By Levi Loesch, Product and Materials Engineer, Product and Materials Division, DDL, Inc.
When labeling a product, ensuring that you are using the best combination of materials to present the product as intended to the end user and reduce cost as much as possible are major considerations. There are a seemingly unlimited number of different types of label materials and inks both with different properties. When it comes to quickly and easily testing the durability of inks and substrates of prospective materials, there’s no better test than ASTM D5264; Standard Practice for Abrasion Resistance of Printed Materials by the Sutherland Rub Tester.
DDL recently added the capability to perform the Sutherland rub test and it became immediately apparent that there is some misunderstanding of what Sutherland rub testing is and the information that it provides. This article will explain the basic purpose of the test and the type of information one should expect to gain from a well-designed test program.
The Sutherland rub test is designed to provide qualitative, comparative data for the abrasion durability of multiple label constructions. The ASTM standard does not provide any pass/fail criteria for the testing as the test is only for comparing relative performance and not designed to set a particular standard. The test is not designed to replace any other tests (transportation simulation testing, for instance) which may, directly or indirectly, give information about the suitability of a label construction.
In order to effectively test multiple label constructions, there are three test variables that must be adjusted in order to optimize the testing. These variables are:
- Test weight (2 lb. or 4 lb.)
- Number of test cycles
- Test speed
- A high test speed is desirable, but the speed must be chosen so that frictional heating doesn’t influence test results.
The goal is to choose the test variables such that when the test is complete, there is a clear difference in the degree of degradation of each label type. For instance, if the test setup is too rigorous, all labels will be degraded to the point that there will be no way to determine which performed the best. On the opposite side, if the test is not stringent enough, even the weakest construction may not show any degradation. Typically, an exploratory test is required to be performed for each different label construction to best determine the optimum test variable settings to use for testing all label constructions.
When qualifying several possible label constructions, it is important to understand the objective of Sutherland rub testing and the information it can provide. A well-designed experiment can help you determine the ink and substrate combination that gives you the most durable and cost-effective solution for your particular application.