JP5721504B2 - Cross-linked polyolefin resin foam sheet and adhesive tape using the same - Google Patents

Description

  The present invention relates to a crosslinked polyolefin resin foam sheet having excellent flexibility and heat resistance, and an adhesive tape using the foam sheet.

A double-sided adhesive tape is used to bond a front plate and a housing installed on a display unit (LCD or the like) in an IT device (mobile phone, camera, game, electronic notebook, etc.).
The frame outside the screen tends to become narrower due to the recent increase in screen size and design. Accordingly, the widths of the double-sided tape and the sealing material described above are becoming narrower.
Patent Document 1 discloses an adhesive tape using a crosslinked polyolefin resin foam sheet having a thickness of 0.05 to 2 mm obtained by foaming and crosslinking a foamable polyolefin resin sheet containing a pyrolytic foaming agent. Has been. However, in this pressure-sensitive adhesive sheet, for example, when slitting or punching to a width of 2 mm or less, sealing performance such as moisture resistance and dust resistance may be insufficient.

International Publication No. 2005/007731 Pamphlet

  The present invention has been made under such circumstances, and has excellent flexibility, heat resistance, and a cross-linked polyolefin resin foam sheet capable of reducing the thickness, and excellent unevenness absorbability of uneven surfaces. An object of the present invention is to provide an adhesive tape having sufficient sealing performance even when slitting or punching.

  As a result of intensive studies to achieve the above object, the present inventors have found that the foamed sheet has an average cell diameter of MD and CD, and a cross-linked polyolefin resin foam sheet in which the aspect ratio of the cell is in a specific range, particularly The present inventors have found that the object can be achieved by a crosslinked polyolefin resin foam sheet containing a polyolefin resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst in a specific ratio. The present invention has been completed based on such findings.

That is, the present invention provides the following [1] to [4].
[1] The aspect ratio 1 of bubbles (average bubble diameter of average P / VD between average bubble diameter of MD and average bubble diameter of CD) is 2 to 18, and aspect ratio 2 (average bubble diameter of MD / CD An average cell diameter) is 0.25 to 4, and an average cell diameter of MD and an average cell diameter P of CD are 140 μm or less.
[2] The crosslinked polyolefin resin foamed sheet according to the above [1], containing 40% by mass or more of a polyolefin resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.
[3] The crosslinked polyolefin resin foam sheet of [1] or [2], wherein the thickness is 0.05 to 2 mm.
[4] A pressure-sensitive adhesive tape in which a pressure-sensitive adhesive layer is laminated on at least one surface of the crosslinked polyolefin resin foamed sheet according to any one of the above [1] to [3].

  According to the present invention, the cross-linked polyolefin resin foam sheet that has excellent flexibility and heat resistance and can be thinned, and the unevenness formed by laminating and integrating the pressure-sensitive adhesive layer on at least one surface of the foam sheet It is possible to provide an adhesive tape that has excellent surface irregularity absorbability and has sufficient sealing performance even when slitting or punching to a width of 2 mm or less, for example.

It is a schematic diagram which shows MD, CD, and VD of a crosslinked polyolefin-type resin foam sheet.

[Crosslinked polyolefin resin foam sheet]
The cross-linked polyolefin resin foam sheet of the present invention (hereinafter also simply referred to as “cross-linked foam sheet”) has a bubble aspect ratio of 1 (average P / VD average cell diameter of MD average cell diameter and CD average cell diameter). ) Is 2-18, the aspect ratio 2 (MD average bubble diameter / CD average bubble diameter) is 0.25-4, and the average P of the average bubble diameter of MD and the average bubble diameter of CD is 140 μm. It is characterized by the following.
FIG. 1 is a schematic diagram showing MD, CD and VD of a cross-linked foam sheet. MD (machine direction) of the cross-linked foam sheet refers to the extrusion direction, and CD (crossing direction) of the cross-linked foam sheet is MD (machine direction). The VD (vertical (thickness) direction) of the crosslinked foamed sheet refers to a direction orthogonal to the surface of the crosslinked foamed sheet.
The crosslinked foamed sheet is formed, for example, by extruding a foamable polyolefin resin composition obtained by supplying a polyolefin resin and a thermal decomposable foaming agent to an extruder and melt-kneading the sheet from the extruder. The foamed polyolefin resin sheet thus obtained can be obtained by crosslinking / foaming.

