JP6220495B2 - Transparent double-sided pressure-sensitive adhesive sheet for image display device and image display device using the same - 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. It is related with the transparent double-sided adhesive sheet which can be used especially suitably in order to bond an image display panel, the structural member for image display apparatuses with a transparent double-sided adhesive sheet using the same, and an image display apparatus using these.

  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, not only the work at the time of filling the liquid is complicated and inferior in productivity, but also the portion where ultraviolet rays are difficult to reach, such as a portion concealed by the printing concealment layer, can cure the liquid composition. It was difficult and it was difficult to obtain stable quality.

  There is also known a method of filling a gap between constituent members for an image display device using an adhesive sheet. 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 a front and back layer, and each layer includes one or more types ( Storage layer elastic 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 layer based on a (meth) acrylate (co) polymer. However, 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 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.

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.

  Patent Document 5 is characterized in that 0.01 to 1.0% by weight of at least a hydrogen abstraction type photoradical initiator of a photoradical initiator is contained with respect to the (meth) acrylic acid ester copolymer. A hot-melt type UV-crosslinked transparent adhesive and a hot-melt type UV-crosslinked transparent adhesive sheet using the adhesive are disclosed.

International Publication Pamphlet WO2010 / 044229 International Publication Pamphlet WO2011 / 129200 JP 2011-184582 A JP 2002-348150 A JP 2004-262957 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, when an image display constituent member such as a liquid crystal panel, a touch panel, or a surface protection panel is attached and integrated with an adhesive sheet, uneven unevenness such as stripes or spots may occur on the display screen. .

  In addition, printing is generally performed on the peripheral portion of the surface protection panel to form a concealing portion in a frame shape, but the portion in contact with the printing portion has a greater stress than other portions. Is applied to the image display device, and there is a possibility that distortion occurs at the periphery of the printing step and adversely affects the optical characteristics. Therefore, it is also required to suppress such distortion.

  Furthermore, the pressure-sensitive adhesive sheet is also required to have foam resistance that does not foam after being bonded to the constituent member for an image display device constituting the image display device.

  Therefore, the present invention is a new one that has foam resistance after bonding with a constituent member for an image display device, and does not cause uneven unevenness such as streaks or spots on the display screen of the image display device. It is intended to provide a transparent double-sided pressure-sensitive adhesive sheet for an image display device.

The present invention is a transparent double-sided pressure-sensitive adhesive sheet used for bonding two facing structural members for an image display device, and is cured by heat or ultraviolet rays while being bonded to the two structural members for an image display device. And the first feature is to use it, and
In the state where the release film is laminated on the front and back surfaces of the transparent double-sided PSA sheet, the average roughness Ra obtained by analyzing the interference fringe image obtained by the laser interferometer is (X), and the release film is peeled off. When the average roughness Ra obtained by analyzing interference fringe images obtained with a laser interferometer is (Y) in a state of being bonded to two constituent members for an image display device, the following (1) to ( A transparent double-sided pressure-sensitive adhesive sheet characterized by having a surface shape that satisfies the condition of 3) is proposed.

(1) 30 nm ≦ (X) ≦ 300 nm
(2) ... 0nm ≦ (Y) ≦ 130nm
(3) (X)-(Y) ≧ 30 nm

  In order to solve the above-mentioned problems, the inventors have examined the cause of the color unevenness phenomenon occurring on the display screen of the image display device in detail. The surface of the transparent double-sided pressure-sensitive adhesive sheet is a surface of the transparent double-sided pressure-sensitive adhesive sheet. It was revealed that the surface of the liquid crystal panel or touch panel was unevenly pressed due to the unevenness, resulting in imprints and unevenness, which caused an appearance defect. In order to improve such appearance defects, it has been found that it is effective to keep the uneven shape of the transparent double-sided pressure-sensitive adhesive sheet within a predetermined range before and after bonding to the constituent member for an image display device. Further, the transparent double-sided pressure-sensitive adhesive sheet in a state before being bonded to the component member so that the surface of the transparent double-sided pressure-sensitive adhesive sheet is flattened following the surface state of the component member when bonded to the component member for image display device It has been found that the above-mentioned problems can be solved by curing the transparent double-sided PSA sheet after pasting in order to impart flexibility to the resin and to maintain the foam resistance after pasting to the constituent members. From such a viewpoint, the present invention has been conceived and the above-mentioned problems have been solved.

