KR102583105B1 - Clear coat composition - Google Patents

Abstract

The present invention includes a first polyester resin, a second polyester resin, a silicone-modified polyester resin, and a melamine resin, wherein the first polyester resin has a hydroxyl value of 200 to 300 mgKOH/g and a glass transition temperature of 15. to 30°C, and the second polyester resin has a hydroxyl value of 80 to 180 mgKOH/g and a glass transition temperature of 1 to 10°C.

Description

Clear coat composition {CLEAR COAT COMPOSITION}

The present invention relates to a clear coat composition that has excellent reactivity and improved pinhole properties, so that the manufactured coating film has excellent appearance properties and excellent mechanical properties such as scratch resistance.

The car body is subjected to multiple coating processes, such as electrodeposition coating, intermediate coating, base coating, and clear coating, in order to improve the exterior characteristics and protect the surface from the external environment. Specifically, it is common to apply and cure an electrodeposited paint and an intermediate paint on a car body, and then continuously apply a base coat and a clear coat on the intermediate coating layer, followed by drying and curing. As described above, it is common to apply the base coat and clear coat after applying and drying the base coat composition, and then curing the clear coat and base coat together at 140 to 150 ° C.

Meanwhile, conventional clear coat compositions are based on a urethane curing system including polyester resin, acrylic resin, melamine curing agent, etc. In addition, the conventional clear coat composition as described above is widely used because the produced coating film has excellent appearance characteristics and excellent scratch resistance. Specifically, Korean Patent Publication No. 2014-0125415 (Patent Document 1) discloses a one-component paint composition containing a hydroxyl group-containing polyester resin and a melamine resin as a crosslinking agent that reacts with the hydroxyl group.

However, conventional clear coat compositions have a short drying time after painting, a short travel distance to the oven for curing after drying the clear coat, or a short distance between car bodies, resulting in poor appearance characteristics of the manufactured paint film, especially poor pinholes and poor gloss. There was a problem, etc.

Therefore, even in cases where the drying time after painting is short due to excellent reactivity, the travel distance to the oven for curing after clear coat drying is short, or the distance between car bodies is short, the produced coating film has excellent appearance characteristics and scratch resistance, etc. There is a need for research and development on clear coat compositions with excellent mechanical properties.

Korean Patent Publication No. 2014-0125415 (Publication date: 2014.10.28.)

The present invention has excellent reactivity, so even when the drying time after painting is short, the distance to the oven for curing after drying the clear coat is short, or the distance between car bodies is short, the produced coating film has excellent appearance characteristics, scratch resistance, etc. The aim is to provide a clear coat composition with excellent mechanical properties.

The present invention includes a first polyester resin, a second polyester resin, a silicone-modified polyester resin, and a melamine resin,

The first polyester resin has a hydroxyl value of 200 to 300 mgKOH/g and a glass transition temperature of 15 to 30 ℃,

The second polyester resin has a hydroxyl value of 80 to 180 mgKOH/g and a glass transition temperature of 1 to 10° C., providing a clear coat composition.

In addition, the present invention relates to the clear coat composition; and a hardener. A clear paint kit is provided.

The clear coat composition according to the present invention has excellent reactivity, so pinholes in the manufactured paint film do not occur even when the drying time after painting is short, the distance to the oven for curing after drying the clear coat is short, or the distance between car bodies is short. The appearance characteristics are excellent as there is no loss of gloss. In addition, the coating film prepared from the clear coat composition has excellent mechanical properties such as hardness, adhesion, and scratch resistance, and can be usefully used for car body painting.

Hereinafter, the present invention will be described in detail.

The “weight average molecular weight” used in this specification is measured by a common method known in the art, and can be measured, for example, by a GPC (gel permeation chromatograph) method.

In addition, “glass transition temperature” is measured by a common method known in the art, and can be measured, for example, by differential scanning calorimetry (DSC).

Functional values such as “acid value” and “hydroxyl value” can be measured by methods well known in the art, and can represent values measured by, for example, titration methods.

clear coat composition

The clear coat composition according to the present invention includes a first polyester resin, a second polyester resin, a silicone-modified polyester resin, and a melamine resin. At this time, the first polyester resin has a higher hydroxyl value (OHv) and glass transition temperature than the second polyester resin. As the clear coat composition contains two types of polyester resins with different glass transition temperatures and hydroxyl values as described above, the appearance characteristics, hardness, adhesion, and resistance of the coating film produced by controlling the drying speed and crosslinking density of the composition The effect of improving mechanical properties such as scratchability can be obtained.

1st polyester resin

The first polyester resin serves as the main resin in the composition and provides film forming properties.

The first polyester resin can be directly synthesized according to a known method, or a commercially available product can be used. For example, the first polyester resin can be produced by reacting a first carboxylic acid and a first polyol.

At this time, the first carboxylic acid is, for example, adipic acid (AA), isophthalic acid (IPA), trimaltic anhydride (TMA), cycloaliphatic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, It may be one or more selected from the group consisting of fumaric acid, maleic anhydride, tetrahydrophthalic anhydride (HHPA), hexahydrophthalic anhydride, and derivatives thereof.

The first polyol is, for example, methoxypolyethylene glycol, 1,6-hexanediol (1,6-HD), neopentyl glycol (NPG), trimethylol propane (TMP), ethylene glycol, propylene glycol, diethylene. It may be one or more selected from the group consisting of glycol, butanediol, 1,4-hexanediol, and 3-methylpentanediol.

