Leveling tester and test method of the hottest rol

2022-08-18
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Roller coating leveling tester and test method

roller coating leveling tester and test method

January 1, 2019

preface

spraying, brushing, roller coating, curtain coating, etc. are all different construction methods of coatings. Roller coating can be divided into same direction roller coating, reverse roller coating, small area roller coating, large area roller coating. As we all know, with different coating methods and construction process conditions, the surface state of the wet film formed by the coating will be different. During the drying process, the reasons for leveling and various defects of the coating film will also vary. This paper discusses the tester and test method of coating leveling in the process of roll coating of tinplate. The method for determining the leveling property of coatings is the national standard GB 1750-79, which is not applicable to the measurement of the leveling property of tinplate coatings. Because gb1750-79 adopts brush coating and spraying, while tinplate sheet adopts roller coating. Brush marks formed by brush coating are basically parallel convex and concave marks, and dot marks formed by spraying. The marks formed by these two coating methods are relatively uniform, and the marks are very similar to the marks, and the thickness of the film formed is 25 μ M or more, and the marks formed by roller coating are like bark, with different lengths and depths, which are much more complex than the above two kinds of marks, and the film thickness is 8 ~ 12 μ M, ratio 25 μ M is much thinner

from the relationship

(where A0 is the initial amplitude; at is the amplitude over time t; h is the average thickness of the coating; λ Is the wavelength; R is the surface tension of coating; η Is the paint viscosity; Δ T is the leveling time) it can be seen that the thickness and wavelength of the coating have a great influence on the leveling process. The thickness is to the third power and the wavelength is to the fourth power. If other parameters remain unchanged, the coating thickness will be doubled and the leveling time will be shortened by 1/8; On the contrary, if the thickness is halved, the leveling time is increased by 8 times. When the wavelength is doubled, the leveling time is increased by 16 times; On the contrary, if the wavelength is halved, the leveling time is shortened by 16 times. According to the relationship t obtained from dimensional analysis= η· L/R (where t is the leveling time; L is the brush mark shape) shows that the leveling time is closely related to the brush mark. The film thickness formed by roller coating is only half of that of brushing and spraying, and the traces are completely different. Therefore, the leveling property of coating measured by GB 1750-79 method can not explain its leveling property in production and application. In order to make the measurement results consistent with the actual application, we have designed a roller coating leveling tester and established a roller coating leveling property test method

2 roller coating leveling tester

for roller coating, the quality of leveling is very important. The coating with poor leveling will form uneven film thickness, poor covering power, large consumption, high cost, and the pattern color painted by the roller is different in depth, bright and dark, with high defective rate, which will also have a negative impact on post-processing. Since GB 1750-79 cannot be used to evaluate the leveling property of roller coating, in order to find a better method to test the leveling property of the first line of epidemic prevention and control in Guangxi Zhuang Autonomous Region, we went deep into the front line of iron printing production, carefully observed and studied the film state and the film forming principle and characteristics during mass production, and designed and manufactured a simple and practical leveling tester (see Figure 1), which can form a film with the same thickness and shape as the actual production

1 - rubber roller; 2 - coating rod; 3 - handle; 4 - Fixed surface of test piece; 5 - guide rail

Figure 1 roller coating leveling tester

3 roller coating leveling test method

3 1. Test instruments, equipment and materials

roller coating leveling tester; Mikrotest thickness gauge; Constant temperature oven (0 ~ 250 ℃); Drying rack timing clock (0 ~ 60 min); Tu - 4 cups; Stopwatch; Thermometer (0 ~ 100 ℃); Coating to be tested (200 ml); Tinplate 120 mm × 180 mm × 0. 2 mm。

3. 2 test method

determine the viscosity of the coating to be tested at room temperature according to GB 1723-79 "determination of viscosity of coatings". Place the clean tinplate on the roll coating leveling tester and fix it. Place a certain amount of coating to be tested on the end of the tinplate close to the roll, and shake the handwheel at a uniform speed to form a film with a thickness and roll trace shape similar to the actual production on the iron plate. Remove the iron sheet, put it on the drying rack, put it into the oven with the temperature adjusted for baking, adjust the timing clock, take out the iron sheet when the clock rings, and cool it. Measure the film thickness with a thickness gauge. Under sufficient light source, observe the leveling property of the film from different angles

