Obtain a 152 x 76 mm (6 x 3 in.) printed sample, representative of the run in ink-lay and coverage. When the printed area permits, the longer direction should be cut across the grain of the sheet, but must not cross scores. Unprinted stock from the same run should be provided in 152 x 51 mm (6 x 2 in.) sizes (for dry rub and wet rub). In both cases, cut the longer dimension across the grain of the board.
Dry rub.Clip a 152 x 51 mm (6 x 2 in.) unprinted specimen to the 1.8-kg (4-lb) test block, with the printing surface away from the rubber pads. Place the printed sample, print side up, on the rubber pad of the base plate.Place the weight over the sample, and make sure that both surfaces are free of dirt. Preset the tester for ten strokes by referring to the chart below the automatic timer.
When the rubs have been completed, examine both the inked surface and the plain surface on the test block for signs of transfer. Repeat the ten stroke sequence until transfer occurs or a predetermined limit is reached. The two test strips should be stapled together and used for visual reference and interpretation. They should be marked plainly with the number of rubs given.
Wet rub.Mount the strips in the same manner as for dry rubs, using the 0.9-kg (2-lb) or 1.8-kg (4-lb) test block. Preset the tester for one rub. Place three to six drops of water on the printed surface so that they will be covered by the test block. 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 board shows fuzzor abrasion. This same test can also be used to determine the wet rub of unprinted surfaces.
Wet bleed or transfer.Make a strip of blotting paper or cotton cloth (see TAPPI T 205 “Forming handsheets for physical tests of pulp”) 152 x 51 mm (6 x 2 in.) on the 0.9 kg (2-lb) or 1.8 kg (4-lb) test block with the felt or smooth side out and saturate the blotter or cotton cloth with water (an eyedropper is convenient).
Place the wet blotter or cotton cloth on the sample to be tested and leave it in place for 4 min. Remove the block without rubbing, and examine for ink transfer to the blotter or cotton cloth. The same blotter or cotton cloth may be used for checking wet smear.
Wet smear.Return the wet-bleed block and blotter to the inked sample and actuate the tester for one stroke.Examine the blotter for color transfer. (The notation of wet bleed should also be recorded on this sample).
Functional rub.Functional rub is a term embracing a number of miscellaneous uses for the Sutherland rub tester. An ink which is acceptable under the outlined test procedures may fail in use as a result of exposure to other 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.” Functional tests are limited only by the ingenuity of the operator and the many uses being found for printed paper or paperboard surfaces. In reporting functional rubs, the operator should specify the number of rubs, the time of contact before rubbing, and the special conditions and testing mediums employed.
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