According to the transparent double-sided pressure-sensitive adhesive sheet proposed by the present invention, the display screen of the image display device is free from uneven unevenness such as stripes and spots, and after being bonded to the constituent member for the image display device. Has foam resistance. In addition, preferably, distortion generated in a portion in contact with the stepped portion can be alleviated, and adverse effects on optical characteristics can be suppressed.
Therefore, the image display device proposed by the present invention and the transparent double-sided pressure-sensitive adhesive sheet for the image display device are thinned and image display devices that are increasingly diversified in design, for example, mobile terminals such as personal computers (PCs), PDAs, mobile phones, It can be suitably used for a game machine, a television (TV), a car navigation system, a liquid crystal pen tablet, and an image display terminal with a touch panel function.

  Hereinafter, although an example of embodiment of this invention is demonstrated, this invention is not restrict | limited to embodiment described below.

<This adhesive sheet>
The transparent double-sided pressure-sensitive adhesive sheet for an image display device according to the present embodiment (hereinafter referred to as “the present pressure-sensitive adhesive sheet”) is a transparent double-sided pressure-sensitive adhesive sheet used for bonding two constituent members for an image display device facing each other. A transparent double-sided pressure-sensitive adhesive sheet that is transparent and has both front and back surfaces as adhesive surfaces and is cured by heat or ultraviolet rays in a state of being bonded to two constituent members for an image display device. It is.

(Average roughness Ra)
The pressure-sensitive adhesive sheet has a specific average roughness in a state in which a release film is laminated on the front and back surfaces of the pressure-sensitive adhesive sheet and in a state in which the release film is peeled off and bonded to two constituent members for an image display device. It has Ra and has a surface characteristic that the difference in average roughness Ra before and after bonding to the constituent member for an image display device is in a specific range.
The average roughness Ra refers to an average roughness obtained by analyzing an interference fringe image obtained by a laser interferometer, and more specifically is a value obtained by the method described in the examples.

First, the pressure-sensitive adhesive sheet preferably has a surface shape that satisfies the following condition (1) when the average roughness Ra in a state in which release films are laminated on the front and back surfaces is (X).
(1) 30 nm ≦ (X) ≦ 300 nm

When (X) is 30 nm or more, when the transparent double-sided pressure-sensitive adhesive sheet with a release film is stored in the state of a scroll or in a state of being cut and stacked, there is a possibility that the release films protecting the surfaces may become stuck. In addition, when (X) is 300 nm or less, when the release film is peeled off and laminated on the constituent member for an image display device, the member is not significantly deformed due to uneven pressing derived from thickness unevenness. Therefore, it is preferable.
From the same viewpoint, it is more preferable that the pressure-sensitive adhesive sheet satisfies 40 ≦ (X) or (X) ≦ 250 in the above range.

In addition, the pressure-sensitive adhesive sheet preferably has a surface shape that satisfies the following condition (2) when the average roughness Ra in a state of being bonded to two constituent members for an image display device is (Y). .
(2) ... 0nm ≦ (Y) ≦ 130nm

  If (Y) is 130 nm or less, unevenness can be reduced to such an extent that the appearance of the display image is not impaired.

Further, the pressure-sensitive adhesive sheet preferably has a surface shape in which the relationship between the above (X) and (Y) satisfies the following condition (3).
(3) (X)-(Y) ≧ 30 nm

  When (X)-(Y) is 30 nm or more, this adhesive sheet itself has not only excellent followability to the adherend surface even if there is unevenness, but also when foreign matter is bitten or image display It can have an advantage that it is easy to adapt to the irregular shape of the adherend surface, such as when there is a step in the component for the apparatus.

(Method for adjusting average roughness Ra)
As a method for adjusting the average roughness Ra of the pressure-sensitive adhesive sheet to the above range, (a) a method of adjusting the surface flexibility of the pressure-sensitive adhesive sheet and imparting surface properties excellent in followability to the adherend member And (b) a method in which the pressure-sensitive adhesive sheet is laminated and the hardness of the intermediate resin layer is adjusted to change the shape according to the flexibility of the intermediate resin layer, or (c) support at the time of sheet molding A method for adjusting the surface roughness of the pressure-sensitive adhesive sheet can be exemplified by adjusting the surface shape and surface roughness of the body and the adherend. From the viewpoint of followability to a fine surface shape and many applicable members, it is preferable to employ the method (a).
Thus, by producing this pressure-sensitive adhesive sheet, the concave-convex shape of the transparent double-sided pressure-sensitive adhesive sheet can be within a predetermined range before and after bonding to the constituent member for an image display device.

