JP2015025064A - Adhesive agent for sticking plastic substrate, adhesive sheet and picture display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive agent for sticking a plastic substrate capable of inhibiting floating or peeling of the plastic substrate on a picture display device even under an environment easily causing vaporization of unreacted materials remaining in the plastic substrate with exposing to high temperature environment, and to provide an adhesive layer and a picture display device using the same.SOLUTION: The above problem is solved by an adhesive agent for sticking a plastic substrate containing at least an acrylic adhesive agent and an isocyanate-based crosslinking agent containing no cyclic structure, and a loss tangent (105°C) of an adhesive layer formed by the adhesive agent is in a range of 0.35 to 0.60 and a storage elastic modulus (105°C) is in a range of 5.5×10Pa to 8.9×10Pa.

Description

  The present invention relates to a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and an image display device using them, which are preferably used when a plastic substrate is bonded to an image display element or the like.

  Image display devices such as liquid crystal displays and organic EL displays are used in a wide range of fields including personal computers. In particular, mobile devices such as mobile phones and tablet PCs, car navigation systems, and the like include touch sensors that can input information with a finger or the like on the image display surface. A plastic cover member is attached to the image display surface of the touch sensor via an adhesive layer. Such a cover member prevents damage or scattering of the image display surface made of glass or the like due to an impact when a portable device or a car navigation system falls or collides.

  However, an image display device provided with a cover member has a problem that if air bubbles are present between the cover member and the image display surface, light reflection loss due to the air bubbles occurs and the visibility of the image is lowered. It was. Further, the plastic cover member has a problem that unreacted substances contained therein become gas (also referred to as outgas), and particularly when the temperature becomes high, the gas is foamed and the visibility of the image is lowered.

For example, in Patent Document 1, a polyoxyalkylene polymer having at least one alkenyl group in one molecule, a compound having an average of 2 or more and less than 5 hydrosilyl groups in one molecule, A transparent adhesive for a flat panel display comprising a hydrosilylation catalyst, a shear storage modulus (G ′) at 25 ° C. and 1 Hz of 1.0 × 10 ⁵ Pa or less, and a gel fraction of 40% or more A sheet is proposed. According to this technique, it is said that a transparent adhesive sheet for a flat panel display can be provided which has excellent step absorbability and does not cause foaming on the adhesive surface with the plastic plate.

Patent Document 2 proposes a transparent pressure-sensitive adhesive sheet for an image display device disposed between a protective panel and a polarizing film. This pressure-sensitive adhesive sheet has one or more first pressure-sensitive adhesive layers and second pressure-sensitive adhesive layers having different viscoelastic behaviors, and is formed by laminating and integrating these layers, At least one of the second adhesive layers is composed of a composition including an acrylate polymer, a polyfunctional (meth) acrylate crosslinking agent having two or more (meth) acryloyl groups, and a reaction initiator, and is laminated and integrated. The value of the dynamic shear storage elastic modulus G ′ measured by the temperature dispersion at a frequency of 1 Hz is 2 × 10 ^{4 to} 5 × 10 ⁵ Pa in terms of G ′ (20 ° C.). And G ′ (150 ° C.) is in the range of 1 × 10 ⁴ to 1 × 10 ⁵ Pa. According to this technology, even if the adherend is made of a material that generates an outgas such as plastic, it can be stuck so as not to foam, for example, in a high temperature environment of about 80 ° C. Yes.

JP 2010-97070 A International Publication Number WO2010 / 044229

  Although the pressure-sensitive adhesive sheet proposed in Patent Documents 1 and 2 is recognized to some extent, it is exposed to a severer high-temperature environment due to a rise in the temperature of the vehicle, such as a car navigation system installed in the vehicle. Volatilization of unreacted substances and water vapor remaining in the plastic cover member is likely to occur. Air bubbles resulting from the volatilization cause the cover member and the adhesive layer to float and peel off, and are displayed on the display surface. There is a drawback that the visibility of the image is reduced.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to be exposed to a high temperature environment and in an environment in which volatilization of unreacted substances and water vapor remaining in the plastic substrate easily occurs. Even so, an object of the present invention is to provide a pressure-sensitive adhesive for bonding a plastic substrate, a pressure-sensitive adhesive sheet, and an image display device using them, which can suppress the floating and peeling of the plastic substrate on the image display element surface.

