Plunger for a syringe and method of making such a plunger

Abstract

A plunger for advancing a substance in a syringe toward a dispensing nozzle. The plunger has a plunger rod and a seal and being formed of a plastic composition. The plastic composition comprises a polymer and a filler which is non-uniformly distributed within the polymer to provide the plunger rod and the seal with different mechanical properties depending on the filler content in the portions of the plastic composition plunger forming the rod and the seal. The invention preferably provides a dental syringe which can be conveniently used, and further helps minimizing costs in the manufacturing of the dental syringe.

1 . A method of molding a plunger which has a plunger rod and a seal, the method comprising the steps of:
 providing a molten plastic composition, the plastic composition comprising a polymer and a filler distributed within the polymer,   causing a first portion of the plastic composition for forming the seal to reduce in filler content relative to the filler content in a second portion of the plastic composition, such that   the filler is distributed with a first relative filler content by weight in the plunger rod and a second relative filler content by weight in the seal, wherein the first filler content is higher than the second filler content.   
     
     
         2 . The method of  claim 1 , wherein the plunger rod and the seal are monolithically molded in one common cavity of a mold from a total quantity of a plastic composition that includes a polymer and a filler distributed in the polymer to form the plunger as one piece. 
     
     
         3 . The method of  claim 1 , wherein the first filler content of the plunger rod is between 20% by weight and about 60% by weight. 
     
     
         4 . The method of  claim 1 , wherein the total quantity of the plastic composition used to form the plunger rod and the seal has an overall filler content of 50% by weight. 
     
     
         5 . The method of  claim 1 , wherein the plunger rod extends with a generally circular cross-section along a plunger axis, and wherein the seal protrudes from the plunger rod circumferentially around the plunger axis. 
     
     
         6 . The method of  claim 5 , wherein the plunger rod comprises an annular groove about the plunger axis with the seal protruding from the plunger rod in an area of the groove. 
     
     
         7 . The method of  claim 1 , wherein the seal has an annular free edge and tapers from the plunger rod toward the free edge