KR102578457B1 - Adhesive for repeatedly foldable device, adhesive sheet, repeatedly foldable laminate member and repeatedly foldable device - Google Patents

Abstract

The present invention suppresses deformation of the adhesive layer after being released from the bending state when applied to a repetitive bending device and repeatedly bent or when placed in a bending state for a long period of time, and reduces the influence and bending caused by repeated bending of the repetitive bending device. The object is to provide an adhesive and an adhesive sheet for a repetitive bending device that can alleviate the influence of being placed in a state.
As a means to solve this problem, an adhesive for repeatedly bending devices is used to bond one flexible member constituting a repeatedly bent device to another flexible member, and the adhesive is modified by 10% in accordance with JIS K7244-1. The maximum relaxed elastic modulus value measured at this time is set as the maximum relaxed elastic modulus G(t) _max (MPa), and the adhesive is continuously deformed by 10% until 3757 seconds after the maximum relaxed elastic modulus G(t) _max is measured. The minimum relaxed elastic modulus value measured is the minimum relaxed elastic modulus G(t) _min (MPa), and the relaxed elastic modulus fluctuation value ΔlogG(t) calculated from the following equation (I) is 0.85 or less. to provide.
ΔlogG(t)=logG(t) _max -logG(t) _min … (I)

Description

Adhesive for repeatedly bending device, adhesive sheet, repeatedly bent laminated member and repeatedly bent device

The present invention relates to an adhesive and an adhesive sheet for a repeatedly bent device, and to a repeatedly bent laminated member and a repeatedly bent device.

Recently, a bendable display has been proposed as a display body (display) of electronic equipment, which is a type of device. These flexible displays have a wide range of uses, for example, as a stationary display that is curved and installed on a cylindrical pillar, or as a mobile display that can be bent, folded, or rounded and transported. I'm looking forward to it.

Types of flexible displays include, for example, organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), and liquid crystal displays using plastic films as substrates.

In a flexible display as described above, it is generally considered that one bendable member (flexible member) constituting the flexible display is bonded to another flexible member with an adhesive layer of an adhesive sheet. Here, as a conventional display adhesive sheet that cannot be bent, for example, those shown in Patent Documents 1 and 2 are known.

A flexible display is not formed into a curved surface only once, but may be repeatedly bent (bended) as described in Patent Document 3. Additionally, in such repetitively flexible displays, there are cases where the display is fixed in a bent state for a long period of time. When a conventional adhesive sheet is used for a repeatedly flexible display for such purposes, there are cases where the adhesive layer is deformed and the flexible display remains greatly bent, even after being released from the bent state, and becomes hardened in that bent state.

Japanese Patent Application Publication No. 2015-174907 Japanese Patent Application Publication No. 2016-774 Japanese Patent Application Publication No. 2016-2764

The present invention has been made in consideration of the above-described actual situation, and when applied to a repetitive bending device and repeatedly bent or when placed in a bent state for a long period of time, deformation of the adhesive layer is suppressed after release from the bent state, and repeated bending is performed. Adhesives and adhesive sheets for repetitive bending devices that can alleviate the effects of repeated bending of the bending device and the effects of being placed in a bending state, and a device that is free from the bending state in the case of repeated bending and in the case of being placed in a bending state for a long period of time. The object is to provide a repeatedly bent laminated member and a repetitive bending device that can alleviate the effects of repeated bending and the effects of being placed in a bent state.

In order to achieve the above object, firstly, the present invention is an adhesive for a repeatedly bending device for bonding one bendable member and another bendable member constituting a repeatedly bendable device. In accordance with JIS K7244-1, the adhesive is The maximum relaxed elastic modulus value measured when deformed by 10% is set as the maximum relaxed elastic modulus G(t) _max (MPa), and the adhesive is continued at 10% until 3757 seconds after the maximum relaxed elastic modulus G(t) _max is measured. Deformation is performed, and the minimum relaxed elastic modulus value measured in the meantime is set as the minimum relaxed elastic modulus G(t) _min (MPa), and the relaxed elastic modulus fluctuation value ΔlogG(t) calculated from the following equation (I) is 0.85 or less. An adhesive for a repetitive bending device characterized by features is provided (invention 1).

ΔlogG(t)=logG(t) _max -logG(t) _min … (I)

In the invention (invention 1), by satisfying the above-mentioned physical properties, when applied to a repetitive bending device and repeatedly bent, or when placed in a bent state for a long period of time, deformation of the adhesive layer occurs after release from the bent state. It is difficult to do this, and hardening of the repetitive bending device in a greatly bent state is suppressed, and thus the influence due to repeated bending of the repetitive bending device and the influence of being placed in a bent state can be alleviated.

In the above invention (invention 1), it is preferable that the loss tangent (tanδ) at 25°C obtained from dynamic viscoelasticity measurement based on JIS K7244-1 is 0.328 or more and 0.85 or less (invention 2).

In the invention (invention 2), by satisfying the above-mentioned physical properties, it becomes easy to exhibit high adhesive force, and even when applied to a repetitive bending device and repeatedly bent or placed in a bending state for a long period of time, the adhesive layer as described above Peeling of the interface between the adhesive layer and the adherend that occurs at the bent portion can be suppressed by interaction with the material that is less likely to cause deformation.

In the above inventions (inventions 1 and 2), the storage modulus (G') at 25°C is preferably 0.01 MPa or more and 0.25 MPa or less (invention 3).

In the above inventions (inventions 1 to 3), it is preferable that the loss modulus (G") at 25°C is 0.005 MPa or more and 0.10 MPa or less (invention 4).

In the above inventions (inventions 1 to 4), the adhesive is preferably an adhesive formed by crosslinking an adhesive composition containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B) (invention 5).

Second, the present invention is an adhesive sheet having an adhesive layer for bonding one flexible member and another flexible member constituting a repeatedly bent device, wherein the adhesive layer is the adhesive for the repeatedly bent device (inventions 1 to 5). Provides an adhesive sheet characterized by consisting of (invention 6).

In the invention (invention 6), the adhesive sheet includes two release sheets, and the adhesive layer is sandwiched between the release sheets so as to contact the release surfaces of the two release sheets. It is desirable to have it (invention 7).

Thirdly, the present invention is a repeatedly bent laminated member comprising one flexible member and another flexible member constituting a repeatedly bent device, and an adhesive layer for bonding the one flexible member and the other flexible member to each other, wherein the adhesive A repeatedly bent laminated member is provided (invention 8), wherein the layer is the adhesive layer of the above-described pressure-sensitive adhesive sheet (inventions 6 and 7).

In the above invention (invention 8), it is preferable that at least one of the one flexible member and the other flexible member is a display element (invention 9).

Fourthly, the present invention provides a repeatedly bending device characterized by being provided with the above repeatedly bent laminated members (inventions 8 and 9) (invention 10).

The adhesive and adhesive sheet for a repeatedly bending device according to the present invention are unlikely to cause deformation of the adhesive layer after being released from the bending state when applied to a repetitive bending device and repeatedly bent or when placed in a bending state for a long period of time, The influence of repetitive bending of the device and the influence of being placed in a bent state can be alleviated. In addition, the repeatedly bent laminated member and the repeatedly bent device according to the present invention, when repeatedly bent or placed in a bent state for a long period of time, are affected by repeated bending and are affected by being placed in a bent state after being released from the bent state. can be alleviated.

