JP2012211282A - Double-sided pressure-sensitive adhesive tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided pressure-sensitive adhesive sheet in which when a transparent panel and an image display device are fixed, the adhesion at a level difference caused by a decoration part provided at the transparent panel surface or the image display device surface is excellent, and the foaming or peeling at the level difference portion can be controlled under a high temperature environment.SOLUTION: The double-sided pressure-sensitive adhesive tape by which the transparent panel is stuck/fixed to the image display device surface, has the decoration portion at least one of the surface of the transparent panel stuck/fixed to the image display device and the image display device surface, and comprises an adhesive layer in which a pressure-sensitive adhesive composition including an acrylic copolymer containing 50% by mass of n-butyl acrylate is crosslinked, wherein the storage modulus at 70°C of the adhesive layer is 5.0×10to 1.0×10, the storage modulus at 85°C is 4.0×10to 9.0×10, and the total thickness is 50 to 125 μm. In addition, the suitable adhesion to the level difference can be achieved by the double-sided pressure-sensitive adhesive tape, and the foaming and peeling off under the high temperature environment can be controlled.

Description

  The present invention relates to a double-sided pressure-sensitive adhesive tape used when a transparent panel is stuck and fixed to the surface of an image display device.

  Display elements such as liquid crystal displays (LCD) and organic EL displays are used in a wide range of fields including personal computers. In particular, electronic notebooks, cellular phones, portable audio players, and the like have been increasingly reduced in size and thickness in recent years, and further, there has been a demand for higher definition due to support for moving image playback functions and the like. As such a display element, for example, a display having a configuration in which an image display device such as an LCD module or an organic EL module is included in the configuration, and a transparent panel for protecting the image display device is provided above the image display device. The element is used.

  In the display element having the configuration, if an air layer is present between the transparent panel and the image display device, the reflectance is lowered by the air layer. Therefore, the transparent panel and the image display device are bonded with a liquid adhesive or adhesive. The reduction of the reflectance is suppressed by directly bonding and fixing with a tape. In particular, fixing with an adhesive tape is advantageous for cost reduction compared to fixing with an adhesive because there is no facility or process for applying or curing the liquid adhesive during the assembly process of the display element. However, in recent display elements, decorative elements such as various characters and designs are often provided on the back surface of the transparent panel in order to impart designability and distinguishability in the thinned element structure. When an adhesive tape is used for fixing such a transparent panel, there is a problem that the adhesive tape does not follow the stepped portion, peeling or bubbles due to insufficient adhesion occur, and a good image display cannot be obtained.

  A double-sided pressure-sensitive adhesive tape made of a photo-curable pressure-sensitive adhesive having specific viscoelasticity has been disclosed as a pressure-sensitive adhesive tape having good followability to a level difference caused by a decorative part of a transparent panel (see Patent Document 1). The double-sided adhesive tape is excellent in the step following ability of the decorative part provided on the back surface of the transparent panel, but it peels off due to the repulsive force due to the warp of the panel at the time of bonding, and the temperature of the display element part during use of the device When it rises, there is a problem that peeling occurs at the step portion.

  In recent years, display elements such as personal computers, mobile phones, and e-books have become more multifunctional, and their operations are becoming more complicated, so input devices such as touch panels that allow intuitive input are often installed. It has become. In such a touch panel type display element, since the deformation and recovery of the transparent panel due to pressing are repeated, an improvement in peeling resistance at a further step portion has been demanded.

JP2009-155503A

  The problem to be solved by the present invention is that when the transparent panel and the image display device are fixed, they have excellent adhesion at the level difference caused by the decorative portion provided on the surface of the transparent panel or the image display device, and in a high temperature environment. Is to provide a double-sided pressure-sensitive adhesive sheet capable of suppressing foaming and peeling at a step portion.

In the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape, the present invention uses an acrylic copolymer containing 50% by mass or more of n-butyl acrylate at the time of bonding the transparent panel and the surface of the image display device at 70 ° C. By setting the storage elastic modulus in the range of 5.0 × 10 ^{4 to} 1.0 × 10 ⁵ , it is possible to achieve both the fluidity following the stepped portion and the cohesiveness that can withstand the repulsive force caused by the warp of the panel. The present invention, by a range of storage modulus 4.0 × 10 ⁴ ~9.0 × 10 ⁴ under 85 ° C. in a high temperature environment, to ensure the cohesiveness to withstand the strain of the panel due to heat Can do.

  The double-sided pressure-sensitive adhesive tape of the present invention can follow the vicinity of the decorative step at the time of bonding even if any member has a step due to the decorative portion, and can suppress the repulsion of the panel and peeling in a high temperature environment. It is possible to provide an excellent panel member.

