JP5997347B2 - Transparent double-sided pressure-sensitive adhesive sheet for image display device, component for image display device with transparent double-sided pressure-sensitive adhesive sheet using the same, and image display device - Google Patents

Description

  The present invention relates to a transparent double-sided pressure-sensitive adhesive sheet that can be used for bonding constituent members for an image display device. In particular, the present invention relates to a transparent double-sided pressure-sensitive adhesive sheet that can be suitably used for bonding an image display panel, a constituent member for an image display device with a transparent double-sided pressure-sensitive adhesive sheet using the same, and an image display device.

  In recent years, in order to improve the visibility of an image display device, a gap between an image display panel such as an LCD, PDP, or EL and a protective panel or touch panel member disposed on the front side (viewing side) is used as an adhesive sheet. In other words, it is filled with a liquid adhesive or the like to suppress reflection of incident light or outgoing light from a display image at the air layer interface.

As a method for filling the gap between the constituent members for an image display device, a method is known in which a liquid adhesive resin composition containing an ultraviolet curable resin is filled into the gap and then cured by irradiation with ultraviolet rays. .
However, in such a method, the work for filling the liquid is complicated and inferior in productivity, and the liquid adhesive resin composition is cured at a place where ultraviolet rays are difficult to reach, such as a portion hidden in the printing concealment layer. The problem was that it was difficult to obtain a stable quality.

  In addition, a method of filling a gap between constituent members for an image display device using an adhesive sheet is also known. For example, Patent Document 1 discloses a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer having different viscoelastic behavior as a transparent pressure-sensitive adhesive sheet that can be suitably used for bonding a transparent panel such as a protective panel or a touch panel to an image display panel. Each of which is a pressure-sensitive adhesive sheet having a structure in which these layers are laminated and integrated, and the value of the dynamic shear storage elastic modulus G ′ measured by temperature dispersion at a frequency of 1 Hz is A transparent adhesive sheet characterized by being in a specific range is disclosed.

  Patent Document 2 discloses a transparent double-sided PSA sheet having an intermediate resin layer (A) and a pressure-sensitive adhesive layer (B) as a front and back layer, each of which is one or more types of (meta) A layer having an acrylic ester (co) polymer as a base resin, and a storage shear modulus (G ′ (A)) of the intermediate resin layer (A) at a frequency of 1 Hz in a temperature range of 0 ° C. to 100 ° C. There is disclosed a transparent double-sided PSA sheet that is higher than the pressure-sensitive adhesive layer (B) and has an indentation hardness (Asker C2 hardness) of the entire sheet of 10 to 80.

Furthermore, Patent Document 3 discloses a monomer (meth) containing a (meth) acrylic acid ester having an ultraviolet crosslinkable site as a thin (for example, 30 to 50 μm thick) pressure-sensitive adhesive sheet that can be applied to a stepped or raised surface. An ultraviolet-crosslinkable pressure-sensitive adhesive sheet comprising an acrylic copolymer, wherein the storage elastic modulus of the pressure-sensitive adhesive sheet before UV-crosslinking is 5.0 × 10 ⁴ Pa or more and 1.0 × 1010 at 30 ° C. and 1 Hz. ⁶ Pa or less and 80 ° C., 1 Hz, 5.0 × 10 ⁴ Pa or less, and the storage elastic modulus of the pressure-sensitive adhesive sheet after UV crosslinking is 1.0 × 10 ³ Pa or more at 130 ° C., 1 Hz. An ultraviolet crosslinkable pressure-sensitive adhesive sheet is disclosed.

International Publication Pamphlet WO2010 / 044229 International Publication Pamphlet WO2011 / 129200 JP 2011-184582 A

In the field of image display devices centering on mobile phones and mobile terminals, in addition to thinning and high precision, design diversification has progressed, and new problems have arisen accordingly. For example, a black concealment portion is conventionally printed in a frame shape on the peripheral portion of the surface protection panel. However, with the diversification of the design, the frame concealment portion other than black is printed. Forming in color is starting to take place.
However, when the concealing part is formed with a color other than black, the concealing property is low with a color other than black, and therefore the thickness of the concealing part, that is, the printing part, needs to be thicker than that of black. If it does so, the level | step difference followability which can be filled to every corner is required for the adhesive sheet for bonding together the structural member provided with such a printing part. Also, as the thickness of the printing part increases, the part that contacts the printing part is subjected to a larger stress on the image display device than other parts, which may cause distortion and adversely affect the optical characteristics. Therefore, it is also required to suppress such distortion.
In addition, since the thinning of the image display device is progressing, it is necessary to solve such a problem without preventing the thinning.

  Then, this invention relates to the transparent double-sided adhesive sheet for image display apparatuses used in order to bond the image display apparatus structural member which has a level | step-difference part on the bonding surface, under the restrictions of restraining the thickness of an adhesive sheet to 200 micrometers or less, Even if it has a stepped part with a height of 50 μm to 100 μm on the bonding surface, it can relieve the distortion generated in the adhesive sheet after bonding and has foam resistance, and also has cutability and storage stability. It is an object of the present invention to provide an excellent new transparent double-sided pressure-sensitive adhesive sheet for image display devices.

  This invention is for image display apparatuses used in order to bond the image display apparatus structural member which has a level | step-difference part of 50 micrometers-100 micrometers in height, and a flat surface part on the bonding surface, and another image display apparatus structural member. A transparent double-sided pressure-sensitive adhesive sheet, wherein the thickness of the maximum thickness portion of the pressure-sensitive adhesive sheet is 200 μm or less, and has at least a superimposed layer of a pressure-sensitive adhesive layer (A) and a pressure-sensitive adhesive layer (B). And the thickness of the pressure-sensitive adhesive layer (B) satisfy the relationship of (A) / (B)> 1.0, and at least the pressure-sensitive adhesive layer (A) is curable by heat or ultraviolet rays. A transparent double-sided pressure-sensitive adhesive sheet for an image display device is proposed.

