TW202138514A - Adhesive sheet and image display device having a first adhesive layer on one main surface of the transparent film substrate and a second adhesive layer on the other main surface - Google Patents

Abstract

The present invention relates to an adhesive sheet and an image display device. The adhesive sheet (15) has a first adhesive layer (51) on one main surface of the transparent film substrate (59), and a second adhesive layer (53) on the other main surface. The thickness of the first adhesive layer is greater than the thickness of the second adhesive layer, and in the formation of the image display device, the first adhesive layer is arranged in contact with the front transparent plate, and the second adhesive layer is configured in contact with the image display panel.

Description

Adhesive sheet and image display device

The invention relates to a double-sided adhesive sheet for forming an image display device and an image display device.

As various image display devices such as mobile phones, smart phones, car navigation devices, personal computer monitors, and televisions, liquid crystal display devices or organic EL (Electroluminescence) display devices are widely used. In order to prevent the damage of the image display panel caused by the impact from the outer surface, sometimes a transparent resin plate, glass plate, etc. front transparent plate (also called "cover window", etc.) is installed on the visible side of the image display panel.

Sometimes a colored layer (decorative printing layer) is formed on the periphery of the front transparent plate for decoration and shading. When the adhesive is attached to a transparent member with a decorative printing layer, bubbles are likely to be generated around the printing step. Therefore, a method has been adopted that has step absorbability through an adhesive sheet having a large thickness, thereby suppressing defects such as mixing of air bubbles (for example, Patent Document 1). As the brightness of the display device increases, there is a tendency to increase the thickness of the decorative printed layer in order to improve the light-shielding property. Along with this, a thicker and softer adhesive sheet is gradually used in the lamination of the front transparent plate. .

Patent Document 2 proposes the following solution: as an adhesive sheet for attaching a cover window to a polarizing plate of a liquid crystal panel with an in-cell or surface-mounted touch sensor, it is used as an adhesive sheet for the base film. The area layer has an adhesive sheet with a substrate film formed by an adhesive layer with a predetermined thickness.

Previously, as an image display device, the mainstream is the following liquid crystal display device, which has polarizing plates arranged on the front and back of a liquid crystal cell formed by sandwiching a liquid crystal layer between two glass substrates. Combination of income. In recent years, organic EL display devices in which electrodes and light-emitting layers are provided on resin film substrates such as polyimide films have been put into practical use. Organic EL is a self-luminous type and does not require a light source, so it can realize the thinning, curved shape, and softening of the screen. Prior art literature Patent literature

[Patent Document 1] International Publication No. 2013/161666 [Patent Document 2] Japanese Patent Laid-Open No. 2017-160416

[The problem to be solved by the invention]

In the formation of the image display device, pressure processing such as hot pressing or crimping is sometimes performed during or after bonding 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 not easily deformed, the image display panel is hardly deformed even when subjected to local pressure. On the other hand, in an image display panel using a flexible substrate, if a large pressure is locally applied to the connection part of the part during press processing, the substrate will be locally deformed. If the local deformation is not replied after the pressure is released, and the "indentation" remains, it may become a defect in the image display. [Means used to solve the problem]

The double-sided adhesive sheet with base material formed by providing adhesive layers on both sides of the film base material used in the lamination of the image display panel and the front transparent plate can suppress the indentation caused by the deformation of the image display panel The above-mentioned deformation of the image display panel is caused by local pressure from the back side.

The adhesive sheet of the present invention is a double-sided adhesive sheet with a substrate with a first adhesive layer on one main surface of a transparent film substrate and a second adhesive layer on the other main surface. The thickness of the first adhesive layer is greater than the thickness of the second adhesive layer.

The thickness of the first adhesive layer is preferably 80 μm or more, and the thickness of the second adhesive layer is preferably 150 μm or less. The thickness of the transparent film substrate is preferably 15 μm to 150 μm. The frontal retardation of the transparent film substrate is preferably 50 nm or less.

The double-sided adhesive sheet with base material can be used to form an image display device with a front transparent plate arranged on the visible side of the image display panel. In the image display device, the first adhesive layer is attached to the front transparent plate, and the second adhesive layer is attached to the image display panel. The image display panel may have a polarizing plate on the visual recognition side surface of the image display unit. In this case, the polarizing plate is attached to the second adhesive layer.

The image display panel may also be an organic EL display device including an organic EL unit. The organic EL unit may also be one having electrodes and an organic light-emitting layer on a resin film substrate. [Effects of Invention]

By bonding the image display unit and the front transparent plate through the adhesive sheet with the base material of the present invention, it is possible to reduce the residual indentation caused by pressing from the back side.

Figure 1 is a cross-sectional view of a double-sided adhesive sheet with a base material. The double-sided adhesive sheet 15 with a substrate has a first adhesive layer 51 on one main surface of the transparent film substrate 59 and a second adhesive layer 53 on the other main surface of the transparent film substrate 59. In the form shown in FIG. 1, release films 21 and 23 are temporarily adhered to the surfaces of the adhesive layers 51 and 53. 2 is a cross-sectional view showing a configuration example of an image display device that uses a double-sided adhesive sheet 15 with a base material to fix the front transparent plate 7 to the visible side surface of the image display panel.

[Image Display Panel] In the image display device 201 shown in FIG. 2, the image display panel 10 has an image display unit 6 such as a liquid crystal cell or an organic EL cell.

The image display unit 6 has a functional layer for image display and a substrate supporting the functional layer. For example, in a liquid crystal cell, a liquid crystal layer is arranged between two transparent substrates to change the alignment state of the liquid crystal and change the polarization state of the transmitted light, thereby adjusting the amount of light passing through the polarizing plate. In the organic EL unit, a pair of electrodes are arranged on the substrate to adjust the amount of light emitted by the organic light-emitting layer arranged between the electrodes.

The substrate of the image display unit 6 may be a rigid substrate such as glass or a flexible substrate such as a resin film. By using a resin film substrate, thinner and lighter weight can be achieved. Moreover, if a resin film substrate is used, a curved display and a flexible display can also be formed.

As an image display unit using a film substrate, a top-emission type or a bottom-emission type organic EL unit can be exemplified. The top-emission type organic EL unit sequentially has a metal electrode, an organic light-emitting layer and a transparent electrode on the substrate, and emits light from the side of the transparent electrode (the side opposite to the substrate). The bottom-emission type organic EL unit has a transparent electrode, an organic light-emitting layer and a metal electrode on the substrate in sequence, and emits light from the substrate side. The organic light-emitting layer may have an electron transport layer, a hole transport layer, etc., in addition to an organic layer that itself functions as a light-emitting layer. A transparent substrate is used in the bottom emission type organic EL unit. In a top emission type organic EL unit, the substrate does not necessarily have to be transparent.

It is also possible to provide a reinforcing substrate 9 on the back side of the image display unit 6 to protect and strengthen the substrate. As the reinforcing substrate 9, a metal plate, a glass plate, a resin film, etc. can be used. The thickness of the reinforcing substrate is, for example, about 10 μm to about 200 μm.

A flexible printed wiring board (FPC) 95 is connected to the outer peripheral end of the image display unit 6. The FPC 95 is bent so as to go around the back of the image display unit 6, and is connected to the main substrate 90 disposed on the back of the image display unit. In FIG. 2, the FPC and the main substrate are connected by inserting the terminals of the FPC 95 into the connector 91 provided on the main substrate 90. It is also possible to connect the FPC to the main board by soldering or the like. In addition, the FPC and the main board may be connected via wires. In the connection part of the FPC, the thickness of the connector and the welding part may be locally larger and form a convex part.

The optical film 3 may be disposed on the surface of the visual recognition side of the image display unit 6 via the adhesive layer 4. As the optical film 3 arranged on the visible side surface of the image display unit 6, a polarizing plate can be exemplified. The polarizing plate contains a polarizing element, and the double-area layer of the polarizing element usually has a transparent film as a protective film for the polarizing element. It is also possible to omit the polarizing element protective film on one or both sides of the polarizing element.

The polarizing plate may also have an optical function film, which is laminated on one or both surfaces of the polarizing element via an appropriate adhesive layer or adhesive layer as required. As the optical function film, a retardation plate, a viewing angle widening film, a viewing angle restricting (anti-private) film, a brightness enhancement film, etc. may be mentioned.

When the image display unit 6 is an organic EL unit, since the metal electrode of the organic EL unit has light reflectivity, if external light enters the inside of the organic EL unit, the light will be reflected by the metal electrode, which can be seen from the outside. It reflects light like a mirror. By disposing the circular polarizing plate as the optical film 3 on the visible side surface of the organic EL unit, it is possible to prevent the reflected light from being re-emitted to the outside due to the metal electrode, thereby improving the visibility and design of the screen.

The image display panel 10 can also be an image display panel with an in-cell or surface-in-cell touch sensor assembled with a touch sensor. When the image display panel 10 has a touch sensor function, there is no need to additionally provide a touch sensor on the visual recognition side of the image display panel 10. Therefore, in the image display device 201, the front transparent plate 7 is attached to the visible side surface of the image display panel 10 via a double-sided adhesive sheet 15 with a base material.

[Front transparent panel] The front transparent plate 7 is provided with a printing layer 76 on the periphery of one surface of the transparent plate 71. Since the front transparent plate is arranged on the visible side surface of the image display panel, the damage of the image display panel 10 caused by the impact from the outer surface can be prevented. In addition, by providing the printed layer 76, wiring members such as FPC 95 are not visible from the outside, so the design of the image display device can be improved.

For the transparent plate 71, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, a glass plate, or the like can be used. The transparent plate 71 may have rigidity or flexibility. In order to improve the protection of 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, more preferably 300 μm or more. The thickness of the printing layer 76 is about 10 μm to about 100 μm.

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

The adhesive force of the first adhesive layer 51 of the adhesive sheet 15 to the glass is preferably 2 N/10 mm or more, more preferably 4 N/10 mm or more, and even more preferably 5 N/10 mm or more. By setting the adhesive force within the above range, it is possible to prevent the adhesive sheet from peeling off the adherend when the stress caused by strain or the impact caused by falling or the like is generated. The second adhesive layer 53 is also the same as the first adhesive layer, and preferably has a high adhesive force. The next force was obtained by a peel test with a glass plate as the adherend and a tensile speed of 300 mm/min and a peel angle of 180°. Unless otherwise specified, the adhesive force is the value measured at 25°C.

The total light transmittance of the adhesive sheet 15 is preferably 85% or more, more preferably 90% or more. The haze of the adhesive sheet 15 is preferably 1% or less. The thickness of the adhesive sheet 15 (the total thickness of the transparent film substrate 59 and the adhesive layers 51 and 53) is preferably 120 μm to 1000 μm, more preferably 150 μm to 500 μm, and still more preferably 180 μm to 400 μm.