1 is a cross-sectional view of an adhesive sheet according to an embodiment of the present invention.
Figure 2 is a cross-sectional view of a repeatedly bent laminated member according to one embodiment of the present invention.
Figure 3 is an explanatory diagram (side view) illustrating a static bending test.
Figure 4 is an explanatory diagram (side view) illustrating the amount of deformation of the test piece as a test result of a bending test.
Figure 5 is an explanatory diagram (side view) illustrating a dynamic bending test.

Hereinafter, embodiments of the present invention will be described.

[Adhesive for repetitive bending devices]

The adhesive for a repetitive bending device (hereinafter sometimes simply referred to as “adhesive”) according to the present embodiment is an adhesive for bonding one flexible member constituting the repetitive bending device to another flexible member. The repetitive bending device and the bending member will be described later.

For the adhesive according to the present embodiment, the maximum relaxed elastic modulus value measured when the adhesive is deformed by 10% is set as the maximum relaxed elastic modulus G(t) _max (MPa), based on JIS K7244-1, and the maximum relaxed elastic modulus is determined. The adhesive is continuously deformed by 10% until 3757 seconds after G(t) _max is measured, and the minimum relaxed modulus value measured in the meantime is set as the minimum relaxed modulus G(t) _min (MPa), and the following formula is used. The relaxation modulus variation value ΔlogG(t) calculated from (I) is 0.85 or less.

ΔlogG(t)=logG(t) _max -logG(t) _min … (I)

In addition, details of the method for measuring the relaxed elastic modulus G(t) are as shown in the test examples described later.

The pressure-sensitive adhesive according to the present embodiment has a small relaxation modulus fluctuation value as described above, so the property of a perfectly elastic body increases, and the stress fluctuation when deformed by a predetermined amount is small, that is, the force to return to the original state is maintained. easy. Therefore, the deformation is likely to return to its original state when removed. Therefore, the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive is unlikely to cause deformation of the pressure-sensitive adhesive layer even after being released from the bending state when the repeatedly bending device to which the pressure-sensitive adhesive layer is applied is repeatedly bent or is placed in a bending state for a long period of time. Hardening of the bending device in a greatly bent state is suppressed, and thus the influence due to repeated bending of the bending device and the influence due to being placed in the bending state can be alleviated. This effect may hereinafter be referred to as “the effect of alleviating the bending state of the repetitive bending device.” Additionally, as an indicator of the number of times of repeated bending, 30,000 times is exemplified as an example.

In addition, the adhesive according to the present embodiment preferably has a loss tangent (tan δ) of 0.328 or more and 0.85 or less at 25°C, obtained from dynamic viscoelasticity measurement based on JIS K7244-1. In addition, the details of the loss tangent (tanδ) measurement method are as shown in the test examples described later.

The adhesive according to the present embodiment has a particularly large loss tangent (tan δ) as described above, so its viscosity becomes stronger and high adhesive strength is easily exhibited. Therefore, even when a repetitive bending device to which an adhesive layer made of the adhesive layer is applied is repeatedly bent or placed in a bent state for a long period of time, the relaxation modulus fluctuation value is small as described above, and deformation of the adhesive layer is unlikely to occur. This prevents peeling from occurring at the interface between the adhesive layer and the adherend in the bent portion. This effect may hereinafter be referred to as the “interfacial peeling suppression effect.”

From the viewpoint of the bending state relaxation effect of the repetitive bending device, the relaxation modulus fluctuation value ΔlogG(t) is required to be 0.85 or less, preferably 0.82 or less, particularly preferably 0.75 or less, and more preferably 0.50 or less. Moreover, the lower limit of the relaxation modulus fluctuation value is not particularly limited, but is usually preferably 0.10 or more, and 0.15 or more is particularly preferable.

The maximum relaxed elastic modulus G(t) _max of the adhesive according to the present embodiment is an upper limit, preferably 1.0 MPa or less, particularly preferably 0.95 MPa or less, and more preferably 0.9 MPa or less. When the upper limit of the maximum relaxed elastic modulus G(t) _max is the above, the relaxed elastic modulus fluctuation value ΔlogG(t) easily satisfies the above-mentioned value. The lower limit of the maximum relaxed elastic modulus G(t) _max is not particularly limited, but is usually preferably 0.05 MPa or more, particularly preferably 0.10 MPa or more, and more preferably 0.15 MPa or more.

In addition, the minimum relaxed elastic modulus G(t) _min of the adhesive according to the present embodiment is a lower limit, preferably 0.005 MPa or more, particularly preferably 0.01 MPa or more, and more preferably 0.02 MPa or more. When the lower limit of the minimum relaxed elastic modulus G(t) _min is the above, the relaxed elastic modulus fluctuation value ΔlogG(t) easily satisfies the above-mentioned value. The upper limit of the minimum relaxed elastic modulus G(t) _min is not particularly limited, but is usually preferably 0.50 MPa or less, particularly preferably 0.45 MPa or less, and more preferably 0.40 MPa or less.

On the other hand, the loss tangent (tanδ) at 25°C of the adhesive according to the present embodiment is preferably 0.328 or more, particularly preferably 0.45 or more, and more preferably 0.55 as a lower limit, especially from the viewpoint of the effect of suppressing interfacial peeling. desirable. Furthermore, from the viewpoint of maintaining the shape of the adhesive layer, the upper limit of the loss tangent (tanδ) is preferably 0.85 or less, particularly preferably 0.75 or less, and more preferably 0.65.

The type of adhesive according to this embodiment is not particularly limited as long as the above-mentioned physical properties are satisfied, and may be any of, for example, an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, a rubber adhesive, or a silicone adhesive. Additionally, the adhesive may be of an emulsion type, solvent type, or non-solvent type, and may be of a crosslinked type or non-crosslinked type. Among them, an acrylic adhesive that easily satisfies the above-mentioned physical properties and has excellent adhesive properties, optical properties, etc. is preferable.

Additionally, the acrylic adhesive may be one that is active energy ray curable, one that is not active energy ray curable, one that is heat crosslinkable, one that is non-crosslinkable, or a combination of these may be used, but good flexibility is not obtained. For this reason, it is preferable that it is non-curable by active energy rays. As an active energy ray non-curable acrylic adhesive, a crosslinked type is particularly preferable, and a heat crosslinked type is more preferable.

The adhesive according to the present embodiment is, in particular, an adhesive obtained by crosslinking a (meth)acrylic acid ester polymer (A) and an adhesive composition containing a crosslinking agent (B) (hereinafter sometimes referred to as “adhesive composition P”). desirable. With such an adhesive, it is easy to satisfy the above-mentioned physical properties, and since good adhesive force and a certain cohesive force are obtained, durability is also excellent. In addition, in this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same goes for other similar terms. In addition, “polymer” shall also include the concept of “copolymer.”

(1) Components of adhesive composition P

(1-1) (meth)acrylic acid ester polymer (A)

The (meth)acrylic acid ester polymer (A) preferably contains a (meth)acrylic acid alkyl ester and a monomer (reactive functional group-containing monomer) having a reactive functional group in the molecule as a monomer unit constituting the polymer.

