Adhesive sheets for flexible devices, flexible laminates and flexible devices

Abstract

To provide an adhesive sheet which, while comprising a flexible adhesive used in bonding and the like of flexible members, shows suppressed peeling at an undesirable site during peeling of a light release type release sheet and a suppressed dimensional change at an edge part of the adhesive layer during peeling of a heavy release type release sheet.SOLUTION: Provided is an adhesive sheet for flexible device, comprising an adhesive layer and a first release sheet and a second release sheet which hold two principal planes of the adhesive layer therebetween. A storage modulus at 23°C of the adhesive constituting the adhesive layer is 0.2 MPa or less. An Si content on the surface of the adhesive layer is twice or more the amount of the Si content around the center of the adhesive layer. The second release sheet comprises a silicone-based release agent. A migration amount of Si of the second release sheet to the surface of the adhesive layer is 5 to 100 atom%. Peel force of the first release sheet when peeled from the adhesive layer at a peel rate of 2.4 m / min is 150 mN / 25 mm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive sheet for flexible devices, a flexible laminate, and a flexible device.

Background Art

[0002] A display member having a liquid crystal element, a light emitting diode (LED) element, an organic electroluminescence (organic EL) element, etc. is laminated with another member (for example, a protection panel for protecting the display member) to constitute a display (display) of a device such as an electronic device.

[0003] Such a laminate of a display member and another member is generally formed by bonding the display member and another member using an adhesive layer of an adhesive sheet.

[0004] In recent years, as a display of an electronic device, a bendable display, so-called a flexible display, has been proposed. Flexible displays are expected to have a wide range of applications, for example, for stationary displays that are curved and installed on a cylindrical column, or for mobile displays that can be carried by folding or rounding.

[0005] Examples of types of flexible displays include, for example, an organic electroluminescence (organic EL) display, an electrophoretic display (electronic paper), a liquid crystal display using a plastic film as a substrate, and the like.

[0006] Examples of such flexible displays include displays that are bent during molding and maintain a bent state, displays that are repeatedly bent during use, and the like.

[0007] Patent Documents 1 and 2 disclose an adhesive sheet in which the amount of volatile organic compounds contained in the adhesive sheet is reduced and the curved surface adhesiveness is good.

Prior Art Documents

[0008] [Patent Document 1] Japanese Patent Publication No. 2016-26241 [Patent Document 2] Patent No. 5835837 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the adhesive layer of adhesive sheets used in flexible devices such as flexible displays sometimes requires a degree of flexibility that can follow the bending of the flexible component.

[0010] Adhesive sheets used in such flexible devices typically have a configuration in which release sheets are placed on both main surfaces of the adhesive layer, and the peeling force of one release sheet (lightly peelable release sheet) is designed to be smaller than the peeling force of the other release sheet (heavily peelable release sheet).

[0011] When bonding one flexible member to another using an adhesive sheet, first, the light-peel release liner of the adhesive sheet is peeled off, and the exposed adhesive layer is bonded to one flexible member. Then, the heavy-peel release liner is peeled off, and the exposed adhesive layer is bonded to the other flexible member, thereby forming a laminate of flexible members.

[0012] In this case, in order to suppress deformation of the flexible adhesive layer, it is necessary to reduce the peeling force of the release sheet. However, when the peeling force of the release sheet is reduced, the difference in peeling force between the two release sheets tends to become small. As a result, when peeling off the light-peel type release sheet, there was a problem in which the adhesive that should remain on the heavy-peel type release sheet unintentionally adhered to the light-peel type release sheet, a phenomenon known as "separation."

[0013] Furthermore, when the adhesive layer is bonded to one flexible member, and then the heavy-peel release sheet is peeled off to bond the other flexible member to the adhesive, the adhesive stretches and deforms due to the peeling off of the heavy-peel release sheet. As a result, a dimensional change occurs at the edge of the adhesive, causing the position of the adhesive edge to shift outward compared to its position when bonded to one of the members.

[0014] When such dimensional changes occur at the edges of the adhesive, repeated bending of the bonded flexible member further increases the elongation of the adhesive, and consequently, the dimensional changes at the edges also increase. As a result, the thickness of the adhesive layer becomes thinner than the thickness assumed in the design, causing distortions in the positional relationship of the members in the device, and resulting in optical defects in the device.

[0015] This invention has been made in view of the above circumstances, and aims to provide an adhesive sheet that, even when having a flexible adhesive used for bonding flexible members, suppresses separation when peeling off a light-peel type release sheet, and suppresses dimensional changes at the edges of the adhesive layer when peeling off a heavy-peel type release sheet. [Means for solving the problem]

[0016] The embodiments of the present invention are as follows. [1] An adhesive sheet having an adhesive layer and a first release sheet and a second release sheet that sandwich both main surfaces of the adhesive layer, The storage modulus of the adhesive constituting the adhesive layer at 23°C is 0.2 MPa or less. The amount of Si on the surface of the adhesive layer is more than twice the amount of Si near the center of the adhesive layer. The second release sheet contains a silicone-based release agent. The amount of Si transferred to the surface of the adhesive layer of the second release sheet is 5-100 atom%, This is an adhesive sheet for flexible devices in which the peeling force of the first release sheet is 150 mN / 25 mm or less when peeled from the adhesive layer at a peeling speed of 2.4 m / min.

[0017] [2]A flexible member laminate comprising a first flexible member, a second flexible member, and an adhesive layer that bonds the first flexible member and the second flexible member together. The flexible member laminate, wherein the adhesive layer is the adhesive of the adhesive sheet for flexible devices described in [1].

[0018] [3]A flexible device comprising the flexible member laminate described in [2]. [Advantages of the Invention]

[0019] According to the present invention, even if it has a flexible adhesive used for bonding flexible members, etc., it is possible to provide an adhesive sheet for flexible devices in which the separation at the time of peeling of the light-peeling type release sheet is suppressed, and the dimensional change of the end portion of the adhesive layer at the time of peeling of the heavy-peeling type release sheet is suppressed. [Brief Description of the Drawings] [[ID=二十]]

[0020] [Figure 1] FIG. 1 is a cross-sectional view of an adhesive sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a flexible member laminate according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view of a flexible device according to an embodiment of the present invention. [Modes for Carrying Out the Invention] [[ID=三十五]]

[0021] Hereinafter, the present invention will be described in detail based on specific embodiments.

[0022] (1. Adhesive Sheet for Flexible Devices) The adhesive sheet 1 for flexible devices according to this embodiment, as shown in Figure 1, comprises an adhesive layer 10, a first release sheet 11, and a second release sheet 12. The adhesive constituting the adhesive layer 10 will be described later. The two release sheets (first release sheet 11 and second release sheet 12) support the adhesive layer 10, and are arranged so that their release surfaces are in contact with both main surfaces of the adhesive layer, making them removable from the adhesive layer. In other words, the adhesive layer 10 is sandwiched between the two release sheets (first release sheet 11 and second release sheet 12) in a removable manner. In this specification, the release surface of a release sheet refers to the surface of the release sheet that has release properties, and includes both surfaces that have undergone a release treatment and surfaces that exhibit release properties even without a release treatment. The release sheets will be described later.

[0023] The adhesive sheet according to this embodiment is used to bond a first member and a second member. In particular, the adhesive sheet according to this embodiment is suitably used for bonding flexible members.

[0024] Flexible components are components that maintain their function even after being bent, such as by folding. Examples of flexible components include components that are molded to bend during the manufacturing of equipment containing flexible components and maintain that bent state, and components that are repeatedly bent during the use of equipment containing flexible components. Therefore, the adhesive used to bond such flexible components together also needs to be flexible enough to follow the bending.

[0025] To protect the adhesive until use, this embodiment uses an adhesive sheet in which two release sheets are placed on both main surfaces of the adhesive, as shown in Figure 1. The two release sheets typically have different peeling forces from the adhesive, consisting of a release sheet with a relatively small peeling force (light peeling type release sheet) and a release sheet with a relatively large peeling force (heavy peeling type release sheet). By providing this difference in peeling force between the release sheets, the phenomenon of adhesive that should remain on the heavy peeling type release sheet unintentionally adhering to the light peeling type release sheet when the light peeling type release sheet is peeled off, known as "separation," is prevented.

[0026] On the other hand, adhesives used to bond flexible components together are flexible to accommodate bending and are easily deformed when force is applied. Therefore, release sheets that are easy to peel off (with relatively low peeling force from the adhesive) are used.

