Foam sheet of crosslinked polyolefin resin,process for producing the same and pressure-sensitive adhesive tape

Abstract

The present invention provides a crosslinked polyolefin-based resin-extruded foam sheet capable of reducing its thickness while retaining excellent flexibility and heat resistance. The crosslinked polyolefin-based resin foam sheet of the present invention is obtained by feeding a polyolefin-based resin and a thermally degradable blowing agent to an extruder, melting and kneading them, extruding the kneaded material through the extruder into a sheet to form an expandable polyolefin-based resin sheet, and expanding the sheet. Herein, a degree of crosslinking of the crosslinked polyolefin-based resin foam sheet is 5 to 60% by weight, an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) is 0.25 to 1, and the polyolefin-based resin contains 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.

1 . A crosslinked polyolefin-based resin foam sheet obtained by feeding a polyolefin-based resin and a thermally degradable blowing agent to an extruder, melting and kneading them, extruding the kneaded material through the extruder into a sheet to form an expandable polyolefin-based resin sheet, and expanding the sheet, the crosslinked polyolefin-based resin foam sheet comprising the polyolefin-based resin which contains 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, the crosslinked polyolefin-based resin foam sheet having a degree of crosslinking of the crosslinked polyolefin-based resin foam sheet is of 5 to 60% by weight and an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) of 0.25 to 1.  
   
   
       2 . The crosslinked polyolefin-based resin foam sheet according to  claim 1 , wherein an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) is 2 to 18.  
   
   
       3 . A crosslinked polyolefin-based resin foam sheet obtained by feeding a polyolefin-based resin and a thermally degradable blowing agent to an extruder, melting and kneading them, extruding the kneaded material through the extruder into a sheet to form an expandable polyolefin-based resin sheet, and expanding the sheet, the crosslinked polyolefin-based resin foam sheet comprising the polyolefin-based resin which contains 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, the crosslinked polyolefin-based resin foam sheet having wherein a degree of crosslinking of the crosslinked polyolefin-based resin foam sheet is of 5 to 60% by weight[[,]] and an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) of 2 to 18.  
   
   
       4 . The crosslinked polyolefin-based resin foam sheet according to  claim 1 , wherein a 25% compression strength according to JIS K6767 is 4.9×10 4  Pa or less, a tensile strength at 23° C. in at least one direction. of MD and CD is 1.96×10 6  Pa or more, and a thermal dimensional change rate of MD at 90° C. is −10% or more.  
   
   
       5 . The crosslinked polyolefin-based resin foam sheet according to  claim 3 , wherein a 25% compression strength according to JIS K6767 is 4.9×10 4  Pa or less, a tensile strength at 23° C. in at least one direction of MD and CD is 1.96×10 6  Pa or more, and a thermal dimensional change rate at 90° C. is −10% or more.  
   
   
       6 . An adhesive tape comprising a crosslinked polyolefin-based resin foam sheet having a thickness of 0.05 to 2 mm, and an adhesive layer which is layered on and integrated with at least one side of the crosslinked polyolefin-based resin foam sheet, wherein the crosslinked polyolefin-based resin foam sheet is obtained by feeding a polyolefin-based resin and a thermally degradable blowing agent to an extruder, melting and kneading them, extruding the kneaded material through the extruder into a sheet to form an expandable polyolefin-based resin sheet, and expanding the sheet, a degree of crosslinking of the crosslinked polyolefin-based resin foam sheet is 5 to 60% by weight, an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) is 0.25 to 1, and the polyolefin-based resin contains 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.  
   
   
       7 . An adhesive tape comprising a crosslinked polyolefin-based resin foam sheet having a thickness of 0.05 to 2 mm, and an adhesive layer which is layered on and integrated with at least one side of the crosslinked polyolefin-based resin foam sheet, wherein the crosslinked polyolefin-based resin foam sheet is obtained by feeding a polyolefin-based resin and a thermally degradable blowing agent to an extruder, melting and kneading them, extruding the kneaded material through the extruder into a sheet to form an expandable polyolefin-based resin sheet, and expanding the sheet, a degree of crosslinking of the crosslinked polyolefin-based resin foam sheet is 5 to 60% by weight, an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) is 2 to 18, and the polyolefin-based resin contains 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.  
   
   
       8 . A process for producing a crosslinked polyolefin-based resin foam sheet, comprising the steps of: feeding a polyolefin-based resin containing 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, and a thermally degradable blowing agent to an extruder, melting and kneading them, and extruding the kneaded material through the extruder into a sheet to prepare an expandable polyolefin-based resin sheet; crosslinking the expandable polyolefin-based resin sheet so as to have a degree of crosslinking of 5 to 60% by weight; and heating and expanding the crosslinked expandable polyolefin-based resin sheet, and stretching the resulting foam sheet towards any one or both of directions of MD and CD while maintaining the melted state at expansion to stretch a cell of the foam sheet, thereby producing a crosslinked polyolefin-based resin foam sheet in which an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) is 0.25 to 1 or an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) is 2 to 18.  
   
   
       9 . A process for producing a crosslinked polyolefin-based resin foam sheet, comprising the steps of: feeding a polyolefin-based resin containing 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, and a thermally degradable blowing agent to an extruder, melting and kneading them, and extruding the kneaded material through the extruder into a sheet to prepare an expandable polyolefin-based resin sheet; heating the expandable polyolefin-based resin sheet to expand the sheet while crosslinking it so as to have a degree of crosslinking of 5 to 60% by weight; and stretching the resulting foam sheet towards any one or both of directions of MD and CD while maintaining the melted state at expansion to stretch a cell of the foam sheet, thereby producing a crosslinked polyolefin-based resin foam sheet in which an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) is 0.25 to 1 or an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) is 2 to 18.  
   
   
       10 . A process for producing a crosslinked polyolefin-based resin foam sheet, comprising the steps of: feeding a polyolefin-based resin containing 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, and a thermally degradable blowing agent to an extruder, melting and kneading them, and extruding the kneaded material through the extruder into a sheet to prepare an expandable polyolefin-based resin sheet; crosslinking the expandable polyolefin-based resin sheet so as to have a degree of crosslinking of 5 to 60% by weight; heating and expanding the crosslinked expandable polyolefin-based resin sheet to prepare a foam sheet; heating this foam sheet to obtain the melted or softened state; and stretching the foam sheet towards any one or both of directions of MD and CD to stretch a cell of the foam sheet, thereby producing a crosslinked polyolefin-based resin foam sheet in which an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) is 0.25 to 1 or an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) is 2 to 18.  
   
   
       11 . A process for producing a crosslinked polyolefin-based resin foam sheet, comprising the steps of: feeding a polyolefin-based resin containing 40% by weight or more of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, and a thermally degradable blowing agent to an extruder, melting and kneading them, and extruding the kneaded material through the extruder into a sheet to prepare an expandable polyolefin-based resin sheet; heating the expandable polyolefin-based resin sheet to expand the sheet while crosslinking it so as to have a degree of crosslinking of 5 to 60% by weight to prepare a foam sheet; heating the foam sheet to obtain the melted or softened state; and stretching the foam sheet towards any one or both of directions of MD and CD to stretch a cell of the foam sheet, thereby producing a crosslinked polyolefin-based resin foam sheet in which an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) is 0.25 to 1 or an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) is 2 to 18.