The adhesive sheet 15 preferably has ultraviolet shielding properties. Since the adhesive sheet 15 has ultraviolet shielding properties, it is possible to prevent the polarizing plate 3 of the image display panel 10 and the organic layer (such as the organic light-emitting layer) contained in the image display unit 6 from deteriorating due to ultraviolet rays. The transmittance of the adhesive sheet 15 at a wavelength of 380 nm is preferably 20% or less, more preferably 15% or less, and still more preferably 10% or less. In order to make the adhesive sheet 15 have ultraviolet shielding properties, it is only necessary to make any one or more of the first adhesive layer 51, the transparent film base 59, and the second adhesive layer 53 have ultraviolet shielding properties. For example, by using a resin material having ultraviolet shielding properties, such as transparent polyimide and polyethylene naphthalate, as the transparent film substrate 59, ultraviolet shielding properties can be imparted. In addition, an ultraviolet absorber may be contained in any one or a plurality of the transparent film substrate 59 and the adhesive layers 51 and 53.

＜Transparent film base material＞ As the transparent film substrate 59, a transparent resin film can be used. The total light transmittance of the transparent film substrate 59 is preferably 85% or more, more preferably 90% or more. The resin material constituting the transparent film substrate 59 is not particularly limited as long as it has transparency. Examples include polyesters such as polyethylene terephthalate and polyethylene naphthalate; Olefins; cyclic polyolefins such as norene-based polymers; cellulosic polymers such as diacetyl cellulose and triacetyl cellulose; acrylic polymers; styrene-based polymers; polycarbonates, polyamides , Polyimide, polyether ether ketone, etc.

The transparent film substrate 59 may have functional layers such as an easy bonding layer and an antistatic layer on the surface. The transparent film substrate 59 can function as a touch sensor. When the transparent film substrate 59 has a function as a touch sensor, electrodes for position detection are provided on the surface of the film. On the other hand, when the image display panel 10 has a touch sensor function, there is no need to provide a touch sensor on the viewing side of the image display panel 10. Therefore, the transparent film base 59 may not have an electrode for position detection.

Since the transparent film base material is arranged between the two adhesive layers 51 and 53, the elasticity of the adhesive sheet 15 as a whole can be improved, thereby increasing the response force to deformation. Therefore, even when the image display panel is deformed by pressing from the back side of the image display panel 10, the plastic deformation of the adhesive sheet 15 is small, and the indentation can be reduced by the recovery force of the film substrate Residue. The thickness of the transparent film substrate 59 is preferably about 15 μm to about 150 μm, more preferably 25 μm to 120 μm, and still more preferably 35 μm to 100 μm.

In order to suppress rainbow-like coloration (iris phenomenon) when viewing the screen of the image display device, the transparent film substrate 59 preferably has optical isotropy. The frontal retardation of the transparent film substrate 59 at a wavelength of 590 nm is preferably 50 nm or less, more preferably 30 nm or less, still more preferably 10 nm or less, particularly preferably 5 nm or less.

＜Adhesive layer＞ The thickness of the first adhesive layer 51 is greater than the thickness of the second adhesive layer 53. The thickness of the second adhesive layer 53 is preferably 0.2 times to 0.85 times the thickness of the first adhesive layer 51, more preferably 0.3 times to 0.8 times, and still more preferably 0.4 times to 0.75 times.

By making the thickness of the first adhesive layer 51 relatively large, there is a tendency for the step absorbency of the printed layer 76 of the front transparent plate 7 to be improved. To ensure step absorbency and impact resistance, the thickness of the first adhesive layer 51 is preferably 80 μm or more. The thickness of the first adhesive layer 51 may be 100 μm or more or 120 μm or more. When the first adhesive layer 51 is attached to the transparent plate on the front surface of the printed layer 76, the thickness of the first adhesive layer 51 is preferably greater than the thickness of the printed layer 76.

The upper limit of the thickness of the first adhesive layer 51 is not particularly limited. From the viewpoints of productivity and processing dimensional stability, it is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less.

By making the thickness of the second adhesive layer 53 relatively small, the plastic deformation caused by the pressing from the side of the image display panel 10 is reduced. Even when the image display panel 10 is deformed by pressing from the back side, the plastic deformation of the adhesive sheet 15 is small, so that the residual indentation can be reduced.

In order to reduce plastic deformation and reduce indentation, the thickness of the second adhesive layer 53 is preferably 150 μm or less, more preferably 120 μm or less. The thickness of the second adhesive layer 53 may be 100 μm or less or 80 μm or less. In order to impart impact resistance, the thickness of the second adhesive layer 53 is preferably 30 μm or more, more preferably 50 μm or more.

When the image display panel is bonded to the front transparent plate through a single-layer non-substrate adhesive sheet, when the thickness of the adhesive sheet is small, the level difference of the printing step of the front transparent plate is insufficient. When the thickness of the sheet is large, since the plastic deformation of the adhesive sheet is large, the indentation caused by the pressure from the panel side is likely to remain. The adhesive sheet with a base material having a transparent film base material 59 between the two adhesive layers 51 and 53 can ensure the step absorbency by the relatively large thickness of the first adhesive layer 51. In addition, the plastic deformation of the second adhesive layer 53 with a relatively small thickness is small, and the deformation of the second adhesive layer 53 caused by the pressing from the back side can be easily recovered by the elastic recovery force of the transparent film substrate 59. Therefore, it is possible to suppress residual indentation.

To improve the adhesive sheet 15 with the adhesive and then the holding force considerate timely processing and to ensure dimensional stability, shear storage modulus G under the first adhesive layer 51 of _{25 ℃} '25 ℃ preferably less than 0.16 MPa , More preferably, it is 0.18 MPa or more, still more preferably 0.20 MPa or more, and particularly preferably 0.21 MPa or more.

On the other hand, in order to make the adhesive sheet 15 having an appropriate viscosity to ensure the wettability and having the step absorbability, for cushioning the impact such as falling, G of the first adhesive layer 51 _{'25 ℃} preferably 0.5 MPa or less, more preferably 0.4 MPa or less, still more preferably 0.3 MPa or less, particularly preferably 0.28 MPa or less.

In order to make the adhesive sheet 15 have step absorbency, the loss tangent tanδ _{70 °C at} 70°C of the first adhesive layer 51 is preferably 0.25 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. The 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 retention, the tanδ _{70 °C is} preferably 1.0 or less, more preferably 0.9 or less, and still more preferably 0.85 or less. The tanδ _{70 °C} may be 0.80 or less, 0.75 or less, or 0.70 or less.

The peak top value of tanδ of the first adhesive layer 51 is preferably 1.5 or more, more preferably 1.6 or more, and still more preferably 1.7 or more. Adhesives with a larger peak top value of tanδ tend to have larger viscous behavior and excellent impact resistance. The upper limit of the peak top value of tanδ of the first adhesive layer 51 is not particularly limited, and is usually 3.0 or less. From the viewpoint of adhesive retention, the peak top value of tanδ is preferably 2.7 or less, more preferably 2.5 or less.

The glass transition temperature of the first adhesive layer 51 is preferably -3°C or lower, more preferably -4°C or lower. The glass transition temperature of the first adhesive layer 51 is preferably -20°C or higher, more preferably -15°C or higher, and still more preferably -13°C or higher. By setting the glass transition temperature within the above-mentioned range, the adhesive has an appropriate viscosity even in a low-temperature region, and it tends to suppress the peeling of the adherend due to impact such as falling.

Shear storage modulus G', loss tangent tanδ, and glass transition temperature can be determined by viscoelasticity measurement at a frequency of 1 Hz. tanδ is the ratio G''/G' of the loss modulus G" to the storage modulus G', and the glass transition temperature is the temperature at which tanδ reaches its maximum (peak top temperature). The storage modulus G'is equivalent to the part that is stored in the form of elastic energy when the material is deformed, and is an index indicating the degree of hardness. The greater the storage modulus, the higher the subsequent retention, and the more likely it is to suppress the peeling caused by strain. Loss modulus G" is equivalent to the part of lost energy lost due to internal friction when the material is deformed, and it represents the degree of viscosity. The larger the tanδ, the stronger the viscosity tendency, and the deformation behavior becomes the liquid deformation behavior, so the rebound energy tends to decrease.

To make G _{'25 ℃} 0.16 MPa or more processing stability and to ensure at the same time having a suitable flexibility for imparting the step absorbability of the gel fraction of the adhesive is preferably 30% to 80%, more preferably 35%～70%. The gel fraction may be 40% or more or 45% or more, and may be 65% or less or 60% or less.

Regarding the gel fraction of the adhesive, it can be determined in the form of insoluble components in solvents such as ethyl acetate. Specifically, it is determined from the insoluble components after immersing the adhesive in ethyl acetate at 23°C for 7 days Relative to the weight fraction of the sample before immersion (unit: wt%). Generally, the gel fraction of a polymer is equal to the degree of cross-linking, and the more cross-linked parts in the polymer, the greater the gel fraction. The gel fraction (introduction amount of the cross-linked structure) can be adjusted to a desired range by the method of introducing the cross-linked structure, the type and amount of the cross-linking agent, and the like.

The second adhesive layer 53 is not particularly limited as long as it is a transparent adhesive layer having the above-mentioned thickness. The adhesive of the first adhesive layer 51 and the adhesive of the second adhesive layer 53 may be the same or different. Then in order to improve retention, dimensional stability and impact resistance, a second adhesive layer having a shear storage modulus G of 53 of the _{25 ℃} '25 ℃, loss tangent at 70 ℃ the tanδ _{70 ℃,} tanδ peak of The value, the glass transition temperature, and the gel fraction are preferably within the aforementioned ranges described with respect to the first adhesive layer 51.

＜The composition of the adhesive＞ The composition of the adhesives constituting the first adhesive layer 51 and the second adhesive layer 53 is not particularly limited, and acrylic polymer, silicone polymer, polyester, polyurethane can be appropriately selected and used. , Polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based, natural rubber, synthetic rubber and other rubber-based polymers are used as adhesives for base polymers. In particular, if it is excellent in optical transparency, and exhibits moderate wettability, cohesiveness, and adhesive properties, and also excellent in weather resistance, heat resistance, etc., it is preferable to use an acrylic system with a cross-linked structure introduced. Acrylic adhesive for base polymer.

The acrylic base polymer contains alkyl (meth)acrylate as the main constituent monomer component. Furthermore, in this specification, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid.