[0027] However, when using easily removable release sheets, the difference in peeling strength between the two release sheets tends to become small. As a result, there was a problem in that the easily removable release sheets were more likely to separate when peeled off.

[0028] Furthermore, when peeling off the light-peel release sheet and bonding one component to the adhesive, and then peeling off the heavy-peel release sheet and bonding the other component to the adhesive, the adhesive stretches and deforms due to the peeling off of the heavy-peel release sheet. As a result, a dimensional change occurs at the edge of the adhesive, causing the position of the adhesive edge to shift outward compared to its position when bonded to one component.

[0029] When such dimensional changes occur at the edges of the adhesive, unintended adhesion to other components is likely to occur. If adhesion occurs, the elongation of the adhesive increases further, and the dimensional changes become even greater. As a result, the bonding accuracy between components decreases, and the yield decreases.

[0030] In particular, if dimensional changes occur at the edges of the adhesive during the bonding of flexible components, repeated bending of the bonded flexible components afterward will further increase the elongation of the adhesive, and consequently, the dimensional changes at the edges will also increase. As a result, the thickness of the adhesive layer becomes thinner than the thickness assumed during the design phase, causing distortions in the positional relationship of the components in the device, and resulting in optical defects in the device. Therefore, in order to improve the optical reliability of the device, it is necessary to suppress dimensional changes at the edges of the adhesive before and after peeling of the heavy-peel release sheet.

[0031] To address the above-mentioned problems, the physical properties of the release sheet and the adhesive layer are controlled in the adhesive sheet according to this embodiment. The components of the adhesive sheet according to this embodiment will be described in detail below.

[0032] (1.1. Adhesive layer) The adhesive layer bonds the first member and the second member. In this embodiment, it is preferable that the adhesive layer bonds the first flexible member and the second flexible member.

[0033] The adhesive layer may consist of one layer (single layer) or of two or more layers. If the adhesive layer has multiple layers, these layers may be identical or different from each other, and there are no particular restrictions on the combination of layers that make up these multiple layers.

[0034] In this embodiment, the adhesive layer has the following physical properties, which allows for sufficient bonding between the first flexible member and the second flexible member, and effectively suppresses peeling and other issues even when the bonded members are bent.

[0035] The thickness of the adhesive layer 10 is preferably 1 to 300 μm, more preferably 5 to 180 μm, even more preferably 10 to 100 μm, particularly preferably 15 to 60 μm, and most preferably 20 to 40 μm. This makes it easier to adjust the peeling force described above and the difference in peeling force described later to a desired value. Furthermore, it provides good adhesion between the first flexible member and the second flexible member, and consequently, excellent flexibility.

[0036] (1.2. Adhesive) In this embodiment, the adhesive layer 10 consists of the adhesive described below.

[0037] (1.3. Physical properties of adhesives) In this embodiment, the adhesive constituting the adhesive layer 10 has the following physical properties.

[0038] (1.3.1. Storage modulus) In this embodiment, it is preferable that the storage modulus (G') of the adhesive at 23°C and a frequency of 1 Hz is 0.2 MPa or less. The storage modulus is one indicator of how easily the adhesive layer deforms (hardness). By keeping the storage modulus of the adhesive at 23°C within the above range, the adhesive layer can adequately follow the bending even when repeatedly bent, and lifting or peeling from the bonded member is suppressed.

[0039] The upper limit of the storage modulus of the adhesive is preferably 0.2 MPa or less, more preferably 0.15 MPa or less, even more preferably 0.1 MPa or less, particularly preferably 0.08 MPa or less, and most preferably 0.06 MPa or less. On the other hand, the lower limit of the storage modulus of the adhesive is preferably 0.001 MPa or more, more preferably 0.005 MPa or more, even more preferably 0.01 MPa or more, particularly preferably 0.02 MPa or more, and most preferably 0.04 MPa or more, from the viewpoint of dimensional stability, processability, and prevention of splitting. The storage modulus of the adhesive can be adjusted, for example, by changing the composition of the adhesive (type and amount of reactive functional groups, molecular structure of the monomer composition used, glass transition temperature, etc.), the molecular weight of the materials constituting the adhesive, etc.

[0040] The storage modulus (G') can be measured by known methods. For example, the adhesive layer is prepared as a sample of a predetermined size, and the elastic modulus is measured by applying strain to the sample at a predetermined frequency within a predetermined temperature range using a dynamic viscoelasticity measuring device. From the measured elastic modulus, the storage modulus under the above conditions can be calculated.

[0041] (1.3.2. Si content on the second release sheet side surface of the adhesive layer) In this embodiment, it is preferable that Si is present on the second release sheet side surface of the adhesive layer. This reduces the peeling force of the second release sheet (lightly peelable release sheet). As a result, the difference in peeling force between the heavily peelable release sheet and the lightly peelable release sheet becomes larger, and separation during peeling of the lightly peelable release sheet can be suppressed.

[0042] The second release sheet side surface of the adhesive layer refers to the main surface of the adhesive sheet on which the second release sheet is located, out of the two main surfaces of the adhesive layer. In Figure 1, the second release sheet side surface is the main surface 10b.

[0043] The Si present on the second release sheet side surface of the adhesive layer may be Si originating from the adhesive layer or Si migrated from the release sheet. In this embodiment, it is preferable that the Si present on the second release sheet side surface is Si migrated from the release sheet. Whether the Si present on the second release sheet side surface is Si originating from the adhesive layer or Si migrated from the release sheet can be determined, for example, by comparing the amount of Si on the surface of the adhesive layer with the amount of Si near the center of the adhesive layer. In this embodiment, if the amount of Si on the surface of the adhesive layer is twice or more the amount of Si near the center of the adhesive layer, it can be determined that the Si migrated from the release sheet.

[0044] The amount of Si on the surface of the adhesive layer on the second release sheet side can be measured, for example, as follows: Surface analysis is performed on the surface of the adhesive layer exposed by peeling the second release sheet from the adhesive sheet using X-ray photoelectron spectroscopy (XPS), and the Si ratio is calculated from the obtained spectrum to determine the amount of Si. The specific measurement method will be described in detail in the examples below.

[0045] (1.3.3. Dimensional changes at the edges of the adhesive layer) The dimensional change at the edge of the adhesive layer of the adhesive sheet according to this embodiment is preferably 0 μm or more at the lower limit, less than 100 μm at the upper limit, more preferably less than 70 μm, and preferably less than 30 μm. This indicates that the adhesive sheet has suppressed dimensional changes at the edge of the adhesive layer. Having such characteristics suppresses further dimensional changes at the edge when the bonded flexible member is repeatedly bent, thereby making it less likely for the thickness of the adhesive layer to become thinner than the thickness assumed at the time of design, causing distortion in the positional relationship of the members in the device, and resulting in optical defects in the device. Specific evaluation methods will be described in detail in the embodiments described later.

[0046] (1.4. Composition of the adhesive) The composition of the adhesive is not particularly limited as long as it possesses the above-mentioned physical properties. For example, it may be any of the following: acrylic adhesive, polyester adhesive, polyurethane adhesive, rubber adhesive, silicone adhesive, etc. Furthermore, the adhesive may be of emulsion type, solvent type, or solvent-free type. In addition, the adhesive may or may not have a cross-linked structure.

[0047] In this embodiment, from the viewpoint of ease of realizing the above-mentioned physical properties, and from the viewpoint of adhesive properties, optical properties, etc., an acrylic adhesive is preferred as the adhesive, and an acrylic adhesive having a crosslinked structure is more preferred.

[0048] Specifically, the adhesive is preferably an adhesive obtained by crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B). Such an adhesive is likely to satisfy the above-mentioned physical properties and easily provide good adhesive strength. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the concept of "polymer" is also included in the concept of "polymer".

[0049] (1.4.1. (meth)acrylic acid ester polymer) The (meth)acrylic acid ester polymer (A) preferably contains an alkyl (meth)acrylic acid ester and a monomer having a reactive functional group in its molecule (a monomer containing a reactive functional group) as monomer units constituting the polymer.

[0050] By including an alkyl (meth)acrylate ester, the resulting adhesive can exhibit desirable tackiness. Preferably, the alkyl (meth)acrylate ester has an alkyl group with 1 to 20 carbon atoms. The alkyl group may be linear, branched, or have a cyclic structure.

