JP5534854B2 - Adhesive sheet for electronic equipment - Google Patents

Description

  The present invention relates to an adhesive sheet for electronic equipment.

  Conventionally, in the assembly of a liquid crystal panel, a cushion material is used for the purpose of absorbing an impact. The liquid crystal display device described in Patent Document 1 includes a rubber cushion material between the housing and the front plate. The liquid crystal display device described in Patent Document 2 includes a cushion material between the liquid crystal panel and the panel guide.

  Detailed studies are being conducted on such cushioning materials and shock absorbing materials. For example, Patent Document 3 discloses a shock absorbing sheet having a rubber foam and a bubble-containing adhesive layer. Further, it is described that this shock absorbing sheet is interposed between the image display panel and the transparent front plate.

  In recent years, with the demand for downsizing / thinning electronic devices, display panels are generally getting thinner. In a thin display panel, the cushion material used is required to have a high impact absorbing ability while being thin.

  In particular, display panels used for portable electronic components and display panels used for household appliances used around water are required to be thinner and more watertight. However, it has been difficult to achieve both excellent shock absorption and water tightness while being thin.

JP 2007-047620 A JP 2005-346061 A JP 2006-110773 A

  The present invention provides a pressure-sensitive adhesive sheet for electronic equipment that has sufficient shock absorption, adhesiveness, and water tightness while being thin.

  The pressure-sensitive adhesive sheet for electronic equipment according to the present invention is a pressure-sensitive adhesive sheet for electronic equipment in which an acrylic pressure-sensitive adhesive layer is laminated and integrated on at least one surface of a crosslinked polyolefin resin foamed sheet. 100 parts by weight of an acrylic pressure-sensitive adhesive containing 30 to 70% by weight of a butyl acid component, 10 to 50% by weight of a 2-ethylhexyl acrylate component and 5 to 30% by weight of a radical polymerizable monomer component having a bicyclo ring structure in the molecule; And 3 to 60 parts by weight of a tackifier.

  The polyolefin resin constituting the crosslinked polyolefin resin foamed sheet is preferably one containing 40% by weight or more of a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.

  By using a polyolefin resin containing 40% by weight or more of a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, the polyolefin resin is not increased in adhesiveness. Flexibility can be imparted.

  Moreover, the polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst has a narrow molecular weight distribution, and in the case of a copolymer, the proportion of the copolymer component is almost equal to any molecular weight component. Introduced in. Therefore, the foamed sheet can be uniformly crosslinked. And since the foamed sheet is uniformly crosslinked, the foamed sheet can be uniformly stretched as necessary, and the thickness of the resulting crosslinked polyolefin resin foamed sheet can be made uniform as a whole. .

  In the polyolefin resin, the content of the polyethylene resin obtained using the metallocene compound containing a tetravalent transition metal as a polymerization catalyst is preferably 40% by weight or more, more preferably 50% by weight or more, % By weight or more is particularly preferable, and 100% by weight is most preferable. The content of the polyethylene resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst is 100% by weight. As a polyolefin resin, a metallocene compound containing a tetravalent transition metal as a polymerization catalyst The case where only the polyethylene-type resin obtained using is used is meant.

  As a polyethylene resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, a metallocene compound containing a tetravalent transition metal is used as a polymerization catalyst, and ethylene and a small amount of an α-olefin are used together. A linear low density polyethylene obtained by polymerization is preferred.

  Examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene.

  Here, the metallocene compound containing a tetravalent transition metal generally means a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds, and a bis (cyclopentadienyl) metal complex is typical. Is.

  As a metallocene compound containing a tetravalent transition metal, specifically, a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, platinum, or one or more cyclopentadienyl rings or Examples thereof include compounds in which the analog is present as a ligand (ligand).

  Examples of such metallocene compounds containing tetravalent transition metals include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, Dimethylsilyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-t-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium chloride , Methylphenylsilyltetramethylcyclopentadienyl-t-butylamido hafnium dichloride, indenyl titanium tris (dimethylamide), indenyl titanium tri (Diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

  Metallocene compounds containing tetravalent transition metals can act as catalysts during the polymerization of various olefins by changing the type of metal and the structure of the ligand and combining them with specific cocatalysts (cocatalysts). . Specifically, the polymerization is usually performed in a catalyst system in which methylaluminoxane (MAO), a boron compound, or the like is added as a cocatalyst to a metallocene compound containing a tetravalent transition metal. In addition, 10 to 1,000,000 mol times is preferable and the usage-amount of the cocatalyst with respect to the metallocene compound containing a tetravalent transition metal has more preferable 50 to 5,000 mol times.

The method for polymerizing the polyethylene resin is not particularly limited, and examples thereof include a solution polymerization method using an inert medium, a bulk polymerization method substantially free of an inert medium, and a gas phase polymerization method. The polymerization temperature is usually from −100 ° C. to 300 ° C., and the polymerization pressure is usually from normal pressure to 100 kg / cm ² .

  Metallocene compounds containing tetravalent transition metals have uniform active site properties and the same activity at each active site. Therefore, the molecular weight, molecular weight distribution, composition, and composition distribution of the polymer to be synthesized are uniform. Rise. Therefore, the polyolefin resin polymerized using these metallocene compounds as a polymerization catalyst has a narrow molecular weight distribution, and in the case of a copolymer, the copolymer component is introduced in almost equal proportion to any molecular weight component. Have

  Furthermore, the polyolefin resin constituting the crosslinked polyolefin resin foamed sheet contains a polyolefin resin other than the polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. Also good. Examples of such polyolefin resins include polyethylene resins and polypropylene resins. In addition, polyolefin resin may be used independently or 2 or more types may be used together.

  The polyethylene resin is not particularly limited as long as it is other than a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. For example, linear low density polyethylene, low density polyethylene , Medium density polyethylene, high density polyethylene, ethylene-α-olefin copolymer containing 50% by weight or more of ethylene, ethylene-vinyl acetate copolymer containing 50% by weight or more of ethylene, and the like. Even if it is used, 2 or more types may be used together. 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.

  In addition, the polypropylene resin is not particularly limited, and examples thereof include polypropylene and a propylene-α-olefin copolymer containing 50% by weight or more of propylene. The above may be used in combination. 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 and 1-octene. Can be mentioned.

  If the degree of crosslinking of the crosslinked polyolefin resin foamed sheet is small, when the foamed sheet is stretched, bubbles in the vicinity of the surface of the foamed sheet are broken to cause surface roughness, and adhesion to the acrylic pressure-sensitive adhesive layer When the foamable polyolefin resin composition is too large, the melt viscosity of the foamable polyolefin resin composition described later becomes too large, and the foamable polyolefin resin composition foams when the foamable polyolefin resin composition is heated and foamed. The cross-linked polyolefin resin foam sheet having a desired expansion ratio cannot be obtained, and as a result, the impact absorbability is poor. Therefore, 5 to 60% by weight is preferable, and 10 to 40% by weight is more preferable.

In addition, the degree of crosslinking of the crosslinked polyolefin resin foamed sheet refers to that measured in the following manner. About 100 mg of a test piece is taken from the crosslinked polyolefin resin foam 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, 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. Based on the obtained value, the degree of crosslinking (% by weight) of the crosslinked polyolefin resin foam sheet is calculated by the following formula.
Crosslinking degree (% by weight) = 100 × (B / A)

  Further, the cross-linked polyolefin-based resin foam sheet preferably has an air bubble aspect ratio (MD average cell diameter / CD average cell diameter) of 0.25 to 1, and a cell aspect ratio (MD average cell). More preferably, the diameter / average bubble diameter of CD is 0.25 to 1 and the aspect ratio of bubbles (average bubble diameter of CD / average bubble diameter of VD) is 2 to 18.

  Specifically, when the ratio of the average bubble diameter of MD and the average bubble diameter of CD in the crosslinked polyolefin resin foam sheet, that is, the aspect ratio of the bubbles (average bubble diameter of MD / average bubble diameter of CD) is small, The expansion ratio of the cross-linked polyolefin resin foam sheet is reduced and flexibility is reduced, or the thickness, flexibility and tensile strength of the cross-linked polyolefin resin foam sheet may vary. Since the softness | flexibility of a resin foam sheet falls, 0.25-1 are preferable and 0.25-0.60 are more preferable.

