JP7180714B2 - Adhesive sheet, laminate sheet, flexible image display device member, and flexible image display device - Google Patents

Description

The present invention uses an adhesive sheet or adhesive layer, a flexible image display device member, and the adhesive sheet or adhesive layer that can be suitably used for an image display device having a curved surface, a bendable flexible image display device, or the like. The present invention relates to a laminated sheet and a flexible image display device using the laminated sheet.

In recent years, curved image display devices and bendable flexible image display devices using organic light emitting diodes (OLED) and quantum dots (QD) have been developed and are being widely commercialized.
Such a display device has a laminated structure in which multiple sheet members such as a cover lens, a circularly polarizing plate, a touch film sensor, and a light-emitting element are bonded together with a transparent adhesive sheet. When applied, it can be regarded as a laminated sheet in which the member sheet and the adhesive sheet are laminated.

As for the foldable flexible image display device, various problems arise due to interlayer stress when the device is folded. For example, there is a case where the layers are separated when folded (delamination, a phenomenon in which the layers are separated is called "delamination"), and there is a demand for a laminated sheet that does not separate even when folded.
In addition, there is a demand for a laminated sheet that quickly restores a flat state when the screen is unfolded from a folded state.
Furthermore, as the folding operation is repeated, stress is applied to the member sheet, which is the adherend of the pressure-sensitive adhesive sheet, which may cause cracks and eventually breakage. It is also required to be a laminated sheet.

Regarding the foldable flexible image display device, for example, in Patent Document 1, by setting the product value of the creep compliance fluctuation value and the relaxation elastic modulus fluctuation value to a suitable range, it can be applied to a repeatedly bending device and can be bent for a long period of time. A pressure-sensitive adhesive for a repeatedly bending device, which exhibits high resilience such as suppressing deformation of the pressure-sensitive adhesive layer after being released from the bending state when placed in a state and mitigating the effects of being placed in the bending state; and Adhesive sheets and flex laminate members and repeat flex devices are disclosed.

JP 2019-123826 A

However, even if the product of the creep compliance fluctuation value and the relaxation elastic modulus fluctuation value of the adhesive sheet is controlled within a suitable range at room temperature as disclosed in Patent Document 1, when the folding operation is performed at a high temperature, bending occurs. If the effect of being placed in a state remains and the resilience is insufficient, or if the member sheet is repeatedly folded at a low temperature, stress will be applied to the member sheet, which is the adherend of the adhesive sheet. Problems such as cracking may occur.

In particular, devices containing adhesive sheets are expected to be used under high temperatures due to heat generated by the devices, or under high and low temperatures depending on the environment such as region and season. There is a demand for a pressure-sensitive adhesive sheet that expresses strength and durability.

Therefore, according to the present invention, when a laminated sheet having a configuration in which a member sheet and an adhesive sheet are laminated is folded in a high-temperature environment, it is possible to improve the resilience when the sheet is unfolded from the folded state. An adhesive sheet or an adhesive layer, a laminated sheet using these, a flexible image display device member, and a flexible image display device are provided.

The present invention proposes a pressure-sensitive adhesive sheet that satisfies the following requirements (1) and (2).
(1) The storage shear modulus at 60°C (G' (60°C)) obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 0.005 MPa or more and less than 0.20 MPa, and at 60°C Loss tangent (tan δ (60° C.)) is less than 0.60.
(2) The creep compliance value measured when a stress of 3,000 Pa is applied is the minimum creep compliance J(t)min (MPa ^-1 ), and 3757 seconds after the minimum creep compliance J(t)min is measured. A stress of 3,000 Pa continues to be applied until the end of the stress, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J(t)max (MPa ⁻¹ ), the minimum creep compliance J(t)min and the maximum creep compliance J(t)max is less than 1.0.

The present invention further proposes a laminated sheet comprising a member sheet on at least one side of the pressure-sensitive adhesive sheet. At this time, it is preferable that (3) the member sheet has a tensile strength of 10 MPa to 900 MPa at 25° C. measured according to ASTM D882.

The present invention also provides a laminated sheet comprising a member sheet on at least one side of an adhesive layer, wherein the adhesive layer satisfies the requirements of (1) and (2) below, and the member sheet satisfies (3) below. We propose a laminated sheet that satisfies the requirements.
(1) The storage shear modulus at 60°C (G' (60°C)) obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 0.005 MPa or more and less than 0.20 MPa, and at 60°C Loss tangent (tan δ (60° C.)) is less than 0.60.
(2) The creep compliance value measured when a stress of 3,000 Pa is applied is defined as the minimum creep compliance J(t)min (MPa-1), and 3757 seconds after the minimum creep compliance J(t)min is measured. When a stress of 3,000 Pa is continuously applied until later, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J (t) max (MPa-1), the minimum creep compliance J (t) min and the maximum creep compliance J(t)max is less than 1.0.
(3) Tensile strength at 25° C. measured according to ASTM D882 is 10 MPa to 900 MPa.

The present invention also proposes a flexible image display device comprising the laminated sheet.

The adhesive sheet or adhesive layer proposed by the present invention has a creep compliance variation value ΔlogJ(t) of less than 1.0, and by adjusting the storage elastic modulus and loss tangent at 60 ° C. to specific ranges, Good resilience can be shown even in a static bending test at high temperature, which is a more severe condition than the above.

Next, the present invention will be described based on embodiments. However, the present invention is not limited to the embodiments described below.

<<This adhesive sheet>>
A pressure-sensitive adhesive sheet according to an embodiment of the present invention (hereinafter sometimes referred to as "the present pressure-sensitive adhesive sheet") satisfies the following requirements (1) and (2).
(1) The pressure-sensitive adhesive sheet has a storage shear modulus at 60°C (G' (60°C)) of 0.005 MPa or more and less than 0.20 MPa, obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz; Also, the loss tangent at 60°C (tan δ (60°C)) is less than 0.60.
(2) Regarding the adhesive sheet, the creep compliance value measured when a stress of 3,000 Pa is applied is defined as the minimum creep compliance J (t) min (MPa ^-1 ), and the minimum creep compliance J (t) min is measured. A stress of 3,000 Pa continues to be applied for 3,757 seconds after the minimum creep compliance, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J (t) max (MPa ^-1 ). A creep compliance variation value ΔlogJ(t) calculated from the difference between J(t)min and maximum creep compliance J(t)max is less than 1.0.

<<This flexible image display device member>>
A flexible image display device member according to an example of an embodiment of the present invention (hereinafter sometimes referred to as "present flexible image display device member") has a configuration in which two flexible members are bonded together via an adhesive layer. and the adhesive layer (hereinafter sometimes referred to as "this adhesive layer") satisfies the following requirements (1) and (2).
(1) The adhesive layer has a storage shear modulus at 60°C (G' (60°C)) of 0.005 MPa or more and less than 0.20 MPa, obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz; Also, the loss tangent at 60°C (tan δ (60°C)) is less than 0.60.
(2) Regarding the adhesive layer, the creep compliance value measured when a stress of 3,000 Pa is applied is defined as the minimum creep compliance J (t) min (MPa ^-1 ), and the minimum creep compliance J (t) min is measured. A stress of 3,000 Pa continues to be applied for 3,757 seconds after the minimum creep compliance, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J (t) max (MPa ^-1 ). A creep compliance variation value ΔlogJ(t) calculated from the difference between J(t)min and maximum creep compliance J(t)max is less than 1.0.
The form of the adhesive layer is not limited, and the flexible image display device may be formed by laminating a sheet-shaped adhesive product that has been molded into a sheet in advance to the flexible image display device member. The adhesive layer may be directly formed on the member.

<<This adhesive sheet and this adhesive layer>>
First, the present adhesive sheet and the present adhesive layer will be described.

