Factors affecting the accuracy of coating performance tests are discussed

For those engaged in testing work, it is necessary to continuously improve the accuracy of testing and data reliability, which requires not only advanced testing equipment, complete standard specifications, environmental conditions to meet the requirements, but also high-quality practitioners and strict on-site management. Because in any one testing process, the accuracy of the test results in addition to the use of instruments, equipment, environment and other hardware, but also by many factors, and some of these human factors are uncontrollable, some can be controlled, only to minimize the impact of these controllable factors, in order to improve the accuracy of the test. This paper mainly expounds the controllable human factors that affect the test results in the course of coating testing, that is, several aspects that site management should pay attention to
the
.1 test
1.1 Surface treatment of the pre-coated substrate
to obtain good coating quality, the substrate must be pre-treated before painting. The surface of the substrate will often have oil, moisture, rust, if not removed clean will seriously affect the adhesion between the substrate and the coating, thereby affecting its performance. Different treatment methods are often required for different substrates, such as the application of 120 spaper sandpaper along the longitudinal grinding rust removal, and then cleaned with 120 s solvent gasoline, dry with a lint-free cloth for use. Glass plate application of hot soapy water washing, water flushing, drying, paint with skimmed cotton solvent wipe drying use. Treatment of clean substrate in a state of active, easy to react with moisture in the air, oxygen and hand grease, sweat stains, so, can not be directly contact with the treatment of clean test board, and test board once treated clean as soon as possible paint. Aluminum plate often needs yellow anode and arlodin treatment to improve its corrosion resistance. These treatments are chemically or electrochemically to form a dense oxide film on the surface of the aluminum plate to prevent air corrosion of the aluminum plate, the facts also proved that the corrosion resistance of the treated aluminum plate significantly improved, but under the microscope observation will find that there are many gaps in the oxide film, so there will still be moisture into the gap and corrosion of the aluminum plate, so the treated aluminum plate should be used within the specified period, more than the cycle should be disabled. During storage, apply clean cal paper to wrap the test piece and place it in the dryer for storage, and take the test piece to be clamped with tweezers.
1.2 Sample preparation
to remove a representative sample from a barrel of paint, the sample in the barrel must be fully stirred before sampling, can be used mechanical vibration method; Before preparation, the coating should also be adjusted according to the relevant regulations, placing the sample under the specified temperature and humidity conditions and maintaining a predetermined time. Because the performance of organic products is sensitive to environmental changes, state adjustment is necessary to obtain accurate test data. Paint should be adjusted to the appropriate viscosity, sticky through small, coating film will flow hanging, poor cover force, thickness can not meet the requirements; Polyurethane coatings in water or alcohols will cross into blocks and germinate, in the storage or painting process should always avoid contact with water or alcohol, sampling containers, rods, etc. should always always be dry, storage coating containers should be tightened to avoid moisture contact with the air.
1.3 Paint
The control of the paint environment is difficult for dry and dusty areas, first of all, in order to avoid the air dust particles adhere to the undried paint film to form defects, it is best to keep the laboratory closed, close doors and windows to avoid natural wind entry, And often clean to keep the room clean and dust-free, indoor floor waxing, into the laboratory operators should wear clean work clothes, soft cloth shoes, so as not to dust pollution paint or sprayed to the substrate wet paint film, especially when the paint fineness test, dropped dust will affect the fine meter reading. The inner wall of the pumping cabinet can be protected by obsorisive paper and so on, because paint mist can contaminate the cabinet wall when painting, often replace obsori paper and keep clean so as not to cure the coating dust particles to pollute the coating film. Spraying time can not be sprayed to the specified thickness, which will cause the paint film flow, uneven gloss, paint film drying is not thoroughly caused by the hair stick, bubbles, affecting the gloss and drying time of the test, but should cross thin spray several times to reach the specified thickness. Turn the paint cabinet inside the disc cross-spraying, and after spraying once stay 1 min and then turn the disc, so as not to turn and make the lacquer liquid flow, and turn the disc force should not be too strong to avoid the test plate wiggle each other, affecting the quality of the coating. The compressed air used in painting should be oil-free and waterless, check the cleanliness of compressed air before painting, and replace the filter of the oil-water separator in time if oil or water is found.
