KR101194665B1 - Primer/clearcoat free painting process of monocoat top-coating material - Google Patents

Abstract

The present invention relates to a medium / clear coat erasing coating method, and more particularly, a base coat paint including a sunscreen composition, a block isocyanate and melamine is coated on a substrate having an electrodeposition coating with a single film having a thickness of 25 to 70 μm. The present invention relates to a medium / clear coat erasing type coating method for a monocoat top coat which can protect the electrodeposition coating film from ultraviolet rays and can secure physical properties and appearance quality even if the intermediate and clear coats are eliminated.

Description

Medium / clear coat clear coating method for monocoat top coat {PRIMER / CLEARCOAT FREE PAINTING PROCESS OF MONOCOAT TOP-COATING MATERIAL}

The present invention relates to a medium / clear coat erasing coating method, and more particularly, a base coat paint including a sunscreen composition, a block isocyanate and melamine is coated on a substrate having an electrodeposition coating with a single film having a thickness of 25 to 70 μm. The present invention relates to a medium / clear coat erasing type coating method for a monocoat top coat which can protect the electrodeposition coating film from ultraviolet rays and can secure physical properties and appearance quality even if the intermediate and clear coats are eliminated.

In a typical coating method applied to automobiles and the like, many coating films are formed. Each paint film is designed to impart specific properties to the paint system. The substrate is first coated with an electrodeposition (ED) paint, and the electrodeposition film serves to control corrosion. Next, the intermediate (primer / surface) paint is coated on the electrodeposition coating film, which plays an essential role in blocking ultraviolet rays (UV) from the sun reaching the electrodeposition coating film. Next, one or more basecoat coatings are applied over the intermediate coating, which provides the color required for the substrate. Finally, one or more clearcoat coatings are coated over the basecoat coating, which provides the basecoat coating with scratch resistance, acid resistance, weather resistance, gloss, and distinctness of image (DOI). This conventional coating method is shown in FIG.

On the other hand, the electrodeposition coating film is usually not resistant to ultraviolet rays. When ultraviolet light reaches the electrodeposited coating and reacts, the electrodeposited coating is degraded and the entire coating system can be peeled off from the substrate. This problem occurs when the electrodeposition coating film is used alone or when ultraviolet rays are not blocked by other coating films. The base coat coating film of the conventional coating method does not block the ultraviolet light that reaches the electrodeposition coating film, the coating film formed through the intermediate serves to protect the electrodeposition coating film from ultraviolet light and prevent peeling. To protect the electrodeposition coating, the intermediate coating typically has a thickness of at least 25 μm to reduce the percentage of ultraviolet light transmitted through the intermediate coating to less than 0.1% at 290-360 nm wavelength and less than 0.5% at 360-400 nm wavelength. Should have For example, when the thickness of the intermediate coating film is 15 μm or less, more than about 10% of ultraviolet rays are transmitted through the intermediate coating film.

In such a situation in which an intermediate application for protecting the electrodeposition coating film is essential, a cost for forming the multilayer coating film is inevitably incurred. First, since the intermediate coating film must contain a considerable amount of ultraviolet (absorbing) material, there is a cost for the material constituting the intermediate coating film. Next, energy is also consumed in the curing step for curing the intermediate coating (also referred to as "baking") before the basecoat paint is applied. In addition, the intermediate paint system includes a prep-deck, a paint booth, a midcoat baking oven, a midcoat sand and an inspection workshop, which requires additional space in the paint line. In addition, since the intermediate paint is usually an oil-soluble solvent-based material, there is also a problem in that the amount of volatile organic compounds (VOC) emitted from the coating process increases.

Accordingly, in the coating system, a 3Coat 1Bake (3C1B) coating method and a water-soluble intermediate removing coating method have been proposed as a technique capable of protecting the electrodeposition coating film from ultraviolet rays while eliminating the intermediate. The 3Coat 1Bake method consists of electrodeposition, midway, basecoat 1, basecoat 2, and clearcoat, and it is a method of coating basecoat and clearcoat with wet on wet without paint drying oven. On the other hand, the water-soluble intermediate erasing type coating method is composed of electrodeposition, base coat 1, base coat 2, clear coat, is a coating method to eliminate the intermediate itself and implement the intermediate function in the base coat 1.