  In addition, when the ratio of the average bubble diameter of CD and the average bubble diameter of VD, that is, the aspect ratio of bubbles (average bubble diameter of CD / average bubble diameter of VD) in the crosslinked polyolefin resin foamed sheet is small, When the flexibility of the polyolefin-based resin foam sheet is reduced and is large, the expansion ratio of the crosslinked polyolefin-based resin foam sheet is decreased and the flexibility is decreased, or the thickness, flexibility and tensile strength of the crosslinked polyolefin-based resin foam sheet are decreased. 2 to 18 is preferable, and 2.5 to 15 is more preferable.

  The MD (machine direction) of the cross-linked polyolefin resin foam sheet refers to the extrusion direction, and the CD (crossing direction) of the cross-linked polyolefin resin foam sheet is orthogonal to the MD (machine direction) and cross-linked polyolefin resin foam. The direction along the surface of the sheet is referred to, and the VD (vertical (thickness) direction) of the crosslinked polyolefin resin foamed sheet refers to a direction orthogonal to the surface of the crosslinked polyolefin resin foamed sheet.

  Next, the average cell diameter of MD of the cross-linked polyolefin resin foamed sheet is measured in the following manner. That is, the cross-linked polyolefin resin foam sheet is cut over the entire length in a plane parallel to VD at a substantially central portion of the CD.

  Thereafter, the cross section of the cross-linked polyolefin resin foam sheet is magnified 60 times using a scanning electron microscope (SEM), and a photograph is taken so that the full length of the VD of the cross-linked polyolefin resin foam sheet is accommodated.

  In the obtained photograph, a straight line having a length of 15 cm on the photograph (actual length of 2500 μm before enlargement) corresponding to the central portion of the VD of the crosslinked polyolefin resin foamed sheet is obtained by foaming the crosslinked polyolefin resin foam. Draw to be parallel to the sheet surface.

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 polyolefin-type resin foam sheet means what was measured in the following way. That is, photography is performed in the same manner as the procedure for calculating the average cell diameter of MD of the crosslinked polyolefin resin foam sheet.

  In the obtained photograph, three straight lines that divide the cut surface of the photographed crosslinked polyolefin resin foam sheet into four parts in MD are foamed in a direction (VD) perpendicular to the surface of the crosslinked polyolefin resin foam sheet. Draw over the entire length of the 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 bubbles 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.
VD average bubble diameter (μm) = length of straight line on photo (μm) / (60 × number of bubbles (pieces))

  Next, the average cell diameter of CD of the cross-linked polyolefin resin foam sheet is measured in the following manner. That is, the cross-linked polyolefin resin foam sheet is cut over the entire length in the thickness direction on a plane parallel to the CD and parallel to the direction (VD) perpendicular to the surface of the cross-linked polyolefin resin foam sheet.

  Thereafter, the cross section of the cross-linked polyolefin resin foam sheet is magnified 60 times using a scanning electron microscope (SEM), and a photograph is taken so that the total length in the thickness direction of the cross-linked polyolefin resin foam sheet is accommodated.

  Then, based on the obtained photograph, the average cell diameter of CD is calculated in the same manner as when the average cell diameter of MD of the crosslinked polyolefin resin foamed sheet is measured.

  In the above-described procedure 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, even if the bubbles seem to be completely separated from each other by the cell wall on the cut surface of the cross-linked polyolefin resin foam sheet, they communicate with each other at a portion other than the cut surface of the cross-linked polyolefin resin foam sheet. However, in the present invention, the cross-linked polyolefin resin foam sheet is not considered whether or not it is in communication with each other in the portion other than the cut surface, and based only on the cross section of the bubble film shown on the photograph. The bubble form is judged, and one void portion completely surrounded by the bubble film cross section appearing on the photograph is judged as one bubble.

  Positioning on a straight line means that the straight line completely penetrates the bubble at any part of the bubble, and the straight line does not completely penetrate the bubble at both ends of the straight line. In the case where the end of is located in the bubble, this bubble is counted as 0.5.

  When taking a photograph of the cut surface of the cross-linked polyolefin resin foam sheet, coloring the cut surface of the cross-linked polyolefin resin foam sheet facilitates the discrimination of air bubbles and enlarges the 2500 μm scale together to take a photo. This makes it easier to specify the straight line length on the photograph.

  By using the cross-linked polyolefin resin foam sheet as described above, the pressure-sensitive adhesive sheet for electronic equipment of the present invention has extremely excellent shock absorption and excellent water-tightness even if its thickness is thin. .

  If the closed cell ratio of the crosslinked polyolefin resin foam sheet is low, the water-tightness of the pressure-sensitive adhesive sheet for electronic devices is lowered, so 80% or more is preferable, and 95% or more is more preferable. In addition, the closed cell rate of a crosslinked polyolefin-type resin foam sheet means what was measured in the following way.

As a method for measuring the closed cell ratio of the cross-linked polyolefin resin foam sheet, first, a test piece having a flat square shape with a side of 5 cm and a constant thickness is cut out from the cross-linked polyolefin resin foam sheet. Subsequently, the weight W ₁ of the test piece is measured, and the thickness of the test piece is further measured to calculate the apparent volume V ₁ of the test piece.

Next, the value obtained as described above is substituted into the following equation (1) to calculate the apparent volume V ₂ occupied by the bubbles. The density of the polyolefin resin constituting the test piece is ρg / cm ³ .
Apparent volume occupied by bubbles V ₂ = V ₁ −W ₁ / ρ (1)

Subsequently, the test piece is submerged in distilled water at 23 ° C. so that the distance from the upper surface of the test piece to the water surface is 100 mm, and a pressure of 15 kPa is applied to the test piece for 3 minutes. After that, the test piece is taken out from the distilled water, the water adhering to the surface of the test piece is removed, the weight W _{2 of the} test piece is measured, and the open cell ratio F ₁ is calculated based on the following formula (2). Thus, the closed cell rate F ₂ is obtained from the open cell rate F ₁ .
Open cell ratio F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂ (2)
Closed cell ratio F ₂ (%) = 100−F ₁ (3)

In addition, when the 25% compressive strength of the crosslinked polyolefin resin foamed sheet in accordance with JIS K6767 is large, the impact absorbability may be lowered. Therefore, 4.9 × 10 ⁴ Pa or less is preferable. Since it may be inferior to thickness uniformity in a step, 2 * 10 < ⁴ > -4 * 10 < ⁴ > Pa is more preferable.

Furthermore, if the tensile strength at 23 ° C. in at least one direction of MD or CD in the cross-linked polyolefin resin foam sheet is small, the cross-linked polyolefin resin foam sheet may be cut during the bonding operation. × 10 ⁶ Pa or more is preferable, and if it is too large, the handleability of the pressure-sensitive adhesive sheet for electronic equipment may be lowered, and thus 2.2 × 10 ^{6 to} 8.0 × 10 ⁶ Pa is more preferable. In addition, the tensile strength in 23 degreeC in MD or CD of a crosslinked polyolefin-type resin foam sheet says what was measured based on JISK6767.

  Next, a method for producing a crosslinked polyolefin resin foam sheet will be described. The method for producing the crosslinked polyolefin resin foam sheet is not particularly limited. For example, a polyolefin resin containing 40% by weight or more of a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. And a foamable polyolefin resin composition containing a thermally decomposable foaming agent is supplied to an extruder, melt-kneaded, and extruded into a sheet form from the extruder; A step of crosslinking the foamable polyolefin resin sheet, and a step of melting or softening the obtained foamed sheet and stretching the foamed sheet in the direction of either or both of MD and CD. The method of containing is mentioned. In addition, the process of extending | stretching the bubble of a foam sheet should just be performed as needed.

  And as a method of crosslinking the expandable polyolefin resin sheet, for example, a method of irradiating the expandable polyolefin resin sheet with ionizing radiation such as electron beam, α ray, β ray, and γ ray, expandable polyolefin resin Examples include a method in which an organic peroxide is blended in advance in the composition, 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-butyl) Peroxy) hexyne-3, benzoyl peroxide, cumyl peroxyneodecanate, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di (ben (Zoylperoxy) hexane, t-butylperoxyisopropyl carbonate, t-butylperoxyallyl carbonate and the like may be mentioned, and these may be used alone or in combination of two or more.

