JPWO2018181498A1 - Polyolefin foam sheet, production method thereof and pressure-sensitive adhesive tape - Google Patents

Abstract

The polyolefin foam sheet of the present invention is a polyolefin foam sheet obtained by foaming a foamable composition containing a polyolefin resin, and has a strength of 0.02 to 0.07 at a time of 20 milliseconds measured by a pulsed NMR Hahn Echo method. In the range.

Description

  The present invention relates to a polyolefin foam sheet, a method for producing the same, and an adhesive tape having the polyolefin foam sheet.

BACKGROUND ART In electronic devices such as mobile phones, cameras, game machines, electronic organizers, and personal computers, a sealing material or a shock absorbing material made of a foamed sheet, and an adhesive tape made of a foamed sheet as a base material are used. For example, a display device used in the above-described electronic device generally has a structure in which a protection panel is installed on a display panel such as an LCD, and the protection panel is attached to a frame portion outside the display panel. For this purpose, an adhesive tape based on a foamed sheet is used.
BACKGROUND ART Conventionally, as a foamed sheet used inside an electronic device, a crosslinked polyolefin-based resin foamed sheet obtained by foaming and cross-linking a foamable polyolefin-based resin sheet containing a pyrolytic foaming agent is known (for example, see Patents). Reference 1).

International Publication No. 2005/007731

  By the way, in recent years, electronic devices have been miniaturized, while various components have advanced functions, and the space inside the electric devices has been increasingly restricted. For example, the frame portion outside the display panel has been reduced in space due to the downsizing of the electronic device and the upsizing of the display device. Therefore, a foamed sheet is required to have high flexibility and durability even when it is made not only relatively thick but also thin.

  Foamed sheets are known to reduce apparent density to increase flexibility. In addition, in the case of a shock absorbing material or the like, attempts have been made to increase the delamination strength in order to increase durability such as impact resistance. However, the apparent density and the mechanical strength of the foamed sheet are generally in a trade-off relationship.For example, if the apparent density is reduced to increase the flexibility, the delamination strength decreases, so It is difficult to achieve both good performance and mechanical strength.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a foamed sheet having excellent flexibility and mechanical strength even in a thin foamed sheet.

As a result of intensive studies, the present inventors have found that when the strength at a time of 20 milliseconds by pulse NMR measurement is within a certain range, the value of the delamination strength / density increases, and both the flexibility and mechanical strength of the foamed sheet are reduced. The present inventors have found that it is easy to improve the condition, and have completed the present invention described below.
That is, the present invention provides the following [1] to [11].
[1] A polyolefin foam sheet obtained by foaming a foamable composition containing a polyolefin resin, wherein the strength at a time of 20 milliseconds measured by the pulsed NMR Hahn Echo method is in the range of 0.02 to 0.07. Polyolefin foam sheet.
[2] The polyolefin foam sheet according to the above [1], wherein the polyolefin resin is a polyethylene resin.
[3] The polyolefin foam sheet according to the above [2], wherein the polyolefin resin contains a linear low-density polyethylene polymerized with a metallocene compound polymerization catalyst.
[4] The polyolefin foam sheet according to the above [3], wherein the polyolefin resin further contains an ethylene-vinyl acetate copolymer.
[5] The polyolefin foam sheet according to any one of [1] to [4], wherein the degree of crosslinking is 30 to 70% by mass.
[6] The polyolefin foam sheet according to any one of [1] to [5], wherein the thickness is 0.02 to 0.8 mm.
[7] The polyolefin foam sheet according to any one of the above [1] to [6], which has an expansion ratio of 1.2 to 12 cm ³ / g.
[8] The polyolefin foam sheet according to any one of the above [1] to [7], which is obtained by foaming a foamable composition further containing a pyrolytic foaming agent.
[9] The method for producing a polyolefin-based foamed sheet according to any one of the above [1] to [8], wherein the crosslinked foamable composition comprises a polyolefin-based resin and a pyrolytic foaming agent. A method for producing a polyolefin-based foam sheet, wherein the foam is heated to foam the pyrolytic foaming agent.
[10] The method for producing a polyolefin foam sheet according to [9], wherein the foamable composition is foamed and further stretched.
[11] An adhesive tape, comprising: the polyolefin-based foam sheet according to any one of [1] to [8]; and an adhesive layer provided on at least one surface of the polyolefin-based foam sheet.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where a sheet | seat is thinned, it is possible to provide a foamed sheet with favorable both flexibility and durability.

