U.S. patent application number 10/337139 was filed with the patent office on 2004-07-08 for vibratory molding process and product.
Invention is credited to Hankins, James Kendall, Pemberton, Christopher L., Wright, Donald K..
Application Number | 20040128806 10/337139 |
Document ID | / |
Family ID | 46298924 |
Filed Date | 2004-07-08 |
United States Patent
Application |
20040128806 |
Kind Code |
A1 |
Wright, Donald K. ; et
al. |
July 8, 2004 |
Vibratory molding process and product
Abstract
A fastener strip is disclosed having a permanently sealed,
airtight portion and a reclosable portion capable of maintaining an
airtight seal when closed. The permanently sealed portion is
generally planar and essentially impervious to air flow. The
reclosable portion includes a ridge and a trough joined at their
adjacent ends to a plug, which prevents air from leaking from the
adjacent end of the reclosable portion. Additionally, a dam joins
the plug to the first backing in an essentially airtight seal, and
joins the plug to the second backing in an essentially airtight
seal. A method and apparatus for sealing portions of a
thermoplastic fastener strip are also disclosed. A method is
additionally disclosed for vibrating and molding thermoplastic
materials in which a flow of malleable thermoplastic material is
initiated and molded with an effectively dimensioned vibrator that
is unitary with a first matrix for guiding and molding the
malleable polymer.
Inventors: |
Wright, Donald K.;
(Murphysboro, IL) ; Pemberton, Christopher L.;
(Marion, IL) ; Hankins, James Kendall;
(Harrisburg, IL) |
Correspondence
Address: |
VEDDER PRICE KAUFMAN & KAMMHOLZ
222 N. LASALLE STREET
CHICAGO
IL
60601
US
|
Family ID: |
46298924 |
Appl. No.: |
10/337139 |
Filed: |
January 7, 2003 |
Current U.S.
Class: |
24/584.1 |
Current CPC
Class: |
B29C 66/80 20130101;
B29C 66/8242 20130101; B29C 66/346 20130101; B29L 2005/00 20130101;
B29C 66/9513 20130101; B29C 65/08 20130101; Y10T 24/2532 20150115;
Y10T 24/45152 20150115; B29C 66/8322 20130101; B29C 66/43 20130101;
B29C 66/81431 20130101; B29C 67/0044 20130101; B29C 66/03241
20130101; B29C 66/1248 20130101; B29C 66/73921 20130101 |
Class at
Publication: |
024/584.1 |
International
Class: |
A44B 021/00; A44B
017/00 |
Claims
We claim:
1. A method for sealing portions of a thermoplastic fastener strip,
which method comprises the steps of: providing a thermoplastic
fastener strip; vibrating a portion of the fastener strip so as to
increase the malleability of said portion, as compared to the
malleability of the fastener strip before vibrating; pressing a
first matrix against the malleable portion to produce a first
shape; and pressing a second matrix against the malleable portion
to produce a second shape.
2. The method of claim 1 in which the vibrating is caused by an
oscillating vibrator in contact with the fastener strip.
3. The method of claim 2 in which the vibrator vibrates at a
frequency which produces a measurable increase in the temperature
of the vibrated portion.
4. The method of claim 2 in which the vibrator oscillates at a
frequency of at least about 20,000 cycles per second.
5. The method of claim 2 in which the vibrator includes a generally
planar face having a plurality of cutouts and a groove extending
from one of the cutouts to another of the cutouts.
6. The method of claim 2 in which the vibrator is positioned over
the fastener strip and an anvil is positioned under and in contact
with the fastener strip.
7. The method of claim 6 in which the vibrator does not touch the
anvil during the vibrating.
8. The method of claim 1 in which the vibrating is caused by two or
more oscillating vibrators in contact with the fastener strip, one
of the vibrators positioned over and in contact with the fastener
strip and the other of the vibrators positioned under and in
contact with the fastener strip.
9. The method of claim 1 in which the first matrix is pressed
against the malleable portion at a first location to produce the
first shape, the malleable portion is subsequently transferred to a
second location and the second matrix is pressed against the
malleable portion at the second location to produce the second
shape.
10. The method of claim 1 in which the vibrating and the first
matrix to produce the first shape are performed at the same
location.
11. The method of claim 1 in which the first matrix is pressed
against the malleable portion, the malleable portion is
subsequently heated and the second matrix is then pressed against
the malleable portion.
12. The method of claim 1 which includes heating the fastener strip
to a temperature warmer than room temperature and cooler than the
melting range of the fastener strip before the vibrating.
13. The method of claim 1 which includes tensioning the fastener
strip and maintaining the tension during sealing of the portions of
the fastener strip.
14. The method of claim 1 which includes pressing a third matrix
against the malleable portion to produce a third shape.
15. The method of claim 1 in which each of the matrices includes a
die, and at least one of the dies has a generally planar face and a
plurality of cutouts.
16. The method of claim 15 in which at least one of the dies has a
generally planar face and a channel extending substantially across
the face.