It is a schematic sectional drawing of the image display panel which fixed the transparent panel which has a decoration part, and the image display apparatus using the double-sided adhesive sheet of this invention. It is a schematic sectional drawing of the image display panel which fixed the transparent panel and the image display apparatus which has a decoration part using the double-sided adhesive sheet of this invention. It is a schematic sectional drawing of the panel which fixed the transparent panel which has a decoration part, and films, such as an electroconductive metal film, using the double-sided adhesive sheet of this invention. It is a schematic sectional drawing of the panel which fixed the transparent panel and films, such as an electroconductive metal film which has a decoration part, using the double-sided adhesive sheet of this invention.

The double-sided pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape for sticking and fixing a transparent panel to the surface of an image display device, and has a decorative portion on at least one of the surface to be attached and fixed to the image display device of the transparent panel and the surface of the image display device. And a double-sided pressure-sensitive adhesive tape having no core substrate formed from a pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition containing an acrylic copolymer. The acrylic copolymer contains 50% by mass or more of n-butyl acrylate as a monomer component, and the storage elastic modulus at 70 ° C. of the dynamic viscoelastic spectrum measured at a frequency of 1 Hz of the pressure-sensitive adhesive layer is 5.0. Double-sided pressure-sensitive adhesive tape having a storage elastic modulus of 4.0 × 10 ^{4 to} 9.0 × 10 ⁴ at × 10 ^{4 to} 1.0 × 10 ⁵ and 85 ° C. and a total thickness of the double-sided pressure-sensitive adhesive tape of 50 μm to 125 μm It is.

[Adhesive composition]
The pressure-sensitive adhesive composition used in the present invention is a pressure-sensitive adhesive composition containing an acrylic copolymer, and contains n-butyl acrylate as a main monomer component as a monomer component constituting the acrylic copolymer. Content of n-butyl acrylate is 50 mass% or more in the monomer component which comprises an acrylic copolymer, Preferably it is 55-98 mass%, More preferably, it is 60-90 mass%. The double-sided pressure-sensitive adhesive tape of the present invention can achieve both fluidity and cohesion by using the acrylic copolymer.

  In the acrylic copolymer used in the present invention, it is preferable to use other (meth) acrylate monomers for n-butyl acrylate. As the other (meth) acrylate monomer, a monomer usually used for an acrylic copolymer of an acrylic pressure-sensitive adhesive can be used as appropriate, and a (meth) acrylate monomer that does not deteriorate the visibility of the image display device can be preferably used. Examples of the (meth) acrylate monomer used in combination with n-butyl acrylate include, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, sec-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, Octyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, t -Butyl methacrylate, n-hexyl methacrylate, cyclohexylme Acrylate, n- octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, isodecyl methacrylate, lauryl methacrylate and the like.

  Among these, it is preferable to use methyl acrylate, methyl methacrylate, or 2-hydroxyethyl acrylate. By using the above acrylic copolymer as a component, the storage elastic modulus and gel fraction of the obtained pressure-sensitive adhesive layer are suitable. It becomes easy to control within a range.

  Furthermore, it is preferable to add a vinyl monomer having a functional group such as a hydroxyl group, a carboxyl group, or an amino group in the side chain in a range of 0.01 to 15% by mass in the monomer component constituting the acrylic copolymer. For example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, crotonic acid, fumaric acid , Carboxypropyl acrylate maleate, dimethylaminoethyl acrylamide, N-vinyl pyrrolidone, acrylonitrile, N-vinyl caprolactam, acrylamide, styrene, vinyl acetate, N-methylol acrylic amide, glycidyl methacrylate, etc. The above can be used in combination. Among these, a hydroxyl group-containing vinyl monomer or a carboxyl group-containing vinyl monomer is preferable because it is easy to obtain suitable adhesion to an adherend, and a hydroxyl group-containing vinyl monomer can be particularly preferably used when the adherend is easily oxidized or corroded. . 2-hydroxyethyl (meth) acrylate can be preferably used as the hydroxyl group-containing vinyl monomer, and acrylic acid can be preferably used as the carboxyl group-containing monomer.

  The acrylic copolymer can be obtained by copolymerization by a solution polymerization method, a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method, an ultraviolet irradiation method, or an electron beam irradiation method.

  Mass average molecular weight measured in terms of standard polystyrene measured by gel permeation chromatography (GPC) of acrylic copolymer (gel permeation chromatography, SC-8020 manufactured by Tosoh Corporation, high molecular weight column TSKgelGMHHR-H, The solvent (tetrahydrofuran) is preferably 300,000 to 1,000,000, and more preferably 400,000 to 700,000. By setting the molecular weight of the polymer in this range, it is easy to increase the cohesive force of the pressure-sensitive adhesive in a high temperature environment, and it is possible to suppress peeling in a high temperature environment.

