FIELD OF THE INVENTION

The present invention relates generally to filaments, in particular bristles and more particularly tooth-cleaning bristles comprising a surface structure with at least one surface recess such as dimples and pittings, and to a method for manufacturing such a filament. Moreover, the present invention also relates to a toothbrush head including a plurality of tufts of such bristles.

BACKGROUND OF THE INVENTION

In brushes, particularly toothbrushes, which may be used for cleaning and/or the application of liquids or powders, usually a plurality of bristles forming a bristle field with a plurality of bristle tufts, are provided for effecting the desired function. The bristles are often filaments, in particular monofilaments made of plastic and comprise a smooth, cylindrical circumferential surface. However, such filaments also may have non-circular cross-sections e.g. with a polygonal shape, a star shape, an oval shape etc.

For some applications, it is desired to give the circumferential surface a specific surface structure having a desired roughness and/or a relief-like structure having projections and recesses like dimples and pittings. Such a surface structure may have different functions. Basically, such a surface structure increases the surface area of the filament in comparison to a filament with a smooth, cylindrical surface. Such a surface area increase provides larger adhesive forces, so in cleaning applications, debris and dust particles are better held on the filament or, in other applications, liquids or powder may be better held on the filament. Furthermore, the surface structure may improve the cleaning efficiency in particular for plaque and other particles strongly bonded to the teeth. Particularly, by means of an appropriate surface structure the filament provides an abrasive effect. For some applications it is desired that the cross-section of the filament varies along the longitudinal extension of the filament.

Document DE 19818345 Al describes bristles for a toothbrush which bristles include a plastic core which is covered by a rubber-elastic cover layer. So as to achieve a high cleaning efficiency and an abrasive effect despite the soft surface, the said rubber-elastic cover layer is provided with a surface structure including dimples and pittings which are created in a hot pressing process.

Such a hot pressed surface structure has, however, some disadvantages. In particular, there are certain restrictions with regard to the achievable shapes of the surface structure. Usually, only shallow dimples and pittings with a smooth, rounded edge may be provided, what is also due to the rubber-elastic material of the cover layer which shows a certain resilience and tends to regain its original shape after a hot pressing treatment. Due to the shape limitations, such a surface structure may achieve limited abrasive effects and thus a limited cleaning efficiency only. Moreover, such a hot pressing process is rather complicated for filaments having a tiny diameter and thus rather expensive.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide an improved filament with a surface structure of the aforementioned type and an improved method for manufacturing such a filament which avoid the disadvantages of the prior art and further develop the latter in an advantageous way. More particularly, the present invention aims to provide an improved surface structure on a bristle achieving high cleaning efficiency without sacrificing easy and cost- efficient manufacturing.

According to the present invention, this objective is achieved by a method as defined in claim 1, a filament as defined in claim 9 and a toothbrush head as defined in claim 16. Preferred embodiments of the present invention are laid down in the dependent claims.

To achieve the aforementioned objective, it is suggested to produce the desired surface structure in an etching process and to provide the filament with at least one etch recess or etch pitting. To allow an easy control of the shape of such etch recesses or etch pittings, the filament body basically consists of a material which is soluble by a corrosive agent, wherein certain portions of the filament body's surface are shielded against contact by the corrosive agent whereas other portions are not shielded so that the corrosive agent may act on the soluble material of the filament body only in selected surface portions. According to the present invention, the method for manufacturing the filament is characterized in that a filament body with at least a portion made of a material soluble by a corrosive agent is covered in part with a cover layer stable to said corrosive agent such that a surface portion of said filament body substantially corresponding to said at least one surface recess is uncovered, and said filament body is contacted with said corrosive agent for a limited time to create the surface recess in said uncovered surface portion. Correspondingly, a filament according to the present invention is characterized in that its surface structure includes at least one etch pitting or etch recess in a filament body made at least in part of a material soluble by a corrosive agent. Advantageously, such etch recesses or etch pittings differ from mechanically produced recesses or pittings in their shape and contour. Mechanically produced recesses and pittings such as drilled bores, hot pressed depressions or milled slots or cut slots usually have an absolutely regular and even shape exactly corresponding to a basic geometrical structure with straight or at least evenly bowing contour lines, whereas etch recesses or etch pittings according to the present invention may show some surface roughness and fuzzy contour lines with deviations from precisely geometrical shapes with straight or absolutely evenly curved lines what may even further increase adhesive forces to dust particles and the desired abrasive effect for cleaning surfaces with strongly bonded pollution such as plaque.

