Brief analysis on the testing method of recoating

Brief analysis of testing methods for recoating performance of marine coatings

brief analysis of testing methods for recoating performance of marine coatings

December 15, 2018

overview in recent 20 years, China's marine coating testing technology has achieved rapid development, reached a certain level, formulated a series of coating testing standards, and improved the standard system. At the same time, the application of testing standards has also greatly improved the level of coating testing technology and coating quality, and shortened the gap with the coating testing technology of industrial developed countries. Since the late 1980s, China's marine heavy-duty coatings have entered a golden period of rapid growth, and become one of the fastest-growing areas in the coating industry, the earliest to be in line with international standards, and accounting for the largest market share of industrial coatings. It is expected that in the next 5-10 years, the heavy-duty anti-corrosion coatings and coatings for ships in China will still show a trend of rapid development

the popularization and application of long-term heavy-duty anti-corrosion coating system often makes the antirust performance reach the effect of 10 years or even more. Therefore, primers and topcoats with different service lives cause recoatability problems in the maintenance process of chemical curing topcoats, usually with 45 ° (± 22.5 °), 90 ° (± 45 °), 180 ° (± 90 °), 180 ° (± 90 °) 540 ° and other standard test modes and user-defined test modes and other power lines are tortuously selected. The chemical curing coating has the limitation of the longest coating interval during coating. The subsequent coating requires polishing, which is not only time-consuming and reduces the coating efficiency, but also causes environmental pollution, and its effect is often not satisfactory, far inferior to the chemical combination of the same kind of coating. In order to overcome the recoating problem of the longest coating interval, recoating coatings came into being [1]

recoating coating is a new generation of coating. The detection method of its recoating performance, especially the recoating detection of ship hull topcoat, has not formed a unified standard at home and abroad. Therefore, it seriously restricts the development and application of a new generation of coating in our country. Combined with my own work experience and referring to relevant data, the author recommends several practical test methods for the recoating performance of ship hull topcoats and interior coatings of several important parts, so as to speed up the development and application of recoatable coatings and make a modest effort to promote the progress of coating testing technology

1 test part 1.1 test method for recoating performance of ship hull topcoat

1.1.1 test principle

(1) thermally accelerated curing

thermally accelerated curing recoating test principle is to simulate the recoating test of the coating after complete curing under the condition of long cycle

(2) atmospheric exposure (gb/t 9276-1996)

the principle of atmospheric exposure recoating test is to assess the recoating test of coatings after exposure in outdoor natural environment

(3) UV aging (gb/t 14522-1993)

the principle of UV aging recoating test is to simulate the outdoor solar UV light to test the recoating property of the coating after aging

1.1.2 sample preparation

the test plate required for sample preparation shall meet the technical requirements of gb/t 912-1989 ordinary carbon steel, the specification shall be determined by the measured performance test requirements, and its surface treatment shall be carried out in accordance with the provisions of gb/t 9271-1988

(1) preparation of thermally accelerated curing specimen

the recoatable finish paint is directly coated on the test plate, placed at room temperature for 24 hours, and the dried specimen is treated at (80 ± 2) ℃ for 200 hours, then a recoatable finish paint is coated on the surface of the specimen, and the recoat adhesion test is carried out after curing at room temperature for 7 days

(2) preparation of atmospheric exposure samples

paint the test plate according to the supporting system of recoating ship hull finish, maintain the samples indoors for 7 days, and then conduct Xiamen marine atmospheric exposure test for 6 months and 12 months respectively. Wipe off the dust on the surface of the paint film of the exposed sample with a dry cloth, and then apply one layer of recoating paint on the surface of the sample. After curing at room temperature for 7 days, conduct the recoating adhesion test

(3) preparation of UV aging samples

paint the test plate according to the supporting system of recoating hull finish. The samples are maintained indoors for 7 days, and the UV aging tests of 200 h, 500 h and 1000 h are carried out respectively according to gb/t 14522-1993. After the test, the surface of the sample is coated with one layer of recoating finish paint, and the recoating adhesion test is carried out after curing at room temperature for 7 days