  In order to increase the cohesive strength of the pressure-sensitive adhesive layer, it is preferable to add a crosslinking agent. Examples of the crosslinking agent to be added include an isocyanate crosslinking agent, an epoxy crosslinking agent, a chelate crosslinking agent, and an aziridine crosslinking agent. As addition amount of a crosslinking agent, it is preferable that it is 0.01-1.0 mass part with respect to 100 mass parts of said (meth) acrylic acid ester type copolymers. The cohesive force of the pressure-sensitive adhesive layer can be adjusted by adding these cross-linking agents.

  These cross-linking agents can be appropriately selected as long as the storage elastic modulus and gel fraction of the pressure-sensitive adhesive layer can be in a suitable range, and among them, an isocyanate cross-linking agent or an epoxy cross-linking agent can be preferably used. Moreover, when using an isocyanate type crosslinking agent, it is preferable to use 0.05-0.5 mass part with respect to 100 mass parts of acrylic copolymers, and 0.1-0.4 mass part is used. More preferably it is used. When using an epoxy-type crosslinking agent, it is preferable to use 0.01-0.2 mass part with respect to 100 mass parts of acrylic copolymers, and 0.02-0.1 mass part is used. It is more preferable. By setting it as these ranges, it becomes easy to control the storage elastic modulus and gel fraction of the adhesive layer obtained to a suitable range.

[Adhesive layer]
The pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape of the present invention is a pressure-sensitive adhesive layer (obtained by heat drying) the pressure-sensitive adhesive composition, and has a storage elastic modulus at a dynamic viscoelastic spectrum of 70 ° C. measured at a frequency of 1 Hz. Is in the range of 5.0 × 10 ^{4 to} 1.0 × 10 ⁵ , and the storage elastic modulus in a high temperature environment of 85 ° C. is in the range of 4.0 × 10 ^{4 to} 9.0 × 10 ⁴ , The thickness of the agent layer is 50 μm to 125 μm. By setting the storage elastic modulus at 70 ° C. within this range, it is possible to achieve both the fluidity following the stepped portion and the cohesiveness to withstand the repulsive force caused by the warp of the panel, and the adhesion at the stepped portion can be improved. Moreover, by making the storage elastic modulus in the high temperature environment of 85 degreeC into the said range, the cohesiveness which resists the distortion | strain of a panel is made compatible, and it is excellent in the peeling resistance in a high temperature environment. Adjustment of these viscoelasticity can be adjusted with the component, weight average molecular weight, gel fraction, etc. of an adhesive composition.

Furthermore, it is particularly preferable that the storage elastic modulus at 70 ° C. of the dynamic viscoelastic spectrum measured at a frequency of 1 Hz is included in the range of 5.0 × 10 ^{4 to} 1.0 × 10 ⁵ . When the storage elastic modulus is included in this range, both the fluidity following the stepped portion and the cohesiveness to withstand the repulsive force due to the warp of the panel can be achieved, and the adhesion at the stepped portion can be further improved.

Further, it is particularly preferable that the loss storage elastic modulus at 85 ° C. of the dynamic viscoelastic spectrum measured at a frequency of 1 Hz is included in the range of 4.0 × 10 ^{4 to} 9.0 × 10 ⁴ . By including the storage elastic modulus within this range, it is possible to secure cohesiveness that can withstand panel distortion due to heat, and to further improve peeling resistance under a high temperature environment.

  The dynamic viscoelasticity of the pressure-sensitive adhesive layer in the present invention is obtained by sandwiching a test piece between parallel disks, which are measuring parts of the tester, using a viscoelasticity tester (manufactured by Rheometrics, trade name: Ares 2KSTD). , Obtained by measuring the storage elastic modulus (G ′) and loss elastic modulus (G ″) at a frequency of 1 Hz. However, in the latter case, the thickness of the pressure-sensitive adhesive is adjusted to be in the above-mentioned range. .