  The present invention also provides an image display device with a transparent double-sided pressure-sensitive adhesive sheet obtained by bonding the transparent double-sided pressure-sensitive adhesive sheet for an image display device proposed by the present invention to a constituent member for an image display device and curing by heat or ultraviolet rays. Proposed structural members.

  The present invention further includes at least two image display device constituent members facing each other, and at least one of the image display device constituent members has a stepped portion having a height of 50 to 100 μm on the bonding surface, and a flat surface excluding the stepped portion. The present invention proposes a space between the two image display device constituent members in an image display device having a surface portion and having an interval of 200 μm or less formed by the flat surface portions of the two image display device constituent members facing each other. The present invention proposes an image display device having a configuration filled with the above-mentioned transparent double-sided pressure-sensitive adhesive sheet for image display devices.

The transparent double-sided pressure-sensitive adhesive sheet proposed by the present invention suppresses the thickness of the pressure-sensitive adhesive sheet to 200 μm or less even when it has a stepped portion having a height of 50 μm to 100 μm on the bonding surface of the constituent members for an image display device to be bonded. Under constraints, the adhesive layer (A) and the adhesive layer (B) have a superimposed layer, the thickness of the adhesive layer (A) is larger than the adhesive layer (B), and the adhesive layer ( A) is provided with curability by heat or ultraviolet rays, so that distortion generated in the portion in contact with the stepped portion can be alleviated, and it has excellent foam resistance, and also has cutability and storage stability. It has the advantage of being excellent.
Therefore, the transparent double-sided pressure-sensitive adhesive sheet for image display devices proposed by the present invention is an image display device that is becoming thinner and diversified in design, for example, mobile terminals such as personal computers (PCs), PDAs, mobile phones, game machines, and televisions. (TV), car navigation systems, liquid crystal pen tablets, and image display terminals with a touch panel function.

FIG. 1 is a cross-sectional view showing a transparent double-sided PSA sheet for an image display device according to an example of the present invention. Fig.1 (a) is an example of the transparent double-sided adhesive sheet for image display apparatuses of 2 layer structure, FIG.1 (b) is an example of the transparent double-sided adhesive sheet for image display apparatuses of 3 layer structure. FIG. 2 is a cross-sectional view illustrating an example of a state after bonding two constituent members for an image display device using the transparent double-sided pressure-sensitive adhesive sheet for an image display device according to an example of the present invention.

  Hereinafter, although an example of embodiment of the present invention is explained, the present invention is not limited to the following embodiment.

[This adhesive sheet]
The transparent double-sided pressure-sensitive adhesive sheet for image display device according to the present embodiment (hereinafter referred to as “the present pressure-sensitive adhesive sheet”) has a step portion having a height of 50 μm to 100 μm on the bonding surface, and the like. A pressure-sensitive adhesive sheet used for bonding and integrating the constituent members for an image display device, having a superimposed layer of the pressure-sensitive adhesive layer (A) and the pressure-sensitive adhesive layer (B), being transparent and It is a transparent double-sided pressure-sensitive adhesive sheet in which both front and back surfaces are adhesive surfaces.

<Configuration of this adhesive sheet>
This pressure-sensitive adhesive sheet has at least a superimposed layer of a pressure-sensitive adhesive layer (A) and a pressure-sensitive adhesive layer (B). Specifically, in addition to the two-layer structure of the pressure-sensitive adhesive layer (A) / pressure-sensitive adhesive layer (B), the three-layer structure of the pressure-sensitive adhesive layer (A) / pressure-sensitive adhesive layer (B) / pressure-sensitive adhesive layer (A). Can be mentioned. Moreover, this adhesive sheet may have other layers other than an adhesive layer (A) and an adhesive layer (B), specifically, an adhesive layer (A) / adhesive layer (B ) / Adhesive layer (C).

  As a suitable example, in addition to the two-layer structure of the pressure-sensitive adhesive layer (A) and the pressure-sensitive adhesive layer (B), the three-layer structure of the pressure-sensitive adhesive layer (A) / the pressure-sensitive adhesive layer (B) / the pressure-sensitive adhesive layer (A). And the like.

<Adhesive layer (A)>
The pressure-sensitive adhesive layer (A) is in contact with a step portion having a height of 50 μm to 100 μm and an image display device constituent member having a flat surface portion on the bonding surface, and the role of the step following property and foaming resistance on the bonding surface. It is a layer that bears.
The pressure-sensitive adhesive layer (A) preferably has curability by heat or ultraviolet light in order to play such a role. If the adhesive sheet is cured with heat or ultraviolet light after being bonded to the image display device constituent member by having heat or ultraviolet curable properties, it can follow the level difference with foaming resistance on the bonding surface. Sex can be secured.

  In order for the pressure-sensitive adhesive layer (A) to be curable by heat or ultraviolet rays, for example, as described below, the light-sensitive pressure-sensitive adhesive composition or the thermosetting pressure-sensitive adhesive composition can be used to form the pressure-sensitive adhesive layer (A). ).

As described above, the pressure-sensitive adhesive layer (A) has curability by heat or ultraviolet rays, and has a relatively flexible property.
Therefore, the pressure-sensitive adhesive layer (A) follows the step of such a constituent member even if the image display device constituent member has a step portion having a height of 50 to 100 μm, and is subjected to stress received by being pressed by the step portion. Can be relaxed, and distortion that occurs in this part can be reduced,
Has step following ability.

