TWI862630B - Adhesive sheet, repeatedly bent laminated component, and repeatedly bent device - Google Patents

Abstract

The present invention provides an adhesive sheet, a repeatedly bent laminated component and a repeatedly bent device, wherein the adhesive layer in the bent portion is not easily peeled off at the interface with the adherend, and light leakage and visibility reduction caused by bending are suppressed. The adhesive sheet 1 comprises: an adhesive layer 11 for bonding a bendable component constituting a repeatedly bending device to other bendable components; the adhesive constituting the adhesive layer 11 has a storage modulus G'(-20) of not less than 0.01 MPa and not more than 0.2 MPa at -20°C; and the adhesive constituting the adhesive layer 11 has an absolute value of a photoelastic coefficient of not more than 9.9×10 ^-10 m ² /N at a measured wavelength of 400 nm at 23°C.

Description

Adhesive sheet, repeatedly bent laminated component, and repeatedly bent device

The present invention relates to an adhesive sheet for a repetitive bending device, a repetitive bending laminate component and a repetitive bending device.

In recent years, a bendable display has been proposed as a display body (display) of electronic equipment, which is one of the devices. As a curved display, in addition to a display having a single curved surface, a repeatedly curved display for repeatedly bending (folding) has been proposed.

In the above-mentioned reciprocating bending display, a bendable component (flexible component) constituting the flexible display is attached to other flexible components via an adhesive layer of an adhesive sheet. However, when using conventional adhesive sheets in reciprocating bending displays, there is a problem of peeling off at the interface between the adhesive layer at the bending portion and the adherend.

Patent document 1 discloses an adhesive for the purpose of suppressing the occurrence of peeling during repeated bending. [Prior art document] [Patent document]

Patent document 1: Japanese Patent Application Publication No. 2016-108555

[Problem to be solved]

On the other hand, in the above-mentioned repeatedly bent display, light leakage may occur around the bent portion during and after bending, and visibility may be reduced. The adhesive described in Patent Document 1 cannot fully solve the problems of light leakage and reduced visibility.

The present invention was completed in view of the above situation, and its purpose is to provide an adhesive sheet, a repeatedly bent laminated component, and a repeatedly bent device, in which the interface between the adhesive layer and the adherend at the bent portion is not easily peeled off, and light leakage and visibility reduction caused by bending are suppressed. [Means for solving the problem]

In order to achieve the above-mentioned purpose, first, the present invention provides an adhesive sheet having: an adhesive layer for bonding a bendable component constituting a repetitively bending device to other bendable components, the adhesive constituting the adhesive layer having a storage modulus G'(-20) of not less than 0.01 MPa and not more than 0.2 MPa at -20°C, and an absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measured wavelength of 400 nm of not more than 9.9×10 ^-10 m ² /N (Invention 1).

In the above invention (Invention 1), the adhesive constituting the adhesive layer has the above-mentioned physical properties, so that when a laminate formed by bonding a flexible component to other flexible components by the adhesive layer is repeatedly bent or is in a bent state for a long time, the interface between the adhesive layer and the adherend at the bent portion is not easy to peel off, and light leakage and reduced visibility caused by bending (after bending) are suppressed.

In the above invention (Invention 1), the absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer when measured at 23°C and a wavelength of 500 nm is preferably 9.9×10 ^-10 m ² /N or less (Invention 2).

In the above inventions (Inventions 1 and 2), the absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer when measured at 23°C and a wavelength of 600 nm is preferably 9.9×10 ^-10 m ² /N or less (Invention 3).

In the above inventions (Inventions 1 to 3), the storage modulus G'(85) of the adhesive constituting the adhesive layer at 85°C is preferably greater than 0.005 MPa and less than 0.2 MPa (Invention 4).

In the above inventions (Inventions 1 to 4), the storage modulus G'(25) of the adhesive constituting the adhesive layer at 25°C is preferably greater than 0.01 MPa and less than 0.2 MPa (Invention 5).

In the above inventions (Inventions 1 to 5), the gel fraction of the adhesive constituting the adhesive layer is preferably greater than 30% and less than 95% (Invention 6).

In the above inventions (Inventions 1 to 6), the adhesive constituting the adhesive layer is preferably an acrylic adhesive (Invention 7).

In the above inventions (Inventions 1 to 7), the adhesive sheet has two peeling sheets, and the adhesive layer is preferably clamped on the peeling sheet in a manner of contacting with the peeling surfaces of the two peeling sheets (Invention 8).

Second, the present invention provides a repeatedly bent laminated component, which comprises: a bendable component and other bendable components constituting a repeatedly bent device, and an adhesive layer for bonding the above-mentioned one bendable component and the above-mentioned other bendable components to each other, wherein the above-mentioned adhesive layer is formed by the adhesive layer of the above-mentioned adhesive sheet (Inventions 1 to 8) (Invention 9).

Third, the present invention provides a repeated bending device, which is a device having the above-mentioned repeated bending layered component (Invention 9) (Invention 10) [Effect of the invention]

The adhesive sheet, repeatedly bent laminated component and repeatedly bent device related to the present invention are unlikely to be peeled off at the interface between the adhesive layer and the adherend at the bent portion, and light leakage and visibility reduction caused by bending are suppressed.

The following describes an embodiment of the present invention. [Adhesive sheet] An adhesive sheet according to an embodiment of the present invention comprises: an adhesive layer for bonding a bendable component constituting a repetitive bending device to other bendable components, preferably a peeling sheet formed by laminating one or both sides of the adhesive layer. The repetitive bending device and the bendable component are as follows.

The adhesive constituting the adhesive layer has a storage modulus G'(-20) of 0.01 MPa or more and 0.2 MPa or less at -20°C, and an absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measurement wavelength of 400 nm is 9.9×10 ^-10 m ² /N or less. The storage modulus and photoelastic coefficient measurement methods in this specification are shown in the following test examples.

The adhesive constituting the adhesive layer in the present embodiment has the above-mentioned physical properties, so that when a laminate formed by bonding a flexible component to other flexible components by the adhesive layer is repeatedly bent or is in a bent state for a long time, the interface between the adhesive layer and the adherend at the bent portion does not peel off, and light leakage and reduced visibility caused by bending (after bending) are suppressed. In particular, when the storage modulus G'(-20) is 0.2 MPa or less, deformation due to repeated bending can be suppressed, that is, stress (which becomes particularly large at low temperatures) is small, because the interface between the adhesive layer and the adherend at the bent portion becomes less likely to peel off. In addition, in particular, when the photoelastic coefficient is 9.9× ^{10-10 m2} /N or less, the occurrence of birefringence caused by residual stress accompanying bending can be suppressed, and light leakage and visibility reduction caused by bending are suppressed.

From the viewpoints of the above-mentioned peel resistance, light leakage resistance and visibility, especially from the viewpoint of peel resistance, the storage modulus G'(-20) of the adhesive constituting the above-mentioned adhesive layer at -20°C must be 0.2MPa or less, preferably 0.15MPa or less, especially 0.10MPa or less, and further preferably 0.08MPa or less. In addition, from the viewpoint of cohesion, the storage modulus G'(-20) of the adhesive constituting the above-mentioned adhesive layer at -20°C must be 0.01MPa or more, preferably 0.03MPa or more, especially 0.05MPa or more, and further preferably 0.07MPa or more.

