JP6499586B2 - Double-sided adhesive tape for portable electronic devices - Google Patents

Description

The present invention relates to a double-sided pressure-sensitive adhesive tape for portable electronic devices that has high adhesive strength after thermocompression bonding and can exhibit excellent impact resistance even if it is narrow.

In an electronic device (for example, a mobile phone, a portable information terminal, etc.) equipped with an image display device or an input device, an adhesive tape is used for assembly. Specifically, for example, an adhesive tape is used to bond a cover panel for protecting the surface of an electronic device to a touch panel module or a display panel module, or to bond a touch panel module and a display panel module. Yes. Such an adhesive tape is used, for example, by being punched into a frame shape or the like and arranged around the display screen.

Adhesive tapes used in electronic devices are required to have various performances including high adhesive strength. For example, even if an impact is applied, the tape does not peel off and a strong impact is applied to the parts. No impact resistance is needed.

In recent years, with the downsizing of electronic devices and the increase in the size of display screens, the area of the opening has increased, thereby narrowing the joint fixing portion around the display screen. For this reason, the pressure-sensitive adhesive tape is becoming narrower year by year, and when it is used with a narrow width, the adhesion area is lowered. If the adhesive area decreases, it becomes difficult for the adhesive tape to reach the acceptable standard value in the adhesive strength test, drop impact test, etc. at the electronic equipment design manufacturer, so the design manufacturer should design the adhesive tape to the narrow width desired. Is becoming difficult.

As an adhesive tape that can maintain a high adhesive force even if it is narrow, an adhesive tape made of a heat-sensitive adhesive has been studied.
Patent Document 1 describes a heat-adhesive film made of a polymer having a urethane group, an amide group, and an acrylic group. Further, Patent Document 2 describes a thermal adhesive sheet in which a release film is provided on each surface of a double-sided adhesive sheet having both surfaces of a heat-sensitive adhesive layer made of a polyester-based thermoplastic adhesive.
However, in general, heat-sensitive adhesives are less susceptible to impacts than pressure-sensitive adhesives and have a problem that they are easily peeled off when dropped.

JP 2013-79305 A JP 2009-242562 A

An object of the present invention is to provide a double-sided pressure-sensitive adhesive tape for portable electronic devices that has a high adhesive strength after thermocompression bonding and can exhibit excellent impact resistance even if it is narrow.

The present invention is a double-sided pressure-sensitive adhesive tape for portable electronic devices having a pressure-sensitive adhesive layer on both sides of a substrate, wherein at least one pressure-sensitive adhesive layer is 45 to 90% by weight of structural units derived from butyl acrylate, and 2-ethylhexyl. Containing 5 to 40% by weight of structural units derived from acrylate, 100 parts by weight of acrylic copolymer having a weight average molecular weight of 400,000 to 1 million, and 40 to 60 parts by weight of tackifying resin, The shear modulus G ′ of the resin is 1.0 × 10 ^{6 to} 8.0 × 10 ⁶ Pa, and 40 to 60 parts by weight of the tackifying resin 5 is a tackifying resin (a) having a softening point of 100 ° C. or less. It is a double-sided pressure-sensitive adhesive tape for portable electronic devices containing -30 parts by weight.
The present invention is described in detail below.

In the double-sided pressure-sensitive adhesive tape for portable electronic devices having a pressure-sensitive adhesive layer on both surfaces of the substrate, the present inventor blends a predetermined amount of a specific acrylic copolymer and a specific tackifying resin in at least one pressure-sensitive adhesive layer. By adjusting the shear modulus G ′ at 23 ° C. of the pressure-sensitive adhesive layer to a specific range, even if it is narrow, the portable electronic device has high adhesive strength after thermocompression bonding and can exhibit excellent impact resistance. The inventors have found that a double-sided pressure-sensitive adhesive tape for equipment can be obtained, and have completed the present invention.

The double-sided pressure-sensitive adhesive tape for portable electronic devices of the present invention (also simply referred to as “double-sided pressure-sensitive adhesive tape” in the present specification) has pressure-sensitive adhesive layers on both surfaces of a substrate.
In the double-sided pressure-sensitive adhesive tape of the present invention, at least one pressure-sensitive adhesive layer contains 45 to 90% by weight of structural units derived from butyl acrylate and 5 to 40% by weight of structural units derived from 2-ethylhexyl acrylate. It contains 100 parts by weight of an acrylic copolymer having an average molecular weight of 400,000 to 1,000,000 and 40 to 60 parts by weight of a tackifier resin.
By making the said adhesive layer into such a composition, the adhesive force after thermocompression-bonding of a double-sided adhesive tape and impact resistance can be improved.

