JP2024046697A - Adhesive sheets for flexible devices, flexible laminates and flexible devices - Google Patents

Abstract

[Problem] To provide an adhesive sheet which, even if it has a soft adhesive used for laminating flexible materials, suppresses tearing when a light release type release sheet is peeled off, and suppresses dimensional changes at the ends of the adhesive layer when a heavy release type release sheet is peeled off. [Solution] An adhesive sheet for flexible devices which has an adhesive layer and a first release sheet and a second release sheet which sandwich both main surfaces of the adhesive layer, wherein the storage modulus at 23°C of the adhesive constituting the adhesive layer is 0.2 MPa or less, the amount of Si at the surface of the adhesive layer is at least 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 to 100 atom %, and the peel force of the first release sheet when peeled off from the adhesive layer at a peel speed of 2.4 m/min is 150 mN/25 mm or less. [Selected Figure] Figure 1

Description

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

Display members having liquid crystal elements, light-emitting diode (LED) elements, organic electroluminescence (OLED) elements, etc. are laminated with other members (such as a protective panel for protecting the display member) to form a display for a device such as an electronic device.

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

In recent years, bendable displays, or so-called flexible displays, have been proposed as displays for electronic devices. Flexible displays are expected to have a wide range of applications, for example as stationary displays that are curved and installed on a cylindrical pillar, or as mobile displays that can be folded or rolled up for easy portability.

Examples of flexible display types include organic electroluminescence (OLED) displays, electrophoretic displays (electronic paper), and liquid crystal displays that use plastic films as substrates.

Examples of such flexible displays include displays that are bent during molding and maintained in a bent state, and displays that are repeatedly bent during use.

Patent Documents 1 and 2 disclose pressure-sensitive adhesive sheets in which the amount of volatile organic compounds contained in the pressure-sensitive adhesive sheets is reduced and which have good curved surface adhesion.

JP 2016-26241 A Patent Publication No. 5835837

However, the adhesive layer of the adhesive sheet used for flexible devices such as flexible displays may be required to have enough flexibility to follow the bending of the flexible member.

Adhesive sheets used in such flexible devices usually have a configuration in which release sheets are arranged on both main surfaces of the adhesive layer, and the release force of one release sheet (light release type release sheet) is The release force is designed to be smaller than that of the other release sheet (heavy release type release sheet).

When bonding one flexible member and the other flexible member using an adhesive sheet, first peel off the easy-release type release sheet of the adhesive sheet and bond the exposed adhesive layer to one flexible member. . Thereafter, the heavy release type release sheet is peeled off and the exposed adhesive layer is bonded to the other flexible member to form a laminate of flexible members.

At this time, 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 smaller. As a result, when the light-release release sheet is peeled off, the adhesive that should remain on the heavy-release release sheet unintentionally adheres to the light-release release sheet, which is a problem that occurs. Ta.

Furthermore, after the adhesive layer is attached to one flexible member, when the heavy release release sheet is peeled off to attach the adhesive to the other flexible member, the adhesive stretches and deforms due to the peeling of the heavy release release sheet. As a result, there is a problem in that the adhesive end changes in dimension and the position of the adhesive end shifts outward compared to the position when it was attached to one of the members.

If such a dimensional change occurs at the end of the adhesive, if the bonded flexible member is repeatedly bent, the elongation of the adhesive will further increase, and the dimensional change at the end will also increase accordingly. . As a result, the thickness of the adhesive layer becomes thinner than the expected thickness at the time of design, which causes distortions in the positional relationships of components in the device, which causes optical defects in the device. there were.

The present invention has been made in view of the above circumstances, and even if it has a flexible adhesive used for laminating flexible members, it is possible to suppress the tear separation during peeling of a light release type release sheet, An object of the present invention is to provide a pressure-sensitive adhesive sheet in which dimensional change at the end of the pressure-sensitive adhesive layer is suppressed when the release sheet is peeled off.

The aspects of the present invention are as follows.
[1] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, and a first release sheet and a second release sheet sandwiching both main surfaces of the pressure-sensitive adhesive layer,
The pressure-sensitive adhesive layer has a storage modulus of 0.2 MPa or less at 23°C,
the amount of Si at the surface of the pressure-sensitive adhesive layer is at least twice the amount of Si near the center of the pressure-sensitive adhesive layer;
the second release sheet contains a silicone-based release agent;
the amount of Si transferred to the surface of the pressure-sensitive adhesive layer of the second release sheet is 5 to 100 atom %,
This is a pressure-sensitive adhesive sheet for flexible devices, in which the peel strength of the first release sheet when peeled from the pressure-sensitive adhesive layer at a peel 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 to each other,
The adhesive layer is a flexible member laminate that is an adhesive included in the adhesive sheet for flexible devices according to [1].

[3] A flexible device comprising the flexible material laminate described in [2].

According to the present invention, even if a flexible adhesive used for laminating flexible members is used, separation during peeling of a light release type release sheet is suppressed, and adhesiveness during peeling of a heavy release type release sheet is suppressed. It is possible to provide a pressure-sensitive adhesive sheet for flexible devices in which dimensional changes at the edges of the agent layer are suppressed.

FIG. 1 is a sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. FIG. 2 is a sectional view of a flexible member laminate according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a flexible device according to an embodiment of the present invention.

The present invention will be described in detail below based on specific embodiments.

(1. Adhesive sheets for flexible devices)
The adhesive sheet 1 for flexible devices according to the present embodiment has an adhesive layer 10, a first release sheet 11, and a second release sheet 12, as shown in FIG. 1. The adhesive constituting the adhesive layer 10 will be described later. In addition, 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 contact both main surfaces of the adhesive layer, and are peelable from the adhesive layer. In other words, the adhesive layer 10 is sandwiched between two release sheets (first release sheet 11 and second release sheet 12) so as to be peelable. In this specification, the release surface of the release sheet refers to a surface of the release sheet that has peelability, and includes both a surface that has been subjected to a release treatment and a surface that exhibits peelability even without being subjected to a release treatment. The release sheet will be described later.

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 bendable members (flexible members).

A flexible member is a member that maintains its functionality even when it is bent, such as folded. Examples of flexible members include members that are molded to bend during the manufacture of a device that includes the flexible member and that maintain a bent state, and members that are repeatedly bent during the use of a device that includes the flexible member. Therefore, the adhesive that bonds such flexible members together must also have the flexibility to follow the bending.

In order to protect the adhesive until it is used, in this embodiment, as shown in FIG. 1, an adhesive sheet is used in which two release sheets are arranged on both main surfaces of the adhesive. The two release sheets usually have different peel strengths from the adhesive, and are composed of a release sheet with a relatively small peel strength from the adhesive (light release type release sheet) and a release sheet with a relatively large peel strength from the adhesive (heavy release type release sheet). By providing a difference in peel strength between the release sheets in this way, it is possible to prevent the adhesive that should remain on the heavy release type release sheet from unintentionally adhering to the light release type release sheet when the light release type release sheet is peeled off, a phenomenon known as tearful separation.

