JP2018091974A - Polarizing plate with adhesive, and image display device - Google Patents

Abstract

A polarizing plate with an adhesive which is used between a front transparent member such as a front transparent plate or a touch panel and an image display cell, and which can achieve both a thinner image display device and high durability of a polarizer. I will provide a. A polarizing plate (1) with an adhesive comprises a polarizer (11) made of a polyvinyl alcohol-based film containing iodine, and a transparent protective film (15) bonded to a first main surface of the polarizer. And a front-side pressure-sensitive adhesive sheet (20) provided in contact with the second main surface of the polarizer. The front-side pressure-sensitive adhesive sheet is a laminated pressure-sensitive adhesive sheet in which at least two pressure-sensitive adhesive layers are laminated, and a first pressure-sensitive adhesive layer (21) disposed in contact with the polarizer and a second pressure-sensitive adhesive layer disposed apart from the polarizer. A second adhesive layer (22). The storage elastic modulus G'80 at 80C of the front-side pressure-sensitive adhesive sheet is preferably 1 x 105 Pa or less, and the moisture permeability of the first pressure-sensitive adhesive layer is preferably 150 g / m2 · 24 h or less. [Selection diagram] Fig. 1

Description

  The present invention relates to a polarizing plate with an adhesive used for forming an image display device including a transparent plate, a touch panel and the like on the front surface of an image display panel. Furthermore, this invention relates to the image display apparatus using the said polarizing plate with an adhesive.

  Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile phones, smart phones, car navigation devices, personal computer monitors, and televisions. For the purpose of preventing damage to the image display panel due to impact from the outer surface, a front transparent plate (also referred to as “window layer” or the like) such as a transparent resin plate or a glass plate is provided on the viewing side of the image display panel. Sometimes. 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 member such as a front transparent plate or a touch panel on the front surface of the image display panel, the polarizing plate disposed on the viewing side surface of the image display panel and the front transparent member are bonded together with an adhesive. An “interlayer filling structure” has been proposed. In the interlayer filling structure, since the space between the polarizing plate and the front transparent member is filled with the adhesive, the difference in the refractive index at the interface is reduced, and the reduction in visibility due to reflection and scattering is suppressed.

  A colored layer (decorative printing layer) for the purpose of decoration and light shielding is formed on the peripheral edge of the panel-side surface of the front transparent member. When an adhesive is bonded to a transparent member having a decorative print layer, bubbles are likely to be generated around the printing step portion. In addition, local stress is applied to the image display panel directly below the stepped portion of the print through the adhesive, and mechanical distortion occurs at the edge of the screen, which may cause display unevenness at the periphery of the screen. is there.

  In order to solve these problems caused by printing steps, a soft and thick adhesive sheet is used as an interlayer filler (see, for example, Patent Document 1). In Patent Document 2, a film with a double-sided pressure-sensitive adhesive comprising a pressure-sensitive adhesive layer for bonding to an image display panel on one surface of a polarizing plate and a pressure-sensitive adhesive layer for interlayer filling having a predetermined storage elastic modulus on the other surface Has been proposed.

JP2011-219665A JP 2014-115468 A

  In mobile display applications such as mobile phones and smartphones that are often used outdoors, the use of an interlayer filling structure using an adhesive is spreading. In mobile displays, there is a great demand for thinner and lighter components, and displays that employ an interlayer filling structure are also required to be thinner. However, since the pressure-sensitive adhesive layer used as an interlayer filler is required to have a step absorbability, there is a limit to reducing the thickness of the pressure-sensitive adhesive layer.

  The present inventors use a single protective polarizing plate having a protective film only on one side of the polarizer as a polarizing plate provided on the viewing side of the image display panel, and directly laminate an adhesive as an interlayer filler on the polarizer. I tried to make it thinner. However, it has been found that in the configuration in which the conventional interlayer filling pressure-sensitive adhesive sheet is provided on the polarizer without a protective film, the polarizer fades in the humidification durability test, and there is a problem in durability. In view of this problem, an object of the present invention is to provide a polarizing plate with an adhesive that can achieve both reduction in thickness and humidification durability of an image display device.

  The above problem can be solved by providing a laminated pressure-sensitive adhesive sheet in which a low-moisture-permeable pressure-sensitive adhesive layer and a pressure-sensitive adhesive layer having a predetermined viscoelastic behavior are laminated on a polarizing plate.

  The polarizing plate with an adhesive of the present invention is in contact with a polarizer composed of a polyvinyl alcohol film containing iodine, a transparent protective film bonded to the first main surface of the polarizer, and a second main surface of the polarizer. A front-side pressure-sensitive adhesive sheet provided. The front-side pressure-sensitive adhesive sheet is a laminated pressure-sensitive adhesive sheet in which at least two pressure-sensitive adhesive layers are laminated, a first pressure-sensitive adhesive layer disposed in contact with the polarizer, and a second pressure-sensitive adhesive disposed away from the polarizer. And a layer.

Front-side pressure-sensitive adhesive sheet is preferably a storage elastic modulus G _'80 at 80 ° C. is not more than 1 × ¹⁰ 5 Pa. The front-side pressure-sensitive adhesive sheet preferably has a moisture permeability of 150 g / m ² · 24 h or less. The thickness of the front side pressure-sensitive adhesive sheet is preferably 250 μm or less. The front side pressure-sensitive adhesive sheet preferably has a ratio G ′ ₂₅ / G ′ ₈₀ of the storage elastic modulus G ′ _{80 at 80} ° C. and the storage elastic modulus G ′ ₂₅ at 25 ° C. of 2 to 100.

  The front-side pressure-sensitive adhesive sheet preferably has a light transmittance at a wavelength of 380 nm of 15% or less. For example, when at least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer contains an ultraviolet absorber, the front-side pressure-sensitive adhesive sheet can be provided with ultraviolet absorptivity.

The first pressure-sensitive adhesive layer provided in contact with the polarizer preferably has a moisture permeability of 150 g / m ² · 24 h or less. The thickness of the first pressure-sensitive adhesive layer is preferably 50 μm or less. In order to realize low moisture permeability with a small thickness, the first pressure-sensitive adhesive layer is preferably a pressure-sensitive adhesive layer containing a rubber-based polymer as a main component. In the first pressure-sensitive adhesive layer, the ratio G ′ ₂₅ / G ′ ₈₀ of the storage elastic modulus G ′ _{80 at 80} ° C. and the storage elastic modulus G ′ ₂₅ at 25 ° C. may be 3 or less.

  The thickness of the second pressure-sensitive adhesive layer provided away from the polarizer (provided on the side close to the front transparent member) is preferably 50 μm or more. The thickness of the second pressure-sensitive adhesive layer is preferably larger than the thickness of the first pressure-sensitive adhesive layer.

The second adhesive layer preferably has a storage elastic modulus G ′ _{25 at} 25 ° C. of 1 × 10 ⁴ or more, and preferably has a storage elastic modulus G ′ _{80 at} 80 ° C. of 1 × 10 ⁵ Pa or less. The second pressure-sensitive adhesive layer preferably has a ratio G ′ ₂₅ / G ′ ₈₀ of storage elastic modulus G ′ _{80 at 80} ° C. and storage elastic modulus G ′ ₂₅ at 25 ° C. of 3.5 or more. The second pressure-sensitive adhesive layer is preferably a pressure-sensitive adhesive layer containing an acrylic polymer as a main component.

  The polarizing plate with an adhesive of the present invention is preferably used by being disposed between a front transparent plate or a touch panel and an image display cell. The polarizing plate with the pressure-sensitive adhesive of the present invention may be a polarizing plate with a double-sided pressure-sensitive adhesive provided with a cell-side pressure-sensitive adhesive sheet on the transparent protective film.

  Furthermore, this invention relates to an image display apparatus provided with said polarizing plate with an adhesive, and a front transparent member on the surface of an image display cell. In the image display device of the present invention, a polarizing plate and a front transparent member such as a front transparent plate and a touch panel are bonded together by a front side adhesive sheet.

  As for the polarizing plate with an adhesive of this invention, the front side adhesive sheet is provided without the transparent protective film on the polarizer of the single protective polarizing plate in which the transparent protective film was provided only on one side of the polarizer. Therefore, it contributes to thinning of an image display apparatus provided with a polarizing plate between the front transparent member and the image display cell. Since the first pressure-sensitive adhesive layer of the front-side pressure-sensitive adhesive sheet has low moisture permeability, even when the image display device is exposed to a high-humidity environment, moisture transfer to the polarizer is suppressed, and the polarizer is less likely to fade. . In addition, by providing the second adhesive sheet on the first adhesive sheet, the front side adhesive sheet has step absorbability, and air bubbles are mixed near the printing step of the front transparent member, and display unevenness of the image display device is reduced. Can be suppressed.

It is typical sectional drawing showing one form of a polarizing plate with an adhesive. It is sectional drawing which represents typically one Embodiment of an image display apparatus. It is a typical sectional view showing one form of a polarizing plate with a double-sided adhesive. It is a microscope observation image in the humidification durability (edge part color omission) evaluation of a polarizing plate with an adhesive.

  FIG. 1 is a cross-sectional view showing one embodiment of a polarizing plate with an adhesive. The polarizing plate with an adhesive 1 includes a front-side adhesive sheet 20 on the first main surface of the polarizing plate 10. The front side pressure-sensitive adhesive sheet 20 is a pressure-sensitive adhesive sheet for attaching a front transparent member to the viewing side of the polarizing plate in the formation of the image display device. The front pressure-sensitive adhesive sheet 20 includes a first pressure-sensitive adhesive layer 21 disposed in contact with the polarizer 11 of the polarizing plate 10 and a second pressure-sensitive adhesive layer 22 provided on the first pressure-sensitive adhesive layer 21. The first pressure-sensitive adhesive layer 21 is disposed in contact with the polarizer 11 of the polarizing plate 10.

  FIG. 2 is a schematic cross-sectional view showing an embodiment of an image display device including a front transparent member on the viewing side surface. In the image display device 100, the polarizing plate 10 is disposed between the front transparent member 70 provided with the printing unit 76 on the transparent plate 71 and the image display cell 60. The polarizing plate 10 and the image display cell 60 are bonded together via the cell-side pressure-sensitive adhesive sheet 30, and the polarizing plate 10 and the front transparent member 70 are bonded together via the front-side pressure-sensitive adhesive sheet 20.

[Single protective polarizing plate]
As the polarizing plate 10, one having a transparent protective film 15 bonded to only one side of the polarizer 11 is used (hereinafter, the polarizing plate 10 having a transparent protective film provided only on one side of the polarizer is referred to as “single protective polarizing”. Sometimes referred to as “board”). By using a single protective polarizing plate as the polarizing plate disposed on the viewing side of the image display cell, the image display device can be thinned.