As the pyrolytic foaming agent, known ones can be used without particular limitation. Examples thereof include azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide, and the like, and azodicarbonamide is preferable. These pyrolytic foaming agents can be used alone or in combination of two or more.
The average particle size of the pyrolytic foaming agent is preferably 6 μm or less, and more preferably 4 μm or less.
The content of the thermally decomposable foaming agent in the foamable polyolefin resin composition can be appropriately determined according to the foaming ratio of the crosslinked foamed sheet. Usually, 1-40 mass parts is preferable with respect to 100 mass parts of polyolefin resin, and 1-30 mass parts is more preferable.
When a cross-linked foam sheet is used as a sealing material for the display part of an IT device, the expansion ratio is preferably 1.1 to 2.5 cm ³ / g. Therefore, foaming in the expandable polyolefin resin composition 1-8 mass parts is preferable with respect to 100 mass parts of polyolefin resin, and 1.5-5 mass parts is more preferable. When it is more than 1 part by mass, it is possible to obtain unevenness followability, and when it is 8 parts by mass or less, it is possible to obtain the tensile strength and impact absorption of the crosslinked foamed sheet.

<Polyolefin resin>
There is no restriction | limiting in particular in polyolefin resin which comprises a crosslinked foamed sheet, Polyethylene resin, a polypropylene resin, etc. can be used.
Examples of the polyethylene resin include linear low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-α-olefin copolymer containing 50% by mass or more of ethylene, and 50% by mass or more of ethylene. Examples thereof include an ethylene-vinyl acetate copolymer.
Examples of the α-olefin constituting the ethylene-α-olefin copolymer include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Can be mentioned.

Examples of the polypropylene resin include polypropylene and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. The propylene-α-olefin copolymer may be any of a block copolymer, a random copolymer, and a random block copolymer.
Examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene and the like. Can be mentioned.
Said polyolefin resin can be used individually or in combination of 2 or more types.

(Metallocene polyolefin resin)
The polyolefin resin preferably contains a polyolefin resin synthesized using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (hereinafter also referred to as “metallocene polyolefin resin”).
Examples of the metallocene polyolefin resin include metallocene polypropylene resin, metallocene polyethylene resin, metallocene linear low density polyethylene obtained by copolymerizing ethylene and a small amount of α-olefin, and metallocene. A linear low density polyethylene is more preferable. A commercially available metallocene-based polyolefin resin can be used. Metallocene polyolefin resins and other polyolefin resins can be used in combination.
The content of the metallocene polyolefin resin in the polyolefin resin is preferably 40% by mass or more, more preferably 50% by mass or more, from the viewpoint of reducing the thickness while maintaining flexibility and heat resistance. 60 mass% or more is still more preferable, and 100 mass% is especially preferable. Note that the content of the metallocene polyolefin resin of 100% by mass means that only the metallocene polyolefin resin is used as the polyolefin resin.
The following (a) and (b) are the reasons why the content of the metallocene polyolefin resin in the polyolefin resin is preferably 40% by mass or more.

(A) A crosslinked foamed sheet can be produced by stretching a foamable polyolefin resin composition in a predetermined direction while foaming. When the foamed sheet is stretched, the foamed cells are expanded in the stretching direction so that the cell walls are close to each other. Therefore, an adhesive resin (for example, ethylene-vinyl acetate copolymer) is used as the polyolefin resin. When coalescing is used, the bubble walls are tightly integrated with each other, and the aspect ratio of the bubbles in the desired range cannot be obtained.
Therefore, by using a polyolefin resin containing 40% by mass or more of a metallocene polyolefin resin, even if the cell walls of the foam sheet are close to each other, the cell walls are closely integrated with each other. Can be generally prevented. As a result, the mechanical strength can be improved and the flexibility can be improved while keeping the aspect ratio of the bubbles within a predetermined range.
(B) The metallocene polyolefin-based resin has a characteristic that the sheet is hardly cut when stretched. Further, the foamed sheet can be stretched uniformly, and the thickness of the resulting crosslinked foamed sheet can be made substantially uniform as a whole. Moreover, it is possible to obtain a crosslinked foamed sheet having a substantially uniform aspect ratio of bubbles and generally uniform quality such as mechanical strength and flexibility.

