U.S. patent number RE38,652 [Application Number 08/868,762] was granted by the patent office on 2004-11-16 for hook for hook and loop fasteners.
This patent grant is currently assigned to Velcro Industries B.V.. Invention is credited to George A. Provost.
United States Patent |
RE38,652 |
Provost |
November 16, 2004 |
Hook for hook and loop fasteners
Abstract
A plastic molded hook for use with a hook and loop fastening
system especially adapted for use with low profile loops. The hook
design includes a base, a stem and a crook whereby the volume of
the portion of the hook penetrating into a pile of loops is defined
as the displacement volume. Hooks especially adapted for use with
low profile loops have a displacement volume of less than
6.times.10.sup.-6 cubic inches.
Inventors: |
Provost; George A. (Litchfield,
NH) |
Assignee: |
Velcro Industries B.V.
(Curacao, AN)
|
Family
ID: |
25462632 |
Appl.
No.: |
08/868,762 |
Filed: |
June 4, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
932633 |
Aug 20, 1992 |
05315740 |
May 31, 1994 |
|
|
Current U.S.
Class: |
24/452; 24/442;
24/446; 24/447; 24/449 |
Current CPC
Class: |
A44B
18/0061 (20130101); Y10T 24/2792 (20150115); Y10T
24/27 (20150115); Y10T 24/2742 (20150115); Y10T
24/2767 (20150115); Y10T 24/275 (20150115) |
Current International
Class: |
A44B
18/00 (20060101); A44B 018/00 () |
Field of
Search: |
;24/452,442,444,446,447,448,450,306 ;2/912 ;128/DIG.15 |
References Cited
[Referenced By]
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Oct 1994 |
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WO |
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Primary Examiner: Sakran; Victor
Attorney, Agent or Firm: Fish & Richardson P.C.
Claims
I claim: .[.
1. A hook for a hook and loop fastening system comprising: a base;
a stem connected at its lower end to the base, the stem having an
outer side and an inner side; a crook having a first end and a hook
tip, the first end connected to the stem, the crook projecting
upwards from the stem and then downwards towards the base in a
substantially smooth curve ending at the hook tip; the hook having
a width, a height, and a displacement volume, wherein displacement
volume is the volume of a rectangular parallelepiped having a
bottom plane, first and second side planes, first and second end
planes and a top plane; the bottom plane orientated parallel to the
base and tangent to the hook tip, the top plane parallel to the
base and tangent to the top of the hook at the point where the
crook achieves its maximum distance from the base, the side planes
laying in the plane of the sides of the hook; the first end plane
perpendicular to the bottom plane at the point where the bottom
plane intersects the stem at its outer side, the second end plane
perpendicular to the bottom plane and tangent to the outermost
portion of the hook tip; wherein the displacement volume of the
hook is less than 6.times.10.sup.-6 cubic inches
(9.83.times.10.sup.-5 cc)..]. .[.
2. The hook of claim 1 wherein the crook height is less than 0.012
inches..]..[.
3. The hook of claim 1 wherein the thickness of the hook is less
than 0.010 inches..]..[.
4. The hook of claim 1 wherein the footprint of the hook is less
than 1.5.times.10.sup.-4 square inches..]..[.
5. A hook for a hook and loop fastening system comprising: a base;
a stem connected at its lower end to the base, the stem having an
outer side and inner side; a crook having a first end and a hook
tip, the first end connected to the stem, and then downwards
towards the base in a substantially smooth curve ending at the hook
tip; the hook having a width, a height and a displacement volume,
wherein displacement volume is the volume of a rectangular
parallelepiped having a bottom plane, first and second side planes,
first and second end planes and a top plane; the bottom plane
orientated parallel to the base and tangent to the hook tip, the
top plane parallel to the base and tangent to the top of the hook
at the point where the crook achieves its maximum distance from the
base, the side planes laying in the plane of the sides of the hook;
the first end plane perpendicular to the bottom plane at the point
where the bottom plane intersects the stem at its outer side, the
second end plane perpendicular to the bottom plane and tangent to
the outermost portion of the hook tip; wherein the displacement
volume of the hook is less than 4.times.10.sup.-6 cubic inches..].
