WO1998000048A1

WO1998000048A1 - A brush

Info

Publication number: WO1998000048A1
Application number: PCT/US1997/010664
Authority: WO
Inventors: David Victor Cann
Original assignee: The Procter & Gamble Company
Priority date: 1996-06-28
Filing date: 1997-06-19
Publication date: 1998-01-08
Also published as: GB9613724D0

Abstract

A brush comprising a bristle bearing portion (8) having a plurality of bristles (10) extending therefrom, wherein one or more of the bristles are fastened into the bristle bearing portion (8) by an anchor (1) having a surface and at least one formed protrusion (2) extending from the surface. The protrusions (2) serve to improve the retention of the bristle tufts (9) within the brush head, which is particularly useful when the tufts are being inserted into soft materials. The anchors can be made by a conventional process adapted to introduce cuts in the anchor at the same time as it is separated from a continuous wire.

Description

A BRUSH

Field of the Invention

The present invention relates to a brush comprising an anchor for holding bristles into the brush, more particularly to a brush comprising an an anchor having one or more protrusions or barbs extending therefrom to improve its retention in soft materials.

Background of the Invention

Bristles are fastened into brushes, such as toothbrushes, in a number of different ways. Those described in the art include stapling, fusion and injection moulding of the brush head around the bristles.

The most commonly practised method for toothbrushes, and one of the most efficient, is the stapling method. A small flat staple, or anchor, is driven into a tuft hole in the toothbrush head. As the anchor is driven in it pushes against the centre portion of a tuft of pre-cut bristles laid across the hole, simultaneously folding them into a 'U' shape and carrying the centre portion down into the hole. Thus a tuft is formed of U- shaped lengths of bristle wrapped around the anchor and with their free ends extending outwardly from the brush head. The anchor, which is primarily held in place by friction, secures the bristles in the brush head. For most purposes this is sufficient. Tufts of bristles in commercial toothbrushes produced by this method can withstand a pulling force of typically 20 to 25 Newtons before being pulled out of the brush head. Of course, significant reductions in this value can lead to individual bristles or even whole tufts being inadvertently pulled out of the brush head, for example if the free end of a bristle gets caught between the teeth, leading to considerable consumer dissatisfaction.

GB-A-2,247,400 discloses a toothbrush in which the cross-section of the tuft cavity narrows towards its base in order to improve retention of the anchored bristles.

Recently, brushes utilising softer material in the brush head than the conventional polypropylenes have been described. WO-A-96/02165, for example, describes a toothbrush having a resiliently flexible, bristle-bearing head which can use appreciable amounts of thermoplastic elastomers, such as Santoprene® and Thermoflex®, in the brush head. Ensuring good bristle retention in such softer materials presents considerable challenges.

It is accordingly an object of this invention to provide anchors, and brushes utilising them, which have improved retention in brushes. It is a further object of this invention to provide anchors suitable for securing bristles into soft materials.

It is yet a further object of this invention to provide a process for making such anchors.

Summary of the Invention

According to one aspect of the present invention there is provided a brush comprising a bristle-bearing portion having a plurality of bristles extending therefrom, wherein one or more of the bristles are fastened into the bristle-bearing portion by an anchor having a surface and at least one formed protrusion extending from the surface.

According to a second aspect of the invention there is provided a process for making a brush comprising the steps of: i) cutting a section of wire having a rectangular or trapezoid cross-section from the free end of a continuous feedstock; ii) prior to, at the same time as, or subsequent to step (i), forming the section of wire to make a generally planar anchor having one or more formed protrusions extending therefrom; and iii) thereafter inserting the anchor into the bristle-bearing portion of said brush so that it secures one or more bristles into the brush.

The anchors of the invention have improved retention in the brush and are particularly suitable for securing bristle tufts in soft materials.

Detailed Description of the Invention

The brush of this invention can be of any form where bristles are secured into a portion of the brush using an anchor. Preferably the brush is, or is intended for use in, a toothbrush having an elongated handle and, at one end thereof, a head having a bristle- bearing portion with a plurality of bristles extending therefrom. The bristle-bearing portion of the head can be integrally formed with the rest of the brush or it can, for example, be a replaceable insert.

