KR102249906B1 - Image display device - Google Patents

Abstract

In the image display device 100, the transparent film base material 25 is bonded to the polarizing plate 10 provided on the surface of the image display cell 50 through the first adhesive sheet 21, and the transparent film base material 25 is The transparent resin plate 71 of the front transparent member 70 is bonded to each other via the second adhesive sheet 22. The second pressure-sensitive adhesive sheet has a thickness of 50 µm or more, and a storage modulus of the pressure-sensitive adhesive at 105° C. in a portion bonded to the front transparent member of the second pressure-sensitive adhesive sheet is 3×10 ⁴ Pa or more. The storage modulus of the second pressure-sensitive adhesive sheet at 25°C is greater than that of the first pressure-sensitive adhesive sheet at 25°C.

Description

Image display device {IMAGE DISPLAY DEVICE}

The present invention relates to an image display device including a front transparent member such as a transparent plate or a touch panel on the front surface of the image display panel.

As various image display devices such as mobile phones, car navigation devices, personal computer monitors, and televisions, liquid crystal displays and organic EL displays are widely used. In some cases, a front transparent plate (also referred to as a "window layer" or the like) is provided on the viewer side of the image display panel for the purpose of preventing damage to the image display panel due to impact from the outer surface. In addition, in recent years, devices having a touch panel on the viewer side of an image display panel have been spreading.

As a method of disposing a front transparent plate on the front surface of an image display panel, a ``interlayer filling structure'' has been proposed in which a polarizing plate disposed on the outermost surface of the image display panel and a front transparent plate are bonded through an adhesive (example For example, Patent Document 1). Further, even when the touch panel is disposed on the front surface of the image display panel, a configuration in which the polarizing plate and the touch panel are interlayer filled with an adhesive is adopted. In the interlayer filling structure, since the space between the image display panel and the front transparent member is filled with an adhesive, the difference in the refractive index of the interface decreases, and a decrease in visibility due to reflection or scattering is suppressed. In recent years, the adoption of an interlayer filling structure using an adhesive has been expanded for mobile displays such as mobile phones and smart phones, which are often used outdoors.

Due to the increasing demand for visibility, adoption of a configuration in which an image display panel and a front transparent member are interlayered with an adhesive in vehicle-mounted displays such as car navigation devices has been studied. In general, vehicle-mounted displays are required to have higher durability at a higher temperature than mobile displays, and recently, it is required that the display performance does not deteriorate even after a high-temperature durability test of 100°C or higher.

When an image display device in which an image display panel and a front transparent member are interlayered using an adhesive is provided for a long-term high-temperature endurance test required for a vehicle-mounted display, the transmittance of the in-plane central portion of the polarizing plate constituting the image display panel is increased. There is a case of deterioration. It is thought that the decrease in the transmittance of the polarizing plate is caused by the acid liberated from the polarizer protective film, etc., becoming a catalyst due to the retention of moisture in a high temperature environment, and the polyvinyl alcohol constituting the polarizer is dehydrated to generate polyene (e.g. Patent Document 2).

Japanese Patent Publication No. 2011-219665 Japanese Patent Publication No. 2014-102353

The present inventors have found that when a resin-made front transparent plate is used in an image display device having an interlayer filling configuration using a pressure-sensitive adhesive, a decrease in the transmittance of the polarizing plate can be suppressed even under a high temperature environment. On the other hand, in the case of using a resin-made front transparent plate, after a heating test at a high temperature, outgas from the front transparent plate remains as bubbles at the interface between the front transparent plate and the adhesive sheet, resulting in a decrease in visibility. There are cases. In addition, the resin-made front transparent plate is easily warped due to temperature changes, and the adhesive may be peeled off due to the warpage of the front transparent plate.

In view of the above, the present invention is unlikely to cause deterioration of the polarizing plate even when exposed to a high temperature environment for a long time, and also mixing of air bubbles in the pressure-sensitive adhesive used for bonding the polarizing plate and the front transparent member, or the front surface due to bending. It is an object of the present invention to provide an image display device in which peeling of a transparent member is unlikely to occur.

The present invention relates to an image display device in which an image display panel including a polarizing plate on a surface of an image display cell and a front transparent member are integrated. The transparent film base material is bonded on the polarizing plate of the image display panel through the first adhesive sheet, and the front transparent member is bonded on the transparent film base material through the second adhesive sheet. The transparent member includes a transparent resin plate, and the transparent resin plate is in contact with the second adhesive sheet. The second pressure-sensitive adhesive sheet has a thickness of 50 µm or more, and a storage modulus of the pressure-sensitive adhesive at 105° C. in a portion bonded to the front transparent member of the second pressure-sensitive adhesive sheet is 3×10 ⁴ Pa or more.

The storage modulus of the second pressure-sensitive adhesive sheet at 25°C is greater than that of the first pressure-sensitive adhesive sheet at 25°C. The storage modulus of the second pressure-sensitive adhesive sheet at 25° C. ^{is preferably 1×10 4} Pa or more. The storage modulus of the second pressure-sensitive adhesive sheet at 105° C. ^{is preferably 2×10 5} Pa or less.

The thickness of the first pressure-sensitive adhesive sheet is preferably 5 μm to 50 μm. The thickness d ₁ of the first adhesive sheet is preferably 0.5 times or less of _{the thickness d 2 of the second adhesive sheet.}

In the image display device of the present invention, since a transparent resin plate is used as the front transparent member, even when exposed to a high temperature environment for a long time, moisture retention in the polarizing plate is suppressed, and deterioration due to polyene conversion of the polarizer, etc. can be suppressed. have. Since the image display panel and the front transparent member are bonded to each other through an adhesive sheet provided with a substrate having an adhesive sheet having a different storage elastic modulus on the front and back of the transparent film substrate, there is no retention of air bubbles due to outgas to the transparent resin plate. Warpage of the transparent resin plate is suppressed.

1 is a cross-sectional view schematically showing an embodiment of an image display device.
2 is a cross-sectional view schematically showing a laminated configuration of a polarizing plate provided with a double-sided pressure-sensitive adhesive.
3 is a cross-sectional view schematically showing a lamination configuration of a laminated pressure-sensitive adhesive sheet with a base material.

1 is a schematic cross-sectional view showing an embodiment of an image display device of the present invention. The image display device 100 includes an image display panel 60 and a front transparent member 70. The image display panel 60 includes a polarizing plate 10 on the surface of the image display cell 50 on the viewer side.

Between the polarizing plate 10 of the image display panel 60 and the front transparent member 70, the transparent film base material 25 is arrange|positioned, and the polarizing plate 10 and the transparent film base material 25 of the image display panel 60 ) Is bonded through the first pressure-sensitive adhesive sheet 21, and the transparent film substrate 25 and the front transparent member 70 are bonded through the second pressure-sensitive adhesive sheet 22. In this way, in the image display device 100, the image display panel 60 and the front transparent member 70 are bonded to each other by the adhesive sheets 21 and 22 disposed on both sides of the transparent film base material 25 to be integrated. Has been.

[Image Display Panel]

(Image display cell)

The image display cells 50 of the image display panel 60 are, for example, liquid crystal cells or organic EL cells. In a liquid crystal display panel, a polarizing plate provided on the viewing side of a liquid crystal cell adjusts the transmittance according to the polarization state of light that has passed through the liquid crystal cell. In the organic EL panel, by providing a circularly polarizing plate on the viewing side of the organic EL panel, it is possible to improve the visibility of the display by shielding the emission of external light reflected from the metal electrode layer of the organic EL cell to the viewing side.