The storage modulus G'(85) of the adhesive constituting the adhesive layer at 85°C is preferably 0.2 MPa or less, more preferably 0.1 MPa or less, particularly preferably 0.05 MPa or less, and further preferably 0.03 MPa or less. Thereby, the force acting on the adherend by the adhesive layer decreases with bending, and a device with good peeling resistance at high temperatures can be obtained. On the other hand, the storage modulus G'(85) at 85°C is preferably 0.005 MPa or more, more preferably 0.010 MPa or more, and particularly preferably 0.015 MPa or more. Thereby, the adhesive layer does not become too soft even at high temperatures and maintains cohesion.

The storage modulus G'(25) of the adhesive constituting the adhesive layer at 25°C is preferably 0.2 MPa or less, more preferably 0.1 MPa or less, particularly preferably 0.08 MPa or less, and further preferably 0.05 MPa or less. This makes it easier for the adhesive to be exhibited. On the other hand, the storage modulus G'(25) at 25°C is preferably 0.01 MPa or more, more preferably 0.02 MPa or more, and particularly preferably 0.03 MPa or more. This makes it possible to improve the peel resistance in the standard ambient temperature range and the processability such as stripping processing.

Furthermore, from the viewpoints of the above-mentioned peeling resistance, light leakage resistance and visibility, in particular from the viewpoints of light leakage resistance and visibility, the absolute value of the photoelastic coefficient of the adhesive constituting the above-mentioned adhesive layer at 23°C and a measured wavelength of 400nm must be 9.9× ^{10-10 m2} /N or less, preferably 8.0× ^{10-10 m2} /N or less, more preferably 6.0× ^{10-10 m2} /N or less, and particularly preferably 5.0× ^10-10 m2/N or less. The lower limit of the absolute value of the above-mentioned photoelastic coefficient is not particularly limited, and may be ^{0 m2} /N. However, from the viewpoint of easily obtaining an adhesive having a storage modulus G'(-20) at -20°C satisfying the above value, the absolute value of the above photoelastic coefficient is preferably 1.0×10 ^-10 m ² /N or more, more preferably 2.0×10 ^-10 m ² /N or more, further preferably 3.0×10 ^-10 m ² /N or more, and particularly preferably 4.0×10 ^-10 m ² /N or more.

From the viewpoint of better light leakage resistance and visibility, the absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer when measured at 23°C and a wavelength of 500nm is preferably 9.9× ^{10-10 m2} /N or less, more preferably 8.0× ^{10-10 m2} /N or less, particularly preferably 6.0× ^{10-10 m2} /N or less, and further preferably 5.0× ^{10-10 m2} /N or less. The lower limit of the absolute value of the photoelastic coefficient is not particularly limited, and may be 0 ^m2 /N. However, from the viewpoint of easily obtaining an adhesive having a storage modulus G'(-20) at -20°C satisfying the above value, the absolute value of the above photoelastic coefficient is preferably 1.0×10 ^-10 m ² /N or more, more preferably 2.0×10 ^-10 m ² /N or more, particularly preferably 3.0×10 ^-10 m ² /N or more, and further preferably 3.5×10 ^-10 m ² /N or more.

From the viewpoint of better light leakage resistance and visibility, the absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer when measured at 23°C and a wavelength of 600nm is preferably 9.9× ^{10-10 m2} /N or less, more preferably 8.0× ^{10-10 m2} /N or less, particularly preferably 6.0× ^{10-10 m2} /N or less, and further preferably 4.0× ^{10-10 m2} /N or less. The lower limit of the absolute value of the photoelastic coefficient is not particularly limited, and may be 0 ^m2 /N. However, from the viewpoint of easily obtaining an adhesive having a storage modulus G'(-20) at -20°C satisfying the above value, the absolute value of the above photoelastic coefficient is preferably 0.8×10 ^-10 m ² /N or more, more preferably 1.5×10 ^-10 m ² /N or more, particularly preferably 2.0×10 ^-10 m ² /N or more, and further preferably 3.0×10 ^-10 m ² /N or more.

The absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C at a wavelength of 400nm, the absolute value of the photoelastic coefficient at a wavelength of 500nm, and the difference between the maximum value and the minimum value of the absolute value of the photoelastic coefficient at a wavelength of 600nm are preferably 8× ^{10-10 m2} /N or less, more preferably 4× ^{10-10 m2} /N or less, particularly preferably 2.0× ^{10-10 m2} /N or less, and even more preferably 1.5× ^{10-10 m2} /N or less. Thereby, the light leakage resistance and visibility affected by the different types of the light emitting body used can be suppressed.

The gel fraction of the adhesive constituting the adhesive layer is preferably 30% or more, more preferably 40% or more, particularly preferably 50% or more, and further preferably 60% or more. Thereby, the adhesive exerts a suitable cohesive force capable of withstanding repeated bending. As a result, the above-mentioned peel resistance becomes better. On the other hand, the gel fraction of the adhesive in the present embodiment is preferably 95% or less, more preferably 90% or less, particularly preferably 80% or less, further preferably 75% or less, and most preferably 70% or less. Thereby, it is inferred that the destruction of the cross-linked structure in the adhesive caused by repeated bending is suppressed, resulting in better visibility. Moreover, the method for measuring the gel fraction in this specification is shown in the following test example.

The specific structure of an example of an adhesive sheet related to the present embodiment is shown in FIG1. As shown in FIG1, an adhesive sheet 1 related to an embodiment is composed of two peeling sheets 12a and 12b, and an adhesive layer 11 clamped between the two peeling sheets 12a and 12b in a manner of contacting the peeling surfaces of the two peeling sheets 12a and 12b. In addition, the peeling surface of the peeling sheet in this specification refers to a surface having a peeling property in the peeling sheet, including any one of a surface subjected to a peeling treatment and a surface showing a peeling property even if a peeling treatment is not performed.

1. Constituent elements 1-1. Adhesive layer The adhesive layer 11 is formed by an adhesive having the above-mentioned physical properties. The type of adhesive constituting the adhesive layer 11 is not particularly limited as long as it satisfies the above-mentioned physical properties (especially the storage modulus G'(-20) at -20°C and the photoelastic coefficient at 23°C and a measured wavelength of 400nm), and may be, for example, any of acrylic adhesives, polyester adhesives, polyurethane adhesives, rubber adhesives, silicone adhesives, etc. In addition, the adhesive may be any of an emulsion type, a solvent type, or a solvent-free type, and may be any of a crosslinked type or a non-crosslinked type. Among these, acrylic adhesives are preferred because they easily satisfy the above-mentioned physical properties and have excellent adhesive properties and optical properties, and solvent-type acrylic adhesives are particularly preferred.

Specifically, the adhesive in the present embodiment is preferably an adhesive obtained by crosslinking an adhesive composition containing a (meth)acrylate polymer (A) and a crosslinking agent (B) (hereinafter, sometimes referred to as "adhesive composition (P)"). As long as it is a relevant adhesive, the above-mentioned physical properties can be satisfied, and good adhesion can be easily obtained. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. In addition, "polymer" is a concept that also includes "copolymer".

