CN108230900B

CN108230900B - Image display device

Info

Publication number: CN108230900B
Application number: CN201711376423.3A
Authority: CN
Inventors: 宝田翔; 山本真也; 泽崎良平; 保井淳
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2016-12-21
Filing date: 2017-12-19
Publication date: 2021-08-10
Anticipated expiration: 2037-12-19
Also published as: CN108230900A; JP2018101117A; KR102249906B1; JP6850601B2; TW201825625A; KR20180072556A; TWI750259B

Abstract

The present invention relates to an image display device. In an image display device (100), a transparent film substrate (25) is bonded to a polarizing plate (10) provided on the surface of an image display unit (50) via a first adhesive sheet (21), and a transparent resin plate (71) of a front transparent member (70) is bonded to the transparent film substrate (25) via a second adhesive sheet (22). The second adhesive sheet has a thickness of 50 [ mu ] m or more, and the adhesive in the portion bonded to the front transparent member of the second adhesive sheet has a storage elastic modulus of 3X 10 at 105 ℃⁴Pa or above. The storage elastic modulus at 25 ℃ of the second adhesive sheet is greater than the storage elastic modulus at 25 ℃ of the first adhesive sheet.

Description

Image display device

Technical Field

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

Background

Liquid crystal display devices and organic Electroluminescence (EL) display devices are widely used as various image display devices such as mobile phones, car navigation devices, monitors for personal computers, and televisions. In order to prevent damage or the like of the image display panel due to an impact from the outer surface, a front transparent plate (also referred to as a "window layer" or the like) may be provided on the viewing side of the image display panel. In recent years, devices having a touch panel on the viewing side of an image display panel have become widespread.

As a method of disposing a front transparent plate on the front surface of an image display panel, an "interlayer filling structure" has been proposed in which a polarizing plate disposed on the outermost surface of the image display panel is bonded to the front transparent plate via an adhesive (for example, patent document 1). When the touch panel is disposed on the front surface of the image display panel, the polarizing plate and the touch panel are filled with an adhesive between layers. In the interlayer filling structure, since the space between the image display panel and the front transparent member is filled with the adhesive, the difference in refractive index at the interface is reduced, and the deterioration of visibility due to reflection or scattering can be suppressed. In recent years, an interlayer filling structure using an adhesive has been widely used for mobile display applications such as mobile phones and smart phones which are often used outdoors.

In order to meet the demand for visibility, a structure in which an image display panel and a front transparent member are filled with an adhesive between layers has been studied in an in-vehicle display such as a car navigation system. In general, a vehicle-mounted display is required to have higher durability at higher temperatures than a mobile display (ディスプレイ for モバイル), and in recent years, it has been required that display performance does not deteriorate even after a high-temperature durability test at 100 ℃.

When an image display device in which an image display panel and a front transparent member are interlayer-filled with an adhesive is subjected to a long-time high-temperature durability test required for an in-vehicle display, the transmittance of the central portion in the plane of a polarizing plate constituting the image display panel may decrease. It is considered that the decrease in transmittance of the polarizing plate is caused by dehydration of polyvinyl alcohol constituting the polarizer to generate polyene, because acid released from a polarizer protective film or the like acts as a catalyst due to retention of moisture in a high-temperature environment (for example, patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2011-

Patent document 2: japanese patent laid-open publication No. 2014-102353

Disclosure of Invention

Problems to be solved by the invention

The present inventors have found that, in an image display device having an interlayer filling structure using an adhesive, when a front transparent plate made of a resin is used, a decrease in transmittance of a polarizing plate can be suppressed even in a high-temperature environment. On the other hand, when a resin front transparent plate is used, outgas from the front transparent plate may be trapped as bubbles at the interface between the front transparent plate and the adhesive sheet after a heating test at a high temperature, and visibility may be degraded. In addition, the front transparent plate made of resin is likely to warp due to a temperature change, and the adhesive may peel off along with the warp of the front transparent plate.

In view of the above circumstances, an object of the present invention is to provide an image display device in which deterioration of a polarizing plate is not easily caused even when exposed to a high-temperature environment for a long time, and mixing of air bubbles in an adhesive used for bonding a polarizing plate and a front transparent member and peeling of the front transparent member due to warping are not easily caused.

Means for solving the problems

The present invention relates to an image display device in which an image display panel having a polarizing plate on a surface of an image display unit is integrated with a front transparent member. A transparent film substrate is bonded to a polarizing plate of an image display panel via a first adhesive sheet, and a front transparent member is bonded to the transparent film substrate via a 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 adhesive sheet has a thickness of 50 [ mu ] m or more, and the adhesive in the portion bonded to the front transparent member of the second adhesive sheet has a storage elastic modulus of 3X 10 at 105 ℃⁴Pa or above.

The storage elastic modulus at 25 ℃ of the second adhesive sheet is greater than the storage elastic modulus at 25 ℃ of the first adhesive sheet. The storage elastic modulus at 25 ℃ of the second adhesive sheet is preferably 1 × 10⁴Pa or above. The storage elastic modulus at 105 ℃ of the second adhesive sheet is preferably 2X 10⁵Pa or less.

The thickness of the first adhesive sheet is preferably 5 μm to 50 μm. Thickness d of first adhesive sheet₁Preferably the thickness d of the second adhesive sheet₂Less than 0.5 times of the total amount of the active ingredient.

Effects of the invention

In the image display device of the present invention, since the transparent resin plate is used as the front transparent member, even when exposed to a high-temperature environment for a long time, the retention of moisture in the polarizing plate can be suppressed, and deterioration due to the polyalkyleneition of the polarizer and the like can be suppressed. Since the image display panel and the front transparent member are bonded to each other via the adhesive sheet with a substrate having the adhesive sheet having different storage elastic modulus on the front surface and the back surface of the transparent film substrate, the retention of bubbles due to outgassing from the transparent resin plate and the warping of the transparent resin plate can be suppressed.

Drawings

Fig. 1 is a cross-sectional view schematically showing one embodiment of an image display device.

Fig. 2 is a cross-sectional view schematically showing a lamination structure of polarizing plates with double-sided adhesive.

Fig. 3 is a cross-sectional view schematically showing a laminated structure of a laminated adhesive sheet with a base material.