(Polarizing plate)

The polarizing plate 10 provided on the visual-recognition side surface of the image display cell 50 includes a polarizer 11. The polarizer 11 is a polyvinyl alcohol-based film containing a dichroic material such as iodine or a dichroic dye. As the material of the polyvinyl alcohol-based film applied to the polarizer, polyvinyl alcohol or a derivative thereof is used. Polyvinyl alcohol derivatives include polyvinyl formal, polyvinyl acetal, and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, alkyl esters, acrylamide, etc. The thing that was transformed into is mentioned. Polyvinyl alcohol is generally used having a degree of polymerization of about 1000 to 10000 and a degree of saponification of about 80 to 100 mol%.

By performing dyeing and stretching with a dichroic material to a polyvinyl alcohol-based film, a polarizer is obtained. As the polarizer 11, a thin polarizer having a thickness of 10 μm or less may be used. As a thin polarizer, for example, Japanese Patent Application Laid-open (Small) 51-069644, Japanese Patent Laid-Open No. 2000-338329, International Publication No. 2010/100917 pamphlet, Japanese Patent No. 4691205 Specification, Japanese Patent No. 4751481 The polarizer described in the specification of a call or the like is mentioned. Such a thin polarizer is obtained, for example, by a manufacturing method including a step of stretching a polyvinyl alcohol-based resin layer and a resin substrate for stretching in a laminated state, and a step of dyeing with a dichroic material such as iodine.

It is preferable that the polarizing plate 10 is adjacent to the polarizer 11 and provided with the transparent protective films 12 and 13. It is preferable that the polarizer 11 and the transparent protective films 12 and 13 are bonded together via an appropriate adhesive (not shown). As a material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, and thermal stability can be mentioned. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, Polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene resin), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

When the transparent protective films 12 and 13 are provided on both surfaces of the polarizer 11, the materials of the transparent protective films on the front and back may be the same or different. An optically anisotropic film such as a retardation plate (stretched film) may be used as the transparent protective film 13 provided on the image display cell 50 side of the polarizer 11 for the purpose of optical compensation or expanding the viewing angle. By using a 1/4 wavelength plate as the transparent protective film 13 on the image display cell 50 side of the polarizer 11, the polarizing plate 10 is used as a circular polarizing plate, resulting in reflection of external light incident on the image display cell. The decrease in visibility can be suppressed. By using a 1/4 wavelength plate as the transparent protective film 12 provided on the viewer side of the polarizer 11, the light emitted from the image display device to the viewer side is circularly polarized, and also for the viewer wearing polarized sunglasses, Appropriate image display can be visually recognized.

The transparent protective film 12 provided on the visible side of the polarizer 11 preferably has a moisture permeability of 300 g/m 2 ·24 h or more, more preferably 500 g/m 2 ·24 h or more, and even more preferably 700 g/m 2 ·24 h. . When the moisture permeability of the transparent protective film 12 is high, retention of moisture in the polarizing plate 10 can be suppressed, and a decrease in transmittance due to polyenization of the polyvinyl alcohol constituting the polarizer can be suppressed.

For example, by using a cellulose resin as the material of the transparent protective film 12, the moisture permeability can be adjusted to the said range. Examples of the cellulose resin include esters of cellulose and fatty acids. As a specific example of a cellulose ester, cellulose acetate, such as triacetyl cellulose and diacetyl cellulose, cellulose propionate, cellulose butyrate, etc. are mentioned.

Functional coating layers, such as a hard coating layer, an antireflection layer, an anti-sticking layer, an antistatic layer, and an easy adhesion layer, may be added to the surface of the polarizing plate 10. However, from the viewpoint of maintaining high moisture permeability, the transparent protective film 12 provided on the visible side of the polarizer 11 is preferably not provided with a functional coating layer that reduces moisture permeability such as a hard coating layer or an antireflection layer.

(Cell side adhesive sheet)

In the image display panel 60, it is preferable that the image display cell 50 and the polarizing plate 10 are bonded to each other via an adhesive sheet 30. The thickness of the cell-side adhesive sheet 30 used for bonding the image display cell and the polarizing plate is preferably 3 µm to 30 µm. As the pressure-sensitive adhesive constituting the cell-side pressure-sensitive adhesive sheet, an acrylic pressure-sensitive adhesive is preferably used.

Cell side pressure-sensitive adhesive sheet 30, and more preferably a storage elastic modulus G _'25 at 25 ℃ of 1 × 10 ⁴ Pa to 1 × 10 should preferably ⁷ Pa, and 5 × 10 ⁴ Pa to 5.0 × 10 ⁶ Pa , More preferably 1×10 ⁵ Pa to 1×10 ^{6 Pa.} Of the at which the G _'25 of the cell side pressure-sensitive adhesive sheet to a predetermined pressure-sensitive adhesive sheet or pressure-sensitive adhesive comprising a polarizing plate cut into a size with a represents a suitable adhesive is the range cut edge or the like pressure-sensitive adhesive yichak or to inhibit, such as cracks and breakage of the pressure-sensitive adhesive I can.

(Other members that make up the image display panel)

The image display panel 60 may contain optical elements such as an optical compensation film and a viewing angle enlargement film in addition to the adhesive sheet 30 between the image display cell 50 and the polarizing plate 10. Optical elements, such as a backlight, a rear-side polarizing plate, and a brightness enhancing film, may be disposed on the rear side of the image display cell 50.

[Front transparent member]

Examples of the front transparent member 70 include a front transparent plate (window layer), a touch panel, and the like. The front transparent member 70 includes a transparent resin plate 71 on a surface on the side of the image display panel, and the transparent resin plate 71 is in contact with the second adhesive sheet 22.

When the front transparent member 70 is a front transparent plate, the resin material constituting the transparent resin plate 71 is preferably an acrylic resin, a polycarbonate resin, or the like. From the viewpoint of achieving both transparency and mechanical strength, a plurality of transparent resin plates containing different resin materials may be laminated and used. For example, by using a laminated resin plate of an acrylic resin plate and a polycarbonate resin plate, the mechanical strength of the transparent plate can be improved by the polycarbonate resin while maintaining the transparency of the acrylic resin.

The thickness of the transparent resin plate 71 is preferably 500 µm or more, more preferably 700 µm or more, and even more preferably 800 µm or more. By increasing the thickness of the transparent resin plate 71, even when the image display device is exposed to a high temperature environment of 100° C. or higher, warpage is less likely to occur, and peeling of the front transparent member from the image display panel can be suppressed. From the viewpoint of suppressing warpage due to temperature change, the larger the thickness of the transparent resin plate 71 is, the more preferable. On the other hand, if the thickness is excessively large, the transparency may be lowered. Therefore, the thickness of the transparent resin plate 71 is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less.

The surface of the transparent resin plate 71 may be provided with a coating layer for imparting functions such as antireflection properties, scratch resistance, and antifouling properties. In general, a printing layer 76 for the purpose of decoration or light shielding is provided at the periphery of the bonding surface of the transparent resin plate 71 with the adhesive sheet 22. The thickness of the printing layer 76 is, for example, about 5 to 30 µm.