(1) Components of the adhesive composition P (1-1) (Meth)acrylate polymer (A) The (meth)acrylate polymer (A) preferably includes, as monomer units constituting the polymer, an alkyl (meth)acrylate for exhibiting good adhesiveness and a monomer having a reactive functional group serving as a crosslink (a monomer containing a reactive functional group). Here, a general alkyl (meth)acrylate exhibits negative birefringence, and although the resulting polymer becomes birefringent, by introducing a monomer exhibiting positive birefringence into the polymer, the birefringence can be eliminated by the positive and negative offset. In this way, the absolute value of the photoelastic coefficient of the resulting adhesive can be suppressed from decreasing, making it easier to satisfy the above-mentioned photoelastic coefficient. In addition, the (meth)acrylic acid alkyl ester tends to reduce the storage modulus of the obtained polymer, while the monomer showing positive birefringence (particularly the monomer containing an aromatic ring described below) tends to increase the storage modulus of the obtained polymer. By introducing both into the polymer, it becomes easy to satisfy the physical properties related to the storage modulus G'. Therefore, the (meth)acrylic acid ester polymer (A) preferably contains, as monomer units constituting the polymer, an alkyl (meth)acrylic acid ester, a monomer showing positive birefringence, and a monomer containing a reactive functional group.

As the alkyl (meth)acrylate, an alkyl (meth)acrylate having an alkyl group with a carbon number of 1 to 20 is preferred. The alkyl group is preferably in a straight chain or branched chain form.

As the (meth)acrylic acid alkyl esters having an alkyl group with 1 to 20 carbon atoms, there can be enumerated, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, tetradecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, etc. Among them, from the viewpoint of the above-mentioned storage modulus G' and the photoelastic coefficient, (meth)acrylic acid esters having an alkyl group with 1 to 8 carbon atoms are preferred, and (meth)acrylic acid esters having an alkyl group with 4 to 8 carbon atoms are particularly preferred. Specifically, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. Furthermore, these may be used alone or in combination of two or more.

The (meth)acrylate polymer (A) preferably contains 50% by mass or more of an alkyl (meth)acrylate having an alkyl group with a carbon number of 1 to 20 as a monomer unit constituting the polymer, more preferably 70% by mass or more, particularly preferably 80% by mass or more, and further preferably 90% by mass or more. In addition, it is preferably 99% by mass or less of the alkyl (meth)acrylate, more preferably 98% by mass or less, particularly preferably 97% by mass or less, and further preferably 96% by mass or less. When the alkyl (meth)acrylate having an alkyl group with a carbon number of 1 to 20 is contained in the above amount, the (meth)acrylate polymer (A) can be given appropriate adhesion and can easily satisfy the above storage modulus G' and photoelastic coefficient.

As monomers showing positive birefringence, monomers having a ring structure, particularly monomers having an aromatic ring (monomers containing an aromatic ring) are preferred. As aromatic rings, benzene rings, naphthalene rings, anthracene rings, biphenyl rings, fluorene rings, etc. are exemplified, among which benzene rings are preferred from the viewpoint of positive birefringence.

Examples of the monomer containing an aromatic ring include phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, benzyl (meth)acrylate, naphthyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, ethoxylated o-phenylphenol acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, biphenyl di(meth)acrylate, pentafluorobenzyl (meth)acrylate, etc. Among them, from the viewpoint of positive birefringence, 2-phenoxyethyl (meth)acrylate or phenoxypolyethylene glycol (meth)acrylate is preferred, 2-phenoxyethyl (meth)acrylate is particularly preferred, and 2-phenoxyethyl acrylate is further preferred. These may be used alone or in combination of two or more.

The (meth)acrylate copolymer (A) preferably contains 0.1% by mass or more of an aromatic ring-containing monomer as a monomer unit constituting the polymer, more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, and further preferably 2% by mass or more. In addition, it is preferred to contain 30% by mass or less of an aromatic ring-containing monomer, more preferably 20% by mass or less, particularly preferably 15% by mass or less, and further preferably 9% by mass or less. By having the content of the aromatic ring-containing monomer within the above range, the negative birefringence of the (meth)acrylate alkyl ester is offset, the birefringence can be further eliminated, and it becomes easier to satisfy the above-mentioned optical elastic coefficient. In addition, the adhesion is also well maintained.

Since the (meth)acrylate polymer (A) contains a monomer containing a reactive functional group as a monomer unit constituting the polymer, the reactive functional group from the monomer containing the reactive functional group reacts with the crosslinking agent (B) described below to form a crosslinking structure (three-dimensional mesh structure), thereby obtaining an adhesive having a desired cohesive force. The adhesive becomes one that easily satisfies the physical properties related to the storage modulus G' and the photoelastic coefficient (and gel fraction) described above.

The (meth)acrylate polymer (A) preferably includes a monomer having a hydroxyl group in the molecule (a hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (a carboxyl group-containing monomer), a monomer having an amino group in the molecule (an amino group-containing monomer), etc. Such monomers having a reactive functional group may be used alone or in combination of two or more.

Among the above-mentioned monomers containing reactive functional groups, hydroxyl-containing monomers or carboxyl-containing monomers are preferred, and hydroxyl-containing monomers are particularly preferred. Hydroxyl-containing monomers are likely to satisfy the physical properties related to the above-mentioned storage modulus G. That is, as long as it is a hydroxyl-containing monomer, the storage modulus G' at low temperature will become smaller, and the fine adjustment of the storage modulus G' of the obtained adhesive becomes easy.

As the monomer containing a hydroxyl group, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and other hydroxyalkyl (meth)acrylates can be listed. Among the above, from the viewpoint of easily satisfying the physical properties related to the above-mentioned storage modulus G', hydroxyalkyl (meth)acrylates having a hydroxyalkyl group with a carbon number of 1 to 4 are preferred. Specifically, for example, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and the like are preferably listed, and 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate can be particularly preferably listed. These can be used alone or in combination of two or more.

Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citric acid. Of these, acrylic acid is preferred from the viewpoint of the adhesion of the resulting (meth)acrylate polymer (A). These monomers may be used alone or in combination of two or more.

Furthermore, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and acrylic acid show positive birefringence. Therefore, together with the above-mentioned monomers showing positive birefringence (monomers containing an aromatic ring), negative birefringence of the alkyl (meth)acrylate can be offset.

The (meth)acrylate polymer (A) preferably contains 0.1% by mass or more of a monomer containing a reactive functional group as a monomer unit constituting the polymer, particularly preferably 0.4% by mass or more, and further preferably 0.8% by mass or more. In addition, the (meth)acrylate polymer (A) preferably contains 18% by mass or less of a monomer containing a reactive functional group as a monomer unit constituting the polymer, particularly preferably 9% by mass or less, and further preferably 3% by mass or less. When the (meth)acrylate polymer (A) contains a monomer containing a reactive functional group in the above-mentioned group as a monomer unit, the cohesive force of the obtained adhesive becomes appropriate through the crosslinking reaction with the crosslinking agent (B), and it becomes easy to satisfy the physical properties related to the above-mentioned storage modulus G' (and gel fraction), especially the storage modulus G' (-20) at -20°C.

The (meth)acrylate polymer (A) preferably does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. Since carboxyl groups are slightly acidic components, by not containing carboxyl group-containing monomers, even if defects are generated due to acid on the adhesive attachment object, for example, when transparent conductive films such as tin-doped indium oxide (ITO), metal films, and metal meshes exist, such defects (corrosion, resistance value changes, etc.) caused by acid can be suppressed.

Here, "containing no carboxyl group-containing monomers" means substantially containing no carboxyl group-containing monomers. In addition to containing no carboxyl group-containing monomers at all, the carboxyl group-containing monomers are allowed to be contained to such an extent that corrosion of the transparent conductive film, metal wiring, etc. caused by the carboxyl group does not occur. Specifically, in the (meth)acrylate polymer (A), the amount of the carboxyl group-containing monomers allowed to be contained as a monomer unit is 0.1 mass % or less, preferably 0.01 mass % or less, and further preferably 0.001 mass % or less.