  If the amount of the organic peroxide added is small, the foamable polyolefin resin sheet may be insufficiently crosslinked. If the amount is large, decomposition residues of the organic peroxide are present in the resulting crosslinked polyolefin resin foam sheet. Since it may remain, 0.01-5 weight part is preferable with respect to 100 weight part of polyolefin resin, and 0.1-3 weight part is more preferable.

  The amount of the thermally decomposable foaming agent in the foamable polyolefin resin composition may be appropriately determined according to the expansion ratio of the cross-linked polyolefin resin foam sheet. Is reduced, it may not be possible to obtain a crosslinked polyolefin resin foam sheet having a desired expansion ratio, and if so, the tensile strength and compression recovery of the resulting crosslinked polyolefin resin foam sheet may decrease, 1-40 weight part is preferable with respect to 100 weight part of polyolefin resin, and 1-30 weight part is more preferable.

  The foamable polyolefin resin composition includes an antioxidant, a foaming aid such as zinc oxide, a cell core adjuster, and a heat stabilizer as necessary as long as the physical properties of the crosslinked polyolefin resin foam sheet are not impaired. Further, a colorant, a flame retardant, an antistatic agent, a filler and the like may be contained.

  Further, 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, and a method using an oil bath. May be used in combination.

  The stretching of the foam sheet may be performed after the foamable polyolefin resin sheet is foamed to obtain the foam 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 the foam sheet is cooled, the foam sheet may be heated again to be in a molten or softened state 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. By stretching the foamed sheet, it is possible to produce a crosslinked polyolefin resin foamed sheet in which the foam sheet has an aspect ratio within a predetermined range by stretching and deforming the foamed cells in a predetermined direction.

  Furthermore, in the extending | stretching direction of a foam sheet, it is extended toward MD or CD of a long-shaped expandable polyolefin resin sheet, or toward MD and CD. In addition, when extending a foamed sheet toward MD and CD, you may extend | stretch a foamed sheet toward MD and CD simultaneously, 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.

  Further, as a method of extending the foam sheet into the CD, the both ends of the CD of the foam sheet are gripped by a pair of grip members, and the foam sheet is moved by gradually moving the pair of grip members in directions away from each other. A method of stretching to CD 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, if the draw ratio in MD of the cross-linked polyolefin resin foam sheet is small, the flexibility and tensile strength of the cross-linked polyolefin resin foam sheet may be reduced. If large, the foam sheet may be cut during the stretch. Or, the foaming gas escapes from the foaming sheet being foamed, the expansion ratio of the resulting crosslinked polyolefin resin foam sheet is significantly reduced, the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet are reduced, and the quality is poor. Since it may become uniform, 1.1 to 2.0 times are preferable, and 1.2 to 1.5 times are more preferable.

In addition, the draw ratio in MD of a crosslinked polyolefin-type resin foam sheet is computed in the following way. That is, while obtaining the cube root F of the expansion ratio of the crosslinked polyolefin resin foamed sheet, the ratio of the winding speed to the supply speed (winding speed / supply speed) R is determined, and the crosslinked polyolefin resin foam is calculated based on the following formula. The draw ratio in the MD of the sheet can be calculated. However, the expansion ratio of the cross-linked polyolefin resin foam sheet is obtained by dividing the specific gravity of the expandable polyolefin resin sheet by the specific gravity of the cross-linked polyolefin resin foam sheet.
Stretch ratio (times) in MD of foam sheet = R / F

  Moreover, if the draw ratio in the CD of the crosslinked polyolefin resin foamed sheet is small, the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet may be reduced. If it is large, the foamed sheet may be cut during stretching or Foaming gas escapes from the foamed sheet during foaming, the expansion ratio of the resulting crosslinked polyolefin resin foam sheet is significantly reduced, and the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet are reduced and the quality is not uniform. 1.2 to 4.5 times is preferable, and 1.5 to 3.5 times is more preferable.

In addition, the draw ratio of CD in the crosslinked polyolefin resin foamed sheet is the length of CD of the crosslinked polyolefin resin foamed sheet obtained by heating and foaming the expandable polyolefin resin sheet without stretching the MD and CD. one to W _3, the length of the CD of the crosslinked polyolefin-based resin foam sheet was stretched in CD and W _4, it can be calculated based on the following equation.
Stretch ratio (times) of CD of foam sheet = W ₄ / W ₃

  The thickness of the crosslinked polyolefin resin foam sheet is not particularly limited, but if it is thin, the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet are reduced, and the impact of the resulting adhesive sheet for electronic devices is reduced. Even if the absorbability, texture, mechanical strength, etc. are reduced and the thickness is increased, the improvement of the performance of the pressure-sensitive adhesive sheet for electronic devices cannot be expected, and the economic efficiency is lowered, so 0.08 to 0.5 mm is preferable.

  An acrylic pressure-sensitive adhesive layer is laminated and integrated on at least one surface, preferably both surfaces of the crosslinked polyolefin-based resin foam sheet. The acrylic pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive and a tackifier. The acrylic pressure-sensitive adhesive contains a butyl acrylate component, a 2-ethylhexyl acrylate component, and a radical polymerizable monomer component having a bicyclo ring structure in the molecule.

  If the content of the butyl acrylate component in the acrylic pressure-sensitive adhesive is small, the heat resistance of the acrylic pressure-sensitive adhesive may decrease, and if it is large, the initial pressure-sensitive adhesive property of the acrylic pressure-sensitive adhesive may decrease. , 30 to 70% by weight, preferably 40 to 70% by weight.

  If the content of the 2-ethylhexyl acrylate component in the acrylic pressure-sensitive adhesive is small, the acrylic pressure-sensitive adhesive may be difficult to adhere to an adherend having a low polarity. Is limited to 10 to 50% by weight, and preferably 15 to 40% by weight.

  The acrylic pressure-sensitive adhesive contains a radical polymerizable monomer component having a bicyclo ring structure in the molecule as a monomer component. The bicyclo ring structure refers to a saturated alicyclic hydrocarbon structure in which two rings share two or more atoms.

  As described above, by incorporating a radical polymerizable monomer component having a bicyclo ring structure in the molecule as a monomer component in the acrylic pressure-sensitive adhesive, impact resistance at a low temperature (−20 ° C.) of the acrylic pressure-sensitive adhesive layer can be obtained. While being able to improve, the adhesiveness of an acrylic adhesive layer can be improved.

  The radical polymerizable monomer having a bicyclo ring structure in the molecule is not particularly limited as long as radical polymerization is possible. For example, isobornyl (meth) acrylate, norbornyl (meth) acrylate, bicyclo [3.2.1] Octyl-2- (meth) acrylate, bicyclo [3.3.1] nonyl-9- (meth) acrylate, and the like, a radical polymerizable monomer having an isobornyl group is preferable, and isobornyl (meth) acrylate is more preferable. Isobornyl acrylate is particularly preferred. In addition, (meth) acrylate means a methacrylate or an acrylate.

  In the acrylic adhesive, even if the content of the radical polymerizable monomer component having a bicyclo ring structure in the molecule is at least, the effect of improving the impact resistance at low temperatures of the acrylic adhesive layer is manifested. Therefore, it is limited to 5 to 30% by weight, and more preferably 10 to 25% by weight.

  The acrylic pressure-sensitive adhesive may contain an ethyl acrylate component. If the content of the ethyl acrylate component in the acrylic pressure-sensitive adhesive is small, the water-tightness of the pressure-sensitive adhesive sheet for electronic equipment may decrease. May decrease, or the acrylic pressure-sensitive adhesive layer may become too hard, so 5 to 15% by weight is preferable, and 5 to 10% by weight is more preferable.

  The acrylic pressure-sensitive adhesive may contain butyl acrylate, 2-ethylhexyl acrylate, and other components copolymerizable with the radical polymerizable monomer component having a bicyclo ring structure in the molecule. As the other component, for example, it is added for the purpose of increasing the cohesive force of the obtained pressure-sensitive adhesive, and contributes to forming a crosslinked structure between the main chains of the resin constituting the acrylic pressure-sensitive adhesive layer. And those which increase the glass transition temperature (Tg) of the resin constituting the acrylic pressure-sensitive adhesive layer.

  Other components that contribute to the formation of a crosslinked structure between the main chains of the resin constituting the acrylic pressure-sensitive adhesive layer are not particularly limited. For example, (meth) acrylic acid-2-hydroxyethyl, (meta ) Vinyl monomers such as glycidyl acrylate and allyl glycidyl ether.

