JP7309006B2 - Repetitive bending device, method for manufacturing the same, and method for suppressing bending marks - Google Patents

Description

TECHNICAL FIELD The present invention relates to a repeatedly bending device, a method for manufacturing the repeatedly bending device, and a method for suppressing bending traces in the repeatedly bending device.

In recent years, bendable displays have been proposed as display bodies (displays) for electronic equipment, which are a type of device. Such a bendable display is expected to have a wide range of uses, for example, as a stationary display that is curved and installed on a columnar pillar, or as a portable display that can be folded, folded, or rolled up.

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

In the bendable display as described above, it is common to bond one bendable member (flexible member) constituting the bendable display and another bendable member with an adhesive layer of an adhesive sheet. It is considered to be a target. Here, for example, those disclosed in Patent Documents 1 and 2 are known as conventional non-bendable pressure-sensitive adhesive sheets for displays.

A bendable display may be repeatedly bent (bent) as described in US Pat. In addition, such a repeatedly bendable display may be fixed in a bent state for a long period of time. If a conventional adhesive sheet is used for such a repeatedly bendable display, the adhesive layer will be deformed even after it is released from the bent state, and the bendable display will remain largely bent, leaving traces of bending. I had a problem.

JP 2015-174907 A JP 2016-774 A JP 2016-2764 A

The present invention has been made in view of the actual situation as described above, and a repeatedly bending device that does not easily leave a bending mark after being released from a bending state when repeatedly bent or when placed in a bent 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 traces that can suppress the formation of bending traces in the repeatedly bending device.

To achieve the above objects, firstly, the present invention provides a repeatedly bending device comprising one or more pressure-sensitive adhesive layers, wherein at least one pressure-sensitive adhesive layer complies with JIS K7244-1. Then, the maximum relaxation modulus value measured when the adhesive is strained by 10% is defined 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 strained by 10% until 3757 _seconds after being applied. (Invention 1).
ΔlogG(t)=logG(t) _max −logG(t) _min (I)

In the repeatedly bending device according to the above invention (invention 1), at least one of the adhesive layers of the repeatedly bending device is made of the above adhesive, so that stress fluctuation when distorted by a predetermined amount is small, that is, The force that tends to return to the original state is easily retained, and therefore the deformation is easily restored when the load is removed. Therefore, when the repeatedly bending device is repeatedly bent or left in a bent state for a long period of time, the device can be easily restored after being released from the bent state, and it is possible to suppress the formation of bending marks due to hardening in the bent state. can be done.

In the above invention (Invention 1), the creep compliance value measured when a stress of 3000 Pa is applied to the adhesive is defined as the minimum creep compliance J (t) _min (MPa ^-1 ), and the minimum creep compliance J (t) A stress of 3000 Pa continues to be applied until 3757 seconds after _min is measured, and the maximum creep compliance value measured during that time is defined as the maximum creep compliance J (t) _max (MPa ^-1 ), and the following formula (II) 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 an 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), it is preferable that 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 10% or more. (Invention 4).

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

The second aspect of the present invention is a method for manufacturing a repeatedly bending device having one or more pressure-sensitive adhesive layers, wherein at least one of the pressure-sensitive adhesive layers is coated with a pressure-sensitive adhesive in accordance with JIS K7244-1. The maximum relaxation modulus value measured when strained by 10% is the maximum relaxation modulus G (t) _max (MPa), and 3757 seconds after the maximum relaxation modulus G (t) _max is measured The pressure-sensitive adhesive continues to be strained by 10% until later, the minimum relaxation modulus value measured during that time is the minimum relaxation modulus G (t) _min (MPa), and the relaxation calculated from the following formula (I) Provided is a method for manufacturing a repeatedly bending device, characterized in that the device is made of an adhesive having an elastic modulus variation value ΔlogG(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 that a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive is used to bond constituent members of the repeatedly bending device (invention 7).

The third aspect of the present invention is a method for suppressing bending traces in a repeatedly bending device provided with one or more adhesive layers, wherein at least one of the adhesive layers is coated in accordance with JIS K7244-1. , the maximum relaxation modulus G (t) _max (MPa) is the maximum relaxation modulus value measured when the adhesive is strained by 10%, and the maximum relaxation modulus G (t) _max is measured. The pressure-sensitive adhesive is continuously strained by 10% until 3757 seconds, and the minimum relaxation modulus value measured during that time is defined as the minimum relaxation modulus G (t) _min (MPa), and is calculated from the following formula (I) Provided is a method for suppressing bending traces in a repeatedly bending device, characterized in that the device is composed of an adhesive having a relaxed elastic 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 constituent members of the repeatedly bending device (invention 9).

The repeatedly bending device according to the present invention is less likely to leave bending marks after being released from the bent state when repeatedly bent or when left in the bent state for a long period of time. Further, according to the method for manufacturing a repeatedly bending device according to the present invention, such a repeatedly bending device can be manufactured. Furthermore, according to the method for suppressing bending marks according to the present invention, it is possible to suppress the formation of bending marks in the repeated bending device.

1 is a cross-sectional view of an adhesive sheet according to one embodiment for manufacturing a repeatedly bending device according to the present invention; FIG. 1 is a cross-sectional view of a repeat bending device according to one embodiment of the present invention; FIG. FIG. 10 is a cross-sectional view of a repeat bending device according to another embodiment of the invention; FIG. 10 is a cross-sectional view of a repeat bending device according to another embodiment of the present invention; FIG. 3 is a cross-sectional view of a laminate manufactured in Examples. It is an explanatory view (side view) explaining a static bending test. FIG. 4 is an explanatory diagram (side view) explaining the amount of deformation of a test piece as a test result of a bending test;

Embodiments of the present invention will be described below.
[Repeated bending device]
The repeatedly bending device according to this embodiment is a device that is repeatedly bent or placed in a bent state for a long period of time, and includes one or more adhesive layers. A plurality of constituent members (flexible members having flexibility) are adhered by this pressure-sensitive adhesive layer, thereby forming a repeatedly bending device.

