JP2022100334A - Repeat bending device, manufacturing method therefor and suppression method of bent trace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a repeat bending device hardly generating bent trace after releasing the same from a bent state, when repeatedly bent, or stood at a bending state for long time.

SOLUTION: There is provided a repeat bending device 10A having one or a plurality of adhesive layers 111, 112 and 113, at least one layer of the adhesive layers is constituted by an adhesive having relaxation modulus variation ΔlogG(t) calculated from the following formula (I), wherein a maximum relaxation modulus value measured when the adhesive is strained at 10% is G(t)_max (MPa), a minimum relaxation modulus value measured during keeping straining the adhesive at 10% from when the maximum relaxation modulus G(t)_max is measured to 3757 sec. later is minimum relaxation modulus G(t)_min(MPa), of 1.20 or less. ΔlogG(t)=logG(t)_max-logG(t)_min (I).

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a repetitive bending device, a method for manufacturing a repetitive bending device, and a method for suppressing bending marks in the repetitive bending device.

In recent years, a bendable display has been proposed as a display body (display) of an electronic device, which is a kind of device. Such a flexible display is expected to be widely used, for example, for a stationary display that is curved and installed on a columnar pillar, or for a mobile display that can be folded, folded, or rolled to be carried.

Examples of the type of the flexible display include an organic electroluminescence (organic EL) display, an electrophoretic display (electronic paper), and a liquid crystal display using a plastic film as a substrate.

In a flexible display as described above, it is common that one flexible member (flexible member) constituting the flexible display and another flexible member are bonded to each other by an adhesive layer of an adhesive sheet. It is considered to be the target. Here, as a conventional non-bendable adhesive sheet for a display, for example, those shown in Patent Documents 1 and 2 are known.

The flexible display may be repeatedly bent (bent) as described in Patent Document 3, instead of being curved only once. Further, in such a repeatedly flexible display, it may be fixed in a bent state for a long period of time. When a conventional adhesive sheet is used for a repetitive flexible display for such applications, the adhesive layer is deformed and the flexible display remains largely bent even after being released from the bent state, and a bending mark is attached. There was a case that it ended up.

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

The present invention has been made in view of the above-mentioned actual conditions, and is a repetitive bending device that does not easily leave a bending mark after being released from the bending state when repeatedly bending or being placed in the bending state for a long period of time. It is an object of the present invention to provide a method for manufacturing such a repeatedly bending device, and a method for suppressing bending marks capable of suppressing the formation of bending marks in the repeatedly bending device.

In order to achieve the above object, firstly, the present invention is a repetitive bending device including one layer or a plurality of pressure-sensitive adhesive layers, and at least one layer of the pressure-sensitive adhesive layer conforms to JIS K7424-1. Then, the maximum relaxation elastic modulus value measured when the pressure-sensitive adhesive is distorted by 10% is set as the maximum relaxation elastic modulus G (t) _max (MPa), and the maximum relaxation elastic modulus G (t) _max is measured. The pressure-sensitive adhesive is continuously distorted by 10% until 3757 seconds after the preparation, and the minimum relaxation elastic modulus value measured during that period is defined as the minimum relaxation elastic modulus G (t) _min (MPa), and the following formula (I) is used. Provided is a repetitive bending device characterized in that the relaxation elastic modulus fluctuation value ΔlogG (t) calculated from the above is composed of a pressure-sensitive adhesive having a modulus of 1.20 or less (Invention 1).
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I)

In the repetitive bending device according to the above invention (Invention 1), since at least one layer of the pressure-sensitive adhesive layer of the repetitive bending device is made of the above-mentioned adhesive, the stress fluctuation when distorted by a predetermined amount is small, that is, that is, The force to return to the original state is easily maintained, and therefore the deformation is likely to return to the original state when the load is removed. Therefore, when the repeatedly bent device is repeatedly bent or left in the bent state for a long period of time, it is easy to recover after being released from the bent state, and it is possible to prevent the device from solidifying in the bent state and forming a bending mark. Can be done.

In the above invention (Invention 1), the creep compliance value measured when a stress of 3000 Pa is applied to the pressure-sensitive adhesive is set to the minimum creep compliance J (t) _min (MPa ^-1 ), and the minimum creep compliance J (t) is set. A stress of 3000 Pa is continuously applied until 3757 seconds after _min is measured, and the maximum creep compliance value measured during that period is defined as the maximum creep compliance J (t) _max (MPa ^-1 ), and the following equation (II) is used. The creep compliance fluctuation value ΔlogJ (t) calculated from the above is preferably 2.84 or less (Invention 2).
ΔlogJ (t) = logJ (t) _max -logJ (t) _min ... (II)

In the above inventions (Inventions 1 and 2), the pressure-sensitive adhesive is a pressure-sensitive adhesive obtained by cross-linking a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester polymer (A) and a cross-linking agent (B). It is preferable that there is (Invention 3).

In the above inventions (Inventions 1 to 3), the ratio of the number of pressure-sensitive adhesive layers composed of the pressure-sensitive adhesive to the total number of pressure-sensitive adhesive layers contained in the repeatedly bending device is preferably 10% or more. (Invention 4).

In the above inventions (Inventions 1 to 4), the ratio of the total thickness of the pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive to the thickness of the repeatedly bending device is 1% or more and 50% or less. Preferred (Invention 5).

Secondly, the present invention is a method for manufacturing a repetitive bending device including one or a plurality of pressure-sensitive adhesive layers, wherein at least one layer of the pressure-sensitive adhesive layer is a pressure-sensitive adhesive in accordance with JIS K7244-1. The maximum relaxation elastic modulus value measured when is distorted by 10% is defined as the maximum relaxation elastic modulus G (t) _max (MPa), and 3757 seconds after the maximum relaxation elastic modulus G (t) _max is measured. The pressure-sensitive adhesive is continuously distorted by 10% until later, and the minimum relaxation modulus value measured during that period is set to the minimum relaxation modulus G (t) _min (MPa), and the relaxation calculated from the following formula (I) is performed. Provided is a method for manufacturing a repetitive bending device, which comprises a pressure-sensitive adhesive having an elastic modulus fluctuation value Δlog G (t) of 1.20 or less (Invention 6).
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I)

In the above invention (Invention 6), it is preferable to use a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive to bond the constituent members of the repeatedly bending device (Invention 7).

Thirdly, the present invention is a method for suppressing bending marks in a repeatedly bending device including one or a plurality of pressure-sensitive adhesive layers, wherein at least one layer of the pressure-sensitive adhesive layer is based on JIS K7424-1. The maximum relaxation modulus G (t) max (MPa) measured when the pressure-sensitive adhesive is distorted by 10% is set as the maximum relaxation modulus G (t) _max (MPa), and the maximum relaxation modulus G (t) _max is measured. The pressure-sensitive adhesive is continuously distorted by 10% until 3757 seconds later, and the minimum relaxation elastic modulus value measured during that period is defined as the minimum relaxation elastic modulus G (t) _min (MPa), and is calculated from the following formula (I). Provided is a method for suppressing bending marks in a repetitive bending device, which comprises a pressure-sensitive adhesive having a relaxed modulus fluctuation value ΔlogG (t) of 1.20 or less (Invention 8).
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I)

In the above invention (Invention 8), it is preferable to use a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive to bond the constituent members of the repeatedly bending device (Invention 9).

The repetitive bending device according to the present invention is unlikely to have a bending mark after being released from the bending state when repeatedly bending or being left in the bending state for a long period of time. Further, according to the method for manufacturing a repetitive bending device according to the present invention, such a repetitive bending device can be manufactured. Further, according to the method for suppressing bending marks according to the present invention, it is possible to suppress bending marks from being formed in a repeatedly bending device.

It is sectional drawing of the adhesive sheet which concerns on one Embodiment for manufacturing the repeated bending device which concerns on this invention. It is sectional drawing of the repeated bending device which concerns on one Embodiment of this invention. It is sectional drawing of the repeated bending device which concerns on other embodiment of this invention. It is sectional drawing of the repeated bending device which concerns on another Embodiment of this invention. It is sectional drawing of the laminated body manufactured in an Example. It is explanatory drawing (side view) explaining the static bending test. It is explanatory drawing (side view) explaining the amount of deformation of a test piece as a test result of a bending test.

