The causes and solutions of color difference in anti-corrosion coatings

introduction

Chromatic aberration refers to the difference
in color given by 2 or more colors to a person's vision.
Anti-corrosion coatings In the process of coating, the color difference of the top coat is difficult to control
.
There are two main methods for chromatic aberration measurement, one is visual inspection, that is, visual vision with eyes; The second is to use a colorimeter to measure the online coatingol.
com
of coatings.
In order to measure the degree of color difference, the measurement must be based on the standard color swatch, which is a color card approved by both parties, so that it is easy to compare with the physical object and identify whether the physical object has color difference
.
The color difference of anti-corrosion coating is generally divided into: color difference of different parts of the same workpiece, color difference between different workpieces, color difference between steel and concrete, etc.
, color difference
during repair.
Based on the experience in practical work, this article discusses the causes and solutions
of various chromatic aberrations.

Factors that produce chromatic aberration

1.
1 The influence of the painting construction environment on the color difference of the top paint

In the process of spraying the topcoat, the temperature and humidity of the spraying environment are different, which has a great impact on the color difference of the topcoat, that is, the same can of adjusted paint, sprayed in different temperature and humidity environments, after drying to measure the color difference, ΔE is very different
.
This is because the temperature and humidity of the environment affect the volatilization rate of the paint solvent, the solvent volatilizes quickly at high temperature, and the solvent volatilizes slowly at low temperature, which in turn affects the surface drying time of the paint film; Similarly, if the solvent volatilizes slowly with high humidity, the solvent volatilizes quickly with low humidity, which will also affect the surface drying time of the paint film, resulting in color difference
in the paint film.

1.
2 The influence of paint film thickness on color difference During the spraying process, due to the difference in spraying distance, paint output, gun speed or operation skills, the thickness of the paint film has a great impact, some places are thicker, some places are thinner, and some places even appear bottom exposure phenomenon, the appearance of thick paint film is plump and the gloss is high; The thin part of the paint film is not bright, and the gloss is poor, resulting in color difference
.

1.
3 Compressed air pressure During the painting process, the difference in compressed air pressure has a great
influence on the color difference of the paint film.
This is because the size of the air pressure will affect the size of the paint atomization particles, the smaller the compressed air pressure, the worse the atomization effect, the larger the paint atomization particles, the paint film formed by the paint spraying on the coated object is not smooth, rough and dull; If the compressed air pressure is large, although the paint mist particles formed are fine, the paint mist will fly everywhere, which not only affects the quality of the paint film, but also affects the paint rate, and will also affect
the color difference.

1.
4 Influence of drying temperature During the drying process, the difference in temperature of the paint film has a certain impact
on the color difference of the paint film.
Because the drying process is a physical and chemical process from quantitative change to qualitative change, the temperature and the length of time have a greater impact on the process of physical and chemical change, the temperature is low, the crosslinking reaction is slow, the temperature is lower than the specified range, the paint film can not be completely dried, affecting the performance of the paint film; The high drying temperature of the paint film can accelerate the process of crosslinking reaction, but because the paint film is formed too quickly, which affects the leveling effect, the paint film will be rough
.

1.
5 The influence of solvent volatilization rate The volatilization rate of solvent is directly related to the boiling point of the solvent, and the higher the boiling point of the solvent, the slower its volatilization; The lower the boiling point of the solvent, the faster
it evaporates.
If the same paint is diluted with a solvent with different boiling points and sprayed, under the same process conditions, the two paint films obtained have color differences
.
This is because the evaporation rate of the diluent affects the surface drying time of the paint film, which in turn affects the leveling
of the paint film.

1.
6 Influence of construction viscosity Construction viscosity also has an effect
on color difference.
The same kind of paint, using different viscosities for construction, the color difference value of the coating is not the same, and the difference is very large
.
This is because the application viscosity affects the appearance quality of the paint film
.
When a company's "Engineering Yellow" waterborne topcoat was sprayed with swatches of different viscosities, among which the viscosity of 1# swatch was 45 s, the viscosity of 2# swatch was 75 s, and the viscosity of 3# swatch was 102 s, the color difference effect was compared, and the comparison results are shown in the following table
.

It can be seen from the table that when the paint viscosity is 75 s, the color difference value is the smallest, and the ΔE is less than 1; When the viscosity is 45 s and 102 s, the chromatic difference value ΔE is greater than 2, which shows that the viscosity has a great influence
on the chromatic aberration.

Viscosity chromatic difference statistical comparison table

1.
7 The influence of uneven mixing on the color difference of paint during construction Before construction, the paint should be adjusted, and the paint should be stirred evenly during the painting process, and the purpose of stirring is to stir up the sediment at the bottom of the barrel and fully stir evenly
.
If not stirred, the coloring dye at the bottom of the barrel will precipitate at the bottom of the barrel and cannot be evenly dispersed in the paint, which will affect the hiding power of the coating and affect the color difference
of the paint.

1.
8 The influence of the underlying surface condition Before painting, the condition of the underlying surface has a great impact on the color difference of the coating, if the color of the bottom layer is different, or flowering, or different colors of the middle coating (if there is no middle coating, it refers to the primer), the color difference of the upper surface coat is very different, and some can be identified from the naked eye
.
For example, the top coat sprayed in gray and white is blackened and the other is white
.
Sometimes partial repair is to touch up the surface of the topcoat, and the color difference of the repaired paint surface will be very serious
.
There is also a difference in the roughness of the underlying surface, which will also cause color difference
to the topcoat.

1.
9 The influence of other factors Different batches of color paint and overprint paint, due to the difference in paint production process conditions, or raw material factors, will also cause color difference
to the paint coating.
In addition, the difference in the interval between the "wet touch" construction process between topcoat and overprint paint will also affect
the paint coating.
The size of the vertical wind speed of the paint booth also has an impact
on the color difference of the top paint.