The (meth)acrylic acid ester polymer (A) can exhibit desirable adhesiveness by containing (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. As the (meth)acrylic acid alkyl ester, (meth)acrylic acid alkyl ester whose alkyl group has 1 to 20 carbon atoms is preferable. The alkyl group may be linear or branched, and may have a cyclic structure.

As alkyl (meth)acrylic acid esters with an alkyl group having 1 to 20 carbon atoms, those containing a homopolymer glass transition temperature (Tg) of -40°C or lower (hereinafter sometimes referred to as "low Tg alkyl acrylate") desirable. By containing such a low Tg alkyl acrylate as a constituent monomer unit, the flexibility of the obtained adhesive can be improved.

Low Tg alkyl acrylates include, for example, n-butyl acrylate (Tg -55°C), n-octyl acrylate (Tg -65°C), isooctyl acrylate (Tg -58°C), and 2-ethylhexyl acrylate (Tg). -70℃), isononyl acrylate (Tg -58℃), isodecyl acrylate (Tg -60℃), isodecyl methacrylate (Tg -41℃), n-lauryl methacrylate (Tg -65℃) ), tridecyl acrylate (Tg -55°C), tridecyl methacrylate (Tg -40°C), etc. are preferably mentioned. Among them, from the viewpoint of more effectively improving flexibility, as a low Tg alkyl acrylate, it is more preferable that the Tg of the homopolymer is -45°C or lower, and it is especially preferable that it is -50°C or lower. Specifically, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. These may be used individually, or two or more types may be used in combination.

The (meth)acrylic acid ester polymer (A), as a monomer unit constituting the polymer, preferably contains 50% by mass or more of low Tg alkyl acrylate as the lower limit, and particularly preferably contains 55% by mass or more, It is more preferable to contain 60% by mass or more. By containing 50% by mass or more of the low Tg alkyl acrylate, it becomes easier to set the glass transition temperature (Tg) of the (meth)acrylic acid ester polymer (A) within the above-mentioned range.

On the other hand, the (meth)acrylic acid ester polymer (A) preferably contains 99.9% by mass or less of the above-mentioned low Tg alkyl acrylate as the monomer unit constituting the polymer, as the upper limit, and particularly preferably contains 99% by mass or less. And, it is more preferable to contain 98% by mass or less. By containing 99.9% by mass or less of the low Tg alkyl acrylate, it is possible to introduce an appropriate amount of other monomer components (particularly reactive functional group-containing monomers) into the (meth)acrylic acid ester polymer (A).

In addition, the above-mentioned alkyl (meth)acrylic acid alkyl esters having 1 to 20 carbon atoms in the alkyl group are monomers whose glass transition temperature (Tg) as a homopolymer exceeds 0°C (hereinafter sometimes referred to as “high Tg alkyl acrylates”). It may contain. By containing such a high Tg alkyl acrylate as a constituent monomer unit, the relaxation modulus fluctuation value of the obtained pressure-sensitive adhesive may easily satisfy the above-mentioned value.

Additionally, as a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms, it is also preferable to use a combination of low Tg alkyl acrylate and high Tg alkyl acrylate. As a result, the relaxation modulus fluctuation value and loss tangent of the obtained pressure-sensitive adhesive easily satisfy the above-mentioned values.

When the (meth)acrylic acid ester polymer (A) contains a high Tg alkyl acrylate as a monomer unit constituting the polymer, the content is preferably 5% by mass or more, and particularly preferably 10% by mass or more, It is more preferable that it is 15 mass% or more. Moreover, the content is preferably 30 mass% or less, particularly preferably 25 mass% or less, and more preferably 20 mass% or less.

Examples of the high Tg alkyl acrylates include methyl acrylate (Tg 10°C), methyl methacrylate (Tg 105°C), ethyl methacrylate (Tg 65°C), and n-butyl methacrylate (Tg 20°C). ), isobutyl methacrylate (Tg 48℃), t-butyl methacrylate (Tg 107℃), n-stearyl acrylate (Tg 30℃), n-stearyl methacrylate (Tg 38℃), acrylic acid Cyclohexyl (Tg 15℃), cyclohexyl methacrylate (Tg 66℃), benzyl methacrylate (Tg 54℃), isobornyl acrylate (Tg 94℃), isobornyl methacrylate (Tg 180℃) , adamantyl acrylate (Tg 115°C), adamantyl methacrylate (Tg 141°C), and morpholine acrylate (Tg 145°C). Among the above, methyl acrylate, methyl methacrylate and isobornyl acrylate are preferred from the viewpoint of cohesive force. These may be used individually, or two or more types may be used in combination.

Additionally, when using a combination of low Tg alkyl acrylate and high Tg alkyl acrylate as a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms, the (meth)acrylic acid ester polymer (A) is As a constituting monomer unit, it is preferable to contain the low Tg alkyl acrylate in an amount of 85% by mass or less as an upper limit, particularly preferably 75% by mass or less, and more preferably 65% by mass or less. As a result, the relaxation modulus fluctuation value and loss tangent of the obtained adhesive become more likely to satisfy the above-mentioned values.

The (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, and reacts with a crosslinking agent (B) described later through a reactive functional group derived from the reactive functional group-containing monomer, As a result, a crosslinked structure (three-dimensional network structure) is formed, and an adhesive having the desired cohesive force is obtained.

The reactive functional group-containing monomer contained in the (meth)acrylic acid ester polymer (A) as a monomer unit constituting the polymer includes a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), and a monomer having a carboxyl group in the molecule (carboxy group-containing monomer). , a monomer having an amino group in the molecule (amino group-containing monomer), etc. are preferably mentioned. These reactive functional group-containing monomers may be used individually or in combination of two or more types.

Among the above reactive functional group-containing monomers, hydroxyl group-containing monomers and carboxyl group-containing monomers are preferable, and hydroxyl group-containing monomers are particularly preferable. Since the hydroxyl group-containing monomer has a relatively low glass transition temperature (Tg) as a homopolymer, it is easy to maintain high flexibility of the obtained (meth)acrylic acid ester polymer (A), and the carboxyl group-containing monomer is used to obtain a (meth)acrylic acid ester polymer (A). The adhesive strength of A) can be increased.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, ( (meth)acrylic acid hydroxyalkyl esters such as 3-hydroxybutyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate. Among them, from the viewpoint of flexibility of the resulting (meth)acrylic acid ester polymer (A), 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are preferable. These may be used individually, or two or more types may be used in combination.

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

When the (meth)acrylic acid ester polymer (A) contains a hydroxyl group-containing monomer as a monomer unit constituting the polymer, the content of the hydroxyl group-containing monomer is preferably 0.1% by mass or more, and particularly preferably 0.3% by mass or more. do. Additionally, the content of the hydroxyl group-containing monomer is preferably 30% by mass or less, particularly preferably 25% by mass or less, and more preferably 20% by mass or less. On the other hand, when the (meth)acrylic acid ester polymer (A) contains a carboxyl group-containing monomer as a monomer unit constituting the polymer, the content of the carboxyl group-containing monomer is preferably 0.5% by mass or more, and is 1% by mass or more. Particularly desirable. Additionally, the content of the carboxyl group-containing monomer is preferably 10 mass% or less, particularly preferably 7 mass% or less, and more preferably 5 mass% or less. Since the contents of the hydroxyl group-containing monomer and the carboxyl group-containing monomer are respectively as above, the flexibility and adhesiveness of the obtained (meth)acrylic acid ester polymer (A) are better, and the bending state relaxation effect of the repeatedly bending device of the obtained pressure-sensitive adhesive layer is more effective. Achieved at a high level.

