Resin molded articles and method of manufacturing the same

Abstract

In a method of manufacturing a resin molded article, resin including a foaming agent is injected into a cavity defined in a mold assembly. Then, a movable mold of the mold assembly is moved to partly expand the cavity so that the foaming is promoted at the part where the cavity is expanded. Therefore, a high foamed portion having voids therein and a low foamed portion having an expansion ratio less than that of the high foamed portion are integrally formed in the resin molded article.

1 . A method of manufacturing a resin molded article comprising: 
 injecting resin including a foaming agent into a cavity defined in a mold assembly; and    foaming the injected resin in the mold assembly, wherein the foaming of the resin is partly promoted in the cavity by a foam-promoting device provided in the mold assembly, thereby creating expansion ratio difference in the molded article.    
   
   
       2 . The method according to  claim 1 , wherein the foam-promoting device includes a movable core, wherein the movable core moves to partly expand the cavity after the resin injection, thereby increasing the expansion ratio of the resin at the part where the cavity is expanded.  
   
   
       3 . The method according to  claim 1 , wherein the foam-promoting device includes a vibrator disposed to partly vibrate a mold wall defining the cavity, wherein the vibrator operates during the foaming, thereby increasing the expansion ratio of the resin at a vibrated part.  
   
   
       4 . The method according to  claim 1 , wherein the foam-promoting device includes a temperature difference generating means disposed to create temperature difference in a mold wall defining the cavity during the foaming, thereby increasing the expansion ratio at a portion where temperature is higher than the other in the mold wall.  
   
   
       5 . The method according to  claim 4 , wherein the temperature difference generating means includes a heater disposed to partly heat the mold wall.  
   
   
       6 . The method according to  claim 1 , wherein the foaming agent includes supercritical liquid nitrogen.  
   
   
       7 . The method according to  claim 1 , wherein the foaming agent includes supercritical liquid carbon dioxide.  
   
   
       8 . A method of manufacturing a resin molded article comprising: 
 injecting resin including a foaming agent into a cavity defined in a mold assembly; and    foaming the injected resin in the mold assembly, wherein during the foaming the cavity is partly narrowed by a movable core provided in the mold assembly, thereby reducing an expansion ratio of the molded article at a part where the cavity is narrowed.    
   
   
       9 . The method according to  claim 8 , wherein the foaming agent includes supercritical liquid nitrogen.  
   
   
       10 . The method according to  claim 8 , wherein the foaming agent includes supercritical liquid carbon dioxide.  
   
   
       11 . A method of manufacturing a resin molded article comprising: 
 preparing injection material including resin and a foaming agent;    defining a cavity in a mold;    injecting the prepared injection material into the cavity so that the cavity is filled with the injection material;    foaming the injection material injected in the cavity by the foaming agent;    while the foaming process, differentiating a foaming ratio of the injection material filled in at least two locations in the cavity; and    opening the mold to eject a molded article which has integrally molded at least two portions having different foaming ratio.    
   
   
       12 . The method according to  claim 11 , wherein the mold defines a thicker portion and a thinner portion in the cavity, and the differentiating step provides a higher foaming ratio in the injection material filled in the thicker portion.  
   
   
       13 . The method according to  claim 12 , wherein the differentiating step is performed by adjusting a thickness of the cavity after the cavity is filled with the injection material.  
   
   
       14 . The method according to  claim 12 , wherein the differentiating step is performed by widening the cavity to define the thicker portion during the foaming step, widening the cavity being capable of increasing the foaming ratio of the injection material filled in the thicker portion.  
   
   
       15 . The method according to  claim 14 , wherein the widening the cavity is performed after the injecting step and is performed during the foaming step.  
   
   
       16 . The method according to  claim 12 , wherein the differentiating step including the step of vibrating a portion of the mold defining the thicker portion to increase the foaming ratio of the injection material filled in the thicker portion.  
   
   
       17 . The method according to  claim 12 , wherein the differentiating step differentiates temperature of portions of the mold such that a portion defining the thicker portion is higher temperature than a portion defining the thinner portion, the higher temperature being capable of increasing the foaming ratio of the injection material filled in the thicker portion.  
   
   
       18 . The method according to  claim 12 , wherein the differentiating step including the step of heating the portion of the mold defining the thicker portion to increase the foaming ratio of the injection material filled in the thicker portion.  
   
   
       19 . The method according to  claim 12 , wherein the differentiating step is performed by narrowing the cavity to define the thinner portion during the foaming step, the narrowing the cavity being capable of decreasing the foaming ratio of the injection material filled in the thinner portion.  
   
   
       20 . The method according to  claim 19 , wherein the narrowing the cavity is performed after the injecting step and is performed during the foaming step.