Active energy ray curable adhesive sheet for optical components

Abstract

To provide a novel adhesive sheet capable of achieving a low dielectric constant and excellent printing step absorption while having excellent handleabilty as an adhesive sheet.SOLUTION: There is provided an active energy ray-curable adhesive sheet for an optical member which is an active energy ray-curable adhesive sheet containing an acrylic resin A, wherein the acrylic resin (A) is a (co)polymer of a monomer component containing a (meth)acrylic ester monomer (a) having an active energy ray-crosslinkable structural site and a linear alkyl group having 10 to 24 carbon atoms and the active energy ray-curable adhesive sheet has all of the following characteristics (1) to (3): (1) the tensile elasticity at a temperature of 23°C is 0.03 MPa or more, (2) the displacement length by a holding power test in which the adhesive sheet is adhered to a stainless steel plate with an adhesion area of 25 mm×20 mm and a load of 500 gf (4.9 N) is applied in a vertical direction for 30 minutes is 1 mm or more and (3) the relative dielectric constant at a frequency of 100 kHz is 3.7 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet having a low dielectric constant and excellent step absorption properties and handling properties (e.g., ease of cutting, reworking, and storage). In particular, the present invention relates to an active energy ray-curable pressure-sensitive adhesive sheet for optical components that can be suitably used in forming image display devices such as personal computers, mobile terminals (PDAs), game consoles, televisions (TVs), car navigation systems, touch panels, and pen tablets. [Background technology]

[0002] BACKGROUND ART In recent years, image display devices equipped with a touch sensor function, particularly an electrostatic capacitance type touch sensor function, have become widespread, particularly in mobile phones and mobile terminals.

[0003] This type of capacitive touch sensor detects position by detecting changes in the capacitance of a capacitor formed between two opposing electrodes separated by an insulating film, as a conductor such as a finger approaches from the surface protection panel side.

[0004] However, with the recent trend toward thinner components, the gap between the electrode and the surface of the protective panel has narrowed, and as the change in capacitance in response to touch increases, the problem of noise easily occurring in the detection signal has arisen. Therefore, there is a demand for adhesive sheets used to fill the gap between the electrode and the surface protective panel with a low dielectric constant to absorb changes in touch detection sensitivity and suppress noise in the detection signal.

[0005] Furthermore, as electrodes become lighter and cheaper, electrode substrates are being replaced by resin films. In the case of electrodes with a conductive thin film pattern formed on only one side, two film electrodes or a glass electrode and a film electrode must be laminated together using an adhesive sheet or the like, and the adhesive sheet used in this process must also have a low dielectric constant.

[0006] As an example of a low dielectric constant pressure-sensitive adhesive sheet, Patent Document 1 discloses a double-sided pressure-sensitive adhesive sheet characterized by containing an acrylic compound (A) having a relative dielectric constant of 3.0 or less at a frequency of 100 kHz and an acrylic acid ester copolymer (B) obtained by copolymerizing a (meth)acrylic acid ester monomer and / or a vinyl ether monomer having a linear or branched alkyl group having 1 to 9 carbon atoms on the side chain.

[0007] By using an acrylic compound (A) with a low dielectric constant of 3.0 or less at a frequency of 100 kHz, this double-sided pressure-sensitive adhesive sheet not only reduces the dielectric constant of the entire sheet, but also improves handleability (ease of handling) by forming a crosslinked structure throughout the entire pressure-sensitive adhesive sheet, allowing the sheet to maintain its shape even when heated. Furthermore, by incorporating an acrylic ester copolymer (B) obtained by copolymerizing a (meth)acrylic ester monomer and / or a vinyl ether monomer having a linear or branched alkyl group having 1 to 9 carbon atoms in its side chain, favorable adhesive properties can be obtained, such as preventing foaming or peeling of bonded members due to environmental changes such as temperature and humidity, and providing appropriate elasticity and dent recovery.

[0008] Patent Document 2 also discloses a pressure-sensitive adhesive characterized by containing a (meth)acrylic polymer obtained by polymerizing a monomer component including an alkyl(meth)acrylate (a1) having a branched alkyl group having 8 to 24 carbon atoms at the ester terminal and an alkyl(meth)acrylate (a2) having a linear alkyl group having 8 to 24 carbon atoms at the ester terminal.

[0009] With such a pressure-sensitive adhesive, the action of the long-chain branched alkyl group and the long-chain linear alkyl group makes it possible to realize a pressure-sensitive adhesive layer with a low dielectric constant and to achieve satisfactory adhesive performance.

[0010] Thus, up until now, attempts have been made to lower the dielectric constant of pressure-sensitive adhesive sheets while maintaining the original functions of the pressure-sensitive adhesive sheets.

[0011] Incidentally, a touch panel type image display device is usually configured by combining a surface protection panel, a touch panel, and an image display panel (collectively referred to as "components for an image display device").

[0012] In recent years, surface protection panels for touch panel type image display devices such as smartphones and tablet terminals have been made of tempered glass as well as plastic materials such as acrylic resin plates and polycarbonate plates, and the peripheral edges of the surface protection panels other than the visible opening surface are printed in black.

[0013] In addition, touch panels use plastic film sensors together with glass sensors, components in which the touch panel function is integrated with the surface protection panel (e.g., touch-on-lens (TOL)), and components in which the touch panel function is integrated with the image display panel (e.g., in-cell or on-cell).

[0014] In the field of image display devices, primarily mobile phones and mobile terminals, thinner walls, higher precision, and increasingly diverse designs are being developed. While it was previously common for surface protection panels to have a black frame-shaped concealing portion printed around the periphery, the increasing diversity of designs has led to the formation of frame-shaped concealing portions in colors other than black. When concealing portions are formed in colors other than black, the concealing properties are low, so the height of the concealing portion, i.e., the printed portion, tends to be higher than in black. Therefore, adhesive sheets for bonding components with such printed portions are required to conform to large printing steps and fill every corner.

[0015] Therefore, various methods for filling the printing step have been proposed. For example, Patent Document 3 discloses an ultraviolet-crosslinkable adhesive sheet containing a (meth)acrylic copolymer of a monomer containing a (meth)acrylic acid ester having an ultraviolet-crosslinkable moiety, in which the storage modulus of the adhesive sheet before ultraviolet crosslinking is 5.0 × 10 at 30°C and 1 Hz. 4 Pa or more, 1.0×10 6 Pa or less, and at 80°C and 1 Hz, 5.0 x 10 4 Pa or less, and further, the storage modulus of the pressure-sensitive adhesive sheet after UV crosslinking is 1.0 × 10 at 130°C and 1 Hz. 3 The document discloses an ultraviolet-crosslinkable adhesive sheet having a compressive strength of 100 MPa or more.

[0016] Such an adhesive sheet can be heated and / or pressurized before UV crosslinking, so that even if its thickness is approximately the same as the height of the step or protrusion (e.g., 20 to 30 μm), it can adequately conform to the step or protrusion. As a result, no voids or the like are formed near the step or protrusion, and the internal residual stress of the adhesive sheet near the step or protrusion does not become unnecessarily high. Furthermore, highly reliable adhesion can be achieved by performing UV crosslinking after bonding the pressure-sensitive adhesive sheet to the adherend, which allows the thickness of the laminate including the adherend to be kept thin and enables bonding without defects such as voids or color unevenness in the liquid crystal. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-040240 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-194170 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-184582 Summary of the Invention [Problem to be solved by the invention]

[0018] The pressure-sensitive adhesive sheets disclosed in Patent Documents 1 and 2 aim to lower the dielectric constant of the pressure-sensitive adhesive sheet while maintaining the original functions of the pressure-sensitive adhesive sheet, but do not take into consideration the ability to absorb printing step differences.

[0019] Furthermore, when print step absorbency is taken into consideration, it is conceivable that by imparting flexibility to the adhesive sheet, as in the adhesive sheet disclosed in Patent Document 3, excellent print step absorbency can be imparted to the adhesive sheet despite its thinness (e.g., 30 to 50 μm), but when print step absorbency is taken into consideration, there is a risk that handling properties (e.g., ease of cutting, ease of reworking, ease of storage) may be deteriorated. In addition, the pressure-sensitive adhesive sheet of Patent Document 3 does not take into consideration the reduction of the dielectric constant.

