Studies on Folding Test (Part 1)

Abstract

As a part of the studies on folding tests, a new folding tester was manufactured for trial and its performance was tested. The new tester-called here “roller tester” - (Fig. 1) consisting of a reciprocating head with two wire-like miniature rollers, folds the paper strip continuously under a preset tension.The length of paper strip subjected to actual folding test is 12mm, and paper strip tested does not have ruptured end of straight lineshaped as with conventional folding testers but has irregular line-shaped end like that with tensile test, (Fig. 2).The characteristics of the roller tester could be summarized as follows : (1) Good correlations exist between the folding tests made with the roller tester and those made with M.I.T.- or Schopper-tester for most of the papers with a few exception. This exception can likely be explained by the fact that the roller tester actuaes a paper so as to loosen its fiber bonding and is less sensitive to fiber length, (Table 1, 2 and Fig. 5, 7). (2) Coefficient of variation of measurements with the roller tester was estimated at about 16%, which is smaller than M.I.T.- and Schopper-tester, coefficient of variation of which were both about 25%, (Table 3). (3) Folding endurance with the roller tester increases to a certain extent with increasing humidity in machine direction, but decreases with increasing humidity in cross machine direction, (Table 5, Fig. 8) (4) Folding speed affects only in cross machine direction. Folding endurance reaches to the maximum value at a speed of 100 double folds per minute and falls to some lower volue at either higher and lower speeds, (Table 69, Fig. 9).(5) There are good linear correlations between tension and double logarithm of folding endurarance. It is recognized that folding endurance in cross machine direction has a tendency to go larger than that in machine direction under the smaller tension (Table 10, Fig. 11). (6) Coefficient of variation of measurements is not affected by the change of relative humidity and folding speed, but it becomes larger under the smaller tension. For samples from the same paper, coefficient of variations are equivarent, in machine direction and cross machine direction, (Table 1214). Coefficient of variation tends to increse with increasing of folding endurance value, (Fig. 12).