Injection molding method and injection mold

Abstract

An injection molding method and an injection mold used therefor are provided, in which a molded product free from burrs, whitening and gate marks can be obtained with a simple structure mold, and it can adequately serve the needs for multicavity molding as well. The injection molding method comprises the steps of: introducing and charging a molten resin material into a resin reservoir and a molding cavity of an injection mold, a depth of the resin reservoir being larger than a thickness of a communicating portion; and moving a cut punch, when a portion of the resin material in the resin reservoir is still molten, to push the molten resin in the resin reservoir back from a gate into a runner so that the cut punch not only closes the communicating portion but also cuts a resin solidified portion in the resin reservoir away from a resin molded product in the molding cavity at the communicating portion.

1 . An injection mold comprising: 
 a fixed die and a movable die which form a cavity into which a molten resin material is injected to form a resin molded product;    a runner through which the molten resin material supplied to said fixed die flows, said runner being provided in said fixed die and passing through inside of said fixed die;    a resin reservoir formed by recessing said fixed die toward a opposite side of said movable die and communicating with said runner and said cavity;    a communicating portion formed on a boundary between said resin reservoir and said cavity and allowing said resin reservoir and said cavity to communicate with each other so that the molten resin material is introduced into said cavity via said resin reservoir;    a gate formed on a boundary between said runner and said resin reservoir and at an end portion of said runner in said fixed die and injecting to said resin reservoir the molten resin material supplied to said fixed die and flowed through said runner in said fixed die to charge the molten resin material into the cavity through said communicating portion from said resin reservoir;    a cut punch provided on a side of said movable die that confronts said gate through said resin reservoir and having a distal end, said cut punch being movable between a first position to close said communicating portion, in which said distal end of said cut punch is inserted into said resin reservoir so as to be in slidable contact with said resin reservoir and a second position to open said communicating portion, in which said distal end of said cut punch is drawn out of and apart from said resin reservoir;    an undercut portion provided at a periphery of said distal end of said cut punch, disposed closer to an edge portion of said distal end than a center portion of said distal end, said undercut portion serving to hold a resin solidified portion formed in said resin reservoir at the time of mold opening; and    means for driving said cut punch between said first position and said second position in a moving direction of said cut punch toward the resin reservoir,    wherein said driving means drives said cut punch to locate said distal end at said second position between said resin reservoir and said cavity to open said communicating portion in such a way that when the molten resin material is being charged into said cavity, said resin reservoir and said cavity are allowed to communicate with each other so that the molten resin material is introduced into said cavity via said resin reservoir,    wherein said driving means drives said cut punch to move said distal end of said cut punch toward said first position after the molten resin material has been charged into said cavity and said resin reservoir, and to locate said distal end at said first position in said resin reservoir to close said communicating portion in such a way that when an inner portion of the resin material that is present in said resin reservoir is still molten, a portion of the resin material thereof that is in direct contact with said cooled dies is gradually solidified and thereby the portion of the resin material at said communicating portion between said cavity and said resin reservoir is semi-solidified, said cut punch is inserted into said resin reservoir, whereby said cut punch not only closes said communicating portion while forcibly pushing the still molten resin material present in said resin reservoir back through said gate into said runner, but also cuts the resin material at said communicating portion so that said resin molded product formed in said cavity is separated from said resin solidified portion formed in said resin reservoir, and    wherein said undercut portion of said distal end of said cut punch holds the resin solidified portion formed in said resin reservoir.    
     
     
         2 . The injection mold according to  claim 1 , further comprising: 
 a sprue bush provided on said fixed die and having an introducing hole that introduces the molten resin material supplied to said fixed die,    wherein said runner communicates with said introducing hole of said sprue bush and the molten resin material supplied to said fixed die and introduced into said introducing hole of said sprue bush flows through said runner in said fixed die.    
     
     
         3 . The injection mold according to  claim 2 , wherein said sprue bush introduces into said introducing hole thereof the molten resin material supplied to said fixed die from an injection nozzle of an injection molding machine.  
     
     
         4 . The injection mold according to  claim 1 , comprising plural pairs of the cavities, the resin reservoirs and the cut punches.  
     
     
         5 . The injection mold according to  claim 1 , wherein said runner is a cold runner and has a tapered portion on an end side of said runner inside said fixed die, and said gate is formed at said end portion of said tapered portion of said runner.  
     
     
         6 . The injection mold according to  claim 5 , wherein said gate is closed with a semi-solidified resin material or a solidified resin material after said cut punch has moved to said first position.  
     
     
         7 . The injection mold according to  claim 1 , wherein said runner is a hot runner. ( 8 )  
     
     
         8 . The injection mold according to  claim 7 , wherein said hot runner has a valve gate structure. ( 9 )  
     
     
         9 . The injection mold according to  claim 8 , wherein said gate is closed by means of said valve gate structure after said cut punch has moved to said first position.  
     