17. A method for making a fastener strip having a permanently
sealed, airtight portion adjacent a reclosable portion that is
essentially airtight when fastened, which method comprises the
steps of: providing a reclosable thermoplastic fastener strip that
is essentially airtight when fastened; vibrating a portion of the
fastener strip so as to increase the malleability of said portion,
as compared to the malleability of the fastener strip before
vibrating, the malleable portion being adjacent an end of a
reclosable portion; pressing the malleable portion to produce a
generally planar portion that is essentially airtight; displacing
at least some of the malleable portion to produce an essentially
airtight plug that joins the planar portion in an essentially
airtight seal, which extends from the planar portion to the
adjacent end of the reclosable portion and joins the adjacent end
of the reclosable portion in an essentially airtight seal; and
cooling the fastener strip to make a fastener strip having a
permanently sealed, airtight portion adjacent a reclosable portion
that is essentially airtight when fastened.
18. The method of claim 17 in which the reclosable portion
includes: a) an elongated first backing, including a trough
extending lengthwise along the first backing; and b) an elongated
second backing, including a ridge extending lengthwise along the
second backing, the ridge removably insertable into the trough to
essentially prevent air flow across the trough; and the planar
portion includes essentially no ridge and essentially no trough;
said method including the steps of joining the ridge of the
reclosable portion and the trough of the reclosable portion at the
adjacent end of the reclosable portion so as to create the a plug
in the seal that prevents air from leaking from the adjacent end of
the reclosable portion.
19. The method of claim 18 which includes displacing at least some
of the malleable portion to produce an essentially airtight dam
that joins the plug to the first backing in an essentially airtight
seal, and joins the plug to the second backing in an essentially
airtight seal.
20. The method of claim 17 in which displacing the malleable
portion includes pressing a first matrix against the malleable
portion to produce a first shape.
21. The method of claim 20 in which plug is formed by pressing the
first matrix against the malleable portion.
22. The method of claim 17 in which displacing the malleable
portion includes pressing a second matrix against the malleable
portion to produce a second shape.
23. The method claim 22 in which the dam is formed by pressing the
second matrix against the malleable portion.
24. An apparatus for sealing portions of a fastener strip, which
apparatus comprises: a vibrator for vibrating a portion of the
fastener strip so as to increase the malleability of said portion,
as compared to the malleability of the fastener strip before
vibrating; a first matrix constructed and arranged for pressing
against the malleable portion to produce a first shape for sealing
the fastener; and a second matrix constructed and arranged for
pressing against the malleable portion to produce a second shape
for sealing the fastener.
25. The apparatus of claim 24 in which the vibrator oscillates in
contact with the fastener strip.
26. The apparatus of claim 24 in which the vibrator is suitable for
vibrating at a frequency which produces a measurable increase in
the temperature of the vibrated portion.
27. The apparatus of claim 24 in which the vibrator is suitable for
oscillating at a frequency of at least about 20,000 cycles per
second.
28. The apparatus of claim 24 in which the vibrator includes a
generally planar face having a plurality of cutouts and a groove
extending from one of the cutouts to another of the cutouts so as
to facilitate flow of thermoplastic material.
29. The apparatus of claim 24 in which the vibrator includes is
positioned over the fastener strip and an anvil is positioned under
and in contact with the fastener strip so as to facilitate
sealing.
30. The apparatus of claim 29 in which the vibrator does not touch
the anvil during the vibrating.
31. The apparatus of claim 24 in which the vibrator includes two or
more ultrasonic horns in contact with the fastener strip, one of
the horns being positioned over and in contact with the fastener
strip and the other of the horns being positioned under and in
contact with the fastener strip.
32. The apparatus of claim 24 in which includes a first stage at a
first location for pressing the first matrix against the malleable
portion, and a second stage at a second location for pressing the
second matrix against the malleable portion so as to produce the
second shape.
33. The apparatus of claim 24 in which the first stage is suitable
for the vibrating and the malleable portion pressing so as to
produce the first shape.
34. The apparatus of claim 24 which comprises a heater for
pre-heating the fastener strip.
35. The apparatus of claim 24 and comprising a tensioner for
tensioning the fastener strip.
36. The apparatus of claim 24 which comprises a third matrix for
pressing against the malleable portion so as to produce a third
shape.
37. The apparatus of claim 24 in which each of the matrices
includes a die, and at least one of the dies has a generally planar
face and a plurality of cutouts.
38. The apparatus of claim 37 in which the first matrix includes a
die that is unitary with the vibrator.
39. The apparatus of claim 37 in which at least one of the dies has
a generally planar face and a channel extending substantially
across the face for pressing the fastener strip so as to form a
generally planar portion and for displacing at least some of the
malleable portion beyond the planar portion so as to form an
airtight seal.