<Physical properties of crosslinked foamed sheet>
(Aspect ratio of bubbles in cross-linked foam sheet)
The cross-linked foam sheet has an air bubble aspect ratio 1 (average of MD average bubble diameter and CD average bubble diameter / VD average bubble diameter) of 2 to 18, preferably 2.5 to 15, more preferably. Is 5-10. When the aspect ratio 1 of the bubbles is 2 or more, it is possible to obtain the flexibility of the crosslinked foamed sheet, and when it is 18 or less, it is possible to obtain the dustproof property and the preventive property. Furthermore, when the aspect ratio 1 is 15 or less, it is possible to obtain shock absorption.
The cross-linked foam sheet has an air bubble aspect ratio of 2 (average cell diameter of MD / average cell diameter of CD) of 0.25 to 4. The aspect ratio 2 of the bubbles is preferably 0.5 to 2 and more preferably 0.7 to 1.3 since the anisotropy is close to 1 and the anisotropy is small. If the aspect ratio 2 is in the above range, it is preferable that variations in mechanical properties such as flexibility and tensile strength hardly occur.

  Since the bubble aspect ratio is 1 (average P / VD average bubble diameter of the average bubble diameter of MD and the average bubble diameter of CD) is 2 to 18, the average of the average bubble diameter of MD and the average bubble diameter of CD In order for P to be 140 μm or less, the average cell diameter is preferably in the range of 76 to 686 μm, more preferably in the range of 95 to 572 μm, and still more preferably in the range of 190 to 380 μm. The average bubble diameter is a bubble diameter when the bubble is assumed to be a sphere.

The average cell diameter of MD of the crosslinked foamed sheet is a value measured by the following method.
That is, after cutting the cross-linked foam sheet over the entire length in a plane parallel to VD at a substantially central portion in the CD, the cut surface of the cross-linked foam sheet is magnified 60 times using a scanning electron microscope (SEM), A photograph is taken so that the full length of the VD of the crosslinked foamed sheet is accommodated.
In the obtained photograph, a straight line having a length of 15 cm (actual length of 2500 μm before enlargement) on the photograph is parallel to the surface of the crosslinked foamed sheet at a portion corresponding to the central portion of the VD of the crosslinked foamed sheet. Draw like so. Next, the number of bubbles located on the straight line is visually counted, and the average bubble diameter of bubbles MD is calculated based on the following formula.
Average bubble diameter of MD (μm) = 2500 (μm) / number of bubbles (pieces)

Moreover, the average cell diameter of VD of a crosslinked foamed sheet is the value measured by the following method.
That is, the photograph is taken in the same manner as the procedure for calculating the average cell diameter of MD of the crosslinked foamed sheet, and in the obtained photograph, three straight lines that divide the cut surface of the crosslinked foamed sheet into MD are divided into four. And drawn over the entire length of the foam sheet in a direction (VD) perpendicular to the surface of the crosslinked foam sheet. Thereafter, the length of each straight line is measured and the number of bubbles located on each straight line is visually counted, and the average bubble diameter of the bubble VD is calculated for each straight line based on the following formula, and the arithmetic mean of these is calculated. Is the average bubble diameter of the VD of the bubbles.
Average bubble diameter of VD (μm) = length of straight line on photograph (μm) / (60 × number of bubbles (pieces))

The average cell diameter of CD of the crosslinked foamed sheet is a value measured by the following method.
That is, the cross-linked foam sheet is cut over the entire length in the thickness direction along a plane parallel to the CD and parallel to the direction (VD) perpendicular to the cross-linked foam sheet surface, and then the cross-section of the cross-linked foam sheet is scanned. Using a scanning electron microscope (SEM), the image is magnified 60 times and photographed so that the entire length in the thickness direction of the crosslinked foamed sheet is accommodated.
Then, based on the obtained photograph, the average bubble diameter of CD is calculated in the same manner as when the average bubble diameter of MD of the crosslinked foamed sheet is measured.

