JP7428494B2 - Repeated bending laminate member and repeatable bending device - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive sheet for a device that is repeatedly bent, a repeatedly bent laminate member, and a repeatedly bent device.

In recent years, bendable displays have been proposed as displays for electronic equipment, which is a type of device. As flexible displays, in addition to displays that are curved only once, there have also been proposed displays that are repeatedly bent (folded).

In the above-mentioned repeated bending display, it is considered that one bendable member (flexible member) constituting the bendable display and another bendable member are bonded together using an adhesive layer of an adhesive sheet. It will be done. However, when a conventional adhesive sheet is used in a repeatedly bent display, a problem arises in that peeling occurs at the interface between the adhesive layer and the adherend at the bent portion.

Patent Document 1 discloses an adhesive intended to suppress the occurrence of peeling during repeated bending.

Japanese Patent Application Publication No. 2016-108555

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

The present invention has been made in view of the above-mentioned circumstances, and provides a method that prevents peeling at the interface between the adhesive layer and the adherend at the bent portion, and suppresses light leakage and visibility deterioration due to bending. The present invention aims to provide a pressure-sensitive adhesive sheet, a repeatedly bent laminate member, and a repeatedly bent device.

In order to achieve the above object, the present invention first provides an adhesive sheet having an adhesive layer for bonding one flexible member and another flexible member constituting a device that is repeatedly bent. The storage modulus G'(-20) at -20°C of the adhesive constituting the adhesive layer is 0.01 MPa or more and 0.2 MPa or less, and the adhesive constituting the adhesive layer has a Provided is a pressure-sensitive adhesive sheet characterized in that the absolute value of the photoelastic coefficient at a temperature of 400 nm at a measurement wavelength of 9.9×10 ⁻¹⁰ m ² /N or less is provided (invention 1).

In the above invention (invention 1), the adhesive constituting the adhesive layer has the above-mentioned physical properties, so that the adhesive layer forms a laminate in which one flexible member and another flexible member are bonded together. When the body is repeatedly bent or left in a bent state for a long period of time, peeling does not easily occur at the interface between the adhesive layer and the adherend at the bent part, and light leakage due to bending (after bending) is prevented. and visibility deterioration is suppressed.

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

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

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

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

In the above inventions (Inventions 1 to 5), the gel fraction of the adhesive constituting the adhesive layer is preferably 30% or more and 95% or less (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 includes two release sheets, and the adhesive layer is sandwiched between the release sheets such that it is in contact with the release surfaces of the two release sheets. (Invention 8).

Second, the present invention provides one flexible member and another flexible member constituting a device that is repeatedly bent, and an adhesive layer that bonds the one flexible member and the other flexible member to each other. Provided is a repeatedly bent laminated member comprising: (Invention 9), the adhesive layer comprising the adhesive layer of the adhesive sheet (Inventions 1 to 8).

Thirdly, the present invention provides a repeatedly bending device (invention 10) characterized by comprising the above-mentioned repeatedly bending laminated member (invention 9).

Advantageous Effects of Invention The adhesive sheet, the repeatedly bent laminated member, and the repeatedly bent device according to the present invention are unlikely to cause peeling at the interface between the adhesive layer and the adherend at the bent portion, and suppress light leakage and decrease in visibility due to bending. Ru.

FIG. 1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a repeatedly bent laminated member according to an embodiment of the present invention. 1 is a cross-sectional view of a repetitive bending device according to an embodiment of the invention. FIG. It is an explanatory view (side view) explaining a static bending test.

Embodiments of the present invention will be described below.
[Adhesive sheet]
The adhesive sheet according to one embodiment of the present invention has an adhesive layer for laminating one flexible member and another flexible member constituting a repeatable bending device, and preferably the adhesive A release sheet is laminated on one or both sides of the agent layer. The repetitive bending device and flexible member will be described later.

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

Since the adhesive constituting the adhesive layer in this embodiment has the above-mentioned physical properties, the adhesive layer can repeatedly bend a laminate formed by laminating one flexible member and another flexible member. When bent or left in a bent state for a long period of time, peeling does not easily occur at the interface between the adhesive layer and the adherend at the bent part, and light leakage and visibility decrease due to bending (after bending) are prevented. suppressed. In particular, when the storage elastic modulus G'(-20) is 0.2 MPa or less, the strain, that is, the stress (which becomes especially large at low temperatures) caused by repeated bending can be suppressed to a small level, thereby making it possible to suppress the adhesive at the bent part. Peeling is less likely to occur at the interface between the layer and the adherend. In particular, when the photoelastic coefficient is 9.9×10 ⁻¹⁰ m ² /N or less, the occurrence of birefringence due to residual stress due to bending can be suppressed, and light leakage and visibility reduction due to bending can be suppressed. suppressed.

From the viewpoint of the above-mentioned peel resistance, light leakage resistance and visibility, especially from the viewpoint of peel resistance, the storage modulus G' (-20) at -20°C of the adhesive constituting the adhesive layer is 0. .2 MPa or less, preferably 0.15 MPa or less, particularly preferably 0.10 MPa or less, and even more preferably 0.08 MPa or less. In addition, from the viewpoint of cohesive force, the storage modulus G' (-20) at -20°C of the adhesive constituting the adhesive layer needs to be 0.01 MPa or more, and is 0.03 MPa or more. It is preferably 0.05 MPa or more, particularly preferably 0.07 MPa or more.

The storage elastic modulus G' (85) at 85°C of the adhesive constituting the adhesive layer is preferably 0.2 MPa or less, more preferably 0.1 MPa or less, particularly 0.05 MPa or less. The pressure is preferably 0.03 MPa or less, and more preferably 0.03 MPa or less. As a result, the force acting from the adhesive layer on the adherend due to bending is reduced, and a device with excellent 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. This allows the adhesive layer to maintain its cohesive strength without becoming too soft even at high temperatures.

The storage modulus G'(25) at 25°C of the adhesive constituting the adhesive layer is preferably 0.2 MPa or less, more preferably 0.1 MPa or less, and particularly 0.08 MPa or less. The pressure is preferably 0.05 MPa or less, and more preferably 0.05 MPa or less. This makes it easier to exhibit adhesiveness. 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, particularly preferably 0.03 MPa or more. This not only provides excellent peeling resistance in the standard environmental temperature range, but also improves workability such as punching.