The acrylic copolymer can be prepared by copolymerizing a monomer mixture.
The monomer mixture contains 45 to 90 parts by weight of butyl acrylate and 5 to 40 parts by weight of 2-ethylhexyl acrylate.
If the butyl acrylate content is less than 45 parts by weight, the adhesive strength of the double-sided pressure-sensitive adhesive tape after thermocompression bonding decreases. When the content of butyl acrylate exceeds 90 parts by weight, the double-sided pressure-sensitive adhesive tape is easily peeled off from the adherend when a strong impact is applied to the adhesive surface.
When the content of 2-ethylhexyl acrylate is less than 5 parts by weight, the double-sided pressure-sensitive adhesive tape is easily peeled off from the adherend when a strong impact is applied to the adhesive surface. When content of 2-ethylhexyl acrylate exceeds 40 weight part, the adhesive force after the thermocompression bonding of a double-sided adhesive tape will fall.

The monomer mixture may contain other polymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate as necessary.
Examples of other polymerizable monomers that can be copolymerized include, for example, carbon number of alkyl groups such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and isopropyl (meth) acrylate. 1 to 3 (meth) acrylic acid alkyl ester, tridecyl methacrylate, and (meth) acrylic acid alkyl ester having 13 to 18 carbon atoms such as stearyl (meth) acrylate, hydroxyalkyl (meth) acrylate , Glycerin dimethacrylate, glycidyl (meth) acrylate, 2-methacryloyloxyethyl isocyanate, (meth) acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid and the like.

Especially, it is preferable that the said monomer mixture contains further less than 20 weight part ethyl acrylate or methyl acrylate with respect to a total of 100 weight part of butyl acrylate and 2-ethylhexyl acrylate. By adding less than 20 parts by weight of ethyl acrylate or methyl acrylate to the above monomer mixture, the adhesive strength after thermocompression bonding of the double-sided adhesive tape is increased, and it is difficult to peel off from the adherend when a strong impact is applied to the adhesive surface. be able to. The minimum with preferable content of ethyl acrylate or methyl acrylate is 5 weight part, and a more preferable upper limit is 15 weight part.

In order to copolymerize the monomer mixture to obtain the acrylic copolymer, the monomer mixture may be radically reacted in the presence of a polymerization initiator. As a method of radical reaction of the monomer mixture, that is, a polymerization method, a conventionally known method is used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like.
The said polymerization initiator is not specifically limited, For example, an organic peroxide, an azo compound, etc. are mentioned. Examples of the organic peroxide include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5 -Dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy Examples include isobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These polymerization initiators may be used alone or in combination of two or more.

The acrylic copolymer has a weight average molecular weight (Mw) of 400,000 to 1,000,000. When the weight average molecular weight is less than 400,000, the double-sided pressure-sensitive adhesive tape is easily peeled off from the adherend when a strong impact is applied to the adhesive surface. If the weight average molecular weight exceeds 1,000,000, the adhesive strength of the double-sided adhesive tape after thermocompression bonding will decrease. The preferable lower limit of the weight average molecular weight is 500,000, the preferable upper limit is 950,000, the more preferable lower limit is 600,000, and the more preferable upper limit is 900,000.
In order to adjust the weight average molecular weight within the above range, polymerization conditions such as a polymerization initiator and a polymerization temperature may be adjusted.
In addition, a weight average molecular weight (Mw) is a weight average molecular weight of standard polystyrene conversion by GPC (Gel Permeation Chromatography: gel permeation chromatography).

The pressure-sensitive adhesive layer contains 40 to 60 parts by weight of a tackifier resin with respect to 100 parts by weight of the acrylic copolymer.
When the content of the tackifying resin is less than 40 parts by weight, it is difficult for the double-sided pressure-sensitive adhesive tape to exhibit sufficient adhesive strength after thermocompression bonding. When the content of the tackifying resin exceeds 60 parts by weight, the pressure-sensitive adhesive layer becomes brittle, and the double-sided pressure-sensitive adhesive tape is easily peeled off from the adherend due to an impact such as dropping. The minimum with preferable content of tackifying resin is 45 weight part, and a preferable upper limit is 55 weight part.

40 to 60 parts by weight of the tackifying resin contains 5 to 30 parts by weight of a tackifying resin (a) having a softening point of 100 ° C. or less. The softening point is a softening point measured by the JIS K2207 ring and ball method.
When the content of the tackifying resin (a) having a softening point of 100 ° C. or less is less than 5 parts by weight, the flexibility of the pressure-sensitive adhesive layer is lowered, and the double-sided pressure-sensitive adhesive tape is adhered to the adherend by an impact such as dropping. Easily peels off. When the content of the tackifying resin (a) having a softening point of 100 ° C. or less exceeds 30 parts by weight, the pressure-sensitive adhesive layer becomes excessively flexible, and the double-sided pressure-sensitive adhesive tape exhibits sufficient adhesive strength after thermocompression bonding. It becomes difficult. The upper limit with preferable content of the tackifying resin (a) whose softening point is 100 degrees C or less is 25 weight part.