Some or all of the brush will generally, though not necessarily, be made from conventional hard toothbrush materials such as plastics materials having a modulus of elasticity of at least about 500 MPa, more preferably at least about 1000 MPa. Suitable plastics materials include, for example, polyamides and polypropylenes. Polypropylene is preferred. Suitable polypropylenes include the material 'Polypropylene PM 1600' (marketed by Shell), having a modulus of elasticity (ISO 178) of 1500 MPa and Apryl 3400 MAI from Elf Atoche . Preferably, at least the handle of the brush and at least a supporting frame in the head will be so constructed.

However, some or even all of the brush can be made from a soft material, such as plastics materials, having a modulus of elasticity of less than about 500 MPa. Preferred examples of such soft materials include elastomers. The term 'elastomer' herein refers to a material which is both elastically compressible and elastically extensible. Brushes using such an elastomer in the head are described, for example, in WO-A-96/02165 where the elastomer is used to make the head flexible. The present invention is particularly useful where it is required to secure bristle tufts into a soft material, especially an elastomer rather than into a hard plastics materials such as described above. Being able to securely fasten bristle tufts into a soft material gives greater versatility in head design.

Suitable elastomers for use herein include thermoplastic elastomers with a Shore hardness of 30 - 80 and a modulus of elasticity of less than about 500 MPa, preferably less than about 300 MPa, such as Santoprene and Thermoflex. An exemplary elastomer is 'PTS Thermoflex 75' (marketed by Plastic Technologie Service, Germany), having a modulus of elasticity (ISO 178) of 100 MPa and a hardness (ISO 868) of 80 Shore A. Elastomers PL12291, PL12292, and PL12293 (marketed by Multibase, Saint Laurent Du Pont, France) are also suitable for use herein. In general, choosing the elastomer so that is based upon the same chemical class of polymers as material of the head segments assists in bonding the elastomer to the head segments. For example, when the head segments are made from polypropylene, the elastomer is preferably based upon polypropylene. The elastomers can optionally be mixed with a suitable plasticiser or foaming agent to make them more compressible.

Bristles for use herein can be made of any of the materials well known in the art. Suitable bristle materials herein include polyester and nylon, such as Dupont Nylon 612. The bristles are preferably of circular cross-section but can also be of other cross-sections including, but not limited to, rectangular, hexagonal and trilocular. Furthermore, the diameter and length of the bristles can vary within the usual dimensions known by a person skilled in the art. Cutting and end-rounding of the bristles can be done using any of the methods commonly known in the art.

Some bristles can be secured to the brush by means other than stapling, such as fusion. Fusion methods are described and reviewed in, for example, WO-A-93/ 12690. However, it is an essential requirement of the invention that one or more of the bristles are fastened into the bristle-bearing portion of the brush by an anchor as herein described. Bristles can be secured into the brush via the anchor by any suitable means. For example, the bristles can be physically entrapped in the brush by the anchor, without being fixed to it, as described in more detail below, or they can be attached to the anchor such as by tying or glueing. The anchor can be inserted into the brush using conventional methods. When soft brush materials are used then the anchor can be inserted directly into the material. Alternatively, and especially when hard materials are used it will may be necessary to create, for example by moulding, a slot or hole in the brush material to receive the anchor and associated bristle(s). The anchor should be inserted such that the protrusion(s) point away from the plane of the anchor towards the surface of the brush into which the tuft is inserted. In this way the anchor is still relatively easy to insert but is much more difficult to remove.

One or more bristles can be secured by the same anchor. As used herein, "tuft" refers to a set of one or more bristles secured into the bristle-bearing portion of the brush by the same anchor. The brush can comprise one or more of such tufts.

