Date of Award
Bachelor of Science
Paper Science and Engineering
Dr. Ellsworth H. Shriver
This senior engineering problem is the study of the mechanism of blackening and methods of measurement for blackening. The effect of blackening is the loss of color and opacity in the sheet. The loss of color results as a darker sheet. There are 3 major variables which cause blackening: moisture content, nip pressures, and roll temperatures. The increase in any of these variables results in blackening. In this experiment, the increase of moisture content produced the most significant blackening. The increase of pressure and increase of temperature produced slight blackening effects. The most blackened sheet occurred at 10% moisture, 200°F, and 900 psi. An unblackened sheet resulted at 6% moisture, 200°F, all pressures. Blackening became evident at 8% moisture, 200°F. Safe nip loadings would be between 300-600 psi to prevent blackening. A safe moisture level would be 6%. A safe temperature range would be 150-175°F. The most valid method of blackening measurement is with a color meter. The opacity measurement can also be used, but in this experiment, blackening was not severe enough to procedure widely variable opacity values.
Bland, Valerie, ""Supercalendering: The Blackening Reaction and Its Effect on Strength and Optical Properties of Rotogravure Paper"" (1988). Paper Engineering Senior Theses. 23.