<Storage shear modulus and loss tangent>
The pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer have a storage shear modulus at 60°C (G' (60°C)) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz of 0.005 MPa or more and less than 0.20 MPa. It is preferable that

The 60° C. storage shear modulus (G′(60° C.)) of the present pressure-sensitive adhesive sheet and the present pressure-sensitive layer is preferably less than 0.20 MPa, more preferably 0.18 MPa or less, and more preferably 0.18 MPa or less. It is more preferably 15 MPa or less, and even more preferably 0.12 MPa or less.
On the other hand, the lower limit of the storage shear modulus (G′ (60° C.)) is preferably 0.005 MPa or more from the viewpoint of maintaining the shape.

By setting the storage shear modulus (G′ (60° C.)) within the above range, for example, when the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer is adhered to a member sheet to form a laminated sheet or flexible image display device member, It is possible to reduce the interlaminar stress during bending of the laminated sheet or the flexible image display device member at a temperature of from to high, and to suppress delamination and cracking of the member sheet or the flexible member.

The loss tangent at 60° C. (tan δ (60° C.)) of the present pressure-sensitive adhesive sheet and the present pressure-sensitive layer in shear measurement at a frequency of 1 Hz is preferably less than 0.60, more preferably 0.55 or less, and 0 It is more preferably 0.50 or less. On the other hand, the lower limit of the loss tangent (tan δ (60° C.)) is preferably 0.20 or more from the viewpoint of maintaining adhesive strength.

By setting the loss tangent (tan δ (60 ° C.)) within the above range, the flow of the adhesive sheet or adhesive layer can be suppressed. When the image display device member is formed, it is possible to improve the resilience when the laminated sheet or the flexible image display device member is unfolded from the folded state.
Even if the storage shear modulus (G′ (60° C.)) of the present pressure-sensitive adhesive sheet and the present pressure-sensitive layer is less than 0.20 MPa, if the loss tangent (tan δ (60° C.)) is large, the present pressure-sensitive adhesive sheet and the This pressure-sensitive adhesive layer undergoes creep deformation during high-temperature bending.
However, by setting the loss tangent (tan δ (60° C.)) to less than 0.60, it is possible to suppress creep deformation and to improve the restorability when unfolded from the folded state.

Furthermore, the present pressure-sensitive adhesive sheet and the present pressure-sensitive adhesive layer have a -20°C storage shear modulus (G' (-20°C)) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, which is 1.0 MPa or less. is preferred, 0.70 MPa or less is more preferred, and 0.60 MPa or less is even more preferred. On the other hand, the lower limit of the storage shear modulus (G′ (−20° C.)) is preferably 0.05 MPa or more from the viewpoint of shape retention at high temperatures.

By setting the storage shear modulus (G′ (−20° C.)) of the present pressure-sensitive adhesive sheet and the present pressure-sensitive adhesive layer to 1.0 MPa or less, the interlaminar stress during bending at low temperatures can be reduced, and the member sheet or flexible Delamination and cracking of members can be suppressed.
In general, the adhesive sheet and adhesive layer have a glass transition temperature (Tg) between low temperature and room temperature, so the storage shear elastic modulus (G' (-20 ° C.)) is the storage shear elastic modulus (G' (60 ° C.) ).
However, if the storage shear modulus (G' (-20°C)) is 1.0 MPa or less, the member sheet or the flexible member can be prevented from cracking even when the bending operation is performed at a low temperature.

<Maximum point of loss tangent (tan δ) and glass transition temperature (Tg)>
The maximum point of the loss tangent obtained by dynamic viscoelasticity measurement in shear mode at a frequency of 1 Hz for the pressure-sensitive adhesive sheet and pressure-sensitive layer is preferably -25° C. or lower.
The maximum point of the loss tangent (tan δ) can be interpreted as the glass transition temperature (Tg). −20° C.)) can be easily adjusted to 1.0 MPa or less.

The “glass transition temperature” is the temperature at which the peak of the principal dispersion of the loss tangent (tan δ) appears. Therefore, when only one maximum point of the loss tangent (tan δ) obtained by dynamic viscoelasticity measurement is observed in a shear mode with a frequency of 1 Hz, in other words, when the tan δ curve exhibits a unimodal shape, the glass transition temperature ( Tg) can be assumed to be unity.

The “maximum point” of the loss tangent (tan δ) is the peak value in the tan δ curve, that is, the maximum value in a predetermined range or the entire range among the inflection points that change from positive (+) to negative (-) when differentiated. is the meaning of a point with a value of .

Elastic modulus (storage modulus) G', viscous modulus (loss modulus) G" and tan ? = G"/G' at various temperatures can be measured using a strain rheometer.

The storage shear elastic modulus (G') and loss tangent (tan δ) are determined by the type of resin (for example, an acrylic (co)polymer and a curable compound described later) that constitutes the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer and its mass average molecular weight. and the like, and further by adjusting the gel fraction of the pressure-sensitive adhesive sheet, etc., it is possible to adjust the above range. However, it is not limited to this method.

<Creep compliance>
Regarding this adhesive sheet and this adhesive layer, the creep compliance value measured when a stress of 3,000 Pa is applied is defined as the minimum creep compliance J (t) min (MPa ^-1 ), and the minimum creep compliance J (t) min is When a stress of 3,000 Pa is continuously applied for 3757 seconds after the measurement, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J (t) max (MPa ^-1 ), the minimum creep The creep compliance variation value ΔlogJ(t) calculated from the difference between the compliance J(t)min and the maximum creep compliance J(t)max is preferably less than 1.0.

In order to reduce the creep compliance fluctuation value ΔlogJ(t), the number of cross-linking points is increased in the cross-linking structure of the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer, or a cross-linking structure having a long chain structure is used. It is preferable to employ a method of increasing the molecular weight to form an entangled molecular chain structure or increasing the gel fraction.

The creep compliance fluctuation value ΔlogJ(t) can also be adjusted by adjusting the type of polymer forming the present pressure-sensitive adhesive sheet and the present pressure-sensitive adhesive layer and the weight average molecular weight thereof.
However, the method of adjusting the creep compliance variation value ΔlogJ(t) is not limited to these methods.

In recent years, due to the demand for weight reduction of image display devices, the member sheets to be used tend to be thinner, and it is important to reduce the stress on the member sheets.
Here, the member sheet included in the image display device and adhered to the present adhesive sheet and the present adhesive layer mainly includes, for example, cycloolefin resin, triacetylcellulose resin, polymethyl methacrylate resin, epoxy resin, polyimide resin, and the like. The sheet used as a component can be mentioned.
Among them, the tensile strength at 25° C. of the sheet mainly composed of cyclic olefin resin is as low as 40 MPa to 60 MPa at a thickness of 100 μm, and in the case of laminated sheets using member sheets with such low tensile strength, cracks occur when folded. It was difficult to eliminate the cracks within the range of the conventional technology.

In addition, the above-mentioned "main component" refers to a component that occupies the largest mass ratio among the resin components that constitute the member sheet, and specifically, the member sheet or the resin composition that forms the member sheet. 50% by mass or more, preferably 55% by mass or more, and more preferably 60% by mass or more.

However, regarding the present pressure-sensitive adhesive sheet and the present pressure-sensitive adhesive layer, the creep compliance value measured when a stress of 3,000 Pa is applied is defined as the minimum creep compliance J (t) min (MPa ^-1 ), and the minimum creep compliance J (t) A stress of 3,000 Pa continues to be applied until 3757 seconds after min is measured, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J(t)max (MPa ^-1 ). If the creep compliance variation value ΔlogJ(t) calculated from the difference between the minimum creep compliance J(t)min and the maximum creep compliance J(t)max is less than 1.0, the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer are Even when the adhesive sheet is attached to a member sheet and folded at a high temperature, the adhesive sheet and the present adhesive layer can be provided with excellent resilience that does not remain affected by being placed in a bent state.
From this point of view, the creep compliance variation value ΔlogJ(t) is preferably less than 1.0, more preferably 0.9 or less, more preferably 0.8 or less.