(1) The pressure-sensitive adhesive for plastic base material bonding according to the present invention for solving the above-mentioned problems is a pressure-sensitive adhesive containing at least an acrylic pressure-sensitive adhesive and an isocyanate-based crosslinking agent not containing a cyclic structure, The loss tangent (105 ° C.) of the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive is in the range of 0.35 to 0.60, and the storage elastic modulus (105 ° C.) is 5.5 × 10 ⁴ Pa to 8.9 ×. It is within the range of 10 ⁴ Pa or less.

(2) The pressure-sensitive adhesive sheet for laminating a plastic substrate according to the present invention for solving the above problems is formed of a pressure-sensitive adhesive containing at least an acrylic pressure-sensitive adhesive and an isocyanate-based cross-linking agent not containing a cyclic structure. An adhesive sheet having an adhesive layer, wherein the loss tangent (105 ° C.) of the adhesive layer is in the range of 0.35 to 0.60, and the storage elastic modulus (105 ° C.) is 5.5 × 10 ^4. It is in the range of Pa or more and 8.9 × 10 ⁴ Pa or less.

  (3) In the image display device according to the present invention for solving the above-described problems, the plastic substrate is bonded to the display surface using the above-described adhesive for bonding a plastic substrate or an adhesive sheet according to the present invention. It is characterized by being.

  According to the adhesive, the adhesive sheet, and the image display device for laminating a plastic substrate according to the present invention, volatilization of unreacted substances and water vapor remaining in the plastic substrate due to exposure to a high temperature environment is likely to occur. Even under the environment, the floating and peeling of the plastic substrate bonded to the image display element surface can be suppressed.

It is typical sectional drawing which shows an example of the adhesive sheet for plastic base material bonding which concerns on this invention. It is typical sectional drawing which shows an example of the image display apparatus using the adhesive sheet for plastic base material bonding which concerns on this invention.

  The adhesive for sticking a plastic substrate, an adhesive sheet and an image display device according to the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment, In the range of the summary, various deformation | transformation can be implemented.

[Adhesive for bonding plastic substrates]
The pressure-sensitive adhesive for laminating a plastic substrate according to the present invention contains at least an acrylic pressure-sensitive adhesive and an isocyanate-based cross-linking agent having no cyclic structure. And when the adhesion layer was formed with the adhesive, the loss tangent (105 degreeC) of the adhesion layer is in the range of 0.35 or more and 0.60 or less, and the storage elastic modulus (105 degreeC) is 5. It is in the range of 5 × 10 ⁴ Pa or more and 8.9 × 10 ⁴ Pa or less.

  This pressure-sensitive adhesive has a loss tangent (105 ° C.) and a storage elastic modulus (105 ° C.) of the pressure-sensitive adhesive layer formed of a pressure-sensitive adhesive containing at least an acrylic pressure-sensitive adhesive and an isocyanate-based crosslinking agent not containing a cyclic structure. In some cases, even when unreacted substances remaining in the plastic substrate or vaporization of water vapor occurs in a harsh environment, the plastic substrate can be prevented from floating or peeling on the image display element surface. . That is, the present invention solves the floating and peeling of the plastic substrate that is likely to occur particularly when exposed to a high temperature environment by specifying the elasticity and viscosity of the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive.

  Since this pressure-sensitive adhesive for bonding a plastic substrate contains the above-mentioned acrylic pressure-sensitive adhesive and isocyanate-based crosslinking agent, the pressure-sensitive adhesive layer 2 for bonding a plastic substrate formed with the pressure-sensitive adhesive for bonding a plastic substrate. And an adhesive sheet 10 (see FIG. 1) for laminating a plastic substrate including an adhesive layer 2 for laminating the plastic substrate is used for laminating a touch panel constituting an image display device such as a mobile phone or a tablet PC. When used, the plastic base material constituting the cover member of the touch panel can be prevented from floating and peeling, and is excellent in practicality.

  Hereafter, the component of the adhesive for plastic base material bonding is demonstrated in detail.

