A common complaint among users of facial tissues is that loose dust particles and/or lint fall off the tissue before use. They accumulate on the tissue carton top and counter surfaces. They cling to eyeglass lens when the tissue is used to clean them. They are, of course, considered unacceptable by the consumer.
The terms "dust particles" and "lint" which are used here are relatively general when considered out of context. For purposes of discussing this invention, however, dust is considered to be discrete particles of 0.4 mm or less in length, while lint is considered to be composed of longer particles or fibers, most of which are tissue making fibers.
In the process by which facial tissue, for example, is manufactured, dust and lint are found in several contexts. The tissue web has a quantity of loose dust and lint embedded or entangled in its surfaces, much of it a by-product of the creping step. As the web travels through the tissue reeling and rewinding operations, a boundary layer of air attaches to each of the web surfaces and becomes contaminated with dust and lint entrained in the air flow. Finally, the larger environment in which the manufacturing operations take place also contains a certain amount of environmental dust and lint.
Regardless of where the dust and lint is found, producing tissue with a minimum amount of loose dust and lint remaining on the surface of the finished product has long been an aim of the manufacturing process. Most systems and methods for reducing dust and lint on tissue during production have relied primarily on area containment and removal which would meet OSHA air quality standards. Some systems have been employed which attempt to remove loose dust and lint directly from tissue during its manufacture, however. For example, it is known to simply direct air jets at the surfaces of a web in both the tissue forming machine and the rewinding machine in attempts to clean the web. Examples of web cleaners which employ such air jets are found in Doran et al. U.S. Pat. No. 3,078,496, Olbrant et al. U.S. Pat. No. 3,775,806 and Warfvinge U.S. Pat. No. 4,594,748.
It is also known to employ the Coanda effect to dry tissue webs and to remove dust and other particulate materials clinging to tissue webs in the tissue forming machine. The Lindstrom U.S. Pat. No. 4,247,993 and the Lepisto U.S. Pat. No. 4,932,140 describe Coanda effect airflow used in drying. The Overly U.S. Pat. No. 3,587,177 employs the Coanda effect for web cleaning, although without using the term "Coanda". Recently, Thermo Wisconsin, Inc., a Wisconsin company, has manufactured and sold a device called a FiberMaster web cleaner which employs the Coanda effect to control airflow for web cleaning. The FiberMaster web cleaner is constructed and operates substantially along the lines disclosed in the Pollack U.S. Pat. No. 5,466,298 and U.S. Pat. No. 5,577,294. It employs a Coanda effect nozzle and stepped airfoil to direct a turbulent stream of air in counterflow to the boundary layer of air accompanying the tissue on one side of the tissue. FiberMaster web cleaners are normally used in tissue reeling operations and utilize air pressures of 20 inches H.sub.2 O or less. Yet another web cleaner employing the Coanda effect is disclosed in the Horn U.S. Pat. No. 5,490,300.
Although it seems clear that significant amounts of environmental dust and lint can be removed using air cleaners of one type or another, the incidence of customer complaints about loose dust and lint in the finished product persists. The present invention is directed toward overcoming the shortcomings of existing web cleaners and methods for removing dust and lint, and producing tissue which is lower in dust and lint content than heretobefore considered possible.
USPTO Backgrounds
USPTO Backgrounds