It is explanatory drawing of the interlayer strength measuring method.

Hereinafter, the present invention will be described in detail using embodiments.
[Polyolefin foam sheet]
The crosslinked polyolefin-based foam sheet according to the present invention (hereinafter, also simply referred to as “foam sheet”) is a foam obtained by foaming a foamable composition containing a polyolefin resin, and the foamed sheet is measured by a pulse NMR Hahn Echo method. The intensity at a time of 20 milliseconds is in the range of 0.02 to 0.07.
In the present invention, when the above-mentioned strength exceeds 0.07, the value of delamination strength / density described later becomes low, and it is difficult to improve both flexibility and durability. On the other hand, if the strength is less than 0.02, it is difficult to control the foaming state, and it is difficult to produce a foam sheet practically.
In addition, from the viewpoint of improving both the durability and the flexibility, the strength is preferably from 0.03 to 0.07, and more preferably from 0.04 to 0.065.

(Polyolefin resin)
Examples of the polyolefin resin used for the foamed sheet include a polyethylene resin, a polypropylene resin, an ethylene-vinyl acetate copolymer, and the like. Among these, a polyethylene resin is preferable.
Examples of the polyethylene resin include a polyethylene resin polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, and a chromium oxide compound. Preferably, a polyethylene resin polymerized with a metallocene compound polymerization catalyst is used.

As the polyethylene resin, a linear low-density polyethylene is preferable. By using a linear low-density polyethylene, the obtained foamed sheet can have high flexibility and can have a reduced thickness. This linear low-density polyethylene is more preferably obtained using a polymerization catalyst such as a metallocene compound. The linear low-density polyethylene is obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more with respect to the total amount of monomers) and a small amount of α-olefin as required. The resulting linear low density polyethylene is more preferred.
Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene and the like. Among them, α-olefins having 4 to 10 carbon atoms are preferred.
Polyethylene resin, for example the density of the linear low density polyethylene as described above is preferably 0.870~0.910g / cm ^3, more preferably 0.875~0.907g / cm ^3, 0.880~0.903g / Cm ³ is more preferred. As the polyethylene resin, a plurality of polyethylene resins can be used, and a polyethylene resin having a density other than the above-described range may be added.

(Metallocene compound)
Examples of the metallocene compound include compounds such as a bis (cyclopentadienyl) metal complex having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, and platinum has one or more cyclopentadienyl rings or analogs thereof as a ligand (ligand). Can be mentioned.
Metallocene compounds have uniform active site properties, and each active site has the same activity. Since the polymer synthesized using the metallocene compound has high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, etc., when the sheet containing the polymer synthesized using the metallocene compound is cross-linked, the cross-linking is uniform. Proceed to The uniformly cross-linked sheet is uniformly foamed, so that it is easy to reduce the variation in the cell diameter. Further, since the stretching can be performed uniformly, the thickness of the foamed sheet can be made uniform.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted by a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group. Examples of the hydrocarbon group include a methyl group, an ethyl group, various propyl groups, various butyl groups, various amyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. , Various cetyl groups, phenyl groups and the like. In addition, "various" means various isomers including n-, sec-, tert-, and iso-.
Further, a compound obtained by polymerizing a cyclic compound as an oligomer may be used as a ligand.
Further, besides the π-electron unsaturated compounds, monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, aryls Phosphides and the like may be used.

Examples of the metallocene compound containing a tetravalent transition metal or a ligand include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethyl And silyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride.
The metallocene compound, when combined with a specific co-catalyst (co-catalyst), exhibits a function as a catalyst when polymerizing various olefins. Specific co-catalysts include methylaluminoxane (MAO), boron compounds and the like. The use ratio of the cocatalyst to the metallocene compound is preferably 100,000 to 1,000,000 times, more preferably 50 to 5,000 times.

