Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-11-30
2003-02-11
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S290000, C156S308400, C156S553000, C156S555000, C156S580200, C156S582000
Reexamination Certificate
active
06517650
ABSTRACT:
BACKGROUND
The present invention relates to apparatus and methods for effecting ultrasonic bonding on at least one continuously moving web or work piece attached to a continuously moving web using ultrasonic bonding apparatus. The invention more particularly concerns apparatus and methods for ultrasonically bonding at least one continuously moving web using a rotary ultrasonic horn.
It is known to bond at least one continuously moving substrate web by constrictively passing the web between a rotating ultrasonic horn and a rotating anvil roll. Typically, the anvil roll includes one or more arrays of raised projections configured to bond the web in a predetermined bond pattern. The rotary ultrasonic horn is capable of expressing ultrasonic energy at a bonding surface to ultrasonically bond the web as the web constrictively travels between the rotary ultrasonic horn and the anvil roll. Representative examples of rotary ultrasonic horns which have been used to bond at least one web are described in U.S. Pat. No. 5,096,532 to Neuwirth et al issued Mar. 17, 1992; and U.S. Pat. No. 5,110,403 to Ehlert issued May 5, 1992.
The consistency and quality of the bond when using such rotary bonding techniques is dependent on the consistency of the force exerted on the web by the combination of the anvil roll and the bonding roll; the time during which the web is being pressed in the constrictive nip which is dependent on the operating speed; and the types of materials being bonded. The consistency and quality of the bonds are also dependent on the frequency and amplitude of the vibrations of the ultrasonic horn, and the percent bond area which is the area of the pins (projections) in the bond region divided by the surface area of the bond region.
Conventional methods for rotary bonding include a rotating ultrasonic horn which is mounted in a cantilevered configuration such that the horn is not supported about the surface of the bonding roll. However, such conventional methods have not always been sufficiently satisfactory.
The inventors herein have discovered that, while a variety of factors can be adjusted and controlled in defining a more uniform bonding pattern, stiffness/rigidity of the entirety of the bonding apparatus is a critical factor in achieving desired bond uniformity.
Use of a cantilevered bonding roll has inherent limitations which adversely affect the bond quality and which in this invention can be at least partially corrected by replacing the cantilever configuration with an in-line or balanced force application which avoids application of forces through cantilevered configurations. In cantilevered configurations, it has been very difficult to maintain the desired degree of consistency and stability of nip force between the bonding roll and the anvil roll. As a result, in many conventional methods for rotary bonding, bond quality and/or consistency has been undesirably variable both along the length of the bond region and across the width of the bond region. In addition, processes using cantilevered rotary ultrasonic horns have not been as robust as desired for a manufacturing environment.
Consistency and quality of bonds when using conventional rotary ultrasonic bonding methods and apparatus has been particularly variable where the desired bond pattern is intermittent because the nip pressures inherently change in concert with the intermittent nature of the bonding operation.
When using conventional methods for rotary bonding in such configuration, the bond quality has typically been less than satisfactory along the length of the bond pattern. Such inconsistency in the bond pattern has been due, at least in part, to inconsistent levels of force being effectively applied along the length of respective intermittent bond regions of the bond pattern. Typical of such inconsistency is excessive nip loading at the leading edge of the bond region, and insufficient nip loading behind the leading edge of the respective element as the bonding apparatus flexes or deflects in combination with development of the respective bonding region at the nip. Both the excessive nip loading and the insufficient nip loading have resulted in poor bond quality and poor bond consistency.
Under excessive loading, so much energy may be applied to the materials being bonded as to burn through or otherwise excessively soften the materials being bonded, as well as to apply excessive pressure to the softened materials, whereby bonds so formed may be weak, and/or may be uncomfortably harsh to the touch of a wearer's skin. In the alternative, excessive loading can physically damage, as by tearing, the material being bonded. Additionally, excessive loading can increase wear and thus damage the ultrasonic horn. Finally, ultrasonic horns are generally driven by piezoelectric crystals that convert electrical energy at high frequency into mechanical vibrations. When an excessive impulse load is applied to the horn, the process works in reverse and the resulting electrical spike can overload and shut down the electrical frequency generator.
Generating ultrasonic bonds depends on the combination of frequency and amplitude of the vibrations, the amount of pressure applied, and the time during which pressure is applied. Under conditions of insufficient loading at the nip, too little pressure is applied to the materials to be softened thereby, whereby the amount of energy transferred to the elements to be bonded together is insufficient to develop sufficiently strong bonds.
Conventional methods for rotary bonding have used different approaches to diminish the variations in consistency of the interference. For example, the bonding roll, anvil roll, and support frames have been precisely machined to minimize runout in the bonding system.
As used herein, the term “runout” expresses changes in the radius of the anvil roll and/or the rotary ultrasonic horn about the circumference of the respective rotary element.
The above-mentioned difficulties of maintaining desired bond quality and consistency along both the length and width of the web become even more acute when intermittently bonding at least one continuously moving web using a rotary ultrasonic horn. Operation of a rotary ultrasonic horn includes movement inherent in the continuous vibration of the horn at a given frequency and amplitude to efficiently bond the web. as well as rotation of the horn along the length of a web which may vary in thickness along the length of the web, thus to impose varying resistance to the nip pressure applied by the combination of the horn and the anvil on the web. Under certain conditions, such vibratory movement of the horn, and variation of web thickness, either alone or in combination, may adversely affect bond consistency and quality in the web.
For example, because the ultrasonic horn must vibrate at its resonant frequency like a bell. the shaft supporting the horn cannot be rigidly mounted e.g. to a frame. The need to provide non-rigid mounts for e.g. non-rigid mounting corresponds with a tendency for the horn to be deflected from a desired position under the nip forces required to achieve bonding using ultrasonic energy to develop the desired bonds or to be deflected, under its own dead weight. Typically, the rotary ultrasonic horn has conventionally been mounted in a cantilevered configuration which enhances the amount by which the position of the horn is changed when going from a dead-weight self-supporting mass being acted on by gravity to a fully loaded bond nip.
For example, a horn assembled in a conventional and typical mount extends from a generally horizontal shaft. The shaft rests on rubber O-rings. When the horn is so mounted in a generally horizontal orientation, with the O-rings taking the load, the axis of the horn sags out of true alignment with the shaft support structure which supports the shaft, the horn, and optionally the drive mechanism. Such sag is typically about 0.015 inch at the horn face for a 20 pound horn.
In addition, where the web advancing through the nip, defined between the horn and the anvil,
Abel Kent William
Coenen Joseph Daniel
Couillard Jack Lee
Lohoff Michael Lee
Nason Robin Kurt
Kimberly--Clark Worldwide, Inc.
Sells James
Wilhelm Thomas D.
Wilhelm Law Service
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