Crosslinked polyolefin-based resin foam sheet and process for producing the same as well as 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.

Claims

1. An electronic appliance comprising: an electronic appliance main body, an electronic part mounted in the electronic appliance main body, and an adhesive tape which prevents application of impact on the electronic part and prevents entrance of dust into the electronic appliance main body, wherein the adhesive tape comprises: a crosslinked polyolefin-based resin foam sheet, and an adhesive layer that 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 into an extruder, melting and kneading the polyolefin-based resin and the thermally degradable blowing agent, extruding the kneaded material through the extruder into a sheet to form an expandable polyolefin-based resin sheet, expanding the sheet to form the crosslinked polyolefin-based resin foam sheet, and stretching the crosslinked polyolefin-based resin foam sheet in a melted state after the expansion of the sheet to obtain a thickness of 0.05 to 2 mm, wherein the crosslinked polyolefin-based resin foam sheet comprises the polyolefin-based resin, wherein the polyolefin-based resin consists of a polyethylene-based resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, wherein the crosslinked polyolefin-based resin foam sheet has a degree of crosslinking of the crosslinked polyolefin-based resin foam sheet of 10 to 60% by weight, a first aspect ratio of a cell (MD average cell diameter/CD average cell diameter) of 0.25 to 0.60, and a second aspect ratio of a cell (CD average cell diameter/VD average cell diameter) of 2.5 to 15, wherein the expandable polyolefin-based resin sheet is continuous and the crosslinked polyolefin-based resin foam sheet is continuous, and wherein the crosslinked polyolefin-based resin foam sheet is stretched towards both of directions of MD and CD.

2. The electronic appliance according to claim 1, wherein the crosslinked polyolefin-based resin foam sheet comprises 40% by weight or more of the polyolefin-based resin.

3. The electronic appliance according to claim 1, wherein the crosslinked polyolefin-based resin foam sheet has a stretching ratio in CD of 1.2 to 4.5 times.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic view showing MD, CD and VD of a crosslinked polyolefin-based resin foam sheet.

EXPLANATION OF SYMBOLS

(2) 1: crosslinked polyolefin-based resin foam sheet.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples 1 to 4, Comparative Example 4

(3) An expandable polyolefin-based resin composition consisting of 100 parts by weight of linear low density polyethylene (made by Exxon Chemical Company, trade name: EXACT3027, density: 0.900 g/cm.sup.3, weight-average molecular weight: 2.0, melting point: 98 C., softening point: 85 C.) obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, 5 parts by weight of azodicarbonamide, 0.3 part by weight of 2,6-di-t-butyl-p-cresol and 1 part by weight of zinc oxide was fed to an extruder, melted and kneaded at 130 C., and extruded into a continuous expandable polyolefin-based resin sheet having a width of 200 mm and a thickness of 0.8 mm.

(4) Then, both sides of the continuous expandable polyolefin-based resin foam sheet were irradiated with an electron beam of an acceleration voltage of 800 kV at 5 Mrad to crosslink the expandable polyolefin-based resin sheet, and this expandable polyolefin-based resin sheet was continuously sent into an expanding furnace retained at 250 C. with a hot air and an infrared heater, followed by heating and expansion.

(5) Thereafter, after the resulting foam sheet was continuously sent out from the expanding furnace, this foam sheet was stretched in its CD in the state where a temperature of both sides of the foam sheet was maintained at 200 to 250 C. and, at the same time, the foam sheet was wound at a winding speed faster than a speed of sending the expandable polyolefin-based resin sheet into the expansion furnace (feeding speed), thereby, the foam sheet was stretched in MD to stretch and deform a cell of the foam sheet in CD and MD, to obtain a crosslinked polyolefin-based resin foam sheet having a width, a thickness, a degree of crosslinking and an expansion ratio shown in Table 1. The winding speed of the foam sheet was adjusted while an inflation portion in MD by expansion of the expandable polyolefin-based resin sheet itself was taken into consideration. In addition, a ratio of the winding speed and the feeding speed of the foam sheet (winding speed/feeding speed), as well as a stretching ratio of MD and CD of the crosslinked polyolefin-based resin foam sheet are shown in Table 1.