Reference numerals

10 polarizing plate

11 polarizer

12. 13 transparent protective film

20 laminated adhesive sheet with base

21. 22, 30 adhesive sheet

25 transparent film substrate

41. 42, 43 protective sheet

80 polarizing plate with double-sided adhesive

50 image display unit

60 image display panel

70 front transparent member

71 transparent resin plate

76 print layer

100 image display device

Detailed Description

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

The transparent film base 25 is disposed between the polarizing plate 10 and the front transparent member 70 of the image display panel 60, the polarizing plate 10 and the transparent film base 25 of the image display panel 60 are bonded via the first adhesive sheet 21, and the transparent film base 25 and the front transparent member 70 are bonded via the second 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 and integrated by the

adhesive sheets

21 and 22 disposed on both surfaces of the transparent film base 25.

[ image display Panel ]

(image display Unit)

The image display unit 50 of the image display panel 60 is, for example, a liquid crystal unit or an organic EL unit. In the liquid crystal display panel, a polarizing plate provided on the viewing side of the liquid crystal cell adjusts the transmittance according to the polarization state of light transmitted through the liquid crystal cell. In the organic EL panel, by providing the circularly polarizing plate on the viewing side of the organic EL panel, the emission of external light reflected by the metal electrode layer of the organic EL cell to the viewing side can be shielded, and the visibility of the display can be improved.

(polarizing plate)

The polarizing plate 10 disposed on the viewing-side surface of the image display unit 50 includes a polarizer 11. The polarizer 11 is a polyvinyl alcohol film containing a dichroic material such as iodine or dichroic dye. As a material of the polyvinyl alcohol-based film used in the polarizer, polyvinyl alcohol or a derivative thereof is used. Examples of the derivative of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal, and modified compounds of olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, alkyl esters thereof, and acrylamide. Polyvinyl alcohol having a polymerization degree of about 1000 to about 10000 and a saponification degree of about 80 to about 100 mol% is generally used.

The polarizer is obtained by dyeing and stretching a polyvinyl alcohol-based film with a dichroic material. As the polarizer 11, a thin polarizer having a thickness of 10 μm or less may be used. Examples of the thin polarizer include polarizers described in jp 51-069644 a, jp 2000-a 338329 a, WO2010/100917 a single file, japanese patent No. 4691205, and japanese patent No. 4751481. Such a thin polarizer can be obtained, for example, by a production method including a step of stretching a polyvinyl alcohol resin layer and a stretching resin substrate in a state of a laminate and a step of dyeing with a dichroic material such as iodine.

The polarizing plate 10 preferably includes transparent protective films 12 and 13 adjacent to the polarizer 11. The polarizer 11 and the transparent protective films 12 and 13 are preferably bonded to each other via an appropriate adhesive (not shown). Examples of the material constituting the transparent protective film include thermoplastic resins having excellent transparency, mechanical strength, and thermal stability. Specific examples of such thermoplastic resins include cellulose resins such as triacetylcellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, cyclic polyolefin resins (norbornene resins), 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 surfaces may be the same or different. As the transparent protective film 13 provided on the image display unit 50 side of the polarizer 11 for the purpose of optical compensation, expansion of viewing angle, or the like, an optically anisotropic film such as a phase difference plate (stretched film) may be used. By using the 1/4 wave plate as the transparent protective film 13 on the image display unit 50 side of the polarizer 11, the polarizing plate 10 is made a circularly polarizing plate, and a reduction in visibility due to reflection of external light incident on the image display unit can be suppressed. By using the 1/4 wave plate as the transparent protective film 12 provided on the viewing side of the polarizer 11, light emitted from the image display device to the viewing side is circularly polarized, and thus, even a viewer wearing polarized sunglasses can view an appropriate image display.

The moisture permeability of the transparent protective film 12 provided on the viewing side of the polarizer 11 is preferably 300g/m²24 hours or longer, more preferably 500g/m²24 hours toMore preferably 700g/m²24 hours or longer. When the transparent protective film 12 has a high moisture permeability, the retention of moisture in the polarizing plate 10 can be suppressed, and the decrease in transmittance due to polyene formation of polyvinyl alcohol constituting the polarizer can be suppressed.

For example, by using a cellulose-based resin as the material of the transparent protective film 12, the moisture permeability can be adjusted to the above range. Examples of the cellulose-based resin include esters of cellulose and fatty acids. Specific examples of the cellulose ester include cellulose acetate, cellulose propionate, and cellulose butyrate such as triacetyl cellulose and diacetyl cellulose.

A hard coating layer, an anti-reflection layer (reflection preventing body frame), a release layer, an anti-static layer, an easy adhesion layer, and other functional coatings 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 viewing side of the polarizer 11 is preferably not provided with a functional coating layer that reduces moisture permeability, such as a hard coat layer or an antireflection layer.

(Unit side adhesive sheet)

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

The storage elastic modulus G 'at 25 ℃ is preferable for the unit-side pressure-sensitive adhesive sheet 30'₂₅Is 1 × 10⁴Pa～1×10⁷Pa, more preferably 5X 10⁴Pa～5.0×10⁶Pa, more preferably 1X 10⁵Pa～1×10⁶Pa. G 'if unit side adhesive sheet'₂₅Within the above range, the adhesive sheet or the adhesive-attached polarizing plate exhibits appropriate adhesiveness, and can suppress the adhesive from transferring to a dicing blade or the like and the adhesive from breaking or chipping when the adhesive sheet or the adhesive-attached polarizing plate is cut into a predetermined size.

(other Components constituting the image display Panel)

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

[ front transparent Member ]

The front transparent member 70 may be a front transparent plate (window layer), a touch panel, or the like. The front transparent member 70 includes a transparent resin plate 71 on the image display panel side surface, 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, an acrylic resin, a polycarbonate resin, or the like is preferable as a resin material constituting the transparent resin plate 71. From the viewpoint of compatibility between transparency and mechanical strength, a plurality of transparent resin plates containing different resin materials may be stacked 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 still 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 ℃ or higher, warping does not easily occur, and peeling of the front transparent member from the image display panel can be suppressed. From the viewpoint of suppressing the warpage due to the temperature change, the larger the thickness of the transparent resin plate 71 is, the more preferable. On the other hand, since the transparency may be lowered when the thickness is too large, the thickness of the transparent resin plate 71 is preferably 5mm or less, more preferably 4mm or less, and further preferably 3mm or less.