In the above-described method for measuring the average bubble diameter, when counting the number of bubbles located on a straight line, the bubble diameter is determined based only on the bubble cross section appearing on the photograph.
That is, the bubbles may appear to be completely separated from each other by the cell wall on the cut surface of the crosslinked foamed sheet, but may be communicated with each other at a portion other than the cut surface of the crosslinked foamed sheet. However, in the present invention, without considering whether or not the parts other than the cut surface of the cross-linked foam sheet are in communication with each other, the bubble form is judged based only on the bubble film cross section appearing on the photograph, and on the photograph One void portion completely surrounded by the appearing bubble film cross section is determined as one bubble.
Here, “located on a straight line” means that the straight line completely penetrates the bubble at any part of the bubble, and the straight line completely penetrates the bubble at both ends of the straight line. In the case where the end of the straight line is located in the bubble without any problem, the number of bubbles was counted as 0.5.
When taking a photograph of the cut surface of the crosslinked foamed sheet, coloring the cut surface of the crosslinked foamed sheet facilitates the discrimination of bubbles, and when taking a photograph with the 2500 μm scale enlarged together, It becomes easy to specify the straight line length at.

(Crosslinking degree of crosslinked foamed sheet)
If the degree of crosslinking of the crosslinked foamed sheet is too small, bubbles in the vicinity of the surface of the foamed sheet are broken when the foamed sheet is stretched to cause surface roughness, and the appearance of the resulting crosslinked foamed sheet is deteriorated. On the other hand, if the degree of crosslinking is too large, the melt viscosity of the expandable polyolefin resin composition becomes too high, and the expandable polyolefin resin composition follows foaming when the foamable polyolefin resin composition is heated and foamed. It becomes difficult to obtain a crosslinked foamed sheet having a desired expansion ratio. Therefore, the crosslinking degree of the crosslinked foamed sheet is preferably 5 to 60% by mass, and more preferably 10 to 40% by mass.
In addition, the crosslinking degree of a crosslinked foamed sheet is a value measured by the following method.
That is, about 100 mg of a test piece is taken from the crosslinked foamed sheet, and the mass A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in 30 cm ³ of xylene at 120 ° C. and allowed to stand for 24 hours, and then filtered through a 200-mesh wire mesh to collect the insoluble matter on the wire mesh, vacuum dried, and the mass of the insoluble matter. Weigh B (mg) precisely. From the obtained value, the degree of crosslinking (mass%) is calculated by the following formula.
Crosslinking degree (% by mass) = 100 × (B / A)

(25% compressive strength of crosslinked foamed sheet)
The 25% compressive strength based on JIS K6767 of the crosslinked foamed sheet is preferably 49 kPa or less because the feel of the crosslinked foamed sheet may be lowered or the impact absorbability may be lowered if it is too large. When the foamed sheet is wound, it may be crushed in the thickness direction and the thickness may be reduced, so 20-40 kPa is more preferable.

(Tensile strength of crosslinked foamed sheet at 23 ° C)
If the tensile strength at 23 ° C. in at least one direction of MD or CD in the crosslinked foamed sheet is too small, the crosslinked foamed sheet may be cut during use when the crosslinked foamed sheet is used as a base material for an adhesive tape. Therefore, 196 kPa or more is preferable, and if it is too large, when the crosslinked foamed sheet is used as the base material of the adhesive tape, it may be difficult to cut the adhesive tape by hand and the handleability may be reduced, so 220 to 8000 kPa. Is more preferable.
In addition, the tensile strength in 23 degreeC in MD or CD of a crosslinked foamed sheet is the value measured based on JISK6767.

(Heat dimensional change rate of MD of crosslinked foamed sheet at 90 ° C.)
If the MD dimensional change rate at 90 ° C. of the crosslinked foamed sheet is too small, when the crosslinked foamed sheet is used as a base material for the adhesive tape, the heat resistance of the crosslinked foamed sheet is lowered and heat is applied. -10% or more is preferable, and when the cross-linked foamed sheet is used as the base material of the pressure-sensitive adhesive tape, heat is generated in the cross-linked foamed sheet. When added, the adhesive tape may expand and shift from the sticking position, so -10 to 5% is more preferable, and -2.0 to 2.0% is particularly preferable. Moreover, when MD heating dimensional change rate is -10% or more, it is excellent in touch, impact absorption, and heat resistance.
In addition, the heating dimensional change rate of MD at 90 ° C. of the crosslinked foamed sheet is a value measured according to JIS K6767 except that the measurement temperature is 90 ° C.