<Gel fraction>
The gel fraction of the present adhesive sheet and the present adhesive layer is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more.
When the gel fraction of the present adhesive sheet and the present adhesive layer is 70% or more, the shape can be sufficiently retained.

<Total light transmittance, haze>
The total light transmittance of the present adhesive sheet and the present adhesive layer is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more.

The haze of the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer is preferably 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.5% or less.
Since the present pressure-sensitive adhesive sheet and the present pressure-sensitive adhesive layer have a haze of 1.0% or less, they can be used for image display devices.
In order to keep the haze of the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer within the above range, it is preferable that the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer do not contain particles such as organic particles.

<Thickness>
The thickness of the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer is not particularly limited. can contribute to
Therefore, the thickness of the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer is preferably 5 µm or more, more preferably 8 µm or more, and particularly preferably 10 µm or more.
On the other hand, the upper limit is preferably 1000 μm or less, more preferably 500 μm or less, particularly 250 μm or less.

<Acrylic (co)polymer>
The pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer are preferably formed by curing a resin composition containing an acrylic (co)polymer having (meth)acrylate as a monomer component and a curable composition described later.
By including an acrylic (co)polymer as a pre-curing component, the adhesive strength and cohesive strength of the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer can be enhanced.

Further, the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer are formed by curing a resin composition containing a mixture of monomer components constituting the acrylic (co)polymer or a partial polymer thereof, and a curable resin described later. can also

Examples of the (meth)acrylate include monofunctional (meth)acrylate (a1) having one (meth)acryloyl group and polyfunctional (meth)acrylate (a2) having two or more (meth)acryloyl groups. Among them, the monofunctional (meth)acrylate (a1) is preferred.

In the present invention, "(meth)acryl" means acryl and methacryl, "(meth)acryloyl" means acryloyl and methacryloyl, and "(meth)acrylate" means acrylate and methacrylate, respectively. .
Further, the term "(co)polymer" is meant to include both homopolymers and copolymers.

The monomer components forming the acrylic (co)polymer are described in detail below.

(Monofunctional (meth)acrylate (a1))
In addition to alkyl (meth)acrylates, monofunctional acrylates that are constituent monomers of acrylic (co)polymers include carboxyl group-containing (meth)acrylates, hydroxyl group-containing (meth)acrylates, epoxy group-containing (meth)acrylates, amino (Meth)acrylates having functional groups such as group-containing (meth)acrylates and amide group-containing (meth)acrylates can be mentioned.

In the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer, alkyl (meth)acrylate is used as a monofunctional acrylate, which is a constituent monomer of the acrylic (co)polymer, from the viewpoint of adjusting the glass transition temperature of the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer. preferably included.

Either linear or branched alkyl (meth)acrylate can be employed as the alkyl (meth)acrylate. Examples include n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate Acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl ( meth)acrylate, t-butylcyclohexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, isobornyl (meth) acrylate, 3,5,5-trimethylcyclohexane (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl ( meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and the like. These may be used singly or in combination of two or more.

Among these alkyl (meth)acrylates, from the viewpoint of adjusting the viscoelasticity of the pressure-sensitive adhesive sheet within the above range, the monofunctional (meth)acrylate (a1) has an alkyl group having 4 to 20 carbon atoms. An acrylate is preferred, and an alkyl (meth)acrylate having an alkyl group of 4 to 18 carbon atoms is more preferred.
When the number of alkyl carbon atoms in the monofunctional (meth)acrylate (a1) is within the range of 4 to 20, it becomes easy to adjust the viscoelasticity of the pressure-sensitive adhesive sheet within the above range. Alkyl (meth)acrylates having a branched alkyl group are particularly preferred because they lack crystallinity and have a low glass transition temperature even when they have a large number of carbon atoms.

(Polyfunctional (meth)acrylate (a2))
As a constituent monomer of the acrylic (co)polymer, in addition to the monofunctional (meth)acrylate (a1), a polyfunctional (meth)acrylate having a plurality of (meth)acrylate groups may be contained.

The polyfunctional (meth)acrylate (a2) is not particularly limited, but the storage shear elastic modulus (G' (60 ° C.)) of the present pressure-sensitive adhesive sheet and the present pressure-sensitive adhesive layer at 60 ° C. is less than 0.20 MPa. Polyfunctional urethane (meth)acrylate is preferred from the viewpoint of ease of adjustment.

In order to adjust the creep compliance variation value ΔlogJ(t) to less than 1.0, it is necessary to form a crosslinked network.
By selecting polyfunctional urethane (meth)acrylate as a monomer component in addition to the alkyl (meth)acrylate described above, it becomes easier to form an appropriate network.
Therefore, it is preferable to use a urethane acrylic (co)polymer containing a polyfunctional urethane (meth)acrylate as a monomer component as the acrylic (co)polymer.
In particular, the polyfunctional (meth)acrylate (a2) has 2 to 3 (meth) Bifunctional to trifunctional urethane (meth)acrylates having an acrylate group are more preferred, and bifunctional urethane (meth)acrylates are particularly preferred.

The type of polyfunctional urethane (meth)acrylate is not particularly limited, but preferably a polyol compound having two or more hydroxyl groups in the molecule, a compound having two or more isocyanate groups in the molecule, and at least a molecule It is preferably a polyfunctional urethane (meth)acrylate consisting of a reaction product with a (meth)acrylate containing one or more hydroxyl groups therein.

Examples of polyol compounds having two or more hydroxyl groups in the molecule include polyether polyols, polyester polyols, caprolactone diols, bisphenol polyols, polyisoprene polyols, hydrogenated polyisoprene polyols, polybutadiene polyols, and hydrogenated polybutadiene polyols. , castor oil polyol, polycarbonate diol, and the like.
Among them, polycarbonate diol, polybutadiene polyol, and hydrogenated polybutadiene polyol are preferred because of their excellent transparency and durability, and particularly preferred are polycarbonate diol and hydrogenated polybutadiene from the viewpoint of not causing cloudiness even under high-temperature and high-humidity conditions. Mention may be made of polyols. These may be used singly or in combination.

Compounds having two or more isocyanate groups in the molecule include, for example, aromatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates, among which flexible cured products can be obtained. From the point of view, aliphatic polyisocyanates and alicyclic polyisocyanates are preferred. These may be used singly or in combination.

Here, examples of the aromatic polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate and tetramethylxylylene diisocyanate. , diphenylmethane diisocyanate, naphthalene-1,5-diisocyanate, triphenylmethane triisocyanate, and the like.

Examples of the alicyclic polyisocyanate include isophorone diisocyanate, bis(4-isocyanatocyclohexyl)methane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, norbornane diisocyanate. , bicycloheptane triisocyanate, and the like.

Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate, 1,3,6-hexamethylene triisocyanate and 1,6,11-undecatriisocyanate.

Among these, diisocyanates such as isophorone diisocyanate and hexamethylene diisocyanate are preferred because they give a cured product that does not cause white turbidity in the adhesive layer when placed under high temperature and high humidity conditions.

The (meth)acrylates containing at least one hydroxyl group in the molecule are, for example, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, polyethylene glycol. and mono(meth)acrylates of dihydric alcohols such as trimethylolethane, trimethylolpropane, and mono(meth)acrylates or di(meth)acrylates of trihydric alcohols such as glycerin. These may be used singly or in combination.