<Adhesive layer (B)>
The pressure-sensitive adhesive layer (B) is a layer that plays a role of imparting cutability and storage stability to the pressure-sensitive adhesive sheet. In order to play such a role, the pressure-sensitive adhesive layer (B) preferably has a harder property than the pressure-sensitive adhesive layer (A). In order to impart such desired properties, the physical properties of the pressure-sensitive adhesive sheet may be adjusted as described below.

<Thickness>
In the present adhesive sheet, the thickness of the maximum thickness portion of the adhesive sheet is 200 μm or less, and the thickness of the adhesive layer (A) and the thickness of the adhesive layer (B) are (A) / (B)> 1.0. It is preferable to satisfy the relationship.
The pressure-sensitive adhesive sheet includes a pressure-sensitive adhesive layer (A) and a pressure-sensitive adhesive layer (B) that satisfy this thickness relationship, so that the thickness of the pressure-sensitive adhesive sheet is 200 μm or less, and the height difference is 50 to 100 μm. Even if it is bonded to an image display device constituting member having a portion, it is not inferior in conformity to unevenness or a bent surface, and it is difficult to foam at a stepped portion immediately after being attached to an adherend or over time. Has an effect.

From this viewpoint, it is more preferable that the thickness of the pressure-sensitive adhesive layer (A) and the thickness of the pressure-sensitive adhesive layer (B) satisfy the relationship of 1.0 <(A) / (B) <8.0. More preferably, the relationship 0 <(A) / (B) <4.0 is satisfied.
In addition, in the case of a configuration such as pressure-sensitive adhesive layer (A) / pressure-sensitive adhesive layer (B) / pressure-sensitive adhesive layer (A), the thickness of one pressure-sensitive adhesive layer (A) and the pressure-sensitive adhesive layer (B) The thickness should satisfy the above relationship.

(Adhesive composition)
An example of a constituent material that can be suitably used to form the present pressure-sensitive adhesive sheet (hereinafter referred to as “the present pressure-sensitive adhesive composition”) will be described. However, this is only an example, and the present invention is not limited to this.

  The pressure-sensitive adhesive layer (A) is provided with a base polymer having a molecular weight within a predetermined range, a photocrosslinking initiator, and a cross-linking agent as necessary in order to have curability by heat or ultraviolet light. It is preferable to use a photocurable pressure-sensitive adhesive composition or a thermosetting pressure-sensitive adhesive composition containing a base polymer and a thermal crosslinking agent.

(Base polymer)
The base polymer of this pressure-sensitive adhesive composition is a (meth) acrylic acid ester-based polymer (including a copolymer, “acrylic acid ester-based (co) polymer” from the viewpoints of adhesiveness, transparency, and weather resistance. It is also referred to as “union”.
The acrylic ester-based (co) polymer as the base resin is selected by appropriately selecting the kind of acrylic monomer or methacrylic monomer used to adjust the base resin, the composition ratio, and the polymerization conditions. ) And molecular weight, etc., can be appropriately adjusted for production.

Examples of the acrylic monomer constituting the acrylic ester (co) polymer include 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, n-butyl acrylate, ethyl acrylate, and the like as main raw materials.
In addition to these, a (meth) acrylic monomer having various functional groups may be copolymerized with the acrylic monomer according to the purpose of imparting cohesive force or imparting polarity.
Examples of the (meth) acrylic monomer having the functional group include methyl methacrylate, methyl acrylate, hydroxyethyl acrylate, acrylic acid, glycidyl acrylate, N-substituted acrylamide, acrylonitrile, methacrylonitrile, fluorine-containing alkyl acrylate, and organosiloxy group. An acrylate etc. can be mentioned.
In addition, various vinyl monomers such as vinyl acetate, alkyl vinyl ether, and hydroxyalkyl vinyl ether that can be copolymerized with the acrylic monomer and methacrylic monomer can be used as appropriate.

This pressure-sensitive adhesive composition has a suitable adhesive force when it is first cured after being formed into a sheet, and has flexibility to follow unevenness and foreign matter on the surface of the adherend. Is preferred.
Even if the molecular weight of the base polymer is too large or too small, the effects of the present invention cannot be exhibited.
If the molecular weight of the base polymer is too small, the adhesive force may not be exhibited during curing (crosslinking) before bonding, or it may be too soft and inferior in handling properties, and conversely if the molecular weight is too large, There is a possibility that it becomes hard at the stage of curing (crosslinking) before bonding and cannot follow irregularities and foreign matter on the surface of the adherend.
Therefore, from this viewpoint, the acrylic polymer (co) polymer having a mass average molecular weight of the base polymer of 100,000 to 700,000, particularly 200,000 or more, or 600,000 or less, particularly 250,000 or more or 500,000 or less. It is preferable to use it.

  Among them, it is more preferable to use an acrylic acid ester (co) polymer having a mass average molecular weight (Mw) / number average molecular weight (Mn) of 5 to 10, especially 6 or 9 or less. A large mass average molecular weight / number average molecular weight means that the molecular weight distribution is wide. If this value is as large as about 5 to 10, each of the low molecular weight component and the high molecular weight component is fluid and viscous. This contributes to the performance of matching the molecular weight such as the property and cohesive force, and therefore, the workability and the adhesive performance tend to be better than those having a narrow (uniform) molecular weight distribution.

(Crosslinking agent)
As a crosslinking agent used when the acrylic ester (co) polymer is crosslinked, for example, a polyfunctional (meth) acrylate having two or more (meth) acryloyl groups is preferable.

