Web cleaning method

Cleaning and liquid contact with solids – Processes – Longitudinally traveling work of bar – strip – strand – sheet...

Reexamination Certificate

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C134S021000, C134S032000, C134S036000, C134S037000, C015S309100, C015S345000

Reexamination Certificate

active

06193810

ABSTRACT:

FIELD OF THE INVENTION
This invention is generally in the field of paper manufacturing. It relates particularly to the manufacturing of tissue paper products such as facial tissue and the like.
BACKGROUND OF THE INVENTION
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
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.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved Coanda effect web cleaner for removing dust and lint from a web of tissue during the manufacture of facial tissues or the like.
Another object is to provide a Coanda effect web cleaner for removing dust and lint from a web of tissue wherein air, dust and lint flow into an exhaust plenum in a controlled and improved manner.
Still another object is to provide a Coanda effect web cleaner which stabilizes the web as it passes and prevents web pull-down into the exhaust area.
A further object is to provide a Coanda effect web cleaner and web cleaning system which find particularly advantageous application for removing dust and lint from a web of tissue in a rewinding machine.
Still a further object is to provide a new and improved method for removing dust and lint from a web of tissue in a rewinding machine.
Yet a further object is to provide an improved tissue product having a surprisingly low dust and lint count.
The foregoing and other objects are realized in accord with the present invention by providing an improved Coanda effect web cleaner and system, a new and improved web cleaning method, and a resultant low dust and lint count tissue product. The improved Coanda effect web cleaner comprises an elongated, curved airfoil formed adjacent a narrow slit defining a Coanda nozzle out of which a jet of air is forced. The curved airfoil is a continuous, uninterrupted surface extending from adjacent the slit to an exhaust outlet for the unit. From about 15 to 35 cfm of air per foot of slit length exits the slit, under a relatively low pressure of between 20 and 80 inches H
2
O. The air exits the slit, which is 0.002 to 0.015 inches wide, in a thin layer and at a velocity of 18,000-34,000 fpm. The thin layer of air attaches to the airfoil surface as a result of the Coanda effect. As it does so, it scrubs away, and carries with it, the boundary layer of air which is traveling with an adjoining surface of a tissue web. This boundary layer air is laden with dust and lint. It also scrubs away dust and lint which is partially embedded, i.e., mechanically entangled, in the tissue surface. The Coanda effect air flow, with the dust and lint “scrubbed” from the web with the boundary layer, and with loose dust and lint physically pulled from the web surface, travels to the exhaust outlet along the airfoil surface and is drawn into an exhaust plenum.
A system of two of these improved web cleaners are mounted in a tissue web rewinding machine, one above and one below the web path. Each of these web cleaners includes a Coanda nozzle slit which is preferably 0.012 inches in width. According to the method of the invention, about 15 to 35 cfm of air per foot of slit under a pressure of between 20 and 80 inches H
2
O in an air supply plenum is forced out of each slit next to the adjacent airfoil surface. The resultant air jets create thin, stable, non-turbulent layers of air which attach to respective curved surfaces, creating low pressure zones adjacent each nozzle which tends to draw the tissue web toward that nozzle. The air jet created layers, traveling at high exit flow velocities of 18,000-34,000 fpm, carry dust and lint to exhaust plenums from both surfaces of the multiple-ply web in the rewinding machine. Meanwhile, slightly upstream of these air foil surfaces, each web cleaner has a web stabilizer airfoil which attracts and supports the moving web while preventing the web from being drawn far out of its path by the effect of the exhaust. The two web cleaners are offset from each other relative to web travel, the lower one being upstream, although they may be reversed or opposed to each other.
A multiple ply tissue is produced with an unexpectedly low dust and lint count. In practice, it has been found that a multiple ply tissue having an MD Slope of less than 8.0 Kg can be produced with a dust and lint count of less than 10,000 per eight square feet of tissue surface.


REFERENCES:
patent: 2082411 (1937-06-01), Merrill
patent: 2515223 (1950-07-01), Hollick
patent: 3078496 (1963-0

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