JP2013185023A - Transparent double-sided pressure-sensitive adhesive sheet and image display using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new transparent double-sided pressure-sensitive adhesive sheet, which has, even when a laminating surface includes a stepped part 50-100 μm in height under a limitation such that the thickness of the adhesive sheet is kept at 250 μm or less, a tendency to follow the stepped part by absorbing distortion caused within the adhesive sheet after laminating, and further has high workability as well as excellent foaming resistance after laminating.SOLUTION: A substrate-less transparent double-sided pressure-sensitive adhesive sheet includes different adhesive layers (A) and (B) on both surface sides, and has a total thickness of 250 μm or less. The adhesive layer (A) on one surface side is larger in the slippage length at 40°C to a SUS plate in a retention force measurement according to JIS-Z-0237 than that of the adhesive layer (B) on the other surface side, and has curability by heat or ultraviolet ray. The adhesive layer (B) of the other surface side has a slippage length at 40°C to the SUS plate of less than 1 mm in the retention force measurement according to JIS-Z-0237.

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, and an image display device using the same.

  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 pressure-sensitive adhesive sheet having an intermediate resin layer (A) and a pressure-sensitive adhesive layer (B) as front and back layers, each of which is composed of 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. A transparent double-sided PSA sheet is disclosed which is higher than the pressure sensitive adhesive layer (B) and has an indentation hardness (Asker C2 hardness) of 10 to 80 of the entire sheet.

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 at 80 ° C. and 1 Hz, 5. An ultraviolet crosslinkable pressure-sensitive adhesive sheet that is 0 × 10 ⁴ Pa or less and further has a storage elastic modulus of 1.0 × 10 ³ Pa or more at 130 ° C. and 1 Hz is disclosed. .

Further, Patent Document 4 has at least one UV-curable pressure-sensitive adhesive layer, and (a) a storage elastic modulus G ′ (1 Hz) at a measurement temperature of 20 ° C. and a frequency of 1 Hz in a state before UV curing. Storage elastic modulus G ′ (10 ⁻⁷ Hz) at 5 × 10 ^{3 to} 5 × 10 ⁵ Pa (pascal) and (b) reference temperature 20 ° C. and frequency 10 ⁻⁷ Hz is 5 × 10 ^{1 to} 5 × 10 ^3. (C) Storage elastic modulus G ′ (1 Hz) at a measurement temperature of 20 ° C. and a frequency of 1 Hz is 1 × 10 ⁴ to 1 × 10 ⁶ Pa (pascal) with viscoelastic properties of Pa and after UV curing. And (d) a pressure-sensitive adhesive sheet for an interlayer film having a viscoelastic property of a storage elastic modulus G ′ (10 ⁻⁷ Hz) at a reference temperature of 20 ° C. and a frequency of 10 ⁻⁷ Hz of 1 × 10 ⁴ Pa or more. Yes.

International Publication Pamphlet WO2010 / 044229 International Publication Pamphlet WO2011 / 129200 JP 2011-184582 A JP 2002-348150 A

In the field of image display devices, mainly mobile phones and portable terminals, lightening, thinning, and high precision are progressing, 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.

  In addition, since the thinning of the image display device is progressing, it is necessary to solve such a problem without preventing the thinning.

  In addition, the transparent double-sided pressure-sensitive adhesive sheet used for bonding such an image display device, particularly an image display device constituent member having a stepped portion on the bonding surface, has foam resistance after bonding to the component member. Is also required.

  Here, the transparent pressure-sensitive adhesive sheet disclosed in Patent Document 1 is a pressure-sensitive adhesive sheet having a relatively hard property in order to have a property of good foam resistance by a heat durability test, and can follow a printing step. There was still room for improvement in terms of sex.

  On the other hand, the transparent double-sided pressure-sensitive adhesive sheet described in Patent Document 2 is a relatively soft pressure-sensitive adhesive sheet in order to have excellent followability with respect to the level difference due to the printing site, but is resistant to foaming after bonding. Moreover, there was room for improvement about the ease of bonding at the time of bonding, and punching workability.

  In addition, the pressure-sensitive adhesive sheet described in Patent Document 3 has both the followability to the step and the reliability after the member bonding by making the storage elastic modulus different before and after the crosslinking. The storage stability in the state was inferior and was not always satisfactory.

  Furthermore, the pressure-sensitive adhesive sheet for an interlayer film described in Patent Document 4 has high fluidity and poor stability before being cured, so that it easily deforms due to dents and the like, and still has room for improvement.