.[.
6. The hook of claim 5 wherein the crook height is less than 0.012
inches..]..[.
7. The hook of claim 5 wherein the thickness of the hook is less
than 0.010 inches..]..[.
8. The hook of claim 5 wherein the footprint of the hook is less
than 1.5.times.10.sup.-4 square inches..].
9. In a hook for a hook and loop fastener having a profile defined
by an inner generally concave face and an outer generally convex
face, the hook comprising a planar base member intimately engaging
a tapered base portion and extending there from to join, in a
transition region, a tapered hook portion able to engage a loop
applying a force to the hook portion substantially normal to the
planar base member and terminating in a free end, the taper of the
hook portion being much less than the taper of the base portion
wherein the hook tapers continuously downwardly in width from the
tapered base portion to the free end such that a loop engaging the
hook in tension, with the force being substantially normal to the
planar base member, will cause the hinging or buckling of the hook
at a location adjacent the outer face in the transition region as
the hook deforms under the applied force and such that a loop
engaging the hook in shear, with the force substantially parallel
to the planar base member, will transmit bending force through the
tapered base portion between the location of buckling and the
planar base member, the hook being of substantially constant
thickness and having a substantially rectangular traverse cross
section and a displacement volume, wherein displacement volume is
the volume of a rectangular parallelepiped having a bottom plane,
first and second side planes, first and second end planes and a top
plane; the bottom plane oriented parallel to the base and tangent
to the hook tip, the top plane parallel to the base and tangent to
the top of the hook at the point where the hook achieves its
maximum distance from the base, the side planes laying in the plane
of the sides of the hook; the first end plane perpendicular to the
bottom plane at the point where the bottom plane intersects the
stem at its outer side, the second end plane perpendicular to the
bottom plane and tangent to the outermost portion of the hook tip;
wherein the volume displacement of the hook is less than
6.times.10.sup.-6 cubic inches (9.83.times.10.sup.-5 cubic
centimeters).
10. The hook according to claim 9 wherein the inner face in the
transition region has an angle to the direction normal to the base
member orientated to encourage a loop engaging the hook in shear to
move toward the base member.
11. The hook according to claim 9 wherein the crook height of the
hook is less than 0.012 inches.
12. The hook according to claim 9 wherein the inner generally
concave face is so shaped as to encourage a loop engaging the hook
in shear to engage the hook at about the location of buckling.
13. The hook portion of a hook and loop assembly comprising a
multiplicity of hooks, having the configuration of the hook of
claim 9 assembled into a multiplicity of hooks onto and extending
from a common integral planar base.
14. The hook portion of a hook and loop assembly according to claim
13 wherein the multiplicity of hooks are aligned in a given
direction so that adjacent rows of hooks face in opposite
directions.
15. The hook portion of a hook and loop assembly according to claim
13 wherein the multiplicity of hooks are aligned in a given
direction so that all hooks face in the same direction..Iadd.
16. A plastic hook product for a hook and loop fastening system
having hooks sized and shaped to be capable of engaging loops of a
loop product with a pile height of approximately 0.04 inches or
less, the hook product comprising a multiplicity of plastic hooks
in adjacent rows and extending from a common integral planar base,
each of the multiplicity of hooks comprising: a stem connected at
its lower end to the base by being molded integrally with the base,
the stem having an outer side and an inner side; a crook having a
first end and a hook tip, the first end connected to the stem, the
crook projecting upwards from the stem and then downwards towards
the base in a substantially smooth curve ending at the hook tip;
the hook having a width, a height, and a displacement volume,
wherein displacement volume is the volume of a rectangular
parallelepiped having a bottom plane, first and second side planes,
first and second end planes and a top plane; the bottom plane
orientated parallel to the base and tangent to the hook tip, the
top plane parallel to the base and tangent to the top of the hook
at the point where the crook achieves its maximum distance from the
base, the side planes laying in the plane of the sides of the hook;
the first end plane perpendicular to the bottom plane at the point
where the bottom plane intersects the stem at its outer side, the
second end plane perpendicular to the bottom plane and tangent to
the outermost portion of the hook tip; wherein the displacement
volume of the hook is less than 6.times.10.sup.-6 cubic inches
(9.83.times.10.sup.-5 cc)..Iaddend..Iadd.