The first polyester resin may have an acid value (Av) of 15 to 25 mgKOH/g, or 18 to 22 mgKOH/g. When the acid value of the first polyester resin is within the above range, rapid hardening due to heat treatment is prevented, which has the effect of preventing poor appearance of the coating film and reducing the occurrence of bubbles (popping). If the acid value of the first polyester resin is less than the above range, the curing reaction speed is lowered, which causes a problem in that the hardness and appearance characteristics of the produced coating film are lowered, and if it exceeds the above range, the curing reaction speed is accelerated and the coating film becomes brittle. ), scratch resistance may decrease, and as hydrophilicity improves, water resistance may decrease.

Additionally, the first polyester resin may have a hydroxyl value (OHv) of 200 to 300 mgKOH/g, or 220 to 280 mgKOH/g. When the hydroxyl value of the first polyester resin is within the above range, it is effective in improving the spreadability of the coating film and improving chemical resistance due to urethane reaction. In addition, when the hydroxyl value of the first polyester resin is less than the above range, there is a problem in that the durability, recoating adhesion, and solvent resistance of the produced coating film are reduced due to insufficient crosslinking density due to insufficient reactivity with the melamine resin. If the range is exceeded, problems may arise where the coating film becomes brittle due to overcuring and the appearance and scratch resistance deteriorate.

The first polyester resin may have a glass transition temperature (Tg) of 15 to 30 °C, or 18 to 25 °C. When the glass transition temperature of the first polyester resin is within the above range, workability (spray feel) is excellent and there is an effect of imparting flexibility to the coating film. If the glass transition temperature of the first polyester resin is less than the above range, the drying speed of the paint decreases, causing a problem in that the mechanical properties of the coating film deteriorate. If it exceeds the above range, the drying speed becomes faster, the appearance deteriorates, and the coating film becomes brittle. (Brittle), a problem of deterioration in scratch resistance may occur.

Additionally, the first polyester resin may have a weight average molecular weight (Mw) of 800 to 1,500 g/mol, or 1,000 to 1,300 g/mol. When the weight average molecular weight of the first polyester resin is within the above range, the paint has the effect of forming a smooth and soft coating film. If the weight average molecular weight of the first polyester resin is less than the above range, there is a problem that the mechanical properties of the produced coating film are deteriorated due to the small molecular weight, and if it exceeds the above range, the flowability decreases due to the increase in molecular weight, and the coating film becomes hard and becomes smooth. This may lead to problems such as decreased scratch resistance.

The first polyester resin may have a solid content (NV) of 60 to 85% by weight, or 70 to 80% by weight, based on the total weight of the resin. When the solid content of the first polyester resin is within the above range, there is an effect of reducing the total volatile organic compound (TVOC) content due to the high solid content. If the solid content of the first polyester resin is less than the above range, there is a problem that curing reactivity is lowered due to a decrease in the solid content of the composition, and if it exceeds the above range, the solid content of the paint is excessively high, resulting in poor workability. Problems may arise where the exterior properties of the coating film deteriorate.

Additionally, the first polyester resin may be included in an amount of 20 to 30% by weight, or 22 to 28% by weight, based on the total weight of the clear coat composition. When the first polyester resin is included within the above content range, there is an effect of improving appearance, scratch resistance, and coating film smoothness. If the content of the first polyester resin in the composition is less than the above range, the crosslink density is lowered, leading to a problem of deterioration of mechanical properties and appearance, and if it is more than the above range, the viscosity of the composition is excessively high, resulting in poor workability and drying properties. Degraded pinhole characteristics may become poor.

2nd polyester resin

The second polyester resin serves to improve the appearance characteristics of the manufactured coating film.

The second polyester resin can be directly synthesized according to a known method, or a commercially available product can be used. For example, the second polyester resin can be produced by reacting a second carboxylic acid and a second polyol.

At this time, the second carboxylic acid is, for example, adipic acid (AA), isophthalic acid (IPA), trimaltic anhydride (TMA), cycloaliphatic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, It may be one or more selected from the group consisting of fumaric acid, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride (HHPA), isononanoic acid (INA), and derivatives thereof.

The second polyol is 1,6-hexanediol (1,6-HD), pentaerythritol, sorbitol, methoxypolyethylene glycol, neopentyl glycol (NPG), trimethylol propane (TMP), and ethylene. It may be one or more selected from the group consisting of glycol, propylene glycol, diethylene glycol, butanediol, 1,4-hexanediol, and 3-methylpentanediol.

The second polyester resin may have an acid value (Av) of 20 to 30 mgKOH/g, or 20 to 25 mgKOH/g. When the acid value of the second polyester resin is within the above range, rapid hardening due to heat treatment is prevented, which has the effect of preventing poor appearance of the coating film and reducing the occurrence of bubbles (popping). If the acid value of the second polyester resin is less than the above range, there is a problem that the hardness and appearance characteristics of the produced coating film decrease due to the curing reaction speed, and if it exceeds the above range, the water resistance decreases as the hydrophilicity improves. may occur.

