KR20210097625A - Adhesive sheet and image display device - Google Patents

Abstract

An adhesive sheet (15) has a first adhesive layer (51) on one main surface of a transparent film base material (59) and a second adhesive layer (53) on the other main surface. In the formation of an image display device in which the thickness of the first adhesive layer is thicker than the thickness of the second adhesive layer, the first adhesive layer is disposed in contact with a front transparent plate, and the second adhesive layer is disposed in contact with an image display panel.

Description

Adhesive sheet and image display device {ADHESIVE SHEET AND IMAGE DISPLAY DEVICE}

TECHNICAL FIELD The present invention relates to a double-sided pressure-sensitive adhesive sheet used for forming an image display device and an image display device.

DESCRIPTION OF RELATED ART Liquid crystal display devices and organic electroluminescent display devices are widely used as various image display apparatuses, such as a cellular phone, a smart phone, a car navigation apparatus, a personal computer monitor, and a television. For the purpose of preventing damage to the image display panel due to impact from the outer surface, etc., a front transparent plate (also referred to as a “cover window”) such as a transparent resin plate or a glass plate is provided on the visual display side of the image display panel there may be cases

A colored layer (decorative printing layer) for the purpose of decoration or light shielding may be formed on the periphery of the front transparent plate. When a pressure-sensitive adhesive is bonded to a transparent member having a decorative printed layer, air bubbles are likely to be generated around the printed step portion. Therefore, the method of suppressing problems, such as a bubble mixing, is employ|adopted by giving step water absorption by a thick adhesive sheet (for example, patent document 1). As the luminance of the display device increases, the thickness of the decorative printed layer tends to increase in order to increase the light-shielding property, and as a result, a thicker and more flexible adhesive sheet is used for bonding the front transparent plate. .

In Patent Document 2, as a pressure-sensitive adhesive sheet for bonding a cover window to a polarizing plate of a liquid crystal panel having an in-cell or on-cell touch sensor, an adhesive sheet with a base film in which an adhesive layer having a predetermined thickness is laminated on both sides of a base film It is suggested to use

Conventionally, as an image display device, the liquid crystal display device which arrange|positioned the polarizing plate on the front and back of the liquid crystal cell which clamped the liquid crystal layer between two glass substrates, and combined it with light sources, such as a backlight, has been mainstream. In recent years, the organic electroluminescent display which provided the electrode and the light emitting layer on resin film board|substrates, such as a polyimide film, is put to practical use. Since organic EL is a self-luminous type and does not require a light source, the screen can be made thinner, curved, flexible, or the like.

International Publication No. 2013/161666 Japanese Patent Laid-Open No. 2017-160416

In the formation of an image display device, pressure processing such as hot pressing or crimping may be performed at the time or after bonding of the image display panel and the front transparent plate. In an image display panel using a rigid substrate such as a glass substrate, since the substrate is hardly deformed, the image display panel hardly deforms even when a local pressure is applied. On the other hand, in the image display panel using a flexible substrate, when a large pressure is locally applied to the connection location of components, etc. at the time of press processing, the board|substrate deform|transforms locally. If the local deformation does not recover after releasing the pressure and remains as an "indentation", it may become a defect in image display.

By using a double-sided adhesive sheet provided with a base material having adhesive layers on both surfaces of the film base material for bonding the image display panel and the front transparent plate, indentation caused by deformation of the image display panel due to local pressure from the back side is suppressed. possible.

The adhesive sheet of this invention is a base material-equipped double-sided adhesive sheet which equips one main surface of a transparent film base material with a 1st adhesive layer, and equips the other main surface with a 2nd adhesive layer. The thickness of the first pressure-sensitive adhesive layer is larger than the thickness of the second pressure-sensitive adhesive layer.

The thickness of the first pressure-sensitive adhesive layer is preferably 80 µm or more, and the thickness of the second pressure-sensitive adhesive layer is preferably 150 µm or less. As for the thickness of a transparent film base material, 15-150 micrometers is preferable. As for front retardation of a transparent film base material, 50 nm or less is preferable.

The double-sided adhesive sheet with a base material can be used for formation of the image display apparatus by which the front transparent plate was arrange|positioned on the visual recognition side of an image display panel. In the image display device, the first adhesive layer is bonded to the front transparent plate, and the second adhesive layer is bonded to the image display panel. The image display panel may be equipped with the polarizing plate on the visual recognition side surface of an image display cell. In this case, the polarizing plate is bonded to the second pressure-sensitive adhesive layer.

The image display panel may be an organic EL display device including an organic EL cell. The organic EL cell may include an electrode and an organic light emitting layer on a resin film substrate.

By bonding the image display cell and the front transparent plate via the adhesive sheet with a base material of this invention, the residual|survival of the indentation resulting from the press from the back side can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the example of the lamination|stacking structure of the double-sided adhesive sheet with a base material.
Fig. 2 is a cross-sectional view showing a configuration example of an image display device;
It is sectional drawing which shows the laminated|stacked structural example of an optical film with an adhesive sheet.
It is sectional drawing which shows the laminated|stacked structural example of an optical film with an adhesive sheet.
It is a schematic diagram which shows the arrangement|positioning of the sample in an impact resistance test.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing of the double-sided adhesive sheet with a base material. The double-sided pressure-sensitive adhesive sheet 15 provided with a substrate includes a first pressure-sensitive adhesive layer 51 on one main surface of the transparent film substrate 59 , and a second pressure-sensitive adhesive layer 53 on the other main surface of the transparent film substrate 59 . ) is provided. In the form shown in FIG. 1, the release films 21 and 23 are temporarily attached to the surface of the adhesive layers 51 and 53. As shown in FIG. FIG. 2 is a cross-sectional view showing a configuration example of an image display device in which a front transparent plate 7 is fixed to the viewer-side surface of an image display panel using a double-sided adhesive sheet 15 with a base material.

[Image display panel]

In the image display device 201 shown in FIG. 2 , the image display panel 10 includes image display cells 6 such as liquid crystal cells and organic EL cells.

The image display cell 6 is provided with the functional layer for image display, and the board|substrate which supports the functional layer. For example, in a liquid crystal cell, a liquid crystal layer is provided between two transparent substrates, and the quantity of the light which permeate|transmits a polarizing plate is adjusted by changing the orientation state of a liquid crystal and changing the polarization state of transmitted light. In an organic EL cell, a pair of electrodes is provided on a board|substrate, and the light emission amount of the organic light emitting layer provided between the electrodes is adjusted.

The board|substrate of the image display cell 6 may be rigid board|substrates, such as glass, and flexible board|substrates, such as a resin film, may be sufficient as it. By using a resin film board|substrate, thickness reduction and weight reduction are attained. Moreover, if a resin film board|substrate is used, it is also possible to form a curved display and a flexible display.

As an image display cell using a film substrate, a top emission type or a bottom emission type organic electroluminescent cell is mentioned. The top emission type organic EL cell is provided with a metal electrode, an organic light emitting layer, and a transparent electrode in order on a board|substrate, and light is radiate|emitted from the transparent electrode side (opposite side to a board|substrate). A bottom-emission type organic EL cell is equipped with a transparent electrode, an organic light emitting layer, and a metal electrode in order on a board|substrate, and radiates|emits light from the board|substrate side. The organic light emitting layer may be provided with an electron transport layer, a hole transport layer, etc. in addition to the organic layer which itself functions as a light emitting layer. In the bottom emission type organic EL cell, a transparent substrate is used. In the top emission type organic EL cell, the substrate is not necessarily transparent.

On the back surface side of the image display cell 6, the board|substrate 9 for reinforcement may be provided for the purpose of protection and reinforcement of a board|substrate. As the reinforcing board|substrate 9, a metal plate, a glass plate, a resin film, etc. are used. The thickness of the reinforcing substrate is, for example, about 10 to 200 µm.

A flexible printed wiring board (FPC) 95 is connected to the outer peripheral end of the image display cell 6 . The FPC 95 is bent so as to return to the back surface of the image display cell 6 and is connected to the main board 90 arranged on the back surface of the image display cell. In FIG. 2 , the FPC and the main board are connected by inserting the terminals of the FPC 95 into the connector 91 provided on the main board 90 . The FPC may be connected on the main board by soldering or the like. It is also possible to connect the FPC and the main board through a lead wire. In the connection place of the FPC, the thickness of the connector or soldering part is locally large, and a convex part may be formed.

The optical film 3 may be arrange|positioned on the visual recognition side surface of the image display cell 6 via the adhesive layer 4 . As the optical film 3 arrange|positioned on the visual recognition side surface of the image display cell 6, a polarizing plate is mentioned. A polarizing plate contains a polarizer, and the transparent film as a polarizer protective film is generally laminated|stacked on both surfaces of a polarizer. You may abbreviate|omit the polarizer protective film of one surface or both surfaces of a polarizer.

The polarizing plate may be equipped with the optical function film laminated|stacked on one or both surfaces of a polarizer via a suitable adhesive bond layer or an adhesive layer as needed. As an optical function film, a retardation plate, a viewing angle expansion film, a viewing angle restriction|limiting (peep prevention) film, a brightness improvement film, etc. are mentioned.

When the image display cell 6 is an organic EL cell, since the metal electrode of the organic EL cell is light-reflecting, when external light is incident on the inside of the organic EL cell, the light is reflected by the metal electrode, and the reflected light from the outside is mirrored and admitted together. By arranging the circularly polarizing plate as the optical film 3 on the visual side surface of the organic EL cell, re-emission of the reflected light from the metal electrode to the outside can be prevented, and the visibility and designability of the screen can be improved.

The image display panel 10 may be an in-cell type or on-cell type image display panel with a touch sensor having a built-in touch sensor. When the image display panel 10 has a touch sensor function, it is not necessary to separately provide a touch sensor on the viewer side of the image display panel 10 . Therefore, in the image display device 201 , the front transparent plate 7 is bonded to the viewer-side surface of the image display panel 10 via the double-sided adhesive sheet 15 provided with the substrate.

[Front transparent plate]

The front transparent plate 7 is provided with a printing layer 76 on the periphery of one side of the transparent flat plate 71 . By disposing the front transparent plate on the viewer-side surface of the image display panel, it is possible to prevent damage to the image display panel 10 due to an impact from the outer surface. Moreover, since wiring members, such as the FPC 95, are not visually recognized from the outside by providing the printing layer 76, the designability of an image display apparatus increases.

As the transparent plate 71, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate is used. The transparent plate 71 may have rigidity or may be flexible. From the viewpoint of enhancing the protection against the image display panel 10, the transparent plate 71 is preferably a rigid substrate, and the thickness of the transparent plate 71 is preferably 200 µm or more, and more preferably 300 µm or more. . The thickness of the printed layer 76 is about 10-100 micrometers.