[0051] Examples of alkyl (meth)acrylate esters having 1 to 20 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

[0052] Among these, (meth)acrylic acid esters with 1 to 8 carbon atoms in the alkyl group are preferred, and (meth)acrylic acid esters with 4 to 8 carbon atoms in the alkyl group are particularly preferred, from the viewpoint of physical properties related to the storage modulus G' at 23°C. Specifically, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. These may be used individually or in combination of two or more.

[0053] The (meth)acrylic acid ester polymer (A) preferably contains 50 to 99.9% by mass of alkyl (meth)acrylic acid ester having 1 to 20 carbon atoms in the alkyl group as monomer units constituting the polymer, more preferably 70 to 99.5% by mass, even more preferably 90 to 99% by mass, and particularly preferably 94 to 98.5% by mass. This allows for the imparting of suitable tackiness to the (meth)acrylic acid ester polymer (A) and facilitates the adjustment of the storage modulus G' of the resulting adhesive to a lower value. Furthermore, other monomer components can be introduced into the (meth)acrylic acid ester polymer (A) in desired amounts, making it easier to design an adhesive that exhibits the desired performance.

[0054] The (meth)acrylic acid ester polymer (A) contains a monomer containing a reactive functional group as a monomer unit constituting the polymer. Through the reactive functional group derived from the reactive functional group containing the monomer, the (meth)acrylic acid ester polymer (A) reacts with the crosslinking agent (B) described later, forming a crosslinked structure (three-dimensional network structure) in the adhesive. As a result, an adhesive with the desired cohesive force is obtained. This adhesive is likely to satisfy the physical properties related to the storage modulus G' described above, as well as the desired peel force and peel force difference.

[0055] Preferred monomers containing reactive functional groups include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomers), monomers having a carboxyl group in the molecule (carboxyl group-containing monomers), and monomers having an amino group in the molecule (amino group-containing monomers). These reactive functional group-containing monomers may be used individually or in combination of two or more.

[0056] Among the above-mentioned monomers containing reactive functional groups, monomers containing hydroxyl groups or monomers containing carboxyl groups are preferred, and monomers containing hydroxyl groups are particularly preferred. By including monomers containing hydroxyl groups, it is easier to satisfy the physical properties related to the storage modulus G' described above, and fine-tuning of the storage modulus G' becomes easier.

[0057] Examples of hydroxyl group-containing monomers include hydroxyalkyl methacrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0058] Among these, hydroxyalkyl (meth)acrylate esters having a hydroxyalkyl group with 1 to 4 carbon atoms are preferred from the viewpoint of easily achieving the physical properties related to the storage modulus G' described above. Specifically, for example, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred, and 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate are particularly preferred. These may be used alone or in combination of two or more.

[0059] Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred from the viewpoint of the adhesiveness of the resulting (meth)acrylic acid ester polymer (A). These may be used individually or in combination of two or more.

[0060] The (meth)acrylic acid ester polymer (A) preferably contains 0.1 to 10% by mass of reactive functional group-containing monomers as monomer units constituting the polymer, more preferably 0.5 to 7% by mass, and even more preferably 1 to 5% by mass.

[0061] By setting the content ratio of the reactive functional group-containing monomer within the above range, the cohesive force of the adhesive obtained by the crosslinking reaction with the crosslinking agent (B) becomes appropriate, making it easier to satisfy the physical properties related to the storage modulus G', the desired peeling force, and the difference in peeling force as described above.

[0062] Furthermore, it is preferable that the (meth)acrylic acid ester polymer (A) does not contain carboxyl group-containing monomers as monomer units constituting the polymer. Since carboxyl groups are acidic components, by not containing carboxyl group-containing monomers, it is possible to suppress problems caused by acid (corrosion, changes in resistance, etc.) even when the object to which the adhesive is applied contains transparent conductive films such as tin-doped indium oxide (ITO), metal films, or metal meshes.

[0063] Here, "carboxy group-containing monomer-free" means substantially free of carboxy group-containing monomers, including not only complete absence of carboxy group-containing monomers, but also the possibility of containing carboxy group-containing monomers to an extent that does not cause corrosion of transparent conductive films or metal wiring due to carboxyl groups. Specifically, it means that the (meth)acrylic acid ester polymer (A) may contain carboxy group-containing monomers as monomer units in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less.

[0064] In this embodiment, the (meth)acrylic acid ester polymer (A) may optionally contain other monomers as monomer units constituting the polymer. As other monomers, monomers that do not contain reactive functional groups are preferred in order not to inhibit the effects of the reactive functional group-containing monomers described above. Examples of such monomers include unreactive nitrogen atom-containing monomers such as N-acryloylmorpholine and N-vinyl-2-pyrrolidone, alkoxyalkyl (meth)acrylate esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used individually or in combination of two or more.

[0065] The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

[0066] The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 300,000 to 3,000,000, more preferably 500,000 to 2,200,000, even more preferably 700,000 to 1,800,000, particularly preferably 900,000 to 1,500,000, and most preferably 1,100,000 to 1,300,000. This makes it easier to satisfy the physical properties related to the storage modulus G', the desired peel strength, and the peel strength difference in the resulting adhesive. Note that the weight-average molecular weight in this specification is the value on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0067] In the adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more types.

[0068] (1.4.2. Crosslinking agents) The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) upon heating or other triggers of the adhesive composition P containing the crosslinking agent (B), forming a crosslinked structure (three-dimensional network structure). As a result, the cohesive force of the resulting adhesive is improved, and the physical properties related to the storage modulus G', as well as the desired peel force and peel force difference, are more easily satisfied.

[0069] The crosslinking agent (B) can be any agent that reacts with the reactive groups of the (meth)acrylic acid ester polymer (A). Examples include isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, and ammonium salt crosslinking agents. Among these, it is preferable to use an isocyanate crosslinking agent that exhibits excellent reactivity with monomers containing reactive functional groups. Note that the crosslinking agent (B) can be used alone or in combination of two or more types.

[0070] Isocyanate-based crosslinking agents include 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; alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate; and their biuret and isocyanurate forms, as well as 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.

[0071] The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 to 2 parts by mass, more preferably 0.06 to 1 part by mass or more, even more preferably 0.12 to 0.7 parts by mass, and particularly preferably 0.15 to 0.5 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). This makes it easier to satisfy the physical properties related to the storage modulus G', the desired peeling force, and the difference in peeling force.

[0072] (1.4.3. Other Additives) The adhesive composition P may optionally contain additives commonly used in acrylic adhesives. Examples of such additives include silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, rust inhibitors, fillers, and refractive index modifiers. Polymerization solvents and diluent solvents described later are not included in the additives constituting the adhesive composition P.

[0073] In this embodiment, the adhesive composition P preferably contains a silane coupling agent. This improves the adhesion between the resulting adhesive layer and the flexible member to be adhered, resulting in a more desirable adhesive strength and excellent flexibility.

[0074] The silane coupling agent is preferably an organosilicon compound having at least one alkoxysilyl group in its molecule. Furthermore, the silane coupling agent is preferably one that has good compatibility with the (meth)acrylic acid ester polymer (A) and is light-transmitting.

[0075] Examples of such silane coupling agents include polymerizable unsaturated silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and mercaptopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropyldimethoxymethylsilane. Examples include silicon compounds containing a pt group, amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, or condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. These may be used individually or in combination of two or more.

[0076] The content of the silane coupling agent in the adhesive composition P is preferably 0.01 to 1 part by mass, more preferably 0.05 to 0.6 parts by mass, and even more preferably 0.1 to 0.3 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). As a result, the resulting adhesive layer has improved adhesion to the flexible member that is adhered to, and the adhesive strength is greater.

[0077] (1.5. Release Sheet) In this embodiment, the adhesive sheet has at least two release sheets. As described above, the two release sheets have a difference in peeling force, with one release sheet being a light-peel type and the other being a heavy-peel type. In the adhesive sheet 1 shown in Figure 1, the first release sheet 11 is a heavy-peel type, and the second release sheet 12 is a light-peel type. That is, the peeling force of the first release sheet 11 from the adhesive layer 10 is greater than the peeling force of the second release sheet 12 from the adhesive layer 10.

[0078] (1.5.1 First release sheet) The first release sheet may consist of one layer (single layer) or two or more layers of substrate, or the surface of the substrate may be treated to control its release properties. That is, the surface of the substrate may be modified, or a material not derived from the substrate (for example, a release agent layer) may be formed on the surface of the substrate.

[0079] (1.5.2. Physical properties of the first release sheet) In this embodiment, the first release sheet (heavy-peel type release sheet) has the following physical properties.