According to preferred embodiments of the present invention, the said etch recesses and etch pittings, respectively, may have different shapes and arrangements on the filament. According to a first preferred embodiment of the invention, a plurality of basically circular dimples may be provided in the circumferential surface of the filament, wherein such dimples may have a random distribution over the circumferential surface area or, in the alternative, may be positioned in a matrix-like distribution. In addition to such dimples or in the alternative thereto, the surface structure may include at least one etch recess with an elongate shape that extends over at least 1/3, preferably at least 1/2 of the filament's longitudinal extension. Such an elongate etch recess basically may have a slot-like shape. However, according to a preferred embodiment of the present invention, the at least one elongate etch recess may have a shape such that the filament's cross section varies in shape over the longitudinal extension of the filament. More particularly, cross-sections taken at different longitudinal positions may differ from each other. Such varying cross-sections may be achieved by an elongate recess that varies in width and/or which has a curved longitudinal shape preferably with a curved longitudinal shape. According to a particularly preferred embodiment of the invention, an elongate etch recess having a helical contour may be provided in the circumferential surface of the filament. More particularly, at least two such elongate, helically configured etch recesses may be provided on different sides of the circumferential surface of the filament.

In addition or in the alternative to the aforementioned embodiment, the filament may have etch recesses or etch pittings of other shapes. For example, according to another preferred embodiment of the invention, certain portions of the circumferential surface of the filament corresponding to a desired pattern may be recessed by etching so that a pattern of preferably bar- shaped and/or rib-shaped and/or pin-shaped projections formed by the non-recessed portions project in radial direction from the circumferential surface of the filament.

In addition or in the alternative to at least one of the aforementioned surface structures, the filament may have etch recesses which form preferably bore-like channels inside the filament body. Such bore-like channels may perforate the filament completely and/or may have a limited depth and/or may be interconnected with each other so a channel system is provided inside the filament body.

So as to achieve easy, but nevertheless precise control of the shape of the etch recesses, a corrosive agent resistant cover layer is provided on the filament body which basically consists of a material soluble by said corrosive agent, so certain portions of the surface of the filament body made of such a soluble material are protected against contact with the corrosive agent. Consequently, the said cover layer made of a material stable to the corrosive agent, covers only certain portions of the surface area of the filament body to be contacted with the corrosive agent. In other words, the cover layer includes at least one void that gives the corrosive agent access to a respective portion of the soluble material of the filament body as said filament body is exposed to the surrounding and thus the corrosive agent in the region of said void in the cover layer.

The said cover layer covering certain portions of the filament body and not covering certain other portions thereof, may be applied to the filament body in different ways. According to an advantageous embodiment, the said cover layer may be applied in a multiple-step process, wherein particularly in a first step the entire portion of the filament to be contacted with the corrosive agent is covered with a continuous cover layer and wherein in a further step certain portions of said initially continuous cover layer are removed to provide voids in said cover layer through which the corrosive agent gets access to the filament body's material under the cover layer. Completely covering the filament portion to be contacted with the corrosive agent first and removing certain cover layer portions then in a second step provides for easy manufacturing with still reliable covering of the portions to be protected against etching. However, in the alternative it also would be possible to provide the cover layer in a one-step process, wherein the cover layer material is deposited on the filament body only in the portions to be covered, whereas no material is deposited on the surface portions which are not to be covered. Nevertheless, the aforementioned application of the cover layer in a multiple-step process is preferred in terms of process handling, cost efficiency and reliable covering of the surface portions to be protected against etching.

According to a preferred embodiment, a photosensitive material may be used for the cover layer so certain portions of the cover layer may be removed or fixed by irradiating the respective portions with light or any other appropriate radiation. More particularly, it is a preferred embodiment of the invention to completely cover the filament's surface, or at least the portion of the filament's surface to be contacted with the corrosive agent, with a photosensitive cover layer material in a first step and then, in another step, to subject only portions of said photosensitive cover layer material to light so the respective irradiated portions are changed in their material properties compared to the non-irradiated portions, whereas the other portions not irradiated do not change their properties. If a positively photosensitive material is used, the irradiated portions may be removed by a photographic developer. In the alternative, it is also possible to use a negatively photosensitive material which is fixed by light irradiation. In this case, the portions of the initially continuous cover layer which are to be removed are not irradiated, whereas the remaining portions which are subjected to light irradiation are fixed on the filament surface.