[Double-sided adhesive sheet with base material]

As shown in FIG. 2 , in the double-sided pressure-sensitive adhesive sheet 15 with a base material, the first pressure-sensitive adhesive layer 51 provided on one main surface of the transparent film base material 59 is bonded to the front transparent plate 7 , and is transparent The second pressure-sensitive adhesive layer 53 bonded to the main surface of the other side of the film substrate 59 is bonded to the image display panel 10 .

As for the adhesive sheet 15, it is preferable that the adhesive force with respect to the glass of the 1st adhesive layer 51 is 2 N/10 mm or more, 4 N/10 mm or more is more preferable, 5 N/10 mm or more is still more preferable. When adhesive force is the said range, peeling of the adhesive sheet from a to-be-adhered body in the case where the impact by stress by deformation|transformation, a fall, etc. generate|occur|produces can be prevented. It is preferable that the 2nd adhesive layer 53 also has high adhesive force similarly to a 1st adhesive layer. Adhesive force is calculated|required by the peel test of 300 mm/min of tensile velocity and 180 degrees of peeling angles using a glass plate as a to-be-adhered body. Unless otherwise stated, adhesion is a measurement at 25°C.

85 % or more is preferable and, as for the total light transmittance of the adhesive sheet 15, 90 % or more is more preferable. As for the haze of the adhesive sheet 15, 1 % or less is preferable. 120-1000 micrometers is preferable, as for the thickness (the total thickness of the transparent film base material 59 and the adhesive layers 51, 53) of the adhesive sheet 15, 150-500 micrometers is more preferable, 180-400 micrometers is more preferably.

It is preferable that the adhesive sheet 15 has ultraviolet-ray shielding property. Since the pressure-sensitive adhesive sheet 15 has UV-shielding properties, deterioration due to UV rays of the organic layer (eg, organic light emitting layer) included in the polarizing plate 3 of the image display panel 10 or the image display cell 6 can be suppressed. there is. 20 % or less is preferable, as for the transmittance|permeability of wavelength 380 nm of the adhesive sheet 15, 15 % or less is more preferable, and its 10 % or less is still more preferable. In order to provide the pressure-sensitive adhesive sheet 15 with UV-shielding properties, any one or more of the first pressure-sensitive adhesive layer 51 , the transparent film substrate 59 and the second pressure-sensitive adhesive layer 53 may have UV-shielding properties. For example, ultraviolet shielding properties can be imparted by using a resin material having ultraviolet shielding properties, such as transparent polyimide and polyethylene naphthalate, as the transparent film base material 59 . Moreover, you may include a ultraviolet absorber in any one or multiple of the transparent film base material 59 and the adhesive layers 51 and 53.

<Transparent film substrate>

As the transparent film base material 59, a transparent resin film is used. 85% or more is preferable and, as for the total light transmittance of the transparent film base material 59, 90% or more is more preferable. The resin material constituting the transparent film base material 59 will not be particularly limited as long as it has transparency, and polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; Cyclic polyolefins, such as a norbornene-type polymer; Cellulose polymers, such as a diacetyl cellulose and a triacetyl cellulose; acrylic polymer; styrenic polymer; Polycarbonate, polyamide, polyimide, polyether ether ketone, etc. are mentioned.

The transparent film base material 59 may have functional layers, such as an easily bonding layer and an antistatic layer, on the surface. The transparent film base material 59 may have a function as a touch sensor. When the transparent film substrate 59 has a function as a touch sensor, an electrode for position detection is provided on the surface of the film. On the other hand, when the image display panel 10 has a touch sensor function, it is not necessary to provide a touch sensor on the visual recognition side of the image display panel 10 . Therefore, the transparent film base material 59 does not need to be equipped with the electrode for position detection.

When the transparent film base material is arrange|positioned between the two adhesive layers 51 and 53, the elasticity of the adhesive sheet 15 whole becomes high, and the restoring force with respect to a deformation|transformation becomes large. Therefore, even when the image display panel is deformed by the pressure from the back side of the image display panel 10, the plastic deformation of the pressure-sensitive adhesive sheet 15 is small, and the residual indentation can be reduced by the restoring force of the film substrate. there is. About 15-150 micrometers is preferable, as for the thickness of the transparent film base material 59, 25-120 micrometers is more preferable, and its 35-100 micrometers are still more preferable.

It is preferable that the transparent film base material 59 has optical isotropy from a viewpoint of suppressing rainbow-like coloring (iris phenomenon) when the screen of an image display apparatus is visually recognized. 50 nm or less is preferable, as for the front retardation in wavelength 590 nm of the transparent film base material 59, 30 nm or less is more preferable, 10 nm or less is still more preferable, and its 5 nm or less is especially preferable.

<Adhesive layer>

The thickness of the 1st adhesive layer 51 is larger than the thickness of the 2nd adhesive layer 53. As shown in FIG. 0.2 to 0.85 times of the thickness of the 1st adhesive layer 51 is preferable, as for the thickness of the 2nd adhesive layer 53, 0.3 to 0.8 times are more preferable, 0.4 to 0.75 times are still more preferable.

When the thickness of the first pressure-sensitive adhesive layer 51 is relatively large, the step absorbency of the front transparent plate 7 with respect to the printed layer 76 tends to increase. From the viewpoint of securing step absorption and impact resistance, the thickness of the first pressure-sensitive adhesive layer 51 is preferably 80 μm or more. The thickness of the 1st adhesive layer 51 may be 100 micrometers or more or 120 micrometers or more. When bonding the first pressure-sensitive adhesive layer 51 to the front transparent plate having the printed layer 76 , the thickness of the first pressure-sensitive adhesive layer 51 is preferably larger than the thickness of the printed layer 76 .

Although the upper limit in particular of the thickness of the 1st adhesive layer 51 is not restrict|limited, From a viewpoint of productivity, processing dimensional stability, etc., 500 micrometers or less are preferable, 300 micrometers or less are more preferable, and 250 micrometers or less are still more preferable.

When the thickness of the second pressure-sensitive adhesive layer 53 is relatively small, the plastic deformation with respect to the pressure from the image display panel 10 side is reduced. Even when the image display panel 10 is deformed by the pressure from the back side, since plastic deformation of the pressure-sensitive adhesive sheet 15 is small, the residual indentation can be reduced.

From a viewpoint of making plastic deformation small and reducing an indentation, 150 micrometers or less are preferable and, as for the thickness of the 2nd adhesive layer 53, 120 micrometers or less are more preferable. The thickness of the 2nd adhesive layer 53 may be 100 micrometers or less or 80 micrometers or less. From a viewpoint of providing impact resistance, 30 micrometers or more are preferable and, as for the thickness of the 2nd adhesive layer 53, 50 micrometers or more are more preferable.

In the case of bonding an image display panel and a front transparent plate through a single-layer non-substrate adhesive sheet, if the thickness of the adhesive sheet is small, the step absorbability for the printing step of the front transparent plate is insufficient, and the thickness of the adhesive sheet is When it is large, since the plastic deformation of an adhesive sheet is large, it is easy to remain|survive the indentation by the press from the panel side. The adhesive sheet with a base material provided with the transparent film base material 59 between the two adhesive layers 51 and 53 can ensure the step absorbency by the 1st adhesive layer 51 with a relatively large thickness. In addition, the relatively small thickness of the second pressure-sensitive adhesive layer 53 has small plastic deformation, so that the deformation of the second pressure-sensitive adhesive layer 53 due to pressure from the back side by the elastic restoring force of the transparent film substrate 59 is restored. Since it is easy, the residual|survival of an indentation can be suppressed.

_{The shear storage modulus G' 25 ° C} of the first pressure-sensitive adhesive layer 51 at 25 ° C. 0.16 MPa or more is preferable, 0.18 MPa or more is more preferable, 0.20 MPa or more is still more preferable, and 0.21 MPa or more is especially preferable.

On the other hand, from the viewpoint of providing appropriate viscosity to ensure wettability and providing cushioning properties against impacts such as step absorption and dropping, G' _{25° C.} of the first pressure-sensitive adhesive layer 51 is preferably 0.5 MPa or less. and 0.4 MPa or less is more preferable, 0.3 MPa or less is still more preferable, and 0.28 MPa or less is especially preferable.

From the viewpoint of providing the pressure-sensitive adhesive sheet 15 with step absorbency, the loss tangent tan δ _{70° C.} of the first pressure-sensitive adhesive layer 51 at 70° C. is preferably 0.25 or more, more preferably 0.30 or more, and furthermore 0.35 or more. desirable. tanδ _70°C may be 0.40 or more, 0.45 or more, 0.50 or more, or 0.55 or more. From the viewpoint of adhesive holding force, tan δ _70°C is preferably 1.0 or less, more preferably 0.9 or less, and still more preferably 0.85 or less. tanδ _70°C may be 0.80 or less, 0.75 or less, or 0.70 or less.

1.5 or more are preferable, as for the peak top value of tan-delta of the 1st adhesive layer 51, 1.6 or more are more preferable, and 1.7 or more are still more preferable. An adhesive having a large peak top value of tan δ has a large viscous behavior and tends to be excellent in impact resistance. Although the upper limit of the peak top value of tan-delta of the 1st adhesive layer 51 is not specifically limited, Generally, it is 3.0 or less. From a viewpoint of adhesive holding force, 2.7 or less are preferable and, as for the peak top value of tan-delta, 2.5 or less are more preferable.

-3 degreeC or less is preferable and, as for the glass transition temperature of the 1st adhesive layer 51, -4 degrees C or less is more preferable. -20 degreeC or more is preferable, as for the glass transition temperature of the 1st adhesive layer 51, -15 degreeC or more is more preferable, and -13 degreeC or more is still more preferable. When a glass transition temperature is in the said range, also in a low-temperature area|region, an adhesive has moderate viscosity, and there exists a tendency for peeling of the to-be-adhered body by impacts, such as a fall, to be suppressed.

The shear storage modulus G', loss tangent tan δ, and glass transition temperature are determined by viscoelasticity measurement at a frequency of 1 Hz. tan δ is the ratio G"/G' of the storage elastic modulus G' and the loss elastic modulus G", and the glass transition temperature is the temperature (peak top temperature) at which tan δ becomes the maximum. The storage modulus G' corresponds to a portion stored as elastic energy when the material is deformed, and is an index indicating the degree of hardness. The larger the storage elastic modulus, the higher the adhesive holding force and the tendency for peeling due to deformation to be suppressed. The loss elastic modulus G" corresponds to the portion of the loss energy dissipated by internal friction or the like when the material is deformed and indicates the degree of viscosity. The larger tan δ, the stronger the tendency of viscosity, the deformation behavior becomes liquid, and the rebound elastic energy tends to be smaller.

