PAPER CHEMISTRY LABORATORY, INC.
Making Hand Sheets That Realistically Reflect Machine Performance
The task of making hand sheets that accurately reflect the effective use of functional chemical additives, using any of the traditional hand sheet molds, is not easy. The problem arises because of stock dilution in order to obtain good formation. The low molecular weight cationic additives are quickly de-sorbed from the fibers, fines and fillers into the dilution water with disastrous impact on physical properties. For example, a Hercules Sizing Test (HST) value, which is normally 150 seconds, can be reduced to a negligible value, for example a fraction of a second.
Several means have evolved which more or less effectively cope with the problem. A major international supplier of filler increases the size loading by 3X to compensate for the de-sorption. A leading international supplier of internal size discards the first five hand sheets, each time saving the white water for continuing use. Many investigators have become accustomed to this practice or some variation thereof.
On a different note, a major US paper manufacturer has given away three M/K automated hand sheet molds to educational institutions and purchased a CanPa "formatique" which deposits stock in a spinner, thereby imparting directionality. It is also reputed to emulate other characteristics of a paper machine. (When I repeated this to one authority, he asked "which paper machine?"). The CanPa unit includes a press and a drum dryer, produces a hand sheet 10" x 30" and costs around $100K. It uses big blotters for pressing.
For my part, when I recognized the difficulty, I developed the Dynamic Paper Chemistry Jar Mk IV, which makes dynamic hand sheets 4" in diameter, as well as performing all the normal Jar functions. And more recently, perhaps 6-8 years ago, in response to customer demand, we started supplying the Dynamic Paper Chemistry Jar® Mk V, priced under $10K, which makes dynamic hand sheets 8" in diameter. All of the hand sheet work reported on this web site is done with the Mark V which, like the Mark IV and the CanPa, obtains good formation from agitation rather than dilution.
The Mark III, IV and V Dynamic Paper Chemistry Jars® are described in detail elsewhere on this web site. The Mark III and IV meet TAPPI Spec T-261 and have traditionally been used for fines determination. They are supported by Operating Manuals which provide a comprehensive description of the fundamentals of papermaking wet end chemistry.
Now that we have the capability of truly optimizing papermaking wet end chemistry, it becomes even more consequential that we be able to definitively evaluate candidate chemicals. This is an issue of vital importance to wet end chemists, and is one on which we need to develop a common approach.
Please Email your experience and suggestions, and I’ll put them on the web site with attribution, so that others can respond. Perhaps we can sort this out together.