The (meth)acrylate polymer (A) may contain other monomers as monomer units constituting the polymer as desired. As other monomers, monomers containing no reactive functional groups are preferred in order not to hinder the above-mentioned effects of monomers containing reactive functional groups. As related monomers, for example, non-reactive nitrogen-containing monomers such as N-acryloylformoline and N-vinyl-2-pyrrolidone, (meth)acrylate alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, styrene, etc. can be listed. These can be used alone or in combination of two or more.

The polymerization state of the (meth)acrylate polymer (A) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth)acrylate polymer (A) is preferably 600,000 or more, more preferably 800,000 or more, particularly preferably 1,000,000 or more, and further preferably 1,200,000 or more. In addition, the weight average molecular weight of the (meth)acrylate polymer (A) is preferably 2,500,000 or less, more preferably 2,000,000 or less, particularly preferably 1,700,000 or less, and further preferably 1,400,000 or less. When the weight average molecular weight of the (meth)acrylate polymer (A) is within the above range, the physical properties (and gel fraction) related to the above storage modulus G' are easily satisfied, especially the storage modulus G'(25) at 25°C and the storage modulus G'(85) at 85°C. In addition, the weight average molecular weight in this specification is a value converted into standard polystyrene measured by gel permeation chromatography (GPC).

In the adhesive composition P, the (meth)acrylate polymer (A) may be used alone or in combination of two or more.

(1-2) Crosslinking agent (B) When the adhesive composition P containing the crosslinking agent (B) is heated or the like, the (meth)acrylate polymer (A) is crosslinked to form a three-dimensional mesh structure. As a result, the cohesive force of the resulting adhesive is improved, making it easier to satisfy the physical properties related to the storage modulus G' and the gel fraction.

As the crosslinking agent (B), any crosslinking agent that reacts with the reactive group of the (meth)acrylate polymer (A) may be used, for example, isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, ethyleneimine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, ammonium salt crosslinking agents, etc. Among the above, it is preferred to use an isocyanate crosslinking agent that has good reactivity with the monomer containing a reactive functional group. Moreover, the crosslinking agent (B) may be used alone or in combination of two or more.

Isocyanate crosslinking agents are those containing at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, and xylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate; and diurea products and isocyanurate products thereof, and adducts thereof as reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trihydroxymethylpropane, and castor oil. Among them, trihydroxymethylpropane-modified aromatic polyisocyanates, particularly trihydroxymethylpropane-modified toluene diisocyanate or trihydroxymethylpropane-modified xylene diisocyanate are preferred from the viewpoint of reactivity with hydroxyl groups.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 parts by mass or more, particularly 0.06 parts by mass or more, and further preferably 0.12 parts by mass or more, relative to 100 parts by mass of the (meth)acrylate polymer (A). In addition, the content is preferably 5 parts by mass or less, more preferably 2 parts by mass or less, particularly 1 part by mass or less, and further preferably 0.4 parts by mass or less. When the content of the crosslinking agent (B) is within the above range, it becomes easy to satisfy the physical properties related to the storage modulus G' and the gel fraction.

(1-3) Various additives The adhesive composition P may contain various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, thickeners, antioxidants, light stabilizers, softeners, fillers, and refractive index adjusters, as desired. The following polymerization solvents and dilution solvents are not included in the additives constituting the adhesive composition P.

The adhesive composition P preferably contains the above-mentioned silane coupling agent. Thereby, in the obtained adhesive layer, the adhesion with the flexible member as the adherend is improved, and the adhesive force is better.

The silane coupling agent is an organic silicon compound having at least one alkoxysilyl group in the molecule, and preferably has good compatibility with the (meth)acrylate polymer (A) and light transmittance.

Examples of the relevant silane coupling agents include polymerizable unsaturated group-containing silicon compounds such as ethylene trimethoxysilane, ethylene triethoxysilane, and methacryloyloxypropyl trimethoxysilane, 3-glycidyloxypropyl trimethoxysilane, 3-glycidyloxypropyl methyl dimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 3-butylpropyl trimethoxysilane, 3-butylpropyl triethoxysilane, and 3-butylpropyl dimethoxysilane. A silicon compound containing an alkyl group such as methylsilane, an amine group-containing silicon compound such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, or a condensate of at least one of them and an alkyl group-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, etc. These may be used alone or in combination of two or more.

The content of the silane coupling agent in the adhesive composition P is preferably 0.01 parts by mass or more, particularly 0.05 parts by mass or more, and further preferably 0.1 parts by mass or more, relative to 100 parts by mass of the (meth)acrylate polymer (A). In addition, the content is preferably 1 part by mass or less, particularly 0.5 parts by mass or less, and further preferably 0.3 parts by mass or less. When the content of the silane coupling agent is within the above range, the adhesion between the obtained adhesive layer and the flexible component as the adherend is improved, resulting in a higher adhesion.

(2) Production of adhesive composition P The adhesive composition P can be produced by producing a (meth)acrylate polymer (A), mixing the obtained (meth)acrylate polymer (A) with a crosslinking agent (B), and adding desired additives.

The (meth)acrylate polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a general free radical polymerization method. The polymerization of the (meth)acrylate polymer (A) is preferably carried out by a solution polymerization method using a polymerization initiator as required. By polymerizing the (meth)acrylate polymer (A) by a solution polymerization method, it becomes easy to increase the molecular weight of the resulting polymer and adjust the molecular weight distribution, and further, the generation of low molecular weight products can be reduced. Therefore, even when the gel fraction is relatively small and the degree of crosslinking is moderate, the deviation of the adhesive due to repeated bending is unlikely to occur, and an adhesive with good peel resistance can be obtained.

Examples of the polymerization solvent used in the solution polymerization method include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, and the like, and two or more thereof may be used in combination.

As the polymerization initiator, there can be mentioned azo compounds, organic peroxides, etc., and two or more kinds can be used in combination. As the azo compounds, there can be mentioned, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane 1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methyl propionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazolin-2-yl)propane], etc.

Examples of the organic peroxide include benzoyl peroxide, tert-butyl perbenzoate, isopropyl hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl) peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, (3,5,5-trimethylhexyl) peroxide, dipropionyl peroxide, and diacetyl peroxide.

Furthermore, in the above polymerization step, by adding a chain transfer agent such as 2-hydroxyethanol, the weight average molecular weight of the obtained polymer can be adjusted.

After obtaining the (meth)acrylate polymer (A), a crosslinking agent (B) and, if necessary, an additive and a diluting solvent are added to the solution of the (meth)acrylate polymer (A), and the mixture is fully mixed to obtain an adhesive composition P (coating solution) diluted with a solvent.

Furthermore, when any of the above components is used in a solid state or is mixed with other components in an undiluted state to produce precipitation, the component may be dissolved or diluted in a diluent in advance and then mixed with other components.

As the above-mentioned diluting solvent, for example, aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methyl chloride and ethyl chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, butanone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosol-based solvents such as ethylcellosol.

The concentration and viscosity of the coating solution thus prepared are not particularly limited as long as they are within the coating range, and can be appropriately selected according to the situation. For example, the adhesive composition P is diluted in such a way that the concentration becomes 10 to 60% by mass. Moreover, when obtaining the coating solution, the addition of a diluting solvent is not a necessary condition, and as long as the viscosity of the adhesive composition P is coatingable, a diluting solvent may not be added. At this time, the adhesive composition P becomes a coating solution in which the polymerization solvent of the (meth)acrylate polymer (A) is directly used as a diluting solvent.

