1 In the premise that the film thickness meets the requirements of hiding power, the paint film thickness of the metallic paint should be reduced as much as possible, and at the same time, the thickness of the varnish coating film should be increased as much as possible.
Metallic paints are usually sprayed using a combination of high-speed automatic electrostatic cup spray paint (ESTA) and automatic spray guns (Spraymate). Generally, the film thickness of the ESTA paint shall be 60% to 70% of the total film thickness of the metallic paint, and the thickness of the spraymate shall be 30% to 40% of the total film thickness of the metal paint. The proportion of spray paint for each metallic paint is different. It is necessary to find out the best ratio in practice. Generally, the film thickness of metallic paint is controlled from 12 to 18 μm, and the film thickness of varnish is controlled from 25 to 35 μm.
2 Add additives
The spray environment has an effect on the orange peel process of the paint film. In the condition that the constant temperature/humidity of the spray booth cannot be guaranteed, the orange peel process can be reduced by adding additives. For example, in the case of high temperature, high boiling point additives (such as diethylene glycol butyl ether and ethylene glycol butyl ether acetate, etc.) can be added to improve the orange peel defects of the paint film produced during the spraying process due to the excessive volatilization of the solvent.
In addition, it is better to spray the varnish after the metallic paint has been dried to 85%, so it is possible to improve the drying process of the metallic paint by adding flow modifying additives. However, attention should be paid to the control of the addition of flow modification aids. Insufficient amount of additives will cause orange peel and pinholes in the coating. Excessive amount of additives will cause loss of light and haze on the coating. Efforts also have some program influence. 3 Control of Electrostatic Sprayer Process
At present, most auto manufacturers' paint lines use high-voltage electrostatic automatic spray systems. In the actual production process, it is important to select the cooperative automatic sprayer process control parameters for different topcoat coatings.
3.1 Rotation speed of cup
The rotation speed of the ESTA cup is the factor that has the most influence on the atomization particle size of the coating. When the rotational speed of the rotary cup is too low, the paint is poorly atomized and the paint film is rough; the larger the rotational speed, the smaller the atomized particle size of the paint and the smoother the paint film, but the fine atomization will cause the loss of the paint mist, and This can cause excessive wear on the automatic sprayer turbine bearings. Therefore, for the solvent-based coatings, the spinner speed of the ESTA should be controlled between 20000 and 300000r/min when spraying the middle paint and the paint. When the varnish is sprayed, the rotation speed of the ESTA should be controlled between 20000 and 35000r/min. .
3.2 Shaping air volume
Adjusting the shaping air volume of ESTA can control the size of the paint fan. The lower the shaping air volume, the larger the paint fan area. The amount of shaping air is reduced, which can reduce the long-wave orange peel of the paint film. However, when the shaping air volume is too low, the sprayed paint mist can contaminate the screw cup.
3.3 spraying distance
Spray distance between spray cup and body should generally be controlled at 250-300mm. Excessive distance will not only affect the utilization of the coating, but also adversely affect the smoothness of the coating.
3.4 Spray flow
Increasing the thickness of the varnish in the middle and varnish can increase the fullness of the coating and effectively reduce the orange peel of the coating, and the spraying flow rate is an important factor that affects the thickness of the varnish. In fact, when the spray flow reaches the critical state of sagging, the coating surface has the best effect. Therefore, several sets of different spray control parameters can be determined according to the actual production conditions, so that the spray flow is always guaranteed to be in the state of flow-like non-flow.
3.5 electrostatic voltage
ESTA electrostatic voltage coating also has an effect on the coating orange peel, generally controlled at 30 ~ 1000kV better.
Metallic paints are usually sprayed using a combination of high-speed automatic electrostatic cup spray paint (ESTA) and automatic spray guns (Spraymate). Generally, the film thickness of the ESTA paint shall be 60% to 70% of the total film thickness of the metallic paint, and the thickness of the spraymate shall be 30% to 40% of the total film thickness of the metal paint. The proportion of spray paint for each metallic paint is different. It is necessary to find out the best ratio in practice. Generally, the film thickness of metallic paint is controlled from 12 to 18 μm, and the film thickness of varnish is controlled from 25 to 35 μm.
2 Add additives
The spray environment has an effect on the orange peel process of the paint film. In the condition that the constant temperature/humidity of the spray booth cannot be guaranteed, the orange peel process can be reduced by adding additives. For example, in the case of high temperature, high boiling point additives (such as diethylene glycol butyl ether and ethylene glycol butyl ether acetate, etc.) can be added to improve the orange peel defects of the paint film produced during the spraying process due to the excessive volatilization of the solvent.
In addition, it is better to spray the varnish after the metallic paint has been dried to 85%, so it is possible to improve the drying process of the metallic paint by adding flow modifying additives. However, attention should be paid to the control of the addition of flow modification aids. Insufficient amount of additives will cause orange peel and pinholes in the coating. Excessive amount of additives will cause loss of light and haze on the coating. Efforts also have some program influence. 3 Control of Electrostatic Sprayer Process
At present, most auto manufacturers' paint lines use high-voltage electrostatic automatic spray systems. In the actual production process, it is important to select the cooperative automatic sprayer process control parameters for different topcoat coatings.
3.1 Rotation speed of cup
The rotation speed of the ESTA cup is the factor that has the most influence on the atomization particle size of the coating. When the rotational speed of the rotary cup is too low, the paint is poorly atomized and the paint film is rough; the larger the rotational speed, the smaller the atomized particle size of the paint and the smoother the paint film, but the fine atomization will cause the loss of the paint mist, and This can cause excessive wear on the automatic sprayer turbine bearings. Therefore, for the solvent-based coatings, the spinner speed of the ESTA should be controlled between 20000 and 300000r/min when spraying the middle paint and the paint. When the varnish is sprayed, the rotation speed of the ESTA should be controlled between 20000 and 35000r/min. .
3.2 Shaping air volume
Adjusting the shaping air volume of ESTA can control the size of the paint fan. The lower the shaping air volume, the larger the paint fan area. The amount of shaping air is reduced, which can reduce the long-wave orange peel of the paint film. However, when the shaping air volume is too low, the sprayed paint mist can contaminate the screw cup.
3.3 spraying distance
Spray distance between spray cup and body should generally be controlled at 250-300mm. Excessive distance will not only affect the utilization of the coating, but also adversely affect the smoothness of the coating.
3.4 Spray flow
Increasing the thickness of the varnish in the middle and varnish can increase the fullness of the coating and effectively reduce the orange peel of the coating, and the spraying flow rate is an important factor that affects the thickness of the varnish. In fact, when the spray flow reaches the critical state of sagging, the coating surface has the best effect. Therefore, several sets of different spray control parameters can be determined according to the actual production conditions, so that the spray flow is always guaranteed to be in the state of flow-like non-flow.
3.5 electrostatic voltage
ESTA electrostatic voltage coating also has an effect on the coating orange peel, generally controlled at 30 ~ 1000kV better.
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