A method for synthesizing the polyfunctional urethane (meth)acrylate is not particularly limited, and a known method can be used. For example, a polyol compound having two or more hydroxyl groups in the molecule and an isocyanate compound having two or more isocyanate groups in the molecule, preferably in a molar ratio (polyol compound: isocyanate compound) of 3:1 to 1: 3, more preferably at a ratio of 2:1 to 1:2, by reacting in a diluent (eg, methyl ethyl ketone, methoxyphenol, etc.) to obtain a urethane prepolymer. Polyfunctional urethane is obtained by reacting the isocyanate groups remaining in the obtained urethane prepolymer with a sufficient amount of (meth)acrylate containing at least one hydroxyl group in the molecule to react therewith. A (meth)acrylate is obtained.

Examples of catalysts used at this time include lead oleate, tetrabutyltin, antimony trichloride, triphenylaluminum, trioctylaluminum, dibutyltin dilaurate, copper naphthenate, zinc naphthenate, zinc octylate, zinc octoate, and naphthenic acid. Zirconium, cobalt naphthenate, tetra-n-butyl-1,3-diacetyloxydistannoxane, triethylamine, 1,4-diaza[2,2,2]bicyclooctane, N-ethylmorpholine and the like.

The above acrylic (co)polymer is an acrylic (co)polymer containing urethane (meth)acrylate as a monomer component, and among them, an acrylic (co)polymer containing polyfunctional urethane (meth)acrylate as a monomer component. ) polymers are one preferred example.

(Other monomer components)
The pressure-sensitive adhesive sheet may contain (meth)acrylate components other than those described above as monomer components of the acrylic (co)polymer.
For example, it is preferable to contain a monomer having a polar functional group in order to improve adhesion to the member sheet or flexible member.

Examples of polar functional groups possessed by monomers include hydroxyl groups, thiol groups, carboxyl groups, carbonyl groups, ester groups, amino groups, amide groups, glycidyl groups, and silanol groups. Among them, a hydroxyl group, an amino group, an amide group, a carbonyl group, an ester group, a glycidyl group, and a silanol group are preferable as a polar functional group that improves adhesion to members and hardly corrodes peripheral members. Among them, a hydroxyl group, an amino group, an amide group, and a glycidyl group are particularly preferable as those having a high effect in improving adhesion.

Monomers containing such polar functional groups include, for example, 4-hydroxybutyl acrylate glycidyl ether, 4-hydroxybutyl acrylate, diethylacrylamide, hydroxyethylacrylamide, acryloylmorpholine, 4-t-butylcyclohexyl acrylate, and the like. can be done. Among them, 4-hydroxybutyl acrylate, diethylacrylamide, hydroxyethylacrylamide and acryloylmorpholine are particularly preferred from the viewpoint of cost and adhesion.
In addition to the above monofunctional monomers, a bifunctional or higher acrylate may also be contained.

<Curable compound>
A curable compound is a compound that has the property of being cured by heat or light irradiation. In the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer, the curable compound preferably forms a crosslinked structure with the acrylic (co)polymer.
In addition, "forming a crosslinked structure" means not only the case where polymer chains are crosslinked via chemical bonds, but also hydrogen bonding within or between polymer chains, electrostatic interaction, vandel It also includes (pseudo) cross-linking by non-covalent bonding due to interaction such as Waals force.

The curable compound is preferably a compound having an ethylenically unsaturated group in the molecule from the viewpoint of curing to form a crosslinked structure with the acrylic (co)polymer.
In particular, the curable compound is preferably a (meth)acrylate, more preferably a monofunctional (meth)acrylate. For example, urethane (meth)acrylate can be mentioned.
In addition, monofunctional (meth)acrylate means the (meth)acrylate which has one (meth)acryloyl group here.

The curable compound preferably has a glass transition temperature of −40° C. or lower, more preferably −45° C. or lower when homopolymerized.
When the curable compound has a glass transition temperature within this range, the glass transition temperature of the acrylic (co)polymer can be set relatively high.
Therefore, the present pressure-sensitive adhesive sheet and the present pressure-sensitive adhesive layer can exhibit a particularly excellent effect of ensuring adhesiveness, imparting flexibility to withstand buckling during bending deformation, and being able to have bending resistance. can.

Among them, the curable compound is preferably a (meth)acrylate having a glycol skeleton. A (meth)acrylate having a glycol skeleton tends to lower the glass transition temperature after curing, and easily imparts flexibility and the like by adjusting the molecular weight of the skeleton component.

Examples of the glycol skeleton include ethylene glycol skeleton, propylene glycol skeleton, diethylene glycol skeleton, butanediol skeleton, hexanediol skeleton, 1,4-cyclohexanedimethanol skeleton, glycolic acid skeleton, and polyglycol skeleton. Among these, a polyethylene glycol skeleton and/or a polypropylene glycol skeleton are more preferable.

Furthermore, the curable compound is preferably a (meth)acrylate having a mass average molecular weight (MW) of 5,000 or more, more preferably 7,000 or more, and still more preferably 9,000 or more.

If the curable compound is such a (meth)acrylate, it can be a curable compound with a low glass transition temperature due to the long-bonded skeleton of the linear structure, and can impart good flexibility.
Urethane (meth)acrylates having a glycol skeleton with a mass average molecular weight of 5,000 or more, more preferably 7,000 or more, and even more preferably 9,000 or more are particularly preferred. By using such a urethane (meth)acrylate, it is possible to impart good wettability to an adherend.

The curable compound is preferably contained in a proportion of more than 15 parts by mass and less than 75 parts by mass with respect to 100 parts by mass of the (meth)acrylic (co)polymer. By containing the photocurable compound in such a ratio, it is possible to achieve both adhesive strength and bending resistance in a well-balanced manner.
From this point of view, the curable compound is preferably contained in a proportion of more than 15 parts by mass and less than 75 parts by mass with respect to 100 parts by mass of the (meth)acrylic (co)polymer. It is preferably contained in a ratio of 30 parts by mass or more or 65 parts by mass or less.

Two or more curable compounds may be used in combination.

<Radical initiator>
As the radical initiator used for curing the curable compound to obtain the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer, for example, light such as ultraviolet rays and visible light, more specifically, light having a wavelength of 200 nm to 780 nm can be irradiated. Preferred examples include compounds that generate more active radical species.

As the radical initiator, both a cleavage type initiator and a hydrogen abstraction type initiator can be used. However, when a hydrogen abstraction type initiator is used, a hydrogen abstraction reaction also occurs from the acrylic (co)polymer, and not only the curable compound but also the acrylic (co)polymer is incorporated into the crosslinked structure, and the crosslink point It is preferable because it is possible to form a crosslinked structure with a large amount.

In addition, even after being used for a photocuring reaction once, the hydrogen abstraction type initiator can repeatedly function as an active species by irradiating with light again. When a sheet is used as the type, it is preferable in that it can serve as a starting point for photoreaction during post-curing.

Examples of the hydrogen abstraction type initiator include benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3′-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyl Oxybenzophenone, methyl 2-benzoylbenzoate, methyl benzoylformate, bis(2-phenyl-2-oxoacetic acid)oxybisethylene, 4-(1,3-acryloyl-1,4,7,10,13-pentaoxo tridecyl)benzophenone, thioxanthone, 2-chlorothioxanthone, 3-methylthioxanthone, 2,4-dimethylthioxanthone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, or derivatives thereof etc. can be mentioned.

The lower limit of the content of the radical initiator is preferably 0.01 parts by mass or more, preferably 0.03 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic (co)polymer. More preferably, it is at least 0.05 parts by mass.
The upper limit is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and 2 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic (co)polymer. is most preferred.

