GB/T16995-1997 "Determination of livering time of thermosetting coating powder at a given temperature"

(1 Scope

This standard specifies the method for determining the gelling time of thermosetting powder coatings at a given temperature (generally 180 °C).

The determination of gel time is a very simple method of expressing the characteristics and quality control of powder coatings. However, the gel time determined by this method cannot directly reflect the nationalization time of powder coatings in actual application.

This method is not suitable for powder coatings with ultra-short gelation time (less than 15s).

(2) Definition

The time required for a certain volume of powder to paint to become indeformable after melting under specified conditions.

(3) Principle

A certain volume of powder coating sample is heated to the specified temperature at the drawing pit of the heating block, and the time when it can no longer be drawn into wire from the melt is measured.

(4) Material

① Checking substance: a substance whose melting point is known and used for testing to check the temperature of the heating block. If the temperature of 180°C is checked by a child, D-camphor is a more suitable material.

②Release agent such as polytetrafluoroethylene air-port rubber dispersion.

(5) Instrument

Heating block: It is composed of an electric heating steel block with sufficient mass (to keep the temperature stable). This steel block needs to be able to change its temperature at a constant temperature within the range of 130~230°C. This temperature shall be controllable with a thermostat. The heating block has a circular polished pit with a diameter of 16mm ± 0.1mm and a radius of 10mm ± 0.1mm, located at the center of the upper surface for placing test samples. The heating block should have a hole of sufficient mesh diameter to place the temperature Detector, and the hole should be close to the center of one side of the heating block. It extends horizontally below the upper surface to near the center of the heating block, and its terminal is not more than 2mm away from the center of the painting pit.

A suitable heating block (example) is shown in Figure 6-10.

The heating block is often thermally insulated. For the heating block shown in Figure 6-10, a 500W heating device is suitable.

Thermometer: It should have a sufficient measurement range, and the reading value should be accurate to 1°C.

Measuring spoon: with a capacity of 0.25mL ± 0.01mL, used to transfer the sample to the pit of the heating block.

Timer: accurate to 1s.

Stirrer: Very low heat capacity, good size. A stirrer with a 1 mm diameter circular needle mounted on an insulating rod may be used. A small wooden whisk can also be used.

Squeegee: Made of soft sub heating block material. Used to remove the sample on the heating block without scratching the surface of the heating block.

(6) Sampling

According to the provisions of GB3120, take a representative sample of the tested product.

(7) Operation steps

Parallel assays were performed in duplicate samples.

Unless otherwise specified or otherwise agreed between the US and the US, the test shall be carried out at 180°C ± 1°C

Place the heating block in a non-ventilated room temperature environment, heat the heating block to the specified temperature and allow it to stabilize for at least 10min. To check whether the surface temperature of the heating block has reached the required temperature, a small piece of material with the required melting point temperature can be placed on the Heating Plate.

If necessary, according to the instructions of the manufacturer, the pit and the upper surface of the heating block can be treated with a release agent.

Use a measuring spoon to move 0.25mL of the sample of the product under test to the pit of the heating block, start the timer immediately after all the samples are melted and use the stirrer to melt the material in a small circular motion. When the test object starts to thicken, while keeping stirring, lift the batch mixer up to about 10mm from the melt every 2~3 seconds. If the drawn wire formed during the increase becomes brittle and breaks, and can no longer be drawn into a wire from the melt, stop timing and record the time, accurate to 1 second. This time is the gelation time of the sample.

Scrape the test sample immediately from the heating block with a spatula, taking care not to scratch the surface of the heating block.

Resample to repeat the above assay. If the difference between the two results does not exceed 5% of the minimum value, the arithmetic mean may be calculated and reported. If the difference between the two results exceeds 5% of the minimum value, a third measurement is required and the arithmetic mean of the three results is calculated and reported.