The pressure-sensitive adhesive layer preferably has a gel fraction of 30 to 70%. In particular, it is preferably 40 to 60%, and most preferably 45 to 55%. By setting the gel fraction within this range, the storage elastic modulus of the dynamic viscoelastic spectrum measured at a frequency of 1 Hz can be adjusted to the target range. The gel fraction is expressed as a percentage with respect to the original mass by immersing the cured adhesive layer in toluene, measuring the mass after drying of the insoluble matter left after standing for 24 hours, and measuring the mass.
Gel fraction = [(mass after dipping toluene in double-sided pressure-sensitive adhesive tape) / (mass before dipping toluene in double-sided pressure-sensitive adhesive tape)] × 100

[Double-sided adhesive tape]
The double-sided pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape for sticking and fixing a transparent panel and the surface of an image display device, and the surface of the transparent panel to be stuck and fixed to the image display device, or at least one surface of the surface of the image display device It is used for sticking and fixing in a mode having a decorative part. The double-sided pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape that does not have a core base material composed of the above-mentioned pressure-sensitive adhesive layer, and suitably follows the step of the decorative portion in application to this aspect, and the panel rebound or high temperature Since peeling in the environment can be suppressed, it is possible to provide a panel member having an excellent appearance.

  The double-sided pressure-sensitive adhesive tape of the present invention may be composed of a single pressure-sensitive adhesive layer or may be a laminate of a plurality of pressure-sensitive adhesive layers.

  The thickness of the double-sided pressure-sensitive adhesive tape of the present invention is 50 to 125 μm, preferably 75 to 100 μm. By setting the thickness of the double-sided pressure-sensitive adhesive tape within the above range, it is possible to achieve both conformability to the stepped portion decorated on the transparent panel and thinning of the electronic device. If the thickness of the double-sided pressure-sensitive adhesive tape is less than 50 μm, it is difficult to follow the step because the pressure-sensitive adhesive cannot secure a volume for filling the step portion. On the other hand, since electronic devices are becoming smaller, it is difficult to use a double-sided pressure-sensitive adhesive tape having a thickness exceeding 125 μm.

  The double-sided pressure-sensitive adhesive tape of the present invention preferably has a 180 ° peel adhesive strength of 5 to 50 N / 25 mm measured by the following measurement. When the adhesive force of the double-sided pressure-sensitive adhesive tape of the present invention is within the above range, peeling from the pressure-sensitive adhesive layer to the transparent panel can be suppressed. 180 ° peeling adhesive strength is a round trip with one round of pressure bonding using a 2kg roller to a glass plate in an environment with a temperature of 23 ° C and relative humidity of 50% RH on a PET substrate with a thickness of 25μm. It is the adhesive force at a peeling rate of 5 mm / min after pressure bonding and leaving it to stand for 1 hour in an environment of a temperature of 23 ° C. and a relative humidity of 50% RH.

  It is preferable that the double-sided pressure-sensitive adhesive tape of the present invention does not drop in a holding force test at 70 ° C. for 24 hours. Furthermore, it is preferable that the tape shift distance is 2 mm or less without falling. In the holding force test, a load is applied in the shearing direction of the double-sided pressure-sensitive adhesive tape, and the shift distance of the double-sided pressure-sensitive adhesive tape after a lapse of a certain time or the falling time of the double-sided pressure-sensitive adhesive tape is measured. In this test, the double-sided adhesive tape that does not drop and has a small displacement distance has excellent adhesion and cohesion even in an environment of 70 ° C. Even when deformed, no peeling or elongation occurs.

  The double-sided pressure-sensitive adhesive tape of the present invention preferably has high transparency from the viewpoint of use in an image display device.

  The total light transmittance (JIS K 7361) in the visible light wavelength region of the double-sided pressure-sensitive adhesive tape of the present invention is preferably 85% or more, more preferably 90% or more. When the total light transmittance is within the above range, the double-sided pressure-sensitive adhesive tape has high transparency, and high definition of the display screen is possible.

[Usage]
The double-sided pressure-sensitive adhesive tape of the present invention has a decoration part on at least one surface of the surface of the image display device or the surface of the image display device that is attached and fixed to the image display device of the transparent panel when the transparent panel is fixed to the image display device surface. It can be suitably applied to sticking and fixing with. As a specific embodiment, for example, there is an image display panel as shown in FIG. In FIG. 1, 1 is a transparent panel, 2 is a decorative part attached to the transparent panel, 3 is a double-sided pressure-sensitive adhesive tape of the present invention, and 4 is an image display device. In recent years, with the diversification of panel configurations of electronic terminals, there are cases in which a decorative portion is provided on the image display apparatus side as shown in FIG. Even in this case, the double-sided pressure-sensitive adhesive tape of the present invention can obtain the same effect.

[Decoration]
The decorative part provided on the surface of the image display device that is pasted and fixed to the image display device of the transparent panel or the surface that is pasted and fixed to the transparent panel of the image display device is a character or figure that is visually recognized around the screen display unit of the portable electronic terminal, Alternatively, there are black and white bases provided on the back surfaces thereof. These decorative portions are preferable because they can be easily provided by printing on a transparent panel. The printing method and printing ink are not particularly limited, and a commonly used printing method such as silk printing or pad printing or printing ink can be used.