(3) Preparation of adhesive In this embodiment, the adhesive constituting the adhesive layer 11 is preferably formed by crosslinking the adhesive composition P. The crosslinking of the adhesive composition P can generally be performed by heat treatment. In addition, the heat treatment can be performed by drying the film of the adhesive composition P applied on the desired object to volatilize the diluted solvent.

The heating temperature of the heat treatment is preferably 50 to 150° C., particularly 70 to 120° C. Moreover, the heating time is preferably 10 seconds to 10 minutes, particularly 50 seconds to 2 minutes.

After the heat treatment, if necessary, a 1 to 2 week aging period may be set at room temperature (e.g., 23°C, 50%RH). When the aging period is necessary, the adhesive is formed after the aging period. When the aging period is unnecessary, the adhesive is formed after the heat treatment.

By the above-mentioned heat treatment (and aging), the (meth)acrylate polymer (A) can be fully crosslinked through the crosslinking agent (B) to form a crosslinked structure, thereby obtaining an adhesive.

(4) Thickness of adhesive layer The thickness of the adhesive layer 11 in the adhesive sheet 1 according to the present embodiment (measured in accordance with JIS K7130) is preferably 1 μm or more as the lower limit, more preferably 5 μm or more, particularly preferably 10 μm or more, and further preferably 15 μm or more. When the lower limit of the thickness of the adhesive layer 11 is as described above, it is easy to exert the desired adhesive force, and the peeling resistance is better.

In addition, the thickness of the adhesive layer 11 is preferably 300 μm or less, more preferably 150 μm or less, and particularly preferably 90 μm or less. From the perspective of obtaining a thinner repetitive bending device, it is further preferably 40 μm or less. When the upper limit of the thickness of the adhesive layer 11 is as described above, the stress generated in the adhesive layer due to repetitive bending is suppressed from being excessive, and the peeling resistance can be improved. Furthermore, the adhesive layer 11 can be formed as a single layer or by laminating a plurality of layers.

1-2. Peeling sheet The peeling sheets 12a and 12b are used to protect the adhesive layer 11 until the adhesive sheet 1 is used. When the adhesive sheet 1 (adhesive layer 11) is used, it is peeled off. In the adhesive sheet 1 related to this embodiment, one or both of the peeling sheets 12a and 12b are not necessarily required.

As the peeling sheets 12a and 12b, for example, polyethylene film, polypropylene film, polybutylene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene-(methyl)acrylic acid copolymer film, ethylene-(methyl)acrylate copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. can be used. In addition, crosslinked films thereof can also be used. Furthermore, laminated films thereof can also be used.

It is preferred that the peeling surfaces of the peeling sheets 12a and 12b (particularly the surfaces in contact with the adhesive layer 11) be subjected to a peeling treatment. Examples of the peeling agent used in the peeling treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based peeling agents. Furthermore, it is preferred that the peeling sheet on one side of the peeling sheets 12a and 12b be a heavy-peeling type peeling sheet with a large peeling force, and the peeling sheet on the other side be a light-peeling type peeling sheet with a small peeling force.

Although there is no particular limitation on the thickness of the peeling sheets 12a and 12b, it is generally about 20 to 150 μm.

2. Physical properties (adhesion) The adhesion of the adhesive sheet 1 of this embodiment to sodium calcium glass is preferably 1N/25mm or more, more preferably 3N/25mm or more, particularly preferably 5N/25mm or more, and further preferably 8N/25mm or more as the lower limit. When the lower limit of the adhesion of the adhesive sheet 1 to sodium calcium glass is as above, the peeling resistance is better. On the other hand, although there is no special restriction on the upper limit of the above adhesion, rework is sometimes necessary. From this point of view, the above adhesion is preferably 30N/25mm or less, more preferably 25N/25mm or less, and particularly preferably 20N/25mm or less. In addition, the adhesive force in this specification basically refers to the adhesive force measured by the 180-degree pull-off method based on JIS Z0237:2009. The specific test method is shown in the following test example.

The adhesive sheet 1 according to the present embodiment has an adhesion to polyimide of preferably 1 N/25 mm or more, more preferably 3 N/25 mm or more, particularly preferably 5 N/25 mm or more, and further preferably 10 N/25 mm or more. When the lower limit of the adhesion of the adhesive sheet 1 to polyimide is as described above, the adhesive sheet 1 has better peeling resistance even when a polyimide film or the like is used as an adherend. On the other hand, although there is no particular restriction on the upper limit of the adhesion, sometimes reworkability is necessary. From this point of view, the adhesion is preferably 30 N/25 mm or less, more preferably 25 N/25 mm or less, and particularly preferably 20 N/25 mm or less.

3. Production of adhesive sheet As a production example of the adhesive sheet 1, the case of using the above-mentioned adhesive composition P is described. On the peeling surface of the peeling sheet 12a (or 12b) on one side, a coating liquid of the adhesive composition P is applied, and the adhesive composition P is heat-treated to thermally crosslink to form a coating layer, and then the peeling surface of another peeling sheet 12b (or 12a) is superimposed on this coating layer. When the aging period is necessary, the aging period is passed, and when the aging period is unnecessary, the coating layer becomes the adhesive layer 11 as it is. In this way, the above-mentioned adhesive sheet 1 can be obtained. The conditions for heat treatment and aging are as described above.

As another manufacturing example of the adhesive sheet 1, a coating liquid of an adhesive composition P is applied on the peeling surface of a peeling sheet 12a on one side, and a heat treatment is performed to heat-crosslink the adhesive composition P to form a coating layer, thereby obtaining a peeling sheet 12a with a coating layer. In addition, a coating liquid of the adhesive composition P is applied on the peeling surface of another peeling sheet 12b, and a heat treatment is performed to heat-crosslink the adhesive composition P to form a coating layer, thereby obtaining a peeling sheet 12b with a coating layer. Then, the peeling sheet 12a with the coating layer and the peeling sheet 12b with the coating layer are attached so that the two coating layers are in contact with each other. When the aging period is necessary, the coating layer of the above-mentioned layer becomes the adhesive layer 11 as it is, and when the aging period is unnecessary, the above-mentioned adhesive sheet 1 can be obtained. According to this manufacturing example, even if the adhesive layer 11 is relatively thick, it can still be manufactured stably.

As a method for applying the coating liquid of the adhesive composition P, for example, a rod coating method, a knife coating method, a roller coating method, a flap coating method, a die coating method, a gravure coating method, etc. can be used.

[Repeatedly curved laminated component] As shown in FIG. 2 , the repeatedly curved laminated component 2 according to the present embodiment is composed of an adhesive layer 11 located between a first curved component 21 (a curved component) and a second curved component 22 (another curved component) to bond the first curved component 21 and the second curved component 22 to each other.

The adhesive layer 11 in the repeatedly bent laminated member 2 is the adhesive layer 11 of the adhesive sheet 1 .

The repeatedly bending laminated component 2 is the repeatedly bending device itself, or a component constituting a part of the repeatedly bending device. The repeatedly bending device is preferably a display (repeatedly bending display) that can be repeatedly bent (including bending), but is not limited to this. As related repeatedly bending devices, for example, organic electroluminescent (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays using plastic substrates (films) as substrates, foldable displays, etc., can also be touch panels.