As the alkyl (meth)acrylate, it is preferable to use an alkyl (meth)acrylate having 1 to 20 carbon atoms in the alkyl group. The alkyl (meth)acrylate may have a branched alkyl group or a cyclic alkyl group.

As specific examples of alkyl (meth)acrylate having a chain alkyl group, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (methyl) ) Isobutyl acrylate, second butyl (meth)acrylate, tertiary butyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, neopentyl (meth)acrylate Ester, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, (meth) ) Nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate Base ester, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, ( Cetyl meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isoostearyl (meth)acrylate, ten (meth)acrylate Nonaalkyl esters and so on.

Specific examples of alkyl (meth)acrylates having alicyclic alkyl groups include: cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate , Cyclooctyl (meth)acrylate and other cycloalkyl (meth)acrylates; iso(meth)acrylate and other (meth)acrylates with a bicyclic aliphatic hydrocarbon ring; (meth) Dicyclopentyl acrylate, dicyclopentyloxyethyl (meth)acrylate, tricyclopentyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl (meth)acrylate (Meth)acrylates having three or more aliphatic hydrocarbon rings, such as 2-adamantyl ester and 2-ethyl-2-adamantyl (meth)acrylate.

The amount of the alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic base polymer is preferably 50% by weight or more, more preferably 55% by weight or more, and still more preferably 60% by weight or more. In order to make the glass transition temperature (Tg) into an appropriate range, the acrylic base polymer has an alkyl (meth)acrylate having a chain alkyl group with 4 to 10 carbon atoms relative to the total amount of constituent monomer components. The amount is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 55% by weight or more. Furthermore, the monomer component constituting the acrylic base polymer means the monomer used to form the crosslinked structure is removed from all the monomer components constituting the polymer (the following polyfunctional (meth)acrylate, (methyl) ) Monomer components after acrylic urethane etc.) and crosslinking agent.

The acrylic base polymer may contain a hydroxyl group-containing monomer and a carboxyl group-containing monomer as constituent monomer components. When the crosslinked structure is introduced by the isocyanate crosslinking agent, the hydroxyl group becomes the reaction point with the isocyanate group. When the crosslinked structure is introduced by the epoxy-based crosslinking agent, the carboxyl group becomes the same as the epoxy group. Reaction point.

Examples of hydroxyl-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyethyl (meth)acrylate. Hydroxyhexyl ester, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl) (meth)acrylate ) (Meth) acrylates such as methyl esters. When introducing the cross-linked structure based on the urethane-based segment into the acrylic base polymer, in order to improve the compatibility with the urethane-based segment and the transparency of the adhesive, acrylic The base polymer preferably contains (meth)acrylate having a hydroxyalkyl group having 4 to 8 carbons as a constituent monomer component.

By making the acrylic base polymer have a hydroxyl-containing monomer as a constituent monomer component, the transparency of the adhesive is improved and the white turbidity in a high-temperature and high-humidity environment is suppressed. In addition, the hydroxyl group of the hydroxyl group-containing monomer can form physical crosslinks based on hydrogen bonds with acrylic polymers and crosslinked segments. Thus, by increasing the base polymer of the monomer component in the acrylic monomer containing hydroxyl group ratio, the cohesive force has improved, G 'tends to increase the _{25 ℃.} With respect to the total amount of monomer components constituting the acrylic base polymer, the amount of the hydroxyl-containing monomer is preferably 5% by weight to 30% by weight, more preferably 8% by weight to 25% by weight, and still more preferably 10% by weight ~20% by weight.

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

The acrylic base polymer may contain a nitrogen-containing monomer as a constituent monomer component. Examples of nitrogen-containing monomers include: N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperidine, vinylpyrrolidone, Vinyl pyrrole, vinyl imidazole, vinyl azole, vinyl oxoline, (meth) acryloyl oxoline, N-vinyl carboxylic acid amides, N-vinyl caprolactam and other vinyl series Monomers; cyano group-containing acrylic monomers such as acrylonitrile and methacrylonitrile. Among them, N-vinylpyrrolidone is preferred in order to have a higher adhesive force improvement effect due to increased cohesive force.

By the acrylic base polymer containing a hydroxyl group-containing monomers, carboxyl group-containing monomer and a nitrogen-containing highly polar monomer as a constituent monomer a monomer component has improved cohesive force of the adhesive, G 'increases _{25 ℃,} followed by The tendency to improve retention. On the other hand, when the content of the high-polarity monomer is too large, the glass transition temperature may increase and the impact resistance may decrease. Therefore, the amount of the highly 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 monomer components constituting the acrylic base polymer is preferably 15% by weight to 45% by weight %, more preferably 20% by weight to 40% by weight, and still more preferably 25% by weight to 37% by weight. It is particularly preferable that the total of the hydroxyl-containing monomer and the nitrogen-containing monomer is within the above-mentioned range. With respect to the total amount of monomer components constituting the acrylic base polymer, the amount of the nitrogen-containing monomer is preferably 7 wt% to 30 wt%, more preferably 10 wt% to 25 wt%, and still more preferably 12 wt% ~22% by weight.

The acrylic base polymer may also contain the following monomer components as monomer components other than the above, that is, an acid anhydride group-containing monomer, a caprolactone adduct of (meth)acrylic acid, a sulfonic acid group-containing monomer, Phosphoric acid monomers; vinyl acetate, vinyl propionate, styrene, α-methylstyrene and other vinyl monomers; cyano group-containing acrylic monomers such as acrylonitrile and methacrylonitrile; (methyl ) Epoxy group-containing monomers such as glycidyl acrylate; polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxy glycol (meth)acrylate, methoxy Polypropylene glycol (meth)acrylate and other glycol-based acrylate monomers; tetrahydrofurfuryl (meth)acrylate, fluorine-containing (meth)acrylate, polysiloxane (meth)acrylate, (meth) Acrylic monomers such as 2-methoxyethyl acrylate and the like.

Among the above-mentioned monomer components of the acrylic base polymer, it is preferable that the content of alkyl (meth)acrylate is the largest. The properties of the adhesive are easily affected by the type of monomer (main monomer) with the largest content among the constituent monomers of the base polymer. For example, when the main monomer is an alkyl (meth)acrylate having a chain alkyl group with a carbon number of 6 or less, the tanδ at _{70 °C} tends to increase and the step absorbency tends to increase. Especially butyl acrylate and the like to C ₄ alkyl acrylate ester monomer of the main case, there is a tendency of increasing tanδ _{70 ℃.} The amount of the alkyl (meth)acrylate having a chain alkyl group with a carbon number of 6 or less relative to the total amount of monomer components constituting the acrylic base polymer is preferably 40% by weight to 85% by weight, more preferably 45 wt% to 80 wt%, more preferably 50 wt% to 75 wt%. In particular, the content of butyl acrylate as a constituent monomer component is preferably within the above-mentioned range.

The theoretical Tg of the acrylic base polymer is preferably -50°C or higher. The theoretical Tg of the acrylic base polymer is preferably -10°C or lower, more preferably -20°C or lower, and still more preferably -25°C or lower. Theoretical Tg by the following Fox formula based, according to the glass transition temperature of the homopolymer of the monomer components constituting the base polymer Tg of the acrylic monomer component _I and each of the weight fraction W _i is calculated. 1/Tg=Σ(W _i /Tg _i )

Tg is the glass transition temperature of the polymer (unit: K), W _i is the weight fraction of monomer component i (copolymerization ratio on a weight basis) constituting the chain segment, and Tg _i is the glass of homopolymer of monomer component i Transition temperature (unit: K). As the glass transition temperature of the homopolymer, the value described in the third edition of the Polymer Handbook (John Wiley & Sons, Inc., 1989) can be used. For the Tg of the homopolymer of the monomer not described in the above-mentioned literature, the peak top temperature of the loss tangent (tanδ) obtained by the dynamic viscoelasticity measurement may be used.

The polymer introduced with the crosslinked structure can be obtained, for example, by the following method: (1) Polymerizing a polymer with a functional group capable of reacting with the crosslinking agent, and then adding a crosslinking agent to make the polymer react with the crosslinking agent. Method; and (2) a method of introducing a branched structure (crosslinked structure) by making the polymer component of the polymer include a polyfunctional compound; and so on. It is also possible to use these methods to introduce various cross-linked structures into the base polymer.

Specific examples of the crosslinking agent in the method of reacting the base polymer and the crosslinking agent in the above (1) include: isocyanate-based crosslinking agent, epoxy-based crosslinking agent, azoline-based crosslinking agent, An aziridine-based cross-linking agent, a carbodiimide-based cross-linking agent, a metal chelate-based cross-linking agent, etc. Among them, in order to have high reactivity with the hydroxyl group and carboxyl group of the base polymer and easily introduce a cross-linked structure, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are preferred. These crosslinking agents form a crosslinked structure by reacting with functional groups such as hydroxyl and carboxyl groups introduced into the base polymer. For an acid-free adhesive without a carboxyl group in the base polymer, it is preferable to use an isocyanate-based crosslinking agent, and a crosslinked structure is formed by the 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 can be used. As the isocyanate-based crosslinking agent, for example, lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; cyclopentyl diisocyanate, cyclohexyl diisocyanate, isophorone diisocyanate, etc. Alicyclic isocyanates such as isocyanates; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate; trimethylolpropane/toluene diisocyanate three Polymer adducts (for example, "Coronate L" manufactured by Tosoh Corporation), trimethylolpropane/hexamethylene diisocyanate trimer adducts (for example, "Coronate HL" manufactured by Tosoh Corporation), Trimethylolpropane adduct of xylylene diisocyanate (for example, "Takenate D110N" manufactured by Mitsui Chemicals), isocyanurate form of hexamethylene diisocyanate (for example, manufactured by Tosoh Corporation) "Coronate HX") and other isocyanate adducts. In addition, by using a urethane prepolymer having an isocyanate group at the terminal as an isocyanate-based crosslinking agent, a crosslinked structure based on the urethane-based segment can be introduced.

In the above (2) method of including the polyfunctional compound in the polymerization component of the base polymer, the entire amount of the monomer component constituting the acrylic base polymer and the polyfunctional compound for introducing the crosslinked structure can be reacted at once , It can also be aggregated in multiple stages. As a method of performing polymerization in multiple stages, the following method is preferred: the monofunctional monomer constituting the base polymer is polymerized (prepolymerization) to prepare a partial polymer (prepolymer composition), and the prepolymer is combined A polyfunctional compound such as a polyfunctional (meth)acrylate is added to it, and the prepolymer composition and the polyfunctional monomer are polymerized (main polymerization). The prepolymer composition is a partial polymer containing a polymer with a low degree of polymerization and unreacted monomers.