Moreover, when the (meth)acrylic acid ester polymer (A) contains only a hydroxyl group-containing monomer as a reactive functional group-containing monomer as a monomer unit constituting the polymer, the content is preferably 1% by mass or more, and is 3% by mass. It is more preferable that it is more than 5 mass%, it is especially preferable that it is 5 mass% or more, it is more preferable that it is 10 mass% or more, and it is most preferable that it is 15 mass% or more.

The (meth)acrylic acid ester polymer (A) may contain a nitrogen atom-containing monomer as a monomer unit constituting the polymer. Examples of the nitrogen atom-containing monomer include monomers having an amino group, monomers having an amide group, monomers having a nitrogen-containing heterocycle, etc. Among these, monomers having a nitrogen-containing heterocycle are preferable.

Examples of monomers having a nitrogen-containing heterocycle include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, and N-(meth) Acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylaziridine, aziridinyl ethyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, 2- Examples include vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, and N-vinylphthalimide. Among them, N-(meth)acryloylmorpholine, which exhibits better adhesiveness, is preferred. , N-acryloylmorpholine is particularly preferred. These may be used individually, or two or more types may be used in combination.

When the (meth)acrylic acid ester polymer (A) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer, the content of the nitrogen atom-containing monomer is preferably 1% by mass or more, and 3% by mass or more. Particularly desirable. Additionally, the content of the nitrogen atom-containing monomer is preferably 20% by mass or less, particularly preferably 15% by mass or less, and more preferably 10% by mass or less.

The (meth)acrylic acid ester polymer (A) may, if desired, contain other monomers as monomer units constituting the polymer. As other monomers, monomers that do not contain reactive functional groups are preferred so as not to inhibit the above-described actions of the monomers containing reactive functional groups. Examples of such monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used individually, or two or more types may be used in combination.

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

The lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 100,000 or more, particularly preferably 300,000 or more, and more preferably 500,000 or more. If the lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is above, the adhesive will have better durability. In addition, the weight average molecular weight in this specification is a standard polystyrene conversion value measured by gel permeation chromatography (GPC) method.

Additionally, the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 1.5 million or less, particularly preferably 1.2 million or less, and more preferably 1 million or less. If the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is above, the resulting adhesive will have better flexibility and adhesive strength.

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

(1-2) Cross-linking agent (B)

The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) as a trigger, such as by heating the adhesive composition P containing the crosslinking agent (B), and forms a three-dimensional network structure. As a result, the cohesive strength of the obtained adhesive is improved, and the adhesive layer becomes excellent in durability.

The crosslinking agent (B) may be any that reacts with the reactive group of the (meth)acrylic acid ester polymer (A), for example, an isocyanate crosslinking agent, an epoxy crosslinking agent, an amine crosslinking agent, a melamine crosslinking agent, an aziridine crosslinking agent, and hydrazine. Examples include cross-linking agents, aldehyde-based cross-linking agents, oxazoline-based cross-linking agents, metal alkoxide-based cross-linking agents, metal chelate-based cross-linking agents, metal salt-based cross-linking agents, and ammonium salt-based cross-linking agents. Among the above, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with reactive functional group-containing monomers, which are the constituent monomer units of the (meth)acrylic acid ester polymer (A), especially with hydroxyl group-containing monomers. In addition, the crosslinking agent (B) can be used individually or in combination of two or more types.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate. Adducts are reactants with alicyclic polyisocyanates such as isocyanates, and their biuret and isocyanurate forms, as well as low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Sieves, etc. may be mentioned. Among them, from the viewpoint of reactivity with hydroxyl groups, trimethylolpropane-modified aromatic polyisocyanates, especially trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate, are preferable.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.1 parts by mass or more, particularly preferably 0.4 parts by mass or more, and 1.0 parts by mass or more, based on 100 parts by mass of the (meth)acrylic acid ester polymer (A). It is more desirable. Moreover, the content is preferably 10 parts by mass or less, particularly preferably 8 parts by mass or less, and more preferably 5 parts by mass or less. When the content of the crosslinking agent (B) is within the above-mentioned range, the cohesive force of the obtained adhesive becomes appropriate, and the bending state relaxation effect of the repeatedly bending device of the obtained adhesive layer is achieved at a high level.

(1-3) Various additives

The adhesive composition P may contain, if desired, various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index regulators, etc. It can be added. In addition, the polymerization solvent and dilution solvent described later are not included in the additives constituting the adhesive composition P.

(2) Preparation of adhesive composition P

Adhesive composition P can be prepared by preparing a (meth)acrylic acid ester polymer (A), mixing the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent (B), and adding additives as desired. there is.

The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a normal radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer (A) is preferably performed by a solution polymerization method using a polymerization initiator as desired. Examples of polymerization solvents 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 polymerization initiators include azo-based 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), and 1,1'-azobis(cyclohexane 1-carbon). tril), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl2,2'- Azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'- Azobis[2-(2-imidazoline-2-yl)propane] etc. can be mentioned.

Organic peroxides include, for example, benzoyl peroxide, t-butylperbenzoate, cumene hydroperoxide, diisopropylperoxydicarbonate, di-n-propylperoxydicarbonate, and di(2-ethoxyethyl)peroxydicarbonate. , t-butyl peroxyneodecanoate, t-butyl peroxypivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide, etc.

Additionally, in the polymerization step, the weight average molecular weight of the obtained polymer can be adjusted by mixing a chain transfer agent such as 2-mercaptoethanol.

Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinking agent (B) and, if desired, additives and a diluting solvent are added to the solution of the (meth)acrylic acid ester polymer (A), and mixed sufficiently to form a solvent. Obtain the diluted adhesive composition P (application solution).

In addition, when using any of the above components in solid form, or when precipitation occurs when mixed with other components in an undiluted state, the component is dissolved or diluted alone in a diluted solvent in advance. Afterwards, you may mix it with other ingredients.

Examples of the diluting solvent 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, and 1-mer. Alcohols such as toxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, cellosolve solvents such as ethyl cellosolve, etc. This is used.

The concentration and viscosity of the coating solution prepared in this way are not particularly limited as long as it is within a range that can be coated, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted so that the concentration is 10 to 60% by mass. In addition, in obtaining the coating solution, addition of a diluting solvent, etc. is not a necessary condition, and if the adhesive composition P has a coatingable viscosity, etc., there is no need to add a diluting solvent. In this case, the adhesive composition P is an application solution in which the polymerization solvent of the (meth)acrylic acid ester polymer (A) is used as a dilution solvent.

