WO2015152222A1

WO2015152222A1 - Polyolefin foam sheet and pressure-sensitive adhesive tape

Info

Publication number: WO2015152222A1
Application number: PCT/JP2015/060085
Authority: WO
Inventors: 康司谷内
Original assignee: 積水化学工業株式会社
Priority date: 2014-03-31
Filing date: 2015-03-31
Publication date: 2015-10-08
Also published as: JPWO2015152222A1; CN106133040A; CN106133040B; CN110256746A; KR102125916B1; KR20160140648A; JP6469085B2

Abstract

This polyolefin foam sheet is obtained by foaming a resin composition containing a polyolefin resin (A) and a styrene thermoplastic elastomer (B) for which the temperature that maximizes the peak value of tan δ, as per dynamic-viscoelasticity measurement, is between −30°C and 10°C, inclusive. The ratio (A/B) of the mass of the polyolefin resin (A) to the mass of the styrene thermoplastic elastomer (B) is between 50:50 and 90:10, inclusive, and the thickness of the polyolefin foam sheet is between 0.05 and 1.0 mm, inclusive.

Description

Polyolefin foam sheet and adhesive tape

The present invention relates to a polyolefin-based foamed sheet used in, for example, electronic equipment applications, and an adhesive tape provided with an adhesive layer on the foamed sheet.

Foamed sheets in which a large number of bubbles are formed inside the resin are widely used as sealing materials and shock absorbing materials in electronic devices used in the information technology field such as mobile phones, tablet terminals, and personal computers. The foamed sheet used in these electronic devices is required to have high flexibility in order to maintain the sealing performance by improving the followability to the level difference and to improve the shock absorption. In addition, it is also necessary to increase the breaking strength in order to prevent the foam sheet itself from being damaged when subjected to a strong impact.
Conventionally, polyolefin-based resins are widely used for foam sheets, and flexibility and mechanical strength are enhanced by adjusting the expansion ratio and the degree of crosslinking. In addition, as in Patent Document 1, it is also known to improve the flexibility and breaking strength of a foamed sheet by mixing two types of resins having different densities as a polyolefin resin (see, for example, Patent Document 1). ).

JP 2014-28925 A

In recent years, electronic devices used in the information technology field have been reduced in size and the display area has been increased, and the foam sheet has been made thinner and narrower accordingly. In addition, electronic devices may be defective due to the influence of static electricity. In particular, in mobile phones and tablet terminals, since a touch panel type display device is often used, problems such as the display device not being turned on due to the influence of static electricity are likely to occur. For this reason, the foam sheet is also required to have a function of increasing the electrostatic resistance of the electronic device.

However, foam sheets are becoming thinner and narrower, and shortages of flexibility, breaking strength, and withstand voltage characteristics have become apparent. Simply adjusting the expansion ratio and degree of crosslinking is sufficient. It is becoming difficult to obtain a good flexibility and breaking strength. Moreover, in the method described in Patent Document 1, although flexibility and breaking strength are improved, it is difficult to increase electrostatic resistance.

The present invention has been made in view of the above circumstances, and the problem of the present invention is that it has good flexibility, breaking strength, and withstand voltage characteristics even when it is thinned and narrowed. It is providing the polyolefin-type foam sheet which can be made.

As a result of intensive studies, the present inventors have found that the above problem can be solved by mixing a styrene-based thermoplastic elastomer having a maximum peak of tan δ within a predetermined temperature range into the polyolefin-based resin constituting the foam sheet, The following invention was completed.
That is, the present invention provides the following (1) to (7).
(1) Foaming a resin composition containing a polyolefin resin (A) and a styrene thermoplastic elastomer (B) having a maximum tan δ peak temperature in the range of −30 to 10 ° C. by dynamic viscoelasticity measurement. The ratio (A / B) of the polyolefin resin (A) to the styrene thermoplastic elastomer (B) is 50/50 to 90/10 in terms of mass ratio, and the thickness is 0.05 to 1.0 mm. A polyolefin foam sheet.
(2) The polyolefin-based foamed sheet according to the above (1), wherein the styrene-based thermoplastic elastomer (B) has a styrene content of 5 to 25% by mass.
(3) The styrenic thermoplastic elastomer (B) is selected from a styrene / isoprene block copolymer, a hydrogenated styrene / isoprene block copolymer, and a hydrogenated styrene / isoprene / butadiene block copolymer or The polyolefin-based foamed sheet according to the above (1) or (2), which is two or more kinds.
(4) The polyolefin-based foamed sheet according to any one of (1) to (3), wherein the polyolefin-based resin (A) is a polyethylene-based resin.
(5) The polyolefin-based foamed sheet according to (4) above, wherein the polyethylene-based resin is polymerized with a metallocene compound polymerization catalyst.
(6) The polyolefin foamed sheet according to any one of the above (1) to (5), wherein the polyolefin foamed sheet is crosslinked.
(7) A pressure-sensitive adhesive tape comprising the polyolefin-based foamed sheet described in any of (1) to (6) above and a pressure-sensitive adhesive layer provided on at least one surface of the polyolefin-based foamed sheet.