(Acrylic adhesive)
Acrylic pressure-sensitive adhesive is mainly composed of (meth) acrylic acid ester, specifically (meth) acrylic acid alkoxyalkyl ester, and copolymerized with carboxyl group-containing monomer copolymerizable with (meth) acrylic acid alkoxyalkyl ester. An acrylic polymer obtained by A main component means containing 51 mass% or more of (meth) acrylic-acid alkoxyalkylesters.

  Examples of the (meth) acrylic acid alkoxyalkyl ester include, for example, 2-methoxyethyl (meth) acrylate, 2-methoxypropyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, and (meth) acrylic acid 2- Examples include methoxybutyl, 4-methoxybutyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate, 4-ethoxybutyl (meth) acrylate, and the like. These may be used alone or in combination of two or more.

  In this invention, it is preferable to use what copolymerized the hydroxyl-containing (meth) acrylate monomer in addition to above-mentioned (meth) acrylic acid ester.

  Examples of the hydroxyl group-containing (meth) acrylate monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1-dimethyl-3-butyl (meth) acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl- 3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl (meth) acrylate, glycerin mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, poly (ethylene glycol) Lumpur - propylene glycol) mono (meth) acrylate, N- methylol acrylamide, allyl alcohol, mention may be made of methallyl alcohol and the like. One or more of these hydroxyl group-containing (meth) acrylate monomers may be contained. By including such a hydroxyl group-containing (meth) acrylate monomer, the reworkability of the acrylic pressure-sensitive adhesive can be improved.

  The hydroxyl group-containing (meth) acrylate monomer can be added to the (meth) acrylic acid ester in consideration of the adhesiveness and reworkability of the acrylic pressure-sensitive adhesive. In that case, it is preferable to add the hydroxyl group-containing (meth) acrylate monomer within a range of 0.1% by mass or more and 20% by mass or less with respect to the (meth) acrylic acid ester monomer.

  In the present invention, in addition to the monomers described above, glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, glycidyl vinyl ether, 3,4-epoxycyclohexyl vinyl ether, glycidyl (meta ) Glycidyl group-containing (meth) acrylate monomers such as allyl ether and 3,4-epoxycyclohexyl (meth) allyl ether, acrylamide, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-propoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-tert-butylacrylamide, N-o Chill acrylamide may be included containing amide groups of diacetone acrylamide (meth) acrylate monomer.

  The acrylic pressure-sensitive adhesive (copolymer) used in the present invention can be obtained by polymerizing the above monomers by a method such as ordinary solution polymerization, bulk polymerization, emulsion polymerization or suspension polymerization. However, it is preferable to manufacture by the solution polymerization from which the said acrylic adhesive is obtained as a solution. By obtaining the acrylic pressure-sensitive adhesive as a solution, it can be used as it is for the production of the pressure-sensitive adhesive composition of the present invention.

  The mass average molecular weight of the acrylic polymer obtained by copolymerization of the (meth) acrylic acid alkoxyalkyl ester and the hydroxyl group-containing monomer is not particularly limited as long as the adhesive layer exhibits a specific range of elasticity and viscosity. It is preferably 150,000 or more, more preferably in the range of 150,000 to 1,500,000, and even more preferably in the range of 150,000 to 1,000,000. If it is the said range, when it exposes to a high temperature environment, it can suppress that gas is generated from a plastic base material with the adhesive strength of an adhesion layer. The mass average molecular weight is a value measured by gel permeation chromatography (GPC). “High temperature” means, for example, a high temperature rising in a car, and an image display device such as a car navigation mounted in the car is exposed to the high temperature.

  The acrylic pressure-sensitive adhesive that is a copolymer may be produced by appropriately selecting various radical polymerizations such as solution polymerization, bulk polymerization, emulsion polymerization, etc., and as a commercial product, for example, EXK11-468 (TOYOCHEM Co., Ltd.), SK Dyne 2950 (manufactured by Soken Chemical Co., Ltd.), CT-6030 (manufactured by DIC Corporation) and the like can be suitably used.

  In radical polymerization, a polymerization initiator, a chain transfer agent, an emulsifier and the like are used, but they are not particularly limited and can be appropriately selected and used. The weight average molecular weight of the methacrylic polymer can be controlled by the amount of the polymerization initiator and the chain transfer agent used and the reaction conditions, and the amount used is appropriately adjusted according to these types.