By setting the softening point of the tackifier resin (a) having a softening point of 100 ° C. or lower to 100 ° C. or lower, the adhesive strength after thermocompression bonding can be maintained while maintaining the impact resistance and flexibility of the pressure-sensitive adhesive layer. Can be increased.
Especially, it is preferable that the softening point is 80 degrees C or less about the tackifying resin (a) whose said softening point is 100 degrees C or less. By setting the softening point to 80 ° C. or less, the impact resistance of the pressure-sensitive adhesive layer can be further increased.

The tackifier resin preferably contains a rosin tackifier resin and / or a terpene tackifier resin. However, in addition to rosin-based tackifier resins and / or terpene-based tackifier resins, examples of the tackifier resins include coumarone indene resins, alicyclic saturated hydrocarbon resins, C5-based petroleum resins, and C9-based resins. Examples thereof include petroleum resins and C5-C9 copolymer petroleum resins.
The rosin-based tackifying resin is not particularly limited, but a rosin ester-based resin is preferable. The rosin ester-based resin includes a rosin resin mainly composed of abietic acid, a disproportionated rosin resin and a hydrogenated rosin resin, and a dimer (polymerized rosin resin) of a resin acid such as abietic acid. It is a resin obtained by esterification with a kind.
Esterified rosin resin is rosin ester resin, disproportionated rosin resin is esterified disproportionated rosin ester resin, hydrogenated rosin resin is esterified hydrogenated rosin ester resin, polymerized rosin resin The esterified product is a polymerized rosin ester resin. Examples of the alcohols used for the esterification include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol.

Examples of the hydrogenated rosin ester resin include Pine Crystal KE-359 (hydroxyl value 42, softening temperature 100 ° C.) manufactured by Arakawa Chemical Industries, and ester gum H (hydroxyl value 29, softening temperature 68 ° C.) manufactured by the same company. .
Examples of the polymerized rosin ester resin include Pencel D135 (hydroxyl value 45, softening temperature 135 ° C.) manufactured by Arakawa Chemical Industries, Pencel D130 (hydroxyl value 45, softening temperature 130 ° C.) manufactured by Arakawa Chemical Co., Ltd. , Softening temperature 125 ° C.), Pencel D160 (hydroxyl value 42, softening temperature 160 ° C.) manufactured by the same company.
These rosin-based tackifier resins may be used alone or in combination of two or more.

The terpene-based tackifier resin is not particularly limited, but a terpene phenol-based resin is preferable. The terpene phenol-based resin is a resin obtained by polymerizing terpene in the presence of phenol.
As the terpene-based tackifying resin, for example, YS Polystar G150 (softening point 150 ° C.) manufactured by Yashara Chemical Co., Ltd. YS Polystar T100 (softening point 100 ° C.) manufactured by Yasuhara Chemical Co., Ltd. YS Polystar G125 (softening point 125 ° C.) manufactured by Yasuhara Chemical Co. (Softening point 115 ° C.), YS Polystar T130 (softening point 130 ° C.) manufactured by the same company.

In the pressure-sensitive adhesive layer, a crosslinking structure may be formed between main chains of the resin (the acrylic copolymer and / or the tackifying resin) constituting the pressure-sensitive adhesive layer by adding a crosslinking agent. preferable.
The said crosslinking agent is not specifically limited, For example, an isocyanate type crosslinking agent, an aziridine type crosslinking agent, an epoxy-type crosslinking agent, a metal chelate type crosslinking agent etc. are mentioned. Of these, isocyanate-based crosslinking agents are preferred. By adding an isocyanate-based crosslinking agent to the pressure-sensitive adhesive layer, the isocyanate group of the isocyanate-based crosslinking agent reacts with the alcoholic hydroxyl group in the resin constituting the pressure-sensitive adhesive layer, thereby cross-linking the pressure-sensitive adhesive layer. It becomes loose. Therefore, the pressure-sensitive adhesive layer can disperse the peeling stress applied intermittently, and has a resistance to peeling from the adherend against the peeling stress caused by the deformation of the adherend when a strong impact is applied. More improved.
The addition amount of the crosslinking agent is preferably 0.1 to 15 parts by weight and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the acrylic copolymer.

