VIETNAM STANDARD TCVN 2096:1993
METHOD OF DETERMINATION OF DRY STATE AND DRY TIME
Method for determination of dry state and dry time
1. Classification and definition
1.1. Surface dryness
The coating film is considered to have reached surface dryness when dry sand particles can be gently brushed off the film surface without leaving defects on it.
The time from the time the film is applied to the sample plate to the time the film reaches surface dryness is called the surface drying time.
1.2. Penetrative dryness
The state in which the film dries along with the entire thickness of the film.
According to the purposes of this standard, films are considered to have attained class I (or class II) dryness when a cloth, under a specified pressure, twist and time, does not leave marks or defects on the membrane surface.
The time when the film is applied to the sample plate to when the film dries to grade I (grade II) dryness is called class I (or class II) drying time.
2. Tools
Clean sand with a particle diameter of 130 - 180 mm is classified by sieves with holes 130 mm and 180 mm wide.
The brush is soft, flat, approximately 25 mm wide, and about 3 mm yarn long.
Compressor: consists of a freely sliding ball, the top is flat on which the weight is placed, and the bottom is attached to a semi-rigid, round rubber pad. The rubber pad has a radius of 22 ± 1mm, and a thickness of 5 ± 0.5 mm. Figure 1 is a sample of the compressor suitable for class I and class II dryness tests.
Single strand polyamide fabric with minimum size 100 x 100 mm. The weights have masses of 200g and 1500g.
The stopwatch is accurate to 0.1 seconds.
3. Sampling
Sampling test according to TCVN 2090 - 1993.
Prepare test specimens and examine them according to TCVN 5669 - 1992.
4. Sample plate
Select the sample sheet according to TCVN 5670 - 1992 and process the sample onto the sample plate according to TCVN 2094 - 1993 to the specified thickness of the dry film (in mm and specified separately for each type of paint).
5. Test conduction
5.1. Dry the sample plate
Leave the painted specimen sheet to dry in a standing position in a dust-free, drafts-free room and direct sunlight, at a temperature of 25 ± 20 °C and relative humidity of 70 ± 5% unless otherwise agreed upon among the interested parties.
5.2. Assess the dry state of the surface.
5.2.1. After the specified time, place the specimen to be tested horizontally.
5.2.2. Pour about 0.5g of sand (section 2) onto the membrane surface from a height between 100 - 150 mm. A test tube of 25 mm diameter and suitable length may be sprinkled with sand to avoid excessive spillage of sand particles.
5.2.3. After 10s, hold the sample plate at a horizontal angle of 200C and gently sweep the sand away with a soft-bristled brush.
5.2.4. The film is considered to have reached surface dryness if all sand particles are swept away without leaving defects on the membrane surface.
5.3. Determine the drying time of the surface.
At suitable intervals, just before the film is expected to be surface-dry, perform the test as described in 6.2 until surface dryness is reached and record the time.
5.4. Determination of dry state class I
5.4.1. After drying, place the test piece on a flat base.
5.4.2. Place the cloth over the test area on the sample plate.
5.4.3. Place the weight on the top of the compressor so that a pressure of 50G/cm2 is created, and lower the compressor so that the rubber pad fits inside the cloth. Press the clock and leave the compressor in this position 10 ± 1s.
5.4.4. After 10s, rotate the compressor 90 degrees for 2 ± 0.5s. Lift up the compressor, remove the test sample and check.
5.4.5. Repeat this test three times. If the membrane shows no defects or marks on all three tests, the membrane is considered to have achieved class I dryness.
5.5. Determine the dry time grade I.
5.5.1. After a suitable period of time, carry out the test as described in 5.4. Check the membrane for defects, if so, stop the inspection.
5.5.2. If no defects are left on the film, repeat the test on two other specimens.
5.5.3. Record the longest time measured after three attempts to reach class I dryness, recording the ambient temperature and humidity.
5.6. Determine the grade II dry state and grade II dry time.
The test steps are carried out in the same way as in section 5.5. and section 5.4. and the weight used has a mass such that a compressive pressure on the specimen plate is 500 G/cm2.
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