40. An apparatus for sealing a portion of a reclosable
thermoplastic fastener strip that is essentially airtight when
fastened, the fastener strip comprising: a) an elongated first
backing, including a trough extending lengthwise along the first
backing; and b) an elongated second backing, including a ridge
extending lengthwise along the second backing, the ridge removably
insertable into the trough to essentially prevent air flow across
the trough; the apparatus comprising: a vibrator for vibrating a
portion of the fastener strip so as to produce a portion that is
relatively more malleable, as compared to the malleability of the
fastener strip before vibrating, the malleable portion being
adjacent an end of a reclosable remainder portion of the fastener
strip; and at least one matrix for pressing against the malleable
portion so as to produce a planar portion that includes essentially
no ridge and essentially no trough and to displace at least some of
the malleable portion to form a plug which joins the ridge of the
reclosable portion and the trough of the reclosable portion at the
adjacent end in an airtight seal that prevents air from leaking
from the adjacent end.
41. The apparatus of claim 40 which comprises a second matrix for
displacing at least some of the malleable portion displacing at
least some of the malleable portion to produce an essentially
airtight dam that joins the plug to the first backing of the
reclosable portion in an essentially airtight seal, and joins the
plug to the second backing of the reclosable portion in an
essentially airtight seal.
42. The apparatus of claim 40 which comprises a cooler for cooling
the fastener strip.
43. An apparatus for vibrating a portion of a thermoplastic
fastener strip, which apparatus comprises: a vibrator suitable for
oscillating at a frequency in the range of normal human hearing or
higher, the vibrator including a generally planar face having a
plurality of spaced apart cutouts; and a groove extending from one
of the cutouts to another of the cutouts, the groove sized to
receive a portion of a fastener strip including thermoplastic
material and to displace a predetermined volume of the material
along the fastener strip when the vibrator is oscillated and
pressed into the fastener strip.
44. The apparatus of claim 43 in which the groove is sized
appropriately for the vibrator to displace the volume of material
when the vibrator is oscillated and pressed into the fastener strip
with a predetermined pressure.
45. The apparatus of claim 43 in which the groove is sized
appropriately for the vibrator to displace the volume of material
when the vibrator is oscillated and positioned at a predetermined
distance from the fastener strip.
46. The apparatus of claim 43 in which the cutouts are generally
arcuate in section and spaced apart at a predetermined distance,
each of the cutouts arching toward the other of the cutouts.
47. The apparatus of claim 43 in which at least one of the cutouts
includes a transition volume having a depth which increases as a
function of distance from the groove.
48. The apparatus of claim 43 in which the groove has a depth which
decreases as a function of distance from the closest of the
cutouts.
49. The apparatus of claim 43 in which the vibrator is suitable for
pneumatically actuated oscillation at frequencies in the range of
about 10,000 to about 100,000 cycles per second.
50. The apparatus of claim 47 in which the fastener strip includes
an elongated first backing having a longitudinally extending
trough; and an elongated second backing having longitudinally
extending ridge, the ridge removably insertable into the trough to
essentially prevent air flow across the trough.
51. The apparatus of claim 50 in which the groove has an axis is
oriented to receive the ridge and the trough, and each of the
cutouts has an axis of symmetry that is generally parallel and
offset with respect to the groove axis.
52. The apparatus of claim 43 in which the vibrator is a
resonator.
53. The apparatus of claim 43 which also includes an anvil, and the
vibrator is positioned over the anvil.
54. A fastener strip, which comprises: a reclosable portion
including a) an elongated first backing, including a trough
extending lengthwise along the first backing; and b) an elongated
second backing, including a ridge extending lengthwise along the
second backing, the ridge removably insertable into the trough to
essentially prevent air flow across the trough; and a generally
planar portion including essentially no ridge and essentially no
trough; and a plug that joins the ridge of the reclosable portion
and the trough of the reclosable portion at the adjacent end of the
reclosable portion to the plug in an airtight seal that prevents
air from leaking from the adjacent end of the reclosable
portion.
55. The fastener strip of claim 54 which comprises an essentially
airtight dam that joins the plug to the first backing in an
essentially airtight seal, and joins the plug to the second backing
in an essentially airtight seal.
56. The fastener strip of claim 54 in which the planar portion is
essentially impervious to air flow.
57. The fastener strip of claim 54 in which the plug is essentially
impervious to air flow.
58. The fastener strip of claim 55 in which the dam is essentially
impervious to air flow.
59. The fastener strip of claim 54 in which the at least some of
the plug is located between the ridge of the reclosable portion and
the trough of the reclosable portion.
60. A fastener strip, which comprises: a reclosable portion
including a) an elongated first backing, including a trough
extending lengthwise along the first backing; and b) an elongated
second backing, including a ridge extending lengthwise along the
second backing, the ridge removably insertable into the trough to
essentially prevent air flow across the trough; a generally planar
portion including essentially no ridge and essentially no trough; a
plug that joins the ridge of the reclosable portion and the trough
of the reclosable portion at the adjacent end of the reclosable
portion to the plug in an airtight seal that prevents air from
leaking from the adjacent end of the reclosable portion; and a dam
that joins the plug to the first backing in an essentially airtight
seal, and joins the plug to the second backing in an essentially
airtight seal.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to a process for permanently
sealing portions of reclosable fastener strips that includes the
use of a vibrating horn to heat and mold the fastener strip. The
invention also relates generally to an apparatus for permanently
sealing portions of reclosable fastener strips and to reclosable
fastener strips that include permanently sealed airtight
portions.