The ethylene-vinyl acetate copolymer used as the polyolefin resin includes, for example, an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene. The ethylene-vinyl acetate copolymer has a vinyl acetate content of, for example, 5 to 50% by mass, preferably 10 to 40% by mass, and more preferably 15 to 35% by mass. The vinyl acetate content is measured according to JIS K6924-1.
Examples of the polypropylene resin include polypropylene and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. These may be used alone or in combination of two or more.
As the α-olefin constituting the propylene-α-olefin copolymer, specifically, ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1- Octene and the like can be mentioned, and among these, α-olefins having 6 to 12 carbon atoms are preferable.

The polyolefin resin contained in the foamed sheet, when using the above-described linear low-density polyethylene, the above-described linear low-density polyethylene may be used alone, or may be used in combination with another polyolefin resin. For example, you may use together with the other polyolefin resin mentioned above.
When containing another polyolefin resin, the ratio of the other polyolefin resin to the total amount of the linear low-density polyethylene and the other polyolefin resin is preferably 75% by mass or less, and more preferably 50% by mass or less. Is more preferable, and it is further preferable that it is 20 mass% or less. Here, the other polyolefin resin is preferably an ethylene-vinyl acetate copolymer.

  As the resin contained in the foamable composition, a polyolefin resin may be used alone, but may include a resin other than the polyolefin resin as long as the effects of the present invention are not impaired. In the foamed sheet, the ratio of the polyolefin resin to the total amount of the resin is preferably from 60 to 100% by mass, more preferably from 70 to 100% by mass, and still more preferably from 80 to 100% by mass. Examples of the resin other than the polyolefin resin include a styrene-based thermoplastic elastomer, a thermoplastic elastomer such as EPDM, and a rubber component.

  In the present invention, although the principle is not clear, for example, by increasing the tensile strength of the resin sheet after crosslinking, the strength at a time of 20 milliseconds by the pulse NMR measurement tends to decrease. Further, for example, by using a polyethylene resin such as a linear low-density polyethylene polymerized with a polymerization catalyst of a metallocene compound as described above, and by using a relatively high degree of crosslinking as described below, by pulse NMR measurement The intensity at a time of 20 milliseconds tends to be 0.07 or less as described above.

(Degree of crosslinking)
The foamed sheet is a crosslinked foam, and the degree of crosslinking is preferably 30 to 70% by mass, more preferably 35 to 65% by mass, and still more preferably 40 to 60% by mass. When the degree of crosslinking is equal to or more than the lower limit, the intensity at a time of 20 milliseconds measured by the pulse NMR method tends to be 0.07 or less. Further, when the degree of crosslinking is equal to or more than the lower limit, fine bubbles are easily formed.

(Expansion ratio)
The expansion ratio of the foam sheet is preferably 1.2~12cm ³ / g, more preferably 1.3~10cm ³ / g. In the present invention, by setting the strength at a time of 20 milliseconds by the pulse NMR measurement within the above-mentioned predetermined range, mechanical strength such as impact resistance can be secured while securing desired flexibility in a wide range of expansion ratios. Can be improved.
Further, the foamed sheet has a high mechanical strength and a further improved durability by reducing the foaming ratio even within the above range. From such a viewpoint, the expansion ratio of the foam sheet is more preferably 1.5 to ³ cm ³ / g.
The foam sheet preferably has a higher expansion ratio from the viewpoint of flexibility, and from that viewpoint, preferably has a foaming ratio of 7 to 12 cm ³ / g.
In the present invention, the apparent density of the foam sheet is determined according to JIS K7222, and the reciprocal thereof is defined as the expansion ratio.

(Closed cell rate)
In the foam sheet, the cells are preferably closed cells. The expression that the bubbles are closed cells means that the ratio of the closed cells to all the bubbles (referred to as a closed cell ratio) is 70% or more. The closed cell rate is preferably at least 75%, more preferably at least 90%.
The closed cell rate can be determined based on ASTM D2856 (1998). A commercially available measuring instrument includes a dry automatic densimeter Acupic 1330.