The front transparent member 70 may be a touch panel having the transparent resin plate 71 as a substrate. As the touch panel, any type of touch panel such as a resistive film type, a capacitive type, an optical type, and an ultrasonic type is used. In a resistive or capacitive touch panel, an electrode for position detection may be provided on a transparent resin plate.

[Composition between the image display panel and the front transparent member]

The image display device 100 includes a first adhesive sheet 21, a transparent film substrate 25, and a second adhesive sheet from the image display panel 60 side between the image display panel 60 and the front transparent member 70. (22) is provided. The polarizing plate 10 and the transparent film base 25 of the image display panel 60 are bonded to each other by the first adhesive sheet 21, and the transparent film base 25 and the front surface are transparent by the second adhesive sheet 22. The member 70 is joined.

(Transparent film base)

The transparent film substrate 25 disposed between the two pressure-sensitive adhesive sheets 21 and 22 prevents stress generated at the bonding interface between the transparent resin plate 71 of the front transparent member 70 and the second pressure-sensitive adhesive sheet 22. It balances and has an action of suppressing the warpage of the transparent resin plate. The transparent film substrate 25 also functions as a moisture passage for dispersing moisture from the polarizing plate 10 out of the system. In order to have flexural rigidity that can contribute to the suppression of warpage of the transparent resin plate and to effectively act as a passage for moisture on the side of the film, the thickness of the transparent film substrate 25 is preferably 10 μm or more, and 20 μm. The above is more preferable. From the viewpoint of maintaining transparency, dispersing moisture from the main surface of the film, and suppressing retention of moisture in the polarizing plate 10, the thickness of the transparent film substrate 25 is preferably 150 μm or less, and 100 μm or less. Is more preferable, and 80 micrometers or less are still more preferable.

As a material constituting the transparent film base material 25, various thermoplastic resin materials described above are preferably used as a material for a transparent protective film of a polarizer. In order to make the transparent film substrate 25 function effectively as a passage for moisture, similar to the transparent protective film 12 provided on the visible side of the polarizer 11, the material of the transparent film substrate 25 is made of a cellulose resin. desirable.

(Adhesive sheet)

The first adhesive sheet 21 installed between the polarizing plate 10 on the surface of the image display panel and the transparent film substrate 25, together with the transparent film substrate 25, is a stress at the bonding interface of the transparent resin plate 71 It has the effect of alleviating and suppressing warpage. The second adhesive sheet 22 provided between the transparent film substrate 25 and the transparent resin plate 71 resists the pressure of outgassing from the transparent resin plate 71 and prevents the retention of air bubbles at the bonding interface. It has an inhibitory effect. When the printing layer 76 is provided on the periphery of the front transparent member 70, the second pressure-sensitive adhesive sheet 22 prevents the retention of air bubbles in the vicinity of the printing level difference of the printing layer, or the display unevenness caused by the printing level difference. It also has an action as a cushioning layer (step absorbing layer) for suppressing it.

In order to resist outgassing from the transparent resin plate, the second pressure-sensitive adhesive sheet 22 needs to have an appropriate hardness at a high temperature. Specifically, the second adhesive sheet 22 is the bonding part of the transparent resin plate 71 of the front transparent member 70, and that the storage elastic modulus G _'105 at 105 ℃ more than 3 × 10 ⁴ Pa preferably , It is more preferable that it is 5×10 ⁴ Pa or more, and it is still more preferable that it is ^{6×10 4 Pa or more.}

In the present specification, the storage elastic modulus G'is a temperature increase rate of 5°C in the range of -50 to 150°C under a condition of a frequency of 1 Hz in accordance with the method described in JIS K7244-1 "Plastic-Dynamic Mechanical Properties Test Method". It is obtained by reading the value at a predetermined temperature when measured in minutes.

The second pressure-sensitive adhesive sheet 22 may be a laminated pressure-sensitive adhesive sheet obtained by laminating a plurality of pressure-sensitive adhesive layers. For example, by the _'105 G as a pressure-sensitive adhesive layer disposed on the bonding portion between the transparent resin plate 71 using the adhesive of the above-mentioned range, and laminating a relatively soft pressure-sensitive adhesive layer was provided on the transparent film substrate 25 side, the 2 You may give cushioning property to the whole adhesive sheet. When the second pressure-sensitive adhesive sheet includes a single-layer pressure-sensitive adhesive layer _{, it is preferable that G'105} of the second pressure-sensitive adhesive sheet is within the above range. When the storage elastic modulus of the second pressure-sensitive adhesive sheet is excessively high, display unevenness may occur due to a difference in printing at the periphery of the front transparent member. Thereby, the storage elastic modulus G _'105 at 105 ℃ of the second adhesive sheet is 2 × 10 ⁵ Pa or less is preferable, more preferably 1 × 10 ⁵ Pa or less.

As the first pressure-sensitive adhesive sheet 21, by using a material having a storage elastic modulus at room temperature smaller than that of the second pressure-sensitive adhesive sheet 22, the stress at the bonding interface of the transparent resin plate 71 is relieved, and the transparent resin plate 71 ) It is possible to suppress the peeling of the end caused by bending. Specifically, the second storage at 25 ℃ of the adhesive sheet 22, the elastic modulus G _'25, the storage elastic modulus at 25 ℃ of the first adhesive sheet G' greater than _25. Claim 2 G of a pressure-sensitive adhesive sheet 22, is more preferably, ₂₅ is a first pressure-sensitive adhesive sheet 21 of the G _'25 or more than 5 × 10 ³ Pa and preferably greater, 1 × 10 ⁴ Pa or more larger.

In the image display device of the present invention, since the front transparent plate is made of a resin material, retention of moisture in the polarizing plate 10 is suppressed, and the polyvinyl alcohol constituting the polarizer 11 is denatured (polyeneization, etc.). It is possible to suppress a decrease in transmittance. On the other hand, the resin-made transparent plate is less rigid than the glass-made transparent plate, and the dimensional change upon heating is large, so that warpage is liable to occur. In particular, when the temperature is returned to room temperature from the heating environment, stress is generated at the bonding interface and the elastic modulus of the transparent resin plate is increased due to temperature change, so that the transparent resin plate is liable to be warped. In addition, when a laminated resin plate in which a resin layer containing other materials is laminated, such as a laminated plate of an acrylic resin layer and a polycarbonate resin layer, is used as the transparent resin plate, the amount of change in size of the resin layer on the front and back due to temperature change Because they are different, warpage is liable to occur. When warping occurs in the transparent resin plate, the transparent resin plate may peel from the adhesive sheet at the periphery (cross-section).

In the image display device of the present invention, since the storage elastic modulus in the bonding portion of the transparent resin plate 71 of the second pressure-sensitive adhesive sheet 22 is large, outgas is released from the transparent resin plate 71 in a heating environment. By resisting the pressure, the retention of air bubbles at the bonding interface can be suppressed. In addition, since the second adhesive sheet 22 has a relatively high storage modulus, when it is returned to room temperature (near 25°C) from a heating environment, the bonding interface between the transparent resin plate 71 and the second adhesive sheet 22 It reacts to the stress and can suppress the warpage of the transparent resin plate. In addition, since the transparent film substrate 25 and the first adhesive sheet 21 having a relatively low storage elastic modulus are provided between the second adhesive sheet 22 and the polarizing plate 10, the transparent resin plate 71 and The stress in the bonding interface of the 2nd adhesive sheet 22 can be absorbed and dissipated, and warpage can be suppressed.