  Therefore, the present invention has the property of following the step portion even if it has a step portion having a height of 50 μm to 100 μm on the bonding surface under the constraint that the thickness of the pressure sensitive adhesive sheet is suppressed to 250 μm or less. It is intended to provide a new transparent double-sided pressure-sensitive adhesive sheet that can relieve the distortion generated therein, has excellent foam resistance, and has high processability.

  The present invention is a baseless transparent double-sided pressure-sensitive adhesive sheet having different pressure-sensitive adhesive layers (A) and (B) on the front and back sides and having an overall thickness of 250 μm or less, and the pressure-sensitive adhesive layer (A) on one side is In the holding force measurement according to JIS-Z-0237, the deviation length at a temperature of 40 ° C. with respect to the SUS plate is larger than that of the pressure-sensitive adhesive layer (B) on the other side, and is cured by heat or ultraviolet rays. The pressure-sensitive adhesive layer (B) on the other side is transparent, with a deviation length of less than 1 mm at a temperature of 40 ° C. relative to the SUS plate in the holding power measurement according to JIS-Z-0237. Propose a double-sided PSA sheet.

  The present invention also includes at least two image display device components facing each other, and at least one of the image display device components has a stepped portion having a height of 50 to 100 μm on the bonding surface and a flat surface portion. In the image display device in which the distance between the flat surface portions of the two image display device constituent members facing each other is 250 μm or less, the present invention proposes a space between the two image display device constituent members. The image display apparatus provided with the structure filled with the transparent double-sided adhesive sheet of this is proposed.

The transparent double-sided pressure-sensitive adhesive sheet proposed by the present invention has a step 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 the constraint that the thickness of the pressure-sensitive adhesive sheet is suppressed to 250 μm or less. Even if it exists, it is set as the structure which has different adhesive layers (A) and (B) in the front and back, adjusts the shift length of the adhesive layer of the front and back, and enlarges the shift length of at least one adhesive layer (A). In addition, by keeping the curability by heat or ultraviolet rays, it is possible to follow the stepped portion, relieve distortion generated in the portion in contact with the stepped portion, have foam resistance, and have high workability. It has the advantage of comprising.
Therefore, the transparent double-sided pressure-sensitive adhesive sheet proposed by the present invention is an image display device that is becoming thinner and diversified in design, such as a personal computer (PC), a PDA, a mobile terminal such as a mobile phone, a game machine, a television (TV), It can be suitably used for a car navigation system, a liquid crystal pen tablet, and an image display terminal with a touch panel function.

  Hereinafter, although an example of an 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 (hereinafter referred to as “the present pressure-sensitive adhesive sheet”) according to this embodiment includes different pressure-sensitive adhesive layers (A) and pressure-sensitive adhesive layers (B) on the front and back sides, and the pressure-sensitive adhesive layer (A) is heated. Or it has the sclerosis | hardenability by an ultraviolet-ray, it is transparent, and both front and back are formed as an adhesive surface.

(Holding power)
The pressure-sensitive adhesive layer (A) on the one surface side of this pressure-sensitive adhesive sheet has a displacement length at a temperature of 40 ° C. relative to the SUS plate in the holding power measurement according to JIS-Z-0237. ) And the adhesive layer (B) on the other surface side has a displacement length of less than 1 mm at a temperature of 40 ° C. with respect to the SUS plate in the same holding force measurement.

In this pressure-sensitive adhesive sheet, in order to adjust the shift length of the pressure-sensitive adhesive interface, the adhesive force or cohesive force of the pressure-sensitive adhesive composition to the adherend may be adjusted.
Specifically, in order to keep the deviation length small, for example, the polar component in the base polymer that forms an adhesive interface with the adherend is increased, or the wettability and adhesion to the adherend are increased by the oligomer. In addition, increase the cohesion of the base polymer and increase the degree of cross-linking of the base polymer to such an extent that it does not impair the adhesion, making it difficult to deform. That's fine.
Conversely, to increase the displacement length, for example, reduce the amount of highly agglomerated components in the acrylate ester copolymer that is the base polymer, reduce the degree of crosslinking to make it easier to deform, and add tack fire etc. Then, fluidity may be imparted in a predetermined temperature range.

<Adhesive layer (A)>
The pressure-sensitive adhesive layer (A) constituting this pressure-sensitive adhesive sheet is a layer that plays a role of step following and foaming resistance. In the holding power measurement according to JIS-Z-0237, the temperature relative to the SUS plate is 40 ° C. The deviation length is larger than that of the pressure-sensitive adhesive layer (B).

