Patent Publication Number: US-2003221271-A1

Title: Bristle sub-assemblies and method of making same

Description:
RELATED APPLICATIONS  
     [0001] This is a continuation-in-part of U.S. Ser. No. 09/092,092, filed Jun. 5, 1998. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] The present invention relates generally to articles made of polymeric monofilaments, and more particularly, to looped bristles, methods for making looped bristles and bristle sub-assemblies, and monofilament bristle sub-assemblies connected to brush bodies.  
       [0003] The aforementioned co-pending application describes a manufacturing technique in which a base string is fed axially along a mandrel while at the same time a monofilament is wrapped around the mandrel, thereby producing a plurality of “wraps” which are transported along the mandrel by the base string. The wraps are then bonded to the base string using an ultrasonic welder, and subsequently cut to thereby form an article having two rows of monofilament segments connected to the base string.  
       [0004] This article, called a “bristle string,” can then be cut to lengths and used to make a variety of brushes or other products requiring bristles. In one example, several rows of bristles are formed in a toothbrush by mounting the bristle string segments in the head portion of a toothbrush. Typically, the proximal ends of the bristles are connected to the brush head and the distal ends extend freely upwardly.  
       [0005] Brushes with looped bristles have been used in the past. For example, U.S. Pat. No. 4,211,217 to Gueret describes a hair and massage brush in which the bristles are bent to form loops which are anchored in perforations formed in the brush head fusing the ends together. As another example, U.S. Pat. No. 4,406,032 to Diamant describes a toothbrush which includes a filament wrapped around the head to form a plurality of circular loops.  
       [0006] U.S. Pat. No. 4,493,125 to Collis describes a toothbrush having a combination of curved bristles and straight bristles. The curved bristles were formed by having opposite ends of straight filaments embedded in the head of the toothbrush in groups, thereby forming loops. The loops are then cut axially to form two rows of curved bristles. Other examples where looped bristles are used in a toothbrush are shown in U.S. Pat. No. 4,030,845 to Deckert, U.S. Pat. No. 2,599,191 to Meunier, and U.S. Pat. No. 4,438,541 to Jacob et al.  
       [0007] While these show various forms of loop bristles, a need exists for a looped bristle structure that is relatively easy to manufacture and cost effective to produce.  
       SUMMARY OF THE INVENTION  
       [0008] An object of the present invention is to provide means to expand brush design beyond the range possible with current tufting techniques.  
       [0009] Another object of the present invention is to provide a bristle subassembly for a brush in which individual filaments are positionally fixed with respect to each other prior to connection to a brush body.  
       [0010] Still another object of the present invention is to provide a method of assembling brushes in which bristle sub-assemblies can be permanently connected to the brush body or, alternatively, detachably connected for subsequent replacement, thereby avoiding wastefully discarding otherwise functional brush bodies.  
       [0011] Yet another object of the invention is to provide a brush that has a combination of arched bristles, looped bristles and straight bristles, whereby both types of bristles can be assembled without using conventional tufting techniques.  
       [0012] These and other objects are met by providing a bristle sub-assembly which includes two substantially parallel base strings and a plurality of polymeric monofilaments connected transversely between the two base strings. When the two base strings are juxtaposed to each other, they form a single row of arched monofilaments. The row of arched monofilaments can be sized to a desired length by cutting the two base strings and then connecting them to a brush head in desired patterns.  