Additionally, the second polyester resin may have a hydroxyl value (OHv) of 80 to 180 mgKOH/g, or 100 to 150 mgKOH/g. When the hydroxyl value of the second polyester resin is within the above range, it is effective in improving the spreadability of the coating film and improving chemical resistance due to urethane reaction. In addition, when the hydroxyl value of the second polyester resin is less than the above range, there is a problem that the appearance, durability, and chemical resistance of the manufactured coating film are deteriorated due to insufficient crosslinking density with the melamine resin, which is a curing agent, and when it is above the above range, Overcuring may cause the paint film to become brittle, which may result in reduced paint workability and cold chipping resistance.

The second polyester resin may have a glass transition temperature (Tg) of 1 to 10°C, or 3 to 7°C. When the glass transition temperature of the second polyester resin is within the above range, workability (spray feel) is excellent and there is an effect of imparting flexibility to the coating film. If the glass transition temperature of the second polyester resin is less than the above range, the drying speed of the paint decreases, causing a problem in that the mechanical properties of the coating film deteriorate. If it exceeds the above range, the drying speed becomes faster, the appearance deteriorates, and the coating film becomes brittle. (Brittle), a problem of deterioration in scratch resistance may occur.

Additionally, the second polyester resin may have a weight average molecular weight (Mw) of 800 to 1,600 g/mol, or 1,000 to 1,500 g/mol. When the weight average molecular weight of the second polyester resin is within the above range, the paint has the effect of forming a smooth and soft (SOFT) coating film. If the weight average molecular weight of the second polyester resin is less than the above range, there is a problem that the mechanical properties of the produced coating film are deteriorated due to the small molecular weight, and if it exceeds the above range, the flowability decreases as the molecular weight increases, and the coating film becomes hard and smooth. This may lead to problems such as decreased scratch resistance.

The second polyester resin may have a solid content (NV) of 60 to 80% by weight, or 65 to 75% by weight, based on the total weight of the resin. When the solid content of the second polyester resin is within the above range, there is an effect of reducing the total volatile organic compound (TVOC) content due to the high solid content. If the solid content of the second polyester resin is less than the above range, there is a problem that the curing reactivity is lowered due to a decrease in the solid content of the paint, and if it exceeds the above range, the workability of the paint is inferior, and the appearance characteristics of the manufactured coating film deteriorate. Problems may arise.

Additionally, the second polyester resin may be included in the composition in an amount of 15 to 25% by weight, or 17 to 23% by weight, based on the total weight of the clear coat composition. When the second polyester resin is included within the above content range, there is an effect of improving appearance, scratch resistance, and coating film smoothness. If the content of the second polyester resin in the composition is less than the above range, the crosslink density of the coating film decreases, causing a problem of reduced recoating adhesion and scratch resistance, and if it exceeds the above range, the viscosity of the composition becomes excessively high. Problems may arise in which the appearance characteristics of the manufactured coating film are deteriorated due to reduced workability and drying properties.

Silicone modified polyester resin

Silicone-modified polyester resin is highly reactive and prevents pinholes from forming in the manufactured coating film, thereby improving the appearance characteristics.

The polyester resin of the silicone-modified polyester resin can be directly synthesized according to a known method, or a commercially available product can be used, and the polyester resin prepared by reacting the third carboxylic acid and the third polyol can be used as an organic polysiloxane. It may have been transformed into .

At this time, the third carboxylic acid is, for example, adipic acid (AA), isophthalic acid (IPA), trimaltic anhydride (TMA), cycloaliphatic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, It may be one or more selected from the group consisting of fumaric acid, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride (HHPA), isononanoic acid (INA), and derivatives thereof.

The third polyol is 1,6-hexanediol (1,6-HD), pentaerythritol, sorbitol, methoxypolyethylene glycol, neopentyl glycol (NPG), trimethylol propane (TMP), and ethylene. It may be one or more selected from the group consisting of glycol, propylene glycol, diethylene glycol, butanediol, 1,4-hexanediol, and 3-methylpentanediol.

The organic polysiloxane may include functional groups and non-functional organic groups. For example, the organic polysiloxane may include one or more functional groups selected from the group consisting of silanol and alkoxy groups, and may include one or more non-functional organic groups selected from the group consisting of methyl, propyl, and phenyl groups. The alkoxy group includes, for example, methoxy, ethoxy, and butoxy groups.

The silicone-modified polyester resin may have an acid value (Av) of 10 mgKOH/g or less, 8 mgKOH/g or less, or 1 to 8 mgKOH/g. If the acid value of the silicone-modified polyester resin is less than the above range, the surface tension of the paint is high, which causes a problem in that the appearance characteristics of the manufactured paint film are deteriorated. If it exceeds the above range, the surface tension of the paint is too low, causing mechanical problems of the manufactured paint film. Problems with deterioration of physical properties may occur.

Additionally, the silicone-modified polyester resin may have a hydroxyl value (OHv) of 150 to 250 mgKOH/g, or 190 to 210 mgKOH/g. If the hydroxyl value of the silicone-modified polyester resin is less than the above range, there is a problem that the durability and chemical resistance of the produced coating film is reduced due to insufficient reactivity with the melamine resin and the crosslinking density is lowered, and if it exceeds the above range, overcuring occurs. As a result, the coating film becomes brittle, which may cause problems with deterioration in appearance characteristics and scratch resistance.