G' The gel fraction of the pressure-sensitive adhesive is preferably 30 to 80%, more preferably 35 to 70%, from the viewpoint of ensuring processing stability while ensuring processing stability _{at G' 25° C. of 0.16 MPa or more and providing adequate flexibility for imparting step water absorption.} do. The gel fraction may be 40 % or more or 45 % or more, and 65 % or less or 60 % or less may be sufficient as it.

The gel fraction of an adhesive can be calculated|required as an insoluble content with respect to solvents, such as ethyl acetate, and specifically, the weight fraction with respect to the sample before immersion of the insoluble component after immersing an adhesive in ethyl acetate at 23 degreeC for 7 days (unit : % by weight). In general, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked portions in the polymer, the greater the gel fraction. The gel fraction (introduction amount of the crosslinked structure) can be adjusted to a desired range depending on the method of introducing the crosslinked structure, the type and amount of the crosslinking agent, and the like.

The 2nd adhesive layer 53 will not be specifically limited if it is a transparent adhesive layer which has the said thickness. The adhesive of the 1st adhesive layer 51 and the adhesive of the 2nd adhesive layer 53 may be same or different. From the viewpoint of improving adhesive retention, dimensional stability and impact resistance, the second pressure-sensitive adhesive layer 53 has a shear storage modulus G' at _{25°C at 25°C} , loss tangent at _70°C tanδ 70°C, a peak top value of tanδ, glass It is preferable that a transition temperature and a gel fraction exist in the range mentioned above with respect to the 1st adhesive layer 51.

<Composition of adhesive>

The composition of the pressure-sensitive adhesive constituting the first pressure-sensitive adhesive layer 51 and the second pressure-sensitive adhesive layer 53 is not particularly limited, and acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/chloride A polymer such as a vinyl copolymer, a modified polyolefin, an epoxy-based polymer, a fluorine-based polymer, a natural rubber, or a synthetic rubber may be appropriately selected and used as the base polymer. In particular, since it is excellent in optical transparency, shows adhesive properties such as moderate wettability, cohesiveness and adhesiveness, and is also excellent in weather resistance and heat resistance, an acrylic pressure-sensitive adhesive containing an acrylic base polymer having a crosslinked structure is preferably used.

The acrylic base polymer contains (meth)acrylic acid alkylester as a main constituent monomer component. In addition, in this specification, "(meth)acryl" means acryl and/or methacryl.

As (meth)acrylic-acid alkylester, the (meth)acrylic-acid alkylester of C1-C20 of an alkyl group is used suitably. In the (meth)acrylic acid alkyl ester, an alkyl group may have a branch, and may have a cyclic alkyl group.

Specific examples of the (meth)acrylic acid alkyl ester having a chain alkyl group include (meth) methyl acrylate, (meth) ethyl acrylate, (meth) butyl acrylate, (meth) acrylate isobutyl, (meth) acrylate s-butyl, (meth) t-butyl acrylate, (meth) pentyl acrylate, (meth) acrylate isopentyl, (meth) acrylate neopentyl, (meth) acrylate hexyl, (meth) acrylate heptyl, (meth) acrylic acid 2-ethylhexyl, (meth) acrylic acid Octyl, (meth) acrylate isooctyl, (meth) acrylate nonyl, (meth) acrylate isononyl, (meth) acrylate decyl, (meth) acrylate isodecyl, (meth) acrylate undecyl, (meth) acrylate dodecyl, (meth) acrylic acid isotridodecyl, (meth) acrylic acid tetradecyl, (meth) acrylic acid isotetradecyl, (meth) acrylic acid pentadecyl, (meth) acrylate cetyl, (meth) acrylic acid heptadecyl, (meth) acrylic acid octadecyl Decyl, (meth)acrylic acid isooctadecyl, (meth)acrylic acid nonadecyl, etc. are mentioned.

As a specific example of the (meth)acrylic acid alkylester which has an alicyclic alkyl group, (meth)acrylic acid cycloalkyl, such as (meth)acrylic acid cyclopentyl, (meth)acrylic acid cyclohexyl, (meth)acrylic acid cycloheptyl, (meth)acrylic acid cyclooctyl, ester; (meth)acrylic acid ester having a bicyclic aliphatic hydrocarbon ring such as (meth)acrylic acid isobornyl; Dicyclopentanyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, tricyclofentanyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl ( and (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings such as meth)acrylate and 2-ethyl-2-adamantyl (meth)acrylate.

50 weight% or more is preferable, as for the quantity of the (meth)acrylic acid alkylester with respect to the monomer component whole quantity which comprises an acrylic base polymer, 55 weight% or more is more preferable, and its 60 weight% or more is still more preferable. From the viewpoint of setting the glass transition temperature (Tg) in an appropriate range, the amount of (meth)acrylic acid alkylester having a chain alkyl group having 4 to 10 carbon atoms with respect to the total amount of the constituent monomer components in the acrylic base polymer is preferably 40% by weight or more. and more preferably 50% by weight or more, and still more preferably 55% by weight or more. In addition, the monomer component constituting the acrylic base polymer is a monomer used to form a crosslinked structure from all monomer components constituting the polymer (polyfunctional (meth)acrylate, urethane (meth)acrylate, etc. described later) and a crosslinking agent is excluded.

The acrylic base polymer may contain a hydroxyl group-containing monomer or a carboxyl group-containing monomer as a constituent monomer component. When a crosslinked structure is introduced by an isocyanate crosslinking agent, a hydroxyl group becomes a reaction point with an isocyanate group, and when a crosslinked structure is introduce|transduced by an epoxy-type crosslinking agent, a carboxy group becomes a reaction point with an epoxy group.

As the hydroxyl group-containing monomer, (meth)acrylic acid 2-hydroxyethyl, (meth)acrylic acid 2-hydroxypropyl, (meth)acrylic acid 4-hydroxybutyl, (meth)acrylic acid 6-hydroxyhexyl, (meth)acrylic acid 8 -hydroxyoctyl, (meth)acrylic acid 10-hydroxydecyl, (meth)acrylic acid 12-hydroxylauryl or (4-hydroxymethylcyclohexyl)-methyl (meth)acrylate (meth)acrylic acid ester can be heard When a crosslinked structure by a urethane-based segment is introduced into the acrylic base polymer, compatibility with the urethane-based segment is high and from the viewpoint of improving the transparency of the pressure-sensitive adhesive, the acrylic base polymer, as a constituent monomer component, has 4 to 8 carbon atoms It is preferable that the (meth)acrylic acid ester which has a hydroxyalkyl group is included.

When an acrylic base polymer has a hydroxyl-containing monomer as a structural monomer component, while transparency of an adhesive improves, there exists a tendency for the cloudiness in a high-temperature, high-humidity environment to be suppressed. In addition, the hydroxyl group of a hydroxyl-containing monomer can form an acryl-type polymer or a bridge|crosslinking segment, and physical bridge|crosslinking by hydrogen bonding. Therefore, by increasing the ratio of the hydroxyl group-containing monomer in the monomer component constituting the acrylic base polymer, the cohesive force _{tends to increase and the G' 25°C} tends to increase. The amount of the hydroxyl group-containing monomer relative to the total amount of the monomer components constituting the acrylic base polymer is preferably 5 to 30% by weight, more preferably 8 to 25% by weight, and still more preferably 10 to 20% by weight.

Examples of the carboxyl group-containing monomer include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

The acrylic base polymer may contain a nitrogen-containing monomer as a constituent monomer component. Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmor. vinyl-based monomers such as poline, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, and N-vinylcaprolactam; and cyano group-containing acrylic monomers such as acrylonitrile and methacrylonitrile; can Among these, N-vinylpyrrolidone is preferable because the adhesive strength improvement effect by the cohesive force improvement is high.

When the acrylic base polymer contains high polarity monomers such as a hydroxyl group-containing monomer, a carboxyl group-containing monomer and a nitrogen-containing monomer as a constituent monomer component, the cohesive force of the pressure-sensitive adhesive increases, and the G' _{25 ° C.} there is. On the other hand, when content of a highly polar monomer is too large, a glass transition temperature may become high and impact resistance may fall. Therefore, the amount of the high polar monomer (the total of the hydroxyl group-containing monomer, the carboxyl group-containing monomer and the nitrogen-containing monomer) relative to the total amount of the monomer components constituting the acrylic base polymer is preferably 15 to 45 wt%, and 20 to 40 wt% It is more preferable, and 25 to 37 weight% is still more preferable. In particular, it is preferable that the sum total of a hydroxyl-containing monomer and a nitrogen-containing monomer exists in the said range. The amount of the nitrogen-containing monomer relative to the total amount of the monomer component constituting the acrylic base polymer is preferably 7 to 30% by weight, more preferably 10 to 25% by weight, and still more preferably 12 to 22% by weight.

The acrylic base polymer is a monomer component other than the above. of vinyl-based monomers; cyano group-containing acrylic monomers such as acrylonitrile and methacrylonitrile; Epoxy group-containing monomers, such as (meth)acrylic-acid glycidyl; glycol-based acrylic ester monomers such as (meth)acrylic acid polyethylene glycol, (meth)acrylic acid polypropylene glycol, (meth)acrylic acid methoxyethylene glycol, and (meth)acrylic acid methoxypolypropylene glycol; (meth)acrylic acid tetrahydrofurfuryl, fluorine (meth)acrylate, silicone (meth)acrylate, (meth)acrylic acid ester-based monomers such as 2-methoxyethyl (meth)acrylic acid may be included.

The acrylic base polymer preferably has the highest content of (meth)acrylic acid alkyl ester among the monomer components. The characteristics of the pressure-sensitive adhesive are easily influenced by the type of the monomer (main monomer) having the highest content among the constituent monomers of the base polymer. For example, when the main monomer is a (meth)acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms, the tan δ _{70° C.} is large, and the step absorbency tends to be improved. In particular, when an acrylic acid C ₄ alkyl ester such as butyl acrylate is the main monomer, tan δ _{70° C.} tends to increase. The amount of (meth)acrylic acid alkylester having a chain alkyl group having 6 or less carbon atoms relative to the total amount of the monomer components constituting the acrylic base polymer is preferably 40 to 85% by weight, more preferably 45 to 80% by weight, and 50 to 75 weight% is more preferable. In particular, it is preferable that content of butyl acrylate as a structural monomer component is the said range.

As for the theoretical Tg of an acryl-type base polymer, -50 degreeC or more is preferable. The theoretical Tg of the acrylic base polymer is preferably -10°C or less, more preferably -20°C or less, and still more preferably -25°C or less. _{The theoretical Tg is calculated from the glass transition temperature Tg i} of the homopolymer of the monomer component constituting the acrylic base polymer and the weight fraction W _i of each monomer component by the following Fox's formula.

