Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-03-17
2001-10-02
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S267000, C156S290000, C156S308400
Reexamination Certificate
active
06296727
ABSTRACT:
I. BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to binders and other articles of manufacture having sheets of plastic bonded together and, in particular, a method for ultrasonically sealing a plastic film during the manufacture of a binder.
B. Prior Art
The manufacturing process of polypropylene clear view binders involves ultrasonically sealing and cutting sheets of plastic at the edges of the binders. Waste material is then stripped away from the edge. U.S. Pat. No. 5,476,570, which issued on Dec. 19, 1995 to Widmann and which is incorporated by reference herein, discloses a method for manufacturing folders or binder jackets that utilizes ultrasonic welding.
An important aspect of a commercial binder manufacturing operation is the speed with which binders can be produced. While high rates of production are desired, production is typically limited by the need to ensure that the plastic sheets are well-sealed, that the cuts are clean, and that the edges are smooth after the waste material is stripped. In particular, problems that occur at high production rates of greater than about 20 binders per minute include ragged, bumpy edges, blemishes and stringiness.
There is therefore a need for an improved method of ultrasonically sealing a plastic film composed of polypropylene that can be performed at higher production rates and yield products that are free of defects such as ragged or bumpy edges, blemishes, or stringiness.
II. SUMMARY OF THE INVENTION
Broadly considered, the present invention relates to employing a nucleating agent to raise the recrystallization temperature of the plastic sheets from which office products such as binders are formed.
One aspect of the present invention is a method of making a cover comprising a pair of welded thermoplastic polymer sheets having therebetween a stiffener. A stiffener is provided such that the stiffener has a leading edge, a trailing edge, and two side edges. The stiffener may be made of any suitable stiffening material such as clipboard or fiberboard. A pair of thermoplastic polymer sheets are positioned on opposite sides of the stiffener. The thermoplastic polymer sheets each have two side edges substantially parallel to the side edges of the stiffener. The thermoplastic polymer sheets are ultrasonically welded around the periphery of the stiffener. The polymer sheets are cut to form a leading edge and trailing edge which are substantially parallel to the leading edge and trailing edge of the stiffener. A cover is then formed thereby in which the two thermoplastic polymer sheets have substantially the same length and width as the stiffener.
The thermoplastic polymer is selected from the group consisting of polypropylene and a copolymer of ethylene or butene and propylene, the weight percent of ethylene or butene being between about 1 wt. % to about 10 wt. %, and containing a sufficient amount of a nucleating agent to raise the recrystallization temperature to between about 100° C. to about 140° C.
Embodiments of this aspect of the invention may include additional features. The amount of nucleating agent present in the thermoplastic polymer may be between about 0.05% and about 1% by weight.
The nucleating agent may be selected from the group consisting of mineral nucleating agents, salts of aliphatic acids, aralkyl acids, and sorbitol derivatives. The nucleating agent may alternatively be a compound selected from the group consisting of benzylidene sorbitol and bis(alkylbenzylidene) sorbitol wherein the alkyl moiety has from 2 to 18 carbon atoms.
The thermoplastic polymer sheet containing the nucleating agent is typically stiffer than the thermoplastic polymer sheet without the nucleating agent as shown by the Gurley stiffness in the following Table 1, where the Gurley stiffness is the average of the stiffness measured in the machine direction (MD) and in the cross-direction (CD). Generally speaking, the Gurley stiffness will be between about 350 or 400 and 525 or 550.
Gurley stiffness is determined by T 543 pm-84. As is known in the art, the Gurley stiffness tester consists of a balanced pendulum or pointer, pivoted at its center of gravity, mounted in jewel bearings and provided with holes for attaching weights at one inch, two inches and four inches below the center pivot. In practice, the sample to be measured is centrally clamped to the tester. A suitable weight is attached in one of the three positions, giving arm ratios of 4 to 5, 2 to 5, or 1 to 5. The control switch is pressed to drive the arm carrying the clamped sample. The test is completed when the end of the sample clears the vane.
The melt flow index of the thermoplastic polymer sheets may be between about 1 and 10. The melting point of the thermoplastic polymer sheet may be between about 130° C. to about 170° C.
One or more stiffeners may be provided to define a front cover stiffening panel, a spine stiffening panel and a rear cover stiffening panel.
Other objects and features of the invention will become apparent from a review of the Detailed Description below, from the drawings, and from the claims.
REFERENCES:
patent: 5476570 (1995-12-01), Widmann
patent: 6009925 (2000-01-01), Hall et al.
patent: 4313875-C2 (1994-11-01), None
patent: 0622170-A2 (1994-02-01), None
Chang Eng-Pi
Podosek Edward
Sun Edward I.
Avery Dennison Corporation
Oppenheimer Wolff & Donnelly LLP
Sells James
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