As described above, in the image display device of the present invention, deterioration of the polarizing plate in a high-temperature environment can be suppressed by using a resin material for the front transparent member. Regarding outgassing and warpage caused by the resin material, the polarizing plate 10 and the transparent resin plate 71 are provided with a transparent film base 25 between the two-layer pressure-sensitive adhesive sheets 21 and 22 having predetermined viscoelastic properties. It can be solved by bonding using the laminated pressure-sensitive adhesive sheet 20 provided with the substrate.

Prevent the pressure-sensitive adhesive of the cut edge or the like at the time of cutting the pressure sensitive adhesive sheet or pressure-sensitive adhesive comprising a polarizing plate into a predetermined size, and also to ensure the initial adhesive properties at the time of bonding, G _'25 of the first adhesive sheet 21, 1×10 ⁴ Pa to 2×10 ⁵ Pa is preferable, and 5×10 ⁴ Pa to 1.5×10 ⁵ Pa is more preferable. As described above, G 2 of the adhesive sheet 22 is larger than _"25 G of the first adhesive sheet 21, _25, also, is preferably not less than 1 × 10 ⁴ Pa. Claim 2 G _'25 of the adhesive sheet 22 is 3 × 10 ⁴ Pa to 8 × 10 ⁵ Pa is preferably, 5 × 10 ⁴ Pa to ⁵ × 10 5 Pa is and more preferably, 7 × 10 ⁴ Pa to 3 ×10 ⁵ Pa is more preferable.

From the viewpoint of suppressing protrusion of the pressure-sensitive adhesive sheet from the end face in the heating environment when the second pressure-sensitive adhesive sheet 22 and the front transparent member 70 are bonded or the image display device is actually used, the first each adhesive sheet 21 and the second pressure-sensitive adhesive sheet 22 has a storage modulus G _'105 at 105 ℃, 5 × 10 ³ Pa to 2 × 10 ⁵ Pa are preferred, 8 × 10 ³ Pa to 1.5 × 10 ⁵ Pa is more preferable.

In order to provide step absorption with respect to printing steps by functioning as a cushion layer, the thickness d2 of the second pressure-sensitive adhesive sheet 22 is preferably 50 µm or more, more preferably 70 µm or more, and even more preferably 80 µm or more. . The upper limit of the thickness of the second pressure-sensitive adhesive sheet 22 is not particularly limited, but is preferably 500 μm or less from the viewpoint of productivity of the pressure-sensitive adhesive sheet and prevention of protrusion from the end face. In the case where the second pressure-sensitive adhesive sheet is a laminated sheet of a plurality of pressure-sensitive adhesive layers, the thickness of the pressure-sensitive adhesive layer installed in contact with the transparent resin plate 71 is 5 in terms of resistance against outgas from the transparent resin plate 71 and warpage suppression. It is preferably µm or more, more preferably 10 µm or more, and even more preferably 15 µm or more.

_{The thickness d 1} of the first adhesive sheet 21 is preferably 3 to 50 µm, more preferably 5 to 40 µm, and even more preferably 10 to 30 µm. It is preferable that the thickness of the 1st adhesive sheet 21 is smaller than the thickness of the 2nd adhesive sheet 22. Claim the first adhesive sheet 21, the thickness d ₁ and a second ratio d ₁ / d ₂ of the thickness of the adhesive sheet (22), d ₂ is less than or equal to 0.5 are preferred, and 0.3 or less are more preferred, more preferably not more than 0.2 .

(Composition of adhesive)

As long as the first adhesive sheet 21 and the second adhesive sheet 22 have the above-described characteristics, the composition of the adhesive is not particularly limited, and acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether , Vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based, natural rubber, a pressure-sensitive adhesive having a rubber-based polymer such as synthetic rubber as the base polymer may be appropriately selected and used.

As a pressure-sensitive adhesive having excellent optical transparency and adhesiveness, an acrylic pressure-sensitive adhesive having an acrylic polymer as a base polymer is preferably used. In the acrylic pressure-sensitive adhesive composition, the content of the acrylic base polymer relative to the total solid content of the pressure-sensitive adhesive composition is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more.

As the acrylic polymer, those having a monomer unit of an alkyl (meth)acrylate as the main skeleton are suitably used. In addition, in this specification, "(meth)acryl" means acrylic and/or methacrylic. As the alkyl (meth)acrylate, an alkyl (meth)acrylate having 1 to 20 carbon atoms in the alkyl group is suitably used.

In the alkyl (meth)acrylate, the alkyl group may have a branch. Branched alkyl (meth)acrylic acid esters include 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isotetradecyl (meth)acrylate, and (meth) Isooctadecyl acrylate, etc. are suitably used.

The content of the alkyl (meth)acrylate in the acrylic base polymer is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more with respect to the total amount of the monomer components constituting the base polymer. The acrylic base polymer may be a copolymer of a plurality of alkyl (meth)acrylate esters, or may be a copolymer of a linear alkyl (meth)acrylic acid ester and a branched alkyl (meth)acrylic acid ester. The arrangement of single-phase constituent monomers in the copolymer may be random or may be a block.

The acrylic polymer may contain a polyfunctional monomer component as a constituent monomer component. By having a polyfunctional monomer as a copolymerization monomer component, the storage modulus of the pressure-sensitive adhesive tends to be improved. By changing the type or content of the polyfunctional monomer component, the storage modulus of the first adhesive sheet and the second adhesive sheet can be adjusted to a desired range. The polyfunctional monomer is a monomer having at least two polymerizable functional groups having an unsaturated double bond such as a (meth)acryloyl group or a vinyl group.

In order to adjust the molecular weight of the polymer, a chain transfer agent may be used. The chain transfer agent receives radicals from the growing polymer chain to stop elongation of the polymer, and the chain transfer agent that receives the radicals attacks the monomers to initiate polymerization again. When a chain transfer agent is used, an increase in molecular weight can be suppressed without lowering the radical concentration in the reaction system, and the storage modulus of the pressure-sensitive adhesive sheet tends to decrease. As a chain transfer agent, for example, α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, thioglycolic acid 2-ethylhexyl, 2,3-dimercapto Thiols such as -1-propanol are suitably used.

The acrylic base polymer may contain an acrylic monomer unit having a crosslinkable functional group as a copolymerization component. When the base polymer has a crosslinkable functional group, curing by ultraviolet irradiation can be easily performed. Examples of the acrylic monomer having a crosslinkable functional group include a hydroxy group-containing monomer and a carboxy group-containing monomer. Among them, the pressure-sensitive adhesive constituting the second pressure-sensitive adhesive sheet preferably contains a hydroxy group-containing monomer as a copolymerization component of the base polymer. When the base polymer has a hydroxy group-containing monomer as a monomer unit, the crosslinking property of the base polymer is improved, and the pressure-sensitive adhesive in a high-temperature, high-humidity environment tends to be suppressed, and a pressure-sensitive adhesive having high transparency is obtained.