Even if the degree of cross-linking (gel fraction) of the pressure-sensitive adhesive layer is too high or too low, the pressure-sensitive adhesive layer can be easily peeled off from the adherend due to the peeling stress caused by the deformation of the adherend. Therefore, 5 to 60% by weight is preferable, 10 to 50% by weight is more preferable, and 20 to 45% by weight is particularly preferable.
The degree of cross-linking (gel fraction) of the pressure-sensitive adhesive layer was determined by collecting W1 (g) of the pressure-sensitive adhesive layer and immersing this pressure-sensitive adhesive layer in ethyl acetate at 23 ° C. for 24 hours to give an insoluble content of 200 mesh. The residue on the wire mesh is vacuum-dried, and the weight W2 (g) of the dry residue is measured and calculated by the following formula (1).
Cross-linking degree (gel fraction) (% by weight) = 100 × W2 / W1 (1)

The pressure-sensitive adhesive layer has a shear elastic modulus G ′ at 23 ° C. of 1.0 × 10 ^{6 to} 8.0 × 10 ⁶ Pa. By adjusting the shear elastic modulus G ′ at 23 ° C. of the pressure-sensitive adhesive layer within the above range, the impact resistance of the double-sided pressure-sensitive adhesive tape at room temperature can be enhanced.
When the shear elastic modulus G ′ at 23 ° C. is less than 1.0 × 10 ⁶ Pa, the double-sided pressure-sensitive adhesive tape hardly exhibits sufficient adhesive strength after thermocompression bonding. When the shear elastic modulus G ′ at 23 ° C. exceeds 8.0 × 10 ⁶ Pa, the flexibility of the pressure-sensitive adhesive layer is lowered, and the double-sided pressure-sensitive adhesive tape is easily peeled off from the adherend due to an impact such as dropping. End up. In addition, the initial tack of the pressure-sensitive adhesive layer is reduced, the adhesive force to the release paper bonded to the pressure-sensitive adhesive layer during punching of the double-sided pressure-sensitive adhesive tape is reduced, and the workability is significantly reduced. The preferred lower limit of the shear modulus G ′ at 23 ° C. is 1.1 × 10 ⁶ Pa, the preferred upper limit is 7.0 × 10 ⁶ Pa, and the more preferred lower limit is 1.2 × 10 ⁶ Pa, the more preferred upper limit. Is 6.0 × 10 ⁶ Pa.
The shear modulus G ′ at 23 ° C. is a value measured at a measurement frequency of 10 Hz using, for example, DVA-200 manufactured by IT Measurement Control Co., Ltd.

In order to adjust the shear elastic modulus G ′ at 23 ° C. of the pressure-sensitive adhesive layer to the above range, the composition of the pressure-sensitive adhesive layer may be adjusted within the above range.

The pressure-sensitive adhesive layer may be colored for the purpose of shielding light from a display screen such as a liquid crystal display (LCD). The color pigment used for coloring the pressure-sensitive adhesive layer is not particularly limited, and examples thereof include carbon black and titanium oxide.

Although the thickness of the said adhesive layer is not specifically limited, It is preferable that the thickness (thickness of the adhesive layer of one side) of an adhesive layer is 10-150 micrometers. When the thickness is less than 10 μm, the pressure-sensitive adhesive layer may have reduced impact resistance. When the thickness exceeds 150 μm, the pressure-sensitive adhesive layer may have impaired reworkability or workability.

In the double-sided pressure-sensitive adhesive tape of the present invention, as long as at least one pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer as described above, the double-sided pressure-sensitive adhesive layers may have the same composition or may have different compositions. .

The said base material is not specifically limited, For example, a resin film with comparatively high rigidity, a resin film with comparatively low rigidity, a sheet-like foam etc. are mentioned.
The resin film having relatively high rigidity is not particularly limited, and examples thereof include a polyethylene terephthalate (PET) film and an axially stretched polypropylene (OPP) film. Since the double-sided pressure-sensitive adhesive tape of the present invention has the pressure-sensitive adhesive layer as described above, it is sufficient even when the base material is a resin film having such a relatively high rigidity and a low impact absorption. It is possible to have adhesive strength after heat and pressure bonding and impact resistance.

The thickness of the relatively rigid resin film is not particularly limited, but is preferably 5 to 100 μm. When the thickness is less than 5 μm, the base material may have a reduced strength, and may be broken or subjected to punching workability when a strong impact is applied. When the thickness exceeds 100 μm, the base material is reduced in flexibility, and may be peeled off at the interface with the pressure-sensitive adhesive layer when a strong impact is applied, and the double-sided pressure-sensitive adhesive tape is attached to the adherend. It may be difficult to stick together along the shape.

