Causes and prevention of sick orange peel and sagging phenomenon in painting

De-painting sickness refers to the abnormal phenomenon that may occur during the coating construction process and after the coating dries and forms a film.

There are many factors that cause morbidity, such as: raw material performance, formula design, manufacturing process, storage and storage, surface treatment, construction technology, and environmental climate. No matter what the reason is, it may affect the quality of the material or the membrane. If there is a diseased state, it will not only affect the appearance of the paint film, but also reduce its protective performance. In order to make better use of material removal, avoid morbidity, and give full play to the decorative and protective performance of coatings, the common treatment methods of spraying construction are introduced here.

orange peel

The finger layer forms an orange-peel-like bumpy surface as it dries

(1) Reasons

Orange peel is caused by poor leveling of the paint. The removal materials that are prone to bridge skin mainly include nitro varnish, amino alkyd resin varnish, etc.

(2) Prevention methods

1. To ensure that the paint has a certain leveling time after painting, the solvent should not volatilize too quickly, choose the corresponding supporting diluent or add part of the medium and high boiling point solvent that volatilizes slowly (such as 1 Buxitong), or add an appropriate amount Leveling agents (these parts need to be selected according to strict technical product quality requirements, and cannot be added randomly); the temperature of the surface of the coated object should not be too high, and it cannot be dried immediately after spraying, and there must be sufficient room temperature leveling time; when spraying The indoor temperature should not be too high, about 20°C. The wind speed should not be too high. Otherwise, it will accelerate the volatilization of the solvent and shorten the leveling time of the paint.

2. The surface to be coated should be fully polished and smooth to ensure the consistency of the coating and the leveling effect of the coating; each coating must have a certain thickness, not too thin. Generally, it should be more than 20µm; choose the appropriate spraying pressure , urban coating distance, nozzle size, and then ensure good atomization of the paint; the paint should have a moderate degree of resistance and not too large. A lower coating viscosity should be selected after the experiment. If the high-viscosity nitro method does not call for coating but brushing, it will cause orange peel if it is too late to brush evenly or level.

Sagging

Streaming refers to the phenomenon that part of the paint on the surface of the object to be coated is in the shape of wine or stalagmites under the action of gravity, also known as sagging. It is more common in facade painting, and there are more depressions in the corners and corners.

(1) Reasons

1. The ambient temperature of the coating is high. Or the diluent volatilizes too slowly, the construction viscosity of the coating is too small, and the fluidity is too large, which is easy to cause sagging. (Related instruments: Sag Tester)

2. When painting, the rattan paint is too much and not evenly painted. If the bristles are too soft, the paint liquid will be too thick to open, or if the bristles are too short, the paint liquid will be thin.

3. When spraying, the caliber of the nozzle of the gun is too large, the air pressure is too small, and it is barely sprayed; the distance from the object is too close, the speed of the gun is too slow; the oily paint and drying paint dry slowly, and there is too much overlap when spraying.

4. During construction, the wet temperature is low, the humidity is high, and the material removal and drying are slow when the ventilation is poor. (Related instruments: temperature and humidity meter)

(2) Prevention methods

1 Thinner should be selected according to the construction environment. Adjust the appropriate viscosity of the material. For example, the spraying viscosity of the base paint should be about 18-26s, and the baking paint should be 20-30s. (Related instruments: drying time Tester)

2. Do not dip the paint brush too much at one time, the paint liquid is thin, and the bristles should be large; the paint liquid is thick, and the bristles should be short.

3. The diameter of the nozzle for spraying nitro paint is slightly larger, the air pressure is 0.4-0.5MPa (4-5kgf/cm'), and it is about 25m away from the high workpiece. The nozzle diameter of the oil spray method should be smaller, and the distance from the workpiece is more than 30cm. Oil-spraying rattan or drying paint should not be painted too much, and the gun speed should be slightly faster.

4. Try to increase the ambient temperature (above 10°C) and improve the ventilation conditions. If necessary, do the drying and subtraction test of the coating film before painting.