[0020] Therefore, the object of the present invention is to realize both a low dielectric constant and excellent print step absorption, and at the same time, to provide a pressure-sensitive adhesive sheet that is easy to handle (for example, easy to cut, easy to rework, easy to store, etc.). The object of the present invention is to provide a new adhesive sheet that is also excellent in adhesive properties. [Means for solving the problem]

[0021] The present invention is an active energy ray-curable pressure-sensitive adhesive sheet containing an acrylic resin (A), wherein the acrylic resin (A) is a (co)polymer of monomer components including an active energy ray-crosslinkable structural moiety and a (meth)acrylic acid ester monomer (a) having a linear alkyl group having 10 to 24 carbon atoms, and is mainly characterized by the following:

[0022] The present invention provides an active energy ray-curable pressure-sensitive adhesive sheet for optical members, which contains an acrylic resin (A), wherein the acrylic resin (A) is a (co)polymer of monomer components including a (meth)acrylic acid ester monomer (a) having an active energy ray-crosslinkable structural moiety and a linear alkyl group having 10 to 24 carbon atoms, and which has at least all of the following properties (1) to (3): (1) Tensile modulus at 23°C is 0.03 MPa or more (2) Affixed to a stainless steel plate with an adhesive area of ​​25mm x 20mm, and subjected to a vertical load of 500gf (4.9N) for 30 minutes. The displacement is 1mm or more in the holding strength test. (3) A dielectric constant of 3.7 or less at a frequency of 100 kHz

[0023] The present invention also provides an active energy ray-curable pressure-sensitive adhesive sheet for optical components, which contains an acrylic resin (A), wherein the acrylic resin (A) has an active energy ray-crosslinkable structural moiety and is a (co)polymer of monomer components including a (meth)acrylic acid ester monomer (a) having a linear alkyl group having 10 to 24 carbon atoms, and which has, in the thickness direction from at least one sheet surface, regions containing the acrylic resin (A) that have different storage moduli G' at a frequency of 1 Hz and a temperature of 20°C, and which has a relative dielectric constant of 3.7 or less at a frequency of 100 kHz. [Effects of the Invention]

[0024] The active energy ray-curable pressure-sensitive adhesive sheet for optical members of the present invention can achieve both low dielectric constant characteristics and excellent print step absorbency. Furthermore, since it also has excellent handling properties as an adhesive sheet (for example, ease of cutting, reworking, and storage), it can be suitably used when forming image display devices such as personal computers, mobile terminals (PDAs), game consoles, televisions (TVs), car navigation systems, touch panels, and pen tablets. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of a sample for a tensile modulus measurement test in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described in detail, but the following description is one example (typical example) of the embodiment of the present invention, and the present invention is not limited to the contents thereof in any way.

[0027] In addition, "(meth)acrylic" encompasses acrylic and methacrylic, "(meth)acryloyl" encompasses acryloyl and methacryloyl, and "(meth)acrylate" encompasses acrylate and methacrylate, respectively, and "(co)polymer" encompasses polymers and copolymers. Furthermore, the term "sheet" conceptually encompasses sheets, films, and tapes.

[0028] <<Active energy ray curable adhesive sheet for optical components>> The active energy ray-curable pressure-sensitive adhesive sheet for optical members of the present invention (hereinafter also referred to as "the pressure-sensitive adhesive sheet") contains an acrylic resin (A), which is a (co)polymer of monomer components including a (meth)acrylic acid ester monomer (a) having an active energy ray-crosslinkable structural moiety and a linear alkyl group having 10 to 24 carbon atoms.

[0029] Furthermore, the pressure-sensitive adhesive sheet has at least all of the following properties (1) to (3).

[0030] (1) Tensile modulus at 23°C is 0.03 MPa or more (2) Affix the tape to a stainless steel plate with an adhesive area of ​​25 mm wide x 20 mm long, and apply a load of 500 gf (4.9 N) vertically for 30 minutes. The tape is tested for a misalignment of 1 mm or more. (3) A dielectric constant of 3.7 or less at a frequency of 100 kHz

[0031] The adhesive sheet possesses the above properties, allowing it to achieve both low dielectric constant characteristics and excellent print step absorption, while also ensuring ease of handling as an adhesive sheet (e.g., ease of cutting, reworking, and storage).

[0032] This pressure-sensitive adhesive sheet uses, as the acrylic resin (A), a (co)polymer of monomer components including a (meth)acrylic acid ester monomer (a) having an active energy ray-crosslinkable structural moiety and a linear alkyl group having 10 to 24 carbon atoms, thereby making it possible to obtain a pressure-sensitive adhesive sheet in which the tensile modulus of elasticity and holding power are adjusted to fall within a predetermined range while the dielectric constant is reduced.

[0033] (tensile modulus) The pressure-sensitive adhesive sheet has a tensile modulus of 0.03 MPa or more at a temperature of 23°C. By setting the tensile modulus within this range, excellent handleability can be ensured. From this perspective, the tensile modulus of the pressure-sensitive adhesive sheet is preferably 0.03 MPa or more and 1.0 MPa or less, and more preferably 0.03 MPa or more and 0.5 MPa or less.

[0034] (holding force) The pressure-sensitive adhesive sheet has a slippage length of 1 mm or more in the above-mentioned holding power test. A slippage length of 1 mm or more allows the pressure-sensitive adhesive sheet to have print step absorbency. From this perspective, the slippage length of the pressure-sensitive adhesive sheet is preferably 1.0 mm or more and 20 mm or less. The slippage length determined by the holding power test is a value determined by the method described in the Examples below.

[0035] By using a specific acrylic resin (A), the pressure-sensitive adhesive sheet has a flexible property with a slippage length of 1 mm or more, and at the same time has a strong property with a tensile modulus of elasticity of 0.03 MPa or more. In this way, by using a specific acrylic resin (A), the pressure-sensitive adhesive sheet can achieve a low dielectric constant, while being flexible and having excellent handling properties such as ease of cutting, and can possess the contradictory properties of print step absorption and ease of handling. More specifically, by designing a pressure-sensitive adhesive sheet having a laminated structure as described below while having the above properties (1) to (3), it is possible to achieve higher print step absorbency and ease of handling.

[0036] For example, by using a specific acrylic resin (A) and forming an area with a different storage modulus G' at a frequency of 1 Hz and a temperature of 20°C in the thickness direction from at least one sheet surface, it is possible to achieve higher levels of print step absorbency and handleability.

[0037] The tensile modulus refers to the value determined by the method described in the Examples below, and the storage modulus G' refers to the storage modulus when dynamic viscoelasticity is measured in shear mode, and refers to the value determined by the method described in the Examples below.

[0038] The region having different storage moduli G' includes, for example, a case where two or more layers having different storage moduli G' are stacked, or a case where there is no clear interface between the layers but there are parts having different storage moduli G'.

[0039] An example of the region containing the acrylic resin (A) and having a different storage modulus G' is a configuration having at least n layers containing the acrylic resin (A), in which the storage modulus G' at a frequency of 1 Hz and a temperature of 20°C of the first layer and the i-th layer are different from each other (hereinafter also referred to as a "laminated configuration"). Here, n is an integer of 2 or more, and i is an integer of 2 or more that satisfies the relationship n>i when n is 3 or more.

[0040] In the above laminated structure, the ith layer preferably has a storage modulus G' of 40 kPa or more and 1 MPa or less at a frequency of 1 Hz and a temperature of 20° C. Having the ith layer have a storage modulus G' within this range gives the adhesive sheet itself stiffness, and prevents problems such as the adhesive resin adhering to a cutting die or slit blade, the adhesive material wrapping around the cut edges and making it impossible to peel off the release film, or glue spilling out from the edges.

[0041] In the above embodiment, the first layer preferably has a storage modulus G' of 30 kPa to 70 kPa at a frequency of 1 Hz and a temperature of 20° C. Having the first layer have a storage modulus G' within this range can provide advantages such as good conformability to printing irregularities and reduced optical distortion near irregularities after lamination.

[0042] The storage modulus G' can be adjusted to fall within the above range by changing the type, molecular weight, and composition ratio of each component constituting the pressure-sensitive adhesive sheet, as well as by adjusting the degree of crosslinking by adjusting the amount of active energy ray irradiation, adjusting the amount of active energy ray-crosslinkable structural moieties, or adjusting the amount of crosslinking agent.

[0043] Among these, it is preferable to contain the acrylic resin (A) described below.

[0044] (Layer structure) The pressure-sensitive adhesive sheet of the above laminated configuration has a configuration in which n or more layers are laminated, and specific examples include laminated configurations having a first layer / second layer, a first layer / second layer / third layer, or a first layer / second layer / ... / i-th layer. Note that it is not necessary for all layers to be pressure-sensitive adhesive layers, but it is preferable that at least the first layer (surface layer) and / or the n-th layer (back layer) be a pressure-sensitive adhesive layer.

[0045] Therefore, for example, the film may have a two-layer structure where n is 2 and the first and second layers contain the acrylic resin (A), or a three-layer structure where n is 3 and the first and second layers (i=2) contain the acrylic resin (A) (n=3, i=2), or may have a three-layer structure where n is 3 and the first and third layers contain the acrylic resin (A).

[0046] Among the above structures, a two-layer structure where n is 2 and the first and second layers contain the acrylic resin (A), and a three-layer structure where n is 3 and the first and second layers (i=2) contain the acrylic resin (A) (n=3, i=2) are preferred from the viewpoint of ease of production.

[0047] The present adhesive sheet having the above laminated structure is most preferably in a form in which the intermediate layer contains the above acrylic resin (A) in comparison with the front and back layers, and the storage modulus G' of the front and back layers and the intermediate layer are different, since the intermediate layer, having a moderate hardness, gives the adhesive sheet itself stiffness, and the flexible front and back layers ensure conformability to uneven surfaces.

[0048] From the above, it is preferable that n is 3 or more, that is, n=3 or more, i=2 or more, and the relationship n>i is satisfied.

[0049] From the above, the present pressure-sensitive adhesive sheet is most preferably a two-layer structure where n is 2, the first and second layers containing the acrylic resin (A), the first layer having a storage modulus G' of 30 kPa to 70 kPa at a frequency of 1 Hz and a temperature of 20°C, and the second layer having a storage modulus G' of 40 kPa to 1 MPa at a frequency of 1 Hz and a temperature of 20°C, or a three-layer structure where n is 3, the first and second layers (i=2) containing the acrylic resin (A) (n=3, i=2), the first layer having a storage modulus G' of 30 kPa to 70 kPa at a frequency of 1 Hz and a temperature of 20°C, and the second layer having a storage modulus G' of 40 kPa to 1 MPa at a frequency of 1 Hz and a temperature of 20°C. In this case, the storage modulus G' of the third layer at a frequency of 1 Hz and a temperature of 20°C may be the same as or different from that of the first layer, but is more preferably the same.