Hereinafter, embodiments of the present invention will be described.
[Repeat bending device]
The repetitive bending device according to the present embodiment is a device that is repeatedly bent or placed in a bent state for a long period of time, and includes one layer or a plurality of layers of an adhesive layer. By this pressure-sensitive adhesive layer, a plurality of constituent members (flexible members having flexibility) are bonded together, thereby forming a repeatedly bending device.

1. 1. Adhesive layer (flexible adhesive layer)
(1) Physical properties of the pressure-sensitive adhesive layer (flexural-resistant pressure-sensitive adhesive layer) At least one of the above-mentioned pressure-sensitive adhesive layers is the maximum measured when the pressure-sensitive adhesive is distorted by 10% in accordance with JIS K7424-1. The relaxation modulus is set to the maximum relaxation modulus G (t) _max (MPa), and the adhesive is continuously distorted by 10% until 3757 seconds after the maximum relaxation modulus G (t) _max is measured, during which time. The minimum relaxation elastic modulus value to be measured is defined as the minimum relaxation elastic modulus G (t) _min (MPa), and the relaxation elastic modulus fluctuation value Δlog G (t) calculated from the following equation (I) is 1.20 or less. It consists of a certain adhesive.
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I)
In the present specification, the pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive may be referred to as a "bending-resistant pressure-sensitive adhesive layer". Further, the pressure-sensitive adhesive layer other than the bending-resistant pressure-sensitive adhesive layer may be referred to as a “non-bending-resistant pressure-sensitive adhesive layer”. The details of the method for measuring the relaxed elastic modulus G (t) are as shown in the test examples described later.

In the repetitive bending device according to the present embodiment, since at least one layer of the adhesive layer of the repetitive bending device is made of the above-mentioned adhesive, the stress fluctuation when distorted by a predetermined amount is small, that is, it is restored. The force to try is easily maintained. Therefore, the deformation is likely to be restored when the load is removed. Therefore, when the repeatedly bent device is repeatedly bent or left in the bent state for a long period of time, it is easy to recover after being released from the bent state, and it is possible to prevent the device from solidifying in the bent state and forming a bending mark. Can be done. As an index of the number of times of repeated bending, 30,000 times is exemplified.

From the viewpoint of the bending trace suppressing effect of the repetitive bending device, the relaxation elastic modulus fluctuation value ΔlogG (t) needs to be 1.20 or less, preferably 1.00 or less, and particularly 0.80 or less. It is preferably 0.50 or less, and more preferably 0.50 or less. The lower limit of the relaxation elastic modulus fluctuation value is not particularly limited, but is usually preferably 0.10 or more, and particularly preferably 0.15 or more.

The maximum relaxed elastic modulus G (t) _max is preferably 1.0 MPa or less, particularly preferably 0.95 MPa or less, and further preferably 0.90 MPa or less as an upper limit value. Since the upper limit value of the maximum relaxed elastic modulus G (t) _max is the above, the relaxed elastic modulus fluctuation value Δlog G (t) can easily satisfy 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 further preferably 0.15 MPa or more. Is preferable.

The minimum relaxed elastic modulus G (t) _min is preferably 0.005 MPa or more, particularly preferably 0.020 MPa or more, and further preferably 0.035 MPa or more as the lower limit value. .. Since the lower limit value of the minimum relaxed elastic modulus G (t) _min is the above, the relaxed elastic modulus fluctuation value Δlog G (t) can easily satisfy 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 further preferably 0.40 MPa or less. Is preferable.

In the present embodiment, the creep compliance value measured by the pressure-sensitive adhesive constituting the bending-resistant pressure-sensitive adhesive layer when a stress of 3000 Pa is applied to the pressure-sensitive adhesive is set to the minimum creep compliance J (t) _min (MPa ^-1 ). , The stress of 3000 Pa is continuously applied until 3757 seconds after the minimum creep compliance J (t) _min is measured, and the maximum creep compliance value measured during that period is the maximum creep compliance J (t) _max (MPa ^-1 ). ), And the creep compliance fluctuation value ΔlogJ (t) calculated from the following equation (II) is preferably 2.84 or less.
ΔlogJ (t) = logJ (t) _max -logJ (t) _min ... (II)
The term "when a stress of 3000 Pa is applied to the pressure-sensitive adhesive" means a time when the stress is applied to the pressure-sensitive adhesive and the stress reaches 3000 Pa. The details of the creep compliance J (t) measuring method are as shown in the test examples described later.

Since the creep compliance fluctuation value of the pressure-sensitive adhesive is small as described above, the strain fluctuation when a predetermined stress is applied is small, that is, the pressure-sensitive adhesive layer is less likely to be deformed. Therefore, when the repeatedly bent device is repeatedly bent or left in the bent state for a long period of time, the deformation itself is suppressed after being released from the bent state, and it is more effective that the repeatedly bent device has a bending mark. Can be suppressed.

From the viewpoint of the bending trace suppressing effect of the repetitive bending device, the creep compliance fluctuation value ΔlogJ (t) is preferably 2.84 or less, more preferably 2.50 or less, and particularly 2.00 or less. It is preferably 1.80 or less, and more preferably 1.80 or less. The lower limit of the creep compliance fluctuation value is not particularly limited, but is usually preferably 1.00 or more, and particularly preferably 1.20 or more.

The minimum creep compliance J (t) _min is preferably 1.00 MPa ^-1 or more, particularly preferably 1.10 MPa ^{-1 or more, and further 1.15 MPa -1 or} more as the lower limit value. Is preferable. Since the lower limit value of the minimum creep compliance J (t) _min is the above, the creep compliance fluctuation value Δlog J (t) can easily satisfy the above-mentioned value. The upper limit of the minimum creep compliance J (t) _min is not particularly limited, but is usually preferably 5.0 MPa ^-1 or less, particularly preferably 4.5 MPa ^-1 or less, and further 4.0 MPa ⁻ . It is preferably ¹ or less.

Further, the maximum creep compliance J (t) _max is preferably 900 MPa ^-1 or less, particularly preferably 500 MPa ^-1 or less, and further preferably 300 MPa ^-1 or less as an upper limit value. Most preferably, it is 200 MPa ^-1 or less. Since the upper limit of the maximum creep compliance J (t) _max is the above, the creep compliance fluctuation value Δlog J (t) can easily satisfy the above-mentioned value. The lower limit of the maximum creep compliance J (t) _max is not particularly limited, but is usually preferably 10 MPa ^-1 or more, particularly preferably 15 MPa ^-1 or more, and further preferably 20 MPa ^-1 or more. preferable.

The product (ΔlogG (t) × ΔlogJ (t)) of the above-mentioned relaxation elastic modulus fluctuation value ΔlogG (t) and the creep compliance fluctuation value ΔlogJ (t) is preferably 3.3 or less, and particularly 2.0. It is preferably less than or equal to, and more preferably 1.0 or less. Since the above product value is small as described above, the stress fluctuation or strain fluctuation at the time of bending is small, so that the deformation is likely to be restored when the load is unloaded, or the deformation itself is unlikely to occur. As a result, it is possible to more effectively suppress the formation of bending marks on the repeatedly bending device. The lower limit of the product value is not particularly limited, but is usually preferably 0.1 or more, and particularly preferably 0.2 or more.

The ratio of the number of the bending-resistant pressure-sensitive adhesive layers to the total number of pressure-sensitive adhesive layers contained in the repeatedly bending device according to the present embodiment is preferably 10% or more, more preferably 25% or more, and particularly preferably 25% or more. It is preferably 35% or more, and more preferably 50% or more. Since the ratio of the number of the bending-resistant adhesive layer is as described above, the effect of the restoring action and the deformation suppressing action of the bending-resistant adhesive layer is greatly exerted on the repeatedly bending device, and the bending mark is left on the repeatedly bending device. It is possible to suppress the sticking more effectively. The upper limit of the ratio of the number of bending-resistant adhesive layers is 100%.