(Crosslinking agent)
As the crosslinking agent, an isocyanate-based crosslinking agent having no cyclic structure is used. An isocyanate-based crosslinking agent having no cyclic structure in the structure may reduce the storage elastic modulus at a high temperature within a range of 5.5 × 10 ⁴ Pa or more and 8.9 × 10 ⁴ Pa or less at 105 ° C. it can. An adhesive layer having a low storage elastic modulus at 105 ° C. is soft and has a high adhesive strength. As a result, the adhesive strength of the adhesive layer when the loss tangent at 105 ° C. is in the range of 0.35 or more and 0.60 or less is high, and is attributed to unreacted substances contained in the plastic substrate. Foaming can be suppressed.

  Preferred cross-linking agents include hexamethylene diisocyanate (HDI) cross-linking agents and metal chelate cross-linking agents. The cyclic structure means an aromatic ring such as a 5-membered ring or a 6-membered ring, or a structure containing one or more saturated or unsaturated carbon rings.

  On the other hand, a tolylene diisocyanate (TDI) -based cross-linking agent or a xylene diisocyanate (XDI) -based cross-linking agent having a cyclic structure in the structure hardly reduces the storage elastic modulus at high temperatures. An adhesive layer having a large storage elastic modulus at 105 ° C. is hard and has a low adhesive strength. As a result, the adhesive strength of the adhesive layer when the loss tangent at 105 ° C. is in the range of 0.35 or more and 0.60 or less is low, such as unreacted substances and water vapor contained in the plastic substrate. In some cases, foaming due to the above cannot be suppressed.

  In order to suppress lifting and peeling, specifically, an isocyanate-based cross-linking agent having no cyclic structure is used as a cross-linking agent, and the viscoelastic properties (loss tangent, storage elastic property) of the formed adhesive layer at 105 ° C. Rate) is within a specific range. In this specific range of viscoelastic characteristics, it is considered that the hardness and softness of the adhesive layer prevent the plastic substrate from floating and peeling off.

(Adhesive)
The pressure-sensitive adhesive is obtained by blending the above-mentioned acrylic pressure-sensitive adhesive and the above-mentioned crosslinking agent so as to be within a predetermined viscoelastic property range. The range of such viscoelastic properties varies depending on the type of acrylic resin and cross-linking agent. As an example, the cross-linking agent is 0.175 parts by mass or more and 0.450 parts by mass with respect to 100 parts by mass of the acrylic resin. It can be within the following ranges.

  In the pressure-sensitive adhesive, for example, a tackifier, a metal chelating agent, a colorant, a pigment, a dye, a surfactant, a plasticizer, a surface lubricant, a leveling agent, and a softening agent may be used within a range not impairing the effects of the present invention. Additives such as antioxidants, silane coupling agents, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, fillers, metal powders, particles, foils, and the like may be blended.

[Adhesive layer for bonding plastic substrates]
As shown in FIG. 2, the pressure-sensitive adhesive layer for bonding a plastic substrate can be formed using the pressure-sensitive adhesive according to the present invention described above. The method for forming the adhesive layer is not particularly limited. For example, roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat, lip Examples thereof include a coat and a die coater.

  The thickness of the adhesive layer can be appropriately selected in consideration of the state, shape, etc. of the layer in contact with the adhesive layer. Usually, it is 5 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less. If it is this range, an adhesive physical property can be stabilized. When the thickness is less than 5 μm, sufficient adhesive strength may not be obtained. When the thickness exceeds 500 μm, the optical characteristics such as cost increase and light transmittance may be adversely affected.

(Viscoelastic properties)
The adhesive layer has a loss tangent at 105 ° C. in the range of 0.35 or more and 0.60 or less, and a storage elastic modulus at 105 ° C. of 5.5 × 10 ⁴ Pa or more and 8.9 × 10 ⁴ Pa. Within the following range. The storage elastic modulus (E ′) is one of the physical properties that reflect the hardness of the adhesive layer. For example, a solid viscoelasticity analyzer RSA-III manufactured by T.A.
It can be measured by a dynamic viscoelasticity measurement method (attachment mode: compression mode, frequency: 1 Hz, temperature: −50 to 150 ° C.) based on K7244-1.