<Other ingredients>
The pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer can contain components (also referred to as “other components”) other than the acrylic (co)polymer and the curable compound. Other components are not particularly limited, and the adhesive sheet and the adhesive layer may contain other monomer components and polymer components.

The pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer may contain a rust inhibitor as another component.
Triazoles and benzotriazoles are particularly preferable as rust preventives, and can prevent the transparent electrodes on the touch panel from corroding.
A preferable addition amount is preferably 0.01 to 5% by mass, more preferably 0.1% by mass or more or 3% by mass or less, based on the total pressure-sensitive adhesive sheet and pressure-sensitive adhesive layer.

The pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer may contain a silane coupling agent as another component.
As the types of silane coupling agents, those containing a glycidyl group, or those containing a (meth)acrylic group or a vinyl group are particularly preferred.
By containing these, when forming a laminate using the adhesive sheet and the present adhesive layer, the adhesiveness to the member sheet or flexible member is improved, and the foaming phenomenon in a moist and hot environment can be suppressed.

The content of the silane coupling agent is preferably 0.01 to 3% by mass with respect to the entire pressure-sensitive adhesive sheet and pressure-sensitive adhesive layer, and more preferably 0.1% by mass or more or 1% by mass or less. More preferred. Depending on the adherend, the effect of the silane coupling agent can be exhibited even at a content of 0.01% by mass.
On the other hand, by adjusting the content to 3% by mass or less, foaming due to dealcoholization can be suppressed.

The pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer contain, as other components, curing accelerators, fillers, coupling agents, ultraviolet absorbers, ultraviolet stabilizers, antioxidants, stabilizers, pigments, or some combination thereof. may
The amounts of these additives are typically preferably selected so as not to adversely affect the curing of the adhesive sheet and adhesive layer or adversely affect the physical properties of the adhesive sheet and adhesive layer.

<Preferred uses of the adhesive sheet>
The present pressure-sensitive adhesive sheet is preferably used for laminating a member constituting a display member (also referred to as a "display member"), especially a flexible member for a display used for producing a display, and is used for producing a flexible display. It is particularly preferable to use it as an adhesive part for a flexible display used for.
As for the flexible member, the same one as described later can be used.

<Constituent elements of this flexible image display device member>
Next, among the constituent elements of the present flexible image display device member, elements other than the present adhesive layer will be described.

(flexible member)
Flexible members constituting the present flexible image display device members include, for example, flexible displays such as organic electroluminescence (EL) displays, cover lenses (cover films), polarizing plates, polarizers, retardation films, barrier films, and viewing angle compensation. Examples include flexible members for displays such as films, brightness enhancement films, contrast enhancement films, diffusion films, transflective films, electrode films, transparent conductive films, metal mesh films, and touch sensor films. Any one of these may be used, or two of the two may be used in combination. Examples include a combination of a flexible display and other flexible members, and a combination of a cover lens and other flexible members.

The flexible member means a bendable member, especially a repeatedly bendable member. In particular, a member that can be fixed in a curved shape with a bending radius of 25 mm or more, particularly a member that can withstand repeated bending with a bending radius of less than 25 mm, more preferably less than 3 mm, is preferred.

In the above configuration, the main component of the flexible member may be, for example, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, epoxy resin, polyimide resin, or the like. , or two or more resins.
Here, the "main component" refers to a component that accounts for the largest mass ratio among the components that constitute the flexible member, and specifically accounts for 50% by mass or more of the resin composition that forms the flexible member. 55% by mass or more, more preferably 60% by mass or more.
Also, the flexible member may be made of thin glass.

In the above-described configuration, one of the two flexible members, that is, the first flexible member, preferably has a tensile strength of 10 MPa to 900 MPa at 25° C. measured according to ASTM D882, especially 15 MPa or more. Alternatively, it is 800 MPa or less, more preferably 20 MPa or more or 700 MPa or less.

In addition, the other flexible member, that is, the second member sheet, preferably has a tensile strength of 10 MPa to 900 MPa at 25° C. measured according to ASTM D882, especially 15 MPa or more or 800 MPa or less, especially 20 MPa or more. Alternatively, it is more preferably 700 MPa or less.

Examples of flexible members having high tensile strength include polyimide films and polyester films, and the tensile strength of these films is generally 900 MPa or less.
On the other hand, flexible member sheets having a slightly low tensile strength include triacetyl cellulose (TAC) films, cyclic olefin polymer (COP) films, etc., and these have a tensile strength of 10 MPa or more.
Even if the present flexible image display device member has such a flexible member made of a material having a slightly low tensile strength, problems such as cracking can be suppressed by the action of the present adhesive layer.

<<This laminated sheet>>
A laminated sheet according to an example of the embodiment of the present invention (hereinafter sometimes referred to as "this laminated sheet") includes a member sheet that satisfies the requirements of (3) on at least one side of the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer. Prepare.
(3) Tensile strength at 25° C. measured according to ASTM D882 is 10 MPa to 900 MPa.

The laminate sheet includes a member sheet (hereinafter sometimes referred to as a "first member sheet"), the present adhesive sheet or the present adhesive layer, and an optional member sheet (hereinafter referred to as a "second member sheet"). (a) and (b) are preferably laminated sheets having a configuration in which the above are laminated in this order.
In this case, the second member sheet also preferably satisfies the above requirement (3).
The first member sheet and the second member sheet may be the same or different.

The thickness of this laminated sheet is not particularly limited. For example, when used in an image display device, the laminated sheet is in the form of a sheet. If there is, it can contribute to thinning of the laminate.
Therefore, the thickness of the laminated sheet is preferably 0.01 mm or more, more preferably 0.03 mm or more, particularly 0.05 mm or more.
On the other hand, the upper limit is preferably 1.0 mm or less, more preferably 0.7 mm or less, particularly 0.5 mm or less.

The laminate sheet can be produced by adhering the pressure-sensitive adhesive sheet or the pressure-sensitive adhesive layer to the first member sheet or the second member sheet. However, it is not limited to such a manufacturing method.

<Material sheet>
Depending on the configuration of the flexible image display device and the position of the adhesive sheet or the adhesive layer, the first member sheet and the second member sheet may include a cover lens, a polarizing plate, a retardation film, a barrier film, and a touch sensor. A film, a light emitting element, etc. can be mentioned.

In particular, considering the configuration of image display, the first member sheet preferably has a touch input function. When the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer has the above-described second member sheet, the second member sheet may also have a touch input function.

Main components of the member sheet include, for example, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, epoxy resin and polyimide resin. may be a resin of
Here, the “main component” refers to a component that accounts for the largest mass ratio among the components constituting the member sheet, and specifically, the component sheet or the resin composition forming the member sheet. % by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more.

Also, the member sheet may be a thin film glass. Here, thin-film glass refers to glass having the thickness of the member sheet mentioned above.

Furthermore, with respect to the first member sheet, the tensile strength at 25° C. measured according to ASTM D882 is preferably 10 MPa to 900 MPa, especially 15 MPa or more or 800 MPa or less, especially 20 MPa or more or 700 MPa or less. More preferred.

When the present pressure-sensitive adhesive sheet or the present pressure-sensitive layer has the above-described second member sheet, the second member sheet preferably has a tensile strength of 10 MPa to 900 MPa at 25 ° C. measured according to ASTM D882, Among them, it is more preferably 15 MPa or more or 800 MPa or less, and more preferably 20 MPa or more or 700 MPa or less.

Member sheets having high tensile strength include polyimide films, polyester films, and the like, and their tensile strength is generally 900 MPa or less.
On the other hand, member sheets having a slightly low tensile strength include triacetyl cellulose (TAC) films, cyclic olefin polymer (COP) films, and the like, and these have a tensile strength of 10 MPa or more.
Even if the present laminated sheet has a member sheet made of such a material having a slightly low tensile strength, it is possible to suppress troubles such as cracking due to the action of the adhesive sheet.