When the base material is the resin film or sheet-like foam having a relatively low rigidity, the base material itself has a buffer property, so that the impact resistance of the double-sided pressure-sensitive adhesive tape can be further improved.
The resin film having relatively low rigidity is not particularly limited, and examples thereof include rubber-based or urethane-based resin films.

As the sheet-like foam, a polyolefin foam is particularly preferable.
The polyolefin foam is not particularly limited as long as it is a foam containing a polyolefin resin, and examples thereof include a polyethylene foam, a polypropylene foam, an ethylene-propylene foam, and the impact resistance is improved. Therefore, a foam containing a polyolefin resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (also referred to as “metallocene polyolefin foam” in the present specification) is preferable. Among these, a foam containing a polyethylene resin obtained by using a metallocene compound (also referred to as “metallocene polyethylene foam” in the present specification) is more preferable.
Examples of the metallocene compounds include Kaminsky catalysts.

As a polyethylene resin obtained using the metallocene compound contained in the metallocene polyethylene foam, for example, using the metallocene compound, ethylene and another α-olefin blended as necessary may be used. Examples thereof include polyethylene-based resins obtained by polymerization. Examples of the other α-olefin include propene, 1-butene, 1-pentene, 1-hexene and the like.

The metallocene polyethylene foam may further contain another olefin resin in addition to the polyethylene resin obtained using the metallocene compound. Examples of the other olefin-based resin include polyethylene, polypropylene, ethylene-propylene copolymer, and the like.
In this case, the content of the polyethylene resin obtained by using the metallocene compound in the metallocene polyethylene foam is preferably 40% by weight or more. When the content of the polyethylene resin obtained by using the metallocene compound is 40% by weight or more, high compressive strength can be obtained even if the metallocene polyethylene foam is thin.

The polyolefin foam is preferably cross-linked. By cross-linking the polyolefin foam, impact resistance can be improved.
The method for crosslinking the polyolefin foam is not particularly limited. For example, a method of irradiating the polyolefin foam with ionizing radiation such as electron beam, α ray, β ray, γ ray, Examples include a method of decomposing the organic peroxide by heating.

The method for producing the polyolefin foam is not particularly limited, but a foamable resin composition containing a polyolefin resin and a foaming agent is prepared, and the foamable resin composition is extruded into a sheet using an extruder. In this case, it is preferable to foam the foaming agent and crosslink the obtained polyolefin foam as necessary.

Although the thickness of the said sheet-like foam is not specifically limited, 60-300 micrometers is preferable. When the thickness is less than 60 μm, the substrate may be broken when strength is lowered and a strong impact is applied. When the thickness exceeds 300 μm, the base material is reduced in flexibility and may peel off at the interface with the pressure-sensitive adhesive layer when a strong impact is applied. It may be difficult to adhere and adhere together.

The double-sided pressure-sensitive adhesive tape of the present invention preferably has a push adhesive strength at room temperature of 120 N or more after being punched into a frame shape having a width of 1 mm and thermocompression bonded to an aluminum plate at 70 ° C.
If the push adhesive strength is within the above range, the adhesive strength equal to or better than the adhesive strength in the 2 mm width of the double-sided adhesive tape made of a normal pressure-sensitive adhesive is achieved with a half width (1 mm width). Thus, even when the width is reduced, the double-sided adhesive tape easily reaches the acceptable standard value in an adhesive strength test, a drop impact test or the like at an electronic device design manufacturer. Further, when the double-sided pressure-sensitive adhesive tape is strongly bonded, it is possible to suppress the floating or peeling of the adherend (eg, front plate (cover panel) or component) over time. The push adhesive force is more preferably 125N or more, and further preferably 130N or more.
The push adhesive strength at room temperature after punching into a frame shape with a width of 1 mm and thermocompression bonding to an aluminum plate at 70 ° C. is a value measured by the method shown in FIG. 2 as described below.

In FIG. 2, the schematic diagram of the push test of a double-sided adhesive tape is shown. First, a double-sided adhesive tape is punched into an outer diameter of 46 mm, a length of 61 mm, an inner diameter of 44 mm, and a length of 59 mm to produce a frame-shaped test piece having a width of 1 mm. Next, as shown in FIG. 2 (a), the square hole is approximately in the center of the test piece 1 from which the release paper has been peeled off from the polycarbonate plate 3 having a thickness of 38 mm and a square hole having a width of 50 mm and a thickness of 2 mm. Then, an aluminum plate 5 having a width of 55 mm, a length of 65 mm, and a thickness of 2 mm is pasted from the upper surface of the test piece 1 so that the test piece 1 is located substantially at the center, and the test apparatus is assembled.
Thereafter, a pressure of 30 kgf is applied at 70 ° C. for 10 seconds from the side of the aluminum plate 5 positioned on the upper surface of the test apparatus, and the aluminum plate and the polycarbonate plate positioned on the top and bottom are thermocompression bonded and left at room temperature for 24 hours.
As shown in FIG. 2 (b), the push test is determined by turning the manufactured test apparatus upside down and fixing it to the support base, and pushing the lower aluminum plate 5 from the opening side at a speed of 10 mm / min. This can be done by measuring the load when the plate 5 is peeled off. If measurement temperature is normal temperature, it will not specifically limit, For example, 23 degreeC etc. are mentioned.

