Note: Descriptions are shown in the official language in which they were submitted.
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MONOFILAMENTS WITH SPLIT ENDS
BACKGROUND OF THE INVENTION
' 1. Field of the Invention
This invention relates generally to monofilaments, and riiore
particularly to monofilaments having split ends, which may be used for example
as
toothbrush bristles.
2. Description of the Related Art
Thermoplastic polymers have long been used to form brush
bristles in a wide variety of configurations. To increase the effectiveness of
these
brushes, the ends of such bristles have been split or "feathered" to provide a
soft
bristle tip. In the past, however, various difficulties have been encountered
in
splitting bristle tips.
In particular, various techniques have been used to split paintbrush
bristles to improve painting performance. Such procedures have been
particularly
suited to paintbrush bristles because long splits which propagate along a
large
portion (up to one inch) are particularly desirable. With certain bmshes,
however,
only splitting of the tips is desirable. For example, the length of a typical
toothbrush bristle is about (or less than) one half inch. If splitting were to
occur
along a large portion of a toothbrush bristle, the bristles would not be
sufficiently
rigid to adequately clean teeth. Accordingly, currently available splitting
techniques fail to adequately address difficulties associated with splitting
the tips of
toothbrush bristles and other bristles in which long splits are undesirable.
SUMMARY OF THE INVENTION
' This invention relates to a monofilament having a portion
with a plurality of internal fusion lines and at least four voids, wherein the
voids
comprise between 5 and 20 % of the cross-sectional area of the monofilament.
This invention also relates to a monofilament having a
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diameter in a range of 0.0025 to 0.012 inches, wherein the monofilament has a
hexalocular, an octalocular, or a near circular shape.
In addition, this invention relates to a method of
manufacturing extruded monofilaments having split ends, including the steps of
extruding a plurality of thermoplastic polymeric streams to form a plurality
of
monofilaments, spinning a plurality of cutting blades above 1000 rpm, and
placing
a plurality of cutting blades in contact with end portions of the
monofilaments to
form split ends. In one embodiment of the present invention, the blades are
spun
at or near the natural frequency of the monofilaments.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. la is a cross-sectional view of a hexalocular monofilament of
the present invention.
Fig. 1b is a cross-sectional view of a spinnerette capillary used to
extrude the monofilament of Fig la.
Fig. 2a is a cross-sectional view of another hexalocular
monofilament of the present invention.
Fig. 2b is a cross-sectional view of a spinnerette capillary used to
extrude the monofilament of Fig 2a.
Fig. 3a is a cross-sectional view of another hexalocular
monofilament of the present invention.
Fig. 3b is a cross-sectional view of a spinnerette capillary used to
extrude the monofilament of Fig 3a.
Fig. 4a is a cross-sectional view of another hexalocular
monofilament of the present invention.
Fig. 4b is a cross-sectional view of a spinnerette capillary used to
extrude the monofilament of Fig 4a.
Fig. 5a is a cross-sectional view of another hexalocular
monofilament of the present invention.
Fig. 5b is a cross-sectional view of a spinnerette capillary used to
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extrude the monofilament of Fig Sa.
Fig. 6a is a front view of a spinrlerette having a plurality of
spinnerette capillary locations.
Fig. 6b is a side view of the spinnerette of Fig. 6a.
Fig. 7a is a plan view of a blade used in manufacturing a
monofilament having split ends.
Fig. 7b is a front view of a structure having three blades mounted on
a common shaft for use in splitting the ends of the monofilaments of the
present
~vention.
Fig. 7c is a side view of the structure of Figure 7b.
Fig. 8 is a graph of the natural frequency for a 612 monofilament
with a 550,000 psi modulus and various lengths and diameters.
Fig. 9 is a perspective view of a toothbrush having a plurality of
fathered bristles.
Fig. 10 is a side view of a plurality of bristles with split ends that
produce a plurality of soft fme tips.
Fig. 11 is a side view of a comparison of a feathered toothbrush
bristle which spreads-out on a tooth surface with an ordinary solid tip which
provides only a single contact point.
Fig. 12 is a view of feathered toothbrush bristles which penetrate
deeper at the gum line for better cleaning without hurting the gum of a
patient.
Fig. 13 is a cross-sectional view of an octalocular monofilament in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMgpDIMENTS
OF THE PRESENT INVENTION
Which reference to the drawings, several embodiments of the present
invention, and their corresponding method of manufacture, will now be
described
° in greater detail. Which reference to Figs. la, 2a, 3a, 4a and Sa,
examples of a
monofilament having a hexalocular shape are shown. Such shapes were achieved
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thxough an extrusion procxss using the respective spinne~ette capillaries of
Figs.
