Tufting oral brushes

Details Tufting oral brushes Tufting oral brushes

2001-05-23

2003-06-17

Warden, Sr., Robert J. (Department: 1744)

Brush, broom, and mop making

Brush-making machines

C300S021000

Reexamination Certificate

active

06578929

ABSTRACT:

TECHNICAL FIELD
This invention relates to methods and devices for tufting oral brushes.
BACKGROUND
Conventional toothbrushes generally include tufts of bristles mounted on the head of an oral brush handle. Until recently, the bristles were generally mounted perpendicular to the top surface of the head of the brush, and the tufts were of the same length. Methods and devices for mounting bristles in this orientation are well known.
Recently, the oral care industry has recognized the benefits of toothbrushes having tufts of varying lengths and/or tufts extending at different angles relative to the head of the toothbrush. A toothbrush having tufts extending at different angles is shown in FIG.
1
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One method of manufacturing toothbrushes involves placing tufts of finished (end-rounded) bristles so that their unfinished ends extend into a mold cavity, and forming the toothbrush body around the unfinished ends of the tufts by injection molding, thereby anchoring the tufts in the toothbrush body. The tufts are held in the mold cavity by a mold bar having blind holes that correspond to the desired positioning of the tufts on the finished brush. The finished bristles may be formed by a process that includes unwinding a rope of filaments from a spool, end-rounding the free end of the filaments, cutting off a portion of the rope that is adjacent the free end of the filaments to form bristles having the desired length, and placing the bristles into a rectangular box, called a magazine. Tufts are then formed by picking groups of bristles from the magazine.
The bristles are tamped as they are put into the magazine, in an effort to obtain height uniformity among the thousands of bristles that can eventually occupy a magazine. However, height irregularities tend to occur, which may result in unacceptable flaws in the finished toothbrush. For example, if a single bristle protrudes from the magazine when it is picked from the magazine and inserted into the mold bar, the protruding bristle may protrude from the back of the finished toothbrush.
Problems may also occur when the bristles are picked from the magazine and transferred to the machine that fills the moldbar. A picker device attempts to repeatedly choose the proper number of bristles to form a tuft. However, the inherent difficulty in this task may result in tufts of bristles that are either too small or too large for the blind holes in the moldbar. If a tuft is too small, the blind hole is not sufficiently filled and plastic will flow into the hole when the handle is formed. If a tuft is too large, one or several bristles may not enter the moldbar, but rather curl to the side and prevent the complete insertion of the tuft into the moldbar, which may then interfere with molding.
The problems inherent in transferring pre-cut tufts from a magazine to a moldbar are generally exacerbated when the tufts must be positioned so that in the finished toothbrush they will have different lengths and/or extend at different angles.
SUMMARY
The present invention features methods and machines for manufacturing toothbrushes. These methods and machines are particularly useful for forming toothbrushes with tufts of bristles that have varying lengths and/or extend from the toothbrush head at varying angles. The inventors have found that such toothbrushes can be manufactured relatively easily and economically by an injection molding process that includes advancing free ends of strands of continuous filaments into a moldbar. The filaments are not cut to bristle-length until after the free ends of the filaments have been advanced into the holes in the moldbar, thus reducing or eliminating the problems that tend to occur when handling cut tufts, as discussed above. As a result, the machine and methods of the invention are efficient and economical and tend to reduce the number of toothbrushes that must be rejected due to tufting problems. In some implementations, the free ends are selectively advanced into blind holes of different depths using a single selective clamping device. Use of a single device to perform the selective advancement results in a relatively small, compact tufting machine.
In one aspect, the invention features a method for manufacturing a toothbrush including: (a) feeding each free end of a plurality of long, continuous strands of filaments into a corresponding blind hole in a moldbar, at least some of the blind holes having different depths, the strands being advanced until the free ends are adjacent bottom surfaces of the blind holes; (b) during step (a), selectively clamping one or more of the strands with a single selective clamping device while advancing the selected strands; (c) cutting the strands of filaments so that an anchoring portion of each cut strand extends above a surface of the moldbar; (d) placing the moldbar in a molding machine so that the anchoring portion of the filaments extends into a molding cavity defined in part by the moldbar, the molding cavity being shaped to form the body of the toothbrush; and (e) delivering resin to the molding cavity to form a toothbrush body around the anchoring portion.
Some implementations include one or more of the following features. The method further includes end rounding the free ends prior to inserting the free ends into the blind holes. The dimensions of each strand correspond to predetermined dimensions of a tuft of bristles on the toothbrush. Each strand fits sufficiently tightly in the corresponding blind hole so that resin is hindered from flowing into the hole when resin is delivered to the mold. At least some of the blind holes are constructed to extend at an angle relative to a top surface of the moldbar. At least some of the blind holes are constructed to extend at different angles than others. The method further includes unwinding the plurality of strands from a single spool. The method further includes tensioning the strands so that the strands are under substantially uniform tension during unwinding. The tensioning step includes feeding the strands through a chamber in which a compressed gas, e.g., compressed air, is blown over the strands. The delivering step includes injection molding.
In another aspect, the invention features a method for manufacturing a toothbrush including: (a) feeding each free end of a plurality of long, continuous strands of filaments into a corresponding blind hole in a moldbar, at least some of the blind holes extending into the moldbar at different angles with respect to a top surface of the moldbar; (b) during step (a), selectively clamping one or more of the strands while advancing the selected strands; (c) cutting the strands of filaments so that an anchoring portion of each cut strand extends above a surface of the moldbar; (d) placing the moldbar in a molding machine so that the anchoring portion of the filaments extends into a molding cavity defined in part by the moldbar, the molding cavity being shaped to form the body of he toothbrush; and (e) delivering resin to the molding cavity to form a toothbrush body around the anchoring portion.
Some implementations include one or more of the following features. The method further includes end rounding the free ends prior to inserting the free ends into the blind holes. The method further includes unwinding the plurality of strands from a single spool. The method further includes tensioning the strands so that the strands are under substantially uniform tension during unwinding. The tensioning step includes feeding the strands through a chamber in which a compressed gas is blown over the strands. The delivering step includes injection molding.
In a further aspect, the invention features a device for manufacturing a plurality of toothbrush tufts from strands of continuous filaments, by feeding free ends of the strands into a moldbar constructed to define a portion of a molding cavity, the moldbar having a plurality of blind holes, at least some of the blind holes having different depths and each blind hole being dimensioned to receive a single strand. The device includes a feeding device inclu

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