(6) In Comparative Example 4, since a stretching ratio of MD and CD of the foam sheet was too great, an expansion gas was escaped, and an expansion ratio of the resulting crosslinked polyolefin-based resin foam sheet results in a low level of 5.2 times.

Example 5

(7) According to the same procedure as that of Example 1 except that an amount of azodicarbonamide to be added was 3 parts by weight in place of 5 parts by weight, extrusion was performed so that a thickness of the expandable polyolefin-based resin sheet was 0.32 mm, and a ratio of a feeding speed and a winding speed (feeding rate/winding rate) of the foam sheet, as well as a width of CD in the crosslinked polyolefin-based resin foam sheet was 1050 mm, a crosslinked polyolefin-based resin foam sheet was obtained.

Example 6

(8) An expandable polyolefin-based resin composition consisting of 100 parts by weight of linear low density polyethylene (made by Exxon Chemical Company, trade name: EXACT3027, density: 0.900 g/cm.sup.3, weight-average molecular weight: 2.0, melting point: 98 C., softening point: 85 C.) obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, 5 parts by weight of azodicarbonamide, 0.3 part by weight of 2,6-di-t-butyl-p-cresol and 1 part by weight of zinc oxide was fed to an extruder, and melted and kneaded it at 130 C., which was extruded into a continuous expandable polyolefin-based resin sheet having a width of 200 mm and a thickness of 0.8 mm.

(9) Then, both sides of the continuous expandable polyolefin-based resin sheet were irradiated with an electron beam of an acceleration voltage of 800 kV at 5 Mrad to crosslink the expandable polyolefin-based resin sheet, this expandable polyolefin-based resin sheet was continuously sent into an expansion furnace retained at 250 C. by a hot air and an infrared heater, was heated and expanded, and was cooled to prepare a continuous foam sheet, which was wound in a coil.

(10) The resulting foam sheet was successively fed to a stretching step, the foam sheet was heated so that a temperature of its both sides became 110 C., the foam sheet was stretched in its CD and, at the same time, the foam sheet was stretched in MD by winding the foam sheet at a winding speed faster than a feeding speed of the foam sheet, to stretch and deform a cell of the foam sheet in CD and MD to obtain a crosslinked polyolefin-based resin foam sheet having a width, a thickness, a degree of crosslinking and an expansion ratio shown in Table 1. In addition, a ratio of a winding speed and a feeding speed of the foam sheet (winding speed/feeding speed), as well as a stretching ratio of MD and CD of the crosslinked polyolefin-based resin foam sheet are shown in Table 1.

Comparative Example 1

(11) According to the same procedure as that of Example 1 except that the foam sheet was not stretched in CD, a crosslinked polyolefin-based resin foam sheet was obtained.

Comparative Example 2

(12) According to the same procedure as that of Example 1 except that a width of CD of the foam sheet became 2000 mm, a crosslinked polyolefin-based resin foam sheet was tried to be prepared, but the foam sheet was cut in CD, and a crosslinked polyolefin-based resin foam sheet could not be obtained.

Comparative Example 3

(13) According to the same procedure as that of Example 2 except that a polyolefin-based resin consisting of 20 parts by weight of linear low density polyethylene (made by Exxon Chemical Company, trade name: EXACT3027, density: 0.900 g/cm.sup.3, weight-average molecular weight: 2.0) obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, and 80 parts by weight of a polyethylene resin (density: 0.923 g/cm.sup.3) was used in place of 100 parts by weight of linear low density polyethylene (made by Exxon Chemical Company, trade name: EXACT3027, density: 0.900 g/cm.sup.3, weight-average molecular weight: 2.0) obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, a crosslinked polyolefin-based resin foam sheet was tried to be prepared, but the foam sheet was cut in CD in a step of stretching the foam sheet, and a crosslinked polyolefin-based resin foam sheet could not be obtained.