The closed cell ratio is measured more specifically as follows. From the foamed sheet, a test piece having a square shape with a side of 5 cm and a constant thickness is cut out. The thickness of the test piece was measured, to measure the weight W ₁ of the specimen to calculate the apparent volume V ₁ of the test piece. Then calculated based on the apparent volume V ₂ occupied by the bubbles in the following formula. The density of the resin constituting the test piece is 1 g / cm ³ .
Apparent volume occupied by bubbles V ₂ = V ₁ −W ₁
Subsequently, the test piece is immersed in distilled water at 23 ° C. to a depth of 100 mm from the water surface, and a pressure of 15 kPa is applied to the test piece for 3 minutes. Thereafter, the test piece is taken out of the water to remove water adhering to the surface of the test piece, the weight W _{2 of the} test piece is measured, and the open cell rate F ₁ and the closed cell rate F ₂ are calculated based on the following equation. I do.
Open cell rate F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂
Closed cell rate F ₂ (%) = 100−F ₁

(Dimensions of foam sheet)
The thickness of the foam sheet is preferably 0.02 to 0.8 mm. According to the present invention, even in such a relatively wide thickness range, by setting the strength at the above-mentioned time of 20 milliseconds within a predetermined range, it is possible to secure the flexibility of the foamed sheet while maintaining mechanical strength such as impact resistance. Strength can be improved. Further, the thickness of the foamed sheet is more preferably 0.08 to 0.50 mm, and further preferably 0.10 to 0.40 mm.
The foamed sheet is not particularly limited, but may be processed into a fine line shape. For example, the foamed sheet may be used with a width of 10 mm or less. Also, for example, it may be 5 mm or less, or even 1 mm or less. When the width of the foam sheet is reduced, the foam sheet can be suitably used inside a miniaturized electronic device. Further, the foamed sheet of the present invention maintains good durability even when the width is reduced. The lower limit of the width of the foam sheet is not particularly limited, but may be, for example, 0.1 mm or more, or 0.2 mm or more. The planar shape of the foam sheet is not particularly limited, and may be an elongated rectangular shape, a frame shape, an L shape, a U shape, or the like, or may be any shape such as a square or a circle.

(Mechanical properties)
The 25% compressive strength of the foam sheet is preferably from 10 to 2,000 kPa, more preferably from 1,000 to 1,500 kPa, and still more preferably from 500 to 1,500 kPa. By setting the 25% compressive strength to 2000 kPa or less, the foamed sheet is provided with a shock absorbing property and a sealing property, and can be suitably used as a buffer absorbing material and a sealing material. Further, by increasing the compressive strength, it becomes easy to improve the mechanical strength. The 25% compressive strength refers to a value obtained by measuring a foamed sheet in accordance with JIS K6767.

The foamed sheet preferably has an interlayer peel strength of 0.7 MPa or more, more preferably 0.8 MPa or more, and even more preferably 4.5 MPa or more. In addition, the value of the delamination strength was measured according to the method of Examples described later.
In the foamed sheet, the value (interlayer peel strength / density) obtained by dividing the interlayer peel strength (MPa) by the apparent density (g / cm ³ ) is preferably 8 or more, and more preferably 8.5 or more. More preferred. The higher the delamination strength / density, the higher the delamination strength while having the same apparent density, which means that it is easier to achieve both flexibility and mechanical strength. The higher the delamination strength / density, the better, but practically it is about 15 or less.

(Pyrogenic foaming agent)
The foamed sheet of the present invention is preferably formed by foaming a foamable composition containing a pyrolytic foaming agent in addition to the resin.
As the thermal decomposition type foaming agent, an organic foaming agent and an inorganic foaming agent can be used. Examples of the organic blowing agent include azo compounds such as azodicarbonamide, metal salts of azodicarboxylic acid (such as barium azodicarboxylate), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine, Examples thereof include hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, anhydrous sodium citrate and the like.
Among these, azo compounds are preferred, and azodicarbonamide is particularly preferred, from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety. These pyrolytic foaming agents can be used alone or in combination of two or more.
The amount of the thermal decomposition type foaming agent in the foamable composition is preferably 1 to 15 parts by mass, more preferably 1 to 12 parts by mass, and still more preferably 1.5 to 5 parts by mass with respect to 100 parts by mass of the resin. It is.

