Study on the method of measuring wash resistance of synthetic resin emulsion exterior coating

0 Introduction
Synthetic resin emulsion exterior paint products have the advantages of beautiful decoration, convenient construction, low pollution, relatively low cost, etc. , in recent years widely used in the decoration and decoration of building exterior walls, they play an increasingly important role in beautifying the environment and building decoration, decoration. However, because China's environmental conditions are not very ideal, air pollution is heavy, in order to make the exterior paint products have a beautiful appearance, need to be cleaned from time to time, but can not affect its service life, therefore, wash-resistant brushing has become an important technical indicator to investigate the performance level of exterior paint products. At present, China's synthetic resin emulsion outer wall coating products to implement the standard is GB /T 9755-2001
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. This standard has been issued for more than ten years, has not been able to adapt to the current continuous development of synthetic resin emulsion exterior coating products technology level, so it needs to be revised. Due to some defects in the current method of measuring wash resistance, when revising GB/T 9755-2001, it is necessary to focus on and study the wash resistance project.
1 Introduction and comparison of wash-resistant scrub determination methods at home and abroad
1.1 Domestic existing methods
The coating is applied to the substrate by scraping or brushing method, and after drying according to the prescribed conditions, it is determined by the wash-resistant brusher in accordance with GB/T 9266-2009, so as to be assessed by whether the middle 100 mm area of the test board length is exposed after the specified number of times.
1.2 Foreign methods
Differences between wash-resistant methods in JIS K 5663: 2003, ASTM D 2486-2006, and methods in GB/T 9266-2009 It is a hard vinyl chloride plate or its film as a substrate, with a trench depth of 150 m or 175 m wet film preparer scraping 1 coating, the assessment method is similar to GB/T 9266-2009. According to ISO 11998:2006 method to determine moisture-resistant scrubability, the use of sufficient thickness of the gap-type wet film preparer scraping film, maintenance 7 d after the fixed sanding pad on the wash-resistant brush for wash-resistant scrub determination. The results are expressed as the mass loss or average film thickness loss of the coating per unit area after 200 scrub cycles.
1.3 Comparison of methods at home and abroad
a comprehensive comparison of wash-resistant methods at home and abroad can be found in Table 1. As can be seen from Table 1: The current domestic use of wash-resistant scrubbing measurement methods due to uneven substrate and make the results of the repetition and reproducibility of the problem is poor, for this reason, in the GB/T 9755-2001 and other product standards revised, for wash-resistant projects, can be combined with some methods abroad after comprehensive consideration to improve.
2 Study on the new measurement method of wash resistance of synthetic resin emulsion exterior coating products
2.1 Determination of basic test conditions
Washing project, taking into account ISO 11998:2006, GB/T 9266-2009 and ASTM D 2486-2006 3 methods After the advantages and disadvantages, the basic conditions determined are: the substrate using black PVC (PVC) or other materials of plastic sheets, to solve the problem of the flatness of the substrate; More flat, when measuring, under the test plate to pad thin sheets, accelerate the destruction process, washing media using 2.5 g/L of positive decosyl benzoate sodium water solution, to avoid differences in the quality of different brands of washing powder and affect the measurement results. Four routes were selected for the study.
2.2 route 1
route 1, the substrate using black PVC plastic sheet, with different clearance depth of the wet film preparation film, after maintenance 7 d to determine wash resistance. When measuring, a layer of 12.7 mm wide, 0.25 mm thick sheet under the test plate, with the existing domestic brush and scrub machine to determine, to observe the test plate surface damage when the number of washes required. The test results measured along this route are in table 2. During the test, several samples of different PVC (pigment volume concentration) were selected for determination, wet film preparers with different gap depths were replaced, and damage to the paint film was examined from different areas of the test plate. From the test data, no matter what kind of gap depth of wet film preparation, and no matter from what area to investigate the damage of the paint film, for most of the exterior paint samples need a long number of tests, not only time-consuming, and different grades of paint products are more difficult to distinguish. Therefore, route 1 should not be used.
2.3 route 2
route 2, on the basis of route 1, the brush will be replaced with GB/T 9780-compliant interior wall pollution resistance test grinding head (load 1.5 kg, 8 layers of medical gauze), that is, the substrate using black PVC plastic sheet, with different clearance depth of wet film preparation, maintenance 7 d after the determination of wash resistance. During the determination, a thin sheet 12.7 mm wide and 0.25 mm thick is positioned under the test plate, and the test grinding head is used to determine the number of times required for damage to the test plate surface. The test results measured along this route are in table 3. During the test, several samples of different PVC were selected for determination, wet film preparers with different clearance depths were replaced, and damage to the paint film was examined from different areas. From the test data, no matter what kind of gap depth wet film preparation, and no matter from what area to investigate the damage of paint film, for most exterior paint products need a long number of tests, not only time-consuming, and different grades of paint products are more difficult to distinguish. In addition, the frequency of gauze replacement, the drip addition of scrubs have an impact on the measurement results. Therefore, route 2 is not used.
