Pigments are important materials widely used in painting, printing and other industrial fields, and their properties have a profound impact on the quality and stability of the final product. This article will focus on the method of measuring the alkali resistance of pigments. Through the evaluation of staining grades and discoloration grades, we can comprehensively understand the stability of pigments in alkaline environments and their applicability in different application scenarios.
1. Measurement scope and description
The alkali resistance of pigments refers to the ability of pigments to resist the action of alkali causing staining of alkali solutions and discoloration of pigments, expressed in terms of staining series and/or discoloration series. This method is suitable for testing the alkali resistance of most organic pigments. Through this method, we can accurately evaluate the performance of pigments in alkaline environments and provide scientific basis for their application.
2. Instruments and materials
Balance: sensitivity 0.01g.
Electric heating blast box: sensitivity ±0.1°C.
Box type resistance furnace.
Automatic grinding machine (flat grinding machine).
Paint Film Applicator: wet film thickness 100μm.
The adjusting knife is made of medium carbon steel or spring steel.
Syringe: Capacity 1mL.
Crucible: capacity 30mL.
Pictorial printing paper: complies with GB 2249-1996.
Ink-adjusting oil (made from pure linseed oil): viscosity 2600~2800mPa·s (25°C).
The gray sample card used to evaluate staining complies with GB 251-2008.
The gray sample card used to evaluate discoloration complies with GB 250-2008.
Sodium hydroxide complies with the requirements of GB 629, 2% solution.
3. Measurement method
1. Preparation of test solution and filter cake
Carry out parallel measurements of two samples.
Weigh two samples, each of 0.5g, accurate to 0.001g, and put them into test tubes respectively. Add 20mL of distilled water to one of them, and 20mL of 2% sodium hydroxide solution to the other. Close the ground stopper tightly and level it. Fix it on an electric oscillator, shake for 5 minutes, take it off, pour it into a fine-pore crucible with three layers of filter paper, and vacuum filter until a clear filtrate is obtained.
Note: If you cannot obtain clean filtrate by filtering with filter paper, you can use other methods of filtration, such as glass filters.
2. Assessment of staining and discoloration levels
Fill the cuvette with 2% sodium hydroxide solution and the prepared clear filtrate respectively, and perform operation, observation and evaluation. Refer to Chapter 6, Section 2, No. 10, Chapter 6.
Take out the filter cakes from the two crucibles after filtration, place them on a white porcelain plate, press them with colorless glass, and use the same method as (2) to compare the discoloration with a gray sample card to visually evaluate the discoloration progression of the sample.
3. Parallel test results
The series obtained from parallel tests should be the same.
4. Result expression
The alkali resistance of the sample is expressed by the staining progression of the filtrate, the discoloration progression of the filter cake, or both the staining progression of the filtrate and the discoloration progression of the filter cake. For the staining of the filtrate and the discoloration of the filter cake, level 5 is the best and level 1 is the worst. The method of expressing the degree of staining of the filtrate and the degree of discoloration of the filter cake has been explained before and will not be described again.
5. Reference standards
This experiment was conducted in accordance with the national standard GB 5211.7-85 "Determination of Pigment Alkali Resistance", ensuring the scientificity and comparability of the experiment.
The alkali resistance of pigments is a crucial performance indicator in the pigment application process. Through the alkali resistance measurement method introduced in this article, we can comprehensively understand the performance of pigments in an alkaline environment, providing a scientific basis for selecting pigments suitable for different application scenarios. This contributes to the optimization of the production process, improving the quality and stability of the final product.