Further, the ratio of the total thickness of the bending-resistant pressure-sensitive adhesive layer to the thickness of the repeatedly bending device according to the present embodiment is preferably 1% or more, more preferably 2% or more, as a lower limit value. In particular, it is preferably 3% or more, and more preferably 5% or more. The "total thickness of the bending-resistant adhesive layer" means the thickness of one layer when the repeating bending device contains only one bending-resistant adhesive layer, and the repeated bending device has bending resistance. When multiple adhesive layers are included, it means the total thickness. Since the lower limit of the ratio of the total thickness of the bending-resistant adhesive layer is as described above, the effect of the restoring action and the deformation suppressing action of the bending-resistant adhesive layer is greatly exerted on the repeatedly bending device, and the bending is repeated. It is possible to more effectively suppress the formation of bending marks on the device.

On the other hand, the upper limit of the ratio of the total thickness of the bending-resistant adhesive layer to the thickness of the repeatedly bending device according to the present embodiment is preferably 50% or less, more preferably 30% or less. In particular, it is preferably 20% or less, and more preferably 10% or less. This makes it possible to secure the thickness of each component other than the bending-resistant adhesive layer, which is required for the repeatedly bending device.

(2) Adhesive The type of the adhesive constituting the bending-resistant adhesive layer is not particularly limited as long as the above-mentioned physical properties are satisfied, and for example, an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, and a rubber. It may be either a based pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, or the like. Further, the pressure-sensitive adhesive may be an emulsion type, a solvent type or a solvent-free type, and may be either a crosslinked type or a non-crosslinked type. Among them, an acrylic pressure-sensitive adhesive that easily satisfies the above-mentioned physical properties and is excellent in adhesive physical properties, optical properties, and the like is preferable.

Further, the acrylic pressure-sensitive adhesive may be an active energy ray-curable one, an active energy ray non-curable one, or a heat-crosslinkable one. It may be non-crosslinkable or a combination thereof, but it is preferably active energy ray non-curable in order to obtain good flexibility. As the active energy ray non-curable acrylic pressure-sensitive adhesive, a crosslinked type is particularly preferable, and further, a thermally crosslinked type is preferable.

The pressure-sensitive adhesive constituting the bending-resistant pressure-sensitive adhesive layer is, in particular, a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester polymer (A) and a cross-linking agent (B) (hereinafter referred to as “sticky composition P””. In some cases, it is preferable that the adhesive is obtained by cross-linking). With such an adhesive, it is easy to satisfy the above-mentioned physical properties, and since good adhesive force and a predetermined cohesive force can be obtained, the durability is also excellent. In addition, in this specification, (meth) acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. In addition, the concept of "polymer" shall be included in "polymer".

(2-1) Component (2-1-1) (meth) acrylic acid ester polymer (A) of the adhesive composition P
The (meth) acrylic acid ester polymer (A) is a (meth) acrylic acid alkyl ester and a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer) as a monomer unit constituting the polymer. And are preferably contained.

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

The (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms has a glass transition temperature (Tg) of −40 ° C. or lower as a homopolymer (hereinafter, may be referred to as “low Tg alkyl acrylate”). ) Is preferably contained. By containing such a low Tg alkyl acrylate as a constituent monomer unit, the flexibility of the obtained pressure-sensitive adhesive can be improved.

Examples of the low Tg alkyl acrylate include n-butyl acrylate (Tg-55 ° C.), n-octyl acrylate (Tg-65 ° C.), isooctyl acrylate (Tg-58 ° C.), and 2-ethylhexyl acrylate (Tg). -70 ° C), isononyl acrylate (Tg-58 ° C), isodecyl acrylate (Tg-60 ° C), isodecyl methacrylate (Tg-41 ° C), n-lauryl methacrylate (Tg-65 ° C), tridecyl acrylate (Tg-55 ° C.), tridecyl methacrylate (Tg-40 ° C.) and the like are preferably mentioned. Above all, from the viewpoint of more effectively improving the flexibility, the homopolymer Tg of the low Tg alkyl acrylate is more preferably −45 ° C. or lower, and more preferably −50 ° C. or lower. Is particularly preferred. Specifically, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable. These may be used alone or in combination of two or more.

The (meth) acrylic acid ester polymer (A) preferably contains low Tg alkyl acrylate as a lower limit value of 50% by mass or more, and particularly 55% by mass or more, as a monomer unit constituting the polymer. Is preferable, and more preferably 60% by mass or more is contained. By containing 50% by mass or more of the low Tg alkyl acrylate, the glass transition temperature (Tg) of the (meth) acrylic acid ester polymer (A) can be easily set within the above range.

On the other hand, the (meth) acrylic acid ester polymer (A) preferably contains the above low Tg alkyl acrylate as a monomer unit constituting the polymer in an upper limit of 80% by mass or less, and particularly in an amount of 75% by mass or less. It is preferable that the content is 70% by mass or less. By containing the low Tg alkyl acrylate in the above content, it is possible to introduce a suitable amount of other monomer components (particularly the reactive functional group-containing monomer) into the (meth) acrylic acid ester polymer (A). can.

Further, as the (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group, a monomer having a glass transition temperature (Tg) of more than 0 ° C. as a homopolymer (hereinafter referred to as "high Tg alkyl acrylate") may be used. It is preferable to contain.). By containing such a high Tg alkyl acrylate as a constituent monomer unit, the obtained pressure-sensitive adhesive layer can easily satisfy the above-mentioned physical properties.

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

Examples of the high Tg alkyl acrylate include methyl acrylate (Tg10 ° C.), methyl methacrylate (Tg105 ° C.), ethyl methacrylate (Tg65 ° C.), n-butyl methacrylate (Tg20 ° C.), and isobutyl methacrylate (Tg48 ° C.). ), T-butyl methacrylate (Tg 107 ° C), n-stearyl acrylate (Tg 30 ° C), n-stearyl methacrylate (Tg 38 ° C), cyclohexyl acrylate (Tg 15 ° C), cyclohexyl methacrylate (Tg 66 ° C), methacrylic acid. Examples thereof include benzyl (Tg 54 ° C.), isobornyl acrylate (Tg 94 ° C.), isobornyl methacrylate (Tg 180 ° C.), adamantyl acrylate (Tg 115 ° C.), and adamantyl methacrylate (Tg 141 ° C.). Among the above, methyl acrylate, methyl methacrylate and isobornyl acrylate are preferable from the viewpoint of cohesive force. These may be used alone or in combination of two or more. The high Tg alkyl acrylate does not contain the nitrogen atom-containing monomer described later.

The (meth) acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, and thus via the reactive functional group derived from the reactive functional group-containing monomer. , Will react with the cross-linking agent (B) described later, thereby forming a cross-linked structure (three-dimensional network structure), and a pressure-sensitive adhesive having a desired cohesive force can be 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 (monomer containing a hydroxyl group) and carboxy in the molecule. Preferred examples thereof include a monomer having a group (monomer containing a carboxy group) and a monomer having an amino group in the molecule (monomer containing an amino group). These reactive functional group-containing monomers may be used alone or in combination of two or more.

Among the above reactive functional group-containing monomers, a hydroxyl group-containing monomer and a carboxy group-containing monomer are preferable, and a hydroxyl group-containing monomer is particularly preferable from the viewpoint of flexibility.

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

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 5% by mass or more, particularly. It is preferably 10% by mass or more, and more preferably 15% by mass or more. The content of the hydroxyl group-containing monomer is preferably 30% by mass or less, and particularly preferably 25% by mass or less. When the content of the hydroxyl group-containing monomer is as described above, the flexibility and adhesiveness of the obtained (meth) acrylic acid ester polymer (A) are improved, and the obtained pressure-sensitive adhesive layer satisfies the above-mentioned physical properties. It will be easy.

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 a monomer having an amino group, a monomer having an amide group, a monomer having a nitrogen-containing heterocycle, and the like, and among them, a monomer having a nitrogen-containing heterocycle is preferable. Further, from the viewpoint of increasing the degree of freedom of the portion derived from the nitrogen atom-containing monomer in the higher-order structure of the constituent pressure-sensitive adhesive, the nitrogen atom-containing monomer constitutes the (meth) acrylic acid ester polymer (A). It is preferable that no reactive unsaturated double-bonding group is contained other than one polymerizable group used for the polymerization of.