The brush according to the invention can include one or more tuft holes to facilitate insertion of such tufts into the brush, each tuft hole having a closed base and an open end and being of such a diameter that it can securely accommodate the number of bristles desired to be inserted therein without either excess free space or placing undue stress on the bristles. The tuft hole can have a slot diametrically across it, as is generally known in the art and commercially practised. The slot acts to reduce the probability of stress cracking upon insertion of an anchor. Preferably, bristle tufts are physically restrained in the brush by being folded around the anchor in the manner generally used for commercial brushes. That is, one or more bristles are pre-cut to the desired length and laid with their centre portions across a pre-formed tuft hole. A plugging tool then punches the anchor towards the base of the tuft hole, driving the bristles of the tuft down with it and folding them into a 'U' shape, of which the centre portion is carried down into the hole. Thus a tuft is formed of U-shaped lengths of bristle wrapped around the anchor and with their free ends extending outwardly from the bristle-bearing portion of the brush. Each bristle passes underneath the base of the anchor and is trapped between it and the base of the tuft hole.

The brush can include bristle tufts anchored into a hard plastics material as described above or into a soft material such as an elastomer, or there can be tufts anchored into each type of material. In certain embodiments the tuft may extend through both types of material, such as for example when a plastics material is coated with an elastomer. In these cases the anchor can lie wholly within one material or the other or across the boundary between the materials. Of course, the brush may include some tufts anchored with the anchors according to the invention and additional tufts secured using conventional anchors. For the purposes of manufacturing simplicity the anchors are preferably all according to the invention. The tufts can be round on cross-section or polygonal, such as rectangular. Typically they will be round and tufts suitable for use in a toothbrush will typically contain from about 10 to about 20 bristles, generating from about 20 to about 40 free working ends, and have a diameter of from about 1 to about 2 mm. The free ends of the bristles extend from the surface of the brush so as to form a working surface which is used for brushing. The working surface may be variously profiled as is known in the art.

The anchor of this invention is of generally planar form and is typically rectangular or trapezoid in shape, preferably rectangular. The anchor further includes one or more protrusions directed out of its plane. By "generally planar" is meant herein that the anchor is of substantially plate-like appearance, having one dimension, the thickness, which is generally smaller than the two dimensions, the length and the width, orthogonal to it. Thus the ratio of the width to the thickness is preferably from about 2: 1 to about 20: 1 , more preferably from about 4: 1 to about 10: 1 , typically about 6: 1.

Preferred anchors are rectangular in shape having a thickness of from about 0.15 to about 0.25 mm, preferably about 0.2 mm. Suitably, the length of the anchor is from about 1.5 to about 2.5 mm, preferably from about 1.5 to about 2 mm; and the width of the anchor is from about 0.9 to about 1.5 mm, preferably from about 1.0 to about 1.4 mm. It is envisaged that the anchor, excepting the protrusion (s), need not be completely flat, there may be some degree of curvature to it, for example residual curvature resulting from wire fed from a tightly wound spool. Such nonplanarity will generally be inconsequential compared to the formed protrusions.

In general, anchors according to the invention can be produced by any suitable process. For example, flat anchors can be punched from a sheet of metal and concurrently formed to create one or more protrusion (s) by an adapatation of the punching tool. Alternatively the protrusions can be post-formed in a separate step. In a typical process of the art for making known anchors, a strip of wire of rectangular cross-section is fed towards a cutting tool. The cutting tool cuts a length of wire from the free end of the strip, the length generally being slightly greater than the diameter of the tuft hole for which the anchor is intended. In a process according to the invention the conventional process is modified such that, prior to, after or, preferably, at the time as cutting the wire, protrusions are formed on the anchor. Thus the process according to the invention includes the steps of: i) cutting a section of wire having a rectangular or trapezoid cross-section from the free end of a continuous feedstock; ii) prior to, at the same time as, or subsequent to step (i), forming the section of wire to make a generally planar anchor having one or more formed protrusions extending therefrom; and iii) thereafter inserting the anchor into the bristle-bearing portion of said brush so that it secures one or more bristles into the brush.

Anchors according to the invention are preferably in the form of a planar strip having at least one formed protrusion extending from the surface. The formed protrusions can be of any size and shape. In preferred embodiments the protrusions are like barbs, being approximately triangular with a pointed apex which will engage with the material of the bristle-bearing portion of the brush. Preferably they are sufficiently large to give the anchor a Holding Index of at least 110, preferably at least 120, more preferably at least 130 and especially of 150 or more. The Holding Index is 100 times the ratio of the Average Tuft Pull Strength of the anchor to the Average Tuft Pull Strength of an anchor of the same general dimensions but not having the protrusions formed thereon. Measurement of Average Tuft Pull Strength is described below.

