Determination of water permeability of coating film with indicator
This method is based on measuring the time for the change of the indicator under the paint film due to the penetration of water through the paint film.
A readily water-soluble aniline dye or a rubber (rubber latex) solution 26 can be used as an indicator. According to the 30th test method of OCT10086-39, the water permeability of the paint film can be measured by the following method using rubber mortar.
On a glass plate measuring 50 x 100 mm that has been effectively degreased, apply an aqueous solution of rubber cement, taking care to obtain a thin layer of water-sensitive emulsion.
When preparing the rubber solution, put it in a cup filled with 100 ml of hot water, heat it on a Water Bath and stir it, and dissolve it in small portions with 8 grams of gelatin. After the gelatin is dissolved, drop 15 parts of rubber (specific gravity 10) into the cup while stirring continuously. The solution is boiled under stirring for 8-~10 minutes, and then quickly filtered through cotton (relevant instrument: stirrer). Pour the filtered hot solution onto glass plates to make a thin layer, approximately 5 mL per plate.
On the test panel prepared by the above method, apply two coats of the paint sample; when the second coat is dry, apply paraffin wax along the edges, and then immerse the test panel in the Water Bath of the Tester (Fig. 170). In the Water Bath, after a predetermined period of time, the siphon pipe 2 injects an accurately calculated amount of water. The size of the siphon and Water Bath should be appropriately selected so that each new batch of water can cause an 8-10 mm change in the level of the Water Bath. The water filling speed of the siphon is regulated by the cock 3. After 24 hours from the beginning of the measurement, check the test plate wells to determine the earlier signs of rubber bleaching in those areas. After finding this area, calculate how long the test panel has been placed in the water, that is, calculate the time necessary for water to penetrate the paint film. (Related instruments: constant temperature Water Tank)
EB Antoshin (EBAHTomHH) 27 proposed a special instrument for measuring the water permeability of the paint film; this instrument was later improved by CH Xie Lie Briannikov.
In the HHnnK instrument (Figure 171), the moment the water penetrates the paint film (the closure of the current), a blue mark can appear on the thread or paper strip of the starch (this is due to the decomposition of the potassium iodide solution). The free iodine precipitated as a result). Several paint films can be tested simultaneously on one instrument.
Determination of water permeability and vapor permeability of coating film (paint film) by water-absorbing substances
Now, the method of measuring the water permeability and vapor permeability of the paint film based on the wide absorption of water vapor diffused through the paint film by the water-absorbing substance has been widely used.
