Packages rely on printed labels to route them to their destinations. Those labels are usually comprised of ink on paper and must survive the trip. Loading and unloading, traveling down conveyor belts, and sharing tight quarters with other packages exposes those printed labels to significant wear and tear. One way that ink manufacturers and printers ensure their products will last is the rub test.
The benchmark piece of laboratory equipment for rub testing inks is the Sutherland rub tester. As demonstrated on the manufacturer’s site, rubtester.com, the machine is available in the original configuration, a newer model with a broader range of tests, and even custom design. Because no standardized tests exist within the industry printers and ink manufacturers have several options for designing tests. Companies can experiment with various papers, inks, and coatings using precise measurements of weight and amount of wear. For example, an ink manufacturer experimenting with label printing may test an ink and paper combination with a 2-pound weight for 40 strokes at 45 strokes per minute to simulate a given package and its estimated wear from sender to receiver. This simulation provides the manufacturer with an idea of how crisp and clear the image will remain. Text and barcodes must remain legible, and logos should maintain design integrity. Another useful test an ink manufacturer or printer can perform is to find how much ink smears or transfers to another surface during contact. Results of such tests help manufacturers, sellers, and consumers trust a product will perform as expected time after time.
Friction plays an integral part in the printing process and the application. Some packaging will have large amounts of images and text printed directly on the surface. As with labels, the ink must withstand a considerable amount of abrasion during shipping and storage. Therefore, this printed material requires relatively thick, tough ink which sometimes forms a solid coating on the surface of the container. If this resulting coating is slick, the package may become challenging to stack and grip because it has lost the paper’s friction properties. Should these slick spots occur, the ink producer might introduce polymer additives to give the inked images a slight tooth. This tooth, or rough surface, could cause a problem during the testing phase related again to friction. The rub tester equipment is programmable to move at different speeds such as 85 strokes per minute or faster. The faster the test is performed, the more friction the process produces. Additionally, changes in weight affect the friction coefficient. Friction causes heat and heat damages ink; therefore, consideration of the ink composition and characteristics during the testing process is necessary.
Lack of industry testing standards makes the use of reliable equipment an essential part of consistent quality control. Because rub testing performed in a lab with calibrated equipment can produce comparable results with controlled variables, it is a valuable tool for all involved in the ink and printing industries. However, package handlers and online shoppers benefit from it as well.