On the other hand, the adhesive used to bond flexible members together has flexibility to accommodate bending, and is easily deformed when force is applied. Therefore, as the release sheet, a release sheet that is easy to peel off (relatively low peeling force from the adhesive) is used.

However, when a release sheet that is easy to peel is used, the difference in peeling force between the two release sheets tends to be small. As a result, there has been a problem in that tear separation tends to occur when the easy-release type release sheet is peeled off.

Furthermore, after peeling off the light release type release sheet and laminating one member and the adhesive, when peeling off the heavy release type release sheet and laminating the other member and the adhesive, the heavy peeling Due to the peeling of the mold release sheet, the adhesive stretches and becomes deformed. As a result, there is a problem in that the end of the adhesive undergoes a dimensional change, and the position of the end of the adhesive shifts outward compared to the position when bonded to one member.

When such a dimensional change occurs at the end of the adhesive, unintended adhesion to other members is likely to occur, and when adhesion occurs, the elongation of the adhesive becomes even greater and the dimensional change becomes even larger. As a result, the bonding accuracy between the members is reduced, and the yield is reduced.

In particular, if a dimensional change occurs at the end of the adhesive when flexible members are laminated, then if the laminated flexible member is repeatedly bent, the elongation of the adhesive will further increase, and the dimensional change at the end will also occur. It gets even bigger. As a result, the thickness of the adhesive layer becomes thinner than the expected thickness at the time of design, distortion or the like occurs in the positional relationship of the members in the device, and optical defects due to this occur in the device. Therefore, in order to improve the optical reliability of the device, it is necessary to suppress the dimensional change of the adhesive end before and after peeling off the heavy release type release sheet.

In order to deal with the above problem, in the adhesive sheet according to this embodiment, the physical properties of the release sheet and the adhesive layer are controlled. Below, the constituent elements of the adhesive sheet according to this embodiment will be explained in detail.

(1.1. Pressure-sensitive adhesive layer)
The adhesive layer bonds the first member and the second member together. In this embodiment, the adhesive layer preferably bonds the first flexible member and the second flexible member together.

The adhesive layer may be composed of one layer (single layer) or may be composed of two or more layers. When the adhesive layer has multiple layers, these multiple layers may be the same or different, and there are no particular limitations on the combination of layers that make up these multiple layers.

In this embodiment, the adhesive layer has the following physical properties, which allows the first flexible member and the second flexible member to be sufficiently bonded together and effectively prevents peeling or other problems from occurring when the member is bent after bonding.

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 especially 20 to 180 μm. Preferably, it is 40 μm. This makes it easier to adjust the above-mentioned peeling force and the difference in the peeling force described below to a desired value. Moreover, it has adhesiveness that allows the first flexible member and the second flexible member to be bonded together well, and furthermore, it has excellent flexibility.

(1.2. Adhesive)
In this embodiment, the adhesive layer 10 is made of an adhesive described below.

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

(1.3.1. Storage Modulus)
In this embodiment, the storage modulus (G') of the adhesive at 23°C and a frequency of 1 Hz is preferably 0.2 MPa or less. The storage modulus is one of the indicators of the ease of deformation (hardness) of the adhesive layer. By setting the storage modulus of the adhesive at 23°C within the above range, even if the adhesive layer is repeatedly bent, it can sufficiently follow the bending, and lifting or peeling from the member to which it is attached is suppressed.

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 even more preferably 0.06 MPa or less. On the other hand, from the viewpoint of dimensional stability, processability, and prevention of tearful separation, 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 even more preferably 0.04 MPa or more. 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 and glass transition temperature of the monomer composition used, etc.), molecular weight of the material constituting the adhesive, etc.

The storage modulus (G') may be measured by a known method. For example, the adhesive layer is treated as a sample of a given size, and a dynamic viscoelasticity measuring device is used to apply strain to the sample at a given frequency within a given temperature range to measure the modulus. From the measured modulus, the storage modulus under the above conditions can be calculated.

(1.3.2. Amount of Si in the surface of the pressure-sensitive adhesive layer facing the second release sheet)
In this embodiment, it is preferable that Si exists on the surface of the pressure-sensitive adhesive layer on the side of the second release sheet. This can reduce the peeling force of the second release sheet (light release type release sheet). As a result, the peeling force difference between the heavy release type release sheet and the light release type release sheet becomes large, and the tearing when the light release type release sheet is peeled off can be suppressed.

The second release sheet side surface of the adhesive layer refers to the main surface on which the second release sheet is disposed, of the two main surfaces of the adhesive layer in the adhesive sheet. In FIG. 1, the second release sheet side surface is the main surface 10b.

The Si present on the surface of the adhesive layer facing the second release sheet may be Si originating from the adhesive layer, or Si migrated from the release sheet. In this embodiment, the Si present on the surface facing the second release sheet is preferably Si migrated from the release sheet. Whether the Si present on the surface facing the second release sheet 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 at least twice the amount of Si near the center of the adhesive layer, it can be determined that it is Si migrated from the release sheet.

The amount of Si on the surface of the adhesive layer facing the second release sheet can be measured, for example, as follows. The surface of the adhesive layer exposed by peeling the second release sheet from the adhesive sheet is subjected to surface analysis using X-ray photoelectron spectroscopy (XPS), and the amount of Si is determined by calculating the ratio of Si from the obtained spectrum. Specific measurement methods are described in detail in the examples below.

(1.3.3. Dimensional change at the end of the adhesive layer)
The lower limit of the dimensional change at the end of the adhesive layer of the adhesive sheet according to the present embodiment is usually 0 μm or more, and the upper limit is preferably less than 100 μm, more preferably less than 70 μm, and less than 30 μm. It is preferable that there be. This indicates that the pressure-sensitive adhesive sheet has suppressed dimensional changes at the end portions of the pressure-sensitive adhesive layer. Having such characteristics suppresses further changes in end dimensions when the bonded flexible member is repeatedly bent, thereby reducing the thickness of the adhesive layer from the expected thickness at the time of design. As a result, the problem that distortion or the like occurs in the positional relationship of members in the device and optical defects due to this occur in the device is less likely to occur. A specific evaluation method will be explained in detail in Examples described later.

(1.4. Composition of Adhesive)
The adhesive composition is not particularly limited as long as it has the above-mentioned physical properties. For example, it may be any of acrylic adhesives, polyester adhesives, polyurethane adhesives, rubber adhesives, silicone adhesives, etc. In addition, the adhesive may be any of emulsion type, solvent type, and solventless type. Furthermore, the adhesive may have a crosslinked structure or may not have a crosslinked structure.

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

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 is likely to provide good adhesive strength. 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."

(1.4.1. (meth)acrylic acid ester polymer)
The (meth)acrylic acid ester polymer (A) includes (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. It is preferable to contain the following.

By including a (meth)acrylic acid alkyl ester, the resulting adhesive can exhibit desirable adhesiveness. As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms is preferred. The alkyl group may be linear or branched, or may have a cyclic structure.