In the foamed sheet of the present invention, it is possible to improve the flexibility, breaking strength, and withstand voltage characteristics even when it is thinned and narrowed.

It is a schematic diagram which shows the measuring method of fracture strength.

Hereinafter, the present invention will be described in more detail using embodiments.
The polyolefin foam sheet of the present invention (hereinafter sometimes simply referred to as “foam sheet”) includes a polyolefin resin (A) and styrene having a maximum peak temperature of tan δ of −30 to 10 ° C. as measured by dynamic viscoelasticity. A resin composition containing the thermoplastic elastomer (B) is foamed.

In the present invention, the ratio (A / B) of the polyolefin resin (A) to the styrene thermoplastic elastomer (B) is 50/50 to 90/10 in mass ratio. If the mass ratio is less than 50/50, the amount of the component (A) is insufficient and it becomes difficult to obtain the mechanical strength required for the foamed sheet. If the mass ratio exceeds 90/10, the amount of the component (B) is insufficient, and it becomes difficult to obtain a foam sheet having good withstand voltage characteristics and flexibility. From these viewpoints, the mass ratio is preferably 60/40 to 80/20.

[Polyolefin resin (A)]
Examples of the polyolefin resin (A) include a polyethylene resin, a polypropylene resin, or a mixture thereof. Among these, a polyethylene resin is preferable. More specifically, examples thereof include polyethylene resins, polypropylene resins, or mixtures thereof polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, and a chromium oxide compound. Among these, polymerization of a metallocene compound is included. A polyethylene resin polymerized with a catalyst is preferred.
The melting point of the polyolefin resin (A) is not particularly limited, but is preferably 60 ° C. or higher, and more preferably 80 to 110 ° C. Thereby, the thermal stability of the resin composition is increased, stickiness and blocking during the production of the foamed sheet are prevented, and the processability is easily improved. In the present specification, the melting point is measured by a differential scanning calorimetry (DSC) method.

The polyethylene resin preferably has a low density in order to increase the flexibility of the foam sheet. The density of the polyethylene resin, particularly preferably from 0.920 g / cm ³ or less, more preferably 0.865 ~ 0.915g / cm ^3, particularly preferably at 0.870 ~ 0.910g / cm ³ is there. The density is measured in accordance with JIS K 7112.

Examples of the polyethylene resin include an ethylene homopolymer, an ethylene-vinyl acetate copolymer, and an ethylene-α-olefin copolymer. Of these, an ethylene-α-olefin copolymer is preferable. The ethylene-α-olefin copolymer is a polyethylene-based copolymer obtained by copolymerizing ethylene with a small amount of α-olefin as required (for example, 30% by mass or less, preferably 10% by mass or less of all monomers). Among them, linear low density polyethylene obtained by a polymerization catalyst of a metallocene compound is preferable.
Specific examples of the α-olefin constituting the polyethylene resin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. . Of these, α-olefins having 4 to 10 carbon atoms are preferable, and among these, 4-methyl-1-pentene, 1-hexene, and 1-octene are more preferable.
The ethylene-vinyl acetate copolymer usually includes a copolymer containing 50% by mass or more of ethylene units.

In the present invention, a foamed sheet having high flexibility and high breaking strength can be easily obtained by using a polyethylene-based resin, particularly a linear low density polyethylene, obtained by a polymerization catalyst of a metallocene compound. Moreover, as will be described later, it is easy to maintain high performance even if the foam sheet is thinned.
The polyethylene resin obtained by the polymerization catalyst of the metallocene compound is preferably contained in the foamed sheet in an amount of 50% by mass or more of the entire polyolefin resin (A), more preferably 70 to 100% by mass, and still more preferably 90 to 90% by mass. 100% by mass, most preferably 100% by mass is contained.

Examples of the polypropylene resin include a propylene homopolymer, a propylene-α-olefin copolymer containing 50% by mass or more of propylene units, and the like. These may be used alone or in combination of two or more.
Specific 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- Among these, α-olefins having 6 to 12 carbon atoms are preferable.