The pressure-sensitive adhesive constituting the second pressure-sensitive adhesive sheet 22 preferably contains a highly polar monomer unit such as a nitrogen-containing monomer in addition to the above-described alkyl (meth)acrylate and hydroxyl group-containing monomer units. By containing a highly polar monomer unit such as a nitrogen-containing monomer unit in addition to the hydroxy group-containing monomer unit, the pressure-sensitive adhesive has high adhesiveness and retaining power, and there is a tendency to suppress clouding in a high temperature and high humidity environment.

The acrylic base polymer can be prepared by known polymerization methods such as solution polymerization, UV polymerization, bulk polymerization, and emulsion polymerization. Solution polymerization method or active energy ray polymerization method (for example, UV polymerization) is preferable from the viewpoint of transparency, water resistance, cost, etc. of the pressure-sensitive adhesive. As a solvent for solution polymerization, ethyl acetate, toluene, and the like are generally used.

A crosslinked structure may be introduced into the base polymer of the ultraviolet curable pressure-sensitive adhesive. The storage modulus of the pressure-sensitive adhesive sheet tends to increase due to the introduction of a crosslinked structure. Formation of a crosslinked structure is performed, for example, by adding a crosslinking agent after polymerization of the base polymer, followed by heating. As the crosslinking agent, those generally used such as an isocyanate crosslinking agent, an epoxy crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, and a metal chelate crosslinking agent can be used. Further, a radical polymerizable functional group can be introduced into the base polymer by mixing with the base polymer a radical polymerizable compound having a functional group bondable to the functional group of the base polymer and a radical polymerizable functional group. An isocyanate group is preferable as the functional group bondable to the functional group of the base polymer. Since the isocyanate group forms a urethane bond with the hydroxy group of the base polymer, the radical polymerizable functional group can be easily introduced into the base polymer.

The adhesive composition may contain a silane coupling agent or a tackifier for the purpose of adjusting adhesive force. In addition, additives such as plasticizers, softeners, deterioration inhibitors, fillers, colorants, antioxidants, surfactants, and antistatic agents may be contained in the pressure-sensitive adhesive composition.

The adhesive constituting the first adhesive sheet 21 and/or the second adhesive sheet 22 may be a photocurable or thermosetting adhesive. When a curable adhesive containing an unpolymerized component is used as the second adhesive sheet 22, the storage elastic modulus is small and fluidity is high at the time of bonding with the front transparent plate 71, so that the adhesive easily enters the vicinity of the steps. , It is possible to suppress the mixing of air bubbles in the vicinity of the step. If curing is performed after bonding, the storage modulus increases, so that the second pressure-sensitive adhesive sheet 22 can have a counter force against outgas and an action of suppressing warpage as described above.

It is preferable that the curable pressure-sensitive adhesive is photo-curable from the viewpoint of easy curing after bonding with the front transparent member. As a method of photocuring, a method of irradiating a system containing a photocurable compound and a photopolymerization initiator with active light such as ultraviolet rays is preferable. In particular, a system using an ethylenically unsaturated compound and a photo radical generator is preferred because of the high light sensitivity and abundant materials to choose from.

When the pressure-sensitive adhesive of the second pressure-sensitive adhesive sheet 22 is a photocurable type, the content of the photocurable compound is preferably 0.01 to 50 parts by weight, more preferably 0.05 to 30 parts by weight, based on 100 parts by weight of the total pressure-sensitive adhesive composition. In order to make the storage modulus of the pressure-sensitive adhesive after curing in an appropriate range, the content of the photo-curable polyfunctional monomer in the pressure-sensitive adhesive composition is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, based on the total 100 parts by weight of the pressure-sensitive adhesive composition, More preferably 2 parts by weight or less.

The pressure-sensitive adhesive sheet is obtained, for example, by applying the pressure-sensitive adhesive composition on a substrate and drying the solvent as necessary. As the substrate, the transparent film substrate 25 may be used, or another substrate may be used. As an application method, extrusion coating by roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coater, etc. Methods, such as a law, are mentioned. Among these, it is preferable to use a die coater, and it is particularly preferable to use a die coater using a fountain die or a slot die.

When the base polymer of the pressure-sensitive adhesive composition is a solution polymerization polymer, it is preferable to dry the solvent after application. As the drying method, a method appropriately appropriate according to the purpose may be adopted. The heating drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and more preferably 70°C to 170°C. As for the drying time, an appropriate time may be adopted as appropriate. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and still more preferably 10 seconds to 10 minutes.

When the pressure-sensitive adhesive composition contains a crosslinking agent, after application onto a substrate, crosslinking by heating may be performed. The heating temperature and the heating time are appropriately set depending on the type of crosslinking agent to be used, but crosslinking is performed by heating in a range of usually 20°C to 160°C for about 1 minute to 7 days. Heating for drying the pressure-sensitive adhesive after application may also serve as heating for crosslinking.

On the pressure-sensitive adhesive sheet, the protective sheet is peelably bonded as necessary. The protective sheet is used for the purpose of protecting the exposed surface of the pressure-sensitive adhesive until the pressure-sensitive adhesive is used for bonding to an adherend. The base material used at the time of formation (coating) of the pressure-sensitive adhesive layer may be used as it is as a protective sheet for the pressure-sensitive adhesive layer.

[Formation of an image display device]

The polarizing plate 10 is bonded to the surface of the image display cell 50 through the cell-side adhesive sheet 30, and the polarizing plate 10 and the front transparent member 70 are interposed through the transparent film base material 25. An image display device is obtained by bonding with the 1 adhesive sheet 21 and the 2nd adhesive sheet 22.

The order of bonding is not particularly limited. As shown in FIG. 2, a cell side adhesive sheet 30 is provided on one side of the polarizing plate 10, and a first adhesive sheet 21, a transparent film base 25, and a second adhesive sheet are provided on the other side. When the installed polarizing plate with double-sided adhesive is used, the step of attaching the polarizing plate to the surface of the image display cell and then attaching a separate adhesive sheet on the polarizing plate can be omitted, and the manufacturing process of the image display device can be simplified.

The method of installing the 1st adhesive sheet 21, the transparent film base material 25, and the 2nd adhesive sheet 22 on the polarizing plate 10 is not specifically limited. As shown in Fig. 3, a laminated adhesive sheet 20 with a substrate provided with a first adhesive sheet 21 on one side of the transparent film base 25 and a second adhesive sheet 22 on the other side. It is preferable to form in advance, and to bond this laminated pressure-sensitive adhesive sheet 20 with a base material onto the polarizing plate 10.

As for the laminated pressure-sensitive adhesive sheet 20 with a base material, as shown in FIG. 3, it is preferable that protective sheets 41 and 42 are attached to each of the surface of the first pressure-sensitive adhesive sheet 21 and the surface of the second pressure-sensitive adhesive sheet 22. . By peeling the protective sheet 41 provided on the surface of the first adhesive sheet 21 and bonding it to the polarizing plate 10, the first adhesive sheet 21, the transparent film substrate 25, and the second The pressure-sensitive adhesive sheet 22 is provided, and a polarizing plate with a pressure-sensitive adhesive to which the protective sheet 42 is attached to the surface of the second pressure-sensitive adhesive sheet 22 is obtained. In the polarizing plate provided with a double-sided adhesive, it is preferable that the protective sheet 43 is attached to the surface of the cell-side adhesive sheet as shown in FIG. 2.

