example 3 22 ○ △ 74 X 2B X △

As shown in Table 3, it was found that the coating compositions for intermediates of Examples 1 to 8 were excellent in dispersibility. In particular, the coating compositions for intermediates of Examples 1 to 4 were excellent in durability such as dispersibility, storage stability, impact resistance and chipping resistance.

On the other hand, the coating film prepared from the coating composition of Comparative Example 1 not containing the urethane-modified polyester resin was very poor in gloss, impact resistance, and chipping resistance. Further, the coating film prepared from the coating composition of Comparative Example 2, which did not contain a polyester resin, lacked adhesion, impact resistance and chipping resistance. Furthermore, the coating composition of Comparative Example 3 that did not contain an acrylic resin was poor in storage stability, and the coating film prepared therefrom was very poor in adhesion, impact resistance, and chipping resistance.

Claims (7)

A coating composition for intermediate use, comprising urethane-modified polyester resin, polyester resin, acrylic resin, melamine resin, and isocyanate resin. The method according to claim 1,
The urethane-modified polyester resin has a hydroxyl value of 70 to 100 mgKOH/g, an acid value of 1 to 10 mgKOH/g, a solid content of 50 to 70% by weight based on the total weight of the resin, and a viscosity of 850 at 25°C. To 1,290 cps, intermediate coating composition. The method according to claim 1,
The polyester resin has a hydroxyl value of 100 to 170 mgKOH/g, an acid value of 0.1 to 8 mgKOH/g, a solid content of 70 to 85% by weight based on the total weight of the resin, and a viscosity of 500 to 4,000 at 25°C. cps, intermediate coating composition. The method according to claim 1,
The acrylic resin has a hydroxyl value of 50 to 100 mgKOH/g, an acid value of 1 to 30 mgKOH/g, a solid content of 15 to 35% by weight based on the total weight of the resin, and a viscosity of 50 to 250 cps at 25°C Phosphorus, intermediate coating composition. The method according to claim 1,
The melamine resin comprises a butoxy-methoxy mixed melamine resin and a methylate melamine resin, a coating composition for intermediate use. The method according to claim 1,
The isocyanate resin has a viscosity of 1,500 to 7,500 cps at 25° C., and a solid content of 70 to 80% by weight based on the total weight. The method according to claim 1,
The intermediate coating composition comprises 10 to 20 parts by weight of a urethane-modified polyester resin, 5 to 15 parts by weight of a polyester resin, 10 to 30 parts by weight of an acrylic resin, 1 to 15 parts by weight of melamine resin, and 1 to 5 parts by weight of an isocyanate resin. Containing, intermediate coating composition.