<<Method for producing the present pressure-sensitive adhesive sheet and the present laminate sheet>>
Next, a method for producing the present pressure-sensitive adhesive sheet and the present laminated sheet will be described. However, the following description is an example of the method for producing the present pressure-sensitive adhesive sheet and the present laminated sheet, and the present pressure-sensitive adhesive sheet and the present laminated sheet are not limited to those produced by such a production method.

In preparing the pressure-sensitive adhesive sheet, a resin composition for forming the pressure-sensitive adhesive sheet containing an acrylic (co)polymer, a curable compound, a radical initiator, other components, etc. is prepared, and the resin composition is formed into a sheet. The present pressure-sensitive adhesive sheet may be produced by molding into a shape, curing the curable compound by cross-linking or polymerization reaction, and subjecting it to appropriate processing as necessary.

Further, in the preparation of the present adhesive layer, the resin composition for forming the present adhesive layer is prepared in the same manner as described above, the member sheet or the flexible member is coated with the resin composition, and the resin composition is cured to obtain the present adhesive layer. An adhesive layer may be formed.
However, it is not limited to this method.

When preparing the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer-forming resin composition, the raw materials are mixed with a temperature-controllable kneader (e.g., single-screw extruder, twin-screw extruder, planetary mixer, twin-screw mixer, pressure kneader, etc.). ) may be used for kneading.
When mixing various raw materials, various additives such as silane coupling agents and antioxidants may be blended in advance with the resin and then supplied to the kneader, or all the materials may be melted and mixed in advance. Alternatively, a masterbatch in which only the additive is concentrated in the resin in advance may be prepared and supplied.

In order to impart curability to the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer, as described above, the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer-forming resin composition is polymerized, in other words, crosslinked using a radical initiator. preferable.
At this time, the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer-forming resin composition may be applied to the first member sheet to the second member sheet and polymerized, or the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer-forming resin composition may be applied. may be attached by polymerizing.

As a method for forming the present pressure-sensitive adhesive sheet-forming resin composition into a sheet, known methods such as a wet lamination method, a dry lamination method, an extrusion casting method using a T-die, an extrusion lamination method, a calendering method, an inflation method, an injection method, a Molding, injection hardening method, etc. can be employed. Among them, the wet lamination method, the extrusion casting method, and the extrusion lamination method are suitable for producing a sheet.

Further, when the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer-forming resin composition contains a radical initiator, a cured product can be produced by curing by irradiation with heat and/or active energy rays.
In particular, the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer is produced by irradiating heat and/or active energy rays to a molded article, for example, a sheet formed from the present pressure-sensitive adhesive sheet or the present pressure-sensitive adhesive layer-forming resin composition. be able to.
Here, the active energy rays to be irradiated include α rays, β rays, γ rays, ionizing radiation such as neutron rays and electron beams, ultraviolet rays, visible rays, and the like. Ultraviolet rays are preferable from the viewpoint of suppression and reaction control.

Moreover, the irradiation energy, irradiation time, irradiation method, and the like of the active energy ray are not particularly limited as long as the monomer component can be polymerized by activating the radical initiator.
When a hydrogen abstraction initiator is used as the radical initiator, a hydrogen abstraction reaction also occurs from the acrylic (co)polymer, and not only the photocurable compound but also the acrylic (co)polymer is incorporated into the crosslinked structure. A crosslinked structure with many crosslinked points can be formed.
Therefore, the pressure-sensitive adhesive sheet or pressure-sensitive adhesive layer is preferably cured using a hydrogen abstraction initiator.

Moreover, as another embodiment of the method for producing the pressure-sensitive adhesive sheet, the resin composition for forming the pressure-sensitive adhesive sheet described later can be dissolved in an appropriate solvent, and various coating techniques can be used.
When a coating method is used, the pressure-sensitive adhesive sheet can also be obtained by thermal curing in addition to the active energy ray irradiation curing described above. In the case of coating, the thickness of the adhesive sheet can be adjusted by the thickness of the coating and the solid content concentration of the coating liquid.

From the viewpoint of preventing blocking and adhesion of foreign matter, a protective film having a release layer laminated thereon may be provided on at least one side of the pressure-sensitive adhesive sheet or pressure-sensitive adhesive layer.
Also, if necessary, embossing or various irregularities (conical, pyramidal, hemispherical, etc.) processing may be performed. In addition, various surface treatments such as corona treatment, plasma treatment and primer treatment may be performed on the surface for the purpose of improving adhesion to various member sheets.

<<Manufacturing method of the present flexible image display device member>>
The method for producing the present flexible image display device member is not particularly limited. After the resin composition is formed into a sheet, it may be bonded to the flexible member.

<<Image display device>>
By incorporating the lamination sheet, for example, by laminating the lamination sheet to other constituent members of the image display device, a flexible image display device having the lamination sheet can be formed.
A flexible image display device is an image display device that does not leave a trace of bending even if it is repeatedly bent, can quickly recover to the state before bending when the bending is released, and can display images without distortion even when bent. Say.
More specifically, an image composed of a member capable of a fixed curved shape with a bending radius of 25 mm or more, particularly a member capable of withstanding repeated bending action with a bending radius of less than 25 mm, more preferably less than 3 mm. A display device.
In particular, this laminated sheet can prevent delamination and cracking of the laminated sheet even when folded in a high-temperature environment, and has good restorability, so it is possible to manufacture an image display device with excellent flexibility. be.

<<Description of terms, etc.>>
In the present invention, the term "film" includes the "sheet", and the term "sheet" includes the "film".
In addition, the expression "panel" such as an image display panel, a protective panel, etc. includes a plate, a sheet and a film.

In this specification, when described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, "X or more and Y or less" and "preferably larger than X" or "preferably It also includes the meaning of "smaller than Y".
In addition, when described as "X or more" (X is an arbitrary number), it includes the meaning of "preferably greater than X" unless otherwise specified, and is described as "Y or less" (Y is an arbitrary number). If not otherwise specified, it also includes the meaning of "preferably smaller than Y".

The invention is further illustrated by the following examples. However, the present invention is not limited to the examples shown below.

<raw materials>
First, the details of the raw materials of the resin compositions prepared in the examples will be described.

1. Acrylic (co)polymer Acrylic copolymer a; acrylic copolymer consisting of 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, 2-hydroxyethyl acrylate and 4-hydroxy acrylate (mass average molecular weight: about 700,000 )
-Acrylic copolymer b: 600 ppm of 2-methacryloyloxyethyl isocyanate ("Karenzu MOI" manufactured by Showa Denko Co., Ltd.) was added to a copolymer consisting of about 85 mol% of butyl acrylate and about 15 mol% of 2-hydroxyl acrylate. Urethane acrylic copolymer (mass average molecular weight: about 900,000)
・ Acrylic copolymer c: commercially available 2-ethylhexyl acrylic copolymer (mass average molecular weight: about 540,000))
- Acrylic copolymer d: a commercially available 2-ethylhexyl-based acrylic copolymer having an acryloyl group in the side chain

2. Curable compound Urethane acrylate a: propylene glycol skeleton-containing monofunctional urethane acrylate, PEM-X264 (manufactured by AGC), weight average molecular weight: about 10,000, glass transition temperature: -53°C
・Urethane acrylate b: bifunctional urethane acrylate (bifunctional urethane acrylate in which hydroxyethyl acrylate is added to the terminal of polypropylene glycol and hexamethylene diisocyanate polymer, mass average molecular weight: about 8,000)

3. Radical initiator 4-methylbenzophenone (hydrogen abstraction initiator)
4. Silane coupling agent KBM403 (manufactured by Shin-Etsu Silicone Co., Ltd.)
5. Anti-rust agent ・1,2,3-benzotriazole6. Solvent ・Ethyl acetate

[Preparation of adhesive sheet 1]
In Examples 1 and 2, adhesive sheets were obtained as follows.
A resin composition was prepared by blending the raw materials at the mass ratio shown in Table 1, and the thickness of the resin composition was placed on a release film (PET film manufactured by Mitsubishi Chemical Corporation) having a thickness of 100 μm that had been subjected to silicone release treatment. It was developed into a sheet so as to have a thickness of 50 μm.

