COSMETIC BRUSH COMPRISING BRISTLES HAVING EXTERNAL DEPRESSIONS FIELD OF THE INVENTION The present invention relates to a cosmetic brush, and more specifically, to a brush comprising bristles having external depressions. BACKGROUND OF THE INVENTION Several international applications described brushes made by the injection molding process and the processes therefore. Examples include: WO 02/03831 Al, titled Method and Device For Producing Bristle Products and Bristle Products; assigned to Coronet-Werke GmbH of Germany, Herman patent application DE 10201635.6, titled Method and Device For the Production of Bristles, assigned to Coronet-Werke GmbH of Germany; German patent application DE 10212701.8, titled Bristle, Method and Device For Its Production and Bristle Product, assigned to Coronet-Werke GmbH of Germany; and German patent application 10221869.2, titled Method of Manufacturing a Bristle Structure on a Carrier, assigned to Coronet-Werke GmbH of Germany, the disclosures of all of which are incorporated herein by reference. Generally, plastic brushes can be made by a two-step process. First, a hollow core having a multiplicity of orifices through its surface can be formed from a first plastic material. Second, a second plastic material can be injected, under pressure, into the hollow core, so that the escaping (or "extruded") through the recesses soft plastic forms individual bristles as the second material solidifies. The first and second materials can be identical, or different. The position of the orifices and their shapes can be chosen to define the position of the bristles and their cross-sectional configuration. Now, it has been discovered that cosmetic brushes, such, for example, as those used for mascara application to eye lashes, can be improved by providing, at least partially, individual bristles that have a concave portion thereon. It is believed that such a brush will deliver a more refined application of liquid mascara to the lashes and reduce the potential for the lashes to "stick" to one another when the liquid mascara is applied to the lashes. SPEC-796905.doc BDJ_10.06.2011 2 Accordingly, the present invention provides a cosmetic brush comprising a plurality of bristles, wherein selected bristles have at least one external depression oriented in a direction parallel to the longitudinal axis of the selected bristle, and the process for making such a brush. A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims. Throughout the description and claims of the specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps. SUMMARY OF THE INVENTION A cosmetic brush of the present invention comprises a substantially longitudinal stem and a plurality of bristles extending therefrom. Each bristle has a base associated with the stem and a free end opposite to the base. Each bristle has external walls and a longitudinal axis oriented along the length of the bristle. The walls of the bristle can be concave, round, planar, or convex. The brush as a whole has a major axis disposed along the stem of the brush. According to the present invention, at least some of the bristles, termed herein as "selected bristles," have at least one external depression in their walls. The depression of each of the selected bristles is oriented in a direction substantially parallel to the longitudinal axis of the bristle. The selected bristle can have any suitable shape in its cross-section perpendicular to the bristle's longitudinal axis. For example, the selected bristle can have a cross section that includes oblong, polygon, circular, curbed, rhombic, trapezoid, or any other shape. The number of the depressions per bristle can also vary. For example, the bristle can have on, two, three, four, and more depressions. In one embodiment, the depression or depressions extend through the entire length of the selected bristle. In another embodiment, the depression or depressions extend only through a portion of the selected bristle. In still another embodiment, the depression is located at the free end of the selected bristle. SPEC-796905.doc BDJ_10.06.2011 2a In the selected bristles having more than one depression, the location of the depressions may vary. For example, in the selected bristles having two depressions, the depressions can be located opposite to each other. In the selected bristle having three or SPEC-796905.doc BDJ_10.06.2011 WO 2006/039575 PCT/US2005/035338 3 four depressions, the depressions can be spaced substantially equidistantly from one another, as viewed in the cross-section perpendicular to the longitudinal axis of the selected bristle. The bristles may have differential lengths. In one embodiment, for example, the s lengths of the bristles are such that the ends of several bristles consecutively disposed next to one another, as viewed in a cross-section of the brush perpendicular to the major axis, form an imaginary line that is straight. In another embodiment, such a line can be concave or convex. The bristles may be made to gradually taper from the base towards the free end. 10 Alternatively, the bristles may have a generally uniform thickness (with the exception of the selected bristles cross-sections of which are at least partially affected by the longitudinal depression), or taper from the free ends towards the bases of the bristles. In one embodiment, the ends of at least some of the bristles, either selected or otherwise, have concave depression. Those depressions are different and distinct from is the depressions in the walls of the bristles, for the depressions in the free ends of the bristles are not disposed longitudinally in relation to the longitudinal axes of the bristles. The longitudinal axes of the