<Metalocene compounds>
Suitable metallocene compounds include compounds such as bis (cyclopentadienyl) metal complexes having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum have one or more cyclopentadienyl rings or their analogs as ligands (ligands). The compound to be mentioned is mentioned.
Such metallocene compounds have uniform active site properties and each active site has the same activity. A polymer synthesized using a metallocene compound has high uniformity such as molecular weight, molecular weight distribution, composition, and composition distribution. Therefore, when a sheet containing a polymer synthesized using a metallocene compound is crosslinked, crosslinking occurs. Progress evenly. The uniformly cross-linked sheet is easily stretched uniformly, so that the thickness of the foamed sheet is easily uniformed, and high performance is easily maintained even when the thickness is reduced.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted with 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. The “various” means various isomers including n-, sec-, tert-, and iso-.
Moreover, what polymerized the cyclic compound as an oligomer may be used as a ligand.
In addition to 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 Phosphide or the like may be used.

Examples of metallocene compounds containing tetravalent transition metals and ligands include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethyl And silyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride.
The metallocene compound exhibits an action as a catalyst in the polymerization of various olefins by combining with a specific cocatalyst (co-catalyst). Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron compounds. The proportion of the cocatalyst used with respect to the metallocene compound is preferably 100,000 to 1,000,000 mole times, more preferably 50 to 5,000 mole times.

<Ziegler-Natta compound>
The Ziegler-Natta compound is a triethylaluminum-titanium tetrachloride solid composite, which is obtained by reducing titanium tetrachloride with an organoaluminum compound and then treating with various electron donors and electron acceptors. A method of combining a composition, an organoaluminum compound, and an aromatic carboxylic acid ester (see JP-A 56-1000080, JP-A 56-120712, JP-A 58-104907), halogens Method of supported catalyst in which magnesium tetrachloride is brought into contact with magnesium tetrachloride and various electron donors (see JP-A-57-63310, JP-A-63-43915, JP-A-63-83116), etc. What was manufactured by is preferable.

[Styrenic thermoplastic elastomer (B)]
The styrenic thermoplastic elastomer (B) used in the present invention has a structural unit derived from styrene, specifically, a co-weight of styrene and a conjugated diene selected from isoprene, butadiene and the like. Coalescence is mentioned.

The styrenic thermoplastic elastomer (B) has a maximum peak temperature of tan δ of −30 to 10 ° C. as measured by dynamic viscoelasticity. As described above, when the maximum peak temperature of tan δ is relatively low, heat loss in a high-speed deformation region such as impact fracture increases, and the fracture strength of the foamed sheet is easily improved. On the other hand, if the maximum peak temperature of tan δ is outside the above range, it may be difficult to improve the fracture strength and flexibility of the foam sheet. From the above viewpoint, the maximum peak temperature of tan δ of the styrenic thermoplastic elastomer is preferably −25 to 5 ° C., and more preferably −20 to 0 ° C.
In the present specification, “the maximum peak temperature of tan δ” refers to a value measured by a dynamic viscoelasticity measuring device in a tensile mode, a temperature rising rate of 10 ° C./min, and a frequency of 10 Hz. Examples of the dynamic viscoelasticity measuring apparatus that can be used for the measurement include “Leovibron DDV-III” manufactured by Orientec Co., Ltd.

When the styrene-based thermoplastic elastomer (B) has a structural unit derived from styrene, it is possible to improve the withstand voltage characteristics of the foamed sheet. The styrene content in the styrenic thermoplastic elastomer (B) is preferably 5 to 25% by mass. By setting the styrene content to be the upper limit or less, the compatibility with the polyolefin resin (A) is improved, and the crosslinkability and the foamability are easily improved. Moreover, it becomes possible to improve a withstand voltage characteristic more by setting it as the said lower limit or more. From these viewpoints, the styrene content in the styrene-based thermoplastic elastomer (B) is more preferably 7 to 20% by mass, and further preferably 7 to 15% by mass.
The number average molecular weight of the styrenic thermoplastic elastomer (B) is not particularly limited, but is preferably 30,000 to 800,000, more preferably 120,000 to 180,000 from the viewpoints of fracture strength and processability.
In addition, a number average molecular weight is a pothistyrene conversion value measured using gel permeation chromatography (GPC).

The styrenic thermoplastic elastomer (B) may or may not be hydrogenated.
Hydrogenation can be performed by a known method. Specifically, it can be obtained by dissolving a hydrogen-free styrene-based thermoplastic elastomer in a solvent inert to the hydrogenation reaction and hydrogenation catalyst, and reacting hydrogen using a known hydrogenation catalyst. . As a catalyst, a heterogeneous catalyst in which a metal such as Raney nickel, Pt, Pd, Ru, Rh, Ni is supported on a carrier such as carbon, alumina, diatomaceous earth, or a transition metal and an alkylaluminum compound, an alkyllithium compound, etc. And Ziegler-based catalysts composed of the above combinations. The hydrogen pressure is preferably from normal pressure to 200 kg / cm ² , the reaction temperature is preferably from room temperature to 250 ° C., and the reaction time is preferably from 0.1 to 100 hours. The polymer after the reaction is solidified with methanol or the like and then heated or dried under reduced pressure, or the reaction solution is poured into boiling water and the solvent is removed azeotropically, and then heated or dried under reduced pressure. Obtainable.

