Measuring Durability in Coatings with Abrasion Testing

How do we best test to predetermine the durability of printed/coated graphic arts products?

Abrasion tests can determine the durability of printed and coated graphic arts. The durability of a printed coating is typically defined by such terms as, scuff, wear, rub, smudge, abrasion, blotching, and/or pick-off resistance. Historically a problem, defacing abrasion damage is an even greater issue as international firms face the challenge of servicing global markets.

A variety of shaker boxes, tumblers, and rub testers i.e., the Sutherland and Taber Abraser, have been developed and used in order to stimulate damage occurring in the field. While in widespread use, most practitioners agree that all of these devices suffer from the inability to provide reproducible, repeatable results.

Development of Abrasion Testing Machines

Consider the Sutherland, its up and back motions simply do not reproduce the scuff markings and pick-off seen in field damage, and today’s tougher finishes can produce rubs in the thousands with long test times. Further, test results have not been able to be reliably reproduced between operators, laboratories, and instruments. Nevertheless, the Sutherland rub tester has been an industry standard since 1951 and it was used to develop ASTM D5264-98 (2019).

Testing Coatings using a Sutherland Rub Tester

In testing, a flat printed specimen is mounted to a platform with a second printed specimen attached to a weighted test strip (2 or 4 lbs.) placed in contact over it. The Sutherland’s drive moves the weighted test strip in an arc to produce a rubbing action. The rub test simulates and measures the amount of abrasion that might result from shipping, handling, and storage. Printed labels, folding cartons, corrugated, other packaging, and other flat graphic arts items have been subject to Sutherland rub testing.

The Taber Abraser is used on a Wide Variety of Materials

The Taber Abraser too, with its rotating wheels and test bed, does not reproduce the look of field-found abrasion. Additionally, the abrasive wheels may clog, leading to test repeatability issues and an inability to reliably correlate lab and field results.

While developed in the 1930s, it remains a standard for testing abrasion resistance under ASTM D4060-19. It is used to test a wide range of materials including ceramics, coatings, carpeting, laminates, leather paper, book covers, etc.

Taber testing is done by mounting a flat specimen to a turntable platform that rotates at a fixed speed on a vertical axis. A rub-wear motion results when the test specimen is in contact with a sliding rotation produced by the device’s two abrading wheels.

Comprehensive Abrasion Tester: Reproducible Results

The GA-CAT Comprehensive Abrasion Tester was developed in the 1980s to determine the abrasion resistance of printed materials, especially that of beer and beverage cans. It has also proved its’ worth as a test method applicable to flat substrates such as packaging labels, books, catalog and magazine covers, bar codes, corrugated boxes, folding cartons, etc.

In many cases, the GA-CAT has become the test instrument of choice over coming reproducibility issues. The GA-CAT is fast and easy to use, and produces test results that are easily reproducible across different operators, instruments, and laboratories. The GA-CAT can reproduce or simulate the 5 most common types of field abrasion damage seen, which are: complete and partial image transfer, random image transfer, pick-off and blotching. All types of flat printed and/or coated materials including paper, paper board, film, foil, and corrugated can be tested for abrasion resistance or abrasiveness.

The Four Factors that contribute to Abrasion Damage

The GA-CAT instrument combines the 4 factors found to contribute to abrasion damage when a product is handled and shipped. These are:

• AMPLITUDE – defined as the movement in either direction that occurs when two surfaces are in contact.
• FREQUENCY – defined as the speed at which the movement is occurring when two surfaces rub against one another.
• PRESSURE – defined as the energy pressing surfaces together.
• TIME – defined as the period surfaces are rubbing.

What is the GA-CAT Test Method?

Fast and simple, the GA-CAT test method consists of facing a test specimen against a receptor panel, both of which are then sandwiched between two protective foam sheets. This sandwich is then placed between two center spacer panel holders. Once mounted, pressure can be applied to top and bottom sides. Preset frequency, amplitude, and time test conditions (default values) are then run, with the option of selecting a range of default values.

During the test, the GA-CAT’s bottom carriage moves from left to right, cycling back and forth, setting up a rubbing motion as the tops of the spacer panels are held and pivot. Upon test completion, the test specimen is examined for wear and the receptor for deposition of ink or other transferred material.

Rating the Results

The results can be rated to a comparative control or they can be quantified by making a comparison on a ranking scale of 0 to 10 with 0 being the most abrasion resistant. Product-to-product test panels may also be tested, placing the test surfaces face to face for wet or dry testing.

Standard receptors are available that provide a range of abrasiveness, which when properly selected, reduce test time and eliminate frictional heat build-up. A ranking book containing comparative test specimens is also available.

The GA-CAT has proven to be a reliable test procedure that has been able to replicate the actual abrasion damage resulting from the handling, storage, and shipping of various packaging and other printed materials.

The test method is also proving to be useful when comparing a variety of test parameters, under laboratory conditions. The GA-CAT has shown to be able to differentiate very fine degrees of rub. This produces the ability to quantify the abrasion differences between printed inks, varnishes, coatings, laminates, and the surfaces of substrates, a value when seeking improvements.

Acceptance of the GA-CAT by the printing industry has been accelerated by the adoption of a Standard Test Method by the American Society for Testing and Materials (ASTM) in 1991. See ASTM D5181-09

It’s a wrap on abrasion

Abrasion tests can determine the durability of printed and coated graphic arts.  So we’ve gone through the major testing devices and procedures involved with measuring and testing the projected durability of these printed and coated graphic arts products and packaging.  All of these systems are in use today.  Some systems have limited useful results, while others may be more suited for the individual requirements of the coatings.  It is important to understand these standardized tests, including their uses and limitations as you provide the best result for your clients.

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