Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Of varying cross-sectional area or with intermittent...
Reexamination Certificate
1997-08-22
2001-08-28
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Of varying cross-sectional area or with intermittent...
C264S040500, C264S040700, C264S146000, C264S210200, C264S210500, C264S294000, C264S296000, C428S100000, C428S119000
Reexamination Certificate
active
06280670
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the continuous forming of fastener products with elements extending from a base, and has particular application to the production of fastener elements for touch fasteners and the like.
Some fastening elements are capable of engaging fibrous loops to form a fastening, while some are termed “self-engaging” as they are constructed and arranged to releasably engage similar fastener elements. Sometimes the latter are employed on fastening strips that are thereby looped to overlay, and fasten with, themselves.
Some fastening elements are hook-shaped, with distal ends that extend in discrete directions from their stems. Fastening elements with heads that overhang their stems generally equally in all directions are sometimes referred to as “mushroom” fastening elements. Some hook-shaped fastening elements have more than one distal end. Hooks with two oppositely-directed distal ends are sometimes called “palm-tree” hooks.
Hook-shaped fastener elements for touch fasteners and other products are effectively produced by the machine and method of Fischer U.S. Pat. No. 4,794,028, which is hereby incorporated by reference. In commercial production, fastener products are effectively produced in a continuous molding process employing a rotating mold roll. The mold roll has a large number of thin, disk-shaped mold rings and spacer rings which are stacked concentrically about a central barrel. At the periphery of the mold rings are hook-shaped cavities for molding the fastening elements. Molten resin is introduced to the surface of the mold roll and, under pressure, fills the cavities. The outer surface of the mold roll simultaneously forms one side of the strip-form base which, after being trained about the mold roll a sufficient distance and time to permit sufficient cooling of the resin, is stripped from the mold roll surface, pulling the formed fastener elements from their cavities without opening the cavities themselves.
Mushroom-type fastening elements are often produced by weaving a plastic fiber into a sheet form base to form a series of loops, cutting the loops to form stems, and melting the distal ends of the stems. In part because the plastic fiber (e.g., polypropylene) is a drawn fiber with high molecular alignment and residual strain along its axis, the molten resin of the stem ends draws back to form free-form, hemispherical heads overhanging the unmelted lower portions of the stems. Frequently the distal ends of the stems are melted by passing them near a hot wire or heated platen.
Because of their omni-directional overhanging portions, mushroom-type fastening elements are especially suitable for loop-engaging applications requiring shear strength in many different directions.
SUMMARY OF THE INVENTION
The invention features fastener elements produced by a method employing a rotating mold roll to mold preform stems extending from a strip-form base, and subsequently re-forming the distal ends of the stems in shaped cavities in a rotating heading roll to form engageable heads. The resulting fastener product is efficiently and cost-effectively produced in strip form in a continuous molding process.
According to one aspect of the invention, a method is provided for producing a fastener product having a multiplicity of fastening members with stems integrally molded with a strip-form base. The method comprises applying molten resin to a rotating mold roll having an outer surface for forming one side of the base, and a multiplicity of cavities extending inward from the outer surface for molding the stems; stripping from the mold roll a preform product having the strip-form base and a multiplicity of upstanding, preform stems extending from a side of the base; and passing the preform product through a post-forming nip between a heading roller and a backing member to form overhanging heads at the distal ends of the upstanding stems. The heading roller has a multiplicity of cavities about its periphery for forming the heads.
In one embodiment, the preform stems are registered with respect to the rotational position of the heading roll, such as by molding a alignment feature in the preform product with the mold roll and using the alignment feature to position the preform stems with respect to the rotational position of the heading roll.
In another embodiment, the rotational position of the heading roll is registered with respect to the preform stems, such as by mechanically coupling a registration means on each of the mold and heading rolls to register the rotational position of the heading roll with respect to the mold roll. This can include sensing (e.g., optically) an alignment feature of the preform product.
Generally, the cavities of the heading roller are substantially the shape of the formed heads. For instance, in one embodiment the formed, overhanging heads are of conical shape, having uppermost surfaces forming apices. The apices each preferably define an included angle of less than about 90 degrees, more preferably less than about 60 degrees.
The heading roll should be maintained at an elevated temperature to soften the distal ends of the upstanding stems of the preform product.
Preferably, the formed, overhanging heads each overhang their respective stems in elevational view by an overhang distance of at least about 25 percent (more preferably, at least about 50 percent) of the width of their respective stems.
After passing the preform product through the post-forming nip, the strip-form base can be trimmed between the alignment feature and the fastening members to produce a strip-like fastener product without the alignment feature.
The cavities of the mold roll can have many different shapes. For instance, in one embodiment the cavities of the mold roll comprise cylindrical holes extending inward from the surface of the mold roll. In another embodiment, the cavities of the mold roll comprise axial slots extending through the peripheral edges between broad sides of disk-form mold plates.
In one embodiment, the cavities of the heading roll are arranged to randomly intercept the preform stems. At least some of the preform stems may be bent by the heading roll to form hook-shape fastener elements, with at least some of the preform stems being headed by the heading roll without being bent. Preferably, the preform stems are arranged in spaced, parallel rows extending in the machine direction and the cavities of the heading roll have an overall depth of less than about 0.5 times the spacing between adjacent, machine direction rows of stems. Adjacent cavities of the heading roll are preferably spaced at a cavity spacing distance of less than about 0.8 times the spacing between adjacent, machine direction rows of stems.
In one configuration, the cavities of the heading roll extend into the heading roll from rectangular bases, the bases of the heading roller occupying at least 90 percent of the circumferential area of the heading roll along the length of the cavity portion (i.e., the length of the roll having cavities) of the heading roll.
According to another aspect of the invention, an apparatus is provided for performing the above-described method. The apparatus has a rotating mold roll having an outer surface for forming one side of a strip-form base, and a multiplicity of cavities extending inward from the outer surface for integrally molding stems extending from the base. Also included is means for applying molten resin to the mold roll, and a heading roll having a multiplicity of cavities about its periphery for forming heads on the preform stems to form fastener members.
The apparatus preferably includes means for aligning the preform stems with the heading roll. Such means can include means for registering the preform product to the heading roll, such as by interlocking alignment features molded into the preform product. Alternatively, the alignment means can register the rotational position of the heading roll to the preform product, such as by controlling the rotation of the heading roll based upon sensed alignment features
Buzzell Keith G.
Dowd Clinton
Provost George A.
Eashoo Mark
Fish & Richardson P.C.
Heitbrink Jill L.
Velcro Industries B.V.
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