  Moreover, it does not specifically limit as another component which raises the glass transition temperature (Tg) of resin which comprises the said acrylic adhesive layer, For example, (meth) acrylic acid, crotonic acid, maleic acid, itaconic acid, etc. Carboxy group-containing monomers; hydroxyl group-containing monomers such as n-methylolacrylamide; maleic anhydride, vinyl acetate, styrene and the like, and acrylic acid is preferred.

  And in acrylic adhesive, the content of butyl acrylate component, 2-ethylhexyl acrylate component and other components (except for ethyl acrylate) copolymerizable with radical polymerizable monomer component having bicyclo ring structure in the molecule If the amount is small, the pressure-sensitive adhesive force and tack of the resulting acrylic pressure-sensitive adhesive may be reduced, and if it is large, the resulting acrylic pressure-sensitive adhesive may be insufficiently crosslinked and the cohesive force may be reduced. -15 wt% is preferable, and 2-10 wt% is more preferable.

  In the acrylic adhesive, the main chain of the acrylic adhesive resin is a butyl acrylate component, a 2-ethylhexyl acrylate component, and other components copolymerizable with a radical polymerizable monomer component having a bicyclo ring structure in the molecule. If the content of other components that contribute to the formation of a cross-linked structure in between is small, the resulting acrylic pressure-sensitive adhesive may be insufficiently cross-linked and the cohesive force may be reduced. Since the adhesive strength and tack of the pressure-sensitive adhesive may decrease, 0.01 to 10% by weight is preferable, and 0.05 to 5% by weight is more preferable.

  Furthermore, if the weight average molecular weight measured as a polystyrene-equivalent molecular weight by the GPC (Gel Permeation Chromatography) method of the acrylic pressure-sensitive adhesive is small, the formed pressure-sensitive adhesive layer will deform the adherend. It is easy to peel off from the adherend due to the accompanying peeling stress, and the water tightness of the pressure-sensitive adhesive sheet for electronic equipment may be reduced. If it is large, the adhesive strength of the pressure-sensitive adhesive is reduced. In addition, the peeling stress generated along with the deformation of the adherend tends to peel from the adherend, and the water tightness of the pressure-sensitive adhesive sheet for electronic equipment may be lowered, so 300,000 to 1,500,000 are preferable, and 300,000 to 100 Is preferable, 350,000 to 900,000 is more preferable, and 400,000 to 650,000 is particularly preferable.

  In addition, the weight average molecular weight measured as a polystyrene conversion molecular weight by GPC method of the said acrylic adhesive was obtained by filtering a diluted solution obtained by diluting the acrylic adhesive with tetrahydrofuran (THF) 50 times through a filter. Based on the obtained filtrate, it can be obtained by measuring the polystyrene equivalent molecular weight of the acrylic pressure-sensitive adhesive by gel permeation chromatography. As the gel permeation chromatograph, for example, a product commercially available from Water under the trade name “2690 Separations Model” can be used.

  And in order to obtain the said acrylic adhesive, butyl acrylate, 2-ethylhexyl acrylate, and the radically polymerizable monomer which has a bicyclo ring structure in a molecule | numerator together with other vinyl monomers as needed, presence of a polymerization initiator What is necessary is just to carry out radical polymerization under. In addition, as a polymerization method, a conventionally well-known method is used, for example, solution polymerization, emulsion polymerization, suspension polymerization, block polymerization, etc. are mentioned.

  When radically polymerizing butyl acrylate, 2-ethylhexyl acrylate, and a monomer containing a radical polymerizable monomer having a bicyclo ring structure in the molecule, radical polymerization is performed in the presence of a chain transfer agent to produce an acrylic adhesive. It is preferable to do.

  By making this chain transfer agent exist at the time of radical polymerization, the resulting acrylic pressure-sensitive adhesive increases in the proportion of low molecular weight components and becomes excellent in impact resistance at low temperatures.

  The chain transfer agent is not particularly limited, and examples thereof include dodecyl mercaptan, t-butyl mercaptan, n-octyl mercaptan, isooctyl thioglycolate, and dodecyl mercaptan is preferable.

  If the amount of the chain transfer agent used at the time of radical polymerization is small, the weight average molecular weight of the resulting acrylic pressure-sensitive adhesive becomes high, the acrylic pressure-sensitive adhesive becomes hard at low temperatures, and the impact resistance at low temperatures of the acrylic pressure-sensitive adhesive is reduced. If the amount is too large, the molecular weight of the resulting acrylic pressure-sensitive adhesive may decrease too much, and the pressure-sensitive adhesive property of the acrylic pressure-sensitive adhesive may decrease. 0.01 to 0.2 parts by weight is preferable, and 0.03 to 0.08 parts by weight is more preferable.

  The polymerization initiator is not particularly limited. For example, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylper Oxypivalate, 2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate And t-butyl peroxyisobutyrate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate and the like. 1,1-bis (t-hexylper Oxy) -3,3,5-trimethylcyclohexane and t-hexylperoxypivalate are preferred. In addition, the said polymerization initiator may be used independently, or 2 or more types may be used together.

  The acrylic pressure-sensitive adhesive layer contains a tackifier for the purpose of suppressing the fluidity of the acrylic pressure-sensitive adhesive and improving the water tightness in the shear direction to improve the water-stopping property.

  And if there is little content of the tackifier in an acrylic adhesive layer, an acrylic adhesive layer will become easy to peel from a to-be-adhered body by the peeling stress which arises with a deformation | transformation of an to-be-adhered body, and an electronic device The water-tightness of the pressure-sensitive adhesive sheet decreases, and if it is large, the acrylic pressure-sensitive adhesive layer becomes hard and the adhesive strength and tack may decrease, so 3 to 60 parts by weight with respect to 100 parts by weight of the acrylic pressure-sensitive adhesive It is limited to 10 to 40 parts by weight, and 20 to 35 parts by weight is more preferable.

  Examples of tackifiers include rosin ester resins, polymerized rosins, disproportionated rosins, hydrogenated rosins, rosin resins such as partially disproportionated rosins, terpenes such as terpene phenol resins, aromatic modified terpene resins, and rosin phenol resins. Rosin ester resin, polymerized rosin, and terpene phenol resin are preferable, and two or more of rosin ester resin, polymerized rosin, and terpene phenol resin are preferably used in combination.

  Examples of the polymerized rosin include dimers of resin acids such as abietic acid. The rosin ester resin is a rosin resin mainly composed of abietic acid, a disproportionated rosin resin, a hydrogenated rosin resin, a dimer of a resin acid such as abietic acid (polymerized rosin), an alcohol It is a resin obtained by esterification. The rosin ester-based resin includes those in which a part of the hydroxyl group of the alcohol used for esterification is contained in the resin without being used for esterification. A resin obtained by esterifying a rosin resin is a rosin ester resin. A product obtained by esterifying a disproportionated rosin resin is a disproportionated rosin ester resin. A hydrogenated rosin ester resin is obtained by esterifying a hydrogenated rosin resin. A polymerized rosin ester resin is obtained by esterifying a polymerized rosin resin.

  Examples of alcohols used for the esterification include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol.

  If the content of the rosin ester-based resin in the acrylic pressure-sensitive adhesive layer is small, the acrylic pressure-sensitive adhesive layer may be easily peeled off from the adherend against the peeling stress in the shear direction, or The pressure-sensitive adhesive of the acrylic pressure-sensitive adhesive layer with respect to the polyolefin-based resin molded product may decrease, and if it is large, the acrylic pressure-sensitive adhesive layer may become hard and the initial tackiness may decrease. The amount is preferably 3 to 30 parts by weight, more preferably 10 to 20 parts by weight with respect to parts.

  If the content of the polymerized rosin in the acrylic pressure-sensitive adhesive layer is small, the acrylic pressure-sensitive adhesive layer may be easily peeled off from the adherend against the peeling stress in the shear direction, or the polyolefin-based Since the adhesiveness of the acrylic pressure-sensitive adhesive layer to the resin molded product may decrease, and in many cases, the acrylic pressure-sensitive adhesive layer may become hard and initial tackiness may decrease, so that the acrylic pressure-sensitive adhesive is reduced to 100 parts by weight. 3-30 weight part is preferable with respect to it, and 5-15 weight part is more preferable.