Comparative Example 5

(14) According to the same procedure as that of Example 1 except that a polyolefin-based resin consisting of 20 parts by weight of linear low density polyethylene (made by Exxon Chemical Company, trade name: EXACT3027, density: 0.900 g/cm.sup.3, weight-average molecular weight: 2.0) obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst and 80 parts by weight of an ethylene-vinyl acetate copolymer (ethylene content: 18% by weight) was used in place of 100 parts by weight of linear low density polyethylene (made by Exxon Chemical Company, trade name: EXACT3027, density: 0.900 g/cm.sup.3, weight-average molecular weight: 2.0) obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, a crosslinked polyolefin-based resin foam sheet was prepared.

(15) Average cell diameters of MD, CD and VD in the resulting crosslinked polyolefin-based resin foam sheet, an aspect ratio of a cell (MD average cell diameter/CD average cell diameter) (expressed as MD/CD in Table 1) and an aspect ratio of a cell (CD average cell diameter/VD average cell diameter) (expressed as CD/VD in Table 1), a 25% compression strength according to JIS K6767, tensile strengths at 23 C. in MD and CD, as well as a thermal dimensional change rate in MD at 90 C. are shown in Table 1.

(16) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Winding speed/ 2.50 2.50 3.10 4.30 2.15 2.50 feeding speed Stretching MD 1.2 1.2 1.4 2.0 1.3 1.2 ratio CD 2.0 3.0 1.4 1.5 2.4 2.0 (times) Average MD 112 110 145 200 165 115 cell CD 210 330 142 150 370 218 diameter VD 38 24 44 30 28 36 (m) Aspect MD/CD 0.53 0.33 1.02 1.33 0.45 0.53 ratio CD/VD 5.53 13.75 3.23 5.00 13.21 6.06 Width (mm) 860 1300 600 640 1050 860 Thickness (mm) 0.6 0.4 0.75 0.5 0.1 0.6 Degree of 25 25 25 25 25 25 crosslinking (wt %) Expansion ratio 9.8 9.6 9.9 9.6 4.7 9.9 (times) 25% compression 3.92 2.94 4.90 3.92 2.94 3.88 strength (10.sup.4 Pa) Tension MD 3.03 2.94 3.92 4.41 6.88 2.98 strength CD 2.94 3.92 2.45 2.50 6.96 2.90 (10.sup.6 Pa) Thermal MD 2.0 0.5 3.0 3.5 3.7 2.0 dimensional CD 5.0 8.0 3.0 3.5 9.5 7.0 change rate (%) Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Winding speed/ 2.50 2.50 2.50 4.10 2.50 feeding speed Stretching MD 1.2 1.2 1.2 2.4 1.2 ratio CD 1.0 5.8 2.0 (times) Average MD 115 190 305 cell CD 100 310 300 diameter VD 78 15 48 (m) Aspect MD/CD 1.15 0.61 1.02 ratio CD/VD 1.28 20.67 6.25 Width (mm) 430 1300 860 Thickness (mm) 1.2 0.25 0.6 Degree of 25 25 25 crosslinking (wt %) Expansion ratio 10.0 5.2 9.9 (times) 25% compression 9.80 5.88 2.94 strength (10.sup.4 Pa) Tension MD 2.99 5.88 1.27 strength CD 2.06 4.90 0.69 (10.sup.6 Pa) Thermal MD 3.0 6.0 20 dimensional CD 1.0 8.0 40 change rate (%)

INDUSTRIAL APPLICABILITY

(17) The crosslinked polyolefin-based resin foam sheet of the present invention is suitable for using as an adhesive tape wherein an adhesive layer is layered on and integrated with at least one side of the crosslinked polyolefin-based resin foam sheet, or using as a medical patch wherein a medicament is applied on one side of the crosslinked polyolefin-based resin foam sheet.