KR20080107099A - A powder coating material composition having exellent scratch resistance and storage stability - Google Patents

Abstract

A powder coating composition is provided to ensure excellent durability and appearance and to perform a low temperature curing by using a glycidyl methacrylate acrylic resin. A powder coating composition comprises a glycidyl methacrylate acrylic resin 50~85 weight%; a hardener having an acid group 10~40 weight%; an acryl leveling agent 0.1~3.0 weight%; metal oxide nano particles 0.1~5.0 weight%; an antioxidant 1.0~4.0 weight%; a photostabilizer 1.0~4.0 weight%; and an anti-pinhole agent 0.1~2.0 weight%. The glycidyl methacrylate acrylic resin has an epoxy equivalent of 350~600g / eq, a melting viscosity of 100~1,000cps and a glass transition temperature of 30~50‹C.

Description

Powder coating composition excellent in scratch resistance and storage stability {A POWDER COATING MATERIAL COMPOSITION HAVING EXELLENT SCRATCH RESISTANCE AND STORAGE STABILITY}

The present invention relates to a powder coating composition excellent in scratch resistance and storage stability, and more particularly glycidyl methacrylate acrylic resin, a curing agent having an acid group, acrylic leveling agent, metal oxide particles, antioxidant, light stabilizer And it relates to a powder coating composition comprising a pinhole inhibitor.

There are many types of paints for automotive topcoats, and suitable paints are selected and used according to the policies of each car manufacturer. Recently, in order to cope with regulations on volatile organic compounds, a lot of environmentally friendly paints are used, and representative examples are water-soluble paints and powder paints. Water-soluble paints have advantages such as excellent appearance, but there is a drawback of poor paintability, powder coating has a disadvantage that can not use the existing coating equipment.

However, since the powder coating does not generate volatile organic compounds at all, the possibility of using it in the future is very high, and it is still being used as a coating for automotive coatings in foreign countries. However, powder coating has a disadvantage in that scratch resistance is inferior to conventional oil-soluble liquid coating. Such a drop in scratch resistance may cause a problem of deterioration in surface glossiness and deterioration of durability when the vehicle body is exposed to a rapidly increasing automatic car wash.

The currently applied powder acrylic clear paint has a skeleton in which an epoxy group and an acid group are bonded as a main skeleton, and there is a limit in improving scratch resistance due to a limitation in increasing the crosslinking density due to molecular weight.

In addition, the acrylic transparent powder coating has a much lower molecular weight than the conventional powder coating and the glass transition temperature of the coating is around 40 ° C., so the paint storage stability is very weak. To use this paint, air conditioners are installed in the storage and coating booths. There is a problem to lower the temperature to 20 ℃ or less.

The present invention has been made to solve the above problems, it is an object of the present invention to provide a powder coating composition excellent in scratch resistance and storage stability.

In order to achieve the above object,

Powder coating composition of the present invention is 50 to 85% by weight of glycidyl methacrylate acrylic resin, 10 to 40% by weight of a curing agent having an acid group (acid group), 0.1 to 3.0% by weight of an acrylic leveling agent, 0.1 to 4.0 nano metal oxide particles 5.0 wt%, 1.0 to 4.0 wt% antioxidant, 1.0 to 4.0 wt% light stabilizer and 0.1 to 2.0 wt% pinhole inhibitor.

Examples of the glycidyl methacrylate acrylic resin include methyl methacrylate, ethyl methacrylate, butyl methacrylate and 2-hydroxyethyl methacrylate in glycidyl methacrylate homopolymer or glycidyl methacrylate. One or more types of polymers selected from the group consisting of rates can be used. Glycidyl methacrylate acrylic resin is characterized by excellent durability, low temperature curing, and excellent appearance. It is preferable that the epoxy equivalent of glycidyl methacrylate acrylic resin is 350-600 g / eq, melt viscosity is 100-1,000 cps (200 degreeC, ICI viscometer), and glass transition temperature is 30-50 degreeC. If the epoxy equivalent is less than 350g / eq may be a rapid reactivity can occur pinhole phenomenon, etc., if it exceeds 600g / eq the adhesion of the paint is poor. When the melt viscosity is less than 100 cps, the melt viscosity of the paint is too low, causing a problem that the paint flows down. When the melt viscosity exceeds 1,000 cps, the melt viscosity is too high and the leveling of the paint drops a lot. If the glass transition temperature is less than 30 ° C., the blocking of the resin becomes severe and difficult to handle, and the properties may change. If the glass transition temperature is higher than 50 ° C., the viscosity of the resin becomes high, resulting in poor leveling.