[0080] (1.5.3. Peeling force from the adhesive layer) In this embodiment, it is preferable that the peeling force when the first release sheet is peeled from the adhesive layer at a peeling speed of 2.4 m / min is 150 mN / 25 mm or less. This peeling force corresponds to the peeling force when peeling the heavy-peel release sheet in order to peel off the light-peel release sheet from the adhesive sheet, bond the adhesive layer to the first member, and then bond it to the second member. Because the above peeling force is within the above range, deformation (elongation) of the adhesive is less likely to occur when peeling the heavy-peel release sheet from the adhesive layer. As a result, dimensional changes at the edges of the adhesive layer can be suppressed.

[0081] The above peeling force is preferably 150 mN / 25 mm or less, more preferably 140 mN / 25 mm or less, and even more preferably 130 mN / 25 mm or less. Furthermore, the lower limit of the above peeling force is not particularly limited as long as it is greater than the peeling force of the light-peel type release sheet (second release sheet). In this embodiment, from the viewpoint of making it easier to satisfy the peeling force difference described later and from the viewpoint of separation and storage stability in roll form, the lower limit of the above peeling force is preferably 30 mN / 25 mm or more, more preferably 50 mN / 25 mm or more, even more preferably 70 mN / 25 mm or more, and particularly preferably 80 mN / 25 mm or more.

[0082] The peeling speed of the release sheet is set appropriately depending on the type of member to which the adhesive layer is bonded and the type of bonding device. Therefore, it is preferable that the peeling force of the first release sheet at a predetermined peeling speed is within a predetermined range.

[0083] When the peeling speed is 10 m / min, the peeling force when peeling the first release sheet from the adhesive layer is preferably 600 mN / 25 mm or less, more preferably 400 mN / 25 mm or less, even more preferably 300 mN / 25 mm or less, particularly preferably 260 mN / 25 mm or less, and most preferably 220 mN / 25 mm or less. By keeping the above peeling force within the above range, deformation (elongation) of the adhesive is less likely to occur when peeling the heavy-peel type release sheet from the adhesive layer, and dimensional changes at the edges of the adhesive layer can be suppressed. Furthermore, the lower limit of the above peeling force is not particularly limited as long as it is greater than the peeling force of the light-peel type release sheet (second release sheet). In this embodiment, from the viewpoint of easily satisfying the peeling force difference described later and from the viewpoint of storage stability in the form of separation and rolls, the lower limit of the peeling force is preferably 30 mN / 25 mm or more, more preferably 80 mN / 25 mm or more, even more preferably 110 mN / 25 mm or more, and particularly preferably 140 mN / 25 mm or more.

[0084] When the peeling speed is 0.3 m / min, the peeling force when peeling the first release sheet from the adhesive layer is preferably 80 mN / 25 mm or less, more preferably 70 mN / 25 mm or less, even more preferably 60 mN / 25 mm or less, particularly preferably 50 mN / 25 mm or less, and most preferably 45 mN / 25 mm or less. By keeping the above peeling force within the above range, deformation (stretching) of the adhesive is less likely to occur when peeling the heavy-peel type release sheet from the adhesive layer, and dimensional changes at the edges of the adhesive layer can be suppressed. Furthermore, the lower limit of the above peeling force is not particularly limited as long as it is greater than the peeling force of the light-peel type release sheet (second release sheet). In this embodiment, from the viewpoint of making it easier to satisfy the peeling force difference described later and from the viewpoint of storage stability in the form of splitting and roll form, the lower limit of the above peeling force is preferably 5 mN / 25 mm or more, more preferably 10 mN / 25 mm or more, and even more preferably 20 mN / 25 mm or more.

[0085] From the viewpoint of adjusting the peeling force within the above range, the thickness of the first release sheet is preferably 30 to 100 μm, more preferably 40 to 80 μm, and even more preferably 45 to 60 μm. Furthermore, from the viewpoint of making the peeling force of the first release sheet greater than that of the second release sheet, the thickness of the first release sheet is preferably equal to or greater than the thickness of the second release sheet, and more preferably greater than the thickness of the second release sheet.

[0086] Note that the thickness of the first release sheet refers to the total thickness of the first release sheet. For example, if the first release sheet is composed of multiple layers, the thickness refers to the sum of the thicknesses of all the layers that make up the first release sheet.

[0087] In this embodiment, the first release sheet is preferably configured to include a base material, more preferably the surface of the base material is peel-treated, and even more preferably the base material has a release agent layer, from the viewpoint of making it easier to keep the peeling force within the above range. The presence of a release agent layer makes it easier to impart good peelability to the surface (peel surface) on which the release agent layer is formed in the first release sheet.

[0088] (1.5.4. Base material) The base material of the first release sheet is not particularly limited as long as it is a material that can support the adhesive layer until the adhesive layer is attached to the adherend (for example, a flexible member), and is usually composed of a film mainly made of a resin-based material (hereinafter referred to as "resin film").

[0089] Specific examples of resin films include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate copolymer film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. Crosslinked films of these are also used. Furthermore, laminated films of these may also be used. In this embodiment, polyethylene terephthalate film is preferred from the viewpoint of suppressing coiling due to stretching of the substrate, in addition to environmental safety and cost.

[0090] The base material may contain various additives in the resin film, such as colorants, flame retardants, plasticizers, antistatic agents, lubricants, and fillers.

[0091] The thickness of the substrate is not particularly limited as long as it is thick enough to support the adhesive layer, within the range of the thickness of the first release sheet described above. From the viewpoint of adjusting the peeling force of the first release sheet within the above range, the thickness of the substrate is preferably 30 to 100 μm, more preferably 40 to 80 μm, and even more preferably 45 to 60 μm.

[0092] (1.5.5. First release agent layer) When the first release sheet has a substrate and a release agent layer, the release agent layer of the first release sheet (which may be referred to as the "first release agent layer" in this specification) imparts the ability to release the first release sheet from the adhesive layer. The first release agent layer is not particularly limited as long as it is composed of a material that can impart release properties, but in this embodiment, the first release agent layer is preferably a layer obtained by curing the first release agent layer composition described later.

[0093] The thickness of the first release agent layer is not particularly limited as long as it is thick enough to exhibit the desired release properties. However, from the viewpoint of adjusting the release force of the first release sheet within the above range, it is preferably 1 to 1000 nm, more preferably 10 to 500 nm, even more preferably 30 to 300 nm, and particularly preferably 50 to 200 nm.

[0094] (1.5.6. Composition for the first release agent layer) The composition for the first release agent layer may include, for example, an alkyd release agent, a silicone release agent, a fluorine release agent, an unsaturated polyester release agent, a polyolefin release agent, or a wax release agent. In this embodiment, from the viewpoint of adjusting the release force of the first release sheet and the release force difference described later to be within the above range, the composition for the first release agent layer preferably contains a silicone release agent, and more preferably contains a silicone release agent and a heavy release additive.

[0095] (1.5.7. Silicone-based release agents) As a silicone-based release agent, it is preferable to use a silicone-based release agent that contains silicone having dimethylpolysiloxane as its basic structure. This allows the release force of the first release sheet to be adjusted within the above range.

[0096] The content of dimethylpolysiloxane silicone in the first release agent layer composition (excluding the catalyst described later), when the total weight is 100 parts by mass, is preferably less than 100 parts by mass, more preferably less than 90 parts by mass, even more preferably less than 80 parts by mass, and particularly preferably less than 70 parts by mass. The lower limit of this content is 0 parts by mass. This makes it easy to adjust the release force of the first release sheet within the above range.

[0097] The silicone may be of the addition reaction type, condensation reaction type, or energy ray curing type such as ultraviolet curing type or electron beam curing type, but an addition reaction type silicone is preferred. Addition reaction type silicones have high reactivity and excellent productivity, and compared to condensation reaction type silicones, they have advantages such as stable release force after manufacturing and no curing shrinkage, making it easier to adjust the release force of the first release sheet within the above range.

[0098] Specific examples of addition-type silicones include organopolysiloxanes, which have two or more C2-C10 alkenyl groups, such as vinyl groups, allyl groups, propenyl groups, and hexenyl groups, at the ends and / or side chains of the molecule.

[0099] When using such addition-reaction type silicones, it is preferable to use a crosslinking agent and a catalyst in combination.

[0100] Examples of crosslinking agents include organopolysiloxanes having at least two hydrogen atoms bonded to silicon atoms in one molecule. Specifically, these include dimethylhydrogensiloxy group-ended dimethylsiloxane-methylhydrogensiloxane copolymers, trimethylsiloxy group-ended dimethylsiloxane-methylhydrogensiloxane copolymers, trimethylsiloxy group-ended methylhydrogenpolysiloxanes, and poly(hydrogensilsesquioxanes).