  5-30 micrometers is preferable, as for the thickness of a decoration part, 5-25 micrometers is more preferable, and 5-20 micrometers is still more preferable. When the thickness of the decorative portion is within the above range, the step following property of the double-sided pressure-sensitive adhesive tape of the present invention is particularly suitable, and effects such as the suppression of bubble generation can be suitably expressed even when applied to a thin electronic terminal. . Moreover, the decoration part may be laminated | stacked by the some decoration part, and the magnitude | size and shape of the decoration part laminated | stacked may differ. In the case where a plurality of decorative portions are stacked, the effects of the present invention are easily achieved when the maximum thickness of the stacked decorative portions is within the above range.

[Transparent panel]
The transparent panel is not particularly limited, but commonly used panels include glass plates, (meth) acrylic resins, polycarbonate resins, polyethylene terephthalate resins, and the like.

  The thickness of the transparent panel is preferably 50 μm to 3 mm, preferably 75 μm to 2 mm, and more preferably 100 μm to 1 mm. When the thickness of the transparent panel is within the above range, the panel is deformed at the time of bonding, so that the force is easily transmitted to the adhesive tape, and the step-following effect of the double-sided adhesive tape of the present invention is easily exhibited. Further, by making the thickness within this range, it is possible to achieve both protection against impact on the electronic terminal and thinning of the terminal.

[Image display device]
Although it does not specifically limit as an image display apparatus, For example, the LCD module, organic EL module, touch panel module, etc. which are used for image displays, such as a small electronic terminal, are mentioned. Since the double-sided pressure-sensitive adhesive tape of the present invention can reduce the thickness of portable electronic devices, it is preferably used for these modules. The surface bonded to the transparent panel of these image display devices is a surface of a glass panel or an optical film provided on the surface of the glass panel. Moreover, as shown in FIGS. 3 and 4, the image display device using the touch panel module has a structure in which a conductive metal film such as ITO is provided on the surface of the touch panel module to be bonded to the transparent panel. There is. In this configuration, the present invention can achieve the same effect even when the transparent panel provided with the decoration and the conductive metal film on the surface of the image display device are bonded together.

[Panel fixing method]
When fixing the transparent panel and the image display device, it is preferable to perform a heating and pressurizing process in order to remove bubbles mixed in due to the step of the decorative portion of the transparent panel.

  As for the temperature conditions which perform said heating-pressing process, 40-80 degreeC is preferable. Furthermore, 50-70 degreeC is preferable and it is especially preferable that it is 60-70 degreeC. When the temperature at which the heat and pressure treatment is performed is in the above range, the adhesive layer of the double-sided pressure-sensitive adhesive tape of the present invention has both the fluidity to follow the step portion of the decoration and the cohesiveness to withstand the repulsive force due to the warp of the panel. can do.

  The pressure condition for performing the heating and pressurizing treatment is preferably 3 to 5 atm, and more preferably 4 to 5 atm. When the pressure for performing the heating and pressurizing treatment is within the above range, the pressure-sensitive adhesive deforms greatly due to the pressure, so that the pressure-sensitive adhesive layer easily follows the step portion of the decoration.

  10-50 minutes are preferable and, as for the conditions of the time which performs said heat pressurization process, 20-30 minutes are more preferable. When the time for performing the heating and pressing treatment is within the above range, the adhesive layer, the transparent panel, and the image display device can be fixed efficiently.

[Preparation of acrylic copolymer, etc.]
An acrylic copolymer and an acrylic mixture were prepared as shown below with the composition shown in Table 1 (the amount in the table is part by mass).

<Acrylic copolymer (1)>
Preparation of acrylic copolymer In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 65 parts by mass of butyl acrylate, 30 parts by mass of methyl acrylate, 5 parts by mass of 2-hydroxyethyl acrylate It melt | dissolved in ethyl acetate and superposed | polymerized and obtained the acrylic copolymer (1) of mass mean molecular weight (Mw) 700,000 (solid content 30%).

<Acrylic copolymer (2)>
Preparation of acrylic copolymer In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 65 parts by mass of butyl acrylate, 30 parts by mass of methyl acrylate, 5 parts by mass of 2-hydroxyethyl acrylate It melt | dissolved in ethyl acetate and superposed | polymerized and obtained the acrylic copolymer (2) of mass mean molecular weight (Mw) 400,000 (solid content 48%).