By performing prepolymerization of the constituent components of the acrylic base polymer, the branch point (crosslinking point) of the polyfunctional compound can be uniformly introduced into the base polymer. In addition, it is also possible to apply a mixture of low molecular weight polymers or partial polymers and unpolymerized monomer components (adhesive composition) on the substrate, and then perform the main polymerization on the substrate to form an adhesive Agent layer. Due to the low viscosity and excellent coating properties of oligomeric compositions such as prepolymer composition, it is based on the application of the adhesive composition which is a mixture of prepolymer composition and polyfunctional compound and then the main polymerization on the substrate. The method can improve the productivity of the adhesive layer and make the thickness of the adhesive layer uniform.

As a polyfunctional compound for introducing a crosslinked structure, a compound containing two or more polymerizable functional groups (ethylenically unsaturated groups) having an unsaturated double bond in one molecule can be exemplified. The polyfunctional compound is preferably a polyfunctional (meth)acrylate in order to facilitate copolymerization with the monomer components of the acrylic base polymer. In the case of introducing a branched (crosslinked) structure by active energy ray polymerization (photopolymerization), a multifunctional acrylate is preferred.

Examples of polyfunctional (meth)acrylates include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate. , Bisphenol A ethylene oxide modified two (meth) acrylate, bisphenol A propylene oxide modified two (meth) acrylate, alkanediol two (meth) acrylate, tricyclodecane two Methanol di(meth)acrylate, ethoxylated isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri( Meth) acrylate, di(trimethylolpropane) tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth) ) Acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate ) Acrylate, isoprene (meth)acrylate, etc.

By using a (meth)acrylate urethane having a (meth)acrylic acid group at the end of the urethane chain as a polyfunctional (meth)acrylate, it is possible to introduce a urethane-based The cross-linked structure of the chain segment. By using the urethane-based segment to cross-link the acrylic base polymer, it is easy to obtain an adhesive that can have both a low glass transition temperature and high adhesive retention. The urethane-based segment is a molecular chain with a urethane bond. By covalently bonding the two ends of the urethane-based segment with the acrylic base polymer, the amino group-based The formate is a cross-linked structure of the chain segment. The urethane-based segment typically contains a polyurethane chain obtained by reacting a diol with a diisocyanate.

The molecular weight of the polyurethane chain in the urethane-based segment is preferably 5,000 to 30,000, more preferably 6,000 to 23,000, and still more preferably 7,000 to 20,000. The greater the molecular weight of the polyurethane chain in the urethane series segment, the longer the distance between crosslinking points. If the molecular weight of the polyurethane chain is within the above-mentioned range, the polymer with the cross-linked structure introduced has moderate cohesiveness and fluidity, so it can take into account adhesion, step absorbency, and impact resistance.

When the molecular weight of the polyurethane chain is too small and the distance between the cross-linking points is short, as the cohesive force increases, the tanδ decreases, and there is a tendency for step absorbency and impact resistance to decrease. On the other hand, when the molecular weight of the polyurethane chain is too large and the distance between the cross-linking points is long, the storage modulus may be small and then the retention force may be insufficient. Even when the molecular weight of the polyurethane chain is relatively large, the gel fraction can be increased by increasing the amount of the urethane chain segment, thereby increasing the storage modulus. However, the compatibility of polyurethane chains with larger molecular weights and acrylic polymers is low, so sometimes as the amount of urethane chain segments increases, the haze of the adhesive increases And the transparency is reduced.

If the amount of the urethane-based segment becomes too large, the viscosity of the adhesive may decrease as the gel fraction increases, thereby decreasing the step absorbency and impact resistance. In addition, if the amount of the urethane-based segment becomes too large, the transparency of the adhesive may decrease and the haze may increase. Therefore, relative to 100 parts by weight of the acrylic polymer, the amount of the urethane-based segment in the base polymer is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, and even more preferably 5 parts by weight the following. On the other hand, in order to increase 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 relative to 100 parts by weight of the acrylic polymer. More preferably, it is 0.4 part by weight or more, and even more preferably 0.5 part by weight or more. With respect to 100 parts by weight of the acrylic polymer, the amount of the urethane-based segment in the base polymer may be 4 parts by weight or less or 3 parts by weight or less, and may be 0.7 parts by weight or more or 1 part by weight or more.

As the glycol used to form the polyurethane chain, low molecular weight glycols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, hexylene glycol, etc.; polyester polyols, polyethers, etc. Polyols, polycarbonate polyols, acrylic polyols, epoxy polyols, caprolactone polyols and other high molecular weight polyols.

The diisocyanate used to form the polyurethane chain may be any one of aromatic diisocyanate and aliphatic diisocyanate. As the diisocyanate, derivatives of isocyanate compounds can also be used. Examples of derivatives of isocyanate compounds include: dimer of polyisocyanate, trimer of isocyanate (isocyanurate), polymeric MDI, adduct with trimethylolpropane, and biuret modification Compounds, allophanate modified compounds, urea modified compounds, etc. As a diisocyanate component, it can also be used for the urethane prepolymer which has an isocyanate group at the terminal.

In the exemplified polyurethane chain, in order to have higher compatibility with the acrylic polymer, it is preferable to include a polyether urethane having a polyether polyol as the diol component, and/ Or polyester urethane with polyester polyol as the diol component. Especially when the cross-linked structure based on polyester urethane is introduced, the storage modulus at room temperature increases, and the subsequent retention and processability tend to increase. As one of the reasons, a molecular structure that has rigidity compared with polyether and the like polyester can be exemplified. It is believed that if the cross-linked structure is introduced by rigid segments, the movement of the polymer will be restricted and the storage modulus will increase. On the other hand, since the distance between the cross-linking points of the polymer is maintained, it exhibits impact resistance, Step absorbency.

By using a compound having a functional group capable of copolymerizing with the monomer components constituting the acrylic polymer at the end of the polyurethane chain, or having a functional group capable of cooperating with the acrylic polymer at the end of the polyurethane chain Compounds containing reactive functional groups such as carboxyl groups and hydroxyl groups can introduce crosslinked structures based on urethane-based segments into acrylic polymers. In order to easily introduce the crosslinking points into the acrylic polymer uniformly, and to make the acrylic polymer and the urethane-based segment excellent in compatibility, it is preferably used for both of the polyurethane chains. A urethane di(meth)acrylate having a (meth)acryloyl group at the end is used as the polyfunctional (meth)acrylate to introduce a crosslinked structure based on the urethane-based segment.

Urethane di(meth)acrylates having (meth)acrylic groups at both ends can be used, for example, by using (meth)acrylates having hydroxyl groups in addition to diol components in the polymerization of polyurethane. Base) Acrylic compound. In order to control the chain length (molecular weight) of the urethane chain segment, it is preferable to synthesize isocyanate-terminated polyurethane by reacting diol and diisocyanate in such a way that the isocyanate becomes excessive, and then add a polyurethane having a hydroxyl group. The (meth)acrylic compound reacts the terminal isocyanate group of the polyurethane with the hydroxyl group of the (meth)acrylic compound.

A polyurethane chain having an isocyanate group at the end is obtained by reacting a polyol and a polyisocyanate compound in such a way that the polyisocyanate compound becomes excessive. In order to obtain an isocyanate-terminated polyurethane, the diol component and the diisocyanate component may be used so that the NCO/OH (equivalent ratio) is preferably 1.1 to 2.0, and more preferably 1.15 to 1.5. It is also possible to add a diisocyanate component after mixing roughly equal amounts of the diol component and the diisocyanate component and reacting them.

Examples of the (meth)acrylic compound having a hydroxyl group include: hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and hydroxyhexyl (meth)acrylate. Ester, hydroxymethacrylamide, hydroxyethylacrylamide, etc.

As the (meth)acrylate urethane, Arakawa Chemical Industry, Shin Nakamura Chemical Industry, Toagosei, Kyoeisha Chemical, Nippon Kayaku, Nippon Synthetic Chemical Industry, Negami Industry, Daicel-Zenxin, etc. can be used Commercial products sold by various companies. The weight average molecular weight of the (meth)acrylate urethane is preferably 5,000 to 30,000, more preferably 6,000 to 23,000, and still more preferably 7,000 to 20,000.

The glass transition temperature of (meth)acrylate urethane is preferably 0°C or lower, more preferably -10°C or lower, and still more preferably -20°C or lower. By using low-Tg (meth)acrylate urethane, even when the cross-linked structure based on the urethane-based segment is introduced to increase the cohesive force of the base polymer, low temperature can be obtained Adhesive with excellent adhesion. The lower limit of the glass transition temperature of (meth)acrylate urethane is not particularly limited. To obtain an adhesive with excellent high-temperature retention, it is preferably -100°C or higher, more preferably -90°C or higher, and more Preferably, it is above -80°C.

When (meth)acrylic urethane is used to introduce the cross-linked structure based on the urethane-based segment into the acrylic polymer, the glass of the urethane-based segment of the base polymer The transition temperature is approximately equal to the glass transition temperature of (meth)acrylate urethane.

＜Adhesive composition＞ The adhesive composition containing the base polymer is coated on the substrate, and the solvent is dried, and the base polymer is cross-linked and hardened as needed, thereby forming an adhesive layer.

The base polymer can be prepared by known polymerization methods such as solution polymerization, photopolymerization (UV polymerization), bulk polymerization, and emulsion polymerization. In view of the transparency, water resistance, and cost of the adhesive, solution polymerization or photopolymerization is preferred. In the case of photopolymerization, the polymer can be prepared without using a solvent, so there is no need to dry and remove the solvent when forming the adhesive layer, and the adhesive layer with a large thickness can be uniformly formed.

系光聚合起始劑、醯基氧化膦系光聚合起始劑等。作為熱聚合起始劑，可以使用偶氮系起始劑、過氧化物系起始劑、將過氧化物與還原劑組合而成之氧化還原系起始劑(例如，過硫酸鹽與亞硫酸氫鈉之組合、過氧化物與抗壞血酸鈉之組合等)。When preparing the base polymer, polymerization initiators such as photopolymerization initiators and thermal polymerization initiators can be used according to the type of polymerization reaction. As the photopolymerization initiator, benzoin ether-based photopolymerization initiator, acetophenone-based photopolymerization initiator, α-ketol-based photopolymerization initiator, aromatic sulfonyl chloride-based photopolymerization initiator can be used , Photoactive oxime-based photopolymerization initiator, benzoin-based photopolymerization initiator, benzophenone-based photopolymerization initiator, benzophenone-based photopolymerization initiator, ketal-based photopolymerization initiator, 9 -Oxygen Sulfur𠮿

It is a photopolymerization initiator, an phosphine oxide-based photopolymerization initiator, etc. As the thermal polymerization initiator, an azo-based initiator, a peroxide-based initiator, and a redox-based initiator (for example, persulfate and sulfurous acid) formed by combining a peroxide and a reducing agent can be used. The combination of sodium hydrogen peroxide, the combination of peroxide and sodium ascorbate, etc.).