Examples of the monomer having a nitrogen-containing heterocycle include N- (meth) acryloylmorpholine, N-vinyl-2-pyrrolidone, N- (meth) acryloylpyrrolidone, N- (meth) acryloylpiperidin, and N- (meth) acryloyl. Pyrrolidine, N- (meth) acryloyl aziridine, aziridinyl ethyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, N-vinylphthalimide, etc. Among them, N- (meth) acryloylmorpholine, which exhibits more excellent adhesive strength, is preferable, and N-acryloylmorpholine is particularly preferable. These may be used alone or in combination of two or more.

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. In particular, it is preferably 3% by mass or more. The content of the nitrogen atom-containing monomer is preferably 20% by mass or less, particularly preferably 15% by mass or less, and further preferably 10% by mass or less.

If desired, the (meth) acrylic acid ester polymer (A) may contain another monomer as a monomer unit constituting the polymer. As the other monomer, a monomer containing no reactive functional group is preferable so as not to inhibit the above-mentioned action of the reactive functional group-containing monomer. Examples of such monomers include (meth) acrylic acid alkoxyalkyl esters such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate, vinyl acetate, styrene and the like. 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 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 further preferably 500,000 or more. When the lower limit of the weight average molecular weight of the (meth) acrylic acid ester polymer (A) is the above, the durability of the pressure-sensitive adhesive becomes more excellent. The weight average molecular weight in the present specification is a value in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method.

Further, 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 further preferably 1 million or less. preferable. When the upper limit of the weight average molecular weight of the (meth) acrylic acid ester polymer (A) is as described above, the flexibility of the obtained pressure-sensitive adhesive becomes more excellent.

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

(2-1-2) Crosslinking agent (B)
The cross-linking agent (B) cross-links the (meth) acrylic acid ester polymer (A) with the heating of the adhesive composition P containing the cross-linking agent (B) as a trigger to form a three-dimensional network structure. .. As a result, the cohesive force of the obtained pressure-sensitive adhesive is improved, and the pressure-sensitive adhesive layer becomes excellent in durability.

The cross-linking agent (B) may be any as long as it reacts with the reactive group of the (meth) acrylic acid ester polymer (A), and for example, an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, and an amine-based cross-linking agent. , Melamine-based cross-linking agent, aziridine-based cross-linking agent, hydrazine-based cross-linking agent, aldehyde-based cross-linking agent, oxazoline-based cross-linking agent, metal alkoxide-based cross-linking agent, metal chelate-based cross-linking agent, metal salt-based cross-linking agent, ammonium salt-based cross-linking agent, etc. Can be mentioned. Among the above, it is preferable to use an isocyanate-based cross-linking agent having excellent reactivity with a reactive functional group-containing monomer, particularly a hydroxyl group-containing monomer. The cross-linking agent (B) may be used alone or in combination of two or more.

The isocyanate-based cross-linking 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, isophorone diisocyanates, and alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate. , And their biurets, isocyanurates, and adducts, which are reactants with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Of these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate, are preferable from the viewpoint of reactivity with hydroxyl groups.

The content of the cross-linking agent (B) in the adhesive composition P is preferably 0.1 part by mass or more with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A), and is 0.3. It is more preferably parts by mass or more, particularly preferably 0.5 parts by mass or more, and further preferably 1.0 part by mass or more. The content is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, particularly preferably 5 parts by mass or less, and further preferably 3 parts by mass or less. .. When the content of the cross-linking agent (B) is in the above range, the cohesive force of the obtained pressure-sensitive adhesive becomes appropriate, and the pressure-sensitive adhesive layer easily satisfies the above-mentioned physical properties.

(2-1-3) Various Additives The tacky composition P may contain various additives usually used for acrylic pressure-sensitive adhesives, for example, silane coupling agents, ultraviolet absorbers, antistatic agents, if desired. A tackifier, an antioxidant, a light stabilizer, a softener, a filler, a refractive index adjuster and the like can be added. The polymerization solvent and the diluting solvent described later are not included in the additives constituting the adhesive composition P.

(2-2) Production of Adhesive Composition P The adhesive composition P produced a (meth) acrylic acid ester polymer (A), and the (meth) acrylic acid ester polymer (A) obtained by producing the (meth) acrylic acid ester polymer (A). It can be produced by mixing with the cross-linking agent (B) and adding an additive if desired.

The (meth) acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by an ordinary radical polymerization method. The polymerization of the (meth) acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method using a polymerization initiator, if desired. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone and the like, and two or more of them may be used in combination.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more of them may be used in combination. Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane1-carbonitrile), and 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] and the like.

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

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

Once the (meth) acrylic acid ester polymer (A) is obtained, the cross-linking agent (B) and, if desired, an additive and a diluting solvent are sufficiently added to the solution of the (meth) acrylic acid ester polymer (A). To obtain a tacky composition P (coating solution) diluted with a solvent.

If any of the above components is in the form of a solid, or if precipitation occurs when the component is mixed with another component in an undiluted state, the component is used alone as a diluting solvent in advance. It may be dissolved or diluted and then mixed 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 and 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 may be any range as long as it can be coated, and may be appropriately selected depending on the situation. For example, the adhesive composition P is diluted to a concentration of 10 to 60% by mass. It should be noted that the addition of a diluting solvent or the like is not a necessary condition when obtaining the coating solution, and the diluting solvent may not be added as long as the adhesive composition P has a viscosity that allows coating. In this case, the adhesive composition P becomes a coating solution using the polymerization solvent of the (meth) acrylic acid ester polymer (A) as it is as a diluting solvent.

(2-3) Production of Adhesive The pressure-sensitive adhesive constituting the bending-resistant pressure-sensitive adhesive layer is preferably obtained by cross-linking the pressure-sensitive adhesive composition P. Crosslinking of the adhesive composition P can usually be carried out by heat treatment. It should be noted that this heat treatment can also be used as a drying treatment for volatilizing the 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, particularly preferably 70 to 120 ° C. The heating time is preferably 10 seconds to 10 minutes, and particularly preferably 50 seconds to 2 minutes.

After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be provided at room temperature (for example, 23 ° C., 50% RH). If this curing period is required, the adhesive is formed after the curing period has elapsed, and if the curing period is not required, 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 cross-linked via the cross-linking agent (B) to form a cross-linked structure, and a pressure-sensitive adhesive is obtained. Such a pressure-sensitive adhesive has a predetermined cohesive force.

(2-4) Physical Properties of Adhesive The storage elastic modulus (G') of the adhesive constituting the bending-resistant adhesive layer at 25 ° C. is preferably 0.01 MPa or more as a lower limit, and is particularly 0.03 MPa. The above is preferable. The upper limit of the storage elastic modulus (G') is preferably 0.30 MPa or less, and particularly preferably 0.25 MPa or less.

The elastic modulus (G ") of the pressure-sensitive adhesive constituting the bending-resistant pressure-sensitive adhesive layer at 25 ° C. is preferably 0.005 MPa or more, and particularly preferably 0.01 MPa or more, as a lower limit value. The upper limit of the loss elastic modulus (G ") is preferably 0.1 MPa or less, and particularly preferably 0.08 MPa or less.

Further, the loss tangent (tan δ) of the pressure-sensitive adhesive constituting the bending-resistant pressure-sensitive adhesive layer at 25 ° C. is preferably 0.25 or more, and particularly preferably 0.28 or more, as a lower limit value. Further, the upper limit of the loss tangent (tan δ) is preferably 0.85 or less, and particularly preferably 0.80 or less.

When the storage elastic modulus (G'), the loss elastic modulus (G ") and the loss tangent (tan δ) of the pressure-sensitive adhesive constituting the bending-resistant pressure-resistant adhesive layer are within the above ranges, the obtained pressure-sensitive adhesive layer has the above-mentioned physical characteristics. The method for measuring the storage elastic modulus (G'), the loss elastic modulus (G ") and the loss tangent (tan δ) is as shown in the test example described later.

(3) Adhesive Sheet In the repetitive bending device according to the present embodiment, a desired constituent member (flexible member having flexibility) is bonded by using the pressure-sensitive adhesive sheet having the above-mentioned bending-resistant adhesive layer. , Can be preferably manufactured.

A specific configuration as an example of the adhesive sheet is shown in FIG.
As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 according to the embodiment is in contact with the two release sheets 12a and 12b and the release surfaces of the two release sheets 12a and 12b. , 12b and the bending resistant pressure-resistant adhesive layer 11R. The peeling surface of the release sheet in the present specification refers to a surface having peelability in the release sheet, and includes both a surface subjected to peeling treatment and a surface exhibiting peelability even without peeling treatment. ..