It is preferable that the content of glycidyl methacrylate acrylic resin is 50 to 85% by weight. When the content is less than 50% by weight, yellowing and leveling may drop a lot. Falling problem occurs.

As a hardening | curing agent which has the said acidic radical, dodecanedioic acid, sebacic acid, etc. can be used, for example.

It is preferable that the hardening | curing agent which has an acidic radical has acidity of 100-500 mgKOH / g, and melt temperature is 100-150 degreeC. If the acidity is less than 100mgKOH / g, the reactivity is too fast, may cause pinholes and wrinkles in the appearance, when the acidity exceeds 500mgKOH / g, the reactivity is poor and the adhesion deteriorates. If the melting temperature is less than 100 ℃, the viscosity of the paint is lowered, the problem of the paint flowing down occurs, and if it exceeds 150 ℃ there is a problem that the leveling of the paint falls.

It is preferable that the content of the curing agent having an acid group is 10 to 40% by weight. When the content is less than 10% by weight, the reactivity is poor and adhesion defects occur, and when the content exceeds 40% by weight, yellowing occurs.

As said acrylic leveling agent, a polyacrylate polymer or a polymethacrylate polymer can be used individually or in mixture.

The acrylic leveling agent has a melting temperature of 50 to 150 ° C and a density of 0.5 to 1.5 g / ml. If the melting temperature is less than 50 ℃ the storage stability of the paint in the powder form is poor, the problem of agglomeration of the paint occurs, if the temperature exceeds 150 ℃, the leveling is greatly reduced and the problem of creering. If the density is out of the above range, there is a problem that the problem of creering on the coating film.

The content of the acrylic leveling agent is preferably 0.1 to 3.0% by weight. If the content is less than 0.1% by weight, there is a problem that creering occurs, and when it exceeds 3.0% by weight, a tackiness occurs in the coating film.

The metal oxide particles are preferably at least one selected from the group consisting of tin oxide oxide powder, tungsten oxide oxide powder, aluminum oxide oxide powder, molybdenum oxide powder, and nickel nanooxide powder.

Since the metal nanoparticles are very small in size, when the powder paint melts and the epoxy group reacts with the acid group, the metal nanoparticles are located between the crosslinks of the paint, which increases the degree of crosslinking of the coating film. By doing so, scratch resistance can be greatly improved. In addition, since the metal nanoparticles contained in the powder coating composition are located between the paint particles, the phenomenon that the paint agglomerates with each other by heat or the like can be suppressed. This effect leads to improved storage stability, making powder coatings less susceptible to heat than conventional paints.

It is preferable that the metal oxide particles have a purity of 99.99% or more and an average particle size of 10 to 300 nm. If the purity is less than 99.99%, impurities may cause a defect in appearance. When the average particle size is less than 10nm, the cohesive force of the nanoparticles becomes strong, so that it is difficult to mix with other components of the powder coating composition, so that the dispersibility worsens, and when the average particle size exceeds 300nm, the appearance becomes cloudy.

The content of the metal nanoparticles is preferably 0.1 to 5.0% by weight. When the content is less than 0.1% by weight, the effect of scratch improvement and appearance improvement is lost. Appears.

Examples of the antioxidant include 9,10-dihydro-9-oxa-10-phosphaperenene-10-oxide, 2-benzothiazol-2-yl-thio-succinic acid di-alkyl ammonium or organophospho. Examples include antioxidants, and serves to improve external durability after painting.

It is preferable that the content of the antioxidant is 1.0 to 4.0% by weight. If the content is less than 1.0% by weight, the durability and yellowing of the coating film occur. If the content exceeds 4.0% by weight, the hardness is poor and the mechanical strength is deteriorated. .

Examples of the light stabilizer include 2-hydroxyphenyltriazole, 2-hydroxyphenyltriazine, and the like, and serve to improve external durability after coating.

It is preferable that the content of the light stabilizer is 1.0 to 4.0% by weight. If the content is less than 1.0% by weight, the durability and yellowing of the coating film occur, and when the content exceeds 4.0% by weight, the curing property is poor and the mechanical strength is deteriorated. .

As the pinhole inhibitor, for example, benzoin and the like are preferable, and serve to release volatile substances from the coating film during curing.