In order to adjust the molecular weight of the base polymer, a chain transfer agent can also be used. As the chain transfer agent, there may be mentioned: α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, thioglycolic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolic acid, 2 ,3-Dimercapto-1-propanol and other mercaptans; α-methylstyrene dimer, etc.

When a multifunctional monomer is used as the monomer component of the base polymer in addition to the monofunctional monomer, the monofunctional monomer may be polymerized first to form a prepolymer composition with a low degree of polymerization (prepolymerization). ), adding a multifunctional monomer to the slurry of the prepolymer composition to polymerize the prepolymer and the multifunctional monomer (main polymerization). By performing the prepolymerization of the prepolymer in this way, the branch points generated by the polyfunctional monomer component can be uniformly introduced into the base polymer. In addition, a mixture of the prepolymer composition and unpolymerized monomer components (adhesive composition) may be coated on the substrate, and then the main polymerization may be performed on the substrate to form an adhesive layer. Due to the low viscosity of the prepolymer composition and excellent coating properties, it can be improved according to the method of main polymerization on the substrate after coating the mixture of the prepolymer composition and the unpolymerized monomer, that is, the adhesive composition. The productivity of the adhesive layer and the uniform thickness of the adhesive layer.

The prepolymer composition can be partially polymerized (prepolymerized) by mixing the monomer components constituting the acrylic base polymer and the polymerization initiator (referred to as the "prepolymer forming composition"), for example. ) And prepared. Furthermore, the monomer in the composition for forming a prepolymer is preferably a monofunctional monomer such as an alkyl (meth)acrylate or a polar group-containing monomer among the monomer components constituting the acrylic polymer. The composition for prepolymer formation may also contain a polyfunctional monomer. For example, the composition for forming a prepolymer may contain a part of the polyfunctional monomer component as the raw material of the base polymer, and after the prepolymer is obtained by polymerization, the remaining part of the polyfunctional monomer component may be added and used for the main polymerization.

In addition to the monomer and the polymerization initiator, the composition for forming a prepolymer may contain a chain transfer agent and the like as necessary. The polymerization method of the prepolymer is not particularly limited. In order to adjust the reaction time so that the molecular weight (polymerization rate) of the prepolymer falls within a desired range, it is preferable to perform polymerization by irradiating active light such as UV light. The polymerization initiator and chain transfer agent used for the prepolymerization are not particularly limited, and for example, the above-mentioned photopolymerization initiator and chain transfer agent can be used.

The polymerization rate of the prepolymer is not particularly limited. In order to make the viscosity suitable for coating on the substrate, it is preferably 3% by weight to 50% by weight, more preferably 5% by weight to 40% by weight. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity of active light such as UV light, and the irradiation time. The polymerization rate of the prepolymer is calculated by the following formula based on the weight before and after heating when heated at 130°C for 3 hours. The polymerization rate of the adhesive is also calculated by the same method. Polymerization rate (%) = weight after drying / weight before drying × 100

It is formed by mixing the remaining monomer components (post-added monomers) constituting the acrylic base polymer in the above-mentioned prepolymer composition and polymerization initiator, chain transfer agent, silane coupling agent, crosslinking agent, etc. as required Adhesive composition. The post-added monomer preferably contains a multifunctional monomer. When urethane di(meth)acrylate is used to introduce a crosslinked structure based on the urethane-based segment, it is preferable to add urethane di(meth)acrylate As a post-add monomer.

The photopolymerization initiator and chain transfer agent used in the main polymerization are not particularly limited. For example, the above-mentioned photopolymerization initiator and chain transfer agent can be used. When the polymerization initiator used in the prepolymerization is not inactivated and remains in the prepolymer composition, the addition of the polymerization initiator used for the main polymerization can be omitted.

In the main polymerization, it is preferable to adjust the molecular weight by including a chain transfer agent in the adhesive composition. The chain transfer agent used in the main polymerization is not particularly limited, and for example, the above-mentioned chain transfer agent can be used. The amount of the chain transfer agent in the adhesive composition is preferably 0.001 parts by weight to 2 parts by weight, more preferably 0.005 parts by weight to 1 part by weight, and more preferably 0.01 parts by weight relative to 100 parts by weight of the constituent components of the base polymer Parts by weight-0.5 parts by weight. Furthermore, when the chain transfer agent used in the prepolymerization is not inactivated and remains in the prepolymer composition, the addition of the chain transfer agent to the adhesive composition can be omitted.

The chain transfer agent is a self-growing polymer chain that accepts free radicals to stop the elongation of the polymer, and after receiving the free radicals, the chain transfer agent will attack the monomer and start the polymerization again. By using a chain transfer agent, it is possible to suppress the increase in the molecular weight of the polymer without reducing the concentration of free radicals in the reaction system.

When the ratio of monofunctional monomer to polyfunctional monomer is fixed, the higher the molecular weight, the higher the probability of the crosslinking point (branching point) formed by the polyfunctional monomer in a polymer chain, so there is condensation. The tendency of gel fraction to increase. By using a chain transfer agent to suppress the elongation of the polymer, there is a tendency that the molecular weight of the polymer becomes smaller and the increase in the gel fraction is suppressed. Therefore, by including the chain transfer agent in the adhesive composition, it is easy to form an adhesive having a large tan δ and excellent step absorbency.

(Ultraviolet absorber) In order to make the adhesive layers 51 and 53 have ultraviolet absorbing properties, an ultraviolet absorber may also be used. Examples of ultraviolet absorbers include: benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, tris-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers剂 etc. In order to have high UV absorption and excellent compatibility with acrylic polymers, it is easy to obtain high-transparency acrylic adhesives, preferably three-type ultraviolet absorbers and benzotriazole-type ultraviolet absorbers, among which Preferably, it is a triple-type ultraviolet absorber containing a hydroxyl group and a benzotriazole-type ultraviolet absorber having a benzotriazole skeleton in one molecule.

As the ultraviolet absorber, a commercially available product can be used. As a commercially available product of tri-series ultraviolet absorbers, there can be exemplified: 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-tris-2-yl)- The reaction product of 5-hydroxyphenyl and [(alkoxy)methyl]oxirane ("TINUVIN 400" manufactured by BASF), 2-(2,4-dihydroxyphenyl)-4,6- The reaction product of bis(2,4-dimethylphenyl)-1,3,5-tris and glycidic acid (2-ethylhexyl) ester ("TINUVIN 405" manufactured by BASF Corporation), 2,4 -Bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3,5-tris ("TINUVIN 460" manufactured by BASF Corporation), 2-(4,6-Diphenyl-1,3,5-tris-2-yl)-5-[(hexyl)oxy]-phenol ("TINUVIN 577" manufactured by BASF Corporation), 2-( 2-Hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-tris (tinuvin manufactured by BASF 479」), 2,4-bis[{4-(4-ethylhexyloxy)-4-hydroxy}-phenyl]-6-(4-methoxyphenyl)-1,3,5- Tris ("Tinosorb S" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-tris-2-yl)-5-[2-(2-ethylhexyl) Oxy)ethoxy]-phenol ("ADK STAB LA-46" manufactured by ADEKA) and the like.

As a commercially available product of a benzotriazole-based ultraviolet absorber, 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4 may be mentioned. -(1,1,3,3-Tetramethylbutyl)phenol ("TINUVIN 928" manufactured by BASF), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotris Azole ("TINUVIN PS" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (manufactured by BASF) "TINUVIN 900"), 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetra Methylbutyl)phenol ("TINUVIN 928" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol ("TINUVIN 928" manufactured by BASF) TINUVIN 571''), 2-(2H-benzotriazol-2-yl)-p-cresol ("TINUVIN P" manufactured by BASF), 2-(2H-benzotriazol-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-butylphenol ("TINUVIN 326" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-amylphenol (BASF) Manufactured "TINUVIN 328"), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol ("TINUVIN 329" manufactured by BASF Corporation ), phenylpropionic acid and 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy (C7-9 side chain and straight chain alkyl) The ester compound ("TINUVIN 384-2" manufactured by BASF company), 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl) methyl propionate The reaction product of ester and polyethylene glycol ("TINUVIN 1130" manufactured by BASF), 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl ) The reaction product of methyl propionate and polyethylene glycol 300 ("TINUVIN 213" manufactured by BASF Corporation), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalic acid) Iminomethyl)-5-methylphenyl]benzotriazole ("Sumisorb250" manufactured by Sumitomo Chemical Co., Ltd.), etc.

When a UV absorber is added to the adhesive composition, the amount of the UV absorber added is usually about 0.05 parts by weight to about 10 parts by weight, preferably 0.1 parts by weight to 5 parts by weight, relative to 100 parts by weight of the base polymer share. By setting the content of the ultraviolet absorber within the above-mentioned range, the decrease in transparency caused by bleeding of the ultraviolet absorber and the like can be suppressed, and the ultraviolet shielding property of the adhesive layer can be improved.

(Oligomer) The adhesive composition may also contain various oligomers to adjust the adhesive force or viscosity of the adhesive. As the oligomer, for example, an oligomer having a weight average molecular weight of about 1,000 to about 30,000 can be used. As the oligomer, in order to have excellent compatibility with the acrylic base polymer, an acrylic oligomer is preferred.

The acrylic oligomer contains alkyl (meth)acrylate as the main constituent monomer component. Among them, as constituent monomer components, it is preferable to include (meth)acrylic acid alkyl ester having a chain alkyl group ((meth)acrylic acid chain alkyl ester) and (meth)acrylic acid having an alicyclic alkyl group. Alkyl acrylate (alicyclic alkyl (meth)acrylate). 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.

The glass transition temperature of the acrylic oligomer is preferably 20°C or higher, more preferably 40°C or higher. The glass transition temperature of the acrylic oligomer can be 60°C or higher, 80°C or higher, 100°C or higher, or 110°C or higher. By introducing a cross-linked structure of low-Tg acrylic base polymer and high-Tg acrylic oligomer, there is a tendency to improve the adhesive retention. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, and it is usually 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. The glass transition temperature of the acrylic oligomer is calculated by the above-mentioned Fox formula.

Among the exemplified alkyl (meth)acrylates, as the chain alkyl (meth)acrylates, if the glass transition temperature is high and the compatibility with the base polymer is excellent, methyl methacrylate is preferred. ester. As the alicyclic alkyl (meth)acrylate, dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. That is, as the constituent monomer component of the acrylic oligomer, it is preferable to include the selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. More than one kind, and methyl methacrylate.

