Common problems and prevention methods in UV roller coating 

Mechanical coating production has been achieved in a mature mode, especially roller coating, in terms of production efficiency and paint loss, the advantages are more obvious, is one of the board furniture and wood door enterprises to apply more mechanized coating methods. However, roller coating in the construction process can also appear a series of paint film maladies, now summarise a few common defect, and put forward prevention methods for reference.

Problem 1:  Roll marks

Causes

The main reasons for roller marks are: one is the substrate, the substrate is poorly sanded and uneven before coating; the second is the coating, the viscosity of the coating is too high in the low temperature environment; the third is the equipment operation, the construction of quantitative roller and coating roller spacing is too wide, the coating volume is too large, the speed of the conveyor belt and the speed of the coating roller are not consistent; the fourth is the process, between the coating is not fully cured sanding, multiple repeated roller coating caused by the accumulation of coating.

Prevention methods

The following methods are relevant to prevent roller marks.

Firstly, the substrate is sanded by a fixed thickness sander before painting to improve the flatness of the substrate, in general, the curvature of 1m length of substrate must be controlled within ±2mm and the thickness error must be controlled within ±0.05mm.

Secondly, in the case of low room temperature or high viscosity, UV paint can be pre-tempered to reduce the viscosity of the paint.

Third, the amount of coating during construction is related to the roller speed, quantitative roller and coating roller spacing, coating roller and the spacing of the coated object, which can be properly adjusted according to the actual situation. The speed of the coating roller and the conveyor belt should be checked regularly and the two speeds should be synchronised.

Fourthly, the process is recommended to be applied several times thinly, with the best two coats of primer (including putty) between the coating and the coating, fully cured once and then sanded, followed by the next process.

Problem 2: Poor adhesion

Causes

Poor adhesion is generally related to the following aspects: Firstly, the substrate is not nourished and special treatment before painting, the substrate water content, oil content is high; Secondly, the UV coating contains high powder, construction of thick coating; Thirdly, the construction process of the substrate, coating surface pollution; Fourthly, between the coating sanding is not good, there is a sand leakage phenomenon or sanding placed after too long.

Prevention methods

To prevent poor adhesion, the following points should be done.

Firstly, the substrate should be nourished and specially treated before painting, and the moisture content of the substrate should be controlled within 12%. Oil and special substrates should be closed to the substrate first, reasonable choice of coating products and process design.

Second, UV roller coating construction recommended single coating amount: transparent primer 20-25g/㎡, transparent top coat 5-8g/㎡, solid colour primer 15-25g/㎡, solid colour top coat 8-14g/㎡.

Third, the construction process of the substrate surface or coating between the oil, water pollution is strictly prohibited, pay special attention to the summer construction personnel lifting the board after the sticky sweat stains, oil and water separator timely drainage.

Fourth, the sanding should be suitable sandpaper, sanding belt (primer sanding generally with 320#-400# sandpaper), sanding should be careful, no sand leakage, sanding should be carried out within 4 hours after the next process construction, overnight construction to re-sanding.