A coating layer for imparting functions such as antireflection, scratch resistance, and stain resistance may be provided on the surface of the transparent resin plate 71. A printed layer 76 for the purpose of decoration or light shielding is usually provided on the peripheral edge of the surface of the transparent resin plate 71 that is in contact with the adhesive sheet 22. The thickness of the printed layer 76 is, for example, about 5 μm to about 30 μm.

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

[ constitution between image display Panel and front surface transparent Member ]

The image display device 100 includes a first adhesive sheet 21, a transparent film substrate 25, and a second adhesive sheet 22 between the image display panel 60 and the front transparent member 70 from the image display panel 60 side. The polarizing plate 10 of the image display panel 60 is bonded to the transparent film substrate 25 with the first adhesive sheet 21, and the transparent film substrate 25 is bonded to the front transparent member 70 with the second adhesive sheet 22.

(transparent film substrate)

The transparent film base 25 disposed between the two

adhesive sheets

21 and 22 has a function of balancing stress generated at the bonding interface between the transparent resin plate 71 of the front transparent member 70 and the second adhesive sheet 22, thereby suppressing warpage of the transparent resin plate. Transparent film substrate 25 also functions as a moisture channel for allowing moisture from polarizing plate 10 to escape to the outside of the system. The thickness of the transparent film base material 25 is preferably 10 μm or more, and more preferably 20 μm or more, in order to have bending rigidity that can contribute to suppression of warpage of the transparent resin plate and to make the film side function effectively as a moisture channel. From the viewpoint of maintaining transparency, dissipating 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, more preferably 100 μm or less, and even more preferably 80 μm or less.

As the material constituting the transparent film base material 25, various thermoplastic resin materials described above as the material of the transparent protective film of the polarizer are preferably used. In order to allow the transparent film substrate 25 to effectively function as a moisture channel, the material of the transparent film substrate 25 is preferably a cellulose-based resin, as in the case of the transparent protective film 12 provided on the viewing side of the polarizer 11.

(adhesive sheet)

The first adhesive sheet 21 provided between the polarizing plate 10 and the transparent film substrate 25 on the surface of the image display panel has a function of relaxing the stress at the bonding interface of the transparent resin plate 71 together with the transparent film substrate 25 to suppress warping. The second adhesive sheet 22 provided between the transparent film substrate 25 and the transparent resin plate 71 has a function of suppressing stagnation of air bubbles at the bonding interface by a release pressure against outgas from the transparent resin plate 71. When the printed layer 76 is provided on the periphery of the front transparent member 70, the second adhesive sheet 22 also functions as a cushion layer (step absorption layer) for suppressing the retention of air bubbles in the vicinity of the print step of the printed layer and the display unevenness caused by the print step.

In order to resist outgassing from the transparent resin plate, the second adhesive sheet 22 needs to have appropriate hardness at high temperature. Specifically, the storage elastic modulus G 'at 105 ℃ is preferably set at the portion of the second adhesive sheet 22 bonded to the transparent resin plate 71 of the front transparent member 70'₁₀₅Is 3 x 10⁴Pa or more, more preferably 5X 10⁴Pa or more, more preferably 6X 10⁴Pa or above.

In the present specification, the storage elastic modulus G' is obtained by reading a value at a predetermined temperature measured at a temperature rise rate of 5 ℃/min within a range of-50 to 150 ℃ under a frequency of 1Hz according to the method described in JIS K7244-1 "test method for Plastic-dynamic mechanical Properties".

The second adhesive sheet 22 may be a laminated adhesive sheet obtained by laminating a plurality of adhesive layers. For example, G 'may be used'₁₀₅The pressure-sensitive adhesive having the above range is used as a pressure-sensitive adhesive layer located at a portion to be bonded to the transparent resin plate 71, and a relatively flexible pressure-sensitive adhesive layer is laminated on the transparent film substrate 25 side, so that the second pressure-sensitive adhesive sheet has cushioning properties as a whole. When the second adhesive sheet is composed of a single adhesive layer, G 'of the second adhesive sheet is preferable'₁₀₅Within the above range. When the storage elastic modulus of the second adhesive sheet is too high, display unevenness may occur due to a print step at the peripheral edge of the front transparent member. Thus, storage at 105 ℃ of the second adhesive sheetElastic modulus G'₁₀₅Preferably 2X 10⁵Pa or less, more preferably 1X 10⁵Pa or less.

By using a pressure-sensitive adhesive sheet having a storage elastic modulus at room temperature smaller than that of the second pressure-sensitive adhesive sheet 22 as the first pressure-sensitive adhesive sheet 21, stress at the bonding interface of the transparent resin plate 71 can be relaxed, and peeling of the edge portion due to warping of the transparent resin plate 71 can be suppressed. Specifically, the storage elastic modulus G 'at 25 ℃ of the second adhesive sheet 22'₂₅Storage elastic modulus G 'of 25 ℃ or higher of the first adhesive sheet'₂₅. G 'of the second adhesive sheet 22'₂₅Preferably G 'of the first adhesive sheet 21'₂₅Large 5X 10³Pa or more, more preferably 1X 10 or more⁴Pa or above.

In the image display device of the present invention, since the front transparent plate contains a resin material, retention of moisture in the polarizing plate 10 can be suppressed, and a decrease in transmittance due to modification (e.g., polyalkylene) of polyvinyl alcohol constituting the polarizer 11 can be suppressed. On the other hand, a resin transparent plate has a smaller rigidity and a larger dimensional change during heating than a glass transparent plate, and therefore is likely to be warped. In particular, when the temperature returns from the heating environment to room temperature, stress is generated at the bonding interface with a temperature change, and the elastic modulus of the transparent resin plate is increased, so that warpage is likely to occur in the transparent resin plate. In addition, when a laminated resin sheet obtained by laminating resin layers containing different materials, such as a laminated sheet of an acrylic resin layer and a polycarbonate resin layer, is used as the transparent resin sheet, the amount of change in the size of the resin layer on the front surface and the back surface due to a change in temperature is different, and therefore warping is likely to occur. When the transparent resin plate is warped, the transparent resin plate may be peeled from the adhesive sheet at the peripheral edge (end face).

