U.S. patent application number 10/649385 was filed with the patent office on 2004-03-04 for method and apparatus for making articles having bristles.
Invention is credited to Chambers, Jeffrey Allen, Edwards, Mark Stephen.
Application Number | 20040040643 10/649385 |
Document ID | / |
Family ID | 26928620 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040040643 |
Kind Code |
A1 |
Edwards, Mark Stephen ; et
al. |
March 4, 2004 |
Method and apparatus for making articles having bristles
Abstract
Methods and apparatus for making elongated articles are
disclosed. One method includes feeding at least one base string
along an axis, wrapping at least one monofilament around the axis
to produce a number of monofilament wraps per length of base string
which are transported by the base string, bonding the wraps to the
base string with ultrasonic energy, and cutting the wraps at a
point downstream of where the wraps are bonded to the base string.
The result is an article having two rows of monofilament segments
connected to the base string.
Inventors: |
Edwards, Mark Stephen;
(Hockessin, DE) ; Chambers, Jeffrey Allen;
(Hockessin, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
26928620 |
Appl. No.: |
10/649385 |
Filed: |
August 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10649385 |
Aug 27, 2003 |
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09956689 |
Sep 20, 2001 |
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6660117 |
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60235155 |
Sep 22, 2000 |
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Current U.S.
Class: |
156/174 ;
156/175; 156/72 |
Current CPC
Class: |
Y10T 428/23979 20150401;
A46D 1/04 20130101; A46B 5/06 20130101 |
Class at
Publication: |
156/174 ;
156/072; 156/175 |
International
Class: |
B65H 081/00 |
Claims
1. A method for making an elongated article comprising the steps
of: feeding at least one base string along an axis; wrapping at
least one monofilament around the axis to produce a number of
monofilament wraps per length of base string which are transported
by the base string; bonding the wraps to the base string; and
cutting the wraps at a point downstream of where the wraps are
bonded to the base string to thereby form an article having two
rows of monofilament segments connected to the base string.
2. A method for making an elongated article comprising the steps
of: feeding a base string along a first support; wrapping at least
one monofilament around a second support to form a plurality of
loops; feeding the loops transversely over the at least one base
string; pressing the loops into contact with the base string,
whereby the loops are transported by and with the at least one base
string; and bonding the wraps to the base string to form an article
having two rows of monofilament loops connected to the base string.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/235,155, filed Sep. 22, 2000 and U.S. Patent
Application No. 90/956,689, filed Sep. 20, 2001, of which the
present application is a division.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to articles made of
polymeric monofilaments, and more particularly, to methods for
making brush bristles and bristle sub-assemblies, and apparatuses
for making brush bristles and bristle sub-assemblies.
[0003] Brush making involves the attachment of bristles to a brush
body. In one type of brush, known as the "solid block/staple set,"
a solid block acting as the brush body is drilled, molded, or
otherwise worked to form an array of holes, Individual tufts are in
individual holes and secured to the block by wire staples, plugs or
other anchoring means. Hand drawn brushes are similar except that
the tufts are secured by drawing them through the holes with an
elongated strand.
[0004] Another type of brush employs a "ferrule and monofilaments"
technique for attaching the bristles to the brush body. A cluster
of monofilaments and cavity creating spacers are inserted into a
ferrule and set with a binding resin. Ferrule brushes, such as the
paint brush, are used to primarily apply liquid or viscous
solutions.
[0005] In metal strip brushes, fibers are held in a "U" shaped
channel of a metal strip by an anchoring wire, string, or
monofilament. The channel is then crimped closed to mechanically
clamp the proximal end portions of the monofilaments and anchor
wire within the strip. Once formed, the brush-strips can be
attached to brush bodies or otherwise shaped for specific
applications.
[0006] Fused brushes are those in which polymeric tufts are fused
directly to a brush body that is preferably made of the same
material. One variation of fused brushes employs ultrasonic welding
to secure polymeric fibers directly to a base.
[0007] With respect to the toothbrush, it is now commonplace to
employ nylon monofilaments that are grouped together to form
"bristle tufts." Each bristle tuft is typically arranged in a
circular cluster, and a complete bristle head includes a matrix of
bristle tufts arranged in rows or other patterns. The folded
proximal bases of the bristle tufts are typically embedded and held
in place by an anchor wire that extends across the field of the
tufts and into the polymeric material that forms the head portion
of the toothbrush body, while the distal ends extend upwardly
therefrom, often terminating in a common plane. A more recent
tufting method employs the process of cutting the tuft of
monofilaments to the desired length, heat fusing the proximal ends
and embedding the fused proximal ends into the polymeric material
of the toothbrush head.
[0008] More recent innovations in the toothbrush art have included
bristle tufts cut to provide differing lengths to provide an array
of shorter and longer tufts to achieve a desired action on the
user's teeth. In some tufts the monofilaments are of differing
length. While these improvements can result in better functional
aspects of the toothbrush, few innovations have been made over the
years in techniques for manufacturing the toothbrush head; this is
particularly evident in the manner in which bristles are assembled
with the brush body.
