GB/T 20623-2025Emulsions for architectural coatings (English PDF)

6.1 Sampling

Sampling shall be performed according to the provisions of GB/T 3186, or according to an agreed method. The sampling quantity shall be determined according to the test requirements.

Each specimen shall be inspected and prepared according to the provisions of GB/T 20777; and the final specimen shall be prepared in the "to be tested" state.

6.2 Test environment

Unless otherwise specified, tensile strength and elongation at break (standard state) shall be tested under the standard conditions specified in GB/T 9278; other items shall be tested under the conditions specified in the relevant test method standards.

6.3 General requirements

Unless otherwise specified, only reagents confirmed to be chemically pure or higher and distilled or deionized water meeting the Class III water requirements of GB/T 6682 shall be used in the test. The test solution shall be pre-adjusted to the test temperature before the test.

6.4 Preparation of coating

Unless otherwise specified, preparation of coating shall be performed according to the provisions of GB/T 1727.After thoroughly mixing the specimen, apply 1~2 coats to a PTFE sheet (approximately 200 mm x 150 mm x (4 ~ 6) mm, or other suitable sizes) using a 100mm wire bar coater. When applying 2 coats, the interval between each coat shall not exceed 24 h.

Once the coating is smooth, use a steel or plastic coating mold (see Figure 1, consisting of multiple molds with a thickness of 0.3 mm or 0.5 mm) or an intermittent wet film preparation device (interval depth of 0.3 mm or 0.5 mm) to apply multiple coats; with the interval between each coat not exceeding 24 h. The final dry film thickness shall be (0.5 ± 0.1) mm. For specimens that are difficult to form a continuous film, the PTFE sheet can be sanded with P400 wet sandpaper to increase roughness before preparation of coating. The coating surface shall be smooth and free of defects such as bubbles and cracks. After the final film preparation, cure for 48 h under the standard conditions specified in GB/T 9278.After peeling off the film, place it face down in a constant temperature drying oven at (80±2) °C, ensuring the distance between the test piece and the oven wall is no less than 50 mm. After 96 h, remove it and cure for 24 h under the standard conditions specified in GB/T 9278.

6.5 State in container

6.10 Freeze-thaw resistance

It shall be performed according to Method A in GB/T 9268-2008.The specimen quantity is approximately 50 g. The specimen container is a cylindrical plastic or glass container with a volume of approximately 100 mL and a height of approximately 80 mm.

6.11 Storage stability

Place approximately 0.5 L of the specimen into a cylindrical plastic or glass container with a height of approximately 130 mm, leaving approximately 10% space inside. After sealing, place it in a constant temperature drying oven at (50±2) °C. After 14 d, remove it and place it at (23±2) °C for 3 h. Open the container and observe for any stratification, skinning, hardening, or flocculation. The specimen can be spread into a uniform thin layer on a clean glass plate using a stirring rod, and then the presence of flocculent matter can be observed.

6.12 Dilution stability

The specimen was prepared into a homogeneous dilution with a non-volatile matter mass fraction of (3±0.5)%. The dilution was poured into a 100 mL stoppered graduated cylinder to the 100 mL mark and stand at (23±2) °C for 72 h. The volumes of the supernatant and the sediment were then recorded. Dilution stability is expressed as the volume fraction of the supernatant and sediment in 100 mL of the dilution, and the results are rounded-off to the nearest integer.

6.13 Mechanical stability

At 10 °C ~ 30 °C, the specimen was filtered through a 177 µm pore size filter. (400 ± 0.5) g of the filtered specimen was weighed into an approximately 1000 mL suitable container (approximately 10 cm in diameter). The container containing the specimen was fixed to the base of a high-speed disperser (with a disc-shaped stirring head, 40 mm diameter) using clamps.

The high-speed disperser was started; and the speed was gradually adjusted to 2500 r/min within 1 min. After dispersion for 0.5 h, the specimen was filtered through a 177 µm pore size filter. Residue on the inner wall of the container was rinsed into the filter with tap water. The filter was then rinsed with tap water; and the presence of emulsion demulsification and obvious flocculent matter was observed.

6.14 Calcium ion stability

Add 30 mL of emulsion to a 50 mL beaker and stir with a stir bar. Simultaneously, slowly add 6 mL of 0.5% calcium chloride solution over 10 s. After thorough mixing, pour the solution into a 50 mL stoppered graduated cylinder. Incubate at (23±2) °C for 48 h and observe for any stratification, precipitation, or flocculation. Spread the specimen evenly onto a clean glass plate using a stir bar to form a thin, uniform layer and observe for any flocculation.

6.15 Tensile strength and elongation at break

6.15.1 Instruments and equipment

6.15.1.1 Tensile testing machine. Meets the requirements of GB/T 528.

6.15.1.2 Low temperature chamber. Used in conjunction with the tensile testing machine.

During tensile test in the low temperature chamber, the temperature shall be maintained within the range of (-10±2) °C.

6.15.1.3 Cutting knife. A type 2 dumbbell-shaped specimen cutter conforming to the provisions

of GB/T 528.

6.15.1.4 Thickness gauge. Conforms to the provisions of ISO 23529, with a graduation of 0.01 mm.

6.15.1.5 Steel ruler. Measuring range 0 cm ~ 30 cm, with a graduation of 0.5 mm.

6.15.2 Test piece marking and thickness determination

It shall be performed according to the provisions of GB/T 528.Use a cutting knife (6.15.1.3) to cut the prepared and cured coating from 6.4 into type 2 dumbbell-shaped test pieces. Use a steel ruler (6.15.1.5) to measure the test length from the center of the dumbbell-shaped test piece to both ends and mark it. Measure the thickness at three points of center and both ends (1 mm from the marked line) along the test length using a thickness gauge (6.15.1.4). Take the arithmetic mean as the test piece thickness t. The distance between the blades at the narrow part of the cutting knife is taken as the test piece width W.

6.15.3 Tensile strength and elongation at break under standard conditions

Mount the test piece in the fixture of a tensile testing machine (6.15.1.1). Record the distance L0 between the marked lines on the tensile testing machine. Stretch the test piece at a tensile speed of 200 mm/min until fracture. Record the distance L1 between the marked lines at this point, accurate to 0.01 mm. Record the maximum load F of the test piece that occurs during the tensile process until fracture.

6.15.4 Elongation at break at -10 °C

Place the test piece in a low-temperature chamber (6.15.1.2) and maintain it at (-10±2) °C for 1 h. Open the low-temperature chamber door and install the test piece in the tensile testing machine (6.15.1.1) fixture. Record the distance L0 between the marking lines on the tensile testing machine. Close the low-temperature chamber door; lower the chamber temperature to (-10±2) °C and maintain it for 2 min. Stretch the test piece at a tensile speed of 30 mm/min until fracture; and record the distance L1 between the marking lines at this point. The reading shall be accurate to 0.01 mm.

6.15.5 Calculation of test results

6.15.5.1 Tensile strength P is calculated according to Formula (1). ......