1/Tg=Σ(W _i /Tg _i )

Tg is the glass transition temperature of the polymer (unit: K), W _i is the weight fraction (copolymerization ratio by weight) of the monomer component i constituting the segment, Tg _i is the glass transition temperature of the homopolymer of the monomer component i (unit: K). As a glass transition temperature of a homopolymer, the numerical value described in Polymer Handbook 3rd edition (John Wiley & Sons, Inc., 1989) is employable. As for the Tg of the homopolymer of the monomer not described in the above literature, the peak top temperature of the loss tangent (tanδ) by dynamic viscoelasticity measurement may be employed.

The polymer to which the crosslinked structure is introduced is, for example, (1) a method of polymerizing a polymer having a functional group capable of reacting with a crosslinking agent, then adding a crosslinking agent to react the polymer with the crosslinking agent; and (2) a method of introducing a branched structure (crosslinked structure) by including a polyfunctional compound in the polymerization component of the polymer. You may use these together and introduce|transduce multiple types of crosslinked structures into a base polymer.

Specific examples of the crosslinking agent in the method of reacting the base polymer and the crosslinking agent in (1) above include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an oxazoline-based crosslinking agent, an aziridine-based crosslinking agent, a carbodiimide-based crosslinking agent, a metal chelate-based crosslinking agent, and the like. can be heard Especially, since the reactivity with the hydroxyl group and a carboxy group of a base polymer is high and introduction|transduction of a crosslinked structure is easy, an isocyanate type crosslinking agent and an epoxy type crosslinking agent are preferable. These crosslinking agents react with functional groups, such as a hydroxyl group and a carboxy group, introduced into the base polymer to form a crosslinked structure. In the acid-free adhesive in which the base polymer does not contain a carboxyl group, it is preferable to use an isocyanate-based crosslinking agent to form a crosslinked structure by reaction of the hydroxyl group in the base polymer with the isocyanate crosslinking agent.

As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule is used. As an isocyanate type crosslinking agent, For example, Lower aliphatic polyisocyanate, such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; Trimethylolpropane/tolylene diisocyanate trimer adduct (e.g., dosing agent "Coronate L"), trimethylolpropane/hexamethylene diisocyanate trimer adduct (e.g., dosing agent "Coronate HL") , a trimethylolpropane adduct of xylylene diisocyanate (for example, "Takenate D110N" manufactured by Mitsui Chemicals), an isocyanurate body of hexamethylene diisocyanate (for example, "Coronate HX" manufactured by Tosoh), etc. of isocyanate adducts, and the like. Moreover, as an isocyanate type crosslinking agent, the crosslinked structure by a urethane type segment can be introduce|transduced by using the urethane prepolymer which has an isocyanate group at the terminal.

In the method including the polyfunctional compound in the polymerization component of the base polymer of (2) above, the monomer component constituting the acrylic base polymer and the entire amount of the polyfunctional compound for introducing the crosslinked structure may be reacted at once, or in multiple steps You may superpose|polymerize. As a method of performing polymerization in multiple steps, a monofunctional monomer constituting the base polymer is polymerized (pre-polymerized) to prepare a partial polymer (prepolymer composition), and a polyfunctional compound such as polyfunctional (meth)acrylate is added to the prepolymer composition. In addition, the method of superposing|polymerizing (main polymerization) a prepolymer composition and a polyfunctional monomer is preferable. The prepolymer composition is a partial polymer comprising a polymer having a low polymerization degree and an unreacted monomer.

By performing preliminary polymerization of the constituent components of the acrylic base polymer, the branching point (crosslinking point) of the polyfunctional compound can be uniformly introduced into the base polymer. Further, after coating a low molecular weight polymer or a mixture of a partially polymerized product and an unpolymerized monomer component (adhesive composition) on a substrate, the main polymerization is performed on the substrate to form a pressure-sensitive adhesive layer. Since the low-polymerization composition such as the prepolymer composition has low viscosity and excellent coatability, the productivity of the pressure-sensitive adhesive layer can be improved by applying the pressure-sensitive adhesive composition, which is a mixture of the prepolymer composition and the polyfunctional compound, and then performing the polymerization on the substrate. Together with this, the thickness of the pressure-sensitive adhesive layer can be made uniform.

As a polyfunctional compound used for introduction|transduction of a crosslinked structure, the compound which contains 2 or more of polymerizable functional groups (ethylenically unsaturated group) which has an unsaturated double bond in 1 molecule is mentioned. As a polyfunctional compound, since copolymerization with the monomer component of an acryl-type base polymer is easy, polyfunctional (meth)acrylate is preferable. When introducing a branched (crosslinked) structure by active energy ray polymerization (photopolymerization), polyfunctional acrylates are preferable.

Examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, and bisphenol A ethylene oxide-modified di(meth)acryl. rate, bisphenol A propylene oxide modified di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, penta erythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, ethoxylated pentaerythritoltetra(meth)acryl rate, pentaerythol tetra (meth) acrylate, dipentaerythol poly (meth) acrylate, dipentaerythol hexa (meth) acrylate, neopentyl glycol di (meth) acrylate, glycerin di (meth) acrylic a rate, an epoxy (meth)acrylate, a butadiene (meth)acrylate, an isoprene (meth)acrylate, etc. are mentioned.

By using the urethane (meth)acrylate which has a (meth)acryloyl group at the terminal of a urethane chain as a polyfunctional (meth)acrylate, the crosslinked structure by a urethane-type segment can be introduce|transduced. When the acrylic base polymer is crosslinked by the urethane-based segment, an adhesive capable of achieving both a low glass transition temperature and a high adhesive retention force is easily obtained. The urethane-based segment is a molecular chain having a urethane bond, and when both ends of the urethane-based segment are covalently bonded to an acrylic base polymer, a crosslinked structure by the urethane-based segment is introduced. The urethane-based segment typically includes a polyurethane chain obtained by reacting a diol with a diisocyanate.

5000-30000 are preferable, as for the molecular weight of the polyurethane chain in a urethane-type segment, 6000-23000 are more preferable, 7000-20000 are still more preferable. The distance between crosslinking points becomes long, so that the molecular weight of the polyurethane chain in a urethane-type segment is large. When the molecular weight of the polyurethane chain is within the above range, since the polymer having the crosslinked structure introduced therein has moderate cohesiveness and fluidity, it is possible to achieve both adhesive strength, step absorption and impact resistance.

When the molecular weight of the polyurethane chain is excessively small and the distance between the cross-linking points is short, tan δ decreases with an increase in cohesive force, and there is a tendency that the step absorbency and impact resistance decrease. On the other hand, when the molecular weight of the polyurethane chain is excessively large and the distance between crosslinking points is long, the storage elastic modulus is small and the adhesive holding force may be insufficient. Even when the molecular weight of the polyurethane chain is large, the storage elastic modulus can be increased by increasing the amount of the urethane-based segment to increase the gel fraction. However, since a polyurethane chain with a large molecular weight has low compatibility with an acrylic polymer, the haze of an adhesive may become large with increase in the amount of a urethane type segment, and transparency may fall.

When the amount of the urethane-based segment becomes excessively large, the viscosity of the pressure-sensitive adhesive may decrease with an increase in the gel fraction, and the step water absorption and impact resistance may decrease. Moreover, when the quantity of a urethane-type segment becomes large excessively, transparency of an adhesive may fall and a haze may rise. Therefore, the amount of the urethane segment in the base polymer is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, and still more preferably 5 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. On the other hand, from the viewpoint of increasing the gel fraction to have adhesive retention, the amount of the urethane-based segment in the base polymer is preferably 0.3 parts by weight or more, more preferably 0.4 parts by weight or more, and 0.5 parts by weight or more with respect to 100 parts by weight of the acrylic polymer. More preferably not less than parts by weight. The quantity of the urethane-type segment in a base polymer may be 4 weight part or less or 3 weight part or less, and 0.7 weight part or more, or 1 weight part or more may be sufficient with respect to 100 weight part of acrylic polymers.

Examples of the diol used for forming the polyurethane chain include low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol and hexamethylene glycol; and high molecular weight polyols such as polyester polyol, polyether polyol, polycarbonate polyol, acrylic polyol, epoxy polyol, and caprolactone polyol.

The diisocyanate used for formation of a polyurethane chain may be either aromatic diisocyanate and aliphatic. As the diisocyanate, a derivative of an isocyanate compound may also be used. As a derivative of an isocyanate compound, a dimer of polyisocyanate, a trimer of isocyanate (isocyanurate), polymeric MDI, an adduct with trimethylolpropane, a biuret modified product, an allophanate modified product, a urea modified product, etc. can be heard As a diisocyanate component, you may use the urethane prepolymer which has an isocyanate group at the terminal.

Among the exemplary polyurethane chains, since compatibility with the acrylic polymer is high, it is preferable to include a polyether urethane having a polyether polyol as a diol component and/or a polyester urethane having a polyester polyol as a diol component. In particular, when a crosslinked structure is introduced with polyester urethane, the storage elastic modulus at room temperature becomes large, and adhesion retention and workability tend to improve. As one reason, polyester has a rigid molecular structure compared with polyether etc. is mentioned. When a crosslinked structure is introduced by a rigid segment, the storage elastic modulus is increased because the movement of the polymer is restricted, and on the other hand, since the distance between the crosslinking points of the polymer is maintained, it is thought that impact resistance and step absorbency are exhibited.

By using a compound having a functional group copolymerizable with the monomer component constituting the acrylic polymer at the end of the polyurethane chain, or a compound having a functional group capable of reacting with the carboxyl group, hydroxyl group, etc. contained in the acrylic polymer at the end of the polyurethane chain, acrylic A crosslinked structure by a urethane-based segment can be introduced into the polymer. Since it is easy to introduce a crosslinking point uniformly into the acrylic polymer and the compatibility between the acrylic polymer and the urethane segment is excellent, as the polyfunctional (meth)acrylate, (meth)acryloyl groups at both ends of the polyurethane chain It is preferable to introduce a crosslinked structure by a urethane-based segment by using a urethane di(meth)acrylate having

The urethane di(meth)acrylate which has a (meth)acryloyl group at both terminals is obtained by using the (meth)acryl compound which has a hydroxyl group in addition to a diol component in the superposition|polymerization of a polyurethane, for example. From the viewpoint of controlling the chain length (molecular weight) of the urethane-based segment, diol and diisocyanate are reacted so as to have an excess of isocyanate to synthesize isocyanate-terminated polyurethane, and then a (meth)acrylic compound having a hydroxyl group is added to the polyurethane. It is preferable to make a terminal isocyanate group react with the hydroxyl group of a (meth)acrylic compound.

