ASTM D724-99 pdf free.Standard Test Method for Surface Wettability of Paper (Angle-of-Contact Method).
In considering the results of the angle of contact test,the following factors that all affect the results in differentdegrees shall be considered: (a) the wetting power of the testliquid used,(b) the wettability of the sizing agent used in sizingthe paper, and (c) the surface texture of finish of the paper.10.2 The standard ink will give smaller angles of contactthan water, indicating that it wets the paper more readily thanwater. Papers surfacesized with starch will generally showsmaller angles than papers of about the same finish tube-sizedwith glue.A machine-finished paper with a grainy surfacewould have a greater angle of contact than a plated orcalendered paper of equal sizing. It is known that in practice,ruling results will depend on both the surface wettability andfinish of the paper.Thus，the angle of contact should give avery good idea of what is to be expected. It has been found thatexcellent ruling will prevail when the average angle of contactwith water lies between 90 and 100°; when the angle of contactis greater than 110°,breaks are likely to occur in the ruledlines; when the angle is smaller than 90°, the ruling fluid islikely to feather.
In determining the writing qualities of paper by meansof the angle-of-contact method, it is necessary to take intoaccount that medium-sized papers will at times show feathering only after the ink has partly penetrated the paper. Thetendency of a writing paper to feather will be indicated by thedecrease in the angle of contact between measurement after 5and 60 s. In hard-sized papers, the angle of contact will notchange perceptibly between the measurements at 5 and 60 s. Ifthe initial wettability is less than 90°, it is quite likely the paperwill feather as soon as it is written upon.
As the range in contact angle for specific conditions issmall, a refined technique is required in performing the test.This is indicated by the above examples as well as bytheoretical considerations.ASTM D724 pdf download.