<Polarizer>
The polarizer 11 is a polyvinyl alcohol film containing iodine. As a material for the polyvinyl alcohol film applied to the polarizer, polyvinyl alcohol or a derivative thereof is used. Derivatives of polyvinyl alcohol 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 thereof, acrylamide and the like. Can be mentioned. Polyvinyl alcohol having a polymerization degree of about 1000 to 10000 and a saponification degree of about 80 to 100 mol% is generally used.

  A polarizer is obtained by subjecting the polyvinyl alcohol film to iodine staining and stretching treatment. The thickness of the polarizer is preferably about 1 to 50 μm. As the polarizer, a thin polarizer having a thickness of 10 μm or less can be used. Thin polarizers are described in, for example, JP-A-51-069644, JP-A-2000-338329, WO2010 / 100917, Japanese Patent No. 4691205, Japanese Patent No. 4751481, and the like. A polarizer can be mentioned. Such a thin polarizer can be obtained, for example, by a production method including a step of stretching a polyvinyl alcohol-based resin layer and a stretching resin base material in the state of a laminate and a step of dyeing with iodine.

<Transparent protective film>
A transparent protective film 15 for protecting the polarizer 11 is provided on one surface (first main surface) of the polarizer 11. The transparent protective film 15 may have functions such as an optical compensation film for the purpose of widening the viewing angle, a quarter wavelength plate for constituting a circularly polarizing plate together with the polarizer 11, and the like.

  Examples of the material constituting the transparent protective film 15 include resin materials that are excellent in transparency, mechanical strength, and thermal stability. Specific examples of such resin materials include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, Examples include (meth) acrylic resins, cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Although the thickness of the transparent protective film 15 is not specifically limited, About 5-100 micrometers is preferable from points, such as workability | operativity, such as intensity | strength and handleability, and thin film property. It is preferable that the polarizer 11 and the transparent protective film 15 are bonded together via an appropriate adhesive layer (not shown).

[Front side adhesive sheet]
The polarizing plate with the pressure-sensitive adhesive of the present invention includes a front-side pressure-sensitive adhesive sheet 20 on the surface of the single protective polarizing plate 10 on which the transparent protective film 15 is not provided. The front side adhesive sheet 20 is used for bonding the front transparent member 70 to the viewing side of the single protective polarizing plate 10. The front side pressure-sensitive adhesive sheet 20 is a laminated pressure-sensitive adhesive sheet having at least two pressure-sensitive adhesive layers. The first pressure-sensitive adhesive layer 21 is provided in contact with the polarizer 11, and the second pressure-sensitive adhesive layer 22 is provided on the first pressure-sensitive adhesive layer 21. When the front-side pressure-sensitive adhesive sheet 20 is composed of two layers, a first pressure-sensitive adhesive layer 21 and a second pressure-sensitive adhesive layer 22, the pressure-sensitive adhesive polarizing plate 1 is formed on the piece protective polarizing plate 10 with the first pressure-sensitive adhesive layer 21 and the first pressure-sensitive adhesive layer 21. The two adhesive layers 22 are provided in this order.

The front pressure-sensitive adhesive sheet 20 preferably has a moisture permeability of 150 g / m ² · 24 h or less. By providing the front-side pressure-sensitive adhesive sheet 20 with low moisture permeability in contact with the polarizer 11, moisture migration from the outside to the polarizer 11 can be reduced, and deterioration of the polarizer in a high-humidity environment can be suppressed. The front-side pressure-sensitive adhesive sheet 20 preferably has a storage elastic modulus G ′ _{80 at} 80 ° C. of 1 × 10 ⁵ Pa or less. Even when the front transparent member 70 has a printing step, the front-side pressure-sensitive adhesive sheet 20 having a low storage elastic modulus at a high temperature is used for bonding the polarizing plate 10 and the front transparent member 70 to each other. In addition, it is possible to suppress bubbles from being mixed in the vicinity of the printing step and occurrence of display unevenness due to stress strain. From the viewpoint of thinning, the thickness of the front side pressure-sensitive adhesive sheet 20 is preferably 250 μm or less.

<First adhesive layer>
The first pressure-sensitive adhesive layer 21 disposed in contact with the polarizer 11 preferably has a moisture permeability of 150 g / m ² · 24 h or less. By providing the adhesive layer having a low moisture permeability in contact with the polarizer 11, deterioration of the polarizer 11 can be suppressed even when the image display device is exposed to a high humidity environment. Moisture permeability of the first adhesive layer 21, more preferably not more than ^{120g / m 2 · 24h, 100g} / m more preferably less 2 · 24h or less, and particularly preferably ^{60g / m 2 · 24h, 40g} / m 2 · 24h The following are most preferred. The moisture permeability is a value measured according to a moisture permeability test (cup method) of JIS Z0208, and is the weight of water vapor that passes through a sample of 1 m ² in 24 hours at 40 ° C. and a relative humidity of 92%. .

  The image display cell 60 is bonded to the surface of the single protective polarizing plate 10 with the transparent protective film 15, and the front transparent member 70 is bonded to the polarizer 11 of the single protective polarizing plate 10 via the front adhesive sheet 20. In the display device 100, moisture may migrate to the polarizer 11 from the surface with the transparent protective film 15 (first main surface) and the surface with the front-side adhesive sheet 20 (second main surface). In the single protective polarizing plate, generally, the amount of moisture transferred from the second main surface side where the transparent protective film is not provided to the polarizer tends to increase.

  As for the transfer of moisture from the second main surface side to the polarizer 11, the transfer from the attachment surface (main surface) of the front side adhesive sheet 20 and the transfer of moisture from the side surface of the front side adhesive sheet 20 can be considered. In the image display device in which a front transparent member such as a front transparent plate or a touch panel is provided on the surface on the viewing side, the front transparent member 70 has an action of suppressing moisture intrusion from the main surface of the image display device. Therefore, the transfer of moisture from the front surface-side adhesive sheet-attached surface of the second main surface can be suppressed to some extent. On the other hand, the front side pressure-sensitive adhesive sheet 20 as an interlayer filler provided between the polarizing plate 10 and the front transparent member 70 has a thickness-absorbing property by increasing the thickness. In some cases, the amount of moisture transferred to the polarizer 11 through the substrate increases.

  When the conventional interlayer filling pressure-sensitive adhesive sheet is disposed on the single protective polarizing plate, fading is likely to occur near the end face of the polarizer due to the influence of moisture transferred from the side surface of the pressure-sensitive adhesive sheet to the polarizer. In contrast, by providing the first pressure-sensitive adhesive layer 21 with low moisture permeability in contact with the polarizer 11, the amount of moisture transferred to the polarizer 11 through the side surface of the front-side pressure-sensitive adhesive sheet 20 is reduced, It is possible to suppress the deterioration of the polarizer due to. When the moisture permeability of the second pressure-sensitive adhesive layer 22 is large, moisture may enter from the side surface of the second pressure-sensitive adhesive layer 22, but the moisture that has entered the second pressure-sensitive adhesive layer 22 is a low moisture-permeable first. Since it is blocked by the pressure-sensitive adhesive layer 21, the transition to the polarizer 11 is suppressed. Therefore, if the 1st adhesive layer 21 is low humidity, even when the thickness of the front side adhesive sheet 20 is large, the transfer of the water | moisture content to the polarizer 11 can be reduced and deterioration of a polarizer can be suppressed.

From the viewpoint of reducing the thickness, the thickness d ₁ of the first pressure-sensitive adhesive layer 21 is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less. From the viewpoint of thinning, the thickness of the first pressure-sensitive adhesive layer is preferably as small as possible. On the other hand, moisture permeability and thickness are in an inversely proportional relationship, and in a sheet-like material made of the same material, moisture permeability tends to increase as the thickness decreases. In order to make the moisture permeability within the above range, the thickness of the first pressure-sensitive adhesive layer 21 is preferably 5 μm or more, and more preferably 10 μm or more.

The storage elastic modulus G ′ ₂₅ at 25 ° C. of the first pressure-sensitive adhesive layer 21 is preferably 1 × 10 ⁴ Pa to 1 × 10 ⁸ Pa, more preferably 5 × 10 ⁴ Pa to 1 × 10 ⁷ Pa, and 1 × 10. ⁵ Pa to ⁵ × 10 ⁶ Pa is more preferable. The storage elastic modulus G ′ ₈₀ at 80 ° C. of the first pressure-sensitive adhesive layer 21 is preferably 5 × 10 ³ Pa to 5 × 10 ⁷ Pa, more preferably 1 × 10 ⁴ Pa to 5 × 10 ⁶ Pa, and 3 × 10. ⁴ Pa to 1 × 10 ⁶ Pa is more preferable.

(Composition of the first pressure-sensitive adhesive layer)
The composition of the pressure-sensitive adhesive constituting the first pressure-sensitive adhesive layer 21 is not particularly limited as long as it satisfies the above moisture permeability. Acrylic polymer, rubber polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl Those having a base polymer such as ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy-based, or fluorine-based polymer can be appropriately selected and used. Since the front-side pressure-sensitive adhesive sheet is disposed on the front surface of the image display device, the first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 are preferably excellent in optical transparency. Specifically, each of the first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 preferably has a haze of 1.0% or less and a total light transmittance of 90% or more.

  Since the low moisture permeability can be realized even with a small thickness, the first pressure-sensitive adhesive layer 21 is preferably a rubber-based pressure-sensitive adhesive layer containing a rubber-based polymer as a main component. Here, the “main component” means that the rubber-based polymer is 40% by weight or more in the first pressure-sensitive adhesive layer (or based on the total solid content of the pressure-sensitive adhesive composition for forming the first pressure-sensitive adhesive layer). It is included.

  The rubber-based polymer is a polymer that exhibits rubber elasticity in a temperature range near room temperature. As the rubber-based polymer, it is preferable to use one or more selected from the group consisting of natural rubber, synthetic rubber, and thermoplastic elastomer.

  Synthetic rubbers include polyisobutylene (PIB), butadiene rubber (BR), isoprene rubber (IR), isobutylene-isoprene rubber (IIR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber ( NBR), butadiene-isoprene-styrene random copolymer, isoprene-styrene random copolymer, binary ethylene-propylene rubber (EPR), ternary ethylene-propylene rubber (EPT), acrylic rubber, urethane rubber, etc. Can be mentioned. Among these, from the viewpoints of transparency and light resistance, polyisobutylene (PIB) and butyl rubber (IIR) are preferable, and polyisobutylene (PIB) is particularly preferable.