1.4 Dry curing of the paint film
after spraying the paint to allow the paint film to cure, it is solvent evaporation, resin and substrate between the process of generating a solid chemical bond, only fully cured paint film can play its anti-corrosion properties, paint film curing can be divided into 2 cases: room temperature curing and temperature curing. Before heating and curing, place the paint film at room temperature 0.5 h and then enter the oven, the oven at room temperature will be put into the test film, let the test film with the oven to heat up and maintain the specified time at the specified temperature. Undrided test pieces can not be placed directly into the high temperature oven, because just after spraying the paint contains a large number of highly volatile solvents, directly into the oven at sudden high temperature solvent rapid evaporation, too intense to spread to the air in the paint film inside the formation of bubbles. The most important thing about room temperature curing is that natural wind flow is not allowed in the environment, and the interior should be closed and clean. Hand contact is not allowed to affect the uniformity of gloss before thorough drying, sweat stains and grease on the hands will affect the adhesion test. Need to spray primer and finish matching coating, after applying primer to let it cure, curing time should be appropriate, time is too long, paint film surface pollution will increase, impact and paint adhesion;2 Dry film performance test
2.1 state adjustment
the test plate removed from the drying chamber can not be tested immediately, should be under the prescribed conditions of state adjustment, the standard conditions of temperature (23±2) degrees C, relative humidity (50±5 percent), only in the same environmental conditions measured data are comparable, arbitration test should select standard conditions.
2.2 test process
test process should be carried out in strict accordance with the test method, paint test results are mostly conditional parameters, different test conditions obtained by the test results are very different, the following adhesion test as an example detailed.
adhesion as the most important performance of paint film, test methods are many kinds, the current more commonly used is tape method adhesion, that is, in the paint surface first carved different forms of scratches, and then in the scratch area close tape, force to tear off the tape, by checking the integrity of the paint film to judge adhesion grading, the factors affecting this method are:
1) before the test paint surface cleanness, should use the appropriate solvent cleaning and drying test surface
2) scratching form; Different, commonly used are two parallel dashes 25 mm apart, two parallel dashes 25 mm apart with a 45 degree slash, four lines 1 mm apart and four parallel dashes perpendicular to them, five dashes 1 mm apart and five parallel dashes 45 degrees apart, six dashes 1 mm apart and six parallel lines perpendicular to them, with different forms of dashing.
3) the use of tape and pressing tape used force, tape more than 3M company 250 tape, pressing tape using coated rubber tweezers naturally rolled over the surface of the subject.
4) The action of tearing off the tape should be fast and intense, and the above parameters should be selected according to the requirements in order to obtain accurate test results.
equipment used shall comply with the requirements of the documentation, be verified on a regular basis and during the validity period, and shall also be checked periodically to ensure the measurement stability of the equipment during its service. The difference in the parameters of the instrument and equipment model will make the results of the test very different. If different impact test methods specify different hammer impact tester parameters: the impact head diameter is 16mm and 8 mm respectively, under the same impact force, the force of the test surface is different, in the test should be carried out in accordance with the prescribed test method to choose the impact tester.
of mechanical properties such as shock and pencil hardness should be considered, the edge effect of the test plate should be considered, the test should generally be avoided within 15 mm from the edge, and several parallel test points on the same test piece are at least 15 mm apart. Because the edge of the paint film is generally thicker than the interior, various mechanical properties are lower than the interior, can not represent the performance of the entire paint film. Paint film thickness on the performance of the test has a great impact, before the test must be carried out thickness test, to ensure that the thickness of the paint film in line with the specifications, otherwise the test results are not comparable.
The luster of the paint film is the ability of the paint film surface to reflect the light on it in one direction, is one of the important indicators to measure the appearance performance of the paint film, in the test should pay attention not to contact the test plate surface directly with bare hands, the sweat stains on the hands will cause the gloss value to decrease.3 personnel
engaged in paint testing personnel should hold the professional induction certificate, and should be regularly trained, familiar with the professional standards and norms. Staff-to-person tests within and between laboratories should be carried out on a regular basis, in particular capacity verification, to improve the accuracy of laboratory personnel's measurements by identifying controllable factors affecting test results through comparing analyses.
4 Conclusion
above talked about a few paint film preparation, testing process affecting the test results of the factors, a summary is to choose the correct test method, the use of equipment and environmental conditions to meet the requirements, in accordance with the prescribed procedures for operation, qualified personnel, of which personnel are the most important factors, because these specific problems seem simple, but not easy to do, and no matter how advanced test equipment, standards and norms how complete, all work must be done by personnel, so strict management and high-quality staff to improve the level of testing.