Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common...
Reexamination Certificate
1998-09-21
2001-05-01
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
C264S328700, C264S328800, C425S572000, C425S573000
Reexamination Certificate
active
06224364
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to molded products with fastener elements for use in hook-and-loop fastening and the like.
Hook-and-loop fasteners typically have two components: a “loop” component with engageable fiber loops, either of a woven or non-woven fabric or matt, and a mating “hook” component with a large number of miniature fastener elements, sometimes of hook form or mushroom form, adapted to engage and retain the loops of the loop component. Although early hook components were woven, many advances have been made in their manufacture, such that now many hook components are economically molded, with the fastener elements integrally molded upon a common sheet-form base. Fischer, for example, teaches such a method in U.S. Pat. No. 4,794,028, in which the fastener elements are molded in individual closed cavities in a mold roll, and then stripped from their closed cavities by peeling the fastener “tape” from the surface of the mold roll. Molded fastener elements of fasteners intended for repetitive use are generally engineered with shapes and resins selected to provide an appropriate amount of strength and flexibility, such that the fastener will have the required retention strength and yet not tend to damage the engaged loops when peeled apart. Customarily, such sheet-form fastener components have been formed in continuous strips, and then cut and affixed to the surfaces wished to be separably joined.
In some cases, loop-engageable fastener elements have been injection molded as part of a relatively stiff product. For example, Mcvicker, in U.S. Pat. No. 5,656,226, illustrates an array of fastener elements being integrally molded with a surface of an ankle brace.
Although injection molding fastener elements integrally and in place upon a product avoids the step of subsequently attaching a strip of fastener “tape” to the product for assembly, such a process places some limitations upon the structure of the fastener elements that are not present with some continuous forming techniques. For example, filling very small fastener element cavities can require high pressures and fast flows to avoid chilling the resin before the cavities have sufficiently filled. Depending upon the size and geometry of the overall injected product, filling an array of such cavities in a relatively small region of a surface of the product can complicate the design of the gate and runner systems. If the entire mold cavity is filled in one shot, the molten plastic may initially flow across the openings of the fastener element cavities, without completely filling them. The plastic may then cool to a temperature that prevents further flow or requires extremely high pressures to fill the cavities. In addition, one-shot injection of an entire product having a small array of miniature fastener elements from a single flow of resin requires the resin of the entire product to have qualities appropriate for fastener element strength and flexibility. In some instances there may be a more economical choice of resins for the bulk of the product which will be foregone in order to ensure reliable fastener elements, and in some other cases the quality of the fastener elements may be mitigated in the selection of a resin more suitable for the rest of the product.
SUMMARY OF THE INVENTION
The invention features an injection mold for forming a molded product having an array of fastener elements integrally molded with and extending from a surface of the product.
According to one aspect of the invention, an injection mold is provided, having first and second mold parts. The first mold part has a mold surface with a region having an array of fastener element cavities extending therefrom for molding the fastener elements. The second mold part has a mold surface aligned with the mold surface of the first mold part to define therebetween, in a closed condition, a mold cavity constructed to receive molten plastic for molding the product. The mold cavity includes a first portion comprising a majority of the volume of the mold cavity, and a second portion contiguous with the first portion and defined in part by the region of the first mold part surface having the array of fastener element cavities. At least one of the first and second mold parts has a moveable segment constructed to be retracted across the mold cavity, between filling of the first portion of the mold cavity with the plastic and filling of the fastener element cavities with the plastic, to enable the fastener element cavities and the first portion of the mold cavity to be filled under different molding conditions.
For molding some products, the first portion of the mold cavity comprises more than about 75 percent, and in some cases more than 90 percent, of the volume of the mold cavity.
In some embodiments, the moveable segment is constructed to be retracted across the mold cavity, after the first portion of the mold cavity has substantially filled with plastic, from a flow-inhibiting position to a the flow-enabling position. In its flow-inhibiting position, moveable segment inhibits flow of the molten plastic into the second portion of the mold cavity and the fastener element cavities while the first portion of the mold cavity is substantially filled with plastic. In its flow-enabling position, the moveable segment enables flow of the plastic into the second portion of the mold cavity and the fastener element cavities.
In some cases the first mold part includes the moveable segment, the segment having a surface including the region with the array of fastener element cavities. In some of these cases, the movable segment is constructed to further retract, after the fastener element cavities have filled, from its flow-enabling position to pull the molded fastener elements from their cavities.
In some other instances, the second mold part includes the moveable segment, the segment being arranged opposite the array of fastener element cavities of the first mold part. In some of these instances the moveable segment also includes a gate for filling the second portion of the mold cavity.
In some embodiments in which the moveable segment is constructed to be retracted across the mold cavity, after the first portion of the mold cavity has substantially filled with plastic, from a flow-inhibiting position to a flow-enabling position, the moveable segment inhibits flow of the molten plastic, in its flow-inhibiting position, into some of the second portion of the mold cavity while the fastener element cavities are filled with plastic. In its flow-enabling position, the moveable segment then enables flow of the molten plastic into all remaining unfilled regions of the second portion of the mold cavity.
In some embodiments, the fastener element cavities are defined entirely by surfaces which remain in fixed position relative to each other throughout molding and release of the fastener elements.
The segment is preferably constructed, in some cases, to be moved across the mold cavity to contact, in its flow-inhibiting position, an opposite surface defining the mold cavity. The segment and the opposite surface may together define a seal to block flow to the fastener element cavities with the segment in its flow-inhibiting position.
In some embodiments, the mold defines both a first gate and a second gate arranged to provide molten plastic to the mold cavity, with the first gate arranged to provide molten plastic to substantially fill the fastener element cavities and the second gate arranged to provide molten plastic to substantially fill the first portion of the mold cavity. In some particularly advantageous examples, the first gate is constructed to provide a different type of molten plastic than the second gate.
According to another aspect of the invention, a method of forming a molded product having an array of fastener elements integrally molded with and extending from a surface of the product is provided. The method employs the above-described mold, having various combinations of the above-described mold features, and includes the steps of:
Fish & Richardson P.C.
Heitbrink Tim
Velcro Industries B.V.
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