The styrenic thermoplastic elastomer (B) is usually a block copolymer. As the block copolymer, block portions at both ends are made of polystyrene, and an intermediate block is a block of isoprene or a conjugated diene such as isoprene and butadiene. The thing which is is mentioned. In the block copolymer, the intermediate block preferably contains vinyl-polyisoprene.
Specific examples of the block copolymer include styrene / isoprene block copolymers and styrene / isoprene / butadiene block copolymers. Among these, styrene / isoprene / butadiene block copolymers are exemplified. Is preferred.

The styrene / isoprene block copolymer may be a hydrogenated hydrogenated styrene / isoprene block copolymer or may not be hydrogenated. As a commercial product of a non-hydrogenated styrene / isoprene block copolymer, Kuraray Co., Ltd., trade name “HIBLER (registered trademark) 5125” (styrene content 20 mass%, maximum peak temperature of tan δ = −3 ° C.) ). As a commercially available product of hydrogenated styrene / isoprene block copolymer, Kuraray Co., Ltd., trade name “HIBLER (registered trademark) 7125” (styrene content 20 mass%, maximum peak temperature of tan δ = −5 ° C.) Is mentioned.
On the other hand, the styrene / isoprene / butadiene block copolymer is preferably hydrogenated. As a commercially available product of the hydrogenated styrene / isoprene / butadiene block copolymer, there is a product name “HIBLER (registered trademark) 7311” (styrene content 12 mass%, maximum peak temperature = −17 ° C.) manufactured by Kuraray Co., Ltd. Can be mentioned.

The styrenic thermoplastic elastomer (B), which is a block copolymer, can be produced, for example, by anionic copolymerization of styrene and a conjugated diene such as isoprene and / or butadiene with an alkyl lithium compound as an initiator.
Examples of the alkyl lithium compound include alkyl lithium having an alkyl group having 1 to 10 carbon atoms such as methyl lithium, ethyl lithium, pentyl lithium, and butyl lithium, and dilithium compounds such as naphthalenedi lithium and dithiohexylbenzene.
As a polymerization method, (1) a method in which an alkyl lithium compound is used as an initiator followed by styrene, then isoprene, and if necessary, further butadiene or isoprene-butadiene is successively polymerized, and then styrene is sequentially polymerized; (2) styrene Subsequently, a method of polymerizing isoprene and, if necessary, further butadiene or isoprene-butadiene, and coupling this with a coupling agent can be mentioned. Examples of the coupling agent include dichloromethane, dibromomethane, dibromobenzene and the like.

In the polymerization, it is preferable to use a solvent in order to appropriately control the reaction. Examples of the solvent include organic solvents inert to the polymerization initiator, for example, hexane, heptane, cyclohexane, methylcyclohexane, benzene, and other aliphatic, alicyclic, and aromatic hydrocarbons having 6 to 12 carbon atoms. It is preferable to use it.
The polymerization is preferably performed at a temperature range of 0 to 80 ° C. for 0.5 to 50 hours.

The maximum peak temperature of tan δ of the block copolymer can be adjusted by a method of adjusting the number of 3, 4 bonds or 1, 2 bonds of isoprene or butadiene, and a Lewis base is used as a cocatalyst. Can be adjusted relatively easily. Examples of Lewis bases include ethers such as dimethyl ether, diethyl ether and tetrahydrofuran, glycol ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether, triethylamine, N, N, N ′, N′-tetramethylethylenediamine (TMEDA), and N-methyl. Examples thereof include amine compounds such as morpholine. These Lewis bases are preferably used in an amount of 0.1 to 1000 times the number of moles of lithium in the polymerization initiator. The maximum peak temperature can also be adjusted by adjusting the presence or absence of hydrogenation and the hydrogenation rate.

The resin component of the resin composition may be composed of the component (A) and the component (B), but contains a resin component other than the components (A) and (B) as long as the object of the present invention is not impaired. Also good. In such a case, the total amount of the components (A) and (B) is usually 70% by mass or more, preferably 90% by mass or more based on the total amount of the resin components. Moreover, various additives other than a resin component may be mix | blended with the resin composition so that it may mention later.

