Abstract:
A method for efficiently producing injection molded toothbrush handles wherein two or more adjacent cavities in a mold are respectively configured to mold a first portion of a handle and a second portion of a handle, wherein upon injection molding of the first portion in a first cavity, the second portion is simultaneously injected into a second cavity into which a previously molded fist portion has been placed after its removal from the first cavity, thereby to immediately contact the previous first portion with the newly injected second portion. A third portion may also be injected into a third cavity into contact with a previously injection molded contacting first and second toothbrush handle portion. In this manner, seriatim transfer of the said portions between cavities enhances product output. The handle may include transparent or translucent portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The subject application is based upon International Application PCT/CH01/00720 filed Dec. 17, 2001, now WO 02/052982 dated Jul. 11, 2002. 
   BACKGROUND OF THE INVENTION 
   WO-A-94/05183 discloses a method for producing a toothbrush consisting of two different material components, in which method, in a first step, the main body of the toothbrush is injected from a first material component, for which purpose a first cavity is provided. Thereafter, in a second cavity, a further material component, for example an elastic and/or nonslip material, is injected onto various parts of the main body. The main body has a relatively narrow cross section both in its area supporting the bristles and also in its handle area. 
   In order to improve the grip of toothbrushes and to permit comfortable handling, it is advantageous to make the toothbrush relatively solid in its handle area, i.e. to give the handle a relatively large cross section. However, this kind of handle design entails a number of disadvantages from the point of view of production technology. Not only is more material used as a result of the greater volume of the handle; the injection time and cooling time are also hugely increased by the greater mass, and the injection-molding process is thus prolonged (longer molding time). In addition, such handle parts with a relatively large cross section have a tendency to cavitation (i.e. formation of air bubbles) which are visible in handles made of a transparent material and detract from the esthetic effect of the toothbrush. 
   BRIEF SUMMARY OF THE INVENTION 
   The object of the present invention is to propose a method of the type mentioned at the outset which guarantees short injection intervals when producing a toothbrush with a solid handle of large cross section. 
   In this regard, two or more toothbrush handle portions are separately and serially injection molded in a plural cavity die set to facilitate the formation of handles having distinct differing portions. Further, the die set may effect the simultaneous similar molding of plural handles, and wherein one or more plastic supply injectors may be employed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in greater detail below with reference to the drawing. 
     Three variants of the method according to the invention are illustrated in the drawing and are described in greater detail below. 
     In the drawing, which is purely diagrammatic: 
       FIG. 1  is illustrative of a first molding method wherein the first step comprises injection molding a toothbrush handle first insert element; 
       FIG. 2  illustrates the second step of a first molding method wherein the molded insert element of  FIG. 1  is associated with a newly injected handle portion; 
       FIG. 3  illustrates the third step of a first molding method wherein the handle with the first molded insert element of  FIG. 2  is associated with a newly injected second insert element; 
       FIG. 4  shows in a side view, and partially in cross section, a toothbrush produced according to the method steps in  FIGS. 1 to 3 ; 
       FIG. 5  shows a plan view of part of an injection mold for the first method variant; 
       FIG. 6  is illustrative of a second molding method wherein the first step comprises injection molding a major handle portion of a toothbrush; 
       FIG. 7  illustrates the second step of a second molding method wherein the major handle portion of  FIG. 6  is associated with respective injection molded terminal and lateral inserts thereto. 
       FIG. 8  shows in a side view, and partially in cross section, a toothbrush produced according to the method steps in  FIGS. 6 and 7 ; 
       FIG. 9  shows a plan view of part of an injection mold for the second method variant; and 
       FIG. 10  shows a plan view of part of an injection mold for a third method variant. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   To produce a toothbrush  1  which is shown in  FIG. 4  and whose handle  2  has a larger cross section than the front head part  3  provided for securing the bristles or tufts, an inner part  4  of the handle  2  is first prepared in a first step shown in  FIG. 1 . For this purpose, a first portion of the first material component provided for the handle  2  (and if appropriate also for the head part  3 ) is injected into a first cavity a formed between two parts  5 ,  6  of an injection mold  7 . The first injection point for the first material component delivered from a first unit A 1  is indicated by AP 1  in  FIG. 1 , while the injection channel or injection nozzle provided for this is indicated by  9 . 