An object of the present invention is to suppress the influence of bubbles generated from a plastic substrate when exposed to a high temperature environment. Therefore, the value of the storage elastic modulus (E ′) at a temperature of 105 ° C. was used as an index. When the storage elastic modulus (E ′) at a temperature of 105 ° C. is in the range of 5.5 × 10 ⁴ Pa or more and 8.9 × 10 ⁴ Pa or less, the adhesive layer is soft and has high adhesive strength. As a result, the adhesive strength of the adhesive layer when the loss tangent at 105 ° C. is in the range of 0.35 or more and 0.60 or less is high, and unreacted substances, water vapor, etc. contained in the plastic substrate It is possible to suppress foaming caused by.

If the storage elastic modulus at 105 ° C. is less than 5.5 × 10 ⁴ Pa, the adhesive layer is too soft, and the adhesive layer cannot withstand the foaming stress caused by unreacted substances or water vapor contained in the plastic substrate, The plastic substrate may float or peel off. On the other hand, if the storage elastic modulus at 105 ° C. exceeds 8.9 × 10 ⁴ Pa, the adhesive layer becomes hard and the adhesive strength decreases, so that the plastic substrate may float or peel off.

  Further, the loss tangent (tan δ) at 105 ° C. is preferably in the range of 0.35 or more and 0.60 or less. The loss tangent (tan δ) is one of parameters indicating stress relaxation behavior (deformation delay when force is applied). When the value of loss tangent (tan δ) is small, the stress relaxation of the adhesive layer is fast, and when the value is large, the stress relaxation of the adhesive layer is slow. If the value of the loss tangent (tan δ) at 105 ° C. is within the above range, the restoring behavior against deformation of the adhesive layer does not occur instantaneously. Therefore, even when bubbles are generated when exposed to a high temperature environment, the generation of bubbles can be prevented by pressing the bubbles with the adhesive layer.

  When the loss tangent at 105 ° C. is less than 0.35, the restoring behavior against deformation of the adhesive layer is likely to occur quickly. Therefore, when bubbles are generated when exposed to a high temperature environment, it is difficult to press the bubbles with the adhesive layer. Moreover, when the loss tangent at 105 ° C. exceeds 0.65, the recovery behavior against deformation of the adhesive layer becomes slow, and re-adhesion with the adhesive layer cannot be performed when an extremely fine float is generated due to bubbles. It is considered that the floating is likely to occur from the starting point.

(Plastic substrate)
As the plastic substrate, those which are likely to be generated due to bubbles of unreacted substances, water vapor, etc. remaining in the interior by being exposed to a high temperature environment can be preferably applied. In addition, it is also possible to preferably use a component that easily adheres to bubbles by being exposed to a high-temperature environment when the component attached to the surface of the plastic substrate is exposed.

  Such a plastic substrate is not particularly limited, and can be appropriately selected depending on the application. Generally, a synthetic resin film is used. Synthetic resin film materials include polyester resins, polypropylene resins, polyvinyl chloride resins, fluorine resins, polystyrene resins, poly (meth) acrylic resins, cellulose resins, polycarbonate resins, polyamide resins, Known plastic substrates such as polyolefin resins, polyester resins, polyvinyl alcohol resins, polyimide resins, phenol resins, polyurethane resins, polymethyl methacrylate resins, and the like can be given. These can be used alone or in combination of two or more. Moreover, a single layer may be sufficient and the laminated body of two or more layers may be sufficient. From the viewpoint of mechanical strength and suppression of warpage of the substrate, a uniaxially stretched or biaxially stretched film is preferable. In the present invention, among the above synthetic resins, polyester resins, polycarbonate resins, polymethacrylic acid, from the viewpoint of transparency, heat resistance, moldability, dimensional stability, rigidity, flexibility, stackability, price, etc. It is particularly preferable to use a methyl resin.