[0050] (Thickness of this adhesive sheet) The thickness of the pressure-sensitive adhesive sheet is preferably in the range of 20 μm to 500 μm (excluding the thickness of the substrate sheet, if any). For example, a thickness of 20 μm or more will not impair adhesion to the adherend or impact absorption, while a thickness of 500 μm or less can meet the demand for thinner thickness. Therefore, the thickness of the present pressure-sensitive adhesive sheet is preferably 20 μm to 500 μm, more preferably 30 μm or more or 300 μm or less, and even more preferably 50 μm or more or 200 μm or less.

[0051] In the present pressure-sensitive adhesive sheet having the above laminated structure, the ratio ((S1) / (S2)) of the thickness of the ith layer (S2) to the total thickness of the first and nth layers, i.e., the total thickness (S1) of the front and back layers, is preferably 0.05≦(S1) / (S2)≦2. By setting the thickness ratio in this manner, the contribution of the thickness of the front and back layers in the laminate is not too great, and the laminate is not too flexible, which is preferable as it does not deteriorate workability such as cutting and handling. Furthermore, it is preferable because it is not inferior in ability to conform to uneven or curved surfaces and can maintain adhesive strength and wettability to the adherend. From this perspective, it is more preferable that the ratio of the thickness (S2) of the ith layer to the total thickness (S1) of the front and back layers is 0.1≦(S1) / (S2)≦2, and even more preferable that 0.1≦(S1) / (S2)≦1.

[0052] (dielectric constant) The present pressure-sensitive adhesive sheet preferably has a relative dielectric constant of 3.7 or less at a frequency of 100 kHz. A relative dielectric constant of 3.7 or less allows the present pressure-sensitive adhesive sheet to function as an insulating layer, reducing the loss of high-frequency electrical signals such as touch signals. From this perspective, the relative dielectric constant of the present pressure-sensitive adhesive sheet is more preferably 3.5 or less, and even more preferably 3.2 or less. The relative dielectric constant is a value determined by the method described in the Examples below.

[0053] <Acrylic resin (A)> The pressure-sensitive adhesive sheet contains an acrylic resin (A).

[0054] The acrylic resin (A) is preferably a (co)polymer of monomer components including a (meth)acrylic acid ester monomer (a) having an active energy ray crosslinkable structural moiety and a linear alkyl group having 10 to 24 carbon atoms. The active energy ray-crosslinkable structural moiety is a structural moiety that can react with a part of the acrylic resin (A) or a curing component other than the acrylic resin (A) upon irradiation with active energy rays to form a crosslinked structure.

[0055] Examples of the active energy ray-crosslinkable structural moiety include a structure having a radically polymerizable functional group having a carbon-carbon double bond, such as a functional group having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and a structure that is excited by ultraviolet irradiation and can abstract a hydrogen radical in the excited state, such as a benzophenone structure. When irradiating with active energy rays, light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, and infrared rays, electromagnetic waves such as X-rays and γ-rays, as well as electron beams, proton beams, neutron beams, etc. can be used, but curing by ultraviolet irradiation is advantageous in terms of curing speed, ease of availability of irradiation equipment, cost, etc.

[0056] To introduce a structure having a radically polymerizable functional group having a carbon-carbon double bond, such as a functional group having an unsaturated double bond, a monomer having an unsaturated double bond and a functional group that reacts with the functional group in the acrylic resin, such as 2-isocyanatoethyl (meth)acrylate, may be reacted with the functional group in the acrylic resin. Furthermore, to introduce a compound that is excited by ultraviolet irradiation and can abstract hydrogen radicals in the excited state, a (meth)acrylic acid ester monomer (α) having an active energy ray-crosslinkable structural moiety may be copolymerized as a copolymerization component.

[0057] The (meth)acrylic acid ester monomer (α) containing an active energy ray-crosslinkable structure preferably contains a (meth)acrylic acid ester monomer having a benzophenone structure, since this allows for efficient formation of a crosslinked structure by active energy rays such as ultraviolet rays and electron beams. Specific examples thereof include 4-(meth)acryloyloxybenzophenone.

[0058] The content of the (meth)acrylic acid ester monomer (α) containing an active energy ray-crosslinkable structure moiety is preferably 0.01 to 5 mass% based on the total copolymerization components, and the content of the (meth)acrylic acid ester monomer having a benzophenone structure is preferably 0.01 to 5 mass%, particularly preferably 0.1 to 2 mass%, and even more preferably 0.2 to 1 mass% based on the total copolymerization components. If the content is too low, the holding power when forming a crosslinked structure by active energy rays tends to decrease, while if it is too high, the cohesive force of the entire system tends to increase too much, resulting in a decrease in adhesive strength.

[0059] The acrylic resin (A) having an active energy ray-crosslinkable structural moiety not only allows the acrylic resin (A) to be efficiently cured (crosslinked), but also enhances cohesive strength and provides excellent foaming resistance reliability (especially excellent ultraviolet (UV) foaming resistance) without containing an acid component. From these points of view, a benzophenone structure is most preferred as the active energy ray-crosslinkable structural moiety.

[0060] Examples of the (meth)acrylic acid ester monomer (a) having a linear alkyl group having 10 to 24 carbon atoms include decyl (meth)acrylate (alkyl group having 10 carbon atoms), lauryl (meth)acrylate (having 12 carbon atoms), tridecyl (meth)acrylate (having 13 carbon atoms), hexadecyl (meth)acrylate (having 16 carbon atoms), stearyl (meth)acrylate (having 18 carbon atoms), and behenyl (meth)acrylate (having 22 carbon atoms). These may be used alone or in combination of two or more. Incidentally, a (meth)acrylic acid ester monomer having a linear alkyl group with 10 to 24 carbon atoms and containing a hydroxyl group is considered to be classified as (b) below.

[0061] Among the linear (meth)acrylic acid alkyl ester monomers (a) having an alkyl group with 10 to 24 carbon atoms, it is preferable to use alkyl methacrylates in order to lower the dielectric constant and the glass transition temperature of the acrylic resin, and particularly preferable are those having an alkyl group with 12 to 20 carbon atoms, and most preferable are stearyl methacrylate, lauryl methacrylate, and tridecyl methacrylate.

[0062] The content of the (meth)acrylic acid alkyl ester monomer (a) having a linear alkyl group having 10 to 24 carbon atoms is 50 to 94 mass % of the total (co)polymerization components, preferably 60 to 83 mass %, and particularly preferably 70 to 80 mass %. By keeping it within this range, there is no risk of the dielectric constant increasing or the thermal stability of the resin decreasing.

[0063] (Hydroxyl group-containing (meth)acrylic acid ester monomer) In order to improve resistance to wet heat whitening, the acrylic resin (A) is preferably a copolymer of monomer components that further includes a hydroxyl group-containing (meth)acrylic acid ester monomer (b) as a monomer component other than the above (a).

[0064] Examples of the hydroxyl group-containing (meth)acrylic acid ester monomer (b) include hydroxyalkyl acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, N-methylol (meth)acrylamide, and hydroxyethyl acrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro 2-hydroxypropyl (meth)acrylate; and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate. These may be used alone or in combination of two or more.

[0065] Among the above, primary hydroxyl group-containing monomers are preferred in terms of excellent reactivity with crosslinking agents and improved resistance to wet heat whitening. Furthermore, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred, with 4-hydroxybutyl acrylate being particularly preferred, in terms of low levels of impurities such as di(meth)acrylates and ease of production.

[0066] The content of the hydroxyl group-containing (meth)acrylic acid ester monomer (b) in the copolymerization components is preferably 5 to 15 mass %, particularly preferably 8 to 14 mass %, and even more preferably 10 to 13 mass %, based on the total mass of the copolymerization components. By keeping the content within this range, there is no risk of a decrease in resistance to wet heat whitening or an increase in dielectric constant.

[0067] The content of the monomer components (a) and (b) in the copolymerization components is preferably 50 to 94 mass % for (a) and 5 to 15 mass % for (b).

[0068] The free acid content in the acrylic resin (A) is preferably 1.0% or less, particularly preferably 0.5% or less, and further preferably 0.1% or less. By keeping the content within the above range, there is no risk of a decrease in thermal stability or the progression of corrosion of a metal adherend when the pressure-sensitive adhesive sheet is formed. In order to reduce the content of free acid in the acrylic resin (A) in this way, it is sufficient to reduce the amount of free acid contained in the hydroxyl group-containing (meth)acrylic acid ester monomer (b), and the content is preferably 1.0% or less, particularly preferably 0.5% or less, and even more preferably 0.1% or less.

[0069] In order to efficiently increase the cohesive force while maintaining a low dielectric constant, the acrylic resin (A) is preferably a copolymer of monomer components further containing, as a monomer component other than the above (b), a (meth)acrylic acid alkyl ester monomer (c) having a branched chain-containing alkyl group. In addition, when the (meth)acrylic acid alkyl ester monomer having a branched chain-containing alkyl group has a hydroxyl group, it is treated as a (meth)acrylic acid ester monomer (b) containing a hydroxyl group.