<Method for producing crosslinked foamed sheet>
Next, the manufacturing method of a crosslinked foamed sheet is demonstrated.
The method for producing a crosslinked foamed sheet having an aspect ratio 1 of 2 to 18 and an aspect ratio 2 of 0.25 to 4 is not particularly limited. For example, the following (1) to (4) The method etc. are mentioned.
(1) A foamable polyolefin resin composition obtained by supplying a polyolefin resin containing 40% by mass or more of a metallocene polyolefin resin and a thermally decomposable foaming agent to an extruder and melt-kneading the sheet from the extruder. A process for producing a foamable polyolefin resin sheet by extruding the foamed polyolefin resin sheet, and irradiating the foamable polyolefin resin sheet with ionizing radiation to crosslink the foamable polyolefin resin sheet to a crosslinking degree of 5 to 60% by mass. Heating and foaming the cross-linked foamable polyolefin resin sheet, and stretching the resulting foamed sheet in the MD and / or CD direction while maintaining the molten state during foaming. A method of stretching bubbles.
(2) By supplying a polyolefin resin containing 40% by mass or more of a metallocene polyolefin resin, a thermally decomposable foaming agent and an organic peroxide to an extruder, melt kneading, and extruding the sheet from the extruder A process for producing a foamable polyolefin resin sheet, and heating the foamable polyolefin resin sheet to decompose the organic peroxide, while crosslinking the foamable polyolefin resin sheet to a crosslinking degree of 5 to 60% by mass A process of foaming, and a method of stretching the foamed sheet by stretching the resulting foamed sheet in the MD and / or CD direction while maintaining the molten state during foaming.

(3) A polyolefin resin containing 40% by mass or more of a metallocene polyolefin resin and a thermally decomposable foaming agent are supplied to an extruder, melted and kneaded, and extruded into a sheet form from the extruder, thereby a foamable polyolefin resin. A step of producing a sheet, a step of irradiating this expandable polyolefin resin sheet with ionizing radiation to crosslink the expandable polyolefin resin sheet to a crosslinking degree of 5 to 60% by mass, and a crosslinked expandable polyolefin. A step of heating and foaming the resin sheet and then cooling it to produce a foamed sheet; a step of heating the foamed sheet again to a molten or softened state; and the direction of MD and / or CD of the foamed sheet The method of extending | stretching the bubble of a foam sheet by making it extend toward.
(4) A polyolefin resin containing 40% by mass or more of a metallocene polyolefin resin, a pyrolytic foaming agent and an organic peroxide are supplied to an extruder, melted and kneaded, and extruded from the extruder into a sheet. A process for producing a foamable polyolefin resin sheet, and heating the foamable polyolefin resin sheet to decompose the organic peroxide, while crosslinking the foamable polyolefin resin sheet to a crosslinking degree of 5 to 60% by mass The process of producing a foam sheet by cooling after foaming, the process of heating the foam sheet again to a molten or softened state, and stretching the foam sheet in the MD and / or CD direction A method of stretching bubbles in a foam sheet.

The foamable polyolefin-based resin composition includes, as necessary, an antioxidant such as 2,6-di-t-butyl-p-cresol, a foaming aid such as zinc oxide, a cell core modifier, a heat Stabilizers, colorants, flame retardants, antistatic agents, fillers, and the like may be added as long as the physical properties of the crosslinked foamed sheet are not impaired.
Examples of the method for crosslinking the expandable polyolefin resin sheet include a method of irradiating the expandable polyolefin resin sheet with ionizing radiation such as electron beam, α ray, β ray, γ ray, and the like. In addition, an organic peroxide is blended in advance, and the resulting foamable polyolefin resin sheet is heated to decompose the organic peroxide. These methods may be used in combination.

  Examples of the organic peroxide include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis. (T-butylperoxy) octane, n-butyl-4,4-bis (t-butylperoxy) valerate, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α '-Bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t- Butylperoxy) hexyne-3, benzoyl peroxide, cumylperoxyneodecanate, t-butylperoxybenzoate, 2,5-dimethyl-2,5-di ( Benzoylperoxy) hexane, t-butylperoxyisopropyl carbonate, t-butylperoxyallyl carbonate and the like. These organic peroxides can be used alone or in combination of two or more.

If the amount of the organic peroxide added is too small, crosslinking of the foamable polyolefin resin sheet may be insufficient. On the other hand, if it is too large, decomposition residues of the organic peroxide are present in the resulting crosslinked foamed sheet. Since it may remain, 0.01-5 mass parts is preferable with respect to 100 mass parts of polyolefin resin, and 0.1-3 mass parts is more preferable.
In addition, the method for foaming the foamable polyolefin resin sheet is not particularly limited, and examples thereof include a method of heating with hot air, a method of heating with infrared rays, a method using a salt bath, a method using an oil bath, and the like. May be used in combination.