Plastic films such as polyethylene, polypropylene, and polyethylene terephthalate are preferably used as a constituent material of the protective sheets 41, 42, and 43 to be adhered to the surface of the pressure-sensitive adhesive sheet. The thickness of the protective sheet is usually 5 to 200 µm, preferably about 10 to 150 µm. By appropriately performing a release treatment such as a silicone treatment, a long-chain alkyl treatment, or a fluorine treatment on the surface of the protective sheet to be laid with the pressure-sensitive adhesive sheet, the peelability from the pressure-sensitive adhesive is enhanced.

When using the polarizing plate with double-sided adhesive shown in FIG. 2, the order of bonding is not specifically limited. The bonding on the side of the image display cell 50 may be performed first, or bonding on the side of the front transparent member 70 may be performed first. In addition, both may be bonded at the same time. From the viewpoint of increasing the workability of bonding and the axial accuracy of the polarizing plate, after peeling the protective sheet 43 from the surface of the cell-side pressure-sensitive adhesive sheet 30, the polarizing plate 10 and the image display cell 50 are connected to the pressure-sensitive adhesive sheet 30. ), the cell side bonding process is performed, and then, the protective sheet 42 is peeled from the surface of the second pressure-sensitive adhesive sheet 22, and the polarizing plate 10 and the front transparent member 70 are provided with a base material. It is preferable that the visual side bonding process which is bonded through the sheet 20 is performed.

After bonding of the polarizing plate 10 and the front transparent member 70, the interface between the second adhesive sheet 22 and the front transparent member 70, the printed layer 76 of the front transparent member 70, etc. It is preferable that defoaming is performed to remove air bubbles in the vicinity of the non-flat portion of. As the defoaming method, an appropriate method such as heating, pressurization, and reduced pressure may be employed. For example, it is preferable that bonding is performed under reduced pressure and heating while suppressing the incorporation of air bubbles, and then pressurization is performed simultaneously with heating by an autoclave treatment or the like for the purpose of suppressing delay bubbles or the like. When the pressure-sensitive adhesive sheet is a photocurable type or a thermosetting type, it is preferable to cure the pressure-sensitive adhesive after bonding with the front transparent member and heat treatment.

<Example>

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Preparation of adhesive composition]

<Adhesive A>

In the reaction vessel, 2-ethylhexyl acrylate (2EHA): 65 parts by weight, N-vinylpyrrolidone (NVP): 15 parts by weight, hydroxyethyl acrylate (HEA): 20 parts by weight, and 1-hydroxy as a photopolymerization initiator Roxycyclohexylphenyl ketone ("Irgacure 184" manufactured by BASF): 0.1 part by weight was added, and ultraviolet rays were irradiated under a nitrogen atmosphere to obtain a prepolymer composition having a polymerization rate of 10%. In 100 parts by weight of this prepolymer composition, 2,2-dimethoxy-1,2-diphenylethan-1-one ("Irgacure 651" manufactured by BASF; IRG 651) as a photoinitiator: 0.2 parts by weight, polyfunctional 1,6-hexanediol diacrylate as a monomer (Shin-Nakamura Chemical Co., Ltd. "NK Ester A-HD-N"): 0.3 parts by weight and 3-glycidoxypropyltrimethoxysilane (Shin-Etsu) as a silane coupling agent Chemical agent "KBM-403"): 0.3 parts by weight was added and mixed uniformly to prepare a pressure-sensitive adhesive composition A.

<Adhesive B>

The addition amount of the polyfunctional monomer in the pressure-sensitive adhesive composition was changed to 0.09 parts by weight. Other than that, it carried out similarly to preparation of the adhesive composition A, and prepared the adhesive composition B.

<Adhesive C>

As a chain transfer agent, 0.2 parts by weight of α-thioglycerol (TGR) was added. Except for that, it carried out similarly to preparation of the adhesive composition B, and prepared the adhesive composition C.

<Adhesive D>

The composition of the charged monomer in the preparation of the prepolymer composition was changed to 2HEA:55 parts by weight, NVP:25 parts by weight, and HEA:20 parts by weight, and the amount of the polyfunctional monomer added in the pressure-sensitive adhesive composition was changed to 0.7 parts by weight. Other than that, it carried out similarly to preparation of the adhesive composition A, and prepared the adhesive composition D.

<Adhesive E>

The composition of the charged monomer in the preparation of the prepolymer composition was butyl acrylate (BA): 57 parts by weight, cyclohexyl acrylate (CHA): 12 parts by weight, HEA: 8 parts by weight, and 4-hydroxybutyl acrylate (4HBA). : It changed to 23 parts by weight, and the polyfunctional monomer added in the pressure-sensitive adhesive composition was changed to dipentaerythritol hexaacrylate ("KAYARAD DPHA" manufactured by Nippon Kayaku): 0.12 parts by weight. Other than that, it carried out similarly to preparation of the adhesive composition A, and prepared the adhesive composition E.

<Adhesive F>

As a monomer component in the reaction vessel, BA: 95 parts by weight, acrylic acid (AA): 4.9 parts by weight and HEA: 0.1 parts by weight, and as a thermal polymerization initiator azobisisobutyronitrile (AIBN): 0.2 parts by weight ethyl acetate 233 parts by weight It injected|threw-in together, and it stirred for 1 hour in a 23 degreeC nitrogen atmosphere, and performed nitrogen substitution. Then, it was made to react at 60 degreeC for 5 hours, and the acrylic base polymer was obtained. Trimethylolpropanetolylene diisocyanate ("Coronate L" manufactured by Nippon Polyurethane Kogyo) as an isocyanate-based crosslinking agent: 0.6 parts by weight and KBM-403 as a silane coupling agent: 0.3 parts by weight were added to this acrylic base polymer solution, and then uniformly Then, the pressure-sensitive adhesive composition F (solution) was prepared.

<Adhesive G (cell side adhesive)>

Except that the monomer composition was changed to BA:97 parts by weight and AA:3 parts by weight, the crosslinking agent added to the pressure-sensitive adhesive composition (Coronate L) was changed to 0.8 parts by weight, and the silane coupling agent (KBM-403) was changed to 0.1 parts by weight, The pressure-sensitive adhesive composition G (solution) was prepared in the same manner as in the preparation of the pressure-sensitive adhesive F.

[Production of single layer adhesive sheet]

<Adhesive Sheets A to E>

A coating layer is formed by applying the above pressure-sensitive adhesive composition A to a release-treated side of a separator (a polyester film with a release-treated silicone film on one side) so as to have a thickness of 250 µm, and a release-treated side of a separate separator on this coating layer Was spliced. After that, UV irradiation is performed with a black light positioned so that the irradiation intensity on the irradiation surface immediately under the lamp is 5 mW/cm 2, until the cumulative amount of light reaches 3000 mJ/cm 2 to proceed with polymerization, and separators on both sides. A pressure-sensitive adhesive sheet A1 was obtained.

Except having changed the coating thickness to 20 micrometers, it carried out similarly to the above, and obtained the adhesive sheet A2. After changing the type and thickness of the pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet B1 (thickness 250 μm) using pressure-sensitive adhesive composition B, pressure-sensitive adhesive sheet C1 (thickness 250 μm) and pressure-sensitive adhesive sheet C2 (thickness 20 μm), pressure-sensitive adhesive composition D using pressure-sensitive adhesive composition C A pressure-sensitive adhesive sheet D1 (thickness 250 µm) using and a pressure-sensitive adhesive sheet E1 (thickness 250 µm), a pressure-sensitive adhesive sheet E2 (thickness 100 µm) and a pressure-sensitive adhesive sheet E3 (thickness 500 µm) using the PSA composition E were prepared.