The silicone-modified polyester resin may have a glass transition temperature (Tg) of -20 to 0 °C, or -15 to -5 °C. If the glass transition temperature of the silicone-modified polyester resin is less than the above range, there is a problem that the hardness of the paint decreases due to increased elasticity and the appearance characteristics of the paint film deteriorate due to poor drying, and if it exceeds the above range, the flow of the paint Due to a decrease in properties, the appearance characteristics of the coating film may deteriorate and the elasticity of the coating film may decrease, which may cause problems such as deterioration in adhesion and chipping resistance.

The silicone-modified polyester resin may have a viscosity of 5,000 to 10,000 cps, or 6,000 to 9,000 cps at 25°C. If the viscosity of the silicone-modified polyester resin at 25°C is less than the above range, the viscosity of the composition is too low and there is a problem of deterioration of the adhesion and scratch resistance of the coating film due to non-formation of the manufactured coating film, and if it exceeds the above range. , a problem may occur in which the appearance characteristics of the manufactured coating film are deteriorated due to insufficient workability of the composition.

Additionally, the silicone-modified polyester resin may have a solid content (NV) of 80% by weight or more, or 85 to 95% by weight, based on the total weight of the resin. If the solid content of the silicone-modified polyester resin is less than the above range, there is a problem that the curing reactivity is lowered due to a decrease in the solid content of the composition, and if it exceeds the above range, the workability of the manufactured paint is inferior and the appearance characteristics of the coating film are deteriorated. Problems may arise.

The silicone-modified polyester resin may be included in an amount of 2 to 10% by weight, or 4 to 8% by weight, based on the total weight of the clear coat composition. When the silicone-modified polyester resin is included within the above content range, there is an effect of improving appearance, scratch resistance, and coating film smoothness. If the content of polyester resin in the composition is less than the above range, the crosslink density is lowered, which causes a problem of poor appearance and scratch resistance, and if it is more than the above range, the viscosity of the composition is excessively high, resulting in reduced workability and drying properties. This may cause problems with deterioration of appearance and mechanical properties.

melamine resin

Melamine resin is a curing agent and serves to harden the composition by crosslinking with each component of the clear coat composition.

The melamine resin can be directly synthesized according to a known method, or a commercially available product can be used. For example, melamine resins include methoxy methyl melamine, methyl melamine, butyl melamine, isobutoxy melamine, butoxy melamine, hexamethylol melamine, hexamethoxy methyl melamine, hexabutoxy methyl melamine, and hexamethoxybutoxy methyl. One or more selected from the group consisting of melamine and iminomethoxy methyl melamine may be used.

Additionally, the melamine resin may have a weight average molecular weight (Mw) of 100 to 5,000 g/mol, 500 to 4,500 g/mol, or 1,000 to 4,000 g/mol. When the weight average molecular weight of the melamine resin is within the above range, there is an effect of improving the adhesion and hardness of the manufactured coating film by improving the crosslinking density. In addition, if the weight average molecular weight of the melamine resin is less than the above range, the crosslink density of the coating film decreases, which causes a problem of reduced chemical resistance and scratch resistance, and if it exceeds the above range, the appearance characteristics of the coating film deteriorate as the molecular weight increases. Problems may arise.

The melamine resin may have a viscosity of 400 to 1,200 cps, 500 to 1,100 cps, or 600 to 1,000 cps at 25°C. When the viscosity of the melamine resin at 25°C is within the above range, the produced coating film has excellent gloss and appearance. In addition, if the viscosity of the melamine resin at 25°C is less than the above range, the viscosity is low and the adhesion and scratch resistance of the coating film are reduced due to non-formation of the coating film, and if it exceeds the above range, the workability of the composition is inferior. As a result, a problem may arise in which the appearance characteristics of the manufactured coating film are insufficient.

Additionally, the melamine resin may have an acid value (Av) of 5 mgKOH/g or less, or 0.1 to 3 mgKOH/g. If the acid value of the melamine resin is less than the above range, the hardness and appearance characteristics of the produced coating film may decrease due to a decrease in the curing reaction rate. If the acid value of the melamine resin exceeds the above range, the water resistance may decrease as the hydrophilicity improves. there is.

The melamine resin may have a solid content (NV) of 50 to 70% by weight, or 55 to 60% by weight, based on the total weight of the resin. If the solid content of the melamine resin is less than the above range, the workability of the paint may be reduced, and if it exceeds the above range, the workability may be reduced due to the high solid content during the manufacture of the paint.

Additionally, the melamine resin may be included in an amount of 5 to 15% by weight, or 7 to 13% by weight, based on the total weight of the clear coat composition. When the melamine resin is included within the above content range, there is an effect of improving the adhesion and hardness of the manufactured coating film by improving the crosslinking density. If the content of melamine resin in the composition is less than the above range, there is a problem of deterioration of mechanical properties and chemical resistance due to a decrease in curability, and if it exceeds the above range, the adhesion decreases as the coating film becomes brittle due to excessive curability. And problems such as deterioration in chipping resistance may occur.

The clear coat composition may further include a solvent.

solvent

The solvent controls the viscosity of the composition, improves drying properties, and improves the appearance characteristics and spreadability of the produced coating film.