It is preferable that the content of the pinhole inhibitor is 0.1 to 2.0% by weight. If the content is less than 0.1% by weight, the pinhole and the appearance of the coating are poor, and when the content is more than 2.0% by weight, the yellowing of the coating becomes severe and tacky. .

The powder coating composition of the present invention may include various additives and auxiliaries commonly used in the art, in addition to the above components.

Particle size of the powder coating composition is one of the most important factors for forming the appearance of the powder coating film, the smaller the particle size can be made smoother appearance during curing, the lower particle size can be used to obtain a good coating film. The average particle size of the powder of the powder coating composition of the present invention is preferably 10 to 50 µm, more preferably 10 to 30 µm. When there are many particles smaller than 10 μm, it is difficult to quantitatively transfer the powder, agglomeration occurs in the transfer pipe, which adversely affects the painting workability, and when there are many particles larger than 50 μm, the appearance of the coating film is reduced.

The manufacturing process of the powder coating composition is as follows.

The components of the powder coating composition described above are weighed according to the content range of the present invention and then uniformly premixed for 2-6 minutes in a mixer.

Next, the premixed mixture is melt mixed uniformly using a melt kneader such as a kneader or extruder at a temperature of 50-120 ° C. This melt mixing process is preferably repeated two or more times.

The molten mixture is cooled in a chiller roller, then pulverized using a hammer mill or a fritts mill, and passed through a 325 mesh sieve to obtain a powder coating having an average particle size of 10 to 50 µm.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[ Example ]

1. Preparation of Powder Coating Composition

After blending with the ingredients and contents shown in Tables 1 and 2 below, they were mixed using a mixer to ensure uniform premixing for 5 minutes. This was melt-mixed uniformly using a kneader (BUSS company) at 100 degreeC. The melt mixing was repeated twice. The melt-mixed mixture was cooled in a chill roller, and then ground using a hammer mill to prepare a powder coating composition (Examples 1 to 4 and Comparative Examples 1 to 4) having an average particle size of 10 to 50 µm.

Ingredient (g) Example 1 Example 2 Example 3 Example 4 Fine-clad A254 ¹⁾ 60 40 20 80 Fine-clad A257 ²⁾ 20 40 60 - DDDA ³⁾ 20 25 20 25 BYK-361 ⁴⁾ 0.6 0.6 0.6 0.6 Aluminum Nano Oxide Powder ⁵⁾ 0.5 1.0 0.5 1.0 Igafos 168 ⁶⁾ 1.5 1.5 1.5 1.5 Tinuvin 928 ⁷⁾ 1.5 1.5 1.5 1.5 Benzoin ⁸⁾ 0.5 0.5 0.5 0.5

Ingredient (g) Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Fine-clad A254 ¹⁾ 60 40 20 80 Fine-clad A257 ²⁾ 20 40 60 - DDDA ³⁾ 20 25 20 25 BYK-361 ⁴⁾ 0.6 0.6 1.0 1.0 Igafos 168 ⁶⁾ 1.5 1.5 1.5 1.5 Tinuvin 928 ⁷⁾ 1.5 1.5 1.5 1.5 Benzoin ⁸⁾ 0.5 0.5 0.5 0.5

1) Fine-clad A254: glycidyl methacrylate acrylic resin, epoxy equivalent 525g / eq (DIC Corporation)

2) Fine-clad A257: glycidyl methacrylate acrylic resin, epoxy equivalent 480 g / eq (DIC Corporation)

3) DDDA: Dodecanediosan (DuPont)

4) BYK-361: acrylic leveling agent (BYK company)

5) Aluminum Oxide Nano Powder (NTbase)

6) Igafos 168: Antioxidant (Shibagai Corporation)

7) Tinuvin 928: Light Stabilizer (Shiba Gaiji Corp.)

8) Benzoin: Pinhole preventive agent (US conventional)

2. Coating  Produce

The powder coating composition prepared above was coated on an aluminum plate pretreated with a solution containing no chromium, and then cured at 150 ° C. for 25 minutes (base surface temperature) to prepare a coating film specimen having a thickness of 30 to 40 μm. It was.

3. Property measurement

The coating film properties of the coating films prepared above were measured in the following manner, and the results are shown in Tables 3 and 4.

