Paint Wetting Impairing Substances (PWIS) Test

Paint wetting is the first step of the dispersion process. The dispersion process is the process of mixing at least two substances that are insoluble or barely soluble in each other or that do not chemically interact with each other. During the dispersion process, at least one substance is dispersed into another substance.

Dispersion of solid particles in a liquid is an important process, for example in the production of paints and inks. Various additives are used in the dispersion process, where solid particles such as pigments and fillers are separated from each other and stabilized in a liquid. Solid raw materials (i.e. pigments and fillers) used in paints and inks are usually supplied in powder form. Wetting occurs when the surface tension of the liquid is low relative to the surface energy of the solid particles. When the surface tension is too high, wetting does not occur. Wetting agents are often called surfactants.

Substances that impair the wetting of paint (PWIS) can cause coating defects even in very small amounts and therefore negatively affect the quality of the coating. In the automotive industry, this issue has been a focal point for decades and concerns all paint companies. For this reason, the materials and components used in dyeing facilities are checked and suppliers are given requirements for PWS-compatible products.

Prime examples of substances that impair paint wetting are oils, greases, fluoride, waxes, and silicone. These substances adversely affect painting processes and are not allowed for use in the automotive industry and other production areas. The protective foil of many self-adhesive seals also contains some silicone.

Because silicones were initially recognized primarily as substances that prevent paint from wetting, the term “silicone-free” is still erroneously used today. Whether a substance causes paint to wet depends on its interaction with the paint system.

Ultimately, the intended use is very important. Depending on where a product is used, there may be different requirements for PWIS compliance.

The “VDMA 24364:2018-05 Test for substances that impair the wetting of paint (PWIS compatibility)” standard developed by the Union of German Engineers (VDI) defines the PWIS test requirements, taking into account the intended use of a product, its intended use and classification according to product groups.

This standard describes the requirements for testing products for substances that cause paint wetting impairment. This standard defines a classification based on the intended use of the product in critical areas for substances that cause paint wetting disorders and proposes voluntary labeling for products compatible with substances that cause paint wetting disorders.

This standard was developed to assist suppliers of paint processing companies in testing and classifying their products for paint wetting impairment substances (PWIS) compatibility.

Briefly, paint wetting disorders are defects that occur in the complete and even wetting of a surface with paint. In this context, substances detected during PWIS testing to impair the uniform wetting of a surface with paint (e.g. through crater formation) are defined as substances that impair the wetting of paint. The VDMA 24364 standard, on which this test is based, describes the procedure for testing products for the presence of substances that impair paint wetting, their classification and marking, as well as the qualification of products for PWIS compliance for liquid paint application.

Essentially, a “PWIS-free” claim cannot be made based on a test. However, materials or products may be PWIS compliant depending on the nature or area of ​​their application. PWIS compliance describes the condition of a product or material that does not cause any deterioration in wetting of paint when tested in accordance with that standard.

Among the numerous testing, measurement, analysis and evaluation studies provided to businesses by our organization, there are also paint wetting substances (PWIS) testing services for production and internal controls.