  A terpene phenol resin is a resin obtained by polymerizing a terpene in the presence of phenol, and a hydrogenated terpene phenol resin obtained by subjecting a terpene phenol resin to a hydrogenation treatment is excluded. It is estimated that the aromatic ring in the terpene phenol resin contributes to the improvement of the heat resistance of the pressure-sensitive adhesive. And the heat resistance of an acrylic adhesive layer improves by containing a terpene phenol resin in an acrylic adhesive layer.

  If the softening point of the terpene phenol resin is low, the heat resistance of the acrylic pressure-sensitive adhesive layer may be lowered. Therefore, 140 ° C. or higher is preferable, and if it is too high, the acrylic pressure-sensitive adhesive layer becomes hard and has adhesive strength. In addition, the tackiness is reduced, and the acrylic pressure-sensitive adhesive layer is likely to be peeled off from the adherend due to peeling stress caused by the deformation of the adherend, and the water tightness of the pressure-sensitive adhesive sheet for electronic equipment may be lowered. Therefore, 145-170 degreeC is more preferable. In addition, the softening point of the said terpene phenol resin means what was measured based on JISK2207.

  And if there is little content of the terpene phenol resin in an acrylic adhesive layer, the heat resistance and adhesive force of an acrylic adhesive may fall, and if it is many, an acrylic adhesive will become hard and adhesive force In addition, the tackiness is reduced, and the acrylic pressure-sensitive adhesive layer is likely to be peeled off from the adherend due to peeling stress caused by the deformation of the adherend, and the water tightness of the pressure-sensitive adhesive sheet for electronic equipment may be lowered. Therefore, 3-30 weight part is preferable with respect to 100 weight part of acrylic adhesives, 5-20 weight part is more preferable, and 5-15 weight part is especially preferable.

  30 or more are preferable and, as for the hydroxyl value of a tackifier, 35-60 are more preferable. This is because when the hydroxyl value of the tackifier is small, the acrylic pressure-sensitive adhesive layer is easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend, and the water-tightness of the pressure-sensitive adhesive sheet for electronic devices This is because if the amount is too large, a crosslinking failure may occur when an isocyanate-based crosslinking agent is added to crosslink the pressure-sensitive adhesive as described later. In addition, the hydroxyl value of the said tackifier says the value measured based on JISK0070.

  Moreover, it is preferable to add a crosslinking agent to the acrylic pressure-sensitive adhesive to form a crosslinked structure between the main chains of the resin constituting the acrylic pressure-sensitive adhesive. The crosslinking agent is not particularly limited, and examples thereof include an isocyanate crosslinking agent, an aziridine crosslinking agent, an epoxy crosslinking agent, and a metal chelate crosslinking agent, and an isocyanate crosslinking agent is preferable. This is because the isocyanate group reacts with the alcoholic hydroxyl group in the tackifier, resulting in loose crosslinking of the acrylic pressure-sensitive adhesive. Therefore, the acrylic pressure-sensitive adhesive layer can disperse the peeling stress that is intermittently applied to the acrylic pressure-sensitive adhesive layer. For this reason, the acrylic pressure-sensitive adhesive layer further improves the resistance to peeling from the adherend against the peeling stress caused by the deformation of the adherend, and as a result, improves the water tightness of the pressure-sensitive adhesive sheet for electronic devices. Because it can.

  Whether the acrylic pressure-sensitive adhesive has a high or low degree of crosslinking, the acrylic pressure-sensitive adhesive layer is easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend, and the water-tightness of the acrylic pressure-sensitive adhesive layer 5 to 40% by weight is preferable, 10 to 40% by weight is more preferable, and 15 to 35% by weight is particularly preferable.

Here, as a method for measuring the degree of crosslinking of the acrylic pressure-sensitive adhesive, W ₅ g of the acrylic pressure-sensitive adhesive was sampled, and this acrylic pressure-sensitive adhesive was immersed in ethyl acetate at 23 ° C. for 24 hours to remove the insoluble matter. The mixture is filtered through a 200-mesh wire mesh, the residue on the wire mesh is vacuum-dried, the weight of the dry residue is measured (W ₆ g), and the following formula is used.
Crosslinking degree (% by weight) = 100 × W ₆ / W ₅

  The acrylic pressure-sensitive adhesive may contain additives such as a plasticizer, an emulsifier, a softener, a filler, a pigment, and a dye as necessary.

  Next, the manufacturing method of the adhesive sheet for electronic devices of this invention is demonstrated. As a method for producing a pressure-sensitive adhesive sheet for electronic equipment, an acrylic pressure-sensitive adhesive composition containing an acrylic pressure-sensitive adhesive and a tackifier is applied to one or both sides of a crosslinked polyolefin resin foamed sheet and dried to obtain an acrylic pressure-sensitive adhesive. A method of stacking and integrating the adhesive layers, an acrylic pressure-sensitive adhesive composition is applied on the release-treated surface of the release paper and dried to form an acrylic pressure-sensitive adhesive layer, and this acrylic pressure-sensitive adhesive layer is cross-linked polyolefin-based A method of transferring and integrating the resin foam sheet on one or both sides of the resin foam sheet is exemplified.

  The method for applying the acrylic pressure-sensitive adhesive composition on one or both sides of the crosslinked polyolefin resin foam sheet is not particularly limited. For example, a coating machine such as a coater is used on one or both surfaces of the crosslinked polyolefin resin foam sheet. A method of applying an acrylic pressure-sensitive adhesive composition, a method of spraying and applying an acrylic pressure-sensitive adhesive composition using a spray on one or both sides of a cross-linked polyolefin resin foam sheet, one side or both sides of a cross-linked polyolefin resin foam sheet And a method of applying an acrylic pressure-sensitive adhesive composition using a brush.

And if 90 degree peeling strength of the adhesive sheet for electronic devices is small, since the watertightness of the adhesive sheet for electronic devices may fall, 15N / 10mm or more is preferable, 25N / 10mm or more is more preferable, and an upper limit is It is preferable that it is 60N / 10mm . In addition, 90 degree peeling strength of the adhesive sheet for electronic devices means the value measured based on JISZ0237.

  The 90 ° peel strength of the pressure-sensitive adhesive sheet for electronic devices is the content of the butyl acrylate component, the 2-ethylhexyl acrylate component constituting the acrylic pressure-sensitive adhesive, and the radical polymerizable monomer component having a bicyclo ring structure in the molecule, And it can control by adjusting content of the tackifier with respect to an acrylic adhesive.

Specifically, an acrylic system containing 40 to 50% by weight of a butyl acrylate component, 30 to 40% by weight of a 2-ethylhexyl acrylate component and 10 to 25% by weight of a radical polymerizable monomer component having a bicyclo ring structure in the molecule. By using an acrylic pressure-sensitive adhesive containing 100 parts by weight of a pressure-sensitive adhesive and 20 to 35 parts by weight of a tackifier, the 90 ° peel strength of the pressure-sensitive adhesive sheet for electronic devices can be adjusted to 15 N / 10 mm or more.

If the 90 ° peel strength according to JIS Z0237 in the electronic device pressure-sensitive adhesive sheet immersed in water at 40 ° C. for 120 minutes is small, the water-tightness of the electronic device pressure-sensitive adhesive sheet may decrease, so 15 N / It is preferably 10 mm or more, more preferably 25 N / 10 mm or more, and the upper limit is preferably 60 N / 10 mm .

  The 90 ° peel strength according to JIS Z0237 in the electronic device pressure-sensitive adhesive sheet immersed in water at 40 ° C. for 120 minutes is a butyl acrylate component, a 2-ethylhexyl acrylate component, and an acrylic pressure-sensitive adhesive. It can be controlled by adjusting the content of the radically polymerizable monomer component having a bicyclo ring structure in the molecule and the content of the tackifier relative to the acrylic pressure-sensitive adhesive.

Specifically, an acrylic system containing 40 to 50% by weight of a butyl acrylate component, 30 to 40% by weight of a 2-ethylhexyl acrylate component and 10 to 25% by weight of a radical polymerizable monomer component having a bicyclo ring structure in the molecule. Conforms to JIS Z0237 in the pressure-sensitive adhesive sheet for electronic equipment immersed in water at 40 ° C. for 120 minutes by using an acrylic pressure-sensitive adhesive containing 100 parts by weight of the pressure-sensitive adhesive and 20 to 35 parts by weight of the tackifier. The 90 ° peel strength can be adjusted to 15 N / 10 mm or more.