17. In a plastic hook product for a hook and loop fastener, the
hook product having a multiplicity of plastic hooks sized and
shaped to be capable of engaging loops of a loop product with a
pile height of approximately 0.04 inches or less, hooks of the
multiplicity of hooks each having a profile defined by an inner
generally concave face and an outer generally convex face, the
hooks of the multiplicity of hooks each comprising a planar base
member intimately engaging a tapered base portion, by being molded
therewith, and extending there from to join, in a transition
region, a tapered hook portion able to engage a loop applying a
force to the hook portion substantially normal to the planar base
member and terminating in a free end, the taper of the hook portion
being much less than the taper of the base portion wherein the hook
tapers continuously downwardly in width from the tapered base
portion to the free end such that a loop engaging the hook in
tension, with the force being substantially normal to the planar
base member, will cause the hinging or buckling of the hook at a
location adjacent the outer face in the transition region as the
hook deforms under the applied force and such that a loop engaging
the hook in shear, with the force substantially parallel to the
planar base member, will transmit bending force through the tapered
base portion between the location of buckling and the planar base
member, the hook being of substantially constant thickness and
having a substantially rectangular traverse cross section and a
displacement volume, wherein displacement volume is the volume of a
rectangular parallelepiped having a bottom plane, first and second
side planes, first and second end plates and a top plane; the
bottom plane oriented parallel to the base and tangent to the hook
tip, the top plane parallel to the base and tangent to the top of
the hook at the point where the hook achieves its maximum distance
from the base, the side planes laying in the plane of the sides of
the hook; the first end plane perpendicular to the bottom plane at
the point where the bottom plane intersects the stem at its outer
side, the second end plane perpendicular to the bottom plane and
tangent to the outermost portion of the hook tip; wherein the
volume displacement of the hook is less than 6.times.10.sup.-6
cubic inches (9.83.times.10.sup.-5 cubic centimeters), the
multiplicity of plastic hooks being in adjacent rows, a common
integral planar base of said hook product being formed by base
members of all of the multiplicity of plastic
hooks..Iaddend..Iadd.
18. The hook product of claim 17 wherein the inner face of the
transition region has an angle to the direction normal to the base
member oriented to encourage a loop engaging the hook to move
toward the base member..Iaddend..Iadd.
19. The hook product of claim 17 wherein the inner generally
concave face is so shaped as to encourage a loop engaging the hook
in shear to engage the hook at about the location of
buckling..Iaddend..Iadd.
20. A plastic hook product for a hook and loop fastening system
having hooks sized and shaped to be capable of engaging loops of a
loop product with a pile height of approximately 0.04 inches or
less, the hook product comprising a multiplicity of plastic hooks
in adjacent rows facing in opposite directions and extending from a
common integral planar base, each of the multiplicity of hooks
comprising: a stem connected at its lower end to the base by being
molded integrally with the base, the stem having an outer side and
an inner side; a crook having a first end and a hook tip, the first
end connected to the stem, the crook projecting upwards from the
stem and then downwards towards the base in a substantially smooth
curve ending at the hook tip; the hook having a width, a height,
and a displacement volume, wherein displacement volume is the
volume of a rectangular parallelepiped having a bottom plane, first
and second side planes, first and second end planes and a top
plane; the bottom plane orientated parallel to the base and tangent
to the hook tip, the top plane parallel to the base and tangent to
the top of the hook at the point where the crook achieves its
maximum distance from the base, the side planes laying in the plane
of the sides of the hook; the first end plane perpendicular to the
bottom plane at the point where the bottom plane intersects the
stem at its outer side, the second end plane perpendicular to the
bottom plane and tangent to the outermost portion of the hook tip;
wherein the displacement volume of the hook is less than
6.times.10.sup.-6 cubic inches (9.83.times.10.sup.-5
cc)..Iaddend..Iadd.