(3) Manufacturing of adhesive

The adhesive according to the present embodiment is preferably formed by crosslinking the adhesive composition P. Crosslinking of the adhesive composition P can usually be performed by heat treatment. In addition, this heat treatment can also serve as a drying treatment for volatilizing a diluting solvent or 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, and particularly preferably 70 to 120°C. Moreover, the heating time is preferably 10 seconds to 10 minutes, and particularly preferably 50 seconds to 2 minutes.

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

By the heat treatment (and curing) described above, 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. This adhesive has a predetermined cohesive force.

(4) Physical properties of adhesive

The storage elastic modulus (G') at 25°C of the adhesive according to this embodiment is preferably 0.01 MPa or more as a lower limit. In addition, the upper limit of the storage modulus (G') is preferably 0.25 MPa or less, and particularly preferably 0.20 MPa or less.

In addition, the lower limit of the loss modulus (G") of the adhesive according to the present embodiment at 25°C is preferably 0.005 MPa or more, and particularly preferably 0.01 MPa or more. In addition, the loss modulus (G") The upper limit is preferably 0.1 MPa or less, and is particularly preferably 0.08 MPa or less.

If the storage modulus (G') and loss modulus (G") of the adhesive according to the present embodiment are each in the above range, the adhesive force to the flexible member is good, and the durability of the repeated bending device is improved. In addition, storage The measuring method of elastic modulus (G') and loss modulus (G") is as shown in the test examples described later.

[Adhesive sheet]

The adhesive sheet according to this embodiment has an adhesive layer for bonding one flexible member constituting the repetitive bending device to another flexible member, and the adhesive layer is made of the adhesive described above.

A specific configuration as an example of the adhesive sheet according to this embodiment is shown in Figure 1.

As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 according to one embodiment includes two release sheets 12a and 12b, and the two release sheets 12a and 12b are in contact with the release surfaces of the two release sheets 12a and 12b. It is composed of an adhesive layer (11) sandwiched between release sheets (12a, 12b). In addition, the release surface of the release sheet in this specification refers to the surface of the release sheet that has peelability, and includes both a surface that has been subjected to a peeling treatment and a surface that exhibits peelability even without performing a peeling treatment.

(1) Components

(1-1) Adhesive layer

The adhesive layer 11 is comprised of the adhesive according to the above-mentioned embodiment, and is preferably comprised of the adhesive made by crosslinking the adhesive composition P.

The thickness of the adhesive layer 11 in the adhesive sheet 1 according to the present embodiment (value measured in accordance with JIS K7130) is preferably 2 μm or more as a lower limit, particularly preferably 5 μm or more, and 10 It is more preferable that it is ㎛ or more. If the lower limit of the thickness of the adhesive layer 11 is above, the desired adhesive strength can be easily achieved, and the occurrence of lifting or peeling during repeated bending can be effectively suppressed. Additionally, the upper limit of the thickness of the adhesive layer 11 is preferably 150 μm or less, more preferably 100 μm or less, particularly preferably 70 μm or less, and still more preferably 50 μm or less. If the upper limit of the thickness of the adhesive layer 11 is above, exudation of the adhesive or the components constituting the adhesive from the adhesive layer due to repeated bending can be suppressed. Additionally, 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 the 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, and polyethylene. Naphthalate film, 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, poly Carbonate film, polyimide film, fluororesin film, etc. are used. Additionally, their crosslinked films are also used. Additionally, these laminated films may be used.

It is preferable that the peeling surface of the peeling sheets 12a and 12b (particularly the surface in contact with the adhesive layer 11) is subjected to a peeling 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. Also, among the release sheets 12a and 12b, it is preferable that one of the release sheets is a heavy release type release sheet with a large release force, and that the other release sheet is a light release type release sheet with a small release force.

There is no particular limitation on the thickness of the release sheets 12a and 12b, but it is usually about 20 to 150 μm.

(2) Manufacturing of adhesive sheet

As a production example of the adhesive sheet 1, a case where the adhesive composition P is used will be described. A coating liquid of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), heat treatment is performed to heat crosslink the adhesive composition P to form an application layer, and then another coating layer is added to the application layer. The peeling surfaces of the two release sheets 12b (or 12a) are overlapped. When a curing period is necessary, a curing period is provided, and when a curing period is not necessary, the application layer becomes the adhesive layer 11 as is. As a result, the pressure-sensitive adhesive sheet 1 is obtained. The conditions for heat treatment and curing are as described above.

As another manufacturing example of the adhesive sheet 1, a coating liquid of the adhesive composition P is applied to the peeling surface of one release sheet 12a, heat treatment is performed to heat crosslink the adhesive composition P, and an application layer is formed, A release sheet 12a with an application layer is obtained. Additionally, the coating liquid of the adhesive composition P is applied to the peel surface of the other release sheet 12b, heat treatment is performed to heat crosslink the adhesive composition P, and an application layer is formed, thereby forming a release sheet with an application layer. We get (12b). Then, the release sheet 12a with the application layer and the release sheet 12b with the application layer are bonded so that both application layers contact each other. When a curing period is necessary, a curing period is provided, and when a curing period is not necessary, the above-described laminated applied layer becomes the adhesive layer 11. As a result, the pressure-sensitive adhesive sheet 1 is obtained. According to this manufacturing method, even when the adhesive layer 11 is relatively thick, it becomes possible to manufacture it stably.

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

(3) Adhesion

The lower limit of the adhesive strength of the adhesive sheet 1 according to this embodiment to soda-lime glass is preferably 5.1 N/25 mm or more, particularly preferably 5.5 N/25 mm or more, and even more preferably 6.0 N/25 mm or more. desirable. If the adhesive force of the adhesive sheet 1 is 5.1 N/25 mm or more, the effect of suppressing interfacial peeling is more excellent. On the other hand, the upper limit of the adhesive force is not particularly limited, but usually it is preferably 25 N/25 mm or less, more preferably 20 N/25 mm or less, and especially preferably 15 N/25 mm or less. In addition, the above-mentioned adhesive force basically refers to the adhesive force measured by the 180 degree peeling method based on JIS Z0237:2009, and the specific test method is as shown in the test example described later.

[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), a second flexible member 22 (another flexible member), It is comprised by providing an adhesive layer (11) located between them and bonding the first flexible member (21) and the second flexible member (22) together.

The pressure-sensitive adhesive layer 11 of the repeatedly bent laminated member 2 is the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 described above.

The repetitively bent laminated member 2 is the repetitively bending device itself or a member constituting a part of the repetitively bending device. The repetitive bending device is preferably a display capable of repeated bending (including bending), but is not limited to this. Examples of such repetitive bending devices include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), flexible printed circuit boards, liquid crystal displays using plastic substrates (film) as substrates, and foldable displays. It can be a light, or it can be a touch panel.

The first flexible member 21 and the second flexible member 22 are members capable of repeated bending (including bending), and include, for example, a cover film, barrier film, polarizing film, polarizer, retardation film, and viewing angle. Compensation film, brightness enhancement film, contrast enhancement film, diffusion film, transflective reflective film, electrode film, transparent conductive film, metal mesh film, film sensor, liquid crystal polymer film, light-emitting polymer film, film-like liquid crystal module, organic EL module ( organic EL film), electronic paper module (film-like electronic paper), etc.