The removal of the unstable portions may be achieved in different ways. According to an advantageous embodiment of the invention, the photosensitive cover layer material including so to say stable portions and unstable portions may be contacted with an appropriate liquid such as a photographic developer which removes the unstable portions of the cover layer. Preferably, the filament provided with the respective continuous cover layer including stable and unstable portions may be dipped and drained into a respective bath of liquid.

Use of such a photosensitive material for the cover layer allows precisely shaping the voids in the cover layer. According to a preferred embodiment, light is irradiated onto the filament surface covered with the cover layer of photosensitive material via a mask facing the filament's surface covered with the cover layer. For example, such a mask may have a tubular configuration surrounding the respective filament from all sides and having openings allowing the access of light to certain portions of the filament only. In a preferred embodiment of the invention, lenses may be used to direct the light exactly to the portions to be subjected to irradiation. Such lenses are preferably positioned between the respective mask and the filament surface.

In addition or in the alternative to such masking of the photosensitive cover layer, a light irradiation system providing a precisely focused light beam also may be used to achieve selected irradiation. For example, a laser beam could be used to effect curing of certain portions of the photosensitive cover layer material only. However, the aforementioned embodiment with masking of the cover layer material is more preferred in terms of cost efficiency and safety measures, since no specific safety measures necessary for laser applications are necessary.

In another embodiment of the present invention, the cover layer stable to the corrosive agent may be applied to the filament body made of the material soluble by the corrosive agent in a co- extrusion process. In particular, in such a co-extrusion process, the main filament body made of the material soluble by the corrosive agent, may be co-extruded with a circumferential cover layer made at least in part of a material stable to said corrosive agent. So as to provide the desired voids in the cover layer in a subsequent step, the co-extruded cover layer may be subjected to mechanical treatment. For example, bores may be drilled into the cover layer or desired recesses may be cut into the cover layer by other mechanical tools.

According to another preferred embodiment of the invention, the cover layer is co-extruded from a mixture of at least two materials including a first material stable to the corrosive agent and a second material soluble by the corrosive agent, wherein the co-extrusion process is controlled such that in the co-extruded cover layer there is an inhomogeneous distribution of the said two materials. In particular, the second material soluble by the corrosive agent is distributed in the co- extruded cover layer in a desired pattern which may include a random distribution of basically circular spots or a distribution in longitudinal stripes etc. To produce the desired voids in the co- extruded cover layer, the filament covered with the initially continuous cover layer is contacted with an appropriate corrosive agent for removing the material portions of the cover layer not stable to this corrosive agent. The corrosive agent for producing the voids in the cover layer may be the same corrosive agent used for etching the recesses into the filament body's core made of a respective soluble material. However, in an alternative embodiment the materials may be selected such that different corrosive agents are necessary for and subsequently applied to the filament so as to remove first, by means of a first corrosive agent, only the respective portions of the cover layer to produce the desired voids therein and then, in a second step, by means of a second corrosive agent, to produce the desired recesses in the filament body through the previously produced voids in the cover layer. Such selective etching allows precise control of the depth and shape of the etch recesses in the filament body under the cover layer.

In order to achieve high efficiency and high manufacturing capacities, the aforementioned steps of covering the filament body with the cover layer, providing the desired voids in the cover layer and/or contacting the partly covered filament body with the corrosive agent are effected in a continuous process in which a long filament roving is continuously moved through a plurality of respective stations in a subsequent way. For example, a continuous fiber or filament may be taken from a spool and then moved, e.g. by means of respective deflection wheels, through different treating stations so as to produce the desired surface structure on the continuous filament roving which is then, after having created the surface structure, cut or otherwise separated into a plurality of separate bristles. More particularly, the long filament roving is continuously moved first through a cover layer application station in which preferably liquid photosensitive cover layer material is applied to the filament roving. For example, the filament roving may be moved through a dipping station. After having been covered with the photosensitive cover layer material, the filament roving may then be moved through an irradiation station in which certain portions of the cover layer are subjected to light irradiation. Preferably, light flashes can be applied through a mask and the openings thereof, so that only certain portions of the cover layer material are irradiated even when the filament roving is continuously moving.