If the 90 ° peel strength in accordance with JIS Z0237 in the adhesive sheet for electronic equipment immersed in an aqueous surfactant solution at 5% by weight and 25 ° C. for 120 minutes is small, the watertightness of the adhesive sheet for electronic equipment is low. Since it may fall, 10 N / 10mm or more is preferable, 25 N / 10 mm or more is more preferable, and it is preferable that an upper limit is 60 N / 10 mm .

  The 90 ° peel strength according to JIS Z0237 in the pressure-sensitive adhesive sheet for electronic equipment immersed in an aqueous surfactant solution at 5% by weight and 25 ° C. for 120 minutes is butyl acrylate constituting the acrylic pressure-sensitive adhesive. The content can be controlled by adjusting the content of the component, the 2-ethylhexyl acrylate component and the radical polymerizable monomer component having a bicyclo ring structure in the molecule, and the content of the tackifier relative to the acrylic pressure-sensitive adhesive.

Specifically, an acrylic system containing 40 to 50% by weight of a butyl acrylate component, 30 to 40% by weight of a 2-ethylhexyl acrylate component and 10 to 25% by weight of a radical polymerizable monomer component having a bicyclo ring structure in the molecule. By using an acrylic adhesive containing 100 parts by weight of an adhesive and 20 to 35 parts by weight of a tackifier, an electron immersed in an aqueous surfactant solution at 5% by weight and 25 ° C. for 120 minutes The 90 ° peel strength based on JIS Z0237 in the pressure-sensitive adhesive sheet for equipment can be adjusted to 10 N / 10 mm or more.

When the 90 ° peel strength in accordance with JIS Z0237 of the adhesive sheet for electronic equipment immersed in an aqueous ethyl alcohol solution of 99.5% by weight and 25 ° C. for 120 minutes is small, the water tightness of the adhesive sheet for electronic equipment Is preferably 10 N / 10 mm or more, more preferably 12 N / 10 mm or more, and the upper limit is preferably 40 N / 10 mm .

  90 ° peel strength according to JIS Z0237 in the adhesive sheet for electronic equipment immersed in an ethyl alcohol aqueous solution of 99.5% by weight and 25 ° C. for 120 minutes is acrylic acid constituting the acrylic adhesive It can be controlled by adjusting the content of the butyl component, the 2-ethylhexyl acrylate component and the radical polymerizable monomer component having a bicyclo ring structure in the molecule, and the content of the tackifier relative to the acrylic pressure-sensitive adhesive. .

Specifically, an acrylic system containing 40 to 50% by weight of a butyl acrylate component, 30 to 40% by weight of a 2-ethylhexyl acrylate component and 10 to 25% by weight of a radical polymerizable monomer component having a bicyclo ring structure in the molecule. By using an acrylic pressure-sensitive adhesive containing 100 parts by weight of a pressure-sensitive adhesive and 20 to 35 parts by weight of a tackifier, it was immersed in an aqueous ethyl alcohol solution at 99.5% by weight and 25 ° C. for 120 minutes. The 90 ° peel strength based on JIS Z0237 in the adhesive sheet for electronic equipment can be adjusted to 10 N / 10 mm or more.

If the 90 ° peel strength in accordance with JIS Z0237 of the adhesive sheet for electronic equipment immersed in saline at 3.5% by weight and 25 ° C. for 120 minutes is small, the watertightness of the adhesive sheet for electronic equipment is reduced. Therefore, it is preferably 15 N / 10 mm or more, more preferably 25 N / 10 mm or more, and the upper limit is preferably 60 N / 10 mm .

  90 ° peel strength according to JIS Z0237 in an adhesive sheet for electronic equipment immersed in a salt solution of 3.5% by weight and 25 ° C. for 120 minutes is a butyl acrylate component constituting an acrylic adhesive It can be controlled by adjusting the content of the 2-ethylhexyl acrylate component and the radical polymerizable monomer component having a bicyclo ring structure in the molecule, and the content of the tackifier relative to the acrylic pressure-sensitive adhesive.

Specifically, an acrylic system containing 40 to 50% by weight of a butyl acrylate component, 30 to 40% by weight of a 2-ethylhexyl acrylate component and 10 to 25% by weight of a radical polymerizable monomer component having a bicyclo ring structure in the molecule. An electronic device immersed in a 3.5% by weight and 25 ° C. saline solution for 120 minutes by using an acrylic pressure-sensitive adhesive containing 100 parts by weight of a pressure-sensitive adhesive and 20 to 35 parts by weight of a tackifier 90 ° peel strength in accordance with JIS Z0237 in the pressure-sensitive adhesive sheet can be adjusted to 15 N / 10 mm or more.

  Next, the usage point of the adhesive sheet for electronic devices of this invention is demonstrated. The pressure-sensitive adhesive sheet for electronic equipment according to the present invention has excellent adhesiveness due to the acrylic pressure-sensitive adhesive layer, and has excellent water-tightness at the interface with the adherend. Furthermore, the pressure-sensitive adhesive sheet for electronic devices of the present invention is excellent in water-tightness and flexible because it is a closed-cell foamed resin foamed sheet, and is also excellent in impact resistance.

  Therefore, the pressure-sensitive adhesive sheet for an electronic device according to the present invention can reliably close a gap between components of the electronic device in a watertight state, smoothly absorbs an impact applied to the electronic device, and applies a large impact to the entire electronic device. Can be prevented. Examples of the electronic device include a mobile phone, a portable DVD player, a portable game machine, and a personal computer.

  In particular, the display panel and the transparent protective plate are opposed to each other by interposing the adhesive sheet for electronic equipment of the present invention in the gap between the display panel of the mobile phone and the transparent protective plate disposed on the display panel. The gap between the surfaces can be securely sealed in a watertight state, and the shock applied to the mobile phone can be absorbed smoothly by the adhesive sheet for electronic devices, and the impact applied to the components and members in the mobile phone should be minimized. Can do.

  Since the adhesive sheet for electronic devices of the present invention has the above-described configuration, it has excellent adhesiveness and water tightness. Furthermore, the pressure-sensitive adhesive sheet for electronic equipment of the present invention has impact resistance absorption, particularly shock resistance absorption at low temperatures. Accordingly, it is possible to reliably prevent water from entering the electronic device and to prevent the electronic device from being damaged by smoothly absorbing the impact applied to the electronic device in a wide temperature range.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
A reactor equipped with a thermometer, a stirrer, and a cooling tube was prepared. In this reactor, 10 parts by weight of isobornyl acrylate, 43 parts by weight of butyl acrylate, 35 parts by weight of 2-ethylhexyl acrylate and 2 parts by weight of itaconic acid were prepared. And 70 parts by weight of ethyl acetate were added, and the reactor was heated to start refluxing.

  Subsequently, 0.01 parts by weight of 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane as a polymerization initiator with respect to 100 parts by weight of the total amount of the monomers in the reactor. Then, 0.01 parts by weight of dodecyl mercaptan was added as a chain transfer agent, and polymerization was started under reflux. Next, after 1 hour and 2 hours from the start of polymerization, 0.01 parts by weight of 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane was added, and the polymerization was started. 4 hours later, 0.05 part by weight of t-hexylperoxypivalate was added to continue the polymerization reaction. Then, 8 hours after the start of polymerization, ethyl acetate was added to the reactor and cooled while diluting to obtain an acrylic pressure-sensitive adhesive solution containing an acrylic pressure-sensitive adhesive having a solid content of 30% by weight.

  In the acrylic pressure-sensitive adhesive solution, 14 parts by weight of rosin ester resin (Arakawa Chemical Co., Ltd., hydroxyl value: 38 to 47, softening point: 94 to 104 ° C.) with respect to 100 parts by weight of the acrylic pressure-sensitive adhesive solid content, polymerization 10 parts by weight of rosin (manufactured by Arakawa Chemical Co., Ltd., hydroxyl value: 38 to 47) and 10 parts by weight of terpene phenol resin (trade name “Mighty Ace 150” by Yashara Chemical Co., Ltd., softening point: 145 to 155 ° C.) were added, and ethyl acetate was added. And then adding 1.4 parts by weight of an isocyanate-based crosslinking agent (trade name “Coronate L45” manufactured by Nippon Polyurethane Co., Ltd.), and stirring to obtain an acrylic pressure-sensitive adhesive composition having a solid content of 20% by weight. A solution was obtained. The degree of crosslinking of the acrylic pressure-sensitive adhesive was 25% by weight.