<Acrylic copolymer (3)>
Preparation of acrylic copolymer In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 85 parts by weight of butyl acrylate, 15 parts by weight of methyl methacrylate, 4 parts by weight of acrylic acid, dimethylaminoethyl 1 part by mass of acrylate was dissolved in ethyl acetate and polymerized to obtain an acrylic copolymer (3) having a mass average molecular weight (Mw) of 700,000 (solid content 25%).

[Preparation of pressure-sensitive adhesive composition]
Using the above acrylic copolymer, a pressure-sensitive adhesive composition was prepared as follows with the formulation shown in Table 2 (the blending amount in the table is parts by mass).

<Adhesive composition (a)>
To 100 parts by mass of the acrylic copolymer (1), 0.22 parts by mass of an isocyanate-based crosslinking agent (TD-75 solid content 75%, manufactured by Soken Chemical Co., Ltd.) was added, and the mixture was stirred with a stirrer for 20 minutes. (A) was obtained.

<Adhesive composition (b)>
To 100 parts by mass of the acrylic copolymer (1), 0.20 parts by mass of an isocyanate-based crosslinking agent (TD-75 solid content: 75% by Soken Chemical Co., Ltd.) is added and stirred with a stirrer for 20 minutes to obtain an adhesive composition. (B) was obtained.

<Adhesive composition (c)>
To 100 parts by mass of the acrylic copolymer (1), 0.25 parts by mass of an isocyanate-based crosslinking agent (TD-75 solid content 75%, manufactured by Soken Chemical Co., Ltd.) was added, and the mixture was stirred with a stirrer for 20 minutes. (C) was obtained.

<Adhesive composition (d)>
0.40 parts by mass of an isocyanate-based cross-linking agent (TD-75 solid content 75%, manufactured by Soken Chemical Co., Ltd.) is added to 100 parts by mass of the acrylic copolymer (1), and the mixture is stirred with a stirrer for 20 minutes. (D) was obtained.

<Adhesive composition (e)>
To 100 parts by mass of the acrylic copolymer (2), 0.05 part by mass of an isocyanate-based crosslinking agent (Coronate HL solid content: 75% by Nippon Polyurethane Co., Ltd.) was added and stirred with a stirrer for 20 minutes. e) was obtained.

<Adhesive composition (f)>
0.33 parts by mass of an epoxy-based crosslinking agent (E-2XM solid content 2%, manufactured by Soken Chemical Co., Ltd.) is added to 100 parts by mass of the acrylic copolymer (3), and the mixture is stirred with a stirrer for 20 minutes. (F) was obtained.

<Adhesive composition (g)>
To 100 parts by mass of the acrylic copolymer (1), 0.05 parts by mass of an isocyanate-based crosslinking agent (Coronate HL solid content: 75% by Nippon Polyurethane Co., Ltd.) was added and stirred with a stirrer for 20 minutes to obtain an adhesive composition ( g) was obtained.

<Adhesive composition (h)>
To 100 parts by mass of the acrylic copolymer (1), 0.10 parts by mass of an isocyanate-based crosslinking agent (TD-75 solid content 75%, manufactured by Soken Chemical Co., Ltd.) is added, and the mixture is stirred with a stirrer for 20 minutes. (H) was obtained.

<Adhesive composition (i)>
To 100 parts by mass of the acrylic copolymer (2), 0.20 parts by mass of an isocyanate-based crosslinking agent (Coronate HL solid content: 75% by Nippon Polyurethane Co., Ltd.) was added and stirred with a stirrer for 20 minutes. i) was obtained.

<Adhesive composition (j)>
1.26 parts by mass of an epoxy-based cross-linking agent (E-2XM solid content 2%, manufactured by Soken Chemical Co., Ltd.) is added to 100 parts by mass of the acrylic copolymer (3), and the mixture is stirred with a stirrer for 20 minutes. (J) was obtained.

Example 1
The pressure-sensitive adhesive composition (a) was applied on a polyester film having a thickness of 50 μm (hereinafter referred to as # 50 release film) obtained by peeling one side with a silicone compound so that the thickness after drying would be 75 μm, and at 60 ° C. Dry for 2 minutes at 100 ° C. for 3 minutes. The obtained pressure-sensitive adhesive sheet was bonded to a 38 μm-thick polyester film (hereinafter referred to as # 38 release film) having one surface peel-treated with a silicone compound. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 52%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Example 2)
The pressure-sensitive adhesive composition (b) was applied onto a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 49%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Example 3)
The pressure-sensitive adhesive composition (c) was coated on a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, aging was performed at 23 ° C. for 7 days to obtain a double-sided pressure-sensitive adhesive sheet having a gel fraction of 56%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