(Extension of foam sheet)
The expansion of the foamed sheet may be performed after foaming the foamable polyolefin resin sheet to obtain the foamed sheet, or may be performed while foaming the foamable polyolefin resin sheet. In addition, after foaming a foamable polyolefin resin sheet to obtain a foamed sheet, when the foamed sheet is stretched, the foamed sheet is continuously stretched while the foamed sheet is maintained in a molten state without being cooled. Alternatively, after cooling the foamed sheet, the foamed sheet may be heated again to be melted or softened and then stretched.
Here, the molten state of the foamed sheet refers to a state in which the temperature of both surfaces of the foamed sheet is heated to the melting point of the polyolefin resin constituting the foamed sheet. In addition, melting | fusing point (degreeC) of polyolefin resin means the temperature of the maximum peak among the endothermic peaks accompanying the melting | dissolving of a crystal | crystallization acquired when calorimetric analysis is performed by differential scanning calorimetry (DSC).
Moreover, the softened state of a foam sheet means the state which heated the foam sheet to the temperature from which the both surface temperature T (degreeC) satisfy | fills a following formula.
Softening point of polyolefin resin−10 ° C. ≦ T ≦ Softening point of polyolefin resin + 60 ° C.
The softening point (° C.) of the polyolefin-based resin refers to the Vicat softening point measured based on ASTM D1525.

By stretching the foamed sheet, it is possible to produce a crosslinked foamed sheet in which the foam sheet has an aspect ratio within a predetermined range by stretching and deforming the foam in a predetermined direction.
In extending | stretching a foam sheet, it is made to extend toward MD or CD of a long foamable polyolefin resin sheet, or toward MD and CD. In addition, when extending | stretching a foamable polyolefin resin sheet toward MD and CD, you may extend | stretch a foam sheet simultaneously toward MD and CD, and may extend | stretch separately for every one direction.

As a method of stretching the foam sheet into MD, for example, while cooling the long foam sheet after foaming, rather than the speed (supply speed) at which the long foamable polyolefin resin sheet is supplied to the foaming process. The method of extending the foamed sheet to MD by increasing the winding speed (winding speed), and the speed of winding the foamed sheet (winding speed) rather than the speed of supplying the foamed sheet to the stretching process (supplying speed) Examples thereof include a method of stretching the foam sheet into MD by increasing the speed).
In the former method, the expandable polyolefin resin sheet expands to MD by its own expansion. Therefore, when the foam sheet is stretched to MD, expansion to MD by expansion of the expandable polyolefin resin sheet. In consideration of the amount, it is necessary to adjust the sheet supply speed and the winding speed so that the foamed sheet is stretched to MD more than the expansion amount.

  As a method of stretching the foam sheet into a CD, the both ends of the CD of the foam sheet are gripped by a pair of gripping members, and the pair of gripping members are gradually moved away from each other so that the foam sheet is formed into a CD. A method of stretching is preferred. In addition, since the expandable polyolefin resin sheet expands to CD due to its own foaming, when the expanded sheet is stretched to CD, the expansion to CD due to expansion of the expandable polyolefin resin sheet is taken into consideration. Therefore, it is necessary to adjust so that the foamed sheet is stretched to the CD more than the expansion amount.

  Here, when the draw ratio in MD and CD of the crosslinked foamed sheet is too small, the flexibility and tensile strength of the crosslinked foamed sheet may be lowered, while when too large, the foamed sheet may be cut during stretching, Or the foaming gas escapes from the foaming sheet being foamed, the expansion ratio of the resulting crosslinked foamed sheet is significantly reduced, the flexibility and tensile strength of the crosslinked foamed sheet is reduced, and the quality is uneven. There is. For this reason, the draw ratio in MD is preferably 1.1 to 5.0 times, more preferably 1.2 to 4 times, and the draw ratio in CD is preferably 1.2 to 5 times, and 1.5 to 4 times. More preferred.