Examples of (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and n-(meth)acrylate. Butyl, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, (meth)acrylic acid Examples include n-dodecyl, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

Among these, from the viewpoint of physical properties related to the storage modulus G' at 23°C, (meth)acrylic acid esters having an alkyl group with 1 to 8 carbon atoms are preferred, and (meth)acrylic acid esters having an alkyl group with 4 to 8 carbon atoms are particularly preferred. 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 alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) contains 50 to 99.9% by mass of (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms as a monomer unit constituting the polymer. The content is preferably 70 to 99.5% by mass, more preferably 90 to 99% by mass, and particularly preferably 94 to 98.5% by mass. Thereby, it is possible to impart suitable adhesiveness to the (meth)acrylic acid ester polymer (A), and the storage modulus G' of the resulting adhesive can be easily adjusted to a lower value. Furthermore, desired amounts of other monomer components can be introduced into the (meth)acrylic acid ester polymer (A), making it easier to design an adhesive that exhibits desired performance.

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

Preferred examples of reactive functional group-containing monomers 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 alone or in combination of two or more.

Among the above-mentioned reactive functional group-containing monomers, hydroxyl group-containing monomers or carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are particularly preferred. By containing the hydroxyl group-containing monomer, in addition to making it easier to satisfy the physical properties regarding the storage elastic modulus G' described above, it also becomes easier to finely adjust the storage elastic modulus G'.

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

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

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

The (meth)acrylic acid ester polymer (A) preferably contains 0.1 to 10% by mass, and 0.5 to 7% by mass of a reactive functional group-containing monomer as a monomer unit constituting the polymer. It is more preferable to contain it, and even more preferably to contain it in an amount of 1 to 5% by mass.

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, and the physical properties related to the storage modulus G' mentioned above are achieved. It becomes easier to satisfy the desired peeling force and peeling force difference.

It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. Since a carboxyl group is an acid component, by not containing a carboxyl group-containing monomer, even if the object to which the pressure-sensitive adhesive is applied contains an object that may be damaged by acid, such as a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, or a metal mesh, the damage caused by the acid (corrosion, change in resistance, etc.) can be suppressed.

Here, "free of carboxyl group-containing monomers" means that the polymer does not substantially contain carboxyl group-containing monomers, and in addition to not containing any carboxyl group-containing monomers at all, it is acceptable to contain carboxyl group-containing monomers to the extent that the carboxyl group does not cause corrosion of the transparent conductive film, metal wiring, etc. Specifically, it is acceptable to contain carboxyl group-containing monomers as monomer units in the (meth)acrylic acid ester polymer (A) 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.

In this embodiment, the (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. As the other monomers, monomers that do not contain reactive functional groups are preferred so as not to inhibit the above-mentioned action of the reactive functional group-containing monomer. Examples of such monomers include non-reactive nitrogen atom-containing monomers such as N-acryloylmorpholine and N-vinyl-2-pyrrolidone, (meth)acrylic acid alkoxyalkyl esters 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 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 for the resulting adhesive to satisfy the physical properties related to the storage modulus G' described above, as well as the desired peel strength and peel strength difference. The weight average molecular weight in this specification is a value calculated in terms of standard polystyrene as measured by gel permeation chromatography (GPC).

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

(1.4.2. Crosslinking agent)
The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) by heating the adhesive composition P containing the crosslinking agent (B), thereby forming a crosslinked structure (three-dimensional network structure). ) to form. As a result, the cohesive force of the resulting pressure-sensitive adhesive is improved, and the above-mentioned physical properties regarding the storage modulus G' and the desired peeling force and peeling force difference are more likely to be satisfied.

The crosslinking agent (B) may be any that reacts with the reactive group of the (meth)acrylic acid ester polymer (A). Examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. Among these, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with the reactive functional group-containing monomer. The crosslinking agent (B) may be used alone or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. and their biuret forms, isocyanurate forms, and adduct forms which are reactants with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil.

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, relative to 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' described above, as well as the desired peel force and peel force difference.

(1.4.3. Other additives)
The adhesive composition P may contain additives commonly used in acrylic adhesives, if necessary. Examples of such additives include silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, rust preventives, fillers, and refractive index modifiers. be done. Note that the polymerization solvent and dilution solvent described below are not included in the additives constituting the adhesive composition P.

In this embodiment, the adhesive composition P preferably contains a silane coupling agent. This improves the adhesion of the resulting adhesive layer to the flexible member to be adhered, making the adhesive strength more favorable and providing excellent flexibility.

The silane coupling agent is preferably an organosilicon compound having at least one alkoxysilyl group in the molecule. In addition, the silane coupling agent is preferably one that has good compatibility with the (meth)acrylic acid ester polymer (A) and has optical transparency.

Examples of such silane coupling agents include silicon compounds containing polymerizable unsaturated groups such as vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltrimethoxysilane. Silicon compounds with epoxy structures such as sidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyl Mercapto group-containing silicon compounds such as dimethoxymethylsilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl An amino group-containing silicon compound such as dimethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, or at least one of these, and methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane. Examples include condensates with alkyl group-containing silicon compounds such as methoxysilane. These may be used alone or in combination of two or more.

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

(1.5. Release sheet)
In this embodiment, the adhesive sheet has at least two release sheets. As described above, the two release sheets are provided with a difference in release force, and one release sheet is a light release type release sheet and the other release sheet is a heavy release type release sheet. In the adhesive sheet 1 shown in FIG. 1, the first release sheet 11 is a heavy release type release sheet, and the second release sheet 12 is a light release type release sheet. 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.

(1.5.1 First release sheet)
The first release sheet may be composed of a base material of one layer (single layer) or two or more layers, and the surface of the base material may be subjected to a release treatment from the viewpoint of controlling releasability. That is, the surface of the base material may be modified, or a material not derived from the base material (for example, a release agent layer) may be formed on the surface of the base material.

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

(1.5.3. Peeling force from adhesive layer)
In this embodiment, it is preferable that the peeling force when peeling the first release sheet from the adhesive layer at a peeling speed of 2.4 m/min is 150 mN/25 mm or less. This peeling force is determined by peeling off the light release type release sheet from the adhesive sheet, laminating the adhesive layer to the first member, and then peeling off the heavy release type release sheet in order to laminate it to the second member. This corresponds to the peeling force when When the above-mentioned peeling force is within the above-mentioned range, deformation (elongation) of the pressure-sensitive adhesive is unlikely to occur when the heavy release type release sheet is peeled from the pressure-sensitive adhesive layer. As a result, dimensional changes at the ends of the adhesive layer can be suppressed.

The above peel strength 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. The lower limit of the peel strength is not particularly limited as long as it is greater than the peel strength of the light release type release sheet (second release sheet). In this embodiment, from the viewpoint of making it easier to meet the peel strength difference described later and from the viewpoint of separation and storage stability in roll form, the lower limit of the peel strength 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.

