COEXTRUDED MONOFILAMENTS

This application claims the benefit of U.S. Provisional Application o. 60/005,542, filed October 18, 1995.

BACKGROUND OF THE INVENTION

1 . Field of the Invention

This invention relates to coextruded monofilaments which may be used, for example, in bristles for toothbrushes.

2. Description ofthe Related Art

Bristles made from nylon 6,12 or from polyester are typically circular in cross section with the ends ofthe bristles being well rounded. When used in toothbrushes, the rounded ends have been preferred because using bristles with rounded ends have a lower tendency to damage soft and hard oral tissue.

SUMMARY OF THE INVENTION

This invention relates to a coextruded monofilament having a core material made of a first resin and a sheath material made of a second resin, with the second resin being different from the first resin, and a pocket formed in the end ofthe monofilament.

This invention also relates to a method of forming a pocket in the end of a coextruded monofilament by chemical or mechanical means, or a combination of chemical and mechanical means.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a view in cross sectional view in elevation of a coextruded monofilament made in accordance with this invention;

Figure 2 is a top plan view ofthe coextruded monofilament of Figure 1 ;

Figure 3 is a view in elevation of a conventional monofilament; Figure 4 is a top plan view ofthe conventional monofilament of Figure 3;

Figure 5 is a scanning electron microscope photograph at a magnification of 318x of a pocket formed in the end of a coextruded monofilament of this invention;

Figure 6 is a 50x magnified photograph of a pocket formed in the end of a coextruded monofilament of this invention;

Figure 7 is a scanning electron microscope photograph at a magnification of 242x of a pocket formed in the end of a coextruded monofilament of this invention;

Figure 8 is a magnified photograph of a pocket formed in the end of a coextruded monofilament of this invention;

Figure 9 is a scanning electron microscope photograph at a magnification of 158x of a pocket formed in the end of a coextruded monofilament of this invention; and

Figure 10 is a magnified photograph at a magnification of 419x of a pocket formed in the end of a coextruded monofilament of this invention.

DETAILED DESCRIPTION

This invention relates to a coextruded monofilament of a core material made from a first resin, and a sheath material made from a second resin, wherein the second resin is different from the first resin, and wherein the coextruded monofilament has a pocket formed in the end ofthe coextruded monofilament. The purpose of this pocket is to hold a material, such as a cleaning material, so that the cleaning material in the monofilament has a longer contact with the surface to be cleaned than if the

cleaning material was on the rounded end of a conventional monofilament. For example, if the coextruded monofilament is used in a toothbrush bristle, the pocket will hold toothpaste in contact with a tooth longer than a coextruded monofilament with a conventional rounded end. A used herein, the term "core" refers to the central portion ofthe coextruded monofilament as examined at a cross section. As used herein, the term "sheath" refers to an outer coating layer or layers over the core material on a coextruded monofilament.

Examples of combinations of sheath and core materials include a sheath material of nylon 6; 6,6; 6,10; 6,12; 6,9; 11; 12; copolymers of 6/6,6; 10,10 nylon; and mixtures thereof, and a core material of a copolyester ether such as that sold under the trademark Hytrel® by E.I. du Pont de Nemours and Company of Wilmington, Delaware.

Other examples of combinations of sheath and core materials include a sheath material of a nylon, a polyester, especially polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), a polyurethane, polyvinylidene chloride, or mixtures thereof, and a core material of polyvinyl chloride, polyvinyl acetate copolymer, polystyrene, or mixtures thereof. There is no limitation on the shape ofthe cross section of either the core or the sheath ofthe coextruded monofilament. Either or both may be circular, triangular, square, pentagonal, hexagonal, oval, lobate, triocular, tetraocular or any other shape.

The coextruded monofilament may be made by conventional methods known in the art, such as is disclosed in U.S. Patent No. 5,313,909. It is important that the core and sheath be made from different materials in order to obtain all the benefits ofthe present invention.