(3-1) Component (3-1-1) Bending-Resistant Adhesive Layer The bending-resistant adhesive layer 11R is made of a pressure-sensitive adhesive satisfying the above-mentioned physical properties, and preferably crosslinks the pressure-sensitive adhesive composition P. It is composed of a pressure-sensitive adhesive.

The thickness of the bending-resistant pressure-resistant adhesive layer 11R (value measured according to JIS K7130) in the pressure-sensitive adhesive sheet 1 is preferably 2 μm or more as a lower limit value, particularly preferably 5 μm or more, and further preferably 10 μm or more. It is preferable to have. When the lower limit of the thickness of the bending-resistant pressure-sensitive adhesive layer 11R is the above, it is easy to exert a desired adhesive force, and it is possible to effectively suppress the occurrence of floating and peeling during repeated bending. The thickness of the bending-resistant adhesive layer 11R is preferably 150 μm or less, more preferably 100 μm or less, particularly preferably 70 μm or less, and further preferably 50 μm or less as an upper limit value. preferable. When the upper limit of the thickness of the bending-resistant pressure-sensitive adhesive layer 11R is the above, it is possible to suppress the seepage of the pressure-sensitive adhesive or the components constituting the pressure-sensitive adhesive from the pressure-sensitive adhesive layer due to repeated bending. The bending-resistant adhesive layer 11R may be formed as a single layer, or may be formed by laminating a plurality of layers. Regarding the bending-resistant pressure-sensitive adhesive layer 11R, the bending-resistant pressure-sensitive adhesive layer 11R formed by laminating a plurality of layers is treated as a single layer.

(3-1-2) Release Sheet The release sheets 12a and 12b protect the bending-resistant adhesive layer 11R until the pressure-sensitive adhesive sheet 1 is used, and the pressure-sensitive adhesive sheet 1 (flexion-resistant adhesive layer 11R) is used. Sometimes peeled off. In the pressure-sensitive adhesive sheet 1 according to the present embodiment, one or both of the release sheets 12a and 12b are not always necessary.

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, polyethylene naphthalate film, and polybutylene. Telephthalate 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. In addition, these crosslinked films are also used. Further, 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 bending resistant pressure-sensitive adhesive layer 11R) 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. Of the release sheets 12a and 12b, it is preferable that one of the release sheets is a heavy release type release sheet having a large release force and the other release sheet is a light release type release sheet having a small release force.

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

(3-2) Production of Adhesive Sheet As an example of production of the adhesive sheet 1, a case where the adhesive composition P is used will be described. The coating liquid of the adhesive composition P is applied to the peeling surface of one of the release sheets 12a (or 12b), heat-treated to heat-crosslink the adhesive composition P to form a coating layer, and then the coating thereof. The peeling surface of the other peeling sheet 12b (or 12a) is superposed on the layer. When the curing period is required, the curing period is set, and when the curing period is not required, the coating layer becomes the bending-resistant adhesive layer 11R as it is. As a result, the adhesive sheet 1 is obtained. The conditions for heat treatment and curing are as described above.

As another production example of the pressure-sensitive adhesive sheet 1, a coating liquid of the pressure-sensitive adhesive composition P is applied to the peel-off surface of one of the release sheets 12a, heat-treated to heat-crosslink the pressure-sensitive adhesive composition P, and the coating layer is formed. To obtain a release sheet 12a with a coating layer. Further, the coating liquid of the adhesive composition P is applied to the peeling surface of the other release sheet 12b, heat-treated to heat-crosslink the adhesive composition P to form a coating layer, and the coating layer is attached. To obtain the release sheet 12b of. Then, the release sheet 12a with the coating layer and the release sheet 12b with the coating layer are bonded so that both the coating layers are in contact with each other. When the curing period is required, the curing period is set, and when the curing period is not required, the above-mentioned laminated coating layer becomes the bending-resistant adhesive layer 11R as it is. As a result, the adhesive sheet 1 is obtained. According to this production example, even when the bending-resistant pressure-sensitive adhesive layer 11R is relatively thick, stable production is possible.

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 and the like can be used.

2. 2. Configuration of Repeated Bending Device The repeating bending device according to this embodiment uses, for example, an organic electroluminescence (organic EL) display, an electrophoretic display (electronic paper), a flexible printed substrate, and a plastic substrate (film) as a substrate. A liquid crystal display, a foldable display, a micro LED display, a quantum dot display, or the like, and may be a touch panel.

A configuration as an example of the repetitive bending device according to the present embodiment will be described with reference to the drawings.

The repetitive bending device 10A shown in FIG. 2 includes a first plastic substrate 211, a first pressure-sensitive adhesive layer 111, a second plastic substrate 221 with a gas barrier layer, a thin film thin film 3, and organic light emitting in order from the bottom. A diode 4, a second pressure-sensitive adhesive layer 112 for sealing the organic light-emitting diode 4, a third plastic substrate 222 with a gas barrier layer, a touch sensor 5, a third pressure-sensitive adhesive layer 113, and a fourth It is configured by laminating the plastic substrate 212 of.

In the repetitive bending device 10A, at least one of the first pressure-sensitive adhesive layer 111, the second pressure-sensitive adhesive layer 112, and the third pressure-sensitive adhesive layer 113 is a bending-resistant pressure-sensitive adhesive layer, and the others are non-flexible. It is a bending resistant adhesive layer. The thickness of the second pressure-sensitive adhesive layer 112 that seals the organic light-emitting diode 4 is preferably a thickness that can cover the organic light-emitting diode 4, and is usually 1 to 10 μm, preferably 1 to 10 μm. It is 3 to 5 μm.

The organic light emitting diode 4 may be laminated with a thin film encapsulation (TFE) layer (not shown). The thin film sealing layer usually contains silicon nitride, aluminum oxide, or the like, and can be formed by a PVD (Physical Vapor Deposition) method, a CVD (Chemical Vapor Deposition) method, an ALD (Atomic Layer Deposition) method, or the like. It can be provided with two or more layers. The thickness of the thin film sealing layer is usually 100 nm to 2 μm.

The repetitive bending device 10B shown in FIG. 3 includes a first plastic substrate 211, a first adhesive layer 111, a second plastic substrate 221 with a gas barrier layer, a thin film thin film 3, and organic light emitting in order from the bottom. A diode 4, a second pressure-sensitive adhesive layer 112 for sealing the organic light-emitting diode 4, a third plastic substrate 222 with a gas barrier layer, a touch sensor 5, a third pressure-sensitive adhesive layer 113, and a fourth The plastic substrate 212, the fourth pressure-sensitive adhesive layer 114, and the fifth plastic substrate 231 with a hard coat layer are laminated.

In the repeated bending device 10B, at least one of the first pressure-sensitive adhesive layer 111, the second pressure-sensitive adhesive layer 112, the third pressure-sensitive adhesive layer 113, and the fourth pressure-sensitive adhesive layer 114 is a bending-resistant pressure-sensitive adhesive. It is a layer, and the rest is a non-flexible adhesive layer.

The repetitive bending device 10C shown in FIG. 4 includes a first plastic substrate 211, a first adhesive layer 111, a second plastic substrate 221 with a gas barrier layer, a thin film thin film 3, and organic light emitting in order from the bottom. A diode 4, a second pressure-sensitive adhesive layer 112 for sealing the organic light-emitting diode 4, a third plastic substrate 222 with a gas barrier layer, a touch sensor 5, a third pressure-sensitive adhesive layer 113, and a fourth Plastic substrate 212, a fourth pressure-sensitive adhesive layer 114, a first wavelength plate (λ / 4) 71, a fifth pressure-sensitive adhesive layer 115, and a second wavelength plate (λ / 2) 72. The sixth pressure-sensitive adhesive layer 116, the polarizing plate 81, and the polarizing plate protective film 82 with a hard coat layer are laminated.

In the repetitive bending device 10C, the first pressure-sensitive adhesive layer 111, the second pressure-sensitive adhesive layer 112, the third pressure-sensitive adhesive layer 113, the fourth pressure-sensitive adhesive layer 114, the fifth pressure-sensitive adhesive layer 115, and the sixth Of the pressure-sensitive adhesive layers 116 of the above, at least one layer is a bending-resistant pressure-sensitive adhesive layer, and the other is a non-bending-resistant pressure-sensitive adhesive layer.