1. Adhesive layer (Flexible adhesive layer)
(1) Physical properties of the adhesive layer (flex-resistant adhesive layer) At least one layer of the adhesive layer has the maximum The relaxation modulus value is the maximum relaxation modulus G(t) _max (MPa), and the pressure-sensitive adhesive is continuously strained by 10% until 3757 seconds after the maximum relaxation modulus G(t) _max is measured. The minimum relaxation modulus value to be measured is the minimum relaxation modulus G(t) _min (MPa), and the relaxation modulus fluctuation value ΔlogG(t) calculated from the following formula (I) is 1.20 or less. It consists of an adhesive.
ΔlogG(t)=logG(t) _max −logG(t) _min (I)
In this specification, the pressure-sensitive adhesive layer made of the above pressure-sensitive adhesive may be referred to as a "bend-resistant pressure-sensitive adhesive layer". Moreover, the pressure-sensitive adhesive layer other than the bend-resistant pressure-sensitive adhesive layer may be referred to as a "non-flex-resistant pressure-sensitive adhesive layer". The details of the method for measuring the relaxation modulus G(t) are as shown in the test examples described later.

In the repeatedly bending device according to the present embodiment, since at least one of the adhesive layers of the repeatedly bending device is made of the above-described adhesive, the stress fluctuation when distorted by a predetermined amount is small, that is, the device can be restored to its original shape. The force to try is easily retained. Therefore, the deformation is easily restored when the load is removed. Therefore, when the repeatedly bending device is repeatedly bent or left in a bent state for a long period of time, the device can be easily restored after being released from the bent state, and it is possible to suppress the formation of bending marks due to hardening in the bent state. can be done. As an index of the number of times of repeated bending, 30,000 times is exemplified as an example.

From the viewpoint of the effect of suppressing bending traces of the repeatedly bending device, the relaxation elastic modulus fluctuation value ΔlogG(t) is required to be 1.20 or less, preferably 1.00 or less, and particularly 0.80 or less. is preferably 0.50 or less. Although the lower limit of the relaxation modulus fluctuation value is not particularly limited, it is usually preferably 0.10 or more, and particularly preferably 0.15 or more.

The upper limit of the maximum relaxation 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. By setting the upper limit of the maximum relaxation modulus G(t) _max to the above value, the relaxation modulus fluctuation value ΔlogG(t) easily satisfies the aforementioned value. The lower limit of the maximum relaxation modulus G (t) _max is not particularly limited, but it is usually preferably 0.05 MPa or more, particularly preferably 0.10 MPa or more, and further preferably 0.15 MPa or more. is preferred.

In addition, the minimum relaxation 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 a lower limit. . By setting the lower limit of the minimum relaxation modulus G(t) _min to the above range, the relaxation modulus fluctuation value ΔlogG(t) easily satisfies the aforementioned value. Although the upper limit of the minimum relaxation elastic modulus G (t) _min is not particularly limited, it is usually preferably 0.50 MPa or less, particularly preferably 0.45 MPa or less, and further preferably 0.40 MPa or less. is preferred.

In the present embodiment, the creep compliance value measured when the pressure-sensitive adhesive constituting the bend-resistant pressure-sensitive adhesive layer applies a stress of 3000 Pa to the pressure-sensitive adhesive is defined as the minimum creep compliance J(t) _min (MPa ⁻¹ ). , a stress of 3000 Pa continues to be applied until 3757 seconds after the minimum creep compliance J(t) _min is measured, and the maximum creep compliance value measured during that time is the maximum creep compliance J(t) _max (MPa ⁻¹ ), and the creep compliance fluctuation value ΔlogJ(t) calculated from the following formula (II) is preferably 2.84 or less.
ΔlogJ(t)=logJ(t) _max -logJ(t) _min (II)
In addition, "when a stress of 3000 Pa is applied to the adhesive" refers to the time when stress is applied to the adhesive and the stress reaches 3000 Pa. The details of the method for measuring the creep compliance J(t) 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 is small when a predetermined stress is applied, that is, the pressure-sensitive adhesive layer is less likely to deform. Therefore, when the repeatedly bending device is repeatedly bent or left in a bent state for a long period of time, the deformation itself is suppressed after being released from the bent state, and the repeated bending device is more effective in leaving bending traces. can be effectively suppressed.

From the viewpoint of the effect of suppressing bending traces of the repeatedly bending device, the creep compliance variation 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. Although the lower limit of the creep compliance fluctuation value is not particularly limited, it is usually preferably 1.00 or more, and particularly preferably 1.20 or more.

The minimum creep compliance J(t) _min has a lower limit of preferably 1.00 MPa ⁻¹ or more, particularly preferably 1.10 MPa ⁻¹ or more, further preferably 1.15 MPa ⁻¹ or more. is preferred. Since the minimum creep compliance J(t) _min has the above lower limit value, the creep compliance variation value ΔlogJ(t) easily satisfies the above value. Although the upper limit of the minimum creep compliance J(t) _min is not particularly limited, it is usually preferably 5.0 MPa ⁻¹ or less, particularly preferably 4.5 MPa ⁻¹ or less, and further preferably 4.0 MPa −1 ^{or less.} It is preferably ¹ or less.

In addition, the maximum creep compliance J(t) _max is preferably 900 MPa ⁻¹ or less, particularly preferably 500 MPa ⁻¹ or less, further preferably 300 MPa ⁻¹ or less, as an upper limit value. Most preferably, it is 200 MPa ⁻¹ or less. By setting the upper limit of the maximum creep compliance J(t) _max to the above value, the creep compliance variation value ΔlogJ(t) easily satisfies the above value. The lower limit of the maximum creep compliance J(t) _max is not particularly limited, but it 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 relaxation elastic modulus fluctuation value ΔlogG(t) and the creep compliance fluctuation value ΔlogJ(t) described above is preferably 3.3 or less, particularly 2.0. It is preferably less than or equal to 1.0, more preferably less than or equal to 1.0. Since the product value is small as described above, the stress fluctuation or strain fluctuation during bending is small, so that the deformation is easily restored when the load is removed, or the deformation itself is difficult to occur. As a result, it is possible to more effectively suppress the repeated bending marks from being left on the bending device. Although the lower limit of the product value is not particularly limited, it is usually preferably 0.1 or more, and particularly preferably 0.2 or more.