In the image display device of the present invention, since the storage elastic modulus of the bonded portion of the second adhesive sheet 22 and the transparent resin plate 71 is large, the retention of air bubbles at the bonding interface can be suppressed against the release pressure of outgas from the transparent resin plate 71 in a heated environment. In addition, since the storage elastic modulus of the second adhesive sheet 22 is relatively high, when returning from a heated environment to room temperature (around 25 ℃), the stress at the bonding interface of the transparent resin plate 71 and the second adhesive sheet 22 is cancelled out, and warping of the transparent resin plate can be suppressed. Further, since the transparent film base material 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, it is possible to absorb/dissipate stress at the bonding interface of the transparent resin plate 71 and the second adhesive sheet 22 to suppress warping.

As described above, in the image display device of the present invention, the resin material is used for the front transparent member, whereby the deterioration of the polarizing plate in a high-temperature environment can be suppressed. The problem of outgassing and warpage due to the resin material can be solved by bonding the polarizing plate 10 to the transparent resin plate 71 using a base-attached laminated adhesive sheet 20 having a transparent film base 25 between two

adhesive sheets

21 and 22 having predetermined viscoelastic properties.

G 'of the first adhesive sheet 21 for preventing adhesion of the adhesive to a dicing blade or the like when the adhesive sheet or the adhesive-attached polarizing plate is cut to a predetermined size and ensuring initial adhesive properties at the time of adhesion'₂₅Preferably 1X 10⁴Pa～2×10⁵Pa, more preferably 5X 10⁴Pa～1.5×10⁵Pa. G 'of the second adhesive sheet 22 as described above'₂₅Preferably greater than G 'of the first adhesive sheet 21'₂₅And is 1X 10⁴Pa or above. G 'of the second adhesive sheet 22'₂₅Preferably 3X 10⁴Pa～8×10⁵Pa, more preferably 5X 10⁴Pa～5×10⁵Pa, more preferably 7X 10⁴Pa～3×10⁵Pa。

The storage elastic modulus G 'at 105 ℃ of each of the first adhesive sheet 21 and the second adhesive sheet 22 is considered from the viewpoint of suppressing the protrusion of the adhesive sheet from the end face in a heating environment during heating at the time of bonding the second adhesive sheet 22 to the front transparent member 70 or during actual use of the image display device'₁₀₅Preferably 5X 10³Pa～2×10⁵Pa, more preferably 8X 10³Pa～1.5×10⁵Pa。

To have step absorption of printing step by functioning as a buffer layerThickness d of second adhesive sheet 22₂Preferably 50 μm or more, more preferably 70 μm or more, and further preferably 80 μm or more. The upper limit of the thickness of the second psa sheet 22 is not particularly limited, but is preferably 500 μm or less from the viewpoint of psa sheet productivity, prevention of edge-face protrusion, and the like. In the case where the second adhesive sheet is a laminate sheet of a plurality of adhesive layers, the thickness of the adhesive layer provided in contact with the transparent resin plate 71 is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more, from the viewpoints of resistance to outgassing from the transparent resin plate 71 and suppression of warpage.

Thickness d of first adhesive sheet 21₁Preferably 3 to 50 μm, more preferably 5 to 40 μm, and still more preferably 10 to 30 μm. The thickness of the first adhesive sheet 21 is preferably smaller than the thickness of the second adhesive sheet 22. Thickness d of first adhesive sheet 21₁Thickness d of second adhesive sheet 22₂Ratio of d₁/d₂Preferably 0.5 or less, more preferably 0.3 or less, and still more preferably 0.2 or less.

(composition of adhesive)

The composition of the adhesive is not particularly limited as long as the first adhesive sheet 21 and the second adhesive sheet 22 have the above-described characteristics, and an adhesive having a polymer such as a rubber, e.g., an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyvinyl ether, a vinyl acetate/vinyl chloride copolymer, a modified polyolefin, an epoxy resin, a fluorine-containing resin, a natural rubber, or a synthetic rubber, as a base polymer can be appropriately selected and used.

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

As the acrylic polymer, an acrylic polymer having a monomer unit of an alkyl (meth) acrylate as a main skeleton is preferably used. In the present specification, "(meth) acrylic acid" means acrylic acid and/or methacrylic acid. The alkyl (meth) acrylate preferably has an alkyl group having 1 to 20 carbon atoms.

The alkyl group of the alkyl (meth) acrylate may have a branch. As the branched alkyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, isodecyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate, and the like are preferably 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, based on 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) acrylates, or may be a copolymer of a linear alkyl (meth) acrylate and a branched alkyl (meth) acrylate. The arrangement of the constituent monomer units in the copolymer may be random or block.

The acrylic polymer may contain a polyfunctional monomer component as a constituent monomer component. By having a polyfunctional monomer as a comonomer component, the storage elastic modulus of the adhesive tends to be increased. The storage elastic modulus of the first adhesive sheet and the second adhesive sheet can be adjusted to a desired range by changing the kind and content of the polyfunctional monomer component. The polyfunctional monomer is a monomer having at least 2 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 has a function of receiving a radical from a growing polymer chain to stop the extension of the polymer, and a function of initiating polymerization again by attacking a monomer with the chain transfer agent monomer receiving the radical. By using the chain transfer agent, the increase in molecular weight can be suppressed without decreasing the radical concentration in the reaction system, and the storage elastic modulus of the adhesive sheet tends to be low. As the chain transfer agent, for example, thiols such as α -thioglycerol, lauryl thiol, glycidyl thiol, thioglycolic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2, 3-dimercapto-1-propanol are preferably used.

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

In the adhesive constituting the second adhesive sheet 22, the base polymer preferably contains a highly polar monomer unit such as a nitrogen-containing monomer in addition to the above alkyl (meth) acrylate and hydroxyl group-containing monomer unit. By containing a high-polarity monomer unit such as a nitrogen-containing monomer unit in addition to the hydroxyl group-containing monomer unit, the pressure-sensitive adhesive has high adhesiveness and holding power, and tends to suppress clouding in a high-temperature and high-humidity environment.

The acrylic base polymer can be produced by a known polymerization method such as solution polymerization, UV (ultraviolet) polymerization, bulk polymerization, and emulsion polymerization. From the viewpoint of transparency, water resistance, cost, and the like of the adhesive, solution polymerization or active energy ray polymerization (e.g., UV polymerization) is preferable. As a solvent for the solution polymerization, ethyl acetate, toluene, or the like is generally used.