[Foamed sheet]
<Thickness>
In the present invention, the thickness of the foam sheet is 0.05 to 1.0 mm. If the thickness is less than 0.05 mm, the mechanical strength such as the breaking strength may be deteriorated, or the sealing property and the impact absorption property may be deteriorated. Moreover, when it becomes thicker than 1.0 mm, it becomes difficult to use a foam sheet for the electronic device reduced in size. The thickness of the foam sheet is more preferably 0.06 to 0.5 mm. Within this range, various performances required for the foamed sheet of the present invention can be improved, and it can be suitably used for various electronic devices that have been miniaturized.
In addition, the foamed sheet of the present invention has good sealing properties and impact absorbability even when the width is narrow, but the width of the foamed sheet is specifically 0.5 to 2.5 mm. The thickness is preferably 0.5 to 2.0 mm.

<Apparent magnification>
In the present invention, the apparent magnification of the foamed sheet is preferably 1.1 to 10 cc / g, and more preferably 1.3 to 6 cc / g. When the apparent magnification is in the above range, it becomes possible to have good flexibility while having an appropriate breaking strength, and the sealing performance, impact absorption performance, and the like are improved.

<Gel% (degree of crosslinking)>
The foamed sheet of the present invention is preferably cross-linked. The gel% indicating the degree of cross-linking of the foamed sheet is preferably 10 to 70% by mass, and more preferably 15 to 65% by mass. When the gel% is equal to or higher than the above lower limit value, sufficient crosslinking is formed in the foamed sheet, and the fracture strength and the like can be further improved. Moreover, it becomes possible to make the softness | flexibility of a foam sheet more favorable by setting it as the said upper limit or less, and it becomes easy to improve a sealing performance, an impact-absorbing property, etc.

<Independent bubbles>
The foam sheet of the present invention has a large number of bubbles, but the bubbles are preferably closed cells. In the present specification, the term “bubbles are closed cells” means that the ratio of closed cells to all bubbles (referred to as closed cell ratio) is 70% or more. The closed cell ratio is more preferably 80% or more.
The closed cell ratio is determined according to JIS K 7138 (2006). Commercially available measuring instruments include Beckman's air comparison specific gravity meter MODEL930, dry automatic density meter Accupic 1330, and the like.
The closed cell ratio is measured as follows. A test piece having a flat square shape with a side of 5 cm and a constant thickness is cut out from the foam sheet. The thickness of the test piece is measured, the apparent volume V ₁ of the test piece is calculated, and the weight W _{1 of the} test piece is measured. Next, the apparent volume V ₂ occupied by the bubbles is calculated based on 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 submerged 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 over 3 minutes. After releasing the pressure in water, the test piece is taken out of the water to remove the 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 are calculated based on the following formulas: F ₂ is calculated.
Open cell ratio F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂
Closed cell ratio F ₂ (%) = 100−F ₁

<25% compressive strength>
The 25% compressive strength of the foamed sheet is not particularly limited, but is preferably 10 to 1000 kPa, and more preferably 20 to 800 kPa. When the 25% compressive strength is in the above range, the flexibility of the foamed sheet is likely to be enhanced, and the impact absorption and sealing properties are easily improved. In addition, 25% compressive strength means what measured the foamed sheet based on JISK6767.

<Destructive strength>
In the present invention, the breaking strength of the foam sheet is preferably 2 MPa or more, more preferably 2.5 MPa or more. In this specification, the fracture strength is a value indicating the tensile strength in the thickness direction (Z direction) and is measured by a measurement method described later. When an impact is applied to a thin foam sheet as in the present invention, a large stress acts in the thickness direction due to the impact force. Therefore, by setting the breaking strength to the lower limit value or more, the strength against stress is increased, and the impact resistance of the foamed sheet is easily improved.
Further, the breaking strength is preferably 8 MPa or less, and more preferably 7.5 MPa or less. By making the breaking strength below these upper limit values, the flexibility of the foamed sheet is maintained, and it becomes easy to obtain a foamed sheet having high impact absorption and sealing properties.

[Method for producing foam sheet]
The foamed sheet of the present invention is not particularly limited, but the resin composition is preferably produced by crosslinking and foaming. For example, the production method includes the following steps (1) to (3): Is industrially advantageous.
Step (1): The component (A), the component (B), the pyrolytic foaming agent, and other additives are supplied to an extruder, melt-kneaded, and extruded into a sheet form from the extruder. Step (2): Step of cross-linking the sheet-shaped resin composition Step (3): Heating the cross-linked sheet-shaped resin composition to foam a pyrolytic foaming agent And, preferably, a step of stretching in either or both of the MD direction and the TD direction. In addition to this method, the foam sheet can be manufactured by the method described in WO2005 / 007731. It is.