In addition, from the viewpoints of peel resistance, light leakage resistance, and visibility mentioned above, especially from the viewpoint of light leakage resistance and visibility, the photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measurement wavelength of 400 nm is The absolute value must be 9.9×10 ⁻¹⁰ m ² /N or less, preferably 8.0×10 ⁻¹⁰ m ² /N or less, and 6.0×10 ⁻¹⁰ m ² /N or less is more preferable, and particularly preferably 5.0×10 ⁻¹⁰ m ² /N or less. The lower limit of the absolute value of the photoelastic coefficient is not particularly limited, and may be 0 m ² /N. However, from the viewpoint of making it easier to obtain an adhesive whose storage modulus G'(-20) at -20°C satisfies the above-mentioned value, the absolute value of the photoelastic coefficient should be 1.0×10 ^-10 m ² /N or more. It is preferably 2.0×10 ⁻¹⁰ m ² /N or more, more preferably 3.0×10 ⁻¹⁰ m ² /N or more, especially 4.0×10 ⁻ It is preferable that it is ¹⁰ m ² /N or more.

From the viewpoint of further improving light leakage resistance and visibility, the absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measurement wavelength of 500 nm is 9.9 × 10 ^-10 m ² /N or less, more preferably 8.0×10 ⁻¹⁰ m ² /N or less, particularly preferably 6.0×10 −10 m 2 /N or less, and even more preferably 5.0×10 ⁻¹⁰ m ² /N or less. It is preferably .0×10 ⁻¹⁰ m ² /N or less. The lower limit of the absolute value of the photoelastic coefficient is not particularly limited, and may be 0 m ² /N. However, from the viewpoint of making it easier to obtain an adhesive whose storage modulus G'(-20) at -20°C satisfies the above-mentioned value, the absolute value of the photoelastic coefficient should be 1.0×10 ^-10 m ² /N or more. is preferable, more preferably 2.0×10 ⁻¹⁰ m ² /N or more, particularly preferably 3.0×10 ⁻¹⁰ m ² /N or more, and even more preferably 3.5× It is preferable that it is 10 ⁻¹⁰ m ² /N or more.

From the viewpoint of further improving light leakage resistance and visibility, the absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measurement wavelength of 600 nm is 9.9 × 10 ^-10 m ² /N or less, more preferably 8.0×10 ⁻¹⁰ m ² /N or less, particularly preferably 6.0×10 −10 m 2 /N or less, and even more preferably 4.0×10 ⁻¹⁰ m ² /N or less. It is preferably .0×10 ⁻¹⁰ m ² /N or less. The lower limit of the absolute value of the photoelastic coefficient is not particularly limited, and may be 0 m ² /N. However, from the viewpoint of making it easier to obtain an adhesive whose storage modulus G'(-20) at -20°C satisfies the above-mentioned value, the absolute value of the photoelastic coefficient should be 0.8×10 ^-10 m ² /N or more. It is preferably 1.5×10 ⁻¹⁰ m ² /N or more, more preferably 2.0×10 ⁻¹⁰ m ² /N or more, and even more preferably 3.0× It is preferable that it is 10 ⁻¹⁰ m ² /N or more.

The absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer at 23°C and a measurement wavelength of 400 nm, the absolute value of the photoelastic coefficient at a measurement wavelength of 500 nm, and the absolute value of the photoelastic coefficient at a measurement wavelength of 600 nm. The difference between the maximum value and the minimum value is preferably 8×10 ⁻¹⁰ m ² /N or less, more preferably 4×10 ⁻¹⁰ m ² /N or less, and 2.0×10 ⁻¹⁰ m ² /N or less. It is particularly preferable, and more preferably 1.5×10 ⁻¹⁰ m ² /N or less. This prevents light leakage resistance and visibility from being influenced by differences in the type of light emitters used.

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 even more preferably 60% or more. It is preferable that there be. Thereby, the adhesive exhibits a suitable cohesive force that can withstand repeated bending. As a result, the above-mentioned peeling resistance becomes more excellent. On the other hand, the gel fraction of the adhesive in this embodiment is preferably 95% or less, more preferably 90% or less, particularly preferably 80% or less, and even more preferably 75% or less. It is preferably 70% or less, and most preferably 70% or less. It is presumed that this suppresses the destruction of the crosslinked structure in the adhesive due to repeated bending, resulting in better visibility. Note that the method for measuring the gel fraction in this specification is as shown in the test example described below.

FIG. 1 shows a specific configuration as an example of the adhesive sheet according to the present embodiment.
As shown in FIG. 1, the adhesive sheet 1 according to one embodiment includes two release sheets 12a and 12b, and the two release sheets 12a are in contact with the release surfaces of the two release sheets 12a and 12b. , 12b. Note that the release surface of a release sheet in this specification refers to the surface of the release sheet that has releasability, and includes both a surface that has been subjected to release treatment and a surface that exhibits releasability even without being subjected to release treatment. .

1. Component 1-1. Adhesive Layer The adhesive layer 11 is made of an adhesive having the above-mentioned physical properties. The type of adhesive constituting the adhesive layer 11 is particularly limited as long as the above-mentioned physical properties (particularly the storage modulus G'(-20) at -20°C and the photoelastic coefficient at 23°C and a measurement wavelength of 400 nm) are satisfied. For example, any one of acrylic adhesive, polyester adhesive, polyurethane adhesive, rubber adhesive, silicone adhesive, etc. may be used. Further, the adhesive may be of an emulsion type, a solvent type, or a solvent-free type, and may be a crosslinked type or a non-crosslinked type. Among them, acrylic pressure-sensitive adhesives are preferred because they easily meet the physical properties described above and are also excellent in adhesive properties, optical properties, etc., and solvent-type acrylic pressure-sensitive adhesives are particularly preferred.

Specifically, the adhesive in this embodiment is an adhesive composition (hereinafter referred to as "adhesive composition P") containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B). It is preferable to use an adhesive formed by crosslinking. Such an adhesive can satisfy the above-mentioned physical properties and can easily provide good adhesive strength. In addition, in this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the concept of "copolymer" is also included in "polymer".