[0009] In all types of known brushes, the assembly process can
represent a substantial portion of the cost of manufacture since
individual bristle filaments have to be held in a desired grouping
and then bound to the brush body in a manner that ensures that the
bristle filaments do not become detached during use. Also,
recycling becomes more problematic for brushes which employ metal
staples or other combinations of different classes of materials
(plastics and metals, for example) in one structure. In general,
the presently known techniques for forming monofilament bristle
articles are not suitable for continuous feed, high through-put
production, where labor requirements are relatively slight.
[0010] A machine for making pile articles useful in the field of
floor coverings is described in U.S. Pat. No. 5,547,732 to Edwards
et al. As seen in FIG. 1 herein, the Edwards et al. machine takes a
continuous yarn 20, fed from a source 22 through a tensioner 24,
and passes it through a hollow guide conduit 26 that is rotated
about its center. The conduit 26 is bent to guide the yarn 20 to a
position at 28 radially displaced from the center of rotation. A
mandrel 30 is supported at the center of rotation and accepts the
yarn 20 which is would around the mandrel 30 as it is fed from the
conduit at 28.
[0011] A support strand 32 is fed into the mandrel 30 at 34 and
through a passage 36 in the mandrel 30. The strand 32 exits the
passage at 38 where it is guided to the outside of the mandrel 30
along ridge 40. The mandrel may have two, three, four or more such
ridges where the yarn wrapping on the mandrel bends at an included
angle between 0 and 180 degrees, preferably less than 90 degrees.
The yarn 20 is wrapped over the strand 32 which is pulled along the
mandrel 30 by a windup 41. Additional strands or yarn carriers,
such as 42 and 44 propelled by motor driven pulley 46, are used to
transport the yarn along the other ridges of the mandrel.
[0012] The yarn 20 is wrapped under some tension so it conforms to
the mandrel 30 and is frictionally engaged with the strand and
carriers for transporting before and after bonding. The wrapped
yarn and strand travel together along the mandrel and under
ultrasonic horn 48 where sufficient energy is imparted to the yarn
that it is compacted, the multifilaments are fused together, and
the yarn 20 is fused to the support strand 32. The mandrel ridge
acts as an ultrasonic anvil surface. The wrapped yarn, now bonded
to the strand, continues along the mandrel to cutter 50 which
severs the yarn to define individual bundles of yarn having opposed
ends with each bundle attached to the strand intermediate the
ends.
[0013] In the aforementioned U.S. Pat. No. 5,547,7321, the yarn 20
is described as a multifilament, crimped, bulky, plied-twisted yarn
that has been heat set to retain the ply-twist. The yarn 20 is a
thermoplastic polymer, such as nylon, polypropylene, etc. FIG. 2
shows a typical elongated pile article or tuftstring 52 made with
the machine described with reference to FIG. 1. The tuftstring 52
includes a plurality of bundles of yarn 54 bent into "U" shape and
attached to the support strand 32 at the inside of the "U." Each
bundle defines a pair of upstanding legs or tufts 56 and 58. The
tuftstrings have many advantages of manufacture in making floor
coverings, and in particular, the machine produces continuous
lengths of tuftstring at low cost, and with minimal labor.
SUMMARY OF THE INVENTION
[0014] An object of the present invention is to provide a method of
making bristle articles and bristle sub-assemblies which lends
itself to high productivity and low cost production.
[0015] Another object of the present invention is to provide a
method of making bristle sub-assemblies which are capable of
expanding brush design beyond the range possible with current
tufting techniques. Another object of the present invention is to
provide a method of making a bristle
[0016] sub-assembly for a brush in which individual filaments are
positionally fixed with respect to each other prior to connection
to a brush body.
[0017] Still another object of the present invention is to provide
a method of making bristle sub-assemblies which can be permanently
connected to the brush body or, alternatively, detachably connected
for subsequent replacement, thereby avoiding wastefully discarding
otherwise functional brush bodies.
[0018] These and other objects are met by providing a method for
making an elongated bristle article which comprises the steps of
feeding a base string along an axis, wrapping at least one
monofilament around the axis, thereby producing a number of
monofilament wraps per length of base string which are transported
by the base string, bonding the wraps to the base string, and
cutting the wraps at a point spaced from the bonding point thereby
form an article having two rows of monofilaments connected to the
base string.
[0019] An apparatus for making continuous lengths of bristle
articles of the present invention produces bristle sub-assemblies
which include either a plurality of monofilament segments or
monofilament loops connected to a base string, or combinations of
loops and segments. Each monofilament or monofilament loop is
connected transversely to the base string to form a pair of loop
segments extending outwardly from opposite sides of the base string
to form two rows of loop segments.