<Physical properties of this adhesive sheet>
The pressure-sensitive adhesive sheet is preferably used by being cured by heat or ultraviolet rays in a state of being bonded to two constituent members for an image display device. Therefore, this pressure-sensitive adhesive sheet has a property that it can be cured by heat or ultraviolet rays in a state of being bonded to two constituent members for an image display device.
For example, it can be used after being secondarily cured by heat or ultraviolet rays in a state of being bonded to two constituent members for an image display device using the first cured adhesive sheet.
By using this pressure-sensitive adhesive sheet in this way, it is possible to improve the appearance defect of the display screen without impairing the foam resistance after bonding to the constituent member for an image display device.

  In order for this pressure-sensitive adhesive sheet to have the property of being cured by heat or ultraviolet light, for example, as shown below, it may be formed of a photocurable pressure-sensitive adhesive composition or a thermosetting pressure-sensitive adhesive composition.

(Stress relaxation characteristics)
The pressure-sensitive adhesive sheet preferably has stress relaxation properties as shown in the following (4) and (5).
That is,
(4) The stress relaxation rate after 10 seconds when the adhesive sheet is subjected to 10% strain in the shear direction is 60% or more.
(5) In the temperature range of 30 to 100 ° C., the loss tangent tan δ obtained at a frequency of 1 Hz is 0.5 or more.

Since this pressure-sensitive adhesive sheet has such characteristics as shown in (4) and (5), it has excellent followability to the adherent surface shape when sticking the pressure-sensitive adhesive sheet to the image display device constituting member. The sheet can be bonded without optical distortion even when the sheet has uneven thickness such as unevenness such as a printing step in addition to uneven thickness of the sheet itself and biting foreign matter.
From such a viewpoint, the stress relaxation rate after 10 seconds after applying 10% strain to the pressure-sensitive adhesive sheet in the shear direction is more preferably 70% or more, and more preferably 75% or more.
Further, in the temperature range of 30 to 100 ° C., the loss tangent tan δ obtained at a frequency of 1 Hz is more preferably 0.55 or more, and particularly preferably 0.6 or more.

<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.

  As the present pressure-sensitive adhesive composition, a photocurable pressure-sensitive adhesive composition containing a base polymer having a molecular weight in a predetermined range, a photocrosslinking initiator, and a cross-linking agent as necessary, or a base polymer and a heat cross-linking agent. A thermosetting pressure-sensitive adhesive composition is preferred.

(Base polymer)
The base polymer of this pressure-sensitive adhesive composition is a (meth) acrylic acid ester-based polymer (including a copolymer, hereinafter referred to as “acrylic acid ester-based (co)” from the viewpoints of adhesiveness, transparency, and weather resistance. "Polymer") is preferred.
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 base polymer has a mass average molecular weight of 100,000 to 700,000, particularly 200,000 or more and 600,000 or less, particularly 250,000 or more and 500,000 or less. Is preferred.

  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.

<Laminated structure>
The pressure-sensitive adhesive sheet may be a single-layer sheet or a multilayer sheet in which two or more layers are laminated.

  When the present adhesive sheet is a multilayer transparent double-sided pressure-sensitive adhesive sheet, that is, when a transparent double-sided pressure-sensitive adhesive sheet having a laminated structure including an intermediate layer and an outermost layer is formed, the outermost layer is formed of the above-described main adhesive. It is preferable to form from an agent composition.

(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.

<Constituent Member for Image Display Device with Transparent Double-Sided Adhesive Sheet>
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, and has the following properties (6) and (7) in a state after curing.
(6) ··· In the holding power measurement according to JIS-Z-0237, the deviation length at a temperature of 60 ° C with respect to the SUS plate is 2 mm or less.
(7) The loss tangent tan δ at a frequency of 1 Hz and a temperature of 30 ° C. to 100 ° C. is 0.6 or less.

(Holding power)
The holding force after curing of the present adhesive sheet, that is, the holding force of the adhesive sheet in the constituent member for an image display device with the present adhesive sheet, is 60 ° C. relative to the SUS plate in the holding force measurement according to JIS-Z-0237. It is preferable that the deviation length at is 2 mm or less. The smaller the amount of displacement, the higher the cohesive force of the pressure-sensitive adhesive sheet, and there are advantages such as improved long-term storage and foaming reliability under high temperature environments.
From this point of view, the shorter the deviation length after curing of the pressure-sensitive adhesive sheet, the better. However, by setting it to 2 mm or less, it is possible to obtain foaming reliability that can withstand actual use.