The amount of the alicyclic alkyl (meth)acrylate is preferably 10% by weight to 90% by weight, more preferably 20% by weight to 80% by weight, relative to the total amount of monomer components constituting the acrylic oligomer. More preferably, it is 30% by weight to 70% by weight. Relative to the total amount of monomer components constituting the acrylic oligomer, the amount of (meth)acrylic acid chain alkyl ester is preferably 10% by weight to 90% by weight, more preferably 20% by weight to 80% by weight, and further Preferably it is 30 weight%-70 weight%.

The weight average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,500 to 10,000, and still more preferably 2,000 to 8,000. By using an acrylic oligomer having a molecular weight within this range, there is a tendency for the adhesive force or adhesive retention force of the adhesive to be improved.

Acrylic oligomers can be obtained by polymerizing the above-mentioned monomer components by various polymerization methods. In the polymerization of acrylic oligomers, various polymerization initiators can also be used. In addition, a chain transfer agent can also be used to adjust the molecular weight.

When an oligomer component such as an acrylic oligomer is included in the adhesive composition, the content of the oligomer component is preferably 0.5 to 20 parts by weight, more preferably, relative to 100 parts by weight of the above-mentioned base polymer It is 1 part by weight to 15 parts by weight, more preferably 2 parts by weight to 10 parts by weight. When the content of the oligomer in the adhesive composition is within the above range, the adhesiveness at high temperature and high temperature retention tend to improve.

(Silane coupling agent) A silane coupling agent can also be added to the adhesive composition to adjust the adhesive force. When adding a silane coupling agent to the adhesive composition, relative to 100 parts by weight of the base polymer, the addition amount of the silane coupling agent is usually about 0.01 parts by weight to about 5.0 parts by weight, preferably about 0.03 parts by weight to about 2.0 parts by weight.

(Other additives) In addition to the components exemplified above, the adhesive composition may also contain additives such as adhesion imparting agents, plasticizers, softeners, anti-deterioration agents, fillers, colorants, antioxidants, surfactants, and antistatic agents.

＜Formation of Adhesive Layer＞ When the adhesive composition is photocurable, the adhesive composition is coated on the support substrate, and then photocured by irradiating ultraviolet and/or short-wavelength visible light to form an adhesive layer. When performing light curing, it is preferable to attach a cover sheet to the surface of the coating layer, and irradiate light with the adhesive composition sandwiched between the two cover sheets, so as to prevent the polymerization inhibition caused by oxygen.

As the base material and cover sheet used in the formation of the adhesive layer, any appropriate base material can be used. The base material and the cover sheet may be a release film having a release layer on the contact surface with the adhesive layer. As a base material or a cover sheet, the transparent film base material 59 of the adhesive sheet 15 can also be used.

As the coating method of the adhesive composition, roll coating, touch roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, and bar coating can be used. Method, knife coating method, air knife coating method, curtain coating method, die lip coating method, die nozzle coating machine and other methods.

The main polymerization is performed by irradiating the adhesive composition coated on the substrate in a layered form with active light. In the main polymerization, unreacted monomer components in the prepolymer composition and multifunctional compounds such as urethane di(meth)acrylate react to obtain a polymer with a crosslinked structure introduced.

The active light may be selected according to the type of polymerizable component, the type of photopolymerization initiator, etc. Generally, ultraviolet light and/or short-wavelength visible light are used. The cumulative amount of irradiated light is preferably about 100 mJ/cm ² to about 5000 mJ/cm ² . As a light source for light irradiation, there are no particular restrictions as long as it can irradiate light in the wavelength range of the sensitivity of the photopolymerization initiator contained in the adhesive composition. LED light sources, high-pressure mercury lamps, and ultra-high pressure light sources can be preferably used. Mercury lamps, metal halide lamps, xenon lamps, etc. When large residual amount of unreacted monomers, the adhesive layers may G _{'25 ℃} holding force decreases and then decreased. Therefore, the polymerization rate of the adhesive after the main polymerization is preferably 95% or more, more preferably 97% or more, still more preferably 98% or more, particularly preferably 99% or more. In order to increase the polymerization rate, the adhesive layer can also be heated to volatilize residual monomers and unreacted polymerization initiators.

As mentioned above, the gel fraction of the adhesive is preferably 30% to 80%, more preferably 35% to 70%. By making the gel fraction more than 30%, the adhesive retention force can be improved, and it is not easy to produce glue defects during processing, dislocation between components, and excellent processability and processing dimensional stability. In addition, by making the gel fraction 80% or less, it is possible to exhibit excellent step absorbency.

The weight average molecular weight of the sol component of the adhesive is preferably 150,000 to 450,000, more preferably 180,000 to 420,000. The sol component is a soluble component obtained by extracting a base polymer with tetrahydrofuran (hereinafter referred to as THF). The crosslinked polymer (gel component) is difficult to measure the molecular weight of each polymer chain, so the molecular weight of the sol component (uncrosslinked polymer) becomes an index indicating the degree of elongation of the polymer chain. When the molecular weight of the sol component is too large, the glass transition temperature may increase and the impact resistance may decrease. On the other hand, when the molecular weight of the sol component is too small, the subsequent retention may be reduced.

＜Production of double-sided adhesive sheet with base material＞ A double-sided adhesive sheet with a base material is obtained by laminating the first adhesive layer 51 and the second adhesive layer 53 on the front and back sides of the transparent film base material 59, respectively. As described above, the adhesive composition can be coated on the transparent film substrate 59 when the adhesive layer is formed, thereby forming a laminate of the transparent film substrate and the adhesive layer.

By bonding the release films 21 and 23 on the surfaces of the first adhesive layer 51 and the second adhesive layer 53, as shown in FIG. Adhesive sheet. The release film used as the base material or the cover sheet when forming the adhesive layer can be used as the release film 21, 23 as it is.

[Formation of Image Display Device] As described above, in the formation of the image display device, the adhesive sheet 15 is suitable for attaching the front transparent plate 7 to the visible side surface of the image display panel 10. The order of bonding is not particularly limited. The operation of bonding the adhesive sheet 15 to the image display panel 10 may be performed first, or the operation of bonding the adhesive sheet 15 to the front transparent plate 7 may be performed first. In addition, the bonding of the adhesive sheet 15 and the image display panel 10 and the bonding of the adhesive sheet 15 and the front transparent plate 7 can also be performed at the same time. After bonding the second adhesive layer 53 to the polarizing plate 3, bonding to the polarizing plate 3 and the image display unit 6 via the adhesive layer 4 can also be performed.

Regarding the double-sided adhesive sheet 15 with a base material, in addition to the form in which a release film is temporarily attached to the adhesive layers 51 and 53 as shown in FIG. 1, it can also be used to fix the second adhesive layer 53 to the polarizing plate. Such as optical film with adhesive film. For example, in the form shown in FIG. 3, the release film 21 is temporarily adhered to the surface of the first adhesive layer 51, and the optical film 3 is fixed on the second adhesive layer 53. In the form shown in FIG. 4, an adhesive layer 4 is further provided on the polarizing plate 3, and a release film 24 is temporarily adhered on the adhesive layer 4.

After bonding the image display panel 10 and the front transparent plate 7 via the adhesive sheet 15, pressure processing such as hot pressing and pressure bonding is performed. At this time, when there is a convex part with a large local thickness such as the connection part of the FPC, it will locally receive a large pressure from the back side of the image display panel, which will cause the image display panel 10 to deform. As described above, by bonding the image display panel 10 and the front transparent plate 7 through the double-sided adhesive sheet 15 with a base material, since the plastic deformation of the adhesive sheet 15 is small, the anti-deformation recovery force plays a role, so it can reduce The residue of the indentation caused by the pressure from the back side. [Example]

Hereinafter, examples and comparative examples are given to illustrate the present invention in more detail, but the present invention is not limited to these examples.

[Production of acrylic oligomer] 60 parts by weight of dicyclopentyl 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 as polymerization The solvent toluene was mixed, and stirred at 70°C for 1 hour under a nitrogen atmosphere. Then, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added and reacted at 70°C for 2 hours, and then heated to 80°C and reacted for 2 hours. Then, the reaction liquid was heated to 130° C. to dry and remove the toluene, chain transfer agent, and unreacted monomer, thereby obtaining a solid acrylic oligomer. The weight average molecular weight of the acrylic oligomer is 5100.

[Preparation of prepolymer composition] ＜Prepolymer composition 1＞ Mixing 70 parts by weight of butyl acrylate (BA), 17 parts by weight of N-vinyl-2-pyrrolidone (NVP) and 13 parts by weight of 4-hydroxybutyl acrylate as monomer components for prepolymer formation (4HBA), and a photopolymerization initiator (0.05 parts by weight of "Irgacure 184" manufactured by BASF and 0.05 parts by weight of "Irgacure 651" manufactured by BASF), which are polymerized by irradiating ultraviolet rays until the viscosity (BH viscometer , No. 5 rotor, 10 rpm, measuring temperature 30°C) reached about 20 Pa･s, thereby obtaining prepolymer composition 1 (polymerization rate; about 9%).

＜Prepolymer composition 2＞ The monomer components for prepolymer formation were changed to 68 parts by weight of 2-ethylhexyl acrylate (2EHA), 17 parts by weight of NVP, and 17 parts by weight of 4-hydroxybutyl acrylate (4HBA) in the same manner as above The polymerization was carried out, thereby obtaining a prepolymer composition 2.

[Preparation of light-curing adhesive composition] ＜Adhesive composition A＞ Add 2 parts by weight of polyester urethane diacrylate ("Art Resin UN-350" manufactured by Negami Kogyo Co., Ltd.) with a weight average molecular weight of 12,500 to 100 parts by weight of the above-mentioned prepolymer composition 1; 5 parts by weight Parts of the above-mentioned acrylic oligomer; 0.05 parts by weight of "Irgacure 184" and 0.55 parts by weight of "Irgacure 651" as a photopolymerization initiator; 0.07 parts by weight of α-methylstyrene as a chain transfer agent Polymer ("Nofmer MSD" manufactured by NOF Corporation); and 0.3 parts by weight of "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd. as a silane coupling agent, and then uniformly mixed to prepare an adhesive composition A.

＜Adhesive composition B＞ Add 0.70 parts by weight of ultraviolet absorber ("Tinosorb S" manufactured by BASF), and as a photopolymerization initiator, mix 0.05 parts by weight of "Irgacure 184" manufactured by BASF and 0.05 parts by weight of "Tinosorb S" manufactured by BASF. "Irgacure 651" and 0.40 parts by weight of "Irgacure 819" manufactured by BASF. Except for these changes, the adhesive composition B was prepared in the same manner as the preparation of the adhesive composition A.

