Problem Summary

The MD/CD expansion of Newsprint during the offset printing process is well documented so press operators do expect a degree of expansion and can therefore make the necessary adjustments to accommodate this. However, when changing from 100% TMP Newsprint to 100% recycled Newsprint, some problems of dynamic hygroexpansion and strength retention leading to excessive web breaks on press may occur.  This is mainly due to Newsprint that can have vastly different absorption characteristics and absorb fount at varying rates whilst under press tension. The MD hygroexpansion is due to the applied web tension and, therefore, there is a very good correlation between MD expansion and wetted tensile of Newsprint.

The wetted tensile and the integrity and strength of Newsprint is vital to press performance. Newsprint that absorbs increased levels of moisture will exhibit more fan-out from CD expansion for example, and as a result, it is common to increase press tension to reduce the effects of the press fount.  By increasing tension, the Newsprint will then be subjected to excessive stretch and subsequent web failure. Therefore, the retention of wetted tensile after printing is vital for good press stability and a reduction of web breaks on press where press fount is heavily applied.

Recommended Solutions

The wet tensile problems cannot be solely regarded as a papermaking problem as several press settings and variables can also contribute to these phenomena.  However, for the paper maker there is the possibility to increase the inter-bonding strength and the retention of wet tensile of the fibers with Hercobond® Strength Technology.  This technology can be utilized cost-effectively to minimize dynamic hygroexpansivity of Newsprint.

Key benefits of Hercobond® Strength Technology are:

Reduction in press fount related expansion and web breaks
Improved overall strength properties
Improved drainage and/or reduced steam consumption
Reduced pressroom breaks
Improved retention
Reduced overall production costs