The ratio of the number of bending-resistant adhesive layers to the total number of 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 It is preferably 35% or more, more preferably 50% or more. By setting the ratio of the number of bending-resistant adhesive layers to the above range, the effects of the restoring action and the deformation-suppressing action of the bending-resistant adhesive layer are greatly exerted on the repeatedly bending device, and bending traces are left on the repeatedly bending device. Sticking can be suppressed more effectively. In addition, the upper limit of the ratio of the number of bend-resistant pressure-sensitive adhesive layers is 100%.

In addition, 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 1% or more, more preferably 2% or more, as a lower limit. , particularly preferably 3% or more, more preferably 5% or more. In addition, the "total thickness of the bending-resistant adhesive layer" refers to the thickness of one layer when the repeatedly bending device includes only one bending-resistant adhesive layer. When multiple pressure-sensitive adhesive layers are included, the total thickness is referred to. Since the lower limit of the ratio of the total thickness of the bending-resistant adhesive layer is the 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 device can be repeatedly bent. 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, more preferably 10% or less. This makes it possible to ensure the thickness of each constituent member other than the bending-resistant adhesive layer, which is required for the repeatedly bending device.

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

Further, the acrylic pressure-sensitive adhesive may be active energy ray-curable, active energy ray non-curable, or thermally crosslinkable. It may be non-crosslinkable or a combination thereof, but is preferably non-active energy ray-curable in order to obtain good flexibility. As the active energy ray non-curable acrylic pressure-sensitive adhesive, a cross-linking type is particularly preferable, and a thermal cross-linking type is more preferable.

The pressure-sensitive adhesive constituting the bend-resistant pressure-sensitive adhesive layer is particularly an adhesive composition containing a (meth)acrylic acid ester polymer (A) and a cross-linking agent (B) (hereinafter “adhesive composition P” ) is preferably crosslinked. Such a pressure-sensitive adhesive easily satisfies the physical properties described above, and provides good adhesive strength and predetermined cohesive strength, and thus has excellent durability. 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 "copolymer" is also included in "polymer".

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

The (meth)acrylic acid ester polymer (A) can express preferable adhesiveness by containing a (meth)acrylic acid alkyl ester as a 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. Alkyl groups 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 less as a homopolymer (hereinafter sometimes 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 pressure-sensitive adhesive obtained 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), 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 preferred. Among them, from the viewpoint of improving flexibility more effectively, the low Tg alkyl acrylate is more preferably one having a homopolymer Tg of -45°C or lower, and -50°C or lower. is particularly preferred. Specifically, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains 50% by mass or more, particularly 55% by mass or more, of a low Tg alkyl acrylate as a lower limit as a monomer unit constituting the polymer. is preferable, and more preferably 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 range described above.

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, particularly 75% by mass or less. preferably, more preferably 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 (especially reactive functional group-containing monomers) into the (meth)acrylic acid ester polymer (A). can.

Further, as a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms, a monomer having a glass transition temperature (Tg) exceeding 0 ° C. as a homopolymer (hereinafter referred to as "high Tg alkyl acrylate" may be There is.) is preferably contained. By containing such a high Tg alkyl acrylate as a constituent monomer unit, the obtained pressure-sensitive adhesive layer easily satisfies the physical properties described above.

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, particularly 10% by mass. It is preferably 15% by mass or more, more preferably 15% by mass or more. Also, 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 acrylates include methyl acrylate (Tg 10°C), methyl methacrylate (Tg 105°C), ethyl methacrylate (Tg 65°C), n-butyl methacrylate (Tg 20°C), and isobutyl methacrylate (Tg 48°C). ), t-butyl methacrylate (Tg107°C), n-stearyl acrylate (Tg30°C), n-stearyl methacrylate (Tg38°C), cyclohexyl acrylate (Tg15°C), cyclohexyl methacrylate (Tg66°C), methacrylic acid benzyl (Tg 54°C), isobornyl acrylate (Tg 94°C), isobornyl methacrylate (Tg 180°C), adamantyl acrylate (Tg 115°C), adamantyl methacrylate (Tg 141°C) and the like. Among the above, methyl acrylate, methyl methacrylate and isobornyl acrylate are preferred from the viewpoint of cohesive force. These may be used alone or in combination of two or more. The above high Tg alkyl acrylate does not include a nitrogen atom-containing monomer, which will be described later.

(Meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, so that through the reactive functional group derived from the reactive functional group-containing monomer , reacts with a cross-linking agent (B), which will be described later, to form a cross-linked structure (three-dimensional network structure) and obtain a pressure-sensitive adhesive having desired cohesive strength.

The (meth)acrylic acid ester polymer (A) contains reactive functional group-containing monomers as monomer units constituting the polymer, including monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomer), carboxyl groups in the molecule, A monomer having a group (carboxy group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), and the like are preferable. One of these reactive functional group-containing monomers may be used alone, or two or more thereof may be used in combination.

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

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, (meth) ) hydroxyalkyl (meth)acrylates such as 3-hydroxybutyl acrylate and 4-hydroxybutyl (meth)acrylate; Among them, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are preferable from the viewpoint of the flexibility of the resulting (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, more preferably 15% by mass or more. Moreover, the content of the hydroxyl group-containing monomer is preferably 30% by mass or less, particularly preferably 25% by mass or less. By setting the content of the hydroxyl group-containing monomer to the above range, the resulting (meth)acrylic acid ester polymer (A) has better flexibility and adhesiveness, and the obtained adhesive layer satisfies the physical properties described above. becomes easier.