Among the above, at least one of the first flexible member 21 and the second flexible member 22 is a display element that can be repeatedly bent, specifically, a liquid crystal polymer film, a light-emitting polymer film, a film-like liquid crystal module, and an organic EL module. (organic EL film), or electronic paper module (film-like electronic paper) is preferable.

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 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 5 to 3000 μm, particularly preferably 10 to 1000 μm, and more preferably 10 to 500 μm. By having the thickness of the first flexible member 21 and the second flexible member 22 within this range, it becomes easy to repeatedly bend each flexible member.

In order to manufacture the repeatedly bent laminated member 2, as an 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 placed in the first layer. It is joined to one side of the flexible member 21.

After that, the other release sheet 12b is peeled 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 attached. Combined, a repeatedly bent laminated member 2 is obtained. Additionally, as another example, the joining order of the first flexible member 21 and the second flexible member 22 may be changed.

[Repeated bending device]

The repeatedly bending device according to the present embodiment is provided with 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 another It may be configured with a flexible member. When laminating one repeatedly bent laminated member 2 and another repeatedly bent laminated member 2, or when laminated a repeatedly bent laminated member 2 and another flexible member, the adhesive layer of the above-described adhesive sheet 1 It is preferable to laminate through (11).

Since the repeatedly bending device according to the present embodiment has an adhesive layer made of the above-mentioned adhesive, it can be bent repeatedly (for example, 30,000 times) and when it is bent for a long period of time (for example, at least 24 hours or more). , after being released from the bending state, the repeatedly bending device is suppressed from hardening into a greatly bent state, and the influence of repeated bending and the influence of being placed in the bending state are alleviated. The effect of relieving the bending state of such a repetitive bending device can be evaluated, for example, by the amount of static bending deformation by a static bending test and the amount of dynamic bending deformation by a dynamic bending test.

In the static bending test, a laminate made of two polyethylene terephthalate films (thickness: 12 μm) sandwiching an adhesive layer (thickness: 12 μm) with a size of 200 mm × 50 mm is used as a test piece. As shown in FIG. 3, this test piece S is held in a bent state between holding plates P made of two glass plates placed upright in an environment of 23°C and 50% RH, and held for 24 hours. . At this time, the distance between the two retaining plates P is set to 6 mm (bending diameter of test piece S: 6 mm ϕ), approximately the center of the long side (200 mm) of test piece S becomes the bent portion, and the bending portion on both sides of test piece S is set to 6 mm. Maintain the test piece S so that the short side (50 mm) is located on the upper side. After performing this static bending test, the test piece S is taken out from between the two retaining plates P, and the test piece S is placed on a flat plate so that the convex direction of the bent portion is upward, as shown in FIG. 4. . Then, immediately after the test, 30 minutes after the test, and 24 hours after the test, the height h from the plate surface to the peak of the bent portion (deformed portion) is measured as the static bending deformation amount. This amount of static bending deformation can be used as the test result of the static bending test, and the effect of alleviating the bending state can be evaluated based on this amount of static bending deformation.

The amount of static bending deformation in the static bending test immediately after the test is preferably 3 mm or less, particularly preferably 1 mm or less, and more preferably 0.5 mm or less. Moreover, after 30 minutes of testing, it is preferable that it is 1 mm or less, and it is especially preferable that it is 0.5 mm or less. Moreover, after 24 hours of testing, it is preferable that it is 0.5 mm or less, and it is especially preferable that it is 0.3 mm or less. Moreover, it is preferable that the lower limit of any amount of static bending deformation is 0 mm.

Meanwhile, in the dynamic bending test, a laminate made of two polyethylene terephthalate films (thickness: 12 μm) sandwiching an adhesive layer (thickness: 12 μm), with a size of 150 mm × 50 mm, is used as a test piece. . As shown in FIG. 5, this test piece S is held between two holding plates P of a surface-state no-load U-shaped stretch tester in an environment of 23°C and 50% RH. One of the two holding plates P maintains a parallel relationship with the other holding plate P, and is capable of reciprocating movement toward and away from the other holding plate P. The distance between the two retaining plates P is changed from 86 mm to 6 mm (bending diameter of test piece S: 6 mmϕ, stroke: 80 mm). The test piece S is fixed to the holding plate P so that approximately the center of its long side (150 mm) becomes a bent portion, and the short sides (50 mm) on both sides of the test piece S are located on the upper side. In that state, the test piece S is bent 30,000 times at a bending speed (reciprocating movement speed of the holding plate P) of 30 rpm. After performing this dynamic bending test, the test piece S is taken out from between the two retaining plates P, and the test piece S is placed on a flat plate so that the convex direction of the bent portion is upward, as shown in FIG. 4. Then, immediately after the test and 24 hours after the test, the height h from the plate surface to the peak of the bent portion (deformed portion) is measured as the amount of dynamic bending deformation. This dynamic bending deformation amount is used as the test result of the dynamic bending test, and the bending state relaxation effect can be evaluated based on the dynamic bending deformation amount.

The amount of dynamic bending deformation in the dynamic bending test immediately after the test is preferably 3 mm or less, particularly preferably 1 mm or less, and more preferably 0.5 mm or less. Moreover, after 24 hours of testing, it is preferable that it is 1 mm or less, and it is especially preferable that it is 0.5 mm or less. Moreover, it is preferable that the lower limit of any amount of dynamic bending deformation is 0 mm.

The embodiments described above are described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiment 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 in place of the release sheets 12a and/or 12b.

(Example)

Hereinafter, the present invention will be described in more detail through examples, etc., but the scope of the present invention is not limited to these examples.

[Example 1]

1. Preparation of (meth)acrylic acid ester polymer (A)

47.8 parts by mass of 2-ethylhexyl acrylate, 47.8 parts by mass of n-butyl acrylate, 4 parts by mass of acrylic acid, and 0.4 parts by mass of 2-hydroxypropyl acrylate were copolymerized by solution polymerization to prepare a (meth)acrylic acid ester polymer (A). did. The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described later, and the weight average molecular weight (Mw) was 600,000.

2. Preparation of adhesive composition

100 parts by mass of the (meth)acrylic acid ester polymer (A) obtained in the above step 1 (solid content conversion value; the same applies hereinafter), and trimethylolpropane-modified tolylene diisocyanate (Toyochem Co., Ltd., product name "BHS8515") as a crosslinking agent (B) 3.75 By mixing parts by mass, stirring sufficiently, and diluting with toluene, a coating solution of the adhesive composition (solid content concentration: 30.0% by mass) was obtained.

3. Preparation of adhesive sheet

The coating solution of the obtained adhesive composition was applied using a comma coater (registered trademark) to the peeled side of a medium-release type release sheet (manufactured by Lintec, product name "SP-PET382150"), where one side of the polyethylene terephthalate film was peeled with a silicone-based release agent. did. Then, the application layer was heat treated at 90°C for 1 minute to form an application layer.

Next, the application layer on the heavy release type release sheet obtained above and one side of the polyethylene terephthalate film were treated to release with a silicone-based release agent (manufactured by Lintec, product name "SP-PET381031"). is bonded so that the release treated surface is in contact with the application layer, and cured for 7 days under conditions of 23°C and 50% RH to produce an adhesive sheet having an adhesive layer with a thickness of 12 ㎛, that is, a medium-release type release sheet/adhesive layer (thickness : 12㎛)/A pressure-sensitive adhesive sheet composed of a light-peelable release sheet was produced. In addition, the thickness of the adhesive layer is a value measured using a static pressure thickness meter (product name "PG-02", manufactured by Tech Rock Company) in accordance with JIS K7130.