[0020] Other objects and features of the invention will become more
apparent from the following detailed description when taken in
conjunction with the illustrative embodiments in the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic, perspective view of a known apparatus
for making elongated pile articles useful in the art of making
floor coverings;
[0022] FIG. 2 is a perspective view of a pile article made with the
apparatus of FIG. 1;
[0023] FIG. 3 is a side elevational view of an apparatus for making
bristle sub-assemblies according to the present invention;
[0024] FIG. 4 is an enlarged transverse cross-sectional view taken
along line 4-4 of FIG. 3;
[0025] FIG. 5 is an enlarged transverse cross-sectional view taken
along line 5-5 of FIG. 3;
[0026] FIG. 6 is a top view of a bristle sub-assembly made
according to the present methodology and using the apparatus of
FIG. 3;
[0027] FIG. 7 is an end view of the bristle sub-assembly of FIG.
6;
[0028] FIG. 8 is a longitudinal sectional view taken along line 8-8
of FIG. 7;
[0029] FIG. 9 is a side elevational view of an ultrasonic horn used
in the apparatus of FIG. 7;
[0030] FIG. 10 is a side elevational view of the ultrasonic horn of
FIG. 9 turned 90;
[0031] FIG. 11 is a bottom view of the ultrasonic horn of FIG.
9;
[0032] FIG. 12 is an end view of a bristle sub-assembly of the
present invention and showing the band angle of variance for the
bristles of a given row as .theta..sub.1;
[0033] FIG. 13 is an end view of a multifilament tuftstring of the
prior art and showing the band angle of variance for the tufts of a
given row as .theta..sub.2;
[0034] FIG. 14 is a top, partial view of an apparatus for making
looped monofilament bristle sub-assemblies according to another
embodiment of the present invention;
[0035] FIG. 15 is a side view of the apparatus of FIG. 14;
[0036] FIG. 16 is a top view of a looped monofilament bristle
sub-assembly made with the apparatus of FIG. 14;
[0037] FIG. 17 is an end view of one of the monofilament loops
formed with the apparatus of FIG. 14;
[0038] FIG. 18 is an end view of the monofilament loop of FIG. 17
after ultrasonic heating;
[0039] FIG. 19 is a side elevational view of an apparatus for
making bristle sub-assemblies according to another embodiment of
the present invention;
[0040] FIG. 20 is an enlarged, partial side view showing detail of
one of the string guide grooves of the apparatus of FIG. 19;
[0041] FIG. 21 is an enlarged, partial cross-sectional view showing
detail of the base string residing in the groove with a wrap of
monofilament overlying the groove; and
[0042] FIG. 22 is a view similar to FIG. 21, showing the locking
string being pressed into the groove of the base string.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Referring to FIG. 3, an apparatus 60 for making elongated
bristle sub-assemblies includes a stationary mandrel 62 having four
substantially planar outer surfaces, an interior with at least one
hollow passage, and open opposite axial ends. Four base strings 64,
66, 68 and 70 from four sources 72, 74, 76, and 78, respectively,
are fed from the upper end of the mandrel 62, through the interior,
and out the lower end.
[0044] At the lower end, the base strings are guided by guide
pulleys (not shown) to run along respective grooves in the four
outside corners of the mandrel in the upward direction. The base
strings are caused to translate through the apparatus by servo
drive rollers 80 and drive motor (not shown). A take-up mechanism
81 (only one illustrated) collects elongated bristle sub-assemblies
for further processing or end use. Thus, the pulling force imparted
by the servo drive rollers 80 pays out base strings from their
respective sources and causes the base string to move axially
downwardly through the mandrel and axially upwardly along the
outside of the mandrel 62.
[0045] A rotor 82 driven by a motor 84 through a belt 83 is
provided at the lower end of the mandrel 62. The rotor 82 has a
hollow interior and a hollow arm 85 through which a monofilament 86
passes. The monofilament 86 is supplied from a source 88 and passes
between pinch rollers 87. As the motor 84 rotates the rotor 82, the
monofilament 86 is wrapped around the mandrel 62 to form a
plurality of wraps 89 along the lower end of the mandrel 62. The
upward translation of the base strings causes the wraps 89 to
advance upwardly since the wraps are in frictional contact with the
base strings.
[0046] A servo-circuit is established with the motor of the drive
rollers 80, the motor of the pinch rollers 87 and the motor 84. A
command from controller 90 dictates the speed-10 of the drive
rollers 80, control signals from the controller 90 proportion the
speed of the motor 84 and thus the rotational speed of the rotor
82, and the tension applied the monofilament during wrapping by
controlling the speed of the pinch rollers 80 and 87. Any circuit
and appropriate programming may be employed to ensure a desired
through-put speed and number of wraps per inch on the mandrel.
[0047] The wraps pass beneath four ultrasonic heat sources mounted
on each of the four corners of the mandrel. Only two of the four
ultrasonic heat sources, 91 and 92, are shown in FIG. 1. The heat
sources 91 and 921 include ultrasonic horns 94 and 96,
respectively. The ultrasonic heat sources apply energy to the
monofilaments that causes them to fuse with the respective base
strings in a manner described more fully below. At point spaced
from the horns, a cutting device 98 cuts the monofilament 86 to
thereby for a bristle sub-assembly as a continuous length of
material that is taken up on a spool 81 or other means associated
with the take up mechanism.
