JPS63310673A - Formation of paint film - Google Patents

Abstract

PURPOSE:To improve the smoothness of a paint film by carrying out coating with two kinds of paints having the same compsn. or similar in compsn. to each other and having different surface tensions. CONSTITUTION:Paint I and paint II having the same compsn. or similar in compsn. to each other are prepd. Acrylic resin, polyester resin or the like is used as film forming resin in the paints I, II and the difference in surface tension between the paints I, II is regulated by adding dimethylsilicone, dimethylphenylsilicone or the like. Coating with the paints I, II is carried out by air spraying or electrostatic spraying. The thickness of a layer of the paint I is preferably regulated to 5-30mum and that of a layer of the paint II to 10-30mum. Thus, sagging is suppressed and fine appearance can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating film forming method that is particularly useful for forming coating films with excellent finished appearance such as smoothness and ridges on vertical surfaces such as automobile exterior panels.

Conventionally, two methods such as one-coat finishing and two-coat one-bake method were used.
In coating finishing, each coating film was generally formed by applying a single coating material to a predetermined thickness. Looking at the smoothness of the finished painted surface with this method, on flat surfaces of the object, the applied paint spreads due to gravity and tends to become smooth, but on vertical surfaces, the applied paint tends to sag (sag).
gging), it is common to keep it in a flowing state that does not cause sagging, and as a result, the smoothness and sharpness of the painted surface tend to deteriorate. This is a major issue, and improving the smoothness of vertical surfaces is an important research topic, especially in automotive painting.

The present inventor has studied a method for forming a coating film that is less likely to sag on the vertical portions of an object to be coated and has an excellent finished appearance. As a result, each coating film in the one-coat method or the two-coat method (the latter consists of two layers, and refers to each coating film) has the same or similar composition and has a different surface tension. The above objective could be achieved by coating and forming two types of paints.

That is, in the present invention, a solution-type paint (I) containing a color pigment and a resin as main components is applied to the coated surface, and then a solution-type paint (I) having the same or similar composition as the above-mentioned paint (I) and having a surface tension of The present invention relates to a method for forming a coating film, which comprises applying a solution coating material (II) adjusted to be lower than the coating material CI) and then heating to simultaneously cure both coatings.

In the present invention, the level of surface tension between the paint (I) and paint (II) was determined as follows.

A blasted mild steel plate (0.8 x 300 x 200 mm) was thoroughly degreased with petroleum benzene and air-dried to be used as the object to be coated. On the other hand, regarding paint (I) and paint (II),
Air spray (air spray gun (dynamic type) manufactured by Iwata Painting Machine Co., Ltd.) wider No. on the almost vertical surface of the steel plate.
71, with nozzle #02, atomizing air pressure (gauge pressure) of 3 to 5 kg/c+s, discharge amount adjustment screw fully open, slam width of 20 to 25 cm, distance between gun and surface to be coated of 25 cm.
), the type of solvent, and the amount of solvent used should be adjusted so that when coated continuously, the film thickness (dry) is 30 ± 5, no sagging occurs and the smoothness is almost good. The amount is adjusted.

Next, the blast steel plate was set horizontally and painted with paint (I).
) with air spray (under the above conditions) to M thickness (dry) 30±
Paint it so that it can be used for 5. After leaving it at room temperature for 2 minutes, paint (II) is sprinkled on top of it once under the above-mentioned air spray conditions with the atomizing air pressure reduced to 1 kg/co+2. After leaving it as it is for 5 minutes at room temperature, it is leveled and allowed to harden and dry. Visually observe the painted plate,
When the mist (paint particles) application area of paint (II) is concave, it is said that "the surface tension of paint (II) is lower than that of paint (I)", and when it is completely smooth, there are two It is assumed that the surface tensions of the paints are the same, and when the surface tension is convex, it is assumed that the surface tension of the paint (II) is higher than that of the paint (I).

