Greg Unser

Date of Defense

Spring 4-21-1993

First Advisor

David K. Peterson, paper and Printing Science and Engineering

Second Advisor

William K. Forester, Paper Pilot Plant

Third Advisor

Michael E. McCarville, Chemistry

Abstract

The dramatic increase in the use of photocopiers and laser printers has created a new problem for the paper maker in removing these non-impact inks. The thermo-plastic binder in these inks is difficult to break up causing ink specks to remain in the pulp after deinking, which limits the use of the pulp. This thesis focuses on optimizing the temperature, percent solids and time during mechanical dispersion (mixing) for breaking xerographic printed ink particles up so that they can be removed in subsequent deinking units. A total of thirteen different trials were conducted varying these conditions. Three of these trials were later repeated and a flotation cell added after the dispersion stage. The pieces of paper made after each of these trials were tested using an image analysis system for determining the number and size of the remaining ink particles. The results indicated that the middle temperature (20 C), high consistency (10% solids), and longer residence time (20 minutes) worked best in reducing the average ink particle size. The high solids (10%) condition also proved best in breaking up the ink particles for optimal removal in a flotation cell. These results show that exposing the printed paper for a longer time in a thicker slurry improves the break up of these inks due to more fiber-to-fiber rubbing. Further study in this area might include testing the different flotation surfactant chemicals or comparing the deinking results from the different plastic co-polymers used to bind the ink to the fiber.

Access Setting

Honors Thesis-Campus Only

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