       [0013] Other objects and features of the invention will become more apparent from the following detailed description when taken in conjunction with the illustrative embodiments in the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 is a horizontal sectional view of an apparatus for making bristle sub-assemblies according to a preferred embodiment of the present invention, taken at an ultrasonic welding stage;  
     [0015]FIG. 2 is a horizontal sectional view of an apparatus for making bristle subassemblies according to a preferred embodiment of the present invention, taken at a cutting stage;  
     [0016]FIG. 3 is a plan view of a bristle sub-assembly made with the apparatus of FIG. 1, prior to bending the monofilament segments into arched formations;  
     [0017]FIG. 4 is an end view of a row of arched monofilaments made from the bristle sub-assembly of FIG. 3;  
     [0018]FIG. 5 is a horizontal sectional view of an apparatus for making bristle subassemblies according to another preferred embodiment of the present invention, taken at a cutting stage;  
     [0019]FIG. 6 is an end view of a bristle string sub-assembly made by the apparatus of FIG. 5:  
     [0020]FIG. 7 is an end view of the bristle string sub-assembly of FIG. 6, bent to form an arch section;  
     [0021]FIG. 8 is a plan view of a bristle sub-assembly made according to another embodiment of the present invention;  
     [0022]FIG. 9 is an end view of the bristle sub-assembly according to claim 8, after forming a pair of arched segments;  
     [0023]FIG. 10 is a perspective view of a toothbrush made with the arched bristles made according to the present invention;  
     [0024]FIG. 11 is a partial, longitudinal cross-sectional view of the forward portion of the toothbrush of FIG. 10;  
     [0025]FIG. 12 is an end view of a brush head according to another embodiment of the present invention, and having a row of arched bristles and two flanking rows of straight bristles;  
     [0026]FIG. 13 is an end view of a brush head according to another embodiment of the present invention, and having a first row of arched bristles concentrically disposed with a second row of arched bristles; and  
     [0027]FIG. 14 is an end view of a brush head according to another embodiment of the present invention, and having a row of arched bristles extending over three longitudinal rows of straight bristles. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0028] Referring to FIGS. 1 and 2, a hollow, substantially rectangular mandrel  10  has four beveled corners  12 ,  14 ,  16 , and  18  which include flat surfaces that are at 45° angles to the contiguous flat surfaces of the mandrel  10 . Base strings  20 ,  22 ,  26 ,  28 ,  30 ,  32 ,  34  and  36 , entering one axial end of the mandrel  10 , pass downwardly through the interior of the mandrel  10 . The base strings are turned at the opposite end and guided for movement in the opposite direction in pairs along respective corners of the mandrel  10  as shown.  
     [0029] A monofilament  38  is wrapped around the mandrel  10  as the base strings translate to thereby form a plurality of wraps that are in contact with the base strings. The base strings move the wraps under ultrasonic bonding horns  40 ,  42 ,  44  and  46 , each of which is juxtaposed a respective corner of the mandrel  10 . The horns are energized to thermally fuse the wraps of monofilament to the base strings.  
     [0030] After bonding, the base strings further transport the monofilament wraps, now connected to the base strings, to a cutting station. As seen in FIG. 2, the cutting station includes a cutting blade  48 ,  50 ,  52 , and  54  disposed at respective corners to cut the monofilament wraps between each pair of base strings to form four separate bristle subassemblies. While each cutting blade is shown to be rotatable about an axis illustrated in broken lines in FIG. 2, any suitable mechanical or wave energy cutting device can be employed.  
     [0031] Referring to FIG. 3, one of the bristle sub-assemblies  56  is shown with two base strings  22  and  26 , disposed parallel to each other, and the plurality of wraps bonded to the base strings at substantially right angles to form a plurality of monofilament segments  58 . As seen in FIG. 4, as the parallel base strings  22  and  26  are moved towards each other, the monofilament segments  58  bend to form an arched row  60  of monofilaments.  
     [0032] Other monofilament bristle sub-assemblies can be made by varying the number of base strings and re-positioning the slitters. For example, in FIG. 5 the mandrel  62  has a substantially square cross-sectional shape, with base strings  64 ,  66 ,  68  and  70  disposed respectively at each of the four corners of the mandrel  62 . A monofilament  72  is wrapped around the mandrel  62  and transported by the base strings as before to form a plurality of wraps. After passing under ultrasonic bonders (not shown) and thermally fused to the base strings, the monofilament wraps are transported to a cutting station which includes two cutting blades  74  and  76 .  
     [0033] The cutting blades cut the monofilament wraps on opposite sides of the mandrel  62  to form two nearly identical bristle string sub-assemblies  78 , of which one is shown in FIG. 6. The sub-assembly  78  includes a plurality of monofilament segments  80  connecting to and extending between the two base strings  68  and  70 , and two rows of monofilament segments  82  and  84 . As seen in FIG. 7, when the base strings  68  and  70  are brought together in the direction of the directional arrows, the monofilament segments  80  form an arch.  
     [0034] In another embodiment, seen in FIG. 8, the monofilament wraps are cut to form a bristle string sub-assembly  86  in which the monofilament segments  88  are connected to base strings  90 ,  92  and  94 . As seen in FIG. 9, when the two outer base strings  90  and  94  are moved towards the middle base string  92 , as illustrated by the directional arrows, a pair of arched segments  96  and  98  are formed.  