1) Leveling: Visually determine the smoothness of visual judgment / film

2) Gloss: BYK Glossmeter / 20 Degree Reflectance

3) Impact resistance: measured using an impact tester (DuPont)

4) Adhesiveness: 100 sticks of 1mm intervals are drawn on the coating film to measure adhesion

5) Flexibility: Using the Gardner Flexibility Tester (BYK), 3/16 'of the bar, bend the specimen and check for cracks.

6) Scratch resistance: Glossy preservation rate is calculated after 10 times washing with car washer

7) Solvent resistance: Rub the acetone solution 100 times and observe the gloss and color of coating.

8) Leveling (LW, SW): Measured by Wave Scan DOI (BYK)

9) Acid Resistance: After dropping 0.625ml of 10% sulfuric acid, measure the degree of color change at 70 ℃ using gradient oven.

NT: Good condition without trace on coating

GT: Fine traces remain in the coating film

ST: Some traces remain in the coating film

OT: The coating film is corroded

10) Storage stability: Determination of abnormality such as blocking of paint after storage for 1 month at 25 ° C and 60% relative humidity.

Example 1 Example 2 Example 3 Example 4 Film thickness 30 ~ 35um 35 ~ 40um 35 ~ 40um 30 ~ 35um Exterior Leveling Good Good Good Good Polish 90 92 91 90  Mechanical property Impact resistance 0.5kg / 50cm 0.5kg / 40cm 0.5kg / 50cm 0.5kg / 40cm Adhesion 100/100 100/100 100/100 100/100 Flexibility No crack No crack No crack No crack Scratch resistance Car Wash Test 80% 82% 84% 86% Solvent resistance Acetone Good Good Good Good Leveling Lw 4.3 4.5 4.0 5.0 Leveling Sw 8.2 10.4 9.2 10.2 Acid resistance NT NT GT NT Storage stability 25 ℃, one month clear clear clear clear

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Film thickness 30 ~ 35um 35 ~ 40um 35 ~ 40um 30 ~ 35um Exterior Leveling Slight wrinkles Slight wrinkles Slight wrinkles Slight wrinkles Polish 80 82 81 80 Mechanical properties Impact resistance 0.5kg / 50cm 0.5kg / 40cm 0.5kg / 50cm 0.5kg / 40cm Adhesion 100/100 100/100 100/100 100/100 Flexibility No crack No crack No crack No crack Scratch resistance Car Wash Test 60% 55% 54% 50% Solvent resistance Acetone Good Good Good Good Leveling Lw 20.1 23.8 27.4 20.2 Leveling Sw 35.3 38.7 36.9 32.0 Acid resistance NT NT GT NT Storage stability 25 ℃, one month Blocking occurrence Blocking occurrence Blocking occurrence Blocking occurrence

As shown in the above results, it can be seen that when the metal nanoparticles are used in the powder coating composition, the appearance, scratch resistance, leveling and storage stability are all excellent.

As described in detail above, the powder coating composition according to the present invention is excellent in appearance, scratch resistance, leveling and storage stability when used as a coating for automotive top coat.

Claims (6)

50-85 weight% of glycidyl methacrylate acrylic resins, 10-40 weight% of hardening | curing agents which have an acidic radical, 0.1-3.0 weight% of acrylic leveling agents, 0.1-5.0 weight% of metal nanoparticles, 1.0-4.0 weight% of antioxidants Powder coating composition comprising 1.0 to 4.0% by weight of light stabilizer and 0.1 to 2.0% by weight of pinhole inhibitor. The powder coating composition of claim 1, wherein the glycidyl methacrylate acrylic resin has an epoxy equivalent weight of 350 to 600 g / eq, a melt viscosity of 100 to 1,000 cps, and a glass transition temperature of 30 to 50 ° C. The curing agent of claim 1, wherein the curing agent having an acid group has an acidity of 100 to 500 mgKOH / g, a melting temperature of 100 to 150 ° C, and the acrylic leveling agent has a melting temperature of 50 to 150 ° C and a density of 0.5 to 1.5 g / ml. Powder coating composition, characterized in that. The method of claim 1, wherein the metal oxide particles are selected from the group consisting of tin oxide nanopowder, tungsten oxide nanopowder, aluminum nanooxide powder, molybdenum oxide nanopowder and nickel nanooxide powder. Powder coating composition. The powder coating composition of claim 1, wherein the metal nanoparticles have a purity of 99.99% or more and an average particle size of 10 nm to 300 nm. The powder coating composition according to any one of claims 1 to 5, wherein the average particle size of the powder coating is 10 to 50 µm.