2.4 Route 3
Route 3, on the basis of Route 1 to change the number and width of sheets under the test plate, as well as the load of the brush for determination, that is, the substrate using black PVC plastic sheet, with different clearance depth of wet film preparer film, maintenance after 7 d determination. When the washability is measured, the sheet with different layers and widths is cushioned under the test board, and the load of the domestic brush is changed to observe the number of washes required when the surface of the test plate is damaged. The two samples of the first-class and superior grades were tested, and the test results were found in Table 4. From the test data, the C and D methods can distinguish between first-class and superior samples, but using 3-layer gaskets (3 mm, 6 mm and 10 mm widths from top to bottom, respectively), the gaskets may move during the measurement process to affect the measurement results;
2.5 route 4
route 4, the substrate using black PVC plastic sheet, with a gap depth of 200 m wet film preparer scraped 1 coating, after maintenance of 7 d to determine wash resistance. During the determination, a thin sheet 12.7 mm wide and 0.25 mm thick was padd under the test plate after the paint film was completed, and 2,000 brush cycle measurements were carried out using domestic brushes to observe the removal of the paint film above the sheet after 2,000 brushing tests, as well as the loss of quality of the paint film before and after the washing test. Visual evaluation of paint film damage, combined with quantitative assessment of paint film test before and after the quality loss of the results. Selecting 23 exterior paint samples of different grades provided by different manufacturers (surface 1 to 23) and 5 exterior paint samples of different PVC were tested according to this route and found that the results obtained according to this route are more scientific, more objective, more reasonable, and time-consuming, after a large number of tests confirmed that route 4 is a method that can be adopted when the standard is revised.
2.5.1 Comparing the test results of the same coating sample under the same measurement conditions by route 4
The relative deviation and absolute difference of the two parallel measurements of the same coating sample under the same measurement conditions are given in Table
, from which it can be seen that if the paint film is not damaged, the repetition of the results is better.
2.5.2 Comparing the test results under different measurement conditions of the same coating sample
Table 8 to 9 compares the relative deviation and absolute difference between the measurement results of the same coating sample under different measurement conditions (i.e., changing certain conditions and keeping certain conditions unchanged). From the test results can be seen: in the case of different instruments, different brushes, different wet film preparation, if the paint film is not damaged, the reproduction of the results is also better.
2.5.3 Consideration and treatment of route 4 blank test
When using route 4 for brush resistance determination, do you need to consider the blank test question: that is, the brush does not brush, only consider the quality loss caused by the dissolution of the washing medium? The following methods are used to simulate the blank test process, and the results of the blank test can be found in Table 10.
a method: on the scruber, do not brush, run the same frequency and frequency, paint film width of about 60 mm, according to the same method of washing test, drying, weighing;
b method: on the scruber, do not brush, run the same frequency and frequency, paint film width of about 130 mm, according to the same method of washing test, drying, weighing;
c method: the lacquer film width of about 130 mm test plate in the enamel plate with washing medium soaked about 1 h (equivalent to the time of washing 2,000 times), remove, according to the washing test the same method, drying, weighing.
From table 10 data can generally draw the following conclusions:
(1) blank test value and paint film washing test quality loss
, the greater the quality loss, the greater the blank test value,
that is, the substance in the paint film is more easily dissolved by the washing medium;
This results in the treatment method as determined according to this route: because the substance in the paint film is washed out of the medium, itself can also reflect the paint film wash resistance, it is recommended that if the quality loss of the paint film is assessed without deducting the blank test value, but should be stipulated to prepare the paint film with wet film preparation width. If the blank test value is to be deducted, the c method can be used instead of the b method to shorten the test time.
2.5.4 Comparison of the new method with the results of the current method
compares the results of paint samples with poor results obtained by route 4 with 2.5.4 results obtained under the current method, as seen in Table 11.
From table 11 data can be seen, according to the new method assessed as unqualified paint samples according to the current method, wash resistance is better than GB /T9755-2001 in the requirements of superior products, so if the revised standards use this method, wash resistance requirements will be increased (meet 2, face 6).
3 Conclusion
There are some defects in the current method of measuring the wash-resistant brushing of exterior wall coatings in China, in order to better improve the measurement method of the project, consult the relevant current measurement method standards at home and abroad and analyze and compare them, select several suitable routes for a large number of exterior wall coatings Sample determination found that route 4 is the most appropriate method, that is: the substrate using black PVC plastic sheet, with a gap depth of 200 m wet film preparer scraping 1 coating, after maintenance 7 d to determine wash resistance. The washing medium uses a 2.5 g/L solution of sodium sodium sulphate. During the determination, a thin sheet of 12.7 mm wide and 0.25 mm thick was cushioned under the test plate with the benefit of the finished paint film, and 2,000 wash cycles were measured with a home-made brush. Because the emulsion content of the outer wall coating is relatively high, and PVC is relatively low, the quality loss of the paint film after the washing test is relatively not very high, and part of the quality loss comes from the dissolution effect of the washing medium on certain substances in the paint film, so it is recommended that the external wall coating does not consider the quality loss of the paint film, only after 2,000 wash tests, the paint film above the sheet appears to cross the width of the paint film damage to assess. For other categories of coating products (e.g. interior wall coatings), the final evaluation method can be determined after a large number of tests, depending on the specific circumstances of such products.