  Examples of the thermoplastic elastomer include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-styrene block copolymer (SBS), and styrene. -Ethylene-propylene-styrene block copolymer (SEPS; hydrogenated product of SIS), styrene-ethylene-propylene block copolymer (SEP; hydrogenated product of styrene-isoprene block copolymer), styrene-isobutylene-styrene Styrenic thermoplastic elastomers composed of styrenic block copolymers such as block copolymers (SIBS); polyurethane-based thermoplastic elastomers; polyester-based thermoplastic elastomers; polypropylene and EPT (ternary ethylene-propylene It blends based thermoplastic elastomer, a polymer blend or the like of the beam) and the like. Among these, from the viewpoints of transparency and light resistance, a styrene thermoplastic elastomer is preferable, and a styrene-ethylene-propylene-styrene block copolymer (SEPS) is particularly preferable.

<Second adhesive layer>
The 2nd adhesive layer 22 arrange | positioned away from the polarizer 11 has the effect | action which provides level | step difference absorptivity to the front side adhesive sheet 20. FIG. In order to provide step absorbability, the second adhesive layer 22 preferably has a storage elastic modulus G ′ _{80 at} 80 ° C. of 1.5 × 10 ⁵ Pa or less, preferably 1 × 10 ⁵ Pa or less. Is more preferable, and it is further more preferable that it is 7 * 10 < ⁴ > Pa or less. When the storage elastic modulus at a high temperature of the second pressure-sensitive adhesive layer 22 is low, the fluidity at the time of vacuum heating or heat laminating by autoclave is high, and the pressure-sensitive adhesive easily enters the vicinity of the step. Can be suppressed.

In order to suppress the sticking out of the pressure-sensitive adhesive from the end face of the polarizing plate in the heating state at the time of bonding, the G ′ ₈₀ of the second pressure-sensitive adhesive layer 22 is preferably 1 × 10 ³ Pa or more, and 3 ×× 10 ^3. More than Pa is more preferable.

The storage elastic modulus G ′ ₂₅ at 25 ° C. of the second pressure-sensitive adhesive layer 22 is preferably 1 × 10 ⁴ Pa to 1 × 10 ⁷ Pa, more preferably 4 × 10 ⁴ Pa to ⁶ × 10 ⁶ Pa, and 6 × 10. ⁴ Pa to 1 × 10 ⁶ Pa is more preferable. If the storage elastic modulus at room temperature is 1 × 10 ⁴ Pa or more, it is possible to reduce the adhesion of the adhesive to the cutting blade or the like and the sticking of the adhesive from the end face when the polarizing plate with the adhesive is cut into a predetermined size. . If the storage elastic modulus at normal temperature is 1 × 10 ⁷ Pa or less, it is possible to prevent cracking or chipping of the adhesive on the cut surface when the polarizing plate with the adhesive is cut into a predetermined size. Also, G _'25 of the second pressure-sensitive adhesive layer 22 is within the above range, it is possible to hold the cohesive force necessary for workability and handling properties, etc., can ensure initial tack during bonding.

Second pressure-sensitive adhesive layer 22 is preferably a ratio G _'25 / G' ₈₀ and ₂₅ 'storage modulus G ₈₀ and 25 ° C.' storage modulus at 80 ° C. G is 3.5 or more, 5 or more More preferably, it is more preferably 7 or more. When the temperature dependence of the storage modulus is large and the value of G ′ ₂₅ / G ′ ₈₀ is large, the fluidity is low at normal temperature, and the adhesive is transferred to the cutting blade or the like at the time of cutting or the adhesive from the end face In addition to being able to suppress protrusion, the fluidity is high at the time of heating, and the adhesive easily enters the vicinity of the printing step, so that it is possible to suppress the mixing of bubbles near the printing step and the display unevenness of the image display device. The upper limit of G ′ ₂₅ / G ′ ₈₀ of the second pressure-sensitive adhesive layer 22 is not particularly limited, but is preferably 100 or less and 50 or less in consideration of adhesiveness at the time of bonding at room temperature, fluidity at the time of heating, and the like. More preferred.

  The storage elastic modulus G ′ is a temperature rising rate of 5 ° C. in the range of −50 to 150 ° C. under the condition of frequency 1 Hz in accordance with the method described in JIS K7244-1 “Plastics—Testing method for dynamic mechanical properties”. It is obtained by reading a value at a predetermined temperature when measured at / min.

When the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is a photo-curing type or thermosetting type, and curing is performed after the polarizing plate 10 and the front transparent member 70 are bonded, the pressure-sensitive adhesive before curing (at the time of bonding) The storage elastic modulus (G ′ ₂₅ , G ′ ₈₀ , and G ′ ₂₅ / G ′ ₈₀ ) may be in the above range. Since the cutting of the pressure-sensitive adhesive sheet and the bonding with the front transparent member are performed before curing, the above-described object can be achieved by adjusting the storage elastic modulus of the second pressure-sensitive adhesive layer 22 before curing.

In order to provide step absorbability, the thickness d ₂ of the second pressure-sensitive adhesive layer 22 is preferably 50 μm or more, more preferably 60 μm or more, and further preferably 70 μm or more. By increasing the thickness of the second pressure-sensitive adhesive layer 22, the step absorbability can be enhanced, and the mixing of bubbles near the printing step and the display unevenness of the image display device can be suppressed. The upper limit of the thickness d ₂ of the second pressure-sensitive adhesive layer 22 is not particularly limited, but is preferably 250 μm or less, more preferably 200 μm or less, and more preferably 180 μm or less from the viewpoints of thinning and prevention of sticking of the adhesive from the end face. Is more preferable.

(Composition of the second pressure-sensitive adhesive layer)
The composition of the pressure-sensitive adhesive constituting the second pressure-sensitive adhesive layer 22 is not particularly limited as long as it satisfies the above characteristics, and is an acrylic polymer, rubber-based polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyvinyl ether. Polymers such as vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy-based, and fluorine-based polymers can be appropriately selected and used. As described above, the second pressure-sensitive adhesive layer is preferably excellent in optical transparency.

  The second pressure-sensitive adhesive layer 22 is preferably an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a main component because both the viscoelastic property capable of imparting step absorbability and high transparency can be achieved. . Here, the “main component” is 40% by weight or more of the acrylic polymer in the second pressure-sensitive adhesive layer (or based on the total solid content of the pressure-sensitive adhesive composition for forming the second pressure-sensitive adhesive layer). It is included.

  As the acrylic polymer, a polymer having a monomer unit of (meth) acrylic acid alkyl ester as a main skeleton is preferably used. In the present specification, “(meth) acryl” means acryl and / or methacryl.

  As the (meth) acrylic acid alkyl ester, a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is suitably used. The content of the alkyl (meth) acrylate 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 monomer components constituting the acrylic polymer. The acrylic polymer may be a copolymer of a plurality of (meth) acrylic acid alkyl esters. The arrangement of the constituent monomer units may be random or may be a block.

  In the (meth) acrylic acid alkyl ester, the alkyl group may have a branch. By using a branched (meth) acrylic acid alkyl ester, flexibility is easily imparted to the pressure-sensitive adhesive, and an acrylic pressure-sensitive adhesive layer having the above storage elastic modulus can be easily formed. Examples of branched alkyl (meth) acrylate esters include 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, isodecyl (meth) acrylate, and isotetradecyl (meth) acrylate. , Isooctadecyl (meth) acrylate and the like are preferably used.

  The acrylic polymer preferably contains an acrylic monomer unit having a crosslinkable functional group as a copolymerization component. In the case of having a crosslinkable functional group, the acrylic pressure-sensitive adhesive can have a high cohesive force by thermal crosslinking or photocuring of the acrylic polymer. Examples of the acrylic monomer having a crosslinkable functional group include a hydroxy group-containing monomer and a carboxy group-containing monomer. Especially, it is preferable to contain a hydroxy group containing monomer as a copolymerization component of an acrylic polymer. When the acrylic polymer has a hydroxy group-containing monomer as a monomer unit, the crosslinkability of the acrylic polymer is enhanced, and the white turbidity of the adhesive in a high temperature and high humidity environment tends to be suppressed, and the transparency is high. An adhesive is obtained.

  Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, (meth) Examples include 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate and (4-hydroxymethylcyclohexyl) -methyl acrylate.

  The content of the hydroxy group-containing monomer unit is preferably 0.01% by weight to 20% by weight, more preferably 0.1% by weight to 15% by weight, based on the total amount of the constituent monomer units of the acrylic polymer. More preferred is 10% by weight. When the content of the hydroxy group-containing monomer unit exceeds the above range, the cohesive force of the second pressure-sensitive adhesive layer may increase excessively and the step absorbability may decrease.

  The acrylic polymer preferably contains a highly polar monomer unit such as a nitrogen-containing monomer in addition to the hydroxy group-containing monomer unit. By containing a highly polar monomer unit such as a nitrogen-containing monomer unit in addition to the hydroxy group-containing monomer unit, both high adhesive force and suppression of white turbidity in a high temperature and high humidity environment can be achieved.

  Nitrogen-containing monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth) acryloylmorpholine, N-vinyl. Examples thereof include vinyl monomers such as carboxylic acid amides and N-vinylcaprolactam, and cyanoacrylate monomers such as acrylonitrile and methacrylonitrile. Of these, N-vinylpyrrolidone and (meth) acryloylmorpholine are preferably used. The content of the nitrogen-containing monomer unit is preferably from 3 to 45% by weight, more preferably from 5 to 40% by weight, and even more preferably from 7 to 30% by weight, based on the total amount of the constituent monomer units of the acrylic polymer.

  In the acrylic polymer of the second pressure-sensitive adhesive layer, the total content of the hydroxy group-containing monomer unit and the content of the nitrogen-containing monomer unit with respect to the total amount of the constituent monomer units is preferably 3 to 50% by weight, and 5 to 40 It is more preferable that it is weight%, and it is still more preferable that it is 7-30 weight. When the sum of the content of the hydroxy group-containing monomer unit and the content of the nitrogen-containing monomer unit is in the above range, an acrylic pressure-sensitive adhesive layer having appropriate cohesiveness and flexibility during heating is easily formed.

  The monomer component for forming the acrylic polymer may contain a polyfunctional monomer component. By having a polyfunctional monomer as a copolymerization monomer component, the storage elastic modulus at room temperature tends to be increased. The polyfunctional monomer is a monomer having at least two polymerizable functional groups (for example, vinyl groups). The amount of the polyfunctional monomer used varies depending on the molecular weight, the number of functional groups, etc., but is preferably 5% by weight or less, more preferably 3% by weight or less, based on all monomer components forming the (meth) acrylic polymer. 1% by weight or less is more preferable. When the amount of the polyfunctional monomer used exceeds 5% by weight, the flexibility of the pressure-sensitive adhesive decreases, and air bubbles and display unevenness may occur near the step.