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

The peeling force when peeling the first release sheet from the adhesive layer when the peeling speed is 10 m/min is preferably 600 mN/25 mm or less, more preferably 400 mN/25 mm or less, and 300 mN/25 mm. It is more preferably at most 260 mN/25 mm, particularly preferably at most 220 mN/25 mm, particularly preferably at most 220 mN/25 mm. By having the above peeling force within the above range, deformation (elongation) of the adhesive is less likely to occur when the heavy release type release sheet is peeled from the adhesive layer, and dimensional changes at the edges of the adhesive layer are suppressed. can do. Further, the lower limit of the above peeling force is not particularly limited as long as it is greater than the peeling force of the easy-release type release sheet (second release sheet). In this embodiment, the lower limit of the above peeling force is preferably 30 mN/25 mm or more, and 80 mN/25 mm, from the viewpoint of easily satisfying the peel force difference described below and from the viewpoint of storage stability in the roll form. It is more preferably at least 110 mN/25 mm, even more preferably at least 140 mN/25 mm, and particularly preferably at least 140 mN/25 mm.

When the peeling speed is 0.3 m/min, the peeling force when the first release sheet is peeled 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 especially preferably 45 mN/25 mm or less. When the peeling force is within the above range, the adhesive is less likely to deform (stretch) when the heavy release type release sheet is peeled from the adhesive layer, and dimensional changes at the end of the adhesive layer can be suppressed. In addition, the lower limit of the peeling force is not particularly limited as long as it is greater than the peeling force of the light release type release sheet (second release sheet). In this embodiment, from the viewpoint of making it easier to meet the peeling force difference described later and from the viewpoint of separation and storage stability in a roll form, the lower limit of the 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.

From the viewpoint of adjusting the release 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 release 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 even more preferably greater than the thickness of the second release sheet.

Note that the thickness of the first release sheet means the thickness of the entire first release sheet. For example, the thickness of the first release sheet composed of multiple layers means the total thickness of all the layers constituting the first release sheet.

In this embodiment, the first release sheet preferably includes a base material from the viewpoint of easily controlling the peel force within the above range, and more preferably, the surface of the base material is subjected to a release treatment. More preferably, the structure includes a base material and a release agent layer. By having the release agent layer, it is easy to impart good releasability to the surface (release surface) on which the release agent layer is formed in the first release sheet.

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

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, fluorine A resin film or the like is used. These crosslinked films can also be used. Furthermore, a laminated film of these may be used. In this embodiment, a polyethylene terephthalate film is preferred from the viewpoint of environmental safety, cost, etc., as well as from the viewpoint of suppressing the tightening caused by stretching of the base material.

The base material may contain various additives such as a colorant, a flame retardant, a plasticizer, an antistatic agent, a lubricant, and a filler in the resin film.

The thickness of the substrate is not particularly limited within the range of the thickness of the first release sheet described above, so long as it is thick enough to support the adhesive layer. From the viewpoint of adjusting the release 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.

(1.5.5. First release agent layer)
When the first release sheet has a base material and a release agent layer, the release agent layer of the first release sheet (herein sometimes referred to as "first release agent layer") is adhesive to the first release sheet. Provides releasability from the agent layer. The first release agent layer is not particularly limited as long as it is made of a material that can impart release properties, but in the present embodiment, the first release agent layer is formed by curing the composition for the first release agent layer described below. It is preferable that the layer obtained by

The thickness of the first release agent layer is not particularly limited as long as it can exhibit desired release properties, but 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, particularly preferably 50 to 200 nm.

(1.5.6. Composition for first release agent layer)
The composition for the first release agent layer may contain, for example, an alkyd-based release agent, a silicone-based release agent, a fluorine-based release agent, an unsaturated polyester-based release agent, a polyolefin-based release agent, or a wax-based release agent. In this embodiment, from the viewpoint of adjusting the release force of the first release sheet and the release force difference described below within the above ranges, the composition for the first release agent layer preferably contains a silicone-based release agent, and more preferably contains a silicone-based release agent and a heavy release additive.

(1.5.7. Silicone-based release agents)
As the silicone-based release agent, it is preferable to use a silicone-based release agent containing a silicone having a dimethylpolysiloxane skeleton, which makes it possible to adjust the release force of the first release sheet within the above range.

The content of silicone made of dimethylpolysiloxane is preferably less than 100 parts by mass, and 90 parts by mass when the total weight of the composition for the first release agent layer (excluding the catalyst described below) is 100 parts by mass. It is more preferably less than 80 parts by mass, even more preferably less than 70 parts by mass. Note that the lower limit of the content is 0 parts by mass. This makes it easy to adjust the peeling force of the first release sheet within the above range.

The silicone may be any of addition reaction type, condensation reaction type, and energy ray curing type such as ultraviolet curing type and electron beam curing type, but addition reaction type silicone is preferable. Addition reaction type silicone has high reactivity and excellent productivity, and compared to condensation reaction type, it has the advantage that the release force after production is easily stable and there is no cure shrinkage, so that it is easy to adjust the release force of the first release sheet within the above range.

Specific examples of addition reaction type silicones include organopolysiloxanes that have two or more alkenyl groups with 2 to 10 carbon atoms, such as vinyl groups, allyl groups, propenyl groups, and hexenyl groups, at the ends and/or side chains of the molecule.

When using such an addition reaction type silicone, it is preferable to use a crosslinking agent and a catalyst together.

Examples of crosslinking agents include organopolysiloxanes having at least two hydrogen atoms bonded to silicon atoms in one molecule. Specific examples include dimethylhydrogensiloxane-methylhydrogensiloxane copolymers endblocked with dimethylhydrogensiloxane and trimethylsiloxy group, methylhydrogenpolysiloxane endblocked with trimethylsiloxy group, and poly(hydrogensilsesquioxane).

Examples of catalysts include fine particulate platinum, fine particulate platinum adsorbed on a carbon powder carrier, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, palladium, and platinum group metal compounds such as rhodium. Can be mentioned.

By using such a catalyst, the curing reaction of the composition for the first release agent layer can proceed more efficiently.

When the total weight of the composition for the first release agent layer (excluding the catalyst) is taken as 100 parts by mass, the content of the silicone-based release agent 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 above-mentioned range.

(1.5.8. Heavy release additive)
Examples of heavy release additives include silicone resins and organosilanes such as silane coupling agents. Among these, it is preferable to use silicone resins. Thereby, the peeling force of the first release sheet can be adjusted within the above range, and the peeling force of the first release sheet from the adhesive layer can be made larger than the peeling force of the second release sheet. can.

As the silicone resin, it is preferable to use, for example, an MQ resin containing an M unit that is a monofunctional siloxane unit [R ₃ SiO _1/2 ] and a Q unit that is a tetrafunctional siloxane unit [SiO _4/2 ]. Note that the three R's 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, one or more of the three R's in the M unit is preferably a hydroxyl group or a vinyl group, more preferably a vinyl group.

(1.6. Second release sheet)
Similar to the first release sheet, the second release sheet may be composed of one layer (single layer) or two or more layers of base material, and from the viewpoint of controlling releasability, the surface of the base material may be subjected to release treatment. may have been done. That is, the surface of the base material may be modified, or a material not derived from the base material (for example, a release agent layer) may be formed on the surface of the base material.

