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.

Description

TECHNICAL FIELD [0001] The present invention relates to a crosslinked polyolefin-based resin foam sheet having excellent flexibility and heat resistance and a process for producing the same, as well as an adhesive tape using the crosslinked polyolefin-based resin foam sheet. BACKGROUND ART [0002] Conventionally, polyolefin-based resin foam sheets have been used in a wide range of utility, and examples of this utility may include sealing materials for electronic appliances in addition to a base material of an adhesive tape and a base material of a patch. In these utilities, a polyolefin-based resin foam sheet is required to have a reduced thickness, and flexibility. [0003] As such a polyolefin-based resin foam sheet, Patent Document 1 has proposed a porous sheet with flexibility and mechanical strength improved by adding an inorganic filler to a polyolefin-based resin to form a sheet, and stretching this sheet to render it porous. [0004] However, since it is difficult to realize a hi...

AI Technical Summary

Benefits of technology

[0081] The crosslinked polyolefin-based resin foam sheet of the present invention is 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, and extruding the kneaded material through the extruder into a sheet to form an expandable polyolefin-based resin sheet, and expanding the sheet, wherein a degree of crosslinking of the crosslinked polyolefin-based resin foam sheet is 5 to 60% by weight, an aspect ratio of a cell is within a predetermined range, 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. Therefore, a thickness of the sheet can be reduced while maintaining excellent flexibility and heat resistance.

[0082] In addition, when a 25% compression strength according to JIS K6767 is 4.9 x 104 Pa or less, a tensile strength at 23° C. in at least one direction of MD and CD is 1.96×106 Pa or more, and a thermal dimensional change rate at 90° C. is −10% or more in the crosslinked polyolefin-based resin foam sheet, touch feeding, impact absorbing property and heat resistance are further excellent.

[0083] Further, since an adhesive tape in which an adhesive layer is layered on and integrated with one side of the crosslinked polyolefin-based resin foam sheet having a thickness of 0.05 to 2 mm is excellent property of absorbing irregularities of an irregular plane and, also, can reduce a thickness while retaining excellent flexibility and impact resistance, the tape can be also suitably used as a sealing material for protecting parts of a small electronic appliance.

[0084] A polyolefin-based resin constituting the crosslinked polyolefin-based resin foam sheet of the present invention 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.

[0085] Although the polyethylene-based resin obtained using a metallocene compound is flexible, the resin has little adherability; therefore, the polyolefin-based resin containing 40% by weight or more of this polyethylene-based resin exhibits little adherability in its melted state.

[0086] Therefore, when a crosslinked polyolefin-based resin foam sheet is produced by stretching a foam sheet obtained by expanding the 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, even if cell walls of the foam sheet are in the closed state, situation where cell walls are adhered to and integrated with one another can be generally prevented; therefore, a crosslinked polyolefin-based resin foam sheet having an aspect ratio of a cell within a desired range can be obtained simply.

Problems solved by technology

However, since it is difficult to realize a high expansion ratio of the porous sheet, the sheet has insufficient flexibility.

Further, since the porous sheet has not been subjected to crosslinking treatment, stretching treatment can not be performed at a melting point or more of a polyolefin-based resin constituting a porous sheet; therefore, there is a problem that distortion is occurred in the porous sheet during stretching treatment, and the porous sheet is shrunk during use.

However, the crosslinked ethylene-based resin foam has insufficient flexibility and heat resistance.

It is considered that the flexibility is improved by increasing an expansion ratio, but there is a problem that when the expansion ratio is increased, the resulting foam is thick.

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