[0101] Examples of catalysts include particulate platinum, particulate platinum adsorbed on a carbon powder support, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, palladium, and platinum group metal compounds such as rhodium.

[0102] By using such a catalyst, the curing reaction of the composition for the first release agent layer can be made to proceed more efficiently.

[0103] The content of the silicone-based release agent when the total weight of the first release agent layer composition (excluding the catalyst) is 100 parts by mass is preferably 30 to 100 parts by mass, and more preferably 50 to 100 parts by mass, from the viewpoint of keeping the release force within the range described above.

[0104] (1.5.8. Heavy peeling additive) Examples of heavy release additives include silicone resins and organosilanes such as silane coupling agents, but among these, silicone resin is preferred. This allows the release force of the first release sheet to be adjusted within the above range, and the release force of the first release sheet from the adhesive layer to be greater than the release force of the second release sheet.

[0105] Examples of silicone resins include monofunctional siloxane units [R3SiO 1 / 2 The M unit is [SiO], and the tetrafunctional siloxane unit is [SiO]. 4 / 2 It is preferable to use MQ resin containing Q units, which are ]. The three Rs in the M unit each independently represent a hydrogen atom, a hydroxyl group, or an organic group. From the viewpoint of easily suppressing silicone migration, it is preferable that one or more of the three Rs in the M unit be a hydroxyl group or a vinyl group, and more preferably a vinyl group.

[0106] (1.6. Second release sheet) Similar to the first release sheet, the second release sheet may consist of one layer (single layer) or two or more layers of substrate, or the surface of the substrate may be treated to control its release properties. That is, the surface of the substrate may be modified, or a material not derived from the substrate (for example, a release agent layer) may be formed on the surface of the substrate.

[0107] As long as the peeling force of the second release sheet (lightly peelable release sheet) is less than the peeling force of the first release sheet (heavily peelable release sheet), the physical properties of the second release sheet are not particularly limited. However, in this embodiment, it is preferable that the second release sheet (lightly peelable release sheet) has the following physical properties.

[0108] (1.6.1. Peeling force from the adhesive layer) In this embodiment, the peeling force when the second release sheet is peeled from the adhesive layer at a peeling speed of 10 m / min is preferably 500 mN / 25 mm or less, more preferably 300 mN / 25 mm or less, even more preferably 200 mN / 25 mm or less, particularly preferably 160 mN / 25 mm or less, and most preferably 145 mN / 25 mm or less. This peeling force corresponds to the peeling force when peeling the light-peel type release sheet from the adhesive sheet in order to bond the adhesive layer to the member. By keeping the above peeling force within the above range, separation during peeling of the light-peel type release sheet can be suppressed. In this embodiment, from the viewpoint of making it easier to satisfy the peeling force difference described later and from the viewpoint of storage stability in roll form, the lower limit of the above peeling force is preferably 20 mN / 25 mm or more, more preferably 40 mN / 25 mm or more, even more preferably 60 mN / 25 mm or more, and particularly preferably 80 mN / 25 mm or more.

[0109] The peeling force when the second release sheet is peeled from the adhesive layer at a peeling speed of 0.3 m / min is preferably 70 mN / 25 mm or less, more preferably 50 mN / 25 mm or less, even more preferably 40 mN / 25 mm or less, particularly preferably 30 mN / 25 mm or less, and most preferably 28 mN / 25 mm or less. This peeling force also corresponds to the peeling force when peeling the light-peel type release sheet from the adhesive sheet in order to bond the adhesive layer to the member. By keeping the above peeling force within the above range, it is possible to suppress separation when peeling the light-peel type release sheet. In this embodiment, from the viewpoint of making it easier to satisfy the peeling force difference described later and from the viewpoint of storage stability in roll form, the lower limit of the above peeling force is preferably 3 mN / 25 mm or more, more preferably 8 mN / 25 mm or more, even more preferably 12 mN / 25 mm or more, and particularly preferably 15 mN / 25 mm or more.

[0110] In this embodiment, from the viewpoint of suppressing separation when peeling off the light-peel type release sheet, it is preferable that the peeling force of the first release sheet is greater than the peeling force of the second release sheet, that is, that there is a difference in peeling force. In this specification, a difference in peeling force means a difference in peeling force of more than 1 mN / 25 mm.

[0111] Preferably, the difference in peeling force between the peeling force when the second release sheet is peeled from the adhesive layer at a peeling speed of 10 m / min and the peeling force when the first release sheet is peeled from the adhesive layer at a peeling speed of 10 m / min is greater than 24 mN / 25 mm. This suppresses separation when peeling off a light-peel type release sheet. From the viewpoint of more effectively preventing separation and balancing flexibility and dimensional stability, it is preferable that the difference is 25 to 300 mN / 25 mm, more preferably 30 to 200 mN / 25 mm, even more preferably 50 to 150 mN / 25 mm, particularly preferably 60 to 100 mN / 25 mm, and most preferably 64 to 80 mN / 25 mm.

[0112] The difference in peeling force between the peeling force when the second release sheet is peeled from the adhesive layer at a peeling speed of 0.3 m / min and the peeling force when the first release sheet is peeled from the adhesive layer at a peeling speed of 0.3 m / min is preferably 1.5 to 60 mN / 25 mm, more preferably 2 to 40 mN / 25 mm, even more preferably 2.5 to 30 mN / 25 mm, and particularly preferably 3 to 25 mN / 25 mm. This suppresses separation when peeling off the light-peel type release sheet. Furthermore, from the viewpoint of balancing the prevention of separation with flexibility, the difference in peeling force is preferably 3.5 to 19 mN / 25 mm, and most preferably 4 to 18 mN / 25 mm.

[0113] From the viewpoint of adjusting the peeling force and the difference in peeling forces within the above range, the thickness of the second release sheet is preferably 10 to 100 μm, more preferably 15 to 75 μm, even more preferably 20 to 60 μm, and particularly preferably 24 to 40 μm. Furthermore, from the viewpoint of making the peeling force of the first release sheet greater than the peeling force of the second release sheet, the thickness of the second release sheet is preferably less than or equal to the thickness of the first release sheet, and more preferably less than the thickness of the first release sheet.

[0114] Note that the thickness of the second release sheet refers to the total thickness of the second release sheet. For example, the thickness of a second release sheet composed of multiple layers refers to the sum of the thicknesses of all the layers that make up the second release sheet.

[0115] In this embodiment, the second release sheet is preferably configured to include a base material, more preferably the surface of the base material is peel-treated, and preferably it has a base material and a release agent layer, from the viewpoint of keeping the peeling force within the above range. The presence of a release agent layer makes it easier to impart good peelability to the surface (peel surface) on which the release agent layer is formed in the second release sheet.

[0116] (1.6.2. Base material) The base material for the second release sheet can be appropriately selected from the materials exemplified as the base material for the first release sheet.

[0117] (1.6.3. Second release agent layer) When the second release sheet has a substrate and a release agent layer, the release agent layer of the second release sheet (which may be referred to as the "second release agent layer" in this specification) imparts the ability to release the second release sheet from the adhesive layer. In this embodiment, it is preferable to include Si in order to transfer Si to the surface of the adhesive layer and to keep the amount of Si on that surface within the range described later. As such a release agent layer, it is preferable that it is a layer obtained by curing a composition for the second release agent layer that contains a silicone-based mold release agent.

[0118] (1.6.4. Composition for the second release agent layer) The composition for the second release agent layer can be selected from the materials exemplified in the composition for the first release agent layer, as long as it satisfies the relationship that the peeling force of the first release sheet is greater than the peeling force of the second release sheet. However, it is preferable that the materials exemplified as heavy release additives are present in a smaller amount than in the composition for the first release agent layer, or not present at all.

[0119] When a coating agent containing a composition for a second release layer having a silicone-based release agent is used to form a second release layer on a substrate of a second release sheet, and the second release layer is bonded to an adhesive layer, a phenomenon may occur in which the silicone-based release agent contained in the second release layer migrates to the adhesive layer (transfer phenomenon). In this embodiment, this transfer phenomenon is actively utilized to improve the peelability of the adhesive layer surface by making a predetermined amount of Si present on the surface of the adhesive layer. As a result, the peeling force of the second release sheet (lightly peelable release sheet) from the adhesive layer can be easily adjusted to the above range, and even if the peeling force of the first release sheet (heavily peelable release sheet) from the adhesive layer is within the above range, the difference in peeling force between the first release sheet and the second release sheet can be increased.

