Registering Behaviors of Coated Papers Part 2

Abstract

In spite of the well-established concept in this country that the humidity conditioning of paper before being printed on an offset press is essential to achieve a good registering, increasing number of printers have been working to eliminate this troublesome procedure from their processes. In an effort to assist this movement from the papermaker's standpoint, significance of humidity conditiong has been reexamined, placing emphasis on its effect on the registering characteristics of coated papers. From the results of registering experiment on a commercial offset press, it is indicated that the humidity conditioning of paper can not be a cure-all by itself. A sheet of poor physical condition with high degree of accumulated stresses is partially stress-relieved, but not to a satisfactory extent unless an inefficient long maturing at a very high relative humidity is applied. On the other hand, only a slight effect of conditioning is observed to be supplemental with a sheet of originally gocd registering characteristics. These results are supported by the supple mental data on the effect of humidity cycling in the relative humidity range of 25-65-95% on the physical properties of coated sheets, such as dimensions, moisture content, humidity expansion and contraction, and water expansion. Based on the above observations, the papermaker's part in the project of eliminating humidity conditioning at printing plants is discussed. It is believed to be essential for a papermaker to deliver an originally docile sheet with minimum accumulated stresses, which may not be obtained through a mere moistening treatment afterwards.