21. A plastic hook product for a hook and loop fastening system
having hooks sized and shaped to be capable of engaging loops of a
loop product with a pile height of approximately 0.04 inches or
less, the hook product comprising a multiplicity of plastic hooks
in adjacent rows and extending from a common integral planar base,
each of the multiplicity of hooks comprising: a stem connected at
its lower end to the base by being molded integrally with the base,
the stem having an outer side and an inner side; a crook having a
first end and a hook tip, the first end connected to the stem, the
crook projecting upwards from the stem and then downwards towards
the base in a substantially smooth curve ending at the hook tip;
the hook having a width, a height, and a displacement volume,
wherein displacement volume is the volume of a rectangular
parallelepiped having a bottom plane, first and second side planes,
first and second end planes and a top plane; the bottom plane
orientated parallel to the base and tangent to the hook tip, the
top plane parallel to the base and tangent to the top of the hook
at the point where the crook achieves its maximum distance from the
base, the side planes laying in the plane of the sides of the hook;
the first end plane perpendicular to the bottom plane at the point
where the bottom plane intersects the stem at its outer side, the
second end plane perpendicular to the bottom plane and tangent to
the outermost portion of the hook tip; wherein the displacement
volume of the hook is less than 6.times.10.sup.-6 cubic inches
(9.83.times.10.sup.-5 cc), the hook product being produced by the
method comprising: integrally molding the base and hooks using a
molding roller having open-ended but otherwise closed hook-shaped
mold cavities in its periphery, including filling the mold cavities
with the base in contact with the periphery, and pulling the base
progressively away from the periphery of the molding roller and
progressively pulling the hooks longitudinally from the mold
cavities..Iaddend..Iadd.
22. The hook product of any of claims 16, 18 or 21 wherein the
displacement volume is less than 4.times.10.sup.-6 cubic
inches..Iaddend..Iadd.
23. The hook product of any of claims 16, 18 or 21 wherein for each
hook the crook height is less than 0.012 inches..Iaddend..Iadd.
24. The hook product of any of claims 16, 18 or 21 wherein for each
hook the thickness of the hook is less than 0.010
inches..Iaddend..Iadd.
25. The hook product of any of claims 16, 18 or 21 wherein the
footprint of each hook is less than 1.5.times.10.sup.-4 square
inches..Iaddend..Iadd.
26. The hook product of any of claims 16, 20 or 21 wherein the
multiplicity of hooks face in the same
direction..Iaddend..Iadd.
27. The hook product of any of claims 16, 20 or 21 wherein the
hooks have differing orientations to provide multidirectional shear
operation..Iaddend..Iadd.
28. The hook product of claim 21, wherein the method of producing
the hook product further comprises, prior to pulling, cooling each
of the hooks sufficiently to retain its shape without the aid of
its mold cavity and to be sufficiently resilient to return to its
desired shape after being pulled longitudinally from its mold
cavity while still being flexible enough to permit such removal
without destructive stresses being reached in the
hooks..Iaddend..Iadd.
29. The hook product of claim 21, each hook being tapered and
including concave fillets where the stem is connected to the base,
the taper and the concave fillets coupled with the generally
arcuate shape of the crook portion providing removal easing
clearances facilitating the removal of the hook from its mold
cavity by pulling longitudinally from its mold cavity..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved hook for hook and loop
fasteners and particularly to plastic molded hooks intended for use
with low pile loops. The technology of hook and loop fasteners is
well known wherein a fastener comprised of two separable pile
fastening tapes have interengaging piles on their surfaces, one
pile have loop-elements and the other hook elements, are capable of
co-acting to form a separable bond.
Such pile fasteners have found a wide variety of uses where ease of
opening and closing is desirable such as in clothing, footwear,
home furnishings, medical products, automotive fastening and many
other industrial situations where detachable or permanent
engagement is required. U.S. Pat. No. 3,009,235, U.S. Pat. No.
