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Influence of conductivity in electrophoretic coating


Conductivity is a very important process parameter in cathodic electrophoresis coating process. It has a very close relationship with the throwing power, and they have great influence on the electrophoretic properties, the stability of the bath liquid and the coating effect. Generally speaking, the higher the conductivity of the electrophoresis paint bath, the higher the penetration of the paint will be; on the contrary, it is the opposite. Therefore, the conductivity of the tank liquid should be strictly controlled within the range of process regulations. So in the large production process of electrophoretic coating, the conductivity of the electrophoretic coating of the influence?



Conductivity refers to the amount of conductivity in the 1cm spacing of l square centimeters of the pole surface, in the electrophoretic coating occasions in the tank, UF liquid, pole liquid and the degree of conductivity used in pure water to express the degree of difficulty with the conductivity, but also useful than the electrical resistance to express. Conductivity is the reciprocal of specific resistance.


Specific resistance (Ω - cm) = 6 times 10/conductivity, and conductivity is measured in μS/cm or uΩ- cm-1.


The conductivity of electrophoretic paint tank liquid is related to the solids of tank liquid, pH value and the content of impurity ions, etc. It is one of the important process parameters and should be controlled within a certain range, the size of the range depends on the varieties of electrophoretic paints, and the low or high conductivity of tank liquid is not good, which will directly affect the quality of electrophoretic painting.



Effect of conductivity in electrophoretic coating:


1. To a certain extent, the conductivity can determine the amount of paint that can be applied to the workpiece by swimming to a certain extent.


2. Less conductivity will slightly reduce the amount of cathodic electrophoresis paint deposited, on the contrary, high conductivity will slightly increase the amount of cathodic electrophoresis paint deposited.


3. Tank liquid conductivity is too high or too low, but also on the thickness of the electrophoresis paint film, appearance, swimming penetration, etc., especially with the tank liquid conductivity increases, swimming penetration is also increased, then it is also relatively thicker film thickness.


4. Abnormally high conductivity of the slurry is often caused by high impurity content or low pH, and is also accompanied by abnormal changes in the quality of the coating film, such as orange peel, pinholes, or return to the dissolution of a serious ...... and other abnormal phenomena. It needs to be managed by ultrafilter with anode system.


The above introduction is the conductivity on the cathodic electrophoresis paint some of the effects. Generally speaking, the conductivity should be controlled within the range of 1200±300μs/cm, because the conductivity mainly relies on the quality of deionized water before electrophoresis and the renewal of paint in the electrophoresis tank to be maintained, so when the conductivity is high, it can also be discharged ultrafiltration solution to be adjusted.



Different varieties of cathodic electrophoresis coatings also have the best control range of the conductivity of the bath liquid, based on the conductivity of small changes, such as ± 100us/cm will not affect the performance of the coating film, so the general control range is wider, ± 30us/cm. bath liquid conductivity is too high or too low on the thickness of the coating film, the appearance and the penetration of the film has an impact, with the bath liquid conductivity increases, the penetration of the film is also higher, the thickness of the film is also relatively thicker. The thickness of the film will be relatively thicker. Tank liquid conductivity exceeds the upper limit of the specified value or high, can be used to replace the deionized water ultrafiltration solution to reduce, for example, 300t of tank liquid with deionized water instead of 20t of ultrafiltration solution, the tank liquid conductivity can be reduced by ± 100us/cm.