[0120] (1.6.5. Amount of Si on the surface of the adhesive layer of the second release sheet) In this embodiment, it is preferable that the second release sheet, when bonded to the adhesive layer, can transfer Si to the surface of the adhesive layer. The amount of Si transferred from the second release sheet to the adhesive layer surface can be used as an alternative indicator. For example, the amount of Si obtained by bonding the second release sheet to the surface of an adhesive layer that does not mainly contain Si, leaving it for 24 hours, peeling off the second release sheet, performing surface analysis on the exposed adhesive layer surface by X-ray photoelectron spectroscopy (XPS), and calculating the Si ratio from the obtained spectrum. The Si amount obtained in this way is preferably 5 to 100 atom%, more preferably 7 to 60 atom%, and even more preferably 9 to 30 atom%. By having the Si amount within the above range, the peeling force of the second release sheet (lightly peelable release sheet) can be sufficiently reduced. This allows the peeling force to be adjusted within the range described above. As a result, the difference in peeling force between the heavy-peel type release sheet and the light-peel type release sheet becomes larger, and separation during peeling of the light-peel type release sheet can be suppressed. The specific measurement method for the above Si content will be described in detail in the examples below.

[0121] (1.7. Manufacturing of adhesive compositions) The adhesive composition P can be produced, for example, by first producing a (meth)acrylic acid ester polymer (A), and then mixing the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent (B). Additives may be added as needed.

[0122] (Meth)acrylic acid ester polymer (A) can be produced, for example, by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. Polymerization of (meth)acrylic acid ester polymer (A) can be carried out by solution polymerization using a polymerization initiator as needed. Polymerizing (meth)acrylic acid ester polymer (A) using solution polymerization makes it easier to increase the molecular weight of the resulting polymer, adjust the molecular weight distribution, and further reduce the generation of low molecular weight products. As a result, adhesives with excellent resistance to repeated bending are easily obtained.

[0123] Examples of polymerization solvents used in solution polymerization include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone. One type of polymerization solvent may be used, or two or more types may be used in combination.

[0124] Examples of polymerization initiators include azo compounds and organic peroxides, and two or more may be used in combination. Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane1-carbonitride), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].

[0125] Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl) peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, and diacetyl peroxide.

[0126] Furthermore, in the polymerization process described above, the weight-average molecular weight of the resulting polymer can be adjusted by incorporating a chain transfer agent such as 2-mercaptoethanol.

[0127] Next, a crosslinking agent (B) and a diluent solvent are added to the solution of the obtained (meth)acrylic acid polymer (A) and thoroughly mixed to obtain a solvent-diluted adhesive composition P (coating solution). Additives may be added as needed.

[0128] Furthermore, if any of the above components is a solid component, or if it precipitates when mixed with other components in an undiluted state, that component may be dissolved or diluted in a diluting solvent beforehand before being mixed with the other components.

[0129] Examples of diluent solvents 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 methanol, ethanol, propanol, butanol, and 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.

[0130] The concentration and viscosity of the prepared coating solution can be selected as appropriate depending on the situation, as long as they are within the range of coating. For example, the adhesive composition P is diluted to a concentration of 10 to 60% by mass. Note that the addition of a diluent is not a necessary condition when obtaining the coating solution; if the adhesive composition P has a viscosity suitable for coating, a diluent may not be added. In this case, the adhesive composition P becomes a coating solution where the polymerization solvent of the (meth)acrylic acid ester polymer (A) is used directly as the diluent.

[0131] (1.8. Manufacturing of adhesives) The adhesive constituting the adhesive layer is preferably obtained by crosslinking the adhesive composition P described above. Crosslinking of the adhesive composition P can usually be carried out by heat treatment. This heat treatment can also be combined with the drying treatment used to volatilize the diluent solvent, etc., from the coating film of the adhesive composition P applied to the desired object.

[0132] The heating temperature for the heat treatment is preferably 50 to 150°C, and more preferably 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes.

[0133] After heat treatment, a curing period of 1 to 2 weeks at room temperature (e.g., 23°C, 50% RH) may be allowed, if necessary. If curing is required, an adhesive with a cross-linked structure will be obtained after the curing period. If curing is not required, an adhesive with a cross-linked structure will be obtained after the heat treatment is completed.

[0134] (1.9. Manufacturing of adhesive sheets) The method for manufacturing the adhesive sheet 1 is not particularly limited and can be manufactured by known methods. For example, a coating solution of the adhesive composition P is applied to the release surface of one first release sheet 11 (or second release sheet 12), and a coating layer having a predetermined thickness is formed by crosslinking the adhesive composition P through heat treatment. The release surface of the other second release sheet 12 (or first release sheet 11) is then placed on top of the formed coating layer. If curing is required, after a predetermined curing period, the coating layer becomes an adhesive layer 10. If curing is not required, the coating layer remains an adhesive layer 10. This provides the adhesive sheet 1.

[0135] Another method for manufacturing the adhesive sheet 1 involves applying the adhesive composition P coating solution to the release surface of one first release sheet 11, performing a heat treatment to crosslink the adhesive composition P, and forming a coating layer to obtain the first release sheet 11 with the coating layer. Alternatively, the adhesive composition P coating solution is applied to the release surface of the other second release sheet 12, performing a heat treatment to crosslink the adhesive composition P, and forming a coating layer to obtain the second release sheet 12 with the coating layer. The first release sheet 11 with the coating layer and the second release sheet 12 with the coating layer are then bonded together so that both coating layers are in contact with each other. If curing is required, after a predetermined curing period, the coating layer becomes the adhesive layer 10. If curing is not required, the coating layer remains the adhesive layer 10. This yields the adhesive sheet 1. This manufacturing method allows for stable production even when the adhesive layer 10 is thick.

[0136] Examples of methods for applying the adhesive composition P coating solution include bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0137] (2. Flexible component laminate) As shown in Figure 2, the flexible member laminate 2 according to this embodiment comprises a first flexible member 21 (one flexible member), a second flexible member 22 (another flexible member), and an adhesive layer 10 located between them that bonds the first flexible member 21 and the second flexible member 22 to each other.

[0138] The adhesive layer 10 in the flexible member laminate 2 is the adhesive layer 10 of the adhesive sheet 1 described above.

[0139] The flexible component laminate 2 is either the flexible device itself or a component that constitutes part of the flexible device. The flexible device may include a component that has been bent once during manufacturing and maintains that bent state, or it may include a component that can be repeatedly bent (including folded). Furthermore, the flexible device is preferably a display, but is not limited to this. Examples of flexible devices include organic electroluminescent (OLED) displays, electrophoretic displays (electronic paper), liquid crystal displays using a plastic substrate (film) as the substrate, and foldable displays. These may also be touch panels.

[0140] The first flexible member 21 and the second flexible member 22 are, for example, members that can be repeatedly bent (including folded). Examples of flexible members include cover films, barrier films, hard coat films, polarizing films (polarizing plates), polarizers, phase difference films (phase difference plates), viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transparent reflective films, electrode films, transparent conductive films, metal mesh films, film sensors (touch sensor films), liquid crystal polymer films, light-emitting polymer films, film-type liquid crystal modules, organic EL modules (organic EL films, organic EL elements), electronic paper modules (film-type electronic paper), TFT (Thin Film Transistor) substrates, etc.

[0141] The Young's moduli of the first flexible member 21 and the second flexible member 22 are preferably 0.1 to 10 GPa, more preferably 0.5 to 7 GPa, and even more preferably 1 to 5 GPa, respectively. Having the Young's moduli of the first flexible member 21 and the second flexible member 22 within the above range makes it easy to repeatedly bend each flexible member.

[0142] The thickness of the first flexible member 21 and the second flexible member 22 is preferably 10 to 3000 μm, more preferably 25 to 1000 μm, and even more preferably 50 to 500 μm. By having the thickness of the first flexible member 21 and the second flexible member 22 within the above range, it becomes easy to repeatedly bend each flexible member.

[0143] An example of manufacturing a flexible member laminate 2 is shown. First, one of the second release sheets 12 of the adhesive sheet 1 is peeled off, and the exposed adhesive layer 10 of the adhesive sheet 1 is bonded to one surface of the first flexible member 21.