<Adhesive sheet F>

The above-described pressure-sensitive adhesive composition F was applied onto the release-treated surface of the separator so that the thickness after drying became 250 µm, and heated at 100°C to remove the solvent. Then, it heated at 50 degreeC for 48 hours, and the crosslinking process was performed, and the 250 micrometers-thick adhesive sheet F1 was obtained.

<Measurement of storage modulus>

For each of the pressure-sensitive adhesive compositions A to F, a single-layer pressure-sensitive adhesive sheet having a thickness of 250 µm was prepared, and a plurality of pressure-sensitive adhesive sheets were laminated to have a thickness of about 1.5 mm, as a sample for measurement. Using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific, dynamic viscoelasticity was measured under the following conditions, and the storage modulus at 20°C, 50°C and 105°C (G' ₂₅ , G' ₅₀ and _G'105 ) were read.

(Measuring conditions)

Transformation Mode: Torsion

Measurement frequency: 1Hz

Heating rate: 5℃/min

Measurement temperature: in the range of -50 to 150°C

Shape: Parallel plate 8.0㎜φ

The composition of the pressure-sensitive adhesive compositions A to F and the measurement results of the storage modulus of each pressure-sensitive adhesive sheet are shown in Table 1 as a list.

[Production of polarizing plate with single-sided adhesive]

The pressure-sensitive adhesive composition G was applied onto the release-treated surface of the separator so that the thickness after drying became 20 µm, and heated at 100°C to remove the solvent. Then, it heated at 50 degreeC for 48 hours, and the crosslinking process was performed, and the cell side adhesive sheet was obtained.

A 40㎛-thick triacetylcellulose (TAC) transparent protective film is provided on one side of a polarizer including a 25㎛-thick stretched polyvinyl alcohol film impregnated with iodine, and an acrylic transparent protective film with a thickness of 30㎛ on the other side A polarizing plate provided with a film was used. The cell side adhesive sheet was bonded to the surface of the polarizing plate on the side of the acrylic protective film (the surface on the cell side) using a roll laminator, and a polarizing plate provided with an adhesive sheet on one side of the polarizing plate was obtained.

[Example 1]

<Preparation of laminated adhesive sheet with base material>

The adhesive sheet A1 was bonded to the hard coating layer forming surface of a 40 μm-thick triacetylcellulose (TAC) film having a hard coating layer on one side, and the adhesive sheet F1 was bonded to the other side. A laminated pressure-sensitive adhesive sheet with a substrate provided with a TAC substrate film was produced between the pressure-sensitive adhesive sheets.

<Production of polarizing plate with double-sided adhesive>

The surface of the adhesive sheet F1 side of the laminated adhesive sheet with a base material was bonded to the surface of the polarizing plate with a single-sided adhesive on which the adhesive sheet was not attached (the surface on the side of the TAC transparent protective film) to obtain a polarizing plate with a double-sided adhesive.

<Production of evaluation panel>

After the above-mentioned polarizing plate with double-sided pressure-sensitive adhesive was cut to a size of 200 mm x 140 mm, the cell-side pressure-sensitive adhesive sheet-shaped separator was peeled off, the cell-side pressure-sensitive adhesive sheet surface was superimposed on the central portion of the 0.7 mm-thick glass plate, and bonded using a hand roller. .

Thereafter, the separator on the viewing side of the polarizing plate provided with a double-sided adhesive was peeled off, and the printed surface of the transparent resin plate printed in a frame shape on the periphery of the black ink was mounted on the exposed surface of the adhesive (on the adhesive sheet A1), Bonding was performed with a vacuum thermocompression bonding device (temperature 25°C, pressure in the device 50 Pa, pressure 0.3 MPa, pressure holding time 10 seconds). Then, an autoclave treatment (50°C, 0.5 MPa, 15 minutes) was performed to obtain a panel for evaluation. The transparent resin plate is a laminated transparent resin plate of polymethyl methacrylate (PMMA) and polycarbonate (PC) (1 mm thick × 200 mm × 140 mm), and has a printing surface of black ink on the side of the PC side. (Ink print thickness = 10 µm, ink print width of both short sides (long side direction): 15 mm each, ink print width of both long sides (short side direction): 5 mm each).

[Examples 2 to 6 and Comparative Examples 1 to 3]

The configuration of the laminated pressure-sensitive adhesive sheet with a base material was changed as shown in Table 2. Other than that, the pseudo image display device for evaluation was produced in the same procedure as in Example 1.

[Example 7]

A panel for evaluation was produced in the same procedure as in Example 3, except that a front transparent plate having a thickness of 0.7 mm (a laminated transparent resin plate of PMMA and PC) was used as the front transparent plate.

[Examples 8 and 9]

A panel for evaluation was produced in the same procedure as in Example 1 except that a transparent resin plate having a thickness of 2 mm was used as the front transparent plate. In Example 8, a laminated transparent resin plate of PMMA and PC was used as the front transparent plate. In Example 9, as the front transparent plate, a laminated transparent resin plate including three layers of PMMA/PC/PMMA was used.

[Comparative Example 4]

In the production of a polarizing plate with a double-sided adhesive, as the pressure-sensitive adhesive sheet on the visible side of the polarizing plate, the pressure-sensitive adhesive sheet A1 was used as a single layer instead of the laminated pressure-sensitive adhesive sheet. Other than that, an evaluation panel was produced in the same procedure as in Example 1.

[Comparative Example 5]

A panel for evaluation was produced in the same procedure as in Comparative Example 4 except that a glass plate having a thickness of 0.7 mm was used as the front transparent plate.

[Comparative Example 6]

A panel for evaluation was produced in the same procedure as in Example 3 except that a glass plate having a thickness of 0.7 mm was used as the front transparent plate.

[evaluation]

<Air bubbles>

The inner vicinity of the black ink printing layer of the evaluation panel was observed with a digital microscope at a magnification of 20 times, and the presence or absence of bubbles in the pressure-sensitive adhesive sheet was confirmed. It was set as OK that no air bubble was confirmed, and NG that air bubble was confirmed.

<heating test>

The single transmittance of the in-plane center portion of the evaluation panel (Y value obtained by correcting the luminous sensitivity by the 2-degree field of view (C light source) of JLS Z8701) was measured. The evaluation panel after measuring the single transmittance was put into a hot air oven at a temperature of 105°C, taken out after 500 hours, and allowed to cool until it reached room temperature, and then the following evaluation was performed.

(Transmittance change)

The single transmittance of the in-plane central portion of the evaluation panel was measured, and the rate of change with respect to the single transmittance before the heating test was calculated.

(Adhesive peeling)

The side surface of the evaluation panel in the long side direction was observed, and the presence or absence of peeling of the glass plate and the front transparent plate at the edge was confirmed. About what peeling was confirmed, the amount of peeling from an edge (distance from an edge) was measured. The thing where peeling was not confirmed was made into peeling amount 0.

(Air bubbles in the plane)

From the side of the front transparent plate, the appearance of the central part in the plane of the evaluation panel was visually confirmed, and the part in which air bubbles were confirmed was observed with a digital microscope. It was set as NG that no bubbles were found and that the cells were all confirmed to have a foreign material as a nucleus or that the diameter was less than 300 µm, and that a bubble having a diameter of 300 µm or more was confirmed without a foreign material as a nucleus.

