Basic knowledge of PU color paste

Main properties of PU color paste

1. Tinting strength of PU color paste

For the comparison of different brands of PU colorants, tinting strength is an important indicator, which reflects the color concentration, color development performance and flocculation of pigment dispersions of colorants. Data is measured in parts of pigment paste required to achieve a color of 1/25 the International Standard Depth (ISD), the lower the value, the higher the tinting strength. The value represents the number of grams of color paste that needs to be added to the white base paint: In latex paint - the white base paint has a titanium dioxide content of 25% (1/25ST)

2. Compatibility of PU color paste

The compatibility of PU color paste with the application system is the key to affect the floating color, flocculation and some surface defects of the paint film. Before using the color paste for color matching, a compatibility test must be done, and additives can be used to solve the compatibility problem between the color paste and the paint.

Add the color paste into the white paint, usually in medium and light colors, and apply it on the surface of the object to be coated or the surface of the imitation object to be coated. Color difference (visual). If the fineness of the color paste is not enough, poor dispersion performance will lead to poor color development of the color paste, which will affect the reproducibility of the paint.

3. Dispersion performance of PU color paste

The degree of deflocculation of the pigment particles by the additive determines the size and stability of the colorant dispersion. Generally speaking, it is impossible to achieve complete deflocculation (that is, the pigment exists uniformly and stably as primary particles in the system), and it is only uniformly distributed in the system in the form of agglomerates of pigment particles. A good color paste has a relatively high degree of deflocculation, that is to say, the agglomerates are as small as possible, so that it has good tinting strength, excellent color development and storage stability. Due to the poor dispersion performance of the color paste, the migration difference between the pigment flocs in the color paste and the white pigments and filler particles in the base material is relatively easy to reflect. This difference often makes the pigment flocs no longer evenly distributed. When the film-forming factor There are small differences in temperature, density and surface tension inside the paint film. Pigment flocs and paint base naturally participate in this movement, and the pigment flocs are separated, resulting in floating and blooming. If the dispersion performance of the color paste is good, the occurrence of floating color and blooming can be avoided. In addition, the dispersibility of the paint itself also directly affects the floating and blooming of the paint.

4. One of the structural properties of PU color paste

The light and weather resistance of PU color paste is tested through outdoor exposure (for example, Florida in the United States and Turpan in my country have exposure fields, etc.), but the actual outdoor exposure time is too long, and now most of the general color paste performance testing is through instruments and equipment mock test. Lightfastness: 1/3ISD and 1/25ISD standard color samples are used for exposure using exterior acrylic latex paint. Use xenon lamp light source (1000W) to expose for 72 hours, use 1-8 grade blue wool ruler and standard color sample to expose at the same time, get the color difference for rating, grade 1 is poor, grade 8 is good, (has been evaluated by color measurement software) weather resistance Performance: Use outdoor acrylic latex paint to make 1/3ISD and 1/25ISD standard color samples for exposure. Use the ATLAS artificial aging instrument to expose for 500 hours, and use the ISD gray card to evaluate the color difference. Level 1 is poor and level 5 is good. (Evaluated by color measurement software)

5. The second structural performance of PU color paste

The chemical medium resistance of PU color paste is mainly acid resistance and alkali resistance, that is, chemical migration resistance. This performance depends essentially on the pigment itself and must be taken into account in colorants for exterior use. Generally, water-based coatings also require acid and alkali resistance, and do not require resistance to organic solvents and other chemicals.

Acid resistance and alkali resistance: According to the DIN16524 standard, dry the color paste (at 105 ℃) and put it in 1% sulfuric acid and 2.5% sodium hydroxide solution for 24 hours, then take it out and wash it to measure its acid resistance and alkali resistance . According to the bleeding and color change, it is evaluated according to the 5-level standard. A level 5 indicates excellent acid and alkali resistance, and a level 1 indicates extremely poor acid and alkali resistance.

6. Other physical and chemical parameters of PU color paste

Density: the unit is g/cubic centimeter, and the determination method shall be carried out according to the provisions of GB/T1756. Viscosity: an important indicator reflecting the storage stability of color paste. (STM-Ⅲ Stormer viscometer) pH value: PHB-2 portable PH meter measures the pH value (PH value) of the water-based high-quality color paste system, which is generally between 7-10, so the color paste has a pH value of 7-10 The performance of color retention, tinting strength and color development in the coating system. Fineness and gloss: an intuitive indicator reflecting 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.

7. Quality stability and storage stability of PU color paste

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

8. How to choose PU color paste?

According to the coloring object and environmental requirements, the color paste is mainly divided into two types: light fast and non light fast. Generally, when there is no compatibility in the system for internal use, it is based on the principle of meeting the color requirements and low cost, and does not require light fastness. For external use, the following factors must be considered:

a. Light and weather resistance; b. Chemical medium resistance (mainly acid and alkali resistance); c. Compatibility with the use system; d. Tinting strength, hiding power and color development; e. Color paste and color paste f. The storage stability of the color paste; in general, exterior paints have strict requirements on the color retention of the color, so when selecting the color paste, special attention should be paid to the light resistance, weather resistance and acid and alkali resistance of the color paste sex. Under the premise of good compatibility, tinting strength, hiding power, color development and storage stability, the mutual matching of colorants is also crucial. Single-color colorants with superior performance such as light and weather resistance should be selected as much as possible, but in fact they are often composite colors, so it is generally followed that inorganic and inorganic, organic and organic or light and weather resistance are close (1/25ST diluted, The principle of light fastness should be 7~8 or 8, and weather resistance should be 4~5 or 5), so as to ensure the outdoor color retention and avoid the obvious difference in the weather resistance of the coloring paste, resulting in long time Coating defects such as fading or uneven color and blooming.