The polyurethane chain which has an isocyanate group at the terminal is obtained by making a polyhydric alcohol and a polyisocyanate compound react so that a polyisocyanate compound may become excess. In order to obtain an isocyanate-terminated polyurethane, the diol component and the diisocyanate component may be used so that NCO/OH (equivalent ratio) becomes preferably 1.1 to 2.0, more preferably 1.15 to 1.5. After mixing and reacting a diol component and a diisocyanate component in substantially equal amounts, you may add a diisocyanate component.

Examples of the (meth)acrylic compound having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxymethylacrylamide, hydroxy Ethyl acrylamide etc. are mentioned.

As urethane (meth)acrylate, each company such as Arakawa Chemical High School, Shin-Nakamura Chemical High School, Toa Kosei, Kyoesha Chemical, Nippon Kayaku, Nippon Kosei Chemical High School, Negami High School, Daicel Allnex, etc. Commercially available products may be used. 5000-30000 are preferable, as for the weight average molecular weight of urethane (meth)acrylate, 6000-23000 are more preferable, 7000-20000 are still more preferable.

0 degreeC or less is preferable, as for the glass transition temperature of urethane (meth)acrylate, -10 degreeC or less is more preferable, and its -20 degreeC or less is still more preferable. By using a low-Tg urethane (meth)acrylate, a pressure-sensitive adhesive excellent in low-temperature adhesive strength is obtained even when a cross-linked structure is introduced by a urethane-based segment to increase the cohesive force of the base polymer. Although the lower limit of the glass transition temperature of urethane (meth)acrylate is not specifically limited, From a viewpoint of obtaining the adhesive excellent in high temperature holding power, -100 degreeC or more is preferable, -90 degreeC or more is more preferable, -80 degreeC or more more preferably.

When a urethane (meth)acrylate is used to introduce a crosslinked structure by a urethane-based segment to an acrylic polymer, the glass transition temperature of the urethane-based segment of the base polymer is approximately equal to the glass transition temperature of the urethane (meth)acrylate. .

<Adhesive composition>

An adhesive layer is formed by apply|coating the adhesive composition containing a base polymer on a base material, and performing drying of a solvent or crosslinking and hardening of a base polymer as needed.

The base polymer can be prepared by known polymerization methods such as solution polymerization, photopolymerization (UV polymerization), bulk polymerization, and emulsion polymerization. A solution polymerization method or photopolymerization is preferable from points, such as transparency of an adhesive, water resistance, and cost. In photopolymerization, since a polymer can be prepared without using a solvent, it does not require dry removal of a solvent at the time of formation of an adhesive layer, and can form a large adhesive layer uniformly.

When preparing a base polymer, you may use polymerization initiators, such as a photoinitiator and a thermal polymerization initiator, according to the kind of polymerization reaction. Examples of the photopolymerization initiator include a benzoin ether-based photopolymerization initiator, an acetophenone-based photopolymerization initiator, an α-ketol-based photopolymerization initiator, an aromatic sulfonyl chloride-based photopolymerization initiator, a photoactive oxime-based photopolymerization initiator, a benzoin-based photopolymerization initiator, a benzyl-based photopolymerization initiator, and benzoin. A phenone type photoinitiator, a ketal type photoinitiator, a thioxanthone type photoinitiator, an acylphosphine oxide type photoinitiator, etc. can be used. As the thermal polymerization initiator, an azo-based initiator, a peroxide-based initiator, or a redox-based initiator in which a peroxide and a reducing agent are combined (for example, a combination of a persulfate and sodium hydrogensulfite, a combination of a peroxide and sodium ascorbate, etc.) can be used. .

In order to adjust the molecular weight of the base polymer, a chain transfer agent may be used. Examples of the chain transfer agent include α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, thioglycolic acid 2-ethylhexyl, and 2,3-dimercapto. Thiols, such as 1-propanol, (alpha)-methylstyrene dimer, etc. are mentioned.

As a monomer component forming the base polymer, when a polyfunctional monomer is used in addition to a monofunctional monomer, the monofunctional monomer is first polymerized to form a prepolymer composition with a low degree of polymerization (prepolymerization), and the polyfunctional monomer in the syrup of the prepolymer composition may be added to polymerize the prepolymer and the polyfunctional monomer (main polymerization). In this way, by performing the prepolymerization of the prepolymer, branching points resulting from the polyfunctional monomer component can be uniformly introduced into the base polymer. Moreover, after apply|coating the mixture (adhesive composition) of a prepolymer composition and unpolymerized monomer component on a base material, you may perform main superposition|polymerization on a base material and form an adhesive layer. Since the prepolymer composition has low viscosity and excellent applicability, according to the method of performing main polymerization on the substrate after applying the pressure-sensitive adhesive composition, which is a mixture of the prepolymer composition and the unpolymerized monomer, the productivity of the pressure-sensitive adhesive layer is increased and the thickness of the pressure-sensitive adhesive layer is reduced. can be made uniform.

The prepolymer composition can be prepared by, for example, partial polymerization (prepolymerization) of a composition in which a monomer component constituting an acrylic base polymer and a polymerization initiator are mixed (referred to as "composition for forming a prepolymer"). Moreover, it is preferable that the monomer in the composition for prepolymer formation is a monofunctional monomer, such as (meth)acrylic-acid alkylester and a polar group containing monomer, among the monomer components which comprise an acrylic polymer. The composition for forming a prepolymer may contain the polyfunctional monomer. For example, a part of the polyfunctional monomer component serving as a raw material of the base polymer may be contained in the composition for forming the prepolymer, and the prepolymer may be subjected to the main polymerization by adding the remainder of the polyfunctional monomer component after polymerization.

The composition for prepolymer formation may contain the chain transfer agent etc. other than a monomer and a polymerization initiator as needed. Although the polymerization method of a prepolymer is not specifically limited, From a viewpoint of adjusting reaction time and making the molecular weight (polymerization rate) of a prepolymer into a desired range, polymerization by actinic light irradiation, such as UV light, is preferable. The polymerization initiator and chain transfer agent used for prepolymerization are not specifically limited, For example, the photoinitiator and chain transfer agent mentioned above can be used.

Although the polymerization rate of a prepolymer is not specifically limited, From a 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 a prepolymer can be adjusted to a desired range by adjusting the kind, usage-amount of a photoinitiator, irradiation intensity, irradiation time, etc. of actinic rays, such as UV light. The polymerization rate of the prepolymer is calculated by the following formula from the weight before and after heating when heated at 130°C for 3 hours. The polymerization rate of an adhesive is also computed by the same method.

Polymerization rate (%) = weight after drying / weight before drying x 100

The prepolymer composition is mixed with the remainder of the monomer component constituting the acrylic base polymer (post-addition monomer) and, if necessary, a polymerization initiator, a chain transfer agent, a silane coupling agent, a crosslinking agent, and the like to form a pressure-sensitive adhesive composition. It is preferable that a post-addition monomer contains a polyfunctional monomer. When using urethane di(meth)acrylate to introduce a crosslinked structure by a urethane-based segment, it is preferable to add urethane di(meth)acrylate as a post-addition monomer.

The photoinitiator and chain transfer agent used for this polymerization are not specifically limited, For example, the photoinitiator and chain transfer agent mentioned above can be used. When the polymerization initiator at the time of the prepolymerization remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator for the main polymerization can be omitted.

In this polymerization, it is preferable to adjust molecular weight by including a chain transfer agent in an adhesive composition. The chain transfer agent used for this polymerization is not specifically limited, For example, the chain transfer agent mentioned above can be used. 0.001-2 weight part is preferable with respect to 100 weight part of structural components of a base polymer, as for the quantity of the chain transfer agent in an adhesive composition, 0.005-1 weight part is more preferable, 0.01-0.5 weight part is still more preferable. In addition, when the chain transfer agent used at the time of prepolymerization remains in the prepolymer composition without deactivation, you may abbreviate|omit addition of the chain transfer agent with respect to an adhesive composition.

The chain transfer agent receives a radical from the growing polymer chain to stop the elongation of the polymer, while the chain transfer agent that has received the radical attacks the monomer to initiate polymerization again. By using a chain transfer agent, increase in molecular weight of a polymer can be suppressed, without reducing the radical concentration in a reaction system.

When the ratio of the monofunctional monomer to the polyfunctional monomer is constant, the larger the molecular weight, the higher the probability that one polymer chain contains a crosslinking point (branching point) by the polyfunctional monomer, so the gel fraction tends to increase. By suppressing the elongation of the polymer by using a chain transfer agent, the molecular weight of the polymer decreases and the increase in the gel fraction tends to be suppressed. Therefore, when an adhesive composition contains a chain transfer agent, tan-delta is large and it is easy to form the adhesive excellent in step|step difference water absorption.

(Ultraviolet absorber)

In order to provide the adhesive layers 51 and 53 with ultraviolet absorption, you may use a ultraviolet absorber. Examples of the ultraviolet absorber include a benzotriazole-based ultraviolet absorber, a benzophenone-based ultraviolet absorber, a triazine ultraviolet absorber, a salicylate-based ultraviolet absorber, and a cyanoacrylate-based ultraviolet absorber. A triazine-based UV absorber and a benzotriazole-based UV absorber are preferable, and among them, a triazine-based UV absorber having high UV absorbability, excellent compatibility with an acrylic polymer, and easy to obtain a highly transparent acrylic pressure-sensitive adhesive. A ultraviolet absorber and a benzotriazole-type ultraviolet absorber which has one benzotriazole skeleton in 1 molecule are preferable.

You may use a commercial item as a ultraviolet absorber. Commercially available triazine-based UV absorbers include 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl and [(alkyloxy) Reaction product of methyl]oxirane ("TINUVIN 400" manufactured by BASF), 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5- Reaction product of triazine and (2-ethylhexyl)-glycidic acid ester ("TINUVIN 405" manufactured by BASF), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4) -dibutoxyphenyl)-1,3,5-triazine ("TINUVIN 460" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[ (hexyl)oxy]-phenol ("TINUVIN 577" manufactured by BASF), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl) -1,3,5-triazine ("TINUVIN 479" manufactured by BASF), 2,4-bis-[{4-(4-ethylhexyloxy)-4-hydroxy}-phenyl]-6-(4) -Methoxyphenyl)-1,3,5-triazine ("Tinosorb S" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[ 2-(2-ethylhexanoyloxy)ethoxy]-phenol ("ADK STAB LA-46" by ADEKA) etc. are mentioned.