As for the double-sided adhesive tape of this invention, it is preferable that the total thickness of a double-sided adhesive tape is 100-400 micrometers. When the total thickness is less than 100 μm, the impact resistance of the double-sided pressure-sensitive adhesive tape may be lowered. When the total thickness exceeds 400 μm, the double-sided pressure-sensitive adhesive tape may not be suitable for use in bonding and fixing components constituting the electronic device to the device main body.

As a manufacturing method of the double-sided adhesive tape of this invention, the following methods are mentioned, for example.
First, a solution of adhesive A is prepared by adding a solvent to an acrylic copolymer, a tackifier resin, and a cross-linking agent as necessary, and this adhesive A solution is applied to the release treatment surface of the release film. Then, the solvent in the solution is completely removed by drying to form the pressure-sensitive adhesive layer A. Next, a substrate is bonded to the surface of the formed pressure-sensitive adhesive layer A.
Next, a release film different from the above release film is prepared, the adhesive B solution is applied to the release treatment surface of the release film, and the solvent in the solution is completely removed by drying, thereby releasing the release film. A laminated film in which the pressure-sensitive adhesive layer B is formed on the surface of the mold film is produced. The obtained laminated film is laminated on the back surface of the base material on which the pressure-sensitive adhesive layer A is formed, with the pressure-sensitive adhesive layer B facing the back surface of the base material to produce a laminate. And by pressing the said laminated body with a rubber roller etc., the double-sided adhesive tape which has an adhesive layer on both surfaces of a base material, and the surface of the adhesive layer was covered with the release film can be obtained.

In addition, two sets of laminated films are produced in the same manner, and a laminated body is produced by superposing these laminated films on both sides of the base material with the adhesive layer of the laminated film facing the base material. By pressing the laminate with a rubber roller or the like, a double-sided pressure-sensitive adhesive tape having an adhesive layer on both surfaces of the base material and having the surface of the adhesive layer covered with a release film may be obtained.

The application of the double-sided pressure-sensitive adhesive tape of the present invention is not particularly limited, but an application in which components constituting an electronic device (for example, a mobile phone, a portable information terminal, etc.) are bonded and fixed to the device body is preferable. Specifically, the double-sided pressure-sensitive adhesive tape of the present invention can be used as, for example, a double-sided pressure-sensitive adhesive tape for bonding and fixing a liquid crystal display panel of an electronic device (for example, a mobile phone, a portable information terminal, etc.) to the device body.
Moreover, the shape of the double-sided pressure-sensitive adhesive tape of the present invention in these applications is not particularly limited, and examples thereof include a rectangle, a frame shape, a circle, an ellipse, and a donut shape.

ADVANTAGE OF THE INVENTION According to this invention, even if it is narrow, the adhesive force after thermocompression bonding is high, and the double-sided adhesive tape for portable electronic devices which can exhibit the outstanding impact resistance can be provided.

It is a schematic diagram of the drop impact test of a double-sided adhesive tape. It is a schematic diagram of the push test of a double-sided adhesive tape.

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

Example 1
(1) Preparation of pressure-sensitive adhesive solution To a reactor equipped with a thermometer, a stirrer, and a condenser, the monomers and ethyl acetate shown in Table 1 were added and purged with nitrogen, and then the reactor was heated to start refluxing. Subsequently, 0.1 part by weight of azobisisobutyronitrile was added as a polymerization initiator in the reactor. The mixture was refluxed at 70 ° C. for 5 hours to obtain an acrylic copolymer solution. About the obtained acrylic copolymer, the weight average molecular weight was measured by GPC method using "2690 Separations Model" made from Water as a column.
A predetermined amount of tackifying resin shown in Table 1 is added to 100 parts by weight of the solid content of the acrylic copolymer contained in the obtained acrylic copolymer solution, and 125 parts by weight of ethyl acetate is added and stirred. Furthermore, the isocyanate type crosslinking agent ("Coronate L-45" by Nippon Polyurethane Industry Co., Ltd.) shown in Table 1 was added and stirred to obtain a pressure-sensitive adhesive solution in which the acrylic pressure-sensitive adhesive was dissolved in ethyl acetate.