The pocket in the monofilament may be made by mechanical, or by chemical means, or by a combination of mechanical and chemical means. One method for making the pocket in the end ofthe monofilament is to abrade the ends ofthe monofilament with, for example, a fine stainless steel brush in order to form the pocket. An abrasion resistant additive such as polyethylene, silicone oil, or mineral additives such as talc or titanium dioxide may be added to the sheath material so that the core material is preferentially abraded by the mechanical means.

Another method of forming the pocket is by bringing the end ofthe monofilament into contact with a solvent which will dissolve or degrade the core material, but not the sheath material, in order to form the pocket in the end ofthe monofilament. The time the monofilament is in contact with the solvent and the temperature ofthe solvent both affect on the depth ofthe pocket.

If the core material is a copolyester ether, then a suitable solvent is methylene chloride, antine, carbon tetrachloride, chlorosulfonic acid, ethyl chloride, ethylene dichloride, hydrazine, 37% hydrochloric acid, perchloroethylene, phenol, nitric acid, sulfuric acids, or 11 OF steam. Most of these solvents have little effect on nylons especially for short exposure times.

If the core material is a polyvinyl chloride, polyvinyl acetate copolymer, polystyrene, or mixtures thereof, then a suitable solvent is acetone.

Other examples of sheath and core polymers are a sheath polymer of nylon 6,10 or nylon 6,12 with a core polymer of nylon 6 or nylon 6,6. For such a coextruded monofilament, dilute hydrochloric acid is a suitable solvent to be used to form a pocket in the end ofthe coextruded monofilament.

Another example of a coextruded monofilament of this invention is a sheath polymer of nylon 6,12 and a core polymer of nylon 6, 10. A 90% formic acid solution is a suitable solvent to be used to form a pocket in the end ofthe coextruded monofilament. Another way to form the pocket in a coextruded monofilament is to add a ultraviolet light inhibitor to the sheath polymer but not the core polymer, and expose the coextruded monofilament to intense ultraviolet light to preferentially degrade the core in the end ofthe coextruded monofilament. The coextruded monofilament may then be subject to further mechanical treatment, if necessary, to form the pocket to desired proportions.

The depth ofthe pocket should be from about 0.001 to 0.250 inches (0.025 to 6.4 millimeters).

The diameter ofthe coextruded monofilament should be from about 0.001 to 0.100 inches (0.025 to 2.5 millimeters), and the ratio ofthe area of

the core to the area ofthe coextruded monofilament should be from about 0.1 to about 0.9, with a preferred ratio being from about 0.25 to about 0.75. The monofilaments may be grouped together in tufts, and attached to a brush. Examples ofthe types of brush in which these monofilaments may be used include a toothbrush, and a paintbrush, but this invention is not limited to any specific type of brush, and may be used in any type of brush. The ends ofthe coextruded monofilaments of this invention may be flagged by conventional means. The term "flagging" means that the ends of the inventive coextruded monofilaments having pockets form in their ends may be split by conventional means from the end ofthe monofilament to the bottom ofthe pocket to form what are known as "flags" in the ends of the monofilament. These flags include a concave portion ofthe pocket and provide the same benefits as the coextruded monofilaments having pockets in the ends that are not flagged.

EXAMPLES Example 1

Coextruded monofilaments having a core of Hytrel® 4056 copolyester ether and a sheath of nylon 612 were made using conventional methods. The monofilament was conditioned at 125°C by backwinding it through a conditioner on a spinning line and then processed into hanks. The cross sectional area ofthe core was 25% ofthe total cross sectional area ofthe monofilament.

These coextruded monofilaments were tufted into a tuft toothbrush and the ends ofthe monofilaments were subjected to conventional end rounding.

A fine stainless steel brush having 0.003 inch stainless steel bristles was used to abrade the ends ofthe coextruded monofilaments in the tufts for about 2-3 minutes to form pockets in the end ofthe monofilaments as is shown in Figure 7.

