Abstract

Some paper-mill rewinders use infra-red carbon dioxide laser heads to slit the web into rolls of given widths. However, despite certain advantages, laser slitters are not widely used mainly because of installation and operation costs.

Web breaks on a printing press cause both time and paper waste. Breakings occur because of defects in the edges of the web, such as notches or extra fibers, which offer less resitance to the high tensions existing during the printing of a web at high speed. Since paper edges are much cleaner when cut with an infra-red carbon dioxide laser than when cut with knives, it is possible that laser-cut edges might be stronger and thus reduce the number of breakings of the web.

In order to test this hypothesis, tensile tests were carried out on laser-cut and shear-cut strips for three different types of papers (coated and uncoated stock, and newsprint) and results were compared.

Since direct observation of the effect of a laser beam on cellulose fibers might help in explaining differences in behavior between the two types of paper samples, a scanning electron microscope was used to take photographs of paper areas following treatment with a CO2 laser functioning in pulsed mode. The photographs revealed a drastic change in the structure of hit cellulose: the latter looks melted. This "melted" portion of a laser-cut paper edge is extremely thin (several micrometers) and seems to slow down the combustion of adjacent fibers.

Regarding tensile tests results, laser-cut strips are always stronger, but the relative difference between the two types of specimens is very low (less than 1% in the case of the uncoated stock and the newsprint, and less than 3% in the case of the coated stock).

An analysis of variance proved this 3% difference to be statistically significant, but it remains too low to constitute an incentive for the web printer to order laser-slit paper rolls only, or for the papermaker to replace blade slitters by laser cutting heads.

Library of Congress Subject Headings

Laser printing; Lasers in the graphic arts; Paper--Printing properties; Cutting

Publication Date

1-1-1988

Document Type

Thesis

Student Type

Graduate

Advisor

Chester Daniels

Advisor/Committee Member

Julius Silver

Comments

Physical copy available from RIT's Wallace Library at Z249.4 .P563 1988

Campus

RIT – Main Campus

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