   As can be seen from  FIG. 5 , the injection mold  7  is provided for the production of a plurality of toothbrushes  1 , if appropriate eight tooth brushes  1 . After partial cooling and hardening (as soon as sufficient inherent stability is achieved), the inner parts  4  injected in the first step according to  FIG. 1  are transferred in each case into a second cavity  12 , shown in  FIG. 2 , using a generally known transfer system (not shown in the drawing), for example a so-called internal handling system arranged on the injection-molding tool, an external rotary or linear handling system, or robots. This first transfer is indicated symbolically with an arrow U 1  in  FIG. 5 . 
   The inner part  4  can have support knobs (not shown in  FIG. 1 ) which protrude in the radial direction and by means of which the inner part  4  is supported on the wall of the second cavity  12 , in order to be held centrally there. 
   In a second step shown in  FIG. 2 , a second portion, if appropriate the remaining portion, of the first material component is injected into the second cavity  12  via an injection channel or an injection nozzle  13 . The second injection point AP 2  for the first plastic component is offset in relation to the first injection gate AP 1 , viewed in the longitudinal direction of the toothbrush to be produced. The second portion of the first material component comes into direct contact with the first portion; in the illustrative embodiment shown, material is injected around the inner part  4 , the handle  2  acquires the desired solid shape in its rear area, and the front head part  3  of narrower cross section is also obtained. Thus, a main body of the toothbrush  1  is formed which consists of the first material component and is indicated by  10  in  FIGS. 2 and 5 . To inject both portions of the first material component, only one unit A 1  is preferably used, as is indicated in  FIGS. 1 and 2 . However, the two portions of the same material could also be injected from two different units and could for example have different colors. 
   In the method variant according to  FIGS. 1 to 5 , in a third step, a further material component, for example a material which is more elastically resilient compared to the first material component, e.g. a thermoplastic elastomer (TPE), is finally injected around the front area of the handle  2 . For this purpose, the main body  10  consisting of the first material component is transferred into a third cavity  16  of the injection mold  7  after the second portion has cooled and hardened, in which case once again the second transfer of all eight main bodies  10 , indicated by the arrow U 2  in  FIG. 5 , is effected by means of a suction tool (not shown). 
   According to  FIG. 3 , the second material component is injected into the third cavity  16  from a further unit A 2  via an injection channel or injection nozzle  17  at a third injection point AP 3 , material being injected around a front part  2   a  ( FIGS. 2 and 3 ) of the handle  2  and a kind of coating thus being formed over part of the length of the handle. Such a grip part  20  can contribute, for example, to a further improvement in the gripping of the toothbrush  1 . It is of course possible to add further material components into further cavities. 
     FIGS. 6 ,  7  and  9  show a further method variant for producing a toothbrush  1 ′ which is shown in  FIG. 8  and which once again has a front head part  3  and a handle  2  of greater cross section compared to the latter. In a first step in this variant, according to  FIG. 6 , the head part  3 , a front part  2   a  of the handle  2 , and a part  2   b  of the rear part of the handle with increased cross section, are injection-molded from a first material component and together form a main body  30  of the toothbrush  1 ′. The first cavity provided for this purpose and formed between two parts  25 ,  26  of an injection mold  27  is indicated by  28  in  FIG. 6 . This first cavity  28  is designed in such a way that the part  2   b  of the handle  2  has an upper injection surface  24  extending at an inclination relative to the longitudinal direction of the toothbrush  1 ′ to be produced; the injection surface  24  could of course extend in another direction. At an injection point AP 1 , a first portion of the first material component from a first unit A 1  is injected into the first cavity  28  via an injection channel or injection nozzle  29 . As can be seen from  FIG. 9 , a number of main bodies  30 , possibly eight main bodies, are once again produced in one injection mold  27  and, after partial cooling and hardening, are transferred into a second cavity  32  shown in  FIG. 2  by means of a transfer system (not shown). This transfer is indicated with an arrow U 1  in  FIG. 9 . 