[0070] Examples of the (meth)acrylic acid alkyl ester monomer (c) having a branched chain-containing alkyl group include a branched chain-containing monomer having a tertiary carbon in the alkyl group and a branched chain-containing monomer having a t-Bu group.

[0071] Branched-chain-containing monomers having a tertiary carbon in the alkyl group can efficiently abstract hydrogen during photocrosslinking, thereby increasing cohesive strength, and branched-chain-containing monomers having a t-Bu group, such as tert-butyl (meth)acrylate, can improve cohesive strength by increasing the glass transition temperature. Among these, it is preferable to use iso-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, or tert-butyl(meth)acrylate as the (meth)acrylic acid alkyl ester monomer having a branched chain-containing alkyl group, and particularly preferably 2-ethylhexyl(meth)acrylate or tert-butyl(meth)acrylate.

[0072] The content ratio (weight ratio) of (a) and (c) in the copolymerization components is preferably 100 / 0 to 70 / 30, particularly preferably 100 / 0 to 80 / 20, and further preferably 90 / 10 to 85 / 15. By keeping the ratio within the above range, there is no risk of a decrease in thermal stability or adhesive properties.

[0073] The acrylic resin (A) may be a copolymer further containing other copolymerizable ethylenically unsaturated monomers as copolymerization components, if necessary.

[0074] Other copolymerizable ethylenically unsaturated monomers include, for example, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, nonylphenol ethylene glycol, Aromatic ring-containing monomers such as oxide adduct (meth)acrylate; alicyclic ring-containing monomers such as cyclohexyl (meth)acrylate, cyclohexyloxyalkyl (meth)acrylate, t-butylcyclohexyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate; 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-butoxydiethyleneglycol Ether chain-containing monomers such as methyl acrylate, methyl dimethacrylate, methyl ...Amino group-containing monomers such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and their quaternized derivatives; other examples include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone; These may be used alone or in combination of two or more. From the viewpoint of metal corrosion resistance, it is preferable that the acrylic resin (A) does not contain an acid component such as a carboxyl group.

[0075] The acrylic resin (A) can be produced by polymerizing the above-mentioned polymerization components as appropriate. As a polymerization method for the acrylic resin (A), for example, a conventionally known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. In the present invention, production by solution polymerization is preferred because it allows the acrylic resin (A) to be produced safely and stably with any monomer composition.

[0076] An example of a preferred method for producing the acrylic resin (A) used in the present invention will be described below. First, the copolymerization components and a polymerization initiator are mixed or dropped into an organic solvent, and solution polymerization is carried out to obtain a solution of the acrylic resin (A).

[0077] (organic solvent) Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. Among these solvents, it is preferable to use a solvent having a boiling point of 70°C or less, since this allows for efficient production of a solvent-free acrylic resin by distilling off the solvent from the acrylic resin solution obtained by solution polymerization.

[0078] Examples of organic solvents having a boiling point of 70°C or lower include hydrocarbon solvents such as n-hexane (67°C), alcohol solvents such as methanol (65°C), ester solvents such as methyl acetate (54°C), ketone solvents such as acetone (56°C), diethyl ether (35°C), methylene chloride (40°C), and tetrahydrofuran (66°C). Of these, in terms of versatility and safety, it is preferable to use acetone and methyl acetate, and it is particularly preferable to use acetone. The numbers in parentheses following the names of the above organic solvents are boiling points.

[0079] (Polymerization initiator) As the polymerization initiator used in the above polymerization reaction, azo-based polymerization initiators and peroxide-based polymerization initiators, which are common radical polymerization initiators, can be used. Examples of azo-based polymerization initiators include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), ... ,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and the like, and examples of peroxide polymerization initiators include benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, t-hexyl peroxypivalate, t-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide. These may be used alone or in combination of two or more.

[0080] In the production of the acrylic resin (A), it is preferable to use a reaction solvent for solution polymerization having a boiling point of 70° C. or less and to carry out the polymerization at a relatively low temperature. In this case, if a polymerization initiator with a high 10-hour half-life temperature is used, the polymerization initiator is likely to remain, and if the polymerization initiator remains, gelation of the acrylic resin tends to occur in the step of distilling off the solvent from the acrylic resin (A) solution, which will be described later.

[0081] Therefore, from the viewpoint of stably carrying out the step of distilling off the solvent from the acrylic resin (A) solution obtained by solution polymerization, it is preferable to use a polymerization initiator having a 10-hour half-life temperature of less than 60°C among the above polymerization initiators, and among these, 2,2'-azobis(2,4-dimethylvaleronitrile) (52°C), 2,2'-azobis(2-cyclopropylpropionitrile) (49.6°C), 2,2'-azobis(4-methoxy- ... ) (30°C), t-butyl peroxypivalate (54.6°C), t-hexyl peroxypivalate (53.2°C), t-hexyl peroxyneodecanoate (44.5°C), diisopropyl peroxycarbonate (40.5°C), and diisobutyryl peroxide (32.7°C) are preferred, and 2,2'-azobis(2,4-dimethylvaleronitrile) (52°C) and t-hexyl peroxypivalate (53.2°C) are particularly preferred. The numbers in parentheses following each compound name above are the 10-hour half-life temperatures of each compound.

[0082] The amount of the polymerization initiator used is usually 0.001 to 10 parts by mass, preferably 0.1 to 8 parts by mass, particularly preferably 0.5 to 6 parts by mass, even more preferably 1 to 4 parts by mass, especially preferably 1.5 to 3 parts by mass, and most preferably 2 to 2.5 parts by mass, relative to 100 parts by mass of the polymerization components. By using an amount within this range, there is no risk of the polymerization rate of the acrylic resin decreasing, the amount of residual monomer increasing, or the weight-average molecular weight of the acrylic resin increasing.

[0083] (Polymerization conditions, etc.) The polymerization conditions for solution polymerization may be those known in the art. For example, polymerization components containing a (meth)acrylic monomer and a polymerization initiator may be mixed or dropped into a solvent, and polymerization may be carried out under predetermined polymerization conditions.

[0084] The polymerization temperature in the polymerization reaction is usually 40 to 120° C., but from the viewpoint of ensuring a stable reaction, it is preferably 50 to 90° C., more preferably 55 to 75° C., and particularly preferably 60 to 70° C. By keeping the temperature within the above range, there is no risk of the acrylic resin (A) becoming prone to gelation or the activity of the polymerization initiator decreasing, which would result in a decrease in the polymerization rate and an increase in residual monomers.

[0085] The polymerization time in the polymerization reaction (the time until the start of the follow-up heating, if follow-up heating described below is performed) is not particularly limited, but is preferably 0.5 hours or more, preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 5 hours or more from the addition of the final polymerization initiator. The polymerization reaction is preferably carried out while refluxing the solvent, since this facilitates heat removal.

[0086] In the production of the acrylic resin (A), in order to reduce the amount of residual polymerization initiator, it is preferable to carry out follow-up heating to thermally decompose the polymerization initiator.

[0087] The drive-in heating temperature is preferably higher than the 10-hour half-life temperature of the polymerization initiator, and specifically is usually 40 to 150° C., preferably 55 to 130° C. from the viewpoint of suppressing gelation, and particularly preferably 75 to 95° C. By keeping the temperature within the above range, there is no risk of the acrylic resin (A) turning yellow, or of the polymerization monomer or polymerization initiator remaining, which would reduce the stability over time or the thermal stability of the acrylic resin (A).

[0088] Thus, a solution of the acrylic resin (A) can be obtained. Next, the solvent is distilled off from the resulting acrylic resin (A) solution. The step of distilling off the solvent from the acrylic resin (A) solution can be carried out by a known general method. Examples of the method for distilling off the solvent include a method for distilling off the solvent by heating and a method for distilling off the solvent by reducing pressure. However, from the viewpoint of efficiently distilling off the solvent, a method for distilling off the solvent by heating under reduced pressure is preferred.

[0089] When the solvent is distilled off by heating, the temperature is preferably 60 to 150° C., and it is particularly preferable from the viewpoint of extremely reducing the amount of residual solvent to hold the reaction solution after polymerizing the acrylic resin (A) at 60 to 80° C. to distill off the solvent, and then distill off the solvent at 80 to 150° C. In order to prevent gelation of the acrylic resin (A), it is preferable that the temperature during solvent distillation is not 150° C. or higher.

[0090] When the solvent is distilled off under reduced pressure, the pressure is preferably 20 to 101.3 kPa. In particular, it is preferable to maintain the pressure in the range of 50 to 101.3 kPa to distill off the solvent in the reaction solution, and then distill off the remaining solvent at 0 to 50 kPa, in order to minimize the amount of remaining solvent. In this way, the acrylic resin (A) can be produced.

[0091] The acrylic resin (A) preferably has a weight average molecular weight of 100,000 or more, more preferably 150,000 to 1,500,000, particularly preferably 200,000 to 1,000,000, especially preferably 250,000 to 800,000, and particularly preferably 300,000 to 600,000. By keeping the content within the above range, there is no risk of the viscosity becoming too high, which would result in deterioration in coatability and handling, or a decrease in cohesive force and durability. The weight average molecular weight of the acrylic resin (A) is the weight average molecular weight at the time of completion of production, that is, the weight average molecular weight of the acrylic resin (A) that has not been heated or otherwise subjected to any treatment after production.