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

  In preparing the acrylic polymer, a polymerization initiator such as a photopolymerization initiator or a thermal polymerization initiator may be used depending on the type of polymerization reaction. The photopolymerization initiator is not particularly limited as long as it initiates photopolymerization. For example, benzoin ether photopolymerization initiator, acetophenone photopolymerization initiator, α-ketol photopolymerization initiator, aromatic sulfonyl Chloride photopolymerization initiator, photoactive oxime photopolymerization initiator, benzoin photopolymerization initiator, benzyl photopolymerization initiator, benzophenone photopolymerization initiator, ketal photopolymerization initiator, thioxanthone photopolymerization initiator An acylphosphine oxide photopolymerization initiator can be used. Examples of the thermal polymerization initiator include an azo initiator, a peroxide initiator, a redox initiator in which a peroxide and a reducing agent are combined (for example, a combination of a persulfate and sodium bisulfite, a peroxide) A combination of a product and sodium ascorbate).

  In order to adjust the molecular weight of the acrylic polymer, a chain transfer agent may be used. The chain transfer agent receives a radical from the growing polymer chain to stop the elongation of the polymer, and the chain transfer agent that has received the radical can attack the monomer to start polymerization again. For this reason, by using a chain transfer agent, an increase in the molecular weight of the acrylic polymer is suppressed without reducing the radical concentration in the reaction system, and a pressure-sensitive adhesive having moderate flexibility can be obtained. Examples of the chain transfer agent include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. Are preferably used.

  When a polyfunctional monomer is used in addition to a monofunctional monomer as a monomer component for forming an acrylic polymer, the monofunctional monomer is first polymerized to form a prepolymer composition having a low degree of polymerization (preliminary polymerization). A polyfunctional monomer may be added to the polymer composition (prepolymerized syrup) to polymerize (post-polymerize) the prepolymer and the polyfunctional monomer. Thus, by performing prepolymerization of the prepolymer, the branch points resulting from the polyfunctional monomer component can be uniformly introduced into the acrylic polymer. Moreover, after apply | coating the mixture (adhesive composition) of a prepolymer composition and an unpolymerized monomer component on a base material, post-polymerization may be performed on a base material and an adhesive sheet may be formed. Since the prepolymer composition has a low viscosity and excellent coating properties, the adhesive composition, which is a mixture of the prepolymer composition and the unpolymerized monomer, is subjected to post-polymerization on the substrate after coating, Productivity is improved and the thickness of the pressure-sensitive adhesive sheet can be made uniform.

  The prepolymer composition is, for example, a composition obtained by mixing a monomer component (referred to as “monomer component A”) that constitutes an acrylic polymer and a polymerization initiator (referred to as “prepolymer-forming composition”). It can be prepared by polymerization (preliminary polymerization). The monomer component A in the prepolymer-forming composition is preferably a monofunctional monomer component such as a (meth) acrylic acid alkyl ester or a polar group-containing monomer among the monomer components constituting the acrylic polymer. . The monomer component A may contain not only a monofunctional monomer but also a polyfunctional monomer. For example, a part of the polyfunctional monomer component used as the raw material for the acrylic polymer may be contained in the prepolymer-forming composition, and the remainder of the polyfunctional monomer component may be added to the prepolymer after polymerization to be subjected to post-polymerization.

  The prepolymer-forming composition may contain a chain transfer agent or the like as necessary in addition to the monomer component A and the polymerization initiator. The polymerization method of the composition for forming a prepolymer is not particularly limited, but from the viewpoint of adjusting the reaction time and setting the molecular weight (polymerization rate) of the prepolymer to a desired range, polymerization by irradiation with actinic rays such as UV light is preferable. . The polymerization initiator and chain transfer agent used for the preliminary polymerization are not particularly limited, and for example, the above-described photopolymerization initiator and chain transfer agent can be used.

Although the polymerization rate of a prepolymer is not specifically limited, From the viewpoint of setting it as the viscosity suitable for application | coating on a base material, 3 to 50 weight% is preferable, More preferably, it is 5 to 40 weight%. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity / irradiation time of actinic rays such as UV light, and the like. The polymerization rate of the prepolymer is calculated by the following formula from the weight before and after heating (drying) when the prepolymer composition is heated at 130 ° C. for 3 hours. When the prepolymerization is performed by solution polymerization, the polymerization rate is calculated by subtracting the amount of the solvent from the total weight of the prepolymer composition as the weight before drying in the following formula.
Polymerization rate (%) of prepolymer composition = weight after drying / weight before drying × 100

  A monomer component constituting the acrylic polymer (referred to as “monomer component B”) and, if necessary, a polymerization initiator, a chain transfer agent, a silane coupling agent, a crosslinking agent, and the like are mixed into the prepolymer composition. To form an adhesive composition. The monomer component B preferably contains a polyfunctional monomer. The monomer component B may contain a monofunctional monomer in addition to the polyfunctional monomer.

  The photopolymerization initiator and chain transfer agent used for post-polymerization are not particularly limited, and for example, the above-described photopolymerization initiator and chain transfer agent can be used. When the prepolymerization initiator remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator for post-polymerization can be omitted.

  The acrylic polymer may have a crosslinked structure as necessary. Formation of a crosslinked structure is performed, for example, by adding a crosslinking agent after preliminary polymerization or after polymerization of the base polymer. As the crosslinking agent, generally used ones 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.

  The content of the crosslinking agent is usually in the range of 0 to 5 parts by weight, preferably 0 to 3 parts by weight with respect to 100 parts by weight of the base polymer. When there is too much content of a crosslinking agent, the softness | flexibility of an adhesive will fall and it will become easy to generate | occur | produce the bubble and display nonuniformity near a level | step difference.

  When the pressure-sensitive adhesive composition contains a cross-linking agent, it is preferable that a cross-linking process is performed by heating before bonding to the adherend to form a cross-linked structure. Although the heating temperature and heating time in the crosslinking treatment are appropriately set according to the type of the crosslinking agent to be used, the crosslinking is usually performed in the range of 20 ° C. to 160 ° C. by heating for about 1 minute to 7 days.

  The second pressure-sensitive adhesive layer 22 may be a photocurable or thermosetting pressure-sensitive adhesive. As the second pressure-sensitive adhesive layer 22, a light-curing or thermosetting pressure-sensitive adhesive is used, so that the second pressure-sensitive adhesive is bonded to the polarizing plate 10 and the front transparent member 70 through the front-side pressure-sensitive adhesive sheet 20. The agent layer 22 can be cured to increase the storage elastic modulus of the pressure-sensitive adhesive layer. Therefore, even when the image display device is exposed to a high temperature environment, the flow of the pressure-sensitive adhesive is suppressed, and it is possible to realize long-term reliable adhesiveness in which bubbles are not easily generated or peeled off. In particular, a photo-curing pressure-sensitive adhesive is preferred because it is easy to cure after being bonded to the front transparent member.

  The photocurable pressure-sensitive adhesive contains a photocurable component in addition to the base polymer. As the photocurable component, a radical polymerizable compound (ethylenically unsaturated compound) having a carbon-carbon double bond (C═C bond) is preferably used. The radically polymerizable compound may be present as a monomer or oligomer in the pressure-sensitive adhesive composition, and may be bonded to a functional group such as a hydroxy group of the base polymer. The curable pressure-sensitive adhesive preferably contains a polymerization initiator (photopolymerization initiator or thermal polymerization initiator).

  When the radical polymerizable compound is present as a monomer or oligomer in the pressure-sensitive adhesive composition, a polyfunctional polymerizable compound having two or more polymerizable functional groups in one molecule is preferably used. Polyfunctional polymerizable compounds include compounds having two or more C═C bonds in one molecule, one C═C bond, and polymerizable functional groups such as epoxy, aziridine, oxazoline, hydrazine, and methylol. And the like. Among them, a polyfunctional polymerizable compound having two or more C═C bonds in one molecule, such as a polyfunctional acrylate, is preferable.

  A radical polymerizable functional group having a functional group capable of binding to the functional group of the base polymer and a radical polymerizable functional group is mixed with the base polymer to introduce the radical polymerizable functional group into the base polymer, thereby producing an adhesive composition. Can be used as a curable pressure-sensitive adhesive. The functional group that can be bonded to the functional group of the base polymer is preferably an isocyanate group. Since the isocyanate group forms a urethane bond with the hydroxy group of the base polymer, radically polymerizable functional groups can be easily introduced into the base polymer.

  As a photocuring method, a method of irradiating a system containing a photocurable compound and a photopolymerization initiator with actinic rays such as ultraviolet rays is preferable. In particular, a system using an ethylenically unsaturated compound and a photo radical generator is preferable because of high photosensitivity and abundant materials that can be selected. When the 2nd adhesive layer 22 is a photocurable adhesive, 2-50 weight part is preferable with respect to 100 weight part of the whole adhesive composition, and 5-30 weight part is preferable. Is more preferable.

<Additive in pressure-sensitive adhesive composition>
The pressure-sensitive adhesive composition for forming the first pressure-sensitive adhesive layer 21 and the pressure-sensitive adhesive composition for forming the second pressure-sensitive adhesive layer 22 may contain various additives in addition to the base polymer. For example, a silane coupling agent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting the adhesive force. A silane coupling agent can be used individually by 1 type or in combination of 2 or more types. In particular, when the second pressure-sensitive adhesive layer contains an acrylic polymer as a main component, the pressure-sensitive adhesive composition for forming the second pressure-sensitive adhesive layer preferably contains a silane coupling agent. The addition amount of the silane coupling agent is usually about 0.01 to 5 parts by weight and preferably about 0.03 to 2 parts by weight with respect to 100 parts by weight of the acrylic polymer.

  You may add a tackifier to an adhesive composition as needed. In particular, when the first pressure-sensitive adhesive layer 21 is a pressure-sensitive adhesive layer containing a rubber-based polymer as a main component, a tackifier may be contained in the pressure-sensitive adhesive composition from the viewpoint of improving the adhesion with the polarizer 11. preferable. Examples of tackifiers include terpene tackifiers, styrene tackifiers, phenol tackifiers, rosin tackifiers, epoxy tackifiers, dicyclopentadiene tackifiers, and polyamide tackifiers. An agent, a ketone tackifier, an elastomer tackifier, and the like can be used. In particular, the tackifier used in the first pressure-sensitive adhesive layer is preferably a terpene-based tackifier because it is excellent in compatibility with a rubber material and transparency.

  Examples of the terpene-based tackifier include terpene polymers such as α-pinene polymers, β-pinene polymers, dipentene polymers, terpene phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, and hydrogenated terpenes. Examples thereof include modified terpene resins such as resins (hydrogenated terpene resins).

