Construction Factors Affecting Gloss of High Gloss Polyester Powder Coating Films

Abstract: The principle of gloss formation is introduced, and the effects of coating thickness and surface pit depth on gloss are studied

The lower the gloss; the spraying method, curing time, and coating thickness have no significant effect on the surface gloss of the coating coating online coatingol.

High-gloss paint is deeply loved by consumers for its bright color and brightness, and will occupy the paint market for a long time

In recent years, with the continuous improvement of environmental protection requirements and costs, ordinary solvent-based coatings have gradually turned into powder-based coatings, and powder coatings have gradually occupied a place in the coating market, and their share has continued to expand

At present, powder coatings have gradually expanded from the home appliance industry to the automobile, construction machinery and other industries

How to effectively carry out powder coating construction to ensure that the gloss of the coating film is within the range of process requirements has become the key to the powder coating process

1.

Gloss is the reflection characteristic of the surface of an object to light.

The smoother the surface, the greater the reflectivity and the higher the gloss; the rougher the surface, the worse the reflectivity and the lower the gloss
.

The measure of gloss size is called gloss
.
Gloss is obtained by measuring the ability to reflect light on the surface of an object, and the instrument for measuring gloss is a gloss meter
.

The so-called glossiness refers to the ratio of the amount of regular reflection light on the surface of the sample plate to the amount of regular reflection light on the ideal standard plate surface under the condition of a certain incident angle (usually 45° or 60°), expressed as a percentage.
A 60° gloss meter was taken
.

2.
Introduction to Minitab analysis software

The analysis software used in this paper is Minitab.
Minitab software is the leader of modern quality management statistics and the common language for the implementation of Six Sigma in the world.
It is favored by quality scholars and statistical experts with its powerful functions and simple visualization operations
.

Minitab software is a software tool designed for quality improvement and quality, and it is also a good tool software for continuous quality improvement
.
Minitab software is widely used in our company to analyze the causes of problems, organize data and study process capabilities
.

In this paper, main effect analysis, two-sample T test, variance analysis, correlation and regression are mainly used for statistical analysis of data
.

3.
Analysis of coating process and construction elements

3.
1 Process flow

The coating process adopted by Liugong forklift components is electrostatic powder spraying process.
The main process flow is shot blasting → degreasing → surface conditioning → phosphating → water washing → putty scraping → putty drying → putty polishing → electrostatic spraying → curing → Cool down
.

In this process, the powder used is a high-gloss and bright powder of a well-known domestic brand
.
This paper discusses the construction factors that affect the glossiness of high-gloss powder coatings based on the process flow and existing powders
.

3.
2 The effect of the depth of the pit on the surface of the workpiece on the gloss

At present, the coating line mainly adopts the pass-through shot blasting machine for shot blasting operation
.

By adjusting the speed of the conveyor chain, the depth of the pit on the surface of the workpiece is changed, and the pit depth on the surface of the workpiece is measured before powder coating, and the corresponding surface gloss is measured after powder coating
.

Enter the collected data into the Minitab table, and use Minitab to analyze the main effect diagram of the depth of the workpiece surface pit and the surface gloss of the coating as shown in Figure 1
.

It can be seen from Figure 1 that with the increase of the depth of the pits on the workpiece surface, the gloss of the workpiece surface decreases
.
In order to obtain a more obvious display effect, the depth of the pit on the workpiece surface is discretized (coded), and the main effect diagram of the pit depth on the workpiece surface and the gloss of the coating surface is shown in Figure 2
.

It can be clearly seen that with the increase of the depth of the pits on the surface of the workpiece, the gloss of the workpiece surface tends to decrease
.

Finally, Minitab software is used to analyze the correlation between the two.
The analysis result is shown in Figure 3.
From the screenshot, it can be seen that the correlation coefficient = -0.
838, that is, there is a strong negative correlation between the depth of the workpiece surface pit and the surface gloss
.

3.
3 Influence of spraying method on gloss

Due to the complex structure of the workpiece, robot spraying cannot be used, so the powder coating line adopts manual spraying operation.
Due to the high labor intensity, two spraying employees are arranged for the powder spraying position to work in turn
.