The solvent is not particularly limited as long as it is commonly used in clear coat compositions, and may include, for example, one or more selected from the group consisting of aromatic, acetate-based, alcohol-based, and propionate-based solvents. Specifically, the solvent includes aromatic solvents such as toluene and xylene; 1-methoxy-2-propyl acetate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl glutarate, methyl succinate, methyl adipate, dimethyl glutarate, dimethyl succinate, dimethyl adipate Acetate-based solvents such as pate, butyl carbitol acetate, butyl cellosolve acetate, propylene glycol methyl ether acetate (PMA), and trimethyl-o-acetate; Alcohol-based solvents such as n-butanol, propanol, 1-methoxy-2-propanol, and 2-butoxyethanol; Ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; and propionate-based solvents such as ethyl ethoxypropionate; It may include etc. Additionally, commercially available products of the aromatic solvent include Cocosol #100 and Cocosol #150.

Additionally, the solvent may be included in an amount of 5 to 40% by weight, or 10 to 35% by weight, based on the total weight of the clear coat composition. When the solvent is contained within the above range, the viscosity of the composition is appropriately adjusted, thereby improving workability and drying properties. In addition, if the solvent content is less than the above range, there is a problem of insufficient workability of the composition due to the high solid content in the composition, and if it exceeds the above range, the solid content of the manufactured paint is low, affecting the appearance and adhesion of the manufactured coating film. This shortage problem may occur.

additive

The clear coat composition according to the present invention may further include additives such as flow control agents, ultraviolet absorbers, dispersants, surface conditioners, anti-foaming agents, and curing catalysts. At this time, the additive is not particularly limited as long as it can be added to the paint composition normally.

In addition, the content of the additive is not particularly limited as long as it is within the range that can normally be included in the clear coat composition, for example, the content is 10 to 30% by weight, or 15 to 25% by weight based on the total weight of the clear coat composition. may be included.

The clear coat composition may have a solid content of 40 to 60% by weight, or 45 to 55% by weight. When the solid content of the clear coat composition is within the above range, there is an advantage that the painting workability of the composition becomes appropriate.

Additionally, the clear coat composition may have a viscosity of 15 to 50 seconds, or 20 to 35 seconds, based on Ford Cup No. 4 at 25°C. If the viscosity of the clear coat composition at 25°C is less than the above range, problems such as flowing down vertical surfaces may occur and workability may be insufficient, and if it exceeds the above range, the viscosity of the composition is high and the appearance of the coating film manufactured therefrom may be impaired. This may cause the sprayer to malfunction due to poor characteristics or load on the sprayer.

As described above, the clear paint composition according to the present invention has excellent reactivity, so even when the drying time after painting is short, the travel distance to the oven for curing after drying the clear coat is short, or the distance between car bodies is short, the manufactured paint film It has excellent appearance characteristics as no pinholes occur and no loss of gloss occurs. In addition, the coating film prepared from the clear coat composition has excellent mechanical properties such as hardness, adhesion, and scratch resistance, and can be usefully used for car body painting.

clear paint kit

Additionally, the clear paint kit of the present invention includes the clear coat composition as described above; and a curing agent. That is, the clear paint kit of the present invention is a two-component paint.

The clear paint kit can be used after mixing the clear coat composition and hardener before use.

hardener

The curing agent serves to form a coating film by reacting with the hydroxyl group of the resin as described above to form a urethane bond and curing the composition.

The curing agent may be an isocyanate-based curing agent. At this time, the type of the isocyanate-based curing agent is not particularly limited, and may include, for example, an aliphatic polyisocyanate compound without yellowing phenomenon. Specifically, the isocyanate-based curing agent may include hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl methane diisocyanate, tetramethyl xylene diisocyanate, or mixtures thereof.

In addition, the isocyanate-based curing agent may have an unreacted isocyanate group content (NCO%) of 15 to 30 wt%, or 19 to 24 wt%, based on the total weight of the curing agent. If the NCO% of the isocyanate-based curing agent is less than the above range, the crosslink density of the coating film decreases, which causes a problem in that the impact resistance, water resistance, and cold chipping resistance of the coating film deteriorate. If it exceeds the above range, the curing speed increases and the resin aggregates. This may cause problems such as deterioration in the appearance, gloss, and mechanical properties of the coating film.

The clear paint kit may include a clear coat composition and a curing agent at a weight ratio of 2 to 4:1, or 2.5 to 3.4:1. If the weight ratio of the clear coat composition and the curing agent is less than the above range, that is, if a small amount of the clear coat composition is included relative to the weight of the curing agent, unreacted isocyanate groups are generated in the coating film after curing, causing a problem in which the physical properties of the coating film are deteriorated. If the range is exceeded, that is, if an excessive amount of clear coat composition is included relative to the weight of the curing agent, a problem of low curing density may occur due to insufficient reactivity of the composition.

The clear paint kit may have a solid content of 50 to 70% by weight, or 55 to 65% by weight. When the solid content of the clear paint kit is within the above range, there is an advantage that the painting workability of the composition becomes appropriate.

Additionally, the clear paint kit may have a viscosity of 20 to 50 seconds, or 25 to 45 seconds based on Ford Cup No. 4 at 25°C. If the viscosity of the clear paint kit at 25°C is less than the above range, problems such as dripping on vertical surfaces may occur, and if it exceeds the above range, the viscosity of the paint is high, so the appearance characteristics of the paint film manufactured therefrom deteriorate or the paint may be damaged. The load on the machine may cause the sprayer to malfunction.

