1. Coloring strength of color paste (tinting strength)

For the comparison of water-based color pastes, the coloring strength is an important index, which reflects the color concentration, color development performance and pigment dispersion flocculation. Data are parts of pigment paste required by color to reach 1/25 of International Standard Depth (ISD)To measure, the smaller the value, the higher the tinting strength. The value represents the number of grams of color paste required to be added to the white base paint: in latex paint-the titanium white content of the white base paint is 25% (1/25ST)

2. Compatibility of color paste (color development performance-finger research method)

The compatibility of the color paste with the application system is the key to the floating color, flocculation and surface defects of some paint films. In the use of color paste color matching, must do compatibility experiments, additives can often be used to solve the problem of compatibility of color paste and paint.
Add the color paste to the white paint, generally mix it into medium and light colors, and apply it on the surface of the coated object or the surface of the imitation coated object. When it is about to coagulate, grind the surface part of the coating film with your fingers, and observe whether there is obvious color difference after drying (visual inspection). If the fineness of the color paste is not enough and the dispersion performance is not good, the color development of the color paste is not good, which will affect the reproducibility of the color paint.

3. Dispersion performance of color paste (flocculation degree)

The degree of deflocculation of the pigment particles by the auxiliaries determines the size and stability of the colorant dispersion. In general, it is not possible to achieve complete deflocculation (I. e., a uniform and stable presence of the pigment grade particles in the system), but is uniformly distributed in the system in the form of agglomerates of pigment particles. A good color paste its degree of deflocculation is quite high, that is, the agglomerates are as small as possible, so as to have good color strength, excellent color development and storage stability guarantee. Due to the poor dispersion performance of the color paste, the migration difference between the pigment floc in the color paste and the white pigment and filler particles in the base material is easily reflected. This difference often makes the pigment floc no longer uniformly distributed. When the film is formed due to the slight differences in temperature, density and surface tension inside the paint film, the pigment floc and the paint base naturally participate in this movement, and the pigment floc is separated, resulting in floating color and flowering. If the dispersion performance of the color paste is good, the occurrence of floating color and flower can be avoided. In addition, the dispersion of the coating itself also directly affects the floating color and hair of the paint.

4. One of the structural properties of the color paste (light resistance, weather resistance)

The light and weather resistance of the color paste is tested by outdoor exposure, but the actual outdoor exposure time is too long, and the general color paste performance testing is mostly through the simulation test of instruments and equipment.

Light resistance: Use outdoor acrylic latex paint to make 1/3ISD and 1/25ISD standard color samples for exposure. Xenon lamp light source (1000W) is used for 72 hours of exposure, and 1-8 grade blue wool ruler and standard color sample are used for simultaneous exposure to obtain color difference rating, grade 1 is the worst and grade 8 is the best (evaluated by color measurement software)

Weather resistance: Use outdoor acrylic latex paint to make 1/3ISD and 1/25ISD standard color samples for exposure. ATLAS artificial aging instrument was used for 500 hours, and ISD gray card was used for color difference rating. Grade 1 was the worst and grade 5 was the best.

5. Pigment content of color paste

The pigment content is only for reference and cannot be used as an indicator for evaluating the performance of the color paste. The coloring power of the color paste is not simply proportional to the pigment content. The same pigment content, the fineness of different tinting strength is also very different. In order to ensure the stability of the coloring power of the color paste, the pigment content of the color paste is a change value within a certain range, and the value provided on the color paste data is a typical reference value.

6. Fineness of color paste

Fineness is an intuitive indicator of the dispersion effect and storage stability of the color paste. Generally for the same pigment paste, the smaller the particle size, the larger the specific surface area, thus the covering ability is also increased, the higher the tinting strength; the smaller the fineness, the higher the gloss, the better the dispersion effect and storage stability. Of course, the fineness of the color paste is not the finer the better, because when the particles become smaller and the specific surface area increases, the absorbed light energy increases and the degree of damage increases, resulting in a decrease in weather resistance. And when the particle size is too small, when the coating is dried into a film, with the precipitation of water, the color paste migrates to the surface together, which is easy to cause color matching and wall color difference.

7. Compatibility of color paste and coating

Refers to the grinding method to take 100 grams of white paint, add 2-3 grams of color paste to be tested, fully stir, coat on the surface of the coated object, when it is about to coagulate, grind the surface part of the coating film with your fingers, after the paint film is dry, observe whether there is color difference between the parts rubbed with your fingers and those without. If the difference is large, the compatibility between the color paste and the tested coating is not good, this color paste out of the paint easy to produce floating color phenomenon. If the color is the same, generally does not produce floating color phenomenon.

8. The structural properties of the color paste (chemical resistance)

The chemical resistance of the aqueous color paste is mainly acid and alkali resistance, that is, chemical migration resistance. This property depends essentially on the pigment itself, which must be taken into account in outdoor pastes. General water-based coatings are also required to be acid and alkali resistant, and do not require resistance to organic solvents and other chemicals.

Acid resistance and alkali resistance: according to the DIN16524 standard, the color paste was dried (105 ℃) and placed in 1% sulfuric acid and 2.5 sodium hydroxide solution respectively for 24 hours, then taken out and washed to determine its acid resistance and alkali resistance. According to the change of color bleeding and color, according to the standard of grade 5, it is evaluated that grade 5 indicates excellent acid resistance and alkali resistance, and grade 1 indicates extremely poor acid resistance and alkali resistance.

9. Other physicochemical parameters of color paste

(density, viscosity, PH value, pigment content, solids and fineness and gloss)

Density: the unit is g/cm3, the determination method is carried out according to the provisions of GB/T1756.

Viscosity: an important indicator of the storage stability of the color paste. (STM-III Stormer Viscometer)

PH value: PHB-2 portable pH meter to determine the pH value (PH value) of aqueous high quality color paste system is generally between 7-10, so the color paste has excellent properties such as color retention, tinting strength and color development in the coating system with PH value of 7-10.

Fineness and gloss: a visual indicator of the dispersion effect and storage stability of the color paste. Generally, for the same pigment paste, the smaller the fineness, the higher the gloss, and the better the dispersion effect and storage stability.

10. Quality stability of color paste

Generally, through the strict control of the production formula-raw materials-production process-finished products, the consistency of the solid content, fineness, viscosity, tinting strength, color development, light and weather resistance of the color paste is ensured. (Evaluated by color measurement and matching software, Lab value and color difference control DE <1.0) The storage stability of general water-based color paste is stored at room temperature of about 25 ℃ for one year without obvious defects such as delamination, agglomeration, coarse return, precipitation, etc., and the tinting strength, color development and other physical and chemical properties are not significantly reduced. Usually, the aging judgment can be accelerated by thermal storage and freezing experiments, and the evaluation of the effect of opening cans and the evaluation of color matching software can be carried out.

The selection of color paste should focus on the above factors, other conditions of each brand of color paste can basically reach and the difference is not big. Of course, when choosing color paste, it should also be considered from the perspectives of economy and environmental protection. For example, color paste with poor weather resistance can be selected for interior wall color paste. At the same time, color paste containing heavy metals such as chrome yellow should not be selected for interior wall, but azo, amines, etc.