＜Adhesive composition C＞ Except having changed the compounding amount of the chain transfer agent to 0.03 part by weight, the adhesive composition C was prepared in the same manner as the preparation of the adhesive composition B.

＜Adhesive composition D＞ Except that 0.1 parts by weight of hexanediol diacrylate (HDDA) was prepared instead of polyester urethane diacrylate as a multifunctional monomer, an adhesive was prepared in the same manner as in the preparation of adhesive composition B. Composition D.

＜Adhesive composition E＞ To 100 parts by weight of the prepolymer composition 2 were added 0.1 parts by weight of HDDA, 5 parts by weight of the above acrylic oligomer, 0.04 parts by weight of "Irgacure 184" as a photopolymerization initiator, and 0.04 parts by weight "Irgacure 651", 0.12 parts by weight of "Irgacure 819", and 0.3 parts by weight of silane coupling agent, and then uniformly mixed them to prepare adhesive composition E.

[Production of Adhesive Layer] <Adhesive Layer A1> A 75 μm-thick polyethylene terephthalate (PET) film with a silicone release layer on the surface will be used as the base material. The above-mentioned photocurable adhesive composition was coated on it so that the thickness reached 150 μm to form a coating layer. On the coating layer, a PET film with a thickness of 75 μm, which has been peeled off by polysiloxane on one side, was attached as a cover sheet. By using a black light lamp adjusted in position so that the irradiation intensity of the irradiation surface directly below the lamp reaches 5 mW/cm ^2, the laminate is irradiated with ultraviolet rays from the cover sheet side and photocured to obtain a thickness of 220 μm and a polymerization rate 99% adhesive layer A1.

＜Adhesive layer A2～A4＞ Except that the thickness of the adhesive layer was changed to 150 μm, 100 μm, and 70 μm, the adhesive layers A2, A3, and A4 were produced in the same manner as the production of the adhesive layer A1.

<Adhesive layer B1～B4, C2, C3, D2, D3, E1～E3> Except for changing the type and thickness of the adhesive composition as shown in Table 1, the adhesive layer was produced in the same manner as the production of the adhesive layer A1.

[Evaluation of Adhesive Layer] For each of the above-mentioned adhesive layers, the glass transition temperature, storage modulus, loss tangent, gel fraction, and molecular weight of the sol component were measured by the following methods.

<Storage modulus, loss tangent, and glass transition temperature> Laminate a plurality of adhesive layers after peeling off the release film (base material and cover sheet) on the front and back sides so that the thickness reaches about 1.5 mm, and the laminated one is used as the measurement Use samples. The "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific was used for the dynamic viscoelasticity measurement under the following conditions. (Measurement conditions) Deformation mode: Torsion measurement frequency: 1 Hz Heating rate: 5°C/min Shape: Parallel plate 7.9 mm

Read the shear storage modulus G'at 25°C from the measurement results at _{25 °C} and the loss tangent tanδ at _{70 °C at} 70°C. In addition, the temperature (peak top temperature) at which the loss tangent (tanδ) reaches the maximum is used as the glass transition temperature of the adhesive layer.

＜Gel fraction＞ Scrape about 0.2 g of the adhesive from the adhesive layer and wrap it with a porous polytetrafluoroethylene film ("NTF-1122" manufactured by Nitto Denko Corporation) with a pore size of 100 mm×100 mm and a pore size of 0.2 μm, and use a kite Tie the thread tightly around the mouth. Subtract the weight of the porous polytetrafluoroethylene film and the kite string measured in advance from the weight of the sample (A) to calculate the weight of the adhesive sample (B). A sample of the adhesive wrapped with a porous polytetrafluoroethylene film was immersed in about 50 mL of ethyl acetate at 23°C for 7 days, so that the sol component of the adhesive was dissolved out of the porous polytetrafluoroethylene film. After immersion, take out the adhesive wrapped in a porous polytetrafluoroethylene film, dry at 130°C for 2 hours, cool naturally for about 20 minutes, and then measure the dry weight (C). Calculate the gel fraction of the adhesive according to the following formula. Gel fraction (%)=100×(C－A)/B

×30 cm(合計管柱長度：90 cm) 管柱溫：40℃、流量：0.8 mL/分鐘 注入量：100 μL 溶離液：四氫呋喃 檢測器：示差折射計(RI) 標準試樣：聚苯乙烯<Weight average molecular weight of the sol component> Scrape about 0.2 g of the adhesive from the adhesive layer and immerse it in a 10 mM tetrahydrofuran phosphate solution for 12 hours to extract the sol component. Considering the gel fraction of the adhesive, the amount of the tetrahydrofuran phosphate solution is adjusted so that the content of the sol component in the solution after extraction becomes 0.1% by weight. The extracted solution was filtered with a 0.45 μm membrane filter, the obtained filtrate was used as a sample, and the GPC (Gel Permeation Chromatography) device (product name "HLC-8120GPC") manufactured by Tosoh Corporation was used in the following GPC analysis is performed under the conditions, and the weight average molecular weight Mw of the sol component is calculated. (Measurement conditions) Column: manufactured by Tosoh Corporation, G7000HXL + GMHXL + GMHXL Column size: 7.8 mm each

×30 cm (total column length: 90 cm) column temperature: 40°C, flow rate: 0.8 mL/min injection volume: 100 μL lysate: tetrahydrofuran detector: differential refractometer (RI) Standard sample: polystyrene

Table 1 shows the composition and thickness of each adhesive layer (adhesive composition) and the evaluation results.

[Table 1] A1 A2 A3 A4 B1 B2 B3 B4 C2 C3 D2 D3 E1 E2 E3 composition Prepolymer composition 2EHA - - - - 68 BA 70 70 70 70 - NVP 17 17 17 17 15 4HBA 13 13 13 13 - 2HEA - - - - 17 Multifunctional monomer UN-350 2 2 2 1 - HDDA - - - - 0.1 Acrylic oligomer 5 5 5 5 5 Photopolymerization initiator Irg651 0.55 0.05 0.05 0.05 0.04 Irg184 0.05 0.05 0.05 0.05 0.04 Irg819 - 0.40 0.40 0.40 0.12 UV absorber Tinosorb S - 0.7 0.7 0.7 0.7 Chain transfer agent Nofmer MSD 0.07 0.07 0.03 0.07 - Silane coupling agent KBM-403 0.3 0.3 0.3 0.3 0.3 Thickness (µm) 220 150 100 70 220 150 100 70 150 100 150 100 300 150 100 Evaluation Tg(℃) -5 -5 -5 -5 -5.3 -5.3 -5.3 -5.3 -4.5 -4.5 -5.3 -5.3 -7 -7 -7 G _{'25 ℃} (kPa) 210 210 210 210 230 210 210 210 200 200 230 230 120 120 120 tanδ _{70 ℃} 0.60 0.60 0.60 0.60 0.35 0.33 0.33 0.33 0.28 0.28 0.38 0.38 0.20 0.20 0.20 Gel fraction (%) 54 54 54 54 65 73 73 73 74 74 60 60 85 88 85 Sol composition Mw(×10 ⁴ ) 36 36 36 36 28 twenty four twenty four twenty four 34 34 29 29 18 18 18

[Example 1] A 50 μm thick cycloolefin polymer (COP) film ("ZEONOR Film ZF16" manufactured by Zeon Corporation; front retardation 3 nm) is attached to one main surface of the adhesive layer A2 as the first adhesive layer. The adhesive layer A3, which is the second adhesive layer, is pasted on the other main surface to produce a double-sided adhesive sheet with a film substrate with an adhesive layer on the film substrate.

[Example 2] A biaxially stretched polyethylene terephthalate (PET) film (“Lumirror S10” manufactured by Toray Corporation; front retardation 920 nm) with a thickness of 50 μm was used as the film substrate. Otherwise, the same as in Example 1 In the same way, a double-sided adhesive sheet with a film substrate was produced.

[Examples 3-9, Comparative Examples 3-5] As shown in Table 2, the type of film substrate and the type of adhesive layer were changed to produce a double-sided adhesive sheet with a film substrate.

[Comparative Examples 1, 2, 6, 7] Use single-layer adhesive layers A1, B1, E1, and E3 as substrate-less adhesive sheets.

[Evaluation] The adhesive sheets of the Examples and Comparative Examples were evaluated for adhesion, step absorbency, drop impact resistance, and indentation by the following methods.

＜Adhesive force＞ The release film was peeled off from the second adhesive layer, and a PET film with a thickness of 50 μm was pasted and cut into a width of 10 mm × a length of 100 mm. Then the release film was peeled off from the first adhesive layer, and it was crimped on with a 5 kg roller. A glass plate was used to prepare a sample for adhesion measurement. 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 off and attached to the PET film, and then the release film on the other side was peeled off and attached Glass plate (the same applies to other evaluations thereafter).

Keep the adhesive force measurement sample in an environment of 25°C for 30 minutes, and then use a tensile testing machine to peel the test piece from the glass plate at a tensile speed of 300 mm/min and a peel angle of 180° to measure the peeling force.

＜Haze＞ The release film was peeled off from the second adhesive layer, and then attached to an alkali-free glass with a thickness of 800 μm (total light transmittance 92%, haze 0.4%), and then the release film was peeled off from the first adhesive layer to obtain As a test piece, a haze meter ("HM-150" manufactured by Murakami Color Technology Research Institute Co., Ltd.) was used to measure the haze. The value obtained by subtracting the haze (0.4%) of the alkali-free glass from the measured value is used as the haze of the adhesive sheet.