On the other hand, linear low-density polyethylene obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (trade name “EXACT3027” manufactured by Exxon Chemical Co., Ltd., density: 0.900 g / cm ³ , melting point: 98 ° C., softening point: 85 ° C.) 100 parts by weight, azodicarbonamide 5 parts by weight, 2,6-di-t-butyl-p-cresol 0.3 part by weight and zinc oxide 1 part by weight The resin composition was supplied to an extruder, melted and kneaded at 130 ° C., and extruded into a long foamable polyolefin resin sheet having a width of 200 mm and a thickness of 0.8 mm.

  Next, the foamable polyolefin resin sheet is cross-linked by irradiating an electron beam with an acceleration voltage of 800 kV for 5 Mrad on both surfaces of the long foamable polyolefin resin sheet, and then the foamable polyolefin resin sheet is heated with hot air and infrared rays. The mixture was continuously fed into a foaming furnace maintained at 250 ° C. by a heater to be heated and foamed.

  Then, after continuously feeding the obtained foamed sheet from the foaming furnace, the foamed sheet was stretched to the CD at a stretch ratio of 3 times while maintaining the temperature of both surfaces at 200 to 250 ° C. In addition, the foamed sheet is stretched to MD at a stretch ratio of 3 by winding the foamed sheet at a winding speed faster than the feeding speed (feeding speed) of the foamable polyolefin resin sheet to the foaming furnace, and foamed. The bubbles in the sheet were stretched and deformed to CD and MD to obtain a crosslinked polyolefin resin foam sheet having a width of 1050 mm, a thickness of 0.1 mm, a crosslinking degree of 25% by weight, and an expansion ratio of 4.7 times.

  An acrylic pressure-sensitive adhesive composition solution was applied to both sides of the obtained crosslinked polyolefin resin foamed sheet so that the thickness after drying was 50 μm, and dried at 105 ° C. for 5 minutes. A pressure-sensitive adhesive sheet for electronic devices was obtained by laminating and integrating an acrylic pressure-sensitive adhesive layer having a thickness of 50 μm on each of both surfaces.

(Example 2)
The amount of isobornyl acrylate was 18 parts by weight instead of 10 parts by weight, the rosin ester resin was not used, and dodecyl mercaptan was adjusted to 0.05 parts by weight with respect to 100 parts by weight of the total amount of monomers. Except that, an adhesive sheet for electronic devices was obtained in the same manner as in Example 1.

(Example 3)
Example except that 20 parts by weight of isobornyl acrylate, 43 parts by weight of butyl acrylate, 35 parts by weight of 2-ethylhexyl acrylate and 2 parts by weight of itaconic acid, and 70 parts by weight of ethyl acetate were added to the reactor. In the same manner as in Example 1, an adhesive sheet for electronic equipment was obtained.

Example 4
Example 1 except that the isobornyl acrylate was changed to 23 parts by weight instead of 10 parts by weight, and the dodecyl mercaptan was adjusted to 0.05 parts by weight with respect to 100 parts by weight of the total amount of monomers. Thus, an adhesive sheet for electronic devices was obtained.

(Example 5)
An adhesive sheet for electronic devices was obtained in the same manner as in Example 1 except that 25 parts by weight of isobornyl acrylate was used instead of 10 parts by weight.

(Comparative Example 1)
An acrylic adhesive solid content of 100 wt.% Was prepared in the same manner as in Example 3 except that dodecyl mercaptan was adjusted to be 0.05 wt. Parts with respect to 100 wt. Parts of the total amount of monomers. 1 part by weight of polymerized rosin (Arakawa Chemical Co., hydroxyl value: 38 to 47) and 1 part by weight of terpene phenol resin (trade name “Mighty Ace 150” manufactured by Yashara Chemical Co., softening point: 145 to 155 ° C.) In addition, ethyl acetate was added and stirred, and further, 1.4 parts by weight of an isocyanate-based crosslinking agent (trade name “Coronate L45” manufactured by Nippon Polyurethane Co., Ltd.) was added and stirred to obtain a solid content of 20% by weight. A pressure-sensitive adhesive sheet for electronic equipment was obtained in the same manner as in Example 1 except that an acrylic pressure-sensitive adhesive composition solution was obtained. The crosslinking degree of the acrylic pressure-sensitive adhesive was 30% by weight.

(Comparative Example 2)
In the acrylic pressure-sensitive adhesive solution produced in the same manner as in Example 3, the rosin ester resin (Arakawa Chemical Co., Ltd., hydroxyl value: 38 to 47, softening point: 94 to 104 ° C.) 50 parts by weight and terpene phenol resin (trade name “Mighty Ace 150” manufactured by Yashara Chemical Co., Ltd., softening point: 145 to 155 ° C.) 40 parts by weight are added, and ethyl acetate is added and stirred. Example 1 with the exception that an acrylic pressure-sensitive adhesive composition solution having a solid content of 20% by weight was obtained by adding 1.4 parts by weight of an agent (trade name “Coronate L45” manufactured by Nippon Polyurethane Co., Ltd.) and stirring. Similarly, an electronic device pressure-sensitive adhesive sheet was obtained. The crosslinking degree of the acrylic pressure-sensitive adhesive was 30% by weight.

  The water-tightness A, B, impact resistance, low-temperature impact resistance, workability, and adhesive strength test of the obtained adhesive sheet for electronic devices were measured in the following manner, and the results are shown in Table 1. Moreover, in the crosslinked polyolefin resin foam sheet of the obtained pressure-sensitive adhesive sheet for electronic equipment, the aspect ratio of bubbles (average bubble diameter of MD / average bubble diameter of CD), aspect ratio of bubbles (average bubble diameter of CD / VD) The average cell diameter) and the closed cell ratio were measured, and the results are shown in Table 1.

(Watertightness A)
A test piece was obtained by punching from the pressure-sensitive adhesive sheet for electronic equipment into a ring shape having an outer diameter of 60 mm and an inner diameter of 50 mm over the entire thickness of the pressure-sensitive adhesive sheet for electronic equipment.

  The test piece is sandwiched between two parallel acrylic resin plates so that the compression rate of the test piece becomes 10%, that is, the thickness after compression of the test piece becomes 10% of the thickness before compression. The test piece was compressed with two acrylic resin plates in the thickness direction.

  One acrylic resin plate of the two acrylic resin plates has a through hole in a portion corresponding to the center portion of the test piece. Through this through hole, the opposing surface of the two acrylic resin plates and the test surface are opened. The space surrounded by the pieces was filled with water, and further, the time until water leakage started in accordance with JIS C0920 IPX7 was evaluated in a state where a pressure of 10 kPa was applied.

(Impact resistance)
Two iron plates each having a planar square shape with a side of 100 mm and a thickness of 2 mm were prepared. A test piece having a flat square shape with a side of 50 mm was cut out from the adhesive sheet for electronic equipment, the test piece was attached to the center of the upper surface of the lower iron plate, and the other iron plate was placed on the test piece as the upper iron plate.

  Next, the test piece was compressed with the upper and lower iron plates so that the thickness became 40%. An impact pickup device was attached to an iron ball weighing 15 g. On the upper iron plate, the iron ball is naturally dropped from a position 10 mm vertically upward from the center of the upper iron plate, and the impact acceleration is measured with an impact pickup device, and the absolute value of the positive maximum value of the impact acceleration, The value obtained by arithmetically averaging the absolute value of the negative maximum value was defined as impact acceleration 1.

  On the other hand, with the test piece and the upper iron plate not placed on the lower iron plate, an iron ball having a weight of 15 g is naturally placed on the lower iron plate from a position 10 mm vertically upward from the center of the lower iron plate. The impact acceleration was measured by an impact pickup device after dropping, and the value obtained by arithmetically averaging the absolute value of the positive maximum value of the impact acceleration and the absolute value of the negative maximum value was defined as impact acceleration 2.

The impact absorption rate was calculated based on the following formula from the impact accelerations 1 and 2 measured as described above, and evaluated according to the following criteria. In addition, the adhesive sheet for electronic devices is excellent in shock absorption, so that an impact absorption rate is large.
Impact absorption rate (%) = 100 × [(impact acceleration 2−impact acceleration 1) / impact acceleration 2]

Good: The impact absorption rate was 40% or more.
Impossibility: The impact absorption rate was less than 40%.