[0048] The base strings pass through tubes (not shown) provided in
the interior of the mandrel 62. Proper positioning going into the
tubes, and proper pay off from the supply sources, can be ensured
by strategically located eyelets and/or pulleys, some of which are
shown in FIG. 3. At the lower end of each tube, a pulley is
provided to re-direct the respective base strings upwardly along
the outer corners of the mandrel 62. The center lines of the axles
for the pulleys are positioned appropriately so the strand leaves
the groove of the respective pulleys aligned with the center line
of the groove provided along the ridges or corners of the mandrel
62.
[0049] Although the embodiment of FIG. 3 shows four base strings
and one monofilament, any number of base strings between one and
four could be used. Also, the rotor could carry more than one
monofilament so that several could be wrapped simultaneously.
[0050] The mandrel 62 is supported by a support frame (not shown)
at the end opposite the rotor 82. Shorter mandrels are preferred,
since longer mandrels have a greater moment arm, defined by the
frame attachment point and the point at which the wrapping
monofilament lays onto the mandrel and will, wobble or oscillate as
the wrapper pulls against the mandrel while laying the monofilament
wraps on the mandrel face. As seen in FIG. 4, four shims 100, 102,
104, and 106 are provided axially on respective planar surfaces of
the mandrel 62. The base strings 64, 66, 68, and 70 are shown in
the interior of the mandrel 62, for their downward movement, and
along respective corners of the mandrel 622 for their upward
movement. A "wrap" 108 of monofilament is shown to contact the
shims and the base strings simultaneously.
[0051] Each shim creates a ridge for the distance defined by the
length of the shim in the plane defined between two corners of the
mandrel. Spacers are placed under the shims to provide the desired
relief from the surface plane of the mandrel. This desired relief
is determined through experimentation and is a function of
monofilament wrap density (wraps per inch), filament material
(e.g., nylon, polyester, or polypropylene) and filament diameter.
The shims are relatively short, permitting the wrapped
monofilaments to fall off and relax as they are transported to the
ultrasonic heat sources positioned just downstream from the shims
and at each of the mandrel corners.
[0052] As seen in FIG. 5, the cutter mechanism includes four
rotating cutter wheels 98A, 98B, 98C, and 98D which cut each wrap
108 at four equi-spaced intervals. The wraps are cut after the
monofilament is fused to the base strings by the ultrasonic horns.
After cutting, four bristle subassemblies 108, 110, 112, and 114
are formed.
[0053] FIGS. 6-8 illustrate details of one bristle sub-assembly,
such as bristle sub-assembly 108, which includes the base string 66
and a plurality of monofilament segments 116 connected to the base
string 66. The monofilament segments 116 are preferably connected
to the base string 66 substantially perpendicularly, as shown in
FIG. 6, with the base string 66 dividing each monofilament segment
116 into first and second opposite side legs 118 and 120 which
extend outwardly from the base strings 66 in two rows. In the
illustrated embodiment the legs 118 and 120 are of substantially
equal length. Also, while the base string 66 is shown to be
substantially normal or perpendicular to the monofilament segments
116, in other embodiments the monofilament segments could be placed
at a variety of angles relative to the base string 66, depending on
the brush characteristics desired for the finished product.
[0054] As seen in FIGS. 7 and 8, the legs 118 and 120 are acutely
angled relative to the horizontal plane A-A to form a V-shaped
structure. The polymeric monofilament segments 118 and 120 are
substantially linear and flexible so that when deflected or bent,
spring restoring force is generated to return them to a linear or
substantially linear disposition. The heat imparted by the
ultrasonic horns provides a fusion zone 122 where the individual
monofilament segments 118 and 120 are integrally connected to each
other, if wrapped shoulder to shoulder or overlapping, and/or to
the base string 66.
[0055] The monofilament used in the present invention may be made
of several different thermoplastic polymeric materials, including
aliphatic polyamides, aromatic polyamides, polyesters, polyolefins,
styrenes, fluoropolymers, polyvinylchloride (PVC), polyurethane,
polystyrene and styrene copolymers. Nylon is particularly suitable
for several applications, and the following are examples of nylons
that could be used: 6,12 nylon, 4 nylon, 6 nylon, 11 nylon, 12
nylon, 6,6 nylon, 6,10 nylon, 6,14 nylon, 10, 10 nylon and 12,12
nylon and other nylon co-polymers. The base strings could be made
of the same or similar materials as those used for the
monofilament.
[0056] The monofilament used in the present invention is very
different from the tufted, twisted multi-filaments used to make
tuftstrings of the prior art. The differences in physical features
changes the parameters for ultrasonic welding. Ultrasonic welding
involves high frequency vibration energy. In general, a weld is
generated at the interface between two thermoplastic monofilaments
(or strings) as a result of frictional heating due to the
excitation from the ultrasonic sources described above which are in
contact with one or both of the individual strings.
