Sizing is a paper treatment that causes the surface of the sheet to resist the penetration of liquids, usually aqueous liquids but could also be grease.
Hear about the size press evolution here
The degree of sizing achieved by any of these methods is measured using either the Cobb test, or the Hercules sizing tester.
Surface Sizing is an impregnation process rather than a true surface coating process as the applied solution usually penetrates significantly into the sheet.
A wide range of chemicals or compounds can be applied at this point, examples are
- polyvinyl alcohol
- polyurethane emulsions
- various types of latex
- alkyl ketene dimer
The size press has undergone a significant evolution from the traditional paired rollers, to the modern metered size press.
In order of their development there were the;
Each of these had its disadvantages that led ultimately to the development of the metered size press
Essentially, for the three traditional methods, the sheet passes between two rollers and the sizing agent is added to the ingoing nip on one or both sides. For the metered size press, a quantity of sizing chemical is metered onto a non-stick roll, which then transfers all of it onto the surface of the sheet.
Follow the links above for more detail of each.
The most common material added at the size press is starch. This is prepared in a starch kitchen. In mills where there is more than one machine the starch is then circulated round a starch ring main with local take-offs to individual size presses. A key factor determining the interaction between the sizing agent and the sheet is the rheology of the mix.
Pages in category "Size Press"
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