Further, the foamable composition preferably contains a cell nucleus modifier in addition to the resin and the pyrolytic foaming agent. Examples of the cell nucleus adjusting agent include zinc compounds such as zinc oxide and zinc stearate, and organic compounds of citric acid and urea. Of these, zinc oxide is more preferable. The compounding amount of the cell nucleating agent is preferably 0.4 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, and still more preferably 0.8 to 2.5 parts by mass with respect to 100 parts by mass of the resin. It is. By blending the cell nucleus adjusting agent, it is possible to suppress variations in the cell diameter of the fine cells.
The foamable composition contains, if necessary, additives generally used for foams such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, fillers, etc., in addition to the above. It may be.

[Production method of foam sheet]
The method for producing the foamed sheet is not particularly limited. For example, the foamed sheet contains a polyolefin resin and a thermal decomposition type foaming agent, and is manufactured by heating a crosslinked foamable composition to foam the thermal decomposition type foaming agent. . In addition, the expanded foamable composition may or may not be further stretched. The foamed sheet can be made relatively thin by stretching. Further, the flexibility of the foam sheet can be easily increased while maintaining good durability.

More specifically, the method for producing a foamed sheet includes the following steps (1) to (3).
Step (1): Step of mixing a polyolefin resin and an additive containing a pyrolytic foaming agent to form a sheet-like foamable composition (resin sheet) Step (2): Sheet-like foamable composition (3): irradiating the composition with an ionizing radiation to crosslink the foamable composition, and heating the crosslinked foamable composition to foam the pyrolytic foaming agent to form bubbles.

In the step (1), the method of forming the resin sheet is not particularly limited. For example, a polyolefin resin and an additive are supplied to an extruder, melt-kneaded, and the foamable composition is extruded from the extruder into a sheet. In this way, the resin sheet may be formed.
As a method for crosslinking the foamable composition in the step (2), a method of irradiating the resin sheet with ionizing radiation such as an electron beam, α-ray, β-ray, and γ-ray is used. The irradiation amount of the ionizing radiation may be adjusted so that the degree of crosslinking of the obtained foamed sheet falls within the above-described desired range, but is preferably 5 to 15 Mrad, more preferably 6 to 13 Mrad, More preferably, it is 6 to 8 Mrad.
In this production method, it is preferable to increase the tensile strength of the crosslinked resin sheet. If the tensile strength of the crosslinked resin sheet is increased, its principle is not clear, but the strength at a time of 20 milliseconds by pulsed NMR is easily reduced. The tensile strength of the crosslinked resin sheet at 110 ° C. is preferably 0.2 to 0.7 MPa, more preferably 0.25 to 0.60 MPa, and further preferably 0.25 to 0.50 MPa. The tensile strength of the crosslinked resin sheet can be set within the above range by adjusting the irradiation amount of ionizing radiation while keeping the above-mentioned type of resin.
In the step (3), the heating temperature when the foamable composition is heated to foam the thermal decomposition type foaming agent may be at least the foaming temperature of the thermal decomposition type foaming agent, but is preferably 200 to 300 ° C, Preferably it is 220-280 degreeC.

In addition, the present production method may include a step (step (4)) of stretching the foamed sheet in one or both of the MD direction and the TD direction.
The stretching of the foam sheet in the step (4) may be performed after foaming the resin sheet to obtain a foam sheet, or may be performed while foaming the resin sheet. When the foamed sheet is stretched after foaming the resin sheet to obtain the foamed sheet, the foamed sheet may be continuously stretched while maintaining the molten state at the time of foaming without cooling the foamed sheet. After cooling the foamed sheet, the foamed sheet may be stretched after the foamed sheet is heated again to be in a molten or softened state. At the time of stretching, the foamed sheet may be heated to, for example, 100 to 280 ° C, preferably 150 to 260 ° C.

