In the coatings and pigments industry, the stability of pigments, especially their acid resistance, is a crucial performance parameter. The acid resistance of pigments not only affects the stability of the pigments themselves, but also determines the life, appearance and performance of the final coating. This article discusses in detail the determination method of acid resistance of pigments, the required instrument materials and how to interpret the measurement results.
Definition of acid resistance
The acid resistance of pigments mainly refers to the performance of pigments against acid. This performance includes the staining of acid solutions and the discoloration of pigments, usually expressed in terms of staining series and/or discoloration series. This method is suitable for acid resistance testing of most organic pigments.
Instruments and materials required for determination
In order to determine acid resistance, we require the following instruments and materials:
Basic instrument: acidity meter.
Rating card: Grey sample card (GB 251-2008) for rating staining and grey sample card (GB 250-2008) for rating discoloration.
Hydrochloric acid solution: must meet the requirements of GB 622 2% solution.
Determination process of acid resistance
Preparation of test solution and filter cake
Take two samples, weigh them accurately, and place them in two test tubes. Add distilled water to one tube and hydrochloric acid solution to the other. After a series of oscillations and filtration operations, we will get a clear filtrate.
B. Assessment of staining and discoloration series
First, a 2% hydrochloric acid solution and the resulting filtrate were used for colorimetric evaluation, respectively. Then, the filtered cake was evaluated for discoloration. These evaluations were carried out by comparing gray sample cards.
C. Parallel experiments
The two samples performed should obtain the same evaluation result to ensure the accuracy of the determination.
How to interpret and present the results
The acid resistance of pigments is usually expressed by the staining order of the filtrate, the discoloration order of the filter cake, or a combination of the two. The range of stages is 1 to 5, with 5 indicating the best and 1 indicating the worst. The degree of staining or discoloration between the two stages is expressed in a specific way. For example, if the staining order of the filtrate is 4 and the discoloration order of the filter cake is 3, the result is expressed as 4 [3].
reference standard
This method is based on the national standard GB 5211.6-85 "Determination of acid resistance of pigments".
conclusion
The acid resistance of a pigment is a key parameter that determines its application range and durability. Correct determination and interpretation of this property can help manufacturers and users choose the right pigment for a specific application. In addition, the assay method also provides a standardized way to make fair comparisons between pigments from different sources.