Meanwhile, the intermediate / clear coat removal coating method for the monocoat top coat is that the intermediate itself is eliminated, and the above-described 3Coat is performed in that both the basecoat coating alone performs both the intermediate UV protection and the clearcoat coating protection. It is distinguished from 1Bake coating method and water soluble intermediate removing method.

As shown in Fig. 2, the intermediate / clear coat erasing coating method consists only of electrodeposition and base coat coating. This eliminates spray booths, robot sprayers, circulation systems, tanks, sanding workshops, ovens, etc. No manpower is required for painting and calibration work, and the air conditioning and oven used for painting and curing are omitted, which saves energy and fundamentally blocks the atmospheric environment caused by CO ₂ generated during the curing process. It is a technology that combines both economical and environmentally friendly. That is, the advantages of the medium / clear coat removal coating method are greater than those of the 3C1B coating method or the water-soluble intermediate removal method. Therefore, companies such as automobile companies using the monocoat top coat coating method have a medium / clear coat removal method. Is spurring its application.

However, the intermediate / clear coat erasing coating method is very economical and environmentally friendly as described above, but as a preliminary problem, the protection of the electrodeposited coating film (medium function), the physical properties and the appearance quality through clearing UV rays (clear) The function of the coat) is not fully performed.

Thus, unlike the 3C1B coating method or the water-soluble intermediate-removing coating method, in the medium / clear coat-removing coating method, which removes the clear coat as well as the midway, the intermediate UV protection function and the physical properties and appearance quality of the clear coat are secured. At the same time, it is time to develop a medium / clear coat removal type coating method that can be effectively replaced.

The present invention has been made to solve the problems of the prior art as described above, even if the intermediate and clear coat is eliminated, the intermediate / to the monocoat top coat that can protect the electrodeposition coating film from ultraviolet rays and secure the physical properties and appearance quality It is a technical problem to provide a clear coat removal coating method.

In order to achieve the above technical problem, the present invention is a monocoat top coat, characterized in that to coat a basecoat paint containing a sunscreen composition, block isocyanate and melamine on a substrate electrodeposition coating is completed with a single film of 25 ~ 70㎛ thickness Provides a medium / clear coat removal coating method for paints.

In another aspect of the present invention, there is provided an automobile body coated by the coating method.

By using the intermediate / clear coat erasing coating method for the monocoat top coat of the present invention, it is possible to secure excellent physical properties, appearance quality and workability while protecting the electrodeposition coating film from ultraviolet rays even if the intermediate and clear coats are eliminated. In addition, it can reduce the capital investment, energy and manpower required for the painting process, and reduce CO ₂ emissions as an eco-friendly technology.

Figure 1 shows a conventional coating method.
Figure 2 shows the intermediate / clearcoat clear coating method for the monocoat top coat.
3 is a graph showing ultraviolet transmittance at different wavelengths for the basecoat coating films according to Example 1 and Comparative Example 5. FIG.

Hereinafter, the present invention will be described in detail.

Moderate / clear coat removal coating method for the monocoat top coat of the present invention is a single layer of 25 ~ 70㎛ thick basecoat paint containing a sunscreen composition, block isocyanate (Block NCO) and melamine on the electrodeposition completed substrate It is characterized by painting with a film.

The role of the intermediate paints is weather resistance, chipping resistance, interadhesiveness, and possessive covering power, but the most important role is to prevent ultraviolet rays from reaching the electrodeposition coating film so that the electrodeposited coating film, which is vulnerable to ultraviolet rays, does not whiten or peel off. It is to secure the weather resistance of the coating system for the back. As a result, in the case of the intermediate erasure type method, the ultraviolet ray penetrates the basecoat coating film as a middle member to reach the electrodeposition coating film, and thus, the electrodeposition coating film is destroyed and the aging progresses rapidly due to the ultraviolet light.

3C1B coating method and water-soluble intermediate-deletion coating method have appeared to solve the above problems that occur during the middle deletion. The 3C1B coating method is a wet on wet coating method that eliminates the intermediate curing process. It is a method that continuously coats the base coat and the clear coat through the forced evaporation process of ionized water or solvent contained in the paint instead of the baking process to obtain a dry coating after the intermediate coating. As such, it is distinguished from the intermediate / clear coat removing coating method for the monocoat top coat of the present invention, in which the intermediate process itself is eliminated. In addition, the water-soluble intermediate-clear coating method uses a carbon black pigment in the base coat 1 to perform a moderate function to prevent UV transmission, and the base coat coating alone provides both a moderate UV protection function and a protective function of the clear coat coating film. It is different from the intermediate / clear coat removing coating method for the monocoat top coat of the present invention.