  Loss tangent (tan δ) after curing of the pressure-sensitive adhesive sheet, that is, loss tangent (tan δ) of the pressure-sensitive adhesive sheet in the constituent member for an image display device with the pressure-sensitive adhesive sheet is a frequency of 1 Hz and a temperature range of 30 ° C. to 100 ° C. It is preferable that it is 0.6 or less. When the loss tangent (tan δ) is 0.6 or less, there is an advantage that the elasticity of the pressure-sensitive adhesive sheet is high, and the effect of suppressing the gas pressure due to outgas from the adherend is obtained.

<Image display device>
The pressure-sensitive adhesive sheet can be suitably used for an image display device having two facing image display device components.
Examples of the constituent member for an image display device include a constituent member for an image display device such as a protective panel having a configuration in which a frame-like concealed printing portion is formed at 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 has 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, in addition to a liquid crystal panel having a configuration in which a liquid crystal layer is sandwiched between glass substrates. The thing etc. can be mentioned.
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.

As described above, the pressure-sensitive adhesive sheet has foam resistance after being bonded to the constituent member for an image display device, and non-uniform unevenness such as a streak shape or a spotted pattern occurs on the display screen of the image display device. In view of the contradictory characteristics that there is no such problem, it is preferable to be used by being laminated with an image display panel.
From this point of view, as an image display device, one of the two image display device components facing each other is an image display panel, and the space between the two image display device components is the present. It is preferable to have a structure filled with an adhesive sheet.

  Furthermore, in the said structure, it is more preferable that the other of the said structural member for two image display apparatuses is either a touch panel or a surface protection panel.

(Paste method)
As a method of bonding two image display device constituent members, after sticking an adhesive sheet to one image display device constituent member, the other image display device constituent member is roll-bonded under atmospheric pressure. Examples of the method include fixing each image display constituent member to an opposing stage under an atmospheric pressure or a reduced pressure, and integrating the members.
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 viewpoint, it is preferable to heat to 40 ° C to 100 ° C, more preferably 60 ° C to 80 ° C.

<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 “A to B” (A and B are arbitrary numbers), unless otherwise specified, “preferably greater than A” and “preferably B” together with the meaning of “A to B”. It means “smaller”.
Further, in the present invention, when expressed as “A or more (A ≦)” (A is an arbitrary number), it means “preferably larger than A (A <)” unless otherwise specified, and “B Hereinafter, when expressed as (B ≦) ”(B is an arbitrary number), it means“ preferably smaller than B (B <) ”unless otherwise specified.

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

[Example 1]
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- A pressure-sensitive adhesive composition was prepared by mixing 20 g of 4-methylbenzophenone as an intermolecular hydrogen abstraction type photopolymerization initiator with respect to 1 kg of 50 ° C).
On one side of a polyethylene terephthalate film (Mitsubishi Resin “MRA100”, thickness 100 μm) having one side peel-treated, the adhesive composition is applied and formed with an applicator so that the thickness is 150 μm. The surface of the adhesive material thus coated was coated so that one side of a polyethylene terephthalate film (“MFR75”, thickness 75 μm, manufactured by Mitsubishi Resin Co., Ltd.) having one side peeled off was brought into contact. Then, the pressure-sensitive adhesive composition is cross-linked by irradiating ultraviolet rays on both sides of the pressure-sensitive adhesive sheet through the polyethylene terephthalate film on the front and back so that the integrated light quantity of light with a wavelength of 365 nm is 1000 mJ / cm ² , thereby causing pressure-sensitive adhesive as a primary cured sheet. Sheet 1 (thickness 150 μm) was produced.