As long as the peeling force of the second release sheet (light release type release sheet) is smaller than the peeling force of the first release sheet (heavy release type release sheet), the physical properties of the second release sheet are not particularly limited. Then, the second release sheet (light release type release sheet) preferably has the following physical properties.

(1.6.1. Peeling force from adhesive layer)
In this embodiment, the peeling force when peeling the second release sheet 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, and 200 mN/min. It is more preferably 25 mm or less, particularly preferably 160 mN/25 mm or less, and especially preferably 145 mN/25 mm or less. This peeling force corresponds to the peeling force used when peeling a light-release type release sheet from a pressure-sensitive adhesive sheet in order to bond the pressure-sensitive adhesive layer to a member. When the above-mentioned peeling force is within the above-mentioned range, it is possible to suppress separation when the light-release type release sheet is peeled off. In this embodiment, the lower limit of the above peeling force is preferably 20 mN/25 mm or more, and 40 mN/25 mm or more, from the viewpoint of easily satisfying the peel force difference described later and from the viewpoint of storage stability in roll form. It is more preferable that it be at least 60 mN/25 mm, even more preferably that it is at least 80 mN/25 mm.

The peeling force when peeling the second release sheet 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, and 40 mN/25 mm or less. It is more preferable that it is, and particularly preferably that it is 30 mN/25 mm or less, and especially preferably that it is 28 mN/25 mm or less. This peeling force also corresponds to the peeling force when peeling the easy-release type release sheet from the pressure-sensitive adhesive sheet in order to bond the pressure-sensitive adhesive layer to a member. When the above-mentioned peeling force is within the above-mentioned range, it is possible to suppress separation when the light-release type release sheet is peeled off. In this embodiment, the lower limit of the above peeling force is preferably 3 mN/25 mm or more, and 8 mN/25 mm or more, from the viewpoint of easily satisfying the peel force difference described below and from the viewpoint of storage stability in roll form. It is more preferably at least 12 mN/25 mm, even more preferably at least 15 mN/25 mm.

In this embodiment, from the viewpoint of preventing tearing when the light release type release sheet is peeled off, it is preferable that the peel force of the first release sheet is greater than the peel force of the second release sheet, that is, there is a peel force difference. In this specification, the presence of a peel force difference means that there is a peel force difference of more than 1 mN/25 mm.

The difference in peeling force between the peeling force when peeling the second release sheet from the adhesive layer at a peeling speed of 10 m/min and the peeling force when peeling the first release sheet from the adhesive layer at a peeling speed of 10 m/min is , preferably more than 24 mN/25 mm. Thereby, it is possible to suppress separation when the easy-peel release sheet is peeled off. From the viewpoint of more effectively preventing separation and achieving both flexibility and dimensional stability, it is preferably 25 to 300 mN/25 mm, more preferably 30 to 200 mN/25 mm, and 50 to 150 mN/25 mm. It is more preferably 25 mm, particularly preferably 60 to 100 mN/25 mm, and especially preferably 64 to 80 mN/25 mm.

The peel force difference between the peel force when the second release sheet is peeled from the adhesive layer at a peel speed of 0.3 m/min and the peel force when the first release sheet is peeled from the adhesive layer at a peel 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 makes it possible to suppress tearing when peeling off the light release type release sheet. Furthermore, from the viewpoint of preventing tearing and achieving both flexibility, the peel force difference is preferably 3.5 to 19 mN/25 mm, and most preferably 4 to 18 mN/25 mm.

The thickness of the second release sheet is preferably 10 to 100 μm, more preferably 15 to 75 μm, and 20 to 60 μm from the viewpoint of adjusting the peel force and peel force difference within the above range. is more preferable, and particularly preferably 24 to 40 μm. Further, the thickness of the second release sheet is preferably equal to or less than the thickness of the first release sheet, from the viewpoint of making the peel force of the first release sheet larger than the peel force of the second release sheet. More preferably, the thickness is less than the thickness.

Note that the thickness of the second release sheet means the thickness of the entire second release sheet. For example, the thickness of the second release sheet composed of multiple layers means the total thickness of all the layers that constitute the second release sheet.

In this embodiment, from the viewpoint of setting the release force within the above range, the second release sheet preferably includes a substrate, more preferably has a surface that is release-treated, and preferably has a substrate and a release agent layer. By having a release agent layer, it is easy to impart good releasability to the surface of the second release sheet on which the release agent layer is formed (release surface).

(1.6.2. Substrate)
The substrate of the second release sheet can be appropriately selected from the materials exemplified as the substrate of the first release sheet.

(1.6.3. Second release agent layer)
When the second release sheet has a base material and a release agent layer, the release agent layer of the second release sheet (herein sometimes referred to as "second release agent layer") is adhesive to the second release sheet. Provides releasability from the agent layer. In this embodiment, it is preferable to include Si in order to transfer Si to the surface of the pressure-sensitive adhesive layer and keep the amount of Si on the surface within the range described below. Such a release agent layer is preferably a layer obtained by curing a composition for a second release agent layer containing a silicone mold release agent, for example.

(1.6.4. Composition for second release agent layer)
The composition for the second release agent layer can be selected from the materials exemplified for the composition for the first release agent layer, so long as the relationship that the release strength of the first release sheet is greater than that of the second release sheet is satisfied. However, it is preferable that the material exemplified as the heavy release additive is contained in an amount less than that in the composition for the first release agent layer, or is not contained at all.

When a second release agent layer is formed on the substrate of the second release sheet using a coating agent containing a composition for the second release agent layer having a silicone-based release agent, and the second release agent layer is bonded to the adhesive layer, a phenomenon (transfer phenomenon) may occur in which the silicone-based release agent contained in the second release agent layer migrates to the adhesive layer. In this embodiment, this transfer phenomenon is actively utilized to cause a predetermined amount of Si to be present on the surface of the adhesive layer, thereby improving the releasability of the surface of the adhesive layer. As a result, the release force of the second release sheet (light release type release sheet) from the adhesive layer can be easily adjusted to within the above range, and even if the release force of the first release sheet (heavy release type release sheet) from the adhesive layer is within the above range, the difference in release force between the first release sheet and the second release sheet can be increased.

(1.6.5. Amount of Si on the surface of the pressure-sensitive adhesive layer of the second release sheet)
In the present embodiment, the second release sheet is preferably capable of transferring Si to the surface of the adhesive layer when it is attached to the adhesive layer. The amount of Si transferred to the surface of the adhesive layer of the second release sheet can be, for example, an alternative index, obtained by attaching the second release sheet to the surface of an adhesive layer not mainly composed of Si, leaving it for 24 hours, and then performing surface analysis by X-ray photoelectron spectroscopy (XPS) on the surface of the adhesive layer exposed by peeling off the second release sheet, and calculating the ratio of Si from the obtained spectrum. The amount of Si thus obtained is preferably 5 to 100 atom%, more preferably 7 to 60 atom%, and even more preferably 9 to 30 atom%. By the amount of Si being within the above range, the release force of the second release sheet (light release type release sheet) can be sufficiently reduced, and can be adjusted to within the above-mentioned range of release force. As a result, the difference in release force between the heavy release type release sheet and the light release type release sheet becomes large, and tearful separation during peeling of the light release type release sheet can be suppressed. The specific method for measuring the amount of Si will be described in detail in the examples below.