As a commercially available product of the benzotriazole-based ultraviolet absorber, 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl ) Phenol ("TINUVIN 928" manufactured by BASF), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole ("TINUVIN PS" manufactured by BASF), 2-(2H-benzotriazole- 2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol ("TINUVIN 900" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-(1-methyl -1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol ("TINUVIN 928" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-dodecyl -4-methylphenol ("TINUVIN571" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-p-cresol ("TINUVIN P" manufactured by BASF), 2-(2H-benzotriazole-2- yl)-4-6-bis(1-methyl-1-phenylethyl)phenol ("TINUVIN 234" manufactured by BASF), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl -6-(tert-butyl)phenol ("TINUVIN 326," manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol ("TINUVIN 328," manufactured by BASF) ), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol ("TINUVIN 329" manufactured by BASF), benzenepropanoic acid and 3-(2H-benzoic acid) Triazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy (C7-9 branched and straight-chain alkyl) ester compound ("TINUVIN 384-2" manufactured by BASF), methyl-3- Reaction product of (3-(2H-benzotriazol-2-yl)-5-t-butyl-4-hydroxyphenyl)propionate and polyethylene glycol ("TINUVIN1 130" manufactured by BASF), methyl 3-(3 Reaction product of -(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate and polyethylene glycol 300 ("TINUVIN 213" manufactured by BASF), 2-[2-hydroxyl hydroxy-3-(3,4,5,6-tetrahydrophthalimidemethyl)-5-methylphenyl]benzotriazole (“Sumisorb250” manufactured by Sumitomo Chemical), etc. can

When a ultraviolet absorber is added to an adhesive composition, the addition amount is about 0.05-10 weight part normally with respect to 100 weight part of base polymers, 0.1-5 weight part is preferable. By making content of a ultraviolet absorber into the said range, the ultraviolet shielding property by an adhesive layer can be improved, suppressing the fall of transparency by the bleed-out of a ultraviolet absorber, etc.

(oligomer)

The adhesive composition may contain various oligomers for the purpose of adjustment, viscosity adjustment, etc. of the adhesive force of an adhesive. As an oligomer, the thing of about 1000-30000 weight average molecular weights is used, for example. As an oligomer, since it is excellent in compatibility with an acryl-type base polymer, an acryl-type oligomer is preferable.

The acrylic oligomer contains (meth)acrylic acid alkylester as a main constituent monomer component. Among them, (meth)acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth) acrylate), and (meth) acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl (meth) acrylate) as a constituent monomer component It is preferable to include Specific examples of the chain alkyl (meth) acrylate and the alicyclic alkyl (meth) acrylate are as exemplified above as the constituent monomers of the acrylic polymer.

20 degreeC or more is preferable and, as for the glass transition temperature of an acryl-type oligomer, 40 degreeC or more is more preferable. The glass transition temperature of the acrylic oligomer may be 60°C or higher, 80°C or higher, 100°C or higher, or 110°C or higher. By using the low Tg acrylic base polymer to which the crosslinked structure is introduced and the high Tg acrylic oligomer together, the adhesive retention of the pressure-sensitive adhesive tends to be improved. Although the upper limit of the glass transition temperature of an acryl-type oligomer is not specifically limited, Generally, it is 200 degrees C or less, 180 degrees C or less is preferable, and 160 degrees C or less is more preferable. The glass transition temperature of the acrylic oligomer is calculated by the Fox formula described above.

Among the illustrated (meth)acrylic acid alkylesters, as the chain alkyl (meth)acrylate, methyl methacrylate is preferred because of its high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer contains, as a constituent monomer component, at least one selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate. it is preferable

The amount of the alicyclic alkyl (meth)acrylate relative to the total amount of the monomer component constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and still more preferably 30 to 70% by weight. The amount of the chain alkyl (meth)acrylate relative to the total amount of the monomer component constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and still more preferably 30 to 70% by weight.

1000-30000 are preferable, as for the weight average molecular weight of an acryl-type oligomer, 1500-10000 are more preferable, 2000-8000 are still more preferable. By using the acrylic oligomer having a molecular weight in the range, the adhesive force and adhesion retention of the pressure-sensitive adhesive tend to improve.

An acrylic oligomer is obtained by superposing|polymerizing the said monomer component by various polymerization methods. In the case of superposition|polymerization of an acryl-type oligomer, you may use various polymerization initiators. Moreover, you may use a chain transfer agent for the purpose of adjustment of molecular weight.

When an oligomer component such as an acrylic oligomer is included in the pressure-sensitive adhesive composition, the content thereof is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, and further 2 to 10 parts by weight with respect to 100 parts by weight of the base polymer. desirable. When content of the oligomer in an adhesive composition is the said range, there exists a tendency for the adhesiveness in high temperature and high temperature holding power to improve.

(Silane coupling agent)

You may add a silane coupling agent in an adhesive composition for the purpose of adjustment of adhesive force. When a silane coupling agent is added to an adhesive composition, the addition amount is about 0.01-5.0 weight part normally with respect to 100 weight part of base polymers, and it is preferable that it is about 0.03-2.0 weight part.

(other additives)

In addition to each component illustrated above, the pressure-sensitive adhesive composition may contain additives such as a tackifier, a plasticizer, a softener, an antioxidant, a filler, a colorant, an antioxidant, a surfactant, and an antistatic agent.

<Formation of adhesive layer>

When an adhesive composition is photocurable, after apply|coating an adhesive composition on a support base material, an adhesive layer is formed by irradiating an ultraviolet-ray and/or short wavelength visible light and photocuring. When photocuring, it is preferable to lay a cover sheet on the surface of an application layer, to irradiate light in the state which clamped the adhesive composition between two sheets, and to prevent polymerization inhibition by oxygen.

As the base material and cover sheet used for forming the pressure-sensitive adhesive layer, any appropriate base material is used. The base material and the cover sheet may be a release film provided with a release layer on the contact surface with an adhesive layer. As a base material or a cover sheet, the transparent film base material 59 of the adhesive sheet 15 may be used.

As a coating method of the adhesive composition, 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. Various methods are used.

Main polymerization is performed by irradiating actinic light to the adhesive composition apply|coated in the layered form on the base material. In this polymerization, the unreacted monomer component in a prepolymer composition and polyfunctional compounds, such as urethane di(meth)acrylate, react, and the polymer to which the crosslinked structure was introduce|transduced is obtained.

What is necessary is just to select an actinic light according to the kind of a polymeric component, the kind of photoinitiator, etc., Generally, an ultraviolet-ray and/or visible light of a short wavelength are used. As for the accumulated light quantity of irradiation light, about 100-5000 mJ/cm<2> is preferable. The light source for light irradiation is not particularly limited as long as the photopolymerization initiator contained in the pressure-sensitive adhesive composition can irradiate light in a wavelength range having sensitivity, and an LED light source, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp etc. are preferably used. When there is much residual amount of unreacted monomer, G' ₂₅ degreeC of an adhesive layer may become small, and adhesive holding force may fall. Therefore, 95 % or more is preferable, as for the polymerization rate of the adhesive after this superposition|polymerization, 97 % or more is more preferable, 98 % or more is still more preferable, and 99 % or more is especially preferable. In order to increase polymerization rate, an adhesive layer may be heated and you may volatilize a residual monomer, an unreacted polymerization initiator, etc.

As mentioned above, 30 to 80 % is preferable and, as for the gel fraction of an adhesive, 35 to 70 % is more preferable. When the gel fraction is 30% or more, the adhesive holding force of the pressure-sensitive adhesive is increased, and the adhesive drop-off during processing and the positional shift between members do not occur easily, and the workability and processing dimensional stability are excellent. In addition, when the gel fraction is 80% or less, it is possible to exhibit excellent level difference absorbency.

150,000 to 450,000 are preferable, and, as for the weight average molecular weight of the sol powder of an adhesive, 180,000 to 420,000 are more preferable. The sol powder is a soluble powder obtained by extracting the base polymer with tetrahydrofuran (hereinafter, THF). Since it is difficult to measure the molecular weight of individual polymer chains for a crosslinked polymer (gel powder), the molecular weight of the sol powder (non-crosslinked polymer) is an index indicating the degree of polymer chain elongation. When the molecular weight of sol powder is too large, a glass transition temperature may become high and impact resistance may fall. On the other hand, when the molecular weight of sol powder is too small, adhesive holding force may fall.

<Production of double-sided adhesive sheet with base material>

By laminating the 1st adhesive layer 51 and the 2nd adhesive layer 53 on each front and back of the transparent film base material 59, the double-sided adhesive sheet with a base material is obtained. As mentioned above, when forming an adhesive layer, an adhesive composition may be apply|coated on the transparent film base material 59, and you may form the laminated body of a transparent film base material and an adhesive layer.

By bonding the release films 21 and 23 to the surfaces of the first pressure-sensitive adhesive layer 51 and the second pressure-sensitive adhesive layer 53, as shown in FIG. is obtained The release film used as a base material or a cover sheet at the time of formation of an adhesive layer may be used as the release films 21 and 23 as it is.

[Formation of image display device]

As described above, the pressure-sensitive adhesive sheet 15 is suitably used for bonding the front transparent plate 7 to the viewing-side surface of the image display panel 10 in the formation of an image display device. The order of bonding is not particularly limited, and bonding of the pressure-sensitive adhesive sheet 15 to the image display panel 10 may be performed first, or bonding of the pressure-sensitive adhesive sheet 15 to the front transparent plate 7 may be performed first. do. In addition, it is also possible to perform bonding of both at the same time. After bonding the 2nd adhesive layer 53 and the polarizing plate 3 together, you may bonding the polarizing plate 3 and the image display cell 6 through the adhesive layer 4 .

The double-sided pressure-sensitive adhesive sheet 15 with a substrate has a form in which a release film is temporarily attached to the pressure-sensitive adhesive layers 51 and 53 as shown in FIG. 1 , and the second pressure-sensitive adhesive layer 53 is fixed to an optical film such as a polarizing plate. It can also be used as a film with an adhesive. For example, in the form shown in FIG. 3 , the release film 21 is temporarily attached to the surface of the first pressure-sensitive adhesive layer 51 , and the optical film 3 is fixed to the second pressure-sensitive adhesive layer 53 . In the form shown in FIG. 4, the adhesive layer 4 is further provided on the polarizing plate 3, and the release film 24 is temporarily stuck on it.

After bonding the image display panel 10 and the front transparent plate 7 through the pressure-sensitive adhesive sheet 15, pressure processing such as hot pressing or crimping is performed. At this time, if a convex part with a large thickness partially exists, such as a connection location of an FPC, a large pressure will be locally applied from the back surface side of an image display panel, and the image display panel 10 will deform|transform. As described above, since the image display panel 10 and the front transparent plate 7 are bonded with only the double-sided pressure-sensitive adhesive sheet 15 provided with the substrate interposed therebetween, the plastic deformation of the pressure-sensitive adhesive sheet 15 is small and restoring force against deformation. Because of this action, it is possible to reduce the residual indentation caused by the pressing from the back side.