[0092] The polydispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 15 or less, more preferably 10 or less, particularly preferably 7 or less, and even more preferably 5 or less. By setting it within this range, there is no risk of deterioration in the durability of each layer, foaming, or deterioration in handleability. The lower limit of the polydispersity is usually 1.1 in view of production limitations.

[0093] The weight-average molecular weights mentioned above are those calculated in terms of standard polystyrene molecular weights. The samples were analyzed using high-performance liquid chromatography (Waters Japan, "Waters 2695 (main unit)" and "Waters 2414 (detector)") with a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10 7 Separation range: 100 to 2 × 10 7 The number average molecular weight can also be measured using a similar method. Furthermore, the degree of dispersion can be calculated from the weight average molecular weight and the number average molecular weight.

[0094] The acrylic resin (A) preferably has a glass transition temperature (Tg) of −100 to 50° C., particularly −80 to 0° C., and further preferably −70 to −10° C. By setting the glass transition temperature within the above range, there is no risk of the melt viscosity of the acrylic resin (A) increasing, or the heating temperature required during coating increasing, which would impair the stability of the acrylic resin (A). Furthermore, there is no risk of deterioration in conformability to unevenness, adhesive strength, or heat durability.

[0095] The glass transition temperature is calculated from the following mathematical formula 1 of Fox.

number

[0096] The melt viscosity (mPa·s) of the acrylic resin (A) at 100°C is preferably 1,000 to 10,000,000 mPa·s, particularly preferably 50,000 to 1,000,000 mPa·s, and even more preferably 200,000 to 600,000 mPa·s. By keeping it within this range, there is no risk of insufficient durability due to a decrease in molecular weight, or reduced handleability and difficulty in coating.

[0097] The above viscosity values ​​were measured using a Shimadzu Koka type flow tester under conditions of a load of 30 kg, an orifice diameter of 1.0 mm, a die length of 10 mm, and a measurement temperature of 100°C.

[0098] The acrylic resin (A) is preferably a solvent-free acrylic resin that contains substantially no solvent, and the solvent content of the acrylic resin (A) is preferably 2% by mass or less, more preferably 0.00001 to 2% by mass, particularly preferably 0.0001 to 1% by mass, and even more preferably 0.001 to 0.1% by mass. By keeping the solvent content within this range, there is no risk of bubbles being generated or durability being reduced.

[0099] Furthermore, the amount of residual monomer in the acrylic resin (A) is preferably 2% by mass or less, particularly preferably 0.00001 to 1.5% by mass, and even more preferably 0.0001 to 1.0% by mass. By keeping it within this range, there is no risk of the molecular weight increasing when heated, which would result in a decrease in coatability or adhesive properties, or the generation of bubbles and a decrease in durability.

[0100] The solvent content and residual monomer amount in the acrylic resin (A) are values ​​measured by diluting the acrylic resin (A) 20 times with toluene and using a gas chromatography / mass fragment detector (GC: 7890A GC system manufactured by Agilent Technologies, MSD: 5975 inert manufactured by Agilent Technologies).

[0101] The volatile content of the acrylic resin (A) (usually consisting mainly of solvent and residual monomer) is preferably 2% by mass or less, particularly preferably 0.00001 to 1.5% by mass, and even more preferably 0.0001 to 1.0% by mass. By keeping it within this range, there is no risk of the molecular weight of the acrylic resin (A) increasing when heated, resulting in a decrease in coatability, a decrease in adhesive properties, or the generation of bubbles, which may reduce durability.

[0102] The volatile content of the acrylic resin (A) is a value calculated from the change in weight before and after heating the acrylic resin (A) at 130°C for 1 hour in a hot air dryer.

[0103] <Crosslinking agent> The present pressure-sensitive adhesive sheet may be formed from a composition containing a crosslinking agent (B) in addition to the acrylic resin (A) in order to increase the cohesive strength for improving the handling properties (e.g., cuttability, reworkability, and storage properties) of the pressure-sensitive adhesive sheet.

[0104] Examples of the crosslinking agent (B) include crosslinking agents having at least one crosslinkable functional group selected from a (meth)acryloyl group, an epoxy group, an isocyanate group, a carboxyl group, a hydroxyl group, a carbodiimide group, an oxazoline group, an aziridine group, a vinyl group, an amino group, an imino group, and an amide group, and one or more of these may be used in combination. The crosslinkable functional group may be protected with a deprotectable protecting group.

[0105] Among these, polyfunctional (meth)acrylates having two or more (meth)acryloyl groups, polyfunctional organic functional group resins having two or more organic functional groups such as isocyanate groups, epoxy groups, melamine groups, glycol groups, siloxane groups, and amino groups, and organometallic compounds having metal complexes of zinc, aluminum, sodium, zirconium, calcium, and the like can be preferably used.

[0106] Examples of the polyfunctional (meth)acrylate include 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, glycerin glycidyl ether di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polyalkoxy di(meth)acrylate, and bisphenol F. Polyalkoxydi(meth)acrylate, polyalkylene glycol di(meth)acrylate, trimethylolpropane trioxyethyl(meth)acrylate, ε-caprolactone-modified tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyethylene glycol di(meth)acrylate, tris(acryloxyethyl) isocyanurate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, neopentyl glycol hydroxypivalate Examples of suitable ultraviolet-curable polyfunctional monomers include cholestyryl di(meth)acrylate, di(meth)acrylate of ε-caprolactone adduct of hydroxypivalic acid neopen glycol, trimethylolpropane tri(meth)acrylate, alkoxylated trimethylolpropane tri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate, as well as polyfunctional acrylic oligomers such as polyester(meth)acrylate, epoxy(meth)acrylate, urethane(meth)acrylate, and polyether(meth)acrylate.

[0107] Among the above-mentioned polyfunctional (meth)acrylic acid ester monomers, from the viewpoint of improving adhesion to an adherend and the effect of suppressing wet heat whitening, polyfunctional monomers or oligomers containing a polar functional group such as a hydroxyl group, a carboxyl group, an amide group, etc. are preferred. Among these, it is preferred to use a polyfunctional (meth)acrylic acid ester having a hydroxyl group or an amide group.

[0108] Furthermore, in order to adjust the effects of adhesion, moist heat resistance, heat resistance, etc., a monofunctional or polyfunctional (meth)acrylic acid ester that reacts with the crosslinking agent may be further added.

[0109] From the viewpoint of balancing the flexibility and cohesive strength of the pressure-sensitive adhesive composition, the content of the crosslinking agent is preferably 0.1 to 20 parts by mass relative to 100 parts by mass of the acrylic resin (A), and more preferably 0.5 parts by mass or more or 15 parts by mass or less, and even more preferably 1 part by mass or more or 13 parts by mass or less.

[0110] In order to provide the pressure-sensitive adhesive sheet having the above laminated structure with better handling properties (e.g., ease of cutting, reworking, and storage), it is preferable that the crosslinking agent (B) be contained in the i-th layer, and it is most preferable that the crosslinking agent be contained in a layer other than the first and n-th layers, i.e., a layer other than the front and back layers.

[0111] <Photopolymerization initiator> The pressure-sensitive adhesive sheet contains an acrylic resin (A), but may also be formed from a composition containing a photopolymerization initiator (C) in addition to the acrylic resin (A), in order to stabilize the reaction during irradiation with active energy rays.

[0112] The photopolymerization initiator (C) is not particularly limited as long as it generates radicals by the action of light, and examples thereof include acetophenone-based, benzoin-based, benzophenone-based, thioxanthone-based, and acylphosphine oxide-based photopolymerization initiators. However, it is preferable to use a hydrogen abstraction-type benzophenone-based photopolymerization initiator because it can efficiently crosslink between molecules or within molecules.

[0113] Examples of the benzophenone-based photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. These may be used alone or in combination of two or more.

[0114] Furthermore, as an auxiliary agent for these photopolymerization initiators, for example, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc. can also be used in combination. These auxiliary agents may be used alone or in combination of two or more.

[0115] The amount of the photopolymerization initiator (C) is preferably 0.01 to 10 parts by mass, particularly preferably 0.1 to 5 parts by mass, and even more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the acrylic resin (A). If the amount is too small, the curing rate may decrease or the curing may be insufficient.

[0116] <Other ingredients> In addition to the above, the present pressure-sensitive adhesive sheet may be formed from a composition containing known components blended into ordinary pressure-sensitive adhesive compositions. For example, various additives such as tackifier resins, processing aids (oil components, etc.), silane coupling agents, antioxidants, light stabilizers, metal deactivators, ultraviolet absorbers (UVA), light stabilizers (HALS), rust inhibitors, anti-aging agents, moisture absorbers, hydrolysis inhibitors, and nucleating agents may be appropriately added. Inorganic or organic nanoparticles are also included. Among these, it is more preferable to include a rust inhibitor and a tackifier. Furthermore, a reaction catalyst (such as a tertiary amine compound, a quaternary ammonium compound, or a tin laurate compound) may be appropriately contained as needed.