bristles and the major axis of the brush can be mutually perpendicular. The embodiment is contemplated in which those are not mutually perpendicular, i.e., the axes of at least some of the bristles and the major axis of 20 the brush form an obtuse angle or angles therebetween. The brush of the present invention can be made by a process that includes a so called "injection molding" technique, i.e., a process wherein a molten material is injected, under pressure, into a closed form having a cavity of a desired shape, to fill the cavity, cooled to solidify in the cavity, and released from the cavity. Several patents documents 25 listed herein above and incorporated by reference describe the injection molding process in sufficient detail. More specifically, the process for making the cosmetic brush of the present invention comprises the steps of forming a hollow stem from a first moldable material; providing a plurality of bristle-forming channels surrounding and abutting the hollow 30 stem, each of the bristle-forming channels terminating with an end and having a length, 4 the plurality of bristle-forming channels comprising selected bristle-forming channels, each of the selected bristle-forming channels having at least one protuberance therein; injecting a second moldable material into the hollow stem under pressure sufficient to rapture the hollow stein in predetermined locations corresponding to the bristle-forming channels and to fill the bristle-forming channels with the second moldable material so that the second moldable material assumes the shape of the bristle-forming channels; and solidifying the second moldable material disposed in the bristle-forming channels thereby forming the plurality of bristles of the brush being made, wherein the plurality of bristles comprises selected bristles formed in the selected channels and having at least one external depression thereon. In one embodiment the present invention provides a process for making a cosmetic brush comprising a substantially longitudinal stem and a plurality of bristles extending therefrom, the process comprising steps of: (a) providing a hollow stem from a first moldable material; (b) providing a plurality of bristle-forming channels surrounding and abutting the hollow stem, each of the bristle-forming channels terminating with an end and having a length, the plurality of bristle-forming channels comprising selected bristle-forming channels, each of the selected bristle-forming channels having at least one protuberance therein; (c) injecting a second moldable material into the hollow stem under pressure sufficient to rupture the hollow stem in predetermined locations corresponding to the bristle-forming channels and to fill the bristle-forming channels with the second moldable material so that the second moldable material assumes the shape of the bristle-forming channels; (d) solidifying the second moldable material disposed in the bristle-forming channels thereby forming the plurality of bristles of the brush being made, wherein the plurality of bristles comprises selected bristles formed in the selected channels and having at least one external depression thereon. SPEC-796905.doc BDJ_10.06.2011 4a The protuberances can be disposed along the length of the selected bristle-forming channels and / or at the end of the selected bristle-forming channels, depending on a desired configuration of the bristles being formed. The bristle-forming channel can be formed, for example, by a plurality of plates disposed consecutively adjacent to one another, wherein mutually adjacent plates have surface patterns that form, in combination, a desired profile of the bristle-forming channel. The step of forming a hollow stem from a first moldable material can be accomplished by injecting the first moldable material under pressure into a support form structured to form the hollow stem. The first moldable material and the second moldable material may be identical or, alternatively, may differ from one another. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of an embodiment of a brush according to the invention; Fig. 2 is a cross-sectional view of the brush of Fig. 1, taken along lines 2-2; and Figs. 3 to 6 are perspective views of various embodiments of the selected bristles of the brush of the present invention. Fig. 7 is a plan view of an exemplary embodiment of the bristle having a depression intermediate the base of the bristle and the end thereof. SPEC-796905.doc BDJ 10.06.2011 WO 2006/039575 PCT/US2005/035338 5 Fig. 8 is a schematic cross-sectional view of an embodiment of a support form that can be used for making the brush of the present invention by extrusion molding. Fig. 9 is a schematic cross-sectional and partial view of the form shown in Fig. 8, 5 taken along lines 9-9, and showing a cross-section of a selected bristle forming channel having a protuberance therein. Fig. 10 is a schematic cross-sectional view taken along lines 10-10 of Fig. 9, and showing a plan view of one embodiment of the protuberance of the bristle forming channel. 