When the shift length of the pressure-sensitive adhesive layer (A) is larger than that of the pressure-sensitive adhesive layer (B), there is no possibility that the followability of a step caused by printing ink or the like is impaired.
From this viewpoint, the shift length of the pressure-sensitive adhesive layer (A) is preferably 1 mm or more and less than 15 mm, and more preferably 4 mm or more and less than 15 mm.

(Curing by heat or ultraviolet rays)
Moreover, it is preferable that the adhesive layer (A) has curability by heat or ultraviolet rays.
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.

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 mitigated, and the distortion following this step can be reduced.

  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). ).

<Adhesive layer (B)>
The pressure-sensitive adhesive layer (B) constituting the present pressure-sensitive adhesive sheet is a layer that plays a role of cutability and storage stability (also simply referred to as processability). In the holding power measurement according to JIS-Z-0237, SUS The deviation length at a temperature of 40 ° C. with respect to the plate is preferably less than 1 mm.

  By setting the amount of deviation to less than 1 mm, there is a tendency that the cohesive force is high and the surface tends to be hard, and the foaming resistance under long-term storage and high-temperature environment is improved. Furthermore, processability can be imparted to the present pressure-sensitive adhesive sheet for reasons such as a small elongation of the pressure-sensitive adhesive.

  The pressure-sensitive adhesive layer (B) is not particularly limited in its constituent materials as long as the deviation length is within the above range, and specifically can be formed according to the deviation length adjusting method described above. In particular, it is formed from a pressure-sensitive adhesive resin composition containing a (meth) acrylic acid ester copolymer containing (meth) acrylic acid as a copolymerizable monomer, and an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent. It is preferable to do.

<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) has photocuring pressure-sensitive adhesive containing, for example, a base polymer having a molecular weight in a predetermined range, a photocrosslinking initiator, and, if necessary, a crosslinking agent, in order to have curability by heat or ultraviolet rays. What is necessary is just to be formed by the agent composition and the thermosetting adhesive composition containing a base polymer and a thermal crosslinking agent.
Among these, the pressure-sensitive adhesive layer (A) is formed from a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester copolymer having a mass average molecular weight of 100,000 to 700,000 and an intermolecular hydrogen abstraction type photoinitiator. Is preferred.

(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 type, composition ratio, polymerization conditions, and the like of the acrylic monomer and methacrylic monomer used for the preparation thereof. ) 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 used for the pressure-sensitive adhesive layer (A) has a suitable adhesive force at the stage of primary curing after being formed into a sheet shape, and follows irregularities and foreign matter on the surface of the adherend. It is preferable to have flexibility.
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 known polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, and the like. List urethane prepolymer type isocyanate Door can be.
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.

<Configuration of this adhesive sheet>
This pressure-sensitive adhesive sheet is a base material-less, and has a pressure-sensitive adhesive layer (A) and a pressure-sensitive adhesive layer (B) at least on the front and back sides.
This pressure-sensitive adhesive sheet may have other pressure-sensitive adhesive layers in addition to these, as long as the pressure-sensitive adhesive layers (A) and (B) constitute the front and back surfaces and are substrate-free. Another pressure-sensitive adhesive layer may be interposed between the layers (A) and (B). Furthermore, the pressure-sensitive adhesive layers (A) and (B) may have a single layer structure or a multilayer structure in which two or more layers are laminated.

(Thickness)
From the standpoint that the thickness of the pressure-sensitive adhesive sheet does not hinder the thinning of the image display device, the thickness of the maximum thickness portion is preferably 250 μm or less, and more preferably 200 μm or less.

<Manufacturing method>
This pressure-sensitive adhesive sheet can be prepared by appropriately selecting a base polymer and using a crosslinking method suitable for each as a pressure-sensitive adhesive layer (A) on one side and a pressure-sensitive adhesive layer (B) on the other side. .

  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 By drying or irradiating with ultraviolet rays, the pressure-sensitive adhesive layer (A) forming sheet on one side or the pressure-sensitive adhesive layer (B) forming sheet on the other side can be obtained.