The first flexible component 21 and the second flexible component 22 are components that can be bent repeatedly (including bending), and can include, for example, covering films, gas barrier films, hard coating films, polarizing films (polarizing plates), polarizers, phase difference films (phase difference plates), viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transmitting reflective films, electrode films, transparent conductive films, metal mesh films, flexible glass, thin film sensors (touch sensor films), liquid crystal polymer films, luminescent polymer films, thin film liquid crystal modules, organic EL modules (organic EL films, organic EL elements), electronic paper modules (thin film electronic paper), TET (Thin Film Transistor) substrates, etc.

At least one of the first bendable component 21 and the second bendable component 22 may be a polyimide film, or a laminate having a polyimide film on the side of the adhesive layer 11. Although the polyimide film generally has low adhesion to the adhesive layer, the adhesive layer 11 according to the present embodiment can achieve excellent peeling resistance even when the polyimide film is an adherend.

The Young's modulus of the first bendable component 21 and the second bendable component 22 are preferably 0.1 to 10 GPa, particularly preferably 0.5 to 7 GPa, and further preferably 1.0 to 5 GPa. When the Young's modulus of the first bendable component 21 and the second bendable component 22 are within the relevant range, it becomes easy to repeatedly bend each bendable component.

The thickness of the first bendable component 21 and the second bendable component 22 is preferably 10 to 3000 μm, particularly preferably 25 to 1000 μm, and further preferably 50 to 500 μm. When the thickness of the first bendable component 21 and the second bendable component 22 are within the relevant range, it becomes easy to repeatedly bend each bendable component.

When manufacturing the repeatedly bent laminated member 2, for example, the release sheet 12a on one side of the adhesive sheet 1 is peeled off, and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to the surface of one side of the first flexible member 21.

Thereafter, the release sheet 12b on the other side is peeled off from the adhesive layer 11 of the adhesive sheet 1, and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to the second bendable component 22 to obtain the repeatedly bent laminated component 2. In addition, as another example, the bonding order of the first bendable component 21 and the second bendable component 22 may be replaced.

[Repeated bending device] The repeated bending device related to the present embodiment is a device having the above-mentioned repeatedly bent laminated component 2, which may be composed of only the repeatedly bent laminated component 2, or may be composed of one or more repeatedly bent laminated components 2 and other repeatedly bent laminated components 2. When a repeatedly bent laminated component 2 is laminated with other repeatedly bent components, or when a repeatedly bent laminated component 2 is laminated with other bendable components, it is preferred to laminate them through the adhesive layer 11 of the above-mentioned adhesive sheet 1.

The repeatedly bending device related to this embodiment has an adhesive layer composed of the above-mentioned adhesive. When it is repeatedly bent or in a bent state for a long time, the interface between the adhesive layer and the adherend at the bent portion is not easily peeled off, and light leakage and reduced visibility caused by bending are suppressed.

A repetitive bending device as an example in this embodiment is shown in Fig. 3. In addition, the repetitive bending device related to the present invention is not limited to this repetitive bending device.

As shown in FIG3 , the repetitive bending device 3 according to the present embodiment is composed of, in order from the top, a cover film 31, a first adhesive layer 32, a polarizing film 33, a second adhesive layer 34, a touch sensing film 35, a third adhesive layer 36, an organic EL element 37, a fourth adhesive layer 38, and a TFT substrate 39. The cover film 31, the polarizing film 33, the touch sensing film 35, the organic EL element 37, and the TFT substrate 39 are equivalent to the bendable component.

At least one of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 is the adhesive layer 1 of the adhesive sheet 1. It is preferred that at least two of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 are the adhesive layer 11 of the adhesive sheet 1, and it is most preferred that all of the adhesive layers 32, 34, 36, and 38 are the adhesive layer 11 of the adhesive sheet 1.

Here, for example, when the TFT substrate 39 includes a polyimide film, and particularly when the fourth adhesive layer 38 has a polyimide film, it is preferred that at least the fourth adhesive layer 38 is the adhesive layer 11 of the adhesive sheet 1 .

The embodiments described above are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, the various elements disclosed in the embodiments described above are intended to include all design changes and equivalents within the technical scope of the present invention.

For example, one or both of the peeling sheets 12a and 12b in the adhesive sheet 1 may be omitted. In addition, a desired bendable component may be laminated to replace the peeling sheet 12a and/or the peeling sheet 12b. [Example]

Although the present invention is further specifically described below through embodiments and the like, the scope of the present invention is not limited to these embodiments and the like.

[Example 1] 1. Preparation of (meth)acrylate polymer (A) 46 parts by mass of n-butyl acrylate, 50 parts by mass of 2-ethylhexyl acrylate, 1 part by mass of 4-hydroxybutyl acrylate and 3 parts by mass of 2-phenoxyethyl acrylate were copolymerized by solution polymerization to prepare (meth)acrylate polymer (A). The molecular weight of this (meth)acrylate polymer (A) was measured by the following method, and the weight average molecular weight (Mw) was 1.2 million.

2. Preparation of adhesive composition 100 parts by mass (solid content conversion value; the same below) of the (meth)acrylate polymer (A) obtained in step 1 above, 0.14 parts by mass of trihydroxymethylpropane-modified xylene diisocyanate (XDI: manufactured by Soken Chemical Co., Ltd., product name "TD-75") as a crosslinking agent (B), and 0.20 parts by mass of 3-glycidyloxypropyltrimethoxysilane as a silane coupling agent were mixed, stirred thoroughly, and diluted with butanone to obtain a coating solution of the adhesive composition.

3. Preparation of adhesive sheet The obtained coating solution of the adhesive composition was applied to the peeling-treated surface of a heavy-peel peeling sheet (manufactured by Lintec, product name "SP-PET752150"), one side of which was peeled with a silicone-based peeling agent, using a knife coater. Then, the coating layer was heat-treated at 90°C for 1 minute to form a coating layer.

Next, the coating layer on the heavy-peel release sheet obtained above was placed on a light-peel release sheet (Lintec, product name "SP-PET381130"), one side of which was treated with a silicone-based release agent for release. The adhesive sheet having an adhesive layer with a thickness of 25 μm was prepared by laminating the adhesive layer in contact with the coating layer and aging it at 23°C and 50% RH for 7 days, that is, the adhesive sheet formed by the structure of heavy-peel release sheet/adhesive layer (thickness: 25 μm)/light-peel release sheet. The thickness of the adhesive layer is the value measured by a constant pressure thickness tester (manufactured by TECLOCK, product name "PG-02") based on JIS K7130.

Here, the respective formulations (solid conversion value) of the adhesive composition when the (meth)acrylate polymer (A) is taken as 100 parts by mass (solid conversion value) are shown in Table 1. The details of the abbreviations and the like described in Table 1 are as follows. [(meth)acrylate polymer (A)] BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate 4HBA: 4-hydroxybutyl acrylate PHEA: 2-phenoxyethyl acrylate MA: methyl acrylate MEA: 2-methoxyethyl acrylate AA: acrylic acid HEA: 2-hydroxyethyl acrylate.

[Example 2, Comparative Examples 1-3] Except that the types and ratios of the monomers constituting the (meth)acrylate polymer (A), the weight average molecular weight (Mw) of the (meth)acrylate polymer (A), and the amount of the crosslinking agent (B) were changed as shown in Table 1, the adhesive sheet was produced in the same manner as in Example 1.