  However, the present production method is not limited to the above, and a foamed sheet may be obtained by a method other than the above. For example, instead of irradiating with ionizing radiation, an organic peroxide may be previously blended in the foamable composition, and the foaming composition may be heated and crosslinked by a method of decomposing the organic peroxide. Good.

  The use of the foam sheet is not particularly limited, but is preferably used, for example, inside an electronic device. Since the foamed sheet of the present invention has high durability even when it is thin, it can be suitably used especially in various portable electronic devices having a small space for disposing the foamed sheet. Examples of the portable electronic device include a mobile phone, a camera, a game device, an electronic organizer, a tablet terminal, a notebook personal computer, and the like. The foam sheet can be used as an impact absorbing material and a sealing material inside the electronic device. Moreover, you may use for the adhesive tape which uses a foamed sheet as a base material.

[Adhesive tape]
The pressure-sensitive adhesive tape of the present invention includes, for example, a foamed sheet and a pressure-sensitive adhesive layer provided on at least one surface of the foamed sheet, and is preferably a double-sided pressure-sensitive adhesive tape provided with a pressure-sensitive adhesive layer on both sides.
The thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive tape is preferably from 5 to 200 μm. The thickness of the pressure-sensitive adhesive layer is more preferably 7 to 150 μm, and still more preferably 10 to 100 μm. When the thickness of the pressure-sensitive adhesive layer is in the range of 5 to 200 μm, the thickness of the structure fixed using the pressure-sensitive adhesive tape can be reduced.
The pressure-sensitive adhesive used for the pressure-sensitive adhesive layer is not particularly limited, and for example, an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, or the like can be used.
Further, a release sheet such as release paper may be further laminated on the pressure-sensitive adhesive layer.
The method of forming the pressure-sensitive adhesive layer on at least one surface of the foam sheet is not particularly limited.For example, a method of applying a pressure-sensitive adhesive on at least one surface of the foam sheet using a coating machine such as a coater, and at least one surface of the foam sheet. Examples include a method of spraying and applying an adhesive using a spray, and a method of applying an adhesive using a brush on at least one surface of a foamed sheet. Further, a method of transferring the pressure-sensitive adhesive layer formed on the release sheet to at least one surface of the foamed sheet may be used.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Measuring method]
The measuring method and evaluation method of each physical property are as follows.
<Intensity at time 20 ms>
The intensity at a time of 20 milliseconds was measured by pulsed NMR HahnEcho method measurement. The measurement conditions are as follows.
(Pulse NMR Hahn Echo method measurement)
The measurement was carried out using Bruker Biospin pulse NMR: Minispeccmq20.
1) Sample 100 to 500 mg of the foamed sheet was weighed into an NMR tube having a diameter of 10 mm and used for measurement. The sample was set on a pulse NMR apparatus and cured at 120 ° C. for 10 hours or more.
2) Measurement conditions
Hahn Echo method
First 90 ° -180 ° Pulse Separation: 0.01 msec
Final Pulse Separation: 50msec
Number of Data Points Fitting: 50 points
Scans: 8 to 64 times
Temperature: 120 ° C
(Calculation of intensity at time 20 ms)
The horizontal axis (time) of the decay curve (relaxation curve) of the transverse magnetization vector obtained by the above method was read for an intensity of 20 milliseconds, and was taken as the intensity at a time of 20 milliseconds.

<Apparent density and expansion ratio>
The apparent density of the foam sheet was measured in accordance with JIS K7222, and the reciprocal thereof was defined as the expansion ratio.
<Degree of crosslinking>
About 100 mg of a test piece is collected from the foamed sheet, and the weight 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, then filtered through a 200-mesh wire gauze to collect the insoluble matter on the wire gauze, vacuum-dried, and weighed the insoluble matter. Weigh B (mg) precisely. From the obtained values, the degree of crosslinking (% by mass) was calculated by the following equation.
Degree of crosslinking (% by mass) = 100 × (B / A)
<25% compressive strength>
The 25% compressive strength of the foamed sheet was measured in accordance with JIS K6767.
<Tensile strength of resin sheet after crosslinking>
The tensile strength of the crosslinked resin sheet was measured at 110 ° C. in accordance with JIS K7161.

