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Coating thickness for wood finishing

the dry film thickness measurement

Coating thickness or dry film thickness

The coating thickness is the thickness of the finishing layer which is covering a certain surface. Finishing layer thickness is mainly determined by the application of clear coating on the finishing process, the pigment which form color is only a very thin layer than the film layer produced by the clear coating. In a finishing, the coating thickness will determine the finishing looked. A finishing with thick film layer will have a different appearance with a finishing with a thin film layer. In the process of finishing the film thickness is mostly determined by the number of applications of the clear coatings. It also depend on the type of clear coating used. A clear coating with nitrocellulose types will always produce thin film layer. It needs many time applications to make a thick film layer with the nitrocellulose clear coating. The NC clear coating generally has less solid content then the PU or AC clear coating. The PU or AC clear coating types will be able to produce a thicker layer of the film since he has higher solid content in the same viscosity with the NC or water based clear coating. The PU and AC that dry with reaction also will form thermosetting films which will built thick film faster.
In the wood finishing the film thickness is also influenced by the type and condition of the wood underneath. Wood has pores, grains, and porosity which are varying depending on the species of the wood. Even the same type of timber can have different porosity from one section to another section. Therefore, the measurement of the coating thickness on wood finishing is always resulted in a varied numbers from one point to another. The complex form and shape of the furniture is also cause of the variation measurement result of the coating thickness since the way of difficulty in the application.
The coating thickness is apparently quite important in a finishing. Too thin finishing layer usually will produce a relatively low gloss and may not be sufficient to provide protection to its underneath substrate. Finishing with a high gloss, flat, even and clean appearance usually requires a quite thick film. If we would do a rubbing process on a finishing, we need a sufficient thickness of film layer to avoid the occurrence of sand through on the finish layer.
Nevertheless a finishing film also cannot be too thick, because of the risk of a crack on the finishing. The finishing with NC type clear coating is the most risky to crack due to the film layer that is too thick. This occurs because in his the drying process the NC layer will continue shrinkage to form a very thin layer. The shrinkage of the finishing layer  could cause crack when the film is too thick. In addition the wood will expand and shrink according with the environment changes also potential to cause crack in the finish.
A coating thickness maximum 5 microns is recommended for NC finish to avoid the risk of crack. For the AC or PU finishing a coating thickness of up to 8 microns is still considered safe. Meanwhile, if it is desired a finishing with  very thick film layer a polyester clear coating is recommended.

How to measure the coating thickness

To measure the thickness of the finishing can be done by measuring the film thickness when it wet or when it dry. The measurement when it wet can not determine the thickness of the finishing layer directly. The measurement is done by using a tool called as a wet film thickness gauge. This tool is like a comb that has a size of thickness at any radius. This tool is put on a surface finishing layer when it is still wet, just after a clear coating is finish applied. From this tool, it can be obtained the film thickness when wet. The dry film layer is calculated by multiplying the wet film thickness with the volume solid content of the finishing materials used.
While for measuring the thickness to the dry film is done with an instrument called Prositector or dry film thickness gauge. This tool can measure the dry  film thickness of the finishing layer with more definite results. This tool has a tip which, when attached to a surface finishing layer, the  the thickness of the coating finishing digits can be seen on the screen. But this tool is a lot more expensive than the wet film thickness gauge.

1 comment for "Coating thickness for wood finishing"

  1. The situation that coating film?s thickness can be controlled at a predetermined value is called as the film thickness controllability.
    Because the vacuum sputterin?s discharge current and target current can be controlled separately, so by controlling the target current can control the film thickness.
    For more: film thickness