BACKGROUND OF THE INVENTION
[0002] Reclosable fastener strips are widely used in the packaging
industry as components for reclosable plastic bags, among other
things. Typically, the fastener strips are manufactured in long,
continuous lengths that are wound on reels or accordion-folded in
boxes for storage and shipping.
[0003] These continuous lengths are usually subsequently cut to a
size suitable for attaching to individual bags on, for example, a
form and fill machine. The fastener strips are normally composed of
thermoplastic materials, such as polyethylene, polypropylene,
ethylene vinyl acetate, polyethylene terephthalate, polyvinylidene
fluoride, acrylonitrile butadiene styrene or the like. For example,
the fastener strips often include backings comprised of a
polyethylene-ethylene vinyl acetate blend. The backings often
include a profile portion having ridges and trough composed of
polyethylene terephthalate. A representative fastener strip of the
prior art is depicted in FIGS. 17-19.
[0004] In order for the cut end of the fastener strip to seal
against air leakage in or out of the reclosable bag, the end must
be closed off in some manner. Also, the closed-off portion should
be thinned and flattened to facilitate the cutting operation.
Adhesives and thermal welds, notably "spot seals," have been
utilized in the past. However, neither of these techniques is
entirely reliable, and both of these techniques tend to deform or
obstruct portions of the fastener strips that are intended to
remain unaffected and, therefore, reclosable.
[0005] Vibratory welding processes, including sonic and ultrasonic
processes also have been used in the manufacture of reclosable
thermoplastic plastic bags, as well as other thermoplastic work
pieces using known power supplies, transducers, boosters, and
harmonically balanced horns. Conventional horns used in these
processes are of several different types. These types include flat
horns, knurled horns, and reversed knurled horns. However, each one
of these horns has two major drawbacks. One drawback is that these
horns typically imprint an undesirable contour on vibrated regions
of the thermoplastic work piece. The other drawback is these horns
often deform nearby unvibrated portions of the thermoplastic work
piece. For example, previously disclosed horns typically deform
thermoplastic fastener strips in reclosable portions that adjoin
the vibrated region. This deformation creates gaps that prevent the
fastener strips from forming an airtight seal.
[0006] Ultrasonic processes are also employed to reduce the
thickness of thermoplastic fastener strips to facilitate cutting
and sealing the thermoplastic fastener strips and associated bags.
These previously disclosed processes cannot be relied upon to
create an airtight seal, because the prior art ultrasonic horns
typically a) imprint an undesirable contour on vibrated regions of
the bag so as to create leaks, and b) deform nearby unvibrated
portions of the thermoplastic work piece.
[0007] Therefore, a need exists for a new process for permanently
sealing portions of reclosable thermoplastic fastener strips.
Desirably, the new process provides an airtight seal in both the
vibrated and unvibrated portions of the fastener strip.
SUMMARY OF THE INVENTION
[0008] The present invention provides a fastener strip having a
permanently sealed, airtight portion and a reclosable portion
capable of maintaining an airtight seal when closed. The
permanently sealed portion is generally planar and essentially
impervious to air flow. The reclosable portion includes a ridge and
a trough joined at their adjacent ends to a plug, which prevents
air from leaking from the adjacent end of the reclosable portion.
Additionally, a dam joins the plug to a first backing in an
essentially airtight seal, and joins the plug to a second backing
in an essentially airtight seal.
[0009] The invention also provides a method for sealing portions of
a thermoplastic fastener strip. The method includes vibrating a
portion of a conventional, thermoplastic fastener strip, which is
capable of maintaining an airtight seal, so as to produce a
malleable portion. A first matrix is pressed against the malleable
portion to produce a first shape, and a second matrix is pressed
against the malleable portion to produce a second shape for
permanently sealing a portion of the fastener strip. Preferably, a
dual-purpose vibrator/matrix is utilized to vibrate the fastener
strip and produce the first shape. In addition, the first and
second shapes are also enhanced by other matrices at separate
stages.
[0010] Pressing the malleable portion to produce the first shape
may include flattening the malleable portion and displacing at
least some of the malleable portion to produce an essentially
airtight plug. The plug joins the planar portion in an essentially
airtight seal and joins the adjacent end of the reclosable portion
in an essentially airtight seal.
[0011] Pressing the malleable portion to produce the second shape
may include further flattening the malleable portion and displacing
at least some of the malleable portion to produce an essentially
airtight dam. The dam joins the plug to a first backing of the
reclosable portion in an airtight seal and, also, joins the plug to
a second backing of the reclosable portion.
[0012] The invention also provides an apparatus for sealing
portions of a fastener strip. The apparatus includes a vibrator for
vibrating a portion of the fastener strip so as to increase the
malleability of the portion, a first matrix constructed and
arranged for pressing against the malleable portion to produce a
first shape for sealing the fastener; and a second matrix
constructed and arranged for pressing against the malleable portion
to produce a second shape for sealing the fastener.