The (meth)acrylate polymer (A) may contain a nitrogen atom-containing monomer as a monomer unit constituting the polymer. Nitrogen atom-containing monomers include monomers having an amino group, monomers having an amide group, and monomers having a nitrogen-containing heterocyclic ring, among which monomers having a nitrogen-containing heterocyclic ring are preferred. In addition, 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 pressure-sensitive adhesive, the nitrogen atom-containing monomer constitutes the (meth)acrylic acid ester polymer (A). preferably contains no reactive unsaturated double bond groups other than the one polymerizable group used in the polymerization of .

Examples of monomers having a nitrogen-containing heterocyclic ring include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloyl pyrrolidine, N-(meth)acryloylaziridine, aziridinylethyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, N-vinylphthalimide, etc. Among them, N-(meth)acryloylmorpholine, which exhibits superior adhesive strength, is preferred, and N-acryloylmorpholine is particularly preferred. 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. , particularly preferably 3% by mass or more. Also, 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.

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

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

The 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, 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 above, the durability of the pressure-sensitive adhesive becomes more excellent. In addition, the weight average molecular weight in this specification is the value of standard polystyrene conversion measured by the gel permeation chromatography (GPC) method.

The upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 1,500,000 or less, particularly preferably 1,200,000 or less, and further preferably 1,000,000 or less. preferable. When the upper limit of the weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is 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 heating of the adhesive composition P containing the cross-linking agent (B) as a trigger to form a three-dimensional network structure. . This improves the cohesive strength of the resulting pressure-sensitive adhesive and makes the pressure-sensitive adhesive layer excellent in durability.

The cross-linking agent (B) may be one that reacts with the reactive groups of the (meth)acrylic acid ester polymer (A). Examples include isocyanate cross-linking agents, epoxy cross-linking agents, and amine cross-linking agents. , melamine cross-linking agent, aziridine cross-linking agent, hydrazine cross-linking agent, aldehyde cross-linking agent, oxazoline cross-linking agent, metal alkoxide cross-linking agent, metal chelate cross-linking agent, metal salt cross-linking agent, ammonium salt cross-linking agent, etc. is mentioned. Among the above, it is preferable to use an isocyanate-based cross-linking agent that has excellent reactivity with a reactive functional group-containing monomer, particularly a hydroxyl group-containing monomer. In addition, a crosslinking agent (B) can be used individually by 1 type or in combination of 2 or more types.

The isocyanate-based cross-linking 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; and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. , and their biuret, isocyanurate, and adducts which are reaction products with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among them, trimethylolpropane-modified aromatic polyisocyanate, 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 parts by mass or more, and 0.3 parts by mass with respect to 100 parts by mass of the (meth)acrylic acid ester polymer (A). It is more preferably at least 0.5 parts by mass, and more preferably at least 1.0 parts by mass. In addition, 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 within the above range, the cohesive force of the obtained adhesive becomes moderate, and the adhesive layer easily satisfies the physical properties described above.

(2-1-3) Various Additives The adhesive composition P may optionally contain various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, Tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index modifiers and the like can be added. It should be noted that a polymerization solvent and a dilution solvent, which will be described later, are not included in the additives constituting the adhesive composition P.

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

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

Examples of polymerization initiators include azo compounds and organic peroxides, and two or more of them may be used in combination. Examples of azo compounds include 2,2′-azobisisobutyronitrile, 2,2′-azobis(2-methylbutyronitrile), 1,1′-azobis(cyclohexane 1-carbonitrile), 2 ,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate) , 4,4′-azobis(4-cyanovaleric acid), 2,2′-azobis(2-hydroxymethylpropionitrile), 2,2′-azobis[2-(2-imidazolin-2-yl) propane] and the like.

Examples of organic peroxides include benzoyl peroxide, t-butylperbenzoate, cumene hydroperoxide, diisopropylperoxydicarbonate, di-n-propylperoxydicarbonate, di(2-ethoxyethyl)peroxy dicarbonate, t-butylperoxyneodecanoate, t-butylperoxybivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionylperoxide, diacetylperoxide and the like.

The weight average molecular weight of the resulting polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol in the polymerization step.

After the (meth)acrylic acid ester polymer (A) is obtained, the solution of the (meth)acrylic acid ester polymer (A) is added with the cross-linking agent (B) and, if desired, the additive and the diluent solvent. By mixing, the adhesive composition P (coating solution) diluted with a solvent is obtained.

In any of the above components, if a solid one is used, or if precipitation occurs when mixed with other components in an undiluted state, the component is added alone in advance to a dilution solvent. It may be dissolved or diluted prior to mixing 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; 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/viscosity of the coating solution thus prepared is not particularly limited as long as it is within a range that allows coating, and can be appropriately selected according to the situation. For example, the concentration of the adhesive composition P is diluted to 10 to 60% by mass. When obtaining the coating solution, the addition of a diluent solvent or the like is not a necessary condition, and the diluent solvent may not be added as long as the viscosity of the adhesive composition P allows coating. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent for the (meth)acrylic acid ester polymer (A) is used as the diluting solvent.

(2-3) Production of Adhesive The adhesive constituting the bend-resistant adhesive layer is preferably obtained by cross-linking the adhesive composition P. Crosslinking of the adhesive composition P can usually be performed by heat treatment. This heat treatment can also serve as a drying treatment for volatilizing the diluent solvent and the like from the coating film of the adhesive composition P applied to a 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, more 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 (eg, 23° C., 50% RH). If the 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 crosslinked via the crosslinking agent (B) to form a crosslinked structure, thereby obtaining the pressure-sensitive adhesive. Such an adhesive has a predetermined cohesive force.

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

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

Furthermore, the lower limit of the loss tangent (tan δ) at 25° C. of the pressure-sensitive adhesive constituting the bend-resistant pressure-sensitive adhesive layer is preferably 0.25 or more, particularly preferably 0.28 or more. Also, the upper limit of the loss tangent (tan δ) is preferably 0.85 or less, particularly preferably 0.80 or less.