<Delamination strength>
(Preparation of sample for measuring delamination strength)
As shown in FIG. 1, after applying a primer (“PPX primer” manufactured by Cemedine Co., Ltd.) to a 25 mm square area of the foam sheet 7, an adhesive 8 having a diameter of 5 mm (“PPX manufactured by Cemedine Co., Ltd.”) is applied to the center of the applied portion. )) Was added dropwise. Immediately thereafter, a 25 mm square aluminum jig 9 was placed on the adhesive dropping portion, and the foam sheet 7 and the jig 9 were pressed with the adhesive 8. Thereafter, the foam sheet was cut along the size of the jig 9. A primer was applied to the surface of the cut foam sheet 7 to which the jig 9 was not bonded, and an adhesive 10 having a diameter of 5 mm was dropped at the center of the applied portion. Immediately thereafter, a 10 mm square aluminum jig 11 was placed on the adhesive dropping portion, and the foamed sheet 7 and the jig 11 were pressed with the adhesive 10. After the adhesive protruding around the jig 11 was wiped off, a cut 12 was made in the foam sheet along the size of the jig 11. This was allowed to stand at room temperature for 30 minutes to cure the adhesive, and used as a sample for measuring delamination strength.
(Measurement of delamination strength)
Subsequently, a delamination strength was set on a testing machine (“A Tensilon Universal Material Testing Machine” manufactured by A & D Corporation) having a load cell of 1 kN so that the sheet surface of the foamed sheet 7 was perpendicular to the tensile direction. A measurement sample was attached. The jig 9 was pulled vertically upward at a speed of 100 mm / min, and only a 1 cm square area of the foam sheet was delaminated. The maximum load at this time was measured, and the result was used as the first measurement result. The same operation was repeated three times, and the average value was defined as the delamination strength.

<Delamination strength / density>
The value obtained by dividing the delamination strength (MPa) obtained above by the apparent density (g / cm ³ ) was calculated as delamination strength / density. When the delamination strength / density was 8 or more, the mechanical strength was improved with respect to a foamed sheet having the same apparent density, and was evaluated as “A”. On the other hand, when it is less than 8, it was evaluated as “B” because the mechanical strength was not good for a foamed sheet having the same apparent density. Further, a sheet in which good foamability was not observed and a sheet-like foam could not be produced was evaluated as “C”.

[Example 1]
100 parts by mass of a linear low-density polyethylene resin (manufactured by Dow Chemical Company, trade name “Affinity PL1850”, density: 0.902 g / cm ³ ) obtained by a metallocene compound polymerization catalyst, and a pyrolytic foaming agent 2.1 parts by mass of azodicarbonamide, 1.0 part by mass of zinc oxide as a cell nucleus modifier, and 0.5 part by mass of an antioxidant were supplied to an extruder. These were melt-kneaded at 130 ° C. in an extruder and extruded into a long resin sheet having a thickness of 250 μm.
Next, both sides of the long resin sheet were irradiated with an electron beam having an acceleration voltage of 500 kV for 7 Mrad to crosslink the resin sheet. The tensile strength of the crosslinked resin sheet at 110 ° C. was 0.3 MPa. Thereafter, the crosslinked resin sheet was continuously fed into a foaming furnace maintained at 250 ° C. by hot air and an infrared heater, heated and foamed to obtain a foamed sheet having a thickness of 300 μm.
Next, after continuously feeding the obtained foamed sheet from the foaming furnace, the foamed sheet is deformed by stretching in the TD direction and the MD direction while maintaining the temperature of both sides of the foamed sheet at 200 to 250 ° C. Then, a foamed sheet having a thickness of 150 μm was obtained. The obtained foamed sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