In order to remove the unstable portions of the cover layer material, the continuously moving filament roving can be directed through a photographic developer dipping which forms part of a respective cover layer removal station. Thereafter, the long filament roving may be continuously moved through an etching station which may include a corrosive agent dipping station so as to dip and drain the filament roving with the corrosive agent. Finally, the filament roving can be moved through a cutting station to cut the filament roving into a plurality of bristles. According to another preferred embodiment of the invention, the etched recesses or etched pittings may be filled with a medical treatment medium such as, e.g., an antibacterial liquid or gel that is dispensed and applied to the teeth and the gingiva during cleaning the teeth.

These and other features which may define the invention for themselves or in combination with each other and also in sub-combination different from the definition in the claims, will become apparent in greater detail from the following description and from the figures which illustrate preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show:

Fig. 1: a schematic functional diagram of an installation for manufacturing toothbrush bristles with a surface structure in a continuous process, said installation including a plurality of treating stations through which a bristle roving is continuously moved to apply different treatments to the bristle roving,

Fig. 2: a schematical side view of a bristle, wherein a part of the bristle is shown in a longitudinal-sectional view to illustrate the cover layer for protecting the bristle body's material against application of the corrosive agent, wherein the cover layer is shown with different portions of different curing conditions before producing voids in the cover layer,

Fig. 3: a schematical side view of the bristle portion similar to fig. 2 wherein in the longitudinal-sectional window the cover layer is shown with the voids giving the corrosive agent access to the bristle body material under the cover layer and with etch pittings in the circumferential surface of the bristle,

Fig. 4: a functional diagram of an installation for producing bristles with a surface structure in a continuous process according to an alternative embodiment of the invention according to which the filament is coming from a nozzle, Fig. 5: an enlarged, schematical front view of an irradiation station, wherein said irradiation station includes masks for masking the photosensitive cover layer, a light source for directing flashes of light through said masks and lenses between the masks and the continuously moving bristle roving,

Fig. 6: a schematical side view of the bristle roving coming from a co-extrusion apparatus, wherein in a partly longitudinal-sectional view the co-extruded cover layer including an inhomogeneous mixture of different materials is shown,

Fig. 7: a schematical side view of a bristle roving coming from a co-extrusion apparatus similar to fig. 6, wherein specific tools are used for creating voids in the cover layer shown in the partly longitudinal-sectional view of the bristle roving,

Fig. 8: a longitudinal-sectional view of a bristle illustrating the arrangement of etch recesses providing for a reduced stiffness of the bristle,

Fig. 9: a cross-section of a bristle along line A-A in fig. 10,

Fig. 10: a schematical side view of a bristle having a pattern of rib-like projections created by etching the neighboring portions between the rib-like projections,

Fig. 11: a cross-section of the bristle of fig. 10 along line B-B in fig. 10,

Fig. 12: a schematical side view and partly longitudinal-sectional view of a bristle with a surface structure according to another embodiment of the invention, said surface structure including pin-shaped projections,

Fig. 13: a schematical side view and partly longitudinal-sectional view of a bristle with a surface structure according to another embodiment of the invention, said surface structure including recesses in the shape of through-holes, Fig. 14: a schematical side view and partly longitudinal-sectional view of a bristle according to another embodiment of the invention, said bristle having a surface structure with through-holes interconnected by a longitudinal hole,

Fig. 15: a schematic longitudinal-sectional view of a masking arrangement for creating an etch recess in the form of a reduced diameter section,

Fig. 16: a schematic side view of a bristle having a reduced diameter section as produced by the masking arrangement of fig. 15,

Fig. 17: a schematic side view of a bristle with a surface structure of another preferred embodiment of the invention, said surface structure including a reduced diameter section which, by a further treatment step, has been turned into a needle-like tip,

Fig 18: a cross-sectional view of a bristle according to another preferred embodiment of the invention taken along line A-A in fig. 19,

Fig. 19: a schematic side view of a bristle according to another embodiment of the invention, said side view showing the position of a plurality of cross-sectional planes in which cross-sections of fig. 21-27 have been taken, as well as the helical configuration of a longitudinal recess in the circumferential surface of the bristle,

Fig. 20: a schematic side view of the bristle of fig. 19 showing the helical configuration of a longitudinal recess in the circumferential surface of the bristle,

Fig. 21-27: cross-sectional views of the bristle of fig. 18-20 taken in different planes in fig. 19, and

Fig. 28: a schematical side view of an electric toothbrush having a bristle field with bristles of one of the preceding figures. DETAILED DESCRIPTION OF THE INVENTION

According to the preferred embodiment of the invention shown in fig. 1, a filament or bristle roving 7 much longer than the finished bristle is taken from a spool 11, continuously moved through a plurality of treatment stations and wound around a second storage spool 12. Between the two spools 11 and 12, the said bristle roving 7 runs through a plurality of treatment stations, wherein the bristle roving 7 is deflected by means of a plurality of rollers 13 to direct the bristle or filament roving 7 through the treatment sites.