(Low temperature impact resistance)
A test piece having a plane rectangular shape measuring 100 mm in length and 50 mm in width was cut out from the adhesive sheet for electronic equipment. A polycarbonate resin plate A having a length of 100 mm × width of 50 mm and a thickness of 2 mm and a metal plate having a weight of 90 g and a height of 100 mm × width of 50 mm were prepared.

Next, the polycarbonate resin plate A was laminated and integrated using an adhesive so as to completely overlap the one surface of the metal plate. Then, the pressure-sensitive adhesive sheet for electronic equipment is superposed on one surface of the polycarbonate resin plate A so that the acrylic pressure-sensitive adhesive layer faces the polycarbonate resin plate A, and the electronic equipment is applied at a pressure of 1.01 × 10 ⁵ Pa. The pressure-sensitive adhesive sheet for electronic devices was bonded to one surface of the polycarbonate resin plate A by pressing the pressure-sensitive adhesive sheet for 3 seconds toward the polycarbonate resin plate.

  Furthermore, a polycarbonate resin plate B having a vertical rectangular shape of 100 mm in length and 50 mm in width and having a thickness of 2 mm is prepared, and this polycarbonate resin plate B is completely overlapped with one surface of the crosslinked polyolefin resin foam sheet of the adhesive sheet for electronic devices. Then, a cross-linked polyolefin resin foam sheet and the polycarbonate resin plate B were integrated with each other by piercing a nail from one surface of the polycarbonate resin plate B to prepare a test body. The nail was adjusted so as not to penetrate the crosslinked polyolefin resin foam sheet of the adhesive sheet for electronic devices.

  Then, after leaving the test body to stand at −20 ° C. for 3 hours, the test body was naturally dropped from a height of 1.5 m onto a horizontal plane, and in the test body, the polycarbonate resin plate A and the adhesive for electronic equipment were used. The peeling at the interface between the sheet and the acrylic pressure-sensitive adhesive layer was visually observed.

  When peeling does not occur at the interface between the polycarbonate resin plate A and the acrylic pressure-sensitive adhesive layer of the electronic device pressure-sensitive adhesive sheet, the test specimen is again naturally dropped from a height of 1.5 m onto a horizontal surface, Until the peeling occurs at the interface between the resin plate A and the acrylic pressure-sensitive adhesive layer of the electronic device pressure-sensitive adhesive sheet, the specimen is allowed to fall naturally in the same manner as described above, and the polycarbonate resin plate A and the electronic device pressure-sensitive adhesive sheet The number of times the test specimen dropped until peeling occurred at the interface with the acrylic pressure-sensitive adhesive layer was measured. In addition, when even slight peeling was observed at the interface between the polycarbonate resin plate A and the acrylic pressure-sensitive adhesive layer of the electronic device pressure-sensitive adhesive sheet, it was determined that “peeling occurred”.

(Processability)
After pasting a 160 μm thick polyethylene terephthalate film on both acrylic adhesive layers of the adhesive sheet for electronic devices, the adhesive sheet for electronic devices is punched out into a strip shape with a width of 2 mm and a length of 50 mm, and the adhesive for electronic devices Whether or not the sheet can be punched cleanly was evaluated according to the following criteria.
Excellent: Acrylic pressure-sensitive adhesive layers do not stick together after punching Good: Acrylic pressure-sensitive adhesive layers partially stick after lifting and cannot be lifted: Acrylic pressure-sensitive adhesive layers are completely fused together Was.

(Adhesion test)
Three test pieces were prepared by cutting the obtained pressure-sensitive adhesive sheet for electronic devices into a strip shape having a width of 25 mm. Each of the above test pieces is on a polycarbonate resin (PC) plate, a polyimide resin (PI) plate, and a stainless steel (SUS) plate (hereinafter collectively referred to as “various sticking plates”). After being placed so as to face each of the sticking plates, a test piece and various sticking plates are stuck to each other by reciprocating a 2 kg rubber roller on the test piece at a speed of 300 mm / min. The test body was produced by leaving still at 23 degreeC for 30 minutes. And about these test bodies, according to JISZ0237, the tensile test of a 180 degree direction was performed at peeling speed 300mm / min, and the adhesive force (N / 25mm) with respect to various sticking boards was measured. In addition, the release paper was stuck on the other acrylic adhesive layer of the test piece.

(Watertightness B)
The 90 ° peel strength of the adhesive sheet for electronic devices was measured according to JIS Z0237. In Tables 1 and 2, the measurement results are shown in the column of “non-immersed” for watertightness B.

  The 90 ° peel strength of the electronic device pressure-sensitive adhesive sheet immediately after being immersed in water at 40 ° C. for 120 minutes was measured according to JIS Z0237. In Table 1, the measurement results are shown in the column of “40 ° C. water” for water tightness B.

  Surfactant aqueous solution (37% by weight of a mixture of sodium alkyl ether sulfate, alkylamine oxide and polyoxyethylene alkyl ether) marketed by Procter & Gamble Japan under the trade name “Joy” with water A surfactant aqueous solution of 5% by weight and 25 ° C. was prepared by diluting, and the 90 ° peel strength of the pressure-sensitive adhesive sheet for electronic equipment immediately after being immersed in this surfactant aqueous solution for 120 minutes was defined in JIS Z0237. Measured in conformity. In Table 1, the measurement results are shown in the column of “surfactant” for watertightness B.

  The 90 ° peel strength of the electronic device pressure-sensitive adhesive sheet immediately after being immersed in an ethyl alcohol aqueous solution of 99.5% by weight and 25 ° C. for 120 minutes was measured according to JIS Z0237. In Table 1, the measurement results are shown in the column of “ethyl alcohol” for watertightness B.

  The 90 ° peel strength of the pressure-sensitive adhesive sheet for electronic equipment immersed in saline at 3.5% by weight and 25 ° C. for 120 minutes was measured according to JIS Z0237. In Table 1, the measurement results are shown in the column of “saline solution” for watertightness B.

Claims (8)

A cross-linked polyolefin resin foam sheet having a thickness of 0.08 to 0.5 mm, and laminated and integrated on one surface of the cross-linked polyolefin resin foam sheet, and a butyl acrylate component of 30 to 70% by weight, a 2-ethylhexyl acrylate component Acrylic adhesive containing 100 to 50 parts by weight of an acrylic adhesive containing 10 to 50% by weight and 5 to 30% by weight of a radical polymerizable monomer component having a bicyclo ring structure in the molecule, and 3 to 60 parts by weight of a tackifier An adhesive sheet for electronic equipment, comprising an adhesive layer. The pressure-sensitive adhesive sheet for electronic devices according to claim 1, wherein the tackifier contains two or more of a rosin ester resin, a polymerized rosin, and a terpene phenol resin. 2. The electronic device according to claim 1, wherein the tackifier contains 3 to 45 wt% rosin ester resin, 3 to 35 wt% polymerized rosin, and 3 to 35 wt% terpene phenol resin. Adhesive sheet. 2. The pressure-sensitive adhesive sheet for electronic equipment according to claim 1, wherein a 90 ° peel strength in accordance with JIS Z0237 is 15 N / 10 mm or more. The pressure-sensitive adhesive sheet for electronic devices according to claim 1, wherein the pressure-sensitive adhesive sheet for electronic devices immersed in water at 40 ° C for 120 minutes has a 90 ° peel strength in accordance with JIS Z0237 of 15 N / 10 mm or more. . The 90 ° peel strength in accordance with JIS Z0237 in an adhesive sheet for electronic equipment immersed in an aqueous surfactant solution at 5% by weight and 25 ° C for 120 minutes is 10 N / 10 mm or more. The adhesive sheet for electronic devices according to 1. The 90 ° peel strength according to JIS Z0237 in an adhesive sheet for electronic equipment immersed in an aqueous ethyl alcohol solution at 99.5% by weight and 25 ° C. for 120 minutes is 10 N / 10 mm or more. Item 2. An electronic device pressure-sensitive adhesive sheet according to item 1. The 90 ° peel strength according to JIS Z0237 in an adhesive sheet for electronic equipment immersed in a salt solution of 3.5% by weight and 25 ° C. for 120 minutes is 15 N / 10 mm or more. The adhesive sheet for electronic devices as described in.