[0144] Subsequently, the first release sheet 11 is peeled off from the adhesive layer 10 of the adhesive sheet 1, and the exposed adhesive layer 10 of the adhesive sheet 1 is bonded to the second flexible member 22 to obtain the flexible member laminate 2. Alternatively, as another example, the bonding order of the first flexible member 21 and the second flexible member 22 may be reversed.

[0145] (3. Flexible devices) The flexible device according to this embodiment comprises the flexible member laminate 2 described above, and may consist only of the flexible member laminate 2, or it may be configured with one or more flexible member laminates 2 and other flexible members. When one flexible member laminate 2 is laminated with another flexible member laminate 2, or when a flexible member laminate 2 is laminated with another flexible member, it is preferable to laminate them via the adhesive layer 10 of the adhesive sheet 1 described above.

[0146] In this embodiment, since the flexible device is bonded together by the adhesive layer described above, even when repeatedly bent (for example, 100,000 times), at least the lifting and peeling of the adhesive layer from the bonded members is suppressed.

[0147] Figure 3 shows an example of a flexible device in this embodiment. However, the flexible device according to the present invention is not limited to this example.

[0148] As shown in Figure 3, the flexible device 3 according to this embodiment is constructed by laminating, from top to bottom, a cover film 31, a first adhesive layer 32, a polarizing film 33, a second adhesive layer 34, a touch sensor film 35, a third adhesive layer 36, an organic EL element 37, a fourth adhesive layer 38, and a TFT substrate 39. The cover film 31, polarizing film 33, touch sensor film 35, organic EL element 37, and TFT substrate 39 are all flexible components.

[0149] Preferably, at least one of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 is the adhesive layer 10 of the adhesive sheet 1 described above. Preferably, two or more of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 are the adhesive layer 10 of the adhesive sheet 1 described above, and most preferably, all of the adhesive layers 32, 34, 36, and 38 are the adhesive layer 10 of the adhesive sheet 1.

[0150] In this specification, when "X~Y" (where X and Y are any numbers) is written, unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as "preferably greater than X" or "preferably less than Y." Similarly, when "greater than or equal to X" (where X is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than X," and when "less than or equal to Y" (where Y is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than Y."

[0151] Although embodiments of the present invention have been described above, the present invention is not limited in any way to the embodiments described above, and may be modified in various ways within the scope of the present invention. [Examples]

[0152] The invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0153] (Example 1) 1. Preparation of (meth)acrylic acid ester copolymers A (meth)acrylic acid ester copolymer (A) was prepared by copolymerizing 49 parts by mass of 2-ethylhexyl acrylate, 49 parts by mass of n-butyl acrylate, and 2 parts by mass of 4-hydroxybutyl acrylate. The molecular weight of the obtained (meth)acrylic acid ester copolymer (A) was measured by the method shown below, and the weight-average molecular weight (Mw) was 1.2 million.

[0154] The weight-average molecular weight (Mw) is the weight-average molecular weight on a polystyrene basis, measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement). (Measurement conditions) • GPC measuring device: Tosoh Corporation, HLC-8020 • GPC column (passes through in the following order): Manufactured by Tosoh Corporation TSK Guard Column HXL-H TSK gel GMHXL (x2) TSK gel G2000HXL • Measurement solvent: tetrahydrofuran ·Measurement temperature: 40℃

[0155] 2. Preparation of adhesive composition 100 parts by mass (solid content equivalent; the same applies hereinafter) of the (meth)acrylic acid ester copolymer (A) obtained above and 0.2 parts by mass of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, product name "Takenate D110N") as a crosslinking agent (B) were mixed and thoroughly stirred, and then diluted with methyl ethyl ketone to obtain a coating solution of adhesive composition A with a solid content concentration of 50% by mass.

[0156] 3. Preparation of release sheet As release sheets, two types were prepared: a heavily release sheet, in which one side of a PET film was treated with a silicone-based release agent, and a lightly release sheet, in which one side of a PET film was treated with a silicone-based release agent, as shown below. It has been confirmed that the release force of the heavily release sheet is greater than that of the lightly release sheet. Therefore, in this embodiment, the heavily release sheet is the first release sheet, and the lightly release sheet is the second release sheet. Heavy-duty release sheet 1: Lintec Corporation SP-PET501031 Heavy-duty release sheet 2: Lintec Corporation SP-PET382150 Lightly peelable release sheet 3: Lintec Corporation SP-PET381031 Lightly peelable release sheet 4: Lintec Corporation SP-PET25LT-H Lightly peelable release sheet 5: Lintec Corporation SP-PET381130

[0157] 4. Manufacturing of adhesive sheets The coating solution of the obtained adhesive composition was applied to the release surface of a heavy-peel type release sheet 1 (SP-PET501031) using a knife coater. The coating layer was then heated at 90°C for 1 minute to promote a crosslinking reaction, forming a coating layer consisting of an adhesive having a crosslinked structure composed of a (meth)acrylic acid ester copolymer (A) and a crosslinking agent (B).

[0158] Next, the coating layer on the heavy-peel release sheet 1 obtained above and the light-peel release sheet 4 (SP-PET25LT-H) were bonded together so that the release-treated surface of the light-peel release sheet 4 was in contact with the coating layer, and cured for 7 days under conditions of 23°C and 50% RH to produce an adhesive sheet having an adhesive layer with a thickness of 25 μm. This adhesive sheet had the following configuration: heavy-peel release sheet 1 / adhesive layer A (thickness: 25 μm) / light-peel release sheet 4. The thickness of the adhesive layer was measured in accordance with JIS K7130 using a constant-pressure thickness gauge (Teclock PG-02).

[0159] (Examples 2-4, Comparative Examples 1-3) Adhesive compositions B to D were obtained by changing the composition of the (meth)acrylic acid polymer (A), the amount of crosslinking agent (B), and the amounts of other components as shown in Table 1. As shown in Table 2, an adhesive sheet was manufactured in the same manner as in Example 1, except that the adhesive composition was selected from adhesive compositions A to D shown in Table 1, and the combination of the heavy-peel release sheet (first release sheet) and the light-peel release sheet (second release sheet) was as shown in Table 2. Comparative Example 2 is an adhesive sheet in which ultraviolet light was irradiated through the heavy-peel release sheet to the adhesive layer of the adhesive sheet. The ultraviolet irradiation conditions were as follows. <Ultraviolet irradiation conditions> • Use of high-pressure mercury lamps ·Illuminance 200mW / cm 2 ,Light intensity 1000mJ / cm 2 • The UV irradiance / light intensity meter used is the "UVPF-A1" manufactured by iGraphics Co., Ltd.

[0160] Furthermore, the UV resin used in adhesive composition D was Aronix® M-315, and the photopolymerization initiator used was JRCURE 500.

[0161] [Table 1]

[0162] Details of the abbreviations and other terms listed in Table 1 are as follows: ((meth)acrylic acid ester copolymer (A)) 2EHA: 2-ethylhexyl acrylate BA: n-butyl acrylate HEA: 2-hydroxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate AAc: Acrylic acid (Crosslinking agent (B)) XDI: Isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, product name "Takenate D110N")

[0163] (Storage modulus of adhesive G') Multiple adhesive layers from the adhesive sheets prepared in the examples and comparative examples were laminated to form a 3 mm thick laminate. From the resulting laminate of adhesive layers, a cylindrical object with a diameter of 8 mm (height 3 mm) was punched out and used as a sample for measuring the storage modulus.

[0164] For the samples used for measurement, the storage modulus (G') (MPa) was measured using the torsional shear method with a viscoelasticity analyzer (DYNAMICANALAYZER, manufactured by REOMETRIC) in accordance with JIS K7244-6, under the conditions of a measurement temperature of 23°C and a measurement frequency of 1 Hz. The results are shown in Table 1.

[0165] (Peeling force of release sheet) The peeling force of the first release sheet was measured as follows. The second release sheet was peeled off from the obtained adhesive sheet, and a laminate sample was prepared by heat laminating (70°C, 1 m / min) the good-adhesion side of a 25 μm thick good-adhesion PET (Toyobo Co., Ltd., PET25A-4100) onto the surface of the exposed adhesive layer. The obtained laminate sample was cut into 25 mm wide strips to prepare a sample for measurement. Next, the back surface of the good-adhesion PET of the measurement sample was fixed to a rigid support plate with double-sided tape, and a laminate consisting of the first release sheet / adhesive layer / good-adhesion PET / double-sided tape / rigid support was prepared.