Tuft Pull Strength can be measured for individual tufts and the results can be used to estimate Average Tuft Pull Strength across a given brush type and stapling method. Tuft Pull Strength for a single tuft is determined as follows. The whole tuft is securely clamped within a collet chuck, suitably sized so that the whole of the tuft can be clamped securely with the collet chuck just touching the portion of the brush to which the tuft is attached. The collet chuck is connected through a digital force gauge to equipment capable of providing a smooth upwards pull to the tuft. A suitable gauge for the purpose is the DFS 100 available from John Chatillon & Sons Inc. of Greensboro, Ohio. The brush is securely and independently clamped so that the free end of the tuft points vertically upwards from the brush. If necessary, the brush clamp is adjusted laterally so that the collet chuck is aligned directly above the tuft to be pulled out. The force gauge is set to zero and is set to record the peak tensile force load. A smoothly increasing load is then applied to the tuft by pulling the collet chuck upwards. The operation is continued until the tuft is pulled out of the brush. The peak tensile force is recorded from the force gauge. This is the Tuft Pull Strength. To measure Average Tuft Pull Strength, all tufts on the brush which are anchored by the same anchor type into the same type of material are first numbered in sequence. A random number generator is used to select five of the tufts for individual measurement and the Tuft Pull Strength for each individual tuft is measured as above. If there are five or fewer tufts on the brush then all tufts are measured. The process is repeated for five separate, but like, brushs. Average Tuft Pull Strength is the numerical average of all peak tensile force values thus obtained.

Generally the protrusions will be sufficiently small that the anchor retains an overall impression of planarity and/or does not cause undue obstruction within the plugging process and does not unduly interfere with the bristles or with nearby anchors. A suitable anchor can be made by creating one or more cuts in one or more sides of a flat strip of metal wire and bending out tabs of metal at an angle to the rest of the strip. Conveniently this is done within the same operation as forming the anchor from a continuous feed of wire. Preferably the cut or cuts are made in such a direction that, when the anchor is inserted into the tuft hole, the sides of the tuft hole tend to compress the protrusion towards the general plane of the anchor. When an attempt is made to pull the anchor out, however, the protrusions engage the material of the tuft hole, increasing the retaining power of the anchor. The anchors are thus much easier to insert than to remove. Where there is more than one formed protrusion, the protrusions can lie to one side or both sides of the general plane of the anchor. In a preferred embodiment, there are two or more the protrusions with at least one protrusion extending from each side of the plane of the anchor. More preferably there are just two protrusions which extend to opposite sides of the plane of the anchor, the protrusions having points which are directed towards the open end of the tuft holes such that they will engage in the material of the brush if the anchor is pulled towards the open end of the tuft hole.

The protrusions are preferably at an angle to the general plane of the anchor of from 5° up to 90°, preferably from 10° to 70°, more preferably from 20° to 60°. The angle between the protrusion and the general plane of the anchor is defined by a straight line drawn from the tip of the protrusion to its base, at a right angle to the line of bending. The total area of the protrusions is preferably from about 0.3% to about 25% , more preferably from about 0.5% to about 20%, and especially from about 1 % to about 15% of the total area of the anchor.

The material from which the anchors are made can be the same as those used for making conventional anchors. Suitable materials include brass, nickel alloys and stainless steel alloys. A preferred material is an alloy of copper, nickel and zinc having a tensile strength of from about 650 to about 1000, preferably from about 750 to about 950 Nmπr².

The brush of this invention is suitable for use as or in a toothbrush, including an electric toothbrush.

The invention will now be described by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of an anchor according to the invention.

Fig. 2 is a side elevation of the anchor shown in figure 1.

Fig. 3 exemplifies a process according to the invention in which the protrusions are introduced at the same time as separating the anchor from a continuous wire.