     [0035] The various bristle sub-assemblies described above can be used in a variety of products, including brushes. FIG. 10 shows a toothbrush  100  having a handle portion  102 , a head portion  104 , and a bristle portion which includes straight rows  106 ,  108 ,  110 ,  112 ,  114  and  116  of monofilament bristles, which are alternatingly disposed between arched rows  118 ,  120 ,  122 ,  124  and  126  of monofilament bristles. The straight bristles can be made according to the techniques described in co-pending application Ser. No. 09/092,092 entitled Method and Apparatus For Making Articles Having Bristles, which is incorporated herein by reference. Alternatively, the straight bristles can be made by using the techniques described herein with respect to the embodiment of FIG. 7, whereby the straight bristles are made from the straight segments  82  and  84 .  
     [0036] The straight bristles and arched bristle sub-assemblies are assembled with the head portion  104  by using the techniques described in co-pending application Ser. No. 09/092,094 entitled Monofilament Bristle Assemblies and Methods of Making Brushes Using Same, which is incorporated herein by reference. For example, and as seen in FIG. 11, the head portion  104  is provided with transverse grooves which receive the single base strings of straight rows  106  and  108  and the two base strings of arched rows  118  and  120 . Alternatively, straight rows  106  and  108  can share respective grooves with the corresponding base strings of arched row  118  to form a more compact brush head. Upon placing the base strings in the grooves, chemical, thermal or mechanical means are used to seal the grooves and lock the base strings in place.  
     [0037] The bristle sub-assemblies described herein can be used to construct brushes with a variety of bristle patterns and combinations. FIG. 12, which is a front end view of a toothbrush  128 , has two rows  130  and  132  of straight monofilament bristles which flank a single row  134  of arched monofilament bristles. The rows  130  and  132  extend to a height greater than the apex of the row  134  of arched monofilaments. All three rows extend longitudinally from the upper surface of a head portion  136  of the toothbrush  128 . Each of rows  130  and  132  have a base string mounted in the head portion  136 , while row  134  has two base strings mounted in the head portion, one corresponding to each leg of the arched monofilaments.  
     [0038]FIG. 13, also a front end view of a toothbrush  138 , has two rows  140  and  142  of arched monofilament bristles which are disposed concentrically with respect to each other. Row  140  has an apex greater than that of row  142 , and the legs of row  140  are disposed outside the legs of row  142 . Both rows extend longitudinally from the upper surface of a head portion  144  of the toothbrush  138 . Each of rows  140  and  142  have two base strings mounted in the head portion  144 .  
     [0039]FIG. 14, also a front end view of a toothbrush  146 , has a row  148  of arched monofilament bristles which run longitudinally along the brush head  150 , and three rows  152 ,  154 , and  156  of straight bristles which likewise run longitudinally along the brush head.  
     [0040] The various embodiments described herein can employ virtually any combination of arched and straight bristle sub-assemblies, and may further include the looped bristle sub-assemblies described in U.S. Ser. No. 09/092,092.  
     [0041] An advantage to the present invention is that the bristle sub-assemblies can be mixed and matched to create a variety of desired arched and straight bristle combinations. For toothbrush applications, the arched bristles have the additional advantage that there are no distal ends to be treated, as is the case for straight bristles.  
     [0042] The monofilaments used for both the straight and arched bristle subassemblies are each a single filament, as opposed to a “multi-filament,” such as yarn, twine, etc., although the monofilament may be a co-extrusion of one or more polymers to form a coaxial structure. The monofilaments may be made of several different materials, including aliphatic polyamides, aromatic polyamides, polyesters, polyolefins, polystyrene, polyvinylchloride (PVC), polyurethane, polyvinylidene chloride, fluoropolymers, styrenes and styrene copolymers. A particularly suitable polymeric material for toothbrush applications is 6,12 nylon; other nylons may be used, including 4 nylon, 6 nylon, 11 nylon, 12 nylon, 6,6 nylon, 6,10 nylon, 6,14 nylon, 10,10 nylon and 12,12 nylon and other nylon co-polymers. An example of a preferred polyester is polybutylene terephthalate (PBT).  
     [0043] When the monofilaments are abutting as in FIG. 3, the interconnection of adjacent monofilaments to each other in a flow zone may be relatively strong compared to the interconnection of the base strings to the flow zone which is substantially composed of monofilament material. This feature allows, in some applications, the removal of the base strings from the monofilaments anytime after thermal fusing. Alternatively, the adhesion between the monofilaments and the base string can be at least as strong as the adhesion between monofilaments.  
