PAPER CURL, DIMENSIONAL STABILITY, 
EFFECTS OF SHRINKAGE AND XEROGRAPHIC PAPER

(Note: this website can be reached via www.PaperCurl.com)

CURL BASICS (Read more in article Curl Basics, below )

• Curl is effect of differential dimensional changes between layers in a sheet.
• These are produced by different moisture expansions (usually from differences in fiber orientation); the release of differing amounts of internal strain; or from bending.
• Xerographic (copier) curl is usually toward the print at moistures below 5-5.5% and away from the print at higher moistures for 75gsm papers.
• Balancing amount of hydrophilic binder applied to each surface should reduce curl.
• Adjustment of jet versus wire speed can reduce the difference in wire versus felt side fiber orientation.
• A reduction in inherent moisture expansion of furnish should be helpful in reducing curl (see below).

DIMENSIONAL STABILITY (Read more in article Aspects of Dimensional Stability, below)

• Inherent dimensional stability of a furnish or pulp needs to be measured on free dried sheets. If they are oriented sheets, a calculation of geometric mean expansion should be compared.
• Factors in stability include fibril angle and degree of refining, additives, and filler.
• Paper machine factors include fiber orientation, wet pressing, wet straining and sheet shrinkage.

SHEET SHRINKAGE IN DRYING

Shrinkage is perhaps the most important process effect on the mechanical properties of paper. Recently, Wahlstrom and Fellers showed that tensile stiffness, tensile strength, compressive strength and breaking strain are very closely correlate with sheet shrinkage or wet straining. A most likely explanation is that shrinkage affects micro-compressions, which in turn affects fiber properties, which affect sheet properties.  Read more at "Effects of Paper Shrinkage" and "Property Relationships", below.

XEROGRAPHIC (copy) PAPER

Available electronic articles:

Click below to see descriptions and get access to any of the following articles:

• Loading Curve Variables vs CME (.pdf, 4 pages)
• Effects of Paper Shrinkage (.pdf, 8 pages)
• Property Relationships (.pdf, 5 pages)
• Stiffness Index (.pdf, 5 pages)
• Residual Strain (.pdf, 8 pages)
• Predicting Modulus & Properties (.pdf, 18 pages)
• Residual Strain From Heating (.pdf, 5 pages)
• Accelerating Creep by Heating (.pdf, 6 pages)
• Tensile Loading Tutorial (.pdf, 8 pages)
• Curl From One Sided Drying (.pdf, 4 pages)
• Paper Curl Self-Tutorial (.pdf, 11 pages)
• Curl Basics (.pdf, 5 pages)
• Fundamentals of Paper Curl (.pdf, 18 pages)
• Dimensional Stability (.pdf, 18 pages)
• Aspects of Dimensional Stability (.pdf, 15 pages)
• Measuring Dimensional Stability (.pdf, 2 pages)
• Improving Curl Proposal (.pdf, 20 pages)
• Fuser Curl Mechanisms (.pdf, 8 pages)
• Fuser Curl At Higher Dwell Times (.pdf, 3 pages)
• Curl Terminology (.pdf, 2 pages)
• Hot Bend Curl Test (.pdf, 8 pages)
• Warm Oven Curl Test (.pdf, 2 pages)
• Procedure to Characterize CME (.pdf, 2 pages)
• Curl Tests summarized (.pdf, 3 pages)
• Xerographic Paper Self Tutorial (.pdf, 10 pages)
• Xerographic Paper Properties (.pdf, 4 pages)
• Basis Weight Conversion Factors (.pdf, 1 pages)
• Inkjet Paper Testing (.pdf, 2 pages)
• Static Problems (.pdf, 3 pages)
• Twenty Questions (Copy Paper) (.pdf, 2 pages)
• Imperial Weights and Sizes (.pdf, 3 pages)
• Loose Debris Evaluation Methods (.pdf, 1 pages)
• Twelve Steps to Curl (.pdf, 1 pages)
• Do the Decurl Tango (.pdf, 6 pages)

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