16, 2b, 3b, 4b and 5b. Such monofilaments were prepared by the fusion of six
polymer streams. Fach of these monofilaments 10 include a plurality of voids
20
aced a plurality of weld or fusion lines. The voids result in a void content
of
between S and 20% of the cross-sectional area of the monofilaments.
The brush bristle of the present invention can be prepared from a
wide variety of thermoplastic polymeric materials including polyamides,
polyesters
and polyolefins.
Polyamides for use in brush manufacturing including nylon 6,6,
nylon 610 (polyhexaittethylene sebaccamide), and nylon 612 (hexamethylene,
diamine). Polyesters which have been found particularly well suited to bristle
manufacture include polybutylene terephthalate and polyethylene terephthalate.
A ,
polyolefin which has been found particularly well-suited to bristle
manufacture is
polypropylene.
The overall diameter, or overall maximum cross-sectional
dimension, of the brush bristles of the present invention is in the r~attge of
0.0025
to 0.012 inches (0.0b4 to 0.3 mm).
The bristles of the present invention are preferably formed by
extruding six or more individual streams of polymeric material from a
spinnerettc
including the spinnerette capillaries shown in Figs 1b, 2b, 3b, 4b, and Sb,
and
joining the streams to form a single filamens. A spinnerette, such as the one
shown in Figures 6a and 6b, includes a plurality of spinnerette capillaries.
With
reference to Flgs. 1b, 2b,.3b, and 5b, in the extrusion of the thermoplastic
polymer streams, the polymer is extruded thmugh openings 40. The fusion of the
streams results in fusion lines at the interface of the individual streams,
and the
formation of longitudinal voids along the fusion lines. The general
configuration
of the voids can vary widely.
. After extrusion of the thermoplastic polymer streams at elevated
temperatures into a single filament, the monofilament is quenched and then
drawn
as generally described, for example, in U.S. Pat. No. 2,41$,492.
. ,.
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After extrusion and quenching of the nnonot'dament, the filament is
oriented by stretching to iatlprove the longitudinal strength, Ir addition,
the
filament can be subjected to other treatments to improve physical properties,
such
as treatment with saturated steam as described in ~LJ.S, patent No.
3,595,952,"
The filament may be heat set after drawing for good bend recovery.
T'he heat setting can be carried out either in a gas such as by blowing hot
air over
.the filament, or a liquid bath such as by passing the filament through a bath
of oil.
The filaments are then cut into lengths suitable fvr brush manufacture. The
individual bdsiles are then gathered into bundles, the bundles are tufted into
brushes, and the brUShes are tipped and flagged by a procedure described
below.
With reference to Fig. 7a, a plan view of a cutting blade for use in
Sphtt~g the ends of the bristle of the present invention is shown. An
arrangement
of three such blades which are separated by spacers on a common shaft by about
3! 16 of an inch and which are approximately rotated from one another by 120
degrees is shown in pigs, 7b and 7c. It has been found that by rotating such a
blade above 1000 rpm and placing such a blade in contact with the bristles
achieves
a fine feathering (splitting) effect. In one example of the present invention,
the
blades are rotated at 30,000 rpm with a router motor. The interference between
the bristle and the blade is varied depending an the depth of the split
desired,
although it has been found that 118 to 1/4 of an inch is preferable.
Essentially,.by
spinning the blades at a high rate of speed and placing the blades in .contact
with
the bristle tips, a fast and violent bristle carting action is achieved,
thereby causing
optimal bustle splitting.
It has also been found that by rotating the blades at or near the
3a natural f
requency of a monofiJament wih obtain optimal splitting of the bristles.
~'he natural frequency of a uniform beam is
Natural FXeqc~ency = A
u~ a
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where A=3.52 for a cantilever beam;
_d4
I=area moment of inertia = ~ 64 '
E is Young's Modulus of Elasticity; ~, is mass per unit length; and 1 =
length.
The natural frequency is usually stated in radians per second which can also
be
expressed in revolutions per minute by dividing by 2a and multiplying by 60
seconds per minute.
With reference to Fig. 8, a graph of the natural frequency for a 612
monofilament bristle with a 550,000 psi modulus and various lengths and
diameters
is shown.
The monofilament bristles of the present invention produce a larger
number of smaller ends ("flags") than previously known monofitament bristles
of
the same diameter. The bristles exhibit excellent durability and cleanability,
and
are particularly useful as toothbrush bristles to produce remarkably soft,
fine tips.
By using such a technique, the bristles of the present invention are split
rather than
end rounded to give a plurality of smaller ends that scrub the gingival area
more
effectively. It has also be found that the more dense area achieved by such
flagged
ends scrub major tooth areas better by keeping toothpaste in contact with the
tooth
surface as well as achieving a softer feel when contact is made with soft
tissue in
the mouth.
