How to measure paint viscosity with ISO cup

In the coating industry, viscosity is a key parameter, which directly affects the fluidity and coating performance of the coating. To accurately measure the viscosity of a coating, an ISO cup, also known as an ISO outflow cup, is often used. This article describes how to use ISO cups to measure the viscosity of coatings and describes the relevant instruments, materials and determination methods in detail.

1. Scope and Description

This method is suitable for coating products with Newtonian or nearly Newtonian flow characteristics. The flow characteristics of the coating are the ability of the coating to flow in the case of external application of force. This method specifies four ISO cups with different outflow apertures of 3mm, 4mm, 5mm, and 6mm. The outflow time of the tested sample should not exceed 100 seconds, otherwise the flow breakpoint is difficult to determine due to the delay effect and will increase the repeatability error.

How to measure paint viscosity with ISO cup

2. Instruments and materials

In order to measure the viscosity of coatings, the following instruments and materials are required:

ISO cup: A container having a cylindrical upper part and a conical lower part, with a small cylindrical orifice at the bottom of the cone and an outer protective sleeve to prevent damage.

Thermometer: accurate to 0.2°C, dividing intervals of 0.2°C or finer.

Bracket: Used to support the ISO cup with horizontal adjustment screws.

Stopwatch: 0.2 seconds.

Flat glass plate or straight edge scraper.

Bear the cup.

3. Determination method

Here are the steps to measure the viscosity of a coating using an ISO cup:

(1) Preparation test

After stirring the sample thoroughly, it was poured into the ISO cup of choice. Fill the ISO cup within 5 seconds and release your fingers, using a stopwatch to determine the outflow time.

The assay was repeated once, allowing the sample to remain in the ISO cup for 60 seconds before releasing the finger.

If the difference between the results of the two measurements is greater than 10% of their mean value, it means that the sample does not have Newtonian flow characteristics and is not suitable for viscosity determination by this method.

(2) Determination of outflow time

The outflow aperture of an ISO cup was chosen to ensure that the outflow time of the sample in that ISO cup was between 30 and 100 seconds.

Adjust the temperature of specimen and ISO cup to (23±0.5)°C or as agreed upon.

The ISO cup was placed on the bracket and the horizontal screw on the bracket was adjusted to ensure that the ISO cup was in a horizontal position.

The sample was slowly poured into the ISO cup by blocking the orifice of the ISO cup with one finger to avoid bubble formation. Use a flat glass plate or scraper to scrape off excess sample or air bubbles along the top edge of the ISO cup.

Place the bearing cup under the ISO cup, not less than 100 mm away from the outflow orifice. Quickly remove your finger and start the stopwatch. When the flow out of the hole is interrupted for the first time, the timing is stopped immediately, and the time displayed by the stopwatch is the outflow time, accurate to 0.5 seconds.

How to measure paint viscosity with ISO cup

4. Result representation

The average of the two determinations is the final determination result. The difference between the two measurements should not be more than 5% of the mean value.

5. Reference standards

National standard GB/T 6753.4 “Color lacquer and varnishing with outflow cup determination of outflow time”.

International standard ISO 2431 “Effluence time with Effluence cups for paints and varnishes (fourth edition)”.

Measuring paint viscosity using ISO cups is a common method that can be used for viscosity control and quality assessment in the coating industry. By accurately measuring the viscosity of the paint, manufacturers can ensure the consistency and performance of the product, thereby improving the efficiency and quality of the paint production.

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