As described above, the clear paint kit according to the present invention has excellent reactivity, so even when the drying time after painting is short, the travel distance to the oven for curing after drying the clear coat is short, or the distance between car bodies is short, the manufactured paint film can be used. It has excellent appearance characteristics as no pinholes occur and no loss of gloss occurs.

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

[Example]

Examples 1 to 21 and Comparative Examples 1 to 11. Preparation of clear coat composition

The ingredients in the same amounts as shown in Tables 1 to 3 were mixed to prepare a clear coat composition with a viscosity of 28 seconds at 25°C based on Ford Cup No. 4.

Ingredients (% by weight) Example One 2 3 4 5 6 7 8 9 First polyester resin-1 25 21 29 18 33 25 25 25 25 2nd polyester resin-1 20 20 20 20 20 16 24 12 27 Silicone modified polyester resin 7 7 7 7 7 7 7 7 7 melamine resin 10 10 10 10 10 10 10 10 10 anti-flow agent 14.5 14.5 14.5 14.5 12.8 14.5 14.5 14.5 14.5 UV absorber 2 2 2 2 2 2 2 2 2 surface conditioner 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 defoamer 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 acid catalyst 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Trimethyl o-acetate 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 dimethyl ester 8 10 7 11 5 10 6 12 4.5 Cocosol #100 9.3 11.3 6.3 13.3 6 11.3 7.3 13.3 5.8 Sum 100 100 100 100 100 100 100 100 100

Ingredients (% by weight) Example 10 11 12 13 14 15 16 17 18 19 20 21 First polyester resin-1 25 25 25 25 25 25 25 25 First polyester resin-2 25 1st polyester resin-3 25 1st polyester resin-6 25 1st polyester resin-7 25 2nd polyester resin-1 20 20 20 20 20 20 20 20 2nd polyester resin-2 20 2nd polyester resin-3 20 2nd polyester resin-6 20 2nd polyester resin-7 20 Silicone modified polyester resin 7 7 7 7 7 7 7 7 3 7 One 12 melamine resin 10 10 10 10 10 10 10 10 10 10 10 10 anti-flow agent 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 UV absorber 2 2 2 2 2 2 2 2 2 2 2 2 surface conditioner 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 defoamer 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 acid catalyst 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Trimethyl-o-acetate 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 dimethyl ester 8 8 8 8 8 8 8 8 10 8 10 5 Cocosol #100 9.3 9.3 9.3 9.3 9.3 9.3 9.3 9.3 11.3 9.3 13.3 7.3 Sum 100 100 100 100 100 100 100 100 100 100 100 100

Ingredients (% by weight) Comparative example One 2 3 4 5 6 7 8 9 10 11 First polyester resin-1 25 25 25 25 25 25 1st polyester resin-4 25 1st polyester resin-5 25 No. 1 polyester resin-8 25 1st polyester resin-9 25 2nd polyester resin-1 20 20 2nd polyester resin-4 20 2nd polyester resin-5 20 2nd polyester resin-8 20 2nd polyester resin-9 20 Silicone modified polyester resin 7 7 7 7 7 7 7 7 7 7 melamine resin 10 10 10 10 10 10 10 10 10 10 10 anti-flow agent 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 14.5 UV absorber 2 2 2 2 2 2 2 2 2 2 2 surface conditioner 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 defoamer 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 acid catalyst 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Trimethyl o-acetate 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 dimethyl ester 15 17 11 15 15 15 15 8 8 8 8 Cocosol #100 27.3 20.3 13.3 22.3 22.3 22.3 22.3 9.3 9.3 9.3 9.3 Sum 100 100 100 100 100 100 100 100 100 100 100

Hereinafter, the manufacturer, product name, or ingredient name of each ingredient used in comparative examples and examples is shown in Table 4.