[0166] For the laminate in question, the first release sheet was peeled off using a universal tensile testing machine (Shimadzu Corporation Autograph® AG-IS) at a measurement distance of 100 mm, a peeling angle of 180°, and peeling speeds of 0.3 m / min, 2.4 m / min, and 10 m / min, and the load at which it was peeled was measured. The average value of the load over 80 mm of the measurement distance, excluding the load at the first 10 mm and the load at the last 10 mm, was defined as the peeling force of the first release sheet at each peeling speed. The results are shown in Table 2.

[0167] The peeling force of the second release sheet was measured as follows. The obtained adhesive sheet was cut to a width of 25 mm to prepare a measurement sample. The side of the measurement sample opposite to the peeled surface of the first release sheet was fixed to a rigid support plate with double-sided tape to create a laminate consisting of the second release sheet / adhesive layer / first release sheet / double-sided tape / rigid support plate. Using a universal tensile testing machine (Shimadzu Corporation Autograph® AG-IS), the second release sheet was peeled off at a measurement distance of 100 mm, a peeling angle of 180°, and peeling speeds of 0.3 m / min and 10 m / min, and the load at which it was measured was measured. The average value of the load over 80 mm, excluding the load at the first 10 mm and the load at the last 10 mm of the measurement distance, was taken as the peeling force of the second release sheet at each peeling speed. The results are shown in Table 2.

[0168] Furthermore, the difference in peeling force (peeling force of the first release sheet - peeling force of the second release sheet) was calculated from the peeling force of the first release sheet and the peeling force of the second release sheet obtained. The results are shown in Table 2.

[0169] (Amount of Si transferred from the second release sheet) The adhesive layer surface of an acrylic adhesive tape (manufactured by Nitto Denko Corporation, product name: 31B Tape) was attached to the release-treated surface of the second release sheet and stored for 24 hours. Subsequently, the second release sheet was peeled off, and the silicon atom ratio (atom%) of the exposed adhesive layer surface was calculated using the following formula based on the amount of silicon atoms (Si), carbon atoms (C), and oxygen atoms (O) measured by X-ray photoelectron spectroscopy (XPS) (XPS count). The results are shown in Table 2. Silicon atom ratio (atom%) = [(amount of Si) / {(amount of C) + (amount of O) + (amount of Si)}] × 100

[0170] The measuring device used was the ESCA 5600 manufactured by PerkinElmer, and the measurement conditions were as follows. X-ray source: Mg standard (15kv,400W) Removal angle: 45° Measurement time: 3 minutes Measured elements: Silicon atoms (Si), carbon atoms (C), oxygen atoms (O)

[0171] (Presence or absence of Si on the second release sheet side surface of the adhesive layer) The second release sheet was peeled off from the adhesive sheets obtained from the examples and comparative examples. Then, the silicon atom ratio (atom%) of the exposed adhesive layer surface was calculated using the same method as described above for the Si migration amount of the second release sheet. The presence or absence of Si detection on the adhesive layer surface was determined based on the criteria: Si detection was detected if the silicon atom ratio was greater than 1 atom%, and Si detection was not detected if it was 1 atom or less. The results are shown in Table 2.

[0172] Next, the properties of the adhesive sheet were evaluated as follows.

[0173] (flexibility) Under conditions of 23°C and 50%RH, the light-peel release sheet (second release sheet) was peeled off from the adhesive sheets prepared in the examples and comparative examples, and the exposed adhesive layer was laminated to one side of a polyimide (PI) film (Toray DuPont, product name "Kapton 100PI", thickness: 25 μm, Young's modulus: 3.4 GPa). Next, the heavy-peel release sheet (first release sheet) was peeled off, and the exposed adhesive layer was laminated to one side of a triacetylcellulose (TAC) film (Konica Minolta, product name "KC4UYW", thickness: 40 μm). Then, the laminate was pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., and left for 24 hours under conditions of 23°C and 50%RH. The laminate obtained in this way, consisting of PI film / adhesive layer / TAC film, was cut to a width of 50 mm and a length of 200 mm, and this was used as a sample.

[0174] The obtained samples were repeatedly bent under the following conditions using a durability testing machine (Yuasa System Equipment Co., Ltd., product name "Surface Condition No-Load U-Shape Expansion Testing Machine Model: DLDMLH-FS"). After the test, the interface between the adhesive layer and the adherend at the bent portion was visually inspected for any lifting or peeling, and the repeated bending resistance was evaluated according to the following criteria. The results are shown in Table 2. <Test Conditions> Bending direction: Bending so that the triacetylcellulose film side faces the opposite direction. Minimum bending diameter: 3mmφ Number of flexions: 100,000 Bending speed: 60rpm <Evaluation Criteria for Repeated Flexibility> A... No lifting or peeling (fold angle less than 90°) B... No lifting or peeling (fold angle of 90° or more) F... peeling and lifting present

[0175] (The sad parting when peeling off the second release sheet) The obtained adhesive sheet was cut to a size of 5 x 10 cm to prepare a sample for measurement. Next, the side of the first release sheet in the measurement sample opposite to the release treatment surface was fixed to a rigid support plate with double-sided tape to create a laminate consisting of a second release sheet, an adhesive layer, a first release sheet, double-sided tape, and a rigid support plate.

[0176] For the laminate in question, the second release sheet was peeled from the adhesive layer using a universal tensile testing machine (Shimadzu Corporation Autograph® AG-IS) at a peeling angle of 180° and a peeling speed of 10 m / min. The peeled surface of the second release sheet was visually inspected after peeling, and it was evaluated whether separation had occurred according to the following criteria. The results are shown in Table 2. A... No crying goodbye B...Separation occurs only within 5mm of the longest edge. F...Tearful breakups are widespread.

[0177] (Dimensional change at the edge of the adhesive layer) A 2.5 × 10 cm sample was cut from the obtained adhesive sheet and used as the sample. The second release sheet was peeled off the cut sample and laminated to soda glass using a laminator. After lamination, a line was drawn on the back surface of the soda glass along the edge of the first release sheet using an oil-based marker pen. Nitto Denko Corporation adhesive tape "No. 31B" was applied to the edge of the first release sheet and peeled off at a peeling angle of 90° and a peeling speed of 2.4 m / min. After peeling, the amount of displacement between the center of the line indicating the edge of the first release sheet and the position of the adhesive edge was observed in three arbitrary regions (each 2.2 mm wide) using a digital microscope. The location with the largest amount of displacement within the observation field was measured, and the average value of the three measured points was calculated. The change in edge dimensions of the adhesive layer was evaluated using the calculated average value according to the following criteria. The results are shown in Table 2. A: 0 μm or more and less than 30 μm B: 30 μm or more and less than 70 μm C: 70 μm or more and less than 100 μm F: 100μm or more.

[0178] [Table 2] [Industrial applicability]

[0179] The adhesive sheet of the present invention can be suitably used, for example, for bonding flexible members. [Explanation of Symbols]

[0180] 1…Adhesive sheet 10…Adhesive layer 11…First release sheet 12…Second release sheet 2… Flexible component laminate 21...First flexible member 22...Second flexible member 3. Flexible devices 31…Cover film 32…First adhesive layer 33…Polarizing film 34…Second adhesive layer 35... Touch sensor film 36…Third adhesive layer 37…Organic EL elements 38…Fourth adhesive layer 39…TFT substrate

Claims

1. An adhesive sheet having an adhesive layer and a first release sheet and a second release sheet that sandwich both main surfaces of the adhesive layer, The storage modulus of the acrylic adhesive, which does not mainly consist of Si and constitutes the aforementioned adhesive layer, at 23°C is 0.2 MPa or less. Si is present on the second release sheet side surface of the adhesive layer. The second release sheet contains a silicone-based release agent. The amount of Si transferred from the adhesive layer to the second release sheet side surface is 5 to 30 atom%, The peeling force of the first release sheet when peeled from the adhesive layer at a peeling speed of 10 m / min is greater than the peeling force of the second release sheet when peeled from the adhesive layer at a peeling speed of 10 m / min by more than 24 mN / 25 mm. An adhesive sheet for flexible devices, wherein the peeling force of the first release sheet when peeled from the adhesive layer at a peeling speed of 2.4 m / min is 150 mN / 25 mm or less.

2. A flexible member laminate comprising a first flexible member, a second flexible member, and an adhesive layer for bonding the first flexible member and the second flexible member together, A flexible member laminate in which the adhesive layer is the adhesive of the adhesive sheet for flexible devices described in claim 1.

3. A flexible device comprising a laminate of flexible members as described in claim 2.

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