     
         10 . The injection mold according to  claim 1 , wherein said injection mold is used to mold the resin molded product having an opening and has said resin reservoir and said cut punch inserted into said resin reservoir, said resin reservoir and said cut punch being provided so as to correspond to the opening of the resin molded product. ( 10 )  
     
     
         11 . The injection mold according to  claim 1 , wherein a depth as viewed in a moving direction of said cut punch in said resin reservoir is 1.5 to 10 times an opening distance of said communicating portion. ( 11 )  
     
     
         12 . The injection mold according to  claim 1 , further comprising a pushing device for removing the resin solidified portion which is attached to said distal end of said cut punch, said pushing device being slidably mounted inside said cut punch, so as to be independent of said cut punch. ( 17 )  
     
     
         13 . An injection mold comprising: 
 a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate; and    a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch can be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir,    wherein when the molten resin material is being charged into the cavity, a distal end of the cut punch which extends in a moving direction of the cut punch that is toward the resin reservoir is located between the resin reservoir and the cavity at such a position as to open a communicating portion that allows the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir;    wherein when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with the cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir, the cut punch moves toward the gate so that the cut punch is inserted into the resin reservoir, whereby the cut punch not only closes the communicating portion while forcibly pushing the still molten resin material present in the resin reservoir back into the gate, but also cuts the resin material at the communicating portion so that a resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir,    wherein the runner contacts the resin reservoir, and the gate is disposed at the point where the runner contacts the resin reservoir, such that the gate does not protrude into the resin reservoir, and    wherein an undercut portion is provided at a periphery of the distal end of the cut punch, disposed closer to an edge portion of the distal end than a center portion of the distal end, the undercut portion serving to hold the resin solidified portion formed in the resin reservoir at the time of mold opening.( 6 )    
     
     
         14 . An injection mold comprising: 
 a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate; and    a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch can be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir,    wherein when the molten resin material is being charged into the cavity, a distal end of the cut punch which extends in a moving direction of the cut punch that is toward the resin reservoir is located between the resin reservoir and the cavity at such a position as to open a communicating portion that allows the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir;    wherein when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with the cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir, the cut punch moves toward the gate so that the cut punch is inserted into the resin reservoir, whereby the cut punch not only closes the communicating portion while forcibly pushing the still molten resin material present in the resin reservoir back into the gate, but also cuts the resin material at the communicating portion so that a resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir,    wherein the runner contacts the resin reservoir, and the gate is disposed at the point where the runner contacts the resin reservoir, such that the gate does not protrude into the resin reservoir, and    wherein a depth as viewed in a moving direction of the cut punch in the resin reservoir is 1.5 to 10 times an opening distance of the communicating portion. ( 11 )    
     
     
         15 . An injection mold comprising: 
 a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate;    a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch is operative to be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir, and    a communicating portion, formed between the resin reservoir and the cavity when the cut punch is not in slidable contact with the resin reservoir, the communication portion allowing the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir,    wherein a molded resin product is formed when the cut punch device moves through the resin reservoir towards the gate to close the communication portion, which cuts the resin material at the communication portion so that the resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir,    wherein the cut punch moves at a time when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir and    wherein an undercut portion is provided at a periphery of the distal end of the cut punch, disposed closer to an edge portion of the distal end than a center portion of the distal end, the undercut portion serving to hold the resin solidified portion formed in the resin reservoir at the time of mold opening. ( 15 )    
     
     
         16 . The injection mold according to  claim 15 , further comprising a pushing device for removing the resin solidified portion which is attached to the distal ends of the cut punch, the pushing device being slidably mounted inside the cut punch, so as to be independent of the cut punch. ( 17 )  
     
     
         17 . An injection mold comprising: 
 a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate; and    a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch can be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir and having a distal end which extends in a moving direction of the cut punch that is toward the resin reservoir, the distal end located between the resin reservoir and the cavity at such a position as to open a communicating portion that allows the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir; and    means for driving the cut punch when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with the cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir,    wherein the cut punch is driven toward the gate so that the cut punch is inserted into the resin reservoir, whereby the cut punch not only closes the communicating portion while forcibly pushing the still molten resin material present in the resin reservoir back into the gate, but also cuts the resin material at the communicating portion so that a resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir, and    wherein an undercut portion is provided at a periphery of the distal end of the cut punch, disposed closer to an edge portion of the distal end than a center portion of the distal end, the undercut portion serving to hold the resin solidified portion formed in the resin reservoir at the time of mold opening.( 18 )