The filament roving 7 coming from the first storage spool 11 is preferably a filament or monofilament made of plastic with an e.g. cylindrical shape and/or circular cross section. Particularly, the roving coming from the first spool 11 is a filament made of a material soluble by a corrosive agent. For example, the bristle can be made of a plastic such as polyamide or polybutylene terephthalate.

Coming from the first storage spool 11, the filament or bristle roving 7 runs through a coating bath 14 of a coating station 15. Said coating bath 14 contains a photosensitive liquid which changes its condition when subjected to light. The liquid adhering to the bristle roving 7 leaving said coating bath 14 is dried by means of a drier 16 preferably including a heat source such as a heater. Thus, the bristle roving 7 is covered with a cover layer 5 completely covering the circumferential surface of the filament as shown in fig. 2.

After having dried said cover layer 5, the continuously moving bristle roving 7 runs through a cover layer removing station 17 in which voids are produced in said cover layer 5. Said cover layer removing station 17 includes an irradiation station 18 and a photographic developer station 19.

In said irradiation station 18, only portions of the circumferential surface of the filament are irradiated with light so that the cover layer 5 includes irradiated portions and non-irradiated portions. To control the shape of the irradiated portions, said irradiation station 18 includes a preferably tubular mask 20 through which the bristle roving 7 runs. Said mask 20 is provided with at least one through-hole through which radiation from a light source 50 can be applied to the cover layer 5. As shown in fig. 5, the mask 20 does not need to have a tubular shape, but may comprise a plurality of masking elements 21 facing different sides of the bristle 1, each of said masking elements preferably comprising at least one through-hole through which radiation of a predetermined cross-sectional shape is applied to the circumferential surface of the bristle 1.

Preferably, optical means 52 such as lenses 51, reflectors etc. may be further used to direct light in a predetermined pattern onto the bristle. As fig. 5 shows, lenses 52 may be positioned between the masking elements 21 and the bristle 1 to focus the light beams or light flashes.

Depending on the type of photosensitive coating material, the irradiation may make the photosensitive material stable to developer liquid or unstable to developer liquid. Such photosensitive reaction is known as such as positive photosensitive reaction or negative photosensitive reaction. In case positive photosensitive material is used for the coating layer 5, then the irradiated portions are removed by contacting the cover layer 5 with photographic developer liquid in a developer bath of developer station 19. In contrast, if a negative photographic reaction is utilized, the portions of the cover layer 5 that should remain on the bristle 1 are irradiated and thus so to say cured to make such portions resistant against the photographic developer.

Consequently, when the bristle roving 7 leaves the removing station 17, the cover layer 5 includes a pattern of voids corresponding to the pattern of the surface structure to be produced in the bristle's circumferential surface. In a further cleaning station not explicitly shown and possibly positioned after said developer station 19 and upstream of an etching station 22, remaining developer liquid may be removed from the bristle roving 7.

As shown in fig. 1, the filament then runs through the etching station 22 including a corrosive agent bath 23. As shown in fig. 1, the path of the bristle roving 7 through said corrosive agent bath 23 is adjusted to have a defined length in response to the speed of the filament so that a desired contact time is achieved. For example, the depth 24 and/or the horizontal length 25 of the path in the liquid bath 23 may be adjusted to achieve the desired time period over which the bristle is contacted by the corrosive agent. In addition or in the alternative to such adjustment of the bristle roving path through the bath, also the conveying speed of the bristle roving may be adjusted, wherein, however, the aforementioned adjustment of the length of the dipping path is preferred since adjustment of the speed also affects the other treatment stations. By means of contacting the bristle roving 7 in the etching station 22 with a corrosive agent, the said corrosive agent gets access to the filament 1 under the cover layer 5 through the voids therein and consequently, material of said bristle body 4 is removed in the region of the voids in the cover layer 5. This is basically illustrated by fig. 3 showing dimples or pittings created in the bristle body 4 at positions where the cover layer 5 has voids 3. In neighboring portions where the cover layer 5 has no voids 3, the bristle body 4 is prevented from contacting the corrosive agent so the bristle body 4 can maintain its initial configuration.