  The tackifier contained in the first pressure-sensitive adhesive layer 21 preferably has a softening point of about 70 to 200 ° C, more preferably about 100 to 180 ° C. The softening point is a value measured according to JIS K2207 “ring and ball softening point test method”.

  The content of the tackifier in the first pressure-sensitive adhesive layer 21 is preferably 100 parts by weight or less, more preferably 80 parts by weight or less, and still more preferably 50 parts by weight or less with respect to 100 parts by weight of the rubber-based base polymer. The lower limit of the content of the tackifier is not particularly limited, but is preferably 1 part by weight or more and more preferably 5 parts by weight or more in order to obtain the effect of improving the adhesion with the polarizer.

  The second pressure-sensitive adhesive layer may also contain a tackifier. Use of the tackifier in the second pressure-sensitive adhesive layer can contribute to the adjustment of the temperature dependence of the storage elastic modulus. From the viewpoint of imparting the desired temperature dependence to the storage elastic modulus of the second pressure-sensitive adhesive layer 22, the tackifier contained in the second pressure-sensitive adhesive layer preferably has a softening point of about 50 ° C to 150 ° C. More preferably, the temperature is about 70 ° C to 140 ° C.

  The first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 preferably contain an ultraviolet absorber in at least one of them. Generally, the transparent protective film provided on the surface of the polarizer contains an ultraviolet absorber for the purpose of preventing the polarizer from being deteriorated by ultraviolet rays. On the other hand, since the single protective polarizing plate 10 is not provided with a transparent protective film on the attachment surface of the front side pressure-sensitive adhesive sheet 20, the first pressure-sensitive adhesive layer 21 and / or the second pressure-sensitive adhesive layer 22 is provided with ultraviolet absorptivity. Thus, it is preferable to prevent the polarizer 11 from being deteriorated due to ultraviolet rays.

  Examples of UV absorbers include benzophenone UV absorbers, benzotriazole UV absorbers, salicylic acid UV absorbers, oxalic anilide UV absorbers, cyanoacrylate UV absorbers, and triazine UV absorbers. It is done. 0.01-15 weight part is preferable with respect to 100 weight part of base polymers of an adhesive, and, as for content of a ultraviolet absorber, 0.1-10 weight part is more preferable. The front-side pressure-sensitive adhesive sheet 20 preferably has a light transmittance at a wavelength of 380 nm of 15% or less, and more preferably 10% or less.

  In addition to the components exemplified above, additives such as plasticizers, softeners, deterioration inhibitors, fillers, colorants, antioxidants, surfactants, antistatic agents, and the like are added so long as the properties of the adhesive are not impaired. You may add to an adhesive composition.

  The pressure-sensitive adhesive composition for forming the first pressure-sensitive adhesive layer 21 preferably has a rubber-based polymer content of 40% by weight or more, more preferably 50% by weight, and 60% by weight or more. More preferably. The pressure-sensitive adhesive composition for forming the second pressure-sensitive adhesive layer 22 preferably has an acrylic polymer content of 40% by weight or more, more preferably 50% by weight, and 60% by weight or more. More preferably.

<Formation of adhesive layer>
Various methods are used as a method of forming the pressure-sensitive adhesive layer. Specifically, for example, by roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat, lip coat, die coater, etc. Examples thereof include an extrusion coating method. 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 coating. As a drying method, an appropriate method can be appropriately employed depending on the purpose. The heat drying temperature is preferably 40 ° C to 200 ° C, more preferably 50 ° C to 180 ° C, and particularly preferably 70 ° C to 170 ° C. As the drying time, an appropriate time can be adopted as appropriate. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

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

  The lamination | stacking method of a 1st adhesive layer and a 2nd adhesive layer is not specifically limited. After each of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is individually formed as a pressure-sensitive adhesive sheet, they may be overlapped. After one pressure-sensitive adhesive layer is first formed as a pressure-sensitive adhesive sheet, the other is formed thereon. The pressure-sensitive adhesive layer can be coated to obtain a laminated pressure-sensitive adhesive sheet. Alternatively, the laminated pressure-sensitive adhesive sheet may be formed by coextrusion of the first pressure-sensitive adhesive layer forming composition and the second pressure-sensitive adhesive layer forming composition.

  The front-side pressure-sensitive adhesive sheet 20 may be a laminated pressure-sensitive adhesive sheet composed of two layers, a first pressure-sensitive adhesive layer 21 and a second pressure-sensitive adhesive layer pressure-sensitive adhesive 22, and / or between the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer. Another adhesive layer may be provided on the two adhesive layer adhesive 22. From the viewpoint of productivity and thickness reduction of the pressure-sensitive adhesive sheet, the front-side pressure-sensitive adhesive sheet 20 is preferably composed of two layers, a first pressure-sensitive adhesive layer 21 and a second pressure-sensitive adhesive layer 22.

<Characteristics of adhesive sheet>
The 1st adhesive layer 21 arrange | positioned in contact with the polarizer 11 of the piece protection polarizing plate 10 is comprised with the low moisture-permeable adhesive, and the 2nd adhesive layer 22 arrange | positioned away from the polarizer 11 is high temperature. It is composed of a soft adhesive with a small storage elastic modulus. By providing the first pressure-sensitive adhesive layer 21 with low moisture permeability in contact with the polarizer 11, even when the moisture permeability of the second pressure-sensitive adhesive layer 22 is high, the moisture is transferred to the polarizer 11 by the first pressure-sensitive adhesive layer 21. Is blocked, it is possible to suppress the deterioration of the polarizer due to the movement of moisture from the side surface of the front side pressure-sensitive adhesive sheet 20.

On the other hand, a low moisture-permeable pressure-sensitive adhesive made of a rubber polymer or the like generally has a low glass transition temperature, so that the temperature dependence of the storage elastic modulus of the pressure-sensitive adhesive at normal temperature (25 ° C.) and heating (80 ° C.) is small. the ratio G _'25 / G' ₈₀ of the ₂₅ 'storage modulus G ₈₀ and 25 ° C.' storage modulus at 80 ° C. G is generally 3 or less. Even if a tackifier is used for the first pressure-sensitive adhesive layer 21 containing a rubber-based polymer as a main component, it is difficult to increase G ′ ₂₅ / G ′ ₈₀ . When a large amount of tackifier or plasticizer is contained in the first pressure-sensitive adhesive layer to make G ′ ₈₀ small and have step absorbability, the storage elastic modulus G ′ ₂₅ at room temperature (25 ° C.) also decreases. For this reason, the adhesive sticks out from the end face or is transferred to the cutting blade or the like.

  By laminating a soft pressure-sensitive adhesive as the second pressure-sensitive adhesive layer 22 on the low-moisture-permeable first pressure-sensitive adhesive layer 21, the pressure-sensitive adhesive can enter the vicinity of the printing step of the front transparent member. Bubbles can be prevented from being mixed. Furthermore, since the softness as the whole front surface side adhesive sheet 20 is maintained, the display nonuniformity of the peripheral part of the screen resulting from a printing level | step difference can be suppressed.

As described above, the second adhesive layer 22 has a ratio G ′ ₂₅ / G ′ ₈₀ of the storage elastic modulus G ′ _{80 at 80} ° C. and the storage elastic modulus G ′ _{25 at} 25 ° C. of 3.5 or more. Is more preferably 5 or more, and further preferably 7 or more. G _'25 / G' ₈₀ of the second pressure-sensitive adhesive layer 22 is preferably larger than the G _'25 / G' ₈₀ of the first pressure-sensitive adhesive layer 21. G _'25 / G' ₈₀ of the second pressure-sensitive adhesive layer 22 is preferably at least 2 times the G _'25 / G' ₈₀ of the first pressure-sensitive adhesive layer 21, more preferably at least 3 times, more preferably not less than 4 times . The ratio of G ′ ₂₅ / G ′ ₈₀ between the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is an index representing the difference in temperature dependence of the storage elastic modulus of these pressure-sensitive adhesive layers. It shows that the difference in elastic behavior is large.

The thickness d ₂ of the second pressure-sensitive adhesive layer 22 is preferably larger than the thickness d _{1 of} the first pressure-sensitive adhesive layer 21. The thickness _{d 1} of the first pressure-sensitive adhesive layer 21 the ratio _d 2 / _{d 1} of the thickness _{d 2} of the second pressure-sensitive adhesive layer 22 is preferably from 1.5 to 15, more preferably 2 to 10, 2.5 to 8 Is more preferable. By making the thickness of the second pressure-sensitive adhesive layer relatively larger than that of the first pressure-sensitive adhesive layer, the entire front-side pressure-sensitive adhesive sheet 20 in which the first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 are laminated. In the viscoelastic behavior, the viscoelasticity of the second pressure-sensitive adhesive layer becomes dominant. Therefore, the level difference absorbability of the front side pressure-sensitive adhesive sheet 20 is enhanced, and the mixing of bubbles near the printing level difference and the display unevenness of the image display device can be suppressed.

From the viewpoint of high fluidity during heating and suppressing the sticking of the adhesive from the end face, the storage elastic modulus G ′ ₈₀ at 80 ° C. of the front side pressure-sensitive adhesive sheet 20 is 1 × 10 ³ Pa to 1.5 × 10. ⁵ Pa is preferable, 3 × 10 ³ Pa to 1 × 10 ⁵ Pa is more preferable, and 5 × 10 ³ Pa to 7 × 10 ⁴ Pa is more preferable. From the viewpoint of preventing sticking of the adhesive from the end face and transfer of the adhesive to the cutting blade when the polarizing plate with adhesive is cut to a predetermined size, and suppressing cracking and chipping of the adhesive. The storage elastic modulus G ′ ₂₅ at 25 ° C. of the side adhesive sheet 20 is preferably 1 × 10 ⁴ Pa to 1 × 10 ⁷ Pa, more preferably 4 × 10 ⁴ Pa to ⁶ × 10 ⁶ Pa, and 6 × 10 ⁴ Pa. ˜1 × 10 ⁶ Pa is more preferable.

Front-side pressure-sensitive adhesive sheet storage modulus G 80 ° C. for 20 specific G _'25 / G' ₈₀ and _{25 '80} and the storage modulus G 25 ° C.' is preferably 2 to 100, more preferably from 5 to 50, 7-30 are more preferable. As described above, by making the thickness of the second pressure-sensitive adhesive layer 22 relatively larger than that of the first pressure-sensitive adhesive layer 21, the viscoelastic behavior of the front side pressure-sensitive adhesive sheet 20 as a whole becomes the second pressure-sensitive adhesive layer. Therefore, the temperature dependence of the storage elastic modulus of the front side pressure-sensitive adhesive sheet 20 can be increased, and the value of G ′ ₂₅ / G ′ ₈₀ can be adjusted within the above range.