(1) Component (1-1) (meth)acrylic acid ester polymer (A) of adhesive composition P
The (meth)acrylic acid ester polymer (A) contains, as monomer units constituting the polymer, a (meth)acrylic acid alkyl ester to develop good adhesiveness and a reactive functional group to serve as a crosslinking point. (reactive functional group-containing monomer). Here, ordinary (meth)acrylic acid alkyl esters exhibit negative birefringence, and the resulting polymer has birefringence, but monomers exhibiting positive birefringence are incorporated into the polymer. By doing so, birefringence can be eliminated by canceling the positive and negative polarities. Thereby, the absolute value of the photoelastic coefficient of the obtained adhesive can be suppressed to a small value, making it easier to satisfy the above-mentioned photoelastic coefficient. In addition, (meth)acrylic acid alkyl esters tend to lower the storage modulus of the resulting polymer, while monomers that exhibit positive birefringence (particularly the aromatic ring-containing monomers described below) tend to lower the storage modulus of the resulting polymer. There is a tendency to increase the storage modulus of G', and by incorporating both into the polymer, it becomes easier to satisfy the physical properties regarding the storage modulus G' described above. Therefore, the (meth)acrylic acid ester polymer (A) includes a (meth)acrylic acid alkyl ester, a monomer exhibiting positive birefringence, and a reactive functional group-containing monomer as monomer units constituting the polymer. It is more preferable to contain.

The (meth)acrylic acid alkyl ester preferably contains a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms. The alkyl group is preferably linear or branched.

Examples of (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and n-(meth)acrylate. Butyl, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, (meth)acrylic acid Examples include n-dodecyl, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. Among them, from the viewpoint of the storage elastic modulus G' and photoelastic coefficient described above, (meth)acrylic acid esters in which the alkyl group has 1 to 8 carbon atoms are preferable, and (meth)acrylic acid esters in which the alkyl group has 4 to 8 carbon atoms are preferable. Acid esters are particularly preferred. Specifically, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, with n-butyl acrylate and 2-ethylhexyl acrylate being particularly preferred. Note that these may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains 50% by mass or more of a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms as a monomer unit constituting the polymer. , more preferably 70% by mass or more, particularly preferably 80% by mass or more, and even more preferably 90% by mass or more. Further, it is preferable to contain the (meth)acrylic acid alkyl ester at 99% by mass or less, more preferably at most 98% by mass, particularly preferably at most 97% by mass, and even more preferably at most 96% by mass. It is preferable to do so. When the (meth)acrylic acid alkyl ester whose alkyl group has 1 to 20 carbon atoms is contained in the above amount, the (meth)acrylic acid ester polymer (A) can be given suitable adhesiveness, and the above-mentioned The storage modulus G' and photoelastic coefficient are more likely to be satisfied.

As the monomer exhibiting positive birefringence, a monomer having a cyclic structure is preferably mentioned, and a monomer having an aromatic ring (aromatic ring-containing monomer) is particularly preferably mentioned. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, a biphenyl ring, and a fluorene ring. Among them, a benzene ring is preferred from the viewpoint of positive birefringence.

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

The (meth)acrylic ester copolymer (A) preferably contains 0.1% by mass or more, and preferably 0.5% by mass or more, of an aromatic ring-containing monomer as a monomer unit constituting the polymer. is more preferable, particularly preferably 1% by mass or more, and even more preferably 2% by mass or more. Further, the aromatic ring-containing monomer is preferably contained in an amount of 30% by mass or less, more preferably 20% by mass or less, particularly preferably 15% by mass or less, and even more 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)acrylic acid alkyl ester can be canceled out, and the birefringence can be further eliminated, and the photoelastic coefficient described above can be improved. becomes easier to satisfy. In addition, tackiness is also maintained well.

The (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, so that it can , reacts with a crosslinking agent (B) to be described later, thereby forming a crosslinked structure (three-dimensional network structure) to obtain a pressure-sensitive adhesive having a desired cohesive force. The adhesive easily satisfies the physical properties and photoelastic coefficient (and gel fraction) regarding the storage modulus G' described above.

The reactive functional group-containing monomers contained in the (meth)acrylic acid ester polymer (A) as monomer units constituting the polymer include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomer), carboxylic acid esters in the molecule, etc. Preferred examples include monomers having groups (carboxy group-containing monomers) and monomers having amino groups in the molecule (amino group-containing monomers). These reactive functional group-containing monomers may be used alone or in combination of two or more.

Among the above-mentioned reactive functional group-containing monomers, hydroxyl group-containing monomers or carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are particularly preferred. The hydroxyl group-containing monomer easily satisfies the physical properties regarding the storage modulus G' described above. That is, a hydroxyl group-containing monomer can particularly reduce the low-temperature storage modulus G', making it easy to finely adjust the storage modulus G' of the resulting adhesive.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and ) 3-hydroxybutyl acrylate, 4-hydroxybutyl (meth)acrylate, and other hydroxyalkyl (meth)acrylates. Among the above, preferred are (meth)acrylic acid hydroxyalkyl esters having a hydroxyalkyl group having 1 to 4 carbon atoms, from the viewpoint of ease of satisfying the physical properties regarding the storage modulus G' described above. Specifically, for example, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. are preferably mentioned, and 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate is particularly preferably mentioned. It will be done. These may be used alone or in combination of two or more.

Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred from the viewpoint of the adhesive strength of the resulting (meth)acrylic acid ester polymer (A). These may be used alone or in combination of two or more.

Note that 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and acrylic acid exhibit positive birefringence. Therefore, together with the monomer (aromatic ring-containing monomer) exhibiting positive birefringence described above, it can contribute to canceling out the negative birefringence possessed by the (meth)acrylic acid alkyl ester.

The (meth)acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer in an amount of 0.1% by mass or more, particularly 0.4% by mass or more, as a monomer unit constituting the polymer. The content is preferably 0.8% by mass or more, and more preferably 0.8% by mass or more. Further, the (meth)acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer in an amount of 18% by mass or less, particularly 9% by mass or less, as a monomer unit constituting the polymer. The content is preferably 3% by mass or less, and more preferably 3% by mass or less. When the (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer in the above amount as a monomer unit, the cohesive force of the resulting adhesive increases due to the crosslinking reaction with the crosslinking agent (B). This makes it easy to satisfy the physical properties (and gel fraction) related to the storage modulus G' described above, especially the storage modulus G' (-20) at -20°C.

