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Significance and Use
The ability of polymer films to retain inks, coatings, adhesives, etc. is primarily dependent on the character of their surfaces and can be improved by one of several surface-treating techniques. The electrical discharge treatment, such as corona treatment, has been found to increase the wetting tension of a polymer film. The stronger the treatment, the more actively the surface reacts with different polar interfaces. It is therefore possible to relate the contact angle of a polymer film surface to its ability to accept and retain inks, coatings, adhesives, etc., if the ink, coating, or adhesive contains the polar functionalities. Contact angle in itself is not a completely acceptable measure of ink, coating, or adhesive adhesion.
The wetting tension of a polymer film belongs to a group of physical parameters for which no standard of accuracy exists. The wetting tension of a polymer cannot be measured directly because solids do not change shape measurably in reaction to surface energy. Many indirect methods have been proposed. Different test methods tend to produce different results on identical samples. Practical determination of a solid's surface energy uses this interaction of the solid with test liquids.
Although the level of surface treatment of polymer films has been traditionally defined in the industry in terms of dynes/cm (mN/m), these values are derived from a subjective interpretation of the observed test liquid behavior.
The following ranges of water contact angle values can be used as a guide for defining the level of surface treatment of polyolefins and many other polymer films with initial low surface energies:
|Marginal or no treatment||>90°|
|Low treatment||85 to 90°|
|Medium treatment||78 to 84°|
|High treatment||71 to 77°|
|Very high treatment||<71°|
The suitability of the test for specification acceptance, manufacturing control, and end use of polymer films will have to be established through capability studies for each particular film and treatment.
Almost all materials have variations in contact angle as one moves from point to point. Nonuniform treatment of film with corona treaters may also add variability to the results. Therefore, multiple measurements are necessary to reflect variation in treatment and surface roughness.
1.1 This test method covers measurement of the contact angle of water droplets on corona-treated polymer film surfaces.
Note 1—This test method is identical to ISO 15989.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D618 Practice for Conditioning Plastics for Testing
D724 Test Method for Surface Wettability of Paper (Angle-of-Contact Method)
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
ISO StandardISO15989 Plastics--Film and Sheeting--Measurement of Water-Contact Angle of Corona-Treated Films
ICS Number Code 83.020 (Manufacturing processes in the rubber and plastics industries)
UNSPSC Code 13111200(Films)