Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-03-13
2003-07-08
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S201000, C428S207000
Reexamination Certificate
active
06589634
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to bonding patterns used in the embossing and laminating webs of material in the pin-on-pin process and more particularly to the high speed lamination of two embossed webs with an irregular bonding pattern.
BACKGROUND
Paper products such as facial tissue, baby wipers, paper towels, toilet paper and the like are manufactured widely in the paper industry. Each of these products has unique product characteristics that require appropriate blend of product attributes to ensure that the product can be used for the intended purpose and is desired by consumers. These attributes include tensile strength, water absorbency, softness, thickness, stretch and appearance. One method of modifying and altering these properties or attributes includes providing an artistic pattern in or on the paper product. The artistic pattern typically involves a texture which is provided by either variation of density, height, or thickness variation. This texturing is generally done by a process known as embossing.
Prior art embossing processes typically involve contacting the paper product sheet with embossing equipment, which typically involve opposed rolls having a matched male and female embossing means or a metal male embossing roll and a contacting compliant (e.g., rubber) roll. The rolls operate at equal surface speeds, such that the artistic patterns of the rolls align if male and female. The web is embossed as it passes through the nip created by the two rolls.
The controls that are typically applied during embossment are the nip surface speed of the rolls, the pressure between the two rolls or nip pressure; the moisture level of the paper sheet entering the nip; the temperature of the rolls creating the nip; and the type of sheet of paper entering the nip (thickness, fiber type, smoothness, porosity, and chemical treatments). These controls affect the quality of the embossment, which is frequently judged by the clarity or sharpness of the artistic pattern on the sheet, by its uniformity across the sheet (CD or cross direction) and in the direction of motion of the sheet (MD or machine direction), and by the feel or “hand” of the embossed sheet. Adjusting these process parameters provides product variability but often results in a product without the most desirable or competitive product attributes.
It was found that rather than a single thickness or weight of tissue sheet one could dramatically change the properties of the tissue by laminating together two sheets of half the thickness or weight where each sheet had been embossed separately. The manner of laminating the two separately embossed sheets could deliver significantly different properties, softness, absorbency, feel, etc. Prior art has combined the embossing and laminating processes of separate tissue sheets into a single machine. Three different methods are currently available for commercial use for the manufacture of tissue and paper towels: 1) “Pin-on-Pin” or “Point to Point” or “peg-on-peg”, 2) “Pin to Grove” or “Glued Nested”; and, 3) “Pin Embossed.” The bulk or thickness and absorbency of the laminated two-ply sheet is much greater than the equivalent one-ply. This is shown, for example, by U.S. Pat. No. 3,867,225 to Nystrand.
While the Pin-on-Pin system can produce the best properties, it has associated drawbacks. Pin-on-Pin lamination of two embossed tissue sheets relies upon precise mating or alignment of the artistic patterns of the two separate male embossing elements. After the embossing nip, the two separate sheets are brought together and adhesively attached by pressing the mated protrusions of the male embossing rolls with the sheets between and adhesive between the two tissues. The mating or alignment and pressure at the location where the two male embossing rolls are closest to each other creates the bond points or bond areas of the two tissue sheets. For example, typically there is about a 0.001 inch gap set for the metal protrusions between the two metal rolls for two 20 lb. per ream sheets of tissue. As the production speed increases alignment becomes even more critical because the time of contact is shorter even though the contact forces do not diminish.
If there is even slight rotational or side-to-side misalignment with conventional Pin-on-Pin embossing/laminating, no bonding occurs and hence no acceptable product. Also, as the production speed increases, even when in a state of alignment, the sheet will stop bonding when a limiting speed is reached where vibration produces a “basket-balling” effect, i.e., the laminating rolls appear to bounce apart. This effect opens the gap between the two rolls and relieves the pressure on the bond areas before bonding can occur.
U.S. Pat. No. 3,961,119 to Thomas disclosed that some of the benefit of the Pin-on-Pin embossing/laminating could be achieved by changing from discrete pins to continuous lines for the male artistic patterns of the embossing rolls of the Pin-on-Pin process. By helical design of the line patterns on each of the separate rolls, Thomas caused the two separate bond lines to be approximately 90° to each other. This produced a pinch point, square or diamond, which became a bond and precluded the need for careful alignment of the two rolls. However, this invention did not eliminate the speed limitation as it still caused undue vibration.
U.S. Pat. No. 5,173,851 to Ruppel also addressed the alignment problem by showing how an adequate level of bonding could be achieved by allowing two metal rolls to have dissimilar artistic patterns which can be discontinuous but with a prescribed regularity to produce some minimum level of contact or mating in the nip to create bonded areas of the tissue. Due to the regularity prescribed by Ruppel, the invention still had speed limitations due to deleterious vibrations.
All dynamic machinery and structures have resonant frequencies that can become problems when a regular repeated force excites the resonant condition. See, for example, “Vibration Problems in Engineering” by S. Timoshenko D. Van Nostrand Co. 1928; “Mechanical Vibrations” by William T. Thompson Prentice-Hall, Inc. 1948; “Fundamentals of Vibration Analysis” by N. O. Myklestad, McGraw-Hill 1956. A rather small regular repeating force can induce large amplitude vibration in machinery and supporting structure if the repeated force frequency is just right, i.e., equal or near to one of its critical frequencies or a harmonic of those frequencies.
To offset this adverse phenomena most dynamic machinery is installed with vibration isolation pads or dampers to prevent or mitigate the transmission of deleterious vibrations to other parts of the machinery or supporting structure. Motor mounts and automobile shock absorbers are traditional examples of this. Without shock absorbers the regular repeating force of the paved roadway expansion joints can cause an automobile to bounce wildly and go out of control. This condition does not occur until the automobile has reached or come close to the speed at which these regularly spaced small force pulses are at or near the critical frequency of the automobile suspension system.
Rotating machinery parts are balanced to preclude vibration forces from any small eccentric weight distribution. This is seen in counter weights used on automobile tires and automobile drive shafts. Another method of reducing vibrations includes creating a stiffer, more massive structure to increase the resonant frequency and preclude vibration-induced resonance from being transmitted to the structure or item to be isolated. This is typified by large massive foundation blocks for delicate instruments and for rotating machinery like compressors or turbines. Some machinery can be operated above the critical rotating frequency if one quickly passes through the critical range before the mass can reach a deleterious amplitude of vibration. Some unbalanced machinery vibrates at slow rotational speeds but when it changes from rotation about its geometric center to its dynamic center of inertia the vibration ceases.
The
Biggs David G.
Kressner Bernhardt E.
Perkins Mark D.
Raynor, Jr. William J.
Schultz Walter T.
Dixon Merrick
Garot Judy
Kimberly--Clark Worldwide, Inc.
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