1.1.3 performance test

the recoating performance of the samples shall be tested according to ASTM D 4541 and gb/t 9286-1998 respectively. A series of recoating tests were carried out according to the recoating performance test method of 725-bs recoating polyurethane topcoat made by Xiamen Shuangrui Marine Coatings Co., Ltd

the sample is prepared according to the following supporting system:

primer: 725-h epoxy zinc rich primer, (40 ± 10) μ m。

intermediate paint: 725-h epoxy micaceous iron antirust paint, (100 ± 10) μ m。

finish: 725-bs can be recoated with polyurethane finish, (120 ± 10) μ m。

the test results of recoating adhesion [2] are shown in Table 1, table 2 and table 3 respectively. The self-adhesive stripping force tester is also called tensile testing machine

marine paint detection

1.2 test method for recoating property of marine liquid tank paint

1.2.1 test principle

Test Method for recoating property of marine liquid tank paint is an indoor accelerated test method that simulates the environment in the actual long-term application process and detects the recoating property of the coating in the process of continuous cleaning and maintenance of the cabin

1.2.2 sample preparation

the test plate required for the sample is hot-rolled low carbon steel, and the sand blasting treatment reaches above SA 2.5 level. The specification of the test plate is determined by the measured performance test requirements, and the sample is prepared according to the provisions of gb/t 1727-1992

1.2.3 test method

(1) recoating test procedure of fuel/sea water ballast tank coating ［ 3 ］:

(a) at (27 ± 6) ℃, the sample is soaked in natural sea water or artificial sea water specified in gb/t7790-1996 for 168 h

(b) at (27 ± 6) ℃, soak the sample in the fuel specified in ASTM D 1655 for 168 h, (a) and (b) the interval between the two steps shall not exceed 8 h

(c) at 80 ℃, soak the sample in natural seawater or artificial seawater specified in gb/t 7790-1996 for 2 hours, and the interval between the two steps (b) and (c) shall not exceed 8 hours

(2) special seawater ballast tank coating recoating test procedure [4]:

(a) at (27 ± 6) ℃, the sample is soaked in natural seawater or artificial seawater specified in gb/t7790-1996 for 120 hours

(b) natural drying for 48 h

(c) the oil taken should be highly thin lake oil without impurities and dust. At 80 ℃, the sample should be soaked in natural seawater or artificial seawater specified in gb/t 7790-1996 for 2 hours

(3) test procedure for recoating property of drinking water tank paint [5]:

(a) at (27 ± 6) ℃, the sample is completely immersed in distilled water specified in ASTM d1193 for 120 hours

(b) natural drying for 2 days

(c) soak the sample in distilled water for 2 hours at 80 ℃

procedures (a) to (c) are a complete cycle, repeat 25 cycles, and record the state of the coating after each cycle. After 20 cycles, clean the sample with tap water and dry it for 48 hours, then re coat a layer of test paint on the upper 1/3 area of the sample, and apply a layer of matching finish paint (or a matching system of primer and finish paint) on the lower 2/3 area of the sample, and seal the edge. Dry at standard room temperature for 1 week, and then complete the last five cycles. After 25 cycles, the coating system shall be evaluated for recoating: the recoating adhesion strength shall not be less than 50% of the original coating (ASTM D 4541)

2 results and discussion (1) the recoating test results of recoatable polyurethane hull paint show that the damaged part is mostly the damage of recoated paint film, indicating that this part is an area that should be paid special attention to the recoating problem of paint. The test also shows that after heat accelerated curing, 6 months and 12 months of atmospheric exposure, 200 h, 500 h and 1000 h of UV aging, the adhesion strength of the coating film does not decrease significantly, which is also consistent with the practical application results of the coating for many years. The recoating test method proposed in this paper is reliable

(2) the repainting test of marine liquid tank paint, whether ISO standard or ASTM, mil-prf-23236c standard, is a relatively mature method in the world, and it is evaluated according to not less than 50% of the original adhesion strength. The author believes that it is best to simulate the aging of cabin paint in combination with the most severe conditions in the actual use process, so that the indoor accelerated test results can be consistent with the expected effect of the actual use process

(3) with the continuous progress of science and technology and detection means, detection methods are also constantly improving. Recoating test method is a new test method for common lignin plastics including lignin/pvc with the progress of coating technology. The combination of natural state and indoor accelerated state can not only observe the difference between the two, but also verify the recoating performance of the coating at the same time, which has a certain reference significance for domestic detection of recoating property