There is a big difference in the spraying methods of the two employees, that is, one person adopts the "horizontal, vertical and horizontal" spraying method, and the other person adopts the "horizontal and vertical" spraying method
.

Collect the gloss of the workpiece after spraying by the two employees, input the collected data into the Minitab table, and use Minitab to analyze the main effect diagram of the spraying method and the surface gloss of the coating as shown in Figure 4
.

It can be seen from Figure 4 that among the spraying methods, the "horizontal, vertical and horizontal" spraying method has a relatively higher average gloss than the "horizontal and vertical" spraying method
.

However, the comparison of the two means can only represent the difference between the two samples, so in the long run, is there really a difference between the two?

In order to further confirm whether there is a difference between the two, the two-sample T test in the hypothesis test is used for data analysis.
The screenshot of the analysis result of the two-sample T test is shown in Figure 5
.

It can be seen from Figure 5 that P=0.
09>5%, that is, when the confidence level is 9%, there is currently not enough data to prove that the two spraying methods will cause the difference in the surface gloss of the coating
.

3.
4 Influence of coating thickness on gloss

The complexity of the workpiece determines that the workpiece needs to be manually sprayed, so the spray thickness will fluctuate in a relatively large range during the manual spraying process, so it is necessary to verify the effect of the coating thickness on the gloss
.

Enter the collected data into the Minitab table, and use Minitab to analyze the main effect diagram of coating thickness and coating surface gloss as shown in Figure 6 below
.

It can be seen from Figure 6 that there is no obvious trend between the coating thickness and the surface gloss of the coating, and there is a disorderly relationship between the two
.

In order to verify whether there is a correlation, the correlation analysis between coating thickness and gloss is carried out, and the analysis results are shown in Figure 7
.
It can be seen from Figure 7 that the correlation coefficient between coating thickness and gloss is only -0.
186, and P=0.
308>5%.
Therefore, when the confidence level is 95%, there is no correlation between coating thickness and gloss
.

3.
5 Effect of curing time on gloss

At present, the control of the workpiece curing furnace is manually controlled by the operator.
Because the operator in this position is also responsible for the discharge of the trolley for other post personnel, there is a situation that the trolley has not been discharged from the furnace in time after the specified process baking time
.

Therefore, three curing times (35 minutes, 38 minutes, and 40 minutes) were set for data collection to reproduce the daily baking conditions
.

Enter the collected data into the Minitab table, and use Minitab to analyze the main effect diagram of coating thickness and coating surface gloss as shown in Figure 8 below
.

As can be seen from Figure 8, the gloss is relatively high when the curing time is 36 minutes
.
Since the collected data only represent the sample, in order to infer whether there are differences in the population under different baking times, Minitab was used to perform variance analysis on the data, and the analysis results are shown in Figure 9
.

From the analysis result P=0.
831>0.
05, it can be seen that when the confidence level is 95%, the difference between each temperature will not cause the change between the glossiness
.

4 Conclusion

In this paper, combined with the actual powder coating line and the statistical analysis software Minitab, an exploratory study was carried out on the factors affecting the gloss of the coating film, and the following conclusions were drawn:

(1) With the increase of the depth of the pits on the surface of the workpiece, the gloss shows an obvious downward trend, that is, the depth of the pits on the surface of the workpiece has a great influence on the gloss
.

(2) The effect of spraying method on gloss is small
.

(3) The effect of coating thickness on gloss is small
.

(4) Curing time has little effect on attention
.

(5) In the process of data analysis, the conclusions drawn only by simply comparing the data of the samples are generally wrong
.

It should be based on the data obtained by sampling, using statistical analysis tools for analysis, so as to draw correct conclusions
.

For the object studied in this paper, the glossiness of the coating film can be improved by reducing the depth of the pits on the surface of the workpiece, and it has been proved by practice that when measures are taken to reduce the depth of the pits on the surface, the glossiness of the workpiece surface can reach more than 90%, a great meet process requirements
.