It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxy group-containing monomer as a monomer unit constituting the polymer. Carboxy groups are acid components, so by not containing a carboxy group-containing monomer, the adhesive can be applied to objects that may cause problems due to acids, such as transparent conductive films such as tin-doped indium oxide (ITO), metal films, Even when a metal mesh or the like is present, problems caused by acid (corrosion, change in resistance value, etc.) can be suppressed.

Here, "not containing a carboxyl group-containing monomer" means that it does not substantially contain a carboxyl group-containing monomer, and in addition to not containing any carboxyl group-containing monomer at all, transparent conductive films and metal wiring due to carboxyl groups, etc. It is allowed to contain a carboxy group-containing monomer to the extent that corrosion does not occur. Specifically, the (meth)acrylic acid ester polymer (A) contains a carboxy group-containing monomer as a monomer unit of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less. It is allowed to be contained in an amount of % by mass or less.

The (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. As the other monomers, monomers containing no reactive functional groups are preferred in order not to inhibit the above-described effects of the monomers containing reactive functional groups. Examples of such monomers include non-reactive nitrogen atom-containing monomers such as N-acryloylmorpholine and N-vinyl-2-pyrrolidone, (meth)methoxyethyl (meth)acrylate, and ethoxyethyl (meth)acrylate. Examples include acrylic acid alkoxyalkyl ester, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 600,000 or more, more preferably 800,000 or more, particularly preferably 1,000,000 or more, and even more preferably 1,200,000 or more. It is preferable that it is above. The weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 2.5 million or less, more preferably 2 million or less, particularly preferably 1.7 million or less, and It is preferably 1.4 million or less. When the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is within the above range, the physical properties (and gel fraction) related to the storage elastic modulus G' mentioned above, especially the storage elastic modulus G' ( 25) and the storage modulus G'(85) at 85°C. Note that the weight average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

In adhesive composition P, one type of (meth)acrylic acid ester polymer (A) may be used alone, or two or more types may be used in combination.

(1-2) Crosslinking agent (B)
The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) using heating of the adhesive composition P containing the crosslinking agent (B) as a trigger to form a three-dimensional network structure. . This improves the cohesive force of the resulting adhesive, making it easier to satisfy the physical properties and gel fraction regarding the storage modulus G' described above.

The crosslinking agent (B) may be one that reacts with the reactive group possessed by the (meth)acrylic acid ester polymer (A), such as an isocyanate crosslinking agent, an epoxy crosslinking agent, an amine crosslinking agent. , melamine crosslinking agents, aziridine 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. can be mentioned. Among the above, it is preferable to use isocyanate-based crosslinking agents that have excellent reactivity with monomers containing reactive functional groups. Note that the crosslinking agent (B) can be used alone or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. and their biuret forms, isocyanurate forms, and adduct forms which are reactants with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate or trimethylolpropane-modified xylylene 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 0.01 parts by mass or more, based on 100 parts by mass of the (meth)acrylic acid ester polymer (A). The amount is preferably 0.6 parts by mass or more, and more preferably 0.12 parts by mass or more. Further, the content is preferably 5 parts by mass or less, more preferably 2 parts by mass or less, particularly preferably 1 part by mass or less, and even more preferably 0.4 parts by mass or less. is preferred. When the content of the crosslinking agent (B) is within the above range, the physical properties and gel fraction related to the storage modulus G' described above are easily satisfied.

(1-3) Various additives The adhesive composition P may optionally contain various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, and tackifiers. Agents, antioxidants, light stabilizers, softeners, fillers, refractive index modifiers, etc. can be added. Note that the polymerization solvent and dilution solvent described below are not included in the additives constituting the adhesive composition P.

It is preferable that the adhesive composition P contains the above-mentioned silane coupling agent. As a result, in the resulting adhesive layer, the adhesion to the flexible member that is the adherend is improved, and the adhesive strength becomes more preferable.

As the silane coupling agent, an organosilicon compound having at least one alkoxysilyl group in the molecule, which has good compatibility with the (meth)acrylic acid ester polymer (A) and has light transparency is used. preferable.

Examples of such silane coupling agents include silicon compounds containing polymerizable unsaturated groups such as vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltrimethoxysilane. Silicon compounds with epoxy structures such as sidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyl Mercapto group-containing silicon compounds such as dimethoxymethylsilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl An amino group-containing silicon compound such as dimethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, or at least one of these, and methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane. Examples include condensates with alkyl group-containing silicon compounds such as methoxysilane. 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, based on 100 parts by mass of the (meth)acrylic acid ester polymer (A). It is preferably at least 0.1 part by mass, more preferably at least 0.1 part by mass. Further, the content is preferably 1 part by mass or less, particularly preferably 0.5 part by mass or less, and further preferably 0.3 part by mass or less. When the content of the silane coupling agent is within the above range, the resulting adhesive layer has improved adhesion to the flexible member that is the adherend, and has greater adhesive strength.

(2) Manufacture of adhesive composition P Adhesive composition P is produced by manufacturing a (meth)acrylic acid ester polymer (A), and combining the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent. It can be produced by mixing (B) and adding additives if desired.

The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. The (meth)acrylic acid ester polymer (A) is preferably polymerized by a solution polymerization method using a polymerization initiator if desired. By polymerizing the (meth)acrylic acid ester polymer (A) by a solution polymerization method, it is easy to increase the molecular weight of the obtained polymer and adjust the molecular weight distribution, and further reduce the production of low molecular weight substances. becomes possible. Therefore, even when the gel fraction is relatively small and the degree of crosslinking is relaxed, the adhesive is less likely to be biased due to repeated bending, and it is easy to obtain an adhesive with excellent peeling resistance.

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, etc., and two or more types may be used in combination.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more types may be used in combination. Examples of azo compounds include 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-methylpropionate) , 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazolin-2-yl) Propane], etc.

Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxy Examples include dicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxy bivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like.

In the above polymerization step, the weight average molecular weight of the resulting polymer can be adjusted by incorporating a chain transfer agent such as 2-mercaptoethanol.

Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinking agent (B) and optional additives and diluting solvent are added to the solution of the (meth)acrylic acid ester polymer (A), and sufficient By mixing, a solvent-diluted adhesive composition P (coating solution) is obtained.

In addition, if any of the above components is used in solid form, or if precipitation occurs when mixed with other components in an undiluted state, that component alone must be diluted with a diluting solvent in advance. It may be mixed with other components after being dissolved or diluted.

