Pigment is a chemical product widely used in painting, paint, printing and other fields. Its performance is directly related to the quality and durability of the final product. Among them, the acid resistance of the pigment is an important performance indicator, which directly affects its stability in different environments. This article will introduce a method for measuring acid resistance, which can accurately judge the performance of pigments under acidic conditions by evaluating the staining grade and discoloration grade.
1. Measurement scope and description
The acid resistance of pigments refers to the ability of pigments to resist staining of acid solutions and discoloration of pigments caused by the action of acids, expressed in terms of staining progression and/or discoloration progression. This method is suitable for testing the acid resistance properties of most organic pigments. This approach allows us to understand the stability of pigments in acidic environments, allowing for better pigment selection and 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.
Hydrochloric acid complies with the regulations of GB 622, 2% solution.
3. Measurement method
1. Preparation of test solution and filter cake
Carry out parallel measurements of two samples.
Weigh two samples, each 0.5g, accurate to 0.001g, and put them into two test tubes respectively. Add 20mL distilled water to one of them and 20mL hydrochloric acid solution to the other. After leaving it for 5 minutes, cover it tightly with the ground stopper. Fix them horizontally on an electric oscillator, oscillate for 5 minutes, remove them, pour them into fine-pore crucibles covered with three layers of filter paper, and vacuum filter until a clear filtrate is obtained.
2. Assessment of staining and discoloration levels
Fill the cuvette with the 2% hydrochloric acid solution and the clear filtrate obtained, and perform operation, observation and evaluation. Refer to Chapter 6, Section 2, 10.3, (2).
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 acid 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 staining degree of the filtrate is between two levels, represented by level 45, level 34, level 23, and level 12. The degree of discoloration of the filter cake is between two levels, represented by 4/5, 3/4, 2/3, and 1/2. If the staining degree of the filtrate and the discoloration degree of the filter cake are expressed at the same time, it is expressed as A[B], A represents the staining degree of the filtrate, and [B] represents the discoloration degree of the filter cake.
5. Reference standards
This experiment was conducted in accordance with the national standard GB 5211.6-85 "Method for determination of acid resistance of pigments", ensuring the scientific nature and comparability of the experiment.
Through the acid resistance test method of pigments, we can accurately evaluate the performance of pigments in acidic environments. This provides scientific basis for the application of various pigments in cosmetics, paints, printing and other fields. At the same time, through experimental results, we can better select pigments suitable for specific conditions and ensure the stability of the final product quality.