[0013] In a broader aspect, the invention is an ultrasonic polymer
forming process for thermoplastic materials in which the
improvement includes guiding the flow of malleable polymer to a
predetermined location with an effectively dimensioned vibrator
that is unitary with a first matrix for guiding and molding the
malleable polymer. For example, the predetermined location may be a
location in which additional polymer is desired to render the area
stronger or more aesthetically pleasing, or to fill any gaps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a truncated perspective view of a fastener strip
of the present invention;
[0015] FIG. 2 is an elevation view of the fastener strip depicted
in FIG. 1;
[0016] FIG. 3 is a cross-section taken along line 3-3 of FIG.
2;
[0017] FIG. 4 is a cross-section taken along line 4-4 of FIG.
2;
[0018] FIG. 5 is a cross-section taken along line 5-5 of FIG.
2;
[0019] FIG. 6 is a perspective view of a first stage of an
apparatus of the present invention;
[0020] FIG. 7 is a perspective view of a vibrator of the present
invention;
[0021] FIG. 8 is an end view of the vibrator depicted in FIG.
7;
[0022] FIG. 9 is a partial cross-section of the vibrator taken
along line 9-9 of FIG. 8;
[0023] FIG. 10 is an elevation of the first shape, which is
produced by the first stage;
[0024] FIG. 11 is a perspective view of a second stage, a third
stage, a fourth stage and a fifth stage of the apparatus depicted
in FIG. 6;
[0025] FIG. 12 is a perspective view of a die for the second stage
of the present invention;
[0026] FIG. 13 is an elevation of a second shape, which is produced
by the second stage;
[0027] FIG. 14 is a perspective view of a die for the third stage
of the present invention;
[0028] FIG. 15 is a perspective view of a die for the fourth stage
of the present invention;
[0029] FIG. 16 is a perspective view of a tensioner of the present
invention;
[0030] FIG. 17 is a plan view of a prior art fastener strip,
including two backings;
[0031] FIG. 18 is an elevation view of one of the prior art
backings depicted in FIG. 15; and
[0032] FIG. 19 is an elevation view of the other of the prior art
backings depicted in FIG. 15.
DETAILED DESCRIPTION OF THE INVENTION
[0033] In a preferred embodiment, the invention includes a fastener
strip such as fastener strip 100 depicted in FIG. 1. Fastener strip
100 includes at least one reclosable portion 120 and at least one
permanently sealed, generally planar portion 140. Although the
perspective view shown in FIG. 1 is necessarily truncated, due to
space limitations, it is contemplated that fastener strip 100 may
be wound on a reel or accordion-folded in a box for convenient
shipping and storage and include hundreds or even thousands of
reclosable portions 120 and generally planar portions 140.
[0034] Reclosable portion 120 includes first backing 122 and
troughs 124, which typically extends lengthwise along fastener
strip 100. Reclosable portion 120 also includes second backing 126
and ridges 128 for mating with troughs 124 in an airtight,
reclosable seal that essentially prevents air flow from one side of
the seal to the other. Flap or flange 127 conveniently extends from
second back 122 to an exterior side of fastener 100 in order to
protect trough 124 and ridge 128 from damage and to facilitate a
user's grip for opening fastener strip 100.
[0035] The relative positions of troughs 124 and ridges 128 are
depicted in FIG. 1 are arbitrary and need not be as shown for the
invention to succeed. Also, either first backing 122 or second
backing 126 may be positioned on the exterior side of fastener
strip 100 and either of the backings 122, 124 may extend in the
form of a flange, such as flange 127. The thicknesses of backings
122, 124 are often in the range of about 10 to 20 thousandths of an
inch and the heights of trough 124 and ridge 128 are often in the
range of about 50 to 100 thousandths of an inch. The invention
however is not limited to these ranges.
[0036] Commonly, the thickness of planar portion 140 is about the
thickness of one of the backings 122, 124 to about the combined
thickness of both of the backings. Planar portion 140 is
essentially free of mating ridges and troughs, such as trough 124
and ridge 128, and includes essentially no void spaces.
[0037] Plug 160 joins troughs 124 and ridges 128 in an airtight
seal at adjacent end 130 of reclosable portion 120. Troughs 124 and
ridges 128 define longitudinal interstitial voids (best seen in
FIG. 3) that communicate hydraulically lengthwise along reclosable
portion 120. Even if troughs 124 and ridges 128 mate effectively so
as to prevent air flow between them from one side of fastener 100
to the other (for example, from the interior side of fastener strip
100 to the exterior of fastener strip 100), the ends of trough 124
and ridge 128 must be sealed to prevent air from flowing
longitudinally through these voids and passing through end 130.
Plug 160 provides this seal.
[0038] Dam 180 joins plug 160 to first backing 122 and to second
backing 126 as depicted in FIG. 1. Dam 180 is essentially
impervious to air flow and forms airtight seals where it meets plug
160, first backing 122 and second backing 126, respectively. A
primary purpose of dam 160 is to prevent air one side of fastener
strip 100 from leaking around plug 160 to the other side of
fastener 100.
[0039] The relationship of plug 160 to dam 180 is best seen in FIG.
2. FIG. 2 shows how plug 160 seals end 130 of reclosable portion
120 to prevent longitudinal interstitial voids from passing air
through end 130. Dam 180 joins and seals the backings 122, 126 with
plug 160 and planar portion 140. Lines 3-3, 4-4 and 5-5 correspond
to cross-sections depicted in FIGS. 3-5.