Examples of the diluent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride, and ethylene chloride, methanol, ethanol, propanol, butanol, Alcohols such as 1-methoxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, and cellosolve solvents such as ethyl cellosolve are used.

The concentration and viscosity of the coating solution prepared in this manner are not particularly limited as long as they are within a coating range, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted to a concentration of 10 to 60% by mass. In addition, when obtaining a coating solution, addition of a dilution solvent etc. is not a necessary condition, and if adhesive composition P has a viscosity etc. which can be coated, it is not necessary to add a dilution solvent. In this case, the adhesive composition P becomes a coating solution using the polymerization solvent of the (meth)acrylic acid ester polymer (A) as a diluting solvent.

(3) Manufacture of adhesive The adhesive constituting the adhesive layer 11 in this embodiment is preferably formed by crosslinking the adhesive composition P. Crosslinking of the adhesive composition P can usually be performed by heat treatment. Note that this heat treatment can also serve as a drying treatment when evaporating the diluting solvent and the like from the coating film of the adhesive composition P applied to the desired object.

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

After the heat treatment, a curing period of about 1 to 2 weeks may be provided at room temperature (for example, 23° C., 50% RH), if necessary. If this curing period is necessary, the adhesive is formed after the curing period has elapsed; if this curing period is not necessary, the adhesive is formed after the heat treatment is completed.

By the above heat treatment (and curing), the (meth)acrylic acid ester polymer (A) is sufficiently crosslinked via the crosslinking agent (B) to form a crosslinked structure, and an adhesive is obtained.

(4) Thickness of adhesive layer The lower limit of the thickness of the adhesive layer 11 in the adhesive sheet 1 according to the present embodiment (value measured according to JIS K7130) is preferably 1 μm or more, and preferably 5 μm or more. It is more preferable that it is, it is especially preferable that it is 10 micrometers or more, and it is still more preferable that it is 15 micrometers or more. When the lower limit of the thickness of the adhesive layer 11 is above, it is easy to exhibit the desired adhesive force, and the peeling resistance becomes more excellent.

Further, the upper limit of the thickness of the adhesive layer 11 is preferably 300 μm or less, more preferably 150 μm or less, particularly preferably 90 μm or less, and a thinner repeated bending device can be obtained. From this point of view, it is more preferable that the thickness is 40 μm or less. When the upper limit of the thickness of the adhesive layer 11 is as described above, it is possible to suppress stress generated in the adhesive layer due to repeated bending from becoming too large, and to improve peeling resistance. Note that the adhesive layer 11 may be formed as a single layer, or may be formed by laminating multiple layers.

1-2. Release Sheet The release sheets 12a and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive layer 11) is used. In the adhesive sheet 1 according to this embodiment, one or both of the release sheets 12a and 12b are not necessarily required.

Examples of release sheets 12a and 12b include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, and polybutylene. Terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene/(meth)acrylic acid copolymer film, ethylene/(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluorine A resin film or the like is used. Moreover, these crosslinked films are also used. Furthermore, a laminated film of these may be used.

It is preferable that the release surfaces of the release sheets 12a, 12b (particularly the surfaces in contact with the adhesive layer 11) are subjected to a release treatment. Examples of the release agent used in the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. It is preferable that one of the release sheets 12a and 12b be a heavy release type release sheet with a high peel force, and the other release sheet be a light release type release sheet with a low peel force.

The thickness of the release sheets 12a, 12b is not particularly limited, but is usually about 20 to 150 μm.

2. Physical properties (adhesion)
The adhesive force of the adhesive sheet 1 according to the present embodiment to soda lime glass is preferably 1 N/25 mm or more as a lower limit, more preferably 3 N/25 mm or more, and particularly preferably 5 N/25 mm or more. Preferably, it is more preferably 8N/25mm or more. When the lower limit of the adhesive strength of the adhesive sheet 1 to soda lime glass is as described above, the peeling resistance becomes more excellent. On the other hand, the upper limit of the adhesive force is not particularly limited, but reworkability may be required. From this point of view, the adhesive force 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. In addition, the adhesive strength in this specification basically refers to the adhesive strength measured by the 180 degree peeling method according to JIS Z0237:2009, and the specific test method is as shown in the test example described below. .

The adhesive force of the adhesive sheet 1 according to the present embodiment to polyimide is preferably 1 N/25 mm or more as a lower limit, more preferably 3 N/25 mm or more, and particularly preferably 5 N/25 mm or more, Furthermore, it is preferable that it is 10N/25mm or more. When the lower limit of the adhesive strength of the adhesive sheet 1 to polyimide is as described above, even when a polyimide film or the like is used as an adherend, the peeling resistance becomes more excellent. On the other hand, the upper limit of the adhesive force is not particularly limited, but reworkability may be required. From such a viewpoint, the adhesive force 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. Manufacture of Adhesive Sheet As an example of manufacturing the adhesive sheet 1, a case where the above-mentioned adhesive composition P is used will be described. A coating liquid of the adhesive composition P is applied to the release surface of one of the release sheets 12a (or 12b), heat treatment is performed to thermally crosslink the adhesive composition P, and a coating layer is formed. The release surface of the other release sheet 12b (or 12a) is placed over the layer. If a curing period is required, a curing period is provided, and if a curing period is not required, the coating layer becomes the adhesive layer 11 as is. Thereby, the above-mentioned pressure-sensitive adhesive sheet 1 is obtained. The conditions for heat treatment and curing are as described above.

As another example of manufacturing the adhesive sheet 1, a coating liquid of the adhesive composition P is applied to the release surface of one of the release sheets 12a, and heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer. A release sheet 12a with a coating layer is obtained. Further, the coating liquid of the adhesive composition P is applied to the release surface of the other release sheet 12b, heat treatment is performed to thermally crosslink the adhesive composition P, and a coating layer is formed. A release sheet 12b is obtained. Then, the release sheet 12a with the coating layer and the release sheet 12b with the coating layer are pasted together so that both coating layers are in contact with each other. If a curing period is required, a curing period is provided, and if a curing period is not required, the laminated coating layers described above become the adhesive layer 11 as is. Thereby, the above-mentioned pressure-sensitive adhesive sheet 1 is obtained. According to this production example, even if the adhesive layer 11 is relatively thick, it is possible to stably produce it.