A crosslinked structure may be introduced into the base polymer of the ultraviolet curing type adhesive. By introducing a crosslinked structure, the storage elastic modulus of the adhesive sheet tends to be increased. The formation of the crosslinked structure is performed, for example, by adding a crosslinking agent and heating after the polymerization of the base polymer. As crosslinking agents, it is possible to use isocyanatesCrosslinking agent, epoxy crosslinking agent,

A crosslinking agent generally used such as an oxazoline-based crosslinking agent, an aziridine-based crosslinking agent, a carbodiimide-based crosslinking agent, or a metal chelate-based crosslinking agent. In addition, a radical polymerizable functional group can be introduced into the base polymer by mixing a radical polymerizable compound having a functional group capable of bonding to a functional group of the base polymer and a radical polymerizable functional group with the base polymer. As the functional group capable of bonding with the functional group of the base polymer, an isocyanate group is preferable. The isocyanate group forms a urethane bond with a hydroxyl group of the base polymer, and therefore introduction of a radical polymerizable functional group into the base polymer can be easily performed.

For the purpose of adjusting the adhesive force, a silane coupling agent and a tackifier may be contained in the adhesive composition. The pressure-sensitive adhesive composition may contain additives such as a plasticizer, a softening agent, a deterioration inhibitor, a filler, a colorant, an antioxidant, a surfactant, and an antistatic agent.

The adhesive constituting the first adhesive sheet 21 and/or the second adhesive sheet 22 may be a photocurable type or a thermosetting type adhesive. When a curable adhesive containing an unpolymerized component is used as the second adhesive sheet 22, the adhesive is likely to enter the vicinity of the step due to a small storage elastic modulus and high fluidity when it is bonded to the front transparent plate 71, and the incorporation of air bubbles in the vicinity of the step can be suppressed. If curing is performed after bonding, the storage elastic modulus increases, and therefore the second psa sheet 22 can be made to have the above-described resistance to outgassing and the effect of suppressing warping.

The curable adhesive is preferably photocurable in view of easy curing after bonding to the front transparent member. As the method of photocuring, a method of irradiating a system containing a photocurable compound and a photopolymerization initiator with active light such as ultraviolet light is preferable. In particular, a system using an ethylenically unsaturated compound and a photo radical generator is preferable in terms of high photosensitivity and abundance of selectable materials.

When the adhesive of the second adhesive sheet 22 is a photocurable adhesive, the content of the photocurable compound is preferably 0.01 to 50 parts by weight, and more preferably 0.05 to 30 parts by weight, based on 100 parts by weight of the entire adhesive composition. In order to adjust the storage elastic modulus of the cured adhesive to an appropriate range, the content of the photocurable polyfunctional monomer in the adhesive composition is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and still more preferably 2 parts by weight or less, based on 100 parts by weight of the entire adhesive composition.

The pressure-sensitive adhesive sheet can be obtained by, for example, applying the pressure-sensitive adhesive composition to a substrate and, if necessary, drying the solvent. As the substrate, the transparent film substrate 25 may be used, or another substrate may be used. Examples of the coating method include roll coating, roll lick coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, blade coating, air knife coating, curtain coating, lip die coating, extrusion coating using a die coater, and the like. Among these, a die coater is preferably used, and particularly, a die coater using an injection die or a slit die is more preferably used.

In the case where the base polymer of the adhesive composition is a solution polymerization polymer, it is preferable to perform drying of the solvent after coating. As the drying method, an appropriate method can be adopted according to the purpose. The heating and drying temperature is preferably 40 to 200 ℃, more preferably 50 to 180 ℃, and still more preferably 70 to 170 ℃. The drying time may be suitably employed. 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.

In the case where the adhesive composition contains a crosslinking agent, crosslinking may be performed by heating after coating onto a substrate. The heating temperature and the heating time may be appropriately set according to the kind of the crosslinking agent used, and the crosslinking is usually performed by heating at 20 to 160 ℃ for about 1 minute to about 7 days. The heating for drying the adhesive after coating may also serve as the heating for crosslinking.

A protective sheet is releasably stuck to the adhesive sheet as required. The protective sheet is used for protecting an exposed surface of the pressure-sensitive adhesive before the pressure-sensitive adhesive is used for bonding to an adherend. The substrate used in the formation (coating) of the adhesive layer may be used as it is as a protective sheet for the adhesive layer.

[ formation of image display device ]

The polarizing plate 10 is bonded to the surface of the image display unit 50 via the unit-side adhesive sheet 30, and the polarizing plate 10 and the front transparent member 70 are bonded to each other with the first adhesive sheet 21 and the second adhesive sheet 22 with the transparent film base 25 interposed therebetween, thereby obtaining an image display device.

The order of application is not particularly limited. As shown in fig. 2, if a double-sided adhesive-equipped polarizing plate is used in which a cell-side adhesive sheet 30 is provided on one surface of the polarizing plate 10 and a first adhesive sheet 21, a transparent film substrate 25, and a second adhesive sheet are provided on the other surface, the step of attaching a separate adhesive sheet to the polarizing plate after the polarizing plate is attached to the surface of the image display cell can be omitted, and the manufacturing process of the image display device can be simplified.

A method of disposing the first adhesive sheet 21, the transparent film substrate 25, and the second adhesive sheet 22 on the polarizing plate 10 is not particularly limited. As shown in fig. 3, a substrate-attached laminated adhesive sheet 20 in which a first adhesive sheet 21 is provided on one surface of a transparent film substrate 25 and a second adhesive sheet 22 is provided on the other surface is preferably formed in advance, and the substrate-attached laminated adhesive sheet 20 is bonded to a polarizing plate 10.

In the laminated psa sheet with a substrate 20,

protective sheets

41 and 42 are preferably temporarily attached to the surface of the first psa sheet 21 and the surface of the second psa sheet 22, respectively, as shown in fig. 3. By peeling off the protective sheet 41 provided on the surface of the first adhesive sheet 21 and bonding the same to the polarizing plate 10, a polarizing plate with an adhesive can be obtained in which the first adhesive sheet 21, the transparent film substrate 25, and the second adhesive sheet 22 are provided on the polarizing plate 10, and the protective sheet 42 is temporarily bonded to the surface of the second adhesive sheet 22. In the polarizing plate with a double-sided adhesive, as shown in fig. 2, a protective sheet 43 is preferably temporarily attached to the surface of the unit-side adhesive sheet.