  Examples of the polyester resin include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polyarylate, and polytetramethylene terephthalate. As the polycarbonate resin, a polycarbonate resin obtained by reacting 2,2-bis (4-hydroxyphenyl) propane with diphenyl carbonate, and reacting 2,2-bis (4-hydroxyphenyl) propane with dimethyl carbonate. Obtained by reacting 2,2-bis (4-hydroxyphenyl) propane with diethyl carbonate, obtained by reacting bis (4-hydroxyphenyl) methane with diphenyl carbonate And polycarbonate resins obtained by reacting bis (4-hydroxyphenyl) phenylmethane and diphenyl carbonate. Synthetic polymethyl methacrylate resin using polymethyl methacrylate resin (homopolymer of methyl methacrylate) and methyl methacrylate copolymerized with monomers that can be copolymerized with methyl methacrylate. Resins can be mentioned. Among these, polyethylene terephthalate and polycarbonate are particularly preferable from the viewpoints of easy handling and low cost.

  The thickness of the plastic substrate is not particularly limited and can be appropriately selected depending on the application. Usually, the thickness is about 10 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 10 μm to 200 μm.

  The method for forming the plastic substrate is not particularly limited, and for example, a conventionally known film forming method such as a solution casting method, a melt extrusion method, or a calender method can be used. Moreover, you may use the commercially available plastic base material previously formed into the film form by the said method.

  The plastic substrate may be subjected to known easy adhesion treatment such as corona discharge treatment, plasma treatment, ozone treatment, and the like. Thereby, the adhesiveness with the barrier layer 3 and the transparent conductive film layer 5 such as a layer made of an inorganic oxide vapor-deposited film can be improved.

[Adhesive sheet]
As shown in FIG. 1, the pressure-sensitive adhesive sheet 10 for laminating a plastic substrate according to the present invention is a pressure-sensitive adhesive layer formed of a pressure-sensitive adhesive containing at least an acrylic pressure-sensitive adhesive and an isocyanate-based crosslinking agent that does not contain a cyclic structure. 2 is a pressure-sensitive adhesive sheet. And the loss tangent (105 degreeC) of the adhesion layer 2 exists in the range of 0.35 or more and 0.60 or less, and the storage elastic modulus (105 degreeC) is 5.5 * 10 < ⁴ > Pa or more, 8.9 * It is in the range of 10 ⁴ Pa or less.

  The pressure-sensitive adhesive layer 2 for bonding a plastic substrate can be formed by, for example, applying a pressure-sensitive adhesive for bonding a plastic substrate on a substrate sheet, and drying and removing a polymerization solvent or the like. When applying the adhesive for bonding the plastic substrate, a dilution solvent for application may be added as a solvent other than the polymerization solvent. The adhesive layer 2 is as described above.

  The pressure-sensitive adhesive sheet 10 for bonding a plastic substrate and the pressure-sensitive adhesive layer 2 for bonding a plastic substrate are preferably applied to an optical member, and particularly preferably used for bonding a touch panel. The adhesive sheet for laminating a plastic substrate for a touch panel includes, for example, a transparent conductive film provided with a metal oxide thin film such as ITO and a polymethyl methacrylate resin (PMMA) plate when manufacturing a capacitive touch panel. It is used for bonding hard coat films, glass lenses and the like. Although the kind of touch panel is not specifically limited, For example, a mobile phone, a tablet computer, a portable information terminal etc. can be mentioned.

[Image display device]
As shown in FIG. 2, the image display device 20 according to the present invention includes an adhesive layer 2 for bonding a plastic substrate formed with the above-described adhesive for bonding a plastic substrate according to the present invention, or the plastic substrate. The cover panel 3 which is a touch panel is bonded together using the adhesive sheet 10 for material bonding. In this image display device 20, a touch panel is bonded with an adhesive layer 2 for bonding a plastic substrate or an adhesive sheet 10 for bonding a plastic substrate formed with the adhesive for bonding a plastic substrate of the present invention. In particular, even when exposed to a high temperature environment, it is possible to prevent the plastic base material constituting the touch panel from floating and peeling.

  The image display device 20 shown in FIG. 2 has a configuration of a capacitive touch panel, and includes an image display element 6, a transparent electrode 5a, an adhesive layer 2a for bonding a plastic substrate, a transparent electrode 5b, and a plastic substrate bonding. 2 shows a structural form in which the pressure-sensitive adhesive layer 2b and the touch panel 3 on which the decorative printing 4 is applied are overlapped in that order. Such a touch panel is configured to detect with a touch sensor when the capacitance of the touched position changes when touched with a finger or the like, and the amount of change in the capacitance exceeds a certain threshold. About these each structural member, a general thing can be selected arbitrarily and used.

