ISO 15989 Plastics - Film and Coating - Measurement of Water Contact Angle of Corona Applied Films

The standard "ISO 15989 Plastics - Film and coating - Measurement of water contact angle of corona-treated films" developed by the International Organization for Standardization (ISO) describes a test method for determining the contact angle of water droplets on corona polymer-treated film surfaces and then determining the wetting voltage of the film. . This method can be applied to almost any polymer film. However, if the surface of the film shows a chemical affinity for water, this test method is not valid.

For the purposes of this standard,

• Surface energy refers to the energy associated with intermolecular forces at the interface between two surfaces, measured as free energy per unit area.
• Wetting tension refers to the tension taken equal to the surface tension of the liquid exhibiting a zero contact angle with the surface of the film polymer. This is used to give an estimate of the surface energy of the film.
• Polarity refers to the value that measures the concentration of polar functional groups on the surface of a polymer film. It is expressed as the polar component of the surface energy relative to the total surface energy.
• Static contact angle refers to the angle between a flat solid surface and the tangent drawn in the vertical plane at the interface between the flat solid surface and the surface of a liquid droplet resting on the surface.

While testing, in principle, water droplets are placed on a film sample and the contact angle is measured. The wetting voltage of the film is then determined from a conversion table. Details on the importance and use of contact angle measurements and interference effects in contact angle measurement are included in the standard annexes (Appendix A and Annex B).

These tests use a contact angle meter (goniometer), which includes a light source, optical system, sample stage, and liquid distribution system. The light source can be a halogen, incandescent, or fiber optic type lamp as long as the sample or liquid is not affected by heat from the light source. Imaging optics can be video, CCD camera, ocular lens, or projection optics, and magnifications must be configured to be used.

The sample table must be such that the sample can be positioned so that the test surface is flat and horizontal. When the sample is moved to view a new area, it should be possible to avoid the previously wetted area.

The fluid delivery system is a pump-operated or manual microsyringe. For the highest droplet formation accuracy, small capacity, such as microsyringes, are used. To test liquids that require different droplet sizes, flat-tipped needles are used. Stainless steel needles are preferred, but other types, such as needles coated with polytetrafluoroethylene, can also be used.

The tests also alternatively use a droplet projection contact angle meter. This device is capable of projecting the image of a liquid droplet on the surface of the substrate onto a screen so that the tangent angle of the droplet on the substrate surface can be measured.

Computer-based systems are also used in the tests. These are PC-based systems with automatic image analysis features for contact angle measurement.

Distilled water or ultrapure water is used when performing tests. Reagent grade deionized water can also be used, but the results will not be as accurate. Additionally, any pollution mixed into the water will negatively affect the results.

The minimum amount of film required for this test is approximately one wide and long strip. If the sample is taken from a roll, the orientation of the sample relative to the machine direction of the fabric should be noted. Extreme care should be taken to avoid touching or handling the surface of the sample in areas where testing will be performed. The number of measurements per sample is determined using published tables for sampling plans. The recommended number of readings per sample is ten.

Conditioning is not usually necessary for routine quality assurance or process control measurements because it will affect the measured value so that it no longer represents actual conditions. Conditioning is required for interlaboratory measurements aimed at comparing results. In such cases, samples are conditioned at relative humidity not less than the value before testing. Whenever possible, testing is done under the same conditions used for conditioning. Special testing conditions are generally not required for routine quality assurance.

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