[Paint Inspection]MEK rubbing test method and its limitations

Among the test methods, the most popular and easy to use test method for determining the degree of curing of the coating film would be the MEK rub test.

The term of MEK Rub Test is used much however Solvent Rub Test is the accurate term for MEK Rub Test.

It is called 'MEK Rub Test' because MEK is a strong solvent and mainly used among solvents, since the solvent-MEK is mainly used to evaluate the degree of cure of inorganic Silicate Inorganic Zinc Rich Primer, it is usually called more as MEK rub test than Solvent Rub Test.

Pros and Cons of MEK Rub Test

Pros: Easy, Quick, Simple
Cons: Comparative Evaluation, Lack of Reproducibility

Specifications of Solvent Rub Test

• ASTM D5402 Standard Practice for Assessing the Solvent Resistance of Organic Coatings Using Solvent Rubs
• ASTM D4752 Standard Practice for Measuring MEK Resistance of Ethyl Silicate(Inorganic) Zinc-Rich Primers by Solvent Rub

ASTM D5402 is a standard for evaluating the solvent resistance of organic paints, and ASTM D4752 is a standard for measuring the degree of curing of inorganic zinc primers through the solvent (MEK).

Solvent Rub Test Method (MEK Rub Test Method)

1. Prepare a fully cured control panel and a test panel.
2. Moisten a cotton swab or white cloth with a solvent(MEK) and rub it back and forth at a constant pressure.
3. Test on both panels under identical conditions.
4. Determine the degree of cure by comparing the changed state of gloss, coating loss, etc.

Limitations of Solvent Rubbing Test

MEK rubbing testing has limitations due to its test methods.

In the case of ASTM D4752 listed above, the standard provides a reference table to determine the degree of cure, but when used to determine the degree of cure of a organic paint, a generally comparable standard is required. So the disadvantage here is that the degree of cure must be determined by comparison between the fully-controlled panel and test panel.

In addition, when doing MEK test, it is necessary to know the type of paint. This is because some resins have weak solvent resistance to MEK or some solvent, and so even after proper curing, the gloss, film loss, or softening of the coating may be as if uncured.

The aggressive of solvents

MEK, Acetone >>>>>>> Xylene, Toluene

Depending on the resin type and requirements, solvent selection is also required, but MEK is usually used a lot.

One of the limitations of the MEK test is that it is a test conducted by a human.

As a result, test results may vary due to differences in rubbing speed, force, lasting time and other human factors.

(The pressing force, speed, and rubbing distance can be specified in the above ASTM standards or test requirements.)

However, it is widely used as a very useful test method to easily and quickly determine the degree of curing in the field and the laboratory, and test equipment with minimal human factor has been developed and used for more accurate testing in the laboratory.