Experience last 12 years paper physics consulting to papermills and their suppliers mainly NorthAmerica, 6 years prior to that Senior Research Scientist at world's largest newsprint producer's R&D centre
Organizations Canadian Pulp and Paper Association,
Canadian Association of Physicists
North Shore Mountain Bike Association
Publications TAPPI, Pulp&PaperCanada, Appita, various Physics Journals
Question When the book was freshly glued and bonded, it was in a perfect shape. However, after some time (hours or days), the bonded side twisted (in-plane deformation ?) while no out-of-plane deformation visible. Do you have suggestions regarding possible causes, solutions, or literatures that you can recommend ?
Thanks.
Answer Hello Li;
A few times before, I have seen where the non-bonded free edge side opposite the binding develops waves, in some cases the pages are "cupped" with an in-plane curl of sections of the book with the curl "tunnel" perpendicular to the binding edge. In those cases, you can see these multipage sections alternating the direction of the cupping. This situation is caused by post-binding hygroexpansion of the paper when the paper is bound grain-long perpendicular to the binding edge and the alternating sections are created when there is a hygroexpansivity curl to the paper and the sections correspond different sidedness of the infeed roll of paper.
That's not your case but I mention it to give you some ideas. Your case is curious because the sheets of paper on the non-bound edge are free to slide over each other and so it is hard to see how they could carry any signficant forces to the binding edge. So whatever is happening is likely within a few mm of the binding edge. Your description sounds like a twist curl of the binding edge itself, is that correct? Do the pages themselves lay flat? If the problem is purely a twisting of the binding edge does the coverstock remain perfectly square over the top of the book or does it skew?
I have a paper I published which might give you some other ideas. Do you understand what CD hygroexpansivity means? Off-axis CD hygroexpansivity? These are a bit jargon so don't be offended if you don't.