When the storage elastic modulus (G′), loss elastic modulus (G″), and loss tangent (tan δ) of the pressure-sensitive adhesive constituting the bend-resistant pressure-sensitive adhesive layer are within the above ranges, the resulting pressure-sensitive adhesive layer exhibits the physical properties described above. The storage modulus (G′), loss modulus (G″), and loss tangent (tan δ) are measured by the following test examples.

(3) Adhesive sheet The repeatedly bending device according to the present embodiment is obtained by laminating desired constituent members (flexible members having flexibility) using the above-described adhesive sheet having the bending-resistant adhesive layer. , can be preferably produced.

FIG. 1 shows a specific configuration as an example of the pressure-sensitive adhesive sheet.
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 so as to be in contact with the release surfaces of the two release sheets 12a and 12b. , 12b and a bend-resistant adhesive layer 11R. In this specification, the release surface of the release sheet refers to the surface of the release sheet that has releasability, and includes both the surface that has been subjected to a release treatment and the surface that exhibits releasability without being subjected to a release treatment. .

(3-1) Constituent elements (3-1-1) Flex-resistant adhesive layer The bend-resistant adhesive layer 11R is made of an adhesive that satisfies the physical properties described above, and preferably the adhesive composition P is crosslinked. It is composed of a pressure-sensitive adhesive.

The lower limit of the thickness (value measured according to JIS K7130) of the bend-resistant adhesive layer 11R in the adhesive sheet 1 is preferably 2 μm or more, particularly preferably 5 μm or more, and further preferably 10 μm or more. Preferably. When the lower limit value of the thickness of the bend-resistant adhesive layer 11R is within the above range, the desired adhesive strength can be easily exhibited, and the occurrence of lifting and peeling during repeated bending can be effectively suppressed. The upper limit of the thickness of the bend-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. preferable. When the upper limit value of the thickness of the bend-resistant adhesive layer 11R is the above, it is possible to suppress exudation of the adhesive or components constituting the adhesive from the adhesive layer due to repeated bending. The bend-resistant adhesive layer 11R may be formed as a single layer, or may be formed by laminating a plurality of layers. Regarding the bend-resistant adhesive layer 11R, the bend-resistant adhesive layer 11R formed by laminating a plurality of layers is treated as a single layer.

(3-1-2) Release Sheets The release sheets 12a and 12b protect the bend-resistant adhesive layer 11R until the adhesive sheet 1 is used, and the adhesive sheet 1 (the bend-resistant adhesive layer 11R) is used. sometimes exfoliated. 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, polyethylene naphthalate film, and polybutylene. Terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene/(meth)acrylic acid copolymer film, ethylene/(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluorine A resin film or the like is used. Crosslinked films of these are also used. Furthermore, a laminated film of these may be used.

It is preferable that the release surfaces of the release sheets 12a and 12b (especially the surfaces in contact with the bend-resistant pressure-sensitive adhesive layer 11R) are subjected to a release treatment. Examples of release agents 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 with a large release force, and the other release sheet is a light release type release sheet with a small release force.

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

(3-2) Production of Adhesive Sheet As an example of producing the adhesive sheet 1, the 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 thermally crosslink the adhesive composition P, and a coating layer is formed. The release surface of the other release sheet 12b (or 12a) is placed on the layer. If a curing period is required, the curing period is set, and if the curing period is not required, the coating layer becomes the bend-resistant adhesive layer 11R as it 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 production example of the adhesive sheet 1, a coating liquid of the adhesive composition P is applied to the release surface of one release sheet 12a, and heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer. to obtain a release sheet 12a with a coating layer. Further, the coating liquid of the adhesive composition P is applied to the release surface of the other release sheet 12b, and heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer. to obtain a release sheet 12b. Then, the release sheet 12a with the coating layer and the release sheet 12b with the coating layer are pasted together so that both coating layers are in contact with each other. If a curing period is required, the curing period is set, and if the curing period is not required, the laminated coating layer becomes the bend-resistant adhesive layer 11R as it is. As a result, the pressure-sensitive adhesive sheet 1 is obtained. According to this production example, stable production is possible even when the bend-resistant pressure-sensitive adhesive layer 11R is relatively thick.

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, or the like can be used.

2. Configuration of repeatedly bending device The repeatedly bending device according to the present embodiment includes, for example, an organic electroluminescence (organic EL) display, an electrophoretic display (electronic paper), a flexible printed circuit board, and a plastic substrate (film) as a substrate. It may be 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 this embodiment will be described with reference to the drawings.

The repeatedly bending device 10A shown in FIG. 2 includes, from the bottom, a first plastic substrate 211, a first adhesive layer 111, a second plastic substrate 221 with a gas barrier layer, a thin film transistor 3, and an organic light emitting device. Diode 4, second adhesive layer 112 sealing organic light emitting diode 4, third plastic substrate 222 with gas barrier layer, touch sensor 5, third adhesive layer 113, fourth , and a plastic substrate 212 are laminated.

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

Note that the organic light emitting diode 4 may be laminated with a thin film encapsulation (TFE) layer (not shown). The thin-film encapsulating 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 is possible, and two or more layers may be provided. Also, the thickness of the thin film encapsulating layer is usually 100 nm to 2 μm.

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

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

The repeatedly bending device 10C shown in FIG. 4 includes, from the bottom, a first plastic substrate 211, a first adhesive layer 111, a second plastic substrate 221 with a gas barrier layer, a thin film transistor 3, and an organic light emitting device. Diode 4, second adhesive layer 112 sealing organic light emitting diode 4, third plastic substrate 222 with gas barrier layer, touch sensor 5, third adhesive layer 113, fourth A plastic substrate 212, a fourth adhesive layer 114, a first wave plate (λ/4) 71, a fifth adhesive layer 115, a second wave plate (λ/2) 72, It is configured by laminating the sixth adhesive layer 116, the polarizing plate 81, and the polarizing plate protective film 82 with a hard coat layer.