In this way, a pressure-sensitive adhesive layer (A) -forming sheet on one side and a pressure-sensitive adhesive layer (B) -forming sheet on the other side are prepared in advance, and a transparent double-sided pressure-sensitive adhesive sheet is prepared by superimposing in a subsequent step. You can also.
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.
In addition, a transparent double-sided pressure-sensitive adhesive sheet is prepared by coating a release film in multiple steps with the composition for forming the pressure-sensitive adhesive layer (A) on one side and the composition for forming the pressure-sensitive adhesive layer (B) on the other side in order. You can also
Furthermore, a transparent double-sided pressure-sensitive adhesive sheet can also be produced by co-extrusion of the pressure-sensitive adhesive layer (A) forming composition on one side and the pressure-sensitive adhesive layer (B) forming composition on the other side.

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.

The pressure-sensitive adhesive sheet can also be provided as a component member for an image display device with a pressure-sensitive adhesive sheet by previously laminating on the back surface of the component member for an image display device.
By directly laminating the image display device component during the production of the pressure-sensitive adhesive sheet, the interface between the image display device component and the pressure-sensitive adhesive sheet can be firmly adhered to improve the durability. After this pressure-sensitive adhesive sheet is first laminated on the film side, the adhesive sheet may be brought into close contact with the back surface of the image display device and cured.
The curing conditions at this time are not particularly limited, but may be, for example, left at room temperature for 7 days or left at 40 ° C. for 3 days.

<Image display device>
The pressure-sensitive adhesive sheet can be suitably used for an image display device having two facing image display device components.
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 250 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.

Examples of the structural member for an image display device include a structural member for an image display device such as a surface protection panel having a configuration in which a frame-shaped concealment printing portion is formed on the peripheral edge.
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.

Furthermore, in the said structure, it is more preferable that the said 2 structural member for image display apparatuses is a surface protection panel which has a 50-100 micrometers high level | step-difference part in a bonding surface, and a flat surface part.
In addition, as described above, the pressure-sensitive adhesive sheet has a contradictory characteristic that it has a step following property and a high workability at the time of bonding with a constituent member for an image display device. (A) is preferably filled so as to face the surface protection panel.
Further, the pressure-sensitive adhesive sheet is preferably filled in the image display device so that the pressure-sensitive adhesive layer (B) faces the image display panel or the touch panel.

  From the above, as the image display device, one of the two constituent members for the image display device facing each other is the surface protection panel, the other is the image display panel or the touch panel, and the space between the two constituent members for the image display device is between Most preferably, the adhesive sheet is filled with the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive layer (A) faces the surface protection panel, and the pressure-sensitive adhesive layer (B) faces the image display panel or the touch panel.

(Paste 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, at the stage of bonding, the step portion can be sufficiently followed and is not 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.

[Example 1]
<Preparation of pressure-sensitive adhesive layer (A)>
Acrylate ester copolymer obtained by random copolymerization of 75 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of vinyl acetate, and 5 parts by mass of acrylic acid (Mw = 440000 Mn = 62000 Mw / Mn = 8 Theoretical Tg- 50 kg) 1 kg was mixed with 20 g of 4-methylbenzophenone as an intermolecular hydrogen abstraction type photopolymerization initiator to prepare a front and back layer pressure-sensitive adhesive composition.

  On the other hand, with respect to 1 kg of the acrylic ester copolymer, 200 g of propoxylated pentaerythritol triacrylate which is an ultraviolet curable resin as a crosslinking agent and 10 g of 4-methylbenzophenone as an intermolecular hydrogen abstraction type photopolymerization initiator. The intermediate layer pressure-sensitive adhesive composition was prepared by mixing.

The above-mentioned front and back layer pressure-sensitive adhesive composition and intermediate layer pressure-sensitive adhesive composition are coextruded so as to be <front and back layer pressure-sensitive adhesive composition / intermediate layer pressure-sensitive adhesive composition / front and back layer pressure-sensitive adhesive composition>, and subjected to release treatment. The coating was formed on terephthalate (trade name “MRA100”, manufactured by Mitsubishi Plastics, Inc., thickness 100 μm).
The remaining surface is coated with a peeled polyethylene terephthalate film (Mitsubishi Resin Co., Ltd., trade name “MRF75”, thickness 75 μm), and then a light beam with a wavelength of 365 nm is applied to both sides of the adhesive sheet through the polyethylene terephthalate film on the front and back sides. The pressure-sensitive adhesive composition is crosslinked by irradiating ultraviolet rays so as to be 1000 mJ / cm ^2, and the front and back layer pressure-sensitive adhesive composition / intermediate layer pressure-sensitive adhesive composition / front and back layer pressure-sensitive adhesive composition = from a multilayer structure of 40 μm / 70 μm / 40 μm. Thus, a primary cured sheet of pressure-sensitive adhesive sheet A (having ultraviolet curability, thickness 130 μm) constituting the pressure-sensitive adhesive layer (A) on one side was prepared.