3,083,737 and U.S. Pat. No. 3,154,837 disclose various forms of
separable pile fastener tapes constructed from fibrous forms of
synthetic polymers such as nylon using basic textile weaving
techniques. Such methods create a base fabric into which is woven
the pile surface capable of engaging to form the closure. In more
recent times special hook materials have been made from plastic
molding techniques wherein the hooks are integrally formed with a
base strip as the tape is being formed.
U.S. Pat. No. 3,031,730 describes a closure wherein a surface of
burr like elements are exposed on a surface to be positively
coupled with a fabric. The burr like elements are in the form of
cast or molded flexible or plastic hook like members.
U.S. Pat. No. 3,760,000 to Menzin discloses a hook "eye" having a
sloping surface which functions as a cam surface for extracting the
molded hook from its mold cavity. The shank surface has two flat
sides of equal dimensions and a somewhat larger third side. The
shank portion is larger in cross section nearer the web than at the
tip of the hook and the three flat side portions of the shank are
continuous in smooth curves into and throughout the hook portion
with the shank portion of the three sides laying in the same
continuous plane as the corresponding face of the hook portion.
U.S. Pat. No. 3,312,583 to Rochlis and U.S. Pat. No. 3,708,833 to
Ribich describe other embodiments of hooks having somewhat tapered
shapes. U.S. Pat. No. 3,913,183 to Brumlik describes a self
gripping device wherein the gripping elements are particularly
adapted for self gripping fibers and the like along the entire
length of the fibers.
U.S. Pat. No. 4,894,060 to Nestegard describes a hook design for a
disposable diaper with an improved hook fastener portion wherein
the hook is made by the technique of extruding a profile and
subsequently slitting the profile to form discrete hooks. The
Nestegard patent claims a hook of sufficiently small dimensions for
engaging with low cost loops, particularly loops created by the
nonwoven process. The hook shape of the Nestegard patent is
considerably different than those of the instant invention because
of the method of making the hooks wherein one is dependent upon a
continuous profile prior to the cross cutting process. The
dimensions disclosed and claimed in the Nestegard patent are not
sufficient to calculate a displacement volume.
Even more recently U.S. Pat. No. 4,984,339 to the inventors of the
instant application discloses an improved hook having a profile
defined by an inner, smoothly contoured, generally concave face and
an outer, generally convex face, wherein the hook tapers smoothly
and continuously downward in width from a sturdy base member to its
free end whereby the hook will not deform to release a loop
engaging the hook in shear at or below the desired applied
force.
While the hooks formed according to these patents posses many
useful properties and engage with a wide range of loop
constructions, they possess the limitations of many other prior art
hooks in their inability to function effectively with very low
profile loops constructed with very short individual loops. Such
loops are especially desirable because of their thinness and their
low cost. In some case such loops are laminated to thin layers of
polyurethane foam to provide a resilient base so that hooks can
more easily penetrate into the body of a pile and thus be more
easily surrounded by loops. In general, however, such loops do not
function well with conventional hook structures.
One exception to the above described phenomena is the so-called
mushroom hook. Mushroom hooks are produced by a variety of
processes. Details of these types of products are contained in U.S.
Pat. Nos. 3,138,841, 3,770,359, 4,024,003 and 4,290,832. Generally,
the steps include creating an upstanding filament of polypropylene
monofilament and melting the top of the monofilament with heat
which causes molten polymer to "melt back" or flow down the stem in
a blob which solidifies at the terminal end of the filament to form
a mushroom shape head on top of the stem. The mushroom head acts as
do hooks of conventional hook and loop fasteners by entangling with
loops to form a bond. Because of its small footprint, which will be
discussed more fully below, mushroom fasteners are able to engage
readily with lower pile loops than other hooks of the hook and loop
type. However, mushroom products have many disadvantages. They are
limited to use of orientated polypropylene fibers with associated
limitations of that material, such as a relatively low temperature
operating range. The mushroom heads are easily snapped off their
stems giving such products very limited life in use, and the
mushroom head does not have the flexing capability of a hook shape
and therefore the only way a loop can be removed from the head is
to rupture either the loop or the mushroom head. Other limitations
of mushroom products are well known to those in the art.