(1.7. Manufacture of adhesive composition)
Adhesive composition P is produced by, for example, first producing a (meth)acrylic ester polymer (A), and mixing the obtained (meth)acrylic ester polymer (A) with a crosslinking agent (B). It can be manufactured by Additives may be added if necessary.

The (meth)acrylic acid ester polymer (A) can be produced, for example, by polymerizing a mixture of monomers constituting the polymer by a normal radical polymerization method. The (meth)acrylic acid ester polymer (A) can be polymerized by a solution polymerization method using a polymerization initiator if necessary. By polymerizing the (meth)acrylic acid ester polymer (A) using a solution polymerization method, it becomes easy to increase the molecular weight of the obtained polymer and adjust the molecular weight distribution, and further reduces the production of low molecular weight substances. It becomes possible to do so. As a result, it is easy to obtain an adhesive that is excellent in repeated bending.

Examples of the polymerization solvent used in the solution polymerization method 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.

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), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].

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 peroxypivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide.

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

Subsequently, a crosslinking agent (B) and a diluting solvent are added to the obtained solution of the (meth)acrylic acid ester polymer (A) and mixed sufficiently to form an adhesive composition P diluted with the solvent. (Coating solution) is obtained. Additives may be added as necessary.

If any of the above components is a solid component, or if it is a component that will precipitate when mixed with other components in an undiluted state, that component may be dissolved or diluted in a dilution solvent before being mixed with the other components.

Examples of dilution 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-based solvents such as ethyl cellosolve.

The concentration and viscosity of the prepared coating solution may be within the range that allows coating, and may be appropriately selected depending on the situation. For example, the adhesive composition P is diluted so that the concentration is 10 to 60% by mass. Note that the addition of a dilution solvent or the like is not a necessary condition for obtaining the coating solution, and if the adhesive composition P has a viscosity that allows coating, it is not necessary to add a dilution solvent. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent for the (meth)acrylic acid ester polymer (A) itself serves as the dilution solvent.

(1.8. Production of Adhesive)
The adhesive constituting the adhesive layer is preferably obtained by crosslinking the above-mentioned adhesive composition P. The crosslinking of the adhesive composition P can usually be carried out by a heat treatment. This heat treatment can also serve as a drying treatment for volatilizing a diluting solvent and the like from a coating film of the adhesive composition P applied to a desired object.

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.

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

(1.9. Manufacture of adhesive sheet)
The method for manufacturing the adhesive sheet 1 is not particularly limited, and any known method may be used. For example, a coating liquid of the adhesive composition P described above is applied to the release surface of one of the first release sheets 11 (or the second release sheet 12), and heat treatment is performed to crosslink the adhesive composition P. to form a coating layer having a predetermined thickness. The release surface of the other second release sheet 12 (or first release sheet 11) is placed on the formed coating layer. If curing is required, the coating layer becomes the adhesive layer 10 after a predetermined curing period. Further, when curing is not necessary, the coating layer becomes the adhesive layer 10 as it is. Thereby, the adhesive sheet 1 is obtained.

As another method for producing the adhesive sheet 1, the above-mentioned coating liquid of the adhesive composition P is applied to the release surface of the first release sheet 11, and the adhesive composition P is crosslinked by heat treatment to form a coating layer, thereby obtaining the first release sheet 11 with the coating layer. The above-mentioned coating liquid of the adhesive composition P is applied to the release surface of the other second release sheet 12, and the adhesive composition P is crosslinked by heat treatment to form a coating layer, thereby obtaining the second release sheet 12 with the coating layer. Then, the first release sheet 11 with the coating layer and the second release sheet 12 with the coating layer are bonded together so that both coating layers are in contact with each other. If curing is required, the coating layer becomes the adhesive layer 10 after a predetermined curing period. If curing is not required, the coating layer becomes the adhesive layer 10 as it is. In this way, the adhesive sheet 1 is obtained. According to this manufacturing method, it is possible to stably manufacture the adhesive layer 10 even if the adhesive layer 10 is thick.

Examples of methods for applying the coating liquid of the adhesive composition P include a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, and the like.

2. Flexible Material Laminate
As shown in Figure 2, the flexible material laminate 2 of this embodiment is composed of a first flexible member 21 (one flexible member), a second flexible member 22 (another flexible member), and an adhesive layer 10 located between them and bonding the first flexible member 21 and the second flexible member 22 to each other.

The adhesive layer 10 in the flexible material laminate 2 is the adhesive layer 10 of the adhesive sheet 1 described above.

The flexible material laminate 2 is a flexible device itself, or a material that constitutes part of a flexible device. The flexible device may be a device that includes a material that has been bent once during manufacture and that maintains the bent state, or a device that includes a material that can be repeatedly bent (including folded). In addition, the flexible device is preferably a display, but is not limited to this. Examples of flexible devices include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays that use a plastic substrate (film) as a substrate, and foldable displays. These may be touch panels.

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, retardation films (retardation plates), viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transmissive reflective films, electrode films, transparent conductive films, metal mesh films, film sensors (touch sensor films), liquid crystal polymer films, light-emitting polymer films, film-like liquid crystal modules, organic EL modules (organic EL films, organic EL elements), electronic paper modules (film-like electronic paper), TFT (Thin Film Transistor) substrates, etc.

The Young's modulus of the first flexible member 21 and the second flexible member 22 is preferably 0.1 to 10 GPa, more preferably 0.5 to 7 GPa, and still more preferably 1 to 5 GPa. preferable. When the Young's modulus of the first flexible member 21 and the second flexible member 22 is within the above range, it becomes easy to repeatedly bend each flexible member.

The thickness of the first flexible member 21 and the second flexible member 22 is preferably 10 to 3000 μm, 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 easier to repeatedly bend each flexible member.

An example of manufacturing a flexible member laminate 2 is shown below. First, the second release sheet 12 on one side of the adhesive sheet 1 is peeled off, and the exposed adhesive layer 10 of the adhesive sheet 1 is attached to one side of the first flexible member 21.

Thereafter, the other 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 and the second flexible member 22 are bonded together to form a flexible member laminate. Get 2. Furthermore, as another example, the order of bonding the first flexible member 21 and the second flexible member 22 may be changed.

(3. Flexible Devices)
The flexible device according to the present embodiment includes the above-mentioned flexible material laminate 2, and may be composed of only the flexible material laminate 2, or may be configured to include one or more flexible material laminates 2 and other flexible materials. When laminating one flexible material laminate 2 with another flexible material laminate 2, or when laminating the flexible material laminate 2 with another flexible material, it is preferable to laminate them via the adhesive layer 10 of the above-mentioned adhesive sheet 1.

In the flexible device according to this embodiment, the various components are bonded together using the above-mentioned adhesive layer, so even if the device is repeatedly bent (e.g., 100,000 times), at least the adhesive layer is prevented from peeling off from the bonded components.

