Abrasion, Rub and Scratch Resistance

Damage to surface coatings and printed materials can occur during shipment, storage, handling, or by the end user. This abrasion can result in significant degradation in product appearance, corrosion resistance and legibility of the product information. The durability of variable data printed on labels or packaging is very important for medical device and pharmaceutical products in particular.

The complexity of wear processes has led to the development of numerous standard test methods and test apparatus. Correlation between these methods is not generally possible as each employs a different abrasion technique, although materials are often ranked similarly.

Smithers Pira has a very wide range of testing facilities include the Smithers Pira Rub Tester, the Sutherland Rub Tester, the Taber Abraser, the Sheen Motorised Scratch Tester, the Gavarti Comprehensive Abrasion Tester (CAT), the Satra Rub Tester and the Crockmeter. 

Smithers Pira (PATRA) rub tester

The Smithers Pira (PATRA) rub tester rubs two printed surfaces against each other (face-to-face) in the same plane, at the same speed (60 rpm), under a constant rubbing pressure. The rub test equipment can also be used to evaluate colour transfer from printed or coated surfaces during rubbing and is used by Smithers Pira to evaluate the rub resistance of labels and general printed matter.

The Smithers Pira rub tester conforms to British Standard BS 3110.

Sutherland Rub Tester

Commonly used to determine the amount of scuff or abrasion damage associated with transit shipment, storage, or handling of printed packaging. 

The Sutherland Rub Test is performed by attaching a label to the device while a similar sample label is attached to a weight. The two samples are then rubbed against one another at a controlled speed for a predetermined number of cycles. In contrast to the rotary Smithers Pira Rub Tester, the Sutherland Rub Tester employs a reciprocating arc motion. On completion, the samples are visually inspected to check for ink transfer.

The Sutherland Rub Tester conforms to ASTM D5264 – Standard Practice for Abrasion Resistance of Printed Materials

Taber Abraser

The Taber Abraser is primarily used to evaluate the resistance of surfaces to rubbing abrasion. Specimens are mounted on a rotating turntable and subjected to the wearing action of two abrasive wheels, which are applied at a specific pressure. The severity of the test can be altered by using different wheels under different loads. The end point is either a visual change in appearance or a weight loss associated with material removed by abrasion.

Tappi Standard T476 covering the abrasion loss of paper and board

British Standard BS 3900 for the determination of resistance to abrasion applicable to paints and varnishes

ANSI Standard INCITS 322 applicable to card durability. A Taber abrasion test is specified by the Book Manufacturing Institute (BMI)

Sheen Motorised Scratch Tester

Motorised Scratch TesterA test panel is withdrawn under a constant weighted 1mm tungsten carbide ball-ended needle at a speed of 3.4cm/second using a Sheen 705 mechanised Scratch Tester satisfying the requirements of BS 3900 Part E2 1992/ISO 1518 1992. Failure of the surface coating is examined visually and by electrical surface resistance when the underlying substrate is electrically conductive. 

Coating failure under a given needle profile/weighting is related to coating-substrate adhesion, mechanical properties of substrate and coating, coating thickness, internal stress in coating and friction between stylus-tip and coating. The Practical scratch adhesion value of a coating is defined as the lowest critical load at which the coating fails. 

Gavarti Comprehensive Abrasion Tester

The Gavarti comprehensive abrasion tester or Gavarti CAT was originally designed to test the abrasion resistance of inks and coatings on aluminium beverage cans. The device simulates the motion of a truck or train during shipping and is used by Smithers Pira for assessing the transit scuff resistance of printed cartons and book covers as well as cans.

The printed sheet is sandwiched between oblong blocks of polyurethane rubber. A plain or printed sheet of the same stock is placed in with it and then hydraulic rams push the blocks from the side in a wave motion to simulate transit vibration. At the end of the test, the print-to-print or the print-to-plain-paper can be examined for scuffing.

The Gavarti CAT conforms to ASTM D5181-91.

Satra Rub Tester

The Satra rub tester is a circular rub fastness tester which can also be used for testing the rub/abrasion resistance of inks on printed films, such as plastic carrier bags, under dry and wet conditions.

The machine has a rotating head holding a circular felt pad which is applied to the sample under a defined load.

The rub or abrasion resistance is determined by the extent of damage to the sample material or by the extent of colour or print transfer to the felt pad, using a standard scale where necessary.

The Satra rub tester is used in testing against International Standard ISO 105-X12.

Crockmeter

The Crockmeter is used to assess the transfer from the surface of coloured materials to other surfaces by rubbing. The machine takes its name from the term 'crocking' meaning the transfer of colouring matter or other substances from the test sample to a wet or dry cloth rubbed against it.

The Crockmeter is used in testing against ASTM F1319 and International Standard ISO 105-X12.