[0040] Inspection of FIGS. 1-3 indicate that line 3-3 of FIG. 2 is
at or near end 130. As can be seen in FIG. 3, trough 124 and ridge
128 define interstitial voids that are sealed by plug 160. The view
in FIG. 3 looks away from planar portion 140 and toward reclosable
portion 120. Longitudinal interstitial voids can be seen in
cross-section, with plug 160 filling the voids. Significantly, FIG.
3 shows that trough 124 and ridge 128 are not significantly
deformed at line 3-3 and, therefore, are capable of creating an
airtight, reclosable seal across fastener strip 100. FIG. 3 is
representative of reclosable portion 120, except that plug 160
covers over and/or infiltrates the interstitial voids.
[0041] The view in FIG. 4 is in the same direction as that of FIG.
3, but from a position closer to planar portion 140. Only vestiges
of trough 124 and ridge 128 are apparent, and these are essentially
filled by plug 160. FIG. 4 is representative of plug 160, except
that the vestiges are present.
[0042] FIG. 5 shows a relatively flattened and homogeneous
cross-section, as compared to FIGS. 3 and 4. No vestiges of trough
124 and ridge 128 are visible. FIG. 5 represents the juncture of
dam 180 with planar portion 140.
[0043] Turning now to FIGS. 17-19, prior art fastener strip 10
includes first backing 22, having a plurality of longitudinal
troughs 24 thereon, and second backing 126, which has a plurality
of longitudinal ridges 28 and flap or flange 27. At least one of
the troughs 24 reclosably mates with one of the ridges 28 to
produce an essentially airtight seal that prevents air leakage
between interior and the exterior sides of fastener strip 10.
[0044] Longitudinal interstitial voids commonly exist between
trough 24 and ridge 28. While the voids do not necessarily
interfere with the airtight seal between the sides of fastener
strip 10, the voids permit air flow longitudinally along trough 24
and ridge 28. Fastener strip 10 is composed of a material that
becomes progressively more fluid with increasing temperature,
hereinafter referred to as a "thermoplastic" material.
[0045] FIG. 6 depicts first stage 256 of apparatus 200 of the
present invention for sealing portions of a prior art fastener
strip, such as thermoplastic fastener strip 10 shown in FIGS.
17-19. First stage 256 of apparatus 200 includes vibrator 220 for
vibrating a portion of fastener strip 10 to produce a relatively
more malleable portion 212, best seen in FIG. 9. FIG. 6 also shows
anvil 230, which supports fastener strip 10 from below during the
vibrating, and four pneumatic piston and cylinder assemblies 202.
The use of four pneumatic pistons 202 assures that the anvil 230 is
properly aligned and level, and also helps direct more of the
energy from vibrator 220 to the fastener strip, rather than causing
the anvil 230 to vibrate. First stage 256 is positioned at location
258, which is a short distance away from stages 276, 296, 316 and
320 (best seen FIG. 11) of apparatus 200.
[0046] Vibrator 220, illustrated in FIG. 7, includes pneumatic
actuator 231, ultrasonic horn or resonator 233 and first matrix
240. Actuator 231 receives compressed air and provides energy to
vibrator 220 in the form of mechanical vibrations in the range of
about 10,000 to about 100,000 cycles per second, more preferably at
least about 20,000 cycles per second. Horn or resonator 233 focuses
and intensifies the vibrations at first matrix 240, which is a
single, integral unit with horn 233.
[0047] Horn 233 is also known as a solid resonator, a concentrator,
or a mechanical amplifier. Horn 233 is dimensioned to be resonant
at a predetermined frequency of vibration. When horn 233 is
energized at its proximal input surface by an actuator 231, it
provides ultrasonic energy (vibrations) at its opposite distal end
to a workpiece that is in forced contact with the distal end.
[0048] As depicted in FIGS. 7-9, first matrix 240 is the distal end
of horn 233. Alternatively, first matrix 246 can be constructed as
a separate die and securely mounted on the distal end of horn 233.
It is believed that fashioning first matrix 240 integrally with
horn 23, rather than as a separate die mounted on horn 233, tends
to promotes efficient and reproducible transmission of the
vibrations. In either case, first matrix 240 is located at the
distal end of horn 233 and can be utilized to press and mold a
thermoplastic substrate, such as fastener strip 10, while vibrator
220 is vibrating.
[0049] Details of first matrix 240 are presented in FIG. 8. First
matrix 240 includes a planar face 246 having cutouts 248, 250.
Groove 252 of approximately semicircular cross-section extends
across face 246 from cutout 248 to cutout 250. FIG. 8 illustrates
that groove 252 is generally linear along the longitudinal axis of
fastener strip 10 and that cutouts 248, 250 are each generally
symmetrical and aligned along a shared axis of symmetry. The groove
axis and the cutout axis are offset and generally parallel to each
other. During use, the groove axis is aligned with and positioned
directly over trough 24 and ridge 28.