In addition, the draw ratio in MD of a crosslinked foamed sheet is computed in the following way. That is, while obtaining the cube root F of the expansion ratio of the crosslinked foamed sheet, the ratio of the winding speed to the supply speed (winding speed / supply speed) V is determined, and the draw ratio of the crosslinked foamed sheet in the MD based on the following formula: Can be calculated. However, the expansion ratio of the crosslinked foamed sheet is obtained by dividing the specific gravity of the expandable polyolefin resin sheet by the specific gravity of the crosslinked foamed sheet.
Stretch ratio (times) in MD of foam sheet = V / F
In addition, the draw ratio in the CD of the crosslinked foamed sheet is that the length of CD of the crosslinked foamed sheet obtained by heating and foaming without expanding the foamable polyolefin resin sheet to its MD and CD is W1, The length of the CD of the crosslinked foamed sheet stretched on CD can be calculated based on the following formula, where W2.
Stretch ratio (times) of CD of foam sheet = W2 / W1

[Adhesive tape]
The pressure-sensitive adhesive tape of the present invention is characterized in that a pressure-sensitive adhesive layer is laminated on at least one surface of the crosslinked polyolefin resin foamed sheet of the present invention.
The pressure-sensitive adhesive tape based on the cross-linked foam sheet of the present invention is applied to the pressure-sensitive adhesive tape for absorbing the unevenness of the uneven surface, and an impact is applied to the electronic components incorporated in the electronic device main body such as a mobile phone or a video camera. It can be used as a sealing material for electronic devices for preventing dust and the like from entering the electronic device main body. In particular, since the crosslinked foamed sheet of the present invention can be thinned while maintaining excellent flexibility and heat resistance, it can be suitably used for electronic device applications that are remarkably miniaturized.

When the crosslinked foamed sheet is used as a base material for the adhesive tape, if the thickness of the crosslinked foamed sheet is too thin, the flexibility and tensile strength of the crosslinked foamed sheet are reduced, and the texture and mechanical strength of the resulting adhesive tape are reduced. Decreases. On the other hand, even if the thickness is increased, the performance of the pressure-sensitive adhesive tape cannot be expected and the economic efficiency is lowered. Therefore, 0.05 to 2 mm is preferable, and 0.1 to 8 mm is more preferable.
The adhesive tape formed by laminating and integrating the pressure-sensitive adhesive layer on one side of the cross-linked foam sheet having a thickness of 0.05 to 2 mm is excellent in the absorbability of unevenness on the uneven surface, and has excellent flexibility and impact resistance. Since the thickness can be reduced while being held, it can be suitably used as a sealing material for protecting components of a small electronic device.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer laminated and integrated on one surface or both surfaces of the crosslinked foamed sheet is not particularly limited as long as it is conventionally used for pressure-sensitive adhesive tapes. For example, acrylic pressure-sensitive adhesive Agents, urethane adhesives, rubber adhesives and the like can be used.
As a method of applying a pressure-sensitive adhesive to at least one surface of the crosslinked foamed sheet and laminating and integrating the pressure-sensitive adhesive layers, (i) a method of applying the pressure-sensitive adhesive to at least one surface of the crosslinked foamed sheet using a coating machine such as a coater And (ii) a method of spraying and applying a pressure-sensitive adhesive using at least one surface of the crosslinked foamed sheet, and (iii) a method of applying a pressure-sensitive adhesive using a brush on at least one surface of the crosslinked foamed sheet.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Example 1
(1) Metallocene linear low-density polyethylene (ExxonMobil Chemical Co., Ltd., trade name “EXACT3027”, density: 0.900 g / cm 3, mass average molecular weight (Mw) / number average molecular weight (Mn): 2.0 , Melting point: 98 ° C., softening point: 85 ° C.) 100 parts by mass, 5 parts by mass of azodicarbonamide having an average particle diameter of 2 μm, 0.3 part by mass of 2,6-di-t-butyl-p-cresol, and oxidation A foamable polyolefin resin composition composed of 1 part by mass of zinc is supplied to an extruder and melt-kneaded at 130 ° C. to form a long foamable polyolefin resin sheet having a width of 200 mm and a thickness of 0.8 mm. Extruded.
(2) Next, the foamable polyolefin resin sheet is cross-linked by irradiating both sides of the long foamable polyolefin resin sheet with 5 Mrad of an electron beam with an acceleration voltage of 800 kV to crosslink the foamable polyolefin resin sheet. It was continuously fed into a vertical heating furnace maintained at 250 ° C. by hot air and an infrared heater, and heated and foamed.
(3) After that, after continuously feeding the obtained foam sheet from the heating furnace, the foam sheet is kept on the CD while maintaining the foam sheet at a temperature of 200 to 250 ° C. on both sides. In addition to stretching, the foamed sheet is stretched to MD by winding the foamed sheet at a winding speed higher than the feeding speed (feeding speed) of the foamable polyolefin resin sheet to the heating furnace. CD and MD were stretched and deformed to obtain a crosslinked foamed sheet having the width, thickness, degree of crosslinking and expansion ratio shown in Table 1.
In addition, there exists a tendency which extends in the vertical direction with the weight of the expandable polyolefin resin sheet itself. Therefore, the winding speed of the foam sheet was adjusted in consideration of the amount of expansion to MD due to foaming.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