The tackifying resins used in the examples and comparative examples are shown below.
(Tackifying resin having a softening point of 100 ° C. or lower (a))
・ Hydrogenated rosin ester resin A (Arakawa Chemical Industries, trade name “Ester gum H”, softening point 68 ° C.)
Disproportionated rosin ester resin B (Arakawa Chemical Industries, trade name “Super Ester A-75”, softening point 75 ° C.)
・ Hydrogenated rosin ester resin C (Arakawa Chemical Industries, trade name “Ester gum HP”, softening point 80 ° C.)
・ Hydrogenated rosin ester resin D (Arakawa Chemical Industries, trade name “Pine Crystal KE-359”, softening point 100 ° C.)

(Other tackifying resins)
Disproportionated rosin ester resin E (Arakawa Chemical Industries, trade name “Super Ester A-115”, softening point 115 ° C.)
Polymerized rosin ester resin F (Arakawa Chemical Industries, trade name “Pencel D-135”, softening point 135 ° C.)
Polymerized rosin ester resin G (Arakawa Chemical Industries, trade name “Pencel D-160”, softening point 160 ° C.)
-Terpene phenol resin H (manufactured by Yasuhara Chemical Co., Ltd., trade name “YS Polystar T130”, softening point 130 ° C.)
-Terpene phenol resin I (manufactured by Yasuhara Chemical Co., Ltd., trade name “Mighty Ace G150”, softening point 150 ° C.)

(2) Manufacture of double-sided pressure-sensitive adhesive tape The obtained pressure-sensitive adhesive solution was applied to a release-treated surface of a 75 μm-thick PET film that had been subjected to a release treatment, and dried at 110 ° C. for 3 minutes, whereby a thickness of 90 μm was obtained. An adhesive layer was formed. A 23 μm-thick PET film “FE2002” made by Phutamura Chemical Co., Ltd., which is a base material, is bonded to the surface of the formed adhesive layer with a silicon roller to obtain a single-sided adhesive tape having an adhesive layer on one side of the base material. It was.
Next, a PET film having a thickness of 75 μm that has been subjected to another release treatment is prepared, and an adhesive solution is applied to the release treatment surface of this PET film, followed by drying at 110 ° C. for 3 minutes. An agent layer was formed. This pressure-sensitive adhesive layer was bonded to the base material (PET film “FE2002”) side of the single-sided pressure-sensitive adhesive tape prepared above with a silicon roller. Thereby, the double-sided adhesive tape which had an adhesive layer on both surfaces of the base material, and was covered with 75-micrometer-thick PET film by which the surface of the adhesive layer was given a mold release process was obtained.
In addition, about the adhesive layer, shear elastic modulus G 'was measured at 23 degreeC and the frequency of 10 Hz by DVA-200 made from IT measurement control company. Further, W1 (g) of the formed pressure-sensitive adhesive layer was collected, and this pressure-sensitive adhesive layer was immersed in ethyl acetate at 23 ° C. for 24 hours, and the insoluble matter was filtered through a 200-mesh wire mesh. Was dried in vacuo, the weight W2 (g) of the dry residue was measured, and the degree of crosslinking (gel fraction) of the pressure-sensitive adhesive layer was calculated from the following formula (1).
Cross-linking degree (gel fraction) (% by weight) = 100 × W2 / W1 (1)

(Examples 2-14, Comparative Examples 1-12)
Double-sided adhesion in the same manner as in Example 1 except that the tackifier resins and crosslinking agents listed in Tables 1 and 2 were added to the monomer blends and weight average molecular weight acrylic copolymers listed in Tables 1 and 2. I got a tape.

(Example 15)
Both surfaces were changed in the same manner as in Example 1 except that the base material was changed to Sekisui Chemical Co., Ltd. polyethylene foam “Bollara XLH-0180015” (thickness 150 μm) and the thickness of the adhesive layer was changed to 50 μm. An adhesive tape was obtained.

<Evaluation>
The following evaluation was performed with respect to the double-sided pressure-sensitive adhesive tapes obtained in Examples and Comparative Examples. The evaluation results are shown in Tables 1 and 2.