The stainless steel brush was 3 inches (76.2 mm) in diameter and was rotated at 1200 rpm. About 0.5 inches (12.7 mm) interference between the stainless steel brush and the bristles was used. Hence the sides and ends ofthe bristles were abraded but since the core material was a

softer resin a small 0.002 inch deep pocket was formed in the end ofthe bristle.

Example 2 - Comparative Example A coextruded monofilament having a core of PET and a sheath of nylon 6,12 was made as in Example 1, except that the conditioning temperature was 175°C. The cross sectional area ofthe core was 50% PET. A higher conditioning temperature was used than in Example 1 because the melt point ofthe Example 1 core was 150°C and the PET core of this Example had a higher melt point of 255°C so a standard nylon 6,12 conditioning temperature was used.

The bristles were processed into toothbrushes like Example 1 and were subjected to a similar mechanical treatment with a stainless steel brush. However in this example no pockets were formed because the PET core was not preferentially abraded. Hence the bristle tip had a profile like that as shown in Figure 3. A combined mechanical and chemical treatment would be required to form a pocket in the end ofthe coextruded monofilament having a sheath-core combination of this Example.

Example 3

A coextruded monofilament having a sheath of nylon 6,12 and a core of PBT was made as in Example 2. The cross sectional area of the sheath was 70% ofthe cross sectional area ofthe monofilament.

Toothbrushes were made from the coextruded monofilaments as in Examples 1 and 2, and the ends ofthe monofilaments were abraded with a stainless steel brush for about 2-3 minutes. As may be seen in Figure 5, the monofilaments had an appearance similar to the monofilaments of Example 1 although the pocket formed was not as deep as in Example 1. The 70% core did cause a wider pocket to be formed than the pocket in Example 1.

Example 4

Coextruded monofilaments were made as in Example 1 and were bundled together into approximately two inch diameter bundles. The ends ofthe coextruded monofilament in the bundle were abraded with the

same stainless wire brush as used in Example 1, except that the abrasion took place for about 15 minutes. The center sections ofthe coextruded monofilaments were indented as in Example 1 to form a pocket which demonstrated that the coextruded monofilaments of this invention may be processed as bundles as well as toothbrushes.

Example 5

Toothbrushes having coextruded monofilaments were made as in Example 1, but were treated chemically rather than mechanically. The ends ofthe coextruded monofilaments of a toothbrush were exposed to methylene chloride for about 12 minutes, which is a strong solvent for Hytrel® copolyester ether but is not a solvent for nylon 612. The cores of the ends ofthe coextruded monofilaments were dissolved to form pockets, and the coextruded monofilaments were subjected to mechanical abrasion for about 1-3 minutes to smooth the ends ofthe monofilaments. Photographs ofthe bristles are shown in Figure 6 and Figure 8.

Example 6

A bundle of coextruded monofilaments was made as in Example 4, and the ends ofthe monofilaments were treated by dipping the ends into a shallow bath of methylene chloride for about 10 minutes to form pockets in the ends ofthe monofilaments. The ends ofthe monofilaments were subjected to mechanical treatment with the stainless steel brush of Example 1 to round the ends ofthe monofilaments. These bristles are shown at a magnification of 158x in Figure 9 and a magnification of 419x in Figure 10. By comparison ofthe depth ofthe pocket to the width it was estimated that the pocket formed in this Example was about 0.004 inches (0.1 mm) deep.

Example 7 - Comparative Example

A coextruded monofilament was made having a nylon 6, 12 sheath and a nylon 6, 12 core with the cross sectional area of both the sheath and the core being 50% ofthe cross sectional area ofthe monofilament. The monofilament was extruded and conditioned as in

Example 3, and processed into brushes. The ends ofthe monofilament were abraded with a stainless steel brush as in Example 3. No pocket was formed in the ends ofthe monofilaments, and the ends had a normal rounded appearance such as is shown in Figure 3.