[Example 2]

An adhesive sheet was produced in the same manner as in Example 1, except that the compounding amount of the crosslinking agent (B) was changed to 6.56 parts by mass.

[Example 3]

60 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of methyl methacrylate, and 20 parts by mass of 2-hydroxyethyl acrylate were copolymerized by solution polymerization to prepare a (meth)acrylic acid ester polymer (A). The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described later, and the weight average molecular weight (Mw) was 600,000.

100 parts by mass of the (meth)acrylic acid ester polymer (A) obtained above and 1.88 parts by mass of trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyo Chem Corporation, product name "BHS8515") as a crosslinking agent (B) were mixed, stirred sufficiently, and methyl By diluting with ethyl ketone (MEK), a coating solution of the adhesive composition (solid content concentration: 30.0% by mass) was obtained. An adhesive sheet was produced in the same manner as in Example 1 using the coating solution of the obtained adhesive composition.

[Example 4]

60 parts by mass of butyl acrylate, 20 parts by mass of methyl acrylate, and 20 parts by mass of 2-hydroxyethyl acrylate were copolymerized by solution polymerization to prepare a (meth)acrylic acid ester polymer (A). The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described later, and the weight average molecular weight (Mw) was 600,000.

100 parts by mass of the (meth)acrylic acid ester polymer (A) obtained above and 1.88 parts by mass of trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyo Chem Corporation, product name "BHS8515") as a crosslinking agent (B) were mixed, stirred sufficiently, and added to MEK. By diluting, a coating solution of the adhesive composition (solid content concentration: 30.0% by mass) was obtained. An adhesive sheet was produced in the same manner as in Example 1 using the coating solution of the obtained adhesive composition.

[Example 5]

65 parts by mass of 2-ethylhexyl acrylate, 5 parts by mass of N-acryloylmorpholine, 15 parts by mass of isobornyl acrylate, and 15 parts by mass of 2-hydroxyethyl acrylate are copolymerized by solution polymerization to form (meth)acrylic acid ester. Polymer (A) was prepared. The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described later, and the weight average molecular weight (Mw) was 500,000.

100 parts by mass of the (meth)acrylic acid ester polymer (A) obtained above and 1.20 parts by mass of trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyo Chem Corporation, product name "BHS8515") as a crosslinking agent (B) were mixed, stirred sufficiently, and added to MEK. By diluting, a coating solution of the adhesive composition (solid content concentration: 30.0% by mass) was obtained. An adhesive sheet was produced in the same manner as in Example 1 using the coating solution of the obtained adhesive composition.

[Example 6]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 3 was used and the compounding amount of the crosslinking agent (B) was changed to 0.47 parts by mass.

[Example 7]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 3 was used and the compounding amount of the crosslinking agent (B) was changed to 0.94 parts by mass.

[Example 8]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 4 was used and the compounding amount of the crosslinking agent (B) was changed to 0.47 parts by mass.

[Example 9]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 4 was used and the compounding amount of the crosslinking agent (B) was changed to 0.94 parts by mass.

[Example 10]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 5 was used and the compounding amount of the crosslinking agent (B) was changed to 0.60 parts by mass.

[Comparative Example 1]

An adhesive sheet was produced in the same manner as in Example 1, except that the compounding amount of the crosslinking agent (B) was changed to 0.94 parts by mass.

[Comparative Example 2]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 3 was used and the compounding amount of the crosslinking agent (B) was changed to 0.23 parts by mass.

[Comparative Example 3]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 4 was used and the compounding amount of the crosslinking agent (B) was changed to 0.23 parts by mass.

[Comparative Example 4]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 5 was used and the compounding amount of the crosslinking agent (B) was changed to 0.15 parts by mass.

[Comparative Example 5]

An adhesive sheet was produced in the same manner as in Example 1, except that the (meth)acrylic acid ester polymer (A) prepared in Example 5 was used and the compounding amount of the crosslinking agent (B) was changed to 0.30 parts by mass.

[Comparative Example 6]

Mix 15 parts by mass of isobutylene-isoprene copolymer (product name: "Butyl365", manufactured by Nippon Butyl Corporation) with 3 parts by mass of tackifier (product name: "Kinton A100", manufactured by Nihon Zeon Corporation), stir sufficiently, and dilute with toluene. As a result, a coating solution (solid content concentration: 15% by mass) of the adhesive composition as butyl rubber was obtained. An adhesive sheet was produced in the same manner as in Example 1, except that the coating solution of the obtained adhesive composition was used and the heat treatment temperature was set to 100°C.

In addition, in Table 1, the composition of the (meth)acrylic acid ester polymer (A) and the compounding amount of the crosslinking agent (B) in each Example and Comparative Example (parts by mass relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A)) ) is listed. The abbreviations in Table 1 are as follows.

2EHA: 2-ethylhexyl acrylate

BA: n-butyl acrylate

AA: Acrylic acid

2HPA: 2-hydroxypropyl acrylic acid

MMA: Methyl methacrylate

HEA: 2-hydroxyethyl acrylate

MA: Methyl acrylate

ACMO: N-acryloylmorpholine

IBXA: Isobornyl acrylate

[Test Example 1] (Measurement of relaxed elastic modulus)

The adhesive layers of the adhesive sheets produced in the examples and comparative examples were laminated in multiple layers to form a laminate with a thickness of 0.5 mm. From the obtained laminate of the adhesive layer, a cylindrical body (height 0.5 mm) with a diameter of 8 mm was punched out, and this was used as a sample.

For the above sample, the adhesive was continuously deformed by 10% under the following conditions using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR302") in accordance with JIS K7244-1, and the relaxed elastic modulus G(t) (MPa ) was measured. From the measurement results, the maximum relaxation modulus G(t) _max (MPa) was derived, and the minimum relaxation modulus G(t) _min (MPa) measured 3757 seconds after the maximum relaxation modulus G(t) _max was measured. MPa) was derived.

Measurement temperature: 25℃

Measurement points: 1000 points (logarithmic plot)

From the obtained maximum relaxed elastic modulus G(t) _max (MPa) and minimum relaxed elastic modulus G(t) _min (MPa), the relaxed elastic modulus fluctuation value ΔlogG(t) was calculated based on the following equation (I). The results are shown in Table 1.

ΔlogG(t)=logG(t) _max -logG(t) _min … (I)

[Test Example 2] (Measurement of dynamic elastic modulus)

The adhesive layers of the adhesive sheets produced in the examples and comparative examples were laminated in multiple layers to form a laminate with a thickness of approximately 0.5 mm. From the obtained laminate of the adhesive layer, a cylindrical body (height 0.5 mm) with a diameter of 8 mm was punched out, and this was used as a sample.

For the above sample, the dynamic viscoelasticity was measured under the following conditions using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR302") in accordance with JIS K7244-1, and the storage elastic modulus (G' at 25°C) was measured. )(MPa), loss modulus (G")(MPa), and loss tangent (tanδ) were observed. The results are shown in Table 1.