As the constituent material of the

protective sheets

41, 42, 43 temporarily attached to the surface of the pressure-sensitive adhesive sheet, a plastic film of polyethylene, polypropylene, polyethylene terephthalate, or the like is preferably used. The thickness of the protective sheet is generally from about 5 μm to about 200 μm, preferably from about 10 μm to about 150 μm. The peeling property from the adhesive can be improved by appropriately performing a peeling treatment such as a silicone treatment, a long chain alkyl treatment, or a fluorine treatment on the pasting surface (attached surface) of the protective sheet with the adhesive sheet.

In the case of the polarizing plate using the double-sided adhesive tape shown in fig. 2, the order of lamination is not particularly limited. The image display unit 50 side may be bonded first, or the front transparent member 70 side may be bonded first. Further, the bonding of both may be performed simultaneously. From the viewpoint of improving the workability of bonding and the axis accuracy of the polarizing plate, it is preferable to perform a unit-side bonding step of peeling the protective sheet 43 from the surface of the unit-side adhesive sheet 30, bonding the polarizing plate 10 to the image display unit 50 via the adhesive sheet 30, and then peel the protective sheet 42 from the surface of the second adhesive sheet 22, and bonding the polarizing plate 10 to the front transparent member 70 via the laminated adhesive sheet 20 with a base material.

After the polarizing plate 10 and the front transparent member 70 are bonded to each other, defoaming is preferably performed to remove air bubbles in the vicinity of an uneven portion such as the interface between the second adhesive sheet 22 and the front transparent member 70 and the printed layer 76 of the front transparent member 70. As the defoaming method, an appropriate method such as heating, pressurization, and depressurization can be employed. For example, it is preferable that: bonding is performed while suppressing mixing of bubbles under reduced pressure and heating, and then pressurization is performed while heating by autoclave treatment or the like in order to suppress delayed foaming or the like. When the pressure-sensitive adhesive sheet is a photocurable type or a thermosetting type, the pressure-sensitive adhesive is preferably cured after being bonded to the front transparent member and subjected to heat treatment.

Examples

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

[ preparation of adhesive composition ]

< adhesive A >

Charging a reaction vessel with 2-ethylhexyl acrylate (2 EHA): 65 parts by weight of N-vinylpyrrolidone (NVP): 15 parts by weight, hydroxyethyl acrylate (HEA): 20 parts by weight and 1-hydroxycyclohexyl phenyl ketone ("IRGACURE 184" manufactured by BASF) as a photopolymerization initiator: 0.1 part by weight of an ultraviolet ray was irradiated under a nitrogen atmosphere to obtain a prepolymer composition having a polymerization rate of 10%. To 100 parts by weight of this prepolymer composition, 2-dimethoxy-1, 2-diphenylethan-1-one (IRGACURE 651/IRG 651 manufactured by BASF) was added as a photopolymerization initiator: 0.2 part by weight of 1, 6-hexanediol diacrylate (NK ester A-HD-N manufactured by Mitsumura chemical industries, Ltd.): 0.3 part by weight and 3-glycidoxypropyltrimethoxysilane ("KBM-403" manufactured by shin-Etsu chemical) as a silane coupling agent: 0.3 part by weight, and mixed uniformly, thereby preparing an adhesive composition a.

< adhesive B >

The amount of the polyfunctional monomer added in the adhesive composition was changed to 0.09 parts by weight. Except for this, adhesive composition B was prepared in the same manner as in the preparation of adhesive composition a.

< adhesive C >

0.2 parts by weight of alpha-Thioglycerol (TGR) was added as a chain transfer agent. Except for this, adhesive composition C was prepared in the same manner as in the preparation of adhesive composition B.

< adhesive D >

The composition of the feed monomers in the preparation of the prepolymer composition was changed to 2 HEA: 55 parts by weight, NVP: 25 parts by weight and HEA: 20 parts by weight, the amount of the polyfunctional monomer added in the adhesive composition was changed to 0.7 part by weight. Except for this, adhesive composition D was prepared in the same manner as in the preparation of adhesive composition a.

< adhesive E >

The composition of the charge monomers in the preparation of the prepolymer composition was changed to Butyl Acrylate (BA): 57 parts by weight, cyclohexyl acrylate (CHA): 12 parts by weight, HEA: 8 parts by weight and 4-hydroxybutyl acrylate (4 HBA): 23 parts by weight, the polyfunctional monomer added to the adhesive composition was changed to dipentaerythritol hexaacrylate ("KAYARAD DPHA" manufactured by Nippon chemical Co., Ltd.): 0.12 part by weight. Except for this, adhesive composition E was prepared in the same manner as in the preparation of adhesive composition a.

< adhesive F >

The monomer components BA: 95 parts by weight, Acrylic Acid (AA): 4.9 parts by weight and HEA: 0.1 parts by weight, and Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator: 0.2 part by weight and 233 parts by weight of ethyl acetate were put into a reaction vessel, and stirred at 23 ℃ for 1 hour under a nitrogen atmosphere, followed by nitrogen substitution. Then, the reaction was carried out at 60 ℃ for 5 hours to obtain an acrylic base polymer. To this acrylic base polymer solution was added trimethylolpropane toluene diisocyanate ("Coronate L" manufactured by the japanese polyurethane industry) as an isocyanate-based crosslinking agent: 0.6 part by weight and KBM-403 as a silane coupling agent: 0.3 parts by weight, and then mixed uniformly to prepare an adhesive composition F (solution).

< adhesive G (cell-side adhesive) >

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

[ production of Single-layer adhesive sheet ]

< pressure-sensitive adhesive sheets A to E >

The pressure-sensitive adhesive composition a was applied to the release-treated surface of a separator (polyester film release-treated with polysiloxane on one side) so as to have a thickness of 250 μm, thereby forming a coating layer, and the release-treated surface of the other separator was bonded to the coating layer. Then, the irradiation intensity was controlled so that the irradiation surface directly below the lamp was 5mW/cm²The black light lamp with the position adjusted performs UVIrradiating until the cumulative light amount reaches 3000mJ/cm²Polymerization was allowed to proceed to obtain a psa sheet a1 with separators temporarily attached to both sides.

A psa sheet a2 was obtained in the same manner as described above, except that the coating thickness was changed to 20 μm. Adhesive sheet B1 (thickness 250 μm) using adhesive composition B, adhesive sheet C1 (thickness 250 μm) and adhesive sheet C2 (thickness 20 μm) using adhesive composition C, adhesive sheet D1 (thickness 250 μm) using adhesive composition D, adhesive sheet E1 (thickness 250 μm), adhesive sheet E2 (thickness 100 μm) and adhesive sheet E3 (thickness 500 μm) using adhesive composition E were produced by changing the kind and thickness of the adhesive composition.