[Example 2]
For 1 kg of the acrylate copolymer used in Example 1, 200 g of propoxylated pentaerythritol triacrylate which is an ultraviolet curable resin as a crosslinking agent and 4-methylbenzo as an intermolecular hydrogen abstraction type photopolymerization initiator. The intermediate layer pressure-sensitive adhesive composition was prepared by mixing 10 g of fenne.
The pressure-sensitive adhesive composition prepared in Example 1 and the intermediate layer pressure-sensitive adhesive composition were coextruded so as to be [pressure-sensitive adhesive composition / intermediate layer pressure-sensitive adhesive composition / pressure-sensitive adhesive composition]. A polyethylene terephthalate film (MRF75 manufactured by Mitsubishi Plastics, Inc.) having one side peeled and laminated on the remaining surface of the coextruded sheet of polyethylene terephthalate (Mitsubishi Resin MRA100 thickness 100 μm) having one side peeled. , 75 μm thick). Then, the pressure-sensitive adhesive composition is cross-linked by irradiating ultraviolet rays on both surfaces of the pressure-sensitive adhesive sheet through the polyethylene terephthalate films on the front and back so that the integrated light quantity of light having a wavelength of 365 nm is 1000 mJ / cm ^2. A multilayer pressure-sensitive adhesive sheet 2 (thickness 150 μm) as a primary cured sheet comprising pressure-sensitive adhesive composition / pressure-sensitive adhesive composition = 40 μm / 70 μm / 40 μm was produced.

[Comparative Example 1]
A pressure-sensitive adhesive sheet 3 as a primary cured sheet was produced in the same manner as in Example 1 except that the intermediate layer pressure-sensitive adhesive composition used in Example 2 was used instead of the pressure-sensitive adhesive composition in Example 1. .

[Comparative Example 2]
As adhesive resin, 23 parts by weight of methacrylic group-containing isoprene rubber, 15 parts by weight of isobornyl methacrylate, 5 parts by weight of monohydroxybutyl methacrylate, 25 parts by weight of hydrogenated terpene resin, and 30 parts by weight of butadiene polymer, as a photopolymerization initiator An adhesive resin composition comprising 2 parts by mass of monoacylphosphine oxide was produced.

[Appearance evaluation using interferometer]
First, in a state where polyethylene terephthalate films (release films) are laminated on the front and back surfaces of the pressure-sensitive adhesive sheets 1 to 3 as a primary cured sheet, the surface is used using a laser interferometer (“F601 linear polarization type” manufactured by Fujinon Corporation). The state was observed, and the obtained interference fringe image (interference fringe) was analyzed through a high-pass filter (20 mm) for 40 mm × 40 mm in the adhesive sheet surface using interference fringe analysis software (“A1” manufactured by Fujinon Co., Ltd.). . The in-plane average roughness Ra was determined from the three-dimensional shape of 40 mm × 40 mm obtained by the analysis and defined as (X).

Next, one of the release films of the adhesive sheets 1 to 3 is peeled off from soda lime glass (60 mm × 90 mm × thickness 0.5 mm) as a model of the structural member for the image display device, and the exposed adhesive surface is used as a hand roller. Stuck.
Next, the remaining release film is peeled off, and soda lime glass (60 mm × 90 mm × thickness 0.5 mm) as a model of a component for an image display device is applied to the exposed adhesive surface under reduced pressure (absolute pressure 5 kPa). After press bonding, autoclave treatment (60 ° C., 0.2 MPa for 20 minutes) was applied and finish-bonded to prepare a laminate for evaluation.

For the adhesive resin composition of Comparative Example 2, the adhesive resin was applied in a frame formed by sticking a silicone rubber having a width of 3 mm and a thickness of 150 μm on the periphery of one soda lime glass in a frame shape. Soda lime glass was roll-bonded. A high pressure mercury lamp was used to irradiate the adhesive resin with ultraviolet rays so that the integrated light quantity at a wavelength of 365 nm was 2000 mJ / cm ² to cure the adhesive resin, and a laminate for evaluation after secondary curing was produced.

  The laminated body for evaluation was observed using a laser interferometer (“F601 linear polarization type” manufactured by Fujinon Co., Ltd.), and the evaluation was performed using a laser interferometer (“F601 linear polarization type” manufactured by Fujinon Co., Ltd.). The surface state of the laminate is observed, and the obtained interference fringe image (interference fringe) is subjected to interference pattern analysis software (“A1” manufactured by FUJINON Co., Ltd.) with a high-pass filter (20 mm) for 40 mm × 40 mm in the laminate surface. Analyzed through. The in-plane average roughness Ra was determined from the three-dimensional shape of 40 mm × 40 mm obtained by analysis, and was defined as (Y).