[0050] FIG. 9 is a partial cross-sectional view taken along the
groove axis of FIG. 8. It is evident from FIG. 9 that horn 233 is
unitary with matrix 240. Cutouts 248 and 250 each include a
transition volume 251, 253 having a depth that increases as
distance from groove 252 increases. Each cutout 248, 250 has an
arcuate cross-section, with the arcs positioned convexly to each
other.
[0051] During use, first matrix 240 is placed over fastener strip
10, with groove axis 252, trough 24 and ridge 28 generally aligned.
Moveable anvil 230 includes a generally planar face 23 that
supports fastener strip 10 from below. Alternatively, fastener
strip 10 may be placed between two vibrators 220 (not shown) for
vibrating and pressing between two first matrices 240 (not
shown).
[0052] FIG. 9 depicts vibrator 220 as it initially impinges on
fastener 10. At this time, the tension on fastener strip 10 is
carefully controlled by a conventional tensioner. For example,
dancer roller assembly 216 depicted in FIG. 15 are suitable for
tensioning fastener strip 10. Additionally, as seen as FIG. 16,
fastener 10 has been preheated by means of preheaters 217 and 219
to a temperature greater than room temperature and less than the
melting range or index of the thermoplastic material that composes
fastener 10 so as to remove, curl, and facilitate molding. As
pneumatic assemblies 202 (best seen in FIG. 6) apply calibrated
force to elevated anvil 230, the pressure that face 246 applies to
fastener strip 10 and the distance between face 246 and face 236
are carefully controlled. Preferably, face 246 presses upon
fastener strip 10 with a force of from 10 to 500 pounds per square
inch, ideally about 70 pounds per square inch. Preferably, face 246
and face 236 are not permitted to touch.
[0053] Vibrator 220 vibrates a portion of fastener strip 10 so as
to generate internal friction within fastener strip 10, causing a
portion 212 of fastener strip to become relatively more malleable.
The temperature of the vibrated portion often increases during the
vibrating. The pressure exerted by first matrix 240 tends to
displace some of the malleable portion in predictable directions.
For example, the depth of transition volumes 251, 253 and the depth
of groove 252 are calculated to displace a certain amount of the
malleable portion along groove 252, and displace a certain amount
of the malleable portion to or from the transition volumes 251,
253. Malleable material is also displaced transversely from the
groove axis as first matrix 240 flattens the region between cutouts
248, 250.
[0054] First matrix 240 is properly shaped to press and extrude the
displaced material in desired directions and, also, to mold and
retain the displaced material at desired destinations. Preferably,
the material displaced by first matrix 240 forms plug 160 or dam
180 of fastener strip 100 of the present invention; most preferably
plug 160. The result is a product having first shape 242, depicted
in FIG. 10, which significantly differs from the shape of fastener
strip 10.
[0055] Referring now to FIG. 10, first shape 242 includes flattened
portion 142, elongated hump 144 and a curved portion abutting end
130 of reclosable portion 120. Hump 144 corresponds to the shape of
groove 252. The curved portion corresponds to the shape of
transition volumes 251, 253. First shape 242 facilitates sealing,
and is sufficiently similar to the shape of fastener strip 10 so as
to be reproducibly molded by vibrating and pressing in a single
stage, as described above.
[0056] FIG. 11 is a perspective view of second stage 276, third
stage 296, fourth stage 316 and fifth stage 320 of apparatus 200.
Each of these stages is located a short distance from each other at
locations 278, 298, 318 and 320, respectively. Each of these stages
respectively has a dedicated pneumatic piston and cylinder assembly
261, 281, 301, 321 that forces an anvil down upon the fastener
strip. Second stage 276, third stage 296, and fourth stage 316 are
pressing stages that utilize dies 266, 286, 306 to support the
fastener strip from beneath.
[0057] As with first stage 256, the temperature, pressure, time and
distance between die faces 266, 286, 306 and respectively
associated anvils are carefully controlled. The optimum combination
of these factors depends on the precise nature of the fastener
strip and the specifications of the finished seal portion. However,
die temperatures of about 350 to about 400 degrees F. and pressures
of about 60 to about 80 pounds per square inch have been employed
successfully in pressing stages 276, 296, 316 with a pressing time
of about half a second. Fifth stage 320 cools the finished product,
which is fastener strip 100. Also shown in FIG. 11 is conveyor belt
321 which intermittently advances fastener strip 100. Conveyor belt
321 is preferably constructed of a silicone blend to resist heat,
but also has a surface 323 which sticks to or retains fastener
strip 100 when it is heated sufficiently to be tacky. The fastener
strip when it is heated in malleable-like taffy, but the tension on
conveyor belt 321 and thereof fastener strip 100 is carefully
controlled preferably by a servo motor. As a result, the fastener
strip 100 remains in its original size and configuration, except
where it is shaped by die faces 266, 286 and 306.