As a method for applying the coating liquid of the adhesive composition P, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, etc. can be used.

[Repeatedly bent laminated member]
As shown in FIG. 2, the repeatedly bent laminated member 2 according to the present embodiment includes a first flexible member 21 (one flexible member) and a second flexible member 22 (another flexible member). , and an adhesive layer 11 located between them and bonding the first flexible member 21 and the second flexible member 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 described above.

The repeated bending laminated member 2 is a repeated bending device itself or a member forming a part of a repeated bending device. The repeatable bending device is preferably a display that can be repeatedly bent (including folding) (repetitive bending display), but is not limited thereto. Examples of such repeated bending devices include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays using plastic substrates (films) as substrates, foldable displays, etc. It may be.

The first flexible member 21 and the second flexible member 22 are members that can be repeatedly bent (including bending), and are, for example, a cover film, a gas barrier film, a hard coat film, a polarizing film (polarizing plate). , polarizer, retardation film (retardation plate), viewing angle compensation film, brightness improvement film, contrast improvement film, diffusion film, transflective film, electrode film, transparent conductive film, metal mesh film, flexible glass, film Sensor (touch sensor film), liquid crystal polymer film, light emitting polymer film, film-like liquid crystal module, organic EL module (organic EL film, organic EL element), electronic paper module (film-like electronic paper), TFT (Thin Film Transistor) substrate etc.

At least one of the first flexible member 21 and the second flexible member 22 may be a polyimide film or a laminate including a polyimide film on the adhesive layer 11 side. Polyimide films generally have low adhesion to adhesive layers, but according to the adhesive layer 11 in this embodiment, excellent peeling resistance can be obtained even when polyimide films are adherends.

The Young's modulus of the first flexible member 21 and the second flexible member 22 is preferably 0.1 to 10 GPa, particularly preferably 0.5 to 7 GPa, and more preferably 1.0 to 7 GPa. Preferably it is 5 GPa. When the Young's moduli of the first flexible member 21 and the second flexible member 22 are within this range, it becomes easy to repeatedly bend each flexible member.

The thickness of the first flexible member 21 and the second flexible member 22 is preferably 10 to 3000 μm, particularly preferably 25 to 1000 μm, and more preferably 50 to 500 μm. . When the thicknesses of the first flexible member 21 and the second flexible member 22 are within this range, it becomes easy to repeatedly bend each flexible member.

In order to manufacture the above-described repeatedly bent laminated member 2, for example, one release sheet 12a of the adhesive sheet 1 is peeled off, and the exposed adhesive layer 11 of the adhesive sheet 1 is transferred to one side of the first flexible member 21. Paste on the surface.

Thereafter, the other release sheet 12b is peeled off from the adhesive layer 11 of the adhesive sheet 1, and the exposed adhesive layer 11 of the adhesive sheet 1 and the second flexible member 22 are laminated, and the bent laminated member 2 is repeatedly bent. get. Furthermore, as another example, the order of bonding the first flexible member 21 and the second flexible member 22 may be changed.

[Repetitive bending device]
The repeated bending device according to the present embodiment includes the above-described repeatedly bent laminated member 2, and may be composed of only the repeatedly bent laminated member 2, or may include one or more repeatedly bent laminated members 2 and other repeatedly bent laminated members 2. It may also be configured to include a flexible member. When laminating one repeatedly bent laminated member 2 and another repeatedly bent laminated member 2, or when laminating repeatedly bent laminated member 2 and another flexible member, the adhesive layer 11 of the adhesive sheet 1 described above is It is preferable to laminate the two layers with each other.

In the repeatedly bending device according to the present embodiment, since the adhesive layer is made of the above-mentioned adhesive, even when repeatedly bent or left in a bent state for a long period of time, the adhesive layer at the bent portion and the adherend are Peeling is less likely to occur at the interface with the material, and light leakage and visibility deterioration due to bending are suppressed.

FIG. 3 shows a repetitive bending device as an example of this embodiment. Note that the repetitive bending device according to the present invention is not limited to the repetitive bending device.

As shown in FIG. 3, the repetitive bending device 3 according to the present embodiment includes, in order from the top, a cover film 31, a first adhesive layer 32, a polarizing film 33, a second adhesive layer 34, It is constructed by laminating a touch sensor film 35, a third adhesive layer 36, an organic EL element 37, a fourth adhesive layer 38, and a TFT substrate 39. The above cover film 31, polarizing film 33, touch sensor film 35, organic EL element 37, and TFT substrate 39 correspond to flexible members.

At least any 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 11 of the adhesive sheet 1 described above. be. Any two or more layers 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 described above. Most preferably, all 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, especially when the fourth adhesive layer 38 side is provided with a polyimide film, at least the fourth adhesive layer 38 is made of the adhesive sheet 1 described above. It is preferable that the pressure-sensitive adhesive layer 11 is as follows.

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

For example, one or both of the release sheets 12a and 12b in the adhesive sheet 1 may be omitted, and a desired flexible member may be laminated instead of the release sheets 12a and/or 12b.

Hereinafter, the present invention will be explained in more detail with reference to examples, but the scope of the present invention is not limited to these examples.

[Example 1]
1. Preparation of (meth)acrylic acid ester 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. was copolymerized by a solution polymerization method to prepare a (meth)acrylic acid ester polymer (A). When the molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described below, the weight average molecular weight (Mw) was 1.2 million.

2. Preparation of adhesive composition 100 parts by mass (solid content equivalent; same hereinafter) of the (meth)acrylic acid ester polymer (A) obtained in the above step 1 and trimethylolpropane-modified xylene as a crosslinking agent (B). Mix 0.14 parts by mass of diisocyanate (XDI; manufactured by Soken Kagaku Co., Ltd., product name "TD-75") and 0.20 parts by mass of 3-glycidoxypropyltrimethoxysilane as a silane coupling agent, A coating solution of the adhesive composition was obtained by sufficiently stirring and diluting with methyl ethyl ketone.

3. Manufacture of adhesive sheet The coating solution of the obtained adhesive composition was applied to peel off a heavy release type release sheet (manufactured by Lintec, product name "SP-PET752150") in which one side of a polyethylene terephthalate film was treated with a silicone release agent. It was applied to the treated surface using a knife coater. The coating layer was then heat-treated at 90° C. for 1 minute to form a coating layer.