  The amount of the crosslinking agent is preferably 0 to 30 parts by mass, particularly 20 parts by mass or less, particularly 10 parts by mass or less, and particularly preferably 5 parts by mass or less, with respect to 100 parts by mass of the base polymer.

(Crosslinking initiator)
As a crosslinking initiator used in the present pressure-sensitive adhesive composition, an intermolecular hydrogen abstraction type photopolymerizable initiator (also referred to as “hydrogen abstraction type photoinitiator”) can be mentioned as a particularly preferred example.

  The photopolymerization initiator generates radicals by light irradiation and becomes a starting point for a polymerization reaction in the system. The mechanism of radical generation in (meth) acrylic acid esters and vinyl ester systems is broadly classified into two types: an intramolecular cleavage type that generates a radical by cleaving a single bond of the photopolymerization initiator itself, and a photoexcited initiator. And a hydrogen donor in the system form an exciplex and are broadly classified into a hydrogen abstraction type in which hydrogen of the hydrogen donor is transferred.

  The intramolecular cleavage type decomposes when a radical is generated by light irradiation and becomes another compound. Therefore, once excited, it does not function as a reaction initiator, whereas the hydrogen abstraction type Even if excited, the initiator that has not reacted returns to the ground state and can be reused as a reaction initiator. For this reason, as compared with the intramolecular cleavage type photopolymerization initiator, the hydrogen abstraction type photopolymerization initiator tends to remain as an active species in the system even after the composition is primarily cured by ultraviolet rays. Therefore, it can be used as a reaction initiator when ultraviolet light is applied after bonding and further crosslinking (secondary curing) is performed. Furthermore, the hydrogen abstraction type photopolymerization initiator is superior in that it has fewer low molecular weight decomposition products and less outgassing and elution from the decomposition products than the intramolecular cleavage type.

Examples of the hydrogen abstraction type photoinitiator include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 4-hydroxybenzophenone, 4,4′-dimethylaminobenzophenone, o-benzoylbenzoic acid. Examples include benzophenone compounds such as methyl and dibenzosuberone.
In addition, thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone And anthraquinone compounds such as 2-aminoanthraquinone, and α-dicarbonyl compounds such as benzyl and camphorquinone.
These can also be used as a mixed component comprising two or more types of combinations. However, the hydrogen abstraction type photoinitiator is not limited to the substances listed above. In addition, an intramolecular cleavage type photopolymerization initiator may be used in various proportions.

  The addition amount of the photopolymerization initiator is not particularly limited, and is generally 0.1 to 10 parts by weight, particularly 0.2 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the base resin. In particular, it is preferable to adjust at a ratio of 0.5 parts by mass or more or 3 parts by mass or less. However, this range may be exceeded in balance with other elements.

(Thermal crosslinking agent)
As a thermal crosslinking agent, an isocyanate type crosslinking agent, an epoxy-type crosslinking agent, etc. can be mentioned, for example, These can be used 1 type or 2 types or more.

Examples of the isocyanate-based crosslinking agent include isocyanates such as tolylene diisocyanate, chlorophenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate. Monomers and isocyanate compounds obtained by adding these isocyanate monomers with trimethylolpropane, isocyanurates, burette type compounds, and addition reaction of known polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc. Examples include urethane prepolymer type isocyanate It is possible.
In the isocyanate compounds exemplified above, the isocyanate group may be protected with a suitable blocking agent in order to improve processability and storage stability.
Examples of the blocking agent include phenol, oxime, caprolactam, mercaptan, imide, amide, imidazole, alcohol, active methylene, and various amine compounds. According to this, known ones can be appropriately selected.

  Examples of the epoxy cross-linking agent include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, N, N, N ′, N′-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, m-N, N-diglycidylaminophenylglycidyl ether N, N-diglycidyl toluidine, N, N-diglycidyl aniline and the like.

  In addition, it is preferable that content of these crosslinking agents is the range of 0.5-2 equivalent with respect to the introduction amount of the crosslinkable functional group of a base polymer.

(Other)
When cross-linking the acrylic ester (co) polymer, various additives may be appropriately added as necessary.

<Physical properties of this adhesive sheet>
The pressure-sensitive adhesive sheet preferably has an indentation hardness (C2 Asker hardness) of 40 or more and less than 50, and more preferably 43 or more and less than 47.
When the indentation hardness is 40 or more, the adhesive strength and the cohesive force are sufficient, and when the indentation hardness is less than 50, it is possible to eliminate concerns such as being too hard and inferior in step following ability.
In this pressure-sensitive adhesive sheet, the indentation hardness is reduced by increasing the thickness of the pressure-sensitive adhesive layer (A) relative to the pressure-sensitive adhesive layer (B), that is, by increasing the ratio of the pressure-sensitive adhesive layer (A). Can be adjusted.
In addition, this Asker hardness is a value which can be measured with an Asker hardness meter (Asker C2L) about what laminated | stacked sequentially so that the thickness of this adhesive sheet might be in the range of 2 mm-3 mm.

The present adhesive sheet preferably has a tensile modulus of 0.2 MPa or more.
When this pressure-sensitive adhesive sheet has such properties, it becomes relatively hard and hardly deformed, and can impart excellent cutting properties and storage stability.
From this viewpoint, the tensile elastic modulus of the pressure-sensitive adhesive sheet is preferably from 0.18 MPa to 0.26 MPa, and more preferably from 0.20 MPa to 0.24 MPa.