The constituent members other than the pressure-sensitive adhesive layer constituting the repeated bending devices 10A to 10C are flexible members having flexibility. The Young's modulus of each of these flexible members is preferably 0.1 to 10 GPa, particularly preferably 0.5 to 7 GPa, and further preferably 1.0 to 5 GPa. When the Young's modulus of each flexible member is within such a range, it becomes easy to repeatedly bend each flexible member.

The thickness of each of the flexible members is preferably 5 to 3000 μm, particularly preferably 10 to 1000 μm, and further preferably 10 to 500 μm. When the thickness of the flexible member is within such a range, it becomes easy to repeatedly bend each flexible member.

The repetitive bending devices 10A to 10C can be manufactured by a conventional method except that at least one of the plurality of pressure-sensitive adhesive layers is a bending-resistant pressure-sensitive adhesive layer. When the bending-resistant adhesive layer 11R of the pressure-sensitive adhesive sheet 1 described above is used as the bending-resistant pressure-sensitive adhesive layer, one of the release sheets 12a (12b) of the pressure-sensitive adhesive sheet 1 is peeled off to expose the pressure-resistant adhesive sheet 1. The pressure-sensitive adhesive layer 11R is bonded to a predetermined component. After that, the other release sheet 12b (12a) is peeled from the bending-resistant pressure-resistant adhesive layer 11R of the pressure-sensitive adhesive sheet 1, and the exposed bending-resistant pressure-sensitive adhesive layer 11R of the pressure-sensitive adhesive sheet 1 is bonded to another predetermined component. ..

The pressure-sensitive adhesive layer other than the bending-resistant pressure-sensitive adhesive layer 11R can be formed by using a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of a desired pressure-sensitive adhesive in the same manner as the pressure-sensitive adhesive sheet 1.

The thin film transistor 3 can be constructed by performing thin film deposition or the like on the second plastic substrate 221. Further, the touch sensor 5 can be formed by forming a conductive material such as ITO on the third plastic substrate 222 by subjecting it to a process such as thin film deposition. The touch sensor 5 can also be formed by depositing ITO or the like on the fourth plastic substrate 212. In this case, the third pressure-sensitive adhesive layer 113 is located between the third plastic substrate 222 and the touch sensor 5. Further, the touch sensor 5 may be composed of a plurality of layers, and in that case, an adhesive layer may be present between the touch sensors 5.

Since the repetitive bending device according to the present embodiment has at least one bending-resistant adhesive layer, it is repeatedly bent (for example, 30,000 times) or left in a bent state for a long period of time (for example, at least 24 hours or more). ), After being released from the bent state, it is easy to restore and it is difficult to make a bending mark. The effect of suppressing the bending trace of the repeated bending device can be evaluated by, for example, the amount of static bending deformation by the static bending test. As a bending test, there is also a dynamic bending test in which the repeatedly bending device is repeatedly bent (for example, 30,000 times), but the static bending test is stricter as a test condition for the repeated bending device than the dynamic bending test. If the static bending test gives good results, the dynamic bending test also gives good results. Therefore, it can be said that a static bending test is sufficient to confirm the bending trace suppressing effect of the repeated bending device.

In the static bending test, a laminated body in which an adhesive layer (thickness: 12 μm) is sandwiched between two polyethylene terephthalate films (thickness: 12 μm) and a size of 200 mm × 50 mm is tested. Make a piece. As shown in FIG. 6, this test piece S is held in a bent state for 24 hours between a holding plate P made of two glass plates erected in an environment of 23 ° C. and 50% RH. .. At this time, the distance between the two holding plates P is set to 6 mm (bending diameter of the test piece S: 6 mmφ), and the substantially central portion of the long side (200 mm) of the test piece S becomes the bent part. The test piece S is held so that both short sides (50 mm) of S are located on the upper side. After performing this static bending test, the test piece S is taken out from between the two holding plates P, and as shown in FIG. 7, the test piece S is placed on a flat plate so that the convex direction of the bent portion is on the upper side. Place on. Then, immediately after the test and 24 hours after the test, the height h from the flat plate surface to the apex of the bent portion (deformed portion) is measured as the static bending deformation amount. This static bending deformation amount can be used as the test result of the static bending test, and the bending trace suppressing effect can be evaluated based on the static bending deformation amount.

Immediately after the test, the amount of static bending deformation by the static bending test is preferably 24 mm or less, more preferably 15 mm or less, particularly preferably 10 mm or less, and further preferably 5 mm or less. It is preferably 0.5 mm or less, and most preferably 0.5 mm or less. The lower limit of the static bending deformation amount immediately after the test is preferably 0 mm.

The amount of static bending deformation by the static bending test is preferably 10 mm or less, more preferably 8 mm or less, particularly preferably 6 mm or less, and further preferably 4 mm or less after 24 hours of the test. It is preferably 0.5 mm or less, and most preferably 0.5 mm or less. The lower limit of the static bending deformation amount after 24 hours of the test is preferably 0 mm.

[Method of suppressing bending marks]
In a repetitive bending device having one or more pressure-sensitive adhesive layers, at least one of the pressure-sensitive adhesive layers is formed from a pressure-sensitive adhesive satisfying the above-mentioned physical characteristics, that is, at least one layer of the pressure-sensitive adhesive layer is formed. By using the above-mentioned bending pressure-sensitive adhesive layer, it is possible to suppress the formation of bending marks.

The embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

For example, either or both of the release sheets 12a and 12b in the pressure-sensitive adhesive sheet 1 may be omitted, and desired components may be laminated in place of the release sheets 12a and / or 12b. Further, the repetitive bending devices 10A to 10C may be provided with another layer, or some layers may be omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the scope of the present invention is not limited to these Examples and the like.

[Manufacturing Example 1] (Manufacturing of Adhesive Sheet I)
1. 1. Preparation of (meth) acrylic acid ester polymer (A) Solution polymerization method of 65 parts by mass of 2-ethylhexyl acrylate, 15 parts by mass of isobonyl acrylate, 5 parts by mass of N-acryloylmorpholine and 15 parts by mass of 2-hydroxyethyl acrylate. The (meth) acrylic acid ester polymer (A) was prepared by copolymerizing with the above. When the molecular weight of this (meth) acrylic acid ester polymer (A) was measured by the method described later, the weight average molecular weight (Mw) was 500,000.

2. 2. Preparation of Adhesive Composition 100 parts by mass (solid content conversion value; the same applies hereinafter) of the (meth) acrylic acid ester polymer (A) obtained in the above step 1 and a trimethylolpropane-modified bird as a cross-linking agent (B). Mix with 1.20 parts by mass of range isocyanate (manufactured by Toyochem Co., Ltd., product name "BHS8515"), stir well, and dilute with methyl ethyl ketone (MEK) to obtain a coating solution (solid content concentration) of the adhesive composition. : 30.0% by mass) was obtained.

3. 3. Manufacture of Adhesive Sheet A heavy release type release sheet (manufactured by Lintec Corporation, product name "SP-PET382150") in which one side of a polyethylene terephthalate film is peeled off with a silicone-based release agent from the coating solution of the adhesive composition obtained in the above step 2. ”) Was applied to the peeled surface with a comma coater (registered trademark). Then, the coated layer was heat-treated at 90 ° C. for 1 minute to form a coated layer.

Next, a light release type release sheet (manufactured by Lintec Corporation, product name "SP-PET38131") in which the coating layer on the heavy release type release sheet obtained above and one side of the polyethylene terephthalate film were peeled off with a silicone-based release agent). The adhesive layer having a thickness of 12 μm was formed by laminating the light peeling type peeling sheet so that the peeled surface of the light peeling type peeling sheet was in contact with the coating layer and curing it under the conditions of 23 ° C. and 50% RH for 7 days. An adhesive sheet I having a structure of a heavy release type release sheet, that is, a heavy release type release sheet / an adhesive layer (thickness: 12 μm) / a light release type release sheet was produced. The adhesive layer of the adhesive sheet I is referred to as "adhesive layer I". The thickness of the pressure-sensitive adhesive layer is a value measured using a constant pressure thickness measuring device (manufactured by TECLOCK Co., Ltd., product name "PG-02") in accordance with JIS K7130.

