This section describes coating performance testing, including coating appearance testing, viscosity testing, fineness testing, etc.
Corresponding inspection and acceptance should be carried out before the coating is purchased into the warehouse, so as to avoid possible quality accidents during the coating process, resulting in production delays and a series of economic losses. The product sampling shall be carried out according to GB 3186-88 and the testing items shall be described as follows.
1. Appearance
Visually observe whether the coating has delamination, muddyness, thickening, gelling, anti-coarseness and serious settlement. Corresponding inspections should also be carried out for paint varieties that have been stored for a long time or have reached or exceeded their storage period. Generally, the storage period of paint products is 6-12 months. Due to the high density of pigments, flow drop will inevitably occur during storage. At this time, it is especially necessary to check the degree of sedimentation and agglomeration. Generally, it can be checked with a scraper. If the sedimentation layer is soft and the scraper is easy to insert, the sedimentation layer is easily stirred up and dispersed again. After other properties are checked, the paint can continue to be used.
The sedimentation and agglomeration of the coating is also a means to evaluate the storage stability of the coating, and the degree of settlement can be measured by a force measuring instrument. During the experiment, the sample is placed on the platform of the dynamometer, and the platform moves upward slowly at a speed of 15mm/min. The instrument probe is pressed into the sediment one by one, and the resistance and depth of the probe when inserted into the sediment are recorded, so as to judge the degree of sediment. Softness and thickness. According to the measured penetrating force of the probe, the ability of the sediment to be re-stirred and dispersed can be determined, and the corresponding relationship is shown in the figure. This dynamometer can also be used to measure the amount of sedimentation within a certain period of time, and the relationship between the amount of sedimentation and time is recorded by the Recorder.
2. Viscosity (GB/T1723-93)
For the uniformly stirred original paint, at the specified temperature (such as 25°C1, use the Tu-4 cup to measure the time required for the paint to flow out of the cup in a linear shape. The volume of the cup is 100ml, and the viscometer should be kept horizontal during the test. The liquid level is flush with the edge of the cup mouth (scraped with a glass rod). After each use, the viscometer should be cleaned and dried with a solvent before testing the next sample.
Paint viscosity greatly affects the construction performance of paint, and is an important parameter for paint testing. The viscosity of the original paint is generally relatively high, and the paint with a viscosity below 150s can only be measured with Tu-4 cup. When diluting, it is also necessary to use 4 cups to measure the viscosity, so as to determine the paint dilution ratio under the construction viscosity.
3. Fineness (GB/T6753,1-86)
The fineness seriously affects the smoothness and brightness of the paint film. Moreover, some pigments are easy to flocculate and thicken during storage and dilution, so the detection of fineness becomes particularly important.
The fineness is generally tested with a scraper Fineness Meter. Take a few drops of paint and drop it on the deepest end of the groove, hold the scraper perpendicular to the plate, and quickly pull it from the deep groove to the shallow part (≤3s), so that the paint sample fills the groove of the plate. Observe the exposed particles by sight at 15°-30° on the surface, and record the corresponding graduation line. There shall not be more than 3 particles in the adjacent graduation line above the reading.
The fineness requirements of various coatings are as follows:
1. The high decorative finish is 15-20 microns, the flat paint is 30-40 microns, and the semi-gloss finish is 25-35 microns. The anti-rust primer should be greater than 50 microns.
4. Solid content
Dry the paint sample at the specified temperature to constant weight, and calculate the percentage of residual mass in the total mass of the sample. The solid content of the coating directly affects the fullness and economic benefits of the coating film
See the figure for the standard drying temperature of different types of coatings when measuring the solid content, and see the table for the solid content of various coating products and the dilution rate when they are diluted to the construction viscosity
