Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Of varying cross-sectional area or with intermittent...
Reexamination Certificate
2000-03-03
2003-06-24
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Of varying cross-sectional area or with intermittent...
C264S210700, C264S290200, C264S920000
Reexamination Certificate
active
06582642
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to sheet-form fastening members of synthetic resin and to methods and machines for their manufacture.
An important aspect of the invention concerns hook fastener members for hook and loop fastening. These are formed of synthetic resin in running lengths. Typically there are multitudes of fastener elements, i.e. hundreds or even thousands of discrete hook elements per square inch. These are typically arranged in neat rows in the machine direction, i.e. in the direction in which the forming system produces the product.
These hook elements stand discretely from at least one side of an integral web-form base. The base forms the means of attachment of the fastening member to the article that carries it.
Fastener members with fields of such hooks typically have a pleasing, uniform, commercially acceptable appearance and are widely found in consumer and industrial products.
In a preferred method of manufacture, molding rolls are used in the process shown e.g. in Fischer U.S. Pat. No. 4,794,028. This process produces hook fasteners of commercial appearance in which the rows of hooks are straight and the spacing between the hook elements in both directions is regular.
Mold rolls for forming preferred fastening members of this kind typically comprise a series of thin circular plates, with mold plates alternating with spacer plates. Peripheries of the individual molding plates are machined with cutouts to define small hook profile cavities. The group of plates is held so their peripheries cooperate to define the surface of the roll. Because a large number of such plates is required and the plates must be carefully held in alignment, such mold rolls have been expensive to produce and maintain and have typically been confined to short lengths. The width of the product produced has been correspondingly restricted.
Conventional fastener materials produced in this way have been less than one or two feet in width and have had a web thickness between the hooks greater than 0.005 inch, typically 0.008 inch or more. Typically, in this method of manufacture, the hooks face in the machine direction or in the opposite direction, with the consequence that their major peel and shear strengths have been similarly oriented.
Other advantages and features will be apparent from the following description and claims.
SUMMARY OF THE INVENTION
We have discovered that it is possible to achieve a commercially acceptable sheet-form fastener member of synthetic resin in which the web or base portion lying between the multitude of fastener elements exists in a laterally permanently stretched condition, in many instances the substance of the web having molecular orientation at least partially in the direction of lateral stretch.
We have found that, while preserving the identity and functional shape of integral discrete fastener elements, the web portions between neighboring fastener elements can be stretched to a uniform thickness across the width of the product. In desirable instances, the web portions between the fastener elements are reduced to film thicknesses, and the resulting fastener member is readily conformable about curved or complex surfaces or is otherwise usefully applied to broad areas in an economical manner.
According to one important aspect of the invention a method of producing a sheet-form fastener product comprises the steps of: (1) lengthwise stretching a sheet of heat-softened synthetic resin to pre-orient the molecular structure of the sheet in a longitudinal direction; (2) with a rotating mold roll, molding from the sheet a running web having a base and a multiplicity of discrete fastener elements integral with the base and protruding from at least one side of the base; and (3) thereafter, under conditions in which the web is permanently stretchable, stretching the web widthwise in a manner that permanently stretches the base and increases the widthwise spacing of the fastener elements.
In some particularly useful embodiments, the fastener elements comprise touch-fastener hooks or the like.
Advantageously, in preferred embodiments, the widthwise molecular orientation and peel strength of the fastener product are increased during the widthwise stretching process.
In the presently preferred configuration, the ratio of the final width of the product to the original width of the product before widthwise stretching is between about 2 to 1 and about 10 to 1, and the widthwise stretching reduces the thickness of the base of the web by at least 50%.
In certain configurations, the widthwise stretching widens the web by at least 200% and reduces the thickness of the base of the web between fastener elements by at least two thirds.
In another embodiment, the method also comprises heating the web to render the base of the web permanently stretchable without detrimental change in the shape of the fastener elements. In certain arrangements, the fastener elements protrude from only one side of the web and the web is heated predominantly from a side opposite the side having the fastener elements.
In some examples, the resin is a thermoplastic resin suitable for forming hooks, comprising polypropylene, polyethylene, polyester, polystyrene, PVC, nylon or copolymers or polymer blends thereof.
In certain advantageous configurations, the widthwise stretching process causes molecular orientation and strengthening of the base of the web between fastener elements as it is stretched, such that as a result the base of the web between fastener elements is stretched widthwise substantially uniformly throughout.
In certain situations in which the synthetic resin has a Characteristic Minimum Stretch Ratio, the mold roll defines fastener elements and other stretch-limiting features over the area of the web, according to a predetermined pattern. The pattern is selected such that the ratio of the width of the final web to the width of the web before widthwise stretching is substantially less than the Characteristic Minimum Stretch Ratio. In certain useful embodiments, the fastener elements and stretch-limiting features resist local stretching of the web. In some situations, the stretch-limiting features are physical features of the product formed of synthetic resin integral with the base of the web, with the method including the step of differentially heating the web being formed such that the fastener elements and the stretch-limiting features are rendered less stretchable than the base of the web.
In some configurations, the temperature of the web base is controlled as the web is stretched widthwise. For instance, the fastener elements may be immersed in a temperature-controlled liquid during the widthwise stretching. In other instances, the web base is immersed in a temperature-controlled liquid during the widthwise stretching, or the web base is heated in a heated liquid bath during the widthwise stretching while leaving the fastener elements exposed to air.
In some embodiments a dual stretch process is employed, in which the step of stretching the web widthwise includes stretching the web widthwise in a first stretch zone, maintaining the web at an intermediate, stretched width, and then further stretching the web widthwise in a second stretch zone. Preferably, the rate of widthwise stretching varies along the first stretch zone.
In another aspect of the invention, a method is provided for producing a sheet-form fastener product, comprising (1) forming from synthetic resin a running web having a multiplicity of rows of discrete fastener elements integral with and protruding from at least one side of base of the web, the elements facing in a substantially longitudinal direction, and (2) thereafter, under conditions in which the web is permanently stretchable, stretching the base of the web in a bias direction in a manner that permanently stretches the web base between fastener elements, increasing the spacing of the fastener elements and orienting the rows of fastener elements in a direction diagonal to the machine direction, such that the elements face in a diagonal d
Buzzell Keith G.
Maydra Richard G.
Provost George A.
Eashoo Mark
Fish & Richardson P.C.
Velcro Industries B.V.
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