The present invention paints a basecoat paint containing a sunscreen composition, block isocyanate and melamine to a thickness of 25 ~ 70㎛ in order to perform a moderate UV protection function eliminated, thereby protecting the electrodeposited coating film susceptible to UV rays and conventional It is possible to improve the weather resistance problem of the phosphorus removal method.

Electrodeposited coating protection by sun protection is provided through a basecoat containing a sunscreen composition. As the sunscreen composition, carbon black, iron oxide and titanium dioxide (TiO ₂ ) pigments, a sunscreen package, etc. may be used alone or in combination of two or more, but is not necessarily limited thereto. Preferably, a sunscreen composition comprising at least one of a titanium dioxide pigment and a sunscreen package is used.

There is no particular limitation on the carbon black pigment that can be used, and carbon black pigments generally used in coating compositions can be adopted.

There are no particular restrictions on the iron oxide pigments that can be used, and iron oxide pigments generally used in coating compositions can be adopted. For example, commercially available SICOTRANS RED L2818 red iron oxide, Chroma Red RED R03097, SICOTRANS YELLOW 1916 yellow iron oxide, MAPICO ™ YELLOW 1050 Yellow iron oxide and the like can be used. The iron oxide pigment, when used in admixture with other pigments, is preferably included in the basecoat paint in an amount that provides the required decrease in ultraviolet transmittance.

There is no particular limitation on the titanium dioxide pigment which can be used, and titanium dioxide pigment which is generally used in the coating composition can be adopted. For example, as a commercial item, TI-Pure ™ R-706 titanium dioxide, CR-95 titanium dioxide, or the like can be used. The titanium dioxide pigment, when used in admixture with other pigments, is preferably included in the basecoat paint in an amount that provides the required amount of reduction in ultraviolet transmittance. In one embodiment, the titanium dioxide pigment is used 5 to 90% by weight based on the total weight of the solids of the sunscreen composition, 5 to 40% by weight based on the total weight of the cured coating film, more specifically based on the total weight of the cured coating film 20 to 30% by weight is used. If the amount is too small than this range, peeling of the coating film due to UV transmission may occur. If the amount is excessively larger than this range, the relative content of other components may be reduced, resulting in deterioration of physical properties or appearance quality.

The sunscreen pigments are preferably used 10 to 40% by weight based on the total weight of solids of the basecoat paint. If the amount is too small than this range, peeling of the coating film due to UV transmission may occur. If the amount is excessively larger than this range, the relative content of other components may be reduced, resulting in deterioration of physical properties or appearance quality.

The UV protection package is selected based on the pigment type required to match the color standard of the basecoat coating, and the UV protection capability is measured in the wavelength range of 300 to 420 nm. In one embodiment, a UV blocking package having a 300-360 nm UV transmittance of less than 0.05% in a 10 μm basecoat coating and a 360-420 nm UV transmittance of less than 0.015% in a 15 μm basecoat coating is used. In another embodiment, the UV blocking package may be used to replace the white pigment having excellent UV blocking effect due to its color characteristics and to perform the UV blocking function.

Basecoat paints used in the present invention include block isocyanates and melamine as curing agents. There is no particular limitation on the block isocyanate that can be used, and in one embodiment Bayer PL350 may be used. Meanwhile, an acid catalyst may be further included to adjust the curing temperature at the time of curing. There is no particular limitation on the melamine that can be used, and for example, Cytech 325, Cymel327, INEOS Resimine717, BASF Luwipal 052, Luwipal LR8955, KCC R4270 and the like can be used. It is preferable to use a hardening | curing agent 10-30 weight% based on the total weight of a basecoat coating material. If the content is less than 10% by weight based on the total weight of the basecoat paint may result in poor curing, more than 30% by weight can lead to a decrease in impact resistance and chipping resistance due to brittle coating properties.

