SUTHERLAND® 2000™ Ink Rub Testers

Test Specimen - The test requires two pieces of stock, the test specimen and a test receptor. Cut a test specimen, approximately six by three inches. When printed area permits, the six-inch directions should be cut across the grain of the sheet, but must not cross pressed or cut scores. Prepare test receptor strips of material from the same shipment of stock used in the test sample. Cleanly cut 2x7-inch strips for the four-pound weight are prepared by placing the strip face up against the pin of the scoring device and scoring at the white dot positions to facilitate bending the strip to conform to the test block. To prepare samples for the two-pound weight, 2 x 5-1/4 inch strips are placed face up against the end pin of the scoring device and scored at the red dot position to facilitate bending the strip to conform to the test weight.

Dry Rub - Clip a 2x7-inch inch test strip to the four-pound test block, with the abrasive surface away from the rubber pad (facing the test specimen on base pad). Mount the test specimen securely (if printed material, mount with printed side up) on the rubber pad of the base plate securing with the hold down bracket. Using a camel-hair brush (not included), brush the test strip and the test specimen thoroughly before starting the test to remove any dust or foriegn material. Place the weights over the sample, making sure that the 2x4-inch rubber pad of the test block is over the area that is being tested, and that both surfaces are free of dirt. Preset the tester for ten strokes, or for any number of strokes selected as standard for a particular stroke.

Wet Rub - Mount the strips in the same manner as for a dry rub, using the two-pound test block. Preset the tester for one rub. Place three to six drops of water on the printed surface so that the test block will cover them. Place the block in position and immediately press the “start” button. After one stroke, examine both surfaces for color transfer. Repeat single strokes until ink failure is noted or the surface of the sample shows fuzz or abrasion.

Wet Bleed or Transfer - Mount a 2 x 5-1/4 inch strip on the two-pound test block with the felt or smooth side out, and saturate the blotter with water (an eyedropper is convenient). Place the wet blotter on the sample to be tested and leave in place for four minutes. Remove the block without rubbing and examine for ink transfer to the blotter.

Wet Smear - Use a water-saturated blotter on the two-pound block and actuate the tester for one stroke. Examine the blotter for color transfer. In cases where extreme water resistance is required, more rubs may be specified. An alternate procedure consists of mounting a 2 x 6-inch piece of 80x80 count bleached muslin on the two-pound test block over a blotter as specified above. This procedure has been found particularly useful since it eliminates the effects of surface abrasion on the blotting paper.

Functional Rub - Functional Rub is a term of embracing a number of miscellaneous uses for the SUTHERLAND® Rub Tester. Ink, which is acceptable under the outlined test procedures, may fail under exposure to foreign liquids or pastes. For example, certain inks might be tested to conform to specifications such as “one rub, Cod liver oil” or “three rubs, Jones Antacid Toothpaste.” In reporting functional rubs, the operator must specify the number of rubs, the time of contact before rubbing, and the special conditions and testing mediums employed.

Evaluation of Tests - A practical approach should be emphasized in test evaluation. Few, if any, inks will pass rubbing, wet or dry, without a slight transfer of color. Decisions on the suitability of ink are best made by running comparative tests, checking an acceptable sample at the same time and under the same conditions. A quantitative method of evaluating samples for rub damage has been developed. The test strip (receptor) is measured (zeroed) with a densitometer or a spectrophotometer before the rub test. After the test, the strip is measured again with either the change in density densitometer) or delta E (CIE L*a*b spectrophotometer) reported. The larger the number, the greater the rub damage. Consideration must be given to the time interval between printing and testing, particularly with slow-drying inks. Also prints should be protected from dust and dirt between printing and testing. An attempt should be made to use test samples which are representative of the run, i.e., eliminating the use of sheets with excessive anti-offset materials, or sheets taken from the top of a load which may have collected dust or foreign material.