When the first pressure-sensitive adhesive layer and / or the second pressure-sensitive adhesive layer constituting the front-side pressure-sensitive adhesive sheet 20 is made of a photo-curing type or heat-curing pressure-sensitive adhesive, the storage elastic modulus of the pressure-sensitive adhesive sheet before curing as described above Is preferably in the above range. On the other hand, the moisture permeability of the front side pressure-sensitive adhesive sheet is related to the humidification durability of the image display device after the front transparent plate and the polarizer are bonded together. Thus, it is preferably 150 g / m ² · 24 h or less.

[Formation of polarizing plate with adhesive]
The method for attaching the front side pressure-sensitive adhesive sheet 20 on the single protective polarizing plate 10 is not particularly limited. A laminated adhesive sheet in which the first adhesive layer 21 and the second adhesive layer are laminated may be formed in advance, and the first adhesive layer 21 of the laminated adhesive sheet may be bonded onto the polarizer 11. The first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 may be sequentially bonded onto the child 11. On the polarizer 11, the 1st adhesive layer formation composition may be apply | coated, the 1st adhesive layer 21 may be formed, and the 2nd adhesive layer 22 may be formed on it by application | coating or transcription | transfer. Moreover, a polarizing plate with an adhesive can be obtained by forming a laminated adhesive sheet on the polarizer 11 by co-extrusion of the first adhesive layer forming composition and the second adhesive layer forming composition. .

  As shown in FIG. 1, it is preferable that the protective sheet 41 is detachably pasted on the front side pressure-sensitive adhesive sheet 20 of the polarizing plate 1 with pressure-sensitive adhesive. The protective sheet is used for the purpose of protecting the exposed surface of the adhesive until the adhesive is used for bonding to the adherend. You may use the base material used at the time of formation (application | coating) of an adhesive layer as it is as the protective sheet 41 on a front side adhesive sheet.

  As a constituent material of the protective sheet 41, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, or polyester film is preferably used. The thickness of the protective sheet is usually about 5 to 200 μm, preferably about 10 to 150 μm. Protective sheet can be removed with silicone, fluorine, long chain alkyl or fatty acid amide release agent, silica powder, etc. and antifouling treatment, coating type, kneading type, vapor deposition type, etc. The antistatic treatment can also be performed. In particular, the release property from the pressure-sensitive adhesive can be further improved by appropriately performing a release treatment such as silicone treatment, long-chain alkyl treatment, and fluorine treatment on the surface of the protective sheet.

[Double-sided polarizing plate]
As shown in FIG. 3, the front side adhesive sheet 20 is provided so as to be in contact with the polarizer 11 of the single protective polarizing plate 10, and another adhesive sheet (cell side adhesive sheet) 30 is provided on the attachment surface of the transparent protective film 15. A polarizing plate with a double-sided adhesive is obtained. In the form shown in FIG. 3, the protective sheet 41 is detachably stuck on the front side adhesive sheet 20 of the polarizing plate 2 with double-sided adhesive, and the protective sheet 42 is detachably stuck on the cell side adhesive sheet 30. It is worn.

  As described above, if a polarizing plate with a double-sided adhesive in which a pressure-sensitive adhesive layer is previously provided on both sides of the polarizing plate 10 is used, after the polarizing plate is bonded to the surface of the image display cell, a separate adhesive sheet is provided on the polarizing plate. Can be omitted, and the manufacturing process of the image display device can be simplified.

<Cell side adhesive sheet>
The thickness of the cell-side pressure-sensitive adhesive sheet 30 is preferably 3 μm to 30 μm, more preferably 5 μm to 27 μm, and still more preferably 10 μm to 25 μm. As the cell-side pressure-sensitive adhesive sheet, various pressure-sensitive adhesives used for bonding the polarizing plate and the image display cell can be used. As the pressure-sensitive adhesive constituting the cell-side pressure-sensitive adhesive sheet, an acrylic pressure-sensitive adhesive is preferably used.

The cell-side pressure-sensitive adhesive sheet 30 preferably has a storage elastic modulus G ′ _{25 at} 20 ° C. of 1 × 10 ⁴ Pa to 1 × 10 ⁷ Pa, preferably 5 × 10 ⁴ Pa to 5.0 × 10 ⁶ Pa. It is more preferable that the pressure is 1 × 10 ⁵ Pa to 1 × 10 ⁶ Pa. If the cell-side pressure-sensitive adhesive sheet of G _'25 is within the above range, together they show a moderate adhesion, and transcribing the adhesive to cutting blades or the like during cutting, cracking, chipping, etc. of the adhesive can be suppressed.

[Image display device]
FIG. 2 is a schematic cross-sectional view showing one embodiment of the image display device. The polarizing plate with an adhesive of the present invention comprises a front transparent member 70 such as a touch panel and a front transparent plate on the main surface (viewing side) of the single protective polarizing plate 10 on the polarizer 11 side, and the main surface on the transparent protective film 15 side. It is suitably used for forming an image display device 100 including an image display cell 60 such as a liquid crystal cell or an organic EL cell. In the image display device 100, the front side adhesive sheet 20 is used for bonding the polarizer 11 of the single protective polarizing plate 10 and the front transparent member 70.

  Examples of the front transparent member 70 include a front transparent plate (window layer) and a touch panel. As the front transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. As such a transparent plate, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate is used. As the touch panel, a touch panel of an arbitrary system such as a resistive film system, a capacitance system, an optical system, and an ultrasonic system is used.

  When the double-sided pressure-sensitive adhesive polarizing plate shown in FIG. 3 is used, the method of bonding the image display cell 60 and the pressure-sensitive adhesive polarizing plate 2 and the method of bonding the front transparent member 70 and the pressure-sensitive adhesive polarizing plate 2 are particularly suitable. Without being limited thereto, the protective sheets 41 and 42 attached to the respective surfaces of the front-side pressure-sensitive adhesive sheet 20 and the cell-side pressure-sensitive adhesive sheet 30 can be peeled and then bonded together by various known methods.

  From the viewpoint of improving the workability of bonding and the axial accuracy of the polarizing plate, the protective sheet 42 is peeled off from the surface of the cell-side pressure-sensitive adhesive sheet 30, and then the polarizing plate 10 and the image display cell 60 are bonded via the pressure-sensitive adhesive sheet 30. The cell side bonding process to be combined is performed, and thereafter, the protective sheet 41 is peeled off from the surface of the front side pressure-sensitive adhesive sheet 20, and the polarizing plate 10 and the front transparent member 70 are bonded together via the front side pressure-sensitive adhesive sheet 20. It is preferable that a front side bonding process is performed.

  After the front transparent member 70 is bonded to the front side pressure-sensitive adhesive sheet 20, bubbles near the non-flat portion such as the interface between the front side pressure-sensitive adhesive sheet 20 and the front transparent member 70 and the printing portion 76 of the front transparent member 70 are removed. It is preferable that defoaming is performed. As the defoaming method, an appropriate method such as heating, pressurization, or reduced pressure 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 simultaneously with heating by autoclave treatment or the like for the purpose of suppressing delay bubbles.

  When the front-side pressure-sensitive adhesive sheet 20 contains a photo-curing or thermosetting pressure-sensitive adhesive, it is preferable that curing is performed after the polarizing plate 10 and the front transparent member 70 are bonded. By curing the pressure-sensitive adhesive layer, the reliability of adhesion between the polarizing plate 10 and the front transparent member 70 can be increased. The method for curing the pressure-sensitive adhesive layer is not particularly limited. When photocuring is performed, a method of irradiating actinic rays such as ultraviolet rays through the front transparent member 70 is preferable.

  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.

[Method for evaluating physical properties of pressure-sensitive adhesive and pressure-sensitive adhesive sheet]
<Storage modulus>
A sample for measurement was prepared by laminating a plurality of adhesive sheets to a thickness of about 1.5 mm. In addition, in the measurement of the storage elastic modulus of a lamination adhesive sheet, what laminated | stacked the 1st adhesive layer and the 2nd adhesive layer alternately, and was about 1.5 mm in thickness was used as a measurement sample. About the photocurable adhesive sheet M1, each adhesive sheet before and after hardening was used as a measurement sample. Using “Advanced Rheometric Expansion System (ARES)” manufactured by Rheometric Scientific, dynamic viscoelasticity measurement was performed under the following conditions, and the storage elastic modulus at 25 ° C. and 80 ° C. (G ′ ₂₅ , G ′ ₈₀ ) Was read.
(Measurement condition)
Deformation mode: Torsion Measurement frequency: 1Hz
Temperature increase rate: 5 ° C / min Measurement temperature: -50 to 150 ° C Shape: Parallel plate 8.0mmφ

<Moisture permeability>
The separator on one side of the pressure-sensitive adhesive sheet is peeled off, and a 25 μm thick triacetyl cellulose film (moisture permeability: 1070 g / m ² · 24 h) is bonded to the exposed surface, and then the separator on the other side is peeled off. Based on the Z0208 moisture permeability test (cup method), a moisture permeability test was conducted for 24 hours in a constant temperature and humidity chamber at a temperature of 40 ° C. and a relative humidity of 92%, and the moisture permeability was calculated. About the laminated adhesive sheet of Example 3 using the photocurable adhesive sheet M1 and the adhesive sheet M1, the adhesive sheet was bonded to a triacetyl cellulose film and UV cured, and then a moisture permeability test was performed. The moisture permeability determined by this measurement is the moisture permeability of the laminate of the triacetyl cellulose film and the pressure-sensitive adhesive sheet, but the moisture permeability of the triacetyl cellulose film is sufficiently larger than the moisture permeability of the pressure-sensitive adhesive sheet. Moisture permeability = moisture permeability of the adhesive sheet.

<Ultraviolet transmittance>
The transmittance spectrum of the pressure-sensitive adhesive sheet was measured with a visible ultraviolet spectrophotometer, and the transmittance at a wavelength of 380 nm was read.

[Production of rubber adhesive sheet]
<Preparation of adhesive sheets A1 to A5>
Polyisobutylene (PIB; “OPPANOL B80” manufactured by BASF, weight average molecular weight: about 750,000, glass transition temperature: −63 ° C.): 100 parts by weight, and benzotriazole-based UV absorber (“TINUVIN 384-2” manufactured by BASF) ): A pressure-sensitive adhesive composition A was prepared by mixing 7.8 parts by weight with 300 parts by weight of toluene. After applying the above-mentioned pressure-sensitive adhesive composition A to the release-treated surface of the separator (polyester film peeled with silicone on one side) so as to have the thickness after drying shown in Table 1, it was heated at 130 ° C. for 2 minutes. Then, the solvent was removed to prepare an adhesive sheet.

