Date of Award

8-1972

Degree Name

Bachelor of Science

Department

Pulp and Paper Technology

Abstract

The blocking tendency of polyvinylidene chloride (PVDC) coated paper, front to back, in a rewound roll against a clay-coated surface was investigated. Pressure, temperature, contact time, relative humidity, and thickness of the PVDC layer or layers were all found to be important in the blocking of PVDC coated paper. Autohesion was considered to be the most probable mechanism of blocking. Autohesion involves the interweaving of the polymer molecules of both coated surfaces when they are in contact and under pressure at high temperatures. One way of eliminating blocking is by completely drying (crystallizing) the PVDC film and thereby reducing the effect of contact time and pressure. Another way of eliminating blocking, the one investigated in this paper, is by using an anti-blocking agent in the clay-coating. Anti-blocking agents influence the flow characteristics of the coating and thereby affect adhesive migration. It is this influence that is attributed with reducing the affinity of the polymeric adhesive, in the clay-coating, for the PVDC film and thus preventing blocking. One paraffin wax emulsion, particularly, when used in large amounts and with large amounts of starch prevented blocking.

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