＜Level difference absorbency＞ Cut the adhesive sheet into a size of 75 mm×45 mm, peel off the release film from the second adhesive layer, and use a roll laminator (pressure between rolls: 0.2 MPa, feed speed: 100 mm/min) to stick it on Cut into the center of a PET film with a thickness of 100 mm×50 mm and a thickness of 125 μm. Then, the release film was peeled off from the first adhesive layer, and it was attached to the peripheral portion with black ink printed in a frame shape ( Printing thickness: 25 μm or 40 μm) 500 μm thick glass plate (100 mm×50 mm). The ink printing area of the glass plate is 5 mm from both ends in the short side direction and 15 mm from both ends in the long side direction, and the black ink layer is connected to the area within 5 mm from the four sides of the adhesive sheet. Treat the sample in an autoclave (50°C, 0.5 MPa) for 30 minutes, and then observe the vicinity of the boundary of the black ink printed area with a digital microscope with a magnification of 20 times to confirm whether there are bubbles. For each sample with a printing thickness of 25 μm and 40 μm of black ink, the step absorbency was evaluated according to the following criteria. ◎: No air bubbles are observed throughout the whole week ○: Bubbles are observed at one of the four corners, but no bubbles are observed on all four sides ×: Bubbles are observed at two or more of the four corners or one or more of the four sides

＜impact resistance＞ Cut the adhesive sheet into a size of 75 mm×45 mm, peel off the release film from the second adhesive layer, and use a roll laminator (pressure between rolls: 0.2 MPa, feed speed: 100 mm/min) to stick it on The center of a glass plate (100 mm×70 mm) with a thickness of 500 μm. Then, the release film was peeled off from the first adhesive layer and bonded by vacuum pressure bonding (surface pressure 0.3 MPa, pressure 100 Pa) to a glass plate with a thickness of 500 μm printed with black ink with a thickness of 30 μm in a frame shape on the periphery. (50 mm×100 mm). The ink printing area of the glass plate is 5 mm from both ends in the short-side direction and 15 mm from both ends in the long-side direction, and the black ink layer is connected to the area 5 mm from the four sides of the adhesive sheet. The sample was treated in an autoclave (50°C, 0.5 MPa) for 30 minutes.

As shown in Fig. 5, with the glass plate 7 provided with the printing layer 76 as the lower side, both ends of the test sample 85 in the short-side direction are placed on a table 83 arranged at intervals of 60 mm. An adhesive tape (not shown) is used to fix the upper surface of the end portion of the glass plate 8 without a printing layer on the table 83. Keep the test sample 85 fixed on the table 83 with the adhesive tape at -5°C for 24 hours, and then take it out to room temperature. Within 40 seconds, make a metal ball 87 with a mass of 11 g from 300 The height of mm is dropped on the glass plate 7, and the impact resistance test is performed.

In the impact resistance test, a cylindrical guide 89 is used to fix the drop position of the metal ball, so that the metal ball 87 falls within the frame of the printing area of the printing layer 76 in the short-side direction and the long-side direction The corners of the edges are separated by 10 mm. The test was performed twice, and the case where peeling of the glass plate did not occur in all the tests was evaluated as 0, and the case where peeling of the glass plate occurred in any one or two of the two tests was evaluated as ×.

＜Indentation test＞ The release film is peeled off from the second adhesive layer, and is bonded to a PET film with a thickness of 50 μm using a roll laminator (pressure between rolls: 0.2 MPa, feeding speed: 100 mm/min). Then, the release film was peeled off from the first adhesive layer, and was bonded to a glass plate with a thickness of 500 μm using a roll laminator (pressure between rolls: 0.2 MPa, feed rate: 100 mm/min). The sample was treated in an autoclave (50°C, 0.5 MPa) for 30 minutes.

Using SAICAS manufactured by Daipla Wintes, press a steel ball indenter with a diameter of 1 mm from the PET film side of the above sample at a press-in speed of 5 μm/sec until the vertical load reaches 1 N, hold it for 180 seconds, and then Lift the indenter at a speed of 5 μm/sec. 6 hours after the test, the surface shape of the PET film was measured with a non-contact interference microscope (WYKO), the depth of the indentation of the sample was obtained, and the evaluation was performed according to the following standards. ◎: The depth of the indentation is less than 3 μm ○: The depth of the indentation is greater than 3 μm and less than 4 μm ×: The depth of the indentation is greater than 4 μm

[Evaluation results] Table 1 and Table 2 show the laminated structure and evaluation results of each adhesive sheet. The values in parentheses of the first adhesive layer, film base material and second adhesive layer in Table 2 are the thickness of each layer (unit: μm).

[Table 2] Example 1 Example 2 Example 3 Example 4 Comparative example 1 Example 5 Example 6 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Example 7 Example 8 Example 9 Comparative example 6 Comparative example 7 constitute First adhesive layer A2 (150) A2 (150) A3 (100) A3 (100) A1 (220) B2 (150) B3 (100) B1 (220) B2 (150) B3 (100) B4 (70) C2 (150) D3 (150) E2 (150) E1 (300) E3 (100) Film substrate COP (50) PET (50) COP (50) PET (50) - COP (50) COP (50) - COP (50) COP (50) COP (50) COP (50) COP (50) COP (50) - - Second adhesive layer A3 (100) A3 (100) A4 (70) A4 (70) B3 (100) B4 (70) B1 (220) B1 (220) B1 (220) C3 (100) D4 (100) E3 (100) Evaluation results Adhesion (N/10 mm) 11.4 11.4 11.4 11.4 11.4 12.0 12.0 12.1 14.1 14.1 14.1 10.8 12.5 6.0 9.0 6.0 Haze (%) 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Step absorbency 25 µm ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ 〇 ◎ 〇 ◎ 〇 45 µm ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ 〇 ◎ 〇 ◎ X Drop impact resistance 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 Indentation test ◎ ◎ ◎ ◎ X ◎ ◎ X X X X ◎ 〇 ◎ X ◎

The adhesive layer with a relatively large thickness is provided on the visible side of the transparent film substrate and the adhesive layer with a relatively small thickness is provided on the image display panel side of the transparent film substrate. The double-sided adhesive sheet has excellent step absorbency, and the residual indentation caused by the deformation when the indenter is pressed into the indenter from the side of the second adhesive layer is less, showing good characteristics. On the other hand, the baseless double-sided adhesive sheet of Comparative Example 1 including the adhesive layer A1 with a thickness of 220 μm has good step absorbency, but it is easy to retain the pressure caused by the deformation when the indenter is pressed into the adhesive layer. Marks, resulting in poor indentation.

The same tendency was observed in Example 5, the comparison between Example 6 and Comparative Example 2, and the comparison between Example 9 and Comparative Example 6 in which the composition of the adhesive was changed. In Example 7 and Example 8 in which the composition of the adhesive was changed, similar to the other examples, the step absorbability was excellent and the indentation was not easy to remain, showing good characteristics.

An adhesive layer B1 with a thickness of 220 μm as the second adhesive layer is provided on one main surface of the film substrate, and the thickness of the first adhesive layer B1 is provided on the other main surface of the film substrate. The double-sided adhesive sheet with a substrate of Comparative Examples 3 to 5 of the small adhesive layers B2, B3, and B4 had the same indentation defects as the substrate-less adhesive sheet of Comparative Example 2 including the adhesive layer B2.

Although the substrate-less adhesive sheet of Comparative Example 7 including the adhesive layer E3 with a thickness of 100 μm has good results of the indentation test, the thickness of the adhesive sheet is small, so the step absorbency is poor.

According to the above results, it can be seen that by using an adhesive layer with a relatively large thickness as the first adhesive layer on the visible side of the transparent film substrate, and having a relatively small thickness on the image display panel side of the transparent film substrate The adhesive layer is used as a double-sided adhesive sheet with a base material for the second adhesive layer. It has excellent absorption of the printing step of the front transparent plate and can suppress the impression caused by the pressure from the side of the image display panel. The result is bad.

3: Optical film (polarizing plate) 4: Adhesive layer 6: Image display unit 7: Front transparent board 8: glass plate 9: Reinforced substrate 10: Image display panel 15: Double-sided adhesive sheet with base material 21,23: release film 24: release film 51, 53: Adhesive layer 59: Transparent film substrate 71: transparent board 76: Printing layer 83: Taiwan 85: Test specimen 87: Metal Ball 89: Director 91: main substrate 92: Connection part (connector) 95: FPC 201: Image display device

Fig. 1 is a cross-sectional view showing an example of the laminated structure of a double-sided adhesive sheet with a base material. Fig. 2 is a cross-sectional view showing a configuration example of the image display device. Fig. 3 is a cross-sectional view showing an example of the laminated structure of an optical film with an adhesive sheet. Fig. 4 is a cross-sectional view showing an example of the laminated structure of an optical film with an adhesive sheet. Figure 5 is a schematic diagram showing the configuration of the sample in the impact resistance test.

3: Optical film (polarizing plate)

4: Adhesive layer

6: Image display unit

7: Front transparent board

9: Reinforced substrate

10: Image display panel

15: Double-sided adhesive sheet with base material

51, 53: Adhesive layer

59: Transparent film substrate

71: transparent board

76: Printing layer

90: main substrate

91: Connector

95: FPC

201: Image display device

Claims (16)

An adhesive sheet for an image display device, which is used for attaching an image display panel to a transparent plate in front of the visible side surface of the image display panel, and It has: a transparent film substrate; a first adhesive layer fixed and laminated on the first main surface of the transparent film substrate; and a second adhesive layer fixed and laminated on the second main surface of the transparent film substrate noodle, In the image display device, the first adhesive layer is grounded to the front transparent plate, and The thickness of the first adhesive layer is greater than the thickness of the second adhesive layer. The adhesive sheet of claim 1, wherein the thickness of the first adhesive layer is 80 μm or more. The adhesive sheet of claim 1, wherein the thickness of the second adhesive layer is 150 μm or less. The adhesive sheet of claim 1, wherein the thickness of the transparent film substrate is 15 μm to 150 μm. The adhesive sheet of claim 1, wherein the frontal retardation of the transparent film substrate is 50 nm or less. Such as the adhesive sheet of claim 1, wherein the shear storage modulus of the first adhesive layer at a temperature of 25°C is 0.16 MPa or more. Such as the adhesive sheet of claim 1, wherein the loss tangent of the first adhesive layer at a temperature of 70° C. is 0.25 or more. The adhesive sheet of claim 1, wherein the glass transition temperature of the first adhesive layer is below -3°C. The adhesive sheet according to any one of claims 1 to 8, wherein the first adhesive layer includes an acrylic polymer having a cross-linked structure. Such as the adhesive sheet of claim 9, wherein the gel fraction of the first adhesive layer is 30% to 80%. Such as the adhesive sheet of claim 9, wherein the polymerization rate of the first adhesive layer is more than 95%. The adhesive sheet of claim 9, wherein a cross-linked structure based on a urethane-based segment is introduced into the above-mentioned acrylic polymer. An image display device, wherein a front transparent plate is fixed on the visible side surface of the image display panel via an adhesive sheet as in any one of claims 1 to 12, and The first adhesive layer is attached to the front transparent plate, and the second adhesive layer is attached to the image display panel. Such as the image display device of claim 13, wherein the image display panel has a polarizing plate on the visible side surface of the image display unit, and the polarizing plate is attached to the second adhesive layer. Such as the image display device of claim 13 or 14, wherein the image display panel includes an organic EL unit. The image display device of claim 15, wherein the organic EL unit has electrodes and an organic light-emitting layer on a resin film substrate.

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