As shown by fig. 4, the manufacturing method does not necessarily include use of a spool from which the initial bristle roving is taken. The filament 1 may directly come from the extrusion process, wherein preferably the filament coming from a nozzle 26 of an extruder is preferably cooled in a cooling station 27 which may include a cooling bath into which the filament is extruded. The cooled filament is then preferably lengthened and/or stretched in a tensioning station 28 which may include a plurality of biased rollers about which the filament runs, cf. fig. 4. Thereafter, the process may continue with coating station 15 as shown in fig. 1.

According to an alternative embodiment of the present invention, the cover layer 5 may be provided to the bristle body 4 in a co-extrusion process that is illustrated by fig. 6. The filament 1 is extruded by means of a suitable nozzle 26 which is known as such and adapted to co-extrude a thin circumferential cover layer 5 onto the core body of the extruded filament. Preferably, the co- extruded cover layer 5 is made of at least two different materials including a material stable to at least one corrosive agent and another material not stable to said corrosive agent. The co-extrusion process is controlled in such a way that the said two materials are distributed inhomogeneously in the cover layer 5. Particularly, the material not stable to the corrosive agent may be concentrated in randomly distributed spots 29. When the cover layer 5 is contacted with a suitable corrosive agent, the said spots of material not stable to the corrosive agent are removed so respective voids are created in the cover layer.

As shown in fig. 7, the desired voids in the cover layer 5 also can be produced by means of tools 30 such as laser beams, water jets, sand jets, milling tools, drilling tools or other mechanical or non-mechanical tools etc. Via the drilled or cut voids in the cover layer 5, the corrosive agent gets access to the bristle body 4 under the said cover layer 5 so pittings or other recesses 3 can be etched. As shown in fig. 8, the etch recesses 3 may be distributed in a specific pattern that reduces the column strength or buckling resistance of the bristle 1. For example, on at least two opposite sides, preferably on at least four opposite sides of the circumferential surface, the bristle may have etch recesses or etch pittings spaced from each other in longitudinal direction of the bristle, wherein preferably the recesses on one side are offset in the longitudinal direction relative to the recesses on the opposite side, as is shown in fig. 8.

Such a reduced buckling resistance of the bristles provides advantages in some tooth cleaning applications, e.g. in electric toothbrushes with an oscillating movement of the bristle tufts in the longitudinal direction thereof.

Figures 9 to 11 show another embodiment of a bristle with a surface structure 2 that includes a plurality of bar-shaped projections 31 wherein said bar-shaped projections are arranged in a plurality of rings spaced in the longitudinal direction of the bristle. In the shown embodiment, each ring of projections includes bar-shaped projections extending parallel to the longitudinal direction of the bristle and bar-shaped projections extending parallel to the circumferential direction of the bristle, wherein longitudinally oriented projections alternate with circumferentially oriented projections. Other configurations are possible.

The said projections 31 are surrounded by etched recesses. More particularly, the entire circumferential surface of the bristle 1 with the exception of the aforementioned bar-shaped projections 31 has been subjected to an etching treatment. Advantageously, the said bar-shaped projections 31 are provided with sharp edges 32 at the boundary of their top surfaces. On the other hand, the transition between the recessed circumferential portions and said projections is rounded, cf. fig. 10.

According to fig. 12, the projections 31 also may have the shape of pins. According to fig. 12, the said pins are randomly distributed over the entire circumferential surface. The pin-shaped projections 31 project from the basic circumferential surface in radial direction. The material of the bristle body 4 between the said pin-shaped projections 31 has been removed by etching. Advantageously, the top surface of said pin-shaped projection is surrounded by a sharp edge 32 substantially having a 90° contour or angle. The bottom of the projections is rounded into the basic circumferential surface, cf. fig. 12.

As shown by fig. 13, through-holes 45 may be provided in the bristle body 4, which through- holes 45 may be created by an etching process as described above. As shown by fig. 14, the said through-holes 45 extending through the bristle body 4 substantially perpendicular to the longitudinal axis thereof may be connected to a longitudinal cavity 33 e.g. formed by a cylindrical bore in the center of the bristle body 4.