SUMMARY OF THE INVENTION
The present invention contemplates producing a hook from the method
described in U.S. Pat. No. 4,794,028 to Fischer in which both the
size and shape of the hook is especially suited to low level loops.
It has been found that outstanding and unexpected performance from
such hooks in low level loops is possible. It is further realized
that the selection of the appropriate resin greatly enhances the
performance of such hooks. More specifically I have found that a
hook produced with a displacement volume, discussed more fully
below, of less than 6.times.10.sup.-6 cubic inches and preferably a
displacement volume of less than 4.times.10.sup.-6 cubic inches
will provide unusual and outstanding performance with a loop of the
lowest loop configuration. Displacement volume, as defined herein,
is the volume of a rectangular parallelepiped which delineate the
volume of loop displaced when a hook penetrates into the loop to
just the point where loops may start to fall into the cavity at the
inside of the crook of a hook, as will be more fully appreciated
from the description below.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of a hook of a conventional textile hoop
and loop closure system.
FIG. 2 depicts the hook of FIG. 1 as it would look engaging into a
deep mat of loops in a standard loop strip of a hook and loop
closure where the loop height is great relative to the return
height of the crook.
FIG. 3 depicts the hook of FIG. 1 engaging a low profile loop where
the return of the crook is greater than the height of the
loops.
FIG. 4 is a cross section of a plastic molded hook as described in
the prior art.
FIG. 5 depicts the hook of FIG. 4 as it would look engaging into a
mat of loops in a standard loop element of a hook and loop closure
where the hook is engaged with a single loop.
FIG. 6 depicts the hook of FIG. 1 showing the profile of
displacement, or footprint, required when the hook penetrates into
a mat of loops to a position equal the height of the loops.
FIG. 7 is the cross section of a mushroom hook showing the profile
of displacement.
FIG. 8 depicts the hook of FIG. 4 showing the profile of
displacement.
FIG. 9 is a cross sectional profile of a hook shape of the present
invention and shows the profile of displacement for that hook.
FIG. 10 is the cross section of the hook of the present invention
showing the profile of displacement.
FIG. 11 is a three dimensional illustration of the parallelepiped
which is defined as the displacement volume.
FIG. 12 is a graph depicting the relationship between shear
strength and hook displacement volume for a low profile loop.
BEST MODE FOR CARRYING OUT THE INVENTION
Now referring to FIG. 1, a monofilament (1) strand is bent into a
loop shape which is cut along one side of the loop to create the
crook(2) of a hook with a residual portion(3) of the monofilament
loop separated from the hook end tip(7) of the hook to provide a
spaced opening(4) sufficient to permit loop(5) to enter and become
entangled within the crook(2). In FIG. 6 the dimension "A" of the
hook (1) represents the dimension of the return, or height of the
crook, while "B" represents the total height of the hook from its
base(6) to the top outside of the crook(2). The rectangle "C" of
FIG. 6 represents the footprint of material that penetrates into a
loop structure when penetration is just sufficient to position tip
(7) below the top of a loop. FIG. 2 illustrates what happens when
the hook(1) attempts to penetrate into a mat of loops. The top of
the hook, having a footprint as shown in FIG. 6 "C", pushes aside
the loops(5) and continues to penetrate into the loop pile until it
strikes the base of the loop(8). The loops(5), being resilient,
spring back and some of the loops enter the space(4) provided by
cutting the monofilament. The crook of the hook ensnares the loop
which is well within the interior space(9) formed by the
monofilament. In this manner the loop becomes ensnared by the hook
and when attempting to separate the hook from the loop, separation
is restrained by the two components so engaged. To separate the
components, the hook must be deflected or opened. While the force
to open an individual hook is small, a proper hook and loop
fastener has a sufficient number of hook encounters to require a
substantial force to separate the strips.
