Apparatus for injection molding a plastic monolith

In apparatus for injection molding a plastic monolith comprised of a base of plastic resin material having elongated bristles of the same resin material monolithically relatively upstanding on one side thereof so that the monolith can be used as a brush, the bristles having longitudinal axes relatively transverse the one side of the base, tips spaced apart from the one side of the base along the axes, shank portions relatively upstanding along the axes to points thereon relatively intermediate between the one side of the base and the tips of the bristles, and tip portions extending relatively outwardly along the axes of the bristles from the intermediate points thereon to the tips of the respective bristles,

• a mold comprised of a pair of relatively reciprocable members which are disposed on opposite sides of a plane of the mold and have mutually opposing faces thereon which are operable to define a mold cavity having a cross section corresponding to the base of the monolith when the faces of the members are abutted with one another at the plane of the mold,
• one of the mold cavity defining members having a set of elongated bristle defining branches of the cavity located therein, which extend relatively inwardly of the one mold cavity defining member from the face thereof along longitudinal axes transverse the plane of the mold,
• the branches of the cavity having relatively proximal and distal ends disposed transverse the respective axes thereof at the face of the one mold cavity defining member and at points spaced apart from the face of the one mold cavity defining member, respectively, and annular walls circumposed about the respective axes thereof in the space between the relatively proximal and distal ends of the respective branches,
• the branches having cross sections at the inner peripheries of the walls in planes transverse the axes of the respective branches, including cross sections in spaced first and second planes coinciding with the intermediate points on the axes of the bristles and with the relatively distal ends of the branches, respectively, adapted so that the branches are operable to form the shank and tip portions of the respective bristles,
• means for injecting a mass of plastic resin material into the mold cavity, and in turn into the respective branches thereof through the relatively proximal ends of the branches,
• means disposed at the distal ends of the respective branches to close the distal ends to the flow of resin material therethrough, and
• means disposed about the walls of the respective branches in the space between the respective first and second cross sectional planes of the branches, to discharge gas displaced into the respective branches from the cavity when the plastic resin material occupies the branches through the relatively proximal ends thereof,
• the closure means forming end walls for the relatively distal ends of the branches having cross sectional areas in planes transverse the axes of the branches no greater than the cross sectional areas of the distal ends of the branches in said second cross sectional planes thereof, and the annular walls of the respective branches having cross sections in planes coinciding with the axes of the respective branches that taper along straight lines relatively inwardly of the axes of the respective branches in the direction relatively axially inwardly of the one mold cavity defining member from the face thereof, relatively from the first cross sectional planes of the respective branches to the second cross sectional planes of the respective branches, so that the branches and the respective bristles formed therein relatively slideably disengage from one another when the mold cavity defining members are reciprocated in relation to one another to open the mold and the monolith is relatively retracted from the face of the one mold cavity defining member to remove the bristles therefrom.