The basecoat paint may further include a binder in addition to the sunscreen composition and the curing agent. There are no particular restrictions on the binders that can be used, and binders commonly used in paint compositions can be adopted. For example, blocked isocyanate systems, amines or combinations thereof known in the art can be used as a mixture of hydroxy acrylics, polyester carbamate acrylics, polyesters of two functional groups and the like. In one embodiment, a mixture of hydroxy acrylic polymers, hydroxy polyester polymers crosslinked with monomers or polymerized melamine may be used. The binder is preferably used in an amount of 10 to 50% by weight based on the total weight of the basecoat paint. If the content is less than 10% by weight based on the total weight of the base coat paint, it may cause deterioration of physical properties such as acid resistance and water resistance by the unreacted isocyanate group (NCO), and if it exceeds 50% by weight, the acid resistance may be reduced by the unreacted hydroxyl group. It may cause a decrease in physical properties.

Basecoat paints may include colored pigments to provide the colors and effects required for monocoat topcoats. There is no particular limitation on the colored pigments that can be used, and one or more of the organic and inorganic pigments generally used in the coating composition may be arbitrarily adopted as necessary. In one embodiment, it is possible to use a white pigment excellent in the UV protection effect in addition to the coloring function. It is preferable that the sum total of the pigment which performs coloring and / or a sunscreen function is 5 to 30 weight% based on the total weight of a basecoat paint, More preferably, it is 10 to 25 weight%. If the content is less than 5% by weight based on the total weight of the basecoat paint, there may be a problem of undercoat hiding or weather resistance due to UV transmission. If the content exceeds 30% by weight, the leveling and clearness of the paint may be reduced and brittle. It can result in the impact resistance and chipping resistance fall due to coating characteristics.

Basecoat paints may optionally include additives commonly used in coating compositions as needed. As an additive, for example, a leveling agent, a filler, a stabilizer, a surface modifier, a humectant, a dispersant, an antifoaming agent, an adhesion promoter, a rheology control agent, an ultraviolet absorber, an ultraviolet stabilizer, and a thickener may be used alone or in combination of two or more thereof. It is not limited to this. Among the leveling agents, for example, polyether modified dimethylpolysiloxane, 2,4,7,9-tetramethyl-5-dekin-4,7-diol, modified urea mixture, etc. may be used alone or in combination of two or more. However, the present invention is not limited thereto. The leveling agent is preferably used 0.05 to 0.5% by weight, more preferably 0.1 to 0.2% by weight based on the total weight of the base coat paint. If the content of the leveling agent is less than 0.05% by weight based on the total weight of the basecoat paint, high surface tension may cause deterioration of wettability and appearance quality. If the leveling agent exceeds 0.5% by weight, it may cause adhesion problems with the repaint. have. The additive is preferably used in an amount of 0.1 to 1% by weight based on the total weight of the basecoat paint. If the content is less than 0.1% by weight based on the total weight of the base coat paint, it may be difficult to see the effect of the additives. If the content exceeds 1% by weight, the property or appearance quality may be reduced due to the incompatibility between the additive and the resin or an increase in the additive influence. Can cause.

In one embodiment of the invention, the basecoat paint may be a solvent type liquid composition. There are no particular restrictions on the solvents that can be used, and solvents generally used in coating compositions can be adopted. For example, a general mixed solvent may be used, or xylene, ester, normal butyl alcohol, or the like may be used alone or in combination of two or more thereof. The solvent is preferably used 5 to 40% by weight based on the total weight of the basecoat paint, more preferably 10 to 25% by weight. If the content is less than 5% by weight based on the total weight of the basecoat paint, the resin dissolving power in the paint may be lowered, resulting in deterioration in appearance such as clearness and gloss of the paint. In other embodiments, the basecoat can be a solvent-borne composition containing a high solids content or about 45-65 weight percent nonvolatiles.

On the other hand, the base coat paint as described above is coated with a thickness of 25 ~ 70㎛. In the present invention, in the middle / clear coat erasing coating method for a monocoat top coat composed of electrodeposition and basecoat, after the electrodeposition coating, the basecoat paint including the sunscreen composition is coated with a thickness of 25 to 70 μm. Improves weather resistance by preventing the electrodeposition coating film from reaching. If the coating thickness is less than 25㎛, the UV transmittance is increased, and the weather resistance of the electrodeposition coating film vulnerable to ultraviolet rays is not guaranteed.If the coating thickness is more than 70㎛, problems with workability such as poor flowability and pinholes are generated. Is lowered.