10 Fig. 11 is a schematic perspective view of one embodiment of the bristle-forming channels. DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows an embodiment of a brush 10 of the present invention comprising a substantially longitudinal core, or stem, 260 having a longitudinal, or major, axis A, and a 15 plurality of bristles 50 extending therefrom. Each bristle has a base associated with the stem and a free end opposite to the base. Each bristle has external walls and a longitudinal axis B oriented along the length of the bristle (Fig. 5). The walls of the bristle 50 can be concave, round, planar, or convex, Figs. 3-5. The embodiment of Fig. 1 also has an optional stem 20 that, via an optional 20 locking groove 30, can be attached to a handle (not shown). The brush 10 may be trimmed, to change the length of some bristles or otherwise form a particular configuration of the brush 10 in a cross-section perpendicular to the major axis A. For example, Figs. 2 shows that the trimming can be made to comprise an envelope curve 60 of approximately triangular shape with rounded or skewed corners 70 so that the bristles 25 50 have differential lengths. The same effect can be achieved by using a process of the present invention, and without trimming, as will be discussed in more detail below. According to the present invention, at least some of the bristles 50 have at least one external depression 120 in their walls. These bristles are termed herein as "selected bristles," because the process of the present invention (described herein below) allows 30 one to design what bristles should be structured to have at least one external depression.
WO 2006/039575 PCT/US2005/035338 6 The depressions of the selected bristles can be oriented in a direction parallel to the longitudinal axes B of the bristles, or, alternatively or additionally, can be disposed at free ends of the bristles. Bristles 50 can comprise bristles having a generally round cross-section (Figs. 4 5 and 6), bristles 50b having a generally oblong, or elongated, cross-section (Figs. 3 and 5), or bristles having any other suitable general cross-section, for example, polygonal. As used herein, the term "oblong" refers to a geometrical shape that generally has unequal dimensions in two mutually perpendicular directions. The selected bristle can have any suitable shape in its cross-section perpendicular to the bristle's longitudinal axis. For 10 example, the selected bristle can have a cross-section that includes oblong, polygon, circular, trapezoid, or any other shape. The number of the depressions 120 per the selected bristle can vary. For example, the selected bristle can have one, two, three, four, and more depressions 120. In the selected bristles having more than one depression 120, the location of the depressions 15 may vary. For example, in the selected bristles having two depressions 120, the depressions can be located opposite to each other, Figs. 3 and 5. In the selected bristle having three, four, or more depressions 120, the depressions can be spaced substantially equidistantly from one another, as viewed in the cross-section perpendicular to the longitudinal axis B of the selected bristle (Figs. 3-5) or can be differentially spaced from 20 one another (not shown). In the embodiments shown in Figs. 3-5, the depressions 120 extend through the entire length of the selected bristle. In other embodiments, the depression or depressions 120 can extend only through a portion of the selected bristle, as shown, for example, in Fig. 7. The depression can extend from the base of the selected bristle and terminate before it reaches the free end of the selected bristle; or the 25 depression can extend from the free end of the selected bristle and terminate before it reaches the base of the selected bristle. The embodiment is contemplated in which the selected bristle has more than one depression wherein at least one depression extends through the entire length of the bristle, and the other depression or depressions extends only through a portion of the length of the bristle in any manner described herein above. 30 The bristles 50 may have differential lengths. In one embodiment, for example, the lengths of the bristles 50 are such that the ends of several bristles consecutively WO 2006/039575 PCT/US2005/035338 7 disposed next to one another, as viewed in a cross-section of the brush perpendicular to the major axis A, form an imaginary line that is straight (Fig. 3, line 60). In another embodiment, such a line can be concave: (not shown) or convex (Fig. 3, line 70). Thus, in its cross-section perpendicular to the major axis A, the brush may or may not be 5 circumferentially symmetrical. The bristles 50 can be made to gradually taper from the base towards the free end (Figs. 1-6). Alternatively, the bristles 50 may have a generally uniform thickness (with the exception of the selected bristles, cross-sections of which are at least partially affected by the longitudinal depression), or taper from the free ends towards the bases of the 10 bristles 50 (not shown). In one embodiment, the ends of at least some of the bristles 50 have concave depression 110, Fig. 4. Those concave depressions 110 are different and distinct from the depressions 120 in the walls of the bristles, for the depressions 110 in the free ends of the bristles 50 are not disposed longitudinally in relation to the longitudinal axes B. of the 15 bristles 50. In some embodiments of the brush of the present invention, the selected bristles can have both the longitudinal depression or depressions 120 and the concave depression 110 at the free end of the selected bristle. The longitudinal axes B of the bristles 50 and the major axis A of the brush 10 can be mutually perpendicular. The embodiment is contemplated, however, in which those 20 are not mutually perpendicular, i. e., the axes B of at least some of the bristles 50 and the major axis A of the brush 10 fonn acute or obtuse angle or angles therebetween (not shown). The brush of the present invention can be made by using a technique known as "injection molding." Injection molding is, in essence, a process wherein molten plastic is 25 deposited under pressure, or injected, into a closed form having a cavity of a desired shape, to fill the cavity, then cooled to solidify in the