In the repeat bending device 10C, the first adhesive layer 111, the second adhesive layer 112, the third adhesive layer 113, the fourth adhesive layer 114, the fifth adhesive layer 115 and the sixth adhesive layer At least one of the pressure-sensitive adhesive layers 116 is a bend-resistant pressure-sensitive adhesive layer, and the other layers are non-flex-resistant pressure-sensitive adhesive layers.

The constituent members other than the adhesive layer constituting the repeatedly bending devices 10A to 10C are bendable members having bendability. 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, each flexible member can be easily bent repeatedly.

Each of the flexible members preferably has a thickness of 5 to 3000 μm, particularly preferably 10 to 1000 μm, further preferably 10 to 500 μm. When the thickness of the flexible member is within such a range, each flexible member can be easily bent repeatedly.

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

The pressure-sensitive adhesive layers other than the bend-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 described above.

The thin film transistor 3 can be constructed by performing vapor deposition or the like on the second plastic substrate 221 . Also, the touch sensor 5 can be formed by subjecting a conductive material such as ITO to the third plastic substrate 222 by vapor deposition or the like. 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 adhesive layer 113 will be positioned between the third plastic substrate 222 and the touch sensor 5 . Furthermore, the touch sensor 5 may be composed of multiple layers, in which case an adhesive layer may be present between the touch sensors 5 .

Since the repeatedly bending device according to the present embodiment has at least one bend-resistant adhesive layer, it can ), after being released from the bent state, it is easy to restore and less likely to leave a bent mark. The bending trace suppressing effect of such a repeatedly bending device can be evaluated, for example, by the amount of static bending deformation in a static bending test. As a bending test, there is also a dynamic bending test in which the bending device is repeatedly bent (for example, 30,000 times). If good results are obtained in the static bending test, good results are obtained in the dynamic bending test. Therefore, it can be said that it is sufficient to perform a static bending test in order to confirm the bending mark suppressing effect of the repeatedly bending device.

In the static bending test, a laminate consisting of two polyethylene terephthalate films (thickness: 12 μm) sandwiching an adhesive layer (thickness: 12 μm) and having a size of 200 mm × 50 mm was tested. cut into pieces As shown in FIG. 6, this test piece S is held for 24 hours in a bent state between holding plates P consisting of two standing glass plates 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 (the 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 portion. The test piece S is held so that both short sides (50 mm) of S are positioned on the upper side. After performing this static bending test, the test piece S was taken out from between the two holding plates P, and as shown in FIG. be placed 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 amount of static bending deformation. This amount of static bending deformation is used as the test result of the static bending test, and the effect of suppressing bending traces can be evaluated based on the amount of static bending deformation.

The amount of static bending deformation in 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 immediately after the test. Preferably, it is 0.5 mm or less, most preferably. The lower limit of the amount of static bending deformation immediately after the test is preferably 0 mm.

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

[Method for suppressing bending marks]
In a repeatedly bending device having one or more pressure-sensitive adhesive layers, at least one pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive that satisfies the physical properties described above, that is, at least one pressure-sensitive adhesive layer is By using the bending pressure-sensitive adhesive layer described above, it is possible to suppress the formation of bending traces.

The embodiments described above are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiment is meant 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, or desired constituent members may be laminated instead of the release sheets 12a and/or 12b. Further, the repeat bending devices 10A-10C may include additional layers or may omit some layers.

EXAMPLES 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.

[Production Example 1] (Production of Adhesive Sheet I)
1. Preparation of (meth)acrylic acid ester polymer (A) 65 parts by mass of 2-ethylhexyl acrylate, 15 parts by mass of isobornyl acrylate, 5 parts by mass of N-acryloylmorpholine and 15 parts by mass of 2-hydroxyethyl acrylate were subjected to a solution polymerization method. to prepare a (meth)acrylic acid ester polymer (A). When the molecular weight of this (meth)acrylate polymer (A) was measured by the method described later, it was found to have a weight average molecular weight (Mw) of 500,000.

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 a trimethylolpropane-modified trimethylolpropane-modified trimethylolpropane Diisocyanate (manufactured by Toyochem Co., Ltd., product name "BHS8515") 1.20 parts by mass was mixed, thoroughly stirred, and diluted with methyl ethyl ketone (MEK) to obtain an adhesive composition coating solution (solid content concentration : 30.0% by mass).

3. Production of adhesive sheet The coating solution of the adhesive composition obtained in the above step 2 is applied to a heavy release type release sheet (Lintec Co., Ltd., product name "SP-PET382150") in which one side of a polyethylene terephthalate film is release treated with a silicone release agent. ”) was coated with a comma coater (registered trademark). Then, the coating layer was heat-treated at 90° C. for 1 minute to form a coating layer.

Next, the coating layer on the heavy release release sheet obtained above and a light release release sheet obtained by releasing a polyethylene terephthalate film on one side with a silicone release agent (manufactured by Lintec, product name "SP-PET381031"). was laminated so that the release-treated surface of the light release type release sheet was in contact with the coating layer, and cured for 7 days under the conditions of 23 ° C. and 50% RH to form an adhesive layer with a thickness of 12 μm. A pressure-sensitive adhesive sheet having a structure of heavy-release release sheet/adhesive layer (thickness: 12 μm)/light-release release sheet was prepared. The adhesive layer of this adhesive sheet I is called "adhesive layer I". The thickness of the pressure-sensitive adhesive layer is a value measured in accordance with JIS K7130 using a constant pressure thickness measuring instrument (manufactured by Teclock, product name "PG-02").

[Production Example 2] (Production of Adhesive Sheet II)
Adhesive sheet II was prepared in the same manner as in Example 1, except that the (meth)acrylate polymer (A) prepared in Production Example 1 was used and the amount of the cross-linking agent (B) was changed to 0.30 parts by mass. was made. The adhesive layer of this adhesive sheet II is called "adhesive layer II".