FIG. 3 shows the same hook penetrating a loop strip which has short
loops. The loop height(11) of the low pile type is less than the
return of the crook of the hook, dimension "A" in FIG. 6. In such
cases the loops are deflected as illustrated in FIG. 3 but the
penetration of the hook is stopped when it strikes the base (8) of
the loop strip. However, the loops are so short that, regardless of
how resilient they may be and regardless of how well they spring
back and attempt to enter the space(4) in the hook, their height is
insufficient to permit such to take place. The loops are simply
unable to get above or around the crook(2) of the hook (1). When
this condition prevails there is little or no engagement between
the hook and the loops.
FIG. 4 shows a cross section of a plastic molded hook, formed by
plastic molding techniques in desired shapes as disclosed in U.S.
Pat. No. 4,984,339 assigned to the owner of the instant invention
and incorporated by reference herein. In this instance the
crook(13) is molded into a similar shape as the crook of the
textile monofilament crook(2). However, there is no residual
portion(3) to inhibit the movement of loop into and under the
crook(13) thus providing a much greater opening (14) than is
available from a monofilament textile hook. FIG. 5 is the hook of
FIG. 4 engaged with a standard loop. The hook shown has all the
features of the hook disclosed in U.S. Pat. No. 4,984,339 which
includes the differential tapered profile that results in the
setting of the yield point of the hook and permits flexing of the
hook during disengagement of the hook from a loop. The combination
of the special molded hook shape with small displacement volumes,
as will be described in more detail below, provides a novel and
especially valuable hook fastener for engaging with low profile
loops.
Now turning to FIGS. 6 through 8. As explained above, dimension "A"
represents the height of the crook and it is essential the hook
penetrate into the mat of loops to a depth at least greater than
the height of the crook so that tip (7) will rest below the tops of
loops and the loops can spring into the space(9) and be ensnared by
the hook. If this does not happen there can be no engagement. The
area of loops that must be displaced when the hook penetrates into
loops to this point is depicted by the rectangle "C" in each of
FIGS. 6, 7, 8, and 9. Rectangle "C" is the cross section of the
hook along a plane cut through the hook parallel to the base and
tangent to the point on the hook tip that is nearest the base. For
example, in FIG. 8 the plane is depicted by dashed line (18) which
rests parallel to the base (15), is displaced from the top of the
hook by dimension "A" and displaced from the base (15) by dimension
"D". It can be readily seen that dimension "D" is equal to "B"-"A".
The area of rectangle "C" for any hook will be influenced by
several factors. Looking to FIG. 9, the plane(18) cuts through the
hook such that the plane is parallel to the base (15), upon which
the hook foundation rests, and intersects the back side of the hook
at the point(10). Line 20 projects perpendicular to the
intersecting plane(18) and because plane (18) is parallel to the
base(15), line (20) is also perpendicular to the base(15). If a
second line (21) is drawn perpendicular to the plane(18) and also
tangent to the outermost edge of the hook tip(7), line (21) will be
parallel to line (20). The lines described define the terminal ends
of rectangle "C" (22) and (23). "C" represents the area displaced
by the hook in penetrating the mat of loops, or put another way the
area to which loops must be pushed aside or displaced for
penetration to take place. If the loops into which the hooks
penetrate are very resilient, they will immediately bend around
such a plane and close in behind the face of the plane. However, if
the hook is a solid mass, as in fact it is, the loops simply push
back against the walls of the hook. The penetrating hooks have in
reality a volume and this volume can simply be defined as the
volume of a parallelepiped encasing the crook portion of the hook
above the point where penetration is sufficient to enable
engagement. FIG. 10 shows the position of the parallelepiped "E"
relative to the entire hook configuration. FIG. 11 shows the
parallelepiped standing alone. The volume of the parallelepiped can
be calculated for a single hook by taking the area "C" and
multiplying by the height of the crook "A" where "E"="A".times."C".
We have defined this volume as "displacement volume".
We have found this displacement volume is an important factor in
determining the ability of a hook to engage with certain types of
loops. When the loop height is very low, hooks of low displacement
volume show markedly improved performance even though there is more
than simple loop height to contend with when determining the
ability of a loop to accept a given hook.