Paint CI) and paint (n) are compositionally the same or similar, and are organic solution-type paints containing colored pigments and film-forming resins as main components. That is, these components can be those already known as paint components, and examples of coloring pigments include inorganic pigments, organic pigments, and metallic pigments, and examples of film-forming resins include acrylic resins, polyester resins, etc. base resin and amino resin,
Particularly suitable are thermosetting resin compositions comprising a curing agent such as a block isocyanate compound, and room temperature curable resin compositions comprising a curing agent such as a polyisocyanate compound mixed with a polyol component such as an acrylic resin or a polyester resin. be.

In the present invention, it is necessary to prepare paint (I) and paint (n) to have the same or almost similar components (pigment and/or resin composition). After painting, apply the paint (n
), the two paint layers will be mutually disturbed at the interface, so if the two paints have different compositions, the shrinkage rate of the paint film will differ during drying and curing, resulting in surface defects such as wrinkles. It is from.

The difference in surface tension between paint (I) and paint (II) can be determined by the composition of the resin or solvent in the paint, or by the addition of a surface tension rA modifier such as silicone oil such as dimethyl silicone or dimethylphenyl silicone, or acrylic resin. It is carried out by

In the present invention, paint (I) and paint (rl) can be used as an undercoat, intermediate coat, or top coat. The coatings CI) and (II) are preferably applied by an atomization coating method such as an air spray method, an airless spray method, an electrostatic spray method, or a rotary electrostatic coating method. , since the single dry coating thickness of the paint film is usually 25 to 60 liters, the coating film thickness of the present invention requires 5 to 30 pots of paint CI) and 1 liter of paint (■).
It is appropriate to set it to 0 to 30.

0 to explain examples and comparative examples related to the present invention
As a general rule, parts and percentages are based on weight.

■ Preparation of sample (1) Material to be coated: Polished mild steel plate (300X300XO, 8m+o) thoroughly degreased with petroleum benzine.

(2) Paint ■～■ ■ ■ ■ (Yo1) 50% alkyd resin Yu40 140 140 (t
2) 60% melamine resin 50 50 50 titanium oxide 100 100 100 solvent”) 17
17 □7 (Thursday 4) A composition consisting of 1% silicone oil 0.3 1.2 2.4 was adjusted to a viscosity of 25 seconds (Ford Cup #4/20''O) using Surpetz #150.

(House 1) 50% alkyd resin consisting of 1 mole of phthalic anhydride, 1 mole of trimethylolpropane, and 0.5 mole of coconut oil fatty acid with a hydroxyl value of 85. 50% alkyd resin solution with oil length 31% and acid value 7.3 (Book 2) Melamine resin Knee Buff 20SE manufactured by Mitsui Toatsu Chemical ■ Butanol-modified melamine resin (Zero 3) Solvent Mixed solvent of equal weight ratio of Kijirol and butanol ( 4) Shin-Etsu Chemical Silicone Oil KP-322 made into a 1% solution with Kijiroll 11 Examples and Comparative Examples Paint (I) was applied to a vertically lined surface (polished mild steel plate) with a hardened film of about 10%. Air spray paint as required, let stand for 2 minutes at room temperature, then apply paint (■) with a hardened film at two levels of approximately 15# and 25#L. Approximately 10 at room temperature
After leaving it for a minute, it is heated at 140°C for 30 minutes to harden. (
(The object to be coated shall be held vertically during all operations.) The finish test results of these test pieces are shown in Table 1.

Table 1 Suga Testing Machine - Finishing Measuring Machine r IMAGECLAR
The larger the value measured by ``ITY METERHa-ICM'', the better the finish.

Claims (1)

[Claims] Solution-type paint (I) whose main ingredients are colored pigments and resins
The composition is the same as or similar to the above paint (I), and the surface tension is the same as the above paint (I).
A method for forming a coating film, which comprises applying a solution-type coating material (II) adjusted to a lower temperature than I), and then heating to simultaneously cure both coating films.