This page briefly introduces various phenomena that occur during paint application.
Causes of main phenomena and preventive measures
We can provide solutions to these phenomena.
Phenomenon1：Crack in areas where the paint collects
This phenomenon is seen with UV-curable paints and in sections like the edges of the paint layer, cuts of modified portions, and the corners. UV curing is conducted while extra solvent remains in the paint layer without being fully evaporated because the paint layer is either too thin or too thick. It is considered that cracks are formed because of the internal stress of the paint layer as time passes and the solvent tries to evaporate from the paint layer.
● Perform UV curing with zero solvent residue by thoroughly drying the surface (by raising the temperature or provide a longer time) before UV curing.
● If the phenomenon occurs because of solvent accumulation, adjust the paint solvents or other components or shift to a design that prevents the accumulation of a paint layer at the edges and corners.
● Make the paint layer as thin as possible.
In this phenomenon, part of the paint layer becomes removed from the deposited plating layer and swells. This occurs on the section with lower adhesion force when the swelling force of the gas generated from the material or paint layer is greater than the adhesive force between the material and paint layer or the paint layer and deposited plating layer.
● Baking: To heat the material first to remove gas from it before applying paints.
● Flame treatment: To bake the material as a pretreatment before applying paint to improve adhesion.
Phenomenon3：UV leak out and exposes
Extremely weak UV rays are irradiated in front of a UV lamp, and only the surface of a coating becomes UV-cured. This distorts the balance in the hardness between the surface and the inside, resulting in defects of shrinkage and poor adhesion.
● Adjust the UV device to prevent the paint from being exposed to the UV rays until it is placed in front of the UV device such as providing a shutter.
Phenomenon4：Polymerism is insufficient
In this phenomenon, the paint layer moves and forms wrinkles because it is deposited while the paint layer is deposited in insufficient forms. The luster may seem white and rainbow patterns may be formed once deposited.
● Provide enough curing temperature and curing time for heat-dried paints.
● Provide sufficient UV irradiation for UV curable paints.
In this phenomenon, the paint layer turns white and loses its luster as whiteness or cloudiness forms on the paint surface during the paint coating process or immediately after that. This occurs when moisture in the air mixes with the paint while the paint is applied under hot and humid conditions or when condensation occurs and moisture mixes with the paint.
● Select a solvent with slow evaporation speed.
● Improve the ventilation of the painting area and drying furnace to reduce moisture.
● Thoroughly dry the base material before applying paint to prevent dew condensation.
Solvent attack generates an uneven luster and fine cracks on the surface of the paint layer as the negative effect of the paint solvent dissolves the base material or causes it to swell or soften. This tends to occur when solvent selectivity is poor for each material (non-crystalline plastic: polyethylene, ABS, polycarbonate, etc.) and is likely to occur near the gate, thickened section, and welded section of formed items.
● Solvent attack can be reduced by taking a long coating distance and making sure that the solvent would not remain on the material as much as possible.
● Solvent attack may be reduced by reducing the coating thickness or lowering the drying temperature, although this does not solve the problem completely.
Phenomenon7：Interference patterns in the film
In this phenomenon, rainbow stripes are formed on the layer of deposited topcoat. Certain colors become visible when the paint layer is thin because the interference of the wavelength of light occurs only with limited colors. Conversely, various colors become visible when the paint layer is thick because it causes interference. The interference can be reduced when the paint layer is thicker because light becomes transparent when many colors become mixed.
● Increase the thickness of the paint layer.
Fine splitting refers to the failure to create a normal reflective surface as the undercoat layer expands and penetrates through the diluted solvent of the topcoat. Fine splitting occurs when the high solubility of the solvent component of the topcoat, poor solvent resistance of the undercoat layer, insufficient hardening of the undercoat, and a thin deposition layer.
● Select a topcoat with low solubility of the solvent component.
● Select an undercoat with high solvent resistance.
● Reevaluate undercoat hardening conditions.
● Make the deposition layer as thick as possible.
Shrink marks refer to the formation of unpainted sections as the drying balance become disturbed because of rapid drying immediately after the paint is applied. Possible causes include thickly applied paint, shorter setting time than recommended, and the use of a thinner other than the recommended one.
● Provide recommended setting time after applying paint.
● Dilute a thinner as recommended.
This is the formation of cracks on the painted surface. Cracking occurs when the internal stress of the applied paint exceeds the cohesion or when the shrinkage of the material causes distortion of the applied paint. Possible causes usually include temperature change and repainting.
● Annealing (baking)
● Flame treatment, drying under low temperature
● Reselection of suitable paint for a material or purpose
● Switching to a suitable solvent for a material
Phenomenon11：Cissing Fish eyes
This is the generation of unpainted spots as paint does not spread over the surface but generates spot-like discontinuity (e.g., dent patterns and craters) on the paint surface. This is caused by the adhesion of moisture, dust, oil, and grease on the painted surface or the applied paint.
● Degrease the base surface using thinner to remove moisture and oil.
● Prevent the inclusion of water or oil into compressed air.
● Reevaluate the environment to prevent other paint mist from landing on the surface.
This is a unique phenomenon with the deposition membrane that occurs when paint is deposited on an undercoat and then placed under heat. This is caused by incomplete hardening of the undercoat or the use of a paint that does not satisfy the required conditions (heat resistance).
● Reevaluate hardening conditions.
● Check the heat resistance conditions of a product and select a paint that matches the conditions.
A phenomenon in which a finished paint surface appears bumpy like the skin of an orange.
This happens due to insufficiency in the fluidity of paints during the spray painting process.
● Add a solvent that evaporates slowly. Or, design to slow down evaporation.
● Provide a longer time to set.
● Shorten the spraying distance.
Examples of our solutions to concerns of our clients
From hearing to investigation, analysis, and solution
Paint layers turn white and cloudy when we adjust them to the conditions of the production line of our client.
The inquiry states that defects occur because the production line of a client does not match the conditions that we recommend.
The problem of cloudiness was solved by changing the paint layer hardening speed to the condition of the client’s production line.
Conventional paints cannot hide the surface of base materials and any unevenness will remain visible.
The problem was solved by increasing the concealing performance of the paint layer and improving workability.
There are multiple types of base materials, and we used two types of paints. Yet, work loss was occurring because of the setup change of the paints.
We developed a paint that is compatible with multiple types of base materials to reduce work loss.
Paints become damaged when placing products in bags.
We improved the topcoat applied to the deposition to reduce damage.