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New test method to measure the volatile content in UV-curable coatings and inks



Published December 13, 2011
ASTM D7767 - 11 test method is a newly published extension of Test Method D5403. While Test Method D5403 specifies that a test specimen be cured by exposure to UV or EB as prescribed by the supplier of the material, most radiation curable monomers and oligomers provided as raw materials to formulators are not designed to be used alone but rather as blends of monomers and oligomers so that there are no "supplier prescribed" exposure conditions. Test Method D5403 is not appropriate for the measurement of volatiles from thin radiation-curable coatings because supplier prescribed cure conditions include both a thickness and an exposure specification which are difficult or impossible to achieve in a test lab. Furthermore, inks form a special class of thin radiation curable coatings because they are formulated with known interferences (for example, pigments). As a result, Test Method D5403 does not provide a method for measuring volatiles from monomers and oligomers used as raw materials in the formulation of radiation curable coatings nor does it provide a method for measuring volatiles from thin radiation curable coatings such as inks.

This test method provides a means to measure the volatile content of individual acrylate monomers, oligomers, and blends commonly used to formulate radiation curable coatings such as printing inks. Such coatings comprise liquid or solid reactants that cure by polymerizing, crosslinking, or a combination of both and are designed to be applied as thin coatings in the absence of water or solvent and to be cured by exposing to ultraviolet radiation. There is currently no direct method for measuring the volatiles from the individual materials used or thin coatings made from them.

This test method also provides a means to measure the volatiles from acrylate monomers, oligomers, and blends cured using ultraviolet radiation from which an estimate for the volatiles from a thin coating cured using ultraviolet radiation comprising these acrylate monomers, oligomers, and blends can be calculated. A common exposure step involving a specified amount of ultraviolet radiation in a specific spectral range using a common photoinitiator is called for.

This test method further provides a means to measure the volatiles from thin radiation-curable coatings such as inks in the absence of known interferences such as pigments. A common exposure step involving a specified amount of ultraviolet radiation in a specific spectral range using a common photoinitiator is called for.

If desired, volatile content can be determined as two separate components: processing volatiles and potential volatiles. Processing volatiles are a measure of volatile loss during the actual cure process. Potential (or residual) volatiles are a measure of volatile loss that might occur upon aging or under extreme storage conditions. These volatile content measurements may be useful to the producer of a material, a formulator using such materials, or to environmental interests for determining and reporting emissions.

The validity of this test method for non-acrylated radiation-curable chemistries such as methacrylates, thiol-ene, vinyl ethers, and epoxies cured using ultraviolet radiation has not been verified. Use of an electron beam to cure the acrylate monomers, oligomers, and blends or thin coatings made from them, including inks, has not been verified using this method and cannot be assumed.


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