Next, on the sheet-shaped resin composition, a release film having a thickness of 75 μm (PET film manufactured by Mitsubishi Chemical Corporation) that has been subjected to silicone release treatment is laminated to form a laminate, and a metal halide lamp irradiation device ( Ushio Inc., UVC-0516S1, lamp UVL-8001M3-N) was used to irradiate the resin composition through the release film so that the cumulative irradiation dose at a wavelength of 365 nm was 3000 mJ/cm ² . A pressure-sensitive adhesive sheet laminate was obtained in which release films were laminated on both the front and back sides of a 50 μm pressure-sensitive adhesive sheet (sample).

[Preparation of adhesive sheet 2]
In Examples 3 and 4, adhesive sheets were obtained as follows.
A solvent-containing resin composition was prepared by blending the raw materials at the mass ratio shown in Table 1, and the resin composition was coated on the release film having a thickness of 100 μm that had been subjected to silicone release treatment. It was developed in a sheet form so as to be
Next, the sheet-shaped resin composition was placed in a dryer heated to 90° C. together with the release film and held for 10 minutes to volatilize the solvent contained in the resin composition.
Furthermore, on the sheet-shaped resin composition from which the solvent has been dried, the above-mentioned release film having a thickness of 75 μm that has been subjected to silicone release treatment is laminated to form a laminate, and a metal halide lamp irradiation device (Ushio Inc. Company, UVC-0516S1, lamp UVL-8001M3-N) is used to irradiate the resin composition through the release film so that the cumulative irradiation dose at a wavelength of 365 nm becomes the value shown in Table 1. A pressure-sensitive adhesive sheet laminate was obtained in which a release film was laminated on both the front and back sides of a pressure-sensitive adhesive sheet (sample) having a thickness of 50 μm.

[Preparation of adhesive sheet 3]
In Examples 5 and 6, adhesive sheets were obtained as follows.
A resin composition containing a solvent was prepared by blending raw materials at the mass ratio shown in Table 1, and the thickness of the resin composition was 230 μm on the above-mentioned release film having a thickness of 100 μm that was subjected to silicone release treatment. It was developed in a sheet form so as to be
Next, the sheet-shaped resin composition was placed in a dryer heated to 90° C. together with the release film and held for 10 minutes to volatilize the solvent contained in the resin composition.
Furthermore, on the sheet-shaped resin composition from which the solvent has been dried, the above-mentioned release film having a thickness of 75 μm that has been subjected to silicone release treatment is laminated to form a laminate, and a metal halide lamp irradiation device (Ushio Inc. Company, UVC-0516S1, lamp UVL-8001M3-N) is used to irradiate the resin composition through the release film so that the cumulative irradiation dose at a wavelength of 365 nm becomes the value shown in Table 1. A pressure-sensitive adhesive sheet laminate was obtained in which a release film was laminated on both the front and back sides of a pressure-sensitive adhesive sheet (sample) having a thickness of 50 μm.

[Preparation of adhesive sheet 4]
In Comparative Examples 1 and 2, adhesive sheets were obtained as follows.
A resin composition was prepared by blending the raw materials at the mass ratio shown in Table 1, and the thickness of the resin composition was placed on a release film (PET film manufactured by Mitsubishi Chemical Corporation) having a thickness of 100 μm that had been subjected to silicone release treatment. It was developed into a sheet so as to have a thickness of 50 μm.
Next, on the sheet-shaped resin composition, a release film having a thickness of 75 μm (PET film manufactured by Mitsubishi Chemical Corporation) that has been subjected to silicone release treatment is laminated to form a laminate, and a metal halide lamp irradiation device ( Ushio Inc., UVC-0516S1, lamp UVL-8001M3-N) was applied to the resin composition through the release film so that the cumulative irradiation dose at a wavelength of 365 nm was the value shown in Table 1. Irradiation was performed to obtain a pressure-sensitive adhesive sheet laminate in which release films were laminated on both the front and back sides of a 50 μm pressure-sensitive adhesive sheet (sample).

[Measurement/Evaluation of Adhesive Sheet]
The adhesive sheets (samples) obtained in Examples and Comparative Examples were measured and evaluated as follows.

<Creep compliance>
The release film was removed from each of the pressure-sensitive adhesive sheet laminates prepared in Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets (samples) were laminated to obtain a laminate having a thickness of 1.0 mm. A cylindrical body (height: 1.0 mm) with a diameter of 8 mm was punched out from the laminate of the pressure-sensitive adhesive layers thus obtained, and this was used as a sample. Using a viscoelasticity measuring device (manufactured by TA Instruments, product name “DHR 1”), a stress of 3,000 Pa was continuously applied to the above sample under the following conditions, and the creep compliance J (t) (MPa ^-1 ) was measured.

From the measurement results, the value when a stress of 3,000 Pa is applied is defined as the minimum creep compliance J (t) min (MPa ^-1 ), and 3757 seconds after the minimum creep compliance J (t) min is measured. We derived the maximum creep compliance J(t)max (MPa ⁻¹ ) measured by

(Measurement condition)
・Adhesive jig: Φ8mm parallel plate ・Measurement temperature: 25℃

<Storage shear modulus (G′), loss tangent (tan δ)>
The release film was removed from each of the pressure-sensitive adhesive sheet laminates prepared in Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets (samples) were laminated to obtain a laminate having a thickness of 1.0 mm.
A cylindrical body (height: 1.0 mm) with a diameter of 8 mm was punched out from the laminate of the pressure-sensitive adhesive layers thus obtained, and this was used as a sample.
For the above sample, using a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 1"), the storage shear modulus (G') and loss tangent (tan δ) were measured under the following measurement conditions. It was measured.
From the obtained data, the temperature at which the maximum loss tangent (tan δ) appears (glass transition temperature (Tg)), the storage shear modulus G' at -20 ° C (-20 ° C), the storage shear modulus G at 60 ° C ' (60°C) was obtained.

(Measurement condition)
・Adhesive jig: Φ8mm parallel plate,
・Strain: 0.1%
・Frequency: 1Hz
・Measurement temperature: -60 to 100°C
・Temperature increase rate: 5°C/min

<Gel fraction>
The release film was removed from each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples, and about 0.1 g of the pressure-sensitive adhesive sheet (sample) was collected, impregnated with ethyl acetate for 24 hours, and then 4.5 at 75 ° C. After drying for a certain period of time, the mass fraction of the gel component remaining after that was determined and used as the gel fraction.

<Peel force>
One of the release films was removed from each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples, and a polyethylene terephthalate film ("Cosmoshine A4300" manufactured by Toyobo Co., Ltd., thickness 100 μm) was adhered as a backing film with a hand roller. The sheet (sample) was roll-pressed. Cut this into strips with a width of 10 mm and a length of 150 mm, peel off the remaining release film, and attach the exposed adhesive surface to a stainless steel plate in advance. C_50”, hereinafter referred to as “CPI film”), using a hand roller, to prepare a laminate consisting of CPI film/adhesive sheet (sample)/backing film, and autoclave treatment ( 60° C., gauge pressure 0.2 MPa, 20 minutes), and finished adhesion was performed to prepare a peel force measurement sample.
While pulling at an angle of 180 ° at a peeling speed of 60 mm / min, the backing film was peeled from the CPI film, the tensile strength was measured with a load cell, and the 180 ° peel strength (N /25 mm) was measured and shown in Table 2 as the peel force (60°C).