   In a second step shown in  FIG. 7 , the second, remaining portion of the first material component is injected via an injection channel or an injection nozzle  33 , preferably from the same unit A 1  as the first portion, into the second cavity  32  at a rear, second injection point AP 2  which lies behind the injection surface  24  of the main body  30  located in the cavity  32 . Here too, however, an additional unit could be made available for the second portion. The remaining part  2   c  ( FIG. 7 ) of the handle  2  is formed by the second portion of the first material component injected onto the injection surface  24  of the cooled handle part  2   b . In this variant, the main body  30  is designed in such a way that the space in the second cavity  32  provided for injecting this second portion (or for forming the remaining handle part  2   c ) is separated from a space of the second cavity  32  provided for the injection of a second second material component surrounding the front handle part  2   a , this separation being effected by a peripheral surface  34  of the inserted main body  30  which is located at the transition between the front part  2   a  and the part  2   b  of the handle  2  provided with the injection surface  24 . Thus, simultaneous with the injection of the second, remaining portion of the first material component, it is also possible to inject the second material component, specifically from another unit A 2 , at a third injection point AP 3 , via an injection channel (or injection nozzle)  37  opening into the second cavity  32 . Here too, in order to improve its grip, the handle  2  is provided with the grip part  20  consisting, for example, of an elastically more resilient material component. If necessary, the injection of the first and second material component could take place sequentially. 
   Accordingly, in the second method variant according to  FIGS. 6 ,  7  and  9  (in contrast to the first variant according to  FIGS. 1 to 3  and  FIG. 5 ), only two cavities  28 ,  32  are needed for each toothbrush  1 ′, and only one transfer U 1  is required. 
   Both in the first method variant and in the second method variant, by dividing the injection-molding of the handle  2  of thickened cross section into two operating steps, i.e. by injection-molding the same material in two portions, the injection time and the cooling time are substantially reduced, i.e. shorter injection intervals are permitted, and in addition the formation of cavities is avoided. The last-mentioned advantage is of particular importance in transparent or translucent handles. The separating lines, or in the case of transparent material the separating surfaces, between the handle parts injected in the individual portions are barely visible. Of course, these handle parts (and the cavities required for them) could have a different form than that represented and described in the illustrative embodiments according to  FIGS. 1 to 5  and  FIGS. 6 to 9 . It would also be entirely possible for the handle of thickened cross section to be injected in more than two portions, and to provide an additional cavity for each further portion. 
   The production of a two-component toothbrush  1 ,  1 ′ has been described with reference to  FIGS. 1 to 5  and  FIGS. 6 to 9 , respectively. A one-component toothbrush, i.e. a toothbrush consisting of a single material component, could of course also be injection-molded in two or more portions according to the invention. 
   A two-component toothbrush could also be of a quite different configuration than that shown in  FIG. 4  or  8 . For example, the head part  3  could be made from another material component than the handle  2 . In this case, the material component provided for producing the handle  2  of greater thickness than the head part  3  could advantageously be injected in two portions of approximately the same size. 
   In a multi-component toothbrush, however, a number of material components can according to the invention also be divided into two or more portions which are injected sequentially. For each component which is divided up, an additional cavity per portion is of course required. 
   A further method variant for producing a toothbrush, if appropriate once again a two-component toothbrush  1 ″, is indicated in  FIG. 10 . In a first step, a main body  40  of this toothbrush  1 ″, which has a head part  3  and a handle  2  of larger cross section, is produced by injecting a first material component into a first cavity  41  of an injection mold  42 , the first material component being completely injected into the first cavity  41  in this variant. Accordingly, as soon as sufficient inherent stability is achieved after partial cooling and hardening, the main body  40  is transferred into a cooling cavity  43  by means of a suction tool (not shown), which transfer is indicated with an arrow U 1  in  FIG. 10 . In the cooling cavity  43 , which is not provided with any injection point or injection channel, further cooling and hardening of the main body  40 , in particular of its solid handle  2 , takes place until there is no risk of deformation when, in a further step, the main body  40  is transferred into a further cavity  44  (see arrow U 2  in  FIG. 10 ) into which a second and for example more resiliently elastic material component is injected in order to form the grip part  20 . This variant too permits short injection intervals by means of the transfer U 1  of the main body  40  into the cooling cavity  43 . 
     FIG. 10  again shows by way of example an injection mold  42  provided for the simultaneous production of  8  toothbrushes. Of course, in all the variants, other mold sizes having another number of cavities (e.g. with 16, or 24 cavities per operating step) are conceivable. 
   A wide variety of plastics can be used as suitable material components, and these can be at least partially transparent materials, for example styrene-acrylonitrile, polyester, polystyrene, polyamides, polycarbonates, polymethylmethacrylate or others. Examples of opaque materials that can be used are polypropylene, thermoplastic elastomers or polyethylene.