The pyrolytic foaming agent is not particularly limited, and examples thereof include azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide and the like. Of these, azodicarbonamide is preferred. In addition, a thermal decomposition type foaming agent may be used individually by 1 type, and may use 2 or more types together.
The content of the pyrolytic foaming agent in the resin composition is preferably 0.4 to 12 parts by mass, more preferably 0.6 to 8 parts by mass with respect to 100 parts by mass of the resin component. When the content of the pyrolytic foaming agent is within the above range, the foamability of the resin composition is improved, and it becomes easy to obtain a foamed sheet having a desired foaming ratio.
The method of foaming the resin composition is not particularly limited, and examples thereof include a method of heating the resin composition 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.
The foaming of the resin composition is not limited to the example using the pyrolytic foaming agent, and physical foaming with butane gas or the like may be used.

As a method of crosslinking the resin composition, for example, a method of irradiating the resin composition with ionizing radiation such as electron beam, α ray, β ray, γ ray, and the like, an organic peroxide is blended in advance with the resin composition. Examples of the method include heating the resin composition to decompose the organic peroxide, and these methods may be used in combination. In these, the method of irradiating ionizing radiation is preferable.
The irradiation amount of ionizing radiation is preferably 0.5 to 10 Mrad, more preferably 1 to 8 Mrad so that the gel% is 10 to 70% by mass.

Examples of the organic peroxide used for crosslinking include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, and the like. It is done. These may be used alone or in combination of two or more. The addition amount of the organic peroxide is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the resin component. When the addition amount of the organic peroxide is within the above range, crosslinking of the resin composition is likely to proceed, and the amount of decomposition residue of the organic peroxide is suppressed in the obtained foamed sheet.

The foamed sheet of the present invention is preferably stretched as described above. Stretching may be performed after foaming the resin composition to obtain a foamed sheet, or may be performed while foaming the resin composition. In addition, after foaming the resin composition to obtain a foamed sheet, when the foamed sheet is stretched, it is better to continue stretching the foamed sheet while maintaining the molten state at the time of foaming without cooling the foamed sheet However, after cooling the foamed sheet, the foamed sheet may be stretched again by heating it to a molten or softened state.

Further, the stretch ratio in the MD direction of the foamed sheet is preferably 1.1 to 3.0 times, and more preferably 1.3 to 2.8 times. When the draw ratio in the MD direction of the foamed sheet is set to the above lower limit value or more, the flexibility and tensile strength of the foamed sheet are likely to be good. On the other hand, if the upper limit value is not exceeded, the foamed sheet is prevented from breaking during stretching, or the foaming gas escapes from the foamed sheet being foamed and the foaming ratio is reduced, thereby reducing the flexibility and tensile strength of the foamed sheet. It becomes good and it becomes easy to make the quality uniform. In addition, the foam sheet may be stretched in the TD direction at a stretch ratio in the above range.

Resin compositions include antioxidants such as 2,6-di-t-butyl-p-cresol, foaming aids such as zinc oxide, decomposition temperature regulators, cell core modifiers, and heat stability as needed. Various additives such as a colorant, a colorant, a flame retardant, an antistatic agent, and a filler may be blended within a range that does not impair the physical properties of the foamed sheet. These additives are kneaded together with the components (A) and (B) in the normal step (1).

[Adhesive tape]
The pressure-sensitive adhesive tape of the present invention uses the foamed sheet as a base material, and includes a foamed sheet and a pressure-sensitive adhesive layer provided on at least one surface of the foamed sheet. The thickness of the adhesive tape is usually 0.06 to 2 mm, preferably 0.06 to 1 mm.
The thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive tape of the present invention is preferably 5 to 200 μm. The thickness of the pressure-sensitive adhesive layer is more preferably 7 to 150 μm, still more preferably 10 to 100 μm. When the thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive tape is in the range of 5 to 200 μm, the thickness of the pressure-sensitive adhesive tape can be reduced while ensuring high and stable pressure-sensitive adhesiveness.
There is no restriction | limiting in particular as an adhesive which comprises an adhesive layer, For example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, etc. are mentioned.

Examples of the method of laminating the pressure-sensitive adhesive layer by applying a pressure-sensitive adhesive to at least one surface of the foamed sheet include, for example, a method of applying a pressure-sensitive adhesive using a coating machine such as a coater to at least one surface of the foamed sheet, Examples thereof include a method of spraying and applying an adhesive using a spray on one side, a method of applying an adhesive using a brush on at least one side of a foamed sheet, and the like.
Adhesive tapes using foam sheets are shock absorbers that prevent impacts on the electronic components built in the electronic device bodies such as mobile phones and tablet terminals, and dust and moisture in the electronic device bodies. It can be used as a sealing material that prevents entry.
The foamed sheet of the present invention is excellent in flexibility, and therefore, the adhesive tape is excellent in step following ability and easy to ensure airtightness when used as a fixing tape for fixing various parts in electronic equipment, for example. In addition, it is possible to improve the shock absorption. Moreover, since it is excellent in breaking strength and a withstand voltage characteristic, the malfunction by static electricity at the time of using for an electronic device and the damage of an adhesive tape become difficult to occur.