[0057] Yarn strings, as used in the prior art for making flooring
materials, comprises a bundle of individual filaments. As
ultrasonic energy is applied to a yarn system of filaments, heat is
generated at the interface of all contacting filament surfaces. The
yarn bundle is therefore generating heat within the yarn bundle and
at the interface between the yarn and the base string to which the
attachment is desired. In contrast, for a monofilament, the heating
is localized at the small surface area of the monofilament where
contact is made between the base string and monofilament pair.
[0058] A typical yarn is comprised of many (usually 32-100 or more)
filaments, each having an equivalent diameter of 4-23 denier per
filament, and is often plied and/or twisted to form an even greater
bundle of filaments. Therefore, under the ultrasonic horn surface
of the prior tuftstring apparatus, a typical yarn will generate
heat throughout the bundle of filaments. This heating causes
significant deformation of yarn and individual filament structure
and alteration of the characteristic properties of the yarn in the
weldment area. In fact, the ability to distinguish the individual
filaments comprising the yarn under where ultrasonic bonding has
occurred is difficult and at times impossible.
[0059] A typical monofilament used in the present invention is
2-200 mils in diameter and is not plied or twisted to form bundles.
When ultrasonically bonding a monofilament to the base string, the
surface contact is limited to the small area where the wrap
filaments and the base structure overlap and are compressed into
each other under the pressure of the ultrasonic horn. The result is
that ultrasonic heating becomes localized to the surface at the
desired interface between the monofilaments and base strings. This
small area surface heating and the relatively large mass of the
monofilament as compared to the filaments in a yarn bundle,
preserves much of the physical properties characteristic of the
wrap monofilament prior to bonding. When controlled properly, the
monofilament tufts are sufficiently strong so as not to be
considered frangible.
[0060] Ultrasonic horns typical of those used in the tuftstring
machine were tested for the preferred bristle article made of 6,12
nylon monofilament and were found to be problematic. The bonding
end of these horns are configured with a radius designed to
compress the yarn bundles and then bond the yarn filaments to the
strand all within 2 inch of horn face. The bonding force,
controlled by the pneumatic pressure regulated to an air cylinder
of a flexure assembly (not shown), is distributed over the face of
the horn. Some of the applied force is spent to overcome the
spring-like forces in the matrix of the yarn bundle through the
compression stage of the horn face. Once the fibers are compacted
into intimate contact with one another, the remaining force is
applied to transferring the ultrasonic energy to the fibers. This
occurs in a very narrow zone at the longest tip of the horn.
[0061] The use of monofilaments in the present invention
necessitates different ultrasonic heating conditions. First, the
monofilaments are solid or essentially solid materials, for
example, which need not be compacted to drive energy dissipating
air out of the materials (they could be hollow core or lobed
structures). Second, because the monofilaments are essentially
solid material, and also because they often have circular
cross-sections, the contact area between the wrap monofilament and
the horn, as well as the wrap monofilament and the base strand, is
very small. Assuming little or no compression, they are only
tangentially in contact. The tuftstring horns performed
unsatisfactorily since forces and ultrasonic energy were being
concentrated in these tangential contact areas causing the wrapped
monofilaments to be severed or as known in the art as
"clipped."
[0062] Lower energy levels and lower bonding forces were found to
overcome the clipping problem. At low energy levels, 20-25 watts,
low bonding force, 7-8 psi air pressure, and line speeds of 2-3
yards per minute (ypm), bond strength of the wrap monofilament to
the base strand was very low (0.10-0.20 lbs.) but clipping was
eliminated. As line speeds were increased to 5 ypm, the operating
window was lost. Bond strength deteriorated and any increase in
bond force or bond energy or both generated clipping.
[0063] To solve these problems, the ultrasonic horns 91 and 92 (as
well as the other two that are not shown in FIG. 3) were selected
to have a specific geometry that provided two features. As seen in
FIGS. 9-11, the horn 91 has a body portion 124 and a shank portion
126 which has two flat opposite side surfaces 128 and 130. An end
face 132 has a flat portion defined by the length "A" and a
radiused portion of length "B." Preferably, the length A is 0.25
inch, and the radiused portion has a length of about 0.50 inch.
Also, the width of the face is 0.25 inch.
[0064] The horn 91 is particularly suitable for use with
monofilaments, and differs from those used with tuftstrings in two
significant ways. First, the flat portion represents about 33% of
the face 132 of the horn 91, unlike the faces on tuftstring horns
which are continuously curved. Second, the face 132 is
significantly longer than for horns used optimally for tuftstring
applications. These combine to provide greater surface contact area
and better distribution of the forces and ultrasonic energy over a
larger area. Unlike the chiseling effect of the horns typically
used for tuftstring applications, the horn of FIGS. 9-11
distributes most of the force and energy over a 0.25 inch flat
surface.
[0065] The horn 91 thus has a longer duration of contact and
substantially uniform force with the monofilaments. By way of
example, assuming the contact width for an 8 mil monofilament is
equal to two times its diameter (with compression and partial
melting), the surface area in contact can be estimated. For the
ultrasonic horn 91, the contact area 0.25 inch.times.0.008 inch (8
mils).times.2=0.004 square inches.