[0117] <Method of manufacturing the present pressure-sensitive adhesive sheet> The present pressure-sensitive adhesive sheet can be produced by applying (coating) a resin composition containing the above-mentioned acrylic resin (A) and, if necessary, a crosslinking agent (B) and a photopolymerization initiator (C) in a thermally molten state onto a substrate sheet or a release sheet, and then cooling. Furthermore, for example, the present pressure-sensitive adhesive sheet having a laminated structure, particularly a two-layer structure (n=2), can be produced by a method in which the resin composition is applied (coated) in a thermally molten state onto a substrate sheet or a release sheet, followed by cooling to form a first layer, and then the resin composition is applied (coated) onto the formed first layer, followed by cooling to form a second layer, or by a method in which the resin composition is melted by heating and then co-extrusion molded to simultaneously form the first and second layers. Furthermore, for example, the present pressure-sensitive adhesive sheet having a laminated structure, particularly a structure of three or more layers (n is 3 or more), can be produced by a method in which the resin composition is applied (coated) in a molten state by heat onto a base sheet or a release sheet, then cooled to form a first layer, and then the resin composition is applied (coated) onto the first layer formed, then cooled to form a second layer, and this process is repeated to form the i-th layer; a method in which the resin composition is melted by heat and the first to i-th layers are formed in the same manner as above, and then the coated surfaces of each layer are bonded together; or a method in which the resin composition is melted by heat and the first to i-th layers are simultaneously formed by co-extrusion molding.

[0118] The application (coating) method is not particularly limited as long as it is a common coating method, and examples thereof include roll coating, die coating, gravure coating, comma coating, and screen printing.

[0119] The pressure-sensitive adhesive sheet may be a substrate-sheet-attached pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is provided on a substrate sheet, or a substrate-less pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is provided on a release sheet.

[0120] Examples of substrate sheets include polyester-based resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin-based resins such as polyethylene, polypropylene, and polymethylpentene; polyethylene fluoride resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose-based resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; and synthetic resin sheets such as polyimide; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven and nonwoven fabrics made of glass fiber, natural fiber, synthetic fiber, etc. These substrate sheets can be used as a single layer or as a multi-layered body in which two or more types are laminated together. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction and the like.

[0121] As the release sheet, for example, a release-treated synthetic resin sheet, paper, cloth, nonwoven fabric, etc., exemplified above as the base sheet, can be used. As the release sheet, it is preferable to use a silicone-based release sheet.

[0122] <How to use this adhesive sheet> The present pressure-sensitive adhesive sheet is preferably used by irradiating it with actinic rays after being stuck to an adherend. Therefore, in the case of a two-layer structure (n=2), when the pressure-sensitive adhesive sheet is irradiated with active energy rays so that the cumulative light intensity at 365 nm is 2000 mJ or more, it is preferable that the difference in storage modulus G' of the first layer at a frequency of 1 Hz and a temperature of 80°C before and after irradiation (storage modulus G' after irradiation - storage modulus G' before irradiation) is 5 kPa or more, and the difference in storage modulus G' of the second layer at a frequency of 1 Hz and a temperature of 80°C (storage modulus G' after irradiation - storage modulus G' before irradiation) is 2 kPa or more. Furthermore, when the pressure-sensitive adhesive sheet has a three or more layer structure (n is 3 or more), when the pressure-sensitive adhesive sheet is irradiated with active energy rays so that the cumulative light intensity at 365 nm is 2000 mJ or more, it is preferable that the difference in storage modulus G' at a frequency of 1 Hz and a temperature of 80°C before and after irradiation for the first layer (storage modulus G' after irradiation - storage modulus G' before irradiation) is 5 kPa or more, and the difference in storage modulus G' at a frequency of 1 Hz and a temperature of 80°C (storage modulus G' after irradiation - storage modulus G' before irradiation) is 2 kPa or more for the ith layer.

[0123] Furthermore, in the above configuration, in order to provide step absorption and anti-foaming reliability, in the case of a two-layer configuration (n=2), it is preferable that the difference in storage modulus G' of the second layer at a frequency of 1 Hz and a temperature of 80°C (storage modulus G' after irradiation - storage modulus G' before irradiation) is 5 kPa or more, and it is preferable that the difference in storage modulus G' of the ith layer at a frequency of 1 Hz and a temperature of 80°C (storage modulus G' after irradiation - storage modulus G' before irradiation) is 4 kPa or more. In the case of a three or more layer structure (n is 3 or more), the difference in storage modulus G' of the first layer at a frequency of 1 Hz and a temperature of 80°C (storage modulus G' after irradiation - storage modulus G' before irradiation) is preferably 5 kPa or more, and the difference in storage modulus G' of the ith layer at a frequency of 1 Hz and a temperature of 80°C (storage modulus G' after irradiation - storage modulus G' before irradiation) is preferably 4 kPa or more.

[0124] In this way, the present pressure-sensitive adhesive sheet still has room to be cured by active energy rays, and in particular, by adjusting the degree of curing so that the storage modulus difference is within the above range, it is possible to achieve a low dielectric constant while also having extremely high print step absorption properties. The storage modulus G' can be adjusted by the above-mentioned method.

[0125] (Application) The pressure-sensitive adhesive sheet can be used for optical components, for example, for bonding components of image display devices, such as LCD, PDP, or EL display devices, including personal computers, mobile terminals (PDAs), game consoles, televisions (TVs), car navigation systems, touch panels, and pen tablets.

[0126] To cite a specific example, in the image display device of a mobile phone, a polarizing film or the like is laminated on a liquid crystal panel display (LCD), and a plastic protective panel is laminated on top of that via an adhesive or sheet. In this case, PVA (polyvinyl alcohol) or triacetyl cellulose resin may be used as a constituent material of the polarizing film, and it has been found that these resins are prone to outgassing.

[0127] Therefore, by producing a laminate consisting of a protective panel / the present adhesive sheet / polarizing film and irradiating it with active energy rays through these components of the image display device (protective panel or polarizing film) to increase the storage modulus of the present adhesive sheet, foaming due to outgassing from the protective panel or polarizing film can be effectively suppressed even when used at high temperatures. [Example]

[0128] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples in any way.

[0129] In the following examples and comparative examples, the following physical property measurements and treatments were carried out under the following conditions.

[0130] (Laminated sheet 1 for forming intermediate layer) An acrylic resin A was prepared by randomly copolymerizing 58.5 parts by mass of a mixture of lauryl methacrylate and tridecyl methacrylate (SLMA), 15 parts by mass of 2-ethylhexyl methacrylate (2EHMA), 15 parts by mass of n-stearyl methacrylate (SMA), 11 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 0.5 parts by mass of 4-methacryloyloxybenzophenone (MBP). 1 kg of this acrylic resin A was melt-kneaded with 50 g of an ultraviolet curable resin propoxylated pentaerythritol triacrylate ("ATM-4PL" manufactured by Shin-Nakamura Chemical Co., Ltd.) as a crosslinking agent to prepare a composition (A-1) for an intermediate resin layer. The composition (A-1) was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 90 μm thickness using a laminator at a temperature of 80°C to produce a laminate sheet 1 for forming an intermediate layer (intermediate resin layer (A-1) thickness 90 μm).

[0131] (Laminated sheet 2 for forming intermediate layer) An acrylic resin B was prepared by randomly copolymerizing 44.5 parts by mass of a mixture of lauryl methacrylate and tridecyl methacrylate (SLMA), 10 parts by mass of 2-ethylhexyl methacrylate (2EHMA), 35 parts by mass of n-stearyl methacrylate (SMA), 10 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 0.5 parts by mass of 4-methacryloyloxybenzophenone (MBP). 1 kg of this acrylic resin B was melt-kneaded with 50 g of an ultraviolet curable resin propoxylated pentaerythritol triacrylate ("ATM-4PL" manufactured by Shin-Nakamura Chemical Co., Ltd.) as a crosslinking agent to prepare a composition (B-1) for an intermediate resin layer. The composition (B-1) was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 90 μm thickness using a laminator at a temperature of 80°C to produce a laminate sheet 2 for forming an intermediate layer (intermediate resin layer (B-1) thickness 90 μm).

[0132] (Laminated sheet 3 for forming intermediate layer) An acrylic resin C was prepared by randomly copolymerizing 52.5 parts by mass of a mixture of lauryl methacrylate and tridecyl methacrylate (SLMA), 20 parts by mass of 2-ethylhexyl methacrylate (2EHMA), 15 parts by mass of n-stearyl methacrylate (SMA), 12 parts by mass of 2-hydroxyethyl acrylate (2HEA), and 0.5 parts by mass of 4-methacryloyloxybenzophenone (MBP). 1 kg of this acrylic resin C was melt-kneaded with 50 g of an ultraviolet curable resin propoxylated pentaerythritol triacrylate ("ATM-4PL" manufactured by Shin-Nakamura Chemical Co., Ltd.) as a crosslinking agent to prepare a composition (C-1) for an intermediate resin layer. The composition (C-1) was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 90 μm thickness using a laminator at a temperature of 80°C to produce a laminated sheet 3 for forming an intermediate layer (intermediate resin layer (C-1) thickness 90 μm).

[0133] (Laminated sheet 4 for forming intermediate layer) An acrylic resin D was prepared by randomly copolymerizing 82.6 parts by mass of a mixture of lauryl methacrylate and tridecyl methacrylate (SLMA), 5 parts by mass of t-butyl methacrylate (tBMA), 12 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 0.5 parts by mass of 4-methacryloyloxybenzophenone (MBP). 1 kg of this acrylic resin D was melt-kneaded with 50 g of an ultraviolet curable resin propoxylated pentaerythritol triacrylate ("ATM-4PL" manufactured by Shin-Nakamura Chemical Co., Ltd.) as a crosslinking agent to prepare a composition (D-1) for an intermediate resin layer. The composition (D-1) was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 90 μm thickness using a laminator at a temperature of 80°C to produce a laminate sheet 4 for forming an intermediate layer (intermediate resin layer (D-1) thickness 90 μm).