<Preparation of adhesive sheet B1>
Using the pressure-sensitive adhesive composition B to which no ultraviolet absorber was added, a pressure-sensitive adhesive sheet B1 was produced in the same manner as described above.

<Preparation of adhesive sheets C1 and C2>
Polystyrene-poly (ethylene / propylene) -polystyrene block copolymer (Kuraray “Septon 2063”, styrene content: 13%; SEPS): 100 parts by weight, and triazine UV absorber (“TINOSORB S” manufactured by BASF) ): PSA composition C was prepared by mixing 8.9 parts by weight with 300 parts by weight of toluene. The pressure-sensitive adhesive composition C was applied on the release-treated surface of the separator so as to have a thickness after drying shown in Table 1, and then heated at 130 ° C. for 2 minutes to remove the solvent, thereby preparing a pressure-sensitive adhesive sheet.

  Table 1 shows the composition of the pressure-sensitive adhesive compositions A to C and the properties (thickness, moisture permeability, and storage elastic modulus) of each pressure-sensitive adhesive sheet.

[Production of acrylic adhesive sheet]
<Preparation of adhesive sheets K1 to K3>
(Preparation of adhesive composition)
In the reaction vessel, 2-ethylhexyl acrylate (2EHA): 40 parts by weight, isostearyl acrylate (ISA): 40 parts by weight, N-vinylpyrrolidone (NVP): 19 parts by weight, 4-hydroxybutyl acrylate (4HBA): 1 1 part by weight and 1-hydroxy-cyclohexyl-phenyl-ketone (“Irgacure 184” manufactured by BASF) as a photopolymerization initiator: 0.1 part by weight was injected and irradiated with ultraviolet rays in a nitrogen atmosphere, and the polymerization rate was 10%. A prepolymer composition was obtained. To 100 parts by weight of this prepolymer composition, 2,2-dimethoxy-1,2-diphenylethane-1-one (“Irgacure 651” manufactured by BASF; IRG651) as a photopolymerization initiator and trimethylolpropane tri as a polyfunctional monomer were used. Add acrylate (TMPTA), α-thioglycerol (TGR) as chain transfer agent, and 3-glycidoxypropyltrimethoxysilane (“KBM403” manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent in the amounts shown in Table 2. Then, these were uniformly mixed to prepare an adhesive composition K.

(Preparation of adhesive sheet)
The pressure-sensitive adhesive composition K was applied to the release treatment surface of the separator so as to have the thickness shown in Table 2 to form an application layer, and the release treatment surface of another separator was bonded onto the application layer. After that, UV irradiation is performed with a black light whose position is adjusted so that the irradiation intensity on the irradiation surface immediately below the lamp is 5 mW / cm ² , and the polymerization is advanced by the UV irradiation until the integrated light quantity becomes 3000 mJ / cm ^2, and the acrylic adhesive A sheet was produced.

<Adhesive sheets L1 and L2>
A pressure-sensitive adhesive composition L was prepared by adding 0.7 parts by weight of a triazine-based ultraviolet absorber (“TINOSORB S” manufactured by BASF) to 100 parts by weight of the prepolymer composition. . Using this pressure-sensitive adhesive composition L, coating and UV polymerization were performed in the same manner as described above to prepare a pressure-sensitive adhesive sheet L1 having a thickness of 100 μm and a pressure-sensitive adhesive sheet L2 having a thickness of 125 μm.

<Adhesive sheet M1>
In a reaction vessel, 2EHA: 72 parts by weight, NVP: 13 parts by weight, 2-hydroxyethyl acrylate (2HEA): 14 parts by weight, azobisisobutyronitrile (AIBN): 0.2 parts by weight as a thermal polymerization initiator And TGR: 0.12 parts by weight as a chain transfer agent were added together with 150 parts by weight of ethyl acetate, and the mixture was stirred for 1 hour in a nitrogen atmosphere at 23 ° C. to perform nitrogen substitution. Then, it was made to react at 65 degreeC for 7 hours, and the solution of the acrylic base polymer whose weight average molecular weight (Mw) was 250,000 was obtained. To this acrylic base polymer solution, a trimethylolpropane adduct of xylylene diisocyanate as an isocyanate-based crosslinking agent (“Takenate D110N” manufactured by Mitsui Chemicals) and polypropylene glycol diacrylate (“Shin Nakamura Kogaku” “NK” manufactured as a photopolymerizable polyfunctional monomer) Ester APG400 "), Irgacure 651 as a photopolymerization initiator, and KBM403 as a silane coupling agent were added in the blending amounts shown in Table 2, and then mixed uniformly to prepare an adhesive composition solution. Apply the above-mentioned pressure-sensitive adhesive composition on the release-treated surface of the separator so that the thickness after drying is 100 μm, and heat at 100 ° C. for 6 minutes to dry-remove the solvent and thermally cross-link the isocyanate cross-linking agent. Thus, a photocurable pressure-sensitive adhesive sheet M1 was obtained.

<Adhesive sheets N1 and O1>
The pressure-sensitive adhesive compositions N and O were prepared in the same manner as the pressure-sensitive adhesive composition K except that the prepolymer charged monomer composition and the addition amount of the polyfunctional monomer and the ultraviolet absorber were changed as shown in Table 2. Prepared. Using these pressure-sensitive adhesive compositions, pressure-sensitive adhesive sheets N1 and O1 having a thickness of 125 μm were produced in the same manner as described above.

  Table 2 shows the compositions of the pressure-sensitive adhesive compositions K to O and the properties (thickness, moisture permeability, and storage elastic modulus) of each pressure-sensitive adhesive sheet.

[Preparation of cell side adhesive sheet]
(Preparation of adhesive composition)
In a reaction vessel, 97 parts by weight of butyl acrylate and 3 parts by weight of acrylic acid as monomer components, and 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator were added to ethyl acetate. The mixture was added together with 233 parts by weight and stirred for 1 hour in a nitrogen atmosphere at 23 ° C. to perform nitrogen substitution. Then, it was made to react at 60 degreeC for 5 hours, and the solution of the acrylic average polymer whose weight average molecular weight (Mw) was 1.1 million was obtained. To this acrylic base polymer solution, trimethylolpropane tolylene diisocyanate (“Coronate L” manufactured by Nippon Polyurethane Industry) as an isocyanate-based crosslinking agent: 0.8 part by weight, and a silane coupling agent (“KBM403” manufactured by Shin-Etsu Chemical): 0 After adding 1 part by weight, the mixture was uniformly mixed to prepare an adhesive composition solution.

(Preparation of adhesive sheet)
The pressure-sensitive adhesive composition described above was applied to the release-treated surface of the separator so that the thickness after drying was 20 μm, dried at 100 ° C. for 3 minutes to remove the solvent, and a pressure-sensitive adhesive sheet was obtained. Then, it heated at 50 degreeC for 48 hours, the crosslinking process was performed, and the cell side adhesive sheet was obtained.

[Production of single protective polarizing plate]
A polycycloolefin protective film was bonded to one surface (surface on the cell side) of a polarizer made of a stretched polyvinyl alcohol film having a thickness of 25 μm impregnated with iodine through an adhesive to produce a single protective polarizing plate.

[Example 1]
The pressure-sensitive adhesive sheet A1 was bonded to the exposed surface of the polarizer of the single protective polarizing plate using a roll laminator. Furthermore, said adhesive sheet K1 was bonded together on adhesive sheet A1 using the roll laminator. Then, said cell side adhesive sheet was bonded together on the polycycloolefin protective film of the piece protection polarizing plate using the roll laminator. In this way, the front-side pressure-sensitive adhesive sheet composed of the pressure-sensitive adhesive sheet A1 and the pressure-sensitive adhesive sheet K1 is provided on the polarizer-exposed surface side of the single protective polarizing plate, and the cell side is provided on the surface of the single protective polarizing plate with the transparent protective film. A polarizing plate with a double-sided pressure-sensitive adhesive provided with a pressure-sensitive adhesive sheet was obtained.

[Examples 2-7, Comparative Examples 1-3]
A polarizing plate with a double-sided pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the configuration of the front-side pressure-sensitive adhesive sheet bonded to the polarizer-exposed surface of the single protective polarizing plate was changed as shown in Table 3.

[Comparative Examples 4 and 5]
The double-sided adhesive is the same as in Example 1 except that the adhesive sheet to be bonded to the surface on the viewing side of the single protective polarizing plate is changed to an adhesive sheet having a thickness of 125 μm consisting of a single layer of adhesive sheets A5 and L2, respectively. A polarizing plate with an agent was obtained.

[Evaluation]
<Display unevenness>
Remove the backlight from the replacement upper LCD panel of the Nintendo 3DS, remove the polarizing plate on the opposite side of the LCD panel backlight, and then use a clean cloth soaked in ethanol to adhere the surface of the liquid crystal cell. The agent was removed. After the polarizing plate with a double-sided adhesive is cut to a size of 50 mm x 80 mm, the cell-side separator is peeled off, the cell-side adhesive sheet is overlaid on the center of the liquid crystal cell surface, and bonded using a hand roller It was.

Thereafter, the separator on the viewing side of the polarizing plate with a double-sided pressure-sensitive adhesive was peeled off, and a glass plate (0.7 mm thickness × 50 mm × 100 mm, ink printing thickness = 10 μm, both printed with black ink in a frame shape on the periphery) The printing surface of the short side (long side direction) ink printing width: 15 mm each and the long side (short side direction) ink printing width: 5 mm each is placed on the exposed surface of the adhesive, and vacuum thermocompression bonding Bonding was performed using an apparatus (temperature: 25 ° C., internal pressure: 50 Pa, pressure: 0.3 MPa, pressure holding time: 10 seconds). Thereafter, autoclaving (50 ° C., 0.5 MPa, 15 minutes) was performed to obtain an evaluation panel. For Example 3 using a photo-curing type pressure-sensitive adhesive sheet, after the autoclave treatment, an ultraviolet ray with an integrated light amount of 3000 mJ / cm ² was irradiated through a glass plate on the viewing side using a high-pressure mercury lamp. The panel subjected to UV curing was used as an evaluation panel.

  The evaluation panel was replaced with the image display panel of the Nintendo 3DS main body, and electrical connection was made to obtain an evaluation image display device. When the panel is displayed in white, the presence or absence of display unevenness in the vicinity of the printing frame is visually checked. If there is no display unevenness, ○, if there is slight display unevenness, Δ, What was easily confirmed was set as x.