[Example]

The present invention will be described in more detail below by way of Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Production of acrylic oligomer]

60 parts by weight of dicyclofentanyl methacrylate (DCPMA), 40 parts by weight of methyl methacrylate (MMA), 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent are mixed, and 70 ° C. under a nitrogen atmosphere was stirred for 1 hour. Next, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator, and after reacting at 70° C. for 2 hours, the temperature was raised to 80° C. and reacted for 2 hours. Then, the reaction liquid was heated to 130 degreeC, toluene, a chain transfer agent, and an unreacted monomer were dried off, and the solid acryl oligomer was obtained. The weight average molecular weight of the acryl oligomer was 5100.

[Preparation of prepolymer composition]

<Prepolymer composition 1>

As a monomer component for forming a prepolymer, butyl acrylate (BA): 70 parts by weight, N-vinyl-2-pyrrolidone (NVP): 17 parts by weight, and 4-hydroxybutyl acrylate (4HBA): 13 parts by weight, and A photoinitiator (“Irgacure 184” manufactured by BASF: 0.05 parts by weight, and “Irgacure 651” manufactured by BASF: 0.05 parts by weight) was blended and the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30° C.) Polymerization was carried out by irradiating ultraviolet rays until the value reached about 20 Pa·s to obtain a prepolymer composition 1 (polymerization rate; about 9%).

<Prepolymer composition 2>

The monomer component for forming the prepolymer was changed to 2-ethylhexyl acrylate (2EHA): 68 parts by weight, NVP 17 parts by weight, and 4-hydroxybutyl acrylate (4HBA): 17 parts by weight, polymerization was carried out in the same manner as above, and the prepolymer was Composition 2 was obtained.

[Preparation of photocurable pressure-sensitive adhesive composition]

<Adhesive composition A>

The prepolymer composition 1: 100 parts by weight, polyester urethane diacrylate having a weight average molecular weight of 12500 ("Artresin UN-350" manufactured by Negami Kogyo Co., Ltd.): 2 parts by weight; The acrylic oligomer: 5 parts by weight; As a photoinitiator, "Irgacure 184": 0.05 weight part, and "Irgacure 651": 0.55 weight part; As a chain transfer agent, alpha-methylstyrene dimer (Nichi Oil Co., Ltd. "Nopmer MSD"): 0.07 weight part; And after adding "KBM-403" by Shin-Etsu Chemical as a silane coupling agent: 0.3 weight part, these were mixed uniformly, and the adhesive composition A was prepared.

<Adhesive composition B>

UV absorber ("Tinosorb S" manufactured by BASF): 0.70 parts by weight is added, and as a photopolymerization initiator, "Irgacure 184" manufactured by BASF: 0.05 parts by weight, "Irgacure 651" manufactured by BASF: 0.05 parts by weight, and "Irgacure 819" manufactured by BASF: 0.40 parts by weight was blended. Except for these changes, it carried out similarly to preparation of the adhesive composition A, and prepared the adhesive composition B.

<Adhesive composition C>

Except having changed the compounding quantity of a chain transfer agent into 0.03 weight part, it carried out similarly to preparation of the adhesive composition B, and prepared the adhesive composition C.

<Adhesive composition D>

As a polyfunctional monomer, it replaced with polyester urethane diacrylate, and except having mix|blended 0.1 weight part of hexanediol diacrylate (HDDA), it carried out similarly to preparation of the adhesive composition B, and prepared the adhesive composition D.

<Adhesive composition E>

The prepolymer composition 2: 100 parts by weight, HDDA: 0.1 parts by weight; The acrylic oligomer: 5 parts by weight; As a photoinitiator, "Irgacure 184": 0.04 weight part, "Irgacure 651": 0.04 weight part, and "Irgacure 819": 0.12 weight part; And after adding 0.3 weight part of silane coupling agents, these were mixed uniformly, and the adhesive composition E was prepared.

[Preparation of adhesive layer]

<Adhesive layer A1>

A polyethylene terephthalate (PET) film having a thickness of 75 μm with a silicone-based release layer provided on the surface thereof was applied as a substrate, and the photocurable pressure-sensitive adhesive composition was applied to a thickness of 150 μm on the substrate to form an application layer. On this application layer, a PET film having a thickness of 75 µm on which one side was subjected to a silicone release treatment was bonded as a cover sheet. This laminate was photocured by irradiating ultraviolet rays with a black light whose position was adjusted so that the irradiation intensity on the irradiated surface immediately below the lamp from the cover sheet side was 5 mW/cm 2 , and had a thickness of 220 µm and a polymerization rate 99% of adhesive layer A1 was obtained.

<Adhesive layer A2 to A4>

Except having changed the thickness of an adhesive layer into 150 micrometers, 100 micrometers, and 70 micrometers, it carried out similarly to preparation of adhesive layer A1, and produced adhesive layers A2, A3, and A4.

<Adhesive layer B1 to B4, C2, C3, D2, D3, E1 to E3>

Except having changed the kind and thickness of an adhesive composition as shown in Table 1, it carried out similarly to preparation of adhesive layer A1, and produced the adhesive layer.

[Evaluation of the pressure-sensitive adhesive layer]

For each of the pressure-sensitive adhesive layers, the glass transition temperature, storage elastic modulus, loss tangent, gel fraction, and molecular weight of the sol powder were measured by the following methods.

<Storage modulus, loss tangent and glass transition temperature>

What laminated|stacked two or more adhesive layers which peeled and removed the release film (base material and cover sheet) of the front and back so that thickness might be set to about 1.5 mm was made into the sample for a measurement. Dynamic viscoelasticity was measured under the following conditions using "Advanced Rheometric Expansion System (ARES)" by Rheometric Scientific.

(Measuring conditions)

Deformation mode: torsion

Measuring frequency: 1Hz

Temperature increase rate: 5°C/min

Shape: Parallel plate 7.9mmφ

From the measurement results, the shear storage modulus G' at _25°C and the loss tangent tan δ _70° C at 25°C and 70°C were read. In addition, the temperature (peak top temperature) at which the loss tangent (tan δ) becomes the maximum was made into the glass transition temperature of the adhesive layer.

<Gel fraction>

About 0.2 g of the adhesive was scraped off from the adhesive layer, surrounded by a porous polytetrafluoroethylene membrane with a pore diameter of 0.2 μm (“NTF-1122” manufactured by Nitto Denko Co., Ltd.) cut to a size of 100 mm × 100 mm, and the surrounding mouth was opened. tied with The weight (B) of the pressure-sensitive adhesive sample was calculated by subtracting the total weight (A) of the previously measured porous polytetrafluoroethylene membrane and the smoke thread from the weight of the sample. The pressure-sensitive adhesive sample surrounded by the porous polytetrafluoroethylene membrane was immersed in about 50 mL of ethyl acetate at 23° C. for 7 days to elute the sol component of the pressure-sensitive adhesive out of the porous polytetrafluoroethylene membrane. After immersion, the adhesive surrounded by the porous polytetrafluoroethylene membrane was taken out, dried at 130°C for 2 hours, left to cool for about 20 minutes, and then the dry weight (C) was measured. The gel fraction of the adhesive was computed by the following formula.

Gel fraction (%)=100×(C-A)/B

<Weight average molecular weight of sol powder>

About 0.2 g of the pressure-sensitive adhesive was scraped off from the pressure-sensitive adhesive layer, and sol powder was extracted by immersion in 10 mM tetrahydrofuran phosphate solution for 12 hours. The quantity of the tetrahydrofuran phosphate solution was adjusted so that the content of solution sol powder after extraction might be 0.1 weight% in consideration of the gel fraction of an adhesive. The filtrate obtained by filtering the solution after extraction with a 0.45 µm membrane filter was used as a sample, and GPC analysis was performed under the following conditions with a GPC (gel permeation chromatography) apparatus (product name: "HLC-8120GPC") made by a toner. , the weight average molecular weight Mw of the sol powder was calculated.

(Measuring conditions)

Column: Tosoh Corporation, G7000HXL+GMHXL+GMHXL

Column size: each 7.8 mm φ × 30 cm (total column length: 90 cm)

Column temperature: 40°C, flow rate: 0.8 mL/min

Injection volume: 100 μL

Eluent: tetrahydrofuran

Detector: Differential Refractometer (RI)

Standard Sample: Polystyrene

The composition and thickness of each adhesive layer (adhesive composition), and an evaluation result are shown in Table 1.

[Example 1]

Adhesive layer A2 is bonded as a 1st adhesive layer to one main surface of a 50-micrometer-thick cyclic olefin polymer (COP) film (Nippon Zeon "Zeonoa film ZF16"; front retardation 3 nm), and to the other main surface The adhesive layer A3 was bonded together as a 2nd adhesive layer, and the double-sided adhesive sheet with a film base material in which the adhesive layer was laminated|stacked on both surfaces of the film base material was produced.

[Example 2]

A double-sided adhesive sheet with a film substrate was carried out in the same manner as in Example 1 except that a 50 µm-thick biaxially stretched polyethylene terephthalate (PET) film (“Lumiror S10” manufactured by Toray Industries; front retardation 920 nm) was used as the film substrate. was produced.

[Examples 3 to 9, Comparative Examples 3 to 5]

The kind of film base material and the kind of adhesive layer were changed, as Table 2 showed, and the double-sided adhesive sheet with a film base material was produced.

[Comparative Examples 1, 2, 6, 7]

The single-layered pressure-sensitive adhesive layers A1, B1, E1, and E3 were used as adhesive sheets without a substrate.

[evaluation]

About the adhesive sheet of an Example and a comparative example, the following method evaluated adhesive force, step|step difference absorbency, drop impact durability, and an indentation.

<Adhesiveness>

After peeling the peeling film from the 2nd adhesive layer, bonding a 50-micrometer-thick PET film, and cutting to 10 mm in width x 100 mm in length, the peeling film is peeled from the 1st adhesive layer, and a glass plate with a 5 kg roller. was pressed to prepare a sample for measuring the adhesive force. In Comparative Examples 1, 2, 6, and 7 using a single-layer adhesive sheet without a substrate, the release film on one side was peeled to bond the PET film, and then the release film on the other side was peeled to bond the glass plate ( The same is true for other evaluations thereafter).

After holding the sample for adhesive force measurement for 30 minutes in an environment of 25 ° C., using a tensile tester, the test piece was peeled from the glass plate under the conditions of a tensile rate of 300 mm / min and a peeling angle of 180 °, and the peel force was measured.

<Heize>

After peeling the release film from the 2nd adhesive layer and bonding to 800-micrometer-thick alkali-free glass (total light transmittance 92%, haze 0.4%), what peeled the release film from the 1st adhesive layer was used as a test piece, and a haze meter ( Haze was measured using Murakami Shikisai Kijutsu Genkyujo Co., Ltd. "HM-150"). The value obtained by subtracting the haze (0.4%) of the alkali-free glass from the measured value was defined as the haze of the pressure-sensitive adhesive sheet.