     [0044] While FIG. 3 shows the monofilaments in a single row, shoulder-to-shoulder, the density can be varied such that the adjacent monofilaments do not touch each other. Also, the density may be such that a second or greater number of rows of monofilaments are stacked upon each other. Where eight (8) mil nylon monofilament is used, for example, a density of about 125 monofilaments per inch of base string can be achieved with a single row, shoulder-to-shoulder monofilaments.  
     [0045] While toothbrush embodiments have been described, any of the wide variety of known brushes could be constructed using the arched bristles, arch-and-loop bristle combinations or arch-and-straight bristle combinations according to the present invention. For some brush applications, the monofilaments may include abrasive particles or grit material for particular brush applications. Abrasive monofilaments are commercially available under the name TYNEX® A by E. I. Du Pont De Nemours and Company of Wilmington, Del. USA. Preferably, the abrasive material comprises 0-50% by weight of the polymeric monofilaments. TYNEX® A is a 6,12 nylon monofilament containing particles of silicon carbide or aluminum oxide, which are distributed throughout the monofilament.  
     [0046] When ultrasonic welding is used, at least the monofilament or the base string, preferably both, are made of thermoplastic polymeric materials. These have been described above in reference to other embodiments.  
     [0047] The monofilaments used in any of the above embodiments may be co-extrusions of one or more polymers. Also, to achieve the desired physical characteristics of the bristles used for applications such as cleaning and scrubbing brushes, it has been found that the preferred monofilaments are those having a diameter between 2 and 200 mils, and preferably between 2 and 20 mils. In a particularly preferred embodiment for the toothbrush, the monofilaments are 4-10 mils in diameter. Monofilaments of different diameters, cross-sections, materials, surface properties and/or colors can be combined in one bristle assembly or sub-assembly to achieve specific brushing characteristics and/or appearance.  
     [0048] In embodiments using nylon for either the monofilament or the base string, or both, a preferred nylon is sold under the name TYNEX®, and is manufactured by E. I. Du Pont De Nemours and Company of Wilmington, Del. USA. TYNEX® is polyhexamethylene dodecanamide, which is the technical name for 6,12 nylon. It has a melting point of between 208 and 215° C. and has a specific gravity of 1.05-1.07, and is available commercially in many shapes and diameters.  
     [0049] Monofilaments and/or base strings suitable for use in the present invention can have shapes other than circular cross-sections, and may be hollow or have voids in their cross-section. Embodiments described above show circular cross-sectional shapes for the base string and monofilaments. Either or both the base string and monofilaments could have oval, rectangular, or other shapes. In any shape, the preferred thicknesses for the base string and monofilaments are selected to provide a level of functionality to the individual brush applications.  
     [0050] With respect to the base string, the preferred embodiments described above show a single strand of monofilament material. However, the base string could be a bundle of monofilaments having at least one of the monofilaments made of polymeric thermoplastic material.  
     [0051] The polymeric monofilaments used for bristles in the various embodiments described above can have other additives. For example, the polymeric monofilaments could include 0-50% by weight particles having functional and/or aesthetic quality. One example would be particulate material that provides a color feature that would enhance the visual appearance of the bristles. Other functional particles could also be included such as anti-microbial additives in the polymeric monofilaments. Other particulate materials or coatings may be applied to or embodied within the monofilament such as therapeutic agents or colorants, or other desirable additives. Also, the monofilaments may be surface treated to provide desired properties, such as to alter frictional coefficient.  
     [0052] The embodiments described above require “connection” between the monofilaments and the base string. In this context, “connection” means that the monofilaments are attached to the base string by a frangible joint formed by melting, adhesive bonding, solvent bonding, or similar means. The degree of frangibility can be controlled so that, if desired, the base string can be easily separated from the monofilaments after bonding.  
     [0053] The arched bristles described herein can be put on any brush head in any configuration or pattern. For example, the arched bristles may run parallel to or transverse the longitudinal axis of the brush head, or transverse and longitudinal bristles can be used concurrently. The head itself can have a substantially flat surface from which the bristles extend upwardly, as shown in the illustrated embodiments. Alternatively, the brush head can have a shaped, i.e., curved surface, in which case the bristles would tend to fan outwardly, for the case of a convex surface, or fan inwardly for the case of a concave surface. Also, the two base strings of an arched bristle sub-assembly can be mounted in the brush head in a non-parallel fashion, such that the arched row of bristles adopt a desired profile in which the apex of the arch changes along the length of the row.  
     [0054] Although the invention has been described with reference to several particular embodiments, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.