  Examples of the image display element 6 include display elements such as an organic EL element and a liquid crystal display element. The touch panel 3 is usually provided with decorative printing 4 on a part of the surface on the image display element 6 side. When the touch panel 3 is used for a portable terminal or the like, the decorative printing 4 is provided by various printing means in a strip shape on the entire circumference of the outer peripheral edge. Although the material of the touch panel 3 is not specifically limited, A glass plate and a plastic plate can be mentioned. Examples of the plastic plate include a transparent acrylic plate (PMMA plate). The decorative printing 4 forms a step having a height of about 5 μm to 50 μm on the glass plate or plastic plate, but the step has an arbitrary value depending on the printing method, printing conditions, color type, and the like. .

  Between the image display element 6 and the touch panel 3, normally, transparent electrodes 5a and 5b having a predetermined pattern shape are formed on the entire surface of the image display unit. The pattern of the transparent electrodes 5a and 5b is formed in a pattern that can detect the amount of change in capacitance when touched with a finger or the like. The transparent electrodes 5a and 5b are formed of various transparent conductive films such as ITO. The transparent electrodes 5a and 5b and the adhesive layer 2 for laminating a plastic substrate of the present invention are laminated so as to face each other, and both are provided between the image display element 6 and the touch panel 3.

  Since the image display device 20 according to the present invention configured as described above is unlikely to be lifted or peeled off from the plastic substrate constituting the touch panel 3, it suppresses the occurrence of malfunctions that are likely to occur when the touch panel 3 is peeled off. Can do.

  The present invention will be described in more detail with reference to examples and comparative examples.

[Example 1]
Hexamethylene diisocyanate crosslinking agent (trade name: BXX6450, solid) with respect to 100 parts by mass of acrylic adhesive (trade name: EXK11-468, weight average molecular weight: about 250,000, solid content: 40%, manufactured by TOYOCHEM) The pressure-sensitive adhesive composition was prepared by blending 0.07 part by mass of 100% (manufactured by TOYOCHEM). Next, the pressure-sensitive adhesive composition was applied with an applicator to a PET carrier film (trade name: POL502150, thickness 50 μm, manufactured by Lintec Corporation) subjected to silicone release treatment so that the dried thickness was 250 μm. . Then, after drying at 80 degreeC for 15 minutes, it dried at 120 degreeC for 15 minutes, and formed the adhesion layer. A silicone carrier-treated PET carrier film (trade name: POL501031, thickness 50 μm, manufactured by Lintec Corporation) is bonded onto the formed adhesive layer and aged for 1 week at normal temperature and normal temperature (50% RH, 25 ° C.). Thus, an adhesive sheet was obtained.

  After the obtained pressure-sensitive adhesive sheet was cut out to a size of 50 mm × 50 mm, a PET carrier film (trade name: POL 501031, manufactured by Lintec Corporation) was peeled off, and a 1.0 mm thick polycarbonate having a hard coat layer formed on the surface It bonded together using the rubber roller to the board (brand name: Iupilon IMR05, Mitsubishi Gas Chemical Co., Ltd. product). Next, the other PET carrier film (trade name: POL382020, manufactured by Lintec Corporation) is peeled off, and the exposed adhesive layer is formed of glass having a thickness of 1.0 mm, a size of 55 mm × 55 mm, and a step of 30 μm. Were bonded together using an automatic bonding machine. Thus, a bonded body of a glass plate and a polycarbonate plate was obtained. The autoclave process was performed with respect to this bonding body on conditions of 50 degreeC, 0.5 Mpa, and 30 minutes, and the sample for evaluation of Example 1 was produced. In addition, although the glass in which the level | step difference was formed used the thing of the level | step difference of 30 micrometers in this Example 1, it is applicable similarly also to the glass in which the level | step difference of about 5 micrometers-50 micrometers was formed.

