CA2560512C

CA2560512C - Monofilaments with split ends

Info

Publication number: CA2560512C
Application number: CA002560512A
Authority: CA
Inventors: Robert L. Rackley
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1997-04-24
Filing date: 1997-04-24
Publication date: 2009-07-07
Anticipated expiration: 2017-04-24
Also published as: CA2560512A1

Abstract

Monofilaments with split ends. The monofilaments can be used to form toothbrush bristles having flagged or feathered tips. Each of the monofilaments has 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 monofilaments. Preferably, the monofilaments each have a diameter in a range of 0.0025 to 0.012 inches, and have a hexalocular or an octalocular configuration. The monofilaments are manufactured by extruding a plurality of thermoplastic polymeric streams, rotating a plurality of cutting blades above 1000 rpm, and placing a plurality of cutting blades in contact with end portions of the plurality of thermoplastic polymeric streams to form split ends.

Description

MONOITLEIMENTS WITH SPLIT ENDS
BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates generally to monofilaments, and more 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 fonn 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 brushes, 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 monoflament 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 diameter in a range of 0.0025 to 0.012 i.nches, wherein the nionofilanient has a hexalocular, an octalocular, or a near circular shape.
In addition, this invention relates to a method of manufacturing extruded nionofilarnents 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 nionofilaments to fonn 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. lb 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 capillaiy used to extrude the nionofilament 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 monofilarnent 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 nionofilameiit 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 extrude the monofilament of Fig 5a.
Fig. 6a is a front view of a spinnerette 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 rnonofilament havirg split ends.
Fig. 7b is a front view of a structure having three blades mounted on a conimon shaft for use in splitting the ends of the monofilaments of the present ulvention.
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 feathered bristles.

Fig. 10 is a side view of a plurality of bristles with split ends that produce a plurality of soft fine tips.
Fig. 11 is a side view of a comparison of a feathered toothbrush bristle which spreads-out on a tooth surface witli 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 guni of a patient.
Fig. 13 is a cross-sectional view of an octalocular nionofilarnent in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
OF THE PRESENT INVENTION
Wluch 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 5a, examples of a monofilament having a hexalocular shape are shown. Such shapes were achieved through an extrusion process using the respective spinnerette capillaries of Figs.
1 b, 2b, 3b, 4b and 5b. Such monofilaments were prepared by the fusion of six polymer streams. Each of these monofilaments 10 include a plurality, of voids and a plurality of weld or fusion lines. The voids result in a void content of between 5 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 (polyhexamethylene sebaccamide), and nylon 6I2 (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 overal] maximum cross-sectional dimension, of the brush bristles of the present invention is in the range of 0.0025 to 0.012 inches (0.064 to 0.3 mm).
The bristles of the present invention are preferably forined by extruding six or more individual streams of polymeric material from a spinnerette including the spinnerette capillaries shown in Figs lb, 2b, 3b, 4b, and Sb, and joining the streams to form a single filament. A spinnerette, such as the one shown in Figures 6a and 6b, includes a plurality of spinnerette capillaries.
With reference to Flgs. lb, 2b, 3b, and Sb, in the extrusion of the thermoplastic polymer streams, the polymer is extruded through 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 nionofilament is quenched and then drawn as generally described, for example, in U.S. Pat. No. 2,418,492<

After extrusion and quencliing of the monofilament, the filament is oriented by stretching to iniprove the longitudinal strength. In addition, the filament can be subjected to other treatments to improve physical properties, such as treatment with saturated steam as described in U.S. patent No. 3,595,952, The fila.ment may be heat set after drawing for good bend recovery.
The 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 for brush manufacture. The individual bristles are then gathered into bundles, the bundles are tufted 'uito 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 splitting 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 Figs. 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 on the depth of the split desired, although it has been found that 1/8 to 1/4 of an inch is preferable.
Essentially,.by spinning the blades at a high rate of speed and placiiig the blades in contact with the bristle tips, a fast and violent bristle cutting action is achieved, thereby causing optimal bristle splitting.

It has also been found that by rotating the blades at or near the natural frequency of a monofilament will obtain optimal splitting of the bristles.
The natural frequency of a uniform beam is Natura.l Frequency = A FEI

where A=3.52 for a cantilever beam;
d I= area rnoment of inertia 64 5 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 revolutioris per minute by dividing by 2r and rnuitiplying by 60 seconds per ininute.
With reference to Fig. 8, a graph of the natural frequency for a 612 monoGlarnent bristle with a 550,000 psi modulus and various lengths and diameters is shown.

The monofilatnent bristles of the present invention produce a larger number of smaller ends ("flags") than previously known monofilament bristles of the same diarneter. 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 thaii end rounded to give a plurality of smaller ends that scrub the guigival area more effectively. It has also be found that the rnore dense area achieved by such flagged ends scrub major tooth ar=eas 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 toothbnrsti having a plurality of feathered bristles is shown. Witli 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 ttie present invention also produce a greater atid deeper penetration at the gum line for better cleaning without 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 gumline 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 surfaces, and thus holds toothpaste in contact with teeth. Such an arrangement also provides a unique cushioning effect at the tips whicli adds extra softness to the brush. Such softness reduces bleeding of the gums during brusliing. 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 liaving 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 percetitage of the cross-sectional area occupied by the voids in the monofitaments 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 ici an optiinal splitting of brushes 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 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 monofilainent, 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. lb, 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.
Wiff 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:

% Void Content = 10 0 (1- weight of hollow bristlel weight of solid bristle Although the present invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinar}, skill in the art are also intended to be within the scope of the preseiit invention.
Accordingly, the scope of the present invention is intended to be limited only by the claims appended thereto.

Claims

What is claimed is:

1. A brush monofilament having a portion with a plurality of internal fusion lines and at least four voids, wherein said voids occupy between 5 and 20% of a cross-sectional area of the monofilament.

2. The brush monofilament of claim 1, wherein said monofilament is a toothbrush bristle.

3. The brush monofilament of claim 1 or claim 2, wherein said monofilament is made of a thermoplastic polymeric material.

4. The brush monofilament of claim 3, wherein said thermoplastic polymeric material is selected from the group consisting of nylon 610, nylon 612, a polyamide, and polybutylene terephthalate.

5. The brush monofilament of any one of claims 1 to 4, wherein said brush monofilament has six voids.

6. The brush monofilament of any one of claims 1 to 4, wherein said brush monofilament has eight voids.

7. The brush monofilament of any one of claims 1 to 6, wherein said brush monofilament has a near circular outer shape.

8. The brush monofilament of claims 1 to 7, wherein said brush monofilament has an outer diameter in a range of 0.0064 to 0.030 cm.

9. A toothbrush comprising a plurality of brush monofilaments of any one of claims 1 to 8.