The following table shows displacement volume values for a variety
of hook types sold by Velcro USA Inc., the assignee of the instant
application.
DISPLACEMENT SHEAR IN HOOK TYPE VOLUME LOW LOOP Standard Tensile
6.0 .times. 10.sup.-6 6.5-10.0 Ultra-Mate 15 style 7.4 .times.
10.sup.-6 3.0-8.0 Molded 8 style 14 .times. 10.sup.-6 4.0-9.0
Ultra-Mate 24 style 14 .times. 10.sup.-4 8.0-13.0 Standard Mushroom
1.4 .times. 10.sup.-4 15.0-20.0 Molded 22 style 1.1 .times.
10.sup.-4 22.0-29.0
FIG. 12 is a graph depicting the relationship of shear strength of
hooks to displacement volumes for hooks engaged in a low profile
loop closure system, loop style #3610 sold by Velcro USA Inc. and
having loop height of approximately 0.040 inches. This is a
fraction of standard loops such as loop 1000 sold by Velcro USA
Inc. which has a loop height of approximately 0.100 inches. Data
for the graph is taken from the table above to create the plot
shown in FIG. 12. The ordinate of the graph of FIG. 12 shows shear
strength measured as the strength per square inch of closure. The
abscissa shows displacement volume ranging from 1.1.times.10.sup.-6
to 24.times.10.sup.-6 cubic inches. It is clear from this graph
that displacement volume dramatically influences the ability of a
hook to perform in the shear mode for this loop design. The shear
starts to increase at 6.times.10.sup.-6 and rapidly rises to almost
double at 4.times.10.sup.-6. For engaging into short fine loops a
hook having a displacement volume of less than 6.times.10.sup.-6 is
desirable but preferably the displacement volume will be less than
4.times.10.sup.-6.
These indicators can be very useful in designing new hook shapes
for specific loop geometries. However, hook displacement volume is
by no means the only measure to be used in evaluating the ease of
engagement of a hook in a low profile loop even though it is one of
the important factors. As explained earlier the height of the crook
itself influences the displacement volume of any particular hook,
but in addition, the thickness of the hook has a great effect on
the displacement volume. In addition, the general shape of the hook
can have a major effect on the displacement volume. The hook shape
of U.S. Pat. No. 4,984,339 is especially well suited for engagement
with low profile loops and the molding process for making that hook
is easily adjusted to achieve the modification of the displacement
volume and to produce hooks in the preferred range of displacement
as disclosed herein. For example, in FIG. 9 the location of the
point(10) where the back side of the hook intercepts the lower
plane defining the displacement volume sets the dimension of the
footprint "C". If the hook has a very shallow rearward slope the
point of intersection(10) will be moved rearward also and the
displacement volume will be increased. At the crook tip the
placement of the hook tip sets the relative position of this same
lower plane and the shorter the crook height the lower the
displacement volume. It will be appreciated the displacement volume
may be adjusted by altering many of the dimensions of the hook
shape. Such adjustment is easily accomplished by the methods
disclosed in U.S. Pat. No. 4,794,028.
Heretofore this influence of displacement volume on hook and loop
performance has not been understood. Hook design has been a matter
of trial and error with little rhyme or reason. Hook selection has
been primarily a matter of using the materials available and little
effort has gone into designing hooks with the specific geometry to
accomplish a specific type of performance. It has been known that
using a thicker monofilament would result in greater tape
separation forces than would be the case if finer monofilaments
were used. The development of mushroom tapes and the size of the
head is merely a matter of accident. The head was not designed with
any specific shape or size intended.
Understanding of the principles of the engagement problem in fine
low profile loops has provided the clue to the development of
advanced hook products. I have found that plastic molded hooks with
a displacement volume of less than about 6.times.10.sup.-6, and
preferably less than 4.times.10.sup.-6, engage especially well in
loops with a pile height of less than 0.025 inches. Such fine
molded hooks have never before been produced. Development of such
hooks is a considerable advance in the art, and for the first time,
this understanding permits development of hook tapes which are
specifically designed for the very desirable aesthetic and cost
effective low profile loops.
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