Example 2
A crosslinked foamed sheet was obtained in the same manner as in Example 1 except that the CD width of the crosslinked foamed sheet was 1300 mm.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

Example 3
A crosslinked foamed sheet was obtained in the same manner as in Example 1 except that it was extruded into a long foamable polyolefin resin sheet having a thickness of 0.6 mm, and the CD width of the crosslinked foamed sheet was 640 mm. Obtained.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

Example 4
Extruded into a long foamable polyolefin resin sheet having a thickness of 0.88 mm, the particle size of azodicarbonamide was 5 μm, and the amount of azodicarbonamide added was 3.5 parts by mass instead of 5 parts by mass A crosslinked foamed sheet was obtained in the same manner as in Example 3 except that the foamed polyolefin resin sheet was extruded so that the thickness was 0.32 mm.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

Example 5
Extruding into a long foamable polyolefin resin sheet having a thickness of 1.00 mm, adding azodicarbonamide to 1.5 parts by weight instead of 5 parts by weight, foaming polyolefin resin sheet The sheet was extruded so that the thickness of the foamed sheet became 0.32 mm, the ratio of the supply speed of the foam sheet to the winding speed (supply speed / winding speed), and the CD width of the crosslinked foamed sheet was 640 mm. A crosslinked foamed sheet was obtained in the same manner as in Example 1 except that.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

Comparative Example 1
A crosslinked foamed sheet was obtained in the same manner as in Example 1 except that 3 parts by mass of azodicarbonamide having an average particle size of 10 μm was used.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

Comparative Example 2
A crosslinked foamed sheet was obtained in the same manner as in Example 2 except that azodicarbonamide having an average particle size of 10 μm was used.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

Comparative Example 3
A crosslinked foamed sheet was obtained in the same manner as in Example 2 except that azodicarbonamide having an average particle size of 10 μm was used.
Table 1 shows the ratio (winding speed / feeding speed) between the winding speed and supply speed of the foamed sheet, and the MD and CD stretch ratios of the crosslinked foamed sheet.

From Table 1, Examples 1-5, compared to Comparative Examples 1 to 3, it can be seen a large number of 1mm width inside the bubbles.

  The crosslinked polyolefin resin foam sheet and pressure-sensitive adhesive tape of the present invention can be suitably used not only as a sealing material for electronic equipment by laminating and integrating an adhesive layer on at least one surface of the crosslinked polyolefin resin foam sheet. It is also possible to apply a medicine or the like to one surface of a polyolefin resin foam sheet and use it as a medical patch.

Claims (5)

The aspect ratio 1 of bubbles (average P / VD average bubble diameter of average bubble diameter of MD and average bubble diameter of CD) is 2 to 18, and aspect ratio 2 (average bubble diameter of MD / average bubble diameter of CD) ) is 0.25-4, average cell diameter of the MD is 50～111Myuemu, and Ri average P is der below 110μm of average cell diameter of the average cell diameter and a CD of MD,
The number of 1mm width inside the bubbles in the MD direction Ru 8-16 der, crosslinked polyolefin-based resin foam sheet.   The crosslinked polyolefin resin foamed sheet according to claim 1, comprising 40% by mass or more of a polyolefin resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.   The crosslinked polyolefin resin foam sheet according to claim 1 or 2, wherein the thickness is 0.05 to 2 mm. The adhesive tape by which an adhesive layer is laminated | stacked on at least one surface of the crosslinked polyolefin-type resin foam sheet of any one of Claims 1-3 . The cross-linked polyolefin resin foam sheet according to any one of claims 1 to 4 , wherein the cross-linked polyolefin resin foam sheet is slit or punched to a width of 2 mm or less.

Images