<Level absorbency>

The pressure-sensitive adhesive sheet was cut to a size of 75 mm × 45 mm, the release film was peeled from the second pressure-sensitive adhesive layer, and a roll laminator (pressure between rolls: 0.2 MPa, conveying speed: 100 mm/min). Thereafter, the release film was peeled from the first pressure-sensitive adhesive layer, and a glass plate (100 mm×50 mm) having a thickness of 500 μm on which black ink (printing thickness: 25 μm or 40 μm) was printed on the periphery in the form of a frame was applied with a roll laminator. (Pressure between rolls: 0.2 MPa, feed speed: 100 mm/min) joined. In the ink printing area|region of the glass plate, the short side direction was 5 mm from both ends, the long side direction was 15 mm from both ends, and the black ink layer was in contact with the area|region 5 mm from the edge part of 4 sides of an adhesive sheet. After processing this sample in an autoclave (50 degreeC, 0.5 MPa) for 30 minutes, the vicinity of the boundary of the printing area|region of black ink was observed with the digital microscope of 20 times magnification, and the presence or absence of a bubble was confirmed. For each of the samples having a print thickness of 25 µm and 40 µm of black ink, the following criteria were used to evaluate the level difference absorbency.

(double-circle): Generation|occurrence|production of a bubble was not seen over the whole perimeter.

○: Bubbles were seen in one of the four corners, but the occurrence of bubbles was not seen in any of the four sides.

×: Air bubbles were seen in at least 2 out of 4 corners, or in at least 1 out of 4 sides

<Impact resistance>

The pressure-sensitive adhesive sheet was cut to a size of 75 mm × 45 mm, the release film was peeled from the second pressure-sensitive adhesive layer, and a roll laminator (pressure between rolls: 0.2 MPa, conveyed) in the center of a glass plate (100 mm × 70 mm) having a thickness of 500 µm speed: 100 mm/min). Thereafter, the release film was peeled from the first pressure-sensitive adhesive layer, and a glass plate (50 mm×100 mm) having a thickness of 30 µm and a black ink having a thickness of 30 µm printed in a frame shape on the periphery was subjected to vacuum compression (contact pressure: 0.3 MPa, pressure). 100 Pa). In the ink printing area|region of the glass plate, the short side direction was 5 mm from both ends, the long side direction was 15 mm from both ends, and the black ink layer was in contact with the area|region 5 mm from the edge part of 4 sides of an adhesive sheet. This sample was processed in an autoclave (50 degreeC, 0.5 MPa) for 30 minutes.

As shown in FIG. 5, the both ends of the short side direction of the sample 85 for a test are set|positioned at intervals of 60 mm so that the glass plate 7 in which the printing layer 76 was provided may become the lower side on the die 83. The upper surface of the edge part of the glass plate 8 which is not provided with the printed layer was fixed on the die|dye 83 with adhesive tape (not shown). After hold|maintaining the test sample 85 fixed with the adhesive tape on the die|dye 83 in an environment of -5 degreeC for 24 hours, and after taking it out to room temperature, within 40 seconds, the metal sphere 87 of a mass of 11 g on the glass plate 7 ) was dropped from a height of 300 mm, and an impact resistance test was performed.

In the impact resistance test, a normal guide 89 is used to make the falling position of the metal sphere constant, and from the corner of the inner edge of the frame of the printed area of the printed layer 76 in the short side direction and the long side direction, respectively. The metal sphere 87 was dropped at the position spaced apart by 10 mm. The test of 2 times was done, and also in any test, what peeling of a glass plate generate|occur|produced in (circle) and any one or both times of the thing in which peeling of a glass plate did not generate|occur|produce was made into x.

<Indentation test>

The release film was peeled from the 2nd pressure-sensitive adhesive layer, and it was bonded to a 50-micrometer-thick PET film with the roll laminator (pressure between rolls: 0.2 MPa, feed rate: 100 mm/min). Then, the release film was peeled from the 1st adhesive layer, and it bonded together to the glass plate with a thickness of 500 micrometers with the roll laminator (pressure between rolls: 0.2 Mpa, feed rate: 100 mm/min). This sample was processed in an autoclave (50 degreeC, 0.5 MPa) for 30 minutes.

Using SAICAS manufactured by Daipla Wintes, a steel ball indenter having a diameter of 1 mm was pressed in from the PET film side of the sample at an indentation speed of 5 µm/s until the vertical load became 1 N, and held for 180 seconds. After that, the indenter was pulled up at a speed of 5 µm/s. After 6 hours from the test, the surface shape of the PET film was measured by a non-contact interference microscope (WYKO), the depth of the indentation of the sample was determined, and the following criteria evaluated.

(double-circle): The depth of an indentation is 3 micrometers or less

○: The depth of the indentation is greater than 3 μm and less than or equal to 4 μm.

×: the depth of the indentation is greater than 4 μm

[Evaluation results]

The lamination structure and evaluation result of each adhesive sheet are shown in Table 1 and Table 2. The numerical value in parentheses of the 1st adhesive layer of Table 2, a film base material, and a 2nd adhesive layer is the thickness (unit: micrometer) of each layer.

The double-sided pressure-sensitive adhesive sheet provided with the substrate of Examples 1 to 4 in which a pressure-sensitive adhesive layer having a relatively large thickness is provided on the visual recognition side of the transparent film substrate and a pressure-sensitive adhesive layer having a relatively small thickness is provided on the image display panel side of the transparent film substrate. It was excellent in water absorption, and there was little residual|survival of the indentation by deformation|transformation at the time of press-fitting an indenter from the 2nd adhesive layer side, and the favorable characteristic was shown. On the other hand, the double-sided pressure-sensitive adhesive sheet without a substrate of Comparative Example 1 including the pressure-sensitive adhesive layer A1 having a thickness of 220 μm had good step absorption, but indentations due to deformation when the indenter was pressed into the pressure-sensitive adhesive layer were likely to remain, resulting in poor indentation. occurred.

The same tendency was seen also in the contrast of Examples 5 and 6 and the comparative example 2 which changed the composition of the adhesive, and the contrast of Example 9 and the comparative example 6. Also in Example 7 and Example 8 in which the composition of the adhesive was changed, similarly to another Example, it was excellent in step|step difference absorbency, and it was hard to remain|survive an indentation, and the favorable characteristic was shown.

A pressure-sensitive adhesive layer B1 having a thickness of 220 μm is provided as a second pressure-sensitive adhesive layer on one main surface of the film substrate, and a relatively small pressure-sensitive adhesive layer B2, B3, B4 is provided as a first pressure-sensitive adhesive layer on the other main surface of the film substrate. In the double-sided adhesive sheet with a base material of Comparative Examples 3-5, an indentation defect generate|occur|produced similarly to the base materialless adhesive sheet of Comparative Example 2 containing the adhesive layer B2.

Although the result of the indentation test was favorable for the adhesive sheet without a base material of the comparative example 7 containing the adhesive layer E3 with a thickness of 100 micrometers, since the thickness of an adhesive sheet was small, it was inferior to step|step difference absorbency.

From the above results, a relatively large pressure-sensitive adhesive layer is provided as a first pressure-sensitive adhesive layer on the visual side of the transparent film substrate, and a relatively small pressure-sensitive adhesive layer is provided as a second pressure-sensitive adhesive layer on the image display panel side of the transparent film substrate It can be seen that by using the double-sided pressure-sensitive adhesive sheet with a base material of

51, 53: adhesive layer
21, 23: release film
59: transparent film substrate
15: double-sided adhesive sheet with substrate
3: Optical film (polarizer)
4: adhesive layer
6: Image display cell
10: Image display panel
7: Front transparent plate
9: Reinforcement substrate
95: FPC
91: main board
92: connection part (connector)
201: image display device

Claims (16)

An adhesive sheet for an image display device for bonding an image display panel and a front transparent plate disposed on a viewer-side surface of the image display panel,
A transparent film substrate, a first pressure-sensitive adhesive layer fixedly laminated on the first main surface of the transparent film substrate, and a second pressure-sensitive adhesive layer fixedly laminated on the second main surface of the transparent film substrate,
In the image display device, the first pressure-sensitive adhesive layer is disposed in contact with the front transparent plate,
The adhesive sheet for image display devices whose thickness of a said 1st adhesive layer is larger than the thickness of a said 2nd adhesive layer. According to claim 1,
The thickness of the said 1st adhesive layer is 80 micrometers or more, The adhesive sheet. According to claim 1,
The thickness of the second pressure-sensitive adhesive layer is 150 μm or less, the pressure-sensitive adhesive sheet. According to claim 1,
The thickness of the transparent film substrate is 15 to 150㎛, the pressure-sensitive adhesive sheet. According to claim 1,
The front retardation of the said transparent film base material is 50 nm or less, The adhesive sheet. According to claim 1,
The said 1st adhesive layer is an adhesive sheet whose shear storage modulus at a temperature of 25 degreeC is 0.16 MPa or more. According to claim 1,
The said 1st adhesive layer is an adhesive sheet whose loss tangent at a temperature of 70 degreeC is 0.25 or more. According to claim 1,
The said 1st adhesive layer is an adhesive sheet whose glass transition temperature is -3 degreeC or less. According to claim 1,
The first pressure-sensitive adhesive layer, the pressure-sensitive adhesive sheet comprising an acrylic polymer having a crosslinked structure. 10. The method of claim 9,
The first pressure-sensitive adhesive layer has a gel fraction of 30 to 80%, the pressure-sensitive adhesive sheet. 10. The method of claim 9,
The said 1st adhesive layer is an adhesive sheet whose polymerization rate is 95 % or more. 10. The method of claim 9,
The adhesive sheet in which the crosslinked structure by a urethane-type segment is introduce|transduced into the said acrylic polymer. A front transparent plate is fixed to the surface of the image display panel on the viewer side via the pressure-sensitive adhesive sheet according to any one of claims 1 to 12,
The image display device, wherein the first pressure-sensitive adhesive layer is bonded to the front transparent plate, and the second pressure-sensitive adhesive layer is bonded to the image display panel. 14. The method of claim 13,
The said image display panel is equipped with the polarizing plate on the visual recognition side surface of an image display cell, The said polarizing plate is bonded with the said 2nd adhesive layer, The image display apparatus of Claim. 14. The method of claim 13,
The image display device in which the said image display panel contains organic electroluminescent cell. 16. The method of claim 15,
The said organic electroluminescent cell is equipped with an electrode and an organic light emitting layer on a resin film board|substrate, The image display apparatus of it.

Images