Source: Link Testing Instruments Co.,Ltd.
Latex paint is an organic paint commonly used in the construction industry, also known as synthetic resin emulsion paint. It is classified into different categories according to the production raw materials, use environment and decorative gloss effect, such as polyvinyl acetate latex paint, ethylene propylene latex paint, pure acrylic Latex paint, interior latex paint, exterior latex paint, matte latex paint, matte latex paint, semi-gloss latex paint, mercerized latex paint, etc. No matter what kind of latex paint, in addition to having good protective and decorative functions , and should also have excellent water vapor permeability. After latex paint is applied, the wall usually contains a certain amount of moisture. In rainy and snowy weather or when the indoor humidity is high, moisture will inevitably enter between the wall and the paint film through the paint film. If latex paint is applied, The moisture permeability is poor, and the water vapor in the wall and paint film cannot be lost through the paint film in time, which will produce a certain pressure on the paint film, causing the completed paint film to bubble or even fall off, affecting the construction. Therefore, research and testing of the water vapor transmission performance of latex paint is one of the important ways to improve product and construction quality.
Test methods and instruments
At present, there are four main methods for testing the water vapor transmittance of materials: cup method, electrolysis method, infrared method and humidity method. Among them, the cup method is divided into weight gain method and weight loss method. This article tests the water vapor transmission rate of the sample based on the desiccant method in GB/T 17146 (i.e., the aforementioned weight gain method).
The instrument used in this test is the LTWTC-203H water vapor transmittance test system, which is independently developed and produced by Link Testing Instruments Co.,Ltd.
Test principle: Place a desiccant in the cup, seal the sample at the mouth of the cup, and control the humidity in the test chamber of the equipment to form a certain humidity difference on both sides of the sample to allow water vapor to pass through the test chamber. The water vapor that penetrates into the cup is absorbed by the desiccant, causing the weight of the moisture-permeable cup to change. By testing the increase in the weight of the cup over time, the water vapor transmission rate of the sample is obtained.
Test samples and test process
Test sample: This test uses sheet materials made from a certain brand of latex paint as the test sample.
(1) Use a sample cutter to cut three samples with a diameter of 74mm from the sheet material made of the latex paint sample.
(2) Fill a moisture-permeable cup with a certain amount of dried anhydrous calcium chloride as a desiccant.
(3) Seal the three cut samples on three moisture-permeable cups containing desiccant.
(4) Place the moisture-permeable cup of the sealed sample on the tray in the test chamber of the equipment, close the test chamber door, set parameter information such as sample thickness, test temperature, humidity, etc., click the test option, and the test starts. The equipment automatically performs intermittent weighing of the moisture permeable cup according to the set parameters.
(5) After the test, the equipment calculates and displays the water vapor transmission rates of the three samples based on the weight changes of the three moisture-permeable cups over time.
Test results and analysis
The water vapor transmission rates of the three samples under the test conditions of 23°C and a relative humidity of 50% RH inside and outside the cup were 110.621g/(m2·24h), 108.037g/(m2·24h), and 113.167g/(m2) respectively. ·24h), that is, the water vapor transmission rate of the tested latex paint sample is 110.608 g/(m2·24h).
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