[Test Example 1] (Determination of gel fraction) The adhesive sheets prepared in the embodiment and the comparative example were cut into a size of 80 mm × 80 mm, and the adhesive layer was wrapped in a polyester mesh (product name: Tetron mesh #200). The mass was weighed with a precision balance, and the mass of the adhesive alone was calculated by deducting the mass of the mesh alone. The mass at this time was referred to as M1.

Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. After that, the adhesive was taken out and air-dried for 24 hours at a temperature of 23°C and a relative humidity of 50%, and further dried in an oven at 80°C for 12 hours. After drying, its mass was weighed with a precision balance, and the mass of the adhesive alone was calculated by deducting the mass of the mesh alone. The mass at this time is referred to as M2. The gel fraction (%) is expressed as (M2/M1)×100. The results are shown in Table 2.

[Test Example 2] (Measurement of storage modulus G') The adhesive layers of the adhesive sheets prepared in the embodiment and the comparative example were stacked in multiple layers to form a laminate with a thickness of 3 mm. A cylinder with a diameter of 8 mm (height 3 mm) was punched out from the obtained laminate of adhesive layers and used as a sample.

For the above samples, based on JIS K7244-1, the storage modulus G' was measured by the torsional shear method using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR302") under the following conditions to obtain the storage modulus G'(-20) at -20°C, the storage modulus G'(25) at 25°C, and the storage modulus G'(85) at 85°C (MPa). The results are shown in Table 2. Measurement frequency: 1Hz Measurement temperature: -20°C to 150°C

[Test Example 3] (Measurement of photoelastic coefficient) The adhesive layers of the adhesive sheets prepared in the examples and comparative examples were laminated to form a laminate with a thickness of 0.2 mm. The obtained laminate of adhesive layers was cut into 2 cm × 4.5 cm pieces and placed in a photoelastic coefficient measuring device (manufactured by JASCO, product name "M-220"). Then, under the following conditions, the tensile load was gradually increased while the phase difference at each tensile load was measured. Based on the measurement results, the phase difference values at 400 nm, 500 nm, and 600 nm were taken out and plotted, and the photoelastic coefficient (m ² /N) at each wavelength was calculated from the slope. The results are shown in Table 2. ・Light source: Xe ・Measurement wavelength: 300nm～800nm ・Slit width: 1nm

[Test Example 4] (Measurement of Adhesive Strength) The light-peel release sheet was peeled off from the adhesive sheet obtained in the embodiment and the comparative example, and the exposed adhesive layer was bonded to the easy-adhesive layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET A4300", thickness: 100μm) having an easy-adhesive layer to obtain a laminate of a heavy-peel release sheet/adhesive layer/PET film. The obtained laminate was cut into 25mm wide and 110mm long.

On the other hand, the following two types of adherends were prepared. (1) Sodium calcium glass plate (manufactured by Nippon Sheet Glass Co., Ltd., product name "Sodium Calcium Glass", thickness: 1.1 mm) (2) A laminated body in which a polyimide film with an adhesive layer (manufactured by DUPONT-TORAY CO., LTD., product name "KAPTON 100PI", polyimide film thickness: 25 μm, adhesive layer thickness: 5 μm) was attached to one side of the soda calcium glass plate (manufactured by Nippon Sheet Glass Co., Ltd., product name "Sodium Calcium Glass", thickness: 1.1 mm) (the polyimide film side was the adhered side).

In an environment of 23°C and 50%RH, a heavy-peel release sheet was peeled off from the above-mentioned laminate, and the leaked adhesive layer was attached to the above-mentioned adherends, and then pressurized at 0.5MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd. After that, after being left at 23°C and 50%RH for 24 hours, the adhesive force (N/25mm) when the laminate of the PET film and the adhesive layer was peeled off from the adherend was measured using a tensile tester (TENSILON manufactured by ORIENTEC CORPORATION) at a peeling speed of 300mm/min and a peeling angle of 180 degrees. The conditions other than those described here were measured in accordance with JIS Z0237:2009. The results are shown in Table 2.

[Test Example 5] (Evaluation of peel resistance) In an environment of 23°C and 50% RH, the light peel type peeling sheet was peeled off from the adhesive sheets prepared in the embodiment and the comparative example, and the exposed adhesive layer was bonded to one side of a polyimide (PI) film (manufactured by DUPONT-TORAY CO., LTD., product name "KAPTON 100PI", thickness: 25μm, Young's modulus: 3.4GPa). Next, the heavy peel type peeling sheet was peeled off, and the exposed adhesive layer was bonded to the same PI film. Then, the mixture was pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Manufacturing Co., Ltd., and then placed at 23°C and 50% RH for 24 hours. The laminated body formed by the PI film/adhesive layer/PI film thus obtained was cut into pieces of 50 mm wide and 200 mm long, and used as a sample.

The obtained sample was kept in a bent state for 24 hours between two supporting plates (distance between each other: 4 mm) formed by two standing glass plates in an environment of -20°C as shown in Figure 4. After this static bending test, the interface between the adhesive layer and the adherend at the bent part of the test piece was visually checked to see if there was any peeling. The results are shown in Table 2. 0: No peeling △: Partial peeling (bubbles occurred) ×: Peeling

[Test Example 6] (Light leakage resistance) Prepare a plurality of COP polarizing plates (thickness 60μm) formed by laminating a triacetate cellulose (TAC) film (thickness 25μm), a polyvinyl alcohol (PVA) film polarizer (thickness 12μm), and a cycloolefin polymer (COP) film (thickness 23μm) in this order.

The light peeling release sheet was peeled off from the adhesive sheets prepared in the examples and comparative examples, and the exposed adhesive layer was attached to the TAC film side of one COP polarizing plate. Then, the heavy peeling release sheet was peeled off, and the exposed adhesive layer was attached to the COP film side of another COP polarizing plate in a crossed Nicol state. Then, the pressure was applied at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., and then placed at 23°C and 50% RH for 24 hours. The laminated body of the COP polarizing plate/adhesive layer/COP polarizing plate thus obtained was cut into pieces of 50 mm wide and 200 mm long to serve as a sample.

The obtained sample was repeatedly bent under the following conditions using a durability tester (manufactured by Yuasa System Co., Ltd., product name: "Planar Unloaded U-Shaped Stretch Tester Type: CL09-typeD01-FSC90"). After that, the bent state was released and placed in an environment of 23°C and 50%RH for 24 hours. Then, light leakage was visually confirmed in a dark room by penetrating light from a fluorescent lamp, and light leakage resistance was evaluated based on the following criteria. The results are shown in Table 2. In addition, regarding the adhesive sheet of Comparative Example 2, this evaluation was not performed because the evaluation of peeling resistance was poor.

<Test conditions> Bending direction: bend with the TAC film of one COP polarizing plate as the outside and the COP film of the other COP polarizing plate as the inside Minimum bending diameter: 3mmψ Number of bending times: 100,000 times Test temperature: 23℃ <Evaluation criteria for light leakage resistance> ◎…No light leakage was confirmed at the bent part. ０…Light leakage was slightly generated at the bent part, but it was not a problem in practical use. ×…Clear light leakage was confirmed at the bent part.