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 of each physical property in this specification is as follows.
<Apparent magnification>
For the density of the foam sheet, the apparent density was measured in accordance with JIS K 7222, and the reciprocal thereof was used as the apparent magnification.
<Degree of crosslinking (gel%)>
A test piece of about 50 mg is taken 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 105 ° 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 weight of the insoluble matter. Weigh B (mg) precisely. From the obtained value, the gel% (mass%) is calculated by the following formula.
Gel% (mass%) = 100 × (B / A)
<Closed cell ratio>
Based on JIS K7138 (2006), it measured by the method as described in the specification with the air comparison specific gravity meter MODEL930 by Beckman.
<25% compressive strength>
The 25% compressive strength refers to a foamed sheet measured according to JIS K 6767. In this example, the measurement was performed by stacking a plurality of foam sheets so that the total thickness was 10 mm.

<Destructive strength>
First, a fracture strength measurement sample 10 shown in FIG. 1 was prepared. That is, after applying a primer (trade name. PPX primer, manufactured by Cemedine Co., Ltd.) to a 25 mm square area of the foamed sheet 11, an adhesive for 5 mm in diameter (trade name: 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 A was placed on the adhesive dripping portion, and the foamed sheet 11 and the jig A were pressure-bonded via the adhesive 12. Thereafter, the foam sheet 11 was cut along the size of the jig A. A primer was applied to the surface of the cut foam sheet 11 on which the jig A was not adhered, and an adhesive having a diameter of 5 mm was dropped onto the center of the applied portion. Immediately thereafter, a 10 mm square aluminum jig B was placed on the adhesive dripping portion, and the foamed sheet 11 and the jig B were pressure-bonded via the adhesive 13. After the adhesive sticking out around the jig B was wiped off, cuts 14 were made in the foam sheet 11 along the size of the jig B. This was allowed to stand at room temperature for 30 minutes to cure the adhesive, and the sample 10 for fracture strength measurement shown in FIG. 1 was obtained.
Subsequently, the test piece (manufactured by A & D Co., Ltd., trade name: Tensilon Universal Material Testing Machine) with a 1 kN load cell was broken so that the sheet surface of the foamed sheet 11 was perpendicular to the tensile direction. A sample 10 for strength measurement was attached. Thereafter, one jig A was pulled vertically upward at a speed of 100 mm / min, and only the 1 cm square area of the foamed sheet 11 was delaminated. The maximum load at this time was measured and used as the first measurement result. The same operation was repeated three times, and the average value was taken as the breaking strength.

<Withstand voltage test>
A 1 mm x 100 mm tape-shaped foam sheet is sandwiched in the thickness direction between two acrylic plates, and is sandwiched in the width direction between two aluminum plates arranged between the acrylic plates, withstanding voltage test Kikusui Electronics Using a TOS501 (maximum voltage of 12 kV) manufactured by the company, a voltage is applied in the width direction with a direct current, and if no voltage is applied for 30 seconds at that voltage, the applied voltage is increased in increments of 0.5 kV. The voltage when energized is taken as the result of the withstand voltage. In this measurement, each of MD and TD was measured in the width direction of the tape.
(Evaluation criteria)
If both the measured values of MD and TD were 10 kV or more, it was evaluated as A because the withstand voltage performance was good.
When either one of the measured values of MD and TD was less than 10 kV and both were 8 kV or more, the withstand voltage performance was evaluated as B, and it was evaluated as B.
If either one of the measured values of MD and TD was less than 8 kV, the withstand voltage performance was not good and was evaluated as C.

[Example 1]
Resin component 100 comprising 70 parts by mass of a polyolefin resin (manufactured by Nippon Polyethylene Co., Ltd., trade name: Kernel KF370) and 30 parts by mass of a styrene thermoplastic elastomer (manufactured by Kuraray Co., Ltd., trade name: Hibler (registered trademark) 7311) A resin composition obtained by feeding 1 part by mass of a mass part, 1 part by mass of a pyrolytic foaming agent, 1 part by mass of a decomposition temperature adjusting agent, and 0.5 parts by mass of an antioxidant to an extruder and melt-kneading at 140 ° C. Extrusion molding was performed to form a long sheet having a thickness of 0.3 mm.
Next, the resin composition was crosslinked by irradiating an electron beam with an acceleration voltage of 500 kV for 4.5 Mrad on both surfaces of the long sheet-shaped resin composition.
Thereafter, this resin composition was continuously fed into a foaming furnace maintained at 250 ° C. by hot air and an infrared heater, heated and foamed, and at the same time, stretched in the MD direction and the TD direction. Got.
The obtained foamed sheet was evaluated according to the above evaluation method, and the results are shown in Table 1.