With reference to Fig. 9, a perspective view of a toothbrush having
a plurality of feathered bristles is shown. With reference to Fig. 10, a
plurality of
bristles with split ends that produce a plurality of soft fine tips is also
shown.
These feathered filaments spread-out on tooth surfaces to provide a plurality
of
contact points, unlike ordinary solid tips which provide only one contact
point. A
comparison of these plurality of contact points to the single contact point of
a solid
tip is shown in Fig. 11. The fine feathered filaments of the present invention
also '
produce a greater and deeper penetration at the gum line for better cleaning
without
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hurting the gum line of a patient. Such deeper penetration at the gum line is
shown in Fig. 12. Accordingly, these soft filament tips carry sweeping power
action along with a beneficial interdental and gumiine cleaning. In fact, it
has been
found that such feathered tips reach farther between teeth, provide better
cleaning
coverage than ordinary soft filament tips because of the increase in contact w
surfaces, and thus holds toothpaste in contact with teeth. Such an arrangement
also
provides a unique cushioning effect at the tips which adds extra softness to
the
brush. Such softness reduces bleeding of the gums during brushing. Moreover,
such bristles have proven to be as hygienic as round filaments.
Although the present invention has been described with reference to
a hexalocular bristle structure having six voids, it has also been found that
an
octalocular bristle structure (having eight voids) provides numerous
beneficial
effects. Such an octalocular bristle is shown in Figure 13. It is also to be
understood that although six and eight streams have been used to achieve
hexalocular and octalocular structures, respectively, a greater number of
streams
may be used to produce additional structures having a corresponding greater
number of voids. The outer shape of such hexalocular, octalocular or other
structures may be manufactured so as to have a circular or near circular
shape.
Such a near circular outer shape is shown in Figure 13.
The percentage of the cross-sectional area occupied by the voids in
the monofilaments is determined by the size, location, symmetry and shape of
the
voids. It has been found that a certain level of hollow space (voids) will
result in
an optimal splitting of broshes having relatively short lengths, such as
toothbrushes. The voids optimally result in a void content of between 5 and 20
of the cross-sectional area of the monofilaments. With such brushes, if the
voids
are too small, such as the voids disclosed in U.S. Patent No. 5,128,208, any
feathering effect would result in broken bristle ends rather than in achieving
feathering. If the voids are too large, such as the voids disclosed in U.S.
Patent
No. 4,279,053, the bristle would feather easily, but the splits would likely
propagate down the bristle during use. With use as a toothbrush bristle, it is
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important that the tips of the bristles be split without the split propagating
down the
filament, either during manufacture or use by a patient. This may also be true
of
other types of brushes, depending on the particular use of the brush and/or
length
of the bristles.
With regard to the location of the voids within the monofilament, the
voids should be located about 1/2 way between the center and the outside edge.
It
has also been found that a longer and slender void achieves a greater flagging
effect than a rounded void.
It is also to be noted that the voids may be either symmetrical or
asymmetrical, although it is to be noted that an asymmetrical void may have a
natural curvature which is often undesirable in particular uses, such as a
toothbrush. Preferably, openings 40 of the spinnerette capilaries, as shown in
Figs. 1b, 2b, 3b, have a radius of curvature r in the range of 5 to 12 mils.
Openings 40 of the spinnerette capillary of Fig. 2b have an internal radius
(or
radius of curvature) of 9 mils, while the openings of the spinnerette
capillary of
Fig. 3b have a radius of 8 mils. Interestingly, use of the spinnerette
capillary of
Figure 2b results in the asymmetrical monofilament of Fig. 2a, while use of
the
spinnerette capillary of Fig. 3b results in the symmetrical monofilament of
Fig. 3a.
It is important to note that the asymmetrical monofilament of Fig. 2a is not
due to
problems in the symmetry of the design, but with the large size of the lobes.
With
large lobes, the streams are not knitted together as the center is pulled. As
such,
insufficient space is left for two of the streams to be pulled into the
monofilament.
The void content is determined on the basis of the weight of the
hollow bristle and the weight of a hypothetical solid bristle of the same
exterior
configuration, according to the following formula:
o Void Content = 1 ~ ~ (1- Weight of hollow bristle
weight of solid bristle
Although the present invention has been described in terms of certain
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preferred embodiments, other embodiments that are app2~rent to those of
ordinary
skill in the art are also intended to be withitt the scope of the present
invention.
AcCOrdingly, the scope of the present Invention is intended to be limited only
by
the claims appended thereto.
to
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