[Test Example 7] (Evaluation of visibility) The light-peel-type peeling sheet was peeled off from the adhesive sheets prepared in the embodiment and the comparative example, and the exposed adhesive layer was attached to the TAC film side of the COP polarizing plate similar to that in Test Example 6. Next, the heavy-peel-type peeling sheet was peeled off, and the exposed adhesive layer was attached to a phase difference film (λ/4, thickness 25μm) to obtain a laminate. On the other hand, the light peeling type peeling sheet was peeled off from another adhesive sheet prepared in the embodiment and the comparative example, and the exposed adhesive layer was attached to the aluminum layer of the aluminum film reflector formed by vapor-depositing an aluminum layer (thickness 1 μm) on a PET film (thickness 50 μm). Then, the heavy peeling type peeling sheet was peeled off, and the exposed adhesive layer was attached to the phase difference film of the above-mentioned laminate. Then, the film was pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Manufacturing Co., Ltd., and then placed at 23°C and 50% RH for 24 hours. The laminated body formed by the COP polarizing plate/adhesive layer/retardation film/adhesive layer/aluminum film reflective plate thus obtained was cut into pieces of 50 mm wide and 200 mm long, and used as a sample.

The above sample was bent statically for 24 hours under the following conditions using a durability tester (manufactured by Yuasa System Co., Ltd., product name: "Planar Unloaded U-Shaped Stretch Tester Type: CL09-typeD01-FSC90"). After that, the sample was released from the bending state and the reflected light was visually confirmed under a fluorescent light. The visibility was evaluated based on the following criteria. The results are shown in Table 2.

<Test conditions> Bending direction: bend with the COP polarizing plate on the outside and the aluminum film reflector on the inside Minimum bending diameter: 3mmФ Test temperature: 23℃ <Evaluation criteria for visibility> O…There is no reflected light at the bent part, and visibility is not considered to be reduced. ×…Waves from reflected light are visible at the bent part, and visibility is considered to be reduced.

[Table 1] (Meth)acrylate polymer (A) Crosslinking agent (B) Silane coupling agent Composition M Quality Quality Embodiment 1 BA/2EHA/4HBA/PHEA=46/50/1/3 1.2 million 0.14 0.2 Embodiment 2 BA/2EHA/4HBA/PHEA=41/50/1/8 Comparison Example 1 BA/2EHA/4HBA=49/50/1 Comparison Example 2 BA/MA/MEA/PHEA/AA/HEA=69.8/20/1/8/0.2/1 1.5 million 0.13 Comparison Example 3 BA/2EHA/4HBA/PHEA=33/50/1/16 1.2 million 0.14

[Table 2] Gel fraction (%) Storage modulus G'(MPa) Photoelastic coefficient (×10 ^-10 m ² /N) Adhesion force (N/25mm) Peel resistance [-20℃] Light leakage resistance Visibility G'(-20) G'(25) G'(85) 400nm 500nm 600nm Sodium calcium glass PI film Embodiment 1 67 0.083 0.046 0.024 4.3 4.2 3.8 10.5 15.2 ○ ◎ ○ Embodiment 2 65 0.074 0.033 0.020 4.6 3.7 3.5 10.4 15.7 ○ ◎ ○ Comparison Example 1 73 0.113 0.039 0.027 13.6 12.0 11.2 10.3 10.1 ○ × × Comparison Example 2 85 6.73 0.119 0.075 2.2 2.1 2.0 10.5 12.0 × - × Comparison Example 3 62 0.115 0.045 0.015 -89.0 -89.4 -120 13.4 16.3 ○ × ×

It can be clearly seen from Table 2 that when the adhesive layer of the adhesive sheet of the embodiment is bonded to two bendable components (polyimide film/polyimide film) and placed in a bent state, no peeling occurs at the interface between the adhesive layer and the bendable component, making it excellent in peeling resistance. This effect is fully exerted in a low temperature environment of -20°C. In addition, the adhesive layer of the adhesive sheet of the embodiment is excellent in light leakage resistance and visibility after bending. [Industrial Applicability]

The present invention is suitable for bonding a flexible component (especially a polyimide film or a laminate containing a polyimide film) constituting a repetitive bending device to other flexible components.

1: Adhesive sheet 11: Adhesive layer 12a, 12b: Peeling sheet 2: Repeated bending laminated component 21: First bending component 22: Second bending component 3: Repeated bending device 31: Cover film 32: First adhesive layer 33: Polarizing film 34: Second adhesive layer 35: Touch sensor film 36: Third adhesive layer 37: Organic EL element 38: Fourth adhesive layer 39: TFT substrate S: Test piece P: Support plate

[Figure 1] is a cross-sectional view of an adhesive sheet related to an embodiment of the present invention. [Figure 2] is a cross-sectional view of a repetitive bending laminated component related to an embodiment of the present invention. [Figure 3] is a cross-sectional view of a repetitive bending device related to an embodiment of the present invention. [Figure 4] is an explanatory diagram (side view) for explaining a static bending test.

1: Adhesive sheet

11: Adhesive layer

12a,12b: Peeling film

Claims (10)

An adhesive sheet having an adhesive layer for bonding a bendable component constituting a reciprocating bending device to other bendable components, wherein the adhesive constituting the adhesive layer has a storage modulus G'(-20) of 0.01 MPa or more and 0.2 MPa or less at -20°C and a measurement frequency of 1 Hz, an absolute value of a photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measurement wavelength of 400 nm of 9.9×10 ^-10 m ² /N or less, a gel fraction of the adhesive constituting the adhesive layer of 30% or more and 75% or less, and the adhesive constituting the adhesive layer is an acrylic adhesive. An adhesive sheet having an adhesive layer for bonding a bendable component constituting a reciprocatingly bending device to other bendable components, wherein the adhesive constituting the adhesive layer has a storage modulus G'(-20) of 0.01 MPa or more and 0.10 MPa or less at -20°C and a measurement frequency of 1 Hz, and an absolute value of a photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measurement wavelength of 400 nm of 9.9×10 ^-10 m ² /N or less, and the adhesive constituting the adhesive layer is an acrylic adhesive. The adhesive sheet as claimed in claim 1 or 2, wherein the adhesive constituting the adhesive layer has an absolute value of a photoelastic coefficient of 9.9×10 ^-10 m ² /N or less when measured at 23°C and a wavelength of 500 nm. The adhesive sheet as claimed in claim 1 or 2, wherein the adhesive constituting the adhesive layer has an absolute value of a photoelastic coefficient of 9.9×10 ^-10 m ² /N or less when measured at 23°C and a wavelength of 600 nm. An adhesive sheet as described in claim 1 or 2, wherein the adhesive constituting the adhesive layer has a storage modulus G'(85) of 0.005 MPa or more and 0.2 MPa or less at 85°C and a measurement frequency of 1 Hz. An adhesive sheet as described in claim 1 or 2, wherein the adhesive constituting the adhesive layer has a storage modulus G'(25) of not less than 0.01 MPa and not more than 0.2 MPa at 25°C and a measurement frequency of 1 Hz. The adhesive sheet as described in claim 2, wherein the gel fraction of the adhesive constituting the adhesive layer is greater than 30% and less than 95%. The adhesive sheet as described in claim 1 or 2, wherein the adhesive sheet has two peeling sheets, and the adhesive layer is clamped on the peeling sheets in a manner of contacting with the peeling surfaces of the two peeling sheets. A repeatedly bending laminated component comprises: a bendable component and other bendable components constituting a repeatedly bending device, and an adhesive layer for bonding the above-mentioned one bendable component and the above-mentioned other bendable components to each other, wherein the above-mentioned adhesive layer is composed of an adhesive layer of an adhesive sheet as described in claim 1 or 2. A repeated bending device, comprising: a repeated bending layered component as described in claim 9.

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