[Stress relaxation]
About the adhesive sheets 1 to 3 produced in the examples and comparative examples, the maximum torque (Tq ₀ ) immediately after applying 5% shear strain and the torque after 5 seconds using a rheometer “MARS” manufactured by Eiko Seiki Co., Ltd. (Tq ₅ ) was measured, and the stress relaxation rate (%) was determined by the following equation.
Stress relaxation rate (%) = 100 × (1−T ₅ / T ₀ )

[Retention force]
About the pressure-sensitive adhesive sheets 1 to 3 produced in Examples and Comparative Examples, the pressure-sensitive adhesive material was irradiated with ultraviolet rays with a high-pressure mercury lamp through a release film so that 365 nm ultraviolet rays reached 2000 mJ. An adhesive sheet was prepared.

The pressure-sensitive adhesive sheet was cut into 50 mm × 100 mm, and then the peeled film on one side was peeled off. The pressure-sensitive adhesive sheet was attached with a hand roller so that one side of the pressure-sensitive adhesive sheet overlapped with the PET film for backing (thickness: 38 μm). X A test piece was cut into a strip having a length of 100 mm.
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 60 ° C., a 4.9N weight was attached to the test piece in the vertical direction and left standing for 60 minutes, and then the SUS and the test piece were attached to each other. The length (mm) of the misalignment downward, that is, the misalignment was measured.

[Loss tangent Tan δ]
The pressure-sensitive adhesive sheets 1 to 3 prepared in Examples 1 and 2 and Comparative Example 1 and the pressure-sensitive adhesive sheets 1 to 3 corresponding to the post-secondary curing prepared by holding force measurement were each laminated to approximately 1.2 mm. The thickness was adjusted and the dynamic viscoelasticity was measured by a shearing method using a rheometer “MARS” manufactured by Eihiro Seiki Co., Ltd. under the following conditions.
・ Jig: Φ20mm parallel plate ・ Frequency: 1Hz
・ Temperature: 0 to 100 ° C. (measured at a heating rate of 3 ° C./min)
・ Strain angle: 0.1%

  In the appearance evaluation using the above interferometer, when the state after being bonded to soda lime glass as a model of the structural member for the image display device is observed, foaming is not confirmed for Examples 1 and 2, and There was no occurrence of uneven unevenness such as streaks or spots on the glass surface.

From the results of such examples and comparative examples and the test results conducted by the inventors so far, the uneven shape of the transparent double-sided PSA sheet is controlled within a predetermined range before and after being bonded to the constituent member for the image display device. More specifically, the above (X) is 30 nm to 300 nm, (Y) is 0 nm to 130 nm, and (X)-(Y) is 30 nm or more. It was found that the appearance defect of can be improved. And for that purpose, when bonded to the structural member for an image display device, the transparent double-sided pressure-sensitive adhesive sheet surface follows the surface state of the structural member and is flattened in a state before being bonded to the structural member. It is thought that it is preferable to give the adhesive sheet flexibility.
Furthermore, in order not to impair the foaming resistance after pasting to the structural member, it has been found effective to cure the transparent double-sided PSA sheet after pasting.

Claims (2)

An image display device manufacturing method comprising at least two image display device component members facing each other, wherein one image display device component member is an image display panel,
The other constituent member for the image display device is either a touch panel, a protective panel having a configuration in which a frame-shaped concealed portion printing unit is formed at the peripheral portion, or a surface protective panel in which a touch panel function is integrated,
A primary cured product obtained by curing the pressure-sensitive adhesive composition, that is, an acrylic monomer as a constituent of a (meth) acrylic acid ester-based (co) polymer or a (meth) acrylic acid ester-based (co) polymer; A photocurable pressure-sensitive adhesive composition containing a photopolymerization initiator, or an acrylic monomer as a constituent of a (meth) acrylic acid ester (co) polymer or a (meth) acrylic acid ester (co) polymer; A primary cured product obtained by curing a thermosetting pressure-sensitive adhesive composition containing a thermal crosslinking agent is filled between two component members for an image display device, and two component members for an image display device are bonded. And secondarily curing the primary cured product with heat or ultraviolet rays after the bonding ,
Before SL primary cured product has the properties of the following (4) and (5),
The secondary cured product obtained by the secondary curing has the following (6) .
(4) ··· Stress relaxation rate after 10 seconds when 10% strain is applied is 60% or more
(5). Loss tangent tan δ at a frequency of 1 Hz and a temperature range of 30 ° C. to 100 ° C. is 0.64 or more.
(6). Loss tangent tan δ at a frequency of 1 Hz and a temperature range of 30 ° C. to 100 ° C. is 0.6 or less. The method for manufacturing an image display device according to claim 1, wherein the photopolymerization initiator is a hydrogen abstraction type.