The etch recesses 3 including the aforementioned through-holes 45 as well as the central cavity 33 may be filled with an application medium such as medical liquids and/or gels, cleaning substances or flavors and aromatics. Through said through-holes 45, the substance stored in said central cavity 33 may be dispensed.

According to the embodiment of figures 15 and 16, two sections of the filament or bristle 1 spaced from each other are shielded by means of two shields 34 having no voids. Between the said two shields 34, a portion of the bristle 1 is unshielded so light sources 35 can irradiate the uncovered section of the bristle 1 and consequently the cover layer 5 can be removed completely from said section of predetermined length of the bristle 1.

The bristle is then contacted with the corrosive agent so that in said uncovered bristle section the diameter of the bristle is reduced, i.e. the bristle is given a reduced diameter section. As shown in fig. 16, a section 37 with a reduced diameter alternates with sections 38 of greater or original diameter. As indicated by reference numeral 36, the bristle roving can be cut into pieces at the reduced diameter section. This allows, in a subsequent treatment step as illustrated by fig. 17 to create tapered bristles with a sharpened or needle-like tip.

As can be seen from figures 18 to 27, the aforementioned etching process also may be used so as to manufacture bristles with a cross-section that varies along the longitudinal extension of the bristle. As shown by figures 19 and 20, the filament 1, after having been etched in the aforementioned way, has an unchanged diameter D in cross-sectional plane 76, whereas in cross- sectional plane 84, cf. figure 19, the said filament has a reduced diameter d, cf. figure 20. Moreover, between said two cross-sectional planes 76 and 84, the filament is provided with an etched surface structure including helical recesses which extend from cross-sectional plane 77 to cross-sectional plane 83, cf. figure 19. More precisely, the said helical recesses 3 are formed by etched regions having an elongate shape and a reduced diameter, wherein the borders of said elongate recesses have a helical shape as shown in the figures.

In each of two opposite quadrants 39, there is a step extending between the said planes 77 and 83, wherein said step follows a helical line 40 with a thread pitch in clockwise direction corresponding to a right hand thread. On the other hand, in each of two opposite quadrants 41, there is a step between the said planes 77 and 83, wherein said step follows a helical line 42 with a thread pitch in counterclockwise direction corresponding to a left hand thread.

As can be seen by a comparison of figures 19 and 20, the said helical lines 40 and 42 meet each other in points 43 and 44 which are positioned in plane 77 and plane 83, respectively, cf. figures 19 and 20. Consequently, at the said meeting points 43 and 44 a sort of tip or needle-like contour is defined by the helical lines 40 and 42.

As can be seen from figures 21 to 27, the width of the etched recess 3 between the respective helical lines 40 and 42 varies along the longitudinal extension of the bristle, more precisely increases from plane 78 to plane 82. Consequently, the bristle varies in its cross-section continuosly from cross-sectional plane to cross-sectional plane along the longitudinal extension of the bristle.

The bottom edge of the step defined by the helical lines 40 and 42 and limiting the recesses there between is somewhat rounded, whereas preferably the upper edge 32, cf. e.g. fig. 24, bordering the non-etched diameter section is preferably a sharp edge with an angle of about 90°.

Taking into account the reduced diameter d in the sectors defined by the etched recesses between the helical lines 40 and 42 and, on the other hand, taking into account the large diameter D in the non-etched sectors, a mean diameter can be determined or calculated. In view of the varying width of the etched recess between the helical lines 40 and 42, the said mean diameter and thus the stiffness and/or the column or buckling resistance of the bristle 1 varies continuously from the maximum value in the cross-sectional planes 76 or 77 to the minimum value in the planes 83 and 84. Similar to the illustration given in fig. 17, the bristle having the helical recess as shown in figures 18 to 27 also may be further processed in a subsequent treatment step so as to create a tapered bristle with a sharpened or needle-like tip. The aforementioned etching step producing the reduced diameter section and the helical recesses reduces the necessary amount of work for the said tapering step and thus the manufacturing costs.

The described method may be applied to filaments having a circular cross-section, but also to filaments having a cross-section deviating from a circle. The respective filaments or bristles may be used for brushes and brooms, but also for dental floss, textiles, mattings, pads, nets, sponges, thermal insulations, yarns and threads and other applications. However, a particularly preferred application for the described bristle 1 is use of such bristles in bristle tufts 53 of a toothbrush head 54 and even more particularly use thereof in an electric toothbrush 55 (fig. 28).

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm."

Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.