Brush – broom – and mop making – Processes
Reexamination Certificate
2000-12-21
2004-02-24
Spisich, Mark (Department: 1744)
Brush, broom, and mop making
Processes
C264S243000, C264S255000
Reexamination Certificate
active
06695414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention refers to a method of manufacturing a brush head, in particular for tooth brushes, comprising at least one brush head carrier carrying bristle filaments, by way of an injection molding process, in which a first plastic component is injected into a first mold cavity for forming a bristle carrier, and in which ends of bristle filaments projecting into the first mold cavity are encompassed by the first plastic component. The present invention relates further to a brush head, in particular for a tooth brush, comprising a brush head body carrying brush filaments, in which the fixing-sided ends of bristle filaments are embedded by means of over-molding.
2. Description of the Prior Art
A method of the above-mentioned type is for instance known from DE 845 933 going back to the applicant. The generic method differs from the conventional method of manufacturing a brush head in which recesses are made in the brush head when the brush head is injection molded, wherein bristle filaments are inserted and held into the brush head later by means of anchors, in such a manner that the bristle filaments are joined with the brush head body directly during the injection molding process. In order to obtain as reliable a connection as possible between the brush head body and the bristle filaments usually combined to form bristle bundles, the bristle bundles are regularly melted to a unit at their fixing-sided ends before injecting the plastic component. In the generic process, the enlargement and/or the fixing-sided ends of the bristle filaments are fully or partially encompassed by the first plastic component.
The generic method is particularly suitable for the manufacture of brushes having a relatively thin brush head and this is also preferable for cost reasons. However, the sealing of the ducts of the injection molding tool in which the bristle bundles are held is problematic. In view of an optimal mold filling and a precise design of the mold cavity geometry, as high an injection molding pressure as possible is preferred. The ducts holding the bristle bundles, however, form outlets into which plastic mass is pressed where excessive injection pressure is applied. Thereby the bundle position of the bristle bundles is damaged. The brush is useless. When excessive injection pressure is applied the bundles are also pressed out of the ducts.
Suggestions as to how to solve this problem were not missing in the prior art. It is suggested by DE 38 52 520 that sleeves be inserted into the ducts that have slots at their mold cavity-sided ends and which abut at a conical surface of the injection molding tool and which are pressed radially inward in such a manner to seal the bristle bundle held in the sleeve. It is also known from DE 15 54 925 to hold the bristle bundles in a clamping plate to seal the mold cavity with respect to the bristle bundles in case of injection molding pressure. The proposed solution does, however, require an expensive construction. The solution mentioned last moreover can only be realized in ducts that are arranged in an offset manner to one another. Thereby the geometry of the bristle field is predefined and restricted in an undesired manner.
Moreover, it is known from the prior art to attach the enlargement formed by melting at lie the fixing-sided ends of the bristle bundle directly to the mouth of the ducts holding the bristle bundles (DE 35 11 528). The bundles are held in the brush head body during such a process only with an insufficient expansion force. This should be avoided by an extension of the ducts into the mold cavity as suggested by DE 36 42 124. However, ducts projecting from the bristle surface into the brush body encompassing the individual bristle bundles are produced in which bacteria and dirt can get caught, which is not tolerable in particular in body care brushes, especially tooth brushes.
Besides constructive measures of sealing a mold cavity, it is furthermore known from the prior art to adapt the procedure and to let a relatively low injection pressure act when injecting the plastic mass, said injection pressure being increased after stabilizing the surface of the brush head body penetrated by the bristle bundles in order to counteract a thermal loss and to achieve as complete a design of the mold geometry as possible. Constructive measures at the mold cavity geometry were suggested which should enhance a possibly early stabilization of the surface of the brush head body penetrated by the bristle bundles.
It was for instance suggested in EP 0 749 711 that a collar be formed at the injection molding tool, said collar projecting inwardly into the mold cavity, said collar encompassing each individual bristle bundle. This proposal involves hygiene problems, since this collar is formed at the ready brush as an annular gap encompassing the bristle bundles in which dust and impurities can get caught. According to a further proposal of EP 0 759 711, the shaping tool shall have an annular gap encompassing each bristle bundle to enhance the quick stabilization of shaping mass encompassing the respective bristle bundle. This measure also leads to a contoured, i.e. unplanar, bristle surface. The bristle surface is the surface of the brush head body penetrated by the bristle bundles.
The suggestions discussed above by means of which an emerging of plastic mass from the ducts when over-molding the fixing-sided bristle bundle is prevented, were not capable of fully eliminating the underlying problem. Where injection molding pressure is low at least at the beginning of the filling of the mold, the mold cavity geometry is not formed with the necessary precision If the injection molding pressure is increased, additional sealing measures are required to prevent a penetration of plastic mass into the ducts which hold the bristle bundles. Moreover, the generic method is regularly performed by easily flowing polypropylene having a high melding index (MFI) and which can be easily processed at relatively low injection molding pressures of e.g. 10 to 15 bar at a quite favorable mold filling.
Many brushes, in particular tooth brushes as well as the brush head bodies of these tooth brushes shall, however, be manufactured of plastics having difficult flow properties, which can only be introduced into the mold cavity at relatively high injection pressures of several hundred bar. The use of such high-quality plastics is, up to the present day, restricted to such brush heads at which the brush body is first of all formed by means of injection molding and is subsequently provided with bristle bundles which are fixed in the brush head body by means of metal anchors.
SUMMARY OF THE INVENTION
The present invention is s n the object of solving the above-mentioned problems and of developing a method of manufacturing a brush head of the above-mentioned kind in a manner that a brush head body or a complete tooth brush body containing the brush head body can be manufactured with a perfect surface and a precise design of the mold cavity geometry without the risk of plastic mass penetrating into the ducts holding the bristle bundles and the risk of damaging the bristle filaments projecting over the brush head body. The present invention is furthermore based on the object of providing a brush head of a tooth brush body containing the brush head body complying with these demands.
To achieve the above-mentioned object, the generic method is developed by the invention on file in that the bristle carrier is located into another mold cavity to form the brush head body, said mold cavity being larger than the bristle carrier and which is filled by a hard component. In the method according to the invention, the brush head body is manufactured by means of a two-component or two-color or multi-component injection molding process. During the first step of the two-component injection molding process, an easily flowing plastic material, which preferably has a low pastificabon temperature, is filled into the first mold cavity. This fi
Broecker Gerd
Meyer Berthold
Laubscher, Sr. Lawrence E.
M + C Schiffer GmbH
Spisich Mark
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