<Preparation of pressure-sensitive adhesive layer (B)>
Commercially available solvent-type acrylic pressure-sensitive adhesive (manufactured by Soken Chemical Co., Ltd., trade name “SK Dyne 1882”) with respect to 1000 parts by weight, isocyanate curing agent (manufactured by Soken Chemical Co., Ltd., trade name “L-45”) A pressure-sensitive adhesive solution was prepared by uniformly mixing 1.85 parts by weight and 0.5 parts by weight of an epoxy curing agent (trade name “E-5XM”, manufactured by Soken Chemical Co., Ltd.).
This pressure-sensitive adhesive solution was applied to a release surface of a polyethylene terephthalate film (trade name: MRF75: manufactured by Mitsubishi Plastics) having a thickness of 50 μm using a hot melt coater so as to have a thickness of 20 μm, and the solvent was dried. Thus, the pressure-sensitive adhesive sheet B constituting the pressure-sensitive adhesive layer (B) on the other surface side was prepared by heat reaction crosslinking.

<Production of transparent double-sided PSA sheet>
The pressure-sensitive adhesive layer (A) surface from which the polyethylene terephthalate film (trade name “MRF75”, thickness 75 μm) of the pressure-sensitive adhesive sheet A (thickness 130 μm) was peeled off and the pressure-sensitive adhesive sheet B after drying the solvent were respectively removed. A transparent double-sided pressure-sensitive adhesive sheet 1 having a pressure-sensitive adhesive layer (A) on one side of 150 μm and an adhesive layer (B) on the other side was obtained by integrating with a laminator.

[Comparative Example 1]
In the same manner as in Example 1, a transparent double-sided pressure-sensitive adhesive sheet 3 formed only from a pressure-sensitive adhesive layer (B) having a thickness of 150 μm was obtained.

<Evaluation method>
(Holding force: gap length)
About the transparent double-sided pressure-sensitive adhesive sheets 1 and 2 produced in the examples and comparative examples, the pressure-sensitive adhesive sheet was cut into 50 mm × 100 mm, and then the single-sided release film was peeled off, and one side of the pressure-sensitive adhesive sheet was a polyethylene terephthalate film (thick) The sample was pasted with a hand roller so as to overlap (38 μm), and was cut into a strip having a width of 15 mm and a length of 100 mm to obtain a test piece.
Next, the remaining release film was peeled off, and a test piece was attached to the SUS plate (thickness 120 mm, 5 mm × 1.5 mm) erected vertically by a hand roller so as to overlap the length of 20 mm. . At this time, the sticking area of the transparent double-sided PSA sheet and the SUS plate is 15 mm × 20 mm.
Then, after the test piece was cured for 15 minutes in an atmosphere of 40 ° C., a 4.9N weight was attached to the test piece in a vertical direction and left standing for 60 minutes, and then the SUS and test piece was attached to each other. The length (mm) which shifted | deviated below was measured.

(Step difference)
A glass substrate for evaluation having a width of 10 mm and a thickness of 80 μm was printed on a peripheral portion of soda lime glass having a size of 60 mm × 90 mm × thickness 0.5 mm, and a printing step of 80 μm was formed on the peripheral portion.
Using the polyethylene terephthalate film (thickness: 100 μm) as the other test adherend, the transparent double-sided pressure-sensitive adhesive sheets 1 and 2 prepared in the examples and comparative examples were cut with a cutter in advance, and one side of the pressure-sensitive adhesive sheet was peeled off. The film was peeled off, and the exposed adhesive surface was attached to a polyethylene terephthalate film (thickness: 100 μm) with a hand roller.
Next, the remaining release film is peeled off, pasted with a hand roller so as to cover the printed stepped portion of the glass substrate with the exposed adhesive surface, subjected to autoclaving (60 ° C., 0.3 MPa, 20 minutes), and finally pasted, A laminate was produced.
The laminate was allowed to stand for one day in a normal state (temperature: 23 ° C., humidity: 50%), and then the appearance was visually observed. .