< adhesive sheet F >

The pressure-sensitive adhesive composition F was applied to the release-treated surface of the separator so that the thickness after drying was 250 μm, and the solvent was removed by heating at 100 ℃. Then, the resultant was heated at 50 ℃ for 48 hours to effect crosslinking treatment, thereby obtaining a pressure-sensitive adhesive sheet F1 having a thickness of 250 μm.

< measurement of storage elastic modulus >

For each of the adhesive compositions a to F, a single-layer adhesive sheet having a thickness of 250 μm was produced, and a plurality of adhesive sheets were laminated to produce an adhesive sheet having a thickness of about 1.5mm, which was used as a sample for measurement. Dynamic viscoelasticity measurement was performed using an Advanced Rheological Expansion System (ARES) manufactured by Rheometric Scientific under the following conditions, and the storage elastic modulus (G ') at 25 ℃, 50 ℃ and 105 ℃ was read from the measurement results'₂₅、G’₅₀And G'₁₀₅)。

(measurement conditions)

Deformation mode: torsion

Measuring frequency: 1Hz

Temperature rise rate: 5 ℃ per minute

Measuring temperature: in the range of-50 ℃ to 150 ℃

Shape: parallel plates

The compositions of the adhesive compositions a to F and the measurement results of the storage elastic modulus of the respective adhesive sheets are listed in table 1.

TABLE 1

[ production of polarizing plate with adhesive on one side ]

The pressure-sensitive adhesive composition G was applied to the release-treated surface of the separator so that the thickness after drying was 20 μm, and the solvent was removed by heating at 100 ℃. Then, the sheet was heated at 50 ℃ for 48 hours to carry out a crosslinking treatment, thereby obtaining a unit-side adhesive sheet.

A polarizing plate was used which had a triacetyl cellulose (TAC) transparent protective film having a thickness of 40 μm on one surface of a polarizer comprising a stretched polyvinyl alcohol film impregnated with iodine and having a thickness of 25 μm and an acrylic transparent protective film having a thickness of 30 μm on the other surface. The above-mentioned unit-side adhesive sheet was bonded to the acrylic protective film-side surface (unit-side surface) of the polarizing plate using a roll laminator, thereby obtaining a polarizing plate having an adhesive sheet on one surface of the polarizing plate.

[ example 1]

< preparation of laminated pressure-sensitive adhesive sheet with substrate >

The psa sheet a1 was bonded to a hardcoat-forming side of a 40 μm thick Triacetylcellulose (TAC) film having a hardcoat layer on one side, and the psa sheet F1 was bonded to the other side, thereby producing a laminated psa sheet with a substrate having a TAC substrate film between two psa sheets.

< preparation of polarizing plate with double-sided adhesive >

The surface of the single-sided pressure-sensitive adhesive-equipped polarizing plate without the pressure-sensitive adhesive sheet (TAC transparent protective film side) was bonded to the pressure-sensitive adhesive sheet F1 side surface of the substrate-equipped laminated pressure-sensitive adhesive sheet, thereby obtaining a double-sided pressure-sensitive adhesive-equipped polarizing plate.

< preparation of Panel for evaluation >

The above polarizing plate with a double-sided adhesive was cut into a size of 200mm × 140mm, and then the separator on the unit-side adhesive sheet was peeled off, and the unit-side adhesive sheet was laminated with its surface at the center of a glass plate having a thickness of 0.7mm, and was bonded using a hand roller.

Then, the separator on the viewing side surface of the polarizing plate with the adhesive on both sides was peeled off, and the printed surface of the transparent resin plate having the black ink printed in a frame shape on the peripheral edge portion thereof was placed on the exposed surface of the adhesive (on the adhesive sheet a 1) and bonded by a vacuum thermocompression bonding apparatus (temperature 25 ℃, pressure in the apparatus 50Pa, pressure 0.3MPa, pressure holding time 10 seconds). Then, autoclave treatment (50 ℃, 0.5MPa, 15 minutes) was carried out to obtain a panel for evaluation. The transparent resin plate was a laminated transparent resin plate (1mm thick × 200mm × 140mm) of polymethyl methacrylate (PMMA) and Polycarbonate (PC), and had a black ink printing surface on the PC side surface (ink printing thickness: 10 μm, ink printing widths on both short sides (long side direction): 15mm each, and ink printing widths on both long sides (short side direction): 5mm each).

Examples 2 to 6 and comparative examples 1 to 3

The composition of the laminated adhesive sheet with a substrate was changed as shown in table 2. Except for this, a simulation image display device for evaluation was produced by the same procedure as in example 1.

[ example 7]

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

[ examples 8 and 9]

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

Comparative example 4

In the production of the polarizing plate with a double-sided adhesive, a single layer of the adhesive sheet a1 was used instead of the laminated adhesive sheet as the adhesive sheet on the viewing side of the polarizing plate. Except for this, a panel for evaluation was produced by the same procedure as in example 1.

Comparative example 5

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

Comparative example 6

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

[ evaluation ]

< air bubble >

The vicinity of the inner side of the black ink printed layer of the evaluation panel was observed with a digital microscope at a magnification of 20 times, and it was confirmed whether or not air bubbles were present in the adhesive sheet. The one with no bubble was regarded as "ok", and the one with no bubble was regarded as "not".

< Heat test >

The single-chip transmittance ( body water vapor transmission rate) (Y value obtained by performing visual acuity correction using a 2-degree field of view (C light source) of JlS Z8701) at the center portion in the plane of the panel for evaluation was measured. The evaluation panel after the single sheet transmittance was measured was put into a hot air oven at 105 ℃ and taken out after 500 hours, and was naturally cooled to room temperature, and then the following evaluation was performed.

(transmittance change)

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

(adhesive Release)

The evaluation panel was observed from the side in the longitudinal direction, and it was confirmed whether or not the glass plate was peeled from the front transparent plate at the end. For the person who confirmed peeling, the amount of peeling (distance from the end) from the end was measured. The one not confirmed as peeling was regarded as 0 in the amount of peeling.

