Manufacturing method

Abstract

A method for making products made of plastics comprises the steps of moulding a piece made of polyethylene PE, or made of polypropylene PP, and mechanically folding in a guided manner a flap portion of the aforesaid piece at a folding temperature that is greater than ambient temperature ed less than the alpha-type intermediate physical transition temperature of the material. The method reduces the spring-back of the folded portion and the yield in the folding zone.

1 - 15 . (canceled) 
     
     
         16 . A method for manufacturing products comprising the steps of molding a piece of plastic material comprising at least a semi-crystalline plastic material, said molded piece having at least a skirt portion;
 forming on said skirt portion a facilitated detachment zone that separates an edge portion from the rest of the skirt portion, said forming step including a material removal step, said material removal step being performed with the plastic material of said skirt portion at a removal temperature that is greater than an ambient temperature;   selecting said removal temperature according to at least an intermediate physical transition temperature of said plastic material, said removal temperature being greater than a first limit temperature Tinf, said first limit temperature Tinf being equal to
     T inf=( Tα+T amb)/2, 
   
       or to
     T inf =T α−40° C.,
 
 Tα is the alpha-type physical transition temperature of said plastic material, Tamb is the ambient temperature, for semi-crystalline polymers the transition α representing the crystalline phase, 
 where said removal temperature being less than a second limit temperature Tsup where Tsup=Tα+10° C., 
 
     
     
         17 . A method according to  claim 16 , wherein said removal temperature is greater than
     T inf =T α−40° C.
   
     
     
         18 . A method according to  claim 16 , wherein said material removal temperature is less than Tα. 
     
     
         19 . A method according to  claim 16 , wherein said material removal step comprises a cutting operation along a circumferential extension region of said skirt portion. 
     
     
         20 . A method according to  claim 16 , and further comprising the steps of mechanically folding in a guided manner a part of said edge portion protruding as a flap around a folding zone at a folding temperature, and selecting said folding temperature is a function of said intermediate physical transition temperature Tα. 
     
     
         21 . A method according to  claim 20 , wherein said folding temperature is greater than said first limit temperature Tinf and is less than said second limit temperature Tsup. 
     
     
         22 . A method according to  claim 20 , wherein said folding temperature is less than the alpha-type physical transition temperature of said plastic material. 
     
     
         23 . A method according to  claim 20 , wherein said material removal temperature is within a range equal to said folding temperature plus/minus 15° C. 
     
     
         24 . A method according to  claim 16 , wherein said semi-crystalline plastic material comprises at least a material selected from the following group of materials: polyethylene, high density polyethylene, polypropylene, polyethyleneterephthalate. 
     
     
         25 . A method according to  claim 16 , wherein said material removal temperature is greater than a beta-type physical transition temperature of said plastic material. 
     
     
         26 . A method according to  claim 16 , and further comprising a step of cooling at least a part of said molded piece, said at least part of said molded piece comprising said skirt portion and/or said edge portion, said cooling step being performed before said material removal step and further being performed in a controlled manner in order to bring said at least part of said molded piece said removal temperature. 
     
     
         27 . A method according to  claim 26 , wherein said cooling step comprises directing flow of a cooling fluid to said at least a part of the molded piece to be cooled. 
     
     
         28 . A method according to  claim 26 , wherein said cooling step comprises moving said molded piece along a preset cooling path between a molding zone and a material removal zone.