[0058] FIG. 12 shows die 264, which is typically utilized at second
stage 276. Die 264 includes generally planar face 266 and a pair of
oppositely located arcuate cutouts 268, 270, which are positioned
with their convex sides facing each other. As compared to cutouts
248, 250 of first stage 256, cutouts 268, 270 are positioned closer
together and have greater radii. As seen in FIG. 11, silicone
coated stripper plate 264A is positioned between face 266 and
fastener strip 100, to facilitate separation of face 266 from
fastener strip 100 after compression. Consequently, only stripper
plate 266 of die 260 touches first shape 242. Pressing die 264
against first shape 242 causes flattened portion 142 and hump 144
to become further flattened. Additionally, die 264 displaces
material toward adjacent end 130, which ultimately forms dam 180.
Preferably, plug 160 is not significantly affected by die 264.
[0059] The action of die 264 on first shape 242 produces second
shape 262, which is depicted in FIG. 13. Flattened portion 146 is
thinner, as compared to hump 144. Preferably, dam 180 is formed
primarily by material displaced by die 264 and extends from
backings 122 and 126 and partially surrounds plug 160.
[0060] Overall flatness of the finished fastener strip, such as
fastener strip 100, is an important requirement for many fastening
applications. Third stage 296 works with die 284, as depicted in
FIG. 14, to generally flatten backings 122, 126 of fastener strip
100 and ensure that reclosable portion 120 and planar portion 140
are coplanar. Face 286 defines longitudinal channel 284, which is
significantly deeper and wider than groove 252. Accordingly, die
284 has relatively little effect on plug 160 or dam 180. Third
stage 296 produces third shape 282, which is similar to the shape
of fastening strip 100. Again, a stripper plate 284A is utilized to
facilitate separation after compression.
[0061] Die 304 has a generally planar face 306 with cutouts 308,
310 and is similar to die 262, except that cutouts 308, 310 are
positioned closer together and have greater radii than cutouts 268,
270. When pressed against third shape 282 under proper conditions
of pressure, temperature and spacing, die 304 completes planar
portion 140 and produces fourth shape 302, which is the shape of
fastener strip 100. Fifth stage 316 cools fastener strip 100 so
that it may be more conveniently transported and packaged. Again, a
stripper plate 304A is utilized to facilitate separation. After the
shaping of fastener strip 100 is completed, conveyor belt 321
advances the fastener strip to a second conveyor 101. As it cools,
fastener strip 100 no longer adheres to belt 100, so it can be
removed without stretching or distortion. The lack of tension on
fastener strip 100 is crucial to maintaining the dimensions and
configuration of the fastener strip 100. Fastener strip 100 is then
advanced by second conveyor 101 to a take up reel 103, again
maintaining minimum tension and compression of the fastener strip
100.
[0062] The invention also provides a method for sealing portions of
a thermoplastic fastener strip, which process will now be
described. The invention is not limited to the described process,
starting materials, equipment or products.
[0063] A prior art fastener strip, such as fastener strip 10 is the
starting material. A tensioning assembly, such as a dancer roller
assembly 216 depicted in FIG. 16, is suitable for tensioning
fastener strip 10. Dancer roller assembly 216 applies a precise
tension to fastener strip 100, as will be appreciated and
understood by practitioners. Fastener 100 is preheated by
preheaters 217 and 219 to a temperature warmer than room
temperature and cooler the melting point or index of the
thermoplastic material that composes fastener strip 100. For
example, a temperature in the range of about 120.degree. to about
130 degrees F. is often useful. Control of temperature and tension
prevents distortion of the fastener strip 100. Fastener strip 100
is then advanced by conveyor belt 321.
[0064] A portion of fastener strip 10 is vibrated between a
vibrator and an anvil at a first stage. The vibrating is effective
to increase the malleability of the portion, as compared to the
malleability of fastener strip 100 before vibrating. A first matrix
is pressed against the malleable portion to produce a first shape.
The pressing may be carried out simultaneously with the vibrating.
Second matrix, third and fourth matrices are subsequently pressed
against the malleable portion to produce a second shape, a third
shape and a fourth shape, respectively. Each pressing is
accomplished in a separate stage at a different location. The
fastener strip may be heated before or during the stages. The
finished fastener strip is cooled to room temperature and may then
be wound on a spindle or roll for later use by the bag converter,
again at a precise tension to avoid distortion.
[0065] The vibrator oscillates in contact with the fastener strip
at a frequency of about 10,000 to about 100,000 cycles per second,
preferably at least about 20,000 cycles per second. As described
above, the vibrator includes an actuator, a resonator or horn, and
a first matrix, which is unitary with the horn. The vibrator is
positioned over the fastener strip and an anvil is positioned under
and in contact with the fastener strip. Preferably, the vibrator
does not touch the anvil. Alternatively, two or more vibrators may
be brought in to contact with the fastener strip with the fastener
strip positioned between the vibrators.
[0066] While only a few, preferred embodiments and aspects of the
invention have been described above, those of ordinary skill in the
art will recognize that these embodiments and aspects may be
modified and altered without departing from the central spirit and
scope of the invention. Thus, the preferred embodiments and aspects
described above are to be considered in all respects as
illustrative and not restrictive, the scope of the invention being
indicated by the appended claims, rather than by the foregoing
description, and all changes which come within the meaning and
range of equivalency of the claims are intended to be embraced
herein.
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