[Evaluation results]

In each of the above Examples and Comparative Examples, the configuration of the laminated pressure-sensitive adhesive sheet with a substrate used for bonding the polarizing plate and the front transparent plate (however, Comparative Examples 4 and 5 are single-layered pressure-sensitive adhesive sheets), and the thickness of each pressure-sensitive adhesive sheet (single layer) And storage modulus, the material and thickness of the front transparent plate, and evaluation results are shown in Table 2.

In Comparative Example 5 in which a glass plate was used as the front transparent plate, the polarizing plate was discolored after the heating test, and the transmittance of the central portion in the panel surface was significantly lowered. In Comparative Example 4, the decrease in the transmittance after the heating test was not confirmed, but warpage occurred in the resin plate, and the interface between the resin plate and the pressure-sensitive adhesive was peeled off at the panel end.

In Examples 1 to 9 and Comparative Examples 1 to 3 using a base material-equipped laminated adhesive sheet having an adhesive sheet on both sides of the base film for bonding of the polarizing plate and the resin plate, the decrease in transmittance after the heating test was not observed, and the panel end The peeling of the resin plate in was also suppressed. In Comparative Example 6 in which a polarizing plate and a glass plate were bonded by a laminated pressure-sensitive adhesive sheet with a base material, a decrease in transmittance due to discoloration of the polarizing plate was confirmed after a heating test as in Comparative Example 5.

From the above results, it was found that by using a transparent resin plate as the front transparent plate, deterioration due to polyene conversion or the like of the polarizing plate was suppressed even after a heating test of 100°C or higher. When a transparent resin plate is used, peeling due to warpage of the transparent resin plate may occur, but it has been found that warpage can be suppressed by using a laminated pressure-sensitive adhesive sheet with a base material.

Comparing Example 1, Example 8, and Example 9 using the same laminated pressure-sensitive adhesive sheet, in Examples 8 and 9 where the thickness of the resin plate was large, the amount of peeling due to warping was small. In addition, the same trend was confirmed in the comparison between Example 3 and Example 7. From these results, it was found that by increasing the thickness of the resin plate, warpage caused by temperature change can be reduced.

A first pressure-sensitive adhesive sheet (pressure-sensitive adhesive sheet 1) stored at 25 ℃ as the elastic modulus G 'in the comparative example ₃₂₅ is used for a pressure-sensitive adhesive sheet A2, Comparative Example 4, rather than due to a warp of the resin plate which is provided between the polarizing plate and the film base Although the said peeling was small, the peeling amount was larger than Examples 1-6. Since Examples 1 to 6 and Comparative Example 3 use the same resin plate, it can be seen that a difference occurs in the amount of peeling of the resin plate due to warping depending on the type of the pressure-sensitive adhesive sheet.

Specifically, the second adhesive is the type of sheet In the same manner, the type of the first adhesive sheet in case from the preparation of Comparative Example 3 with an alternative embodiment 3, the smaller the first adhesive sheet of the G _'25, and relieve the stress , It can be seen that peeling caused by warpage can be suppressed. In addition, in the same type of the first adhesive sheet, and the second pressure-sensitive adhesive type of sheet from the preparation of the other Examples 1 and 2, if the G _'25 of the second pressure-sensitive adhesive sheet is large, the peeling due to the bending You can see what can be suppressed. From those results, the second adhesive sheet in case of G is larger than _"25 G of the first adhesive sheet, _25, it may be a high effect of suppressing the peeling due to the bending.

In Comparative Example 1 in which a pressure-sensitive adhesive sheet C1 having a small storage modulus at high temperature was used as the second pressure-sensitive adhesive sheet (adhesive sheet 2) installed between the resin plate and the film substrate, after the heating test, bubbles were formed at the interface between the pressure-sensitive adhesive sheet and the resin plate. Confirmed. Since no air bubbles were found in Comparative Example 6 in which the glass plate was bonded using the same pressure-sensitive adhesive sheet, in Comparative Example 3, it is considered that the outgas generated by heating of the resin plate and remained at the interface of the pressure-sensitive adhesive sheet. In Examples 1 to 8, a resin plate was used, but no retention of air bubbles was observed. From these results, it was found that when the storage modulus of the second pressure-sensitive adhesive sheet at a high temperature is large, the retention of air bubbles at the interface can be suppressed against the discharge pressure of outgassing. On the other hand, in Comparative Example 2, since the storage elastic modulus of the second pressure-sensitive adhesive sheet was excessively large, the step absorbency of the pressure-sensitive adhesive sheet was not sufficient, and the retention of air bubbles was observed in the vicinity of the printing step of the transparent resin plate.

Taking the above results together, by using a resin plate as the front transparent member provided on the surface of the image display cell, it is possible to suppress a decrease in transmittance due to deterioration of the polarizing plate, and a transparent film between the two-layer adhesive sheets. It was found that peeling of the resin plate caused by warping can be suppressed by bonding the polarizing plate and the resin plate through the laminated pressure-sensitive adhesive sheet provided with the substrate. In addition, since the pressure-sensitive adhesive sheet constituting the laminated pressure-sensitive adhesive sheet has a predetermined storage elastic modulus, it is possible to further suppress the peeling caused by the bending of the resin plate, and to suppress the stay of outgas from the resin plate at the bonding interface. In addition, it was found that mixing of air bubbles in the vicinity of the printing step due to the step absorption property can be suppressed.

10: polarizer
11: polarizer
12, 13: transparent protective film
20: laminated adhesive sheet with base material
21, 22, 30: adhesive sheet
25: transparent film substrate
41, 42, 43: protective sheet
80: polarizing plate with double-sided adhesive
50: image display cell
60: image display panel
70: front transparent member
71: transparent resin plate
76: printed layer
100: image display device

Claims (5)

An image display device in which an image display panel having a polarizing plate on the surface of the image display cell and a front transparent member are integrated,
A transparent film substrate is bonded to the polarizing plate of the image display panel through a first adhesive sheet, and a front transparent member is bonded to the transparent film substrate through a second adhesive sheet,
The front transparent member includes a transparent resin plate, and the transparent resin plate is in contact with the second adhesive sheet,
The second pressure-sensitive adhesive sheet has a thickness of 50 μm or more, and a storage modulus of the pressure-sensitive adhesive at 105° C. in a portion of the second pressure-sensitive adhesive sheet bonded to the front transparent member is 3×10 ⁴ Pa or more,
The image display device, wherein the storage elastic modulus at 25°C of the second adhesive sheet is greater than the storage elastic modulus at 25°C of the first adhesive sheet. The image display device according to claim 1, wherein the second pressure-sensitive adhesive sheet has a storage elastic modulus at 25° C. of 1×10 ⁴ Pa or more. The image display device according to claim 1, wherein the second pressure-sensitive adhesive sheet has a storage elastic modulus at 105° C. of 2×10 ⁵ Pa or less. The image display device according to claim 1, wherein the first adhesive sheet has a thickness of 5 µm to 50 µm. The image display device according to any one of claims 1 to 4, wherein a ratio d ₁ /d _{2 of a thickness d 1} of the first adhesive sheet and a thickness d ₂ of the second adhesive sheet is 0.5 or less.

Images