(Foaming resistance test)
Of the laminate produced by the above-described step following evaluation, the transparent double-sided pressure-sensitive adhesive sheet 1 of Example 1 is irradiated with 365-nm ultraviolet light on the pressure-sensitive adhesive sheet via the printed glass substrate. The pressure-sensitive adhesive sheet at the opening was irradiated with ultraviolet rays so as to reach 2000 mJ / cm ^{2, and} a sample for a foam resistance test was produced.
On the other hand, for the transparent double-sided pressure-sensitive adhesive sheet of Comparative Example 1 that has already been sufficiently cured by ultraviolet rays and has only a pressure-sensitive adhesive layer (B) with a small shift length, it was produced by the above-described step following evaluation. The laminate was used as a sample for the foam resistance test as it was.
Each of these samples was allowed to stand for one day in a normal state (temperature: 23 ° C., humidity: 50%), then cured for 6 hours in a constant temperature and humidity machine with a temperature of 85 ° C. and humidity of 25%, and the appearance after curing was visually observed.
The case where a new float or foaming occurred after curing was judged as x, and the case where there was no foam was judged as ○.

(Cutability and storage stability)
About the transparent double-sided adhesive sheets 1 and 2 produced by the Example and the comparative example, 100 sheets were cut with the 55 mm x 85 mm Thomson blade using the Thomson punching machine with the peeling film laminated | stacked. Immediately after cutting, 100 sheets of cut products were stacked, and the shape of the edge was observed after storage for 1 week in an environment of 25 ° C. and 50% humidity. Immediately after pasting or after storage, the case where 10 or more pieces of paste protruded or the edge portion was crushed was judged as x, and the case without paste was judged as o.

The test results are shown in Table 1.

As shown in Table 1, the transparent double-sided pressure-sensitive adhesive sheet 2 of Comparative Example 1 has already been sufficiently cured by ultraviolet rays and has only a pressure-sensitive adhesive layer (B) having a small shift length. Poor foaming property.
On the other hand, from the results of Example 1, it has different pressure-sensitive adhesive layers (A) and (B) on the front and back sides, makes the deviation length of these pressure-sensitive adhesive layers a desired range, and heats the pressure-sensitive adhesive layer (A). Or it turned out that the transparent double-sided adhesive sheet which is excellent in level | step difference followability, foaming resistance, and workability is obtained by providing sclerosis | hardenability by an ultraviolet-ray.
In Example 1, when the state of the pressure-sensitive adhesive layer (A) was observed in the process of forming the transparent double-sided pressure-sensitive adhesive sheet 1, the front and back surfaces formed from the front and back layer pressure-sensitive adhesive composition had soft properties. From this, it is presumed that the transparent double-sided PSA sheet having only the PSA layer (A) formed from the front and back layer PSA composition is inferior in cutting processability and storage stability.

Claims (7)

It is a transparent double-sided pressure-sensitive adhesive sheet having a base material that has different pressure-sensitive adhesive layers (A) and (B) on the front and back sides and has an overall thickness of 250 μm or less,
The adhesive layer (A) on one side has a displacement length at a temperature of 40 ° C. with respect to the SUS plate in the holding power measurement according to JIS-Z-0237, compared to that of the adhesive layer (B) on the other side. And is curable by heat or ultraviolet rays.
The pressure-sensitive adhesive layer (B) on the other side is a transparent double-sided pressure-sensitive adhesive sheet having a displacement length of less than 1 mm at a temperature of 40 ° C. with respect to the SUS plate in the holding power measurement according to JIS-Z-0237.   The transparent double-sided pressure-sensitive adhesive sheet according to claim 1, wherein a shift length of the pressure-sensitive adhesive layer (A) on one side is 1 mm or more and less than 15 mm.   The pressure-sensitive adhesive layer (B) on the other side comprises a (meth) acrylic acid ester copolymer containing (meth) acrylic acid as a copolymerizable monomer, and an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent. The transparent double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, formed from a pressure-sensitive adhesive resin composition to be contained.   The pressure-sensitive adhesive layer (A) on one side is formed from a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester copolymer having a mass average molecular weight of 100,000 to 700,000 and an intermolecular hydrogen abstraction type photoinitiator. The transparent double-sided adhesive sheet as described in any one of Claims 1-3. 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 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 250 μm or less,
The image display apparatus provided with the structure filled with the transparent double-sided adhesive sheet as described in any one of Claims 1-4 between the said two structural members for image display apparatuses.   The image display device according to claim 5, wherein the pressure-sensitive adhesive layer (A) faces a structural member for an image display device having a stepped portion having a height of 50 to 100 μm on the bonding surface and a flat surface portion on the bonding surface.   The image display device according to claim 5 or 6, wherein the other of the two constituent members for the image display device is an image display panel or a touch panel, and the adhesive layer (B) faces the panel.