[0134] (Laminated sheet 5 for forming intermediate layer) An acrylic resin E was prepared by randomly copolymerizing 77 parts by mass of 2-ethylhexyl acrylate (2EHA), 19 parts by mass of vinyl acetate (VA), and 4 parts by mass of acrylic acid (AA). A composition for the intermediate resin layer (E-1) was prepared by melt-kneading 1 kg of this acrylic resin E with 50 g of the ultraviolet-curable resin propoxylated pentaerythritol triacrylate ("ATM-4PL" manufactured by Shin-Nakamura Chemical Co., Ltd.) as a crosslinking agent and 15 g of a mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone ("Ezacure TZT" manufactured by Lamberti) as a photoinitiator. The composition (E-1) was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 90 μm thickness at a temperature of 80°C using a laminator to produce a laminate sheet 5 for forming an intermediate layer (intermediate resin layer (E-1) thickness 90 μm).

[0135] (Laminated sheet 1 for forming outermost layer) The acrylic resin A was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films ("Diafoil MRV-V06" manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / "Diafoil MRQ" manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet with a thickness of 30 μm using a laminator to produce a laminated sheet 1 for forming the outermost layer (adhesive layer A thickness 30 μm).

[0136] (Laminated sheet 2 for forming outermost layer) The acrylic resin B was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 30 μm thickness using a laminator at a temperature of 80°C to produce a laminated sheet 2 for forming the outermost layer (adhesive layer B thickness 30 μm).

[0137] (Laminated sheet 3 for forming outermost layer) The acrylic resin C was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 30 μm thickness using a laminator at a temperature of 80°C to produce a laminated sheet 3 for forming the outermost layer (adhesive layer C thickness 30 μm).

[0138] (Laminated sheet 4 for forming outermost layer) The acrylic resin D was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 30 μm thickness at a temperature of 80°C using a laminator to produce a laminated sheet 4 for forming the outermost layer (adhesive layer D thickness 30 μm).

[0139] (Laminated sheet 5 for forming outermost layer) An outermost resin layer composition E' was prepared by melt-kneading 1 kg of the acrylic resin E with 15 g of a mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone (Ezacure TZT manufactured by Lamberti) as a photoinitiator. The composition was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films (Diafoil MRV-V06 manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / Diafoil MRQ manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet of 30 μm thickness at 80°C using a laminator to produce a laminated sheet 5 for forming the outermost layer (adhesive layer E, thickness 30 μm). [Example]

[0140] <Preparation of adhesive sheet 1> The PET films on both sides of the intermediate resin layer (A-1) in the laminate sheet 1 for forming the intermediate resin layer were sequentially peeled off, and the PET film on one side of the adhesive layer A in the laminate sheet 1 for forming the outermost layer was peeled off, and the exposed adhesive surfaces were sequentially bonded to both surfaces of (A-1) using a laminator to produce a multilayer adhesive sheet consisting of A / (A-1) / A. After lamination, ultraviolet light was irradiated from a high-pressure mercury lamp through the polyethylene terephthalate film remaining on the surface so that the cumulative light intensity at 365 nm was 500 mJ, thereby crosslinking A and (A-1) with ultraviolet light to produce adhesive sheet 1 (total thickness 150 μm). The pressure-sensitive adhesive sheet 1 is in a semi-cured state, that is, in a state where there is room for further curing, by adjusting the amount of ultraviolet light irradiation. [Example]

[0141] <Preparation of adhesive sheet 2> Pressure-sensitive adhesive sheet 2 was produced in the same manner as in Example 1, except that (B-1) was used for the intermediate resin layer and B was used for the outermost layer. [Example]

[0142] <Preparation of adhesive sheet 3> Pressure-sensitive adhesive sheet 3 was produced in the same manner as in Example 1, except that (C-1) was used for the intermediate resin layer and C was used for the outermost layer. [Example]

[0143] <Preparation of adhesive sheet 4> Pressure-sensitive adhesive sheet 4 was produced in the same manner as in Example 1, except that (D-1) was used for the intermediate resin layer and D was used for the outermost layer. [Example]

[0144] <Preparation of adhesive sheet 5> Pressure-sensitive adhesive sheet 5 was produced in the same manner as in Example 1, except that (A-1) was used for the intermediate resin layer and B was used for the outermost layer. [Example]

[0145] <Preparation of adhesive sheet 6> Pressure-sensitive adhesive sheet 6 was produced in the same manner as in Example 1, except that (B-1) was used for the intermediate resin layer and A was used for the outermost layer. [Example]

[0146] <Preparation of adhesive sheet 7> Pressure-sensitive adhesive sheet 7 was produced in the same manner as in Example 1, except that (C-1) was used for the intermediate resin layer and A was used for the outermost layer. [Example]

[0147] <Preparation of adhesive sheet 8> Pressure-sensitive adhesive sheet 8 was produced in the same manner as in Example 1, except that (A-1) was used for the intermediate resin layer and C was used for the outermost layer. [Example]

[0148] <Preparation of adhesive sheet 9> Pressure-sensitive adhesive sheet 9 was produced in the same manner as in Example 1, except that (B-1) was used for the intermediate resin layer and C was used for the outermost layer. [Example]

[0149] <Preparation of adhesive sheet 10> A pressure-sensitive adhesive sheet 10 was produced in the same manner as in Example 1, except that (C-1) was used for the intermediate resin layer and B was used for the outermost layer.

[0150] <Preparation of adhesive sheet 11> The composition (A-1) was sandwiched between two release films, i.e., two release-treated polyethylene terephthalate films ("Diafoil MRV-V06" manufactured by Mitsubishi Chemical Corporation, thickness 100 μm / "Diafoil MRQ" manufactured by Mitsubishi Chemical Corporation, thickness 75 μm), and formed into a sheet with a thickness of 150 μm using a laminator to produce adhesive sheet 11. Comparative Example 2

[0151] <Preparation of adhesive sheet 12> A pressure-sensitive adhesive sheet 12 was produced in the same manner as in Comparative Example 1, except that composition (B-1) was used instead of composition (A-1).

[0152] <Preparation of adhesive sheet 13> A pressure-sensitive adhesive sheet 13 was produced in the same manner as in Comparative Example 1, except that composition (C-1) was used instead of composition (A-1).

[0153] <Preparation of adhesive sheet 14> A pressure-sensitive adhesive sheet 14 was produced in the same manner as in Comparative Example 1, except that composition (D-1) was used instead of composition (A-1).

[0154] <Preparation of adhesive sheet 15> A pressure-sensitive adhesive sheet 15 was produced in the same manner as in Comparative Example 1, except that acrylic resin A was used instead of composition (A-1).

[0155] <Preparation of adhesive sheet 16> A pressure-sensitive adhesive sheet 16 was produced in the same manner as in Comparative Example 1, except that acrylic resin B was used instead of composition (A-1).

[0156] <Preparation of adhesive sheet 17> A pressure-sensitive adhesive sheet 17 was produced in the same manner as in Comparative Example 1, except that acrylic resin C was used instead of composition (A-1).

[0157] <Preparation of adhesive sheet 18> A pressure-sensitive adhesive sheet 18 was produced in the same manner as in Comparative Example 1, except that acrylic resin D was used instead of composition (A-1).

[0158] <Preparation of adhesive sheet 19> A pressure-sensitive adhesive sheet 19 was produced in the same manner as in Comparative Example 1, except that composition E' was used instead of composition (A-1).

[0159] <Preparation of adhesive sheet 20> A pressure-sensitive adhesive sheet 20 was produced in the same manner as in Comparative Example 1, except that composition (E-1) was used instead of composition (A-1).

[0160] <Preparation of adhesive sheet 21> An adhesive sheet 21 was produced in the same manner as in Example 1, except that (E-1) was used for the intermediate resin layer and E' was used for the outermost layer.

[0161] <Tensile modulus> The pressure-sensitive adhesive sheets 1 to 21 produced in the examples and comparative examples were cut into pieces 20 mm wide and 80 mm long, which were attached to a template (60 mm x 80 mm, with a central window) as shown in Figure 1(A). The top and bottom of the template were chucked in a tensile tester (Intesco "205 Model Tester"), and then, as shown in Figures 1(B) and 1(C), diagonal cuts were made on both sides of the template to separate the top and bottom of the template. A tensile test was performed with a chuck distance of 40 mm and a pulling speed of 300 mm / min. In Figure 1, reference numeral 1 denotes the template, and reference numeral 2 denotes the pressure-sensitive adhesive sheet. The tensile modulus (MPa) was then calculated. The calculation results are shown in Table 3.

[0162] <Workability> The pressure-sensitive adhesive sheets 1 to 21 produced in the examples and comparative examples were cut using a Thomson punch with a 50 mm x 80 mm Thomson blade, and the shape of the cut sheet edges was visually observed. Sheets with excess glue at the edge were evaluated as "x", and those without excess glue were evaluated as "o". The evaluation results are shown in Table 3.