Physical properties, or manufacturer and product name First polyester resin-1 Mw: 1,174g/mol, OHv: 250mgKOH/g, Av: 20mgKOH/g, Tg: 22℃, NV: 75% by weight First polyester resin-2 Mw: 1,174g/mol, OHv: 213mgKOH/g, Av: 20mgKOH/g, Tg: 22℃, NV: 75% by weight 1st polyester resin-3 Mw: 1,174g/mol, OHv: 284mgKOH/g, Av: 20mgKOH/g, Tg: 22℃, NV: 75% by weight 1st polyester resin-4 Mw: 1,174g/mol, OHv: 187mgKOH/g, Av: 20mgKOH/g, Tg: 22℃, NV: 75% by weight 1st polyester resin-5 Mw: 1,174g/mol, OHv: 309mgKOH/g, Av: 20mgKOH/g, Tg: 22℃, NV: 75% by weight 1st polyester resin-6 Mw: 1,174g/mol, OHv: 250mgKOH/g, Av: 20mgKOH/g, Tg: 17℃, NV: 75% by weight 1st polyester resin-7 Mw: 1,174g/mol, OHv: 250mgKOH/g, Av: 20mgKOH/g, Tg: 28℃, NV: 75% by weight No. 1 polyester resin-8 Mw: 1,174g/mol, OHv: 250mgKOH/g, Av: 20mgKOH/g, Tg: 13℃, NV: 75% by weight 1st polyester resin-9 Mw: 1,174g/mol, OHv: 250mgKOH/g, Av: 20mgKOH/g, Tg: 33℃, NV: 75% by weight 2nd polyester resin-1 Mw: 1,285g/mol, OHv: 130mgKOH/g, Av: 23mgKOH/g, Tg: 5.7℃, NV: 70% by weight 2nd polyester resin-2 Mw: 1,285g/mol, OHv: 94mgKOH/g, Av: 23mgKOH/g, Tg: 5.7℃, NV: 70% by weight 2nd polyester resin-3 Mw: 1,285g/mol, OHv: 165mgKOH/g, Av: 23mgKOH/g, Tg: 5.7℃, NV: 70% by weight 2nd polyester resin-4 Mw: 1,285g/mol, OHv: 71mgKOH/g, Av: 23mgKOH/g, Tg: 5.7℃, NV: 70% by weight 2nd polyester resin-5 Mw: 1,285g/mol, OHv: 189mgKOH/g, Av: 23mgKOH/g, Tg: 5.7℃, NV: 70% by weight 2nd polyester resin-6 Mw: 1,285g/mol, OHv: 130mgKOH/g, Av: 23mgKOH/g, Tg: 2.7℃, NV: 70% by weight 2nd polyester resin-7 Mw: 1,285g/mol, OHv: 130mgKOH/g, Av: 23mgKOH/g, Tg: 8.4℃, NV: 70% by weight 2nd polyester resin-8 Mw: 1,285g/mol, OHv: 130mgKOH/g, Av: 23mgKOH/g, Tg: -1.6℃, NV: 70% by weight 2nd polyester resin-9 Mw: 1,285g/mol, OHv: 130mgKOH/g, Av: 23mgKOH/g, Tg: 11.7℃, NV: 70% by weight Silicone modified polyester resin OHv: 200mgKOH/g, Av: 5mgKOH/g, Tg: -10℃, NV: 90% by weight, viscosity at 25℃: 7,200cps melamine resin Mw: 3,000g/mol, Av: 1mgKOH/g, NV: 57% by weight, viscosity at 25℃: 870cps anti-flow agent Manufacturer: ALLEX, Product name: C-91756 UV absorber Manufacturer: BASF, Product name: TINUVIN 1130 surface conditioner Manufacturer: BYK, Product name: BYK-322 defoamer Manufacturer: KUSUMOTO, Product Name: OX-60 acid catalyst Manufacturer: KING, Product Name: NACURE-5543

Reference example. Preparation of hardeners

A curing agent was prepared by mixing 49% by weight of hexamethylene diisocyanate (HMDI) as an isocyanate resin, 15% by weight of Cocosol-100, 17% by weight of xylene, and 19% by weight of butyl acetate as an organic solvent.

The prepared curing agent had an unreacted isocyanate group content (NCO%) of 21% by weight.

Experiment example. Evaluation of paint film properties

Primer paint (manufacturer: KCC, product name: FU2290) was applied to the specimen and cured at 140°C for 20 minutes to form a primer film with a thickness of 40㎛. Afterwards, a base coat (manufacturer: KCC, product name: WT3062) was applied on the primer film, and hot air was blown at 80°C for 3 minutes to evaporate the water remaining in the paint, forming a base film with a thickness of 15㎛.

Afterwards, a clear paint was prepared by mixing the clear coat composition prepared in Examples and Comparative Examples and the curing agent of the Reference Example at a weight ratio of 3:1 on the base coating film, and the clear paint was applied and cured at 140°C for 25 minutes to obtain a thickness. The final coating film was prepared by forming a 40㎛ clear coating film. The physical properties of the specimen were measured in the following manner, and the results are shown in Table 5.

(1) Pinhole characteristics

The clear paint was applied in the same manner as described above at a thickness of 10 to 80 ㎛ at 5 ㎛ intervals, and the point where the first pinhole occurred was measured.

Specifically, if a pinhole occurs at a thickness of 60㎛ or more, excellent (◎), if a pinhole occurs at a thickness of 50㎛ or more but less than 60㎛, good (○), and if a pinhole occurs at a thickness of 40㎛ or more but less than 50㎛, then average (△). , if a pinhole occurred at a thickness of less than 40㎛, it was evaluated as defective (×).

(2) Appearance

Gloss (LU), clarity (SH), and orange peel (OP) were measured for the manufactured final coating using an automotive exterior measuring instrument, Wave Scan DOI (BYK Gardner), and comprehensive appearance evaluation values were obtained using the measured physical properties. (CF) was calculated using Equation 1 below.

[Equation 1]

CF = LU

At this time, CF was measured and calculated horizontally and vertically.

If the calculated CF was 65 or more, it was evaluated as excellent (◎), if it was 60 or more but less than 65, it was evaluated as good (○), if it was 55 or more but less than 60, it was evaluated as average (△), and if it was less than 55, it was evaluated as poor (×).

(3) Glossy

The 20° gloss of the final film was measured using a gloss meter. If the 20° gloss was 91 or more, it was excellent (◎), if it was 89 or more but less than 91, it was good (○), and if it was 87 or more but less than 89, it was average (△). ), if it was less than 87, it was evaluated as defective (×).

(4) Recoating adhesion

The base coat and clear coat were applied to the final film in the same manner as described above, and then the adhesion of recoating was evaluated using the checkerboard method.