[0066] For the ultrasonic horn typically used for the tuftstring
applications, assuming there is sufficient force to compress the
monofilament under the longest point of the horn, half its diameter
or 0.004 inches. Contact will be made with 15 monofilaments
assuming each of the monofilaments are in contact with each other
in the plane of the strand. Ignoring the fact that each sequential
trailing monofilament will be compressed less and therefore have a
smaller footprint, the surface area in contact is generously
estimated as 0.126.times.0.008.times.2=0.00- 02 square inches.
Thus, the long duration ultrasonic horn 91 distributes the bonding
force and energy over 20 times the area of the horn typically used
in tuftstring applications. This greater area enables increased
bristle sub-assembly production rate up to 5 ypm beyond the
capability of tuftstring horns.
[0067] In general, bonding conditions are defined by the several
variables. For a given combination of strand and monofilament wrap,
the primary variables are power (watts of energy delivered to the
material passing under the horn), bonding force determined in this
case by the pneumatic pressure supplied to an air cylinder (not
shown) associated with each of the ultrasonic sources, ultrasonic
amplitude, and stop gap setting.
[0068] When the monofilament wraps are shoulder-to-shoulder, as
seen in FIGS. 6-8, the interconnection of adjacent monofilaments
116 to each other in flow zone 122 may be relatively strong
compared to the interconnection of the base string to the flow zone
122 which is substantially composed of monofilament material. This
feature allows, in some applications, the removal of the base
string from the monofilaments anytime after thermal fusing.
Alternatively, the adhesion between the monofilaments and the base
string can be equally as strong as the adhesion between
monofilaments.
[0069] The monofilament wraps 89 seen in FIG. 3 can be disposed in
a single row, shoulder-to-shoulder, or the density can be varied
such that the adjacent monofilaments do not touch each other. Also,
the density may be such that a second or greater number of rows of
monofilaments are stacked upon each other. Where eight (8) mil
nylon monofilament is used, for example, a density of about 125
monofilaments per inch of base string can be achieved with a single
row, shoulder-to-shoulder monofilaments.
[0070] Referring to FIG. 12, the monofilament legs 118 and 120 are
acutely angled relative to the horizontal plane. The legs are each
generally disposed in a linear array or row having a band angle
.theta..sub.1, of relatively small deviation. Experiments have
shown that .theta..sub.1 varies between about 3 and about 10
degrees for 6,12 nylon of 8 mil diameter; and between about 5 and
about 10 degrees for 6,12 nylon of 6.7 mil diameter; and between
about 1 and 12 degrees for 6 nylon of 8 mil diameter.
[0071] In contrast, yarns used in the manufacture of floor
coverings have larger angular deviations as shown in FIG. 13 (the
"legs" in FIG. 13 representing an approximate center line for a
thickened multifilament). Experiments have shown that this angle,
.theta..sub.2, ranges between 12 and 35 degrees for 1375 denier,
2-ply multifilament nylon. This substantial difference is likely
due to the inability to precisely control the thermal history of
each filament within the bundle, forming a wider range of heat set
properties in the bond area and greater loss of position memory. In
addition, the dense packing compresses the bundled filaments,
creating forces on adjacent yarn filaments to displace them,
further contributing to the angular displacement.
[0072] The monofilaments used in the present invention have
elongation features that are significantly different from those of
the tuftstring multifilaments. The apparatuses described herein and
also in the aforementioned tuftstring apparatus operate at tensions
ranging lower than 100 grams. At that level, a thirty-six inch
strand of multifilament nylon having a 1375 denier diameter and a
2-ply construction elongates by about 11%, whereas monofilament
6,12 nylon having an 8 mil diameter elongates by less than 1%. This
property was identified as being critical in early development of
the process, requiring tension control changes and shim
modifications.
[0073] The guiding, processing and winding of elongated or
continuous bristle sub-assemblies made according to the present
invention, having a significant composition of monofilaments, is
greatly improved from those of yarns or yarns with a very low
monofilament count. Monofilaments, being noticeably more rigid than
a yarn or yarn-like bundle of filaments, act like springs or arms
and are an aid to controlling the orientation of the structure
after formation of the individual elongated pile articles.
Operability is significantly enhanced and equipment complexity is
reduced in delivering the elongated bristle sub-assemblies through
subsequent processes (if any) and to its final package form.
[0074] The stiffness of monofilaments is also a significant factor
with regard to the process of wrapping the filaments around the
mandrel and transporting the ladder structure on the mandrel.
Textile yarns or strings are very pliable and will easily wrap and
conform to the straight line, point to point, corners of a
structure such as a mandrel. This is not so with monofilaments
which have a stiffness factor as defined by the following
equation:
Stiffness=.alpha.Df.sup.4
[0075] where a is a constant and Df is filament diameter. The
higher stiffness of the monofilaments used herein creates high
forces at the corners of the mandrel which, if not compensated for,
will stall the transport of the ladder due to the excessively high
friction of the base string along the length of the mandrel to the
cutter mechanism.