[0163] <Retention force test> The adhesive sheets 1 to 21 produced in the examples and comparative examples were cut to 30 mm x 80 mm, the release film on one side was peeled off, and one side of the adhesive sheet was attached with a hand roller so that it overlapped a polyethylene terephthalate film (thickness 38 μm) used as a backing, and this was then cut into strips of 25 mm x 80 mm to prepare test specimens. Next, the remaining release film was peeled off, and the test piece was attached to a vertically placed SUS (stainless steel) plate (120 mm x 50 mm x 1.2 mm thick) with a hand roller, overlapping by 20 mm. At this point, the adhesive area between the transparent double-sided adhesive sheet and the SUS (stainless steel) plate was 25 mm x 20 mm. The test piece was then cured in an atmosphere of 40°C for 15 minutes, after which a 4.9 N weight was attached vertically to the test piece and left to stand for 30 minutes, after which the downward displacement (mm) of the adhesive position between the SUS (stainless steel) plate and the test piece was measured. The measurement results are shown in Table 3.

[0164] <Printing step followability test> A 10 mm wide, 40 μm thick black print (total light transmittance 0%) was applied to the periphery of a 60 mm x 90 mm x 0.5 mm thick soda lime glass to produce a glass substrate for evaluation with a 40 μm printed step on the periphery. This glass substrate for evaluation is a substitute for an image display device component, with a step of 30 μm to 50 μm in height and a flat surface on the bonding surface. A polarizing plate (NWF-KDSEGHC-ST22 manufactured by Nitto Denko Corporation) serving as a component of an image display device was prepared as a test adherend to be bonded to this evaluation glass substrate by completely bonding it to one side of a glass plate (60 x 90 mm x t0.5 mm). One release film was peeled off from each of the pressure-sensitive adhesive sheets 1 to 21 cut for the processability evaluation, and the exposed adhesive surface was attached to the glass substrate with a hand roller so as to cover the print step portion. Next, the remaining release film was peeled off, and untreated soda lime glass was press-attached to the exposed adhesive surface under reduced pressure (5 kPa absolute pressure), and then autoclaved (60°C, 0.2 MPa, 20 minutes) for finish attachment to produce a laminate for evaluating print step followability. The laminate for evaluating print step conformability was left to stand for one day under normal conditions (temperature 23°C, humidity 50%), and then the appearance was visually observed. Those in which lifting or peeling of the adhesive sheet occurred near the print step were evaluated as "×", and those in which lifting or peeling did not occur were evaluated as "◯". The evaluation results are shown in Table 3.

[0165] <Dielectric constant> The PSA sheets 1 to 21 produced in the examples and comparative examples were cut into circles with a diameter of 25 mm, and attached to the measurement section of an LCR meter (manufactured by Keysight Technologies, Inc.) with the release films on both sides removed. The dielectric constant was measured at 23°C, 50% RH, at an applied voltage of 1 V, and at a frequency of 100 kHz. The measurement results are shown in Table 3.

[0166] <Storage modulus (G')> The dynamic storage modulus (G') at 20°C was measured using a rheometer ("MARS" manufactured by Eiko Seiki Co., Ltd.) with a Φ20mm parallel plate adhesive tool, a strain of 0.5%, a frequency of 1 Hz, a temperature of -50 to 200°C, and a heating rate of 3°C / min. The measurement results are shown in Table 1. The dynamic storage modulus (G') at 20° C. was also measured for pressure-sensitive adhesive sheets 11 to 21 in the same manner as above. The measurement results are shown in Table 3. Also, the dynamic storage modulus (G’) at 80°C was measured for the intermediate layer (intermediate layer forming sheet 4 in a semi-cured state) and the outermost layer (outermost layer forming sheet 4 in a semi-cured state) of the active energy ray-curable adhesive sheet 4 obtained in Example 4. Ultraviolet rays were irradiated so that the integrated light quantity of 365 nm became 2000 mJ or more, and the intermediate layer forming sheet 4 and the outermost layer forming sheet 4 after ultraviolet irradiation were produced, and each was measured under the same conditions as above. The measurement results are shown in Table 2.

[0167] <UV Foaming Test> (Preparation of UV Irradiation Test Sample) One release film of the adhesive sheets 1 to 21 prepared in the examples and comparative examples was peeled off and roll-bonded to a soda lime glass with a size of 150 mm × 200 mm and a thickness of 1 mm. Next, the remaining release film was peeled off and roll-bonded to a glass plate with a size of 238 mm × 182 mm × thickness of 0.8 mm, and autoclave treatment (80°C, gauge pressure 0.2 MPa, 20 minutes) was performed for final adhesion. From the glass side with a thickness of 0.8 mm, ultraviolet rays with a wavelength of 365 nm were irradiated onto the adhesive sheet with a high-pressure mercury lamp so that the ultraviolet rays reached 2000 mJ / cm 2 to cure the adhesive sheet and produce a laminate.

[0168] (Test Method) The above laminate was placed in a xenon UV irradiation device (Sun Test CPS: manufactured by Toyo Seiki), and the appearance after UV irradiation treatment at an illuminance of 765 W / m 2 and a temperature of 60°C for 24 hours was observed. Those in which bubbles with a diameter of 5 mm or more occurred in the adhesive sheet were judged as "× (poor)", those in which bubbles with a diameter of less than  5 mm were observed were judged as "△ (usual)", and those without foaming and no change in appearance were judged as "○ (good)".

[0169]

Table 1

[0170]

Table 2

[0171] [Table 3] [Industrial Applicability]

[0172] The active energy ray-curable adhesive sheet for optical members of the present invention is formed using a specific acrylic resin (A) so as to have specific properties, thereby achieving both a low dielectric constant and excellent print step absorption, and can be suitably used when forming image display devices such as personal computers, mobile terminals (PDAs), game consoles, televisions (TVs), car navigation systems, touch panels, and pen tablets. [Explanation of symbols]

[0173] 1. Pattern 2 adhesive sheets

Claims

1. An active energy ray-curable pressure-sensitive adhesive sheet containing an acrylic resin (A), The storage elastic modulus G' at a frequency of 1 Hz and a temperature of 20°C is different from one another. all of the layers contain an acrylic resin (A), and the acrylic resin (A) is the resin component with the largest content among the components constituting the layers; The acrylic resin (A) is a (co)polymer of monomer components including: (a) a (meth)acrylic acid ester monomer having an active energy ray-crosslinkable structural moiety and having a linear alkyl group having 10 to 24 carbon atoms; (b) a hydroxyl group-containing (meth)acrylic acid ester monomer; and (c) a (meth)acrylic acid alkyl ester monomer having a branched chain-containing alkyl group; An active energy ray-curable pressure-sensitive adhesive sheet for optical members, which has at least all of the following properties (1) to (3): (1) A tensile modulus of elasticity at a temperature of 23°C of 0.03 MPa or more (2) Affixed to a stainless steel plate with an adhesive area of ​​25 mm x 20 mm, and subjected to a vertical load of 500 gf (4.9 N) for 30 minutes. The slippage is 1 mm or more in a holding strength test. (3) A relative dielectric constant of 3.7 or less at a frequency of 100 kHz

2. An active energy ray-curable pressure-sensitive adhesive sheet having n layers in a thickness direction from a sheet surface, The active energy ray-curable pressure-sensitive adhesive sheet for optical members according to claim 1, having the following characteristic (4) or (5): wherein n is an integer of 2 or more, and i is an integer of 2 or more that satisfies the relationship n>i: (4) When n=2, the first layer and the second layer have different storage moduli G′ at a frequency of 1 Hz and a temperature of 20°C, and the second layer has a storage modulus G′ of 40 kPa or more and 1 MPa or less at a frequency of 1 Hz and a temperature of 20°C. (5) When n is an integer of 3 or greater, the first layer and the i-th layer have different storage moduli G′ at a frequency of 1 Hz and a temperature of 20°C, and the i-th layer has a storage modulus G′ of 40 kPa or greater and 1 MPa or less at a frequency of 1 Hz and a temperature of 20°C.

3. 3. The active energy ray-curable pressure-sensitive adhesive sheet for optical members according to claim 2, wherein the first layer has a storage modulus G' of 30 kPa or more and 70 kPa or less at a frequency of 1 Hz and a temperature of 20°C.

4. 4. The active energy ray-curable pressure-sensitive adhesive sheet for optical members according to claim 2 or 3, wherein, when irradiated with active energy rays such that the integrated light amount at 365 nm is 2000 mJ or more, the difference in storage modulus G' (storage modulus G' after irradiation - storage modulus G' before irradiation) at a frequency of 1 Hz and a temperature of 80°C before and after irradiation is 5 kPa or more, and the difference in storage modulus G' (storage modulus G' after irradiation - storage modulus G' before irradiation) at a frequency of 1 Hz and a temperature of 80°C for the second layer when n = 2 and for the second layer and the ith layer when n = 3 or more is 2 kPa or more.

5. The active energy ray-curable pressure-sensitive adhesive sheet for optical members according to any one of claims 1 to 4, wherein the active energy ray-crosslinkable structural moiety is a benzophenone-based crosslinked structure.

6. The active energy ray-curable pressure-sensitive adhesive sheet for optical members according to any one of claims 1 to 5, further comprising a crosslinking agent (B).

7. The active energy ray-curable pressure-sensitive adhesive sheet for optical members according to any one of claims 2 to 4, wherein the second layer in (4) or the i-th layer in (5) contains a crosslinking agent (B).

Images