Spots in the Paper (Dirt, Flakes, Tacky substances)
Visible specks and discolored areas in paper can hurt the appearance, interfere with optical reading equipment, and also they can point to other problems on the paper machine, such as the accumulation of deposits on equipment. If you are facing problems that seem to be related to either stickie materials from recycled papers or pitch from mechanical pulps, then it is suggested that you click on the corresponding links.
The first step in overcoming problems related to spots usually is to identify the deposited material. More information is given in the section related to dirt.
In addition to materials usually categorized as "dirt," other possible sources of spots include flakes of incompletely redispersed broke, bits of mineral scale, plastic, and agglomerates of various additives. Much of this kind of material tends to be removed by canister-type filters near to the points of preparation of additives. However, there is a substantial danger of spots if materials are able to accumulate on the surfaces within the headbox, downstream of the main pressure screens. A program of scheduled outages and cleanup of the headbox surfaces may be needed to keep the incidence of spots low. In other cases, spots may be mostly associated with bark, ink, toner, or other materials that ought to be mainly removed during preparation of the pulp. Spots also may be associated with biological growth in the water system (see slime).
Anon., "Identification of Specks and Spots in Paper," TAPPI Useful Method UM 589, 1984.
Rosenberger, R. R., "Putting the New Dirt Count Method into Perspective: A Discussion of TAPPI Method T-563," Prog. Paper Recycling 6 (1): 9 (1996).
Soderhjelm, L., "Dirt and Shives in Pulp, International Standardization," Paper Technol. Ind. 37 (10): 51 (1996).
Zeyer, C., Heitmann, J. A., Venditti, R., and Joyce, T. W., "Image Analysis with an Optical Scanner," Prog. Paper Recycling 3 (3): 29 (1994).
PLEASE NOTE: The information in this Guide is provided as a public service by Dr. Martin A. Hubbe of the Department of Wood and Paper Science at North Carolina State University (firstname.lastname@example.org). Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives. Please send corrections if you find errors or points that need better clarification. Go to top of this page.