  The tensile modulus of the present pressure-sensitive adhesive sheet is preferably adjusted by, for example, the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer (B), particularly the type and amount of the crosslinking agent and photopolymerization initiator, and the crosslinking conditions.

<Manufacturing method>
This pressure-sensitive adhesive sheet can be formed and produced as a pressure-sensitive adhesive layer (A) and a pressure-sensitive adhesive layer (B) by appropriately selecting a base polymer and using a crosslinking method suitable for each.

  For example, select an acrylic ester polymer as the base polymer, add a crosslinking agent and a reaction initiator or reaction catalyst, stir and mix, form a film on the release film to the desired thickness, and heat A pressure-sensitive adhesive layer (A) -forming sheet or a pressure-sensitive adhesive layer (B) -forming sheet can be obtained by drying or irradiation with ultraviolet rays for crosslinking.

In this way, a pressure-sensitive adhesive layer (A) -forming sheet and a pressure-sensitive adhesive layer (B) -forming sheet are prepared in advance, and a transparent double-sided pressure-sensitive adhesive sheet can be prepared by superimposing in a subsequent step.
Moreover, either one sheet | seat is produced and the other composition can be coat | covered with this sheet | seat, and a transparent double-sided adhesive sheet can also be produced.
Alternatively, a transparent double-sided pressure-sensitive adhesive sheet can be produced by coating the release film with the pressure-sensitive adhesive layer (A) forming composition and the pressure-sensitive adhesive layer (B) forming composition in order.
Furthermore, a transparent double-sided pressure-sensitive adhesive sheet can also be produced by coextruding the pressure-sensitive adhesive layer (A) forming composition and the pressure-sensitive adhesive layer (B) forming composition.

This adhesive sheet can also be provided as a form in which release films are laminated on the front and back.
In this case, the release film can be used by appropriately selecting a release film by applying a silicone resin to a polyester-based, polypropylene-based, polyethylene-based cast film or stretched film, or a release paper. In particular, it is preferable to use release films having different peeling forces or release films having different thicknesses on the front and back sides of the pressure-sensitive adhesive sheet.

<Constituent Member for Image Display Device with Transparent Double-Sided Adhesive Sheet>
This pressure-sensitive adhesive sheet can also be provided as a constituent member for an image display device with a transparent double-sided pressure-sensitive adhesive sheet by previously laminating the back surface of the constituent member for an image display device.
A constituent member for an image display device with a transparent double-sided pressure-sensitive adhesive sheet (hereinafter simply referred to as a constituent member for an image display device with a pressure-sensitive adhesive sheet) is bonded to the constituent member for an image display device, and heat or It is a structural member with a transparent double-sided pressure-sensitive adhesive sheet obtained by curing with ultraviolet rays.
The present pressure-sensitive adhesive sheet is cured by heat or ultraviolet light after being bonded to the constituent member for an image display device, whereby excellent foam resistance can be realized.

  From the above, in the constituent member for an image display device with an adhesive sheet, as the constituent member for an image display device to be bonded to the adhesive sheet, a stepped portion having a height of 50 μm to 100 μm and a flat surface portion are used as the bonding surface. What has is preferable.

<Image display device>
This pressure-sensitive adhesive sheet can be suitably used for an image display device having a constituent member for an image display device provided with a step portion.
For example, at least two image display device constituent members that face each other, at least one of the image display device constituent members has a stepped portion having a height of 50 to 100 μm and a flat surface portion on the bonding surface, and two face members that face each other. In the image display device in which the interval between the flat surface portions of the constituent members for the image display device is 200 μm or less, the image display device is configured by filling the adhesive sheet between the two constituent members for the image display device. be able to.

At this time, as a structural member for an image display device having a stepped portion having a height of 50 to 100 μm and a flat surface portion on the bonding surface, for example, a protective panel having a configuration in which a frame-like concealed printing portion is formed on the peripheral portion The structural member for image display apparatuses can be mentioned.
In addition, a touch-on-lens surface protection panel with an integrated touch panel function can also be used.
On the other hand, examples of the constituent member for an image display device to be bonded to this include a touch panel and an image display panel.

The image display panel includes a liquid crystal panel having a configuration in which a liquid crystal layer is sandwiched between glass substrates, and a configuration in which a polarizing film is laminated on the viewing side of the liquid crystal panel in order to prevent deterioration in image quality due to surface reflection. And so on.
In addition to an on-cell type in which a touch panel is incorporated in the image display panel, an in-cell type image display panel in which a touch sensor function is incorporated in a liquid crystal pixel can be used.

  From the above, as the image display device, at least the facing member, the image display device constituent member having a stepped portion and a flat surface portion having a height of 50 to 100 μm on the bonding surface, and either the touch panel or the surface protection panel are displayed. What has the structure filled with this adhesive sheet between apparatus members can be mentioned as a preferable example.

(Bonding method)
As a method of laminating two constituent members for an image display device, this adhesive sheet is roll pasted to one image display device constituent member, and then the other image display device constituent member is roll pasted under atmospheric pressure. Or a method of fixing the image display constituent members to the opposite stages and integrating the members under atmospheric pressure or reduced pressure.
At this time, it is more preferable to carry out the present adhesive sheet and the image display device constituting member while heating. Since the adhesive sheet is softened by heating, the adherence of the adhesive sheet to the adherend surface increases when the adherend has irregularities such as printing steps or entraps foreign matter. The effect of suppressing residual bubbles due to insufficient wetting is obtained. From this point of view, it is preferable to heat from 40 ° C to 100 ° C, more preferably from 60 ° C to 80 ° C.

This pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer (A) having curability by heat or ultraviolet rays. For this reason, when it is applied to an image display device, that is, after being bonded to a member constituting an image display device, it is preferably cured and used by heat or ultraviolet rays.
In particular, when applied to the bonding of the structural member for an image display device having a step portion having a height of 50 to 100 μm, it is possible to sufficiently follow the step portion at the stage of primary curing, and not to be too flexible. By bridging, it is possible to sufficiently permeate every corner without following the step and generate bubbles, and to relieve stress caused by the step. Even if it is exposed to a high humidity environment or exposed to a rapid temperature change, the problem of foaming and peeling at the bonding interface can be prevented.
Further, by secondary curing after bonding, the cohesive force of the flat surface portion, that is, the bonding force can be increased, and the two structural members for the image display device can be firmly bonded as a whole pressure-sensitive adhesive sheet. It can develop foaming properties.

<Explanation of terms>
In general, "film" refers to a thin flat product that is extremely small compared to its length and width and whose maximum thickness is arbitrarily limited, and is usually supplied in the form of a roll (Japan) Industrial standard JISK6900), and in general, “sheet” refers to a product that is thin by definition in JIS and generally has a thickness that is small instead of length and width. However, since the boundary between the sheet and the film is not clear and it is not necessary to distinguish the two in terms of the present invention, in the present invention, even when the term “film” is used, the term “sheet” is included and the term “sheet” is used. In some cases, “film” is included.

In the present invention, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably Y”, with the meaning of “X to Y” unless otherwise specified. It means “smaller”.
Further, in the present invention, when expressed as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and “Y or less” (Y is an arbitrary number). ) Includes the meaning of “preferably smaller than Y” unless otherwise specified.

  Hereinafter, although an Example and a comparative example demonstrate in more detail, this invention is not limited to these.

<Manufacture of components>
First, the structural member for producing the transparent double-sided adhesive sheets 1-4 mentioned later was produced as follows.

(Adhesive layer (A): Composition for pressure-sensitive adhesive)
75 parts by mass of 2-ethylhexyl acrylate (homopolymer Tg (a glass transition point of a polymer obtained by polymerizing only 2-ethylhexyl acrylate): −70 ° C.), 20 parts by mass of vinyl acetate (homopolymer Tg + 32 ° C.), acrylic An acrylic acid ester copolymer A (Mw = 440000, Mn = 62000, Mw / Mn = 8, theoretical Tg-50 ° C.) prepared by random copolymerization with 5 parts by mass of an acid (homopolymer Tg + 106 ° C.) was prepared.
A pressure-sensitive adhesive composition (A) constituting the adhesive layer (A) by adding 20 g of 4-methylbenzophenone as an intermolecular hydrogen abstraction type photopolymerization initiator to 1 kg of this acrylate copolymer A1 -1) was prepared.

(Adhesive layer (B): Composition for intermediate resin layer)
200 g of UV curable resin trimethylolpropane triacrylate as a crosslinking agent and 15 g of 1-hydroxy-cyclohexyl phenyl ketone as a photopolymerization initiator are mixed with 1 kg of the acrylic ester copolymer A, and an adhesive layer An intermediate resin layer composition (B-1) constituting (B) was prepared.

[Example 1]
<Preparation of transparent double-sided pressure-sensitive adhesive sheet 1>
An intermediate resin layer composition (B-1) and a pressure sensitive adhesive composition (A-1) were applied to a release-treated polyethylene terephthalate film (Mitsubishi Resin “MRA75”, thickness 75 μm). Co-extrusion so as to be layer (A-1) / intermediate resin layer (B-1) / pressure-sensitive adhesive layer (A-1), and pressure-sensitive adhesive layer (A-1) / intermediate resin layer ( B-1) / Pressure-sensitive adhesive layer (A-1) = 60/30/60 μm (A polyethylene terephthalate film coated and formed to be a resin layer (A) and subjected to a release treatment (“MRA50” manufactured by Mitsubishi Plastics) A multilayer sheet composed of PET film / (A-1) / (B-1) / (A-1) / PET film was formed (thickness relationship: (A) / (B) = 2.0).
Next, from one polyethylene terephthalate film side, UV light with an integrated light quantity of 1000 mJ / cm ² is irradiated with a high-pressure mercury lamp, and (A-1) and (B-1) are UV-crosslinked to be transparent before secondary curing. Double-sided PSA sheet 1 (total thickness 150 μm) was prepared.

[Comparative Example 1]
<Preparation of transparent double-sided pressure-sensitive adhesive sheet 2>
An intermediate resin layer composition (B-1) and a pressure sensitive adhesive composition (A-1) were applied to a release-treated polyethylene terephthalate film (Mitsubishi Resin “MRA75”, thickness 75 μm). Co-extrusion so as to be layer (A-1) / intermediate resin layer (B-1) / pressure-sensitive adhesive layer (A-1), and pressure-sensitive adhesive layer (A-1) / intermediate resin layer ( B-1) / Pressure-sensitive adhesive layer (A-1) = 50/50/50 [mu] m, and coated with a peeled polyethylene terephthalate film (Mitsubishi Resin "MRA50", thickness 50 [mu] m) Thus, a multilayer sheet composed of PET film / (A-1) / (B-1) / (A-1) / PET film was formed (thickness relationship: (A) / (B) = 1.0).
Next, from one polyethylene terephthalate film side, UV light with an integrated light quantity of 1000 mJ / cm ² is irradiated with a high-pressure mercury lamp, and (A-1) and (B-1) are UV-crosslinked to be transparent before secondary curing. A double-sided pressure-sensitive adhesive sheet 2 (total thickness 150 μm) was produced.