[Manufacturing Example 2] (Manufacturing of Adhesive Sheet II)
The pressure-sensitive adhesive sheet II is the same as in Example 1 except that the (meth) acrylic acid ester polymer (A) prepared in Production Example 1 is used and the blending amount of the cross-linking agent (B) is changed to 0.30 parts by mass. Was produced. The adhesive layer of this adhesive sheet II is called "adhesive layer II".

[Manufacturing Example 3] (Manufacturing of Adhesive Sheet III)
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 a solution polymerization method to prepare a (meth) acrylate ester polymer (A). When the molecular weight of this (meth) acrylic acid ester polymer (A) was measured by the method described later, the weight average molecular weight (Mw) was 600,000.

100 parts by mass of the (meth) acrylic acid ester polymer (A) obtained above and trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyochem, product name "BHS8515") 1.88 mass as a cross-linking agent (B). The parts were mixed with each other, sufficiently stirred, and diluted with MEK to obtain a coating solution (solid content concentration: 30.0% by mass) of the adhesive composition. A pressure-sensitive adhesive sheet III was prepared in the same manner as in Example 1 except that the coating solution of the obtained pressure-sensitive adhesive composition was used. The adhesive layer of this adhesive sheet III is called "adhesive layer III".

[Manufacturing Example 4] (Manufacturing of Adhesive Sheet IV)
The pressure-sensitive adhesive sheet IV is the same as in Example 1 except that the (meth) acrylic acid ester polymer (A) prepared in Production Example 1 is used and the blending amount of the cross-linking agent (B) is changed to 0.60 parts by mass. Was produced. The adhesive layer of this adhesive sheet IV is called "adhesive layer IV".

[Manufacturing Example 5] (Manufacturing of Adhesive Sheet V)
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 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 later, the weight average molecular weight (Mw) was 600,000.

100 parts by mass of the (meth) acrylic acid ester polymer (A) obtained above and trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyochem, product name "BHS8515") 1.88 mass as a cross-linking agent (B). The parts were mixed with each other, sufficiently stirred, and diluted with MEK to obtain a coating solution (solid content concentration: 30.0% by mass) of the adhesive composition. A pressure-sensitive adhesive sheet V was produced in the same manner as in Example 1 except that the coating solution of the obtained pressure-sensitive adhesive composition was used. The adhesive layer of the adhesive sheet V is referred to as "adhesive layer V".

[Manufacturing Example 6] (Manufacturing of adhesive sheet VI)
Mix 15 parts by mass of the isobutylene-isoprene copolymer (manufactured by Nippon Butyl Co., Ltd., product name "Butyl365") and 3 parts by mass of the tackifier (manufactured by Nippon Zeon Co., Ltd., product name "Quinton A100") and stir well. Then, by diluting with toluene, a coating solution (solid content concentration: 15% by mass) of the adhesive composition as butyl rubber was obtained. Using the coating solution of the obtained adhesive composition, an adhesive sheet VI was produced in the same manner as in Example 1 except that the heat treatment temperature was set to 100 ° C. The adhesive layer of this adhesive sheet VI is called "adhesive layer VI".

In Table 1, the composition of the (meth) acrylic acid ester polymer (A) and the blending amount of the cross-linking agent (B) in each production example (mass with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A)). Part) is described. The abbreviations in Table 1 are as follows.
2EHA: 2-ethylhexyl acrylate IBXA: isobornyl acrylate ACMO: N-acryloylmorpholine HEA: 2-hydroxyethyl acrylate BA: n-butyl acrylate MA: methyl acrylate MMA: methyl methacrylate

[Example 1]
Using the pressure-sensitive adhesive sheet I obtained in Production Example 1 and the pressure-sensitive adhesive sheet VI obtained in Production Example 6, the laminate 100 shown in FIG. 5 was manufactured. The laminated body 100 has a first base material 91, a first pressure-sensitive adhesive layer 111, a second base material 92, a second pressure-sensitive adhesive layer 112, and a third base material 93 in this order from the bottom. The third pressure-sensitive adhesive layer 113 and the fourth base material 94 are laminated, and correspond to a simulated repetitive bending device.

Specifically, first, as the first base material 91, the second base material 92, the third base material 93, and the fourth base material 94, the first to fourth polyethylene terephthalate (PET) films (PET) films ( Toray Industries, Inc., product name "S10 Lumirror", thickness: 12 μm) was prepared. Next, the light release type release sheet was peeled off from the pressure-sensitive adhesive sheet VI obtained in Production Example 6 under an environment of 23 ° C. and 50% RH, and the exposed pressure-sensitive adhesive layer VI was applied to one of the first PET films. I stuck it on the surface of. Subsequently, the heavy release type release sheet was peeled off from the pressure-sensitive adhesive sheet VI, and one surface of the second PET film was attached to the exposed pressure-sensitive adhesive layer VI.

Next, the light release type release sheet was peeled off from the pressure-sensitive adhesive sheet I obtained in Production Example 1 under an environment of 23 ° C. and 50% RH, and the exposed pressure-sensitive adhesive layer I was applied to the above-mentioned second PET film. It was pasted on the other side. Subsequently, the heavy-release type release sheet was peeled off from the pressure-sensitive adhesive sheet I, and one surface of the third PET film was attached to the exposed pressure-sensitive adhesive layer I.

Next, the light release type release sheet was peeled off from the pressure-sensitive adhesive sheet VI produced in Production Example 6 under an environment of 23 ° C. and 50% RH, and the exposed pressure-sensitive adhesive layer VI was applied to the other side of the above-mentioned third PET film. I stuck it on the surface of. Subsequently, the heavy release type release sheet was peeled off from the pressure-sensitive adhesive sheet VI, and one surface of the fourth PET film was attached to the exposed pressure-sensitive adhesive layer VI. Finally, after pressurizing with an autoclave manufactured by Kurihara Seisakusho Co., Ltd. at 0.5 MPa and 50 ° C. for 20 minutes, the mixture was left to stand for 24 hours under the conditions of 23 ° C. and 50% RH to obtain the laminate 100 shown in FIG. rice field.

[Examples 2 to 23, Comparative Example 1]
The laminated body 100 shown in FIG. 5 was manufactured using the pressure-sensitive adhesive sheets I to VI manufactured in Production Examples 1 to 6. At this time, the pressure-sensitive adhesive sheets I to VI are formed so that the first pressure-sensitive adhesive layer 111, the second pressure-sensitive adhesive layer 112, and the third pressure-sensitive adhesive layer 113 become the pressure-sensitive adhesive layers I to VI shown in Table 2, respectively. The laminated body 100 was manufactured in the same manner as in Example 1 except that it was used.

[Test Example 1] (Measurement of relaxed modulus)
A plurality of adhesive layers of the adhesive sheet produced in the production example were laminated to form a laminated body having a thickness of 0.5 mm. A cylinder (height 0.5 mm) having a diameter of 8 mm was punched out from the obtained laminated body of the pressure-sensitive adhesive layer, and this was used as a sample.

For the above sample, in accordance with JIS K7424-1, using a viscoelasticity measuring device (manufactured by Antoniopaar, product name "MCR302"), the pressure-sensitive adhesive was continuously distorted by 10% under the following conditions, and the relaxation elastic modulus G. (T) (MPa) was measured. From the measurement result, the maximum relaxation elastic modulus G (t) _max (MPa) is derived, and the minimum relaxation elastic modulus G measured up to 3757 seconds after the maximum relaxation elastic modulus G (t) _max is measured. (T) _min (MPa) was derived.
Measurement temperature: 25 ° C
Measurement points: 1000 points (logarithmic plot)

From the obtained maximum relaxation elastic modulus G (t) _max (MPa) and minimum relaxation elastic modulus G (t) _min (MPa), the relaxation elastic modulus fluctuation value Δlog G (t) is calculated based on the following formula (I). Calculated. The results are shown in Table 1.
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I)

[Test Example 2] (Measurement of creep compliance)
A plurality of adhesive layers of the adhesive sheet produced in the production example were laminated to form a laminated body having a thickness of 0.5 mm. A cylinder (height 0.5 mm) having a diameter of 8 mm was punched out from the obtained laminated body of the pressure-sensitive adhesive layer, and this was used as a sample.

