Multistage process for producing hollow plastic articles from half shells

Abstract

The present invention relates to a multistage process for producing hollow plastic articles, encompassing the following steps: a) producing a tubular plastic parison by means of extrusion or coextrusion; b) cutting open the plastic parison to produce two planar-surface parts; c) molding the planar-surface parts in two mold halves to give half shells, where a removable intermediate frame separates the mold halves from one another at least along the peripheral edges, so that the semifinished products/half shells are not in contact with one another; d) opening the mold halves and removing the intermediate frame; e) closing the mold halves, with the result that the half shells come into contact with one another along a peripheral rim; and f) bonding the half shells to give a hollow article.

1 . A process for producing hollow plastic articles, comprising the following steps: 
 a) producing a tubular plastic parison by means of extrusion or coextrusion;    b) cutting open the tubular plastic parison to produce two planar-surface parts;    c) molding the planar-surface parts in two mold halves to give half shells, where a removable intermediate frame separates the mold halves from one another at least along peripheral edges, wherein the planar-surface parts and half shells are not in contact with one another;    d) opening the mold halves and removing the intermediate frame;    e) closing the mold halves, wherein the half shells come into contact with one another along a peripheral rim; and    f) bonding the half shells.    
     
     
         2 . The process as claimed in  claim 1 , wherein, after removal of the intermediate frame, incorporated parts are attached to the inside of at least one of the molded half shells.  
     
     
         3 . The process as claimed in  claim 2 , wherein the incorporated parts are chosen from ventilation lines for pressure equilibration within a tank, fuel lines for equilibration of liquids within the tank, valves, anti-surge cups, pump-related sensor modules and tank sensor modules.  
     
     
         4 . The process as claimed in  claim 1 , wherein the planar-surface parts are molded in the mold halves to give half shells by means of at least one of thermoforming and blow molding.  
     
     
         5 . The process as claimed in  claim 1 , wherein the bonding of the half shells comprises at least one of adhesive bonding and welding.  
     
     
         6 . The process as claimed in  claim 4 , wherein heat from thermoforming is used to weld the half shells.  
     
     
         7 . The process as claimed in  claim 1 , further comprising molding of the hollow article by at least one of thermoforming and blow molding after bonding of the half shells.  
     
     
         8 . The process as claimed in  claim 1 , wherein the intermediate frame used comprises a plate insert which substantially provides complete filling of an area between the two mold halves.  
     
     
         9 . The process as claimed in  claim 1 , wherein the intermediate frame comprises equipment for cooling or heating.  
     
     
         10 . The process as claimed in  claim 1 , wherein the intermediate frame comprises equipment for controlled heating of the edges of the molded half shells.  
     
     
         11 . The process as claimed in  claim 1 , wherein the intermediate frame comprises equipment for heating a pinch-off edge of at least one mold half.  
     
     
         12 . The process as claimed in  claim 8 , wherein the intermediate frame or the plate insert is of single-part or multipart design.  
     
     
         13 . The process as claimed in  claim 1 , which proceeds without additional heating steps or cooling steps.  
     
     
         14 . The process as claimed in  claim 1 , wherein, during cutting open of the tubular plastic parison, use is made of driven units of a roller type, for guiding over the cutting device.  
     
     
         15 . The process as claimed in  claim 1 , wherein the cutting of the tubular plastic parison takes place before the extrusion process is complete.  
     
     
         16 . The process as claimed in  claim 1 , wherein the plastic parison comprises at least one layer made from polymeric material.  
     
     
         17 . The process as claimed in  claim 1 , wherein the plastic parison comprises a structure of at least two layers.  
     
     
         18 . The process as claimed in  claim 1 , wherein the plastic parison comprises a structure of at least two layers wherein the at least two layers are arranged, from the outside to the inside: 
 (1) a layer made from HDPE with thickness from 5 to 30%,    (2) a regrind layer with thickness from 10 to 82%,    (3) an adhesion-promoter layer with thickness from 1 to 5%,    (4) a barrier layer with thickness from 1 to 10%,    (5) an adhesion-promoter layer with thickness from 1 to 5%,    (6) a layer made from HDPE with thickness from 10 to 40%,    based in each case on a total thickness of the plastic article wall.    
     
     
         19 . A process for producing hollow plastic articles, comprising the following steps: 
 a) producing, by means of extrusion or coextrusion, a tubular plastic parison comprising at least one layer made from polymeric materials;    b) cutting open the tubular plastic parison to give two planar-surface parts by means of a suitable cutting device, and using driven floating rollers for guiding of the parison over the cutting device;    c) molding the planar-surface parts in two mold halves to give half shells, where a removable intermediate frame separates the mold halves from one another, at least along the peripheral edges, wherein the planar-surface parts and half shells are not in contact with one another;    d) opening the mold halves and removing the intermediate frame;    e) closing the mold halves, with the result that the half shells come into contact with one another along a peripheral rim; and    f) welding the half shells.    
     
     
         20 . A hollow plastic article produced by process comprising: 
 a) producing a tubular plastic parison by means of extrusion or coextrusion:    b) cutting open the tubular plastic parison to produce two planar-surface parts:    c) molding the planar-surface parts in two mold halves to give half shells, where a removable intermediate frame separates the mold halves from one another at least along peripheral edges, wherein the planar-surface parts and half shells are not in contact with one another;    d) opening the mold halves and removing the intermediate frame;    e) closing the mold halves, wherein that the half shells come into contact with one another along a peripheral rim; and    f) bonding the half shells.    
     
     
         21 . The article of  claim 20  selected from the group consisting of a plastic fuel tank in motor vehicles, a gasoline canister, a plastic tank for storage or transport of heating oil, diesel, a transport container on a utility vehicle, a solvent container, and a plastic bottle.  
     
     
         22 . The process as claimed in  claim 11  wherein the intermediate frame has equipment for heating a pinch-off edge of both mold halves.  
     
     
         23 . The process as claimed in  claim 14  wherein the driven units are driven floating rollers.  
     
     
         24 . The process as claimed in  claim 16  wherein the polymeric material is selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polyamide, polyketone, polyester, and mixtures thereof.  
     
     
         25 . The process as claimed in  claim 17  wherein the at least two layers comprise a base layer and at least one of a regrind layer, an adhesion-promoter layer and a barrier layer.  
     
     
         26 . The process as claimed in  claim 19  wherein the polymeric materials are selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polyamide, polyketone, polyester, and mixtures thereof.