The intermediate / clay coat removal coating method for the monocoat top coat of the present invention forms an electrodeposition coating film (thickness of about 15 to 25 μm) on the substrate, and then forms only a single basecoat coating film on the electrodeposition coating film. The basecoat coating film formed by the present invention can reduce the transmission of ultraviolet rays generated in the range of 290 ~ 450nm. In one embodiment, it is preferable that the 300-360 nm UV transmittance at 10 μm after the basecoat film is less than 0.05%, and the 360-420 nm UV transmittance at 15 μm after the basecoat film is less than 0.015%. It is also the standard specification (provided by Hyundai Motor Company) for UV transmittance of clear coat-removable monocoat topcoat.

On the other hand, the present invention, in order to perform the protective function of the clear coat cleared, while introducing a block isocyanate in the base coat and coated with a thickness of 25 ~ 70㎛, preferably, by optimizing the ratio of the block isocyanate and melamine will be. By introducing block isocyanate, urethane bonds improve physical properties such as chipping resistance, form a dense bond structure with the acrylic resin, and improve appearance quality.

That is, even if the clear coat is eliminated, the base coat coating film, which is formed to have a thickness of about 15 to 20 μm when the clear coat is included with the introduction of block isocyanate, is secured so as to secure physical properties and appearance quality equivalent to or better than those of the existing coating method. It is formed with a thick coating film of ˜70 μm. Preferably, the weight ratio of the block isocyanate: melamine may be optimized to 1: 1.0 to 1: 1.7 to obtain more excellent physical properties and appearance quality. If the weight ratio of melamine to block isocyanate in the basecoat paint is less than 1.0, the solvent resistance and appearance quality may be lowered, and if it exceeds 1.7, the hardness may be too large, leading to a decrease in impact resistance.

The intermediate / clear coat removing coating method for the monocoat top coat of the present invention is a base coat paint including a sunscreen composition, block isocyanate and melamine in a conventional coating method on a substrate (for example, a car body) on which electrodeposition is completed. What is necessary is just to coat | coat to thickness of 25-70 micrometers, and other coating conditions are not specifically limited. For example, after the electrodeposition paint is applied to the substrate and cured to form an electrodeposition coating film, a basecoat paint containing a sunscreen composition, block isocyanate and melamine may be coated on the electrodeposition coating film in a thickness of 25 to 70 μm. Coating methods that can be used include spray coating, dip coating, roll coating, curtain coating, but are not necessarily limited thereto. Spray coating is preferable from the aspect of panel protection of an automobile body. Also, if a two-tone or multi-tone method is required, after the basecoat coating is cured between each basecoat coating, the mask may be selectively masked before the next basecoat coating is applied. .

The process of stabilizing the coated coating film (flashing process, Flashing) can also be performed at any temperature for any time. For example, the flashing temperature may be at ambient room temperature (room temperature in the coating process zone) or in the range of about 4 to 150 ° C. Flashing can also be facilitated by the application of infrared light or heat. In one embodiment, the flashing is performed for about 5-8 minutes at ambient room temperature after the basecoat paint is applied but before the coating cures.

The curing process of the coating film may also be carried out by any method known in the art, or two or more curing methods may be used in combination. Curing of the coating film may be performed by actinic rays such as heat, infrared rays, ultraviolet rays, electron beams, etc., but is not limited thereto. In one embodiment, curing is performed by passing the coating through an oven. The curing temperature and curing time can also be selected in any combination depending on the chemical nature of the coating composition used.

In one embodiment of the present invention, the base coat paint according to the present invention is coated with a thickness of 25 to 70 μm at a relative humidity of 60 to 70% and a temperature of 20 to 30 ° C. on a substrate where electrodeposition coating is completed, and 5 to 8 minutes. After stabilizing a coating film, it hardens for 20 to 30 minutes at 140-160 degreeC.

There is no particular limitation on the substrate to which the coating method of the present invention can be applied. For example, it can be applied to metal substrates (car body panels, some automobile parts, etc.), plastic substrates (polymer films, some car parts, etc.), wooden substrates, and is particularly suitable for application to the automobile itself.

As described above, the intermediate / clear coat removing coating method for the monocoat top coat of the present invention can remove the intermediate and clear coats, protect the electrodeposition coating film from ultraviolet rays, and secure the physical properties and appearance quality. It can reduce facility investment cost, energy and manpower, and reduce CO ₂ generation as an eco-friendly technology.