[Preparation of laminated sheet]
The release film of each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples was removed, and the first member sheet and the second member sheet were laminated on both sides of the pressure-sensitive adhesive sheet (sample) by a hand roll, and the laminated sheet (sample ).

At this time, in Examples 1, 3, 5, 6 and Comparative Examples 1 and 2, as the first member sheet and the second member sheet, CPI film (main component: transparent polyimide, "C_50" manufactured by KOLON, 25 °C tensile strength: 307 MPa) was used.

Further, in Examples 2 and 4, as the first member sheet and the second member sheet, COP films (main component: cyclic olefin polymer, "ZF-14" manufactured by Nippon Zeon Co., Ltd., tensile strength at 25 ° C.: 59 MPa) were used. Using.

[Evaluation of laminated sheet]
Laminated sheets (samples) prepared as described above using the pressure-sensitive adhesive sheets (samples) obtained in Examples and Comparative Examples were evaluated as follows.

<Dynamic Flexibility>
The laminated sheet (sample) was subjected to a curvature radius R = 3 mm, 60 rpm (1 Hz) setting using a durability system in a constant temperature and humidity chamber and a planar body no-load U-shaped expansion tester (manufactured by Yuasa System Equipment Co., Ltd.). , U-shaped bending cycle evaluation was performed with the CPI film or COP film side facing inside.
The temperature and the number of cycles were evaluated at -20°C and 100,000 times. In addition, the following evaluation criteria evaluated.

◯: None of delamination, breakage, buckling, and flow occurred at the bent portion.
x: Either delamination, breakage, buckling, or flow occurred at the bent portion.

<Static Flexibility>
The laminated sheet (sample) is bent at a radius of curvature R = 3 mm with the CPI film or COP film side facing inward, stored at 60°C and 90% RH for 24 hours, and then restored after 1 hour after opening the jig. evaluated the sex. Delamination and restorability were evaluated according to the following evaluation criteria. Similarly, when the restorability of only the member sheets (CPI film and COP film) was confirmed, the internal angle of the film was 90°.
○: The inner angle of the bent portion was restored to 70° or more and 90° or less.
x: Either the inner angle of the bent portion is less than 70°, or delamination, breakage, buckling, or flow is observed.

Table 2 shows the results obtained by measurement and evaluation of the pressure-sensitive adhesive sheet and laminated sheet.

Creep compliance fluctuation value ΔlogJ (t) is less than 1.0, storage shear modulus at 60°C (G' (60°C)) is 0.005 MPa or more and less than 0.20 MPa, loss tangent at 60°C (tan δ (60°C) ) is less than 0.60, in the laminated sheets of Examples 1 to 6, delamination occurs in a static bending test at high temperature, which is more severe than the room temperature evaluation method of Patent Document 1. It showed good restorability.
In particular, in Examples 1 to 6, in which the -20°C storage shear modulus (G' (-20°C)) is 1.0 MPa or less, it is possible to exhibit excellent performance even in dynamic flexibility at low temperatures. all right.

On the other hand, in Comparative Example 1, the creep compliance variation value ΔlogJ(t) was controlled to be less than 1.0, but the reaction of the curable component was insufficient, the crosslink density was too low, and Tan δ (60°C) was 0.0. Since it exceeded 60, the static flexibility was deteriorated.
In Comparative Example 2, similarly, the creep compliance fluctuation value ΔlogJ(t) was controlled to be less than 1.0, but the reaction of the (meth)acryloyl group in the side chain proceeded too much, resulting in a high crosslink density. It was found that dynamic flexibility and static flexibility deteriorated because G' (60°C) was less than 0.005 MPa.
From the above, the three requirements of the creep compliance variation value Δlog J (t), (G' (60 ° C.)) and the loss tangent at 60 ° C. (tan δ (60 ° C.)) are closely related technical matters, It was found that if any one of these is lacking, both resilience and flexibility cannot be achieved.

Claims (15)

A pressure-sensitive adhesive sheet formed from a resin composition containing an acrylic (co)polymer having a (meth)acrylate having an alkyl group of 4 to 20 carbon atoms as a monomer component and a curable compound, wherein the following (1) and An adhesive sheet that satisfies the requirements of (2).
(1) The storage shear modulus at 60°C (G' (60°C)) obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 0.005 MPa or more and less than 0.20 MPa, and at 60°C Loss tangent (tan δ (60° C.)) is less than 0.60.
(2) The creep compliance value measured when a stress of 3,000 Pa is applied is the minimum creep compliance J(t)min (MPa ^-1 ), and 3757 seconds after the minimum creep compliance J(t)min is measured. A stress of 3,000 Pa continues to be applied until the end of the stress, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J(t)max (MPa ⁻¹ ), the minimum creep compliance J(t)min and the maximum creep compliance J(t)max is less than 1.0. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the storage shear modulus at -20°C (G'(-20°C)) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 1.0 MPa or less. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the maximum point of loss tangent obtained by dynamic viscoelasticity measurement in shear mode at a frequency of 1 Hz is -25° C. or lower. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, which has a gel fraction of 70% or more. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, which is formed from a resin composition containing a urethane acrylic (co)polymer having urethane (meth)acrylate as a monomer component. The adhesive sheet according to claim 5, wherein the urethane (meth)acrylate is a polyfunctional urethane (meth)acrylate. The pressure-sensitive adhesive sheet according to claim 1 , wherein the resin composition contains a radical initiator. The pressure-sensitive adhesive sheet according to claim 1, wherein the curable compound is a monofunctional (meth)acrylate. The pressure-sensitive adhesive sheet according to claim 1, wherein the curable compound is urethane (meth)acrylate. The pressure-sensitive adhesive sheet according to claim 9, wherein the urethane (meth)acrylate has a glycol skeleton. A laminated sheet comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 10 and a member sheet satisfying the requirement (3) on at least one side thereof.
(3) Tensile strength at 25° C. measured according to ASTM D882 is 10 MPa to 900 MPa. A laminated sheet having a member sheet on at least one side of an adhesive layer,
The adhesive layer is formed from a resin composition containing an acrylic (co)polymer having a (meth)acrylate having an alkyl group having 4 to 20 carbon atoms as a monomer component and a curable compound, and the following (1) and meet the requirements of (2),
The member sheet is a laminated sheet that satisfies the following requirement (3).
(1) The storage shear modulus at 60°C (G' (60°C)) obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 0.005 MPa or more and less than 0.20 MPa, and at 60°C Loss tangent (tan δ (60° C.)) is less than 0.60.
(2) The creep compliance value measured when a stress of 3,000 Pa is applied is the minimum creep compliance J(t)min (MPa ^-1 ), and 3757 seconds after the minimum creep compliance J(t)min is measured. A stress of 3,000 Pa continues to be applied until the end of the stress, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J(t)max (MPa ⁻¹ ), the minimum creep compliance J(t)min and the maximum creep compliance J(t)max is less than 1.0.
(3) Tensile strength at 25° C. measured according to ASTM D882 is 10 MPa to 900 MPa. 13. The member sheet according to claim 11 or 12, wherein the main component of the member sheet is one or more resins selected from the group consisting of cycloolefin resins, triacetylcellulose resins, polymethylmethacrylate resins, epoxy resins and polyimide resins. laminated sheets. 13. The laminated sheet according to claim 11 or 12, wherein the member sheet is thin glass. A flexible image display device comprising the laminated sheet according to any one of claims 11 to 14.