(inner surface bubble)

The appearance of the central portion in the plane of the evaluation panel was visually confirmed from the front transparent plate side, and the portion where bubbles were confirmed was observed with a digital microscope. Those with no bubble and those with bubbles confirmed are both centered on foreign matter or with diameters smaller than 300 μm are referred to as "ok", and those with bubbles of diameters 300 μm or more, which are not centered on foreign matter, are referred to as "not ok".

[ evaluation results ]

The composition of the laminated adhesive sheet with a base material used for bonding the polarizing plate and the front transparent plate in each of the above examples and comparative examples (in which comparative examples 4 and 5 are single-layer adhesive sheets), the thickness and storage elastic modulus of each adhesive sheet (single layer), the material and thickness of the front transparent plate, and the 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 heat test, and the transmittance at the central portion in the panel plane was greatly reduced. In comparative example 4, no decrease in transmittance was observed after the heat test, but warpage occurred in the resin plate, and peeling occurred at the interface between the resin plate and the adhesive at the panel end.

In examples 1 to 9 and comparative examples 1 to 3, in which laminated adhesive sheets with substrates having adhesive sheets on both sides of a substrate film were used for bonding a polarizing plate and a resin plate, no decrease in transmittance after a heat test was observed, and peeling of the resin plate at the panel edge was also suppressed. In comparative example 6 in which a polarizing plate and a glass plate were bonded to each other with a laminated adhesive sheet with a base material, a decrease in transmittance due to discoloration of the polarizing plate was observed after a heat test in the same manner as in comparative example 5.

From the above results, it is understood that deterioration due to polyalkyleneition or the like of the polarizing plate can be suppressed even after a heating test at 100 ℃. It is found that, in the case of using a transparent resin plate, although peeling may occur due to warping of the transparent resin plate, warping can be suppressed by using a laminated adhesive sheet with a base material.

When example 1 using the same laminated adhesive sheet was compared with examples 8 and 9, the amount of peeling due to warping was reduced in examples 8 and 9 in which the thickness of the resin plate was large. The same tendency was observed also in the comparison between example 3 and example 7. From these results, it is understood that the warpage due to temperature change can be reduced by increasing the thickness of the resin plate.

Storage elastic modulus G 'at 25 ℃ of use'₂₅In comparative example 3, which is a large adhesive sheet a2 and is the first adhesive sheet (adhesive sheet 1) disposed between a polarizing plate and a film substrate, the peeling caused by the warping of the resin plate was smaller than in comparative example 4, but the amount of peeling was larger than in examples 1 to 6. Examples 1 to 6 and comparative example 3 use the same resin plate, and it is understood that the amount of peeling of the resin plate due to warping varies depending on the type of adhesive sheet.

Specifically, as is clear from comparison of example 3 and comparative example 3 in which the types of the second adhesive sheets are the same and the types of the first adhesive sheets are different, G 'of the first adhesive sheet'₂₅If the amount is small, the stress is relaxed, and peeling due to warpage can be suppressed. Further, as is clear from comparison of example 1 and example 2 in which the types of the first adhesive sheets were the same and the types of the second adhesive sheets were different, G 'of the second adhesive sheet'₂₅In the case of a large size, peeling due to warpage can be suppressed. From these results, it can be said that G 'in the second adhesive sheet'₂₅G 'of greater than first adhesive sheet'₂₅In the case of (3), the effect of suppressing peeling due to warpage is high.

In comparative example 1 in which the adhesive sheet C1 having a small storage elastic modulus at a high temperature was used as the second adhesive sheet (adhesive sheet 2) provided between the resin plate and the film substrate, bubbles were observed at the interface between the adhesive sheet and the resin plate after the heat test. In comparative example 6 in which glass plates were bonded using the same adhesive sheet, bubbles were not observed, and it is considered that outgas generated by heating the resin plate was accumulated at the interface between the resin plate and the adhesive sheet in comparative example 3. In examples 1 to 8, although the resin plate was used, the retention of bubbles was not observed. From these results, it is found that when the storage elastic modulus of the second pressure-sensitive adhesive sheet at high temperature is large, the pressure for releasing outgas can be resisted, and the retention of air bubbles at the interface can be suppressed. On the other hand, in comparative example 2, the storage elastic modulus of the second adhesive sheet was too high, and therefore the step height absorption of the adhesive sheet was insufficient, and bubble retention was observed in the vicinity of the printing step height of the transparent resin plate.

As a result of summarizing the above, it has been found that by using a resin plate as the front transparent member provided on the surface of the image display unit, it is possible to suppress a decrease in transmittance due to deterioration of the polarizing plate, and by bonding the polarizing plate and the resin plate via a laminated adhesive sheet having a base material of a transparent film between two adhesive sheets, it is possible to suppress peeling of the resin plate due to warping. Further, it is found that, by providing the adhesive sheet constituting the laminated adhesive sheet with a predetermined storage elastic modulus, peeling due to warping of the resin sheet can be further suppressed, retention of outgas from the resin sheet at the bonding interface can be suppressed, and mixing of bubbles in the vicinity of the printing step due to the step absorbability can be also suppressed.

Claims

1. An image display device in which an image display panel having a polarizing plate on the surface of an image display unit is integrated with a front transparent member,

a transparent film base material is bonded to the polarizing plate of the image display panel via a first adhesive sheet, and the front transparent member is bonded to the transparent film base material via a second adhesive sheet,

the front surface transparent member comprises a transparent resin plate in contact with the second adhesive sheet,

the second adhesive sheet has a thickness of 50 [ mu ] m or more, and the adhesive in the portion of the second adhesive sheet bonded to the front transparent member has a storage elastic modulus at 105 ℃ of 3X 10⁴Pa or more, and

the second adhesive sheet has a storage elastic modulus at 25 ℃ that is greater than the storage elastic modulus at 25 ℃ of the first adhesive sheet.

2. The image display device according to claim 1, wherein the second adhesive sheet has a storage elastic modulus at 25 ℃ of 1 x 10⁴Pa or above.

3. The image display device according to claim 1, wherein the second adhesive sheet has a storage elastic modulus at 105 ℃ of 2 x 10⁵Pa or less.

4. The image display device according to claim 1, wherein the thickness of the first adhesive sheet is 5 μm to 50 μm.

5. The image display device according to any one of claims 1 to 4, wherein the thickness d of the first adhesive sheet₁And the thickness d of the second adhesive sheet₂Ratio of d₁/d₂Is 0.5 or less.