[Production Example 3] (Production of Adhesive Sheet III)
A (meth)acrylate polymer (A) was prepared by copolymerizing 60 parts by mass of butyl acrylate, 20 parts by mass of methyl acrylate and 20 parts by mass of 2-hydroxyethyl acrylate by a solution polymerization method. When the molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described later, it was found to have a weight average molecular weight (Mw) of 600,000.

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

[Production Example 4] (Production of Adhesive Sheet IV)
Adhesive sheet IV was prepared in the same manner as in Example 1, except that the (meth)acrylate polymer (A) prepared in Production Example 1 was used and the amount of the cross-linking agent (B) was changed to 0.60 parts by mass. was made. The adhesive layer of this adhesive sheet IV is called "adhesive layer IV".

[Production Example 5] (Production of Adhesive Sheet V)
A (meth)acrylate polymer (A) was prepared by copolymerizing 60 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of methyl methacrylate and 20 parts by mass of 2-hydroxyethyl acrylate by a solution polymerization method. When the molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described later, it was found to have a weight average molecular weight (Mw) of 600,000.

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

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

In addition, in Table 1, the composition of the (meth)acrylic acid ester polymer (A) and the amount of the cross-linking agent (B) in each production example (mass relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A) part). 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 adhesive sheet I obtained in Production Example 1 and the adhesive sheet VI obtained in Production Example 6, a laminate 100 shown in FIG. 5 was produced. This laminate 100 includes, in order from the bottom, a first base material 91, a first adhesive layer 111, a second base material 92, a second adhesive layer 112, and a third base material 93. , a third adhesive layer 113, and a fourth base material 94, and corresponds to a simulated repetitive bending device.

Specifically, first, first to fourth polyethylene terephthalate (PET) films ( A product made by Toray Industries, Inc., product name “S10 Lumirror”, thickness: 12 μm) was prepared. Next, in an environment of 23° C. and 50% RH, the light release type release sheet was peeled off from the adhesive sheet VI obtained in Production Example 6, and the exposed adhesive layer VI was placed on one side of the first PET film. It was pasted 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 bonded to the exposed pressure-sensitive adhesive layer VI.

Next, in an environment of 23° C. and 50% RH, the light release type release sheet was peeled off from the adhesive sheet I obtained in Production Example 1, and the exposed adhesive layer I was removed from the 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 bonded to the exposed pressure-sensitive adhesive layer I.

Next, in an environment of 23° C. and 50% RH, the light release type release sheet was peeled off from the adhesive sheet VI produced in Production Example 6, and the exposed adhesive layer VI was transferred to the other side of the third PET film. It was pasted 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 bonded to the exposed pressure-sensitive adhesive layer VI. Finally, after pressurizing at 0.5 MPa and 50° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., it is left under conditions of 23° C. and 50% RH for 24 hours to obtain the laminate 100 shown in FIG. rice field.

[Examples 2 to 23, Comparative Example 1]
Using the adhesive sheets I to VI produced in Production Examples 1 to 6, laminates 100 shown in FIG. 5 were produced. At this time, the pressure-sensitive adhesive sheets I to VI were arranged so that the first pressure-sensitive adhesive layer 111, the second pressure-sensitive adhesive layer 112 and the third pressure-sensitive adhesive layer 113 became the pressure-sensitive adhesive layers I to VI shown in Table 2, respectively. A laminate 100 was manufactured in the same manner as in Example 1, except that it was used.

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

For the above sample, in accordance with JIS K7244-1, using a viscoelasticity measuring device (manufactured by Anton paar, product name "MCR302"), the adhesive was continuously distorted by 10% under the following conditions, and the relaxation elastic modulus G (t) (MPa) was measured. From the measurement results, the maximum relaxation modulus G (t) _max (MPa) is derived, and the minimum relaxation modulus G measured up to 3757 seconds after the maximum relaxation 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 modulus G(t) _max (MPa) and minimum relaxation modulus G(t) _min (MPa), the relaxation modulus fluctuation value ΔlogG(t) is calculated based on the following formula (I): Calculated. Table 1 shows the results.
ΔlogG(t)=logG(t) _max −logG(t) _min (I)

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

Using a viscoelasticity measuring device (manufactured by Anton paar, product name "MCR302"), the above sample was continuously applied with a stress of 3000 Pa under the following conditions, and the creep compliance J (t) (MPa ^-1 ) was measured. . From the measurement results, the value when a stress of 3000 Pa is applied is defined as the minimum creep compliance J (t) _min (MPa ^-1 ), and the minimum creep compliance J (t) _min is measured until 3757 seconds after The maximum measured 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 variation value ΔlogJ(t) is calculated based on the following formula (II): was calculated. Table 1 shows the results.
ΔlogJ(t)=logJ(t) _max -logJ(t) _min (II)

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

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

For the above sample, in accordance with JIS K7244-1, using a viscoelasticity measuring device (manufactured by Anton paar, product name "MCR302"), the dynamic viscoelasticity was measured under the following conditions, and the storage elastic modulus at 25 ° C. (G′) (MPa), loss 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 pieces, which were used as test pieces. The obtained test piece was bent between holding plates (mutual distance: 6 mm) composed of two glass plates set upright as shown in FIG. 6 under an environment of 23° C. and 50% RH. The condition was maintained for 24 hours. After conducting this static bending test, the test piece was placed on a flat plate as shown in FIG. h was measured as the amount of static bending deformation. Based on the measured amount of static bending deformation, the bending resistance (bending mark suppressing effect) was evaluated according to the following criteria. Table 2 shows the results.
◎: The amount of deformation immediately after the bending test is 15 mm or less, the amount of deformation after 24 hours of the test is 1 mm or less ○: The amount of deformation immediately after the bending test is 20 mm or less, and the amount of deformation after 24 hours of the test is 3 mm or less )
△: 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 (except those marked with ◎ and ○).
×: Other than the above

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

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

Reference Signs List 1 Adhesive sheet 11R Flex-resistant adhesive layer 12a, 12b Release sheets 10A, 10B, 10C Repetitive 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 transistor 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 (8)