[0076] To overcome this situation, the shims were configured in the
wrapping section of the mandrel to displace the monofilament from
the mandrel while it is layered onto the mandrel surface during
wrapping, the shims are short and terminate just beyond the
wrapping section to permit slack in the monofilament wraps, thus
lowering the friction between the backbone strands and the
mandrel.
[0077] Together with the shims, the wrap tension is closely
controlled so as not to excessively elongate (stretch) the
monofilament during the wrapping process. When excessive tension
and elongation is generated, the elastic memory of the monofilament
causes the monofilament to shrink to a new equilibrium state, but
not a relaxed state, as it transports off of the shims, where it
places cumulative forces on the base string until they can no
longer transport.
[0078] Some sample operating parameters for the apparatus of FIG. 3
are provided as follows: for polymeric base strings and
monofilaments, line speed is 5 ypm, wraps per inch are 30
wraps/inch, and the rotor speed is 5,400 rpm.
[0079] Referring now to FIGS. 14 and 15, an apparatus 134 according
to another embodiment of the present invention makes looped
monofilament sub-assemblies. The apparatus 134 includes converging
supports 136 and 138 which extend outwardly from, and are fixedly
mounted on, a substantially stationary base 140. The base 140 is
supported by the wrapper mechanism 142 suing bearings and magnetic
fields to prevent rotation. An arm of the wrapper mechanism 142
rotates about an axis "B" to pay out a monofilament 144 around the
supports 1336 and 138 to thereby form a plurality of wraps 146.
[0080] An anvil 148 is juxtaposed the distal end portions of the
supports 136 and 138 on the B axis. A base string 150 supplied from
a source (not shown) passes over a guide pulley 152 and is directed
into a guiding groove provided in a sloped forward surface 154 and
upper flat surface 156 of the anvil 148. The slope and relative
position of the forward surface 154 is selected to form a
sufficient angle between the base string and the loop ends which
maintains the sequence of crossing monofilament while passing under
an ultrasonic horn 158. The slope of surface 154 and the angle of
convergence for the two supports 136 and 138 are matched so as to
maintain tension across wraps 146. Drive belts 160 and 162 assist
in transporting the monofilament loops 146 toward the horn 158.
[0081] A looped monofilament bristle sub-assembly made by the
apparatus, of FIGS. 14 and 15 is shown in FIGS. 16-18. The bristle
subassembly 164 includes a base string 150 and a plurality of
continuously looped monofilaments 168. The looped monofilaments 168
are formed by taking the single strand of monofilament 144 and
forming a plurality of "ovals" along the length of the base string
150. As each oval moves under the horn 158 it is compressed to form
"figure eights" and is then bonded by ultrasonic welding to the
base string 150 so as to bisect the oval and create two individual
loops which provide first and second legs 168A and 168B on opposite
sides of the base string 150. The legs 168A and 168B extend
outwardly and symmetrically or non-symmetrically from the base
string in two rows.
[0082] In the embodiments employing a looped monofilament, it is
preferable to make the length of the loop legs (such as 168A and
168B) substantially greater than the maximum width of the loop
legs. It is also preferable that the monofilament strand is bonded
to the base string at the point where the legs of each loop
intersect the base string, so that a continuous length of looped
bristle sub-assembly can be cut into segments without causing
unraveling of the loops. While not preferred, the bond point may be
at other locations.
[0083] The monofilaments used in any of the above embodiments may
be co-extrusions of one or more polymers. Also, to achieve the
desired physical characteristics of the bristles, it has been found
that the preferred monofilaments are those having a diameter of 2
to 200 mils, and preferably 2 to 20 mils. In a particularly
preferred embodiment for the toothbrush, the monofilaments are 6-10
mils in diameter. Monofilaments of different diameters and/or
colors can be combined in one bristle assembly or sub-assembly to
achieve specific brushing characteristics and/or appearance. For
the base strings, a monofilament having a diameter of 2 to 200 mils
can be used, and in particular, 20 to 30 mils.
[0084] In embodiments using nylon for either the monofilament or
the base string, or both, a preferred nylon filament is sold under
the name TYNEX.RTM. and is manufactured by E. I. Du Pont De Nemours
and Company of Wilmington, Del. USA. TYNEX.RTM. is a 6,12 nylon
filament made from polyhexamethylene dodecanamide. It has a melting
point of between 208 and 215 C and has a specific gravity of
1.05-1.07, and is available commercially in many shapes and
diameters.
[0085] Monofilaments and/or base strings suitable for use in the
present invention can have shapes other than circular
cross-sections, and may be hollow or have voids in their
cross-section. Embodiments described above show circular
cross-sectional shapes for the base string and monofilaments.
Either or both the base string and monofilaments could have oval or
other shapes. In any shape, the preferred thicknesses for the base
string and monofilaments are selected to provide a level of
functionality to the individual brush applications.
[0086] With respect to the base string, the preferred embodiments
described above show a single strand of monofilament material.
However, the base string could be a bundle of monofilaments having
at least one of the monofilaments made of polymeric thermoplastic
material.