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

Experimental apparatus

1. Paint manufacturing equipment

DISPERMAT: High speed dissolver

BALANCE: unit of measurement 0.01 g

DISPERSION EQUIPMENT: Ring Mill

CONVECTION OVEN: Soburo

DURR's ECO BELL (ROBOT): Sprayer

MANUAL GUN

2. Measuring equipment

FORD CUP # 4: Viscosity Measurement

Specific gravity cup

Other: Thermometer, Stopwatch

3. Quality evaluation device

WAVE SCAN DOI: Appearance Quality Measurement

LOSS METER: Gloss Measurement Instrument

FILM BUILD GUAGE: Coating thickness gauge

Example  1 to 5 and Comparative example  1 to 5

After preparing a liquid coating composition of the vanilla white (SJ) color in the formulation shown in Table 1, through the intermediate / clear coat removal coating method to the vehicle body of the electrodeposition coating (20㎛) is shown in Table 1 below It was coated with a single layer of thickness. (In the case of Comparative Example 5, after coating the intermediate paint and the basecoat paint of the formulation shown in Table 1 on the vehicle body in which the electrodeposition coating is completed according to the existing midway application method, the clearcoat paint was applied.)

The coating of paint is 300 ~ 350cc / min discharge rate using electrostatic bell sprayer, external voltage -50 ~ -70kV, shaping air 0.5 ~ 1kg / cm ² , Bell rpm 30000 ~ 35000, Head target distance (HTD) is 200 ~ It was carried out under the conditions of 300 mm. Immediately after the coating, the coating film was set for 5 to 8 minutes, and then cured at 150 ° C. for 20 minutes to form a final coating film.

Table 1 Components, Contents and Coating Thickness of Basecoat Paints

1): Means the coating thickness of the base coat. (Medium is 25 µm, Clear Coat is 40 µm)

* Acrylic 1: CRT54719 (KC's self-synthetic) acrylic polyol resin-low molecular weight

* Acrylic 2: CRT54252 (KC's self-synthesis) acrylic polyol resin-polymer

* Melamine 1: Cymel 325 (Cytech) melamine resin

* Melamine 2: CRK42705 (KC's self-synthesis) Partial Butoxy Melamine Resin

* Block isocyanate: PL350 (Bayer) Blocked aliphatic polyisocyanate on HDI trimer

* TiO ₂ Pigment: TI-Pure ™ R-706 Titanium Dioxide

* UV protection package: a mixture of Tinuvin 384-2 (BASF) and Tinuvin 292 (BASF)

* Flow regulator: Setalux 91756 (Akzo) Acrylic polymer with SCA

* Additives: Mixtures of leveling agents, fillers, stabilizers, surface modifiers, wetting agents, dispersants, defoamers, adhesion promoters, rheology modifiers, thickeners, etc. which are commonly used in automotive water-soluble paints

* Solvent: Mixture of xylene, solvent naphtha, methyl acetate and normal butyl alcohol

Color pigments: Carbon Black, Paliotan Yellow L1945

Test Example  1: UV transmittance evaluation

UV transmittance was measured using UV / VISIBLE SPECTROPHOTOMETER (Model: LAMBDA 950, manufacturer: Perkinelmer) for the basecoat coating films according to Examples and Comparative Examples and the average values are shown in Table 2-1. (Also, ultraviolet transmittances at different wavelengths for the basecoat coating films according to Example 1 and Comparative Example 5 are shown graphically in FIG. 3.

In addition, the results of performing the Super UV Test on the basecoat coating film according to the Examples and Comparative Examples are shown in Table 2-2.

* Super UV Test is a test method for evaluating weather resistance (adhesiveness) by promoting it, and conducts weather resistance test by UV, heat and water for 3 cycles with 120 cycles as 1 cycle, and water resistance test for 24 hours. , To check the adhesion.

Table 2-1 UV transmittance results

[Table 2-2] Super UV Test Results by Film Thickness

As shown in Table 2-1 and Table 2-2, in the case of the embodiment was excellent overall UV blocking effect. On the other hand, Comparative Examples 1 and 2 having a thickness of the base coat film of less than 25 μm and Comparative Example 5, which are existing base coats, could not effectively block ultraviolet rays, resulting in poor adhesion.