A repeatedly bending device comprising one flexible member, another flexible member, and one or more adhesive layers for bonding the one flexible member and the other flexible member, wherein ,
the one bending member and the other bending member are constituent members of the repeated bending device;
At least one layer of the pressure-sensitive adhesive layer is
In accordance with JIS K7244-1, the maximum relaxation modulus value measured when the adhesive is strained by 10% is the maximum relaxation modulus G (t) _max (MPa), and the maximum relaxation modulus G Continue to strain the adhesive by 10% until 3757 seconds after (t) _max is measured, and the minimum relaxation modulus value measured during that time is the minimum relaxation modulus G (t) _min (MPa), The relaxation elastic modulus fluctuation value ΔlogG(t) calculated from the following formula (I) is composed of an adhesive having a value of 1.20 or less,
The pressure-sensitive adhesive is a pressure-sensitive adhesive obtained by cross-linking an adhesive composition containing a (meth)acrylic acid ester polymer (A) and a cross-linking agent (B),
The (meth)acrylic acid ester polymer (A) is a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms as a monomer unit constituting the polymer, and a glass transition as a homopolymer. Containing 50% by mass or more and 80% by mass or less of a low Tg alkyl acrylate having a temperature (Tg) of −40° C. or less,
The (meth)acrylic acid ester polymer (A) has a weight average molecular weight of 100,000 or more and 1,200,000 or less,
The storage modulus (G') of the pressure-sensitive adhesive at 25°C is 0.01 MPa or more and 0.30 MPa or less.
A repeatedly bending device characterized by:
ΔlogG(t)=logG(t) _max −logG(t) _min (I) The creep compliance value measured when a stress of 3000 Pa is applied to the adhesive is defined as the minimum creep compliance J (t) _min (MPa ^-1 ), and 3757 seconds after the minimum creep compliance J (t) _min is measured. A stress of 3000 Pa continues to be applied until the maximum creep compliance value measured during that time is defined as the maximum creep compliance J(t) _max (MPa ⁻¹ ), and the creep compliance fluctuation value ΔlogJ calculated from the following formula (II) 2. The repeat bending device of claim 1, wherein (t) is less than or equal to 2.84.
ΔlogJ(t)=logJ(t) _max -logJ(t) _min (II) 3. The repetition according to claim 1 or 2, wherein 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 included in the repetition bending device is 10% or more. bending device. 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. A repeat bending device according to claim 1. A method for manufacturing a repeatedly bending device comprising one flexible member, another flexible member, and one or more layers of adhesive layers for bonding the one flexible member and the other flexible member and
the one bending member and the other bending member are constituent members of the repeated bending device;
At least one layer of the pressure-sensitive adhesive layer,
In accordance with JIS K7244-1, the maximum relaxation modulus value measured when the adhesive is strained by 10% is the maximum relaxation modulus G (t) _max (MPa), and the maximum relaxation modulus G Continue to strain the adhesive by 10% until 3757 seconds after (t) _max is measured, and the minimum relaxation modulus value measured during that time is defined as the minimum relaxation modulus G (t) _min (MPa), A pressure-sensitive adhesive having a relaxation modulus variation value ΔlogG(t) of 1.20 or less calculated from the following formula (I),
(Meth)acrylic acid ester polymer (A) and a cross-linking adhesive composition containing a cross-linking agent (B),
The (meth)acrylic acid ester polymer (A) is a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms as a monomer unit constituting the polymer, and a glass transition as a homopolymer. Containing 50% by mass or more and 80% by mass or less of a low Tg alkyl acrylate having a temperature (Tg) of −40° C. or less,
The (meth)acrylic acid ester polymer (A) has a weight average molecular weight of 100,000 or more and 1,200,000 or less,
Storage modulus (G') at 25°C is 0.01 MPa or more and 0.30 MPa or less
A method of manufacturing a repeatedly bending device, characterized in that the device is made of an adhesive.
ΔlogG(t)=logG(t) _max −logG(t) _min (I) 6. The method for manufacturing a repeatedly bending device according to claim 5, wherein an adhesive sheet having an adhesive layer made of the adhesive is used to bond constituent members of the repeatedly bending device. Bending marks in a repetitive bending device comprising one flexible member, another flexible member, and one or more layers of adhesive layers bonding the one flexible member and the other flexible member A method of suppressing the
the one bending member and the other bending member are constituent members of the repeated bending device;
At least one layer of the pressure-sensitive adhesive layer,
In accordance with JIS K7244-1, the maximum relaxation modulus value measured when the adhesive is strained by 10% is the maximum relaxation modulus G (t) _max (MPa), and the maximum relaxation modulus G Continue to strain the adhesive by 10% until 3757 seconds after (t) _max is measured, and the minimum relaxation modulus value measured during that time is the minimum relaxation modulus G (t) _min (MPa), A pressure-sensitive adhesive having a relaxation modulus fluctuation value ΔlogG(t) calculated from the following formula (I) of 1.20 or less,
(Meth)acrylic acid ester polymer (A) and a cross-linking adhesive composition containing a cross-linking agent (B),
The (meth)acrylic acid ester polymer (A) is a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms as a monomer unit constituting the polymer, and a glass transition as a homopolymer. Containing 50% by mass or more and 80% by mass or less of a low Tg alkyl acrylate having a temperature (Tg) of −40° C. or less,
The (meth)acrylic acid ester polymer (A) has a weight average molecular weight of 100,000 or more and 1,200,000 or less,
Storage modulus (G') at 25°C is 0.01 MPa or more and 0.30 MPa or less
A method for suppressing bending traces in a repeatedly bending device comprising an adhesive.
ΔlogG(t)=logG(t) _max −logG(t) _min (I) 8. The repeatedly bending device according to claim 7, wherein an adhesive sheet having an adhesive layer made of the adhesive is used to bond constituent members of the repeatedly bending device, thereby suppressing bending traces in the repeatedly bending device. Method.

Images