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

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

At least any one of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 is the adhesive layer 10 of the adhesive sheet 1 described above. It is preferable that there be. Any two or more layers of the first adhesive layer 32, the second adhesive layer 34, the third adhesive layer 36, and the fourth adhesive layer 38 are the adhesive layer 10 of the adhesive sheet 1 described above. Most preferably, all the adhesive layers 32, 34, 36, and 38 are the adhesive layer 10 of the adhesive sheet 1.

In this specification, when it is written "X to Y" (X and Y are any numbers), it means "X or more and Y or less", and also means "preferably greater than X" or "preferably smaller than Y" unless otherwise specified. Furthermore, when it is written "X or more" (X is any number), it means "preferably greater than X" unless otherwise specified, and when it is written "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and may be modified in various ways within the scope of the present invention.

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

Example 1
1. Preparation of (meth)acrylic acid ester copolymer 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 were copolymerized to prepare a (meth)acrylic acid ester copolymer (A). The molecular weight of the obtained (meth)acrylic acid ester copolymer (A) was measured by the method described below, and the weight average molecular weight (Mw) was 1,200,000.

The weight average molecular weight (Mw) is a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC) under the following conditions (GPC measurement).
(Measurement condition)
GPC measuring device: Tosoh Corporation, HLC-8020
GPC columns (passed in the following order): TSK guard column HXL-H manufactured by Tosoh Corporation
TSK gel GMHXL (x2)
TSK gel G2000HXL
Measurement solvent: tetrahydrofuran Measurement temperature: 40°C

2. Preparation of adhesive composition 100 parts by mass of the (meth)acrylic acid ester copolymer (A) obtained above (solid content equivalent; the same applies hereinafter) and an isocyanate-based crosslinking agent (Mitsui By mixing 0.2 parts by mass of Takenate D110N (manufactured by Kagakusha, product name), stirring thoroughly, and diluting with methyl ethyl ketone, a coating solution of adhesive composition A with a solid content concentration of 50% by mass is prepared. I got it.

3. Preparation of Release Sheet As the release sheet, a heavy release type release sheet in which one side of a PET film is treated with a silicone-based release agent for release, and a light release type release sheet in which one side of a PET film is treated with a silicone-based release agent for release were prepared as shown below. It has been confirmed that the release force of the heavy release type release sheet is greater than that of the light release type release sheet. Therefore, in this embodiment, the heavy release type release sheet is the first release sheet, and the light release type release sheet is the second release sheet.
Heavy release type release sheet 1: SP-PET501031 manufactured by Lintec Corporation
Heavy release type release sheet 2: SP-PET382150 manufactured by Lintec Corporation
Light release type release sheet 3: SP-PET381031 manufactured by Lintec Corporation
Light release type release sheet 4: SP-PET25LT-H manufactured by Lintec Corporation
Light release type release sheet 5: SP-PET381130 manufactured by Lintec Corporation

4. Manufacture of Adhesive Sheet The coating solution of the obtained adhesive composition was applied to the release-treated surface of heavy release type release sheet 1 (SP-PET501031) using a knife coater. Then, the coating layer is heat-treated at 90°C for 1 minute to advance the crosslinking reaction, and the adhesive having a crosslinked structure composed of the (meth)acrylic acid ester copolymer (A) and the crosslinking agent (B) is applied. A coating layer consisting of the agent was formed.

Then, the coating layer on the heavy release type release sheet 1 obtained above and light release type release sheet 4 (SP-PET25LT-H) were attached so that the release-treated surface of the light release type 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 a configuration of heavy release type release sheet 1/adhesive layer A (thickness: 25 μm)/light release type release sheet 4. The thickness of the adhesive layer was measured using a constant pressure thickness gauge (PG-02, manufactured by Tecrock Co., Ltd.) in accordance with JIS K7130.

(Examples 2 to 4, Comparative Examples 1 to 3)
Pressure-sensitive adhesive compositions B to D were obtained by changing the composition of the (meth)acrylic acid ester polymer (A), the amount of crosslinking agent (B) and the amount of other components to the amounts shown in Table 1. As shown in Table 2, pressure-sensitive adhesive compositions were selected from the pressure-sensitive adhesive compositions A to D shown in Table 1, and pressure-sensitive adhesive sheets were produced in the same manner as in Example 1, except that the combination of the heavy release type release sheet (first release sheet) and the light release type release sheet (second release sheet) was the combination shown in Table 2. Comparative Example 2 is a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet was irradiated with ultraviolet light through the heavy release type release sheet. The ultraviolet light irradiation conditions were as follows.
<Ultraviolet ray irradiation conditions>
- High pressure mercury lamp used - Illuminance 200mW/ ^cm2 , light quantity 1000mJ/ ^cm2
・UV illuminance/light intensity meter used is "UVPF-A1" manufactured by iGraphics Co., Ltd.

The UV resin used in adhesive composition D was ARONIX (registered trademark) M-315, and the photopolymerization initiator was JRCURE 500.

Details of the abbreviations etc. 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 crosslinking agent (manufactured by Mitsui Chemicals, product name "Takenate D110N")

(Storage modulus G' of adhesive)
The pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets prepared in the Examples and Comparative Examples were laminated together to form a laminate having a thickness of 3 mm. A cylindrical body having a diameter of 8 mm (height of 3 mm) was punched out from the resulting laminate of pressure-sensitive adhesive layers to prepare a sample for measuring the storage modulus.

The storage modulus (G') of the measurement sample was determined in accordance with JIS K7244-6 using a viscoelasticity measuring instrument (DYNAMICANALAYZER, manufactured by REOMETRIC) by the torsional shear method at a measurement temperature of 23°C and a measurement frequency of 1Hz. MPa) was measured. The results are shown in Table 1.

(Release strength of release sheet)
The peel strength of the first release sheet was measured as follows. The second release sheet was peeled off from the obtained pressure-sensitive adhesive sheet, and the good adhesion surface of a 25 μm-thick good adhesion PET (PET25A-4100, manufactured by Toyobo Co., Ltd.) was attached to the exposed surface of the pressure-sensitive adhesive layer by thermal lamination (70° C., 1 m/min) to prepare a laminate sample. The obtained laminate sample was cut into a width of 25 mm to prepare a measurement sample. Next, the back surface of the good adhesion PET of the measurement sample was fixed to a hard support plate with double-sided tape, and a laminate consisting of the first release sheet/pressure-sensitive adhesive layer/good adhesion PET/double-sided tape/hard support was prepared.

The first release sheet of this laminate was peeled off using a universal tensile tester (Shimadzu Corporation, Autograph (registered trademark) AG-IS) at a measurement distance of 100 mm, a peel angle of 180°, and peel speeds of 0.3 m/min, 2.4 m/min, and 10 m/min, and the load at that time was measured. Of the measured loads, 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 peel force of the first release sheet at each peel speed. The results are shown in Table 2.