(1) Drop impact test (production of test equipment)
In FIG. 1, the schematic diagram of the drop impact test of a double-sided adhesive tape is shown. The obtained double-sided pressure-sensitive adhesive tape was punched into an outer diameter of 46 mm, a length of 61 mm, an inner diameter of 44 mm and a length of 59 mm to produce a frame-shaped test piece having a width of 1 mm. Next, as shown in FIG. 1 (a), the square hole is approximately in the center of the test piece 1 from which the release paper has been peeled off from the polycarbonate plate 3 having a thickness of 38 mm and a square hole having a width of 50 mm and a thickness of 2 mm. After being pasted so that the test piece 1 is positioned, a polycarbonate plate 2 having a width of 55 mm, a length of 65 mm, and a thickness of 1 mm is pasted from the upper surface of the test piece 1 so that the test piece 1 is located substantially in the center, and the test apparatus was assembled. .
Thereafter, a pressure of 30 kgf was applied at 110 ° C. for 10 seconds from the side of the polycarbonate plate 2 located on the upper surface of the test apparatus, and the polycarbonate plate located on the top and the bottom and the test piece were heat-pressed and left at room temperature for 24 hours.

(Drop impact test judgment)
As shown in FIG. 1 (b), the produced test apparatus was turned over and fixed to the support base, and an iron ball 4 weighing 300 g passing through the square hole was dropped so as to pass through the square hole. The height at which the iron ball was dropped was gradually increased, and the height at which the iron ball was dropped when the test piece and the polycarbonate plate were peeled off by the impact applied by the dropping of the iron ball was measured.
◎: 60 cm or more ○: 50 cm or more and less than 60 cm Δ: 40 cm or more and less than 50 cm x: less than 40 cm

(2) Push test (production of test equipment)
In FIG. 2, the schematic diagram of the push test of a double-sided adhesive tape is shown. The obtained double-sided pressure-sensitive adhesive tape was punched into an outer diameter of 46 mm, a length of 61 mm, an inner diameter of 44 mm and a length of 59 mm to produce a frame-shaped test piece having a width of 1 mm. Next, as shown in FIG. 2 (a), the square hole is approximately in the center of the test piece 1 from which the release paper has been peeled off from the polycarbonate plate 3 having a thickness of 38 mm and a square hole having a width of 50 mm and a thickness of 2 mm. After pasting so that the test piece 1 is positioned, an aluminum plate 5 having a width of 55 mm, a length of 65 mm, and a thickness of 2 mm is pasted from the upper surface of the test piece 1 so that the test piece 1 is positioned substantially in the center, and the test apparatus was assembled. .
Thereafter, a pressure of 30 kgf was applied at 70 ° C. for 10 seconds from the side of the aluminum plate 5 positioned on the upper surface of the test apparatus, and the aluminum plate and the polycarbonate plate positioned on the top and bottom were thermocompression bonded and left at room temperature for 24 hours.

(Push test judgment)
As shown in FIG. 2 (b), the prepared test apparatus was turned over and fixed to the support base, and the aluminum plate 5 on the lower surface was pushed from the opening side at a speed of 10 mm / min, and the aluminum plate 5 was peeled off. The load was measured. The measurement was performed at 23 ° C.
◎: 130N or more ○: 120N or more and less than 130N Δ: 110N or more and less than 120N ×: less than 110N

ADVANTAGE OF THE INVENTION According to this invention, even if it is narrow, the adhesive force after thermocompression bonding is high, and the double-sided adhesive tape for portable electronic devices which can exhibit the outstanding impact resistance can be provided.

1 Test piece (frame shape)
2 Polycarbonate plate (thickness 1mm)
3 Polycarbonate plate (thickness 2mm)
4 Iron balls (300 g)
5 Aluminum plate (thickness 2mm)

Claims (3)

A double-sided pressure-sensitive adhesive tape for portable electronic devices having a pressure-sensitive adhesive layer on both sides of the substrate,
At least one pressure-sensitive adhesive layer contains 45 to 90% by weight of structural units derived from butyl acrylate and 5 to 40% by weight of structural units derived from 2-ethylhexyl acrylate, and has a weight average molecular weight of 400,000 to 1,000,000. Containing 100 parts by weight of an acrylic copolymer and 40-60 parts by weight of a tackifying resin, and having a shear elastic modulus G ′ at 23 ° C. of 1.0 × 10 ^{6 to} 8.0 × 10 ⁶ Pa,
40 to 60 parts by weight of the tackifying resin contains 5 to 30 parts by weight of a tackifying resin (a) having a softening point of 100 ° C. or less ,
The double-sided pressure-sensitive adhesive tape for portable electronic devices, wherein the tackifying resin (a) having a softening point of 100C or lower has a softening point of 80C or lower . The double-sided pressure-sensitive adhesive tape for portable electronic devices according to claim 1 , wherein the tackifying resin contains a rosin-based tackifying resin and / or a terpene-based tackifying resin. The double-sided pressure-sensitive adhesive tape for portable electronic devices according to claim 1 or 2 , wherein a push adhesive strength at room temperature after punching into a frame shape with a width of 1 mm and thermocompression bonding to an aluminum plate at 70 ° C is 120 N or more.

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