Fig. 4 is a part section of a brush according to the invention showing the anchor in place in a tuft hole with the bristles wrapped around the base of the anchor.

Fig. 5 is a further part section more clearly showing the bristles wrapped around the base of the anchor.

Referring to Fig. 1, a generally planar anchor (1) includes two triangular protrusions (2) formed by creating cuts (3) and bending the resulting tabs so that they are at an angle to the plane of the anchor. In use, the anchor will be inserted into tuft holes along the direction X shown by the arrow.

Referring to Figures 1 and 2, a generally planar anchor (1) includes two triangular protrusions (2) formed by creating cuts (3) and bending the resulting tabs so that they are at an angle to the plane of the anchor. In use, the anchor will be inserted into tuft holes along the direction X shown by the arrow. The protrusions (2) lie at an angle θ to the plane of the anchor (1). The value of θ is preferably, though not necessarily, the same for each protrusion. The effective thickness of the anchor, as shown by the distance y between the two dotted lines, is now significantly greater than the thickness z of the strip from which the anchor is formed. The ratio of y:z, is preferably at least 1.3:1, more preferably at least 1.5: 1, and can be as high as 1.8: 1 or greater.

Referring to Figure 3, a cutting tool (4) is shaped so that it simultaneously severs the anchor (1) from the continuous wire (5), creates cuts (3) in the anchor and forms the protrusions (2) by pressing the wire against template (6) so that they bend away from the general plane of the anchor. A separate plugging tool (not shown) pushes the anchor along the direction X shown by the arrow. In Figure 4 the anchor (1) is located within a tuft hole (7) formed within a brush head (8). The anchor retains a tuft (9) of bristles which are wrapped around its base. The anchor has been inserted such that the points of the protrusions face the open end of the tuft hole and will engage with the material of the brush head if an attempt is made to remove the anchor, for example by pulling on the tuft (9).

In Figure 5 bristles (10) are wrapped around the base of the anchor (1) inserted in brush head (8). For the sake of clarity, both ends of the bristles are shown for only one bristle. It is to be understood that each bristle forms a U-shaped loop around th base of the anchor in this way.

Claims

WHAT IS CLAIMED IS:

1. A brush comprising a bristle-bearing portion having a plurality of bristles extending therefrom, wherein one or more of the bristles are fastened into the bristle-bearing portion by an anchor having a surface and at least one formed protrusion extending from the surface.

2. A brush according to Claim 1 wherein the anchor has a Holding Index of at least 110, preferably at least 120, more preferably at least 130.

3. A brush according to Claim 1 or Claim 2 wherein the anchor is in the form of a planar strip having at least one formed protrusion extending from the surface.

4. A brush according to Claim 3 wherein the anchor comprises two protrusions which extend to opposite sides of the plane of the anchor.

5. A brush according to any one of Claims 1 to 4 wherein the total area of the protrusions is from about 0.3% to about 25%, preferably from about 0.5% to about 20%, more preferably from about 1 % to about 15% of the total area of the anchor.

6. A brush according to any one of Claims 1 to 5 including one or more tuft holes, each having a closed base and an open end, the anchors being located at the base of the tuft holes and securing a tuft of the bristles in each tuft hole.

7. A brush according to Claim 6 wherein the anchor protrusions have points which are directed towards the open end of the tuft holes such that they will engage in the material of the brush if the anchor is pulled towards the open end of the tuft hole.

8. A process for making a brush according any one of Claims 1 to 7 comprising the step of inserting the anchor into the bristle-bearing portion of said brush so that it secures one or more bristles into the brush.

9. A process for making a brush having a bristle-bearing portion comprising the steps of: i) cutting a section of wire having a rectangular or trapezoid cross-section from the free end of a continuous feedstock; ii) prior to, at the same time as, or subsequent to step (i), forming the section of wire to make a generally planar anchor having one or more formed protrusions extending therefrom; and iii) thereafter inserting the anchor into the bristle-bearing portion of said brush so that it secures one or more bristles into the brush.

10. A process according to Claim 9 wherein the section of wire is formed at the same time as cutting it from the continuous feedstock.