Specifically, in the checkerboard method, 100 squares of 2 mm in width and 2 mm in length were made on the surface of the final coating film with a knife, and then the squares were removed using tape to measure adhesion. At this time, the measured adhesion is excellent (◎) when 100 squares are 100% completely attached, good (○) when the remaining squares are between 70% and less than 100%, average (△) when the remaining squares are between 50% and 70%, and 50%. If it is less than that, it was evaluated as defective (×).

(5) Scratch resistance

The initial 20° gloss of the final film was measured using a polisher, and the 20° gloss was measured after 10 reciprocating surface treatments while spraying quartz powder and water using an Amtec Kistler car wash machine. The gloss retention rate of the gloss after surface treatment was calculated based on the gloss before surface treatment.

At this time, if the gloss retention was 70% or more, it was evaluated as excellent (◎), if it was 60% or more but less than 70%, it was evaluated as good (○), if it was 55% or more but less than 60%, it was evaluated as average (△), and if it was less than 55%, it was evaluated as poor (×).

pinhole characteristics Exterior Polish Recoating adhesion Scratch resistance Example One ◎ ◎ ◎ ◎ ◎ 2 ◎ ○ ○ ◎ ○ 3 ○ ○ ◎ ◎ ◎ 4 ○ △ △ ◎ △ 5 △ △ ◎ ○ ◎ 6 ◎ ◎ ◎ ○ ○ 7 ○ ○ ○ ◎ ◎ 8 ○ ◎ ◎ △ △ 9 △ △ △ ○ ◎ 10 ◎ ◎ ◎ ○ ○ 11 ○ ○ ◎ ◎ ○ 12 ○ ◎ ◎ ○ ○ 13 ○ ○ ○ ◎ ○ 14 ○ ◎ ◎ ○ ○ 15 ◎ ○ ○ ○ ○ 16 ◎ ◎ ◎ ○ ○ 17 ○ ○ ◎ ◎ ○ 18 ○ ◎ ○ ◎ ○ 19 ◎ ○ ◎ ○ ○ 20 △ ◎ ○ ○ △ 21 ◎ ○ ○ △ △ Comparative example One X △ △ ○ X 2 △ X X ○ ○ 3 X X △ ○ ○ 4 ○ ○ ○ X X 5 △ X ○ ○ X 6 X ○ ○ X X 7 X X △ ○ X 8 X ○ ○ X X 9 ○ X X X X 10 △ ○ ○ X X 11 X X ○ ○ X

As shown in Table 5, it was found that the coating film prepared from the composition of the example was excellent in all pinhole characteristics, appearance characteristics, gloss, recoating adhesion, and scratch resistance.

On the other hand, Comparative Example 1, which did not contain the first polyester resin, lacked pinhole characteristics and scratch resistance.

Comparative Example 2, which did not contain the second polyester resin, lacked appearance properties and gloss.

Additionally, Comparative Example 3, which did not contain silicone-modified polyester resin, lacked pinhole characteristics and appearance characteristics.

Comparative Example 4, including the first polyester resin-4 with a low hydroxyl value, and Comparative Example 10, including the second polyester resin-8 with a low glass transition temperature, lacked recoating adhesion and scratch resistance.

In addition, Comparative Example 5 including the first polyester resin-5 with a high hydroxyl value and Comparative Example 9 including the second polyester resin-5 with a high hydroxyl value lacked appearance characteristics and scratch resistance. In particular, Comparative Example 9 lacked gloss and recoating adhesion.

Comparative Example 6 including the first polyester resin-8 with a low glass transition temperature and Comparative Example 8 including the second polyester resin-4 with a low hydroxyl value lacked pinhole properties, recoating adhesion, and scratch resistance. did.

In addition, Comparative Example 7 including the first polyester resin-9 having a high glass transition temperature and Comparative Example 11 including the second polyester resin-9 having a high glass transition temperature had pinhole characteristics, appearance characteristics, and scratch resistance. It wasn't enough.

Claims (6)

Based on the total weight of the composition, it contains 22 to 28% by weight of the first polyester resin, 17 to 23% by weight of the second polyester resin, 4 to 8% by weight of the silicone modified polyester resin, and 7 to 13% by weight of the melamine resin; ,
The first polyester resin has a hydroxyl value of 220 to 280 mgKOH/g, a glass transition temperature of 18 to 25 ℃, and a weight average molecular weight of 800 to 1,500 g/mol,
The second polyester resin has a hydroxyl value of 100 to 150 mgKOH/g, a glass transition temperature of 3 to 7° C., and a weight average molecular weight of 800 to 1,600 g/mol. In claim 1,
The first polyester resin has an acid value of 15 to 25 mgKOH/g,
The clear coat composition wherein the second polyester resin has an acid value of 20 to 30 mgKOH/g. In claim 1,
The silicone-modified polyester resin has an acid value of 10 mgKOH/g or less, a hydroxyl value of 150 to 250 mgKOH/g, a glass transition temperature of -20 to 0 ℃, and a viscosity at 25 ℃ of 5,000 to 10,000 cps, clear Coat composition. delete The composition of any one of claims 1 to 3; A clear paint kit containing a hardener. In claim 5,
The composition and the curing agent are included in a weight ratio of 2 to 4:1,
A clear paint kit wherein the curing agent includes an isocyanate-based compound.