3. 3 coating leveling evaluation

the evaluated film thickness is 8 ~ 15 μ m。 The roll mark on the surface of the coating film is obvious, which is the same as the shape painted by the rigid roll, like the bark. If the bottom is exposed seriously and there is a bumpy feeling by hand, the leveling is poor; If the roll mark on the coating surface is obvious, but the roll mark is shallow, sparse, exposed, and the feel is basically smooth, the leveling is unqualified; If the roll marks on the coating surface are few, short, shallow, slightly exposed, and the feel is smooth, the leveling is qualified; If the coating surface is basically free of roll marks, bottom exposure and smooth hand feel, the leveling is good

4 verification of roller coating leveling tester and test method

4 1 adaptability

select a white paint with poor leveling property proved by actual production, and measure its leveling property according to GB 1750-79 method and the method introduced in this paper. The results are shown in Table 1

Table 1 leveling test of white polyester enamel

brushing and spraying have restrictions on the viscosity of the coating. In order to ensure the smooth progress of brushing and spraying, the viscosity of the coating must be in a low range, while roller coating is not limited. As long as the coating is well leveled, it doesn't matter if the viscosity is high. In practical application, the national standard GB 1750-79 test conditions have limitations. The coating prepared according to the test requirements of GB 1750-79 is difficult to obtain 12 μ M, but in practical application, the thickness of roll coating film is generally 6 ~ 18 μ M, with 10 ~ 12 μ M is common. However, the film thickness formed by the coating prepared according to the test requirements of gb1750-79 is beyond this practical range (see Table 1), which is 24 respectively μ M and 30 μ m。 Under this condition, the leveling property of the coating is certainly good, because the leveling time of the film is inversely proportional to the third power of the thickness. In other words, the film thickness with acceptable leveling property measured according to GB 1750-79 is not allowed in the actual roll coating. The same coating is tested according to GB 1750-79. Because the coating prepared according to its test requirements has low viscosity and thick film, it has high requirements for the strength and toughness of the material, and the leveling property is qualified; The results may be different if the method introduced in this paper is used; When the film is thick, the leveling is qualified, but when the film is thin, the leveling is unqualified. The range of film thickness measured by this tester is 5 ~ 30 μ M, which is more suitable for evaluating the leveling property of roller coating

4. 2 accuracy

in order to test the accuracy of this tester, different testers determine the leveling property of the coating according to the method in this paper. The results are shown in Table 2

take the coating with good leveling property tested by this method to the production line for trial machine, observe the leveling property of the coating in practical application, and check whether the laboratory test results are consistent with the actual production situation. During the test run, the leveling property of the coating is evaluated by adjusting the viscosity of the coating and the thickness of the film. The results are shown in Table 3

Table 3 leveling test of white acrylic paint

note: ① the viscosity of production test machine is different from that of laboratory test due to different ambient temperature

② the dry film thickness is different, and the production test machine is quite different, because the production test machine is complex, it is impossible to control the thickness at 1 ~ 2 μ M, the film thickness difference of the same iron plate is 5 μ M is normal

③ the leveling property of the production test machine is better than that of the laboratory, because the oven temperature of the production line has a gradient, which is conducive to leveling, while the laboratory oven is constant temperature. The results of the laboratory are consistent with the production

it can be seen from table 2 and table 3 that the flow of the coating tested with the tester and method introduced in this paper is good in flatness and repeatability according to Dr. Cao min of the company, which is consistent with the actual production situation

amodel a (8) 930 HS PPA is a 30% glass fiber reinforced thermosetting polymer

5 conclusion

(1) the roller coating leveling tester can form a film with a thickness and geometric shape very similar to the actual production situation, and the factors affecting the leveling are basically the same. During the drying process, the micro movement inside the film is roughly the same, and the final film surface condition is very similar to the actual production. This tester and method are very suitable for evaluating the leveling property of roller coating

(2) the roller coating leveling tester and test method have good repeatability and high accuracy, and can correctly evaluate the roller coating leveling

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