- The particles of aliphatic polyurethane topcoat, the protrusions on the paint film, are distributed in granular form on the entire local surface
- A: Reasons:
The spray gun is not cleaned;
The construction environment for spraying polyurethane topcoat is not clean, and dust falls on the paint surface or the adjusted paint;
The temperature in the spray booth is too high or the acrylic polyurethane thinner evaporates too quickly, resulting in dry spraying;
The air circulation design is unreasonable, causing dry paint mist to fall on the wet paint surface;
The viscosity of the polyurethane paint is too high, resulting in poor atomization and large paint droplets.
Prevention and control:
Dust regularly in the paint mixing room, and the paint bucket should be covered with a lid;
Dust thoroughly in the spray booth;
After grinding the workpiece, blow it clean first and then wipe the surface of the workpiece with a dust cloth that does not remove fibers;
Use the matching thinner to clean the spray gun after spraying the paint;
Use a thinner suitable for the ambient temperature;
Adjust the paint viscosity to a reasonable spray viscosity.- Sagging of polyurethane anti-corrosion topcoat. Sagging of polyurethane anti-corrosion topcoat generally occurs on the vertical surface of the construction piece. The wet film flows downward under the action of gravity, forming a local or overall thin top and thick bottom coating. In severe cases, uneven stripes and flow marks appear.
Answer: Reason:
The quality of polyurethane high-gloss paint itself: as an anti-corrosion topcoat, there are generally thick coating design requirements. If the anti-flow performance of the paint itself is too poor, then sagging is inevitable;
Construction of acrylic polyurethane: spraying too thick during construction, or the spraying distance is too close; unnecessary use of large amounts of polyurethane diluents, resulting in low spray viscosity.
Prevention:
If it is caused by factors of the topcoat itself, then acrylic polyurethane paint manufacturers are required to use more reasonable and effective anti-sagging additives in the formula, use less or no high-density fillers, adjust the volatilization rate of the diluent in time, and match the corresponding diluent according to the climate, temperature and construction site conditions.
For sagging caused by construction reasons, spray thinly multiple times (dry film thickness is 20-30μm at a time), control the gun distance (not less than 30cm) and spraying pressure, and strive to achieve uniform gun distance; control the correct acrylic polyurethane topcoat construction viscosity.- Aliphatic polyurethane topcoat shrinkage, the wet film shrinks during the leveling process to form a circular pit, some of which expose the base material, and some particles are found in the middle of the pit, often called “fish eyes”.
Answer: Reason:
Oil, wax or incompatible substances are mixed into the paint;
The surface treatment of the midcoat is not clean, and it is stained with oil, wax, water, machining fluid and other substances;
The air quality in the spray room is too poor, and floating particles fall on the surface of the paint film.
Prevention and control:
Use clean paint mixing tools during the mixing of acrylic polyurethane topcoat;
After the polyurethane midcoat is polished, do not use dirty cloth with oily cloth to touch the midcoat surface;
Ensure that the spray room is clean and there is no floating matter such as dust, oil mist and paint mist in the air.- Pinholes in acrylic polyurethane topcoat, pin-shaped holes on the surface of the paint film, similar to the pores of the skin.
Answer: Reason:
Acrylic polyurethane topcoat itself has poor ability to release bubbles;
The leveling time after thick coating is too short and the paint is baked in the drying room, and the temperature rises too quickly;
Or water is mixed in the paint, etc.;
The air flow rate in the spraying room of acrylic polyurethane topcoat is too fast, resulting in too fast surface drying and too high environmental humidity.
Prevention:
Use slow-drying aliphatic polyurethane topcoat thinner and bake at low temperature;
Strictly follow the construction process to ensure that the paint mixing equipment is clean and free of dirt and moisture. It is not suitable to spray glossy topcoat when the environmental humidity is greater than 80%.- The gloss of aliphatic polyurethane topcoat is uneven, and there is local gloss loss, which seriously affects the overall aesthetic effect.
Answer: Reason:
Some surfaces of the middle coating of aliphatic polyurethane topcoat are too rough, the putty is not applied well, and the polishing work is not done well;
The spraying time interval is too long, and the last coat of paint is sprayed, resulting in paint mist falling on other parts and causing gloss loss; the middle coating is polished before it is completely dry.
Prevention and treatment:
The polishing should be comprehensive and meticulous to eliminate the roughness of the sprayed parts;
The spraying time should not be too long;
The putty and polishing can be applied only after the middle coating is completely dry.- The orange peel of aliphatic polyurethane topcoat, the paint has poor fluidity, the coating film is not leveled well, and there are undulating orange peel-like ripples.
Answer: Reason:
The spray viscosity of aliphatic polyurethane topcoat is too large, the fluidity is poor; the atomization is poor;
The air flow rate in the spray booth is too large, causing the solvent to evaporate too quickly;
During spraying, the distance between the spray gun and the surface of the flag spray part is not appropriate, and the spraying pressure is too high.
Prevention and treatment:
Use the thinner of aliphatic polyurethane topcoat to adjust the paint to the appropriate spraying viscosity;
Adjust the air flow rate in the spray booth, or replace the thinner with a suitable evaporation rate;
The spray distance should not be too close, and the spraying pressure should be moderate.- The acrylic polyurethane magnetic paint has poor vividness, which is mainly manifested in that the paint film has a relatively high gloss, but the reflected shadow is very blurred.
Answer: Reason:
The resin selected for the acrylic polyurethane enamel formula is not good;
Paint mist affects; the coating thickness is insufficient and the fullness is poor.
Prevention and treatment:
Improve the formula and select resins with good gloss and decorative properties;
When repainting, cover the areas other than those to be sprayed;
Apply thinly multiple times to increase the coating thickness to improve the fullness and smoothness of the acrylic polyurethane enamel coating.
FAQs about acrylic polyurethane topcoat
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