Measurement frequency: 1Hz

Measurement temperature range: -20∼150℃

[Test Example 3] (Static bending test)

In an environment of 23°C and 50% RH, the light release type release sheet was peeled from the adhesive sheets produced in the examples and comparative examples, and the exposed adhesive layer was covered with a polyethylene terephthalate film (manufactured by Dore, product name “S10 Lumira”, Thickness: 12 μm) was bonded to one side. Next, the heavy release type release sheet was peeled off, and the exposed adhesive layer was bonded to one side of another polyethylene terephthalate film (manufactured by Doresha, product name "S10 Lumira", thickness: 12 μm). Then, after pressurizing at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakujosha, it was left to stand for 24 hours under conditions of 23°C and 50% RH. The laminated body consisting of PET film/adhesive layer/PET film obtained in this way was cut into 200 mm x 50 mm, and this was used as a test piece.

The obtained test piece was held in a bent state for 24 hours under an environment of 23°C and 50% RH between holding plates made of two glass plates placed upright (distance between them: 6 mm), as shown in Figure 3. did. After performing this static bending test, the test piece is placed on a flat plate as shown in FIG. 4, and immediately after the test, 30 minutes after the test, and 24 hours after the test, the height from the surface of the flat plate to the apex of the bending portion (deformed portion) is h was measured as the static bending deformation amount. Based on the measured amount of static bending deformation, static bending properties were evaluated according to the following criteria. Additionally, in the test piece (Example) after the test, it was visually confirmed whether there was any peeling at the interface between the adhesive layer and the adherend in the bent portion. The results are shown in Table 1.

◎: The amount of deformation immediately after the bending test is 1 mm or less.

○: The amount of deformation immediately after the bending test exceeds 1 mm and is 3 mm or less, and the amount of deformation after 30 minutes of the test is 1 mm or less.

△: The amount of deformation immediately after the bending test is more than 3 mm and less than 6 mm, the amount of deformation after 30 minutes of the test is 5 mm or less, and the amount of deformation after 24 hours of the test is 1 mm or less.

×: Other than the above

[Test Example 4] (Dynamic bending test)

The laminate consisting of PET film/adhesive layer/PET film obtained in the same manner as in Test Example 3 was cut into 150 mm x 50 mm, and this was used as a test piece. As shown in FIG. 5, both ends of the obtained test piece were fixed to two holding plates of a surface-state no-load U-shaped stretching tester (Yasa Systems Kikisha, product name "DLDMLH-FS"). Then, in an environment of 23°C and 50% RH, the test piece was bent 30,000 times with a bending diameter of 6 mmϕ, a stroke of 80 mm, and a bending speed of 30 rpm.

After performing the dynamic bending test described above, the test piece is placed on a flat plate as shown in FIG. 4, and immediately after the test and 24 hours after the test, the height h from the surface of the plate to the apex of the bent portion (deformed portion) is measured as dynamic bending. It was measured as the amount of deformation. Based on the measured amount of dynamic bending deformation, dynamic bending properties were evaluated according to the following criteria. Additionally, in the test piece (Example) after the test, it was visually confirmed whether there was any peeling at the interface between the adhesive layer and the adherend in the bent portion. The results are shown in Table 1.

◎: The amount of deformation immediately after the bending test is 0 mm.

○: The amount of deformation immediately after the bending test is 1 mm or less, and the amount of deformation after 24 hours of the test is 0 mm.

△: The amount of deformation immediately after the bending test exceeds 1 mm and is 3 mm or less, and the amount of deformation after 24 hours of the test is 1 mm or less.

×: Other than the above

[Test Example 5] (Measurement of adhesive force)

The light release type release sheet was peeled from the adhesive sheet produced in the example, and the exposed adhesive layer was replaced with a polyethylene terephthalate (PET) film (manufactured by Toyobo Corporation, product name "PET A4300", thickness) having an easily adhesive layer. : 100 μm) to obtain a laminate of medium-release type release sheet/adhesive layer/PET film. The obtained laminate was cut into 25 mm wide and 100 mm long.

Under an environment of 23°C and 50% RH, a medium-release type release sheet is peeled from the laminate, and the exposed adhesive layer is attached to soda lime glass (manufactured by Nippon Itagarassha) under an environment of 23°C and 50% RH. After leaving for 30 minutes, the laminate of the PET film and the adhesive layer was peeled from the soda-lime glass using a tensile tester (Tensiron, manufactured by Orientex) under the conditions of a peeling speed of 300 mm/min and a peeling angle of 180 degrees. The adhesive force (N/25 mm) was measured. Conditions other than those described here were measured based on JIS Z0237:2009. The results are shown in Table 1.

[Table 1]

As can be seen from Table 1, the adhesive layer of the adhesive sheet of the example had an excellent bending state relaxation effect when two flexible members were bonded together and bent repeatedly and when placed in a bent state for a long period of time. Additionally, the adhesive layer of the adhesive sheets of Examples 3, 5 to 10 was also excellent in the effect of suppressing interfacial peeling.

The present invention is suitable for bonding one flexible member (eg, various films) constituting a repetitive bending device with another flexible member (eg, display element).

1: Adhesive sheet
11: Adhesive layer
12a, 12b: release sheet
2: Repeatedly bent laminated member
21: first flexible member
22: second flexible member
S: test piece
P: retaining plate

Claims (10)

One flexible member and another flexible member constituting a device that is repeatedly bent,
An adhesive layer that bonds the one flexible member and the other flexible member to each other.
A repeatedly curved laminated member provided with,
The maximum relaxed elastic modulus value measured when the adhesive layer is deformed by 10% in accordance with JIS K7244-1 is set as the maximum relaxed elastic modulus G(t) _max (MPa), and the maximum relaxed elastic modulus G(t) _max is Deformation is continued by 10% until 3757 seconds after measurement, and the minimum relaxation modulus value measured in the meantime is set as the minimum relaxation modulus G(t) _min (MPa), and the relaxation modulus variation is calculated from the following equation (I) Made of an adhesive with a value ΔlogG(t) of 0.85 or less.
A repeatedly curved laminated member characterized in that.
ΔlogG(t)=logG(t) _max -logG(t) _min … (I) According to paragraph 1,
A repeatedly bent laminated member characterized in that the loss tangent (tanδ) at 25°C obtained from dynamic viscoelasticity measurement of the adhesive in accordance with JIS K7244-1 is 0.328 or more and 0.85 or less. According to paragraph 1,
A repeatedly bent laminated member characterized in that the storage modulus (G') of the adhesive at 25°C is 0.01 MPa or more and 0.25 MPa or less. According to paragraph 1,
A repeatedly bent laminated member characterized in that the loss modulus (G") of the adhesive at 25°C is 0.005 MPa or more and 0.1 MPa or less. According to paragraph 1,
A repeatedly bent laminated member characterized in that the adhesive is an adhesive obtained by crosslinking an adhesive composition containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B). delete delete delete According to paragraph 1,
A repeatedly bent laminated member, wherein at least one of the one flexible member and the other flexible member is a display element. A repetitive bending device comprising the repeatedly bending laminated member according to claim 1.

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