[Comparative Example 2]
<Preparation of transparent double-sided pressure-sensitive adhesive sheet 3>
An intermediate resin layer composition (B-1) and a pressure sensitive adhesive composition (A-1) were applied to a release-treated polyethylene terephthalate film (Mitsubishi Resin “MRA75”, thickness 75 μm). Co-extrusion so as to be layer (A-1) / intermediate resin layer (B-1) / pressure-sensitive adhesive layer (A-1), and pressure-sensitive adhesive layer (A-1) / intermediate resin layer ( B-1) / Pressure-sensitive adhesive layer (A-1) = 35/70/35 μm Coated with a polyethylene terephthalate film (Mitsubishi Resin “MRA50”, thickness 50 μm) coated and peeled. Thus, a multilayer sheet composed of PET film / (A-1) / (B-1) / (A-1) / PET film was formed (thickness relationship: (A) / (B) = 0.5).
Next, from one polyethylene terephthalate film side, UV light with an integrated light quantity of 1000 mJ / cm ² is irradiated with a high-pressure mercury lamp, and (A-1) and (B-1) are UV-crosslinked to be transparent before secondary curing. A double-sided pressure-sensitive adhesive sheet 3 (total thickness 140 μm) was produced.

[Comparative Example 3]
(Adhesive layer (A): Pressure sensitive adhesive layer)
Acrylate ester copolymer B1 kg (copolymerized) of 73 parts by mass of butyl acrylate (Tg-56 ° C.), 25 parts by mass of methyl methacrylate (Tg 105 ° C.) and 2 parts by mass of acrylic acid (Tg 106 ° C.) Mw = 1,100,000) 0.15 g of a polyisocyanate compound (Asahi Kasei Duranate 24A-100) as a cross-linking agent was added to prepare a pressure-sensitive adhesive composition (A-2), which was subjected to a release-treated polyethylene terephthalate. Polyethylene terephthalate film (Toyobo Co., Ltd.) coated on a film (Mitsubishi Plastics Co., Ltd., trade name “MRF75” thickness 75 μm), coated in a sheet shape to a thickness of 35 μm, and subjected to release treatment on the surface Company-made “E7006” thickness 38 μm) was coated to prepare a pressure-sensitive adhesive layer (A-2). A pressure-sensitive adhesive layer (A-2) having a thickness of 35 μm was produced. In addition, this pressure-sensitive adhesive layer (A-2) does not maintain the curability by heat or ultraviolet rays.

(Adhesive layer (B): laminated sheet for forming an intermediate resin layer)
The intermediate resin layer composition (B-1) is heated and melted on the one side of a polyethylene terephthalate film (Panac PET film “NP75Z01”, thickness 75 μm) treated so that one side is peelable, and the thickness is 80 μm. After coating with an applicator, a polyethylene terephthalate film (Toyobo PET film “E7006”, thickness 38 μm) treated so that one side surface can be peeled is coated so that the one side surface comes into contact with the PET. A laminated sheet for forming an intermediate resin layer, which constitutes an adhesive layer (B), comprising a film / intermediate resin layer (B-1, thickness 80 μm) / PET film was prepared.

<Preparation of transparent double-sided pressure-sensitive adhesive sheet 4>
Laminated the adhesive surface exposed by peeling off the release film for the process of the pressure sensitive adhesive layer (A-2) on the surface exposed by peeling the release film on both sides of the intermediate resin layer (B-1), A pressure-sensitive adhesive layer (A-2) / intermediate resin layer (B-1) / pressure-sensitive adhesive layer (A-2) = 35/80/35 μm transparent double-sided pressure-sensitive adhesive sheet 4 was produced (thickness relationship: ( A) / (B) = 0.4).

<Evaluation method>
The transparent double-sided PSA sheets 1 to 4 obtained as described above were evaluated as follows.

(Evaluation of cutting processability and storage stability)
100 sheets of the transparent double-sided PSA sheets 1 to 4 were cut with a Thomson blade of 55 mm × 85 mm using a Thomson punching machine with the release film laminated. Immediately after cutting and after cutting 100 sheets, the shape of the edge was observed after storage for 1 week in a 25 ° C., 50% humidity environment.
Immediately after pasting or after storage, 10 or more pieces of glue protruding or crushed at the end were evaluated as “×”, and those having no glue protruding or crushed at the edge were “○”. It was determined.

(Printing level followability test)
Evaluation glass having white printing (total light transmittance of 0%) with a width of 10 mm and a thickness of 80 μm on the periphery of soda lime glass of 60 mm × 90 mm × thickness 0.5 mm, and a printing step of 80 μm on the periphery. A substrate was produced.
As a test adherend to be bonded to this glass substrate for evaluation, a polarizing plate (NWF-KDSEGHC-ST22 manufactured by Nitto Denko) was previously bonded to the entire surface of a glass plate (60 × 90 mm × t0.5 mm). Was made.
One release film of the transparent double-sided pressure-sensitive adhesive sheets 1 to 4 cut by the processability evaluation was peeled off, and the exposed pressure-sensitive adhesive surface was stuck with a hand roller so as to cover the printing step portion of the glass substrate. Next, the remaining release film is peeled off, and untreated soda lime glass is press-bonded under reduced pressure (absolute pressure 5 kPa) on the exposed adhesive surface, and then subjected to autoclave treatment (60 ° C., 0.3 MPa, 20 minutes) and finish pasted. The laminated body for printing level | step difference followability evaluation was produced.
After leaving the laminated body for evaluating the printing step following property in a normal state (temperature 23 ° C., humidity 50%) for one day, the appearance was visually observed, and the adhesive sheet was lifted or peeled near the printing step. “×” was evaluated, and “o” was evaluated when there was no lifting or peeling.