Next, the coated layer on the heavy release type release sheet obtained above and a light release type release sheet (manufactured by Lintec, product name "SP-PET381130") in which one side of the polyethylene terephthalate film was treated with a silicone release agent. were laminated so that the release-treated surface of the light-release release sheet was in contact with the coating layer, and cured for 7 days at 23°C and 50% RH to form an adhesive layer with a thickness of 25 μm. A pressure-sensitive adhesive sheet having the structure of heavy release type release sheet/adhesive layer (thickness: 25 μm)/light release type release sheet was prepared. The thickness of the adhesive layer is a value measured in accordance with JIS K7130 using a constant pressure thickness measuring device (manufactured by Techlock Co., Ltd., product name "PG-02").

Here, Table 1 shows each formulation (in terms of solid content) of the adhesive composition when the (meth)acrylic acid ester polymer (A) is 100 parts by mass (in terms of solid content). The details of the abbreviations and the like listed in Table 1 are as follows.
[(meth)acrylic acid ester 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: acrylic 2-hydroxyethyl acid

[Example 2, Comparative Examples 1 to 3]
The type and proportion of each monomer constituting the (meth)acrylic ester polymer (A), the weight average molecular weight (Mw) of the (meth)acrylic ester polymer (A), and the blending amount of the crosslinking agent (B). A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1 except for the changes shown in Table 1.

[Test Example 1] (Measurement of gel fraction)
The adhesive sheets prepared in Examples and Comparative Examples were cut into a size of 80 mm x 80 mm, the adhesive layer was wrapped in a polyester mesh (product name: Tetron Mesh #200), and its mass was weighed using a precision balance. The mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. Let the mass at this time be M1.

Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. Thereafter, 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, the mass was weighed using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. Let the mass at this time be M2. Gel fraction (%) is expressed as (M2/M1)×100. The results are shown in Table 2.

[Test Example 2] (Measurement of storage modulus G')
A plurality of adhesive layers of the adhesive sheets produced in Examples and Comparative Examples were laminated to form a laminate with a thickness of 3 mm. A cylindrical body with a diameter of 8 mm (height: 3 mm) was punched out from the obtained adhesive layer laminate and used as a sample.

The storage modulus G' of the above sample was measured in accordance with JIS K7244-1 using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR302") under the following conditions, and - Storage modulus G'(-20) at 20°C, storage modulus G'(25) at 25°C, and storage modulus G'(85) (MPa) at 85°C were obtained. The results are shown in Table 2.
Measurement frequency: 1Hz
Measurement temperature: -20℃~150℃

[Test Example 3] (Measurement of photoelastic coefficient)
A plurality of adhesive layers of the adhesive sheets prepared in Examples and Comparative Examples were laminated to form a laminate having a thickness of 0.2 mm. The resulting laminate of adhesive layers was cut into 2 cm x 4.5 cm pieces and set in a photoelastic coefficient measuring device (manufactured by JASCO, product name "M-220"). Then, under the following conditions, the phase difference at each tensile load was measured while increasing the tensile load stepwise. Based on the measurement results, the values of the phase difference at 400 nm, 500 nm, and 600 nm were extracted and plotted, and the photoelastic coefficient (m ² /N) at each wavelength was calculated from the slope thereof. The results are shown in Table 2.
・Light source lamp: Xe
・Measurement wavelength: 300nm to 800nm
・Slit width: 1nm

[Test Example 4] (Measurement of adhesive strength)
The easy-release type release sheet was peeled off from the adhesive sheets obtained in Examples and Comparative Examples, and the exposed adhesive layer was replaced with a polyethylene terephthalate (PET) film having an easily adhesive layer (manufactured by Toyobo Co., Ltd., product name "PET A4300"). , thickness: 100 μm) to obtain a laminate of heavy release type release sheet/adhesive layer/PET film. The obtained laminate was cut to a width of 25 mm and a length of 110 mm.

On the other hand, the following two types of adherends were prepared.
(1) Soda lime glass plate (manufactured by Nippon Sheet Glass Co., Ltd., product name: “Soda Lime Glass”, thickness: 1.1 mm)
(2) 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) laminate (polyimide film side is the adhered surface)

Under an environment of 23° C. and 50% RH, the heavy release type release sheet was peeled off from the above laminate, the exposed adhesive layer was applied to each of the above adherends, and the mixture was heated in an autoclave manufactured by Kurihara Seisakusho Co., Ltd. Pressure was applied at 5 MPa and 50° C. for 20 minutes. After that, the PET film was left to stand for 24 hours at 23°C and 50% RH, and then tested using a tensile tester (manufactured by Orientech Co., Ltd., Tensilon) at a peeling speed of 300 mm/min and a peeling angle of 180 degrees. The adhesive force (N/25 mm) when the laminate with the adhesive layer was peeled off from the adherend was measured. The measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 2.

[Test Example 5] (Evaluation of peeling resistance)
In an environment of 23° C. and 50% RH, the light-peel release sheet was peeled off from the adhesive sheets prepared in Examples and Comparative Examples, and the exposed adhesive layer was removed using a polyimide (PI) film (manufactured by DuPont-Toray). , product name "Kapton 100PI", thickness: 25 μm, Young's modulus: 3.4 GPa). Next, the heavy release type release sheet was peeled off, and the exposed adhesive layer was bonded to the same PI film. Then, after pressurizing at 0.5 MPa and 50° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., it was left for 24 hours under the conditions of 23° C. and 50% RH. The thus obtained laminate consisting of PI film/adhesive layer/PI film was cut into 50 mm width and 200 mm length, and this was used as a sample.

The obtained sample was placed in a bent state for 24 hours in a -20°C environment between two holding plates made of upright glass plates (distance between them: 4 mm), as shown in Figure 4. held. After performing this static bending test, it was visually confirmed whether there was any peeling at the interface between the adhesive layer and the adherend at the bent portion of the test piece. The results are shown in Table 2.
〇: No peeling △: Partial peeling (bubbles generated)
×: Peeling

[Test Example 6] (Light leakage resistance)
A COP polarizing plate in which a triacetyl cellulose (TAC) film (thickness 25 μm), a polyvinyl alcohol (PVA) film polarizer (thickness 12 μm), and a cycloolefin polymer (COP) film (thickness 23 μm) are laminated in that order. A plurality of sheets (thickness: 60 μm) were prepared.