[0087] The polymeric monofilaments used for bristles in the various
embodiments described above can have other additives. For example,
the polymeric monofilaments could include 0-50% by weight particles
having functional and/or aesthetic quality. One example would be
particulate material that provides a color feature that would
enhance the visual appearance of the bristles. Other functional
particles could also be included such as anti-microbial additives
in the polymeric monofilaments. Other particulate materials or
coatings may be applied to or embodied within the monofilament such
as therapeutic agents or colorants, or other desirable additives.
Also, the monofilaments may be surface treated to provide desired
properties, such as to alter the frictional coefficient.
[0088] The embodiments described above require "connection" between
the monofilaments and the base string. In this context,
"connection" means that the monofilaments are attached to the base
string by a frangible joint formed by melting, adhesive bonding,
solvent bonding, or similar means. The degree of frangibility can
be controlled so that, if desired, the base string can be easily
separated from the monofilaments after bonding.
[0089] FIG. 19 illustrates apparatus 170 for making bristle
sub-assemblies in which heat fusion of monofilaments is avoided. In
this embodiment, a mandrel 172 has a rectangularly shaped lower
portion 174, a rectangularly shaped upper portion 176, and a
tapered, medial portion 178. The lower portion 174 is wider than
the upper portion 176. The medial portion 178 provides a transition
zone between the upper and lower portions.
[0090] At the lower end of the mandrel 172, a rotor 180 is caused
to rotate by a drive motor (not shown). The rotor 180 is hollow to
receive at least one monofilament 182 supplied from a source (not
shown). As the rotor 180 rotates, the monofilament 182 wraps around
the lower portion 174 of the mandrel 172 to form a plurality of
wraps 184. A pair of pulleys 186 and 188 are disposed at the lower
end of the mandrel 172. The pulleys 186 and 188 are in alignment
with respective grooves 190 and 192 provided longitudinally on the
opposite sides of the mandrel 172. FIG. 20 shows groove 190 in side
194 of the mandrel 172.
[0091] The mandrel 172 is positionally fixed by mounting to an
appropriate frame structure (not shown). A pair of interlocking
guides 196 and 198 are positioned next to respective grooves 190
and 192 at the medial portion 178 of the mandrel 172. Two
monofilament base strings 200 and 202 are fed downwardly into the
mandrel from sources (not shown). The base strings 200 and 202 pass
over pulleys 186 and 188, respectively, and are thereby re-directed
upwardly into respective grooves 190 and 192.
[0092] Two monofilament locking strings 204 and 206 are fed to the
interlocking guides 196' and 198, respectively, from sources (not
shown). Pulleys 208 and 210 provided respectively on the
interlocking guides 196 and 198 re-direct the locking strings 204
and 206 towards the grooves 190 and 192. As the base strings 200
and 202 transport the wraps 184 upwardly, the interlocking guides
196 and 198 force the locking strings together with respective base
strings, to thereby lock or sandwich the wraps between the locking
strings and the base strings. Once locked together, a slitter 212
provided on opposite sides of the mandrel 172 (only one of which is
shown) cuts the wraps 184 causing them to spring outwardly and form
two bristle sub-assemblies having a two-part base string and a
plurality of generally straight monofilament segments. The taper of
the medial portion 178 is established to coincide with the length
of monofilament 182 accumulated in the groove 214 by the
interlocking of locking string 204 into base string 200.
[0093] As seen in FIGS. 21 and 22, the wraps 184 (one visible) are
wrapped around the mandrel 172. In FIG. 21, the base string 200 has
a groove 214 which is open at the top and runs the length of the
mandrel 172. The wraps 184 cross over the open top, and when they
pass under the interlocking guide 196, the locking string 204 is
pressed into the groove 214 thus locking the wrap 184 between the
two strings, as shown in FIG. 22.
[0094] Any appropriate shape of the groove 214 and complementary
shape of the string 204 can be provided to ensure mechanical
interlocking of the two strings. This mechanical interlock is
achieved by using polymeric materials that are resilient to permit
passage of the upper string into the groove of the lower string.
After the two strings are interfitted and the wraps cut by the
slitter, the monofilaments will bend upward to form two rows of
legs as in the other embodiments. The two base strings are disposed
respectively below and above the monofilaments and in alignment
with each other and thus interlock with each other to capture the
monofilaments therebetween.
[0095] The bristle sub-assemblies made according to FIGS. 19-22
preferably use the materials described in the previous embodiments,
along with additional non-thermoplastic and non-polymeric materials
that may be used in the absence of heat, adhesive, or solvent
fusion.
[0096] In the various embodiments described herein the non-looped
monofilaments have been described as linear and parallel, It is
possible to use polymeric monofilaments that are non-linear,
however, such as in the case of monofilaments that have been
crimped wavy or otherwise conditioned to a predisposed non-linear
formation.
[0097] Although the invention has been described with reference to
several particular embodiments, it will be understood to those
skilled in the art that the invention is capable of a variety of
alternative embodiments within the spirit and scope of the appended
claims.
* * * * *