Example 4
The pressure-sensitive adhesive composition (d) was applied onto a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 58%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Example 5)
The pressure-sensitive adhesive composition (e) was coated on a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, aging was performed at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 50%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Example 6)
The pressure-sensitive adhesive composition (f) was coated on a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a double-sided pressure-sensitive adhesive sheet having a gel fraction of 45%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Example 7)
The pressure-sensitive adhesive composition (a) was coated on a # 50 release film so that the thickness after drying was 50 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 2 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 52%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Example 8)
The pressure-sensitive adhesive composition (a) was coated on a # 50 release film so that the thickness after drying was 100 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 4 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 52%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

Example 9
The pressure-sensitive adhesive composition (a) was coated on a # 50 release film so that the thickness after drying was 125 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 5 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 52%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Comparative Example 1)
The pressure-sensitive adhesive composition (g) was applied onto a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, aging was carried out at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 0%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Comparative Example 2)
The pressure-sensitive adhesive composition (h) was coated on a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a double-sided pressure-sensitive adhesive sheet having a gel fraction of 33%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Comparative Example 3)
The pressure-sensitive adhesive composition (i) was coated on a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a double-sided pressure-sensitive adhesive sheet having a gel fraction of 80%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Comparative Example 4)
The pressure-sensitive adhesive composition (j) was applied onto a # 50 release film so that the thickness after drying was 75 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 3 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a double-sided pressure-sensitive adhesive sheet having a gel fraction of 81%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Comparative Example 5)
The pressure-sensitive adhesive composition (a) was coated on a # 50 release film so that the thickness after drying was 40 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 2 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 52%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

(Comparative Example 6)
The pressure-sensitive adhesive composition (a) was coated on a # 50 release film so that the thickness after drying was 150 μm, and dried at 60 ° C. for 2 minutes and at 100 ° C. for 6 minutes. The obtained adhesive sheet and a # 38 release film were bonded together. Thereafter, it was aged at 23 ° C. for 7 days to obtain a baseless double-sided pressure-sensitive adhesive sheet having a gel fraction of 52%. The total light transmittance of the obtained double-sided PSA sheet was 91%.

[Evaluation of double-sided adhesive tape]
The following evaluation was performed on the double-sided pressure-sensitive adhesive tapes prepared in Examples 1 to 9 and Comparative Examples 1 to 6, and the results obtained are shown in Tables 3 to 4.

(1) Measurement of dynamic viscoelasticity The release film of the prepared double-sided pressure-sensitive adhesive tape was peeled off, and the test piece was laminated to a thickness of about 2 mm. A parallel plate having a diameter of 7.9 mm was attached to a viscoelasticity testing machine (ARES 2kSTD) manufactured by T.A. Instruments Japan, and the test piece was sandwiched with a compression load of 40 to 60 g. A frequency range of −30 to 150 ° C. was measured at a frequency of 1 Hz, and a temperature increase rate of 2 ° C./min was measured, and values of storage elastic modulus at 70 ° C. and 85 ° C. were confirmed.

(2) Peeling-off adhesive strength measurement at 180 ° C. The release film on one side of the prepared double-sided pressure-sensitive adhesive tape is peeled off and bonded to a PET substrate having a thickness of 25 μm to produce a pressure-sensitive adhesive tape having a width of 25 mm and a length of 10 cm. Using a 2kg roller, the glass plate is pressed once in one reciprocation using a 2kg roller in an environment of a temperature of 23 ° C and a relative humidity of 50% RH, and left for 1 hour in an environment of a temperature of 23 ° C and a relative humidity of 50% RH. After that, 180 ° peeling adhesion at a peeling speed of 5 mm / min was measured.

(3) Print level followability Peel off the release film on one side of the prepared double-sided pressure-sensitive adhesive tape, and a polyethylene terephthalate film with a thickness of 100 μm, a length of 50 mm and a width of 40 mm in which a printing layer with a thickness of 15 μm and a width of 5 mm is decorated in a frame shape (transparent Panel substitute). The peeled film on one side of the obtained test piece is peeled off and bonded to a glass plate having a thickness of 5 mm, a length of 50 mm, and a width of 40 mm (an alternative to an image display device), and heated at 5 atm, 70 ° C. for 20 minutes. Pressure treatment was performed. Immediately after the heating and pressurizing treatment, the entire printed decorative part was observed with a microscope (magnification 300 times), and it was confirmed whether bubbles were mixed. The evaluation criteria for bubble contamination were as follows.
◎: No bubbles with a diameter of 5 μm or more ○: No bubbles with a diameter of 30 μm or more Δ: Within 10 bubbles with a diameter of 30 μm or more ×: 10 or more bubbles with a diameter of 30 μm or more or peeling