The peeling force of the second release sheet was measured as follows. The obtained adhesive sheet was cut into a width of 25 mm to prepare a measurement sample. The surface of the first release sheet in the measurement sample opposite to the release treatment surface was fixed to a hard support plate with double-sided tape to prepare a laminate consisting of the second release sheet/adhesive layer/first release sheet/double-sided tape/hard support plate. The second release sheet was peeled from the laminate using a universal tensile tester (Shimadzu Corporation Autograph (registered trademark) AG-IS) at a measurement distance of 100 mm, a peeling angle of 180°, and a peeling speed of 0.3 m/min and 10 m/min, and the load at that time was measured. Of the measured loads, 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.

The peel strength difference (the peel strength of the first release sheet - the peel strength of the second release sheet) was calculated from the peel strength of the first release sheet and the peel strength of the second release sheet obtained. The results are shown in Table 2.

(Si transfer amount of second release sheet)
The adhesive layer surface of an acrylic adhesive tape (manufactured by Nitto Denko Corporation, trade name: 31B tape) was attached to the release-treated surface of the second release sheet and stored for 24 hours. Thereafter, the surface of the adhesive layer exposed by peeling off the second release sheet has silicon atoms (Si), carbon atoms (C), and oxygen atoms (O) measured by X-ray photoelectron spectroscopy (XPS). Based on the amount (XPS counts), the silicon atomic ratio (atom%) was calculated using the following formula. The results are shown in Table 2.
Silicon atomic ratio (atom%) = [(Si element amount) / {(C element amount) + (O element amount) + (Si element amount)}] × 100

The measurement was performed using an ESCA 5600 manufactured by PerkinElmer under the following measurement conditions.
X-ray source: Mg standard (15 kv, 400 W)
Take-off angle: 45°
Measurement time: 3 minutes Measurement elements: silicon atom (Si), carbon atom (C), oxygen atom (O)

(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 pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples. Thereafter, the silicon atomic ratio (atom%) of the exposed surface of the adhesive layer was calculated in the same manner as the amount of Si transferred to the second release sheet described above. The presence or absence of Si detection on the surface of the adhesive layer was determined based on the criteria that if the silicon atomic ratio was more than 1 atom %, Si was detected, and if it was less than 1 atom %, Si was not detected. The results are shown in Table 2.

Next, the properties of the adhesive sheet were evaluated as follows:

(flexibility)
In an environment of 23°C and 50% RH, the light-release type release sheet (second release sheet) was peeled off from the adhesive sheets prepared in Examples and Comparative Examples, and the exposed adhesive layer was replaced with a polyimide (PI) film. (manufactured by DuPont-Toray, product name "Kapton 100PI", thickness: 25 μm, Young's modulus: 3.4 GPa). Next, the heavy release type release sheet (first release sheet) is peeled off, and the exposed adhesive layer is attached to one side of a triacetyl cellulose (TAC) film (manufactured by Konica Minolta, product name "KC4UYW", thickness: 40 μm). It was pasted on the surface. Then, after pressurizing at 0.5 MPa and 50° C. for 20 minutes in an autoclave manufactured by Kurihara Seisakusho Co., Ltd., it was left for 24 hours under the conditions of 23° C. and 50% RH. The thus-obtained laminate consisting of PI film/adhesive layer/TAC film was cut to a width of 50 mm and a length of 200 mm, and this was used as a sample.

The obtained sample was repeatedly bent under the following conditions using a durability tester (manufactured by Yuasa System Equipment Co., Ltd., product name: "Surface condition no-load U-shaped expansion/contraction tester type: DLDMLH-FS"). After the test, it was visually confirmed whether there was any lifting or peeling at the interface between the adhesive layer and the adherend at the bent part, and the flexibility was repeatedly evaluated according to the following criteria. The results are shown in Table 2.
<Test conditions>
Bending direction: Bend so that the triacetyl cellulose film sides face each other Minimum bending diameter: 3mmφ
Bending number: 100,000 times Bending speed: 60 rpm
<Evaluation criteria for repeated flexibility>
A...No peeling (bending angle less than 90°)
B…No peeling (bending angle of 90° or more)
F...There is some peeling.

(Sad farewell when peeling off the second release sheet)
The obtained pressure-sensitive adhesive sheet was cut to a size of 5 × 10 cm to prepare a measurement sample. Next, the surface of the first release sheet in the measurement sample opposite to the release treatment surface was fixed to a hard support plate with double-sided tape to prepare a laminate consisting of the second release sheet/pressure-sensitive adhesive layer/first release sheet/double-sided tape/hard support plate.

Regarding the laminate, the second release sheet was removed from the adhesive layer using a universal tensile tester (Autograph (registered trademark) AG-IS manufactured by Shimadzu Corporation) at a peel angle of 180° and a peel speed of 10 m/min. Peeled off. After peeling, the peeled surface of the second release sheet was visually checked, and whether or not separation occurred was evaluated based on the following criteria. The results are shown in Table 2.
A... No break-up B... Break-up occurs only within 5mm of the long side edge F... Break-up occurs over the entire surface

(Dimension change at the edge of the adhesive layer)
A 2.5×10 cm sample was cut out from the obtained adhesive sheet and used as a sample. The second release sheet was peeled off from the cut sample and bonded to soda glass using a laminator. After lamination, a line was drawn on the back side of the soda glass along the edge of the first release sheet using an oil-based marker. Adhesive tape "No. 31B" manufactured by Nitto Denko Corporation was attached to the end 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, using a digital microscope, the amount of deviation 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 areas (each 2.2 mm wide). The location where the amount of deviation was the largest within the observation field of view was measured, and the average value of the three measured points was calculated. Regarding the calculated average value, the end dimensional change of the adhesive layer was evaluated 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: 100 μm or more.

The pressure-sensitive adhesive sheet of the present invention can be suitably used, for example, for bonding flexible members.

DESCRIPTION OF SYMBOLS 1... Adhesive sheet 10... Adhesive layer 11... First release sheet 12... Second release sheet 2... Flexible member laminate 21... First flexible member 22... Second flexible member 3... Flexible device 31... Cover film 32 ...First adhesive layer 33...Polarizing film 34...Second adhesive layer 35...Touch sensor film 36...Third adhesive layer 37...Organic EL element 38...Fourth adhesive layer 39...TFT substrate

Claims (3)

A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, and a first release sheet and a second release sheet sandwiching both main surfaces of the pressure-sensitive adhesive layer,
the pressure-sensitive adhesive layer has a storage modulus at 23° C. of 0.2 MPa or less;
the amount of Si at the surface of the pressure-sensitive adhesive layer is at least twice the amount of Si at the center of the pressure-sensitive adhesive layer,
the second release sheet contains a silicone-based release agent;
the amount of Si transferred to the surface of the pressure-sensitive adhesive layer of the second release sheet is 5 to 100 atom %,
A pressure-sensitive adhesive sheet for flexible devices, wherein the peel strength of a first release sheet when peeled from the pressure-sensitive adhesive layer at a peel speed of 2.4 m/min is 150 mN/25 mm or less. 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 to each other,
A flexible member laminate, wherein the adhesive layer is an adhesive included in the adhesive sheet for flexible devices according to claim 1. A flexible device comprising the flexible member laminate according to claim 2.

Images