Huihong: When choosing a good pigment, what aspects do you need to look at?

Huihong: Good pigments are inseparable from these performance indicators, namely the shade, tinting strength, hiding power, solvent resistance and various fastnesses of the pigment. Let's take a look.

1. Coloring performance is the shade (hue) of the color of the pigment. For a long time, visual judgment has been the basic and advantageous color evaluation method, relying on the eyes trained by professional color personnel. What kind of eyes can be used as a standard? Usually it is difficult to define. The development of color evaluation technology has formed a more scientific evaluation system, such as using a tester, which can be used to describe color qualitatively and quantitatively.

The definition of a color cannot be described verbally, for example, "red", what is red, even if you use more modifiers, such as "magenta", "brick red", "Bordeaux red", it does not precise. To make a color sample, such as a color card, it is more intuitive to define a color. For practical applications, people are more accustomed to determining a standard pigment according to the required color, and then according to a specific dispersion system, the sample to be tested and the standard sample are respectively made into colored samples of color depth, and then the samples are compared. Color difference from the standard sample. Commonly used color systems include CIE*LAB system, and XYZ tristimulus value system, which can be converted to each other.

2. The concept of tinting strength, tinting strength, has pair tinting strength and relative tinting strength. For tinting strength, it is based on the absorbance of the pigment, ie the overall absorption coefficient at the maximum absorption wavelength or across the entire visible spectrum (the latter can be in terms of different spectral components). The relative tinting strength is the relative value obtained by comparing the absorption coefficient between the sample and the standard. The ratio of the amount of sample pigment that matches the amount of standard pigment to achieve the same color depth. It is not always possible to find an exact match, because there is an inherent difference in shade between the two, which cannot be eliminated by quantity, and whose color difference can be expressed by the CIE*LAB system. The color strength of pigments will have different results according to the application conditions of pigments, that is, different color development methods, as well as different measurement methods and evaluation methods.

3. Hiding power or transparency refers to the ability of the pigment medium layer to hide the color difference of the substrate. It is defined as the area covered by a certain amount of pigment-colored paint, and it can also refer to the small size of the layer required to cover a substrate. thickness. For a coating to effectively cover the substrate, scattering is required, and the amount of scattering is related to the thickness of the coating, the absorption of light in the coating, and the size of the color difference of the substrate.

4. Solvent resistance and various application fastness. According to the definition of pigment, it should be insoluble in the application medium, but it is impossible to be insoluble. According to different media or conditions, it will be more or less soluble. Therefore, in the carrier Recrystallization, bleeding, spilling, etc. will occur when the solvent in the medium reaches the amount, and it is very important to prevent the dissolution of the pigment. Factors that control the solubility of a pigment in a medium include: choice of solvent, chemical structure of the pigment, particle size, and temperature. A test method for detecting the resistance of a pigment to a certain solvent: Roll up the pigment toner with a piece of filter paper, put it in a test tube, add the solvent, and determine the weight of the pigment and solvent. After 24 hours at room temperature, the extent to which the solvent was dyed was used to evaluate the solvent resistance of the pigment. This method cannot fully represent the actual application, but it can determine the trend and is instructive. If the pigment is visibly dissolved, and the pigment is used in a medium containing such a solvent, problems such as color, rheology, fastness, etc. will occur.

5. Water resistance, soaping resistance, alkali resistance, acid resistance: there are two meanings, one is the chemical stability in these media, and the second is the solubility in these media. The concept does not need too much explanation. Mainly for the environment and application environment of the pigment, such as the water squeeze phase inversion process of the filter cake, the pigment needs to be water-resistant, and the ink printing requires the pigment to be water-resistant, or alkaline water. For another example, exterior wall coatings require alkali resistance to cement or lime, and car washing requires car paint to be resistant to alkaline water and detergents.

Some lake pigments, or pigments containing free acid or basic groups, will form salts in acids or bases, change color, etc. There are standard detection methods for the detection of these performances, and the evaluation is based on levels 1-5, with 5 being the best. To determine the appropriate detection method according to the application, the pigment is directly exposed to materials such as acid and alkali, and then the pigment and paint are made into a layer, and then exposed to acid and alkali, etc., the results will be very different.