<Bubble>
After the polarizing plate with a double-sided adhesive is cut to a size of 45 mm x 75 mm, the separator on the cell side is peeled off and bonded to the center of a 0.2 mm thick x 50 mm x 100 mm glass plate using a hand roller It was. After that, in the same manner as the production of the display unevenness evaluation panel described above, a glass plate on which black ink is printed in a frame shape is bonded to the peripheral side of the polarizing plate with a double-sided pressure-sensitive adhesive, and an autoclave treatment is performed. A panel for evaluation was obtained. About Example 3, what carried out UV hardening of the adhesive after the autoclave process was made into the panel for evaluation similarly to the panel for display nonuniformity evaluation.

  The vicinity of the inside of the black ink printing portion of the evaluation panel was observed with a digital microscope having a magnification of 20 times to confirm the presence or absence of bubbles in the adhesive sheet (initial evaluation). Further, after being put into an oven at 85 ° C. for 48 hours, the presence or absence of bubbles was confirmed by the same method (evaluation after heating). In the initial stage and after heating, the case where bubbles were not confirmed was marked with ◯, and the case where bubbles were confirmed was marked with x.

<Evaluation of humidification durability (color loss at end)>
After the polarizing plate with a double-sided pressure-sensitive adhesive was cut into a size of 50 mm × 50 mm, an alkali-free glass plate was superposed on each of the double-sided pressure-sensitive adhesive layers, and bonded using a hand roller. Furthermore, about Example 3, UV curing of the adhesive was performed by irradiating ultraviolet rays through the glass plate bonded to the first adhesive layer side. This test piece was put into a constant temperature and humidity chamber having a temperature of 60 ° C. and a relative humidity of 95%, and left to stand for 300 hours, and then taken out. The polarizing plate of the test piece and the standard polarizing plate are arranged in crossed Nicols, and the vicinity of the corner of the polarizing plate of the test piece is observed with an optical microscope (“MX61L” manufactured by Olympus, magnification 10 ×), and color loss occurs. The width of the region (distance from the end of the polarizing plate) was measured. The microscope observation images of Example 1 and Comparative Example 5 are shown in FIG.

[Evaluation results]
The laminated structure of the front-side pressure-sensitive adhesive sheet in the polarizing plates with double-sided pressure-sensitive adhesives of the above Examples and Comparative Examples, the physical properties of the laminated pressure-sensitive adhesive sheets (however, Comparative Examples 4 and 5 are the characteristics of a single-layer pressure-sensitive adhesive sheet) Table 3 shows. Regarding Example 3, the storage elastic modulus is a value before UV curing, and the moisture permeability is a value after UV curing.

  In Comparative Example 5 in which the single-layer acrylic pressure-sensitive adhesive sheet L2 was used as the front side pressure-sensitive adhesive sheet, there was no air bubbles and display unevenness, and the printing step absorbability was exhibited by the pressure-sensitive adhesive sheet. However, as shown in FIG. The color missing at the end of the polarizing plate after the test was large and the humidification durability was inferior. On the other hand, in Comparative Example 4 in which the single-layer rubber-based pressure-sensitive adhesive sheet A5 was used as the front-side pressure-sensitive adhesive sheet, the color leakage at the end of the polarizing plate after the humidification test was suppressed, but the printing level difference of the front transparent plate Due to bubble mixing and display unevenness were observed. From these results, it can be seen that when the front-side pressure-sensitive adhesive sheet provided on the single protective polarizing plate is a single layer, it is difficult to achieve both step absorbency and moisture resistance.

  On the other hand, the rubber-type 1st adhesive layer was provided in contact with the polarizer of a single-sided protective film, and Examples 1-8 by which the acrylic 2nd adhesive layer was provided on the 1st adhesive layer. Then, it turns out that level | step difference absorbability and moisture resistance are compatible.

  In Example 6 and Comparative Example 1, the compositions of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer were the same, but in Comparative Example 1, the amount of color loss at the end portion was large. In Comparative Example 1, since the thickness of the first pressure-sensitive adhesive layer is small and the moisture permeability is high, moisture that has entered from the side surface of the front-side pressure-sensitive adhesive sheet easily migrates to the vicinity of the end face of the polarizer. This is probably because of

  In Example 1, Example 7, Example 8, and Comparative Example 3, the compositions of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are the same, and the thicknesses thereof are different. Also in these examples and comparative examples, the larger the thickness of the first pressure-sensitive adhesive layer, the smaller the amount of color loss at the end of the polarizing plate tends to be reduced, and the first pressure-sensitive adhesive layer with low moisture permeability is durable. It can be seen that it contributes to improvement.

In Comparative Example 3 in which the thickness of the second pressure-sensitive adhesive layer is small and the thickness of the first pressure-sensitive adhesive layer is large, color leakage at the end of the polarizing plate after the humidification test was suppressed, Due to bubble mixing and display unevenness were observed. This is because the viscoelastic behavior of the thick first pressure-sensitive adhesive layer is the dominant factor of the viscoelastic behavior of the entire laminated pressure-sensitive adhesive sheet, and the G ′ _{80 of the} pressure-sensitive adhesive sheet is large, so that the step absorbability is insufficient. This is thought to be due to the fact that

  In Example 8 where the thicknesses of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer were equal, the mixing of bubbles due to the printing step of the front transparent plate was suppressed, but slight display unevenness was confirmed. This is considered to be due to the fact that the pressure-sensitive adhesive sheet of Example 8 has lower step absorbability than other examples in which the thickness of the second pressure-sensitive adhesive layer is large.

  In Example 1, Example 3, Example 4, and Comparative Example 2, the rubber adhesive sheet A1 having a thickness of 25 μm is used as the first adhesive layer, and the acrylic adhesive of the second adhesive layer is used. The composition is different. In these examples and comparative examples, since the amount of color leakage at the end of the polarizing plate after the humidification test is the same, the first pressure-sensitive adhesive layer with low moisture permeability contributes to durability improvement. I understand.

  In Comparative Example 2 in which the storage adhesive modulus of the second pressure-sensitive adhesive layer was high, air bubbles mixed in and display unevenness due to the printing step of the front transparent plate was observed. In Example 4, the mixing of bubbles due to the printing step on the front transparent plate was suppressed, but slight display unevenness was confirmed. On the other hand, in Examples 1 and 2, there were no bubbles and display unevenness, and the pressure-sensitive adhesive sheet had good level difference absorbability.

From the above results, the laminated adhesive of the first pressure-sensitive adhesive layer having a low moisture permeability and the second pressure-sensitive adhesive layer having a large storage elastic modulus temperature dependence and a small G ′ ₈₀ on the polarizer exposed surface of the single protective polarizing plate. It can be seen that by providing the sheet, high durability and step absorbability can be imparted, and the image display device can be thinned.

DESCRIPTION OF SYMBOLS 10 Single side protective polarizing plate 20 Front side adhesive sheet 21,22 Adhesive layer 30 Cell side adhesive sheet 41,42 Protective sheet 1,2 Adhesive polarizing plate 60 Image display cell 70 Front transparent member 71 Plate-like transparent member 76 Printing part 100 Image display device

Claims (14)

A polarizing plate with an adhesive used to be disposed between the front transparent plate or the touch panel and the image display cell,
A polarizer comprising a polyvinyl alcohol film containing iodine, a transparent protective film bonded to the first main surface of the polarizer, and a front side pressure-sensitive adhesive sheet provided in contact with the second main surface of the polarizer And
The front pressure-sensitive adhesive sheet is a laminated pressure-sensitive adhesive sheet in which at least two pressure-sensitive adhesive layers are laminated, a first pressure-sensitive adhesive layer disposed in contact with the polarizer, and a first pressure-sensitive adhesive layer disposed away from the polarizer. With two adhesive layers,
The storage elastic modulus G ′ ₈₀ at 80 ° C. of the front side pressure-sensitive adhesive sheet is 1 × 10 ⁵ Pa or less,
A polarizing plate with an adhesive, wherein the moisture permeability of the first adhesive layer is 150 g / m ² · 24 h or less.   The polarizing plate with an adhesive according to claim 1, wherein the first adhesive layer has a thickness of 50 μm or less.   The polarizing plate with an adhesive according to claim 1 or 2, wherein the second adhesive layer has a thickness of 50 µm or more.   The polarizing plate with the pressure-sensitive adhesive according to any one of claims 1 to 3, wherein a thickness of the second pressure-sensitive adhesive layer is larger than a thickness of the first pressure-sensitive adhesive layer.   The polarizing plate with an adhesive according to any one of claims 1 to 4, wherein the thickness of the front-side pressure-sensitive adhesive sheet is 250 µm or less.   The polarizing plate with an adhesive according to any one of claims 1 to 5, wherein the first adhesive layer is an adhesive layer containing a rubber-based polymer as a main component.   The polarizing plate with the pressure-sensitive adhesive according to any one of claims 1 to 6, wherein the second pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer containing an acrylic polymer as a main component. The second adhesive layer has a storage elastic modulus G ′ _{25 at} 25 ° C. of 1 × 10 ⁴ or more and a storage elastic modulus G ′ _{80 at} 80 ° C. of 1 × 10 ⁵ Pa or less. The polarizing plate with an adhesive of any one of these. The second pressure-sensitive adhesive layer has a ratio G ′ ₂₅ / G ′ ₈₀ of storage elastic modulus G ′ _{80 at 80} ° C. and storage elastic modulus G ′ ₂₅ at 25 ° C. of 3.5 or more. The polarizing plate with an adhesive of any one of Claims 1. 10. The first pressure-sensitive adhesive layer according to claim 1, wherein a ratio G ′ ₂₅ / G ′ ₈₀ of a storage elastic modulus G ′ _{80 at 80} ° C. and a storage elastic modulus G ′ ₂₅ at 25 ° C. is 3 or less. The polarizing plate with an adhesive of 1 item | term. The front-side pressure-sensitive adhesive sheet, the ratio G _'25 / G' ₈₀ of the ₂₅ 'storage modulus G ₈₀ and 25 ° C.' storage modulus G 80 ° C. is from 2 to 100, any one of claims 1 to 10, The polarizing plate with an adhesive of 1 item | term.   The polarizing plate with an adhesive according to any one of claims 1 to 11, wherein the front-side pressure-sensitive adhesive sheet has a light transmittance of 15% or less at a wavelength of 380 nm.   The polarizing plate with an adhesive according to any one of claims 1 to 12, further comprising a cell-side adhesive sheet on the transparent protective film. The surface of an image display cell is equipped with the polarizing plate with an adhesive according to any one of claims 1 to 13, and a front transparent plate or a touch panel,
The image display apparatus by which the said polarizing plate and the said front transparent plate or a touch panel are bonded together by the said front side adhesive sheet.