For the above sample, creep compliance J (t) (MPa ^-1 ) was measured by continuously applying a stress of 3000 Pa under the following conditions using a viscoelasticity measuring device (manufactured by Antoniopaar, product name "MCR302"). .. From the measurement result, the value when a stress of 3000 Pa is applied is set as the minimum creep compliance J (t) _min (MPa ^-1 ), and within 3757 seconds after the minimum creep compliance J (t) _min is measured. The measured maximum creep compliance J (t) _max (MPa ^-1 ) was derived.
Measurement temperature: 25 ° C
Measurement points: 1000 points (logarithmic plot)

From the obtained minimum creep compliance J (t) _min (MPa ^-1 ) and maximum creep compliance J (t) _max (MPa ^-1 ), the creep compliance fluctuation value ΔlogJ (t) is based on the following equation (II). Was calculated. The results are shown in Table 1.
ΔlogJ (t) = logJ (t) _max -logJ (t) _min ... (II)

[Test Example 3] (Calculation of product value)
The product value (ΔlogG (t) × ΔlogJ (t)) of the ΔlogG (t) obtained in Test Example 1 and the ΔlogJ (t) obtained in Test Example 2 was calculated. The results are shown in Table 1.

[Test Example 4] (Measurement of dynamic elastic modulus)
A plurality of adhesive layers of the adhesive sheet produced in the production example were laminated to form a laminated body having a thickness of about 0.5 mm. A cylinder (height 0.5 mm) having a diameter of 8 mm was punched out from the obtained laminated body of the pressure-sensitive adhesive layer, and this was used as a sample.

The dynamic viscoelasticity of the above sample was measured under the following conditions using a viscoelasticity measuring device (manufactured by Antoniopaar, product name "MCR302") in accordance with JIS K7424-1, and the storage elastic modulus at 25 ° C. (G') (MPa), loss elastic modulus (G ") (MPa) and loss tangent (tan δ) were observed. The results are shown in Table 1.
Measurement frequency: 1Hz
Measurement temperature range: -20 to 150 ° C

[Test Example 5] (Static bending test)
The laminates produced in Examples and Comparative Examples were cut into 200 mm × 50 mm, and this was used as a test piece. The obtained test piece was bent between two standing plates (distance between each other: 6 mm) consisting of two glass plates erected as shown in FIG. 6 in an environment of 23 ° C. and 50% RH. It was held in the state for 24 hours. After performing this static bending test, the test piece is placed on a flat plate as shown in FIG. 7, and the height from the surface of the flat plate to the apex of the bent portion (deformed portion) immediately after the test and 24 hours after the test. h was measured as the amount of static bending deformation. Based on the measured static bending deformation amount, the bending resistance (bending mark suppressing effect) was evaluated according to the following criteria. The results are shown in Table 2.
⊚: Deformation amount immediately after bending test is 15 mm or less, deformation amount after 24 hours of test is 1 mm or less 〇: Deformation amount immediately after bending test is 20 mm or less, deformation amount after 24 hours of test is 3 mm or less (excluding those with ◎) )
Δ: The amount of deformation immediately after the bending test is 24 mm or less, and the amount of deformation after 24 hours of the test is 9 mm or less (excluding those with ◎ and 〇).
×: Other than the above

As can be seen from Table 2, the laminated body of the example having at least one adhesive layer of the pressure-sensitive adhesive sheets produced in Production Examples 1 to 5 is excellent in the bending trace suppressing effect.

The repetitive bending device according to the present invention can be suitably used as an organic EL display or the like that can be repeatedly bent.

1 ... Adhesive sheet 11R ... Bending resistant adhesive layer 12a, 12b ... Peeling sheet 10A, 10B, 10C ... Repeated bending device 111, 112, 113, 114, 115, 116 ... Adhesive layer 211,212 ... Plastic substrate 221,222 ... ... Plastic substrate with gas barrier layer 231 ... Plastic substrate with hard coat layer 3 ... Thin film 4 ... Organic light emitting diode 5 ... Touch sensor 71, 72 ... Wave plate 81 ... Polarizing plate 82 ... Polarizing plate protective film 100 ... Laminated body 91, 92, 93, 94 ... Base material S ... Test piece P ... Holding plate

Claims (9)

A repetitive bending device with one or more layers of adhesive.
At least one of the adhesive layers is
In accordance with JIS K7424-1, the maximum relaxation elastic modulus value measured when the pressure-sensitive adhesive is distorted by 10% is set to the maximum relaxation elastic modulus G (t) _max (MPa), and the maximum relaxation elastic modulus G is set. (T) The pressure-sensitive adhesive was continuously distorted by 10% until 3757 seconds after _max was measured, and the minimum relaxation modulus value measured during that period was defined as the minimum relaxation modulus G (t) _min (MPa). A repetitive bending device characterized in that the relaxation elastic modulus fluctuation value Δlog G (t) calculated from the following formula (I) is composed of a pressure-sensitive adhesive having a value of 1.20 or less.
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I) The creep compliance value measured when a stress of 3000 Pa is applied to the pressure-sensitive adhesive is set to the minimum creep compliance J (t) _min (MPa ^-1 ), and 3757 seconds after the minimum creep compliance J (t) _min is measured. The maximum creep compliance value measured during that period is defined as the maximum creep compliance J (t) _max (MPa ^-1 ), and the creep compliance fluctuation value ΔlogJ calculated from the following equation (II) is used. The repetitive bending device according to claim 1, wherein (t) is 2.84 or less.
ΔlogJ (t) = logJ (t) _max -logJ (t) _min ... (II) Claim 1 or 2 is characterized in that the pressure-sensitive adhesive is a pressure-sensitive adhesive obtained by cross-linking a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester polymer (A) and a cross-linking agent (B). The repetitive bending device described in. Any one of claims 1 to 3, wherein the ratio of the number of the pressure-sensitive adhesive layers composed of the pressure-sensitive adhesive to the total number of pressure-sensitive adhesive layers contained in the repeatedly bending device is 10% or more. The repetitive bending device described in the section. Any of claims 1 to 4, wherein the ratio of the total thickness of the pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive to the thickness of the repeatedly bending device is 1% or more and 50% or less. The repetitive bending device according to one item. A method of manufacturing a repetitive bending device including one or more layers of adhesive.
At least one layer of the pressure-sensitive adhesive layer
In accordance with JIS K7424-1, the maximum relaxation elastic modulus value measured when the pressure-sensitive adhesive is distorted by 10% is set to the maximum relaxation elastic modulus G (t) _max (MPa), and the maximum relaxation elastic modulus G is set. (T) The pressure-sensitive adhesive was continuously distorted by 10% until 3757 seconds after _max was measured, and the minimum relaxation modulus value measured during that period was defined as the minimum relaxation modulus G (t) _min (MPa). A method for manufacturing a repeating bending device, characterized in that the relaxation elastic modulus fluctuation value Δlog G (t) calculated from the following formula (I) is composed of a pressure-sensitive adhesive having a value of 1.20 or less.
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I) The method for manufacturing a repetitive bending device according to claim 6, wherein a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive is used to bond the constituent members of the repetitive bending device. A method of suppressing bending marks in a repetitive bending device including one or more layers of adhesive.
At least one layer of the pressure-sensitive adhesive layer
In accordance with JIS K7424-1, the maximum relaxation elastic modulus value measured when the pressure-sensitive adhesive is distorted by 10% is set to the maximum relaxation elastic modulus G (t) _max (MPa), and the maximum relaxation elastic modulus G is set. (T) The pressure-sensitive adhesive was continuously distorted by 10% until 3757 seconds after _max was measured, and the minimum relaxation modulus value measured during that period was defined as the minimum relaxation modulus G (t) _min (MPa). A method for suppressing bending marks in a repetitive bending device, characterized in that the relaxation elastic modulus fluctuation value Δlog G (t) calculated from the following formula (I) is composed of a pressure-sensitive adhesive having a value of 1.20 or less.
ΔlogG (t) = logG (t) _max -logG (t) _min ... (I) The suppression of bending marks in the repeatedly bending device according to claim 8, wherein the pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive is used to bond the constituent members of the repeatedly bending device. Method.

Images