(4) Thermal durability after step following (3) The sample for printing step followability is put into a heater at 85 ° C., and the entire neighborhood of the decorative part printed after one hour has passed is a microscope (magnification 300 times). In the case of observation with, it was confirmed whether bubbles were mixed or peeled off. The evaluation criteria were as follows.
◎: No bubbles larger than 5 μm ○: No bubbles larger than 30 μm in diameter Δ: Less than 10 bubbles larger than 30 μm in diameter ×: Ten or more bubbles larger than 30 μm in diameter or peeling

(5) Holding power test The release film on one side of the prepared double-sided pressure-sensitive adhesive tape was peeled off and bonded to an aluminum foil having a thickness of 50 μm to prepare a pressure-sensitive adhesive tape having a width of 20 mm and a length of 10 cm. The created tape was crimped by a single reciprocation using a 2 kg roller on an area of 20 mm width x 20 mm length of a stainless steel plate in an environment of a temperature of 23 ° C and a relative humidity of 50% RH. After standing for 1 hour, a load of 0.5 kg was applied at 80 ° C., and the presence or absence of a drop of the adhesive tape and a shift after standing for 24 hours was confirmed.
○: No deviation (0.5 mm or less)
Δ: Deviation exceeding 0.5 mm occurs: Adhesive tape falls

(6) Total light transmittance measurement After a double-sided adhesive tape was attached to a glass plate having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm, this was measured with a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm. A sample having a structure of glass plate / adhesive layer / glass plate was prepared by bonding with a glass plate and fixing by heating and pressing under conditions of 5 atm and 70 ° C. for 20 minutes. The total light transmittance was measured based on JIS K7105 and JIS K7136 of the sample using “HR-100 type” manufactured by Murakami Color Research Laboratory.

  As shown in Tables 3 and 4, the double-sided pressure-sensitive adhesive tapes of the present invention of Examples 1 to 9 have excellent followability to the level difference caused by the decorative part when fixing the transparent panel having the decorative part and the image display device, In addition, it is excellent in suppressing foaming and peeling resistance in the vicinity of a step in a high temperature environment. On the other hand, in the double-sided pressure-sensitive adhesive tapes of Comparative Examples 3 and 4, the fluidity was low and the follow-up to the step was poor. Moreover, in Comparative Example 5, the volume for the pressure-sensitive adhesive to fill the step portion could not be ensured, and the follow-up to the step became poor. In the double-sided pressure-sensitive adhesive tapes of Comparative Examples 1 and 2, although following the step, the panel could not withstand the deformation of the panel under a high temperature environment and bubbles were generated at the step. In Comparative Example 6, the followability to a step and the peeling resistance under a high temperature environment were good, but since the tape is thick, it is difficult to cope with the thinning of the electronic device.

1: transparent panel 2: decorative part 3: double-sided adhesive tape 4: image display device 5: conductive metal film 6: image display module

Claims (6)

A double-sided pressure-sensitive adhesive tape for sticking and fixing a transparent panel to the surface of an image display device, having a decorative portion on at least one of the image display device and the surface of the transparent panel and the surface of the image display device. It is composed of a pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition containing a coalescence, wherein the acrylic copolymer contains n-butyl acrylate, and n-butyl acrylate in the monomer component constituting the acrylic copolymer. The storage elastic modulus at 70 ° C. of the dynamic viscoelastic spectrum measured at a frequency of 1 Hz of the pressure-sensitive adhesive layer is 5.0 × 10 ^{4 to} 1.0 × 10 ⁵ . A double-sided pressure-sensitive adhesive tape having a storage elastic modulus at 85 ° C. in the range of 4.0 × 10 ^{4 to} 9.0 × 10 ⁴ and a total thickness of 50 μm to 125 μm.   The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the step of the decorative portion is 5 to 30 μm.   The double-sided pressure-sensitive adhesive tape according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has a gel fraction of 30 to 70%.   The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 3, wherein the acrylic copolymer has a mass average molecular weight (Mw) of 300,000 to 1,000,000.   Using a 2kg roller, the glass plate is pressed once in one reciprocation using a 2kg roller in an environment of a temperature of 23 ° C and a relative humidity of 50% RH, and left for 1 hour in an environment of a temperature of 23 ° C and a relative humidity of 50% RH. The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 4, wherein the adhesive strength at 5 mm / min after peeling is 5 to 40 N.   The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 5, wherein the total light transmittance in the visible light wavelength region of the pressure-sensitive adhesive layer is 90% or more.

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