[Example 2]
The blending amount of the pyrolytic foaming agent was changed to the amount shown in Table 1, and the electron beam applied to the resin composition was changed to 5 Mrad so that the gel% was higher, and the thickness was 0.15 mm. The same operation as in Example 1 was performed except for the points.

[Example 3]
The amount of the pyrolytic foaming agent was changed to the amount shown in Table 1, and the same procedure as in Example 1 was carried out except that the expansion ratio was 3 cc / g and the thickness was 0.15 mm.

[Comparative Example 1]
The resin component supplied to the extruder was changed to only 100 parts by mass of polyethylene resin, and the same procedure as in Example 1 was performed except that the expansion ratio was 2.5 cc / g and the thickness was 0.12 mm.

[Comparative Example 2]
The amount of the pyrolytic foaming agent was changed to the amount shown in Table 1, and the same procedure as in Comparative Example 1 was performed except that the expansion ratio was 3 cc / g and the thickness was 0.15 mm.

[Comparative Example 3]
Of the resin components supplied to the extruder, 30 parts by mass of the styrene thermoplastic elastomer is changed to 30 parts by mass of a polyethylene resin (trade name: Affinity KC8852, manufactured by Dow Chemical Co., Ltd.), and the expansion ratio is 2 cc / g, It carried out similarly to the comparative example 1 except the point which made thickness 0.1mm.

[Comparative Example 4]
The same operation as in Comparative Example 3 was performed except that the thickness was 0.15 mm.

[Comparative Example 5]
The amount of the pyrolytic foaming agent was changed to the amount shown in Table 1, and the same procedure as in Comparative Example 3 was carried out except that the expansion ratio was 2.7 cc / g and the thickness was 0.1 mm.

In addition, the detail of the resin component used by each Example and the comparative example is as follows.
(1) Kernel KF370: linear low density polyethylene which is an ethylene-1-hexene copolymer obtained using a polymerization catalyst of a metallocene compound, density: 0.905 g / cm ³ , melting point (DSC method) Tm: 97 ° C
(2) Affinity KC8852: linear low-density polyethylene which is an ethylene-1-octene copolymer obtained using a metallocene compound polymerization catalyst, density 0.875 g / cm ³ , melting point (DSC method) Tm: 66 ℃
(3) Hibler (registered trademark) 7311: hydrogenated styrene / isoprene / butadiene block copolymer, styrene content: 12% by mass, maximum peak temperature of tan δ: −17 ° C.
Moreover, the additive used by each Example and the comparative example is as follows.
Thermally decomposable foaming agent: Eizo Kasei Co., Ltd., Azodicarbonamide AC # K3
Decomposition temperature regulator: ADEKA Corporation, trade name. ADK STAB (registered trademark) CDA-1
Antioxidant: ADEKA Corporation, trade name. ADK STAB (registered trademark) FP-2000 phosphorus antioxidant

As described above, the foamed sheets of Examples 1 to 3 contain a styrene-based thermoplastic elastomer having a relatively low maximum peak temperature of tan δ in addition to the olefin resin. Became good. In addition, the foam sheets of Examples 1 to 3 had an appropriate value of 25% compressive strength, and had moderate flexibility. On the other hand, Comparative Examples 1 to 5 did not contain a styrenic thermoplastic elastomer, so that at least the withstand voltage characteristics were inferior to those of Examples 1 to 3.

Claims

Foaming a resin composition containing a polyolefin resin (A) and a styrene thermoplastic elastomer (B) having a maximum peak temperature of tan δ of −30 to 10 ° C. measured by dynamic viscoelasticity; A polyolefin having a ratio (A / B) of the polyolefin resin (A) to the styrene thermoplastic elastomer (B) of 50/50 to 90/10 in terms of mass ratio and a thickness of 0.05 to 1.0 mm. Foam sheet.
The polyolefin foam sheet according to claim 1, wherein the styrene thermoplastic elastomer (B) has a styrene content of 5 to 25% by mass.
The styrene thermoplastic elastomer (B) is one or more selected from a styrene / isoprene block copolymer, a hydrogenated styrene / isoprene block copolymer, and a hydrogenated styrene / isoprene / butadiene block copolymer. The polyolefin-based foamed sheet according to claim 1 or 2.
The polyolefin foam sheet according to any one of claims 1 to 3, wherein the polyolefin resin (A) is a polyethylene resin.
The polyolefin-based foamed sheet according to claim 4, wherein the polyethylene-based resin is polymerized with a metallocene compound polymerization catalyst.
The polyolefin foam sheet according to any one of claims 1 to 5, wherein the polyolefin foam sheet is cross-linked.
An adhesive tape comprising the polyolefin-based foam sheet according to any one of claims 1 to 6 and an adhesive layer provided on at least one surface of the polyolefin-based foam sheet.