The easy-release type release sheet was peeled off from the adhesive sheets prepared in Examples and Comparative Examples, and the exposed adhesive layer was attached to the TAC film side of one COP polarizing plate. Next, the heavy release type release sheet was peeled off, and the exposed adhesive layer was bonded to the COP film side of another COP polarizing plate in a crossed nicol state. Then, after pressurizing at 0.5 MPa and 50° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., it was left for 24 hours under the conditions of 23° C. and 50% RH. The thus obtained laminate consisting of COP polarizing plate/adhesive layer/COP polarizing plate was cut into 50 mm width and 200 mm length, and this was used as a sample.

The obtained sample was repeatedly bent under the following conditions using a durability tester (manufactured by Yuasa System Equipment Co., Ltd., product name: "Plane-like object no-load U-shaped expansion and contraction tester, model: CL09-typeD01-FSC90"). . Thereafter, the bent state was released and left for 24 hours in an environment of 23° C. and 50% RH. Then, light leakage was visually confirmed using transmitted light from a fluorescent lamp in a dark room, and the light leakage resistance was evaluated according to the following criteria. The results are shown in Table 2. Note that the pressure-sensitive adhesive sheet of Comparative Example 2 had a poor evaluation of peel resistance, so this evaluation was not performed.

<Test conditions>
Bending direction: Bend so that the TAC film of one COP polarizing plate is on the outside and the COP film of the other COP polarizing plate is on the inside.Minimum bending diameter: 3mmφ
Bending number: 100,000 times Test temperature: 23℃
<Evaluation criteria for light leakage resistance>
◎...No light leakage was observed at the bent portion.
○...Although there was a very slight light leakage at the bent portion, it was at a level that caused no practical problems.
×...Clear light leakage was confirmed at the bent portion.

[Test Example 7] (Evaluation of visibility)
The easy-release type release sheet was peeled off from the adhesive sheets prepared in Examples and Comparative Examples, and the exposed adhesive layer was attached to the TAC film side of the same COP polarizing plate as in Test Example 6. Next, the heavy release type release sheet was peeled off, and the exposed adhesive layer was bonded to a retardation film (λ/4, thickness 25 μm) to obtain a laminate. On the other hand, the light-release type release sheet was peeled off from another adhesive sheet prepared in Examples and Comparative Examples, and the exposed adhesive layer was replaced with an aluminum layer (thickness 1 μm) on a PET film (thickness 50 μm). It was attached to the aluminum layer of an aluminum film reflector. Next, the heavy release type release sheet was peeled off, and the exposed adhesive layer was bonded to the retardation film of the laminate. Then, after pressurizing at 0.5 MPa and 50° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., it was left for 24 hours under the conditions of 23° C. and 50% RH. The thus obtained laminate consisting of the COP polarizing plate/adhesive layer/retardation film/adhesive layer/aluminum film reflection plate was cut into a 50 mm width and 200 mm length, and this was used as a sample.

The above sample was statically bent for 24 hours under the following conditions using a durability tester (manufactured by Yuasa System Instruments Co., Ltd., product name: "Sheet object no-load U-shaped expansion/contraction testing machine, model: CL09-typeD01-FSC90"). . Thereafter, the bent state was released, and the condition of reflected light was visually checked under a fluorescent lamp, and visibility was evaluated according to the following criteria. The results are shown in Table 2.

<Test conditions>
Bending direction: Bend so that the COP polarizing plate is on the outside and the aluminum film reflector is on the inside.Minimum bending diameter: 3mmφ
Test temperature: 23℃
<Visibility evaluation criteria>
○: There was no reflected light at the bent portion, and no decrease in visibility was observed.
×...Unevenness due to reflected light was visible in the bent portion, and a decrease in visibility was observed.

As can be seen from Table 2, when two flexible members (polyimide film/polyimide film) are laminated together and placed in a bent state, the adhesive layer of the adhesive sheet of the example is different from the flexible member. No peeling occurred at the interface with the material, and the peeling resistance was excellent. This effect was fully exhibited in a low temperature environment of -20°C. Moreover, the adhesive layer of the adhesive sheet of the example had excellent light leakage resistance and visibility after bending.

The present invention is suitable for bonding one flexible member (particularly a polyimide film or a laminate containing a polyimide film) and another flexible member constituting a repeatable bending device.

DESCRIPTION OF SYMBOLS 1... Adhesive sheet 11... Adhesive layer 12a, 12b... Release sheet 2... Repeated bending laminated member 21... First flexible member 22... Second flexible member 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...Holding plate

Claims (7)

One flexible member and another flexible member constituting a device that is repeatedly bent;
A repeatedly bent laminated member comprising an adhesive layer for bonding the one flexible member and the other flexible member to each other,
The storage modulus G'(-20) of the adhesive constituting the adhesive layer at -20°C and a measurement frequency of 1 Hz is 0.01 MPa or more and 0.10 MPa or less,
The 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 adhesive constituting the adhesive layer is an adhesive formed by crosslinking an adhesive composition containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B). A laminated member that is repeatedly bent. 2. The adhesive according to claim 1, 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 at 23° C. and a measurement wavelength of 500 nm. Repeatedly bent laminated member. According to claim 1 or 2, the absolute value of the photoelastic coefficient of the adhesive constituting the adhesive layer at 23° C. and a measurement wavelength of 600 nm is 9.9×10 ⁻¹⁰ m ² /N or less. The repeatedly bent laminated member described above. Any one of claims 1 to 3, wherein the adhesive constituting the adhesive layer has a storage modulus G'(85) at 85° C. and a measurement frequency of 1 Hz of 0.005 MPa or more and 0.2 MPa or less. The repeatedly bent laminated member according to item (1). Any one of claims 1 to 4, wherein the adhesive constituting the adhesive layer has a storage modulus G'(25) at 25° C. and a measurement frequency of 1 Hz of 0.01 MPa or more and 0.2 MPa or less. The repeatedly bent laminated member according to item (1). The repeatedly bent laminated member according to any one of claims 1 to 5, wherein the adhesive constituting the adhesive layer has a gel fraction of 30% or more and 95% or less. A repeatedly bending device comprising the repeatedly bending laminated member according to any one of claims 1 to 6.

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