According to the results of report no. 1 in this series, stiffness of paper can be predicted from the equation of
ET3/12
W, if the thickness obtained from mercury buoyancy method is adopted as
T, and sonic modulus adopted as
E (
W : basis weight).
Paper is generally produced in various ways and used under various conditions. Stiffness of paper is, therefore, influenced by a number of factors. Effect of various factors, i. e., kinds of pulp, beating, wet pressing, wet straining, addition of filler, and relative humidity, on stiffness of paper were examined in this study. These factors were mainly analyzed using eq. (1).
Results obtained are as follow.
(1) The order of Clark's stiffness is RGP > LBKP > NBKP, when pulp sheets were made according to the process of JIS P 8209 (wet press : 3.5 kg/cm
2). This seems to be due to the difference of thickness among them.
On the other hand, the order of stiffness is NBKP > LBKP > RGP, when the sheets possess the same thickness by controlling wet pressing. Main reason for this result seems to be caused by the difference of sonic modulus.
(2) Stiffness may be increased under the suitable preparing condition, which includes degree of beating, wet pressing, wet straining, and addition of filler.
When sheet was made by the condition of constant wet pressing 3.5 kg/cm
2, stiffness of paper decreased with increasing in degree of beating. The result indicates that in this condition, thickness of paper is the most important factor on stiffness.
(3) In the case that thickness of paper was varied by changing wet pressing of the samples which possessed the same basis weight and same f reeness, sonic velocity did not depend on paper thickness (density), and in these conditions, stiffnss was proportional to second power of thickness.
(4) Stiffness decreased rapidly at higher than 70% RH, the value at 90% RH, for example, is almost half of that at lower than 50% RH.
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