[Example 2]
The procedure was performed in the same manner as in Example 1 except that the amount of the pyrolytic foaming agent was changed to 10 parts by mass, and the foamed sheet was not stretched in the TD and MD directions.
[Example 3]
The same operation as in Example 1 was carried out except that the electron beam irradiation amount was changed to 6.2 Mrad.
[Example 4]
The resin composition was changed to 30 parts by mass of the above-described linear low-density polyethylene resin and 70 parts by mass of an ethylene-vinyl acetate copolymer ("Ultracene 636" manufactured by Tosoh Corporation, vinyl acetate content: 19% by mass). The procedure was performed in the same manner as in Example 1 except for the following.
[Example 5]
The resin composition was changed to 30 parts by mass of the above-mentioned linear low-density polyethylene resin and 70 parts by mass of an ethylene-vinyl acetate copolymer ("Ultracene 636" manufactured by Tosoh Corporation), and The operation was carried out in the same manner as in Example 1 except that the blending amount was changed to 5.5 parts by mass and the foamed sheet was not stretched in the TD and MD directions.

[Comparative Example 1]
Example 1 was carried out in the same manner as in Example 1 except that the blending amount of the foaming agent was changed to 1.6 parts by mass and the electron beam irradiation amount was changed to 4.2 Mrad.
[Comparative Example 2]
The same as Comparative Example 1 except that the blending amount of the thermal decomposition type foaming agent was changed to 7.5 parts by mass, the electron beam irradiation amount was set to 4.5 Mrad, and the foamed sheet was not stretched in the TD and MD directions. Carried out.
[Comparative Example 3]
The procedure was performed in the same manner as in Comparative Example 1 except that the amount of the pyrolytic foaming agent was changed to 4.5 parts by mass, and the foamed sheet was not stretched in the TD and MD directions.
[Comparative Example 4]
The same operation as in Example 1 was performed except that the electron beam irradiation amount was changed to 9.0 Mrad, but no foam sheet was obtained.

  As described above, in Examples 1 to 5, the strength at a time of 20 milliseconds by the pulse NMR measurement was within the predetermined range, so that the delamination strength / density was 8 or more, and both the flexibility and the mechanical strength Could be good. On the other hand, in Comparative Examples 1 to 3, since the strength at a time of 20 milliseconds by the pulse NMR measurement was increased, the delamination strength / density was less than 8, and both the flexibility and the mechanical strength could be improved. could not. In Comparative Example 4, since the strength at a time of 20 milliseconds by the pulse NMR measurement was small, it was difficult to control the foaming state, and it was difficult to produce a foam sheet practically.

7 Foam sheet 8 Adhesive 9 Jig 10 Adhesive 11 Jig 12 Cut

Claims (11)

  A polyolefin foam sheet obtained by foaming a foamable composition containing a polyolefin resin, wherein the strength at a time of 20 milliseconds measured by a pulsed NMR Hahn Echo method is in the range of 0.02 to 0.07.   The polyolefin foam sheet according to claim 1, wherein the polyolefin resin is a polyethylene resin.   3. The polyolefin foam sheet according to claim 1, wherein the polyolefin resin includes a linear low-density polyethylene polymerized with a metallocene compound polymerization catalyst. 4.   The polyolefin foam sheet according to claim 3, wherein the polyolefin resin further contains an ethylene-vinyl acetate copolymer.   The polyolefin foam sheet according to any one of claims 1 to 4, wherein a degree of crosslinking is 30 to 70% by mass.   The polyolefin foam sheet according to any one of claims 1 to 5, having a thickness of 0.02 to 0.8 mm. Expansion ratio is 1.2~12cm ³ / g, a polyolefin foamed sheet according to any one of claims 1-6.   The foamed polyolefin sheet according to any one of claims 1 to 7, wherein the foamable composition further contains a pyrolytic foaming agent.   The method for producing a polyolefin-based foamed sheet according to any one of claims 1 to 8, comprising heating a crosslinked foamable composition containing a polyolefin-based resin and a pyrolytic foaming agent, and heating the foamed composition. A method for producing a polyolefin foam sheet for foaming a decomposable foaming agent.   The method for producing a polyolefin foam sheet according to claim 9, wherein the foamable composition is foamed and further stretched.   An adhesive tape, comprising: the polyolefin-based foam sheet according to any one of claims 1 to 8; and an adhesive layer provided on at least one surface of the polyolefin-based foam sheet.

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