cavity, and then released from the cavity. One skilled in the art will appreciate that using the injection molding process, it is possible to form virtually any desired configuration of the bristles, including the selected bristles of the present invention. In addition, the injection molding technique allows one 30 to control the length of individual bristles, so that trimming of the finished rush may not WO 2006/039575 PCT/US2005/035338 8 be needed in order to form a certain cross-sectional profile of the brush, as shown, for example, in Fig. 2. The brush of the present invention can be made by an injection-molding process, for example, using a multi-component molding injection machine 200, schematically s shown in Fig. 8. First, a hollow stem 260 is provided. The hollow stem 260 can be made from any suitable material, for example, plastic or resin such as polypropylene, and may include any suitable thermoplastic or thermosetting materials. The hollow stem 260 can be formed by injection-molding or any other means kriown in the art. As an example, in Fig. 8, the hollow stem 260 is formed and disposed in the injection machine 200. The 10 hollow stem 260 may comprise any suitable shape in its cross-section perpendicular to the major axis, for example, cylindrical (shown in the exemplary embodiment of Fig. 1), rectangular, triangular, polygonal, or any combination thereof, or any other shape, including irregular geometric shape (not shown). A plurality of bristle-forming channels 250 is provided. The bristle-forming 15 channels 250 are disposed so that their entrances abut the hollow stem 260 in predetermined locations in which the bristles 50 of the brush being constructed should be disposed after the brush has been constructed. The overall configuration and geometry of the bristle-forming channels 250 corresponds to the desired overall geometry and configuration of the brush being made. Each of the bristle-forming channels 250 20 terminates with an end and has a predetermined lengtl1. Depending on the size and length of the bristle-forming channels 250, the bristle-forminag channels 250 can be made by any means known in the art, for example using conventional drilling techniques, laser, chemical erosion, wire electrical discharge machine (EDM), or any other suitable means. The bristle-forming channels 250 can be formed, for example, by a plurality of coated 25 plates 300 (Fig. 11) disposed consecutively adjacent to one another, wherein mutually adjacent plates 300 have surface patterns that form, in combination, a desired profile of the bristle-forming channels 250. In accordance with the present invention, the plurality of bristle-forming channels 250 include selected bristle-forming channels 250a, i.e., the channels that are structured to 30 form the selected bristles having at least one external depression 120 thereon, as described herein above. For this purpose, each of the selected bristle-forming channels WO 2006/039575 PCT/US2005/035338 9 250a has at least one protuberance 290 therein. The protuberance or protuberances 290 can be disposed along the length of the selected bristle-forming channel 250a, at the end of the selected bristle-forming channels 250a, or both, depending on a desired configuration of the selected bristle being formed. 5 In the next step, a second moldable material 270 is injected, under pressure, into the hollow stem, to form the bristles (Fig. 8). The second moldable material can comprise the material identical to the first moldable material, or, alternatively, may differ therefrom. Only for the purposes for example, the second moldable material can comprise any suitable thermoplastic elastomer (TPE), such as, for example, styrene 10 ethylene-butylene-styrene (SEBS) block copolymer. The pressure under which the second moldable material 270 is injected should be sufficient to rapture the hollow stem 260 and form perforations in locations corresponding to the bristle-forming channels 250 and further to fully fill the bristle-forming channels 250 with the second moldable material 270 so that the second moldable material 270 assumes the shape of the bristle 15 forming channels 250. These perforations formed in the stem 260 serve, in effect, as spinnerets for the second moldable material. The second moldable material 270 that fills, under pressure, the selected bristle-forming channels 250 forms the selected bristles that have external depressions described herein above, the depressions being a "negative" of the protuberances 290 of the selected bristle-forming channels 250a. 20 After the second moldable material 270 solidify in the bristle-forming channels 250, the brush comprising the stem 260 and the plurality oof bristles 50 extending therefrom can be released from the injection machine. If the plurality of plates 300 is used to form the bristle-forming channels 250, the plates 300 can be moved apart from one another, thereby releasing the formed bristles 50. 25 If desired, an optional step of injecting a third moldable material 280 (Fig. 8) into the hollow stem 260 to fill the stem 260, can be used. When the process is completed, the bristles 50 are integrally bound to the third material 280 that has filled the stem 260. The third moldable material can comprise a material identical to at least one of the first moldable material or the second moldable material, or can be chose to be different from 30 either the first moldable material and the second moldable material.
WO 2006/039575 PCT/US2005/035338 10 All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. While particular embodiments of the present invention have been illustrated and 5 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.