Coating liquid performance inspection

Test of liquid properties of coatings - Determination of appearance and lightness of varnishes, varnishes and thinners

1 Definition, Purpose and Significance

Transparency is the ability of a substance to transmit light. Transparency can indicate whether varnishes, varnishes, paints and thinners contain mechanical impurities and floating objects.

Both varnish and varnish are colloidal solutions, and the degree of transparency or turbidity is caused by light scattering on the particles of the dispersed phase. In the production process, the purity of various materials, the mixing of mechanical impurities, the local overheating of materials, the mutual solubility of resins, the solubility of solvents in resins, the precipitation of drier and the infiltration of water will all affect the transparency of the product. Products with a turbid and opaque appearance will affect the gloss and color of the film, as well as reduce the adhesion and resistance to chemical media.

2 Relevant standards

GB/T 1721-79(89) Determination of appearance and transparency of varnishes, varnishes and thinners                               

HGf "3379-2003 Perchlorethylene Diluent Appendix A Transparency Determination

3 Introduction to key points of inspection methods

3.1 GB/T 1721-79(88) Appearance and Transparency Determination of Clean Bran, Clear Oil and Thinner

3.1.1 Determination of appearance

At a certain temperature, visually observe whether the sample contains mechanical impurities under the transmitted light in the dark box.

3.1,2 Determination of transparency

At a certain temperature, visually compare with a series of standard solutions of different degrees of turbidity under the transmitted light in the dark box to evaluate the transparency of the sample.

3.1.3 Materials and enabling equipment

Stoppered colorimetric tube: capacity 25ml

Wooden obscura: 500x400x600mm Transparency standard liquid as shown in Figure 4    ; divided into colorless part and colored part.

3.1.4 Operation points

3.1, 4.1 Determination of Appearance

Put the sample into a dry and clean colorless glass colorimetric tube with a capacity of 25ml, adjust the temperature to (23±2)°C, and observe whether the sample contains mechanical impurities under the transmitted light in the dark box.

3.1.4.2 Determination of transparency

Put the sample into a dry and clean colorless glass colorimetric tube with a capacity of 25ml, adjust the temperature to (23±2)°C, and compare it with a series of standards with different degrees of purity under the transmitted light in the dark box. (Use the primary color part for colorless ones, and the colored part for colored ones), and select the closest primary standard solution for the sample.                                           

3.1.5 Result presentation

3.1.5.1 Appearance By visual comparison, evaluate whether the sample contains mechanical impurities.

3.1 5.2 Transparency standard liquid is divided into three grades, which are transparent, slightly turbid and turbid, namely grades 1, 2 and 3 in the standard. The transparency level of the sample is directly expressed by the level of the closest primary standard solution.

3.1.6 Precautions

3.1.6.1 The standard solution should be properly kept, protected from light, and the effective use period is six months.

3.1.6.2 During the test, if cotton-like suspended solids or sediments are found in the standard solution, it should be well mixed and then compared with the sample.

3.1.6.3 During the measurement, if the sample is turbid due to low hand temperature, it can be heated to (50-55) ℃ on a Water Bath and kept for 5 minutes, then cooled to (23i2 ) CC, and then measured.

3.1.6.4 Before the measurement, the appearance of the colorimetric tube containing the sample should be transparent and clear, otherwise the test result will be affected.

3.2 HG/T3379-2003 Perchlorethylene Thinner Appendix A Determination of Transparency

3.2.1 Principle

Use the instrument to measure the transparency value, and judge the transparency level of the sample based on this value.

3.2.2 Materials and instruments

Copper mesh: 150µlm-180µm.

Transparency Tester: the transparency grade is 20~100, and the measurement accuracy is 2%.

3.2,3 Operation points

3.2.3.1 Turn on the power of the instrument.

3.2, 3.2 Close the cover of the measuring port of the instrument, and adjust the calibration knob to make the display value of the instrument 100%.

3.2.3.3 Stir the sample evenly, filter it with a 150µm-180µm copper mesh, pour the transitional sample into a flat, dry and clean liquid, and the height of the liquid should not be less than four-fifths of the height of the liquid. Insert the liquid stopper into the measuring port, close the differential, and read the value displayed by the instrument. When handling the liquid container, only touch the opaque side of the liquid container with your hands, and keep the transparent side clean.

3.2.4 Result presentation

3.2.4.l Measure twice in parallel, if the difference between the measurement results is not greater than 2, take the average of the two measurement results. .

3.2.4.2 Judge the level of transparency according to Table 1.

Table 1 The relationship between the measured value and the degree of sleep penetration