[Examples 2 and 3 and Comparative Examples 1 to 4]
Each evaluation sample was prepared in the same manner as in Example 1 except that the amount of the hexamethylene diisocyanate crosslinking agent constituting the pressure-sensitive adhesive was changed as shown in Table 1.

[Comparative Examples 5 to 7]
The cross-linking agent constituting the pressure-sensitive adhesive is replaced with tolylene diisocyanate-based cross-linking agent (trade name: Coronate L-45E, solid content: 45%, manufactured by Nippon Polyurethane Industry Co., Ltd.), and the blending amount is shown in Table 1. I did it. The other evaluation samples were prepared in the same manner as in Example 1.

[Comparative Examples 8 to 10]
The cross-linking agent constituting the pressure-sensitive adhesive was changed to xylene diisocyanate-based cross-linking agent (trade name: Takenate D110N, solid content: 75%, manufactured by Mitsui Chemicals, Inc.), and the blending amount thereof was as shown in Table 1. The other evaluation samples were prepared in the same manner as in Example 1.

[Foaming evaluation]
Each of the obtained samples for evaluation was left in an oven at 85 ° C./85% Rh and 105 ° C. dry for 150 hours, and the presence or absence of bubbles (foaming) was visually confirmed. The results are shown in Table 1.

[Measurement of storage elastic modulus (E ′) and loss tangent (tan δ)]
Using the obtained samples for evaluation, the storage elastic modulus (E ′) and the loss tangent (tan δ) of the adhesive layer were measured. A sample for evaluation was set in a solid viscoelasticity analyzer (product name: RSA-III, manufactured by TA Instruments Inc.), and a dynamic viscoelasticity measurement method (attachment mode: compression mode) in accordance with JIS K7244-1. Storage elastic modulus (E ′) and loss tangent (tan δ or tan Δ) were measured at a frequency of 1 Hz and a measurement temperature range of −50 to 150 ° C. The results are shown in Table 2.

The adhesive layers of Examples 1 to 3 in which foaming was not observed had a storage elastic modulus (E ′) at 105 ° C. of 6 within a range where the loss tangent at 105 ° C. was 0.35 or more and 0.60 or less. The loss tangent (tan δ) at 105 ° C. was from 0.373 to 0.568, from .46 × 10 ^{4 to} 8.40 × 10 ⁴ Pa.

From the results shown in Table 1 and Table 2, the loss tangent (105 ° C.) of the adhesive layer 2 formed of an adhesive containing at least an acrylic adhesive and an isocyanate crosslinking agent not containing a cyclic structure is 0.35 or more, When it is in the range of 0.60 or less and the storage elastic modulus (105 ° C.) is in the range of 5.5 × 10 ⁴ Pa or more and 8.9 × 10 ⁴ Pa or less, foaming is not observed, and the plastic The base material was neither lifted nor peeled off.

1 Separator (release film)
2 Adhesive layer for bonding plastic substrates 3 Cover panel (touch panel)
DESCRIPTION OF SYMBOLS 4 Decorative printing 5 Transparent electrode 6 Image display element 10 Adhesive sheet for plastic base material bonding 20 Image display apparatus

Claims (3)

A pressure-sensitive adhesive containing at least an acrylic pressure-sensitive adhesive and an isocyanate-based crosslinking agent not containing a cyclic structure, wherein the loss tangent (105 ° C.) of the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive is 0.35 or more and 0.60 or less. A pressure-sensitive adhesive for laminating a plastic substrate, characterized in that the storage elastic modulus (105 ° C.) is in the range of 5.5 × 10 ⁴ Pa to 8.9 × 10 ⁴ Pa. A pressure-sensitive adhesive sheet formed of a pressure-sensitive adhesive containing at least an acrylic pressure-sensitive adhesive and an isocyanate-based crosslinking agent not containing a cyclic structure, wherein the loss tangent (105 ° C.) of the pressure-sensitive adhesive layer is 0.35 or more and 0.60 or less. And a storage elastic modulus (105 ° C.) within a range of 5.5 × 10 ⁴ Pa or more and 8.9 × 10 ⁴ Pa or less.   A plastic substrate is bonded to a display surface using the adhesive for bonding a plastic substrate according to claim 1 or the adhesive sheet for bonding a plastic substrate according to claim 2. Image display device.

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