(Foaming resistance test)
The laminate for evaluation of print step followability produced in the same manner as in the print step follow-up test is transparent so that the ultraviolet light of 365 nm reaches 2000 mJ / cm ² with the integrated light amount through the printed glass substrate. The double-sided pressure-sensitive adhesive sheets 1 to 3 were irradiated with ultraviolet rays, and the pressure-sensitive adhesive sheet in the inner opening surrounded by the printing part was subjected to ultraviolet crosslinking (secondary curing) to prepare a sample for foam resistance test.
On the other hand, for the transparent double-sided pressure-sensitive adhesive sheet 4 that does not retain curability due to heat or ultraviolet rays, the laminate produced by the above-described printing step follow-up test was directly used as a sample for the foam resistance test.
Each sample was allowed to stand for one day in a normal state (temperature: 23 ° C., humidity: 50%), then cured for 6 hours in a thermostatic device at 85 ° C., and the appearance after curing was visually observed.
The case where a new float or foaming occurred after curing was evaluated as “×”, and the case where a new float or foam did not occur was evaluated as “◯”.

(Indentation hardness)
The indentation hardness of the adhesive sheet is about 2 mm ± 0.3 mm by stacking a plurality of transparent double-sided adhesive sheets 1 to 3, and using a Asker hardness meter, the measuring terminal with a depth of 2.5 mm is used with an indentation load of 1000 g. The measurement was performed by pushing vertically at a pushing speed of 3 mm / min.

(Tensile modulus)
The tensile elastic modulus of the transparent double-sided PSA sheet was cut out with a width of 20 mm and a length of 80 mm for each of the transparent double-sided PSA sheets 1 to 4, and the length direction of the PSA sheet cut out using a tensile tester was tested at a test speed of 300 mm / min. And then measured.
The respective evaluation results are shown in Table 1.

<Discussion>
In the transparent double-sided pressure-sensitive adhesive sheet 1, the relationship between the thickness of the pressure-sensitive adhesive layer (A) and the thickness of the pressure-sensitive adhesive layer (B) is (A) / (B) = 2.0, and printing with a thickness of 80 μm is followed. In addition, it had excellent foam resistance. In addition, the processing and storage stability was excellent.

  The transparent double-sided PSA sheets 2 and 3 have thin adhesive layers (A) on the front and back, and the relationship between the thickness of the PSA layer (A) and the thickness of the PSA layer (B) is (A) / (B ) = 1.0, (A) / (B) = 0.5, and printing with a thickness of 80 μm could not be followed. The processing security stability and foam resistance were excellent.

  In the transparent double-sided pressure-sensitive adhesive sheet 4, the front and back pressure-sensitive adhesive layers (A) are thin, and the relationship between the thickness of the pressure-sensitive adhesive layer (A) and the thickness of the pressure-sensitive adhesive layer (B) is (A) / (B) = 0. Furthermore, since the pressure-sensitive adhesive layer (A) does not retain the curability by heat or ultraviolet rays and has a hard property, it cannot follow the printing with a thickness of 80 μm, and is resistant to foaming. Was inferior.

1 Transparent double-sided pressure-sensitive adhesive sheet for image display device 2 Adhesive layer (A)
3 Adhesive layer (B)
4 Image display device 5 Image display device component (1) Print step portion (2) Print step portion (3) Flat surface portion 6 Image display device component

Claims (6)

An image display device constituent member having a stepped portion and a flat surface portion on a bonding surface, and a transparent double-sided pressure-sensitive adhesive sheet for an image display device used for bonding another image display device constituent member,
The thickness of the maximum thickness part of the adhesive sheet is 200 μm or less,
Having at least a superimposed layer of the pressure-sensitive adhesive layer (A) and the pressure-sensitive adhesive layer (B),
The thickness of the pressure-sensitive adhesive layer (A) and the thickness of the pressure-sensitive adhesive layer (B) satisfy the relationship of (A) / (B)> 1.0,
At least the pressure-sensitive adhesive layer (A) has curability by heat or ultraviolet rays, and
A transparent double-sided pressure-sensitive adhesive sheet for an image display device, having an indentation hardness (C2 Asker hardness) of 40 or more and less than 50.   The image according to claim 1, wherein the pressure-sensitive adhesive layer (A) is formed from a pressure-sensitive adhesive composition containing an acrylic acid ester copolymer having a mass average molecular weight of 100,000 to 700,000 and an intermolecular hydrogen abstraction type photoinitiator. Transparent double-sided adhesive sheet for display devices.   The transparent double-sided pressure-sensitive adhesive sheet for an image display device according to claim 1 or 2 is bonded to a structural member for an image display device, and is cured by heat or ultraviolet rays. Manufacturing method.   The transparent double-sided adhesive according to claim 3, wherein at least one of the constituent members for an image display device according to claim 1 has a stepped portion having a height of 50 µm to 100 µm and a flat surface portion on the bonding surface. A manufacturing method of a constituent member for an image display device with a sheet. At least two image display device constituent members facing each other, at least one of the image display device constituent members has a stepped portion having a height of 50 μm to 100 μm and a flat surface portion on the bonding surface, and two images facing each other In the image display device in which the distance between the flat surface portions of the constituent members for the display device is 200 μm or less,
The image display apparatus provided with the structure filled with the transparent double-sided adhesive sheet for image display apparatuses of Claim 1 or 2 between the said two structural members for image display apparatuses. The image display device according to claim 5, wherein the other of the two image display device components is either a touch panel or an image display panel.

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