Test Example  2: appearance quality evaluation

The coating film according to the Examples and Comparative Examples was measured by the Wave Scan DOI, CF (general appearance evaluation value) value was confirmed by evaluating the appearance quality and the results are shown in Table 3.

* The Wave Scan DOI does not measure subjective quality of automotive paints, but rather measures and combines gloss (LU), image sharpness (SH), and smoothness (OP) with the instrument to perform more objective quality measurement. Since 2001, it has been used as a quality measuring equipment in Hyundai Motors since 2001.

* CF: LU * 15% + SH * 35% + OP * 50%

As shown in Table 3 below, in the case of the embodiment, the appearance quality was excellent overall. In particular, when compared with the existing medium / clear coat application method (Comparative Example 5), it showed an equivalent to better appearance quality. On the other hand, Comparative Examples 1 to 3 containing no block isocyanate or having a coating thickness of less than 25 μm showed poorer appearance quality than the examples.

Test Example  3: Physical property and workability evaluation

The following items were measured for coating films according to Examples and Comparative Examples to evaluate physical properties and workability, and the results are shown in Table 3 below.

* Adhesiveness: Checking for coating after cross cut

* Hardness: measured by pencil hardness method

* Water resistance: Determination of discoloration, swelling, blistering and adhesion failure after immersing the coating film in hot water at 40 ℃ for 240 hours.

* Acid resistance: Set the temperature of GRADIENT OVEN between 30 ~ 45 ℃, add 0.2ml of sulfuric acid 0.1N on the coating film, and heat for 150 minutes to specify the temperature at which coating damage occurs.

* Chipping resistance: chipping test after 3 hours at -40 ℃

* Scratch resistance: 20 ° gloss measurement after 10 round trips with CAR WASH SCRATCH TEST facility with reduced automatic car wash and check gloss retention rate before and after test

(Good: over 60%, normal: 50-60%, poor: less than 50%)

* Impact resistance: Drop the 50g weight at 20, 30, 40, 50cm using DuPont Tester

(Good: more than 30cm, normal: 20-30cm, poor: less than 20cm)

* Overbaking Adhesion: Checking for coating after cross cut

* Flowability: Check the ease of work according to the flow of paint during painting work

* Pinhole: Check whether or not pinholes are generated during paint work

As shown in Table 3 below, in the case of the embodiment, various physical properties and workability were excellent overall. In particular, even in the conventional manner (Comparative Example 5) to remove the intermediate and clearcoat showed the same to better physical properties. On the other hand, Comparative Example 1, which does not contain block isocyanate and also has a coating thickness of less than 25 μm, has poor physical properties such as acid resistance and scratch resistance, while Comparative Example 4 having a coating thickness of more than 70 μm has poor workability and impact resistance. It was.

Table 3 Test Results

As a result, the intermediate / clear coat erasing coating method for the monocoat top coat of the present invention can secure excellent physical properties, appearance quality and workability together with electrodeposited coating protection from ultraviolet rays even after removing the intermediate and clear coats. It was confirmed that the economic and environmental friendliness of the coating process can be greatly improved.

Claims (8)

Medium / clear coat erasing coating method for monocoat top coat paint, characterized in that the basecoat paint containing a sunscreen composition, block isocyanate and melamine is coated on a substrate having a thickness of 25 to 70 μm on the electrodeposition-coated substrate. . The method according to claim 1, wherein the sunscreen composition comprises at least one of a titanium dioxide pigment and a sunscreen package. The method of claim 1, wherein the weight ratio of the block isocyanate: melamine is 1: 1.0 to 1: 1.7. The coating method according to claim 1, wherein the base coat paint is a solvent type liquid composition. The coating method according to claim 1, wherein the UV transmittance of 300 to 360 nm at a thickness of 10 µm of the base coat coating film is less than 0.05%. The coating method according to claim 1, wherein the transmittance of 360 to 420 nm ultraviolet rays at a thickness of 15 μm of the base coat coating film is less than 0.015%. The method of claim 1, wherein the basecoat paint is coated on the substrate to which electrodeposition coating is completed at a relative humidity of 60 to 70% and a temperature of 20 to 30 ° C, and the film is stabilized for 5 to 8 minutes, and then at 140 to 160 ° C. Coating method characterized in that hardened for 20 to 30 minutes. An automobile body coated with a coating method according to any one of claims 1 to 7.

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